N. N. Zemlyanskii

Divalent silicon, germanium, and tin compounds with element--heteroatom bonds

Principal results and trends in chemistry of organic derivatives of divalent silicon, germanium, and tin containing bonds between these elements and the halogen, nitrogen, oxygen, and sulfur atoms are briefly surveyed. Selected characteristics of compounds with the element--phosphorus and element--arsenic bonds are discussed for comparison. Data on the synthesis and structures of new types of these compounds, viz., germanium(ii) diacylates, the alkoxy derivatives E14(OR)2 and E14(OR)Y (E14 = Ge, Sn; R = Me2NCH2CH2; Y = Cl, AcO, (Me3Si)2N), and the ate-complexes Li(+)[E14(OCH2CH2NMe2)3](–) and [Li(thf)2](+)[TsiE14(SBu)2](–) (E14 = Ge, Sn; Tsi = (Me3Si)3C), are presented. It was established for the first time that germanium(ii) and tin(ii) derivatives can be stabilized in the monomeric form only through the intramolecular Nsp3→E14 coordination bonds and the σ-acceptor effect of the oxygen atoms without introduction of bulky substituents.

Heteroorganic betaines: 1. Synthesis of betaines containing the+P−C−Si−S− and+P−C−C−S− fragments and their characterization by multinuclear NMR spectroscopy

A method for the synthesis of a new class of betaines,viz., R31P+CR2R3SiR4R5S−, was developed. The experimental evidence for the intermediate formation of betaines R31P+−CR2R3−CR4R5−S− in the Wittig reaction for a series of thiocarbonyl compounds was obtained. A comparative analysis of the NMR spectra of betaines containing the+P−C−Si−S− and+P−C−C−S− fragments was performed.

Synthesis of the first kinetically stable dibenzosilafulvene

The first stable dibenzosilafulvene, 9-{[8-(dimethylaminomethyl)-1-naphthyl]phenylsil-1-ylium}fluoren-9-ide (7a), was obtained in one step from 9-fluorenyllithium and chloro[8-(dimethylaminomethyl)-1-naphthyl]phenylsilane as a stable solvate with THF. The structure of the zwitterionic compound7a was established by1H,13C, and29Si NMR in solution and in the solid state. The reactions of compound7a with crotonaldehyde, ethanol, and triethylethylidenephosphorane are described. The data on the synthesis of alkoxy- and alkylthiochloro-9-fluorenylsilanes and their phosphonium salts are given.

New Stable Germylenes, Stannylenes, and Related Compounds II. Bis(butylthio)tin(II) and ate-Complexes [(Me3Si)3CE(μ-SBu)2Li(THF)2] (E = Ge,Sn). Synthesis and Structure

By reaction of Me3SiSBu with anhydrous tin(II) chloride bis(butylthio)tin was obtained that exemplified a coordination polymer [Sn(SBu)2]n, whose elementary unit contained according to X-ray diffraction study three independent four-membered rings Sn2S2 of unusual geometry. It was demonstrated that polymeric thiolates [E(SBu)2]n (E = Ge, Sn) readily reacted with TsiLi (Tsi = C(SiMe3)3) in a mixed solvent ether THF affording in a good yield ate-complexes [(Me3Si)3CE(μ-SBu)2Li(THF)2]. Both complexes contain a four-membered ring in a butterfly conformation where the lithium atom is symmetrically bonded to both sulfur atoms, and the coordination polyhedra of Ge and Sn atoms may be regarded as distorted tetrahedra AB3X, where one of coordination places is occupied by unshared electron pair. The structure of the ate-complexes observed in a crystal is conserved also in solution of nonpolar solvents.

New heteroorganic betaines containing the (+)E15—C—E14—X(–) and (+)E15—C—E14(–) structural fragments (E15 = P, As; E14 = Si, Ge, Sn; X = C, S, O, NR)

The review surveys the data on the reactions of phosphorus and arsenic ylides with compounds containing E=X bonds (E = C, Si, Ge, or Sn; X = C or S), cyclic oligomers (R2ES)n (n = 2 or 3), and heavier analogs of carbenes. These reactions give rise to two new classes of heteroorganic betaines containing the (+)E15—C—E14—X(–) (I) and (+)E15—C—E14(–) (II) (E15 = P or As; E14 = Si, Ge, or Sn; X = C or S) structural fragments. Procedures for the synthesis of these compounds, their reactivities, the X-ray diffraction structures, and the electronic structures established by high-level quantum-chemical calculations are considered in detail. The carbon analogs of betaines of type I, viz., compounds bearing the (+)P—C—C—X(–) fragment (III), are also discussed. The latter were long considered as possible intermediates in the reactions of compounds containing the polar C=X bond (X = C, O, S, NR, etc.) with phosphorus ylides (classical Wittig and Corey—Chaykovsky reactions and related processes).

