Binuclear dimethylplatinum(II) complexes: Reactivity and mechanism in protonolysis and oxidative addition reactions

The reaction of [Pt2Me4(mu-SMe2)(2)] with the ligands 1,3- and 1,4-C6H4(CH=NCH2CH2NMe2)(2), 1,3-BAIB, and 1,4-BAIB, respectively, gave the corresponding complexes [Pt2Me4(1,3-BAIB)], 1, and [Pt2Me4(1,4-BAIB)], 2. Complex 1 reacted with 2 equiv of HCl to give [(PtClMe)(2)(1,3-BAIB)], 3, in which the chloride ligands are trans to the imine nitrogen atoms. Complex 1 undergoes oxidative addition with methyl triflate to give, after recrystallization from moist solvent, the diplatinum(IV) aqua complex [{PtMe3(OH2)}(2)(1,3-BAIB)](CF3SO3)(2), 4, which has the anti stereochemistry of the two aqua ligands. Complex 4 forms a dimer of dimers structure in the solid state through hydrogen bonding between aqua ligands and triflate anions. The reactions of 1 and 2 with HCl are shown to proceed through oxidative addition/reductive elimination sequences, and intermediate hydridoplatinum(IV) intermediates have been identified at low temperature by their H-1 NMR spectra. For example, in reactions with complex 1, binuclear hydride complexes of the types [(PtMe2)(PtHClMe2)(1,3-BAIB)], [(PtHClMe2)(2)(1,3-BAIB)], and [(PtClMe)(PtHClMe2)(1,3-BAIB)] were identified. The initial oxidative addition reactions occur with trans stereochemistry, to give hydride trans to chloride, but isomerization was observed in some cases to give complexes with hydride trans to a nitrogen donor of the 1,3-BAIB ligand. The reactions with DCl or CF3SO3D in CD3OD or CD3OD/CD3CN solvent systems gave all isotopomers of methane CHnD4-n, indicating that there is an easy equilibrium between hydrido(methyl)platinum(IV) and (methane)platinum(II) complexes and easy hydrogen- deuterium exchange between hydridoplatinum groups and -OD groups of the solvent.