摘要
本文研究了配位俘获法固载胶体钯催化剂对Heck反应的催化行为,证明了碘苯与胶体钯之间的氧化加成反应引起催化剂颜色及钯的价态变化,钯金属键断裂,生成小分子钯化合物,并为含硫原子高分子配体俘获,进而参加一系列的催化循环。小分子钯化合物的生成,引起胶体催化剂的金属流失,而采用对钯有强配位能力的含硫原子配体,是该催化剂表现出较好稳定性的原因。讨论了影响Heck反应诱导期的各种因素,首次研究了加入三丁基碘化铵,磺对Heck反应诱导期的影响,极大地缩短了诱导期。
Recently a coordination capture method for preparation of immobilized metal catalysts has been reported, thus affording a good opportunity to compare the catalytic behaviors in Heck reaction of the entitled catalyst, (SiO2) - (C3H6SH)nPd0, prepared via coordination capture of PVP-protected palladium colloid with mercapto groups on silica, with Pd?C catalyst and polymeric catalyst (SiO2) -(C3H6SH)nPd(OAc)2. In this paper, the activities and stabilities of the catalysts were investigated for the reaction of ethyl acrylate with phenyl iodide. Elementary analysis, XPS, TEM and kinetic results indicated that the breakdown of the metal-metal bound of the immobilized metallic catalyst caused by oxidative addition of aryl halide to palladium(0) colloidal particle led to the leaching of palladium from the catalyst. The palladium (Ⅱ) species formed in the reaction in turn is coordinated on the surface of silica support by the anchored mercapto ligand and results in the derived material having the catalytic behaviors similar to those of the polymer-supported mononuclear catalyst (SiO2) - (C3H6SH)n Pd (OAc)2. Induction process being one of the elementary steps in Heck reaction was investigated kinetically for the entitled catalyst. XPS data showed that the presence of Pd0 on the surface of colloidal palladium particles owing to the oxidation by air brings about its behavior different from Pd0/ C catalyst. The effect of additive on the induction process was examined experimentally, it was found that the addition of Bu3N ?HI and I2 reduces the induction period of Heck reaction greatly.
出处
《分子催化》
EI
CAS
CSCD
1992年第4期248-254,共7页
Journal of Molecular Catalysis(China)
基金
国家自然科学基金资助课题
关键词
钯
催化剂
配位俘获
诱导期
Heck reaction , Immobilized colloidal palladium catalyst , Coordination capture Induction period.
