Reactivity siloxides

A comprehensive study by Wolczanski [4] and Feher [3] groups has led to the conclusion that siloxide as ancillary ligands show an unusual ability to stabilize the reduced early-TM centers. A combination of high reduction potential and high electrophilicity is responsible for the unusually high reactivity in low-valent siloxide derivatives. 

The reactivity of the samarium hydride complex is evidenced [170] by the formation of [Cp2Sm(THF)]2[/4-72-(OSiMe20SiMe20)] a bridged samarium siloxide, from [Cp2Sm(/r-H)]2. The samarium hydride complex is also used in the polymerization of methyl methacrylate [171]. 

Siloxides, like alkoxides, have been employed as ancillary ligands of transition metal complexes, markedly influencing the reactivity of a metal center by electronic and steric effects of the substituents at the silicon [15, 16]. 

An early report of Ti(SiPh3)476, prepared from TiCl4 and KSiPh3, has since been refuted and the compound reformulated as the siloxide Ti(OSiPh3)467. Further studies have shown that early metal-silicon bonds are quite reactive toward oxygen77, underscoring the importance of excluding air in preparations in early metal silyls. 

Scheme 52 Reactivity of an Fe(iii) siloxide complex with a mesoporous silica.

The chemistry of transition metal siloxide complexes has continued to attract considerable attention in the field of material science [1] and catalysis [2], particularly since 1980. The synthesis, reactivity, and bonding of such complexes in a wide variety of supporting ligand environments continues to be explored. In this regard numerous silanediols, disilanols and silanetriols have been described in the literature [3,4], which could be used as building blocks for the preparation of novel titanium-containing heterocubanes and titanasiloxanes [4-6]. 

Most recently siloxides have become attractive ligands for highly reactive metal fragments [303]. Krempner and coworkers have developed an approach to bidentate siloxides using hydrolysis of oligosilanyl dihalides [62, 304—316]. Reactions of the... 

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