Ligand Design for Aerobic Pd-Catalyzed Styrene Production via the One-Step C–H/C–H Coupling of Benzene and Ethylene

Abstract

This study presents an efficient synthesis of styrene through a one-step C–H/C–H vinyl–aryl bond formation process, aiming to mitigate the need for harsh reaction conditions and the lack of step efficiency of the two-step industrial styrene production. In the ligand accelerated palladium(II)-catalyzed arene alkenylation, tunable 2-hydroxypyridine ligands were shown to enhance catalytic activity, stability, and selectivity. Reaction conditions were designed to obtain turnover numbers toward styrene exceeding 3200 with Pd concentrations ranging from 0.015 to 0.75 mM. Turnover frequencies of over 250 h^–1 were recorded. A thorough mechanistic and spectroscopic study, involving kinetics, DFT calculations, ESI-MS, NMR, and XAS, proved that 2-hydroxypyridine-chelated Pd(II) is the species involved in C–H activation, with concerted metalation-deprotonation as the rate-determining step.