Unimolecular Dissociation of Anions Derived from Maleic Acid (MaH2) in the Gas Phase: MaH− and MaMgCl−—Relationship to Grignard Chemistry and Reductive CO2 Fixation

Abstract

We have conducted collision-induced dissociation experiments on the hydrogen maleate anion (MaH−, m/z = 115) and the anionic maleate–MgCl complex (MaMgCl−, m/z = 173). In addition, we have computationally investigated the observed fragmentation reactions. We find that both anions readily undergo two consecutive decarboxylations resulting in product ions at m/z = 71 and m/z 27 for MaH−, and at m/z = 129 and m/z 85 for MaMgCl−. The first decarboxylation is more facile for MaMgCl− than for MaH−, while loss of CO2 from Ma(–CO2) H− is more facile than that for Ma(–CO2)MgCl−. We also find that MaH− loses water, and we propose a mechanism for this loss. No firstgeneration fragmentation product other than Ma(–CO2)MgCl− is seen for MaMgCl−. Based on the observed unimolecular chemistry, we discuss some of its implications on reductive CO2-fixation and Grignard chemistry.