Electrooxidation of ruthenium cyclopentadienyl PTA complexes in DMF: ESI-MS, cyclic voltammetry and on-line electrochemistry/ESI-MS s

Halogen complexes of ruthenium cyclopentadienyl CpRuPTA2X; CpRuPTAPPh3X; CpRuPPh32Cl, and CpRumPTAPPh3X+ Cp = C5H5; PTA = 1,3,5-triaza-7-phosphaadamantane; mPTA+ = 1-methyl-1,3,5-triaza-7- phosphaadamantane+; X = Cl-, I- were investigated by electrospray mass spectrometry ESI-MS, in flow-cell cyclic voltammetry, by microelectrodes, and by combined online electrochemistry and electrospray mass spectrometry EC/ESI-MS in dimethyl formamide solution. Coordination changes and the structures of the initial compounds and the products of the electrooxidation of the RuII complexes were traced by in situ EC/MSn experiments which revealed their fragmentation pathways. ESI-MS collision-induced dissociation fragmentations of the initial reactants and the oxidation products were explained by soft acid-hard base considerations taking into account the different nature of RuII--RuIV centers. The electrochemical studies show that it is possible to tune the formal potentials for the oxidation of CpRuL2X complexes by over 300 mV by proper selection of the ligands. The increase of the redox potential by the different ligands follows the order PTA PPh3 mPTA+. We demonstrate a similarity between the propensity of the ligand to fragment out in the gas phase and its relationship to the formal potential of the complex.