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.

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen i...

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

Low-valent early transition metals are often intrinsically highly reactive as a result of their strong propensity toward oxidation to more stable high-valent states. Harnessing these highly reducing complexes for productive reactivity is potentially powerful for C–C bond construction, organic reductions, small-molecule activation and many other reactions that offer orthogonal chemoselectivity and/or regioselectivity patterns to processes promoted by late transition metals. Recent years have seen many exciting new applications of low-valent metals through building new catalytic and/or multicomponent reaction manifolds out of classical reactivity patterns. In this Review, we survey new methods that employ early transition metals and invoke low-valent precursors or intermediates in order to identify common themes and strategies in synthesis and catalysis. Low-valent early transition metals are experiencing a renaissance in synthesis and catalysis, finding applications in unusual C–C bond forming reactions, oxidative group-transfer catalysis, proton-coupled electron transfer, photoredox catalysis and more.

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Modern applications of low-valent early transition metals in synthesis and catalysis

Pentafulvenes are a unique class of compounds that originally attracted attention due to their propensity to display nonbenzenoid aromaticity. Subsequently, they were recognized as valuable synthons for the construction of a wide range of compounds by virtue of their ability to display multiple cycloaddition profiles. Naturally, this area of organic chemistry has experienced rapid growth over the last five decades, fueled by elegant work showcasing the unique reactivity of pentafulvenes in a plethora of cycloaddition reactions. In this Review, we have attempted to provide a systematic account of the methods for the generation of pentafulvenes, their rich and varied cycloaddition chemistry, organometallic reactions, and theoretical studies that support their versatility. Further, we have highlighted their applications in the synthesis of a variety of complex structural frameworks. It is our conviction that this Review will be useful to a wide range of chemists, and will spur further research in this promis...

Recent Advances in the Chemistry of Pentafulvenes.

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

Titanaaziridines or η(2)-imine titanium complexes are considered key intermediates of the titanium-catalyzed hydroaminoalkylation of alkenes. Herein, we present an efficient synthetic route to this class of compounds, starting from N-methylanilines and a bis(η(5):η(1)-pentafulvene)titanium complex. Consecutive reactions on the η(2)-methyleneaniline complexes, characterized for the first time, prove a high chemical versatility. In particular, hydroaminoalkylation products were found in reactions of the three-membered titanacycles with alkenes. For the first time, all the intermediates of the hydroaminoalkylation of alkenes were isolated and characterized.

Efficient Access to Titanaaziridines by C ? H Activation of N‐Methylanilines at Ambient Temperature

Titanaaziridine bzw. η2-Imintitankomplexe sind Schlusselintermediate in der titankatalysierten Hydroaminoalkylierung von Alkenen. Hier berichten wir uber einen effizienten Zugang zu dieser Verbindungsklasse, ausgehend von N-Methylanilinen und Bis(η5:η1-pentafulven)titankomplexen. Folgereaktionen der ersten strukturell charakterisierten η2-Methylenanilinkomplexe belegen die vielfaltigen Reaktionsmuster dieser Verbindungsklasse. Insbesondere werden Hydroaminoalkylierungsprodukte in Reaktionen des titanacyclischen Dreiringes mit Olefinen gefunden. Erstmalig konnen alle Intermediate der Hydroaminoalkylierung experimentell zuganglich gemacht werden.

Effizienter Zugang zu Titanaaziridinen durch C-H-Aktivierung vonN-Methylanilinen bei Raumtemperatur

Reactions of Secondary Amines with Bis(η5:η1-pentafulvene)titanium Complexes: Formation of Titanium Amides and Titanaaziridines

Direct Access to Titanocene Imides via Bis(η5:η1-penta-fulvene)titanium Complexes and Primary Amines

From Organic Azides through Titanium Triazenido Complexes to Titanium Imides

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