Monometallic and dimetallic ruthenium(II)-terpyridine complexes employing the tetradentate ligands dipyridylpyrazolyl, dipyridyloxadiazole, and their dimethyl derivatives

The tetradentate ligands, 2,2'-(1H-pyrazole-3,5-diyl)bis(4-methylpyridine) (4,4'-Me(2)dppzH), 2,2'-(1H-pyrazole-3,5-diyl)bis(6-methylpyridine) (6,6'-Me(2)dppzH), 3,5-di(pyrid-2-yl)pyrazole (dppzH), and dipyridyloxadiazole (dpo) react with either Ru(trpy)Cl-3 or trans-Ru(trpy)Cl-2(NCCH3), where trpy is 2,2',2"-terpyridine, to form a variety of Ru(II) complexes. Among these are the symmetrical chloro-bridged Ru(II) dimer and the "in" and "out" geometric isomers of the monometallic Ru(II) containing species where "in" and "out" refer to the orientation of the Ru-Cl vector relative to the centroid of the ligand backbone. Thirteen complexes were prepared and painstakingly purified by. careful recrystallization and/or exhaustive column chromatography. These complexes were characterized by H-1 and C-13 NMR, electronic absorption, and infrared spectroscopy. Additionally, [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-Cl](BF4)(2) (3b(BF4)(2)), [Ru-2(trpy)(2)(4,4'-Me(2)dppz)mu-Cl](PF6)(2).0.5MeOH (3c), [Ru-2(trpy)(2)(6,6'-Me(2)dppz)(CH2C(O)CH3)](PF6)(2.) 0.5(CH3)(2)CO (9b), "in"-[Ru(trpy)(4,4'-Me(2)dppz)Cl](PF6).(CH3)(2)CO (1c), and "out"-[Ru(trpy)(dpo)Cl](PF6).(CH3)(2)CO (2d) were characterized by X-ray crystallography. Several ligand substitution reactions were attempted. For example, [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-Cl](BF4)(2) (3b) was reacted with hydroxide ion to produce [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-OH](PF6)(2) (6b). Complex 6b reacts with benzyl bromide to produce [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-Br](PF6)(2) (7b) or with (CH3)(3)Sil to produce [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-l](PF6)(2) (8b). Reaction of 6b with acetone forms the methyl enolate complex [Ru-2(trpy)2(6,6'-Me(2)dppz)(CH2COCH3)](PF6)(2) (9b) while, analogously to a Cannizarro reaction, the reaction with benzaldehyde forms the bridging benzoate complex [Ru-2(trpy)(2)(6,6'-Me(2)dppz)(C6H4CO2)](PF6)(2) (11b). The bridging azide complex [Ru-2(trpy)(2)(6,6'-Me(2)dppz)mu-N-3](PF6)(2) (10b) is formed by reaction of 6b with (CH3)(3)-SiN3. Additionally, the chloride ligands of the monometallic complexes of "in"-[Ru(trpy)(dpo)Cl](PF6) (1d), "in"-[Ru(trpy)(4,4'-Me(2)dpo)Cl](PF6) (1e), and "out"-[Ru(trpy)(dpo)Cl](PF6) (2d) were substituted with water to form their respective aqua complexes, 4d, 4e, and 5d. All of the complexes exhibit broad unsymmetrical absorption bands in the visible portion of the electromagnetic spectrum. The dimetallic complexes 3b and 3c exhibit two, 1e(-) reversible oxidation waves at +072 and +1.15 V, and at +0.64 and +1.13 V, respectively. These complexes were not emissive.