Preparation And Catalytic Property For Heck Reaction Of Polymer Supported Palladium Complex

Palladium-catalyzed Heck reaction has received considerable attention in recentyears, as it offers a versatile method for the generation of new C-C bonds in organicsynthesis. The reaction is normally carried out with the homogeneous palladium catalystsuch as Pd(OAc)2 and Pd(PPh3)2Cl2. These catalysts have high catalytic activity forHeck reaction; however, they suffer from severe problems related with the separation,recovery and the instability of the homogeneous catalysts at high temperatures, whichhave so far precluded the widespread industrial application of Heck reaction. Theseproblems can be overcome, however, by the use of heterogeneous catalysts, made up ofsupported palladium complex. Polymer-Supported metal complexes having highactivity and selectivity are currently attracting great interest because they can be easilyseparated and recovered. Natural polymers with functional groups are good carriers for mental catalysts.Sesbania gum and starch supported palladium complexes were synthesized with simplemethod and characterized by XPS, IR, TG, DTA and TEM etc. TEM confirms thatpalladium particles have uniform distribution in the catalysts; the average size is 10 nm.Thermal analysis show that both sesbania gum supported palladium complexes andstarch supported palladium complexes have high thermal stability. These two kinds ofcomplexes are efficient catalysts for Heck reactions of acrylic acid,styrene and witharyl iodide at atmospheric condition. The substituted trans-cinnamic acid andtrans-stilbene were obtained in high yield (≥80%). These two kinds of complexescould be separated from the reaction mixture easily and used repeatedly. Three kinds of chitosan derivatives, crosslinked chitosan, chitosan condense withsalilylaldehyde and crosslinked chitosan condense with salilylaldehyde, weresynthesized via simple reactions. Four kinds of catalysts were obtained through theinteraction of chitosan and its derivates with PdCl2. These complexes are efficientcatalysts for Heck reaction under atmospheric condition. The detailed studies show thatthe catalytic performance of chitosan derivatives supported Palladium complexes ismuch more efficient than chitosan supported Palladium complexes under the sameconditions. It remains high catalytic activity for Heck reaction of acrylic acid withiodobenzene even at the low temperature(60 ℃) or with tiny amount of the catalyst(0.1 mol%Pd) and the yields are higher than 90%. Yields of making cinnamic acid wereeven high as 75% for Heck reaction of acrylic acid with iodobenzene by usingcrosslinked chitosan condense with salilylaldehyde supported Palladium complex thatwas recovered for 10 times. Polyvinyl chloride-ethylenediamine, polyvinyl chloride-diethylenetriamine andpolyvinyl chloride-triethylene- tetramine were obtained from polyvinyl chloride viaaminization. Then, three kinds of polyvinyl chloride-polyethylene-polyamine supportedpalladium complexes were synthesized by interacting with PdCl2. These complexes areefficient catalysts for Heck reaction of acrylic acid with aryl iodides in the air at the lowtemperature(50 ℃) using 0.125 mol%Pd of the catalysts and the yields are higher than70%. In the presence of polyvinyl chloride-triethylene-tetramine supported Palladiumcomplex, the reaction can also be carried out at 40 ℃ and the yield of the cinnamicacid is 56%. Using one of the palladium complexes, the Heck reaction of acrylic acidwith iodobenzene can be performed with tiny amount of the catalyst (0.02 mol%Pd)and the yield is about 90%. The complexes can be easily recovered from the reactionmixture by filtration and reused for more than 12 times.