Au center dot center dot center dot H-C Interactions in Gold(I) Complexes with Benzyl Imidazolyl Phosphine Ligands

Secondary interactions in gold(I) compounds have assumed considerable interest, since they have a profound influence on chemical and physics properties, structures and conformations of gold complexes. In the last years a large number of secondary bonding interactions has been discovered in compounds of gold(I), mostly of the general type L-Au-X, where L is a phosphine ligand and X is a halide or a pseudohalide. Distinct kinds of interaction involving gold atoms are: Au•••Au (aurophilic interaction), Au•••X where X is a halide, Au••• -system, Au•••H-C. This last type of contact is very rare either as hydrogen bond or as agostic interaction. The tertiary phosphines (BzIm)Ph2P, 1-benzyl-2-imidazolyl diphenyl phosphine, and (BzIm)3P, tris-(1-benzyl-2-imidazolyl)phosphine, have features to systematically allow Au•••H-C contacts, also coexisting with aurophilic interactions. In fact, they are able to bring the hydrogen atoms of the benzyl groups in close position to the gold atom by a change of conformation. In the complex [(BzIm)Ph2PAuCl] [1], where only one benzyl imidazolyl group is present, the assumed conformation is favourable for the CH2 group to have one hydrogen atom at close distance from Au (2.62 Å). In the complex, [(BzIm)3PAuCl], two benzyl imidazolyl groups position one hydrogen atom of each CH2 group at close distances from gold (2.83 and 2.95 Å). In the tetranuclear gold cluster [{(BzIm)3P}2Au4Cl2]2+ with the two (BzIm)3P phosphines, which act as bihapto ligands, two gold atoms each interact with one hydrogen atom at distances of 2.57 and 2.59 Å. [1] Burini, A.; Pietroni, B. R.; Galassi, R; Valle, G.; Calogero, S. Inorg. Chim. Acta 1995, 229, 299-305.