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Carbene transfer from aliphatic diazoalkanes upon coordinatively unsaturated metal centers is a general synthetic concept that provides straight-forward routes into organo-metallic hydrocarbon chemistry. A comparison focussing on several key reactions of general applicability demonstrates that mononuclear organometal substrates add carbenes that may act as bridging ligands (e.g., compound 6) if they arise from ω,ω'-bisdiazoalkanes. By way of contrast, metal-metal double bonds cleanly form dimetallacyclo-propane-type derivatives under very mild conditions (7-9). The broadest variety of structures is finally encountered with metal-metal triply bonded precursors such as the molybdenum compounds 3: here, the initial diazoalkane adducts are subject to further rearrangement processes commonly leading to metal-metal single bonds (11) or causing irreversible cleavage of the dinuclear metal systems (10).
Thermal decompositions of azo compounds in the gas phase under reduced pressure are further investigated using photoelectron spectroscopic gas analysis. Passing diallyl, diphenyl and phenylmethyl derivatives either through a short-pathway pyrolysis (SPP) apparatus or through an external thermal reactor (ETR) results in the following fragmentations: Under nearly unimolecular conditions (SPP, 10-4 mbar pressure), diallyldiazene decomposes above 600 K to N2 and hexadiene-1,5 with the allyl radical as a detectable intermediate. The PE spectra recorded for diphenyldiazene above 1000 K (ETR, 1-2 mbar pressure) show N2, benzene, as well as traces of diphenyl. Phenylmethyldiazene yields above 800 K (SPP) predominantly N2, toluene, diphenyl and ethane with the methyl radical as the only detectable intermediate. Insertion of quartz wool into the pyrolysis tube (ETR) lowers the fragmentation temperatures, and in addition, above 850 K, HCN and aniline are PE spectroscopically identified. Surprisingly, this second reaction channel can be heterogeneously catalyzed: phenylmethyldiazene decomposes under 10-2 mbar pressure at a [Ni/SiO2] catalyst surface selectively to HCN and aniline.
[Ph3PN(H)Ph][AuI2] (2) is formed by the reaction of AuI with N-Phenyl-iminotriphenylphosphorane, Ph3PNPh in a toluene suspension. 2,3-Bis(triphenylphosphinimino)maleic acid-N-methylimide (3) has been prepared by the Staudinger reaction of 2,3-bis(azido)maleic acid-N-methylimide with PPh3 in THF solution in the form of red crystals. Crystal structure determinations of three iminophosphoranes were carried out by X-ray methods.
Ph3PNPh (1): space group P21/c, Z = 4, 2176 independent observed reflexions, R = 0.057. Lattice dimensions (-30 °C): a = 1126.4, b = 1148.6, c = 1476.0 pm; β = 97.21°. The compound forms monomeric molecules with P=N = 160.2 pm and an PNC angle of 130.4°.
[Ph3PN(H)Ph][AuI2] (2): space group P1̄, Z = 2, 1780 independent observed reflexions, R = 0.057. Lattice dimensions (18 °C); a = 824.9, b = 1022, c = 1476.2 pm; α = 89.23°, β = 87.41°, γ = 85.65°. The compound consists of ions [Ph3PN(H)Ph]⊕ with P=N = 162.4 pm and PNC = 129.3°, and anions [AuI2]⊖ with Au-I = 261.9 and 259.3 pm, IAuI = 176.8°.
(Ph3P)2N2C4O2 (NMe) (3): space group P1̄, Z = 2, 4972 independent observed reflexions, R = 0.050. Lattice dimensions (-90 °C): a = 904.7, b = 993.8, c = 2017.4 pm; α = 101.55°, β = 96.39°, γ = 105.81°. The compound forms monomeric molecules with syn-conformation of the two NPPh3 groups. Bond lengths: P=N = 157.1; 155.3 pm, bond angles: PNC = 133°; 136°.
The title compounds Ph3PNPh · CuCl (1) and (Ph3P)2 N2 C4O2 (NMe) CuCl (2) have been prepared by the reactions of CuCl with the corresponding phosphoranimines Ph3PNPh and 2.3-bis(triphenylphosphoranylideneamino)maleic acid N-methylimide, respectively. Both com-plexes were characterized by their IR spectra as well as by crystal structure determinations.
Ph3PNPh · CuCl (1): space group P1, Z = 4, 3639 independent observed reflexions, R = 0.038. Lattice dimensions (18 °C): a = 1047.6; b = 1251.5; c = 1755 pm; α = 103.43°; β = 97.24°; γ = 101.30°. The compound forms monomeric molecules; the asymmetric unit contains two crystallo-graphically independent molecules. The CuCl molecule is bonded via the N atom of the phos-phoranimine. Bond lengths: Cu-N = 189 pm; Cu-CI = 209 pm; bond angle N - Cu - CI = 177°.
(Ph3P)2N2C4O2(NMe) · CuCl (2): space group Pbca, Z = 8, 5611 independent, observed reflexions, R = 0.069. Lattice dimensions (25 °C): a = 1224.3; b = 1962.5: c = 2994.0 pm. The compound forms monomeric molecules with the CuCl molecule bonded via one of the N atoms of the phosphoranimine groups. Bond lengths: Cu - N = 194 pm; Cu-CI = 212 pm; bond angle N-Cu -CI -175°.
Infrared spectroscopy in combination with a specially developed attenuated total reflection (ATR) flow cell and multivariate analysis was used for the quantitative analysis of beer and other beverages. IR spectra of samples were obtained in the range from below 1000 cm-1 to 4000 cm-1 and subjected to a multivariate analysis based on calibration sets with laboratory reference standards. In the case of beer, this calibration set included 240 beer samples spanning the entire range of ethanol content, extract and CO2. Based on this calibration, an infrared and UV/Vis spectroscopy-based sensor for the quick and quantitative quality control of beer was developed and subjected to extensive tests in breweries. This sensor meets and exceeds all requirements from brewers for the routine control in the production and bottling. Its use for other beverages, for example wine, juices or apple wine, requires only another set of calibration data for the specific beverage.
Dichlorido(3-phenylindenylidene)bis(triphenylphosphane)ruthenium(II) tetrahydrofuran disolvate
(2011)
The RuII atom in the title compound, [RuCl2(C15H10)(C18H15P)2]·2C4H8O, has a distorted square-pyramidal conformation. The P and Cl atoms are at the base of the pyramid and the Ru-Cindenylidene bond is in the axial position. The two Cl ligands and the two phosphane ligands are in trans positions. The Cl-Ru-Cl and P-Ru-P angles are 157.71 (2) and 166.83 (2)°, respectively. The two independent tetrahydrofuran (THF) solvent molecules are disordered. One THF molecule was refined using a split-atom model. The second THF molecule was accounted for by using program PLATON/SQUEEZE [Spek (2009). Acta Cryst. D65, 148-155]. The molecular conformation shows three intramolecular C-H...Cl contacts and two C-H...[pi] interactions while the crystal packing features an intermolecular C-H...Cl contact and two very weak intermolecular C-H...[pi] contacts.
A new procedure for the synthesis of 2-(4-propylphenyl)ethanol is provided. This new procedure significantly reduces side-products as 1-(4-propylphenyl)ethanol and 2-bromoethanol, which are obtained when using the previously known procedure. Only with the new procedure an efficient purification on the large scale needed for avoided-level-crossing muon-spin resonance experiments was possible.
Structural details of the title compound could be derived from an X-ray structure analysis of a crystalline derivative, the nitrobenzoyl ester.
Crystal and molecular structure analysis of the title compound 1, a most electron rich carbosilane, exhibits a shallow boat conformation for the cyclohexadiene ring which is shielded by four bulky Me3Si groups. Multiple hyperconjugative interaction occurs between the two non-conjugated olefinic π systems and the four rather long (192 pm) carbon-silicon o bonds which form an angle of about 34° with the assumed π axis. The HOMO destabilization caused by this unique structural arrangement explains the energetically facile formation and subsequent reactivity of the cation radical 1+ which was found to undergo oxidative desilylation to the aromatic 1,4-bis(trimethylsilyl) benzene precursor in the single electron transfer reaction with TCNE.
[MesnacnacZn(μ-H)]2 (1) was synthesized by reaction of MesnacnacZnI with either an equimolar amount of KNH(iPr)BH3 or an excess of NaH and characterized by multinuclear NMR and IR spectroscopy as well as X-ray diffraction. Two polymorphs of 1 were found and their structures determined on single crystals.
Starting from (MeO)3SiCH2Cl (10) and Ph2(H)SiCH2OH (16), respectively, the (hydroxymethyl)diphenyl(piperidinoalkyl)silanes (HOCH2)Ph2Si(CH2)2NC5H10 (6) and (HOCH2)Ph2Si(CH2)3NC5H10 (8) have been synthesized [10→Ph2(MeO)SiCH2Cl (11)→Ph2(CH2=CH)SiCH2Cl (12)→Ph2(CH2=CH)SiCH2OAc (13)→Ph2(CH2=CH)SiCH2OH (14)→Ph2(CH2=CH)SiCH2OSiMe3 (15)→6; 16→Ph2(H)SiCH2OSiMe3 (17)→8; NC5H10 = piperidino]. N-Quaternization of 6 and 8 with MeI gave the corresponding methiodides 7 and 9, respectively. As shown by IR-spectroscopic studies, compounds 6 and 8 form intramolecular O-H···N hydrogen bonds in solution (CCl4). In the crystal, 6 (space group Pna21; two crystallographically independent molecules) also forms intramolecular O-H···N hydrogen bonds whereas 8 (space group P1̅) forms intermolecular O-H···N hydrogen bonds leading to the formation of centrosymmetric dimers (single-crystal X-ray diffraction studies). The (hydroxymethyl) silanes 6-9 and the related silanols (HO)Ph2Si(CH2)2NC5H 10 (sila-pridinol; 1), sila-pridinol methiodide (2), (HO)Ph2Si(CH2)3NC5H10 (sila-difenidol; 3) and sila-difenidol methiodide (4) were investigated for their antimuscarinic properties. In functional pharmacological experiments as well as in radioligand competition studies, all compounds behaved as simple competitive antagonists at muscarinic M1-, M2-, M3- and M4-receptors. In general, the silanols 1-4 displayed higher receptor affinities (up to 100-fold) than the corresponding (hydroxymethyl) silanes 6-9 . In the (hydroxymethyl)silane series, compound 7 was found to be the most potent muscarinic antagonist [pA2/pKi= 8,71/8,6 (M1), 8,23/7,8 (M2), 8,19/7,8 (M3); pKi = 8,2 (M4)]. In the silanol series, the related compound 2 showed the most interesting antimuscarinic properties [pA2/pKi = 10,37/9,6 (M1), 8,97/8,8 (M2), 9,08/8,8 (M3); pKi = 9,4 (M4)].
