Gas-Phase Reactions of the Group 10 Organometallic Cations, [(phen)M(CH3)]+ with Acetone: Only Platinum Promotes a Catalytic Cycle via the Enolate [(phen)Pt(OC(CH2)CH3)]+

Electrospray ionisation of the ligated group 10 metal complexes [(phen)M(O2CCH3)(2)] (M = Ni, Pd, Pt) generates the cations [(phen)M(O2CCH3)](+), whose gas-phase chemistry was studied using multistage mass spectrometry experiments in an ion trap mass spectrometer with the combination of collision-induced dissociation (CID) and ion-molecule reactions (IMR). A new catalytic cycle has been discovered. In step 1, decarboxylation of [(phen)M(O2CCH3)](+) under CID conditions generates the organometallic cations [(phen)M(CH3)](+), which react with acetone to generate the [(phen)M(CH3)(OC(CH3)(2))](+) adducts in competition with formation of the coordinated enolate for M = Pt (step 2). For M = Ni and Pd, the adducts regenerate [(phen)M(CH3)](+) upon CID. In the case of M = Pt, loss of methane is favored over loss of acetone and results in the formation of the enolate complex, [(phen) Pt(OC(CH2)CH3)](+). Upon further CID, both methane and CO loss can be observed resulting in the formation of the ketenyl and ethyl complexes [(phen)Pt(OCCH)](+) and [(phen)Pt(CH2CH3)](+) (step 3), respectively. In step 4, CID of [(phen)Pt(CH2CH3)](+) results in a beta-hydride elimination reaction to yield the hydride complex, [(phen)Pt(H)](+), which reacts with acetic acid to regenerate the acetate complex [(phen)Pt(O2CCH3)](+) and H-2 in step 5. Thus, the catalytic cycle is formally closed, which corresponds to the decomposition of acetone and acetic acid into methane, CO, CO2, ethene and H-2. All except the last step of the catalytic cycle are modelled using DFT calculations with optimizations of structures at the M0/SDD 6-31G(d) level of theory.