Group 7 transition metal complexes with N-heterocyclic carbenes

Abstract

This tutorial review summarizes all works and highlights recent advances published in the growing field of group 7 N-heterocyclic carbene (NHC) complexes. It provides a valuable source for all scientists that are interested in conducting research with new compounds bearing these metals. The article provides an overview of all manganese NHC complexes that are known to date. There are a lot of examples where manganese NHC complexes show unpredicted behaviour during synthesis, very different from other transition metal NHC complexes and their higher homologues rhenium and technetium. These differences are depicted and discussed. Furthermore, the chemistry of technetium NHC compounds and their chemical behaviour are discussed. To date published work on technetium NHC chemistry has been restricted to the oxidation state +v. It was found that such compounds are very reactive but show great stability in dry air. Their radioactivity makes such compounds interesting candidates for radiochemical applications. Since most group 7 NHC chemistry was conducted on rhenium NHC complexes, this tutorial review highlights the chemical behaviour of such compounds. Rhenium(i) complexes reveal luminescent properties, making them interesting candidates for applications ranging from biological markers to organic light-emitting diodes (OLEDs). Another interesting feature is the radioactivity of some compounds, which makes them excellent candidates for radiopharmaceutical research; hence their synthesis and reactivity are discussed.

N-heterocyclic carbene complexes of Group 6 metals

“…In addition, the stereoelectronic properties of NHCs are easily tuneable by modifying the NHC backbone and the exocyclic nitrogen substituents [7,[21][22][23][24][25][26]. All these beneficial features have popularised the use of NHC ligands in transition metal chemistry [13,14,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Among the metals, Group 6 metals (Cr, Mo, W) have played a classical and central role in the development of carbene chemistry.…”

Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N–C)(CO)3] complexes

“…Subsequently, Compain et al reported the synthesis of two terpyridine-based complexes: one complex that included a dangling pendant pyridine [MnBr(terpyridineκ 2 ,N 1 ,N 2 )(CO) 3 ] and another with all three pyridines bound [Mn(NCMe)(terpyridine-κ 3 ,N 1 N 2 N 3 )(CO) 2 ] + . 18 The resulting complexes of the type: [MnBr(N-C)(CO) 3 ], with imidazole-or benzimidazole-based NHCs, [50][51][52] were found to be catalytic for CO 2 reduction and exhibited a two-electron reduction at a single potential rather than two singlereductions at separate potentials. 17 About the same time, we reported the replacement of one pyridine in bpy with an N-heterocyclic carbene (NHC).…”

The photochemistry of rhenium(i) tricarbonyl N-heterocyclic carbene complexes

“…However, the population of higher excited states results in the cleavage of a Re-CO bond and ligand exchange with the formation of multiple geometrical isomers. The initial explanation involved the coordination of the strongly σ-donating C atom of the NHC ligand, 27,28 thus promoting the labilization of the CO in trans from excited states of possibly LF nature; 23 however, the analysis of the experimental data revealed the formation of three different complexes. 25 We have recently reported the synthesis and photophysical characterization of the tricarbonyl rhenium(I) N-heterocyclic carbene (NHC) complexes 1Cl and 1Br, whose structures are shown in Fig.…”