Synthesis and Properties of Ferrocenyl Allenylidene Complexes: X-ray Structure of [Ru(C=C=CHFc)(PPh3)2(η5-C5H5)][PF6]•CH2Cl2

Reactions of the transition metal halide complexes [MXL2(Cp)] (M = Fe, X = I, L-2 = dppe; M = Ru, X = Cl, L = PPh3; M = Os, X = Br, L = PPh3; Cp = eta-C5H5) with the alkynol HC CCH(OH)(Fc) (1) (Fc = ferrocenyl) in the presence of TlBF4 gave the monosubstituted allenylidene complexes [M(C=C=CHFc)L-2(Cp)][BF4] (2a: M = Ru, L = PPh3; 3: M = Fe, L-2 = dppe; 4: M = Os, L = PPh3). Similarly, the reaction of 1 with [RuCl(PPh3)(2)(Cp)] and NH4PF6 in methanol gave [Ru(C=C=CHFc)(PPh3)(2)(Cp)][PF6] (2b). These highly colored compounds were characterized by spectroscopic and electrochemical techniques and in the case of 2b by a single-crystal X-ray structure determination. Cyclic voltammetry in MeCN in the presence of [(Bu4N)-Bu-n][ClO4] at 100 mV.s(-1) shows a reversible ferrocenyl-based one-electron oxidation, in addition to irreversible oxidation and reduction processes. The NMR spectra of 2b show complex behavior at low temperature, attributed to temperature-dependent chemical shifts and correlated motions of the allenylidene ligand and the ferrocenyl substituent.