1H NMR is not a proof of hydrogen bonds in transition metal complexes

Hydrogen bonding to gold(I) and its effect on the structure and dynamics of molecules have been a matter of long debate. 1 A number of X-ray studies have reported gold compounds with short Au I ···H contacts, but solid spectroscopic evidence for Au I ···H bonding has been missing. 1 Notably, during the revision of this work, Bourissou et al. 2 and Straka et al. 3 have provided evidence of true intramolecular Au I ···H hydrogen bonds in [Cl–Au–L] + complexes, where L is a protonated N-heterocyclic carbene. The studied compounds feature intramolecular Au I ···H + –N bonds detected by means of NMR 2 and infrared spectroscopies. 2 , 3