Synthesis And Performance Research Of Polymer Dual-site Immobilized Hoveyda-Grubbs Catalyst

Olefin metathesis reaction refers to the carbon skeleton rearrangement reaction between unsaturated carbon-carbon bonds catalyzed by metal carbene complexes.Recently,Ru-carbene olefin metathesis catalysts have been widely used in organic synthesis due to their high catalytic activity,good functional group tolerance and compatibilities with most substrates.However,these catalysts are difficult to be recycled and the ruthenium residues in products are difficult to be removed.The immobilization of the catalyst can recycle the catalyst.Common carriers include inorganic rigid material and polymer.The structure of inorganic rigid material has certain binding effect on the catalyst,while polymer has advantages of strong structural design and variable conformation in the reaction medium.By immobilizing the catalyst with polymer as carrier,the micro-environment constructed by the polymer can inhibit the decomposition of the catalyst.Although the catalyst can be recycled by loading a single site of the catalyst,the deactivation of the catalyst during the reaction process reduces its recycling performance.Therefore,tri-block polymer dual-site immobilized catalyst was designed and synthesized in this paper.The excess ligands in the catalyst were used to capture the ruthenium that shed from the catalyst,avoiding the ruthenium loss during the use of catalyst,achieving recycling of the catalyst and avoiding the ruthenium residue in the product.The main research contents and conclusions of this paper were summarized as follows:（1）NHC ligand precursor（p NHC）was synthesized by using4-amino-3,5-xylenol as raw material and functionalized by 6-bromo-1-hexyl acrylate.Benzylidene ligand precursor（p Bzl）was synthesized by using Cbz-L-tyrosine as raw material and functionalized by glycidyl methacrylate.The Grubbs^1st catalyst was synthesized by benzaldehyde p-toluenesulfonyl hydrazone.By FT-IR and ¹H NMR analysis,p NHC,p Bzl and Grubbs^1st catalyst were successfully synthesized,with yields of 80%,85%and 61%,and purities of 92%,90%and 83%,respectively.（2）Firstly,the homopolymerization reaction times of p NHC,p Bzl and flexible monomer tert-butyl acrylate（t BA）were investigated by PET-RAFT.Then,tri-block polymers with different gradients were prepared,and their compositions were analyzed.Finally,Grubbs^1st catalyst was immobilized by tri-block polymer as the carrier.Through FT-IR,UV-vis,NMR(¹H,¹³C and ³¹P),DLS and ICP-MS analysis,it was proved that two kinds of catalysts（Ru1-1 and Ru1-2）with different ruthenium loadings using P(p NHC₉₃-b-t BA₁₈₇-b-p Bzl₄₅)as the carrier were successfully synthesized.The ruthenium loads in Ru1-1 and Ru1-2 were 2.6×10^-2 and 1.4×10^-1mmol g^-1,respectively.（3）Firstly,ROMP,CM and RCM were selected to verify the applicability and catalytic activity of Ru1-1 and Ru1-2.Then,CM was selected to explore the influence of the reaction medium on the catalyst,the cycling performance of the catalyst and the ruthenium residue in the product.The results showed that under the conditions of 0.05 mol%Ru1-1 and 0.05 mol%Ru1-2,the conversion rates of1-octene within 17 h were 88.5%and 74.6%,respectively.The TONs of Ru1-1 and Ru1-2 were 1770 and 1492,respectively.Under the condition of 1 mol%Ru1-1,the conversion rate of diethyl diallylmalonate was 80%within 17 h.The reaction catalyzed by Ru1-1 and Ru1-2 are heterogeneous reaction.After the reaction,the catalyst can be separated and recovered by centrifugation.The activity of the catalyst did not decrease significantly during the 10 cycles,and there was no ruthenium residue in product,which indicated that the catalyst had high stability during the 10cycles.