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Organometallic Chemistry

Organometallic Chemistry. 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

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Organometallic Chemistry

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  1. Organometallic Chemistry

  2. 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 FeCoNiCuZn ZrRuPdHg OSPt

  3. 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.

  4. Useful Metal Alkyls in Organic Synthesis C-M Bond • Organomagnesium – Mg(C--Mg+) • Organolithium - Li (C--Li+) • Organocopper -Cu (C--Cu+)

  5. 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

  6. Reactivity of Alkyl Halides • R-I > R-Br > 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

  7. 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

  8. 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.

  9. Organocuprates CuI, Et2O • 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. -RCu, -LiI

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

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