The title compound, C30H16N4O4, reveals \overline1 crystallographic and molecular symmetry and accordingly the asymmetric unit comprises one half-molecule. The dihedral angle between the planes of the two geminal benzoxazole rings is 74.39 (5)°. The packing features weak C-H...N and [pi]-[pi] interactions [centroid-centroid distance = 3.652 (1) Å].
Transmetallation and oxidative substitution were utilized to prepare examples of group 14, group 6 and group 10 complexes from lithiated or chlorinated 4,4-dimethyl-2-(2-thienyl) oxazoline or its N-alkylated analogs. Two of the product types (2and 5) can be classified as a-thio or remote carbene complexes, depending on the position (3- or 5-) of attachment to the substituted thiophene ring. Spectroscopic measurements as well as crystal and molecular structure determinations clarified the bonding within the new compounds.
Bis(N,N-diethyl-N′-benzoylselenoureato)lead(II) has been prepared and characterized by single-crystal structure analysis. Pb(C12H15N2OSe)2 crystallizes in the non-centrosymmetric orthorhombic space group Iba2. The cell parameters are a = 13.206(3), b = 20.542(4), c = 10.089(2) A and Z = 4. R = 0.025. The direction of the polar axis was determined unambig uously. Pb(II) is bidentally coordinated to two N,N-diethyl-N′-benzoylselenourea molecules. The coordination polyhedron is a distorted pseudo-trigonal bi-pyramid with one equatorial position occupied by an electron lone-pair. The Pb-Se and Pb-O bond lengths are 2.876(1) and 2.444(4) Å, respectively. In the crystal lattice, each Pb atom also shows interactions with two Se atoms of a neighboring molecule. The Pb-Se distance of that interaction is 3.643 Å.
The title solvated salt, C29H41N2+·Br-·2CH2Cl2 was obtained from the reaction of the Arduengo-type carbene 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-4,5-dimethyl-2H-imidazol-2-ylidene with Si2Br6 in dichloromethane. The complete cation is generated by a crystallographic mirror plane and the dihedral angle between the five-membered ring and the benzene ring is 89.8 (6)°; the dihedral angle between the benzene rings is 40.7 (2)°. The anion also lies on the mirror plane and both dichloromethane molecules are disordered across the mirror plane over two equally occupied orientations. In the crystal, the cations are linked to the anions via C-H...Br hydrogen bonds.
The supersilylated ethene trans-(tBu3Si)HC=CH(SitBu3) (triclinic, P ī) is accessible from the reaction of tBu3SiCHBr2 with nBuLi at −78 °C in THF or Et2 O. The reaction of Li(H2NCH2CH2NH2)C≡CH with tBu3SiBr leads to the formation of (tBu3Si)C≡CH and (tBu3Si)C≡C(SitBu3). X-Ray quality crystals of (tBu3Si)C≡C(SitBu3) (triclinic, P ī) were obtained by recrystallization from hexane. In contrast to the structures of the disilane tBu3Si-SitBu3 and the disiloxane tBu3Si-O-SitBu3, the sterically crowded ethene trans-(tBu3Si)HC=CH(SitBu3) and ethyne (tBu3Si)C≡C(SitBu3) feature dihedral angles of 60° in the solid-state structures.
Pyrazolyl-substituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives have been synthesized by reaction of 1,4-benzoquinone and 1,4-naphthoquinone, respectively, with pyrazole. Cyclovoltammetric measurements have shown that 1,4-benzoquinone possesses the potential to oxidize 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene. The 2,5-bis(pyrazol-1-yl)- 1,4-dihydroxybenzene reacts with air to give quantitatively black insoluble 2,5-bis(pyrazol-1-yl)-1,4- quinhydrone. Black crystals of 2,5-bis(pyrazol-1-yl)-1,4-quinhydrone suitable for X-ray diffraction were grown from methanol at ambient temperature (monoclinic C2/c). The poor yields of pyrazolylsubstituted 1,4-dihydroxybenzene and 1,4-dihydroxynaphthene derivatives can be explained by the formation of insoluble black quinhydrons in the reaction of benzoquinone and naphthoquinone with pyrazole. The dianions of 2-(pyrazol-1-yl)- and 2,5-bis(pyrazol-1-yl)-1,4-dihydroxybenzene react with oxygen to give the corresponding semiquinone anions. 2,5-Bis(pyrazol-1-yl)-1,4-benzoquinone shows two reversible one-electron reduction processes in cyclovoltammetric measurements, whereas pyrazolyl-substituted 1,4-dihdroxybenzene and -naphthene derivatives undergo irreversibile electrontransfer processes.
2,5-Diformylbenzene-1,4-diol (5) is a well-suited starting compound for the preparation of ditopic hydroquinone-based ligands. Here, we report an optimized synthesis of 5 which improves the overall yield from published 7% to 42 %. Three new ditopic Schiff base ligands, 2,5-[iPr2N(CH2)2N=CH]2 - 1,4-(OH)2-C6H2 (8), 2,5-(pyCH2N=CH)2-1,4-(OH)2-C6H2 (9), and 2,5-[py(CH2)2N=CH]2-1,4- (OH)2-C6H2 (10), have been synthesized from 5 and structurally characterized by X-ray crystal structure analysis (py = 2-pyridyl).
To examine their luminescence behavior, two air-stable BN addition compounds were synthesized by the reaction of 5-fluoro-2-(2′-pyridyl)indole with 1,4- and 1,3-bis(bromo(methyl)boryl)benzene, respectively. Both BN adducts are luminescent. Their emission maxima (1,3-substituted BN adduct: 495 nm; 1,4-substituted BN adduct: 497 nm) are comparable with the value (490 nm) of the related mono-borylated benzene species, which is composed of a BPh2 fragment and a 5-fluoro-2-(2′-pyridyl) indole unit. The starting materials 1,4- and 1,3-bis(bromo(methyl)boryl)benzene were accessible by treatment of 1,4- or 1,3-bis(dibromoboryl)benzene with two equivalents of SnMe4. In addition, the results of the X-ray structure analyses of the B,B′-bis-5-fluoro-2-(2′-pyridyl)indolyl-complexed meta-bismethylborylbenzene fragment (9, triclinic, P1̅) as well as of 5-chloro-2-(2′-pyridyl)indole (2, monoclinic, P21/c) and 5-fluoro-2-(2′-pyridyl)indole (1, orthorhombic, Pca21) are reported. The pyridylindole derivatives of this approach were synthesized by an optimized two-step procedure from 2-acetylpyridine and 4-fluoro- or 4-chlorophenylhydrazine hydrochloride.
The thermolabile triazenides M[tBu3SiNNNSiMetBu2] (M = Li, Na) are accessible from the reaction of tBu2MeSiN3 with the silanides MSitBu3 (M = Li, Na) at −78 °C in THF. At r. t. N2 elimination from the triazenides M[tBu3SiNNNSiMetBu2] (M = Li, Na) takes place with the formation of M[N(SiMetBu2)(SitBu3)] (M = Li, Na). X-Ray quality crystals of Li(THF)[N(SiMetBu2)(SitBu3)] (orthorhombic, Pna21) are obtained from a benzene solution at ambient temperature. In contrast to the structures of the unsolvated silanides MSitBu3 (M = Li, Na), the THF adduct Li(THF)3SitBu3 is monomeric in the solid state (orthorhombic, Pna21).
The bis(trimethyl)silylamido complex Na(THF){Fe[N(SiMe3)2]3} and the disilane tBu3SiSitBu3 were obtained from the reaction of Fe[N(SiMe3)2]3 with the sodium silanide Na(THF)2[SitBu3] in a mixture of benzene and THF. Single crystals of Na(THF){Fe[N(SiMe3)2]3} suitable for X-ray diffraction were grown from the reaction solution at ambient temperature (orthorhombic, C2221, Z = 4). The solid-state structure features a contact-ion pair with two short N-Na contacts. The THF adducts {M(THF)2[N(SiMe3)2]2} reacted with 2,2´-bipyridine to give the corresponding complexes {M(2,2´bipy)[N(SiMe3)2]2} (M= Mn; Fe). Their structures (M= Fe: orthorhombic, Pca21, Z = 8; M = Mn: orthorhombic, Pbca, Z = 8) feature monomeric units. The cyclic voltammogram of Fe[N(SiMe3)2]3 revealed a reversible redox transition with the potential of -0;523 V (E½), which was assigned to the Fe(III)[N(SiMe3)2]3 → Fe(II)[N(SiMe3)2]-3 redox transition, whereas the compounds {Fe(THF)2[N(SiMe3)2]2} (Eox = -0;379 V) and {Fe(2,2´bipy)[N(SiMe3)2]2} (Eox = -0;436 V) featured irreversible oxidation waves. The related manganese bis(trimethylsilyl)amido complexes {Mn(THF)2[N(SiMe3)2]2} (Eox = -0;458 V) and {Mn(2,2´bipy)[N(SiMe3)2]2} (Eox = -0513 V) also underwent irreversibile electron transfer processes.
Single crystals suitable for X-ray diffraction of (tBu2P)3Ga (monoclinic, space group Cc) were obtained from GaCl3 and two equivalents of Li[PtBu2] at room temperature in benzene. The phosphanylgallane (tBu2P)3Ga was also produced via a one-pot approach by reaction of GaCl3 with three or more than three equivalents of Li[PtBu2]. However, treatment of one equivalent of GaCl3 with one equivalent of Li[PtBu2] and subsequent protolysis yielded [tBu2PH2][tBu2P(GaCl3)2 - Li(Cl3Ga)2PtBu2]. Single crystals of this phosphonium salt (monoclinic, space group Cc) were obtained from benzene at room temperature.
