Synthesis and nuclear magnetic resonance studies of halogeno and hydrido tris(pyrazol-1-yl)borato ruthenium(II) complexes

Abstract

The reaction of polymeric [{RuCl₂(cod)}_n](cod = cycloocta-1,5-diene) with potassium tris(pyrazol-1-yl)borate, KHB(pz)₃, in refluxing tetrahydrofuran leads to [Ru{HB(pz)₃}Cl(cod)]1, and the pyrazole-containing [RuCl₂(Hpz)₂(cod)]2 which arises from thermolysis of pyrazolylborate. Reaction of [RuCl₂(tht)₄](tht = tetrahydrothiophene) with the same salt at room temperature affords a mixture of [Ru{HB(pz)₃}Cl(tht)₂]3 and [Ru{HB(pz)₃}₂(tht)₂]4, which have been efficiently isolated. The product ratio of this process greatly depends on the reaction conditions. The compound [Ru{HB(pz)₃}₂]5 forms by transformation of 4 in chloroform solution, a reaction which is slow but complete in one week. The compound [RuClH(bpzm)(cod)][bpzm = bis(pyrazol-1-yl)methane] reacts with KHB(pz)₃ to give [Ru{HB(pz)₃}H(cod)] as the only ruthenium product. Nuclear Overhauser enhancement (NOE) measurements have been used as a valuable method for the assignment of the H³ and H⁵ resonances of the pyrazolyl groups. Heteronuclear ¹H–¹³C correlation (COSY) experiments have been recorded to determine the assignment of the C³ and C⁵ carbons of the pz groups.