Diphosphetes—substituent stabilized ring systems

Abstract

The mechanism of the formation of σ²P, σ⁴P-1,2-diphosphetes from phosphaacetylene and phosphinocarbene has been explored by quantum chemical methods. A stepwise mechanism has been established, and no transition state for a concerted pathway could be obtained. The electron distribution of the ring can be understood in terms of a MO model, where the two substituents at phosphorus act as a pseudo π center. Amino substituents on the σ⁴ phosphorus and silyl group on the neighbouring carbon change the stability order of the possible isomers, stabilizing the 1,2-diphosphete ring. Substitution at the σ²P—by increasing its valence—destabilizes the diphosphete ring, which remains stable only as a result of the amino and silyl substituents.