The donor-free silanimines tBu2Si=N-SiRtBu2 (R = tBu, Ph), which are prepared from tBu2ClSiN3 and NaSiRtBu2 at −78 ◦C inBu2O, decompose in benzene at room temperature with the formation of isobutene. Products of ene reactions of isobutene and tBu2Si=N-SiRtBu2 (R = tBu, Ph) are formed. X-Ray quality crystals of H2C=C(CH2SitBu2-NH-SiPhtBu2)2 (monoclinic, space group C2/c, Z = 4) were grown from a benzene solution at ambient temperature, whereas single crystals of H2C=C(CH2SitBu2-NH-SitBu3)2 (monoclinic, space group P21, Z = 2) were obtained by recrystallization from THF.
Supersilylated tetrachlorodigermane (tBu3Si)Cl2GeGeCl2(SitBu3) and trigermoxetane (tBu3Si)3Ge3Cl3O
(2004)
In contrast to the tetrachlorodigermane (tBu3Si)Cl2Ge-GeCl2(SitBu3), the cis,transcyclotrigermane (tBu3SiGeCl)3 is sensitive to oxygen. Its treatment with O2 at ambient temperature leads to the trigermoxetane (tBu3Si)3Ge3Cl3O. According to an X-ray structure analysis of single crystals consisting of cocrystallized (tBu3Si)3Ge3Cl3O and (tBu3Si)Cl2Ge-GeCl2(SitBu3) the trigermaoxetane contains an almost planar Ge3O-ring while the tetrachlorodigermane (tBu3Si)Cl2Ge- GeCl2(SitBu3) possesses a Si-Ge-Ge-Si chain which is exactly all trans,
Organodisulfide radical cations R2S2′⊕ and R2C2S2 ′⊕ can be generated from aliphatic as well as aromatic cyclic polysulfides in AlCl3/H2CCl2 solutions and characterized by their ESR spectra. Examples presented are the oxidations of 1,2,3-trithiolanes to 1.2-dithiolane radical cations, in which energetically favored planarized 3 electron/2 center bonds are formed.
Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties. Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K. Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or 1-bromopropene-2. HCl elimination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene. Most interesting, however, is the ring opening of monobromo cyclobutane to 1-bromo-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chemisorbed surface carbene at Raney nickel. The formation of hexadiene-1,5 as a by-product in the HCl elimination of 1-chloropropane, i. e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.
Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties. Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K. Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or l-brom opropene-2. HCl elim ination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene. Most interesting, how ever, is the ring opening of monobromo cyclobutane to 1-brom o-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chem isorbed surface carbene at Raney nickel. The formation of hexadiene-1,5 as a by-product in the HCl elim ination of 1-chloropropane, i.e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.
The enantioselective synthesis of 2-aryl-substituted 2,3-dihydroquinolin-4-ones, a class of heterocyclic compounds with interesting biological activities, has been achieved through a Brønsted acidcatalyzed enantioselective intramolecular Michael addition. The products are available in moderate to high yields and with good enantioselectivities.
1,4-Bis(trimethylsiloxy)benzene has been crystallized both by vacuum sublimation and from «-heptane solution, which each yielded colourless plates with identical monoclinic unit cell dimensions (P2/n, Z = 4). The conformation of C[ symmetry shows the two (H3C)3SiO-substituents to be conrotationally twisted around the O-( C6H4)-O axis by dihedral angles o f ± 60°. According to the photoelectron spectroscopic ionisation pattern and its Koopmans’ assignment, IEVn = -εJAM 1, by AM 1 eigenvalues, the gas phase structure should also be of C, symmetry. The results of geometry-optimized MNDO , AM 1 or PM 3 calculations for the monosubstituted derivative H5C6-OS i(CH3)3 are compared with respect to the quality of their fit to the measured data.
Reduction of naturally occurring para-and ortho-benzoquinone derivatives M to their respective radical anions M·⊖ can be accomplished under largely aprotic conditions either by cautious low-temperature reaction in THF containing an excess of (2.2.2) cryptand at a potassium mirror or by using the "mild" single electron transfer reagent tetrabutylammonium boranate R4N⊕BH4⊖ in DMF. On addition of soluble alkali tetraphenylborates Me⊕[B(C6H5)4]⊖ , their hitherto unknown radical ion pairs [M·⊖ Me⊕]· and/or triple ion radical cations [Me⊕M·⊖Me⊕]·⊕ form, which might be of biological relevance in molecular carrier and "turn off -turn on" switch processes. On addition of metal perchlorates Me⊕n(ClO4⊖)n with multiply charged counter cations Me⊕n the respective paramagnetic species [M·⊖Me⊕n]·(n-1)⊕ result. Assuming exclusive one-electron transfer reductions without any redox fragmentation reactions, ESR, ENDOR and GENERAL TRIPLE spectra are presented and discussed for the following radical anions and radical ion pairs: mitomycin C (M·⊖ and [M·⊖Mex⊕]·(x-1)⊕ with Me⊕ = Li⊕, Na⊕), streptonigrine (M·⊖ and [M·⊖Lix⊕]·(x-1)⊕), Entobex® (M·⊖ and [M·⊖Me⊕n]·(n-1)⊕ with Me⊕n = Li⊕, Na⊕, Cd⊕⊕, (H5C6)2Tl⊕) as well as brucinequinone ([M·⊖ Me⊕n]·(n-1)⊕ with Me⊕n = Li⊕, Cd⊕⊕, Pb⊕⊕, La⊕⊕⊕).
From the electron and proton transfer equilibria network of quinones in solution a novel intermediate can be prepared by deprotonation of 2,5-bis(trimethylsilyl)hydroquinone to its monoanion using sodium metal. The sodium salt crystallizes in polymer strings connected via O⊖···(H)O hydrogen bridges, which are capped additionally by twofold dimethoxy-ethanesolvated Na⊕ countercations. The single crystal structure determination reveals one of the shortest O⊕ ··· HO distances observed so far of only 246 pm. MNDO calculations further confirm the assignment of hydroquinone monoanion building blocks in the polymer chain. For structural comparison as well as for attempts of its sodium reduction, 2,5-bis(trimethylsilyl)-p- benzoquinone has been synthesized. Its single crystal structure is reported, which does not show any cyanine distortion.
The structurally different radical anions M⊖ of peralkylated 1-sila-2,5-diazacyclopentane-3,4-dithione and of tetrakis(isopropylthio)-p-benzoquinone are generated by reduction with potassium/2.2.2-cryptand under aprotic conditions in THF solution. On addition of Li⊕B(C6H5)4⊖, both form hitherto elusive sulfur-containing contact ion pairs, which are characterized by their ESR/ENDOR spectra.
The radical anion of dimesityltetraketone (ERed, I = -0.40 V) is easily generated in THF by potassium mirror/[2.2.2]-cryptand reduction. Its contact ion pairs with Na⊕, Cs⊕ and Ba⊕⊕ counter cations, prepared in THF solution by single electron transfer from the respective metals, are characterized by their ESR/ENDOR spectra, which exhibit temperature-dependent metal couplings of aNa⊕ = 0.061 mT (190 K), aCs⊕ = 0.021 mT (190 K), and aBa⊕⊕ = 0.145 mT (295 K).
Ion pairs of 1,10-phenanthrolin-5,6-dione radical anion [M · ⊖Me⊕n] ·⊕(n−1) with Me⊕n = Mg⊕⊕, Ca⊕⊕, Sr⊕⊕, Zn⊕⊕, Cd⊕⊕, Pb⊕⊕ and La⊕⊕⊕ are advantageously prepared in aprotic DMF solution containing appropriate metal salts Me⊕nX⊖ by using the ‘mild’ single-electron reducing agent tetra(n-butyl)ammonium-boranate R4N⊕BH4⊖ . For comparison, the ‘naked’ radical anion with the largely interaction-free [K⊕(2.2.2)-cryptand]⊕ counter cation is chosen, which is formed on reduction with potassium in THF solution of (2.2.2)-cryptand. Addition of excess Na⊕[B(C6H5)4]⊖ to the reduction solution only yields a solvent-separated ion pair (M · ⊖)DMF ··· (Na⊕)DMF, whereas in the presence of multiply charged counter cations Me⊕n the respective contact ion pair radical cations [M · ⊖Me⊕n] · ⊕(n−1) are formed. Their g values decrease with increasing nuclear charge of Me⊕n and their metal-s-spin densities increase with the effective counter cation charge n⊕/rMe⊕n. The ESR /ENDOR data recorded suggest Me⊕n complexation by the δ⊖OC -COδ⊖ chelate tongs and the ion pair stability, which is modified by the dielectric properties of the solvent used, may be rationalized by the Coulombic attraction between the radical anion M · ⊖ and the counter cations Me⊕n.
Di(methylthio)acetylene H3CS-C≡C-SCH3 reacts with S2C12 in AlCl3/H2CCl2 solution to the tetra(thiomethyl)thiophene radical cation (H3CS)4C4S·⊕ and with H3CSCl to the tetra(thiomethyl)ethene radical cation (H3CS)2C·=⊕C(SCH3)3. Their ESR spectra are assigned by comparison with literature data or those of analogous products obtained from other acetylene derivatives R-C≡C-R with R = SCH2CH3, CH3, C6H5 as well as based on HMO arguments. The possible course of the oxidative sulfuration is discussed.
Cyclovoltammetric measurements of solutions containing the rather basic tetra-(2′-pyridyl)pyrazine allow to detect even traces of water and thus can be used as a touchstone for aprotic (cH⊕ < 1 ppm) conditions. On exchange of the “innocent” tetrabutylammonium R4N⊕ as supporting electrolyte cation by “interactive” ones such as Li⊕) or Na⊕, considerable changes in the reduction potentials are observed due to ion pair formation.
