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Free keywords:
Decarboxylation; Organoplatinum; Collision-induced dissociation; Ion-molecule reaction; Electrospray ionization; Mechanism; DFT calculation
Abstract:
Electrospray ionization of the group 10 complexes [(phen)M(O2CCH3)2] (phen=1,10-phenanthroline, 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). Decarboxylation of [(phen)M(O2CCH3)]+ under CID conditions gen-erates the organometallic cations [(phen)M(CH3)]+, which undergo bond homolysis upon a further stage of CID to generate the cations [(phen)M]+· in which the metal center is formally in the +1 oxidation state. In the case of [(phen)Pt(CH3)]+, the major product ion [(phen)H]+ was formed via loss of the metal carbene Pt=CH2. DFT calculated energetics for the competition between bond homolysis and M=CH2 loss are consistent with their experimentally observed branching ratios of 2% and 98% respectively. The IMR of [(phen)M]+· with O2,N2, H2O, acetone, and allyl iodide were examined. Adduct formation occurs for O2, N2, H2O, and acetone. Upon CID, all adducts fragment to regenerate [(phen)M]+·, except for [(phen)Pt(OC(CH3)2)]+·, which loses a methyl radical to form [(phen)Pt(OCCH3)]+ which upon a further stage of CID regenerates [(phen)Pt(CH3)]+ via CO loss. This closes a formal catalytic cycle for the decomposition of acetone into CO and two methyl radicals with [(phen)Pt]+· as catalyst. In the IMR of [(phen)M]+· with allyl iodide, formation of [(phen)M(CH2CHCH2)]+ was observed for all three metals, whereas for M = Pt also [(phen)Pt(I)]+ and [(phen)Pt(I)2(CH2CHCH2)]+ were observed. Finally, DFTcalculated reaction energetics for all IMR reaction channels are consistent with the experimental observations.
