Binding of CO and NH3 at a five-coordinate Ru(ii) centre in the solid state and in solution

Abstract

The known five-coordinate, square-pyramidal, green trans-RuCl₂(P–N)(PR₃) complexes (P–N = o-diphenylphosphino-N,N′-dimethylaniline; R = Ph (1a), p-tolyl), in the solid state at ambient conditions, or in CDCl₃ solution at low temperatures, coordinate CO (at 1 atm) to form beige-coloured trans-monocarbonyl derivatives. In the solution reactions at room temperature, the PR₃ ligand dissociates and the yellow dicarbonyl complex RuCl₂(CO)₂(P–N) is formed as a mixture of trans,cis- and cis,cis-isomers. With use of ¹³CO, the carbonyls complexes are characterized by variable temperature NMR and IR data, and (for the monocarbonyls) elemental analyses. Similarly, 1a and the dibromo analogue (1b) in the solid state bind NH₃ to form the beige trans-monoammine species RuX₂(P–N)(PPh₃)(NH₃), trans-4a (X = Cl) and trans-4b (X = Br), with cis P-atoms. The solution NH₃ reactions, however, generate a species, speculatively thought to be the unusual, tight ion-pair, bisammine species [RuX(P–N)(PPh₃)(NH₃)₂⋯X], 5a (X = Cl) and 5b (X = Br), in which a halide is considered strongly H-bonded to the cis-ammine ligands, although an alternative RuX(P–N)(PPh₃)(NH₃)₂ formulation with a monodentate P–N ligand cannot be ruled out; dissolution in CDCl₃ of isolated 5a and 5b, which are characterized by NMR, elemental analysis, and conductivity data, results in a partial, reversible loss of NH₃ to form some cis- and trans-4a or -4b, respectively. Treatment of 5a with one mole equivalent of NH₄PF₆ in acetone solution removes the H-bonded chloride to give [RuCl(P–N)(PPh₃)(NH₃)₂]PF₆ (6), and this is converted by thermal loss of NH₃ to generate the extremely air-sensitive, five-coordinate, ionic species [RuCl(P–N)(PPh₃)(NH₃)]PF₆ (7). NMR evidence is presented for formation of the tris(ammine) species [Ru(P–N)(PPh₃)(NH₃)₃](PF₆)₂ (8) via treatment of trans-RuCl₂(P–N)(PPh₃) with an atmosphere of NH₃ in the presence of 2 mole equivalents of NH₄PF₆.