Co-ordination chemistry of dimethylgold(III). Synthesis, structural studies, and fluxional behaviour of complexes with polydentate ligands

Abstract

Dimethylgold(III) nitrate forms complexes [AuMe₂L]NO₃ with polydentate nitrogen-donor ligands (L) containing N-methylimidazol-2-yl (mim) and pyridin-2-yl (py) groups: (mim)₂CHOH, (mim)₃COH, (py)(mim)₂COH, and (py)₂(mim)COH. The structures of [AuMe₂{(py)(mim)₂COH}]NO₃ and [AuMe₂{B(pz)₄}], where [B(pz)₄]^– is tetrakis(pyrazol-1-yl) borate, have been determined by single-crystal X-ray diffraction at 295 K and refined by least-squares methods to R 0.034 and 0.040 for 2 801 and 2 240 independent ‘observed’ reflections, respectively. The complexes have square-planar geometry for gold, ‘cis-Me₂Au(mim)₂’ in the (py)(mim)₂COH complex and ‘cis-Me₂Au(pz)₂’ in the [B(pz)₄]^– complex, with one unco-ordinated pyridine and two unco-ordinated pyrazole rings, respectively. The complexes [AuMe₂L]NO₃[L =(mim)₃COH or (py)₂(mim)COH] in CD₃OD, and monoprotonated complexes of poly(pyrazol-1-yl) borate ligands, [AuMe₂(HB(pz)₂(Hpz)}]⁺ and [AuMe₂{B(Pz)₃(HPz)}]⁺, in (CD₃)₂SO–D₂O, exhibit complex variable-temperature ¹H n.m.r. spectra consistent with fluxional behaviour involving five-co-ordinate intermediates. In addition, the spectra show that [AuMe₂{(py)₂(mim)COH}]NO₃ in solution exists as two structural isomers, involving ‘cis-Me₂Au(py)(mim)’ and ‘cis- Me₂Au(py)₂’ environments in the ratio ca. 5 : 1. Crystal data: [AuMe₂{(PY)(mim)₂COH}]NO₃ triclinic, space group P, a= 11.393(3), b= 10.859(2), c= 7.927(2)Å, α= 89.16(2), β= 74.11(2), γ= 89.87(2)°, and Z= 2; [AuMe₂{B(pz)₄)], monoclinic, space group P2₁/c, a= 12.645(2), b= 8.343(2), c= 17.310(4)Å, β= 99.14(2)°, and Z= 4.