Ru(II) complexes of polyarylated terpyridines: unexpected side-chain C-metallation and photosensitization of electron transfer
作者:Charles Mikel、Pierre G. Potvin
DOI:10.1016/s0020-1693(01)00626-0
日期:2001.12
The new ligands 4,4 " -diphenyl-6,6 " -di(4-ethoxycarbonylphenyl)-2,2':6',2 " -terpyridine (H4), its non-carboxylated 4,6,4 " ,6 " -tetraphenyl analogue (H5) and the 4,4 " -diphenyl-6,6 " -di(4-methoxyphenyl) analogue were prepared in high yields via double Krohnke reactions. Reactions with activated (ttpy)RuCl3 (ttpy is 4'-p-tolyl-2,2':6',2 " -terpyridine) provided the symmetrical N-6-coordinated complexes, [Ru(H4)(ttpy)](PF6)(2) and [Ru(H5)(ttpy)](PF6)2, along with the novel, unsymmetrical C-metallated analogues [Ru(4)(ttpy)]PF6 and [Ru(5)(ttpy)]PF6, in which an unprecedented side-chain metallation occurred in lieu of incomplete substitution. A crystallographic analysis of [Ru(5)(ttpy)]NO3 confirmed the N5C donor set in these products and revealed a distorted binding of 5(-) as well as 'pi -stacking' between its uncoordinated pyridine and the ttpy ligand. The diester [Ru(H4)(ttpy)](PF6)(2) was hydrolyzed to the diacid complex [Ru(H(2)3)(ttpy)PF6)(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(H5)(ttpy)](PF6)(2) and [Ru(H(2)3)(ttpy)](PF6)(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. (C) 2001 Published by Elsevier Science B.V.