【作者】 刘伟；

【导师】 刘晔；

【作者基本信息】 华东师范大学 ， 有机化学， 2010， 硕士

【摘要】 本论文设计合成了一系列离子型金属卟啉,包括锰卟啉、钯卟啉和金卟啉化合物。并针对离子型锰卟啉催化剂,详细考察了卟吩环外围季铵阳离子的吸电子效应、离子型锰卟啉中抗衡阴离子效应、离子液体的溶剂效应、以及卟吩环β位上引入溴原子的空间和电子效应等因素,对锰卟啉催化乙苯(及其衍生物)氧化和环辛烯环氧化反应的催化性能(活性、选择性、锰卟啉催化剂的循环使用)的影响。为了具体明确上述因素的影响,构筑了以下三个催化剂(A3、B2、C2),详细对比考察了催化体剂A3和B2对苯乙烷氧化转化的性能,以及催化剂C2对环辛烯环氧化的催化性能。实验结果表明：与传统有机溶剂中的中性锰卟啉催化的烃类氧化反应相比,离子型锰卟啉和结构相似的离子液体配合使用还具有的以下优点：1)离子液体可以起轴向配体的作用,避免使用易被氧化的吡啶或咪唑及其衍生物作为轴向配体；2)具有芳香共轭结构的咪唑或吡啶离子液体可以通过与卟啉分子之间的π-π作用,抑制锰卟啉自身的π-π聚合(避免锰卟啉μ-氧二聚体的形成),从而提高锰卟啉催化剂的稳定性和催化活性；3)季胺阳离子的强吸电子作用可以降低卟啉环上电子云密度(增强锰卟啉的抗氧化降解能力)；4)磷钨酸根抗衡阴离子的引入可以提高进一步增强锰卟啉阳离子的稳定性和催化活性。具体研究工作包括以下三部分：(一)催化剂A3的合成及其对苯乙烷氧化反应的催化性能以苯乙烷的氧化反应为模板反应,和离子液体[Bmim][PF6]配合使用,考察了锰卟啉环上取代基引入吸电子的季胺阳离子和氯原子,对分散卟啉环上电子云密度,提高金属卟啉催化活性和稳定性的作用,中性锰卟啉四-(2-正丁基-4-氯咪唑基)锰卟啉(A1)和离子型锰卟啉四-(1,3-二甲基-2-正丁基-4-氯咪唑基)锰卟啉六氟磷酸盐([MnTMBuMimP] [PF6]5)(A2)被用来作为对照实验。与中性的锰卟啉催化剂A1相比,带有四个季胺阳离子的离子型锰卟啉催化剂A2和A3,在对不活泼的苯乙烷的催化氧化反应中,具有更好的催化活性和稳定性。紫外光谱分析进一步证明,以离子液体[Bmim][PF6]为反应溶剂,可以避免锰卟啉A2和A3的μ-氧二聚体的形成,A2和A3中咪唑阳离子的强吸电子作用提高了催化剂A2和A3的抗氧化降解能力(稳定性增强)。实验还发现,与引入卤素原子的方法相比,在卟啉环上引入强吸电子的季胺阳离子是一个更有效的降低卟啉环电子云密度,从而增强锰卟啉抗氧化降解能力的有效手段。同时,与在卟啉环外引入体积大的取代基和在反应体系中加入大量轴向配体的方法相比,使用离子液体作反应溶剂能更好地避免反应过程中形成催化活性低的锰卟啉μ-氧二聚体。但是实验发现酒石酸根抗衡阴离子的引入对锰卟啉的催化活性起消极影响。(二)催化剂B2的合成及其对苯乙烷及其衍生物氧化反应的催化性能考察了离子液体[BPy][BF4]溶剂中,锰卟啉[MnTMPyP]5+为阳离子、磷钨酸根[PW12040]3-为阴离子的离子型化合物B2对苯乙烷的催化氧化反应性能。实验结果表明,磷钨酸根[PW12040]3-本身对苯乙烷的氧化没有贡献,但其能明显改善锰卟啉阳离子[MnTMPyP]5+的抗氧化降解能力,从而有利于催化活性。(三)催化剂C2的合成及其对环辛烯氧化反应的催化性能设计催化剂[MnOBTMPyP][PF6]5 (C2)的目的是期望利用在卟吩环上引入大体积的吸电子的溴原子来进一步分散卟吩环上的电子云密度,提高催化剂的抗氧化降解能力,同时体积大的溴原子给卟吩环的平面结构带来扭曲和空间位阻,也能一定程度上阻止卟啉通过π-π堆积聚合,避免在氧化剂存在下形成催化活性惰性的μ-氧二聚体。实验结果表明,催化剂[MnOBTMPyP][PF6]5 (C2)和催化剂[MnTMPyP][PF6]5(C1)在对环辛烯的环氧化催化过程中,无论在离子液体[BPy][BF4]还是在机溶剂介质中,溴代锰卟啉[MnOBTMPyP] [PF6]5 (C2)的催化活性和稳定性均不如[MnTMPyP][PF6]5(C1)。可能由于卟吩环上引入8个大体积的溴原子,使环张力增大,卟啉环更容易开环降解,无法保证锰卟啉结构的稳定性。更多还原

