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The first tricoordinate fluorosilylenoid, (t-Bu2MeSi)2SiFLi.3THF (1), was synthesized, and its X-ray molecular structure was determined. 1 was synthesized in 40% yield by a bromine-lithium exchange reaction in THF of the corresponding fluorobromosilane with t-Bu2MeSiLi. 1 is best described as an R2SiF- anion attracted to a (Li.3THF)+ cation with a small contribution of resonance structure that consists of a silylene fragment and FLi.3THF. 1 reacts as a nucleophile with MeCl, PhH2SiCl, H2O, and MeOH, as an electrophile with MeLi, and as a silylene with Li (or t-BuLi) and Na, yielding alpha-lithium and alpha-sodium silyl radicals, respectively. Either photolysis or thermolysis of 1 yields the corresponding disilene R2Si=SiR2 (R = t-Bu2MeSi), probably via dimerization of R2Si:.

In hexane or benzene leads via a Peterson-type elimination reaction to the sllene bis(trlmethylsllyl)-adamantyMdenesllane (3), which spontaneously dimerizes in a head-to-head fashion (80-90% yield) to 1,1,2,2-tet-

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Reaction of bromoacylsilane 1 (pink solution) with tBu2 MeSiLi (3.5 equiv) in a 4:1 hexane:THF solvent mixture at -78 °C to room temperature yields the solvent separated ion pair (SSIP) of silenyl lithium E-[(tBuMe2 Si)(tBu2 MeSi)C=Si(SiMetBu2 )](-) [Li⋅4THF](+) 2 a (green-blue solution). Removal of the solvent and addition of benzene converts 2 a into the corresponding contact ion pair (CIP) 2 b (violet-red solution) with two THF molecules bonded to the lithium atom. The 2 a⇌2 b interconversion is reversible upon THF⇌ benzene solvent change. Both 2 a and 2 b were characterized by X-ray crystallography, NMR and UV/Vis spectroscopy, and theoretical calculations. The degree of dissociation of the Si-Li bond has a large effect on the visible spectrum (and thus color) and on the silenylic (29) Si NMR chemical shift, but a small effect on the molecular structure. This is the first report of the X-ray molecular structure of both the SSIP and the CIP of any R2 E=E'RM species (E=C, Si; E'=C, Si; M=metal).

A linear Si-Hg-Hg-Si arrangement and a Hg-Hg distance of 265.69 pm are exhibited by the first two-coordinate, dinuclear σ-bonded organomercury(I) compound 1. It was formed unexpectedly in the reaction of two equivalents of the silane (Me3 SiMe2 Si)3 SiH with tBu2 Hg. In contrast if the reagents are allowed to react in a 1:1 ratio the expected mercury(II) compound (Me3 SiMe2 Si)3 SiHgtBu is obtained.

SiH bonds can be activated by organozinc and silylzinc compounds in the presence of minute amounts of radical initiators such as tBu2Hg or AIBN, yielding zinciosilanes in good yields (see scheme). Activation of dihydridosilanes leads to geminal dizinciosilanes. Zincio‐bridged disilyllithium compounds, which have three (1) and four metal–silicon bonds, were also synthesized.

Upon heating of the highly sterically congested 1,1,2,2-tetrakis(trimethylsilyl)dispiro[3,3′,4,4′biadamantane-1,2-disilacyclobutane] (2) in solution in the presence of trapping reagents, such as 1,3-butadienes, styrene, phenylacetylene, and methanol, the trapping products of the silene bis(trimethylsilyl)adamantylidenesilene (1) are formed with high regioselectivity and good yields. Photolysis of 2 at -196 °C in methylcyclohexane in the absence of trapping agents produces tetrakis(trimethylsilyl)disilene (3). Photolysis of 2 in solution in the presence of 1,3-butadiene leads to a 2:1 mixture of 1,1,2,2-tetrakis(trimethylsilyl)-1,2disilacyclohex-4-ene (10)sthe trapping product of the disilene 3sand of 1,1-bis(trimethylsilyl)-1-silacyclopent-3-ene (11)sthe trapping product of bis(trimethylsilyl)silylene (4)stogether with 2,2′-biadamantylidene. The results of laser flash photolysis and of additional trapping experiments suggest that the sole primary product in the photolysis of 2 is the disilene 3, which dissociates under further irradiation to produce the silylene 4. Heating of 1,1,2,2-tetrakis(trimethylsilyl)dispiro[3,3′,4,4′-biadamantane-1,2-digermacyclobutane] ( 14) in solution results in the quantitative formation of 2,2′-biadamantylidene and of germanium-containing oligomers, while neither bis(trimethylsilyl)adamantylidenegermene (15) nor tetrakis(trimethylsilyl)digermene ( 16) or bis-(trimethylsilyl)germylene ( 17) could be trapped. Upon photolysis 14 behaves similarly to 2, leading to 16 and 17, which could be trapped by 1,3-butadiene.