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In the search for novel organic charge transfer salts with variable degrees of charge transfer we have studied the effects of two modifications of the recently synthesized donor–acceptor system [tetramethoxypyrene (TMP)]–[tetracyanoquinodimethane (TCNQ)]. One is of chemical nature by substituting the acceptor TCNQ molecules by F4TCNQ molecules. The second consists in simulating the application of uniaxial pressure along the stacking axis of the system. In order to test the chemical substitution, we have grown single crystals of the TMP–F4TCNQ complex and analyzed its electronic structure via electronic transport measurements, ab initio density functional theory (DFT) calculations and UV/VIS/IR absorption spectroscopy. This system shows an almost ideal geometrical overlap of nearly planar molecules stacked alternately (mixed stack) and this arrangement is echoed by a semiconductor-like transport behavior with an increased conductivity along the stacking direction. This is in contrast to TMP–TCNQ which shows a less pronounced anisotropy and a smaller conductivity response. Our band structure calculations confirm the one-dimensional behavior of TMP–F4TCNQ with pronounced dispersion only along the stacking axis. Infrared measurements illustrating the C[triple bond, length as m-dash]N vibration frequency shift in F4TCNQ suggest however no improvement in the degree of charge transfer in TMP–F4TCNQ with respect to TMP–TCNQ. In both complexes about 0.1e is transferred from TMP to the acceptor. Concerning the pressure effect, our DFT calculations on the designed TMP–TCNQ and TMP–F4TCNQ structures under different pressure conditions show that application of uniaxial pressure along the stacking axis of TMP–TCNQ may be the route to follow in order to obtain a much more pronounced charge transfer.
[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.
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.
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,
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.
Synthesis and crystal structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol
(2022)
The redetermined structure of 2-(2-hydroxyphenyl)-1,3-bis(4-methoxybenzyl)-1,3-diazinan-5-ol, C26H30N2O4, at 173 K has orthorhombic (Pbca) symmetry. It was previously described by Bolte et al. [ Private Communication (refcode EWICEV). CCDC, Cambridge, England]. The title compound resulted from the condensation reaction between 1,3-bis{[(4-methoxyphenyl)methyl]amino}propan-2-ol and 2-hydroxybenzaldehyde in CH3OH. The structure exhibits disorder. One of the 4-methoxybenzyl groups, the hydroxy group bonded to the 1,3-diazinan ring, and the methyl group of the methoxy residue are disordered over two orientations, with occupancies of 0.807 (3)/0.193 (3), 0.642 (5)/0.358 (5), and 0.82 (4)/0.18 (4), respectively. The dihedral angles between the mean planes of the central 1,3-diazinan-5-ol and the 4-methoxyphenyl rings (both occupancy components of the disordered ring) are 88.65 (13), 85.79 (14) and 83.4 (7)°. The crystal packing is sustained by C—H...O and O—H...π interactions, giving rise to infinite chains running along the b-axis direction.
The title compound, C8H16N4·2C11H16O, was synthesized from the corresponding sterically crowded phenol by treatment with the aminal cage polyamine. Single-crystal X-ray diffraction structural analysis revealed the three-molecule aggregate to crystallize in the monoclinic space group P2/c with one half of a 1,3,6,8-tetraaztricyclo[4.4.1.13,8]dodecane (TATD) molecule and one 2-tert-butyl-4-methylphenol molecule per asymmetric unit. The crystal structure features intermolecular O—H...N and C—H...O hydrogen bonds, as well as intermolecular C—H...π interactions.
The asymmetric unit of the title compound, C28H42N2O5·H2O, consists of one half of the organic molecule and one half-molecule of water, both of which are located on a mirror plane which passes through the central C atoms and the hydroxyl group of the heterocyclic system. The hydroxyl group at the central ring is disordered over two equally occupied positions. The six-membered ring adopts a chair conformation, and the 2-hydroxybenzyl substituents occupy the sterically preferred equatorial positions. The aromatic rings make dihedral angles of 75.57 (9)° with the mean plane of the heterocyclic ring. The dihedral angle between the two aromatic rings is 19.18 (10)°. The molecular structure features two intramolecular phenolic O-H...N hydrogen bonds with graph-set motif S(6). In the crystal, molecules are connected via O-H...O hydrogen bonds into zigzag chains running along the a-axis direction.
