Palladium–phosphorus/sulfur nanoparticles (NPs) decorated on graphene oxide: synthesis using the same precursor for NPs and catalytic applications in Suzuki–Miyaura coupling

Abstract

PdP₂ and Pd₄S nanoparticles (NPs) (size: ∼2–6 and 9–15 nm respectively) have been prepared for the first time from a single source precursor complex [Pd(L)Cl₂] (1) by its one pot thermolysis at 200 °C in TOP and OA/ODE (1 : 1) respectively. These NPs were stirred with graphene oxide (GO) at room temperature to prepare NP composites, GO–PdP₂ and GO–Pd₄S. The GO–PdP₂ NPs have been synthesized for the first time. The thioether ligand L prepared by reaction of 1,3-dibromo-2-propanol with the in situ generated PhSNa reacts with [PdCl₂(CH₃CN)₂] in CH₃CN at 70 °C resulting in 1. The L and 1 have been characterized by ¹H and ¹³C{¹H} NMR and HR-MS. The single crystal structure of 1 determined by X-ray diffraction reveals nearly square planar geometry around the Pd metal centre. The catalytic activities of two palladium nano-phases having phosphorus and sulphur respectively as a co-constituent for Suzuki–Miyaura coupling have been found to be exceptionally different, as PdP₂ nanoparticles (NPs) grafted on graphene oxide (GO–PdP₂) are significantly more efficient than Pd₄S NPs grafted on GO. Without grafting PdP₂ and Pd₄S both have low efficiency. This is the first report comparing the influence of P and S on the catalytic activity of Pd NPs. TEM, SEM-EDX and powder-XRD have been used to authenticate all NPs. The GO–PdP₂ NPs have been found to be efficient catalysts for Suzuki–Miyaura coupling reactions (yield up to 96% in 30 min) at room temperature to 80 °C. Their recyclability has been found up to 6 cycles. In contrast, GO–Pd₄S NPs are little active in comparison with GO–PdP₂ NPs. The size of NPs and their distribution on GO appear to be key factors affecting the catalytic efficiency of the composite NPs. Leaching of Pd from GO–PdP₂ NPs contributes significantly to the catalysis as evidenced by the three phase test, hot-filtration and recycling experiments. The catalysis is almost homogeneous.