Transition metal silyl compounds

Early transition-metal silyl compounds have received much less attention, largely due to the fact that general, straightforward synthetic routes have not been available. Syntheses based on oxidative additions are less applicable, given the more electropositive character of the early metals. Particularly for d° silyl complexes, most syntheses are based on nucleophilic displacement of halide by a silyl anion reagent, usually an alkali metal derivative. 

A number of transition-metal silyl compounds possessing M H Si bridges have been structurally characterized. For example, bridging hydrogens have been identified in the dinuclear compounds 27164 and 28165. In 27, the Si-H distances are 1.72 A164. 

Corey JY, Braddock-Wilking J (1999) Reactions of hydrosilanes with transition-metal complexes formation of stable transition-metal silyl compounds. Chem Rev 99 175-292... 

Keywords silyl anions, transition metal silyl compounds, potassium... 

The discovery of the hydrosilation reaction has greatly stimulated research on transition metal-silyl complexes. Currently, there are examples of silyl complexes with almost every transition rnetal. " Silyl hydride complexes are of special interest with respect to the chemistry of the hydrosilation reactions. Such compounds can be seen as the products of oxidative addition into the Si-H bond and thus are intermediates in hydrosilation reactions following the ChaUc-Harrod mechanism. 

The interest in transition metal silyl derivatives stems largely from an interest in how such compounds compare with the very extensive organometallic chemistry of the transition elements and also becanse of the industrial importance... 

M. S. Eisen, Transition-metal silyl derivatives, in The Chemistry of Organic Silicon Compounds (Eds. S. Patai, Z. Rappoport), J. Wiley and Sons, New York, 1998, p. 2037. 

Summary The reactions of undecamethylcyclohexasilylpotassium (1) with various transition metal compounds were examined. Depending on the metal conqiound, 1 can act in four ways (a) as a nucleophile, (b) as a donor ligand, (c) as a strong base, and (d) as a reducing agent. Only (a) and (b) lead to transition metal silyl complexes, while (c) and (d) bring on unwanted side reactions. 

T. D. Tilley, "Transition-Metal Silyl Derivatives", in The Chemistry of Organosilicon Compounds (Eds. S. Patai, Z. Rappoport), Wiley, New York, 1989, p. 1415 and refs, cited therein T. D. Tilley, Appendix to "Transition-Metal Silyl Derivatives", in The Silicon-Heteroatom Bond (Eds. S. Patai, Z. Rappoport), Wiley, New York, 1991, p. 309 and refs, cited therein. 

Novel photochemical (and thermal) reactions of macrocyclic oxa-sila-acetylenic ring systems (expected to show unusual optical properties because of electronic effects arising from orbital overlap of the acetylenic n system with the silicon a bonds and the oxygen lone-pair electrons) were described. While thermolysis in the presence of a transition metal carbonyl compound gave cyclization to both benzenoid and fulvene species, photolysis in the presence of the transition metal carbonyl compound (which catalyzes 1,2-silyl shifts across a carbon-carbon triple bond) gave fulvene and vinylidene products, the latter being readily photolyzed to the fulvene 159 (equation 101). 

Silicon-transition metal chemistry is a relatively new area. The work of Hein and his associates (1941) on Sn—Co derivatives established the possibility of forming bonds between a Group IVB metal and a transition element 139), but it was another fifteen years before CpFe(CO)2SiMej 203), the first of many silyl derivatives, was synthesized. The interest in these compounds derives from (1) comparison with the corresponding alkyl- and Ge-, Sn-, and Pb- transition metal (M) complexes, including the role of ir-back-bonding from filled d orbitals of M into empty d orbitals on Si (or other Group IVB metal), and (2) expectation of useful catalytic properties from such heteronuclear derivatives. 

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