Organometallic Compounds:
Chapter 11
Chapter 11
1
Organometallic Compounds



Most metals are less electronegative than
carbon
In general a carbon bonded to a metal is
nucleophilic and carbanion-like (C–)
Four major classes of organometallic
compounds are:




Organolithium compounds
Grignard reagents
Cuprates
Organopalladium compounds
Chapter 11
2
Grignard & Lithium Reagents



Grignard and lithium Organometallic reagents made
by reacting a halide with elemental metal
Mg essentially slides into C-halogen bond
Li simply replaces halogen
Chapter 11
3
Grignard & Lithium Reagents



Although the carbon–metal bonds are not completely
ionic, organolithium compounds and Grignard reagents
react as if the carbon portion were a carbanion
Consider the reaction of a Grignard reagent with an
ethylene oxide
Ethylene oxide is a good way to extend a carbon chain
by two carbons via use of halide to make
organometallic cpd with negative charge on C
O
CH3CH2CH2CH2MgBr
CH3CH2CH2CH2CH2CH2O
+
CH2
CH2
2+
CH3CH2CH2CH2CH2CH2O
H
-
+ Mg
+ Br
CH3CH2CH2CH2CH2CH2OH
Chapter 11
4
Gilman Reagents
Gilman reagents, also called
organocuprates, are prepared from the
reaction of an organolithium reagent
with copper(I) iodide in diethyl ether or
THF
Chapter 11
5
Gilman Reagents



When a Gilman reagent reacts with an alkyl halide
(except F-) one of the alkyl groups replaces the
halide
Alkyl groups can substitute halogens attached to
alkene or aromatic C with Gilman reagent;
impossible with SN1 or SN2 reaction
Mechanism unknown, probably radical
Chapter 11
6
Suzuki and Heck Reactions


Various palladium catalysts substitute ordinary unfunctionalized
alkenes for Br, I, or triflate (OTf) leaving group attached to benzene or
alkene (Heck).
Reagent can even be made to substitute alkyl groups if a
dialkoxyalkylborane reagent is used with it (Suzuki).
Chapter 11
7
Grubbs & Schrock Metathesis


Terminal alkenes couple eliminating ethylene with rhodium catalyst
(Grubbs).
Terminal alkynes couple eliminating acetylene (ethyne) using
molybdenum or tungsten catalyst (Schrock).
Chapter 11
8
Retrosynthetic Analysis: Using
Ethylene Oxide (EO)







Product has 2 extra C’s plus CN
2 extra C’s mean use EO
Always work back to an ROH for EO analysis
Retro EO addn removes 2 C’s and an OH
Here CN has sub’d for an ROH-derived LG (leav grp)
Make OTs the LG & derive the ROTs from ROH
Cyclohexyl C- attacks EO to make this ROH
Chapter 11
9