[Truncated abstract] This thesis describes various synthetic approaches toward the synthesis of highly conjugated complexes incorporating multiple transition metal centres. Particular attention is given to the synthesis of mononuclear complexes that allow for the facile assembly of discrete oligo- and poly-nuclear complexes in a controlled, stepwise fashion. Conjugated multi-metallic materials are of interest on account of their unique photophysical and electronic properties, with a particular emphasis on elucidating the nature of intramolecular communication between multiple metal centres. Chapter 1 provides a survey of these topics and current research efforts in the field. Chapter 2 describes the synthesis of Group-VIII allenylidene complexes incorporating a terminal bipyridyl moiety that provides a site for further coordination. The new compound 9-hydroxy-9-ethynyl-4,5-diazafluorene was synthesised, and reaction of this proligand with a coordinatively unsaturated metal fragment yields the allenylidene complexes [MCl(PnP)2=C=C=(4,5-diazafluoren-9-yl)]PF6 (M = Ru, PnP = dppm, dppe, dmpe; M = Os, PnP = dppm) and [CpRu(dppe)=C=C=(4,5-diazafluoren- 9-yl)]PF6. The dmpe-ligated complex is particularly susceptible to decomposition, though it was possible to obtain partial spectroscopic characterisation in addition to a single-crystal X-ray structural determination. The remaining allenylidene complexes are stable compounds readily characterised by standard spectroscopic and electrochemical means, with the bis(diphosphine) complexes characterised by single crystal X-ray structural determinations. ... Reactions of the proligand with [RuCl(PnP)2]+ (PnP = dppm, dppe) led to the isolation of a product spectroscopically consistent with the formation of the target cationic allenylidene complexes, though the complexes were not readily purified and the identity of the accompanying anion was not elucidated. The new compound 4-hydroxy-4- ethynyl-cyclopentadithiophene was also prepared, though the compound was found to be highly unstable and susceptible to rapid decomposition. The derived allenylidene complexes [RuCl(PnP)2=C=C=(4-cyclopentadithiophene)]PF6 (PnP = dppm, dppe) were isolated in a pure form and the complexes stable toward spontaneous decomposition. The thienyl-derived allenylidene complexes were characterised by spectroscopic and electrochemical techniques, with a single-crystal X-ray structural determination undertaken for [RuCl(dppm)2=C=C=(4-cyclopentaditiophene)]PF6. Electrochemical properties are significantly different between the complexes, and also show significant variation between electrodes and solvents. The terminal thienyl substituents are electroactive and show one or two oxidation processes consistent with oligomerisation of the thienyl moiety in dichloromethane solvent, and in acetonitrile solvent cyclic voltammograms are consistent with the deposition of an electroactive film on the electrode surface. The electro-polymerisation of the thienylallenylidene complexes offers a promising new route toward multi-metallic allenylidene complexes.