Organometallic Chemistry

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Organometallic Chemistry
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Organometallic Compounds

• Compounds that contain a Metal-Carbon bond.
• Metal Alkyls, e.g. Tetraethyllead - Leaded Gas
• Alkyl methyl, ethyl, tert-butyl, etc.
• Metal Li, Na, K (alkali metals)
• Mg (alkaline earth metals)
• Ti Cr Mn Fe Co Ni Cu Zn
• Zr Ru Pd Hg
• OS Pt

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Metal Alkyls

• General formula R-M (R alkyl, M metal)
• The C-M bond is a covalent bond!
• However, C--M or R--M bond tend to be
  polarized.
• This is especially true for organometallic
  compounds conataining the more electropositive
  metals, i.e. alkali and alkaline earth metals.
• Generally, the alkyl fragment of the
  organometallic compound is very reactive however
  this depends on the metal, changing the metal
  alters the polarization of the R-M bond.
• Thus different organometallic compounds are used
  in many different types of organic reactions.

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Useful Metal Alkyls in Organic Synthesis

• C-M Bond
• Organomagnesium Mg (C--Mg)
• Organolithium - Li (C--Li)
• Organocopper - Cu (C--Cu)

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Organomagnesium Compounds
Grignard Reagents

• Methylmagnesium chloride - CH3Mg Cl-
• Ethylmagnesium bromide - CH3CH2Mg Cl-
• Draw the structures of
• Isopropylmagnesium iodide
• Sec-butylmagnesium chloride
• Formation of Grignard Reagents
• CH3-Cl
  CH3Mg Cl

Mg, Et2O
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Reactivity of Alkyl Halides

• R-I gt R-Br gt R-Cl
• Preparation of Grignards from primary, secondary
  tertiary alkyl halides.
• Grignard formation from aryl halides and allyl
  halides however these may give Wurtz type
  coupling products.
• I2 maybe used to speed-up the formation Grignard
  reagents from alkyl bromides or chlorides

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Organolithium Compounds
Alkyl Lithium Compounds

• Methyllithium CH3Li
• Ethyllithium - CH3CH2Li
• Draw the structures of these Alkyl lithium
  compounds
• n-propyllithium
• tert-butyllithium
• Preparation of organolithium reagents
• CH3-Br CH3Li
  LiBr

2 eq. Li, Et2O
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Organocopper Compounds

• Lithium Dialkylcopper (organocuprate ) (R)2Cu-
  Li
• Cuprates are less reactive than organolithium
• R acts as a Nucleophile
• Oxidation state of copper is Cu(I).
• Nucleophile R will attack various organic
  electrophiles.
• Organocuprates are used in cross-coupling
  reactions to form higher alkanes.
• Cross-Coupling Reaction coupling of two
  different alkyls R and R to yield a new alkane
  (R-R). This type of reaction is used to make
  new C-C between alkyl groups.

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Organocuprates

• Preparation of organocuprates
• 2 CH3Li (CH3)2Cu- Li LiI
• As a reagent for Organic Synthesis
• (CH3)2Cu- Li CH3CH2CH2I CH3CH2CH2CH3
  
• Formation of new C-C bonds
• The electrophile CH3CH2CH2I (R-X) must be a 1
  alkyl halide for a good product yield.

CuI, Et2O
-RCu, -LiI
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Organic Synthesis

• Give a stepwise synthesis for Isobutane.
• 2,2-dimethylheptane