Formation and Reactivity of a Hexahydridosilicate [SiH(6)](2−) Coordinated by a Macrocycle‐Supported Strontium Cation

The cationic benzyl complex [(Me(4)TACD)Sr(CH(2)Ph)][A] (Me(4)TACD=1,4,7,10‐tetramethyltetraazacyclododecane; A=B(C(6)H(3)‐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)(μ‐κ(3) : κ(3)‐SiH(6))][A](2) (3 a). Rapid phenyl exchange between phenylsilane molecules is assumed to generate monosilane SiH(4) 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(SiH(3))(thf)(2)][A], with release of H(2). Upon reaction with a weak Brønsted acid, CO(2), and 1,3,5,7‐cyclooctatetraene SiH(4) 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)(μ(2)‐H)(3)(μ(3)‐SiH(3))(2)][A], while (n)OctSiH(3) led to the trinuclear (n‐octyl)pentahydridosilicate complex [(Me(4)TACD)(3)Sr(3)(μ(2)‐H)(3)(μ(3)‐SiH(5) (n)Oct)][A].