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Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

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.

Iron Catalysis in Organic Synthesis

This critical review discusses historical and contemporary research in the field of transition metal-catalyzed carbon–hydrogen (C–H) bond activation through the lens of stereoselectivity. Research concerning both diastereoselectivity and enantioselectivity in C–H activation processes is examined, and the application of concepts in this area for the development of novel carbon–carbon and carbon–heteroatom bond-forming reactions is described. Throughout this review, an emphasis is placed on reactions that are (or may soon become) relevant in the realm of organic synthesis (221 references).

Transition metal-catalyzed C–H activation reactions: diastereoselectivity and enantioselectivity

The selective oxidation of C-H bonds and the use of O(2) as a stoichiometric oxidant represent two prominent challenges in organic chemistry. Copper(II) is a versatile oxidant, capable of promoting a wide range of oxidative coupling reactions initiated by single-electron transfer (SET) from electron-rich organic molecules. Many of these reactions can be rendered catalytic in Cu by employing molecular oxygen as a stoichiometric oxidant to regenerate the active copper(II) catalyst. Meanwhile, numerous other recently reported Cu-catalyzed C-H oxidation reactions feature substrates that are electron-deficient or appear unlikely to undergo single-electron transfer to copper(II). In some of these cases, evidence has been obtained for the involvement of organocopper(III) intermediates in the reaction mechanism. Organometallic C-H oxidation reactions of this type represent important new opportunities for the field of Cu-catalyzed aerobic oxidations.

Copper-Catalyzed Aerobic Oxidative C ? H Functionalizations: Trends and Mechanistic Insights

Catalytic asymmetric coupling of 2-naphthols by chiral tridentate oxovanadium (IV) complexes.

Catalytic Asymmetric Oxidative Couplings of 2-Naphthols by Tridentate N-Ketopinidene-Based Vanadyl Dicarboxylates

The titled hybrids bearing a central dibenzosuberene optoelectronic unit with functional C3 and C7, N,N-diarylamino appendages, and spiro-fluorene junction act as blue fluorescent OLED materials. Sharp blue fluorescent (464 nm, Δλfwhm = 47−60 nm) OLED devices can thus be furnished with a high ηext of 7.9%, L20 of 2689 cd/m2, ηc of 13.6 (cd/A), and ηp of 8.2 (lm/W) at 20 mA/cm2.

Doubly Ortho-Linked cis-4,4‘-Bis(diarylamino)stilbene/Fluorene Hybrids as Efficient Nondoped, Sky-Blue Fluorescent Materials for Optoelectronic Applications

An unprecedented vanadyl(V) methoxide complex 4 derived from 3,5-dibromo-N-salicylidene-l-tert-leucinate enables highly enantioselective aerobic oxidations of α-hydroxyphosphonates at ambient temperature with selectivity factors ranging from 3 to >99.

Highly Enantioselective Aerobic Oxidation of α-Hydroxyphosphonates Catalyzed by Chiral Vanadyl(V) Methoxides Bearing N-Salicylidene-α-aminocarboxylates

A diverse array of oxometallic species were examined as catalysts for a test direct condensation of benzoic acid and 2-phenylethanol in 1:1 stoichiometry. Besides group IVB MOCl2−xH2O and TiOX2−xH2O, group VB VOCl2−xTHF and group IVB TiO(acac)2 were found to be the most efficient and water-tolerant catalysts for the test reaction. The new neutral catalytic protocol with the optimal TiO(acac)2 tolerates many stereo/electronic structural variations in both (di)acid (1°−3° alkyl and aryl) and (di)alcohol (1°, 2° alkyl, and aryl) components with high chemoselectivity.

Chien-Tien Chen

Papers

Catalytic asymmetric coupling of 2-naphthols by chiral tridentate oxovanadium (IV) complexes.

Catalytic Asymmetric Oxidative Couplings of 2-Naphthols by Tridentate N-Ketopinidene-Based Vanadyl Dicarboxylates

Doubly Ortho-Linked cis-4,4‘-Bis(diarylamino)stilbene/Fluorene Hybrids as Efficient Nondoped, Sky-Blue Fluorescent Materials for Optoelectronic Applications

Highly Enantioselective Aerobic Oxidation of α-Hydroxyphosphonates Catalyzed by Chiral Vanadyl(V) Methoxides Bearing N-Salicylidene-α-aminocarboxylates

Direct atom-efficient esterification between carboxylic acids and alcohols catalyzed by amphoteric, water-tolerant TiO(acac)2.