Conditions for ENDOR measurem ents of organosulfur radical cations are discussed and tested. The one electron oxidation of a variety of aromatic sulfur com pounds comprising benzene-1,2-dithiole, 1,4-dithiine, thianthrene and diphenylsulfide derivatives as well as 33S isotope-marked bis(2,5-dimethoxyphenyl)disulfide is accomplished using the oxygen-free, powerful and selective AlCl3/H2CCl2 reagent. Partly with substantial structural changes, paramagnetic M⊕ species of 1,2-benzodithiete, 1,4-dithiine, thianthrene and diphenyl sulfide result. Their temperature-dependent ENDOR signal patterns provide numerous information e.g. on radical cation structure and dynamics, on the rather high sulfur spin populations or on the spin rotation interaction dominated relaxation behaviour. Accordingly, to obtain optimum ENDOR effects in organosulfur radical cations low temperature measurements are required, and especially for still undiscovered 33S ENDOR couplings, small g factor anisotropies and 33S spin densities appear to be necessary.
For the first time, 107,109Ag ENDOR measurements in solution are reported. In addition, the formation of the known paramagnetic contact ion pair [Ag⊕(PR3)2(R2H2C6O2·⊖] on reduction of 3,5-di(tert-butyl)-o-benzoquinone in THF solution containing soluble silver salts and triphenylphosphine is studied by cyclic voltammetry.
Semiquinone radical anions are prototype compounds for contact ion pair formation with metal counter cations. In order to investigate the still open question whether bulky alkyl groups can sterically interfere, diphenoquinone derivatives O=C(RC=CH)2C=C(HC=CR)2C=O with R = C(CH3)3, CH(CH3)2 and CH3 have been selected and the following ESR/ENDOR results are obtained for the alkaline metal cations: The tetrakis(tert-butyl)-substituted radical anion only adds Li⊕ and Na⊕, while K⊕ forms no ion pair. The 3,3ʹ,5,5ʹ-tetra(isopropyl)diphenoquinone radical anion is accessible to all cations Me⊕, although Rb⊕ and Cs⊕ seem to be present solvent-separated in solution. The tetramethyl-substituted radical anion unfortunately polymerizes rapidly. Additional information concerns the ESR/ENDOR proof for ion triple radical cation formation [Li⊕ M•⊖Li⊕]•⊕, or the difference in the coupling constants upon Me⊕ docking at one δ⊖O=C group, suggesting that about 87% of the spin density is located in the cation-free molecular half of the diphenoquinone radical anion. Based on the wealth of ESR/ENDOR information, crystallization of the contact ion pairs and their structural characterization should be attempted.
The one-electron transfer to large π-delocalized hydrocarbons provides an interesting possibility to crystallize solvent-separated ion-pair salts containing optimally solvated cations. Accordingly, the reduction of 9.9′-bianthryl in aprotic 1.2-dimethoxyethane (DME) solution at a sodium metal mirror allows to grow dark blue, brick-like crystals of its radical anion and threefold DME-solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AM 1 enthalpy hypersurface calculations based on the structural data, the torsion angle between 60° and 120° is determined by the lattice packing and the negative charge is -π-delocalized predominantly within only one anthracene subunit. The counter cation [Na⊕(DME)3], reported only three times so far, shows a sixfold propeller-like coordination of approximate D3 skeletal symmetry with contact distances Na⊕···O between 232 and 243 pm and angles ≮ONa⊕O varying between 69° and 159°. Due to the small repulsion between the chelating DME molecules, the isodesmically calculated Na⊕ solvation enthalpy is more negative than that of the analogous tetrahydrofuran complex [Na⊕(THF)6] - as confirmed by the laboratory experience that salts of less stable anions are preferentially crystallized from a strongly cation solvating DME solution.
The sodium salt of the most simple polynitro-substituted hydrocarbon anion. Na⊕⊖C(NO2)3, (for a hazard warning cf. [***]) crystallizes from ether solutions without and with addition of 18-crown-6 either in a polymer band. [(Na⊕⊖C(NO2)3)dioxane]∞, or as a solvent- separated ion pair, [(Na⊕/18-crown-6)(THF2]⊕[(Na⊕/18-crown-6)(O2N-C⊖(NO2)2)2]⊖. The Na⊕ cations are each 8-fold coordinated in hexagonal bipyramidal arrangement. According to extensive quantum-chemical calculations based on the structure coordinates, the formation of these novel salts can be traced back to the charge distribution in the anions ⊖C(NO2)3. which due to negatively charged oxygen centers are favorable complex ligands. The structure determining effects of solvation are discussed.
The following mixed-stack donor/acceptor complexes {D···A}∞ have been crystallized and their structures determined: {hexamethylbenzene···3,5-dicyano-1-nitrobenzene hexamethylbenzene···3,5-dinitro-1-cyanobenzene}∞, {pyrene···3,5-dinitro-1-cyanobenzene}∞, {anthracene···(3,5-dinitro-1-cyanobenzene)2}∞, {N,N-dimethylanilin···3,5-dinitro- 1-cyanobenzene}∞ and { 1-3-phenylenediamine···3,5-dinitro-1-cyanobenzene}∞. Their lattice packing consists of parallel layers, which contain either donors and acceptors as for hexamethylbenzene and pyrene or composite ones as in the 1:2 complex of anthracene with each one of the acceptors above and below its peripheral rings. The isostructural hexamethylbenzene complexes exhibit almost identical packing coefficients as well as a hexagonal coplanar arrangement of the C6(CH3)6 donors. Weak intermolecular van der Waals interactions are also observed between antiparallel cyano substituents. The interplanar n distances range between 334 and 353 pm, i. e. around 340 pm of two van der Waals n radii. In none of the complexes, however, significant structural changes in either the donor or the acceptor components due to the complex formation are observed. In both the crystals as well as in solution, the donor/acceptor complexes exhibit colours between yellow and red; their long-wavelength charge transfer absorption maxima, therefore, correspond to a lowering in excitation energy of only up to 1 eV relative to that of the components. The different charge transfer in the ground and the CT excited states is also discussed referring to other data such as vertical first ionization energies or interplanar distances {D···A}, as well as to results from semiempirical calculations based on the crystal structure data determined and including approximate configuration interaction.
Tetraphenyl-p-benzoquinone, according to its single crystal structure, shows some steric congestion: its quinone ring is distorted by 7° to a chair conformation, and its phenyl substituents are twisted around their CC axes between 46° and 72°. The half-wave reduction potentials of -0.57 and -1.25 V in acetonitrile confirm negligible π interaction of the phenyl substituents. Addition of alkalimetal tetraphenylborate salts lowers the second reduction potential due to contact ion formation, which can be confirmed by UV/VIS spectra recorded under aprotic conditions. Extensive ESR/ENDOR investigations prove the formation of the following species in THF solution: Tetraphenyl-p-benzosemiquinone radical anion contact ion pairs [M·⊖ Me⊕solv]' (Me⊕: Li⊕, Na⊕, Rb⊕, Cs⊕) and contact triple ion radical cations both with identical cations [M·⊖ (Me⊕solv)2]·⊕ (Me⊕: Li⊕, Na⊕, Cs⊕) and different cations [M·⊖ (Li⊕solv)(Me⊕solv)]·⊕ (Me⊕: Na⊕, Cs⊕). Addition of crown ethers can lead to external solvation of the Me⊕ counter cations, whereas cryptands form internal solvation complexes. The radical anion of 2,6-diphenyl-p-benzosemiquinone adds cations at its phenyl-free molecular half. The radical anion salt [tetraphenyl-p-benzosemiquinone·⊖ (Na⊕(tetrahydropyrane) 2)] could be crystallized and its structure determined at 200 K. In agreement with the Hirota sign rules for contact radicals in solution, the Na⊕ ion is found 62 pm above the π plane and 29° outside the axis of the CO bound, which is elongated due to one-electron reduction by 5 pm to 127 pm.
The following mixed-stack donor/acceptor complexes {D · · · A }∞ have been crystallized and their structures determined: { 1 ,2,4,5-tetramethylbenzene · · · tetrabromo-p -benzoquinone}∞ , {hexamethylbenzene · · · tetrabromo-p-benzoquinone}∞ , { ( 1 ,2 ,4,5-tetramethyl-benzene)2 · · · tetrachloro -p -benzoquinone}∞ , {pyrene · · · tetrafluoro-p-benzoquinone}∞ , {pyrene · · · tetrabromo-p-benzoquinone}∞ and {perylene · · · tetrabromo-p-benzoquinone}∞ . They exhibit an interesting lattice packing, especially the 2:1 tripeldecker sandwich of tetrachloro-p-benzoquinone, which crystallizes in a herringbone pattern. Their interplanar distances are around 340 pm, i. e. two van der Waals π radii. None of them , however, exhibits in neither the donor nor the acceptor components significant structural changes due to complex formation. Their colours range from orange-red to black in the crystal and to green in H2CCl2 solution. Their long-wavelengths charge transfer absorption maxim a correspond to a lowering in excitation energy of up to 2 eV relative to that of the components. The different charge transfer in the ground and excited states of the donor/acceptor complexes investigated is further discussed referring to data such as cyclovoltammetric reduction potentials as w ell as to results from semiempirical calculations based on the crystal structure data determined and including configuration interaction.
In an especially designed and sealed glass apparatus, a combination of UV/VIS and ESR spectroscopy measurements are performed to follow electron transfer reactions in aprotic (cH⊕ < 0,1 ppm) solution. For the sodium metal reductions of the tetracyano-substituted title compounds, the novel technique provides the following detailed information: 1,2,4,5- tetracyanobenzene is uniformly reduced to its radical anion, for which additional geometryoptimized MNDO calculations predict an already significant cyanine disortion. For 7,7,8,8- tetracyano-p-quinodimethane, UV/VIS band shape analysis allows to detect in the saturated THF reduction solution the 16300 cm-1 absorption of the donor/acceptor complex formed in the equilibrium TCNQ·⊖ + TCNQ ⇆ {TCNQ·⊖···TCNQ}, which according to a literature search has been crystallized and structurally characterized in paramagnetic salts such as [Me2⊕ (TCNQ·⊖)2(TCNQ)].
