Gas-Phase Unimolecular Reactions of Pallada- and Nickelalactone Anions

Abstract

Electrospray ionization in combination with multistage mass spectrometry experiments in a linear ion trap mass spectrometer was used to generate and study the gas-phase ion chemistry of the metallalactones [(CH3CO2)Ni(CH2CO2)]− (m/z 175, 5a) and [(CH3CO2)Pd(CH2CO2)]− (m/z 223, 5b). Low-energy collision-induced dissociation (CID) resulted in decarboxylation to produce novel organometallic ions at m/z 131 (Ni) and m/z 179 (Pd). Isotope labeling experiments, bimolecular gas-phase reactions with allyl iodide, and DFT calculations reveal that decarboxylation primarily occurs from the acetato ligand to yield ions of the form [(CH3)M(CH2CO2)]− (M = Pd, Ni). Further CID experiments on [(CH3)M(CH2CO2)]− together with DFT calculations highlight the following. (1) Both palladium and nickel can facilitate C–C bond formation, with elimination of ethylene being observed. (2) The mechanism for formation of ethylene from [(CH3)M(CH2CO2)]− is inherently different for M = Pd versus M = Ni. Elimination of ethylene is compet...