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.