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PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Chem 1140; Catalysis• General Principles• Ziegler-Natta Olefin Polymerization• Mechanism of Hydrogenation with Wilkinson’s Catalyst• Asymmetric HydrogenationCatalysis•Catalysts increase reaction rate without themselves being changed•Can accelerate a reaction in both directions•Do not affect the state of equilibrium of reaction–simply allow equilibrium to be reached fasterActivation energy•Molecules must be activated before they can undergo a reaction–Reactants must absorb enough energy from surroundings to destabilize chemical bonds (energy of activation)•Transition state–Intermediate stage in reaction where the reactant molecule is strained or distorted but the reaction has not yet occurredActivation energy•A catalyst lowers the energy of activation by:–Forcing molecules into conformations that favor the reaction•I.e. the catalyst may re-orientate molecules•Change in free energy is identical to uncatalyzed reaction: the catalyst does not change the thermodynamic equilibrium!Activation energy•Sometimes catalysts cause one large energy barrier to be replaced by two smaller ones–Reaction passes through intermediate stageHow do you correlate rate constants to activation barriers?Arrhenius Equationk (rate constant) = A e(-E/RT)where A = “frequency factor”, and e(-E/RT) = activation energyEyring Absolute Rate Theoryk (rate constant) = [kbT/h]e(-G*/RT) = [kbT/h]e(S*/RT) e(-H*/RT)Energy and TimeG‡reactanttransition stateproductGreleasedkforwardZiegler-Natta Catalysis of Ziegler-Natta Catalysis of Alkene PolymerizationAlkene PolymerizationA typical Ziegler-Natta catalyst is a combination A typical Ziegler-Natta catalyst is a combination of TiClof TiCl44 and (CH and (CH33CHCH22))22AlCl, or TiClAlCl, or TiCl33 and and (CH(CH33CHCH22))33Al.Al.Many Ziegler-Natta catalyst combinations Many Ziegler-Natta catalyst combinations include a metallocene.include a metallocene.Ziegler’s Discovery•1953 K. Ziegler, E. Holzkamp, H. Breil & H. Martin•Angew. Chem. 67, 426, 541 (1955); 76, 545 (1964).Al(Et)3+NiCl2Ni100 atm110 CCH3CH2CH=CH2+ +AlCl(Et)2+ Ni(AcAc) Same result+ Cr(acac) White Ppt. (Not reported by Holzkamp)+ Zr(acac) White Ppt. (Eureka! reported by Breil)TiCl41 atm20-70 CAl(Et)3+CH2CH2"linear"Mw = 10,000 - 2,000,000Natta’s Discovery•1954 Giulio Natta, P. Pino, P. Corradini, and F. Danusso•J. Am. Chem. Soc. 77, 1708 (1955) Crystallographic Data on PP•J. Polym. Sci. 16, 143 (1955) Polymerization described in FrenchCH3TiCl3Al(Et)2ClCH3CH3CH3CH3CH3VCl4Al(iBu)2ClCH3CH3OinCH3- 78 CCH3CH3IsotacticSyndiotacticZiegler and Natta won Nobel Prize in 1963Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationAl(CHAl(CH22CHCH33))33++TiClTiCl44ClAl(CHClAl(CH22CHCH33))22++CHCH33CHCH22TiClTiCl33Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationAl(CHAl(CH22CHCH33))33++TiClTiCl44ClAl(CHClAl(CH22CHCH33))22++CHCH33CHCH22TiClTiCl33HH22CCCHCH22CHCH33CHCH22TiClTiCl33++CHCH33CHCH22TiClTiCl33HH22CCCHCH22Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationCHCH33CHCH22TiClTiCl33HH22CCCHCH22TiClTiCl33CHCH33CHCH22CHCH22CHCH22Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationTiClTiCl33CHCH33CHCH22CHCH22CHCH22TiClTiCl33CHCH33CHCH22CHCH22CHCH22HH22CCCHCH22Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationTiClTiCl33CHCH33CHCH22CHCH22CHCH22HH22CCCHCH22TiClTiCl33CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22Mechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationMechanism of Coordination PolymerizationTiClTiCl33CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22HH22CCCHCH22etc.etc.General Composition of Catalyst SystemGroup I – III MetalsTransition Metals AdditivesAlEt3TiCl4H2Et2AlClEtAlCl2TiCl3MgCl2 Support O2, H2Oi-Bu3Al VCl3, VoCL3,V(AcAc)3R-OHPhenolsEt2MgEt2ZnTitanocene dichlorideTi(OiBu)4R3N, R2O, R3PAryl estersEt4Pb (Mo, Cr, Zr, W, Mn, Ni)HMPA, DMFR C CHMeXX+Al OCH3* *nCH3Al:Zr = 1000Me = Ti, Zr, HfLinear HD PEActivity = 107 g/mol ZrAtactic polypropyleneActivity = 106 g/mol ZrKaminsky Catalyst SystemW. Kaminsky et.al. Angew. Chem. Eng. Ed. 19, 390, (1980); Angew. Chem. 97, 507 (1985)Methylaluminoxane: the Key CocatalystAl(CH3)3+H2Otoluene0 CAl OCH3* *nn = 10-20OAlAlAlCH3OOOAlOAlOAlAlCH3CH3Proposed structureMAONature of active catalystTransition metal alkylationIonization to form active sitesMAONoncoordinating Anion, NCACp2MeXX+Al OCH3* *nCp2MeCH3X+Al OCH3AlXOmCp2MeCH3+Al OCH3AlXOmXAlkene Hydrogenation with Wilkinson’s CatalystCO2MeH2cat. RhCl(PPh3)3H2cat. PtO2CO2MeCO2Me96:449:26MechanismPPh3Rh HPPh3ClHPPh3Rh HPPh3ClHRRHHcoordinationRmigratoryinsertionreductiveeliminationoxidativeaddition-PPh3+PPh3[RhCl(PPh3)2]RhCl(PPh3)3H HPPh3Rh HPPh3HClRR'R'R'R'Enantiomerically Enriched PhosphinesPPh2PPh2HOOHDIOP**PPh2PPh2**CHIRAPHOSDIPAMPPHPPhOMePhPh**NPPh2PPh2O OBPPM**PPh2PPh2BINAPP PRRRRDuPHOSPPRRRRBPEAsymmetric HydrogenationCO2MeNHAcR'RH2Me BPE RhorDuPHOS RhMe90 psi, PhH96-99% eeCO2MeRR'NHAcCO2HR1R3R2H296-99% eeCO2HR3R2R1CO2HMeO97% ee (Naproxen)NHOCO2HR3SiOH H74% de (Thienamycin)Me Me H 91H Me 87H Me Ph 85Ph H H 92H HOCH2 Me 93H CH3 COOCH2CMe 95R1R2R3eeRu(OCOR)2 (binap)Asymmetric HydrogenationMechanism: Halpern, J. Science 1982, 217, 401-407.PRhSP SNHOPhMeO2Cequilibriummust be fast for high eemajork'k'-1MeO2C NHORhLLPhminor<5%diastereoisomersfastH2k2rate limitingstepvery slowH2k'2NHCO2MeORhLLPh>95%k'-1k'Mechanism: Halpern, J. Science 1982, 217, 401-407.majorMeO2C NHORhLLPhminor<5%diastereoisomersfastH2k2rate


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Pitt CHEM 1140 - Catalysis

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