Catalytic Decarboxylative Coupling of Allyl Acetate: Role of the Metal Centers in the Organometallic Cluster Cations [CH3Cu2]+, [CH3AgCu]+, and [CH3Ag2]+

Metal-catalyzed decarboxylative coupling reactions offer new opportunities for formation of C–C bonds. Here, multistage ion trap mass spectrometry experiments together with DFT calculations are used to examine the role of the metal centers in coinage metal cluster catalyzed decarboxylative coupling of allyl acetate in the gas phase via a simple two-step catalytic cycle. In step 1, the metal acetate cluster cation [CH3CO2Cu2]+, [CH3CO2AgCu]+, or [CH3CO2Ag2]+ is subjected to collision-induced dissociation to yield the organometallic cluster cation [CH3Cu2]+, [CH3AgCu]+, or [CH3Ag2]+, respectively. Step 2 involves subjecting these organometallic cluster cations to ion–molecule reactions with allyl acetate with the aim of generating 1-butene and re-forming the metal acetate cluster cations to close the catalytic cycle. Experiment and theory reveal the role of the two metal centers in both steps of the gas-phase catalytic reaction. All three metal acetates undergo decarboxylation (step 1), although when competing reactions are taken into account, the yield of [CH3Cu2]+ is highest (83.3%). Ion–molecule reactions of the organometallic cations with allyl acetate all proceed at the collision rate; however, the types of products formed and their yields vary considerably. For example, only [CH3Cu2]+ and [CH3AgCu]+ undergo the C–C bond-coupling reaction (step 2) in yields of 52.7% and 1.2%, respectively. Overall the dicopper clusters are the superior decarboxylative coupling catalysts, since they give the highest yields of the desired products for both steps 1 and 2. These results highlight that the reactivity of organometallic coinage metal clusters can be “tuned” by varying the composition of the metal core.