Synthesis, Structure and Catalytic Activity of NHC–Ag^I Carboxylate Complexes

Abstract

A general synthetic route was used to prepare 15 new N-heterocyclic carbene (NHC)-Ag(I) complexes bearing anionic carboxylate ligands [Ag(NHC)(O2 CR)], including a homologous series of complexes of sterically flexible ITent ligands, which permit a systematic spectroscopic and theoretical study of the structural and electronic features of these compounds. The complexes displayed a significant ligand-accelerated effect in the intramolecular cyclisation of propargylic amides to oxazolidines. The substrate scope is highly complementary to that previously achieved by NHC-Au and pyridyl-Ag(I) complexes.

Theoretical NMR spectroscopy of N-heterocyclic carbenes and their metal complexes

“…In contrast to Cu and Au, only a few Ag-NHC complexes have been experimentally investigated, due to the easier 'decomposition' reaction of ligand exchange yielding a bis-ligated complex [82]. In addition to the synthesis and catalytic application of these new compounds, a detailed spectroscopic analysis evidenced an unexpected trend in the NMR resonance of the carbene carbon atom in these complexes [83]. 207.9 ppm, while the adamantyl-substituted unsaturated complex, 45, resonates further upfield at 173.5 ppm.…”

“…Calculated versus experimental13 C NMR chemical shifts for selected NHC-Ag-COOCH 3 adducts. Adapted from ref [83]…”

Vinyltrifluoroborate Complexes of Silver Supported by N‐Heterocyclic Carbenes

“…Indeed, structurally well authenticated, monomeric silver complexes of the type (NHC)AgX are relatively less common , . Search of Cambridge Structural Database show that (NHC)Ag(carboxylate) complexes are the better known monomeric (NHC)AgX systems involving oxygen based anions (X),, while the only structurally characterized example of (NHC)Ag with a nitrate anion ligand, is a tetramer, [( i PrIm)Ag(NO 3 )] 4 …”

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

“…[21] Building on these precedents, we wondered whether a silver complex stabilized by the BP DPr ligand could provide a practical catalytic tool for activating the C�C bond in unsubstituted propargylic derivatives. Derived from the attractive structural and steric features of this carbene ligand and the known catalytic utility of other silver carboxylates, [22] we envisioned the preparation of BP DPrAgO 2 C-R (R = Me, Ph) complexes to subsequently evaluate their catalytic performance in CO 2 fixation to propargylic substrates at room temperature in the absence of any co-catalyst (e. g., base, additive).…”

“…[5,23b] The observed C NHC resonances are significantly shifted to lower fields compared to their IPr analogues (δ � 184 ppm). [22] The couplings 1 J( 107 Ag-13 C) = 238-241 Hz and 1 J( 109 Ag-13 C) = 275-278 Hz, increased with respect to the NHC silver bromide complex [ 13 C NMR δ = 230.0 (dd, 1 J( 107 Ag-13 C) = 228 Hz, 1 J-( 109 Ag-13 C) = 263 Hz], demonstrate a significant influence of the carboxylate anion to the Ag-C NHC bond upon halide abstraction.…”