Heteroorganic betaines: Reactions of betaines containing the+P−C−Si−S− fragment

The [Ph3P+−CMe2−SiMe2−SEt]Br− salt was prepared by the reaction of betaine Ph3P+−CMe2SiMeR−S− (1a: R=Me) with EtBr. Acetylation of betaine1a or Et3P+−CHMeSiMe2−S− (2a) afforded 2,2,6-trimethyl-1,3-dioxa-2-silacyclohex-5-ene-4-thione or the [Et3P+−CHMeSiMe2Cl]Cl− salt depending on the reagent ratio. The reactions of betaines1a, b (1b: R=Ph) or2 with compounds (R3Sn)2X (X=O or NMe) can be used for the generation of silanones [RMeSi=O] and silaneimines [RMeSi=NMe] in solutions. The reactivity of betaines Ph3P+−CHR1SiMeR2−S− (R1=H or Me and R2=Me or Ph) is determined by the equilibrium between the zwitterionic and ylide Ph3P=CR1SiMeR2SH tautomers that exist in solutions.

Heteroorganic betaines. 8. Synthesis and structures of silicon- and germanium-containing organoarsenic betaines R13As+—CR2R3—EMe2—S– (E = Si, Ge)

The reactions of ylides R13As=CHR2 with hexamethyl-2,4,6-trisila- and hexamethyl-2,4,6-trigermatrithiacyclohexanes afforded betaines R13As+—CHR2—SiMe2—S– (2) (R1 = Et; R2 = Ph (a), Me3Si (b); R1 = R2 = Ph (c)) and Et3As+—CH(SiMe3)—GeMe2—S– (3), respectively. Betaines 2a,b and 3 were characterized by multinuclear NMR spectroscopy. According to the X-ray diffraction data, in the crystals the As+—C—E—S– main chain (E = Si or Ge) of molecules 2a,b and 3 adopts a twisted cis conformation due to strong intramolecular Coulomb interactions between the anionic and cationic centers. The equilibrium geometries of isolated molecules 2a and 3, which were calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set), are in qualitative agreement with the X-ray data. In solutions, betaines 2a (in the absence of Li salts) and 2c (in the presence of LiBr) selectively decomposed according to the Corey—Chaykovsky reaction, which was accompanied by elimination of R3As and, probably, the intermediate formation of silathiirane. The subsequent transformation of the latter afforded 2,2,4,4-tetramethyl-5-phenyl-2,4-disila-1,3-dithiolane.

Heteroorganic betaines. 7. Synthesis and structure of a germanium-containing organophosphorus betaine Et3P+-CHMe-GeMe2-S-

Germanium-containing organophosphorus betaine Et3P+—CHMe—GeMe2—S– was synthesized by the reaction of hexamethylcyclotrigermatrithiane with Et3P=CHMe. The structure of the betaine was established by X-ray diffraction analysis and multinuclear NMR spectroscopy. In the crystal, the P+—C—Ge—S– main chain of the molecule adopts a folded cis-gauche conformation due to strong Coulomb interactions between the anionic and cationic centers. The equilibrium geometry of the isolated molecule was calculated within the framework of the density functional theory (the PBE functional, the TZ2P basis set). The calculated geometric characteristics are in qualitative agreement with the X-ray data. The structure of the betaine is compared with the structure of its silicon-containing analog studied previously.

Mechanisms and kinetics of the elementotropic rearrangements of tetrahydro-4,4,8,8-tetramethyl-4,8-disila-sym-indacene

The dynamic stereochemistry of silatropic rearrangements of tetrahydro-4,4,8,8-tetra-methyl-4,8-disila-sym-indacene (dimer of 6,6-dimethyl-6-silafulvene), which exists in solution as an equilibrium mixture of two interconverting isomers, was studied. The mechanisms and complete kinetic scheme of rearrangements were established using1H,13C, and29Si 2D quantitative EXSY NMR spectroscopy. It was found that the interconversion and degenerate rearrangements of the observed isomers proceedvia two concurrent pathways due to the formation of different intermediates. The activation parameters of the rearrangements were determined by means of total lineshape analysis of dynamic NMR (DNMR) spectra.

THE SYNTHESIS OF TRISILGERMANIUM AND TRISILTIN CHLORIDES

At present an intensive research is carried out of organometallic compounds containing the trisil group [(MeaSi)3C--, Tsi]. Of the trisil derivatives of the group IVB elements only the compounds of the type RnTsiSiX3-n (I) have been briefly described, whereby interesting rearrangements have been observed for (I) (n = i, 2) [1-3]. The compounds Me3MTsi (M = Ge, Sn) [4, 5] are also known; however, data on their reactivity are not available.