Heterodinuclear ruthenium(II)-cobalt(III) complexes have been prepared as part of investigations into a new approach to selective cancer treatment. A cobalt(III) centre bearing amine ligands, which serve as models for cytotoxic nitrogen mustard ligands, is connected by a bridging ligand to a ruthenium(II)-polypyridyl moiety. Upon excitation of the ruthenium centre by visible light, electron transfer to the cobalt(III) centre results in reduction to cobalt(II) and consequent release of its ligands. We have synthesised several such structures and demonstrated their ability to release ligands upon excitation of the ruthenium centre by visible light.
Two Ru(II)-Co(III) heterodinuclear complexes have been synthesised as model complexes for photoactivated cytotoxins. Photoinduced ligand release has been demonstrated and the rate shown to depend on dioxygen concentration. Emission lifetimes and quantum yields are reported. These results validate the concept and justify further work to synthesise systems containing cytotoxic ligands.
The chiral ligand S-1,2-bis(1H-benzimidazol-2-yl)ethanol, 1, reacts with manganese(II) salts to form cubanes which readily undergo oxidation reactions leading either to a tetranuclear manganese(II,III) mixed valence complex 4 or to a tetranuclear complex of ligand 5 where the secondary alcohol has been oxidised to an enolate. N-methylation of ligand 1 slows the oxidation reaction and stable manganese(II) cubanes may be isolated. The fully methylated ligand 2 gives a cubane of opposite helicity to that found previously for 1 with cobalt. The inversion may be explained by conformational analysis. Cyclic voltammetry suggests that the manganese cubanes reported here are insufficiently robust to store oxidising equivalents as in the oxygen evolving system of photosystem II.
A series of ditopic ligands bearing terpyridyl and polyamine coordination sites have been prepared. Complexes with RuII bound to the terpyridyl sites of many of these ligands have been prepared. RuII complexes of these ligands appear vulnerable to nucleophilic displacement of the polyamine portion of the ligand by BH4
–. A limited study of the coordination chemistry of the polyamine portion of the RuII complexes has been conducted, including the synthesis and characterization of RuII–CoIII heterodinuclear complexes in which the CoIII centre is coordinated by a cyclam macrocycle. The CoIII centre in these systems is unexpectedly labile – it can be removed from the polyamine upon treatment with ethane-1,2-diamine.
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