Recent Advances in the Syntheses and Catalytic Applications of Homonuclear Ru‐, Rh‐, and Ir‐Complexes of C_NHC^C Cyclometalated Ligands

Abstract

In the past few decades, chemistry of cyclometalated species has gained momentum with increased applications in several areas of scientific developments. Cyclometalation reactions result in the formation of stable metallacycles through the generation of metal-carbon covalent bonds by activating the unreactive Csp 2 -H or Csp 3 -H bonds. The extra stability gained by the formation of metallacycles enhances their applicability scopes especially in the area of homogeneous catalysis. In the recent research development in this area, NHC ligands (strong σ-donor and generally, weak πacceptor) have been found to be one of the most suitable candidates for the intramolecular CÀ H activation process which leads to the cyclometalated species. The growth in the area of cyclometalation chemistry that started in the late 20 th century is still continuing and in the past few decades, various examples of NHC derived transition metal-based cyclometalated complexes came into the picture. As covering all the reported literatures in this area (includes mainly late transition metals) will exceed the limits of minireview, we restricted ourselves to the recent (2015 -May 2021) examples of the most common Ru-, Rh-, and Ir-based C NHC ^C cyclometalated complexes and their applications in various homogeneous catalytic conversions such as transfer hydrogenation, amidation, oxidation of alcohols, annulations, and so forth.

Theoretical Study of N–H σ-Bond Activation by Nickel(0) Complex: Reaction Mechanism, Electronic Processes, and Prediction of Better Ligand

“…Transition-metal complexes of N -heterocyclic carbene have been often applied to catalytic reactions, as discussed in many reviews. − Because the knowledge of the ligand effects on the N–H σ-bond activation is indispensable for searching a better catalyst, we investigated here the N–H σ-bond activations of NHMe 2 and NH­(Me)­(Bs) using N -heterocyclic carbene IPr (Scheme ) as a ligand instead of PCy 3 . In Ni­(IPr)­(NHMe 2 ) R5 , the concerted oxidative addition of the N–H σ-bond occurs with a Δ G ° ‡ value of 15.0 kcal/mol and Δ G ° value of 2.1 kcal/mol, as shown in Figure A.…”

N-Heterocyclic carbene supported zinc catalysed N-formylation of diverse N–H functionalities with carbon dioxide under ambient conditions

“…10 f Despite the huge potential of CO 2 functionalization, the above approaches required improvement on several fronts such as robust catalytic protocols based on earth-abundant non-toxic metals with better functional group compatibility, mild reaction conditions etc. It has been well-established that both the metal and ligand play an important role in improving the catalytic activity of a complex and along this line, use of an NHC ligand could be beneficial due to its strong σ-donating nature 12 resulting in a stable metal–ligand complex, which hinders any unwanted ligand dissociation during the catalytic cycle. Further, because of the low abundance, high price, and toxicity of heavier transition metals, there has been a continuous urge for economical but effective base metal derived catalyst systems.…”

Recent advances in C/N-alkylation with alcohols through hydride transfer strategies

“…4 Established pioneers of hydrogen shuttle catalysis have covered these methodologies to some extent in previous reviews focusing on relevant subtopics such as synthesizing heterocycles 5,6 and designing ligands. 7,8 Additionally, previous reviews have been published introducing the background and perspective of each individual metal separately: Co by Kundu 9 and Young, 10 Mn (Mukherjee), 11 Ru and Ir (Rit), 12 and Fe (Anilkumar), 13 to name but a few.…”