Preparation of a N-Heterocyclic Carbene Nickel(II) Complex
Synthetic Experiments in Current Organic and Organometallic Chemistry
Vincent Ritleng, Eric Brenner, and Michael J. Chetcuti
Laboratoire de Chimie Organométallique Appliquée, UMR CNRS 7509, Ecole Européenne de Chimie, Polymères et Matériaux, Université Louis Pasteur, 67087 Strasbourg, France
A four-part experiment that leads to the synthesis of a cyclopentadienyl chloro–nickel(II) complex bearing a N-heterocyclic carbene (NHC) ligand is presented. In the first part, the preparation of 1,3-bis-(2,4,6-trimethylphenyl)imidazolium chloride (IMes·HCl) in a one-pot procedure by reaction of 2,4,6-trimethylaniline with paraformaldehyde, glyoxal, and hydrochloric acid is described. The reaction of NiCl2·6H2O with aqueous ammonia to give [Ni(NH3)6]Cl2, and the reaction of sodium in neat dicyclopentadiene at 160 °C to produce sodium cyclopentadienide in a one-pot synthesis are both delineated in the second part of this experiment. The reaction of [Ni(NH3)6]Cl2, with NaCp to yield [Ni(η5-C5H5)2] forms the third part. Finally, the procedure ends with the reaction of nickelocene with IMes·HCl to afford the nickel(II) half-sandwich complex [Ni(η5-C5H5)(IMes)Cl]. This sequence of experiments provides an excellent example of NHC–ligand preparation and its subsequent complexation to a transition metal and is appropriate for an advanced undergraduate or a graduate lab course. It also provides an opportunity for students to learn standard Schlenk techniques. Furthermore, the characterization of some of the products by 1H NMR spectroscopy demonstrates the utility of 1H NMR in both organic and organometallic chemistry.
Supplement
A student handout containing detailed experimental procedures; notes for the instructor including spectral data for all products; 1H NMR spectra of 1 and 3
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