Reductive C–C Coupling from Molecular Au(I) Hydrocarbyl Complexes: A Mechanistic Study

Abstract

Organometallic gold complexes are used in a range of catalytic reactions, and they often serve as catalyst precursors that mediate C–C bond formation. In this study, we investigate C–C coupling to form ethane from various phosphine-ligated gem-digold(I) methyl complexes including [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ], [Au 2 (μ-CH 3 )(XPhos) 2 ][NTf 2 ], and [Au 2 (μ-CH 3 )( t BuXPhos) 2 ][NTf 2 ] {Ar′ = C 6 H 3 -2,6-(C 6 H 3 -2,6-Me) 2 , C 6 H 3 -2,6-(C 6 H 2 -2,4,6-Me) 2 , C 6 H 3 -2,6-(C 6 H 3 -2,6- i Pr) 2 , or C 6 H 3 -2,6-(C 6 H 2 -2,4,6- i Pr) 2 ; XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl; t BuXPhos = 2-di- tert -butylphosphino-2′,4′,6′-triisopropylbiphenyl; NTf 2 = bis(trifluoromethyl sulfonylimide)}. The gem-digold methyl complexes are synthesized through reaction between Au(CH 3 )L and Au(L)(NTf 2 ) {L = phosphines listed above}. For [Au 2 (μ-CH 3 )(XPhos) 2 ][NTf 2 ] and [Au 2 (μ-CH 3 )( t BuXPhos) 2 ][NTf 2 ], solid-state X-ray structures have been elucidated. The rate of ethane formation from [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ] increases as the steric bulk of the phosphine substituent Ar′ decreases. Monitoring the rate of ethane elimination reactions by multinuclear NMR spectroscopy provides evidence for a second-order dependence on the gem-digold methyl complexes. Using experimental and computational evidence, it is proposed that the mechanism of C–C coupling likely involves (1) cleavage of [Au 2 (μ-CH 3 )(PMe 2 Ar′) 2 ][NTf 2 ] to form Au(PR 2 Ar′)(NTf 2 ) and Au(CH 3 )(PMe 2 Ar′), (2) phosphine migratio...

A dicoordinate gold(i)–ethylene complex

“… 10 In this regard, our group has recently capitalized on the use of sterically demanding phosphine ligands to access unusual Au( i ) structures, including the isolation of bridged cationic digold complexes 11 and the reactivity of gold species as FLP constituents 12 and in C–C bond formation processes. 13 In this study, we have employed the ligand tris-2-(4,4′-di- tert -butylbiphenylyl)phosphine ( 1 ), 14 previously reported by the group of Straub, which allowed us to isolate and structurally characterize the first dicoordinate gold( i )–ethylene complex. This species can be regarded as the simplest model reported to date for the isolobal ethenium cation (C 2 H 5 + ).…”

Coupling photocatalytic water oxidation with organic reduction: strategy for using water to reduce organic molecules

“…9). One undergoes the oxidative addition of ary halides to the transition metals [47][48][49][50][51][52][53][54] . The other starts with the formation of the aryl radical anion (ArX• -) by the single electron transfer (SeT) from catalysts to ary halides 45,46,56 .…”

“…However, it is desired to overcome this problem because a new use of water as the green reducing agent to enable the reductive transformations of organic substances can be developed by this way. In addition, the reductive coupling of aryl or alkyl halides is of great significance in modern organic synthesis [47][48][49][50][51][52][53][54][55][56] , which has prompted us to select this kind of reaction as the model reaction to make our idea come true. Encouraged by prior success in applying carbon nitride-supported transition metal (M/g-C 3 N 4 ) into photocatalytic water splitting, [57][58][59][60][61][62][63][64][65] we selected this kind of semiconductor to achieve our goals.…”

From Waste to Green Applications: The Use of Recovered Gold and Palladium in Catalysis

“…The field of homogeneous gold catalysis remained essentially dormant throughout the 1980s and 1990s, with Dyker's review in 2000 citing as few as 13 reactions catalysed by gold under homogeneous conditions [54]. However, over the past two decades, the scope of homogeneous gold catalysis has expanded significantly, with reports now describing cross-coupling reactions, C-H activation and photoredox catalysis [55][56][57][58][59][60][61]. Despite the advances in homogeneous gold catalysis, the use of heterogeneous supported catalysts has dominated industrial applications of gold catalysts, mainly in the synthesis of bulk chemicals [62].…”