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

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journal contribution
posted on 03.03.2020, 13:06 by Konstantin Koessler, Harald Scherer, Burkhard Butschke
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 PPh3 ligands have been identified. When [(Ph3P)­AuPt­(PPh3)3]­[BAr4F] is heated in solution, the formation of benzene is observed, and a trinuclear, cationic AuPt2 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)4]+ 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].