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 H₂ 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 H₂. All except the last step of the catalytic cycle are modelled using DFT calculations with optimizations of structures at the M06/SDD 6-31G(d) level of theory.