Si=P Double Bonds: Experimental and Theoretical Study of an NHCStabilized Phosphasilenylidene

An experimental and theoretical study of the first compound featuring a SiP bond to a two-coordinate silicon atom is reported. The NHC-stabilized phosphasilenylidene (IDipp)SiPMes* (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, Mes*=2,4,6-tBu(3)C(6)H(2)) was prepared by SiMe3Cl elimination from SiCl2(IDipp) and LiP(Mes*)SiMe3 and characterized by X-ray crystallography, NMR spectroscopy, cyclic voltammetry, and UV/Vis spectroscopy. It has a planar trans-bent geometry with a short SiP distance of 2.1188(7)angstrom and acute bonding angles at Si (96.90(6)degrees) and P (95.38(6)degrees). The bonding parameters indicate the presence of a SiP bond with a lone electron pair of high s-character at Si and P, in agreement with natural bond orbital (NBO) analysis. Comparative cyclic voltammetric and UV/Vis spectroscopic experiments of this compound, the disilicon(0) compound (IDipp)SiSi(IDipp), and the diphosphene Mes*PPMes* reveal, in combination with quantum chemical calculations, the isolobal relationship of the three double-bond systems.