“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 CH‐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 CH 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.