Electrophilic behaviour of nitrosyls: preparation and reactions of six-co-ordinate ruthenium tetra(pyridine) nitrosyl complexes

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Abstract
Reaction of NO2 – with [RuCl2(py)4] gave [Ru(NO2)2(py)4] which on treatment with HCl gave [RuCl(py)4(NO)]2+, isolated as ClO4 – or PF6 – salts. Use of HBr or HClO4, instead of HCl gave [RuBr(py)4(NO)]2+ or [Ru(OH)(py)4(NO)]2+ respectively. The nitrosyl ligand in [RuX(py)4(NO)]2+ behaved as an electrophile [ν(NO) was 1 910 cm–1 for X = Cl, 1 901 cm–1 for X = Br, and 1 868 cm–1 for X = OH]. With OH–[RuX(NO2)(py)4] was formed reversibly. With an excess of N3 – and [RuCl(py)4(NO)][ClO4]2 a mixture of [RuCl(N3)(py)4] and [RuCl(H2O)(py)4]+ was formed, N2 and N2O being evolved. The less soluble [RuCl(py)4(NO)][PF6]2 reacted with an equimolar amount of N3 – to give [RuCl(N2)(py)4]PF6, which was unstable with respect to N2 loss in solution, and was contaminated with a small quantity of a reduced nitrosyl complex, believed to be [Ru(H2O)(py)4(NO)][PF6]2 or [Ru(py)4(NO)][PF6]2·H2O. The formation of [RuCl(N2)(py)4]+ indicates that the reaction between [RuCl(py)4(NO)]2+ and N3 – proceeds via a cyclic [graphic omitted] intermediate, as was confirmed by labelling experiments. Electrochemical one-electron reduction of [RuCl(py)4(NO)]2+ gave [Ru(H2O)(py)4(NO)]2+, isolated as the PF6 – salt; it is not known how strongly the H2O molecule is attached to the ruthenium, if at all. Electrochemical six-electron reduction of [RuCl(py)4(NO)]2+ gave [RuCl(NH3)(py)4]+; this same product could be isolated as the PF6 – salt from zinc amalgam reduction of [RuCl(py)4(NO)]2+. Polarographic, coulometric, and cyclic voltammetry experiments showed that [RuCl(py)4(NO)]2+ is reduced in two successive reversible one-electron steps followed by an irreversible four-electron reduction.

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