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

Abstract

Dimethylgold(III) and methylmercury(II) form complexes Me₂AuL and MeHgL where L are poly-(pyrazol-1-yl)borate ligands [HB(pz)₃]- and [B(pz)₄]-. The structure of Me,Au{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 ¹H n.m.r. spectra in CD₂Cl₂ indicate presence of rapid equilibria between pyrazole ring environments at ambient temperature and, for the MeHg^II complexes, down to -90ºC. For the Me₂Au^III complexes spectra at -90ºC 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) Å, α 117.98(5)º, Z 18.