Preparation Of Activated Carbon Anchored Palladium Complexes And Catalytic Application On Ullmann Reaction

Ullmann reaction is one of the effective methods to build symmetric biaryl via the formation of C-C bonds, while it also plays an important role in the formation of C-O, C-N, C-S bonds. It is generally catalyzed by homogeneous palladium catalyst such as Pd(OAc)2, PdCl2. However, there are separation and recycling problems to limit practical application of the Ullmann reaction. And the development of heterogeneous palladium catalysts has attracted considerable interest.There is an amount of oxygen-containing functional groups in carbon surface, which is able to graft amine functional group. So immobilized metal catalyst is conducted.A ligand-free, without extra added reducing agent, under aerobic conditions, environment-friendly protocol for the Ullmann homcoupling of aryl halides had been developed using commercially available5%Pd/C as the catalyst. The highest coupling product yield of brominated aromatic is88.6%, which of chlorinated aromatic is51.4%. But the performance of palladium-carbon catalyst reuse is poorer, bromobenzene coupling product rate declines from80.8%to36.1%after repeated3times.Activated carbon selected as the carrier, two amine ligands grafted onto the activated carbon, the active species of palladium anchored on activated carbon, the immobilized palladium catalyst (AC-NH(CH2)2NH2-Pd) was prepared. The prepared catalyst was characterized by Bohem titration, elemental analysis (EA), Fourier transform infrared spectroscopy(FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction(XRD) and transmission electron microscopy (TEM). This immobilized catalyst exhibited higher catalytic activity in the Ullmann reaction of aryl halide. The yield of4-Iodoanisole coupling is90.5%. The highest coupling product yield of brominated aromatic is76.7%, which of chlorinated aromatic is41.4%. It can be recovered by simple filtration and reused up to7times with35.9%yield.