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(μ-SMe2)2] are reported.
The reaction with the more rigid ligand phenO gave [PtMe2(κ2N,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)­Me2(phenO)], but
under an inert atmosphere it gave [Pt­(OH)­(OMe)­Me2(phen)],
in a reaction involving N–O bond activation. In contrast, the
reaction of [Pt2Me4(μ-SMe2)2] with bipyO occurred by C–H bond activation to give
methane and [PtMe­(κ2N,C-C5H4N-C5H3NO)­(SMe2)], which underwent ligand substitution with pyridine, triphenylphosphine,
or bis­(diphenylphosphino)­methane (dppm) to give [PtMe­(κ2N,C-C5H4N-C5H3NO)­(NC5H5)], [PtMe­(κ2N,C-C5H4N-C5H3NO)­(PPh3)], or the binuclear
[{PtMe­(κ2N,C-C5H4N-C5H3NO)}2(μ-dppm)],
respectively. With bis­(diphenylphosphino)­ethane (dppe), ligand substitution
gave [PtMe­(κ1C-C5H4N-C5H3NO)­(dppe)], which contains a monodentate
metalated bipyO ligand. The mechanisms of the key reactions are discussed.