From Pyrroles to Isoindolines: Synthesis of a γ-Diimine Ligand for Applications in Palladium Coordination Chemistry and Catalysis

Abstract

The γ-diimine 1,2-(2,6-iPr2-C6H3NC)2-C6H4 (2) was synthesized by the reaction of phthalaldehyde with 2,6-diisopropylaniline. Depending on reaction conditions, 2 can cyclize to form the corresponding iminoisoindoline or isoindolinone. Unlike analogous α- and β-diimine complexes, reaction of the γ-diimine 2 with (MeCN)2PdCl2 results in a dinuclear complex, [(γ-diimine)PdCl(μ-Cl)]2 (5), where the ligand does not coordinate to the Pd(II) center in a chelating fashion but instead adopts a monodentate coordination mode. On the other hand, reaction of 2 with Pd(OAc)2 results in C−H activation and formation of the trinuclear Pd3(OAc)4-based palladacycle {1,2-(2,6-iPr2-C6H3NC)2-C6H3]Pd(μ-OAc)2}2Pd (6). The resulting palladium complexes were tested as precatalysts in Heck and Suzuki coupling reactions.