Gold-Catalysis: Reactions of Organogold Compounds with Electrophiles

Abstract

Different arylgold(i), one alkynylgold(i), and one vinylgold(i) triphenylphosphane complexes were subjected to electrophilic halogenation reagents. With N-chlorosuccinimid, N-bromosuccinimid, and N-iodosuccinimid as well as the Barluenga reagent, selectively halogenated compounds were obtained. Trifluoroacetic acid, as a source of protons, leads to a clean protodeauration. With N-fluorobenzenesulfonimide or Selectfluor, exclusively a homocoupling was observed. For the precursor of the vinylgold(i) complex, a similar oxidative coupling could be induced by gold(iii) chloride. Reactions with silicon or tin electrophiles failed.

Pd(0)/Au(i) redox incompatibilities as revealed by Pd-catalyzed homo-coupling of arylgold(i)-complexes

“…1 With the exception of transmetallation, gold complexes rarely facilitate these basic transformations, a partial consequence of their high barriers for Au( i )/Au(0) and Au( iii )/Au( i ) redox transitions 2 along with their preference for low coordination numbers. Despite these differences Au( i )/Au( iii ) catalyzed cross-coupling reactions have been reported 3,4 under the action of strong oxidants like selectfluor, 5 PhI(OAc) 2 , 6 or peroxy acids. 7 Mechanistic studies by Toste on systems utilizing selectfluor suggest fascinating bimolecular reductive elimination mechanistic possibilities.…”

When gold can do what iodine cannot do: A critical comparison

“…After nucleophilic attack at the gold-activated alkyne and subsequent reorganization steps, the final step typically is a protodeauration [27–30] of the vinylgold intermediate to regenerate the catalytic species. In an analogous way, vinylgold intermediates can be successfully trapped by iodine electrophiles (and other electrophiles) to incorporate I rather than H in the final product (Scheme 1) [27,31–40]. Even though both processes catalyzed by gold give rise to the same scaffolds, iodine incorporation allows for a further functionalization of the scaffold by classical cross-coupling reactions [41–42].…”

Electrochemical monitoring of the oxidative coupling of alkynes catalyzed by triphenylphosphine gold complexes

“…The reaction can be catalyzed by a variety of metal-based catalytic systems [3]. Recently, gold, in spite of its inertness towards ambient conditions, has emerged as a powerful catalytic agent [4][5][6] when combined with oxidizing agents such as selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)) or peracids in homogeneous phase [7][8][9][10][11][12].…”