Pd-PEPPSI Complex Integrated into Hyper-Crosslinked Polymer: A Highly Stable and Reusable Catalyst for Heterogeneous C-C Coupling Reactions.

Abstract

Catalyst deactivation due to aggregation or leaching of active metal species remains a major challenge in heterogeneous catalysis. In this study, a homogeneous Pd-PEPPSI (Pyridine-Enhanced Pre-catalyst Preparation, Stabilization, and Initiation) complex was transformed into a single-site heterogeneous catalyst by incorporating it into a hyper-crosslinked polymer (HCP) via a one-step direct knitting strategy. In the Pd-PEPPSI complex, 3-chloropyridine acts as an ancillary ligand, stabilizing the palladium center and facilitating oxidative addition in C─C coupling reactions, while the N-heterocyclic carbene (NHC) serves as the functional ligand. The HCP's hierarchical pore structure and high surface area enhance catalyst recyclability and reduce metal leaching. The HCP-Pd-PEPPSI-3 catalyst efficiently catalyzed Suzuki-Miyaura cross-coupling reactions of various aryl halides and arylboronic acids at a Pd loading of 0.10 mol%, achieving a 99% yield with a turnover frequency (TOF) of 1.23 × 10⁴ h^-1. Additionally, it achieved up to 98% yield in the Mizoroki-Heck reaction at the same Pd loading. The catalyst maintained a 90% yield after 10 cycles, demonstrating excellent recyclability. This strategy prevents Pd leaching and aggregation, making HCP-Pd-PEPPSI-3 a versatile and sustainable catalyst for Pd-catalyzed reactions.