†Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
‡Exploratory Catalysis Research, UOP LLC, a Honeywell Company, 25 East Algonquin Road, Des Plaines, Illinois 60017, United States.
J Am Chem Soc. 2015 Jun 3;137(21):6770-80. doi: 10.1021/jacs.5b03254. Epub 2015 Apr 30.
Organozirconium complexes are chemisorbed on Brønsted acidic sulfated ZrO2 (ZrS), sulfated Al2O3 (AlS), and ZrO2-WO3 (ZrW). Under mild conditions (25 °C, 1 atm H2), the supported CpZrMe3, CpZrBz3, and CpZrPh3 catalysts are very active for benzene hydrogenation with activities declining with decreasing acidity, ZrS ≫ AlS ≈ ZrW, arguing that more Brønsted acidic oxides (those having weaker corresponding conjugate bases) yield stronger surface organometallic electrophiles and for this reason have higher benzene hydrogenation activity. Benzene selective hydrogenation, a potential approach for carcinogenic benzene removal from gasoline, is probed using benzene/toluene mixtures, and selectivities for benzene hydrogenation vary with catalyst as ZrBz3(+)/ZrS(-), 83% > CpZrMe2(+)/ZrS(-), 80% > CpZrBz2(+)/ZrS(-), 67% > CpZrPh2(+)/ZrS(-), 57%. For CpZrBz2(+)/ZrS(-), which displays the highest benzene hydrogenation activity with moderate selectivity in benzene/toluene mixtures. Other benzene/arene mixtures are examined, and benzene selectivities vary with arene as mesitylene, 99%, > ethylbenzene, 86% > toluene, 67%. Structural and computational studies by solid-state NMR spectroscopy, XAS, and periodic DFT methods applied to supported CpZrMe3 and CpZrBz3 indicate that larger Zr···surface distances are present in more sterically encumbered CpZrBz2(+)/AlS(-) vs Cp*ZrMe2(+)/AlS(-). The combined XAS, solid state NMR, and DFT data argue that the bulky catalyst benzyl groups expand the "cationic" metal center-anionic sulfated oxide surface distances, and this separation/weakened ion-pairing enables the activation/insertion of more sterically encumbered arenes and influences hydrogenation rates and selectivity patterns.
有机锆配合物被化学吸附在 Brønsted 酸性硫酸化的 ZrO2（ZrS）、硫酸化的 Al2O3（AlS）和 ZrO2-WO3（ZrW）上。在温和的条件下（25°C，1 atm H2），负载的 CpZrMe3、CpZrBz3 和 CpZrPh3 催化剂对苯加氢具有很高的活性，活性随着酸性的降低而降低，ZrS＞AlS≈ZrW，这表明更多的 Brønsted 酸性氧化物（那些具有较弱的相应共轭碱）产生更强的表面有机金属亲电体，因此具有更高的苯加氢活性。苯选择性加氢是从汽油中去除致癌苯的一种潜在方法，我们使用苯/甲苯混合物进行了探测，苯加氢的选择性随催化剂而变化，ZrBz3(+)/ZrS(-)为 83%，CpZrMe2(+)/ZrS(-)为 80%，CpZrBz2(+)/ZrS(-)为 67%，CpZrPh2(+)/ZrS(-)为 57%。对于 CpZrBz2(+)/ZrS(-)，它在苯/甲苯混合物中显示出最高的苯加氢活性和中等选择性。还考察了其他的苯/芳烃混合物，苯的选择性随芳烃而变化，间二甲苯为 99%，乙基苯为 86%，甲苯为 67%。通过固态 NMR 光谱、XAS 和周期性 DFT 方法对负载的 CpZrMe3 和 CpZrBz3 进行的结构和计算研究表明，在空间位阻较大的 CpZrBz2(+)/AlS(-)中，Zr···表面距离较大。XAS、固态 NMR 和 DFT 数据的综合结果表明，庞大的催化剂苄基基团扩大了“阳离子”金属中心-阴离子硫酸化氧化物表面的距离，这种分离/减弱离子对使更具空间位阻的芳烃的活化/插入成为可能，并影响加氢反应的速率和选择性模式。
