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Alkene isomerization: hydride mechanism

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Alkene isomerization: hydride mechanism

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    1. Alkene isomerization: hydride mechanism

    2. Alkene isomerization: allyl mechanism

    3. Hydroamination: introduction A [2+2]-cycloaddition of the N-H bond to the alkene is forbidden by the high energy difference between p(C=C) and s(N-H) orbitals. Because of the highly negative reaction entropy, the reaction is not favored at high temperatures. The hydroamination reaction is only slightly exothermic or even thermoneutral.

    4. Early transition metals and lanthanides

    5. Late TMs: oxidative amination

    6. Relative rates of olefin insertion into alkyl, amide and alkoxo complexes

    7. Recently discovered reactions of transition-M–heteroatom bonds

    8. Hydroformylation and oxidation of olefins Chapters 16 and 18

    9. Outline Hydroformylation Thermodynamics Mechanism Phosphine-modified catalysts Wacker reaction Monsanto process Katsuki-Sharpless asymmetric epoxidation of allylic alcohols Jacobsen asymmetric epoxidation of olefins Sharpless asymmetric dihydroxylation of olefins

    10. Hydroformylation: Thermodynamics

    11. Mechanism of the Co-catalyzed hydroformylation

    12. Other mechanistic details

    13. Phosphine-modified catalysts Alkylphosphines are strong electron donors and thus dissociation of CO is retarded, leading to more stable, but also slower catalysts. A very effective ligand for Co is a phobane derivative: The reaction is 100 times slower; The selectivity to linear products increases; The catalyst is more stable; The catalyst acquires activity for hydrogenation Order of activity (195 °C, 36 bar) Ph2EtP > PhBu2P > Bu3P > Et3P > PhEt2P > Cy3P Linear : branched ratio: Bu3P > Et3P = PhEt2P = Cy3P = PhBu2P > Ph2EtP For Rh, PPh3 works very well. HRh(CO)L3 complexes are 100 to 1000 times more active than Co complexes and they operate under milder conditions (15 – 25 atm and 80 °C – 120 °C).

    14. Acetic acid and acetyl chemicals Principal application of acetyl chemicals: solvents and vinyl acetate monomer for polymerization. Early production routes (ca 1850s): fermentation or wood distillation (still used in the USA in the mid-1960s). First synthetic route: Hg2+ catalyzed H2O addition to HC=CH to form CH3CHO.

    15. The Wacker reaction: oxidation with O2

    16. Vinyl acetate synthesis Overall yields: 90 – 95% based on both ethylene and acetic acid. Homogeneous process was abandoned due to corrosion associated with the presence of acetic acid. Heterogeneous process uses PdCl2 / CuCl2 / C or PdCl2 / alumina.

    17. Monsanto carbonylation of methanol

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