Tracing hydrogen bonding Au···H-C at gold atoms: a case study.

It has been shown in preceding experimental work that cyclometalated 6-benzylpyridines with gold(III) centers in the metallacycle (1) adopt a boat conformation reminiscent of the structure of 9,10-dihydroanthracene. There is a conspicuously short Au···H-C contact with a pseudoaxial methyl group suggesting a significant interaction which may be the prototype for Au(III)···H-C hydrogen bonding. Quantum chemical calculations on the B3LYP/def2-TZVP level have now shown that the ground state structures and conformations adopted by the homologues with two hydrogen atoms, two methyl groups, and a hydrogen atom and a methyl group at the carbon atom bridging the two (hetero)arene rings can be explained on the basis of simple conformation rules. There is no evidence that the Au(III)···H-C contact leads to an attractive interaction. The results are discussed in the context of literature data for Pt(II) analogues. Examples for potential Au(III)···H-X interactions presented in other references appear to be of a similar character.