Expanded Ring NHC Silver Carboxylate Complexes as Efficient and Reusable Catalysts for the Carboxylative Cyclization of Unsubstituted Propargylic Derivatives

Abstract

Stabilized by a bulky N-heterocyclic carbene [ BP DPr, 1,3-bis(2,6diisopropylphenyl)-1,3-diazonine-2-ylidene] ligand, new silver carboxylate complexes of the form BP DPrAgO 2 C-R (R = Me, Ph) have been synthesized and fully characterized in solution and in the solid state and implemented as sole catalysts (base-, additive-, and, in some cases, solvent-free) in the challenging fixation of carbon dioxide to unsubstituted propargylic derivatives for the synthesis of oxazolidinones and α-methylene cyclic carbonates. Derived from X-ray diffraction studies, the molec-ular geometry and the concept of buried volume were employed to describe the structural and steric features of these silver complexes. Their stability and efficiency as catalysts have been demonstrated by the synthesis of 29 carboxylation products (72-98 % yield) at low catalyst loadings (0.01-1.5 mol%). Characteristics are high turnover numbers (up to 9400), catalyst recyclability (up to 96 % yield after the 7th cycle with no decomposition of the silver complex), and the possibility to scale-up the reaction.

Catalytic exploration of NHC–Ag(i)HMDS complexes for the hydroboration and hydrosilylation of carbonyl compounds

“…6 Focusing on silver(I)-NHC complexes, their synthetic versatility and application in a wide range of catalytic and organic transformations including A 3 coupling, alkynylation, CO 2 insertions and cyclisation reactions makes them useful reagents in synthesis. [11][12][13][14][15][16][17][18][19] A key aspect to this diverse reactivity is the ease of modularity of the ancillary NHC ligand which can alter its steric and electronic character via modification of the backbone and/or the substituents attached to the N atoms of the azole ring. [20][21][22][23][24] By exploiting the tuneability of NHC ligands, Takaki and co-workers developed a potent silver(I)-NHC pre-catalyst [AgCl(IMes)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene) that allowed β-selective hydroboration of alkynes and allenes to give direct access to a diverse range of organoboron compounds (Scheme 1c).…”

Ag–NHC Complexes in the π-Activation of Alkynes

“… ( A ) Ag(I)−NHC-catalyzed carboxylative cyclization of propargylic alcohols, and ( B ) amines, as reported by Cervantes-Reyes, Hashmi et al [ 61 ]. …”

“…In 2021, an important breakthrough was reported by Cervantes-Reyes, Hashmi et al in identifying ring-expanded Ag(I)–NHC complexes as efficient catalysts for the carboxylative cyclization of propargylic alcohols and amines ( Scheme 13 ) [ 61 ]. The most active complexes were [( BP DPr)(Ag(OAc)] and [( BP DPr)(Ag(OBz)], featuring a nine-membered, bulky NHC ligand ( BP DPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-diazonine-2-ylidene) and carboxylate counterions.…”

“… Heterocyclic scaffolds (4,5-dihydrooxazoles [ 59 , 64 , 85 ]; 1,3-dioxolan-2-ones [ 61 , 86 ]; oxazolidin-2-ones [ 76 , 87 ]; 1,2-dihydroisoquinolines [ 70 , 88 ]; isochromenes [ 71 , 89 ]; quinolines [ 72 , 90 ]; synthesized by Ag(I)−NHC complexes. …”

Synthesis of d10 N-Heterocyclic Carbene Complexes with a Perimidine Scaffold

“…N -Heterocyclic carbenes (NHCs) are critical auxiliary ligands for transition metals, with applications ranging from homogeneous catalysis to surface functionalization. − While unsaturated examples, such as imidazole- and benzimidazole-based NHCs, dominate the literature (Figure A), , there has been a shift to nonstandard NHCs in recent years that have shown greater effectiveness for catalysis. − In particular, saturated NHCs (imidazoline-based) have proven a popular choice due to their increased σ-donor strength, despite saturated NHCs being more challenging to synthesize than imidazole variants. Notable examples where saturated NHCs are highly effective include Grubbs second-generation catalyst for olefin metathesis and reactions that induce chirality. ,− …”