Cobalt–N-Heterocyclic Carbene Complexes in Catalysis

Abstract

Cobalt−N-heterocyclic carbene (NHC) complexes have emerged as an attractive class of 3d transition metal catalysts for a broad range of chemical processes, including cross-coupling, hydrogenation, hydrofunctionalization, and cycloaddition reactions. Herein, we present a comprehensive review of catalytic methods utilizing cobalt−NHC complexes with a focus on the catalyst structure, role of the NHC ligand, properties of the catalytic system, mechanism, and synthetic utility. The survey clearly suggests that the recent emergence of well-defined cobalt−NHC catalysts may have a tremendous utility in the design and application of catalytic reactions using more abundant 3d transition metals.

Recent Developments in Manganese, Iron and Cobalt Homogeneous Catalyzed Synthesis of Primary Amines via Reduction of Nitroarenes, Nitriles and Carboxamides

“…[4,5] Even if such methodologies are well-established, they still suffer from some main limitations such as (i) the lack of selectivity over primary, secondary, and tertiary amines, (ii) the use of tedious multistep process and of harsh reaction conditions, and (iii) sometimes the use of stoichiometric alkali metals. [6] Based on the importance of the reduction of carboxylic and nitro derivatives for the production of primary amines, and in the view of the huge increase of the use of non-noble transition metals such as manganese, [7] iron [8] and cobalt [9] in catalyzed reductions, herein we combined the development of the associated both topics within recent decades, including hydrogenation, hydrosilylation, and transfer hydrogenation methodologies. Thus, this review has several main objectives: (a) to provide a concise overview of the literature in the preparation of primary amines from primary carboxamides, nitriles and nitro derivatives, and (b) to show the potential of manganese, iron and cobalt as subrogate transition metals to the noble ones.…”

Stereoselective C–O Silylation and Stannylation

“…Organozinc reagents are of great important intermediates which display high reactivity and excelleng chemoselectivity in organic synthesis. [38][39][40][41][42][43][44] Hence, we were attracted to developing the well-activated silyl and stannyl zinc reagents via transmetalation of the corresponding lithium reagents, [45][46] and subsequently devising 3d cobaltcatalyzed cross-couplings [47][48][49][50][51][52][53] with polyfunctionalized alkenyl acetates to build synthetically useful C-Si [54][55][56] and C-Sn [57][58][59][60] bonds via umpolung strategy (Figure 1d). In this work, Me 2 PhSi-ZnOPiv•Li 2 (Cl) (OPiv) and ( n Bu) 3 Sn-ZnCl•LiCl show superior reactivity than the other Si-and Sn-based organometallic reagents.…”

Stereoselective C–O silylation and stannylation of alkenyl acetates

“…Organozinc reagents are important intermediates which display high reactivity and excellent chemoselectivity in organic synthesis [38][39][40][41][42][43][44] . Hence, we developed the bench-stable and easy-to-handle silyl and stannylzinc reagents 45,46 , and applied to 3d cobalt-catalyzed cross-couplings [47][48][49][50][51][52][53] with polyfunctionalized alkenyl acetates to build synthetically useful C-Si [54][55][56] and C-Sn [57][58][59][60] bonds (Fig. 1d).…”