Activation of Dioxygen by Dimethylplatinum(II) Complexes

The
ligands RN­(CH2-2-C5H4N)2 (L1, R = CH2CH2OH; L2, R = CH2CH2CH2OH; L3, R = 2-C6H4OH) have been designed to give
dimethylplatinum­(II) complexes that can activate dioxygen in the absence
of a protic solvent. The ligands react with [Pt2Me4(SMe2)2] to give an equilibrium mixture,
with the major constituent being [PtMe2(κ2-N,N′-L)] (1a, L = L1; 1b, L = L2; 1c, L = L3). In the absence of air, 1a reacts with solvent CH2Cl2 to give
[PtMe2(CH2Cl)­(κ3-N,N′,N″-L1]­Cl, while 1c decomposes with loss of methane to give
[PtMe­(κ3-N,N′,N″-L3-H)] and then, by reaction with
solvent, the binuclear complex [{PtMe­(κ3-N,N′,N″-L3-H)}2(μ-H)]­Cl. In the presence of oxygen
the complexes 1 in CH2Cl2 solution
react to give [Pt­(OH)­Me2(κ3-N,N′,N″-L)]­Cl, when L = L1 or L2, or
[Pt­(OH)­Me2(κ3-N,N′,O-L-H)], when L = L3. The complex [Pt­(OH)­Me2(κ3-N,N′,N″-L2)]Cl decomposed in the presence of air to
give the binuclear complex [{PtMe2(2-C5H4NCO2)­(μ-OH)}2]. The factors influencing
reactivity and mechanism in these reactions are elucidated, and the
presence of both a free pyridyl donor (push group) and a free hydroxyl
(pull group) is suggested to give a synergy for dioxygen activation
by dimethylplatinum­(II) complexes.