Iridium phosphinidene complexes: a comparison with iridium imido complexes in their reaction with isocyanides

18-Electron nucleophilic, Schrock-type phosphinidene complexes 3 [Cp*(Xy—N≡C)Ir═PAr] (Ar = Mes*, Dmp, Mes) are capable of unprecedented [1 + 2]-cycloadditions with 1 equiv of isocyanide RNC (R = Xy, Ph) to give novel iridaphosphirane complexes [Cp*(Xy—N≡C)IrPArC═NR]. Their structures were ascertained by X-ray diffraction. Density functional theory investigations on model structures revealed that the iridaphosphirane complexes are formed from the addition of the isocyanide to 16-electron species [Cp*Ir═PAr] forming first complex 3 that subsequently reacts with another isocyanide to give the products following a different pathway than its nitrogen analogue [Cp*Ir≡Nt-Bu] 1.