Focus: Distonic Ions: Research Article

Journal of The American Society for Mass Spectrometry

, Volume 24, Issue 4, pp 502-512

First online:

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

  • Mei LuAffiliated withCenter for Intelligent Chemical Instrumentation, Department of Chemistry and Biochemistry, Ohio University
  • , J. Larry CampbellAffiliated with
  • , Rajat ChauhanAffiliated withDepartment of Chemistry, University of Louisville
  • , Craig A. GrapperhausAffiliated withDepartment of Chemistry, University of Louisville Email author 
  • , Hao ChenAffiliated withCenter for Intelligent Chemical Instrumentation, Department of Chemistry and Biochemistry, Ohio University Email author 

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Transition metal thiolate complexes such as [PPN]+[RuL3]- (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 [PPN]+[RuL3]-. 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 [PPN]+[RuL3]-. 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]+.

Key words

Distonic ion Thiyl radical Mass spectrometry Ion/molecule reaction