Auracarboranes with and without Au−Au Interactions:  An Unusually Strong Aurophilic Interaction

The auracarboranes 1,2-(AuPPh3)2-1,2-C2B10H10 (1) and 1,1‘-(AuPPh3)2-[2-(1‘,2‘-C2B10H10)-1,2-C2B10H10] (2) have been synthesized. Both compounds were characterized by NMR and X-ray crystallography. Compound 2 was found to contain an aurophilic interaction between the gold centers. A variable-temperature NMR investigation indicated that the energy barrier separating the gold−gold bonded state and the nonbonded state is 11 ± 1 kcal/mol. Compound 1 crystallized in the monoclinic space group P21/c with a = 18.3380(9) Å, b = 14.1037(6) Å, c = 19.4716(8) Å, β = 112.003(2)°, V = 4669 Å3, and Z = 4. Data were collected using Mo Kα radiation, to a maximum 2θ = 50°, giving 8865 unique reflections, and the structure was solved by heavy atom methods. The final discrepancy index was R = 0.047, R w = 0.055 for 3423 independent reflections with I > 3σ(I). Compound 2 crystallized in the monoclinic space group P21/c with a = 14.058(6) Å, b = 18.365(8) Å, c = 20.387(9) Å, β = 109.22(1)°, V = 4970 Å3, and Z = 4. Data were collected using Mo Kα radiation, to a maximum 2θ = 45°, giving 5232 unique reflections, and the structure was solved by heavy atom methods. The final discrepancy index was R = 0.066, R w = 0.069 for 2536 independent reflections with I > 3σ(I).