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, Rw = 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, Rw
= 0.069 for
2536 independent reflections with I >
3σ(I).