Pseudo-base formation in the attempted synthesis of a conjugatively coupled bis(nitrosylruthenium) complex and spectroelectrochemistry of bipyrimidine-bridged dinuclear Ru(terpy)X precursor compounds (X = Cl, NO2)

Abstract

Reaction of {(µ-bpym)[RuCl(terpy)]₂}(PF₆)₂, bpym = 2,2′-bipyrimidine and terpy = 2,2′:6′,2″-terpyridine, with NaNO₂ yields {(µ-bpym)[Ru(NO₂)(terpy)]₂}(PF₆)₂. In CH₃CN/0.1 M Bu₄NPF₆ both dinuclear complexes can undergo two reversible bpym-centered one-electron reduction processes and two metal-centered one-electron oxidation steps, the latter involving mixed-valent intermediates with weak intermetallic coupling. Acidification of {(µ-bpym)[Ru(NO₂)(terpy)]₂}(PF₆)₂ does not lead to the expected {(µ-bpym)[Ru(NO)(terpy)]₂}⁶⁺ but, probably because of the high charge, to the insoluble but structurally and IR-spectroscopically characterised pseudo-base product syn-{(µ-bpym-(4-OH))[Ru(NO)(terpy)]₂}(PF₆)₅. The addition of one hydroxide to one of the 4-positions of bis-chelating bpym interrupts the aromatic π conjugation and is accompanied by corresponding intra-pyrimidine bond length variations, however, the effect on the electronic interaction of the two different syn positioned {RuNO}⁶ moieties remains small, possibly due to their situation within the central molecular π plane.