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.

This review describes new reactions catalyzed by recently discovered types of metal complexes and catalytic systems (catalyst + co-catalyst). Works of recent years (mainly 2010–2016) devoted to the oxygenations of saturated, aromatic hydrocarbons and other carbon–hydrogen compounds are surveyed. Both soluble metal complexes and solid metal compounds catalyze such transformations. Molecular oxygen, hydrogen peroxide, alkyl peroxides, and peroxy acids were used in these reactions as oxidants.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

The study of probes for CO sensing of a family of binuclear rhodium(II) compounds of general formula [Rh2{(XC6H3)P(XC6H4)}n(O2CR)4–n]·L2 containing one or two metalated phosphines (in a head-to-tail arrangement) and different axial ligands has been conducted. Chloroform solutions of these complexes underwent rapid color change, from purple to yellow, when air samples containing CO were bubbled through them. The binuclear rhodium complexes were also adsorbed on silica and used as colorimetric probes for “naked eye” CO detection in the gas phase. When the gray-purple colored silica solids containing the rhodium probes were exposed to air containing increasing concentrations of CO, two colors were observed, in agreement with the formation of two different products. The results are consistent with an axial coordination of the CO molecule in one axial position (pink-orange) or in both (yellow). The crystal structure of 3·(CO) ([Rh2{(C6H4)P(C6H5)2}2(O2CCF3)2]·CO) was solved by single X-ray diffraction technique...

/pdf/sensitive-and-selective-chromogenic-sensing-of-carbon-9ny14zxrnu.pdf

Sensitive and selective chromogenic sensing of carbon monoxide via reversible axial CO coordination in binuclear rhodium complexes.

The reduction of nitrite to nitric oxide in dissimilatory denitrification is carried out by copper nitrite reductases (CuNIRs) via a type 2 copper site. Extended studies on CuNIRs in combination with model complexes have allowed for the establishment of two potential mechanisms for this transformation. Recent experimental and computational results have revealed further details of this process. In addition, the interaction of NO with copper sites has recently gained much attention. This review discusses recent results in the context of the known coordination chemistry of CuNIRs.

Binding and activation of nitrite and nitric oxide by copper nitrite reductase and corresponding model complexes

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp3)-H, aryl (aromatic) C(sp2)-H, heteroaryl (heteroaromatic) C(sp2)-H bonds, alkenyl C(sp2)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation. 

Recent advances in transition-metal-catalyzed carbene insertion to C–H bonds

Copper and silver carbonyl and ethylene adducts supported by the highly fluorinated hydridotris(triazolyl)borate ligand [HB(3,5-(CF3)2Tz)3]− have been synthesized and characterized, and compared to the analogous complexes based on the hydridotris(pyrazolyl)borate ligand [HB(3,5-(CF3)2Pz)3]−. 1H and 13C NMR signals of the ethylene moiety of [HB(3,5-(CF3)2Tz)3]Cu(C2H4) and [HB(3,5-(CF3)2Tz)3]Ag(C2H4) appear at a relatively downfield position from the corresponding signals of the [HB(3,5-(CF3)2Pz)3]Cu(C2H4) and [HB(3,5-(CF3)2Pz)3]Ag(C2H4) complexes. This indicates the presence of relatively acidic metal sites in the [HB(3,5-(CF3)2Tz)3]− supported molecules. [HB(3,5-(CF3)2Tz)3]− is also a relatively weaker donor compared to the tris(pyrazolyl)borate version [HB(3,5-(CF3)2Pz)3]−. However, the CO stretching frequency values of [HB(3,5-(CF3)2Tz)3]CuCO (2138 cm−1) and [HB(3,5-(CF3)2Pz)3]CuCO (2137 cm−1) are essentially identical, and did not reflect the differences in the acidity of the metal sites. The analogous silver carbonyl adducts [HB(3,5-(CF3)2Tz)3]AgCO and [HB(3,5-(CF3)2Pz)3]AgCO also show similar νCO values (2178 cm−1). These results illustrate the limitation of using the νCO value of metal carbonyls as a sole indicator of the electronic structure of metal sites in some metal complexes, especially when the metal→CO π-back bonding is less important, and the νCO values of two adducts are unexpectedly similar and appear at a region closer to that of the free CO (2143 cm−1).

