Generating and dimerizing the transient 16-electron phosphinidene complex [Cp*Ir=PAr]: a theoretical and experimental study

The properties of the 16-electron phosphinidene complex CpRIr=PR] were investigated experimentally and theoretically. Density functional theory calculations show a preferred bent geometry for the model complex CpIr=PH], in contrast to the linear structure of CpIr=NH]. Dimerization to give CpIr=PH]2] and ligand addition to afford Cp(L)Ir=PH] (L=PH3, CO) were calculated to give compounds that were energetically highly favorable, but which differed from the related imido complexes. Transient 16-electron phosphinidene complex Cp*Ir=PAr] could not be detected experimentally. Dehydrohalogenation of Cp*IrCl2(PH2Ar)] in CH2Cl2 at low temperatures resulted in the novel fused-ring systems 17 (Ar=Mes*) and 20 (Ar=Mes), with dimeric Cp*Ir=PAr]2] being the likely intermediate. Intramolecular C-H bond activation induced by steric factors is considered to be the driving force for the irreversible formation of 17 and 20. ONIOM calculations suggest this arises because of the large steric congestion in Cp*Ir=PAr]2], which forces it toward a more reactive planar structure that is apt to rearrange.