Theoretical investigation of the mechanisms for the reaction of fused tricyclic dimetallenes containing highly strained E═E (E = C, Si, Ge, Sn, and Pb) double bonds

The potential energy surfaces for the reactions of fused tricyclic dimetallenes that feature a highly strained E═E double bond, Rea-E═E, where E = C, Si, Ge, Sn, and Pb, were studied using density functional theory (B3LYP/LANL2DZ). Three types of chemical reactions (i.e., a self-isomerization reaction, a [2 + 2] cycloaddition with a ketone and a methanol 1,2-addition reaction) were used to determine the reactivity of the Rea-E═E molecules. The theoretical findings reveal that the smaller the singlet-triplet splitting of the Rea-E═E, the lower are its activation barriers and, in turn, the more rapid are its chemical reactions with other chemical molecules. Theoretical observations suggest that the relative reactivity increases in the following order: C═C ? Si═Si < Ge═Ge < Sn═Sn < Pb═Pb. Namely, the smaller the atomic weight of the group 14 atom (E), the smaller is the atomic radius of E and the more stable is its fused tricyclic Rea-E═E to chemical reaction. It is thus predicted that the fused tricyclic Rea-C═C and Rea-Si═Si molecules should be stable and readily synthesized and isolated at room temperature. The computational results show good agreement with the available experimental observations. The theoretical results obtained from this work allow a number of predictions to be made.     

The Insertion of EII and EIV Chlorides (E=Si,Ge) into the Si−Si Bond of Disilylene

Reactions of silicon and germanium dichlorides L ⋅ ECl₂ (E=Si, L=IPr; E=Ge, L=dioxane) with the phosphinoamidinato-supported disilylene ({κ²(N,P)-NNP}Si)₂ resulted in formal tetrylene insertions into the Si−Si bond. In the case of the reaction with silylene, two products were isolated. The first product ({κ²(N,P)-NNP}Si)₂SiCl₂, is the formal product of direct SiCl₂ insertion into the Si−Si bond of ({κ²(N,P)-NNP}Si)₂ and thus features two separated silylamido silylene centers. Over time, migration of the SiCl₂ group to a lateral position afforded the second product, the disilylene {κ²(Si,P)−SiCl₂NNP}Si−Si{κ²(N,P)-NNP}. In contrast, insertion of GeCl₂ resulted only in the isolation of the germanium analogue of {κ²(Si,P)−SiCl₂NNP}Si−Si{κ²(N,P)-NNP}, containing a Ge atom in the central position namely, compound {κ²(Si,P)−SiCl₂NNP}Ge−Si{κ²(N,P)-NNP}, which is a rare example of a silylene-germylene. Finally, reaction of disilylene ({κ²(N,P)−NNP}Si)₂ with SiCl₄ and SiHCl₃ led to the formation of the new bis(silyl)silylene, ({NNP}SiCl₂)₂Si:. All four new products from these insertion reactions have been characterized by multinuclear NMR and single-crystal X-ray diffraction studies.     

Electronic structure of the surface compounds ≡SiOElCl3 (El, = C,Si, Ge,Sn) and their thermal stability

The SCF MO LCA0 method in the MNDO approximation has been used to consider the electronic structure of the surface compounds SlODlCl₃ (El = C, Si, Ge, Sn), modelled by extended clusters. The thermal stabilities of these groups are compared and conclusions ore drawn about the probable mechanism of the interaction of the surface silanol groups of SiO₂ with ElCl₄ molecules.Institute for Surface Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 1, pp. 19–22, January–February, 1991. Original article submitted March 11, 1990.     

Solvent dependence of peak frequencies and bandwidths of the ν4 vibration of the series CH3MCl3, M  C,Si, Ge,Sn

The Raman spectra of the carbon—chlorine symmetric stretching mode, ν₄, of the Group IVA methylmetal trichlorides (CH₃MCl₃, M  C, Si, Ge, Sn) were acquired in a number of solvents of varying molecular properties. Non-linear curve fitting procedures were used to separate the four band components resulting from chlorine isotope splitting.The band maxima of the two lighter members of the series were observed to shift to lower frequency with increasing solvent polarizability, indicating the predominance of solute—solvent dispersion forces. In the germanium and tin compounds, on the other hand, the peak frequencies were correlated, instead, with solvent dipole moment. This result is in contrast to earlier studies on the ν₁ (CH₃ symmetric stretching) vibration, for which dispersion interactions are the dominant frequency displacement mechanism in all four compounds.The bandwidths of the ν₄ vibration were found to depend on dipolar interactions in the germanium and tin compounds. However, this correlation was not observed for the two lighter series members, nor for the carbon—chlorine antisymmetric stretching vibration in CH₃SnCl₃.     

