锚定基团对HKUST-1/TEMPO共催化体系催化性能的影响

用异烟酸(Iso-NTA)为桥接分子, 将有机小分子自由基4-氨基-2,2,6,6-四甲基哌啶-1-氧自由基(4-NH₂-TEMPO)与异烟酸缩合, 合成出含吡啶官能团的TEMPO自由基(Iso-NTA-TEMPO). 与TEMPO相比, Iso-NTA-TEMPO具有较高的氧化电位, 在无Cu(Ⅱ)辅助时, Iso-NTA-TEMPO对苯甲醇的氧化效率高于TEMPO. 在与HKUST-1组成的复合催化体系中, Iso-NTA-TEMPO可通过吡啶基团与HKUST-1孔道中的Cu(Ⅱ)相互作用, 从而在催化过程中(部分)锚定在HKUST-1孔道内部. 与TEMPO/HKUST-1体系相比, Iso-NTA-TEMPO/HKUST-1体系表现出对芳香醇更加高效的催化活性. 采用模板辅助溶剂诱导结晶法合成的HKUST-1晶体表面具有较多缺陷, 更有利于Iso-NTA-TEMPO自由基分子扩散进入HKUST-1孔道内部, 也有助于提高Iso-NTA-TEMPO/HKUST-1体系的催化效率. Iso-NTA-TEMPO/HKUST-1体系可将各种取代基(苄醇、 杂环醇以及二级脂肪醇)高效、 高选择性地氧化成相应的醛或酮.

Effects of Anchoring Group on the Catalytic Activity of HKUST-1/TEMPO Co-catalysts †

By using isonicotinic acid(Iso-NTA) as a bridging molecule, a pyridyl functionalized 2,2,6,6-tetramethylpiperidinyl-1-oxy(TEMPO) radical(Iso-NTA-TEMPO) was synthesized by the condensation of 4-amino-2,2,6,6-tetramethylpiperidino-1-oxy(4-NH₂-TEMPO) and isonicotinic acid. Compared with TEMPO, Iso-NTA-TEMPO exhibited higher oxidation potential, which facilitates the oxidation reaction of benzyl alcohol, without the use of Cu(Ⅱ). In the case of Iso-NTA-TEMPO/HKUST-1 hybrid catalytic system, the Iso-NTA-TEMPO can be(partially) coordinated to Cu(Ⅱ) sites of HKUST-1 by pyridyl group during catalysis. As consequence, the Iso-NTA-TEMPO/HKUST-1 catalytic system shows much higher catalytic activity than that of TEMPO/HKUST-1 system, toward the oxidation of aromatic alcohols. Moreover, HKUST-1 synthesized by template assisted solvent-induced crystallization consists a significant amount of defects, which facilitates the diffusion of Iso-NTA-TEMPO into the pores of HKUST-1, thus, improving the catalytic activity of Iso-NTA-TEMPO/HKUST-1. The Iso-NTA-TEMPO/HKUST-1 system enables the oxidation of a broad range of primary aromatic alcohols with various substituted groups and heteroatoms, as well as secondary aliphatic alcohols with high efficiency and selectivity.