First crystal structure of a Pigment Red 52 compound: DMSO solvate hydrate of the monosodium salt
(2021)
Pigment Red 52, Na2[C18H11ClN2O6S], is an industrially produced hydrazone-laked pigment. It serves as an intermediate in the synthesis of the corresponding Ca2+ and Mn2+ salts, which are used commercially for printing inks and lacquers. Hitherto, no crystal structure of any salt of Pigment Red 52 is known. Now, single crystals have been obtained of a dimethyl sulfoxide solvate hydrate of the monosodium salt of Pigment Red 52, namely, monosodium 2-[2-(3-carboxy-2-oxo-1,2-dihydronaphthalen-1-ylidene)hydrazin-1-yl]-5-chloro-4-methylbenzenesulfonate dimethyl sulfoxide monosolvate monohydrate, Na+·C18H12ClN2O6S−·H2O·C2H6OS, obtained from in-house synthesized Pigment Red 52. The crystal structure was determined by single-crystal X-ray diffraction at 173 K. In this monosodium salt, the SO3− group is deprotonated, whereas the COOH group is protonated. The residues form chains via ionic interactions and hydrogen bonds. The chains are arranged in polar/non-polar double layers.
The title compound, di-μ3-chlorido-tetra-μ2-chlorido-tetrakis(diethyl ether-κO)bis(1,1-dimethylethyl)tetramagnesium, [Mg4(C4H9)2Cl6(C4H10O)4], features an Mg4Cl6 open-cube cluster. The two four-coordinate Mg2+ ions show an almost tetrahedral coordination, whereas the two six-coordinate Mg2+ ions have their ligands in an octahedral environment. The Mg—Cl bond lengths differ depending on the coordination number (2 or 3) of the bridging μ-Cl− ligands. There are few comparable structures deposited in the Cambridge Structural Database.
[1,3-Bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene]triiodoborane benzene hemisolvate
(2020)
Benzene solutions of Me3SnCl when exposed to moisture yield the adduct Me3SnCl·Me3SnOH·H2O. This adduct represents an intermediate in Me3SnCl hydrolysis. The structure of Me3SnCl·Me3SnOH·H2O features an array of Me3Sn units connected alternatingly by bridging Cl and OH ligands.
Treatment of hexachloropropene (Cl2C[double bond, length as m-dash]C(Cl)–CCl3) with Si2Cl6 and [nBu4N]Cl (1 : 4 : 1) in CH2Cl2 results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [nBu4N][Cl2C[double bond, length as m-dash]C(SiCl3)–C(SiCl3)2] ([nBu4N][1]). Tetrachloroallene Cl2C[double bond, length as m-dash]C[double bond, length as m-dash]CCl2 was identified as the first intermediate of the reaction cascade. In the solid state, [1]− adopts approximate Cs symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [1]− of C[double bond, length as m-dash]C–Si//Si–C–Si = 78.3(1)°. One-electron oxidation of [nBu4N][1] with SbCl5 furnishes the distillable blue radical 1˙. The neutral propene Cl2C[double bond, length as m-dash]C(SiCl3)–C(SiCl3)2H (2) was obtained by (i) protonation of [1]− with HOSO2CF3 (HOTf) or (ii) H-atom transfer to 1˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl3 substituents in 2 to Si(OMe)3 (2OMe) or SiMe3 (2Me) substituents was achieved by using MeOH/NMe2Et or MeMgBr in CH2Cl2 or THF, respectively. Upon addition of 2 equiv. of tBuLi, 2Me underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe3 migration and Cl/Li exchange to afford the allenyl lithium compound Me3Si(Li)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiMe3)2 (Li[4]), which is an efficient building block for the introduction of Me, SiMe3, or SnMe3 (5) groups. The trisilylated, monochlorinated allene Cl3Si(Cl)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiCl3)2 (6), was obtained from [nBu4N][1] through Cl−-ion abstraction with AlCl3 and rearrangement in CH2Cl2 (1˙ forms as a minor side product, likely because the system AlCl3/CH2Cl2 can also act as a one-electron oxidant).
