Oxidative Dimerization of Arylalkynyl-Ruthenium Complexes

Chemical oxidation of Ru(C CPh)(PPh3)(2)Cp with [FeCp2]PF6 affords the binuclear cationic complexes [Cp(PPh3)(2)Ru{=C=CHC6H4CPh=C=}Ru(PPh3)(2)Cp] (PF6)(2) (2) and [Cp(PPh3)(2)Ru{C C(C6H4)CPh=C=}Ru(PPh3)(2)Cp]PF6 (3) by radical coupling at sites shown to be electron-rich by DFT studies, particularly involving the acetylide C-beta and C-para atoms and, to a lesser extent, the Cp carbon atoms. Complexes 2 and 3 are related by facile deprotonation/protonation reactions. When the 4-position of the Ph group is blocked, attack by C-beta upon the Cp group occurs to give the bis (vinylidene) [Ru{=C=C(C6H4Me-4)-eta-C5H4[Ru(PPh3)(2){=C=CH(C6H4Me-4)}(PPh3)(2) Cp]}](PF6)(2) (4), which can be deprotonated to give [Ru{=C=C(C6H4Me-4)-eta-CsH4[Ru(PPh3)(2){C C(C6H4Me-4)}(PPh3)(2)Cp]}]PF6 (5). Complex 4 is rapidly oxidized during workup to form [Ru{=C=C(C6H4Me)-eta-C5H4[Ru(CO)(PPh3)(2)]}(PPh3)(2)Cp](PF6)(2) (6). Single-crystal X-ray structure determinations of the salts 2, 3, and 6 are reported.