The SiH radical supported by two N-heterocyclic carbenes.

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)Si[double bond, length as m-dash]Si(Idipp)][B(Ar)] ([B(Ar)], Idipp = C[N(CH-2,6-Pr)CH], Ar = CH-3,5-(CF)) reveal a reversible one-electron reduction at a low redox potential ( = -2.15 V Fc/Fc). Chemical reduction of [B(Ar)] with KC affords selectively the green, room-temperature stable mixed-valent disilicon(0,I) hydride Si(H)(Idipp) (), in which the highly reactive SiH molecule is trapped between two N-heterocyclic carbenes (NHCs). The molecular and electronic structure of was investigated by a combination of experimental and theoretical methods and reveals the presence of a π-type radical featuring a terminal bonded H atom at a flattened trigonal pyramidal coordinated Si center, that is connected a Si-Si bond to a bent two-coordinated Si center carrying a lone pair of electrons. The unpaired electron occupies the Si[double bond, length as m-dash]Si π* orbital leading to a formal Si-Si bond order of 1.5. Extensive delocalization of the spin density occurs conjugation with the coplanar arranged NHC rings with the higher spin density lying on the site of the two-coordinated silicon atom.