The PPh3 ligands in the heterodinuclear AuPt complex [(Ph3P)AuPt(PPh3)(3)][BAr4F] (BAr4F = 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 3 ligands have been identified. When [(Ph3P)AuPt(PPh3)(3)][BAr4F] 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 PPh3 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,(PPh3)(3)](+) results exclusively in the loss of PPh3, the resulting cation [Au,Pt,(PPh3)(3)](+) selectively eliminates C6H6. Thus, the dissociation of a PPh3 ligand from [Au,Pt,(PPh3)(3)](+) 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 [(Ph3P)AuPt(PPh3)(3)][BAr4F].