C-N coupling of methane and ammonia by bimetallic platinum-gold cluster cations

Fourier transform ion-cyclotron resonance mass spectrometry is used to investigate the reactivity of mass-selected bimetallic PtmAun+ clusters (m + n less than or equal to 4) with respect to the C-N coupling of methane and ammonia. To this end, the reactions of the heterometallic carbene species PtmAunCH2+ with NH3 as well as those of the bare clusters with CH3NH2 are studied. On the basis of these experiments augmented by deuterium labeling studies, structural assignments for the reaction products are proposed. Surprisingly, only the dinuclear carbene PtAuCH2+ mediates C-N bond formation to presumably afford the aminocarbene complex PtAuC(H)NH2+, whereas the larger bimetallic carbene clusters mainly yield the carbide species PtmAunC+.NH3 upon reaction with NH3. This difference is rationalized by distinct metal-carbene binding energies. While the pure Au-n+ clusters do not afford C-N coupling either, they undergo degradation reactions with NH3 and CH3NH2 that are subject to pronounced even-odd size effects.