Ylenes in the M(II)→Si(IV) (M=Si, Ge, Sn) coordination mode

The reaction of the methimazolyl (mt, i.e., 2-mercapto-1-methylimidazolide) substituted silane Si(mt)(4) with SnCl(2) and GeCl(2) in dioxane affords the paddlewheel-shaped complexes [ClSi(μ-mt)(4)MCl] (M=Sn (1) and Ge (2), respectively). These compounds represent the first crystallographically characterized hexacoordinate silicon complexes comprising a Sn or Ge atom in the Si coordination sphere. An attempt to synthesize the related silicon compound 3 [ClSi(μ-mt)(4)SiCl] instead afforded the trisilane [ClSi(μ-mt)(4)Si-SiCl(3)] (3a), which provides the first crystallographic evidence for the feasibility of oligosilanes with adjacent hexacoordinate Si atoms. One of the hexacoordinate Si atoms of 3a features the unprecedented (Si(2)S(4))Si skeleton. Natural bonding orbital (NBO) analyses of compounds 1, 2, 3a (and the target compound 3) revealed characteristics of M(II)→Si(IV) (for 2 and 3) or M(I)→Si(IV) (for 3a) dative bonding in the systems with M=Si and Ge, whereas compound 1 exhibits a covalent Sn(III)-Si(III) bond.     

Diverse Reactivity of bis(Silylene) and bis(Germylene) [LE−EL (E=Si and Ge: L=PhC(NtBu)2)] in the Oxidative Activation of C−F Bond: Si−Si Bond is Retained While the Ge−Ge Bond Is Cleaved

Herein we report the reactions of 3,4,5,6-tetrafluoroterephthalonitrile ( 1 ) with bis(silylene) and bis(germylene) LE−EL [E=Si ( 2 ) and Ge( 3 ): L=PhC(N^tBu)₂)]. The reaction of LSi−SiL (L=PhC(N^tBu)₂) ( 2 ) with two equivalents of 1 resulted in an unprecedented oxidative addition of a C−F bond of 1 leading to disilicon(III) fluoride {L(4-C₈F₃N)FSi−SiF(4-C₈F₃N)L}( 4 ), wherein the Si−Si single bond was retained. In contrast, the reaction of LGe−GeL (L=PhC(N^tBu)₂) ( 3 ) with one equivalent of 1 resulted in the oxidative cleavage of Ge−Ge bond leading to L(4-C₈F₃N₂)Ge ( 5 ) and LGeF ( 6 ). All three compounds ( 4 – 6 ) were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. X-ray single-crystal structure determination of compound 4 unequivocally established that the Si^III−Si^III bond remains uncleaved.     

Theoretical studies on the band structures of superconducting solid compounds: Nb3X (X=Si, Ge, Sn, Pb)

The band structures of several analogous superconducting A-15 type solid compounds, Nb3X (X=Si, Ge, Sn, Pb), have been calculated by use of the tight-binding method within the Extended Huckel approximation (EHT). By analysis of their energy bands, densities of states and crystal orbital overlap populations, the dependence of the superconducting transition temperatures (Tc) on the electronic structures and bondings is qualitatively elucidated.     

Molecular Ln(III)−H−E(II) Linkages (Ln=Y,Lu; E=Ge,Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH₃ and trivalent rare-earth-metallocene alkyls [Cp*₂Ln(CH{SiMe₃}₂)] gave complexes [Cp*₂Ln(μ-H)₂SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip₂C₆H₃, Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*₂Ln(μ-H)₂EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)₂] to the rare-earth-metal hydrides [(Cp*₂LnH)₂]. The lead compounds [Cp*₂Ln(μ-H)₂PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.     

