1. Organometallic Chemistry
between organic and inorganic (?)
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Introduction to Organometallic Chemistry

2. Why Organometallic Chemistry ?
Main use in organic synthesis and (homogeneous) catalysis.
Using metals, you can make complicated organic structures that would be hard to make otherwise.
This is because, compared to "standard organic chemistry", metals display new and unusual reaction types.
To understand the "rules" you have to be able to "count electrons".
The "18-electron rule"...
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Introduction to Organometallic Chemistry

3. Introduction to Organometallic Chemistry
Organic Chemistry
more or less covalent C-X bonds
rigid element environments
fixed oxidation states
?Organometallic Chemistry?
Inorganic / Coordination Chemistry
primarily ionic M-X bonds
variable and often fluxional environments
variable oxidation states
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Introduction to Organometallic Chemistry

4. Organometallic Chemistry vs. Organic Chemistry
Many similarities
Many differences
Both can be “understood"
You don’t have to learn everything by heart, but some basic knowledge is required to get anywhere.
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Introduction to Organometallic Chemistry

5. Organometallic Chemistry
There are many metals !
The chemistry of Fe is not much more complicated than that of C, but after that there are 80 more metals... Generalization is important.
We concentrate on the M side of the M-C bond, and on how to tune its reactivity.
Applications: synthesis, catalysis, materials, pharmaceuticals.
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Introduction to Organometallic Chemistry

6. Introduction to Organometallic Chemistry
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Introduction to Organometallic Chemistry

7. Introduction to Organometallic Chemistry
Organic Chemistry
Chemistry of C-X bonds
C-C / C-H : nearly covalent
Cd+-Xd- : polar (partly ionic)
SN1, SN2 and analogous additions/eliminations
Electrocyclic reactions
Woodward-Hoffmann rules
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Introduction to Organometallic Chemistry

8. Introduction to Organometallic Chemistry
Organic Chemistry
Carbon is tetrahedral, trigonal or linear
Reactive intermediates / transition states:
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Introduction to Organometallic Chemistry

9. Organometallic Chemistry: Main group metals
s and p orbitals.
8-e rule, usually.
Metal is the "d+" side of the M-C bond.
"Umpolung" of the organic fragment.
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Introduction to Organometallic Chemistry

10. Organometallic Chemistry: Main group metals
More electropositive and larger: higher coordination numbers, regardless of the number of electrons.
“Early" groups and not very electropositive: lower coordination numbers.
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Introduction to Organometallic Chemistry

11. Organometallic Chemistry: Main group metals
Multiple bonds relatively weak and reactive.
C-C 85 C=C 150 N-N 40 N=N 100 P-P 50 P=P 75
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Introduction to Organometallic Chemistry

12. Organometallic Chemistry: Transition metals
s, p and d orbitals
18-e rule, sometimes 16 e other counts relatively rare
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Introduction to Organometallic Chemistry

13. Organometallic Chemistry: Transition metals
Metal is usually "d+"
Metals are sterically saturated
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Introduction to Organometallic Chemistry

14. Organometallic Chemistry: Transition metals
Often ligands capable of donating 2-8 electrons
Preference for p-system ligands
Bonds relatively weak
Catalysis !
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Introduction to Organometallic Chemistry

15. “Forbidden” reactions ?
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Introduction to Organometallic Chemistry

16. Reactivity of the M-C bond
Polar Þ reactive towards e.g.
Water:
Me3Al explodes with water; Me4Sn does not react.
Oxygen:
Me2Zn inflames in air; Me4Ge does not react.
Carbonyl groups:
MeLi adds at -80°C, Me3Sb not even at +50°C.
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Introduction to Organometallic Chemistry

17. Oxidation and hydrolysis: large driving force
Al-C 65 As-C 55 Si-C 74
Al-O 119 As-O 72 Si-O 108
Al-Cl Si-Cl 91
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Introduction to Organometallic Chemistry

18. Type of reactions in organometallic chemistry (1)
Ligand dissociation / coordination
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Introduction to Organometallic Chemistry

19. Type of reactions in organometallic chemistry (2)
Metal as a ligand
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Introduction to Organometallic Chemistry

20. Type of reactions in organometallic chemistry (3)
Insertion
b-elimination
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Introduction to Organometallic Chemistry

21. Type of reactions in organometallic chemistry (4)
Oxidative addition / Reductive elimination
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Introduction to Organometallic Chemistry

22. Type of reactions in organometallic chemistry (5)
s-bond metathesis
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Introduction to Organometallic Chemistry

23. Type of reactions in organometallic chemistry (6)
Redox reactions
Homolysis
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Introduction to Organometallic Chemistry

24. Type of reactions in organometallic chemistry (7)
Reactivity of coordinated ligands
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Introduction to Organometallic Chemistry

25. Factors governing structure and reactivity of organometallic compounds
M-C, M-X bond strengths
Electronegativity of M
Number of (d) electrons
Coordination number
Steric hindrance
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Introduction to Organometallic Chemistry

26. Trends in the periodic table
Main group metals:
left and down: more electropositive
down: higher oxidation states less stable
Transition metals:
middle: strongest preference for 18-e
2nd and 3rd row: strong preference for paired electrons (low-spin states)
down: higher oxidation states more stable
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Introduction to Organometallic Chemistry

27. Techniques of Organometallic Chemistry
Xray diffraction Þ structure Þ bonding
NMR Þ structure en dynamic behaviour
(calculations) IR MS
EPR
Not: GC LC
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Introduction to Organometallic Chemistry