Synthesis, Structure, Electrochemical, and Spectroscopic Properties of Hetero-Bimetallic Ru(II)/Fe(II)-Alkynyl Organometallic Complexes.

A series of heterobimetallic wire-like organometallic complexes [( tpy-C6H4-R)(PPh3)2Ru-C≡C-Fc]+ ( tpy-C6H4-R = 4'-(aryl)-2,2':6',2''-terpyridyl, Fc = [(η5-Cp)2Fe], R = -H, -Me, -F, -NMe2 in complexes 5-8, respectively) featuring ferrocenyl and 4'-(aryl)-2,2':6',2''-terpyridyl ruthenium(II) complexes as redox active metal termini, have been synthesized. Various spectroscopic tools, such as multinuclear NMR, IR spectra, HRMS, CHN analyses, and single crystal X-ray crystallography have been utilized to characterize the heterobimetallic complexes. The electrochemical and UV-vis-NIR spectroscopic studies have been investigated to evaluate the electronic delocalization across the molecular backbones of the Ru(II)-Fe(II) heterobinuclear organometallic dyads. Electrochemical studies reveal two well-separated reversible redox waves as a result of successive oxidation of the ferrocenyl and Ru(II) redox centers. The spin density distribution analyses reveal that the initial oxidation process is associated with the Fe(II)/Fe(III) couple followed by one electron oxidation of the ruthenium(II) center. The high Kc value (0.11-1.73 × 1012) and intense NIR absorption, with molar absorption coefficient (in the order of 103 M-1 cm-1) for the RuIIFeIII mixed-valence species, signify strong electronic communication between the two metal termini. The electronic coupling constant ( Hab) has been estimated to be 492 and 444 cm-1 for the structurally characterized complexes 6 and 7, respectively. The redox and NIR absorption features indicate that the mixed-valence system of the heterobinuclear dyads belongs to a Robin and Day "class II" system.