Abstract
The new ligands 4,4″-diphenyl-6,6″-di(4-ethoxycarbonylphenyl)-2,2′:6′,2″-terpyridine (H 4), its non-carboxylated 4,6,4″,6″-tetraphenyl analogue (H 5) and the 4,4″-diphenyl-6,6″-di(4-methoxyphenyl) analogue were prepared in high yields via double Kröhnke reactions. Reactions with activated (ttpy)RuCl 3 (ttpy is 4′- p-tolyl-2,2′:6′,2″-terpyridine) provided the symmetrical N 6-coordinated complexes, [Ru(H 4)(ttpy)](PF 6) 2 and [Ru(H 5)(ttpy)](PF 6) 2, along with the novel, unsymmetrical C-metallated analogues [Ru( 4)(ttpy)]PF 6 and [Ru( 5)(ttpy)]PF 6, in which an unprecedented side-chain metallation occurred in lieu of incomplete substitution. A crystallographic analysis of [Ru( 5)(ttpy)]NO 3 confirmed the N 5 C donor set in these products and revealed a distorted binding of 5 − as well as ‘π-stacking’ between its uncoordinated pyridine and the ttpy ligand. The diester [Ru(H 4)(ttpy)](PF 6) 2 was hydrolyzed to the diacid complex [Ru(H 2 3)(ttpy)](PF 6) 2 (H 2 3 is 4,4″-diphenyl-6,6″-di(4-carboxyphenyl)-2,2′:6′,2″-terpyridine). Measurements of the photogeneration of methyl viologen cation radical with [Ru(H 5)(ttpy)](PF 6) 2 and [Ru(H 2 3)(ttpy)](PF 6) 2 as sensitizers showed that the presence of carboxyl groups in the latter provided a distinct benefit, owing to the formation of the neutral form [Ru( 3)(ttpy)] 0 but this was insufficient to overcome the detrimental effect of inter-ligand repulsions.
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