Silylene preparation

The synthetic approach to silylene complexes (Eq. (2)) is versatile and allows a high variability of both the metals and the substituents at the silicon. A whole series of compounds with bulky substituents like 1 -adamantyloxy, 2-adamantyloxy, neopentyloxy, triphenylmethoxy or f-butylthio could be prepared (Table 1). Compounds with sulfur at silicon are particularly interesting however, their synthesis proved to be very difficult. 

Basically the same methods known from the synthesis of classical metal-silyl complexes can also be applied to the preparation of low valent Si compounds. The procedures given here are summarized with the focus on silylene complexes These are a) reactions of appropriate metal anions with halosilanes, which are the most important methods for the formation of M-Si bonds. Alternatively, silyl... 

A fourth preparation for a stable iminosilane as the THF adduct is the reaction of a silylene with trityl azide.23... 

The discovery that soluble high molecular weight polysilanes may be prepared by the reductive coupling of dichlorodialkylsilanes by alkali metals (1,2) has led to considerable work on the properties of this interesting class of polymers (3,4,5). The preparation of the polymers leaves much to be desired as frequently the high polymer is only a minor product. Mechanistic studies of the reaction with a view to improving the relevant yields have been few (6). The major ones by Zeigler (7,8,9) showed that a silylene diradical was not involved in the reaction, and stressed the importance of polymer solvent interactions. 

The chemistry of unsaturated silicon compounds, i.e. silylenes and molecules having (p-p)ic-sili-con element multiple bonds >Si=E (E = C, Si, Ge, Sn, N, P, As, O, S), is an interesting field of research for the theoretician as well as for the preparative chemist because of the unexpected and fascinating results which can be obtained. Yet 30 years ago, such compounds were considered "non existent" because of the classical "double bond rule", established by Pitzer and Mulliken in the early fifties. Since then, the chemistry of unsaturated silicon compounds proceeded from the investigation of small" species in the gas phase to the synthesis and isolation of stable species with bulky substituents at the > Si =E moiety, and to the determination of their structural features. 

The ability to insert in many element-element bonds is an important property of 1 the r -p1 rearrangement of the pentamethylcyclopentadienyl ligands during the reaction is a prerequisite to show a silylene-type reactivity. From a preparative point of view it is worth mentioning that element-silicon bonds which otherwise are difficult to form are easily accessible with the help of 1. In addition, the leaving group character of the pentamethylcyclopentadienyl substituents allows further chemical transformations (vide infra). 

Following a number of stable Si-N silylenes301 and the stable hapto bonded silylene decamethylsilicocene (Me5C5)2Si 107,265 Kira et al. have described the preparation of the first stable sigma-bonded dialkylsilylene,... 

It is an intriguing idea to stabilize low-valent silicon species, such as silyl cations, silylenes, silenes, and disilenes using intramolecularly coordinating ligands. Corriu et al. succeeded in the preparation of the first hypervalent silyl cation [(8-Me2NCioH6)2SiH]+l/2[l8]z 782 by the reaction of the hexacoordinated diorganosilane... 

Attempts have been made to prepare polysilanes containing the 8-dimethylaminonaphth-l-yl ligand.863 The coupling reaction of 8-dimethylaminonaphth-l-yl lithium with MeSiClj has given the dichlorosilane 909, whose mild reduction with Mg has surprisingly yielded the disilane 910 rather than the expected polysilane (Scheme 128). The formation of the disilane may be rationalized by the insertion of a transient silylene 904 into an Si-N bond of... 

Donor-stabilized silylene complexes of manganese include 45 and 46, which have been prepared by the reaction of the corresponding R2SiH2 or RSiH3 compound with (77S-CsH4R)Mn(CO)3 (R = H, Me).71 128... 

Related crown ether-pendant polysilanes 45 were recently prepared by hydrosilylation post-polymerization functionalization of poly[methyl(H)silylene- -methylphenylsilylene], 37, although due to the low molecular weight of 37, the product 45 is also of low molecular weight.153... 

A different methodology using the reactivity of the Si-H bond in 38 was reported in two communications, as COMC (1995) was being completed. Precursor poly[phenyl(H)silylene] 38 is conveniently prepared by the... 

Several examples of carbenoid ion-radicals are discussed within this book. A silylene anion-radical preparation and properties is exemplified here. Scheme 2.5 shows the path to this species. Tetrakis(di-tert-butytmethylsilyl)disilylene was reduced by lithium or sodium salt of naphthalene anion-radical in THF at 78°C and then 12-crown-4 was added to the resulting reaction mixture. The silylene anion-radical was obtained as the corresponding alkali salt. Red crystals of the salt were isolated and characterized by ESR spectroscopy and x-ray crystallography (Inoue et al. 2007). 

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