Reactions of Platinum−Carbene Clusters PtnCH2+ (n = 1−5) with O2, CH4, NH3, and H2O: Coupling Processes versus Carbide Formation

The gas-phase reactions of the platinum−carbene clusters Pt n CH 2 + ( n = 2−5) with the substrates O 2, CH 4, NH 3, and H 2 O have been investigated by FT-ICR mass spectrometry and compared with previous results for the mononuclear homologue PtCH 2 + . The ion−molecule reactions of the clusters Pt n CH 2 + with O 2 and CH 4 are similar to the corresponding processes observed for PtCH 2 + . In contrast, a surprising difference evolves in the reactions with NH 3 and H 2 O. Whereas PtCH 2 + mediates carbon−heteroatom bond formation as an attractive way toward methane functionalization, the homologous clusters fail in this regard and exclusively yield the carbide complexes Pt n C + ·NH 3 and Pt n C + ·H 2 O, respectively. The differences in reactivities have been analyzed further by means of kinetic isotope effects, H/D-exchange reactions, and energy-dependent collision-induced dissociations of Pt n CH 2 + . Essentially, the higher stabilities of the platinum−carbide clusters Pt n C + compared to PtC + cause the change in reactivity. This conclusion is confirmed by the reactions of independently generated clusters Pt n C + ( n = 1−5) with O 2, CH 4, NH 3, and H 2 O. The results underline the importance of carbide structures in these gas-phase reactions, thereby resembling catalyst deactivation by soot formation on heterogeneous platinum catalysts.