A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.
Two subvalent, redox-active diborane(4) anions, [3]4− and [3]2−, carrying exceptionally high negative charge densities are reported: Reduction of 9-methoxy-9-borafluorene with Li granules without stirring leads to the crystallization of the B(sp3)−B(sp2) diborane(5) anion salt Li[5]. [5]− contains a 2,2′-biphenyldiyl-bridged B−B core, a chelating 2,2′-biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na+ salt of the tetraanion [3]4− in which two doubly reduced 9-borafluorenyl fragments are linked via a B−B single bond. Comproportionation of Li[5] and Na4[3] quantitatively furnishes the diborane(4) dianion salt Na2[3], the doubly boron-doped congener of 9,9′-bis(fluorenylidene). Under acid catalysis, Na2[3] undergoes a formal Stone–Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na2[3] shows boron-centered nucleophilicity toward n-butyl chloride. Na4[3] produces bright blue chemiluminescence when exposed to air.
The intriguing (μ-hydrido)diboranes(4) with their prominent pristine representative [B2H5]− have mainly been studied theoretically. We now describe the behavior of the planarized tetraaryl (μ-hydrido)diborane(4) anion [1H]− in cycloaddition reactions with the homologous series of heterocumulenes CO2, iPrNCO, and iPrNCNiPr. We show that a C=O bond of CO2 selectively activates the B−B bond of [1H]−, while the μ-H ligand is left untouched ([2H]−). The carbodiimide iPrNCNiPr, in contrast, neglects the B−B bond and rather adds the B-bonded H− ion to its central C atom to generate a formamidinate bridge across the B2 pair ([3]−). As a hybrid, the isocyanate iPrNCO combines the reactivity patterns of both its congeners and gives two products: one of them ([4H]−) is related to [2H]−, the other ([5]−) is an analog of [3]−. We finally propose a mechanistic scenario that rationalizes the individual reaction outcomes and combines them to a coherent picture of B–B vs. B–H bond activation.
The exhaustive trichlorosilylation of hexachloro-1,3-butadiene was achieved in one step by using a mixture of Si2Cl6 and [nBu4N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu4N]2[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]2− are mainly delocalized across its two carbanionic (Cl3Si)2C termini (α-effect of silicon) such that the central bond possesses largely C=C double-bond character. Upon treatment with 4 equiv of HCl, [1]2− is converted into neutral 1,2,3,4-tetrakis(trichlorosilyl)but-2-ene, 3. The Cl− acceptor AlCl3, induces a twofold ring-closure reaction of [1]2− to form a six-membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X-ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.
Double reduction of the THF adduct of 9H-9-borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M2[1] in essentially quantitative yields (M=Li–K). Even though the added charge is stabilized through π delocalization, [1]2− acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et3SiCl, Me3SnCl) to form B−B/C/Si/Sn bonds. The substrate dependence of open-shell versus closed-shell pathways has been investigated.
The single crystal growth of 19 different intermetallic compounds within the LnT2X2 family (with Ln = lanthanides, T = Co, Ru, Rh, Ir, and X = Si, P) is presented, by employing a high-temperature metal-flux technique. The habitus of the obtained crystals is platelet-like with the crystallographic c direction perpendicular to the surface and with individual masses between 1 and 100 mg. The magnetic properties of these crystals are characterized by magnetization, heat-capacity, and resistivity measurements. These crystals form the materials basis for a thorough study of exciting surface properties by angle-resolved photoemission spectroscopy.
SixGey alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the SixGey heteroadamantanes [0], [1], and [2] through selective one-pot syntheses starting from Me2GeCl2, Si2Cl6, and [nBu4N]Cl. Compound [0] contains six GeMe2 and four SiSiCl3 vertices, whereas one and two of the GeMe2 groups are replaced by SiCl2 moieties in compounds [1] and [2], respectively. Chloride-ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism.
