Mechanism of O₂ activation and methanol production by (di(2-pyridyl)methanesulfonate)Pt^IIMe(OH_n) ^(2-n)- complex from theory with validation from experiment

The mechanism of the (dpms)Pt^IIMe(OH_n) ^(2-n)- oxidation in water to form (dpms)Pt^IVMe(OH) ₂ and (dpms)Pt^IVMe₂(OH) complexes was analyzed using DFT calculations. At pH < 10, (dpms)Pt^IIMe(OH _n)^(2-n)- reacts with O₂ to form a methyl Pt(IV)-OOH species with the methyl group trans to the pyridine nitrogen, which then reacts with (dpms)Pt^IIMe(OH_n)^(2-n)- to form 2 equiv of (dpms)Pt^IVMe(OH)₂, the major oxidation product. Both the O₂ activation and the O-O bond cleavage are pH dependent. At higher pH, O-O cleavage is inhibited whereas the Pt-to-Pt methyl transfer is not slowed down, so making the latter reaction predominant at pH > 12. The pH-independent Pt-to-Pt methyl transfer involves the isomeric methyl Pt(IV)-OOH species with the methyl group trans to the sulfonate. This methyl Pt(IV)-OOH complex is more stable and more reactive in the Pt-to-Pt methyl-transfer reaction as compared to its isomer with the methyl group trans to the pyridine nitrogen. A similar structure-reactivity relationship is also observed for the S_N2 functionalization to form methanol by two isomeric (dpms)Pt^IVMe(OH)₂ complexes, one featuring the methyl ligand trans to the sulfonate group and another with the methyl trans to the pyridine nitrogen. The barrier to functionalize the former isomer with the CH₃ group trans to the sulfonate group is 2-9 kcal/mol lower. The possibility of the involvement of Pt(III) species in the reactions studied was found to correspond to high-barrier reactions and is hence not viable. It is concluded that the dpms ligand facilitates Pt(II) oxidation both enthalpically and entropically.