A dicoordinate gold(i)–ethylene complex

Abstract

The use of the exceptionally bulky tris-2-(4,4’-di-tert-butylbiphenylyl)phosphine ligand allows the isolation and complete characterization of the first dicoordinate gold(I)–ethylene adduct, filling a missing fundamental piece on the organometallic chemistry of...

Dicoordinate Au(I)–Ethylene Complexes as Hydroamination Catalysts

“…In turn, 13 C{ 1 H} NMR resonances are shifted in the same direction with upfield shifts about 7 ppm with respect to free ethylene ( Table 1 ). These relatively small changes suggest little backdonation from Au to the ethylene π*(C=C) orbital, as noted earlier for 1 · C 2 H 4 , 19 and in contrast with the related tricoordinate gold(I)–ethylene complexes, 13f in which the chemical shift differences can reach up to 3 and 55 ppm in 1 H and 13 C NMR spectra, respectively. As for the more sterically hindered complex 1 · C 2 H 4 , 19 the coordinated ethylene presented the largest shift in 1 H NMR resonances, which appear as an AA′BB′ system at 3.79 and 3.66 ppm, contrasting with the rest of the compounds that led to a single broad peak due to four equivalent protons.…”

“…These relatively small changes suggest little backdonation from Au to the ethylene π*(C=C) orbital, as noted earlier for 1 · C 2 H 4 , 19 and in contrast with the related tricoordinate gold(I)–ethylene complexes, 13f in which the chemical shift differences can reach up to 3 and 55 ppm in 1 H and 13 C NMR spectra, respectively. As for the more sterically hindered complex 1 · C 2 H 4 , 19 the coordinated ethylene presented the largest shift in 1 H NMR resonances, which appear as an AA′BB′ system at 3.79 and 3.66 ppm, contrasting with the rest of the compounds that led to a single broad peak due to four equivalent protons. We ascribed the shift in 1 · C 2 H 4 to ring-current effects due to the surrounding aryl rings, which could also hinder the rotation of bound ethylene giving rise to the observed AA′BB′ system.…”

“…Albeit the former are considerably bulky, the tris biaryl tris-2-(4,4′-di- tert -butylbiphenylyl)phosphine phosphine ( L1 ) clearly presents the highest % V bur value of 67.0. 19 As discussed in the following sections, the steric profile of the ligand seems to be crucial to impart stability to the aimed Au(I)–ethylene compounds, having a direct effect on catalytic performance.…”

“… 16 , 17 In fact, we have recently authenticated the first dicoordinate gold(I)–ethylene adduct using the extremely bulky tris-2-(4,4′-di- tert -butylbiphenylyl)phosphine ( L1 ), previously reported by Straub, 18 that kinetically stabilizes the coordination of ethylene. 19 In contrast to related tricoordinate complexes, the bonding interactions are mainly electrostatic (i.e., ionic) with minimal Au → ethylene π-backdonation.…”

“…More precisely, we have used both the commercial ligands trimesityl phosphine ( L2 ) and t BuXPhos ( L3 ), as well as a series of terphenyl phosphines ( L4 – L8 ) prepared by our group ( Figure 1 ). 24 We compare herein the stability of the resulting ethylene adducts with respect to the first of its class constructed around L1 ( 19 ) and examine their catalytic competence for the underdeveloped Au(I)-catalyzed functionalization of ethylene through a model hydroamination reaction.…”