SixGey alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the SixGey heteroadamantanes [0], [1], and [2] through selective one-pot syntheses starting from Me2GeCl2, Si2Cl6, and [nBu4N]Cl. Compound [0] contains six GeMe2 and four SiSiCl3 vertices, whereas one and two of the GeMe2 groups are replaced by SiCl2 moieties in compounds [1] and [2], respectively. Chloride-ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism.
Two salts of the 6,6-difluoro-6H-dibenzo[c,e][1,2]oxaborinin-6-ide anion with different cations
(2020)
The crystal structures are reported of the 6,6-difluoro-6H-dibenzo[c,e][1,2]oxaborinin-6-ide (or 9,9-difluoro-10-oxa-9-boraphenanthren-9-ide) anion with two different cations, namely, potassium 6,6-difluoro-6H-dibenzo[c,e][1,2]oxaborinin-6-ide, K+·C12H8BF2O−, (II), featuring a polymeric structure, and bis(tetraphenylphosphonium) bis(6,6-difluoro-6H-dibenzo[c,e][1,2]oxaborinin-6-ide) acetonitrile trisolvate, 2C24H20P+·2C12H8BF2O−·3CH3CN, (III), which is composed of discrete cations, anions and acetonitrile solvent molecules linked by C—H...O, C—H...N and C—H...F hydrogen bonds. There are only minor differences in the geometrical parameters of the anions in these structures.
NHC supersilyl silver complex [Ag(IPr)SitBu3] as a promising agent for substitution reactions
(2020)
The NHC supersilyl silver complex [Ag(IPr)SitBu3] (IPr = NHCIPr) was prepared by treatment of Ag(IPr)Cl with Na(thf)2[SitBu3] in benzene/thf at room temperature. X‐ray quality crystals of the NHC supersilyl silver complex [Ag(IPr)SitBu3] (monoclinic, space group P21/m) were grown from heptane at room temperature. The 29Si NMR spectrum of a solution of [Ag(IPr)SitBu3] in C6D6 revealed two doublets caused by coupling to 107Ag and 109Ag nuclei. We further investigated the possibility of a conversion of triel halides EX3 by treatment with [Ag(IPr)SitBu3]. At ambient temperature the reaction of [Ag(IPr)SitBu3] with an excess of EX3 yielded tBu3SiEX2 (E = B, Al; X = Cl, Br; E = Ga; X = Cl) and IPr·EX3 (EX3 = BCl3, BBr3, AlCl3, AlBr3, GaCl3). The identity of tBu3SiEX2 and IPr·EX3 was confirmed by comparison with authentic samples.
The tetraaryl μ‐hydridodiborane(4) anion [2H]− possesses nucleophilic B−B and B−H bonds. Treatment of K[2H] with the electrophilic 9‐H‐9‐borafluorene (HBFlu) furnishes the B3 cluster K[3], with a triangular boron core linked through two BHB two‐electron, three‐center bonds and one electron‐precise B−B bond, reminiscent of the prominent [B3H8]− anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M+=Li+, K+) with MeI or Me3SiCl leads to equimolar amounts of 9‐R‐9‐borafluorene and HBFlu (R=Me or Me3Si). Thus, [2H]− behaves as a masked [:BFlu]− nucleophile. The HBFlu by‐product was used in situ to establish a tandem substitution‐hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3‐propylene‐linked ditopic 9‐borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R2BFlu].
The respiratory chain of Escherichia coli contains two different types of terminal oxidase that are differentially regulated as a response to changing environmental conditions. These oxidoreductases catalyze the reduction of molecular oxygen to water and contribute to the proton motive force. The cytochrome bo3 oxidase (cyt bo3) acts as the primary terminal oxidase under atmospheric oxygen levels, whereas the bd‐type oxidase is most abundant under microaerobic conditions. In E. coli, both types of respiratory terminal oxidase (HCO and bd‐type) use ubiquinol‐8 as electron donor. Here, we assess the inhibitory potential of newly designed and synthesized 3‐alkylated Lawson derivatives through L‐proline‐catalyzed three‐component reductive alkylation (TCRA). The inhibitory effects of these Lawson derivatives on the terminal oxidases of E. coli (cyt bo3 and cyt bd‐I) were tested potentiometrically. Four compounds were able to reduce the oxidoreductase activity of cyt bo3 by more than 50 % without affecting the cyt bd‐I activity. Moreover, two inhibitors for both cyt bo3 and cyt bd‐I oxidase could be identified. Based on molecular‐docking simulations, we propose binding modes of the new Lawson inhibitors. The molecular fragment benzyl enhances the inhibitory potential and selectivity for cyt bo3, whereas heterocycles reduce this effect. This work extends the library of 3‐alkylated Lawson derivatives as selective inhibitors for respiratory oxidases and provides molecular probes for detailed investigations of the mechanisms of respiratory‐chain enzymes of E. coli.