Carbon monoxide and ethylene complexes of copper and silver supported by a highly fluorinated tris(triazolyl)borate.

Fluorinated tris(triazolyl)borate [HB(3,5-(CF3)2Tz)3]− (Tz = triazolyl) affords the isolation of [Na(THF)6]{[HB(3,5-(CF3)2Tz)3]2Na} with a ligand sandwiched sodium ion and a copper carbonyl complex [HB(3,5-(CF3)2Tz)3]CuCO with a high C–O stretching frequency.

Sandwiched sodium and half-sandwiched copper carbonyl complexes featuring polyfluorinated tris(triazolyl)borate [HB(3,5-(CF3)2Tz)3]−

The cationic zinc adduct {[HB(3,5-(CF3)2Pz)3]Zn(NCMe)2}ClO4 catalyzes the functionalization of tertiary, secondary, and primary C–H bonds of alkanes via carbene insertion. Ethyl diazoacetate serves as the :CHCO2Et carbene precursor. The counteranion, supporting ligand, and coordinating solvents affect the catalytic activity. An in situ generated {[HB(3,5-(CF3)2Pz)3]Zn}+ species containing a bulkier {B[3,5-(CF3)2C6H3]4}− anion gives the best results among the zinc catalysts used.

https://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.5b02134

Zinc(II)-Mediated Carbene Insertion into C–H Bonds in Alkanes

With the aging of the population intensifying, finding a cure or reasonable treatment for Alzheimer' disease (AD) has become an urgent priority. To target the multi-facets of AD, a class of chrysin derivatives (1-4) were rationally designed and synthesized by the multi-target-directed ligands (MTDLs) strategy, which were characterized by 1H NMR, 13C NMR, MS and elemental analysis. 1-4 showed inhibitory activities on reactive oxygen species, Aβ1-42 aggregation (self-, Cu2+-induced, AChE-induced). They were also potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) with selectivity toward BuChE. Compound 1 as the most promising candidate exhibited the highest selective BuChE inhibition (SI = 15). Furthermore, the kinetic study suggested compound 1 to be a mixed type inhibitor. The results of docking study were consistent with the in vitro results. In addition, compound 1-4 showed favorable blood-brain barrier (BBB) penetration and drug-like property in silico prediction. The corresponding copper complexes of 1-4 have also been synthesized. 1-4 selectively chelated Cu2+, Fe2+, Zn2+ and Al3+ ions, while had no chelating ability to other biometals. The copper complexes also showed good AChE, BuChE and reactive oxygen species inhibitory activities. Notably, the single crystals of 1-Cu(II) complex [Cu(C19H18NO4)2] were prepared for the first time and characterized by X-ray single crystal diffraction. X-ray crystallography analysis of 1-Cu(II) complex provided a reliable structure-activity insight at the molecular level about the antioxidative and Aβ1-42 disaggregation activities. Compound 1 might be a good lead compound to develop promising candidate analogs as AD therapeutics. 

Xiaodi Kou

Papers

Carbon monoxide and ethylene complexes of copper and silver supported by a highly fluorinated tris(triazolyl)borate.

Sandwiched sodium and half-sandwiched copper carbonyl complexes featuring polyfluorinated tris(triazolyl)borate [HB(3,5-(CF3)2Tz)3]−

Zinc(II)-Mediated Carbene Insertion into C–H Bonds in Alkanes

A multifunctional anti-AD approach: Design, synthesis, X-ray crystal structure, biological evaluation and molecular docking of chrysin derivatives.

Novel coumarin derivatives as multifunctional anti-AD agents: Design, synthesis, X-ray crystal structure and biological evaluation