Gold(I) and Palladium(II) Complexes of 1,3,4-Trisubstituted 1,2,3-Triazol-5-ylidene “Click” Carbenes: Systematic Study of the Electronic and Steric Influence on Catalytic Activity

The synthesis of a small family of six electronically and sterically modified 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene gold­(I) chloride complexes is described. Additionally, the corresponding <i>trans</i>-[PdBr₂(iPr₂-bimy)­(1,3,4-trisubstituted 1,2,3-triazol-5-ylidene)] complexes are also generated and used to examine the donor strength of the 1,3,4-trisubstituted 1,2,3-triazol-5-ylidene ligands. All compounds have been characterized by ¹H and ¹³C NMR and IR spectroscopy, high-resolution electrospray mass spectrometry (HR-ESI-MS), and elemental analysis. The molecular structures of four of the gold­(I) and four of the palladium­(II) complexes were determined using X-ray crystallography. Finally, it is demonstrated that these 1,2,3-triazol-5-ylidene gold­(I) chloride complexes (Au­(trz)­Cl) are able to catalyze the cycloisomerization of 1,6-enynes, in high yield and regioselectivity, as well as the intermolecular direct etherification of allylic alcohols. Exploiting the Au­(trz)Cl precatalysts allowed the etherification of allylic alcohols to be carried out under milder conditions, with better yield and regioselectivity than selected commercially available gold­(I) catalysts

Gold(I)-Catalyzed Addition of Thiols and Thioacids to 3,3-Disubstituted Cyclopropenes

Gold­(I)-catalyzed reactions of thiols, thiophenols, and thioacids with 3,3-disubstituted cyclopropenes occur in a regioselective and chemoselective manner to produce either vinyl thioethers or primary allylic thioesters in good yields. A survey of commonly used gold­(I) catalysts shows Echavarren’s cationic gold­(I) catalyst to be most tolerant of deactivation by sulfur. A novel digold with bridging thiolate complex is characterized by X-ray crystallography, shedding light on a possible deactivation pathway

Gold(I)-Catalyzed Addition of Thiols and Thioacids to 3,3-Disubstituted Cyclopropenes

Gold­(I)-catalyzed reactions of thiols, thiophenols, and thioacids with 3,3-disubstituted cyclopropenes occur in a regioselective and chemoselective manner to produce either vinyl thioethers or primary allylic thioesters in good yields. A survey of commonly used gold­(I) catalysts shows Echavarren’s cationic gold­(I) catalyst to be most tolerant of deactivation by sulfur. A novel digold with bridging thiolate complex is characterized by X-ray crystallography, shedding light on a possible deactivation pathway

Gold-Catalyzed Proto- and Deuterodeboronation

A mild gold-catalyzed protodeboronation reaction, which does not require acid or base additives and can be carried out in “green” solvents, is described. As a result, the reaction is very functional-group-tolerant, even to acid- and base-sensitive functional groups, and should allow for the boronic acid group to be used as an effective traceless directing or blocking group. The reaction has also been extended to deuterodeboronations for regiospecific <i>ipso</i>-deuterations of aryls and heteroaryls from the corresponding organoboronic acid. Based on density functional theory calculations, a mechanism is proposed that involves nucleophilic attack of water at boron followed by rate-limiting B–C bond cleavage and facile protonolysis of a Au−σ-phenyl intermediate

Divergent Outcomes of Gold(I)-Catalyzed Indole Additions to 3,3-Disubstituted Cyclopropenes

Depending on the conditions employed, gold(I)-catalyzed addition of indoles to 3,3-disubstituted cyclopropenes can be controlled to yield either 3-(<i>E</i>)-vinylindoles (<b>3</b>) or <i>bis-</i>indolylalkanes (<b>4</b>). If the cyclopropene substituents are sterically bulky, unprecedented gold-catalyzed oxidation under air occurs to yield <i>bis</i>-indolylalkene (<b>5</b>) and epoxide (<b>6</b>) at room temperature