Synthesis, characterization and reactivity studies of electrophilic ruthenium(ii) complexes: a study of H2 activation and labilization

Abstract

Reaction of 2,2′-bipyridine (bpy) with dinuclear complexes [RuCl(dfppe)(μ-Cl)₃Ru(dmso-S)₃] (dfppe = 1,2-bis(dipentafluorophenyl phosphino)ethane (C₆F₅)₂PCH₂CH₂P(C₆F₅)₂; dmso = dimethyl sulfoxide) (1) or [RuCl(dfppe)(μ-Cl)₃RuCl(dfppe)] (2) affords the mononuclear species trans-[RuCl₂(bpy)(dfppe)] (3). Using this precursor complex (3), a series of new cationic Ru(II) electrophilic complexes [RuCl(L)(bpy)(dfppe)][Z] (L = P(OMe)₃ (5), PMe₃ (6), CH₃CN (7), CO (8), H₂O (9); Z = OTf (5, 6, 7, 8), BAr^F₄ (9) have been synthesized via abstraction of chloride by AgOTf or NaBAr^F₄ in the presence of L. Complexes 5 and 6 were converted into the corresponding isomeric hydride derivatives [RuH(PMe₃)(bpy)(dfppe)][OTf] (10a, 10b) and [RuH(P(OMe)₃)(bpy)(dfppe)][OTf] (11a, 11b) respectively, when treated with NaBH₄. Protonation of the cationic monohydride complex (11a) with HOTf at low temperatures resulted in H₂ evolution accompanied by the formation of either solvent or triflate bound six coordinated species [Ru(S)(P(OMe)₃)(bpy)(dfppe)][OTf]_n [(S = solvent (n = 2), triflate (n = 1)] (13a/13b); these species have not been isolated and could not be established with certainty. They (13a/13b) were not isolated, instead the six-coordinated isomeric aqua complexes cis-[Ru(bpy)(dfppe)(OH₂)(P(OMe)₃)][OTf]₂ (14a/14b) were isolated. Reaction of the aqua complexes (14a/14b) with 1 atm of H₂ at room temperature in acetone-d₆ solvent resulted in heterolytic cleavage of the H–H bond. Results of the studies on H₂ lability and heterolytic activation using these complexes are discussed. The complexes 3, 5, 11a, and 14a have been structurally characterized.