A stable silicon-based allene analogue with a formally sp-hybridized silicon atom

Abstract

Carbon chemistry exhibits a rich variety in bonding patterns, with homo- or heteronuclear multiple bonds involving sp-hybridized carbon atoms as found in molecules such as acetylenes, nitriles, allenes and carbon dioxide. Carbon's heavier homologues in group 14 of the periodic table--including silicon, germanium and tin--were long thought incapable of forming multiple bonds because of the less effective p(pi)-p(pi) orbital overlap involved in the multiple bonds. However, bulky substituents can protect unsaturated bonds and stabilize compounds with formally sp-hybridized heavy group-14 atoms: stable germanium, tin and lead analogues of acetylene derivatives and a marginally stable tristannaallene have now been reported. However, no stable silicon compounds with formal sp-silicon atoms have been isolated. Evidence for the existence of a persistent disilaacetylene and trapping of transient 2-silaallenes and other X = Si = X' type compounds (X, X' = O, CR2, NR, and so on) are also known, but stable silicon compounds with formally sp-hybridized silicon atoms have not yet been isolated. Here we report the synthesis of a thermally stable, crystalline trisilaallene derivative containing a formally sp-hybridized silicon atom. We find that, in contrast to linear carbon allenes, the trisilaallene is significantly bent. The central silicon in the molecule is dynamically disordered, which we ascribe to ready rotation of the central silicon atom around the molecular axis.

The Versatile Chemistry of Disilenides: Disila Analogues of Vinyl Anions as Synthons in Low-valent Silicon Chemistry

“…Insertion of the donor-free silylene 3a into a SiCl bond of SiCl 4 had provided the 1,1,1,2-tetrachlorodisilane precursor that was then converted to the trisilaallene 5a upon reduction (Chart 1; 3a, 5a: R = SiMe 3 ). 8 The extension of this prototypical reactivity of silylene 3a to the analogous reaction of 3a with t BuSiCl 3 afforded the 1,1,2-trichlorodisilane 19. Reduction of 19 with the required amount of potassium/graphite furnished the first trialkyldisilenide 20 in acceptable yield (Scheme 6).…”

A Helmeted Dialkylsilylene

“…Stable trisilaallene 52 was synthesized as the first silicon compound with a formal sp-silicon atom starting from stable silylene 1 in 2003. 71 The reaction of 1 with silicon tetrachloride giving Si-Cl bond insertion product 25 (Eq. 10) followed by the reduction with KC 8 affords trisilaallene 52 in overall 42% yield (Eq.…”

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

“…Because the insertion of silylene 1 into C-Cl [43][44][45][46][47][48] and Si-Cl [48][49][50][51][52][53] bonds have been reported, it would be desirable to propose the mechanisms of the present acylsilane formation as being consistent with the features of these precedents. The reactions of isolable dialkylsilylene 1 with chloroalkanes afford rather unusual product mixtures depending on the substrates.…”

“…The insertion reactions of silylene 1 into the Si-Cl bonds of chlorosilanes have been found to occur cleanly [49,50]; hence, the concerted mechanism via three-membered cyclic transition states has been proposed. The mechanism has been supported by the detailed DFT calculations [55][56][57].…”