Hybrid Thiophosphoryl–Benzothiazole Palladium SCN-Pincer Complexes: Synthesis and Effect of Structure Modifications on Catalytic Performance in the Suzuki Cross-Coupling

Abstract

The novel hybrid pincer-type ligands 3, 6, 9, and 11, bearing, as donating sites, a thiophosphoryl group and an imine moiety of the benzothiazole ring bound either directly to the central benzene core or attached to the latter one via O or NH linkers, undergo direct cyclopalladation at the C(2) position of the central benzene core in reaction with (PhCN)2PdCl2 (MeCN or PhCN as a solvent, 80–120 °C) to afford 5,5- and 5,6-membered κ3-SCN-palladium pincer complexes 12–15 in good to high yields. Direct cycloplatination with the related platinum precursor was successful only in the case of N-[3-(1,3-benzothiazol-2-yl)phenyl]-P,P-diphenylthiophosphinic acid amide 9. The Pd(II) complexes 12–15 were found to be highly active (pre)catalysts for the Suzuki cross-coupling of a range of electronically varied aryl bromides with phenylboronic acid. The most active complex, 14a, also promoted efficiently the coupling of chloroacetophenone, ranking among the best pincer complexes suggested for this reaction.