The compound [(PyH)3Br][AlBr4]2 is formed by melting stoichiometric amounts of AlBr/PyHBr in a ratio of 2:3. It crystallizes in the orthorhombic space group Pbca with lattice constants a = 1365.5(2), b = 1616.0(2), c = 2783.7(3) pm, Z = 8, Dc = 2.21 g/cm3. The structure was solved from 2810 diffractometer measured intensities (Cu -Kα radiation) and refined to Rw (F) = 0.071. The cation shows three pyridinium ions attached via N - H - Br hydrogen bonds to a central bromide ion. The N - Br distances are 321(1), 321(2) and 332(2) pm.
Crystals of lemon yellow dipotassium nitranilate and of yellow disodium nitranilate dihydrate have been grown and their structures determined at 290 and 200 K. The six-member- ed, O2N-disubstituted rings show a pronounced cyanine distortion with all four CO bonds identical and the two (OCC(NO2)CO)⊖ chains connected by single CC bonds of each 156 pm length. In the anhydrous K⊕ salt, the ring is planar, but in the Na⊕ hydrate salt it exhibits a twist conformation. Quantum chemical calculations allow to reproduce the structure in every detail, demonstrate strong charge alternation along the cyanine chains with considerable delocalization into the O2N acceptor substituents, and suggest that the rather long connecting CC bonds contain positively charged carbon centers on both ends. In addition, metal ion coordination effects as well as the rather high pKa value of nitranilic acid are rationalized.
The structures of seven di- or tetrasubstituted p-benzoquinone derivatives O=C(XC=CH )2C=O and O=C(XC=CX)2C=O with substituents X = -OCH3, -N(CH2)5, - N(CH2CH2)2O, -Cl, -CN and -⊕N(HC=CH)2C-N(CH3)2 are presented and discussed in comparison with published ones substituted by X = -Si(CH3)3, -C6H5, -N(CH3)2, -⊕N(HC=CH)2CN(CH3)2, -O⊖ , and - NO2. Based on the introduction, in which halfwave-reduction potentials, geometry-optimized quantum-chemical calculations on substituent perturbation and known structural data of p-benzoquinone derivatives are used to characterize their molecular ground states. The structural changes indicate how substituent perturbations might be rationalized. Of the categories defined - imperturbed, donor, donor/acceptor and acceptor perturbed - the donorsubstituted p-benzoquinones do exhibit the largest differences, often called cyanine distorsion. In very satisfactory agreement with extensive semiempirical calculations, all effects determined experimentally are discussed in terms of varying charge distribution. With respect to the biochemical importance of p-benzoquinone derivatives, this first structural summary points out important facets.
Chelate complexes of 1,2-dimesitoylbenzene radical anion with alkali metal cations exhibit in aprotic solution extremely large ESR /ENDOR metal coupling constants. For rationalization, structures of both the neutral molecule (H3C)3H2C6 - CO - C6H4 - CO - C6H2(CH3)3, in which the two carbonyl groups are twisted out of the benzene ring plane by dihedral angles of ± 3̄7̄°, and a sodium contact ion quadruple have been determined. One of the dimers [dimesitoylbenzeneH⊖ (Na⊕H2N H2C - CH2NH2)]2, although generated by Na metal mirror reduction of 1,2-dimesitoylbenzene in aprotic DME solution with added ethylendiamine for better electron transfer, surprisingly contains two 245 pm short (!) hydrogen bridges ⊖O ··· (H)O and in addition two solvation bridges e ⊖O ··· Na⊕(H2NH2C - CH2NH2) ··· O⊖. Results of MNDO calculations based on the experimental coordinates support the proposed concept.
UV/VIS and ESR spectra of electron transfer reaction products in aprotic (cH⊕ < 0,1 ppm) solution can be measured in an especially designed and sealed glass apparatus and provide information on unknown facets of the microscopic pathway through the network of interdependent equilibria. For tetraphenyl-p-benzoquinone in tetrahydrofuran, single-electron reduction by a sodium metal mirror produces a red solution and, unexpectedly, after addition of 2.2.2. cryptand, contact with a potassium metal mirror generates a green (!) one. For both, ESR/ENDOR spectra prove the presence of tetraphenyl-p-benzoquinone radical anion. UV/VIS measurements provide the clue: In the equilibrium revealed by repetetive spectra recording, M·⊖solv + Me⊕solv ⇄ [M·⊖···Me⊖]solv, the radical anion is green (vm = 16900 cm-1) and the contact ion pair red (vm=18900 cm-1 ). On ion pair formation, therefore, the excitation energy of the radical anion increases by 0.25 eV.
The isobaric melting and boiling diagrams for the systems: trimethylchlorosilane/pyridine and trimethylchloromethane/pyridine are reproduced. Some measurements of the molar volume of mixtures between trimethylchlorosilane and pyridine and trimethylchloromethane and pyridine are reported. For both systems the molar excess volume has been calculated as a function of the mole fractions
The isobaric melting and boiling diagrams for the systems: dimethyldichlorosilane/pyridine and 2,2-dichloropropane/pyridine are reproduced. The existence of the incongruently melting addition compounds (CH3)2SiCl2 · (Pyridine)2 and [(CH3)2CCl2]3 · Pyridine could be proved. Some measurements of the molar volume of mixtures of pyridine and dimethyldichlorosilane, and pyridine and 2,2-dichloropropane are reported. For both systems the molar excess volume has been calculated as a function of the mole fractions.
The isobaric melting and boiling diagrams for the systems: pyridine/methyltrichlorosilane and pyridine/1,1,1-trichloroethane are reproduced. The existence of the congruently melting addition compound CH3SiCl3· (Pyridin)2 could be confirmed. Some measurements of the molar volume of mixtures between pyridine and methyltrichlorosilane and pyridine and 1,1,1-trichloroethane, respectively, are reported. For both systems the molar excess volume and for the system pyridine/methyltrichlorosilane the molar excess enthalpie have been calculated as a function of the mole fractions.
By analyzing the phase diagrams of some trimethylhalogenosilane/pyridine- and methyl-trichlorosilane/lutidine-systems the existence of the incongruently melting addition compounds Me3SiF · (Pyridine)2, Me3SiCl · (Pyridine)2, MeSiCl3, · (2.5-Lutidine)2, MeSiCl3, · (2.6-Lutidine)2, (MeSiCl3)2 · 3.5-Lutidine, and the congruently melting compounds MeSiCl3 · 2.4-Lutidine, MeSiCl3 · (3.5-Lutidine)2 was proven.
By analyzing the DSC heating curves and the resulting phase diagrams of the systems of dibromodimethylsilane and 2-, 3- or 4-methylpyridine the existence of the congruently melting addition compounds ((CH3)2SiBr2)2 · (3-methylpyridine) and (CH3)2SiBr2 · (4-methylpyridine)2, and the incongruently melting addition compounds ((CH3)2SiBr2)2 · (2-methylpyridine) and ((CH3)2SiBr2)2 · (4-methylpyridine) could be proved.
Phase equilibrium studies of the Lewis acid-base systems AlCl3/PyHBr and AlBr3/PyHI indicate the existence of congruently melting compounds of the molar ratios 1:1 and 2:3.
These results are quite different from those of our studies of the AlCl3/PyHCl and the AlBr3/PyHBr systems, in which four compounds in the molar ratios 1:1, 1:2, 1:3, and 2:3 could be detected.
The melting point of pyridinium iodide observed at 284,8 °C (decomp.) differs from the previously reported one.
Trimethylbromosilane and 3,4-lutidine form a 1:1 compound which is stable at room temperature. Single crystals of this compound can be isolated by sublimation. It crystallizes in the orthorhombic space group P 2121,21, with lattice constants a = 737,08(9) pm, b = 1295,7(1) pm, c = 1318,8(3) pm. The crystal structure was refined to Rw = 0,042 and proves an ionic structure.
The title compound has been prepared by the reaction of N-trimethylsilyl-iminotriphenylphos-phorane with copper(II) chloride in boiling CCl4 /C2H5OH, and forms moisture sensitive crystals, which are green in transmittance and black in reflexion. [Me3SiNPPh3 · CuCl2 ] 2 was characterized by its IR spectrum as well as by a crystal structure determination (4197 observed, independent reflexions, R = 0.049). The lattice dimensions are at 20 °C: a = 1102.7. b = 1407.3. c = 1560.2 pm; β = 94.27°; space group P21/n with two formula units in the unit cell. The complex consists of centrosymmetric, dimeric molecules with a planar Cu2 Cl2 ring (Cu-CI bond lengths 229 and 231 pm). A terminally bonded CI atom (Cu-CI = 221 pm) and the N atom of the Me3SiNPPh3 ligand (Cu-N = 198.5 pm) complete the coordination number four of the nearly planar surroundings of the Cu atoms.
[MONCl3 · NC - C2Cl3]2 has been prepared by the reaction of MONCl3 with trichloromethyl isocyanidedichloride, CCl3NCCl2 , in CH2Cl2 suspension. The compound forms redbrown. mois-ture sensitive crystals, which were characterized by their IR spectrum as well as by a crystal structure determination (2482 independent observed reflexions, R = 0.048). Crystal data (-70 °C): Space group P21/c, Z = 2, a = 674.2(2); b = 2128.2(11); c = 786.0(4) pm: β = 102.81(3)°. [MONCl3 • NC-C2Cl3]2 forms centrosymmetric dimeric molecules via chloro bridges with Mo-Cl bond lengths of 240.7 and 276.0 pm. The longer MoCl bond of the MOCl2MO ring is caused by the trans influence of the nitride ligand; the MoN bond length of 167 pm corresponds with a triple bond. The 2,3,3-trichloroacrylnitrile ligand is bonded by its nitrogen atom with a bond length of Mo -N = 216 pm; the Mo-N≡C-C sequence is almost linear with a remarkable short C-C bond of 143.0 pm.
(η5-C5H5)Fe(CO)2Br reacts with Se(SiMe3)2 to form the title compound 1, which has been characterized by X-ray crystal structural analysis. 1 crystallizes in the space group P212121 with 4 formula units per unit cell. 1 consists of [Se{Fe(CO)2(C5H 5)}3]+- cations and [Fe4Se4Br4]2--anions, the latter with a heterocubane structure.
