Studies on transition-metal oxo and nitrido complexes. Part 11. New oxo complexes of ruthenium as aerobically assisted oxidants, and the X-ray crystal structure of [Ru2O6(py)4]·3.5H2O

Abstract

The new complexes [Ru₂O₆L₄] [L = 4-t-butylpyridine (4Bu^t-py), nicotinic acid (Hnic), isonicotinamide (isna), pyridine-2-carboxylic acid (Hpyca), or ½(2,2′-bipyridyl) (bipy)] have been prepared and the X-ray crystal structure of another member of the series, [Ru₂O₆(py)]·3.5H₂O, determined [triclinic, space group P, a = 7.943(1), b = 8.952(2), c = 9.257(3) Å, α = 98.76(2), β = 95.75(2), γ = 98.08(1)°, Z = 1, R = 0.065]. New complexes are also reported of the types trans-[RuO₂L₄]²⁺ [L = Hnic, Hpyca, or pyridine-3,4-dicarboxylic acid (H₂pydca)], trans-[RuO₂Cl₂L₂] (L = py, 4Bu^t-py or 4-chloropyridine), trans-[RuO₂(pyca)₂] and trans-[RuO₂Cl₃L]⁻ (L = py, 4Bu^t-py, 3-methylpyridine, or 3,4-dimethylpyridine). Vibrational spectra, structures, and reactions of these species are discussed: they function as overall four-electron oxidants (eight-electron in the case of [Ru₂O₆L₄] ), converting primary alcohols into aldehydes and secondary alcohols into ketones, and function catalytically with N-methylmorpholine N-oxide or iodosylbenzene as co-oxidant. The most soluble of them, trans-[Ru₂O₆(py)₄]·3.5H₂O, trans-[Ru₂O₆(4Bu^t-py)₄], trans-[RuO₂(py)₄]²⁺, and trans-[RuO₂Cl₃(4Bu^t-py)]⁻, will also effect such oxidation of alcohols with dioxygen as co-oxidant.