Cationic, Two‐Coordinate Gold π Complexes

Abstract

Cationic, two-coordinate gold π complexes that contain a phosphine or N-heterocyclic supporting ligand have attracted considerable attention recently owing to the potential relevance of these species as intermediates in the gold-catalyzed functionalization of C-C multiple bonds. Although neutral two-coordinate gold π complexes have been known for over 40 years, examples of the cationic two-coordinate gold(I) π complexes germane to catalysis remained undocumented prior to 2006. This situation has changed dramatically in recent years and well-defined examples of two-coordinate, cationic gold π complexes containing alkene, alkyne, diene, allene, and enol ether ligands have been documented. This Minireview highlights this recent work with a focus on the structure, bonding, and ligand exchange behavior of these complexes.

Ammonium‐Salt‐Tagged IMesAuCl Complexes and Their Application in Gold‐Catalyzed Cycloisomerization Reactions in Water

“…[20,21] To enable access to ammonium-salt-tagged unsaturated NHC ligands, in this paper we present a synthetic pathway to water-soluble IMes derivatives and their conversion into recyclable gold catalysts that activate allenes or alkynes for intramolecular nucleophilic attack in water. [22][23][24] This study complements previous work by our group directed towards sustainable gold catalysis using ionic liquids or micelles as reaction media. [25][26][27] …”

Gold‐Mediated Isomerization of ­Cyclooctyne to Ring Fused Olefinic Bicycles

“…[1][2][3][4][5][6][7][8][9][10][11][12] Cycloisomerization chemistry of 1,n-enynes, in which the alkene acts as the nucleophile towards an alkyne activated by gold(I) is particularly interesting since such reactions lead to intricate scaffolds in an atom economical manner. [1,5,6] An area of major research focus in recent years has been the chemistry of isolable alkyne-gold [13,14] and alkene-gold [13,[15][16][17] complexes since they serve as useful models for key intermediates believed to present in the above mentioned processes. There are several structurally characterized, auxiliary ligand supported and auxiliary ligand free goldalkyne [14,[18][19][20][21][22][23][24][25][26] and gold-alkene adducts presently known.…”

“…N-heterocyclic carbene ligands are particularly useful in this regard. [17,19,53] The cyclooctyne-gold(I) adduct [(SIPr)Au(cyclooctyne)][SbF 6 ] {SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene} [25] reported by us represent one such example. …”

The preference for dual-gold(i) catalysis in the hydro(alkoxylation vs. phenoxylation) of alkynes

“…34,35 In the most common reactivity manifold, a gold-alkyne (oralkene or -allene) complex is activated towards nucleophilic attack by a reagent such as an amine or an alcohol. 36 The counterion has been found to be non-innocent, 37 especially if it has the capacity to coordinate gold directly, [38][39][40][41][42][43][44][45] with the potential power to modify not only the catalytic activity but the regioselectivity and stereoselectivity of the reaction.…”

“…In contrast, the interaction of alkynes and alcohols of aliphatic character follow a monometal mechanism, bearing the nature of the rate determining state. 35,36 but again this preference is really weak since the use of phosphines instead of NHCs can lead to a dual gold mechanism. 35,37,38 For the latter results both gold moieties do not cooperate separately, i.e., each one bonded to either the alcohol or the alkyne, but both are bound to the alkyne.…”