Synthesis and X-ray crystal structures of several dinuclear ruthenium cymene complexes based on the tetradentate ligand, 2,2′-(1H-pyrazole-3,5-diyl)bis(6-methylpyridine) (Me2DppzH)

The complexes [Ru-2(6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)Cl-2](+) (1), [Ru-2(6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)(NO3)(2)](+) (2), [Ru-2(6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)(OH2)(2)](3+) (3), [RU2(6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)(NO2)(2)](+) (4), [Ru-2(6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)(CH3CN)(2)](3+) (5) and [Ru-2(NO2-6,6'-Me(2)dppz) (eta(6)-p-cymene)(2)Cl-2](+) (6), where 6,6'-Me(2)dppzH is 2,2'-(1H-pyrazole-3,5-diyl)bis( 6-methylpyridine) and NO2-6,6'-Me(2)dppzH is 2,2'-(1H-4-nitropyrazole-3,5-diyl)bis(6-methylpyridine), were synthesized and characterized by H-1 NMR and UV-Vis spectroscopy, X-ray crystallography and elemental analysis. Compounds 2 and 4 were additionally characterized by IR spectroscopy. Reaction of compound 1 with an aqueous silver ion produces the corresponding aquo complex 3. Complex 3 can be isolated or further reacted with NaNO2 to form the N-bound nitrite complex 4. Complex 1 can also be reacted with an acetonitrile solution of HPF6 to produce the acetonitrile species (5). Reaction of compound 1 with an excess of NOBF4 produces the corresponding chloro complex with nitration at the pyrazole carbon atom. Attempts to isomerize the geometry of complex 1 from the 'anti-facial' geometry to the 'syn' geometry were unsuccessful using either chemical or photochemical means. All efforts to convert the bound nitro group to the nitrosyl were futile, resulting in either ligand substitution or alteration of the ligand backbone. (C) 2000 Elsevier science Ltd All Rights reserved.