Synthesis and characterisation of unsymmetrical metal (RuII, OsII) and ferrocenyl complexes of 1,3,5-triethynylbenzene

A series of complexes featuring metal (trans-[RuCl(dppm)(2)], trans-[OsCl(dppm)(2)] or [Ru(eta-C5H5)(PPh3)(2)]) and ferrocenyl (C5H5FeC5H4) units unsymmetrically arranged around the periphery of a 1,3,5-triethynylbenzene core have been synthesized in good to reasonable yields by various synthetic routes. A crystal structure determination of trans-[(C5H5FeC5H4C=C)(2)C6H3{C=CRu(dppm)(2)Cl}] shows that the two ferrocenyl units are positioned on the same side of the trisubstituted aromatic core and that all three ethynyl linkages are bent 'down' out of the plane of the central ring. Electrochemical studies show that in the heteronuclear coupling of osmium(II) or ruthenium(II) fragment(s) with ferrocenyl unit(s) the oxidation of Os-II or Ru-II precedes that of the ferrocene unit(s). In addition, whereas in diruthenium or diosmium complexes the oxidation of the two metal centres proceeds separately, in the diferrocenyl complexes the oxidation of the two ferrocene units occurs at the same potential values. This result shows that on appending different groups to the same skeletal core (namely, triethynylbenzene) some can interact electronically (the Ru-II- and Os-II-containing fragments) whereas others do not (the ferrocenyl units).