On the d6-Transition Metal Complex Formation of Electron-Rich Methylenephosphanes, a Quantum Chemical Investigation

Abstract

d(6)-Transition metal fragments M(CO)(5) (M = Cr, Me, W) form mono- and binuclear complexes with methylenephosphanes. In the mononuclear complexes the metal fragment adds to the lone pair at the phosphorus atom without considerable geometrical change of the original phosphaalkene moiety. Amino substitution at the phosphorus atom yields a slightly more stable complex than amino substitution at the carbon atom. The latter substitution pattern causes an inverse polarization of the P-C pi -bond. As a further consequence, in the corresponding transition metal complexes, the phosphorus atom is slightly pyramidalized. In the binuclear complexes the transition metal atoms tend to adopt a distorted bipyramidal arrangement at the phosphorus atom with concomitant lengthening of the P-C bond. The stretching of the P-C pi -bond is required to form a second lone pair for coordination at the phosphorus atom. However, the longest P-C bonds are achieved by C-diamino-substituted methylenephosphanes with overall bulky alkyl groups at the phosphorus and nitrogen atoms. It has the effect of not only extending the P-C bond but also widening the angle at the phosphorus atom.