Stability of metal–metal interactions in dinuclear Pt–Au complexes as a function of bridging Pt–arene ring electronics

Abstract

A series of dinuclear Pt–Au complexes [(bhq-Ph^R)(PPh₃)Pt–Au(PPh₃)]⁺ (R = –H (5), –OMe (5-OMe), –F (5-F), and –CF₃ (5-CF₃)), derived from novel Pt complexes (4, 4-OMe, 4-F, and 4-CF₃), were prepared and analyzed using solution-state NMR spectroscopy and X-ray crystallography. The persistence of three-center Pt–Au–C_ipso bonding interaction in solution and the migration of [Au(PPh₃)]⁺ across electronically distinct arenes of 5, 5-OMe, 5-F, and 5-CF₃ offers a unique opportunity to probe the intermediates of transmetallation as a function of bridging arene ring electronic properties. Analysis of the solid-state X-ray structures of these dinuclear complexes reveal that the degree of arene ring transfer is dictated by whether the [Au(PPh₃)]⁺ bridges the Pt–benzoquinoline or the comparably more flexible Pt–Ph^R ring. Relative thermodynamic stability, evaluated via pyridine titrations, correlates with the electronic donating or withdrawing ability of the R group. A Hammett analysis of the K_eq derived from pyridine titrations reveal a linear relationship between the log(K_R/K_H) and σ_p values. Together, these studies demonstrate how arene ring electronic properties influence the structure and stability of transmetallation intermediates, important progress towards a deeper understanding of transmetallation between transition metal organometallic complexes.