高效Z-选择性钌卡宾烯烃复分解催化剂的合成与催化研究

The design and synthesis of Z-selective olefin metathesis catalyst is one of the most popular topics with challenges in the field of olefin metathesis currently. People have found that ruthenium carbene complexes bearing a benzene dithiol chelating ligand show Z- selectivity and good functional group tolerance. All these remarkable features enable it to be of good prospects in application. However, this kind of catalysts decompose very fast during the reaction process due to its thermal instability, which significantly limits its application in the substrates having bulky substitutions, or electron deficient olefins. Its reactivity and stereo selectivity has yet to be further improved. In this proposal, we expect to improve the stability of this kind of catalysts by raising steric hindrance effect of the sulphur ligand. The nucleophilicity of sulphur will be significantly reduced due to bulky substitutions, and thus the inner decomposition reaction barrier of these catalysts will be increased. The ruthenium center having a trigonal bipyramidal coordination structure would be more close to the coordination structure of the key transition state if the repulsion between the benzene dithiol ligand and NHC ligand were increased by bulky substitution of the dithiol ligand, which will improve the activity of the ruthenium catalyst. The critical transition state will have a more compact space and congestion environment by bulky substitution of the dithiol ligand, the orientation of the substituted groups on the olefin will be strictly controlled in the key transition state, and thus improving the Z-selectivity of the catalyst. Replacing a sulphur in the dithiol ligand by an oxygen, a lower nucleophilic atom, the internal decomposition mechanism of these catalysts will be eliminated, the reactivity as well as the stability of these catalysts will be significantly improved. This research will greatly improve the stability, the catalytic activity, and the Z-selectivity of ruthenium carbene catalyst containing chelating ligand, and expand the application scope. It also provides theory basis for the design of other new Z- selective olefin metathesis catalysts.

Z-选择性烯烃复分解催化剂的设计与合成是当前烯烃复分解领域中最具有挑战性的热门研究课题。含苯二硫酚螯合配体的钌卡宾展现出一定的Z-选择性和良好的官能团适用性，具有良好的应用前景。然而此类催化剂热稳定差，活性、立体选择性也有待进一步提高。本课题期望通过提高双硫配体的空间阻碍作用，显著降低硫的亲核性，提高此类催化剂内在分解反应势垒，提高催化剂的稳定性；通过增加硫酚配体与氮杂环卡宾配体间的空间排斥力，使钌中心拥有接近过渡态的三角双锥型配位结构，从而提高催化活性；通过大空间阻碍作用，使关键过渡态具有更为紧凑的空间环境，提高Z-选择性。通过低亲核性的氧取代双硫酚中的一个硫，可以消除双硫配体催化剂的内在分解机制，提高催化剂的稳定性、反应活性。此项研究可大幅提高含螯合配体的钌卡宾催化剂的稳定性、催化活性、Z-选择性，拓展其适用范围，并为其它新型Z-选择性烯烃复分解催化剂的设计、合成提供理论研究依据。

本课题针对现有的双硫螯合型Z-选择性钌卡宾烯烃复分解催化剂的稳定性不好，催化效率较低等问题，试图设计、合成一类具有大空阻取代基、缺电子的双齿螯合钌卡宾催化剂，期望通过大空阻取代基、缺电子螯合配体提高催化剂的热稳定性、催化活性以及Z-选择性。我们合成了一系列不同邻位取代的2-巯基苯酚及其相应的钌卡宾配合物，发现催化剂的稳定性与取代基有关，含有邻异丙基取代基的钌卡宾配合物稳定性最好。尽管转化率较低，此类催化剂在催化端烯与(Z)-丁-2-烯-1,4-二醇的交叉复分解反应中展示较高的Z-选择性。加入AlCl3助催化剂可以显著提高反应转化率，并逆转为E-选择性。我们巧妙地利用邻碳硼烷的空间和电子效应，设计合成1,2-二巯基-1,2-邻碳硼烷配体及其相应的钌卡宾配合物。发现该催化剂具有较高的热稳定性，可高效率催化降冰片烯类化合物的开环易位聚合反应生成Z-结构的聚合物；可催化端烯与(Z)-丁-2-烯-1,4-二醇的交叉复分解反应中展示高Z-选择性，且产率有所提升。为了考察螯合配体中巯基开合角对催化活性的影响，设计合成了1,8-二巯基萘配体及其钌卡宾配合物。发现相对于1,2-二巯基苯螯合钌卡宾催化剂，此类催化剂的稳定性、催化活性得以提升。另外，合成了3,4-二巯基环丁-3-烯-1,2-二酮配体及其相应的钌卡宾配合物，发现配体的缺电子性质可以降低钌中心的电子密度，提高催化剂的热稳定性及催化活性。所合成催化剂可在室温下高效率地催化降冰片烯和1,5-环辛二烯的开环移位聚合反应（ROMP），且产物具有较高的Z/E比；可催化端烯与(Z)-丁-2-烯-1,4-二醇的交叉复分解反应中展示高Z-选择性，且产率较其它催化剂有大幅提升。此外，我们还发展了一种螯合基团辅助铑催化芳基乙烯与酮的烷基交换反应，在碳-碳键活化方面具有较大的理论研究意义；建立了一种螯合辅助镍催化芳基硼酸酮加成制备叔醇的反应，可简洁、高效的叔醇类化合物，具有良好的应用前景。