Rhodium, iridium and nickel complexes with a 1,3,5-triphenylbenzene tris-MIC ligand. Study of the electronic properties and catalytic activities

Abstract

SummaryThe coordination versatility of a 1,3,5-triphenylbenzene-tris-mesoionic carbene ligand is illustrated by the preparation of complexes with three different metals: rhodium, iridium and nickel. The rhodium and iridium complexes contained the [MCl(COD)] fragments, while the nickel compound contained [NiCpCl]. The preparation of the tris-MIC (MIC = mesoionic carbene) complex with three [IrCl(CO)2] fragments, allowed the estimation of the Tolman electronic parameter (TEP) for the ligand, which was compared with the TEP value for a related 1,3,5-triphenylbenzene-tris-NHC ligand. The electronic properties of the tris-MIC ligand were studied by cyclic voltammetry measurements. In all cases, the tris-MIC ligand showed a stronger electron-donating character than the corresponding NHC-based ligands. The catalytic activity of the tri-rhodium complex was tested in the addition reaction of arylboronic acids to α,β-unsaturated ketones.

Metal Complexes of Click-Derived Triazoles and Mesoionic Carbenes: Electron Transfer, Photochemistry, Magnetic Bistability, and Catalysis

“…A TEP parameter of 2042 cm –1 was determined for the ligand L30 in that work. [96a] This value is in a similar range to what has been observed for monodentate, neutral 1,2,3‐triazol‐5‐ylidene ligands.…”

“…Recently, trinuclear rhodium‐triazolylidene complexes were used as pre‐catalysts for the arylation of 2‐cyclohexen‐1‐one with aryl boronic acids. [96a] Furthermore, mononuclear rhodium(I) complexes with chelating mesoionic carbenes with additional hemilabile donors were used as pre‐catalysts for the hydrothiolation of alkynes. [96b]…”

“…[96a] Furthermore, mononuclear rhodium(I) complexes with chelating mesoionic carbenes with additional hemilabile donors were used as pre‐catalysts for the hydrothiolation of alkynes. [96b]…”

“…[100c] Trinuclear iridium(I) complexes were also reported with ligands of type L30 . [96a] In those complexes the triazolylidene donors bind to each of the central iridium atoms. Additionally, the co‐ligands on iridium were either cyclooctadiene or carbonyl.…”

“…A trinuclear nickel complex, 106 , containing additional cyclopentadienyl (Cp) ligands was also recently reported. [96a] The most recent report on nickel complexes, 107 and 108 , deals with the use of bidentate ligands of type L19a/L20a . These complexes were synthesized by the direct reaction of triazolium salts with NiCp 2 , with one of the Cp ligands acting as a base for the deprotonation of the triazolium salts.…”