Synthesis Of N-heterocyclic Carbene Complexes Research Articles

Synthesis of N-Heterocyclic Carbene Complexes by Oxidative Addition of 4-Iodo-imidazolium Salts Followed by an Unusual Rearrangement

Synthesis of N-Heterocyclic Carbene Complexes by Oxidative Addition of 4-Iodo-imidazolium Salts Followed by an Unusual Rearrangement

Rhodium(I) and Iridium(I) N-Heterocyclic carbene complexes of imidazolium functionalized amino acids and peptides

The conjugation of organometallic complexes to peptides is generally achieved through covalent organic linkages of the metal’s ligand to the peptide. Examples of direct coordination to metal centers by amino acid side chain residues remain rare. In one such example, side chain methylation of the natural amino acid histidine (His) resulted in an imidazolium functionalized amino acid which was used for the synthesis of rhodium(I), iridium(I), iridium(III), palladium(II) and ruthenium(III) N-heterocyclic carbene (NHC) complexes of the single amino acid and peptides containing this amino acid. Here, we have synthesized two new, non-natural imidazolium functionalized amino acid derivatives, which were used for solid phase peptide synthesis and for the synthesis of [M(COD)(NHC)Cl] (COD = 1,5 cyclooctadiene) complexes of Rh(I) and Ir(I). In total, six new complexes of the single amino acids and four complexes where the amino acids are present in a peptide environment were synthesized. Their characterization provides convincing evidence of conversion of the imidazolium moiety to an NHC ligand and thus the presence of a direct metal-carbon bond between the metal center and the amino acid side chain. Therefore, our compounds represent unique examples of peptide-conjugated complexes that bear the potential to be used for the synthesis of N-heterocyclic carbene complexes conjugated to cancer cell targeting peptides.

Nickel and palladium N-heterocyclic carbene complexes. Synthesis and application in cross-coupling reactions

N-Heterocyclic carbenes (NHCs) are widely used as ligands in catalysis by transition metal complexes. The catalytic activity of transition metal NHC complexes is much higher than that of the transition metal complexes bearing the phosphine and nitrogen-containing ligands. They show excellent catalytic performance in different transformations of the organic compounds, especially in the carbon—carbon and carbon—element bond forming reactions. Palladium NHC complexes are very efficient catalysts for the cross-coupling reactions. On the other hand, nickel is less expensive and regarded as a promising alternative to palladium and, therefore, it attracts increasing attention from the researches. The present review is focused on the recent advances in the synthesis of N-heterocyclic carbene complexes of nickel and palladium and their application in catalysis of cross-coupling reactions of organic, organoelement and organometallic compounds with organic halides.

Two-Step Mechanochemical Synthesis of Carbene Complexes of Palladium(II) and Platinum(II)

A mechanochemical strategy for the synthesis of N-heterocyclic carbene complexes is described, in which 1,3-dibenzylimidazole complexes of palladium and platinum are produced in a two-step process by grinding together the reactants with a mortar and pestle. Crystallographic characterization reveals that unlike the solution syntheses, which produce a mixture of products, the solid-state reactions occur under topochemical conditions affording isomerically and polymorphically pure products.

Synthesis of N-Heterocyclic Carbene Complexes of Manganese(I) by Coupling Isocyanide Ligands with Propargylamines and Propargylic Alcohols

A variety of N-heterocyclic carbene (NHC) complexes of general formula fac-[Mn(NHC)(CO)3(bipy)]+ have been prepared by reaction of the manganese(I) isocyanide complexes fac-[Mn(CNR)(CO)3(bipy)]+ with propargylamines and propargylic alcohols and characterized by spectroscopic and X-ray diffraction methods.

Cyclometalated and Alkoxyphenyl-Substituted Palladium Imidazolin-2-ylidene Complexes. Synthetic, Structural, and Catalytic Studies

Some new N,N‘-bis(aryl)imidazolinium salts (3a−h), in which the N-aryl groups have one unsubstituted ortho position and alkyl (Me, Pri) or alkoxy (OMe, OPri) substitution at the other ortho and/or para positions, have been prepared. They were used for the synthesis of N-heterocyclic carbene complexes of palladium in which the N-heterocyclic carbene is attached to cyclometalated or electron-rich aromatic rings (4, 5, 11d,e). The reaction of Pd(tmed)(CH3)2 with the N-heterocyclic carbene generated from 3b and base gave the dimethyl complex 6, which quantitatively eliminated ethane to form the Pd(0) complex 7. The latter was converted to a new type of “pincer” complex (8) by facile cyclometalation of both aromatic groups of the N-heterocyclic carbene ligand. The activities of the new complexes 4 and 9d,e in the Heck reaction of aryl halides were compared. At higher temperatures the complexes 9d,e show low activity in the coupling of aryl chlorides.

Synthesis and reactivity of triethylborane adduct of N-heterocyclic carbene: versatile synthons for synthesis of N-heterocyclic carbene complexes.

The reaction of an imidazolium salt with LiBEt(3)H afforded triethylborane adduct of imidazol-2-ylidene, which can act as a carbene precursor for the synthesis of a transition metal complex as well as a main group element complex.