Carbon-carbon cross-coupling reactions are essential synthetic tools for synthesizing polymers, natural products, agrochemicals, and pharmaceuticals. Therefore, new catalysts that function with greater efficiency and functional group tolerance are being researched. We have prepared new ferrocenylimine monodentate N and P donor ligands and N^N and N^P bidentate chelating ligands (L1 to L4) employed in stabilizing palladium ions for application in Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions. The ferrocenylimine ligands were successfully synthesized by Schiff base condensation reactions of acetyl ferrocene with hydrazine monohydrate to afford ferrocenyl hydrazone (L1). Ligand L1 was further treated with aldehydes to give ferrocenyl(2-diphenylphosphino)imine (L3) and ferrocenyl(pyridyl)imine (L3), while phosphination of L1 with chlorodiphenylphosphine afforded L2. The ligands were used to prepare new palladium(II) complexes (C1 to C4) by complexation with [PdCl2(MeCN)2]. All the ligands and complexes were fully characterized using standard spectroscopic and analytical techniques, including 1H NMR and 13C NMR spectroscopy, FT-IR spectroscopy, mass spectrometry and elemental analysis. The complexes (C1 to C4) were tested for efficacies in catalyzing Mizoroki-Heck and Suzuki-Miyaura C-C cross-coupling reactions and proved to be suitable catalyst precursors. Ferrocenyl(2-diphenylphosphine)imino and ferrocenyl-methyl hydrazone palladium(II) complexes C2 and C3 showed the best activities at TONs of up to 201. The ferrocenyl palladium(II) (pre)catalysts demonstrated moderate activity in Mizoroki-Heck reactions involving substrates with substituents on the olefin and aryl halide (including 4-Cl, 4-CH3, -CO2Me and -CO2Et). Density Functional Theory was used to study the mechanism of the Mizoroki-Heck cross-coupling reactions and have led to confirmation of the widely accepted catalytic cycle. Catalyst precursors (C1 to C4) also displayed good activity and selectivity in Suzuki-Miyaura cross-coupling reactions, at 0.5 mol% catalyst loading, with good tolerance to functional groups present on the aryl halide and boronic acid substrates (such as 4-Cl, 4-CHO, 4-COOH, 3-NO2, 3,5-dimethoxy and 4-CH3).
The cover image, by Asanda C. Matsheku et al., is based on the Full Acridine‐containing RuII, OsII, RhIII and IrIII Half‐Sandwich Complexes: Synthesis, Structure and Antiproliferative Activity, DOI: . Design Credit: Banothile C.E. Makhubela and Hester Roets, UJ Graphic Design Studio.
Research aimed at enhancing the efficacy of organometallic complexes against cancer, has shown that attaching bio-active molecules to (metallo)drugs often enhances their biological properties. New salicylaldimine and 2-pyridylimine ligands (L2 and L3), containing a bio-active acridine scaffold, were synthesized and complexed to Rh(III), Ir(III), Ru(II) and Os(II) metal ion centers. The resulting acridine-containing half-sandwich complexes have been characterized fully by elemental analysis, FT-IR and NMR spectroscopy, HR-ESI mass spectrometry as well as single crystal X-ray diffraction, for the Rh(III) N^N bidentate complex [RhCp*Cl(L3)][BPh 4 ]. The antiproliferative activity of the ligands (L2 and L3) and complexes (C1 to C9) were evaluated in vitro against human promyelocytic leukemia cells (HL60) and normal skin fibroblast cells (FG0). The compounds exhibit good activities against HL60 cells and are consistently selective towards cancerous cells over non-tumorous cells. This study demonstrates the potential of such hybrid compounds to target cancer cells specifically. The most active complex, [RhCp*Cl(L2)], exhibited binding to DNA model guanosine-5'-monophosphate (5'-GMP) which suggests a mode of action involving interaction of the complex with 5'-GMP found on DNA backbone.
Palladium iminophosphorane (C1 – C3) and pyridylimine (C4 – C5) pincer complexes were evaluated for their activity in the conversion of furfural to furfuryl alcohol in the presence of triethylamine...
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