【Abstract】 In this work a series of ionic metalloporphyrins, including manganese porphyrins, palladium porphyrins and gold porphyrins, were designed and synthesized. Empathically, the ionic manganese porphyrins (A3, B2, and C2) were selected as the model catalysts for alkane/alkene oxidations. The influences, like electron-withdrawing nature of the peripheral groups in the porphyrino ring, the incorporated counter anions, and the use of ionic liquid solvents, on the catalytic performance of the ionic manganese porphyrins were investigated in terms of activity, selectivity, and stability. Compared with the conventional neutral manganese porphyrins for alkane/alkene oxidations in organic solvents, the developed ionic manganese porphyrins dissolved in the similar structured IL solvents were endowed with advantageous activity and stability which depended on many factors including that:1) the IL solvent dually acted as the axial ligands, avoiding the involvement of the imidazole or pyridine (derivatives), which is susceptible to oxidation and then sacrificed by excess oxidant; 2) the ILs based on pyridinium or imidazolium with conjugated features could interact with the super-conjugated porphyrins through p-p interactions, which could inhibit the self-aggregation of the manganese porphyrins itselves, avoid the formation of theμ-oxo MnⅣ-porphyrin dimers, and improve the catalytic activity and stability; 3) the strong electron-withdrawing effect of the cations in the ionic manganese porphyrin could decrease the electron density of porphyrino rings and enhance the ability of manganese porphyrins against the oxidative degradation; 4) The involvement of [PW12O40]3- could further increase the stability of porphyrin cations and thus improve catalytic activity of the catalyst. 1. Synthesis and catalytic performance of A3 for ethylbenzene oxidationFor comparison, the corresponding neutral manganese porphyrin (A1), and the ionic manganese porphyrin (A3) with hexafluorophosphates as counteranions, were synthesized and investigated parallelingly in this study. The ionic manganese porphyrin of A2 and A3 featured with imidazolium cations at four meso-carbons proved to be the more efficient and stable catalysts for the oxidation of the less reactive ethylbenzene in contrast to the neutral A1. The UV-visible spectral analysis further proved that the use of [Bmim]PF6 as the solvent could completely inhibit the formation of the inactiveμ-oxo MnⅣ-porphyrin dimer, and the incorporation of imidazolium units with strong electron-withdrawing effect in ionic A2 and A3 gave rise to the stability against oxidation degradation. This work suggested that the incorporation of quaternary ammonium cations (like imidazolium units) with strong electron-withdrawing nature into porphyrino ring was a more effective strategy to suppress the oxidative degradation and then improve the activity of the manganese porphyrin in contrast of the roles of halides, and that the use of the IL with conjugated nature as the solvent was a very effective strategy to inhibit the formation of the inactiveμ-oxo MnⅣ-porphyrin dimer, in contrast to the means like introducing sterically bulky substituents in the porphyrino ring, or using excess N-containing axial ligands. Hoverer, the role of introducing tartrates as the corresponding counter anions was found to be negligible to the catalytic performance of the ionic manganese porphyrin2. Synthesis and catalytic performance of B2 for ethylbenzene (derivatives) oxidationsWithout involvement of the auxiliary axial ligands, the ionic compound B2 combined with the cationic Mn-porphyrin ([MnTMPyP]5+) and the a-Keggin type phosphotungstate ([PW12O40]3-), prove to be an efficient catalyst in room temperature IL of [BPy]BF4 for ethylbenzene oxidation in terms of activity and stability, in comparison to B1 only possessing the catalytic site of [MnTMPyP]5+ alone. The contribution of [PW12O40]3-anions to the activation of ethylbenzene proved to be negligible, but to the stability of [MnTMPyP]5+ against the oxidative degradation was of significance.3. Synthesis and catalytic performance of C2 for cyclooctene epoxidationThe incorporation of Br atoms with bulky size and strong electron-withdrawing nature onβ-positions of the porphine ring was aimed to further decrease the electron density on the porphine ring, which supposedly could give rise to the catalyst stability against oxidative degradation. The distortion of the porphine ring and the increased steric hindrance with introduction of Br atoms could inhibit the manganese porphyrin aggregation through p-p interactions, and avoid the formation ofμ-oxo MnⅣ-porphyrin dimers. However, catalytic experiments and the UV-visible spectral analysis proved that C2was a less efficient and stable catalyst for the epoxidation of cyclooctene in contrast to C1, which did not possess any Br atom. Probably the introduction of eight bulky Br atoms onβ-positions increased the porphine ring’s tension which could made the porphyrin ring structure collapse more easily under oxidative environment.更多还原