User:Benjah-bmm27/degree/3/PGP

=Organometallic Chemistry and Homogeneous Catalysis 2, PGP=

Feedstocks

 * Synthesis gas
 * → aldehydes from alkenes, by Rh catalysis (hydroformylation)
 * → methanol by Cu catalysis
 * → alkanes and alkenes by Fe catalysis (Fischer-Tropsch)


 * Methanol
 * → alkanes, alkenes, aromatics by zeolite catalysis
 * → formaldehyde and ethers, e.g. MTBE
 * → acetic acid by Ir catalysis (Cativa process)

Hydroformylation
Hydroformylation is formally the addition of a molecule of formaldehyde across the C=C double bond of an alkene.


 * R2C=CR2 + H–CHO → R2CH–CR2CHO

Formaldehyde isn't actually used. Synthesis gas (a mixture of hydrogen and carbon monoxide, H2 + CO) is used instead.

Regioselectivity
Hydroformylation of monosubstituted alkenes (vinyl alkanes, if you like: RHC=CH2) can give two possible regioisomers: linear (n) and branched (iso)
 * The regioselectivity of a particular hydroformylation reaction is expressed as the ratio of linear to branched, i.e. n : iso
 * Example: hydroformylation of propene can yield both butyraldehyde (linear) and isobutyraldehyde (branched)
 * Butyraldehyde is a precursor for two very important molecules
 * hydrogenation of butyraldehyde gives n-butanol, an important industrial solvent (4 Mt/year, industry prefers it to EtOH, which is more of a fire risk and is heavily taxed)
 * aldol reaction followed by hydrogenation gives 2-ethylhexanol (2Mt/year, used to make bis(2-ethylhexyl) phthalate, the most important phthalate plasticizer for polymers)

Cobalt carbonyl catalysis of hydroformylation

 * Cobalt added as either dicobalt octacarbonyl, Co2(CO)8, or as a cobalt(II) salt
 * Synthesis gas is a good reducing agent, and rapidly reduces Co(II) to Co2(CO)8
 * Co2(CO)8 + H2 → 2HCo(CO)4
 * HCo(CO)4 is cobalt tetracarbonyl hydride
 * Co(I), d8, 18 e, trigonal bipyramidal molecular geometry
 * volatile
 * unstable above 20 °C unless an atmosphere of CO is present
 * Co catalysis requires high pressures of CO
 * Mechanism begins with the precatalyst HCo(CO)4
 * 1) Dissociation of a CO ligand generates HCo(CO)3: Co(I), d8, 16 e, vacant coordination site
 * 2) Coordination of alkene generates HCo(CO)3(alkene): Co(I), d8, 18 e, coordinatively saturated
 * 3) Migration of hydride from Co to alkene C generates Co(CO)3(alkyl): Co(I), d8, 16 e, coordinatively unsaturated
 * 4) Coordination of a new CO ligand to Co gives Co(CO)4(alkyl): Co(I), d8, 18 e, coordinatively saturated
 * 5) Migratory insertion of alkyl (formally R−) to one of the CO ligands gives Co(CO)3(acyl): Co(I), d8, 16 e, coordinatively unsaturated
 * 6) Oxidative addition of H2 generates H2Co(CO)3(acyl): Co(III), d6, 18 e, coordinatively saturated, octahedral molecular geometry
 * 7) Reductive elimination of acyl hydride (aldehyde!) regenerates HCo(CO)3

Acetic acid synthesis by methanol carbonylation

 * MeOH + CO → MeCO2H
 * Catalysed by {Co, Rh, Ir}-iodine species
 * BASF, 1960: Co-I
 * Monsanto process, 1970: Rh-I
 * Cativa process, 2000: Ir-Ru-I

MMA synthesis

 * Methyl methacrylate for poly(methyl methacrylate) production