Coinage Metal Carbonyls and Isocyanides:  Synthesis and Characterization of the Gold(I) Complexes [HB(3,5-(CF₃)₂Pz)₃]AuCO and [HB(3,5-(CF₃)₂Pz)₃]AuCNBut

Syntheses and IR spectroscopic and X-ray structural data for the gold(I) carbonyl and tert -butyl isocyanide complexes of the fluorinated tris(pyrazolyl)borate ligand [HB(3,5-(CF 3 ) 2 Pz) 3 ] - (where HB(3,5-(CF 3 ) 2 Pz) 3 = hydrotris(3,5-bis(trifluoromethyl)pyrazolyl)borate) are reported. The carbonyl complex [HB(3,5-(CF 3 ) 2 Pz) 3 ]AuCO ( 1 ) crystallizes in a triclinic unit cell, space group P 1̄, with a = 8.3865(6) Å, b = 8.6467(6) Å, c = 19.009(2) Å, α = 98.649(6)°, β = 93.043(7)°, γ = 117.446(6)°, V = 1197.5(2) Å 3, Z = 2, and R = 0.0372. The gold atom adopts a distorted tetrahedral geometry with an Au−C distance of 1.862(9) Å. The 13 C NMR spectrum of 1 displays a signal at δ 172.6 which corresponds to the carbonyl carbon. The ν CO of 1 (2144 cm - 1 ) is similar to that observed for the copper(I) analog. Metal−CO distances and the C−O stretching frequencies of the coinage metal carbonyl adducts of [HB(3,5-(CF 3 ) 2 Pz) 3 ] - follow the orders Ag > Au > Cu and Ag > Au ≥ Cu, respectively. Crystals of [HB(3,5-(CF 3 ) 2 Pz) 3 ]AuCNBu t ( 2 ) are monoclinic, space group P 2 1 / c, with a = 12.082(2) Å, b = 23.551(3) Å, c = 10.780(2) Å, β = 106.683(12)°, V = 2938.4(7) Å 3, Z = 4, and R = 0.0372. The gold atom coordinates to tris(pyrazolyl)borate in a highly asymmetric fashion with one short Au−N bond and two long Au−N separations. Corresponding Cu(I) and Ag(I) adducts display fairly symmetric structures with pseudotetrahedral metal sites. In the isocyanide series, the gold analog exhibits the highest ν CN whereas the Ag adduct has the longest metal−C distance. [HB(3,5-(CF 3 ) 2 Pz) 3 ]ML (M = Cu, Ag, Au; L = CO, CNBu t ) complexes exhibit significantly reduced M-to-L back-bonding.