Heterogeneous catalysis (C9981) Lecture 10 Olefin Metathesis styskalik@chemi.muni.cz styskalik.sci.muni.cz Olefin metathesis • “Two dancing couples exchange their partners” CH2=CH2 + CH3−CH=CH−CH3 CH3−CH=CH2 + CH3−CH=CH2 Olefin metathesis • 1931: Ethylene and 2-butenes found as products of propene heating at 852 °C • 1956−1964: W(CO)6 and Mo(CO)6 supported on alumina for olefin metathesis • 1964: First metal alkylidene complex; Cyclopentene polymerization • Nobel prize in 2005 Richard R. Schrock 1945 Robert H. Grubbs 1942 - 2021 Yves Chauvin 1930 - 2015 Olefin Metathesis • Homogeneous catalysts = metal alkylidene complexes • Grubbs catalysts: Ru based, 1st, 2nd, and 3rd generation P(Cy)3 = tricyclohexylphosphine Olefin Metathesis • Homogeneous catalysts = metal alkylidene complexes • Schrock catalysts: Mo based Olefin Metathesis • Homogeneous catalysts: metal alkylidene complexes – Transition metals Ta, W, Mo, Ru – α-carbon in metal alkylidene complexes is nucleophilic – Bulky ligand (i.e., tricyclohexylphosphine) cannot bind strongly to the metal due to steric reasons – Bulky ligand easily leaves and active species is formed (no. e−?) J. AM. CHEM. SOC. 2006, 128, 16048-16049 Olefin Metathesis • Homogeneous catalysts: metal alkylidene complexes form metallacycles (metallacyclobutane) upon reaction with alkene • Metallacyclobutanes isolated for the first time in 2005 J. AM. CHEM. SOC. 2006, 128, 16048-16049 Olefin Metathesis • Chauvin’s mechanism: Olefin Metathesis • Chauvin’s mechanism: • “Two dancing couples exchanging their partners, but they need the master of ceremony (i.e., the catalyst) for the exchange… Olefin Metathesis • Chauvin’s mechanism: Olefin Metathesis • Chauvin’s mechanism: Olefin Metathesis • Reversible, equilibrium reaction • “Thermoneutral” • We need something that will push the reaction towards desired products – Ethylene as a gaseous product released – Ring strain in cyclic olefins released (i.e., cyclopentene) – … 1,2 = Metathesis reaction 3 = Alkane dehydrogenation Olefin metathesis OM in industrial processes • The Phillips triolefin process/Olefins conversion technology • The Shell higher olefin process • Ring opening metathesis polymerization: Polynorbornene J.C. Mol / Journal of Molecular Catalysis A: Chemical 213 (2004) 39–45 OM in industrial processes • The Phillips triolefin process/Olefins conversion technology (OCT) • WO3/SiO2 OM catalyst, >260 °C, 30−35 bar • Feedstock = ethylene and butenes, MgO isomerization catalyst • Ethylene can be used as a sole feedstock (first partial dimerization to butenes over Ni-based catalyst) • Millions of tons per year CH2=CH2 + CH3−CH=CH−CH3 CH3−CH=CH2 + CH3−CH=CH2 OM in industrial processes • The Shell higher olefin process (SHOP) • C11−C14 alkenes desired = detergent precursors • Production of higher olefins from ethylene in three steps – Ethylene oligomerization over Ni-based catalyst (C4−C40, evennumbered 1-olefins) and distillation to three fractions: C18 – C18 fractions mixed and isomerized (1-olefins useless!) – MoO3/Al2O3 OM, 100−125 °C, 10 bar = statistical distribution of alkenes (both odd and even-numbered), 10−15 % of desired fraction – 1 500 000 tons per year CH3−CH=CH−CH3 + CH3(CH2)7CH=CH(CH2)9CH3 CH3−CH=CH(CH2)7CH3 + CH3−CH=CH(CH2)9CH3 OM in industrial processes • The Shell higher olefin process (SHOP) 1. Oligomerization 2. Isomerization 3. Metathesis 1. Angew. Chem. Int. Ed. 2013, 52, 12492 – 12496 2. J. Chem. Ed., Volume 65 Number 7 July 1988 OM in industrial processes • Ring opening metathesis polymerization: Polynorbornene • First commercial metathesis polymer (1976) • Performed in air • Norsorex® • Elastomer used in oil spill recovery, sound barrier,… Induction period • Heterogeneous catalysts = metals (Mo, W) supported on silica, alumina, silica-alumina in their oxidized form • Only ~1−2 % of all Mo, W, Re atoms form active sites • Metal alkylidene species have to be created first J. Am. Chem. Soc. 2012, 134, 11462−11473R. R. Schrock Induction period • Heterogeneous catalysts = metals (Mo, W) supported on silica, alumina, silica-alumina in their oxidized form • Only ~1−2 % of all Mo, W, Re atoms form active sites • Metal alkylidene species have to be created first J. Am. Chem. Soc. 2012, 134, 11462−11473 Induction period • Heterogeneous catalysts = metals (Mo, W) supported on silica, alumina, silica-alumina in their oxidized form • Only ~1−2 % of all Mo, W, Re atoms form active sites J. Am. Chem. Soc. 2012, 134, 11462−11473 Induction period • Heterogeneous catalysts = metals (Mo, W) supported on silica, alumina, silica-alumina in their oxidized form • Metal alkylidene species have to be created first https://doi.org/10.1021/acscatal.3c02045 Active sites@Lecture 1 • Active sites are often dynamic: They has to be created first! Supported metal alkylidene species • Heterogeneous catalysts = metals (Mo, W) supported on silica, alumina, silica-alumina in their oxidized form • Metal alkylidene species have to be created first OR • Metal alkylidene single site catalysts Basset, Copéret@Lecture 4: Single site catalysts 1. Angew. Chem. Int. Ed. 2006, 45, 6082 – 6085 2. ChemCatChem 2020, 12, 6067–6075 Single site catalyst@Lecture 4 • Grafting on silica – Detailed knowledge of surface (number of OH groups per nm2) – Rigorous water- and oxygen-free environment LnMXx = Chauvin mechanism and? • Chauvin mechanism expects the order of reaction with respect to propylene to be 1 • Studies show the order of reaction ranging from 0.8 to 1.8 • Additional mechanism? https://doi.org/10.1038/s41586-023-05897-w Chauvin mechanism and? • Chauvin mechanism expects the order of reaction with respect to propylene to be 1 • Studies show the order of reaction ranging from 0.8 to 1.8 • Additional mechanism?