C–H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C–H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C–H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C–H activation until summer 2018.

3d Transition Metals for C-H Activation.

Organic reactions that involve the direct functionalization of non-activated C–H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C–H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C–H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C–H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C–H transformations.

/pdf/mild-metal-catalyzed-c-h-activation-examples-and-concepts-2fhc0zulxg.pdf

Mild metal-catalyzed C–H activation: examples and concepts

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure The schemes feature typical substrates used, the products obtained as well as the required reaction conditions Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them Accordingly, this review should be of particular interest also for scientists from industrial R&D sector Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date

/pdf/a-comprehensive-overview-of-directing-groups-applied-in-543u6d0g60.pdf

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry.

Catalytic C–H activation has emerged as a powerful tool for sustainable syntheses. In the recent years, notable success was achieved with the development of cobalt-catalyzed C–H functionalizations with either in situ generated or single-component cobalt-complexes under mild reaction conditions. Herein, recent progress in the field of organometallic cobalt-catalyzed C–H activation is reviewed until November 2015.

Cobalt-Catalyzed C―H Activation

Catalytic C–H bond activation, which was an elusive subject of chemical research until the 1990s, has now become a standard synthetic method for the formation of new C–C and C–heteroatom bonds. The synthetic potential of C–H activation was first described for ruthenium catalysis and is now widely exploited by the use of various precious metals. Driven by the increasing interest in chemical utilization of ubiquitous metals that are abundant and nontoxic, iron catalysis has become a rapidly growing area of research, and iron-catalyzed C–H activation has been most actively explored in recent years. In this review, we summarize the development of stoichiometric C–H activation, which has a long history, and catalytic C–H functionalization, which emerged about 10 years ago. We focus in this review on reactions that take place via reactive organoiron intermediates, and we excluded those that use iron as a Lewis acid or radical initiator. The contents of this review are categorized by the type of C–H bond cleaved...

Iron-Catalyzed C-H Bond Activation.

Carboxylate assistance proved to be the key for the success of efficient cobalt(III)-catalyzed CH cyanations. Thus, an in situ generated cationic cobalt complex was identified as a versatile catalyst for the site-selective synthesis of various aromatic and heteroaromatic nitriles with ample substrate scope.

Cobalt-catalyzed C-H cyanation of arenes and heteroarenes.

The transition metal-catalyzed transformation of otherwise inert C–H bonds into substituted alkenes offers a versatile tool for the synthesis of value added olefinic molecules. Recent developments in the directing group assisted C–H activation approach ensured high levels of positional selectivity. A vast number of coordinating groups have been utilized in directed C–H alkenylation, which are often not removable after the desired transformation. However, the concept of easily removable or traceless directing group strategy overcomes this limitation and enables site-selective C–H alkenylation of relevance to academia and the practitioners in industry. Various easily removable or transformable directing groups utilized in the transition metal-catalyzed oxidative C–H alkenylations are discussed in this review until February 2017.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Expedient C-H aminocarbonylations of unactivated (hetero)arenes and alkenes were accomplished with a cobalt(III) catalyst that shows high functional group tolerance. The C-H functionalization occurred with excellent chemo-, site-, and diastereoselectivity and enabled step-economical reactions with isocyanates or acyl azides.

Cobalt(III)-Catalyzed Aryl and Alkenyl C-H Aminocarbonylation with Isocyanates and Acyl Azides.

https://s3-eu-west-1.amazonaws.com/pstorage-acs-6854636/5308369/ol6b01199_si_001.pdf

Jie Li

Papers

Cobalt-Catalyzed C―H Activation

Cobalt-catalyzed C-H cyanation of arenes and heteroarenes.

Recent advances in positional-selective alkenylations: removable guidance for twofold C–H activation

Cobalt(III)-Catalyzed Aryl and Alkenyl C-H Aminocarbonylation with Isocyanates and Acyl Azides.

Amidines for Versatile Cobalt(III)-Catalyzed Synthesis of Isoquinolines through C-H Functionalization with Diazo Compounds.