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Controlled Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
Reactions in this class of ROP are distinct from those previously considered, both in the fact that the mechanism does not involve ionic intermediates and in the creation of all-carbon backbones (albeit ones that contain double bonds). An olefin metathesis reaction is one in which two carbon–carbon double bonds are removed and two new ones are created. Generically, this can be represented by the following scheme, whereby R1HC = CHR2 reacts with R3HC = CHR4 to produce, for example, R1HC = CHR3 and R2HC = CHR4 .
Functional Bio-Based Lubricant Base Stocks
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Mary Moon, Cyril A. Migdal, Edward Brian Fox, David L. Stonecipher
The efPAO chemistry relies on the use of the well-known Grubbs catalyst technology for olefin metathesis [31,32]. During olefin metathesis, two alkene molecules undergo cycloaddition together while associating with a catalyst; then, they exchange substituents when disassociating from the catalyst. Homogeneous Grubbs catalysts, i.e., ruthenium(II) carbenoid complexes, are used to prepare olefins that are then used to synthesize efPAOs (Figure 25.7). In contrast, most commercial-scale syntheses use heterogeneous catalysts, typically activated metal halides on inert supports such as alumina [69]. Metathesis synthesis.
Ionic Chain-Reaction and Complex Coordination Polymerization (Addition Polymerization)
Published in Charles E. Carraher, Carraher's Polymer Chemistry, 2017
Chauvin, Grubbs, and Schrock won the 2005 Nobel Prize for developing metathesis reactions. Olefin metathesis is a catalytically induced reaction wherein olefins, such as cyclobutene and cyclopentene, undergo bond reorganization, resulting in the formation of so-called polyalkenamers. Since the resulting polymers contain double bonds that can be subsequently used to introduce crosslinking, these materials have been used to produce elastomeric materials as well as plastics. Transition metal catalysts are required for these reactions. Catalysts include typical Natta–Ziegler types and other similar catalysts–cocatalysts combinations. The reactions can be run at room temperature and the stereoregularity controlled through the choice of reaction conditions and catalysts. For instance, the use of a molybdenum-based catalyst with cyclopentene gives the cis product (5.62), whereas the use of a tungsten-based catalyst gives the trans product (5.61).
New latent metathesis catalysts equipped with exchangeable boronic ester groups on the NHC
Published in Journal of Coordination Chemistry, 2018
Revannath Sutar, Danielle Butilkov, N. Gabriel Lemcoff, Ofer Reany
Ruthenium-based catalysts have revolutionized olefin metathesis, which has become one of the most robust and useful reactions for carboncarbon bond formation in total synthesis of natural products, macromolecules, and medicinal chemistry [1, 2]. The introduction of neutral N-heterocyclic carbene (NHC) ligands [3–7] and chelated benzylidenes [8–12] to the ruthenium metal center offers multiple variations to the catalytic properties and thus significantly enhanced the scope of this family of catalysts. Owing to the numerous possibilities of structural modifications by synthetic manipulations, a variety of new symmetric and non-symmetric NHC ligands have been developed and utilized to achieve desired catalytic properties [13–15].
Metathesis reactions with a low-cost spinning disk system
Published in Green Chemistry Letters and Reviews, 2019
Shahid A. Kazi, Peter Clark, Eva. M. Campi, W. Roy Jackson, Milton T. W. Hearn
Olefin metathesis is a well-known, convenient and mild transformation method widely utilized in organic synthesis, whereby carbon–carbon double bonds are converted or redistributed into new products via rupture and reformation. The key step in this process is the reaction between an olefin and a transition metal alkylidene (carbene) complex in a [2 + 2] fashion to generate an unstable metallocyclobutane intermediate. This intermediate can either revert back to the starting materials or open to afford a new carbene and hence produce a new olefin. If this process is repeated then eventually an equilibrium mixture of olefins is produced. Metathesis chemistry is important in the petrochemical and oleo-chemical industry. Unlike petrochemicals, oleo-chemicals are, however, derived from renewable resources, and have improved biodegradability and lower sulphur contents. In terms of oleo-chemical applications, metathesis chemistry has been used (13) to transform natural fats and oils into consumable products, such as lubricants, liquid fuels, paints, surface coatings and surfactants. Metathesis chemistry is also important in the manufacture of other bulk chemicals and polymers (14,15) and has numerous applications in the synthesis of chemical and pharmaceutical lead compounds (16–18). With traditional batch approaches, overall E-factors and other measures of green chemical efficiencies at laboratory scale can, however, be high for ring closing metathesis (RCM) reactions due to the high dilution that is often required, leading to large volumes of solvent waste and related high operational cost. It was anticipated that these constraints could be offset through the scaled-up use of SDR technologies validated at the proof-of-principle stage with smaller laboratory systems.