Carbon Hydrogen versus Nitrogen Oxygen Bond Activation in Reactions of N-Oxide Derivatives of 2,2′-Bipyridine and 1,10-Phenanthroline with a Dimethylplatinum(II) Complex

The reactions of the potential oxygen atom donor ligands 1,10-phenanthroline N-oxide (phenO) and 2,2-bipyridine N-oxide (bipyO) with the dimethylplatinum(II) complex [Pt2Me4(mu-SMe2)(2)] are reported. The reaction with the more rigid ligand phenO gave [PtMe2(2N,O-phenO)], which underwent oxidative addition with 4-t-Bu-C6H4CH2Br to give the platinum(IV) complex [PtBrMe2(CH2C6H4-4-t-Bu)(phenO)]. The complex [PtMe2(phenO)] reacted with methanol in air to give [Pt(OH)(OMe)Me-2(phenO)], but under an inert atmosphere it gave [Pt(OH)(OMe)Me-2(phen)], in a reaction involving NO bond activation. In contrast, the reaction of [Pt(2)Me4(mu-SMe2)(2)] with bipyO occurred by CH bond activation to give methane and [PtMe(kappa N-2,C-C5H4N-C5H3NO)(SMe2)], which underwent ligand substitution with pyridine, triphenylphosphine, or bis(diphenylphosphino)methane (dppm) to give [PtMe(kappa N-2,C-C5H4N-C5H3NO)(NC5H5)], [PtMe(kappa N-2,C-C5H4N-C5H3NO)(PPh3)], or the binuclear [{PtMe(kappa N-2,C-C5H4N-C5H3NO)}2(?-dppm)], respectively. With bis(diphenylphosphino)ethane (dppe), ligand substitution gave [PtMe(kappa C-1-C5H4N-C5H3NO)(dppe)], which contains a monodentate metalated bipyO ligand. The mechanisms of the key reactions are discussed.