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‘-Me2dppzH), 2,2‘-(1H-pyrazole-3,5-diyl)bis(6-methylpyridine) (6,6‘-Me2dppzH), 3,5-di(pyrid-2-yl)pyrazole (dppzH), and dipyridyloxadiazole (dpo) react
with either Ru(trpy)Cl3 or trans-Ru(trpy)Cl2(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 1H
and 13C NMR, electronic absorption, and infrared spectroscopy. Additionally, [Ru2(trpy)2(6,6‘-Me2dppz)μ-Cl](BF4)2
(3b(BF4)2), [Ru2(trpy)2(4,4‘-Me2dppz)μ-Cl](PF6)2·0.5MeOH (3c), [Ru2(trpy)2(6,6‘-Me2dppz)(CH2C(O)CH3)](PF6)2·
0.5(CH3)2CO (9b), “in”-[Ru(trpy)(4,4‘-Me2dppz)Cl](PF6)·(CH3)2CO (1c), and “out”-[Ru(trpy)(dpo)Cl](PF6)·(CH3)2CO
(2d) were characterized by X-ray crystallography. Several ligand substitution reactions were attempted. For example,
[Ru2(trpy)2(6,6‘-Me2dppz)μ-Cl](BF4)2 (3b) was reacted with hydroxide ion to produce [Ru2(trpy)2(6,6‘-Me2dppz)μ-OH](PF6)2 (6b). Complex 6b reacts with benzyl bromide to produce [Ru2(trpy)2(6,6‘-Me2dppz)μ-Br](PF6)2 (7b) or
with (CH3)3SiI to produce [Ru2(trpy)2(6,6‘-Me2dppz)μ-I](PF6)2 (8b). Reaction of 6b with acetone forms the methyl
enolate complex [Ru2(trpy)2(6,6‘-Me2dppz)(CH2COCH3)](PF6)2 (9b) while, analogously to a Cannizarro reaction, the
reaction with benzaldehyde forms the bridging benzoate complex [Ru2(trpy)2(6,6‘-Me2dppz)(C6H4CO2)](PF6)2 (11b).
The bridging azide complex [Ru2(trpy)2(6,6‘-Me2dppz)μ-N3](PF6)2 (10b) is formed by reaction of 6b with (CH3)3SiN3. Additionally, the chloride ligands of the monometallic complexes of “in”-[Ru(trpy)(dpo)Cl](PF6) (1d), “in”-[Ru(trpy)(4,4‘-Me2dpo)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 +0.72 and +1.15 V, and at +0.64 and +1.13 V, respectively. These complexes were not emissive.