H–C–SiH3: Direct Generation and Spectroscopic Identification of Ethylidene’s Cousin.

     Abstract.  Ground-state triplet silaethylidene, generated directly by the reaction of ³P carbon atoms with silane under matrix isolation conditions in solid Ar (10–12 K), has been thoroughly characterized by the EPR and IR spectra of both the parent and perdeuterated isotopologs. A theoretical anharmonic vibrational analysis based on a CCSD(T)/cc-pVTZ complete quartic force field gave remarkable agreement with the experimental IR fundamentals, generally within 10 cm^–1 and without any empirical scaling of the ab initio frequencies. Silaethylidene exhibits a C_S minimum with a H–C–Si angle near 153 °, but the barrier to H–C–Si linearity (C­_3v symmetry) is only 0.24 kcal mol^–1. This minuscule barrier can be surmounted by zero-point vibrations, as evident from the EPR data. The triplet stabilizing effect of the electropositive SiH₃ group amounts to about 15 kcal mol^–1.