Decarboxylative-Coupling of Allyl Acetate Catalyzed by Group 10 Organometallics, [(phen)M(CH3)]+

Gas-phase carbon–carbon bond forming reactions, catalyzed by group 10 metal acetate cations [(phen)­M­(O2CCH3)]+ (where M = Ni, Pd or Pt) formed via electrospray ionization of metal acetate complexes [(phen)­M­(O2CCH3)2], were examined using an ion trap mass spectrometer and density functional theory (DFT) calculations. In step 1 of the catalytic cycle, collision induced dissociation (CID) of [(phen)­M­(O2CCH3)]+ yields the organometallic complex, [(phen)­M­(CH3)]+, via decarboxylation. [(phen)­M­(CH3)]+ reacts with allyl acetate via three competing reactions, with reactivity orders (% reaction efficiencies) established via kinetic modeling. In step 2a, allylic alkylation occurs to give 1-butene and reform metal acetate, [(phen)­M­(O2CCH3)]+, with Ni (36%) > Pd (28%) > Pt (2%). Adduct formation, [(phen)­M­(C6H11O2)]+, occurs with Pt (24%) > Pd (21%) > Ni(11%). The major losses upon CID on the adduct, [(phen)­M­(C6H11O2)]+, are 1-butene for M = Ni and Pd and methane for Pt. Loss of methane only occurs for Pt (10%) to give [(phen)­Pt­(C5H7O2)]+. The sequences of steps 1 and 2a close a catalytic cycle for decarboxylative carbon–carbon bond coupling. DFT calculations suggest that carbon–carbon bond formation occurs via alkene insertion as the initial step for all three metals, without involving higher oxidation states for the metal centers.