Terpyridines functionalised with ferrocenyl groups of different redox potential

2,2':6',2'' -Terpyridines bearing a substituent X in the 4'-position [3a: X = Fc-C=C-p-C6H4; 3b: X = Fc(#)-C=C-p-C6H4; Fc = (C5H5)Fe(C5H4), Fc(#) = (C 5Me4H)Fe(C5Me4)] were prepared by Pd-0-catalysed cross-coupling reactions. 3b was characterised by X-ray structure analysis. [(3a)RuCl2-(DMSO)] (4a) a nd [(3b)RuCl2(DMSO)] (4b) were obtained by reaction of [RuCl2(DMSO)(4)] wit h 1 equivalent of 3a and 3b, respectively, while the analogous reaction wit h 2 equivalents afforded [(3a)(2)Ru][PF6](2) (5a) and [(3b)(2)Ru][PF6](2) ( 5b), respectively, after precipitation with aqueous [NH4][PF6]. Similarly, [(3a)Ru(tpy)][PF6](2) (6) was isolated from the reaction of 4a with 2,2':6' ,2"-terpyridine (tpy). Compounds 3 and 5 were investigated by cyclic voltam metry, which revealed that the introduction of eight methyl groups leads to the expected cathodic shift of the E-0' values of ca. 0.44 V for the ferro cenyl-centered redox processes.