Ring Expansion of a Platinacyclopropane to a Platinacyclopentane by Double Insertion of Isocyanides into Pt−C Bonds

A platinum isocyanide complex bearing a η2-TCNE ligand, (η2-TCNE)Pt(η-CNC6H3-2,6-Me2)2 (1), was synthesized, and its crystallographic study revealed the coordination mode of the η2-TCNE ligand to be a typical metallacyclopropane extreme, in which back-donation from metal to TCNE contributes primarily to the stabilization of 1. Treatment of 1 with 2 equiv of CNC6H3-2,6-Me2 resulted in ring expansion of the platinacyclopropane by insertion of CNC6H3-2,6-Me2 into each Pt−C bond of the metallacycle, leading to formation of a new complex having a platinacyclopentane structure, (TCNE)Pt(η-CNC6H3-2,6-Me2)4 (4). Although the molecular structures of palladium and nickel homologues of 1 were close to the corresponding metallacyclopropane, no metallacyclopentane complex was obtained under similar conditions. Studies on variable-temperature NMR spectroscopy and spin-saturation transfer measurement of 4 showed exchange of the imidoyl CNC6H3-2,6-Me2 group and the coordinated CNC6H3-2,6-Me2 ligand in solution, suggestin...