Redox potentials of photosensitive cyclometalated RuII derivatives of 2-phenylpyridine or 2-(4-tolyl)pyridine are controllably decreased by up to 0.8 V within several minutes. This is achieved by irradiation of the ruthena(II)cycles cis-[Ru(o-X-2-py)(LL)(MeCN)2]PF6 (2, X = C6H4 (a) or 4-MeC6H3 (b), LL = 1,10-phenanthroline or 2,2'-bipyridine). The cis geometry of the MeCN ligands has been confirmed by the X-ray structural studies. The sigma-bound sp2 carbon of the metalated ring is trans to LL nitrogen. Complexes 2 are made from [Ru(o-X-2-py)(MeCN)4]PF6 (1) and LL. This "trivial" ligand substitution is unusual because 1a reacts readily with phen in MeCN as solvent to give cis-[Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (2c) in a 83% yield, but bpy does not afford the bpy-containing 2 under the same conditions. cis-[Ru(o-C6H4-2-py)(bpy)(MeCN)2]PF6 (2e) has been prepared in CH2Cl2 (74%). Studies of complexes 2c,e by cyclic voltammetry in MeOH in the dark reveal RuII/III quasy-reversible redox features at 573 and 578 mV (vs Ag/AgCl), respectively. A minute irradiation 2c and 2e converts them into new species with redox potentials of -230 and 270 mV, respectively. An exceptional potential drop for 2c is accounted for in terms of a photosubstitution of both MeCN ligands by methanol. ESR, 1H NMR, and UV-vis data indicate that the primary product of photolysis of 2c is an octahedral monomeric low-spin (S = 1/2) RuIII species, presumably cis-[RuIII(o-C6H4-2-py)(phen)(MeOH)2]2+. The primary photoproduct of bpy complex 2e is cis-[RuII(o-C6H4-2-py)(bpy)(MeCN)(MeOH)]+, and this accounts for a lower decrease in the redox potential. Irradiation of 2c in the presence of added chloride affords [(phen)(o-C6H4-2-py)ClRuIIIORuIVCl(o-C6H4-2-py)(phen)]PF6, a first mu-oxo-bridged mixed valent dimer with a cyclometalated unit. The structure of the dimer has been established by X-ray crystallography.

Bis‐cyclometalated analogs of tris(2,2′‐bipyridine)ruthenium(II), namely [RuIII(C∩N)2(N∩N)]PF6 complexes 3, are prepared in 52–57 % yield from the mono‐cyclometalated N,N‐dimethylbenzylamine (dmbaH) derivatives [RuII(dmba)(N∩N)(MeCN)2]PF6 (N∩N = bpy or phen) and mercurated 2‐phenylpyridinato‐ or 4‐(2‐tolyl)pyridinato (C∩N) species Hg(C∩N)Cl. Two new bis‐ruthenacycles studied by X‐ray crystallography revealed a C1 symmetry, with the C and N atoms of different C∩N ligands trans to the nitrogen atoms of the N∩N ligand. The reduction potential of the RuII/III feature of 3 is as low as ca.–0.2 V (vs. SCE in MeCN). Complexes 3 display a unique mediating ability in moving electrons from the reduced active site of PQQ‐dependent alcohol dehydrogenase (PQQ‐ADH) to an electrode with 1,2‐propanediol as a substrate at a working potential of +0.1 V. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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