Predesigned Covalent Organic Frameworks as Effective Platforms for Pd(II) Coordination Enabling Cross-Coupling Reactions under Sustainable Conditions

Abstract

The phenanthroline unit in an imine-based covalent organic framework (Phen-COF) offers a robust coordination site for Pd(OAc)2 centers. Coordination of palladium centers is demonstrated by a variety of techniques, including X-ray photoelectron spectroscopy and total X-ray fluorescence. The stable phenanthroline-Pd(II) coordination avoids leaching of metal centers to the reaction medium, where deactivation processes through nanoparticle formation limits the catalytic activities observed for homogeneous systems. Thus, because of isolation and immobilization of catalytic sites in the Pd@Phen-COF the performance of material, the catalytic outputs are dramatically increased with respect to the performance observed for analogous molecular catalysts. This concept is applied in this work to C-C cross-coupling reactions under mild and environmentally benign conditions. The activities found for Suzuki-Miyaura and Mizoroki-Heck reactions allow thousands of turnover numbers in the transformation of a wide scope of precursors with a high degree of recyclability. The results reported in this work contribute to the design of greener protocols for transformations that have a crucial role in the industrial synthesis of high-added value fine chemicals.