Formation and Reactivity of a Hexahydridosilicate [SiH6](2-) Coordinated by a Macrocycle-Supported Strontium Cation
Résumé
The cationic benzyl complex [(Me(4)TACD)Sr(CH2Ph)][A] (Me(4)TACD=1,4,7,10-tetramethyltetraazacyclododecane; A=B(C6H3-3,5-Me-2)(4)) reacted with two equivalents of phenylsilane to give the bridging hexahydridosilicate complex [(Me(4)TACD)(2)Sr-2(thf)(4)(mu-kappa(3) : kappa(3)-SiH6)][A](2) (3 a). Rapid phenyl exchange between phenylsilane molecules is assumed to generate monosilane SiH4 that is trapped by two strontium hydride cations [(Me(4)TACD)SrH(thf)(x)](+). Complex 3 a decomposed in THF at room temperature to give the terminal silanide complex [(Me(4)TACD)Sr(SiH3)(thf)(2)][A], with release of H-2. Upon reaction with a weak Bronsted acid, CO2, and 1,3,5,7-cyclooctatetraene SiH4 was released. The reaction of a 1 : 2 mixture of cationic benzyl and neutral dibenzyl complex with phenylsilane gave the trinuclear silanide complex [(Me(4)TACD)(3)Sr-3(mu(2)-H)(3)(mu(3)-SiH3)(2)][A], while (n)OctSiH(3) led to the trinuclear (n-octyl)pentahydridosilicate complex [(Me(4)TACD)(3)Sr-3(mu(2)-H)(3)(mu(3)-SiH(5)(n)Oct)][A].