Berkson Zachariah J, Bernhardt Moritz, Schlapansky Simon L, Benedikter Mathis J, Buchmeiser Michael R, Price Gregory A, Sunley Glenn J, Copéret Christophe
Department of Chemistry and Applied Bioscience, ETH Zürich, Vladimir-Prelog-Weg 2, Zürich 8093, Switzerland.
Institute of Polymer Chemistry, Universität Stuttgart, Pfaffenwaldring 55, Stuttgart 70569, Germany.
JACS Au. 2022 Mar 9;2(3):777-786. doi: 10.1021/jacsau.2c00052. eCollection 2022 Mar 28.
Molecularly defined and classical heterogeneous Mo-based metathesis catalysts are shown to display distinct and unexpected reactivity patterns for the metathesis of long-chain α-olefins at low temperatures (<100 °C). Catalysts based on supported Mo oxo species, whether prepared via wet impregnation or surface organometallic chemistry (SOMC), exhibit strong activity dependencies on the α-olefin chain length, with slower reaction rates for longer substrate chain lengths. In contrast, molecular and supported Mo alkylidenes are highly active and do not display such dramatic dependence on the chain length. State-of-the-art two-dimensional (2D) solid-state nuclear magnetic resonance (NMR) spectroscopy analyses of postmetathesis catalysts, complemented by Fourier transform infrared (FT-IR) spectroscopy and molecular dynamics calculations, evidence that the activity decrease observed for supported Mo oxo catalysts relates to the strong adsorption of internal olefin metathesis products because of interactions with surface Si-OH groups. Overall, this study shows that in addition to the nature and the number of active sites, the metathesis rates and the overall catalytic performance depend on product desorption, even in the liquid phase with nonpolar substrates. This study further highlights the role of the support and active site composition and dynamics on activity as well as the need for considering adsorption in catalyst design.
分子定义的和经典的非均相钼基复分解催化剂在低温（<100°C）下对长链α-烯烃的复分解反应表现出独特且意想不到的反应模式。基于负载型钼氧物种的催化剂，无论是通过湿浸渍法还是表面有机金属化学（SOMC）制备的，其活性都强烈依赖于α-烯烃的链长，底物链长越长反应速率越慢。相比之下，分子型和负载型钼亚烷基催化剂具有高活性，并且对链长没有如此显著的依赖性。对复分解后催化剂进行的最先进的二维（2D）固态核磁共振（NMR）光谱分析，辅以傅里叶变换红外（FT-IR）光谱和分子动力学计算，证明负载型钼氧催化剂活性降低与内烯烃复分解产物由于与表面Si-OH基团相互作用而产生的强吸附有关。总体而言，这项研究表明，除了活性位点的性质和数量外，复分解速率和整体催化性能还取决于产物解吸，即使在含有非极性底物的液相中也是如此。这项研究进一步强调了载体和活性位点组成及动力学对活性的作用，以及在催化剂设计中考虑吸附作用的必要性。