Vicinally diiodinated polycyclic aromatic hydrocarbons (I2‐PAHs) are accessible from the corresponding diborylated B2‐PAHs through boron/iodine exchange. The B2‐PAHs have been prepared via twofold electrophilic borylation reactions templated by a vicinally disilylated benzene. Our protocol is applicable to fluorenes, acenes, annulated acenes, oligoaryls, and even [5]helicene. Using B2‐naphthalene as the example, we have shown that the reaction scope can, in principle, be expanded to include the synthesis of vicinally dibrominated and dihydroxylated PAHs. The usefulness of the building blocks provided by our method in the field of optoelectronic materials was demonstrated by the successful conversion of I2‐fluoranthene to the analogous doubly alkynylated fluoranthene emitter.
A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ‐bonds and five continuous stereogenic centers are formed in this one‐pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E‐ or a Z‐configured enamide.
A new pseudopolymorph of perchlorinated neopentasilane: the benzene monosolvate Si(SiCl3)4·C6H6
(2020)
A new pseudopolymorph of dodecachloropentasilane, namely a benzene monosolvate, Si5Cl12·C6H6, is described. There are two half molecules of each kind in the asymmetric unit. Both Si5Cl12 molecules are completed by crystallographic twofold symmetry. One of the benzene molecules is located on a twofold rotation axis with two C—H groups located on this rotation axis. The second benzene molecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional interactions beyond normal van der Waals contacts occur in the crystal.
The title compound, C21H26Cl2N2O2, was prepared in a solvent-free microwave-assisted synthesis, and crystallizes in the orthorhombic space group Pna21. The imidazolidine ring adopts an envelope conformation and its mean plane is almost perpendicular to the two pendant aromatic rings [dihedral angles = 84.61 (9) and 86.54 (9)°]. The molecular structure shows the presence of two intramolecular O—H⋯N hydrogen bonds between the phenolic hydroxy groups and imidazolidine N atoms. The two 3-chloro-6-hydroxy-2,4-dimethylbenzyl groups are located in a cis orientation with respect to the imidazolidine fragment. As a result, the lone pairs of electrons on the N atoms are presumed to be disposed in a syn conformation. This is therefore the first example of an exception to the `rabbit-ears' effect in such 2,2′-[imidazolidine-1,3-diylbis(methylene)]diphenol derivatives.
Structural and vibrational studies have been carried out for the most stable conformer of 3,3′-ethane-1,2-diyl-bis-1,3,5-triazabicyclo[3.2.1]octane (ETABOC) at the DFT/B3LYP/6-31G(dp) level using the Gaussian 03 software. In light of the computed vibrational parameters, the observed IR Bolhmann bands for the C2V, C2, and Ci symmetrical structures of ETABOC have been analyzed. Hyperconjugative interaction was done by Natural Bond Orbital Analysis. Interpretation of hyperconjugative interaction involving the lone pairs on the bridgehead nitrogen atoms with the neighboring C–N and C–C bonds defines the conformational preference of the title compound. The recorded X-ray diffraction bond parameters were compared with theoretical values calculated at B3LYP/6-31G(d,p) and HF/6-31G(d,p) level of theory showed that ETABOC adopts a chair conformation and possesses an inversion center.
The asymmetric unit of the title compound, C21H28N4O, consists of two unique molecules linked by an O—H⋯N hydrogen bond. The conformation of both C=N bonds is E and the azomethine functional groups lie close to the plane of their associated benzene rings in each of the independent molecules. The dihedral angles between the two benzene rings are 83.14 (4) and 75.45 (4)°. The plane of the one of the N(CH3)2 units is twisted away from the benzene ring by 18.8 (2)°, indicating loss of conjugation between the lone electron pair and the benzene ring. In the crystal structure, O—H⋯N hydrogen bonds together with C—H⋯O hydrogen bonds link neighbouring supramolecular dimers into a three-dimensional network.