[η5-CpMCl4] (M = Nb, Ta) reacts with E(SiMe3)2 (E = S, Se) to form different multinuclear clusters. The cation [Cp8Ta6S10]2+ (1) consists of a planar Ta2S2-ring of which each Ta is coordi-nated to two Cp2TaS2-fragments. [Cp4Ta4S13] (3) can be derived from [Cp3Ta3S7Cl2] (2) by addition of a CpTaS6-unit to a triangle of Ta-atoms bridged by S- and S2-ligands. The niobium atoms in [Cp3Nb3Se5Cl2] (4) arrange in a chain structure with Nb coordination numbers varying from 4-6.
Zur Reaktion von [(η3-C4H7)PdCl]2 mit Se(SiMe3)2. Die Kristallstruktur von [(η3-C4H7)6Pd6Se3]
(1988)
[(η3-C4H7)PdCl]2 reacts with Se(SiMe3)2 to form [(η3-C4H7)6Pd6Se3] (1). 1 has been characterized by X-ray crystal structure analysis. It contains a distorted trigonal prismatic Pd6-cluster. Three faces of the Pd-prism are occupied by μ4-Se ligands. 1 crystallizes in the space group Pnma with 4 formula units per unit cell. The lattice constants at 200 K are: a = 1175.1(8), b = 1611.4(12), c = 1720.3(12) pm.
The title compound has been prepared by the reaction of N,N,N′-tris(trimethylsilyl)benzamidine with tantalum pentachloride in CH2Cl2 suspension, forming amber-coloured, moisturesensitive crystals, which were characterized by an X-ray structure determination. Space group P 21/n, Z = 2, 4895 observed independent reflexions, R = 0.059. Lattice dimensions (-65°C): a = 1165.2(6), b = 1335.4(6), c = 1629.0(7) pm, β = 93.23(4)°. The complex forms centrosymmetric molecules dimerized via chloro bridges TaCl2Ta with TaCl bond lengths of 247.2(2) and 277.1(2) pm, the longer one being in trans-position to the imido group, which can be formulated as [xxx] (bond lengths Ta=Ν = 183.5(8), C=N = 134(1) pm, bond angle TaNC = 162.7(7)°).
The reaction of [Cp2TiCl2 ] with E(SiMe3)2 leads to dinuclear Ti complexes. In [Cp3Ti2S2Cl] (1) and [Cp3Ti2Se2Cl] (3) two μ2 -S(Se) ligands bridge the Cp2Ti and CpTiCl units, respectively in contrast to these, [Cp4Ti2S2Cl2] (2) contains a μ2η1-S2 bridge connecting two Cp2TiCl fragments. A similar reaction of [CpTiCl3] with Se(SiMe3)2 leads to the tetranuclear cluster [Cp4Ti4Se7O] (4). 4 consists of a Ti4 -tetrahedron which encloses an oxygen atom.
The N,N'-bis(trimethylsilyl)benzamidinato complexes [C6H5 -C(NSiMe3)2MCl3]2(M = Ti. Zr) have been prepared by the reactions of N,N,N'-tris(trimethylsilyl)benzamidine [C6H5-C(NSiMe3)N(SiMe3)2] with titanium tetrachloride, and zirconium tetrachloride, respec-tively. The compounds form moisture sensitive, dark red (Ti) and white (Zr) crystals, which were characterized by crystal structure determinations. [C6H5-C(NSiMe3)2TiCl3]2 : space group P21/rc. Z = 2, 4373 observed independent reflexions, R = 0.034. Lattice dimensions (-90 °C): a - 959.0(8); b = 1196.5(8); c = 1770.9(11) pm; β = 93.79(4)°. [C6H5-C(NSiMe3)2ZrCl3]2 : space group P21/n. Z = 2, 3160 observed independent reflexions, R = 0.031. Lattice dimensions (-90 °C): a = 971.6(7); b = 1222.2(9); c = 1792.9(10) pm; β = 93.51(5)°.
Both complexes crystallize isotypically, forming centrosymmetric dimeric molecules via chloro bridges with bond lengths of 242.0 and 253.8 pm (Ti), and of 253.7 and 264.9 pm (Zr). The metal atoms complete their distorted octahedral surroundings with two chlorine ligands and the nitrogen atoms of the chelating amidinato ligand. The N atoms of the amidinato group are in equatorial and axial positions. This accounts for the different metal-nitrogen bond lengths of 207 pm (ax) and 199 pm (eq) in the titanium compound and 219 pm (ax) and 214 pm (eq) in the zirconium complex.
W2NCl7 has been prepared by the reaction of tungsten pentachloride with the bromide of Millon's base, [Hg2N]Br, in boiling CCl4. The product forms a dark brown, moisture sensitive crystal powder (μeff = 0.7 B.M. at 21 °C). With phosphoryl chloride, the complex W2NCl7·2 POCl3 is formed. The reaction with chlorine leads to the mixed-valenced W(V)/W(VI) complex W2NCl8 (μeff = 0.5 B.M. at 22 °C), which reacts with tetraphenylphosphonium chloride in CH2Cl2 to form (PPh4)2[W2NCl10] ·2CH2Cl2. The reactions of W2NCl7 with PPh4Cl in molar ratios in CH2Cl2 solution lead to several complexes; one of them was identified bv X-ray diffraction methods to be (PPh4)2[W3Cl9(μ3-N)(0)(μ2-NCl)]2 ·1,5 CH2Cl2, which forms black crystals. The compound crystallizes monoclinically in the space group P21/n with two formula units per unit cell (7318 observed, independent reflexions, R = 0.083). The lattice dimensions are (20 °C): a = 994.4; b = 2673; c = 1518.2 pm; β = 101.00°. The compound consists of PPh4⊕ cations and centrosymmetric anions [W3Cl9(μ3-N)(O)(μ2-NCl)]22⊕. The tungsten atoms form a scalene triangle with WW bond lengths of 282 and 278 pm, respectively. The hypothenuse of this triangle is a nearly linear W - N -W bridge with WN distances of 199 and 182 pm. One of the WW edges is bridged by a μ-NCI group with WN bond lengths of 196 und 189 pm. respectively.
[Na-15-Crown-5][MoF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with MoF4(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR and 19F NMR spectra as well as by an X-ray structure determination. Crystal data: space group P21/n, Z = 4 (3736 observed, independent reflexions, R = 0.034). Lattice dimensions at -70 °C: a = 823.5(4). b = 1612.2(9), c = 1383.4(8), β = 99.35(3)°. The compound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether molecule and by two fluorine ligands of the [MoF5(NCl)]- unit with Na-F distances of 228.3 and 249.6 pm. The Mo=N-Cl group of the anion is nearly linear (bond angle 175.8°) with bond lengths MoN = 172.9 and NCl = 161.8 pm.
[Na-15-crown-5][WF5(NCl)] has been prepared as yellow crystals by the reaction of NaF with WC14(NCl) in the presence of 15-crown-5 in acetonitrile solution. The compound was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P 21/n, Z = 4 (2945 observed, independent reflexions, R = 0.035). Lattice dimensions at - 65 °C: a = 827.2(8); b = 1617.3(13); c = 1372.2(10) pm; β = 99.42(5)°. The com pound forms ion pairs, in which the sodium ion is seven-coordinated by the oxygen atoms of the crown ether m olecule, and by two fluorine ligands of the [WF5(NCl)]- unit with Na -F distances of 228.3(6) and 251.3(6) pm. The W ≡ N-Cl group of the anion is nearly linear (bond angle 176.1(5)°) with bond lengths WN = 173.3(6) and NCI = 162.2(7) pm.
WCl4(NCl) has been prepared as a red-brown crystal powder by the reaction of tungsten hexacarbonyl with excess nitrogen trichloride in boiling CCl4. The complex is associated via chloro bridges, forming dimeric units, according to the IR spectrum. Thermal decomposition at 200 °C leads to tungsten nitride trichloride, WNCl3,. With acetonitrile, WCl4(NCl) reacts with formation of the monomeric complex [CH,CN-WCl4(NCl)], which was characterized by its IR spectrum as well as by an X-ray structure determination. Crystal data: space group P21/m, Z = 2 (1387 independent observed reflexions, R = 0.07). Lattice dimensions at 20 °C: a = 590.4(3), b = 729.0(3), c = 1124.6(4) pm, β = 100.63(2)°. The complex forms monomeric molecules, in which the tungsten atom has a distorted octahedral environment of four chlorine atoms in equatorial positions, and the acetonitrile molecule in trans-position to the group. Bond lengths WN = 172 and NCI = 161 pm; bond angle WNCl = 175.5°.
Kristallstruktur von 1,1-Dichlor-3,5-diphenyl-4-H-1,2,4,6-λ4-selenatriazin, SeCl2C2N3H(C6H5)2
(1989)
The title compound has been prepared as a byproduct of the reaction of Se2Cl2 with Ν,Ν,N′-Tris(trimethylsilyl)benzamidine in CH2Cl2 solution. [SeCl2(HNC2N2Ph2)]2 was characterized by an X-ray structure determination. Space group P21/n, Z = 2, 2979 observed independent reflexions, R = 0.032. Lattice dimensions (-65 °C): a = 1050.1(4), b = 1018.9(4), c = 1402.1(6) pm; β = 99.78(3)°. The compound forms centrosymmetric dimeric molecules with SeCl2Se bridges (bond lengths 241.6(1) and 339.3(1) pm), the selenium atoms being members of nearly planar [xxx] selenatriazine rings with Se—N bond lengths of 182.2(2) and 181.5(2) pm.
The PE spectra of the nitrogen-rich title compounds cyanogen azide NC-N3, azodicarbonitrile NC - N = N - CN, azidoacetonitrile NC - H2C - N3, tetrazolo[1,5-a]pyridine (H4C5N)(N )3 and trimethylenetetrazole (H2C)3(CN4) are presented and assigned by radical cation state comparison with related compounds or by Koopmans’ correlation with MNDO eigenvalues. In a low pressure flow system the compounds decompose at higher temperatures, with elimination of the thermodynamically favorable N2 molecule. PE-spectroscopic real-time analysis reveals as further products: NC - N3 → C∞, NC - N = N - CN → NC - CN , NC - H2C - N3 → 2HCN (+ traces NC - HC = NH?) and (H2C)3(CN4) → H2C = N - CN + H2C = CH2. For tetrazolo[1,5-a]pyridine, a preceding ring opening to the corresponding 2-azidopyridine is observed.
