Pd(OAc)2/[C18–DABCO–C18]2Br: a nano palladium catalytic approach for Mizoroki–Heck and Suzuki–Miyaura coupling reactions in water

Abstract

In this study, we have successfully used a new catalytic system comprised of Pd(OAc)₂ and [C₁₈–DABCO–C₁₈]2Br (at a ratio of 1 : 10 mol%) for various types of C–C coupling reactions, including Mizoroki–Heck and Suzuki–Miyaura, in a water-based medium. The catalyst system was analyzed using TEM, which revealed the presence of stable Pd nanoparticles (PdNPs) that were less than 5 nm in size and were protected by a “Gemini” type [C₁₈–DABCO–C₁₈]2Br surfactant. X-ray photoelectron spectroscopy (XPS) was used to determine the oxidation states of Pd. Our optimization study revealed that this catalytic system was highly effective in coupling a range of aryl iodides and bromides with different olefins and aryl boronic acids. The reactions were performed at 80–100 °C with K₂CO₃ as a base, and high yields ranging from 80–93% were obtained. The selectivity of all reactions was excellent, ranging from 92–100%, with a turnover number (TON) of 79.72–92.77 and a turnover frequency (TOF) of 0.997–2.059 min⁻¹. Similarly, the catalytic system was highly efficient in Suzuki–Miyaura coupling of various aryl iodides and bromides with different aryl boronic acids, yielding good to excellent product yields (87–95%) with TON of 86.86–94.84 and TOF of 1.996–3.161 min⁻¹. One of the advantages of this catalyst is that it can be recycled at least three times for Mizoroki–Heck coupling reactions with only a marginal loss in product yields.