Nitrogen ligands: The transition metal catalyzed reaction of aryl halides with olefins (Mizoroki-Heck), phenylboronic acid (Suzuki coupling) and Buchwald-Hartwig amination, new catalysts and effect of co-catalysts<b> </b><b>—</b><b> </b>Aryl halide activation<b> </b><b>—</b><b> </b>Part I

Abstract

Nitrogen ligands are an excellent alternative for the traditional P-ligands in the Pd catalyzed Mizoroki-Heck reaction, Suzuki coupling and Buchwald-Hartwig aryl amination. Pd complexes of dimethyl glyoxime, 8-hydroxyquinoline, salen, picolinic acid, and DAB ligands gave high yields of the <i>E</i>-cinnamates and <i>E</i>-stilbenes from aryl iodides. Acetophenone oxime N, N-dimethybenzylamine and ferrocenyl oxime palladacycle are better catalysts with comparable yields, high TON (95, 000) and TOF's (2, 500 h^-1) to P-ligand catalysts. Aryl bromides and in a few cases, aryl chlorides could also be activated by these complexes by the use of Lewis acid and (C₄H₉)₄NI as additives. Cy-DAB ligands gave good yields with electron rich aryl bromides and the use of ionic liquid improve the yield. These N-ligand metal complexes can be readily synthesized and the ligands possess the advantage of easy functional group modifications and convenient synthetic methods compared to P-ligands. The degradation reactions associated with P-ligands are not observed in the N-ligands, with comparable, high thermal, moisture and air stability and insensitivity. Activation of aryl bromides (Mizoroki-Heck reaction, Suzuki reaction) could be achieved in high yields, TON and TOF (86-94% yield, TON: 36, 000-90, 000, TOF: 6, 000-11, 500 h^-1) catalyzed by monomeric amine and oxime palladacycles (<b>Cat-8, 11, 13 B</b>) with a N-heterocyclic carbene ligand better than a phosphorous ligand. Molten (C₄H₉)₄NBr is an efficient ionic liquid medium for the Mizoroki-Heck reaction of aryl bromides, giving higher yields. Low to moderate yields of aryl amination are obtained with the carbene palladacycle and N, N-dibenzyl piperazine Pd complexes.