Gold(I) Complexes with Eight‐Membered NHC Ligands: Synthesis, Structures and Catalytic Activity

Abstract

A series of expanded‐ring NHC gold complexes of the formula (NaphtDHD−Ar)Au−X (NaphtDHD=4,5‐dihydro‐1H‐naphtho[1,8‐ef][1,3]diazocin‐3(2H)‐ylidene; Ar: Mes=2,4,6‐trimethylphenyl, Dipp=2,6‐diisopropylphenyl or Xyl=2,6‐dimethylphenyl; X=Cl, NCCH3, NTf2) have been synthesized, including the first gold(I) triflimidate complex (5) stabilized by an eight‐membered NHC ligand. The new organogold compounds have been characterized by mass spectrometry, IR spectroscopy, and 1H and 13C NMR spectroscopy. The structural geometries of 3 b–c and 5 have been unequivocally established by crystallographic analysis revealing broad N‐C‐N angles (>121°) and high buried volume values (46–54%). The first catalytic studies were carried out on the cycloisomerization of 1,6‐enynes, obtaining full conversions (0.5 mol% catalyst loading) and excellent endo/exo selectivity (up to 99:1), and on the gold‐catalyzed phenol synthesis. Lastly, the (NaphtDHD‐Dipp)Au+ NTf2− species was subjected to a kinetic experiment in the cyclization of a N‐propargyl carboxamide to evaluate the efficiency of the pre‐formed catalyst (5) and the in situ activated gold complex (3 b+AgNTf2).

Chemoselective H/D exchange catalyzed by nickel nanoparticles stabilized by N-heterocyclic carbene ligands

“…N-heterocyclic carbenes (NHCs) are versatile ligands that have been widely used for the synthesis of a broad variety of metallic complexes or for the functionalization of metallic surfaces. [32][33][34][35][36][37][38] During the last years, NHCs have also shown to be very efficient ligands that strongly coordinate to the surface of MNPs, permitting to modulate their catalytic activity and selectivity. [39][40][41][42][43][44] MNPs stabilized by NHCs have previously been employed as catalysts in H/D exchange reactions.…”

A dicoordinate gold(i)–ethylene complex

“…The percent buried volume (% V Bur ) 16 of the phosphine yielded a large parameter of 67.0 (Fig. S28, ESI † ), which is notably higher than other bulky NHC 17 and phosphine 18 ligands.…”

Tetranuclear Dicationic Aurophilic Gold(I) Catalysts in Enyne Cycloisomerization: Cooperativity for a Dramatic Shift in Selectivity

“…With the gold catalyst, various 1,6‐enynes were converted into five‐membered dienes (type I , Figure 1) at rt; this completed the known reactivity of palladium, platinum, and ruthenium, previously identified for such cyclopentenes formation [47–49] . Following this milestone work, mononuclear cationic gold complexes have been shown to promote mostly the formation of either five and/or six‐membered dienes (type I – III , Figure 1), sometimes with a troublesome selectivity [23,50–61] . Au(I) catalytic systems are occasionally able to form bicyclic strained structures such as bicyclo[4.1.0]hept‐4‐enes (type IV , Figure 1) and cyclobutenes (type V – VI , Figure 1).…”

“…[47][48][49] Following this milestone work, mononuclear cationic gold complexes have been shown to promote mostly the formation of either five and/or six-membered dienes (type I-III, Figure 1), sometimes with a troublesome selectivity. [23,[50][51][52][53][54][55][56][57][58][59][60][61] Au(I) catalytic systems are occasionally able to form bicyclic strained structures such as bicyclo[4.1.0]hept-4-enes (type IV, Figure 1) and cyclobutenes (type V-VI, Figure 1). In these cycloisomerization reactions using 1,6-enyne substrates, a high substrate-dependence is observed for the final selectivity.…”