Do alkali and alkaline earth acetates form organometallates via decarboxylation?: A survey using electrospray ionization tandem mass spectrometry and DFT calculations

Multistage mass spectrometry experiments combined with density functional theory (DFT) calculations were used to examine whether the alkali and alkaline earth acetate ions [Metal(O2CCH3)n]−, formed via electrospray ionization, fragment under collision-induced dissociation conditions to yield the organometallic ions [CH3Metal(O2CCH3)n − 1]−. The alkali earth acetate ions [Metal(O2CCH3)2]− (Metal = lithium, sodium, potassium, rubidium and caesium) all fragment via loss of the acetate anion, with virtually no formation of the organometallate. In contrast, the alkaline earth acetate ions [Metal(O2CCH3)3]− (Metal = magnesium, calcium, strontium and barium) not only fragment via loss of the acetate anion, but also all fragment to form the organometallates [CH3Metal(O2CCH3)2]−. Each of these organometallates [CH3Metal(O2CCH3)2]− react with background water in the quadrupole ion via addition with concomitant elimination of methane to form the metal hydroxide [HOMetal(O2CCH3)2]− ions with a relative reactivity order of: [CH3Ba(O2CCH3)2]− ≈ [CH3Sr(O2CCH3)2]− > [CH3Ca(O2CCH3)2]− > [CH3Mg(O2CCH3)2]−. DFT calculations were used to provide insights into the structures and reactivity of organometallates.