Gold derivatives of scorpionates: comparison with the other coinage metal poly(pyrazolyl)borate analogues

Abstract

Gold derivatives [Au(Tp^x)(PR₃)] (Tp^x = Tp, hydrotris(pyrazol-1-yl)borate or Tp*, hydrotris(3,5-dimethylpyrazol-1-yl)borate; R = Ph or ^tBu) and [Au(pzTp)(PR₃)_x] (pzTp = tetrakis(pyrazol-1-yl)borate, x = 1 or 2, R = Ph or ^tBu) have been synthesised and characterized both in solution (¹H- and ³¹P{¹H}-NMR) and in the solid state (IR, single crystal X-ray structure analysis, ³¹P CPMAS). ³¹P {¹H} NMR solution data suggest greater stability of the tetrakis(pyrazolyl)borate relative to those of tris(pyrazolyl)borate. All compounds are fluxional at room temperature. In order to compare [Au(Tp*)(PPh₃)] with analogous coinage metal adducts we have synthesized and structurally characterized [Cu(Tp*)(PPh₃)]·PPh₃ and [Ag(Tp*)(PPh₃)]·2MeCN. In [Au(Tp*)(PPh₃)] the gold atom adopts a distorted tetrahedral geometry with <Au–P> 2.181(5) and <Au–N> 2.37(2) Å (cf. <Cu–P,N> 2.166(6), 2.098(1) in [Cu(Tp*)PPh₃], 2.156(2), 2.075(7) in [Cu(Tp*)(PPh₃)]·PPh₃; and <Ag–P,N> in [Ag(Tp*)PPh₃]·MeCN 2.347(12), 2.35(5) Å). There are three independent [Au(Tp*)(PPh₃)] molecules in the asymmetric unit of the structure with their PAu⋯B axes lying on the cell diagonal of a cubic P2₁3 cell, two with the same chirality aligned opposed in direction to the third which is of opposite chirality. A number of Cu, Ag and Au complexes containing scorpionate ligands have also been investigated by ³¹P cross-polarization magic-angle-spinning (CPMAS) NMR spectroscopy.