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Updated: Feb 24, 2026

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
The Forgotten Nitroaromatic Phosphines as Weakly Donating P-ligands: An N-Aryl-benzimidazolyl Series in RhCl(CO)
Chongwei Zhu1,2, Emmanuel Gras1,2, Carine Duhayon1,2
1CNRS, LCC (Laboratoire de Chimie de Coordination), 205 route de Narbonne, BP44099, 31077, Toulouse Cedex 4, France.
Abstract:
The coordination chemistry of a priori weakly σ-donating nitroaromatic phosphines is addressed through a series of nitro-substituted (N-phenyl-benzimidazol-1-yl)diphenylphosphines in RhI complexes. From a set of seven such phosphines L=Lxyz(') (x, y, z=0 or 1=number of NO2 substituents at the 5, 6 and N-Ph para positions, respectively), including the non-nitrated parent L000 and its dicationic N-methyl counterpart L000 ', three LRhCl(COD) and seven L2 RhCl(CO) complexes have been obtained in 72-95 % yield. Despite of a cis orientation of the L and CO ligands, the C=O IR stretching frequency νCO varies in the expected sense, from 1967±1 cm-1 for Lxy0 to 1978±1 cm-1 for Lxy1 , and 2005 cm-1 for L000 '. The 103 Rh NMR chemical shift δRh varies from -288 ppm for L000 to -316±1 ppm for L10z or L01z , and -436 ppm for L000 '. The νCO and δRh probes thus reveal moderate but systematic variations, and act as "orthogonal" spectroscopic indicators of the presence of nitro groups on the N-Ph group and the benzimidazole core, respectively. For the dicationic ligand L000 ', a tight electrostatic sandwiching of the Rh-Cl bond by the benzimidazole moities is evidenced by X-ray crystallography (RhClδ- ⋅⋅⋅CN2+ ≈3.01 Å). Along with the LRhCl(CO) complexes, dinuclear side-products (μ-CO)(RhClL)2 were also obtained in low spectroscopic yield: for the dinitro ligand L=L011 , a unique 1:6.7 clathrate structure, with dichloromethane as solvate, is also revealed by X-ray crystallography.
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