The synthesis and single crystal structure of a new cocrystal, which is composed of OHphenolic∙∙∙OHphenolic∙∙∙Naminalic supramolecular heterosynthons assembled from 4-tert-butylphenol and the macrocyclic aminal TATU, is presented. This cocrystal was prepared by solvent-free assisted grinding, which is a commonly used mechanochemical method. Crystal structure, supramolecular assembly through hydrogen bonding interactions as well as the physical and spectroscopic properties of the title cocrystal are presented in this paper.
Remote control of the synthesis of a [2]rotaxane and its shuttling via metal‐ion translocation
(2019)
Remote control in an eight‐component network commanded both the synthesis and shuttling of a [2]rotaxane via metal‐ion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copper‐ion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460 nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a double‐click reaction of acetylenic and diazide compounds. The shuttling frequency in the copper‐loaded [2]rotaxane was determined to k298=30 kHz (ΔH≠=62.3±0.6 kJ mol−1, ΔS≠=50.1±5.1 J mol−1 K−1, ΔG≠298=47.4 kJ mol−1). Removal of zinc(II) ions from the mixture reversed the system back generating the metal‐free rotaxane. Further alternate addition and removal of Zn2+ reversibly controlled the shuttling mode of the rotaxane in this eight‐component network where the ion translocation status was monitored by the naked eye.
The title co-crystal, 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane (HMTA, 1)–4-fluorophenol (4-FP) (1/1), C6H12N4·C6H5FO, shows an unusual asymmetric unit that comprises eight independent molecules (Z′′ = 8), four for each component, with four formula units per asymmetric unit (Z′ = 4). In the molecular packing, each HMTA molecule bridges one 4-FP molecule via an O−H···N hydrogen bond to form a two-molecule aggregate. Differences can be observed between the bond lengths and angles of the independent HMTA and 4-FP molecules and those of the molecules in the aggregate. The C−N bonds exhibit different bond lengths in the tetrahedral cage-like structure of the HMTA molecules, but the largest differences between the molecular aggregates are in the bond lengths in the 4-fluorophenol ring. In the crystal, the HMTA and 4-FP molecules form two hydrogen-bonded (O−H···N, C−H···F and C−H···O) dimers of HMTA and 4-FP molecules, A···D and B···C inversion dimers, which generate enlarged R88(34) ring motifs in both supramolecular structures. In both structures, the crystal packing also features additional C−H···F and C−H···O interactions. The A···D and B···C dimers are linked by additional C−H···F and C−H···O hydrogen bonds, forming columns along the a and b axes, respectively. The importance of the C−H···F interaction to the structure and crystal packing has been demonstrated.
Photolabile protecting groups are widely used to trigger oligonucleotide activity. The ON/OFF‐amplitude is a critical parameter. An experimental setup has been developed to identify protecting group derivatives with superior caging properties. Bulky rests are attached to the cage moiety via Cu‐catalyzed azide–alkyne cycloaddition post‐synthetically on DNA. Interestingly, the decrease in melting temperature upon introducing o‐nitrobenzyl‐caged (NPBY‐) and diethylaminocoumarin‐cages (DEACM‐) in DNA duplexes reaches a limiting value. NMR spectroscopy was used to characterize individual base‐pair stabilities and determine experimental structures of a selected number of photocaged DNA molecules. The experimental structures agree well with structures predicted by MD simulations. Combined, the structural data indicate that once a sterically demanding group is added to generate a tri‐substituted carbon, the sterically less demanding cage moiety points towards the neighboring nucleoside and the bulkier substituents remain in the major groove.
Iodo(triphenyl)silane
(2019)
The molecular structure of the title compound, C18H15ISi, which crystallizes in the space group C2/c, does not exhibit any unusual features. Two weak C—H⋯π interactions may help to consolidate the packing. The present structure is not isostructural with the known Ph3SiX (X = F, Cl or Br) compounds.
