Coordination chemistry of dimethylgold(III) and methylmercury(II). Synthesis, 1H N.M.R. and structural studies of Poly(pyrazol-1-yl)borate complexes

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Abstract
Dimethylgold(111) and methylmercury(11) form complexes Me2AuL and MeHgL where L are poly(pyrazol-1-y1)borate ligands [HB(pz)3]- and [B(pz)4]-. The structure of Me2Au{HB(pz)3} has been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R 0.056 for 2194 independent 'observed' reflections. This complex has square-planar coordination for the gold atom involving two coordinated pyrazole rings and one uncoordinated ring, in contrast to the isoelectronic cation [Me2Au{(pz)3CH)]+ which has square planar coordination with a weak axial Au . .N interaction. Variable temperature 'H n.m.r. spectra in CD2Cl2 indicate presence of rapid equilibria between pyrazole ring environments at ambient temperature and, for the MeHg(II_\ud complexes, down to -90°C. For the Me2Au(III) complexes spectra at -9OoC indicate presence of pyrazole ring environments in ratios 2:1 (L = [HB(pz)3]-) and 2:1:1 (L = [B(pz)4]-). Crystal data for Me2Au{HB(pz)3}: rhombohedral, space group R3c, a 17.98(1) A, alpha 117.98(5), Z 18

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