Palladium(II) complexes bearing 2-(1H-imidazol/oxazol-2-yl)-pyridines: Synthesis, structures and ligand effects in Suzuki–Miyaura cross-coupling

New Bidentate N-Sulfonyl-Substituted Aromatic Amines as Chelate Ligand Backbones: Pd Catalyst Generation in C–C Coupling via In Situ and Precatalyst Modes

A series of six new, bidentate ligands based on N-(2-(R-sulfonamido)benzyl)R-sulfonamide have been isolated as dianionic or monoanionic chelators via condensation of 2-(aminomethyl)aniline with sulfonyl chloride reagents; R=methyl (1 and 1′), tolyl (2 and 2′), 2,4,6-trimethylphenyl (3), or 2,4,6-triisopropylphenyl (4). Complexes of ligands 2–4 reacted at room temperature with palladium(ii) acetate in the presence of various monodentate N-donor co-ligands to form complexes Pd2(2dmap), Pd2′(OAc.py), Pd3(2acn), Pd3(2py), Pd4(2acn), and Pd4(2py), which were structurally confirmed by three X-ray crystal analyses. Results of catalysis studies in water showed high turnover frequencies and yields of up to 98% within 10min and at 0.2 mol-% palladium catalyst loading. Relative to ligand-free catalysis in the presence of only Pd(OAc)2, the ligand-supported palladium species clearly possess positive catalytic advantage. Furthermore, Suzuki coupling efficiencies by 1:1 ‘Pd(OAc)2+ligand’ yielded notably better outcomes than for the 1:2 ‘Pd(OAc)2+ligand’ insitu catalyst generation, which reveals that coordinative saturation is undesirable. The size of the complementing monodentate co-ligand was observed to influence the catalytic efficiency such that bulkier co-ligands consistently yielded improved turnover frequency values, which leads to the conclusion that steric repulsion between the synthesised ligands and the bulkier co-ligands aided the generation of vacant coordination sites for the more active complexes. Moderate Heck coupling activity was recorded for the complexes and better activities appear to correlate with moderate bulkiness of ligand 3.

ESIPT-capable 2,6-di(1H-imidazol-2-yl)phenols with very strong fluorescent sensing signals towards Cr(iii), Zn(ii), and Cd(ii): molecular variation effects on turn-on efficiency

The derivatization influence was studied for twelve 2,6-di(1H-imidazol-2-yl)phenols, whereby a strong fluorescent sensitivity for Cr(iii) was reported, while Zn(ii)/Cd(ii) sensing potentials also appeared.

Camphyl-based α-diimine palladium complexes: highly efficient precatalysts for direct arylation of thiazoles in open-air

Bulky camphyl-based α-diimine palladium complexes have been developed and exhibited high reactivity for the direct arylation of thiazoles in air.

Exhibition of the Brønsted acid–base character of a Schiff base in palladium(ii) complex formation: lithium complexation, fluxional properties and catalysis of Suzuki reactions in water

The Brønsted acid–base character of bis(iminopyrrolylmethyl)amine was shown through the X-ray structures of palladium complexes. The bischelated palladium complex is fluxional as studied by the VT ¹H NMR method and effectively catalyzes Suzuki reactions in water.

Base-promoted protodeboronation of 2,6-disubstituted arylboronic acids

Facile based promoted deboronation of electron-deficient arylboronate esters was observed for arylboronates containing two ortho electron-withdrawing group (EWG) substituents. Among 30 representative boronates, only the diortho-substituted species underwent facile C-B fission in aqueous basic conditions (200 mM hydroxide). These results provide fundamental insight into deboronative mechanisms with implications for cross-coupling reactions, regioselective deuteration/tritiation for isotopic labeling, and the design of new (18)F-trifluoroborate radioprosthetics.