Half-Sandwich Iridium Complexes with Hydrazone Ligands: Synthesis and Catalytic Activity in N-Alkylation of Anilines or Nitroarenes with Alcohols via Hydrogen Autotransfer

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids

A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.

Ruthenium Complexes with NNN-Pincer Ligands for N-Methylation of Amines Using Methanol

A series of ruthenium complexes (Ru1-Ru4) bearing new NNN-pincer ligands were synthesized in 58-78% yields. All of the complexes are air and moisture stable and were characterized by IR, NMR, and high-resolution mass spectra (HRMS). In addition, the structures of Ru1-Ru3 were confirmed by X-ray crystallographic analysis. These Ru(II) complexes exhibited high catalytic efficiency and broad functional group tolerance in the N-methylation reaction of amines using CH3OH as both the C1 source and solvent. Experimental results indicated that the electronic effect of the substituents on the ligands considerably affects the catalytic reactivity of the complexes in which Ru3 bearing an electron-donating OMe group showed the highest activity. Deuterium labeling and control experiments suggested that the dehydrogenation of methanol to generate ruthenium hydride species was the rate-determining step in the reaction. Furthermore, this protocol also provided a ready approach to versatile trideuterated N-methylamines under mild conditions using CD3OD as a deuterated methylating agent.

Co(II) Acetate-Assisted Direct Synthesis of Acyl Hydrazones from Acyl Hydrazides under Mild Conditions

Acyl hydrazones are a class of synthetically important organic compounds that are recurrently in high demand for synthesis and use in various fields of chemistry and biology. We report the first Co(II) catalyzed one-component one-pot sustainable synthesis of acyl hydrazones only from acyl hydrazides under mild reaction conditions. Traditional and contemporary methodologies use two components (usually acyl hydrazides and aldehydes/ketones/alcohols/styrene) as the coupling partners. Our protocol, on the other hand, involves the in situ generation of aldehyde intermediate (detected by gas chromatography) from the acyl hydrazide, which then undergoes condensation with another molecule of the same acyl hydrazide in the same pot to yield acyl hydrazones in presence of mild base K2 CO3 and low-cost Co(OAc)2  ⋅ 4H2 O as catalyst. This method shows good functional group tolerance with good to excellent yield of products. Furthermore, some of the resulting acyl hydrazones have been used as synthetic precursors and explored in various post-synthetic modifications to afford N-heterocyclic compounds. Furthermore, photoswitchable properties of few synthesized acyl hydrazones are also explored using their E/Z isomerization around the C=N bond, as realized by high-pressure liquid chromatography (HPLC) and UV-vis spectroscopic studies.

Metal-organic framework-derived CoNx nanoparticles on N-doped carbon for selective N-alkylation of aniline

N-alkylation of anilines by alcohols can be used as an efficient strategy to synthesise a wide range of secondary amines. In this respect, a hydrogen borrowing methodology has been explored using precious metal-based catalysts. However, the utilisation of cheap and readily available transition metal based catalysts is required for large-scale applications. In this work, we have reported metal-organic framework-derived CoNx@NC catalysts for the selective N-alkylation of anilines with different types of alcohols. The Co-N coordination in CoNx@NC was found to be extremely important to improve the conversion efficiency and yield of the product. As a result, CoNx@NC produced 99% yield of the desired amines, which is far better than that of Co@C (yield = 65%). In addition, CoNx@NC showed remarkable recyclability for six cycles with a minimum drop in the yield of the desired product.

Cyclometalated Half-Sandwich Ruthenium Complexes: Preparation, Structure, and Catalytic Synthesis of Phenolic Esters from Aryl Halides without Using External CO under Air

A series of cyclometalated C,N-chelate half-sandwich ruthenium complexes based on N-heterocyclic ligands were prepared through a simple route with good yields. These air- and moisture-stable cyclometalated ruthenium complexes showed excellent catalytic efficiency in phenoxy carbonylation of aryl halides with phenyl formate derivatives as a CO source and phenol as a coupling partner under air. Ester products were obtained with high yields at room temperature and without the need for an inert atmosphere. The excellent catalytic activity, broad substrate range, and mild reaction conditions made this catalytic system potential for industrial production. In addition, DFT study has been carried out to elaborate the possible mechanism of this Ru-catalyzed reaction.

Half-sandwich iridium complexes with hydrazone ligands: preparation, structure, and catalytic synthesis of cyanosilylethers under air

A series of hydrazone-based N,O-chelate half-sandwich iridium complexes were synthesized through a facile route with good yields. These air- and moisture-stable iridium complexes exhibited excellent catalytic activity in the cyanosilylether synthesis under mild reaction conditions. Under the catalysis of iridium, various cyanosilylethers with different substituents were obtained through a one-pot reaction of trimethylsilyl cyanide (TMSCN) with carbonyl substrates, with good to excellent yields. The excellent catalytic efficiency, wide substrate range, and mild reaction conditions made this type of iridium catalyst have the potential for industrial applications. All the half-sandwich iridium complexes were well characterized by IR, NMR, and EA analyses. The molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.

Transition metal(ii) complexes of halogenated derivatives of (E)-4-(2-(pyridin-2-ylmethylene)hydrazinyl)quinazoline: structure, antioxidant activity, DNA-binding DNA photocleavage, interaction with albumin and in silico studies

Six transition metal(ii) complexes with halogenated quinazoline derivatives as ligands were characterized and evaluated for interaction with calf-thymus DNA, photocleavage of plasmid-DNA, affinity for bovine serum albumin, and antioxidant activity.