"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 gas-phase behavior of cationic [Pt(bipy)(CH(3))((CH(3))(2)S)](+) (1) (bipy=2,2'-bipyridine) has been explored. Losses of CH(4) and (CH(3))(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 DFT-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(4). Activation of a C-H-bond of the (CH(3))(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 (CH(3))(2)S have been examined, and for the major pathway, that is, the dehydrogenative coupling of the two methyl groups to form C(2)H(4), 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 (CH(3))(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 (CH(3))(2)S to C(2)H(4) may serve as a model to obtain mechanistic insight in the dehydrosulfurization of sulfur-containing hydrocarbons.