Probing the Reactivity and Radical Nature of Oxidized Transition Metal-Thiolate Complexes by Mass Spectrometry

Transition metal thiolate complexes such as [PPN] + [RuL 3 ] - (PPN = bis(triphenylphosphoranylidene) ammonium and L = diphenylphosphinobenzenethiolate) are known to undergo addition reactions with unsaturated hydrocarbons via the formation of new C-S bonds in solution upon oxidation. The reaction mechanism is proposed to involve metal-stabilized thiyl radical intermediates, a new type of distonic ions such as [RuL 3 ] + ion in the case of [PPN] + [RuL 3 ] - . This study presents the reactivity and structure investigation of [RuL 3 ] + by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of [RuL 3 ] + with alkenes or methyl ketones in the gas phase are indeed observed, in agreement with the proposed mechanism. Such reactivity is also maintained by several fragment ions of [RuL 3 ] + , indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of [RuL 3 ] + was further verified by the ion/molecule reaction of [RuL 3 ] + with dimethyl disulfide, in which the characteristic CH 3 S• transfer occurs, both at atmospheric pressure and also at low pressure (~mTorr). These results provide, for the first time, clear mass spectrometric evidence of the radical nature of [RuL 3 ] + (i.e., the distonic ion structure of [RuL 3 ] + ), arising from the oxidation of non-innocent thiolate ligands of the complex [PPN] + [RuL 3 ] - . Similar thiolate complexes, including ReL 3 and NiL 2 , were also examined. Although reactions of oxidized ReL 3 or NiL 2 with CH 3 SSCH 3 take place at atmospheric pressure, the corresponding reaction did not occur in vacuum. Consistent with these data, the addition of ethylene was not observed either, indicating lower reactivities of [ReL 3 ] + and [NiL 2 ] + in comparison to [RuL 3 ] + .