Gold(I) Hydrides as Proton Acceptors in Dihydrogen Bond Formation Ignacy Cukrowski,* [a] Jurgens H. de Lange, [a] Ferdinand Groenewald, [b] and Helgard G. Raubenheimer* [b] 1. Introduction The chemistry of Au I complexes is enriched by the important role played by Au···Au interactions, a phenomenon that has been investigated in great detail. [1, 2] Recently the possibility of equally strong Au···H hydrogen bond formation has been rec- ognized as a viable interaction in its own right. Examples have been investigated experimentally in the condensed phase, [3] and theoretically for simple [4] as well as complicated [3] systems. [M] H···HX ([M] = transition metal fragment; X = rest of proton donor molecule) dihydrogen bonding, discovered in the 1990s [5] and later reported for various metals after theoretical and experimental investigations, is presently a topic attracting increased research attention among a large and growing number of participants. [6] Bonding [7] and mechanistic [8] aspects, proton transfer, [9] packing in crystals, [10] and biochemical inves- tigations [11] have all been receiving attention. With two excep- tions, dihydrogen bonding is currently not known for group 11 and 12 transition metal hydride complexes. [8b, 12] The nearest re- semblance of such an interaction in dynamic gold chemistry, has been postulated for a regenerated gold hydride intermedi- ate that is stabilized by a protonated ethanol solvent molecule within a calculated catalytic cycle of olefin hydrogenation. [13] Subsequently, Grabowski and RuipØrez [14] theoretically found the intermediate complexes FH···HCu and FH···HAg upon H 2 cleavage by the two fluorides, MF (M = Cu, Ag). In the context of supramolecular interactions where gold complexes feature prominently, [15] this lack of fundamental knowledge regarding dihydrogen interactions, constitutes a severe shortcoming. If appropriately addressed and accurately resolved, important further developments could follow. Hence, we embarked on such a study involving Au I hydrides. Only a few hydrides of Au I are known. [3] From them, we se- lected as potential anionic proton acceptors the dihydride [AuH 2 ]  (1), [16] the stable, isolobal, cluster-like [AuAuH]  (2), [17] and a complex [C 6 F 5 AuH]  (3), which has not yet been synthe- sized. Furthermore, we included neutral AuH (4) [18] and the sim- plified compound [(MeN K CH =CHNMeC L )AuH] (5) as model for the known carbene complex [(ArN K CH =CHNArC L )AuH] (Ar = 2.6- (iPr) 2 C 6 H 3 ). [19] The conventional proton donors in hydrogen bonding, HF, H 2 O, H 3 N as well as their corresponding protonat- ed analogues were employed. This article focusses primarily on the involvement of HF and H 2 F + in dihydrogen bonding with the selected Au I hydrides, although results obtained with the other proton donors are referred to by way of comparison. Our results highlight the following: 1) a number of previous- ly unreported 1:1, 1:2 and n :1 (n  3) proton acceptor:proton donor interactions realized in isolated systems (full set of struc- tural data for monomers and adducts is provided in Section S1 in the Supporting Information); 2) various competitive and/or 3) stabilizing secondary interactions, and 4) unexpected proton transfers. A major aim of our work was to determine stability trends and bonding preferences between the chosen proton Wavefunction and DFT calculations indicate that anionic dihy- dride complexes of Au I form strong to moderate directed Au  H···H bonds with one or two HF, H 2 O and NH 3 prototype proton donor molecules. The largely electrostatic interaction is influenced by relativistic effects which, however, do not in- crease the binding energy. Very weak Au···H associations—ex- hibiting a corresponding bond path—occur between neutral AuH and HF units, although ultimately F becomes the pre- ferred donor atom in the most stable structure. Increasing the hydridicity of AuH by attachment of an electron donating NHC ligand effects Au-H···H bonding of moderate strength only with HF, whereas competing Au···H interactions dominate for H 2 O and NH 3 . Rare h 2 coordinated and HX (X = F or OH) associ- ated H 2 complexes are produced during interaction with a single ion of stronger acidity, H 2 F + or H 3 O + . Theoretically, re- action of excess [AuH 2 ]  as proton acceptor with H 3 O + or NH 4 + in 3:1 or 4:1 ionic ratios, respectively, affords H···H bonded analogues of Eigen-type adducts. Outstanding analyti- cal relationships between selected bonding parameters sup- port the integrity of the results. [a] Prof. I. Cukrowski, J. H. de Lange Department of Chemistry Faculty of Natural and Agricultural Sciences University of Pretoria, Lynnwood Road Pretoria 0002 (South Africa) E-mail: ignacy.cukrowski@up.ac.za [b] F. Groenewald, Prof. H. G. Raubenheimer Department of Chemistry and Polymer Science University of Stellenbosch Private Bag X1, Matieland 7602 (South Africa) E-mail : hgr@sun.ac.za Supporting Information and the ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/ cphc.201700383. ChemPhysChem 2017, 18, 2288 – 2294  2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2288 Articles DOI: 10.1002/cphc.201700383