Dinuclear Ruthenium Nitrido Complexes Supported by an Oxygen Tripodal Ligand

Dinuclear ruthenium nitrido complexes supported by the Kläui’s tripodal ligand [CpCo­{P­(O)­(OEt)2}3]− (LOEt–) have been synthesized starting from the ruthenium­(VI) nitrido precursor [LOEtRuVI(N)­Cl2] (1). Heating a solution of 1 in CCl4 at reflux, followed by recrystallization from hexane under nitrogen, afforded the mixed-valence ruthenium­(V)–ruthenium­(IV) μ-nitrido complex [LOEtCl2RuV(μ-N)­RuIVCl2LOEt] (2). The cyclic voltammogram of 2 exhibited reversible couples at 0.19 and 1.13 V versus Cp2Fe+/0, which are assigned as the RuV–RuIV/RuIV–RuIV and RuV–RuV/RuV–RuIV couples, respectively. Recrystallization of 2 from Et2O/heptane in air yielded the diamagnetic RuIV–RuIV complex [H13O6]­[{LOEtRuIVCl2}2(μ-N)] ([H13O6]­[2]), which underwent cation exchange with n-Bu4NOH to give [n-Bu4N]­[2]. X-ray diffraction revealed that the complex anions in [H13O6]­[2] and [n-Bu4N]­[2] contain linear, symmetric Ru–N–Ru bridges. Treatment of 1 with [(η6-p-cymene)­RuIICl2]2 in benzene afforded the tetranuclear ruthenium­(IV) complex [LOEtCl2RuIV(μ-N)­RuIV(H2O)­Cl2]2 (3) containing symmetric RuIV–N–RuIV bridges. The reaction of 1 with [RuII(H)­(Cl)­(CO)­(PCy3)2] (Cy = cyclohexyl) gave the ruthenium­(VI)–ruthenium­(II) nitrido complex [LOEtCl2RuVI(μ-N)­RuII(H)­Cl­(CO)­(PCy3)2] (4). The observed short RuII–N bond distance [1.915(5) Å] and high C–O stretching frequency (1985 cm–1) in 4 are suggestive of π interaction between RuII and the nitride.