Synthesis, Electrochemistry, XPS, and DFT Calculations of α-Carbon-Bonded Gold(I) Ferrocenyl- and Ruthenocenyl-Containing β-Diketonato Complexes

Abstract

A series of ferrocenyl- and ruthenocenyl-containing β-diketonato (triphenylphosphine)gold(I) complexes of the type [(RCO)(R′CO)-H^αC-AuPPh₃] were synthesized via the reaction of appropriate β-diketones, RCOC^αH₂COR′, with [(Ph₃PAu)₃][OBF₄]. Complexes with R = R′ = CH₃ (1), or R = Fc = Fe^II(η⁵-C₅H₄)(η⁵-C₅H₅), and R′ = CF₃ (2), CH₃ (3), Ph = C₆H₅ (4), or Fc (5), as well as R = Ru^II(η⁵-C₅H₄)(η⁵-C₅H₅) and R′ = CF₃ (6), CH₃ (7), Ph (8), Rc (9), or Fc (10), were obtained. The Au–^αC bonding mode between gold and β-diketonato ligands was spectroscopically (NMR, FTIR, and XPS) identified as the only bonding mode for all complexes lacking a CF₃ moiety, while a mixture of Au–^αC- and Au–(^κO,^κO)-bonded isomers in equilibrium with each other was observed for CF₃-containing complexes 2 and 6. This experimental observation is supported by a theoretical study utilizing density functional theory. Cyclic and square wave voltammetric studies in CH₂Cl₂/[N(ⁿBu)₄][B(C₆F₅)₄] displayed only the metallocene-based redox processes of 2–10 as reversible, well-resolved ferrocenyl and irreversible ruthenocenyl one-electron transfer steps. XPS spectra for each element in the complexes were measured, and an uncommon indirect proportionality between Au 4f_7/2 binding energies and the sum of R group electronegativities, Σχ_R, as well as between the Fe 2p_3/2 binding energies and formal ferrocenyl reduction potentials, E°′, was obtained.