Use of organomagnesium compounds for the synthesis of organic derivatives of group II–V elements in a nonethereal medium

Summary For the primary alkyl halides (R=from C₂H₅ to n-C₉H₁₉; halogen=C1, Br, and I) and the simplest aryl halides (R=C₆H₅ and p-CH₃C₆H₄) it was shown that the organomagnesium synthesis in absence of catalysts for the Grignard reaction can be applied with success to the preparation of heteroorganic compounds of elements of Groups II–IV (mercury, boron, aluminum, silicon, germanium, tin, phosphorus, arsenic, antimony).     

Quantum-chemical Investigation of the Hyprevalent Intramolecular Coordination X←N (X = C,Si, Ge) in Quasimonocyclic Models of IVa Group Atranes

The structure and the pentacoordination effect in quasimonocyclic models of IVa group atranes were investigated by ab initio[MP2 (full) /6-311+G **] and the density functional [B3LYP/6-311+G **] quantum chemical calculations. The calculations revealed considerable stabilization of the quasimonocyclic conformations relative to their free-of-strain trans-s-transconformations, which is caused by the formation of secondary (R)XN (X=C, Si, Ge) bonds of the hypervalent type. The strength of the intramolecular (R)XN coordination increases in the order X=C, Si, Ge. The nature of attractive (R)XN coordination is determined by donor-acceptor interaction of the nitrogen lone electron pair and antibonding orbital which primary localize at the X-R bond. Energy of X ··· N (X=Si, Ge) contact is about 3-7 kcal mol^-1.     

Recent Progress in the Transition-Metal-Catalyzed Activation of Si−Si Bonds To Form C−Si Bonds

Disilanes possessing a Si−Si bond are unique element–element species. Transition-metal-catalyzed activation of the Si−Si bond allows many useful transformations that generate diverse organosilanes. This Minireview highlights impressive developments in this field over the past decade, with an emphasis on the formation of vinyl-, aryl-, and acylsilanes by C(sp²)−Si bond formation as well as the formation of allyl- and alkylsilanes by C(sp³)−Si bond formation.     

杂硼原子簇XB6+ (X=C,Si, Ge,Sn, Pb)的稳定性和芳香性

利用从头算MP2方法和密度泛函理论B3LYP和B3PW91方法, 研究了杂硼原子簇XB₆⁺ (X=C, Si, Ge, Sn, Pb)的结构、稳定性及化学键合情况. 对C, Si, Ge, B使用6-311+G(d)基组, 对Sn和Pb使用LANL2DZ赝势基组. 研究结果表明, 具有C_s对称性的假平面XB₆⁺ (X=C, Si, Ge, Sn, Pb)结构是势能面上的全域极小点, 其稳定性要高于C_6v对称性的锥形结构和C₂对称性的假锥形结构. 在B3LYP水平上, 对这些异构体的势能面的极小点进行了自然键轨道(NBO)的分析; 对最稳定构型的最高占据分子轨道(HOMO)和最低空轨道(LUMO)能级差、分子轨道(MO)和核独立化学位移(NICS)进行了计算和讨论. 分析了杂原子和硼原子间、相邻硼原子间的键合情况, 讨论了最稳定构型的芳香性质.     

The vibrational spectra of (CH3)3MCCCCM(CH3)3, with M = C,Si, Ge,or Sn

Infrared spectra from 200 to 4000 cm⁻¹ and Raman spectra from 80 to 4000 cm⁻¹ have been recorded for the molecules (CH₃)₃MCCCCM(CH₃)₃ with M = C, Si, Ge, or Sn. Solid samples and solutions in several solvents have been used. Assignments of the fundamentals were made on the assumption of D_3d symmetry, which proved quite satisfactory. In all, 140 of the 188 spectroscopically-active fundamentals for the four molecules have been assigned.The in-phase CC stretch is 115–135 cm⁻¹ higher than the out-of-phase one. This is in sharp contrast to cumulated double bonds, where the in-phase stretch is roughly half the out-of-phase one. A rationalization of this is given.     