Crystal and molecular structure analysis of the electron rich title compound exhibits an undistorted, yet sterically shielded tetra(primary alkyl)-substituted double bond system with alternating anti-periplanar CH2SiMe3 substituents. The diastereotopic methylene protons have been located and their position correlated to the 1HNMR data and to the ESR hyperfine coupling constants of the corresponding radical cation. In contrast to the highly inert all-carbon derivative, tetraneopentylethene, the more electron-rich and more flexible organosilicon title compound reacts with bromine. Close to orthogonal arrangement between the C-C(H2)-Si planes and the ethene plane ensures effective, fourfold σ/π-hyperconjugation.
In order to determine the influence of OH and O2H-radicals on proteins, bovine serum albumin (BSA) in aqueous solution was treated with Fenton’s reagent [Fe(II)SO4+EDTA+H2O2] and with ultraviolet light (λ > 2800 Å) in the presence of H2O2. The action of free radicals produced in this way did not change the properties of the native protein with respect to the sedimentation in the ultracentrifuge or optical rotatory dispersion and electrophoresis under normal conditions. Ampèrometric titration indicated partial oxidation of SH-groups and of 3—5 SS-groups which are not reducible by NaBH4.
Heat aggregation investigated by means of light-scattering was suppressed at pH 7.5 and strongly accelerated at pH 4.6 (range of coagulation), the latter being a result of increased entropy of activation of coagulation velocity.
The difference spectrum against native BSA had positive values of Δε and two maxima at 2480 and 2950 Å.
Ultracentrifugation at room temperature in phosphate buffer (pH 7.3, μ=0.18) furnishes a molecular weight of 63 300. In a solution of 8 M urea and borate buffer (pH 9, μ=0.05) fragments with molecular weights between 25 000 and 37 000 were observed while in phosphate buffer (pH 7.3, without urea) at temperatures higher than 46 °C an anomalous behaviour of the concentration gradient indicated an effect which possibly depends on a dissociation equilibrium.
As a consequence oxygen radicals seem to attack not only SH- and SS-groups but at least one covalent bond of the peptide chain. Some experiments of heat aggregation with BSA treated with γ-rays (60Co) gave the same results as BSA treated with Fenton’s reagent or UV-light+H2O2.
Diluted aqueous solutions of some proteins (bovine serum albumin, β-Lactoglobubin, Peroxidase) show weak phosphorescence lasting over several minutes after they have been irradiated with light in the range 3500-4200 A. Addition of Eosin after the irradiation amplifies in some cases the intensity of luminescence to a value of about hundred. If Eosin is present at the irradiation process the excitation to phosphorescence is possible with light of the wavelength 5460 A.
After denaturation processes which destroy the configuration of proteins (Urea, Guanidine-HCI. detergents, heat at higher pH) the ability of phosphorescence disappears altogether; likewise after blocking the SH-groups by benzochinone or a total oxidation or reduction of the SS-groups which causes an complete unfolding of the peptide chain.
In solutions of bovine serum-albumin irradiated with 3650 Å at room temperature and afterwards frozen to -178°C no radicals could be observed by measurements of electron-spin-resonance but they were detectable if the irradiation took place in the presence of H2O2.
The reactions Xanthinoxidase-Xanthine-O2, Peroxidase-H2O2 and bovine serum-albumin-H2O2-Fe (II) EDTA are accompanied by chemiluminescence. By comparison with the behaviour of oxidised serum-albumin it could be shown that the chemical reaction produces an excited state of the native protein.
The observations lead to the conclusion that the weak phosphorescence of long duration originates from a triplet-state which is sufficiently populated only as the consequence of cooperative phenomena attending the undisturbed α-Helix-structure of the protein.
A phase equilibrium study of the system aluminiumbromide and pyridiniumbromide has been carried out. The phase diagram of the system indicates the existence of three congruently melting com pounds of the molar ratio AlBr3/PyHBr 1:1, 1:3, 2 :3 and one incongruently melting compound of the molar ratio 1:2 and is therefore similar to the AlCl3-PyHCl system [1].
From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX62- . A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A2TeX6 (A = Rb. Cs: X = Cl, Br) the averaged structure (m3̅m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar SnX62 compounds. Distortions therefore are very small and are evident from FTIR spectroscopic measurements only. Here very broad T1u-deformation vibration bands are observed down to temperatures <10 K without splitting: Astatically distorted species could not be frozen out. In contrast to XeF6 for TeX62- the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T1u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments.
The title compound has been prepared from (PPh4)2[Mo2(O2C-Ph)4Cl2] and CCl4 in CH2Cl2 solution as moisture sensitive crystals, which are black in reflexion and yellow in transmission. (PPh4)2[Mo2(O2C-Ph)4Cl4] · 2 CH2Cl2 was characterized by a X-ray crystal structure determination (7873 observed independent reflexions. R = 0.048). It crystallizes in the space group P1̄ with one formula unit in the unit cell; the lattice constants are a = 1186.4; b = 1404.0; c = 1451.0 pm; α = 61.98°; β = 78.91°; γ = 78.26°. The structure consists of PPh4⊕ ions. CH2Cl2 molecules and centrosymmetric anions [Mo2(O2C-Ph)4Cl4]2⊝ containinga molybdenum d3 d3 unit with a relatively long Mo=Mo bond of 249.6 pm. The Mo≡Mo group is spanned in a chelate manner by four O atoms of two benzoate groups and by two further single O atoms of two further benzoate groups. Two terminal Cl atoms on each Mo atom complete the pentagonal bipyramidal coordination spheres about the Mo atoms.
MoF4(NCl) has been prepared as a yellow crystal powder by the reaction of diluted fluorine with MoCl3(N3S2) at room temperature. The compound is associated via fluorine bridges, according to the IR spectrum. With acetonitrile, the monomeric complex [CH3CN -MoF4(NCl)] is obtained, which was characterized by its IR and 19F NMR spectra as well as by an X-ray structure determination. Crystal data: space group Pm, Z = 2 (1068 observed, independent reflexions, R = 0.03). Lattice dimensions at -90 °C: a = 507.1. b = 704.8, c = 995.8 pm, β = 102.02°. The unit cell contains two crystallographically independent molecules [CH3CN -MoF4(NCl)], the Mo≡N-Cl groups being linear (bond angles 176°, 178°) with bond lengths MoN = 172 and NCI = 159, 162 pm. In the trans position to the MoNCl group, the nitrogen atom of the acetonitrile molecule is coordinated.
Cp2TiSe5 has been prepared by the reaction of trim ethyltetradecylammonium-polyselenide with Cp2TiCl2 in ethanol solution and subsequent extraction of the dry residue with dichloromethane. Cp2TiSe5 crystallizes in the space group P1 with two formula units in the unit cell (2559 observed, independent reflexions, R = 0.074). The cell dimensions are a = 808.6, b = 822.6, c = 1190.7 pm, α - 96.28°, β - 106.06°, γ = 108.78°. The structure consists of discrete Cp2TiSe5 molecules with the TiSe5, ring in the chair conformation.
Coordination of substitutionally inert [Ru(bpy)2]2+ fragments (bpy: 2,2′-bipyridine) to the a-iminoketone chelate ligands pyrazine-2-dimethylcarboxamide (4) and 4,7-phenanthroline-5,6-dione (5) yields the complexes [(N,O-4)Ru(bpy)2]2⊕, [(O,O′-5⊖)Ru(bpy)2]⊕ and {(N,O; N′,O′-5)[Ru(bpy)2]2}4⊕ which exhibit a rich electrochemistry. The distinctly different electronic structures of the complexes are evident from the ESR behaviour of paramagnetic intermediates: N.O-coordinated complexes have the unpaired electron residing in the ligand n system upon reduction, albeit with g<2 for the binuclear complex of 5. The paramagnetic O,O′-coordinated mononuclear complex with 5 has its redox potentials shifted positively relative to that of the binuclear system. These results are particularly noteworthy because 4 and 5 can be regarded as model compounds for the flavin and methoxatin dehydrogenase cofactors.
(NBu4)[CoCl3(PPh3)] reacts with Se(SiMe3)2 to form the new clusters [Co8Se8(PPh3)6][CoCl3(PPh3)] (6) and [Co8Se8(PPh3)6][Co6Se8(PPh3)6] (7). The structures of 6 and 7 have been determ ined by X-ray diffraction. 6 and 7 crystallize in the space group P1̄ with two formula units per unit cell and with the following lattice constants at 180 K: 6: a = 1413.8(10), b - 2224.2(23), c = 2348.4(17) pm, α = 86.06(5), β = 86.58(5), γ = 76.11(5)°; 7: a = 1465.9(4), b = 1627.6(6), c = 2505.7(6) pm, α - 98.69(2), β = 96.23(2), γ = 113.06(2)°. The cluster structures of the [Co8Se8(PPh3)6]n (n = 0, 1 +) depend on the total number of electrons in the cluster units.
Photoelektronen-Spektren und Moleküleigenschaften, 110 [1,2]. Tricyanmethan-Derivate X—C(CN)3
(1987)
The photoelectron spectra of tricyanomethane derivatives X-C(CN)3 with substituents X = H, CH3, Br and C6H5 have been recorded and are assigned based on MNDO calculations as well as on radical cation state comparison with the iso(valence)electronic P(CN)3, within the series of cyanomethanes H4-nC(CN)n, and with each other. For HC(CN)3, no traces of the isomeric dicyano, ketimine HN = C=C(CN)2 are detected in the gas phase. Tricyanomethylbenzene, H5C6-C(CN)3, exhibiting the highest first ionization energy of any known singly acceptor substituted phenyl derivative, demonstrates the tremendous electron withdrawing effect of the -C(CN)3 group.
