HETEROBIMETALLIC COMPLEXES FROM THE REACTION OF IRIDIUM(I) AND IRIDIUM(III) 3,5-DIMETHYLPYRAZOLATES WITH GOLD(I) OR GOLD(III)

The reaction of iridium(I) and iridium(III) pyrazolates, IrP2(CO)(pz-N) (1), IrP2(CO)(H)2(pz-N) (2), and IrP2(CO)(H)2(pz′-N) (10) (P = triphenylphosphine; pzH = 3,5-dimethylpyrazole and pz′H = 4-nitro-3,5-dimethylpyrazole), with Au(tht)X (tht = tetrahydrothiophene; X = Cl, Br) affords iridium(I)-gold(I) and iridium(III)-gold(I) derivatives IrP2(CO)(μ-pz-N,N′) AuX (X = Cl (3), X = Br (4)) and IrP2(CO)(H)2(μ-pz-N,N′)AuCl (8). The reaction between 1 and Au(tht)Cl3 gives an unstable yellow bimetallic intermediate, IrAuP2(CO)(pz)Cl3 (5), which is easily decomposed to (Aupz)n (6) and IrP2(CO)Cl3 (7). Iridium(III) cationic pyrazole derivatives [IrP2(CO)(pzH-N)(H)2][A] (A = AuCl4 (9), A = BF4 (12)) and [IrP2(CO)(pz′H-N)(H)2][A] (A = AuCl4 (11), A = BF4 (13)) are obtained by reaction of 2 or 10 with Au(tht)Cl3 or tetrafluoroboric acid. Infrared and NMR (1H and 31P{1H}) data show that compounds 8, 12, and 13 are able to exist in two different forms: in both of them the geometry around the iridium atom is the same with a cis hydride and trans phosphine arrangement. In one of the conformers, 8A, the resonance for the hydride trans to CO is observed at unusually low field (δ -3.72 in deuteriobenzene), suggesting the existence of a Au⋯H interaction. Complex 8A crystallizes in the monoclinic space group P21/n with a = 13.385 (2) Å, b = 16.229 (3) Å, c = 18.376 (3) Å, and β = 101.60 (2)°. Complex 12c is monoclinic, space group P21/c, with a = 9.874 (2) Å, b = 23.951 (4) Å, c = 21.029 (6) Å, and β = 101.25 (2)°. Both structures were solved by Patterson and Fourier methods and refined by full-matrix least squares; R values are 0.044 (for 3954 reflections) and 0.038 (for 4118 reflections) for 8A and 12c, respectively. In 8A a Au⋯H separation of 2.28 Å was calculated, against a value of 2.90 Å resulting from the sum of van der Waals radii.