Are N-heterocyclic carbenes "better" ligands than phosphines in main group chemistry? A theoretical case study of ligand-stabilized E2 molecules, L-E-E-L (L = NHC, phosphine; E = C, Si, Ge, Sn, Pb, N, P, As, Sb, Bi)

A theoretical examination of the L-E-E-L class of molecules has been carried out (E = group 14, group 15 element; L = N-heterocyclic carbene, phosphine), for which Si, Ge, P, and As-NHC complexes have recently been synthesized. The focus of this study is to predict whether it is possible to stabilize the elusive E(2) molecule via formation of L-E-E-L beyond the few known examples, and if the ligand set for this class of compounds can be extended from the NHC to the phosphine class of ligands. It is predicted that thermodynamically stable L-E-E-L complexes are possible for all group 14 and 15 elements, with the exception of nitrogen. The unknown ligand-stabilized Sn(2) and Pb(2) complexes may be considered attractive synthetic targets. In all cases the NHC complexes are more stable than the phosphines, however several of the phosphine derivatives may be isolable. The root of the extra stability conferred by the NHC ligands over the phosphines is determined to be a combination of the NHCs greater donating ability, and for the group 15 complexes, superior π acceptor capability from the E-E core. This later factor is the opposite as to what is normally observed in transition metal chemistry when comparing NHC and phosphine ligands, and may be an important consideration in the ongoing "renaissance" of low-valent main group compounds supported by ligands.     

Determination of the conformation in thioester compounds containing the NSO group through pre-resonance Raman study: Spectroscopic properties of S(N-sulphinylimine)-fluorocarbonylsulphane,FC(O)SNSO

Starting from fluorocarbonylsulphenyl chloride, FC(O)SCl, and N-trimethylsilysulphinylimine, (CH₃)₃SiNSO, the compound S(N-sulphinylimine)-fluorocarbonylsulphane, FC(O)SNSO, has been prepared. The IR, pre-resonant Raman, ¹³C NMR, mass, and UV spectra have been obtained and interpreted.The two bands appearing in the CO stretching fundamental mode region of the vibrational spectra were specially investigated to probe the existence of conformational isomerism in the molecule. From the analysis of the bands and their contours in the vapour-IR spectra, and the depolarization ratios together with the pre-resonant behaviour in the Raman spectrum of the liquid (whose extension is also evaluated), two planar forms can be determined for the molecule.The study of the CO envelope in the IR spectrum of the vapour phase reveals syn conformation (with respect to the CO and SN bonds) as the most stable structure for the molecule, and the anti conformation as the second structure.     

Systematic Access of Ternary Organotetrel-Copper Chalcogenide Clusters by [PhTE3]3− Anions (T=Si,Sn; E=S,Se)

Fragmentation reactions of organotetrel chalcogenide heteroadamantane-type clusters [(PhT)₄E₆] (T/E=Si/S ( 1 ); Si/Se; Sn/S, and Sn/Se) by addition of the corresponding sodium chalcogenide gave salts of the general formula Na₃[PhTE₃], with T/E=Si/S ( 2 ); Si/Se ( 3 ); Sn/S ( A ); Sn/Se ( 4 ). Reaction of these salts with [Cu(PPh₃)₃Cl] gave a series of organotetrel–copper chalcogenide clusters [(CuPPh₃)₆(PhTE₃)₂] with T/E=Si/S; ( 5 ), Si/Se ( 6 ), Sn/S ( 7 ) and Sn/Se ( 8 ). Compounds 5 – 8 share a common structural motif with two intact {PhTE₃} units coordinating a Cu₆ moiety, which was previously reported with other ligands, and for the Sn and Ge congeners only. If the Sn/Se reaction system was allowed to crystallize more slowly, single crystals of compound [(CuPPh₃)₆(PhSnSe₃)₃Cu₃SnSe] ( 9 ) were obtained, which are based on a larger cluster structure. Hence, 9 might form from 8 through incorporation of additional cluster fragments. The experimentally and quantum chemically determined optical properties were compared to related clusters.     

Hypervalent Intramolecular X←N (X = C,Si, Ge) Coordination in Atranes: Quantum-Chemical Study

The structure and pentacoordination effect in atranes containig Group IVa element were studied ab initio [MP2(full)/6-31G**] and in terms of the density functional theory [B3LYP/6-311+G**]. Stabiliza- tion of these compounds is determined mainly by the secondary hypervalent (R)XN bond (X = C, Si, Ge), whose strength increases in the series X = C, Si, Ge. Attractive (R)XN interaction originates from donation of unshared electron pair on the nitrogen atom to the antibonding ^* _XR orbital.