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.

Alkylation reactions represent an important organic transformation to form C–C bonds. In addition to conventional approaches with alkyl halides or sulfonates as alkylating agents, the use of unactivated olefins for alkylations has become attractive from both cost and sustainability viewpoints. This Review summarizes transition-metal-catalyzed alkylations of various carbon–hydrogen bonds (addition of C–H bonds across olefins) using regular olefins or 1,3-dienes up to May 2016. According to the mode of activation, the Review is divided into two sections: alkylation via C–H activation and alkylation via olefin activation.

Transition-Metal-Catalyzed C–H Alkylation Using Alkenes

In the context of atom economy and low environmental impact, synthesis of amines by an efficient catalytic process is of great importance to produce these building blocks for fine chemical industry. The one-pot hydroaminomethylation of alkenes is a tandem reaction which involves three successive steps under CO/H2 pressure to perform the catalyzed hydroformylation of the alkene into the corresponding aldehyde followed by its condensation with a N–H function and the catalyzed hydrogenation of the imine/enamine intermediate into the corresponding saturated amine. Rhodium and more recently ruthenium complexes have been designed to combine high conversions of the reactants and chemoselectivity in the expected amines with high regioselectivity in either the linear or the branched amine. The coordination sphere of the metal according to the presence of ligands, temperature, CO/H2 partial pressures, and nature of the solvent is essential for complying with these selectivity requirements. The rate of the hydroform...

Tandem Hydroaminomethylation Reaction to Synthesize Amines from Alkenes.

Metallo-photoredox catalysis has redefined the available bond disconnections in the synthetic arsenal. By harnessing the one-electron chemistry of photoredox catalysis in tandem with low-valent cobalt catalysts, new methods by which functionalities may be stitched together become available. Herein we describe the coupling of photoredox-generated α-amino radical species with conjugated dienes using a unified cobalt and iridium catalytic system in order to access a variety of useful homoallylic amines from simple commercially available starting materials. We present a series of mechanistic experiments that support the intervention of Co–hydride intermediates that undergo diene insertion to generate Co−π-allyl species.

A Mild Hydroaminoalkylation of Conjugated Dienes Using a Unified Cobalt and Photoredox Catalytic System.

Titanium is the second most abundant transition metal and is already a key player in important industrial processes (e.g. polyethylene). Titanium is an attractive metal to use for catalytic transformations as it is a versatile and inexpensive metal of low-toxicity and of established biocompatibility. However, its potential use as a catalyst for the synthesis of fine chemicals, pharmaceuticals and agrochemicals is often overlooked due to its oxophilic, Lewis acidic character, which renders complexes of titanium less functional group tolerant than their late transition metal counterparts. Nevertheless, three different fields of research in titanium catalysis have drawn attention in recent years: formal redox catalysis, hydroamination and hydroaminoalkylation. For these reactions, titanium offers new approaches and alternative pathways/mechanisms that are complementary to late transition metal-based catalysis. This review focuses on advances in fine chemical synthesis by titanium-catalyzed reactions featuring redox transformations and two important hydrofunctionalization reactions, hydroamination and hydroaminoalkylation. Starting from the late 90s, we provide an overview of historic inspirational contributions, both catalytic and stoichiometric, and the latest insights in catalyst design efforts, mechanistic details and utility of the three different classes of transformations. Insights to enhance catalyst activity as well as catalyst controlled regio- and stereoselectivities are presented. Illustrative examples that highlight substrate scope and the application of titanium catalysis to the synthesis of complex organic small molecules, natural products and materials are shown. Finally, opportunities and strategies for on-going research and development activities in titanium catalysis are highlighted.

Titanium catalysis for the synthesis of fine chemicals – development and trends

An easily accessible formamidinate ligand-bearing titanium complex initially synthesized by Eisen et al. is used as catalyst for intermolecular hydroaminoalkylation reactions of unactivated, sterically demanding 1,1- and 1,2-disubstituted alkenes and styrenes with secondary amines. The corresponding reactions, which have never been achieved with titanium catalysts before, take place with excellent regioselectivity (up to 99 : 1) and in addition, corresponding reactions of 1,3-butadienes with N-methylbenzylamine are also described for the first time.

https://pubs.rsc.org/en/content/articlepdf/2015/dt/c4dt03916e

Intermolecular hydroaminoalkylation of alkenes and dienes using a titanium mono(formamidinate) catalyst

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Intermolecular hydroaminoalkylation of alkenes and dienes using a titanium mono(formamidinate) catalyst