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.