Ferrocene-Containing (η⁶-Hexamethylbenzene)ruthenium(II) Methoxycarbenes:  Synthesis, Structure, and Electrochemistry

The (η⁶-hexamethylbenzene)dichlororuthenium(II) complexes [(η⁶-C₆Me₆)RuCl₂(L)], where L = PMe₃ (1), PPh₃ (2), FcPPh₂ (3; Fc = ferrocenyl), and Hdpf (4; Hdpf = (η⁵-C₅H₄PPh₂)Fe(η⁵-C₅H₄COOH)), were reacted with terminal alkynes (FcC⋮CH, Me₃SiC⋮CH, and PhC⋮CH) in the presence of NaPF₆ and methanol to give (η⁶-hexamethylbenzene)chlororuthenium(II) methoxycarbenes [(η⁶-C₆Me₆)Ru(C(OCH₃)CH₂R)Cl(L)]PF₆ (L/R = PMe₃/Fc (1a), PPh₃/Fc (2a), FcPPh₂/Fc (3a), FcPPh₂/H (3b), FcPPh₂/Ph (3c), Hdpf/Fc (4a), Hdpf/H (4b), and Hdpf/Ph (4c)). All new compounds were characterized by NMR and IR spectroscopy and also studied by mass spectrometry in liquid matrix. The solid-state structure of 4a·CH₂Cl₂ was determined by single-crystal X-ray diffraction. The electrochemical study of these bi- and trimetallic complexes displayed that upon oxidation, the Ru−ferrocenyl phosphine moiety undergoes a ferrocene/ferrocenium redox process followed by a Ru(II) → Ru(III) oxidation which is, however, markedly influenced by the preceding redox change. A redox dissymmetry of carbenes 1a−4c was observed, as these exhibit communication within the Ru−phosphine part while the carbene ferrocenyl group remains isolated and practically unaffected.