Interplay of solvent and metal identity determines rates and stereoselectivities in M(IV)-Beta-catalyzed intramolecular Prins cyclization of citronellal  

M(IV)-Beta分子筛催化香茅醛分子内Prins环化:溶剂与金属中心共同决定活性及立体选择性

作　　者：Shugang Sun Yang Zhu Letian Hong Xuebing Li Yu Gu Hui Shi 孙书钢;朱洋;洪乐天;李学兵;顾宇;施慧(扬州大学化学化工学院,江苏扬州225009;宁波工程学院,材料与化学工程学院,浙江宁波315211)

机构地区：[1]School of Chemistry and Chemical Engineering,Yangzhou University,Yangzhou 225009,Jiangsu,China [2]School of Materials and Chemical Engineering,Ningbo University of Technology,Ningbo 315211,Zhejiang,China

出　　处：《Chinese Journal of Catalysis》2024年第11期233-246,共14页催化学报(英文)

基　　金：国家自然科学基金(22072128,22179134,22308301).

摘　　要：Zeolites of *BEA framework topology containing isomorphously substituted Lewis acidic metal centers catalyze the liquid-phase intramolecular Prins cyclization of citronellal with outstanding catalytic activity and (dia-)stereoselectivity to the commercially most valuable product, isopulegol (IPL). Effects of the metal-center identity and solvent type were occasionally noted, yet without systematic studies hitherto reported. Here, characteristic dependences of catalytic activities and stereoselectivities on solvent and metal identity were uncovered over four M(IV)-Beta catalysts (M = Sn, Ti, Zr and Hf) in four distinct solvents (i.e., acetonitrile, tert-butanol, cyclohexane and n-hexane). Zr^(-) and Hf-Beta were the most active in acetonitrile and the most selective (> 90% to IPL) in tert-butanol, though their activities were generally lower than Ti- and Sn-Beta in solvents other than acetonitrile. By comparison, Ti-Beta was inferior to other catalysts in terms of both activity and IPL selectivity (as previously shown) in acetonitrile but became the most active in other solvents, with markedly increased IPL selectivity from 60% to 70%?80%. Combining multiple site discrimination and quantification techniques, turnover frequencies were determined for the first time in this reaction;such site-based activities, coupled with comprehensive kinetic interrogations, not only enabled a rigorous comparison of catalytic activities across M-Beta catalysts but also provided deeper insights into the free energy driving forces as solvent and metal identity are varied. The activity and selectivity trends, as well as those for the adsorption and intrinsic activation parameters are caused by solvent co-binding at the active site (acetonitrile and tert-butanol) and less quantifiable crowding effects (cyclohexane) due to the limited pore space and the need to accommodate relatively bulky reactant-derived moieties. This work exemplifies how the interplay of metal identity and solvent determines the reactivities and selectivities in Lew右旋香茅醛经历分子内Prins环化, 可生成左旋异蒲勒醇(IPL), 其加氢产物L-薄荷醇具有很高的经济价值. 具有Lewis酸性金属中心的BEA型分子筛(M-Beta)对香茅醛Prins环化反应表现出优异的活性和蒲勒醇化学选择性, 以及较高的IPL立体选择性. 然而, 有关金属中心和溶剂类型对这类材料在该反应中催化性能的影响尚缺乏系统研究. 本文通过考察除金属中心类型外其他性质类似的四种M(IV)-Beta (M = Sn, Ti, Zr, Hf)催化剂以及四种分子尺寸和极性各异的溶剂(乙腈、叔丁醇、环己烷及正己烷)影响, 阐明了催化活性和立体选择性对于金属中心和溶剂类型的依赖关系.Ti-Beta在乙腈溶剂中活性和IPL选择性最低, 与以往报道一致, 但本工作发现Ti-Beta在叔丁醇、环己烷、正己烷溶剂中活性均高于其他三种M-Beta催化剂;此外, Ti-Beta上的IPL立体选择性在三种溶剂中相较乙腈溶剂也大大提升(从60%增至70%‒80%). Zr-Beta和Hf-Beta在乙腈溶剂中活性最高, 在叔丁醇中IPL立体选择性最高(> 90%), 但在除乙腈外的溶剂中两者活性普遍低于Ti-和Sn-Beta. 通过吡啶、氘代乙腈蒸气吸附的红外光谱, 结合环己胺在反应条件下原位滴定的策略, 测定出该反应的转化频率, 从而详细比较M-Beta催化剂的本征活性. 动力学拟合分析进一步得出各催化剂和溶剂体系中香茅醛吸附的平衡常数和环化决速步的本征速率常数, 并量化了反应自由能驱动力在不同金属中心和溶剂中的差异. 催化活性和关键动力学/热力学参数(本征速率常数和吸附平衡常数)结果表明, 不同溶剂中M-Beta的活性顺序截然不同, 从而否定了金属中心Lewis酸强度作为反应性唯一描述符的猜想. 此外, 四种M-Beta的本征速率常数体现出不同幅度的溶剂效应,其中Sn-Beta受溶剂性质的影响明显小于其他三种催化剂. 对不同M-Beta逐一分析表明, 在最常用的乙腈溶剂�

关 键 词：CITRONELLAL Prins cyclization Carbonyl-ene reaction Solid acid Lewis acidic zeolite Solvent effect 

分 类 号：O643.3[理学—物理化学]