Abstract Secondary phosphines, R 2 PH, with R= CH 3, C 6 H 5, Me 3 Si, cleave the SiC 2 ring of hexamethylsilirane in an exothermic reaction at room temperature to give silylphosphines, R 2 PSiMe 2 (CMe 2 CHMe 2). Methylphosphine reacts similarly. The reaction of the silirane with RPCl 2 (R= Me, Et, Ph) proceeds differently, giving Me 2 SiCl 2, Me 2 C CMe 2 and cyclo-[RP] 5. With Ph 2 PCl, the reaction with the silirane gives Ph 2 ...