SYNTHESIS AND NUCLEAR-MAGNETIC-RESONANCE STUDIES OF HALOGENO AND HYDRIDO TRIS(PYRAZOL-1-YL)BORATO RUTHENIUM(II) COMPLEXES

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 H-3 and H-5 resonances of the pyrazolyl groups. Heteronuclear H-1-C-13 correlation (COSY) experiments have been recorded to determine the assignment of the C-3 and C-5 carbons of the pz groups.