Resonance-Assisted but Antielectrostatic Intramolecular Au···H-O Hydrogen Bonding in Gold(I) Complexes: A Computational Verification.

The peculiar Au···H hydrogen bonding has garnered significant interests, but its existence and nature remain an open question in gold chemistry. In this paper, we established and authenticated the first intramolecular Au···H-O hydrogen bonding in gold(I) complexes. Our computational results based on an ab initio valence bond (VB) method, namely the block-localized wave function (BLW) method, clarified that this Au···H-O hydrogen bonding is a new type of resonance-assisted hydrogen bond (RAHB). In this RAHB, π conjugation in the hydrogen bond donor has the capability to modulate the Au···H-O hydrogen bonding. In contrast to conventional RAHBs, however, the Au···H-O hydrogen bonding is antielectrostatic and is dominated by the charge transfer interaction including cooperative σ electron donation from the d orbital of the metal center to the antibonding orbital of the hydroxyl group and π conjugation from the hydroxyl group to adjacent π deficient or strong π electron withdrawing groups. This novel theoretical perspective not only confirms the existence and reveals the nature of intramolecular Au···H hydrogen bonding but also provides a promising strategy to rationally design strong gold hydrogen bonds.