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.