Catalytic applications

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Catalytic applications
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Basic Chemical Concepts
1 The Metal 1.1 Oxidation State and
Electron Count 1.2 Coordinative
Unsaturation 2 Important Properties of Ligands
2.1 CO, R2CCR2, PR3, and H- as Ligands
2.2 Alkyl, Allyl, and Alkylidene Ligands 3
Important Reaction Types 3.1 Oxidative
Addition and Reductive Elimination 3.2
Insertion Reactions 3.3 b-Hydride
Elimination 3.4 Nucleophilic Attack on a
Coordinated Ligand 4 Energy ConsiderationsThermo
dynamics and Kinetics 5 Catalytic Cycle and
Intermediates 5.1 Kinetic Studies 5.2
Spectroscopic Studies 5.3 Model Compounds
and Theoretical Calculations
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The Metal
1.1 Oxidation State and Electron Count
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• 1.2 Coordinative Unsaturation
• When the electron count is lt 18, the metal
  complex is often classified as coordinatively
  unsaturated.
• RhCl(PPh3)3 is coordinatively unsaturated.
• RhH(CO)(PPh3)3 and Co(CO)4- are coordinatively
  saturated.
• Cp2Zr(THF)(CH3) is also coordinatively
  unsaturated because of facile
• displacement of weakly bound solvent molecule.
• Coordinatively unsaturation ? highly reactive
  ? tend to form extra bonds with (CO, PPh3, H-)
  until 18 e- reached.
• Coordinatively unsaturation can be
  induced by bulky ligands.

LPR3
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Steric bulkiness of monodentate phosphine
described by cone angle
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Important Properties of Ligands

• Ligand coordinate onto a metal.
• Lewis base (s donor)
• H2O, NH3, H-
• Lewis acid (p acid ligands)
• CO, NO, H2 and CH2CH2 capable of accepting
  electrons from the metal through back-donation.

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Back-donation donating metal d orbitals and the
ligand p acceptor orbitals match (s for H2) .
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2.2 Alkyl, Allyl, and Alkylidene Ligands
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Important Reaction Type
3.1 Oxidative Addition and Reductive Elimination
Oxidative Addition
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Reductive eliminations
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Insertion
2.10 migratory insertion 2.8 hydrogenation 2.9
polymerization 2.10 CO involving catalytic
reactions 2.11 CO hydrogenation
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note cis insertion
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ß-hydride elimination
1. hydrogenation 2. alkene polymeration
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3.4 Nucleophilic Attack on a Coordinated Ligand
2.12 Wacker Process 2.13 epoxidation 2.14 Models
for water gas shift reaction (rate constant
different can be 109 compared with free CO)
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4 Energy Considerations-Thermodynamics and
Kinetics
Thermodynamics Gibbs free energy ?G (?G lt
0) Kinetic Free energy of activation ?G (?G
accessible)
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In diagram a ?G ?G 2- ?G1 In diagram b I
intermediate lower energy than TS For
spontaneous reaction ?G lt 0 ?G ?H - T?S 1. ?H
lt 0 (enthalpy) 2. ?S gt 0 (entropy)
5 CATALYTIC CYCLE AND INTERMEDIATES

• MLn1 precatalyst or catalyst precursor
• Four Catalytic immediates in the example shown
  below
• How to derive a catalytic cycles??
• Kinetics studies (information on the
  rate-determining step)
• spectroscopic investigation (in situ
  spectroscopic investigation, require certain
  level of concentration, intermediates may never
  be observed)

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3.studies on model compounds (enzymes)
4.computation
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Kinetics Studies Ligand dissociation step
(will addition of more L, rate of reactions
decreased) Spectroscopic investigation
Infrared / multinuclear NMR (eq, 31P, 2H)
Rh porphyrin catalyzed
cyclopropanation
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In situ NMR studies between diazo compound and
catalyst precursor shows the presence of 2.1 and
2.2
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Model Compounds
e.g. 1
The model compound of epoxidation by high-valent
metals ions.
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e.g. 2.
The model compound for studying the reductive
elimination of acetone (Complex 2.5 made from
RhCl(PPh3)3 with propylene oxide, no O.A. with
acetone)
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Theoretical Calculations
Catalytic polymerization physical properties of
the polymer obtained depend on the catalysts.
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The elastomeric property of the polypropylene
depends on the relative amounts of 2.6 and 2.7.
The energy required for the interconversion
between the two states depends on the R group and
can be theoretically calculated. On the basis of
such calculations, for a variety of metallocene
catalysts with different R groups, the
elastomeric property of the final polypropylene
has been correctly predicted.