Facile synthesis of three new palladium(II) complexes bearing heterocyclic hydrazone ligands are presented along with their structural characterization using IR, ¹H and ¹³C NMR spectra. Molecular structures of the complexes determined by single-crystal XRD revealed a distorted square-planar geometry around the metal ion to which the hydrazone was attached in a tridentate fashion. Catalytic activity of these complexes tested towards the Suzuki–Miyaura cross coupling reaction of substituted aryl boronic acids with aryl chlorides in a water–toluene system (90 : 10%) without using any promoting additives or phase transfer agents, proved that they are highly active with 0.01 mol% loading under optimized conditions to afford 99% yield of the coupled product. Effects of temperature, solvent and base on the cross-coupling reaction were carried out as well. These complexes showed significant catalytic activity up to five cycles.

Borylation has become a powerful method to synthesize organoboranes as versatile building blocks in organic synthesis, medicinal chemistry, and materials science. Copper-promoted borylation reactions are extremely attractive due to the low cost and non-toxicity of the copper catalyst, mild reaction conditions, good functional group tolerance, and convenience in chiral induction. In this review, we mainly updated recent advances (from 2020 to 2022) in the synthetic transformations in C=C/C≡C multiple bonds, and C=E multiple bonds mediated by copper boryl systems.

One-pot, tandem C–H and N–H activation of acetanilides with aryl boronic acids to realize functionalized carbazoles was conveniently performed under aerobic conditions using a novel NNO pincer type Pd(II) complex [Pd(L)Cl] (where L = nicotinic acid (phenyl-pyridin-2-yl-methylene)-hydrazide or furan-2-carboxylic acid (phenyl-pyridin-2-yl-methylene)-hydrazide) as a catalyst in neat water and a very low (0.01 mol%) amount of catalyst. It is worth noting that recyclability up to six consecutive runs and column chromatography free isolation of the title heterocycles in an excellent yield are achieved.

Four new palladium(II) complexes featuring ONO pincer type hydrazone ligands were synthesized and characterized by spectroscopic and single-crystal XRD analysis. These complexes showed excellent catalytic activity towards the Suzuki–Miyaura cross coupling reaction of 2-chloroquinoline derivatives with various aryl boronic acids. The main advantages over previous methodologies include low catalyst loading, less problematic reaction media (H₂O–DMF (80 : 20%)) and a lower reaction temperature of 60 °C for optimal performance.

A novel family of 2,6-bis[1-(p-dibenzocycloheptylarylimino)ethyl]pyridylcobalt dichlorides Co1–Co4 were synthesized and fully characterized by FT-IR, ¹H NMR, and elemental analysis as well as X-ray diffraction analysis. The ¹H NMR spectra of these paramagnetic cobalt complexes Co1–Co3 showed similar spectra with one set of signals, while Co4 possessed two sets of signals due to the different conformations caused by different substituents on the ortho-position of the N-aryl group. Crystal structures of Co1, Co2 and Co4 revealed similar square-pyrimidal geometry around the cobalt ion, in which two dibenzocycloheptyl groups adapted as cis-conformers, whereas Co3 possessed bistrigonal geometry and the two dibenzocycloheptyl groups were adapted as trans-conformers. On activation with methylaluminoxane (MAO) or modified MAO (MMAO), all these cobalt complexes displayed high catalytic activities towards ethylene polymerization (up to 1.21 × 10⁷ g (PE) mol⁻¹ (Co) h⁻¹) and produced polyethylenes with narrow molecular distributions (PDI ≈ 2.0). Co3 bearing bulkier isopropyl substituents on the ortho-position gave much higher molecular weight of resultant polyethylene than the other cobalt complexes reported herein. The microstructure analysis of the PEs demonstrated that they are highly linear and contain a vinyl end group as the major group and saturated methyl as the minor group, in which the content of the unsaturated polymer chain relied on the ortho-substituent of the N-aryl group.