Osmium Complexes Containing N-Heterocyclic Carbene-Based C,N,C-Pincer Ligands

Abstract

Osmium(II) complexes bearing C,N,C-pincer ligand 2,6-bis(alkylimidazolin-2-ylidene)pyridine (CNC-Me and CNC-Bu for alkyl = methyl and n-butyl, respectively) or 2,6-bis(3-butylbenzimidazolin-2-ylidene)pyridine (CNC 0 -Bu) and aromatic diimine (2,2 0 -bipyridine (bpy)/1,10-phenanthroline (phen)) have been prepared. The X-ray crystal structure of [Os(CNC-Me)(bpy)Cl](PF 6 ) shows that the Os-C bonds are essentially single (Os-C distances = 2.042(4) and 2.059(4) A ˚). Spectroscopic comparisons of [Os(C,N,C)(diimine)Cl] þ and [Os(tpy)(bpy)Cl] þ (tpy = 2,2 0 ;6 0 ,2 00terpyridine) suggest that the lowest-energy absorption bands for [Os(C,N,C)(diimine)Cl] þ originate from a d π (Os II ) f π*(diimine) metal-to-ligand charge-transfer (MLCT) transition. Density functional theory calculations reveal that the π*(diimine) levels in [Os(C,N,C)(diimine)Cl] þ are lower lying than the π*(C,N,C). The Os(II/III) oxidation waves for [Os(C,N,C)(diimine)Cl] þ are reversible, with E 1/2 = -0.03 to 0.16 V vs Cp 2 Fe þ/0 . The absorption spectra for the Os(III) species have been obtained by spectroelectrochemical methods.

Trinuclear copper(I) complex of 1,3-bis(2-pyridinylmethyl)imidazolylidene as a carbene-transfer reagent for the preparation of catalytically active nickel(II) and palladium(II) complexes

“…These complexes show their enhanced catalytic activity in many organic reactions especially in CeC coupling reactions [16,20,25,28]. Pincer complexes of transition metals such as iridium [31], rhodium [32], ruthenium [33,34], and osmium [35] have found applications in olefin metathesis, hydrogen transfer, hydrosilylation, hydroformylation and polymerization reactions.…”

Osmium Polypyridyl Complexes and Their Applications to Dye-Sensitized Solar Cells

“…1‐Bu, 2‐Bu, and 3‐Bu showed similar weak absorption bands at λ = 500–800 nm due to the C,N,C‐pincer ligands. 1‐Bu and 2‐Bu derivatives are less conjugated than the 3‐Bu derivative, but these have higher energy than the π*(tpy) [25]…”

Synthesis and Characterization of Conformationally Rigid Chiral Pyridine–N‐Heterocyclic Carbene‐Based Palladacycles with an Unexpected Pd–N Bond Cleavage

“…Amino and imino functionalized NHC palladacycles have displayed remarkably enantiomeric excess values of up to 92% in asymmetric allylic alkylation reaction . Pyridine‐functionalized NHCs have also attracted recent interest and have demonstrated good potential in different catalytic scenarios . Crabtree et al and Hahn et al have previously reported a series of palladium tridentate NHC complexes and successfully applied them to the catalysis of the Heck reaction.…”

“…32,33 Pyridine-functionalized NHCs have also attracted recent interest and have demonstrated good potential in different catalytic scenarios. [34][35][36][37][38][39][40][41][42][43][44][45][46] Crabtree et al 47,48 and Hahn et al 49 have previously reported a series of palladium tridentate NHC complexes and successfully applied them to the catalysis of the Heck reaction. A quick literature search revealed that previous efforts in the synthesis of chiral NHC palladacycles typically involved chiral starting materials like (S)-(-)-(1,1'-Binaphthalene-2,2'-diyl)bis(diphenylphosphine); BINAP and oxazolines, and to the best of our knowledge, none of the abovementioned pyridine-NHC palladacycles exhibited any chirality in the carbon chelate backbone.…”