Gold(III) NHC Complexes for Catalyzing Dihydroalkoxylation and Hydroamination Reactions Ashwin G. Nair, Roy T. McBurney, Mark R. D. Gatus, Samantha C. Binding, and Barbara A. Messerle* Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney 2109, Australia * S Supporting Information ABSTRACT: A gold(III) complex of an N-heterocyclic carbene based hemilabile ligand with two pendant pyrazole arms (1,3-bis((1H-pyrazol-3-yl)methyl)-2,3-dihydro-1H-imi- dazole, LH) was synthesized. Complex [LAu(III)Cl 3 ] is an excellent catalyst for promoting dihydroalkoxylation at room temperature, even catalyzing this reaction at 0 °C. [LAu(III)- Cl 3 ] is one of the most efficient catalysts reported to date for the spirocyclization of alkynyl diols. Furthermore, [LAu(III)- Cl 3 ] catalyzed intra- and intermolecular hydroamination reactions, achieving good to excellent conversions. [LAu(III)- Cl 3 ] is a more efficient catalyst than a gold(I) analogue, [LAu(I)Cl]. The dependence of the quantity of weakly coordinating anion [BAr F 4 ] - ((3,5-trifluoromethyl)phenyl borate) present on catalysis efficiency was probed for the dihydroalkoxylation reaction. X-ray diffraction analysis of single crystals demonstrated the solid-state structure of gold complexes [LAu(III)Cl 3 ] and [LAu(I)Cl], which displayed the expected square-planar and linear coordination geometries, respectively. ■ INTRODUCTION Gold catalysis 1 is a vitally important area with many reported examples of gold(I)-catalyzed reactions including C-O 2 and C-N 3 bond formations, C-C bond forming cyclization reactions, 4 applications to total synthesis, 5 and photocatalysis. 6 Conversely, gold(III)-catalyzed reactions are still in their infancy. The vast majority of reports use inorganic gold(III) salts, typically AuCl 3 , primarily for promoting hydroamina- tions, 7 hydroalkoxylations, 8 intramolecular hydroarylation, 9 oxidations, 10 rearrangements, 11 and C-C bond forming cyclizations. 8g,12 There are a growing number of reports using organometallic Au(III) complexes 13 as catalysts, 14 aided by Hashmi’s method for oxidizing Au(I) to Au(III). 14b Organometallic gold(III) complexes have been used for catalyzing isomerizations, 14b,c hydroaminations, 14d C-C cou- plings, 14e-k hydrations, 14l and three component couplings. 14m,n A recent communication by Toste highlighted the need to further develop the area of gold(III) catalysis. 15 Increasing the scope of organogold(III) catalysis is important to enable a greater level of regio-, chemo-, and enantioselectivity over the products generated, to achieve vastly increased reaction rates and to avoid in situ reduction of Au(III) by substrates, intermediates, or products. The choice of ligand to support gold(III) is crucial for achieving optimal catalytic activity. Common structural motifs found in the ligands of reported organogold(III) catalysts include a central N-heterocyclic carbene (NHC); 14k,16 some feature a biphenyl ligand coordinated through a gold-aryl bond, 14g, j or bidentate N, O-donor 17 or N, N′-donor li- gands, 14d,f,h see Figure 1. However, in designing and selecting Au(III) complexes as catalysts, a balance needs to be struck between stability and catalytic activity. Highly efficient Au(III) catalysts offering good stability that operate across a range of reactions would be welcome. We reasoned that a ligand with a strong σ-donor to act as an anchor for gold(III) in combination Received: August 22, 2017 Figure 1. Gold(III) catalysts featuring (a-d) strong and (e) hemilable coordination motifs; (f) our design features both. Article pubs.acs.org/IC © XXXX American Chemical Society A DOI: 10.1021/acs.inorgchem.7b02161 Inorg. Chem. XXXX, XXX, XXX-XXX