Silicon Tetrahydroborate and Silylene Dihydroborate with Interelement B–H–Si and BSi Bonds

Reactions of laser-ablated boron atoms with SiH4 molecules gave silylene dihydroborate (H2BSiH2) in excess argon, which rearranged to silicon tetrahydroborate [Si­(μ-H)2BH2] upon 300–350 nm irradiation. These reaction products were identified by functional group infrared frequencies, isotopic shifts, and comparison to infrared frequencies calculated by using density functional theory. It is found that H2BSiH2 has planar doublet ground state with electron-deficient B–Si double-bond character. Bonding analysis for Si­(μ-H)2BH2 shows that 3c–2e B–H–Si bond is formed by accepting electrons donated from B–H σ bond.