Matrix reactivity of Al and Ga atoms (M) in the presence of silane: generation and characterization of the eta2-coordinated complex M.SiH4, the insertion product HMSiH3, and the MI species MSiH3 in a solid argon matrix

Matrix isolation experiments give evidence for the formation of the loosely bonded metal-silane complex M.SiH(4) by the spontaneous reaction of Al or Ga atoms (M) with silane in a solid Ar matrix at 12 K; however, Ga(2) appears to insert spontaneously into an Si--H bond to form HGaGaSiH(3), probably with the structure HGa(micro-SiH(3))Ga. In M.SiH(4) the metal atom is eta(2)-coordinated by the silane, resulting in a species with C(2v) symmetry. The complex has a distinctive photochemistry: it can be converted on photolysis at lambda approximately 410 or approximately 254 nm to its tautomer, HMSiH(3), which also has a doublet ground electronic state and from which it can be regenerated with lambda approximately 580 nm radiation. Broadband UV-visible photolysis (lambda=200-800 nm) results in decomposition of HMSiH(3), the univalent species MSiH(3) being the only detectable product. The experimental data collected for several silane isotopomers (SiH(4), SiD(4), and SiD(3)H) and different reagent concentrations, together with the results of sophisticated quantum chemical calculations, are used to explore in detail the properties of the detected species and the reaction pathways compassing their formation.