A Catalytic Hydrogel System Reinforced by Palladium Encapsulated Metal-Organic Framework for Suzuki-Miyaura Coupling Reaction

Abstract

환경오염 문제가 점점 대두되면서 휘발성 유기용매의 사용을 감소시킬 수 있는 수용액에서의 화학반응이 주목을 받고 있다. 본 연구에서는 물을 용매로 하는 스즈키-미야우라 반응에 적합한 하이드로젤 촉매를 제조하였다. 팔라듐 나노입자를 도입한 금속-유기 구조체(MOF)를 개질한 후 하이드로젤 제조에 이용하여 기계적 특성과 촉매 활성이 우수한 촉매 시스템을 얻었다. MOF로는 2-aminoterephthalic acid와 zirconium(IV) chloride로부터 합성한 UiO-66-NH2를 이용하였다. 수소 기체를 이용하여 팔라듐 나노입자를 UiO-66-NH2 안에서 생성하고 비닐기를 UiO-66-NH2 에 도입하였다. 비닐기가 도입된 MOF와 아크릴아마이드의 라디칼 중합반응을 소량의 가교제 존재 하에 수행하여 하이드로젤 촉매를 제조하였다. 하이드로젤 촉매의 촉매 활성 및 재사용 가능성을 phenylboronic acid와 iodobenzene의 스즈키-미야우라 반응을 물-에탄올 용매에서 수행하여 조사하였다.

As environmental concerns increase, reactions in aqueous media are moving into the spotlight of synthetic chemistry where the usage of volatile organic solvents is reduced. We developed a catalytic hydrogel system for Suzuki-Miyaura coupling reaction in an aqueous medium. The hydrogel system contained palladium nanoparticle (PdNP) encapsulated metal-organic frameworks (MOFs) as catalytically active species and as reinforcement. The MOF (UiO-66-NH2) was prepared from 2-aminoterephthalic acid and zirconium(IV) chloride. High surface area, chemical modifiability, and numerous hydrogen bonding sites of UiO-66-NH2 made it a good candidate for catalytic cage, chemical crosslinker, and physical filler, respectively. PdNPs were encapsulated inside of UiO-66-NH2 by in situ hydrogen reduction and vinyl moieties for chemical crosslinking were introduced to UiO-66-NH2 by postsynthetic modification. Palladium content and vinyl modification ratio were 2.79 and 96.1 %, respectively. No damage on the crystal structure of UiO-66-NH2 was confirmed by nitrogen adsorption/desorption measurements and X-ray diffraction patterns. A catalytic hydrogel was prepared by free radical polymerization of acrylamide and the vinyl modified, PdNP encapsulated MOF in the presence of a small amount of a chemical cross-linker. The MOF reinforced hydrogel showed higher modulus and elongation by 105 and 25.8 %, respectively than the acrylamide hydrogel without the MOF. The catalytic activity and recyclability of the hydrogel were examined for the Suzuki-Miyaura coupling reaction of phenylboronic acid and iodobenzene.