Silanolate complexes

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

A large effective cation size should suppress the cation-siloxane coordination, favor the Iree ion pair 3 in reaction 10, and enhance charge separation. The anticipated effects would be values of n approaching 1 in the rate equation 9, greatly enhanced rates of polymerization, and suppressed formation of cyclosiloxanes. Evidence that these effects are achieved is indicated by the effects seen with R4N countercations (35), the lithium cryp-tates (25, 27), and the crown ether-potassium silanolate complexes (39, 40). Additional evidence for the influence of the countercation on the equilibria is seen in deviations of the amounts of oligomer produced in equilibrated poly(dimethylsiloxane) from the normal distribution caused by specific interactions between the potassium silanolate chain ends (37, 38). More de-... 

The yttrium silanolate complex 11 shows good catalytic activity with high anti-Markovnikov regioselectivity in the hydrosilylation of 1-decene (Tablet) [59]. Cationic silanolate rare-earth metal alkyl species derived from 11 were either inactive or exhibited significantly diminished activity, possibly as a result of tight binding of the benzene solvent as well as decomposition of the cationic metal hydride intermediate. 

Figure 7.2 Tetrabutylammonium silyloxide salt (E)-206 and the TBAF-silanol complex (E)-205.

XV. GROUP-10 SILICON-CONTAINING COMPLEXES A. Silyl, Bis(silyl) and Silanol Complexes... 

---