Probing the reactivity and radical nature of oxidized transition metal-thiolate complexes by mass spectrometry.

Transition metal thiolate complexes such as PPNRuL3 (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 RuL3 ion in the case of PPNRuL3. This study presents the reactivity and structure investigation of RuL3 by mass spectrometry (MS) in conjunction with ion/molecule reactions. The addition reactions of RuL3 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 RuL3, indicating the preserved thiyl diradical core structure is responsible for the addition reaction. The thiyl radical nature of RuL3 was further verified by the ion/molecule reaction of RuL3 with dimethyl disulfide, in which the characteristic CH3S• 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 RuL3 (i.e., the distonic ion structure of RuL3), arising from the oxidation of non-innocent thiolate ligands of the complex PPNRuL3. Similar thiolate complexes, including ReL3 and NiL2, were also examined. Although reactions of oxidized ReL3 or NiL2 with CH3SSCH3 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 ReL3 and NiL2 in comparison to RuL3.