Cationic Protic Imidazolylidene NHC Complexes of Cp*IrCl+ and Cp*RhCl+ with a Pyridyl Tether Formed at Ambient Temperature

Abstract

Protic NHC (PNHC) complexes with N 1 H, N 2 -alkyl/aryl imidazolylidene ligands are relatively rare, and routes for their synthesis differ from what is used to make non-protic analogs. Prior work from our group and others showed that in the presence of a tethering ligand (phosphine or in one case, pyridine), CpM and Cp*M (M = Ir, Ru) PNHC complexes could be made by heating. Here, we find that the use of ionizing agents to activate [Cp*M III Cl(µ-Cl)] 2 (M = Ir, Rh) allows for what we believe is unprecedented ambient temperature formation of PNHC complexes from neutral imidazoles; the product complexes are able to perform transfer hydrogenation.

Methanol-Mediated Formation of an Iridium(III) NHC/Azolato Chelate Complex: An Experimental and Theoretical Study

“…While such N -protonation , and N -alkylation reactions have been demonstrated with various azolato complexes, the instability of [ 2 ] might be problematic requiring previous modifications at the ligand. However, [ 2 ] itself is a potential pre-catalyst for a variety of bifunctional catalyses such as hydrogenation − and hydrogen-borrowing reactions. …”

Mechanistic insights and comparative analysis of Ru(ii)–NNC pincer complexes with anionic-, protic-, and classical-NHCs for transfer hydrogenation of ketones

“…26 Grotjahn and coworkers revealed that Rh and Ir complexes with pNHC ligands were effective catalysts for the transfer hydrogenation (TH) of acetophenone and chalcone. 27,28 Furthermore, Song and coworkers demonstrated that the NH functionality of protic NHC favors fast and selective hydrogenation of alkenone through hydrogen bonding. 29 Hahn and Morris have recently demonstrated a Ru-NNC complex, with pNHC in a pincer ligand, as an efficient catalyst for TH of ketones.…”

Ru(II)-Anionic-Naked-NHC Complexes as Cooperative Lewis Pairs: Parallels in Structure and FLP-type Chemical Reactivity

“…[64][65][66][67][68][69] These complexes with proton-responsive ligands have shown promising reactivity and selectivity in various catalytic reactions. [70][71][72][73][74][75][76][77] Anionic-naked-N-heterocyclic carbene complexes represent a relatively new and emerging class of compounds obtained from pNHC complexes after deprotonation of the N-H unit and are characterized by negatively charged NHC ligands. [78][79][80][81][82] These complexes have been shown to activate small molecules such as carbon dioxide 83 and dihydrogen.…”