Complexes with Platinum−Iridium Bonds:  Stepwise Formation of a PtIr2 Cluster Complex

The reaction of [Pt(dppm)2]Cl2 (dppm = Ph2PCH2PPh2) with [Ir(CO)4]- and dppm in a 1:2:1 ratio leads in a multistep reaction to the new heteronuclear cluster complex [PtIr2(CO)2(μ-CO)(μ-dppm)3], which contains a triangle of metal atoms with each edge bridged by a dppm ligand and in which only the platinum atom is coordinatively unsaturated. The initial step in the reaction leads to formation of the neutral and cationic binuclear complexes [PtIrCl(CO)2(μ-dppm)2] and [PtIr(CO)3(μ-dppm)2]+, respectively. The binuclear complexes then react with additional [Ir(CO)4]- to form the cluster [PtIr2(CO)4(μ-CO)(μ-dppm)2] by insertion into a Pt−P linkage; this cluster can exist in two isomeric forms, each containing a triangular PtIr2 group with the Ir−Ir and one Pt−Ir edge bridged by dppm ligands but differing in stereochemistry. These isomers equilibrate slowly at room temperature, and each reacts easily with dppm to form the final cluster complex [PtIr2(CO)2(μ-CO)(μ-dppm)3]. The structures of the complexes [PtIr2(CO)2(μ-CO)(μ-dppm)3], [PtIr(CO)3(μ-dppm)2][PF6], and one isomer of [PtIr2(CO)4(μ-CO)(μ-dppm)2] have been determined crystallographically, and the reaction sequence has been determined by monitoring reactions through NMR methods.