We have encountered two polymorphs of the title compound, C24H16B2OS2, both of which display almost the same unit-cell parameters. Compound (I) crystallizes in the non-centrosymmetric space group P21 with four molecules in the asymmetric unit. These molecules are related by pseudosymmetry. As a result, the space group looks like P21/c, but the structure cannot be refined successfully in that space group. Compound (II) on the other hand crystallizes in the centrosymmetric space group P21/c with only two molecules in the asymmetric unit. The crystals studied for (I) and (II) were both non-merohedral twins.
The excellent results of dispersion‐corrected density functional theory (DFT‐D) calculations for static systems have been well established over the past decade. The introduction of dynamics into DFT‐D calculations is a target, especially for the field of molecular NMR crystallography. Four 13C ss‐NMR calibration compounds are investigated by single‐crystal X‐ray diffraction, molecular dynamics and DFT‐D calculations. The crystal structure of 3‐methylglutaric acid is reported. The rotator phases of adamantane and hexamethylbenzene at room temperature are successfully reproduced in the molecular dynamics simulations. The calculated 13C chemical shifts of these compounds are in excellent agreement with experiment, with a root‐mean‐square deviation of 2.0 ppm. It is confirmed that a combination of classical molecular dynamics and DFT‐D chemical shift calculation improves the accuracy of calculated chemical shifts.
Organoboranes are among the most versatile and widely used reagents in synthetic chemistry. A significant further expansion of their application spectrum would be achievable if boron-containing reactive intermediates capable of inserting into C–H bonds or performing nucleophilic substitution reactions were readily available. However, current progress in the field is still hampered by a lack of universal design concepts and mechanistic understanding. Herein we report that the doubly arylene-bridged diborane(6) 1H2 and its B[double bond, length as m-dash]B-bonded formal deprotonation product Li2[1] can activate the particularly inert C(sp3)–H bonds of added H3CLi and H3CCl, respectively. The first case involves the attack of [H3C]− on a Lewis-acidic boron center, whereas the second case follows a polarity-inverted pathway with nucleophilic attack of the B[double bond, length as m-dash]B double bond on H3CCl. Mechanistic details were elucidated by means of deuterium-labeled reagents, a radical clock, α,ω-dihaloalkane substrates, the experimental identification of key intermediates, and quantum-chemical calculations. It turned out that both systems, H3CLi/1H2 and H3CCl/Li2[1], ultimately funnel into the same reaction pathway, which likely proceeds past a borylene-type intermediate and requires the cooperative interaction of both boron atoms.
We have determined the crystal structures of two decachlorocyclopentasilanes, namely bis(tetra-n-butylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C16H36N+·2Cl−·Si5Cl10·2CH2Cl2, (I), and bis(tetraethylammonium) dichloride decachlorocyclopentasilane dichloromethane disolvate, 2C8H20N+·2Cl−·Si5Cl10·2CH2Cl2, (II), both of which crystallize with discrete cations, anions, and solvent molecules. In (I), the complete decachlorocyclopentasilane ring is generated by a crystallographic twofold rotation axis. In (II), one cation is located on a general position and the other two are disordered about centres of inversion. These are the first structures featuring the structural motif of a five-membered cyclopentasilane ring coordinated from both sides by a chloride ion. The extended structures of (I) and (II) feature numerous C—H⋯Cl interactions. In (II), the N atoms are located on centres of inversion and as a result, the ethylene chains are disordered over equally occupied orientations.
A chiral analog of the bicyclic guanidine TBD : synthesis, structure and Brønsted base catalysis
(2016)
Starting from (S)-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound 10. In the crystals of the guanidinium benzoate salt the six membered rings of 10 adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine 10 catalyzes Diels–Alder reactions of anthrones and maleimides (25–30% ee). It also promotes as a strong Brønsted base the retro-aldol reaction of some cycloadducts with kinetic resolution of the enantiomers. In three cases, the retro-aldol products (48–83% ee) could be recrystallized to high enantiopurity (≥95% ee). The absolute configuration of several compounds is supported by anomalous X-ray diffraction and by chemical correlation.