Comparative chemistry of isolable divalent compounds of silicon, germanium, and tin

Abstract

Recent studies of the synthesis, structures, spectroscopic properties, and reactions of a series of isolable metallylenes (R2E:, E = Si (1), Ge (2), and Sn (3); R2 = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) are summarized. Because these group-14 metallylenes bear the same helmet-like ligand, a straightforward discussion of the element-dependence of the intrinsic properties of the group-14 element divalent compounds is possible. All these metallylenes were monomeric both in solution and in the solid state, indicating the effective steric protection by the ligand against dimerization. A small sigma-pi conjugation between C-Si(substituent) sigma orbitals and the vacant npz orbitals of divalent atoms in R2E: exists and the extent decreases in the order E = Si > Ge > Sn, as evidenced by UV-vis and NMR spectroscopies and X-ray crystallography. However, the extent of the sigma-pi conjugation in metallylenes 1-3 was much smaller than the electron-donating effects of neighboring nitrogen atoms in known stable cyclic diamino-substituted metallylenes, and hence metallylenes 1-3 are regarded as the least electronically perturbed. Comparative studies of the unique reactions among these metallylenes are also discussed.

A Helmeted Dialkylsilylene

“…9), indicating that the reaction is not a simple concerted insertion of 1 into a C-Cl bond, while the detailed mechanism remains still open (vide infra). 39 t -BuCl C 6 The diverse reactions of silylene 1 with various haloalkanes suggest the complicated nature of the reaction mechanisms. The initial event in all the reactions may be the formation of a Lewis acid-base complex of the haloalkane with 1 as proposed previously.…”

“…6 Historically, the first convincing evidence for the generation of dimethylsilylene as a representative of dialkylsilylenes was obtained by the high-temperature thermolysis of the corresponding 7-silanorbornadiene derivative in 1964 (Eq. 1).…”

“…9). (1) The Si 1 -Si 2 -Si 3 skeleton is significantly bent with a bond angle of 136.49 (6) , indicating that the bonding at Si 2 atom cannot be described by using simple sp-hybridization anymore. (2) The two Si-Si bond lengths in 52 (2.177(1) and 2.188(1) Å ) are in the range of those for typical stable disilenes.…”

Recent developments in the chemistry of stable silylenes

“…Treatment of the silaallene with water gave the expected 1,3-dihydroxytrisilane 60 [63]. The germanium analogue of 59 has been reported recently [64]. There are as yet no reports of metal coordination complexes of 4.…”

Reactions of an Isolable Dialkylsilylene with Aroyl Chlorides. A New Route to Aroylsilanes

“…The 1:1 reactions of dialkylsilylene 1 [32][33][34][35][36][37] with benzoyl and 4-substituted benzoyl chlorides 2a-2c at −30 • C afforded the corresponding benzoyl(chloro)silanes 3a-3c in high yields, indicating that the C(carbonyl)-Cl bond is much more reactive than the carbonyl group (Equation (4)) [38]. No significant difference was observed in the reactivity among benzoyl chlorides 2a-2c.…”