The use of coordinating moieties as directing groups for the functionalization of aromatic CH bonds has become an established tool to enhance reactivity and induce regioselectivity. Nevertheless, with regard to the synthetic applicability of CH activation, there is a growing interest in transformations in which the directing group can be fully abandoned, thus allowing the direct functionalization of simple benzene derivatives. However, this approach requires the disclosure of new strategies to achieve reactivity and to control selectivity. In this review, recent advances in the emerging field of non-chelate-assisted CH activation are discussed, highlighting some of the most intriguing and inspiring examples of induction of reactivity and selectivity.

Beyond directing groups: transition-metal-catalyzed C-H activation of simple arenes.

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

Homogeneous transition-metal-catalyzed reactions are indispensable to all facets of modern chemical synthesis. It is thus difficult to imagine that for much of the early 20th century, the reactivity and selectivity of all known homogeneous metal catalysts paled in comparison to their heterogeneous and biological counterparts. In the intervening decades, advances in ligand design bridged this divide, such that today some of the most demanding bond-forming events are mediated by ligand-supported homogeneous metal species. While ligand design has propelled many areas of homogeneous catalysis, in the field of Pd(II)-catalyzed C–H functionalization, suitable ligand scaffolds are lacking, which has hampered the development of broadly practical transformations based on C–H functionalization logic. In this Perspective, we offer an account of our research employing three ligand scaffolds, mono-N-protected amino acids, 2,6-disubstituted pyridines, and 2,2′-bipyridines, to address challenges posed by several synthet...

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Developing Ligands for Palladium(II)-Catalyzed C–H Functionalization: Intimate Dialogue between Ligand and Substrate

Der Einsatz von koordinierenden Gruppen als dirigierende Gruppen ist eine zuverlassige Methode zur Kontrolle von Reaktivitat und Selektivitat bei der Aktivierung von Aryl-C-H-Bindungen. Im Hinblick auf die Anwendbarkeit von C-H-Aktivierungen in der Synthese besteht derzeit ein groses Interesse daran, Reaktionen zu entwickeln, in denen vollig auf dirigierende Gruppen verzichtet werden kann und somit die Funktionalisierung einfacher Benzolderivate moglich wird. Dieser Ansatz erfordert jedoch neue Strategien zur Reaktivitats- und Selektivitatskontrolle. In diesem Kurzaufsatz werden aktuelle Fortschritte in dem noch jungen Gebiet der nicht-chelatvermittelten C-H-Aktivierung diskutiert, wobei einige inspirierende Beispiele zur Reaktivitats- und Selektivitatsinduktion hervorgehoben werden.

Ohne dirigierende Gruppen: übergangsmetallkatalysierte C-H-Aktivierung einfacher Arene

Computational studies on carboxylate-assisted C–H activation and functionalization at group 8–10 transition metal centers are reviewed This Review is organized by metal and will cover work published from late 2009 until mid-2016 A brief overview of computational work prior to 2010 is also provided, and this outlines the understanding of carboxylate-assisted C–H activation in terms of the “ambiphilic metal–ligand assistance” (AMLA) and “concerted metalation deprotonation” (CMD) concepts Computational studies are then surveyed in terms of the nature of the C–H bond being activated (C(sp2)–H or C(sp3)–H), the nature of the process involved (intramolecular with a directing group or intermolecular), and the context (stoichiometric C–H activation or within a variety of catalytic processes) This Review aims to emphasize the connection between computation and experiment and to highlight the contribution of computational chemistry to our understanding of catalytic C–H functionalization based on carboxylate-ass

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Computational Studies of Carboxylate-Assisted C-H Activation and Functionalization at Group 8-10 Transition Metal Centers

A systematic theoretical study is carried out on the mechanism for Pd(II)-catalyzed oxidative cross-coupling between electron-deficient arenes and alkenes. Two types of reaction pathways involving either a sequence of initial arene C-H activation followed by alkene activation, or the reverse sequence of initial alkene C-H activation followed by arene activation are evaluated. Several types of C-H activation mechanisms are discussed including oxidative addition, σ-bond metathesis, concerted metalation/deprotonation, and Heck-type alkene insertion. It is proposed that the most favored reaction pathway should involve an initial concerted metalation/deprotonation step for arene C-H activation by (L)Pd(OAc)(2) (L denotes pyridine type ancillary ligand) to generate a (L)(HOAc)Pd(II)-aryl intermediate, followed by substitution of the ancillary pyridine ligand by alkene substrate and direct insertion of alkene double bond into Pd(II)-aryl bond. The rate- and regio-determining step of the catalytic cycle is concerted metalation/deprotonation of arene C-H bond featuring a six-membered ring transition state. Other mechanism alternatives possess much higher activation barriers, and thus are kinetically less competitive. Possible competing homocoupling pathways have also been shown to be kinetically unfavorable. On the basis of the proposed reaction pathway, the regioselectivity predicted for a number of monosubstituted benzenes is in excellent agreement with experimental observations, thus, lending further support for our proposed mechanism. Additionally, the origins of the regioselectivity of C-H bond activation is elucidated to be caused by a major steric repulsion effect of the ancillary pyridine type ligand with ligands on palladium center and a minor electronic effect of the preinstalled substituent on the benzene ring on the cleaving C-H bond. This would finally lead to the formation of a mixture of meta and para C-H activation products with meta products dominating while no ortho products were detected. Finally, the multiple roles of the ancillary pyridine type ligand have been discussed. These insights are valuable for our understanding and further development of more efficient and selective transition metal-catalyzed oxidative C-H/C-H coupling reactions.

Theoretical Analysis of the Mechanism of Palladium(II) Acetate-Catalyzed Oxidative Heck Coupling of Electron-Deficient Arenes with Alkenes: Effects of the Pyridine-Type Ancillary Ligand and Origins of the meta-Regioselectivity

Li Shi

Papers

Theoretical Analysis of the Mechanism of Palladium(II) Acetate-Catalyzed Oxidative Heck Coupling of Electron-Deficient Arenes with Alkenes: Effects of the Pyridine-Type Ancillary Ligand and Origins of the meta-Regioselectivity

A photoluminescent dinuclear phenylquinolyl Ir(II)-Ir(II) complex featuring a μ-η1:η2-phenylquinolyl bridge and an end-on dinitrogen ligand.