Roll-over Cyclometalation of 2,2′-Bipyridine Platinum(II) Complexes in the Gas Phase: A Combined Experimental and Computational Study

In a combined experimental/computational investigation, the gasphase behavior of cationic [Pt(bipy)(CH3)((CH3)(2)S)](+) (1) (bipy=2,2'-bipyridine) has been explored. Losses of CH, and (CH3)(2)S from 1. result in the formation of a cyclometalated 2,2'-bipyrid-3-yl species [Pt(bipy-H)](+) (2). As to the mechanisms of ligand evaporation, detailed labeling experiments complemented by DFF-based computations reveal that the reaction follows the mechanistically intriguing "roll-over" cyclometalation path in the course of which a hydrogen atom from the C(3)-position is combined with the Pt-bound methyl group to produce CH, Activation of a C-H-bond of the (CH3)(2)S ligand occurs as well, but is less favored (35% versus 65%) as compared to the C(3)-H bond activation of bipy. In addition, the thermal ion/molecule reactions of [Pt(bipy-H)](+) with (CH3)(2)S have been examined, and for the major pathway, that is, the dehydrogenative coupling of the two methyl groups to form C2H4, a mechanism is suggested that is compatible with the experimental and computational findings. A hallmark of the gas-phase chemistry of [Pt(bipy-H)](+) with the incoming (CH3)(2)S ligand is the exchange of one (and only one) hydrogen atom of the bipy fragment with the C-H bonds of dimethylsulfide in a reversible "roll-over" cyclometalation reaction. The Pt-II-mediated conversion of (CH3)(2)S to C2H4, may serve as a model to obtain mechanistic insight in the dehydrosulfurization of sulfur-containing hydrocarbons.