Trifluoromethyl azide decomposes in a low-pressure flow system at rather high temperatures by splitting off N2. The nature of the resulting products depends largely on the wall material of the pyrolysis tube: using molybdenum above 1120 K, FCN is observed exclusively. Neither F2C=NF nor F3C-N=N-CF3 can be detected as intermediates by comparing their PE spectra with those continuously recorded while increasing the temperature. F3C-N = N - CF3 fragments already at 870 K to give N2 and F3C-CF3. The PE spectra of F3CN3 and F2C=NF are assigned based on MNDO calculations.
The HCl elimination from β-chloroethyl azide (1-azido-2-chloroethane) over potassium tert. butanolate at 350 K in a low pressure flow system is optimized using PE spectroscopic real-time gas analysis. The highly explosive vinyl azide formed can be purified by cool-trapping the by-products. Its subsequent and virtually hazard-free pyrolysis yields 2H-azirine, which can be isolated at temperatures below 240 K.
In contrast, the direct pyrolysis of β-chloroethyl azide requires temperatures above 710 K and results in a simultaneous split-off of both HCl and N2, yielding acetonitrile as the main thermolysis product. No intermediates such as β-chloroethanimine or ketenimine are observed, a result which is interpreted in terms of chemical activation.
The reactive intermediate methyleneaminoacetonitrile H2C = N - C H2 - CN has been generated via thermal retrotrimerization of N ,N',N"-tris(cyanomethyl)hexahydro-s-triazine and characterized by its photoelectron, mass and low-temperature NMR spectra. A fully geometryoptimized MNDO calculation allows to assign the observed ionization energies and yields estimates for other molecular properties, e.g. a rather high dipole moment.
During photooxidation of polycyclic aromatic hydrocarbons (PAH) products can be formed which develop chemiluminescence on treatment with bases. Flash photolysis experiments show that this is the case only after previous formation of cation radicals, e.g. in the presence of CCl4 as solvent or of e-acceptors in aprotic solvents. These radicals react with oxygen to peroxy-radicals which can combine to several kinds of peroxides. Primary and secondary peroxides are the sources of chemiluminescent activity.
Chemiluminescent peroxides can also be obtained by irradiation of PA H carbonyl com pounds in protic solvents under nitrogen. It is assumed that two excited CO groups combine exceptionally with their O-atom s thus creating a peroxide bond. 24 aromatic aldehydes, ketones, dicarboxylic acid anhydrides and coumarines develop chemiluminescence after illumination with wavelengths ≥ 320 nm with intensities varying 4 magnitudes of order.
The sensitivity of the photochemiluminescent method is sufficient to detect amounts of PA H and their CO derivatives in the ppb to ppm range.
The reduction potentials of 40 aromatic nitro compounds Rπ(NO2)n with Rπ = benzene, naphthalene, anthracene, fluorene and carbazole and n = 1 to 4 nitro groups are determined by cyclic voltammetry in DMF under aprotic conditions. The perturbation by the strongly electron accepting substituents can be rationalized via correlation with HMO eigenvalues. Based on reversibility criteria, the electrochemical behaviour is discussed and the compounds are classified with respect to reversible or irreversible one-electron transfer as well as up to 4 (quasi)-reversible reduction steps. The CV data measured can be used to predict redox reactions of aromatic nitro compounds in inert solvents.
A phase equilibrium study of the system aluminiumchloride and pyridiniumchloride has been carried out. The phase diagram of the system indicates the existence of four congruently melting compounds of the molar ratio AlCl3/PyHCl 1:1, 1:2, 1:3, 2:3.
The synthesis of [Ph4As+]2[Cl4Re(NS)(NSCl)2-] · CH2Cl2 (4) from the reaction of S4N4, Cl4ReN, and Ph4AsCl is reported. CH2Cl2 is used as solvent. The reaction of S4N4 with Re2Cl10 similarly leads to the salt [Ph4As+][Cl2ReNS-] (5) in a smaller yield. 4 crystallizes in the triclinic space group P1̅ with Z = 2, a - 10.434(2), b = 12.1454(6), c = 21.125(2) Å, a = 81.210(6), β = 86.70(1), γ = 76.624(8)°.
The 1:2 molecular complexes formed from 1,4-phenylenebis(dimethylphosphane) and boranes, trialkyl-aluminum and -gallium have been reduced by potassium in THF in the presence of a K+- complexing crown ether. The bis(borane) complex anion radicals proved to be quite persistent, whereas corresponding aluminum radical complexes could only be observed below 240 K. The bis(trimethylgallium) complex gave gallium metal on reduction with potassium. An ESR spectroscopic comparison with the anion radicals of the free ligand, of corresponding chalcogenides, imines and phosphonium salts demonstrates negligible effects of P-complexation on the π spin distribution but high sensitivity of the 31P coupling constant towards coordination of electrophiles at the basic P(III) centers
The neutral title compound, 8,8-bis(dimethylamino)dibenzo-[a,d]-heptafulvene, exhibits a first vertical ionization potential of only 6.98 eV and, therefore, can also be oxidized by AlCl3 in H2CCl2 solution. The radical cation generated shows a complex multiplet signal pattern, which is assigned based on additional ENDOR measurements. The photoelectron (PE) and ESR spectra of the 112 valence electron molecule are interpreted by “pararneter-optimized” HMO and by geometry-optimized MNDO calculations, which both suggest a non-planar π-type ground state with most of the charge and the spin distributed over the dibenzoheptatriene part of the radical cation.
The photoelectron (PE) spectra of bis(dialkylamino) acetylenes R2N-C≡C-NR2 and of tetrakis(dialkylamino) allenes (R2N)2C=C=C(NR2)2 with R = CH3, C2H5 exhibit characteristic ionization patterns which are assigned to π radical cation states of the two molecular halves twisted against each other. The low first ionization potentials between 7.0 eV and 7.7 eV stimulated attempts to oxidize using AlCl3 in H2CCl2 or D2CCl2. The hyperfine structured ESR spectra observed can be unequivocally assigned to the ethylene radical cations R2N-HC=CH -NR2˙⊕ which are formed from the obviously non-persistent species R2N-C≡C-NR2˙⊕ via a hydrogen transfer. During the oxidation of the dialkylamino-substituted allenes no paramagnetic intermediates could be detected, presumably due to a rapid dimerisation of the allene radical cation (R2N)2C=C=C(NR2)2˙⊕.
Das Reduktionsverhalten von Pentacarbonylpyridin-Komplexen des Chroms, Molybdäns und Wolframs
(1984)
The reduction of group VIB metal pentacarbonyl complexes and of iodomethylates of 4- trimethylsilyl-, 4-acetyl- and 4-cyanopyridine has been investigated. Informations on the dissociation of the complexes and on the potential and reversibility of the one-electron reduction were obtained by cyclic voltammetry in DMF, whereas electron spin resonance (ESR) studies of the primary reduction products in the 4-acetylpyridine series revealed the distribution of the unpaired electron. The results suggest that the lowest unoccupied molecular orbital (LUMO) is a ligand centered π*-orbital in the 4-acetyl- and 4-cyanopyridine complexes, thus confirming assignments from photochemistry. The results allow an assessment of both N-coordination and substituent effects at the heterocyclic ligand.
The crystal structure of C12H11N2SiCl3 (monoclinic, P21/m, Z = 2, with a: 9.284(4), b: 7.226(2), c: 10.832(5) Å, β = 115.14(3)°) was refined to R(F) =0.035 from 1228 independent reflections. A trigonal bipyramidal, pentacoordinate silicon is observed. The chelated complex shows two different Si−N bonds, a coordinative bond (1.984(2) Å) between Si and N on the axial position and a Si−N single bond (1.737(3) A, equatorial plane), introduced by chemical reaction. The coordinative bond is 14.2% longer than the Si−N single bond. The lengthening of the coordinative bond in the present case is compared with distances in other extracoordinated silicon compounds.
Crystals of [Al(C5H5N)4Cl2][AlCl4] are orthorhombic, Pna21, Z = 4, a = 18.522(7), b = 15.141(5), c = 9.593(3) Å, V = 2690(2) Å3 , Dc = 1.440 g/cm3 . The structure has been solved from 5968 diffractometer measured intensities and refined by full-matrix least squares to Rw(F) = 0.032. The crystal structure shows the complex to be trans-dichloro-tetrakis(pyridine)aluminium(III) tetrachloroaluminat(III). The mean trans Al-Cl-and trans Al-N-distances in the octahedron are 2.279(3) and 2.070(4) Å, respectively. Crystals of Al(C5H5N)3Cl3 are monoclinic, P21/c, Z = 4, a = 7.261(2), b = 29.961(4), c = 8.624(1) Å, β = 98.12(2)°, V -1857(1) Å3 , DC = 1.326 g/cm3 . The structure has been solved from 4707 diffractometer measured intensities and refined to Rw(F) = 0.028. The crystal structure shows octahedral complexes AlCl3·3 (C5H5N) with trans geometry. The Al-N-distance trans to chlorine (2.096(2) Å) is significantly longer than the two other Al-N-distances (mean 2.072(2) Å).
By analyzing the melting point diagrams of some methylhalogenosilane-pyridine systems the existance of the stable addition compounds CH3SiCl3 · 2 py, CH3SiBr3 · 2 py, (CH3)2SiBr2 · py, (CH3)3SiBr · py was proved. In the systems (CH3)2SiCl2/py and (CH3)2SiBr2/py unstable 1:2-complexes are also found. (CH3)3SiCl forms no complexes with pyridine.
With new X-ray data from a crystal of stoichiometric K0.33MoO3 the crystal structure of this compound was refined until R(anisotropic) = 0.023. The characteristic distortion of the Mo-O octahedra is discussed.
Diadamantyldioxetane, trim ethyldioxetane and tetram ethyldioxetane were photolyzed b y light of A > 260 nm . The spectral distribution o f the quanta emitted during photoinduced decom position of dioxatenes was found to be different from fluorescence and phosphorescence o f ketones. Flash photolysis experim ents showed the absorption of an short-lived interm ediate. It was concluded, therefore, that photolysis o fdioxetanes is not a concerted process but involves at least one precursor o f the final product ketone.