Ni/Pd core/shell nanoparticles supported on graphene as a highly active and reusable catalyst for Suzuki–Miyaura cross-coupling reaction

Monodisperse Ni/Pd core/shell nanoparticles (NPs) have been synthesized by sequential reduction of nickel(Ⅱ) acetate and palladium(Ⅱ) bromide in oleylamine (OAm) and trioctylphosphine (TOP). The Ni/Pd NPs have a narrow size distribution with a mean particle size of 10 nm and a standard deviation of 5% with respect to the particle diameter. Mechanistic studies showed that the presence of TOP was essential to control the reductive decomposition of Ni–TOP and Pd–TOP, and the formation of Ni/Pd core/shell NPs. Using the current synthetic protocol, the composition of the Ni/Pd within the core/shell structure can be readily tuned by simply controlling the initial molar ratio of the Ni and Pd salts. The as-synthesized Ni/Pd core/shell NPs were supported on graphene (G) and used as catalyst in Suzuki–Miyaura cross-coupling reactions. Among three different kinds of Ni/Pd NPs tested, the Ni/Pd (Ni/Pd = 3/2) NPs were found to be the most active catalyst for the Suzuki–Miyaura cross-coupling of arylboronic acids with aryl iodides, bromides and even chlorides in a dimethylformamide/water mixture by using K₂CO₃ as a base at 110 ℃. The G–Ni/Pd was also stable and reusable, providing 98% conversion after the 5^th catalytic run without showing any noticeable Ni/Pd composition change. The G–Ni/Pd structure reported in this paper combines both the efficiency of a homogeneous catalyst and the durability of a heterogeneous catalyst, and is promising catalyst candidate for various Pd-based catalytic applications.