Disassembly of diruthenium(II,III) tetraacetate with P–N donor ligands

Abstract

Valent-averaged diruthenium(II,III) tetraacetate, [Ru2(μ-O2CCH3)4(H2O)2](PF6), was reacted with various bidentate P–N donor ligands. These reactions led to the partial displacement of bridging carboxylate groups and concomitant cleavage of the Ru–Ru bond, producing novel complexes. Disassembly reactions with the aminophosphines; diphenyl-2-pyridylphosphine (dpppy) and 2-(diphenylphosphino)ethylamine (dppea), produced homoleptic tris-chelated species, fac-[Ru(dpppy-P,N)3](PF6)2 (III) and mer-[Ru(dppea-P,N)3](PF6)2 (VI), respectively. Disassembly reactions with aromatic aminophosphines; 2-(diphenylphosphino)methylpyridine (dppmpy) and 2-(diphenylphosphino)ethylpyridine (dppepy), led to heteroleptic tris-chelated complexes cis,cis,trans-[Ru(dppmpy-P,N)2(η2-O2CCH3)](PF6)·MeOH (IV) and cis,cis,trans-[Ru(dppepy-P,N)2(η2-O2CCH3)](PF6) (V), respectively, whereas reaction with the non-cyclic aminophosphine, 3-(diphenylphosphino)-1-propylamine (dpppa) and the non-cyclic iminophosphine, 2-(diphenylphosphino)benzylidinebenzylamine (dppbba), led to the heteroleptic tris-chelated complexes cis,cis,trans-[Ru(dpppa-P,N)2(η2-O2CCH3)](PF6·EtOH (VII) and cis,cis,trans-[Ru(dppbba-P,N)2(η2-O2CCH3)](PF6)·2MeOH·H2O (VIII), respectively. All complexes were fully characterized. Electrochemical studies (CV, OSWV) showed that the homoleptic tris-chelated complexes had higher oxidation potentials (Epa) than the corresponding heteroleptic tris-chelated complexes, due to the weak π-acceptor ability of the acetate group. Complex (III) has the highest Epa as it contains the strongest combination of π-accepting groups. The Epa values of the heteroleptic complexes were found to be in the order: dppbba (CHN)>dppmpy, dppepy (py)>dpppa (NH2), since amines are much poorer π-acceptors than pyridyl and imino groups. Complexes (III), (VI) and (VII) showed irreversible oxidation waves, while complexes (IV), (V) and (VIII) displayed quasi-reversible one electron processes.