Study of the reversible formation of Carbene-Fullerene adducts, Synthesis of a 3-Oxo-1,2,4-Triazolium Carbene

Abstract

In a first project, we optimized the preparation and purification of NHC-fullerene adducts in order to explore the reversible formation of these adducts and investigate their chemistry. Imidazolium salt precursors of NHCs that are very soluble in ordinary non-polar solvents because of their long flexible alkyl chain substituents were first prepared. Then we used the solubilizing NHCs to make pure NHC-fullerene adducts showing high solubility in ordinary organic solvents such as THF, CHCl3, toluene. The reversible formation of adducts was confirmed by thermolysis and trapping experiments in the presence of Brønsted acids, elemental sulfur (S8) or carbon disulfide (CS2). Investigations trapping experiments in the presence of strong Brønsted acids such as CF3COOH and CH3SO3H led to the discovery of new reactivity of NHC-fullerene adducts to give electrophilic functionalization products. Electrophilic functionalization of NHC-fullerene adducts could finally be extended to carbon electrophiles (MeI, MeOTf, BnBr). In a second project, a new type N-heterocyclic carbene was synthesized. This triazolone NHC is more electron-poor than Enders’ triazolium carbene and offers additional opportunities for the tuning of electronic properties through coordination at O by Lewis acids. The triazolone NHC was synthesized from diisopropylphenyl isocyanate, which was reacted with phenylhydrazine to provide N-(2,6-diisopropylphenyl)-2-phenylhydrazine carboxamide. Cyclization using triethyl orthoformate and then N-alkylation with iodomethane gave the desired salt precursor in good yield (97%). Deprotonation and in situ trapping were performed to confirm the formation of the new carbene. Metal complexes and main group adducts were prepared in the same fashion.;첫번째 프로젝트는 NHC-fullerene adducts의 준비와 정제, 그리고 이 adduct의 가역적 형태에 대한 조사를 수행하였다. 먼저, 처음 생성한 NHCs의 전구체인 이미다졸륨염은 길고 유연한 알킬 치환체에 의해 보통의 비극성의 용매에 높은 용해도를 나타냈다. 우리는 이 전구체를 이용하여 NHCs를 생성하고 THF, CHCl3, 톨루엔 같은 일반적인 유기 용매에 높은 용해도를 지닌 정제된 형태의 NHC-fullerene adducts를 생성하였다. 그리고 이 adducts가 가역적 형태임을 브뢴스테드 산과 황(S8), 이황화탄소(CS2)이 각각 존재하는 실험을 통해 증명하였다. 또 한, CF3COOH와 CH3SO3H, CF3SO3H 같은 강한 브뢴스테드 산과 NHC-fullerene adducts가 반응하여 친전자체 작용화 생성물을 생성하는 것 역시 발견하였다. 이것은 결국 탄소 친전자체(MeOTf, BnBr)들로 확장되었다. 두번째 프로젝트는 새로운 형태의 N-heterocyclic carbene(NHC)을 생성하는 것으로, 이 트라이아졸론 NHC은 O를 통해 전기적 특성들을 조정하여 Enders’ 트라이아졸륨 carbene 보다 전자가 부족한 특성을 가진 carbene이다. Diisopropylphenyl isocyanate와 phenyl hydrazine이 반응하여 N-(2,6-diisopropylphenyl)-2-phenylhydrazine carboxamide를 생성한다. 그리고 triethyl orthoformate를 이용한 고리화 반응에 이어, iodomethane에 의한 N-알킬레이션을 통해 전구체가 높은 수득률로 생성된다 (97%). 수소 제거와 금속 복합체, 메인 그룹 adducts 합성을 시도하여 새로운 carbene의 형성을 확인하였다.