Auracarboranes with and without Au-Au interactions: An unusually strong aurophilic interaction

The auracarboranes 1,2-(AuPPh(3))(2)-1,2-C2B10H10 (1) and 1,1'-(AuPPh(3))(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 P2(1)/c with a = 18.3380(9) Angstrom, b = 14.1037(6) Angstrom, 19.4716(8) Angstrom, beta = 112.003(2)degrees, V = 4669 Angstrom(3), and Z = 4. Data were collected using Mo K alpha radiation, to a maximum 2 theta = 50 degrees, 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 > 3 sigma(I). Compound 2 crystallized in the monoclinic space group P2(1)/c with a = 14.058(6) Angstrom, b = 18.365(8) Angstrom, c = 20.387(9) Angstrom, beta = 109.22(1)degrees, V = 4970 Angstrom(3), and Z = 4. Data were collected using Mo K alpha radiation, to a maximum 2 theta = 45 degrees, 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 > 3 sigma(I).