N‐Heterocyclic Carbene Ligands and Iron: An Effective Association for Catalysis

Abstract

Although iron has been known and widely used in coordination and organometallic chemistry for decades and N‐heterocyclic carbenes (NHCs) have also been used for about half a century, their combination surprisingly did not become a hot topic in chemistry until this last decade. This review presents several recent and stimulating developments in homogeneous catalysis done mainly using iron/NHC‐based catalysts. Of particular interest are the roles of iron/NHC complexes in cross‐coupling Kochi reactions, CC bond formation reactions and hydrofunctionalization, and more particularly in hydrosilylation. Our review summarizes the key developments in these fields.

An overview of N-heterocyclic carbenes

“…Reflecting the general trend in cross-coupling reactions, the majority of studies have focused on palladium-catalysed processes [48][49][50][51] although NHC complexes of many other transition metals including nickel 58 and iron 59 have also demonstrated remarkable efficiency. Imidazol-2-ylidene and imidazolin-2-ylidene carbenes remain the most studied classes, with sterically bulky derivatives such as IPr (1d) and SIPr (2b) being particularly widely applied.…”

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.…”

Iron‐Catalyzed gem‐Specific Dimerization of Terminal Alkynes

“…[4g, 8, 9] While the late-metal catalysts are compatible with ab road scope of substrates, [4g, 8] the early metal and aluminum-based catalysts show limited substrate scope,f or example,N Ha nd OH groups cannot be tolerated. [9] Herein we report the first iron-catalyzed [10,11] gem-specific homo-and cross-dimerization of terminal alkynes in the absence of additives.I nterestingly,t his catalytic system is compatible with abroad scope of substrates,including those with OH and NH functional groups.S uch gem specificity applies to the cross-dimerization of terminal alkynes as well.…”