Acceptorless Dehydrogenative Coupling Reactions by Manganese Pincer Complexes

Abstract

Acceptorless dehydrogenative coupling reactions has emerged as one of the promising technique in synthetic organic chemistry to construct carbon‐carbon and carbon‐heteroatom bonds in an environmentally benign and sustainable way. The methodology is highly atom economical and produces water and hydrogen as the byproducts. This protocol, coupled with the earth‐abundant and less toxic manganese catalyst provides a unique opportunity to construct various synthons and biologically important motifs. In recent years, tremendous progress has been made with manganese catalysis based on the pincer ligands for various homogeneous transformations. This review covers the recent progress in the field of manganese catalyzed acceptorless dehydrogenative coupling reactions, their scope and brief mechanistic discussion.

Manganese-catalyzed hydrogenation, dehydrogenation, and hydroelementation reactions

“…[24][25][26][27][28][29][30][31][32][33][34][35][36][37] Currently, the focus has shifted towards the use of molecularly defined lowvalent manganese complexes of pincer and non-pincer ligands for various hydrogenation, dehydrogenation, cross-dehydrogenativecoupling (CDC), hydroelementation, and coupling reactions via direct C-H bond activation. [36][37][38][39][40][41][42][43][44][45][46][47][48] This review will provide a detailed discussion on the emergence of manganese-catalyzed hydrogenation, dehydrogenation, and hydroelementation reactions. Indeed, there are some excellent reviews compiling all the reports on Mn-catalyzed hydrogenative and dehydrogenative transformations.…”

“…Indeed, there are some excellent reviews compiling all the reports on Mn-catalyzed hydrogenative and dehydrogenative transformations. 38,[43][44][45][46][47][49][50][51] However, most of these scattered reviews summarize the research development with minimal analysis of catalyst and reaction development and focus on a particular type of reaction instead of compiling them in a single place. (Scheme 1)…”

“…24–37 Currently, the focus has shifted towards the use of molecularly defined low-valent manganese complexes of pincer and non-pincer ligands for various hydrogenation, dehydrogenation, cross-dehydrogenative-coupling (CDC), hydroelementation, and coupling reactions via direct C–H bond activation. 36–48…”

Towards ligand simplification in manganese-catalyzed hydrogenation and hydrosilylation processes

“…In particular, since the seminal discovery of first efficient Mn-based (de)hydrogenation catalytic systems by Beller [6] and Milstein [7] in the beginning of 2016, this topic became one of the most rapidly emerging areas in catalysis using Earth-abundant transition metal complexes. Despite many impressive results obtained to date, the initial development of Mn(I)-based reduction catalysis was mainly performed using the transposition of chemical concepts previously applied for catalysts containing isoelectronic Fe(II) and Co(I) metal centers, namely the use of pincertype ligands with phosphine donor extremities [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] capable to activate inert chemical bonds via a metal-ligand cooperation [23][24][25][26] (A, Scheme 1). However, the analysis of recent literature provides growing evidence that tridentate ligand architectures are not mandatory for the design of efficient manganese (de)hydrogenation catalysts, as complexes bearing less elaborated bidentate ligands (B, Scheme 1) can be competitive or sometimes even superior in terms of catalytic activity and/or application scope.…”

“…While Mn-catalyzed hydrogenation-type processes have been extensively reviewed [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], these contributions have been essentially focused on the most popular pincer-type systems with a particular attention devoted to the comparison between manganese and their 3d metal congenersiron and cobalt [10][11][12][13]. In contrast, this article is focusing on a systematic overview of the catalytic properties of manganese complexes bearing bidentate donor ligands in (de)hydrogenation processes including the analysis of their relative performance depending on the nature of donor moieties (P-, N-and C-donors) and the comparison, when possible, with structurally related pincer scaffolds.…”