Phenyl-Group Exchange in Triphenylphosphine Mediated by Cationic Gold-Platinum Complexes-A Gas-Phase Mimetic Approach.

The PPh ligands in the heterodinuclear AuPt complex [(PhP)AuPt(PPh)][BAr] (BAr = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) exhibit a high fluxionality on the AuPt core. Fast intramolecular and slow intermolecular processes for the reversible exchange of the PPh ligands have been identified. When [(PhP)AuPt(PPh)][BAr] is heated in solution, the formation of benzene is observed, and a trinuclear, cationic AuPt complex is generated. This process is preceded by reversible phenyl-group exchange between the PPh ligands present in the reaction mixture as elucidated by deuterium-labeling studies. Both the elimination of benzene and the preceding reversible phenyl-group exchange have originally been observed in mass-spectrometry-based CID experiments (CID = Collision-Induced Dissociation). While CID of mass-selected [Au,Pt,(PPh)] results exclusively in the loss of PPh, the resulting cation [Au,Pt,(PPh)] selectively eliminates CH. Thus, the dissociation of a PPh ligand from [Au,Pt,(PPh)] is energetically not able to compete with processes which result in C-H- and C-P-bond cleavage. In both media, the heterobimetallic nature of the employed complexes is the key for the observed reactivity. Only the intimate interplay of the gas-phase investigations, studies in solution, and thorough DFT computations allowed for the elucidation of the mechanistic details of the reactivity of [(PhP)AuPt(PPh)][BAr].