Organometallic Compounds

1
Chapter 14

• Organometallic Compounds

2
Nomenclature

• Organometallic compounds are named as substituted
  derivatives of metals. The metal is the parent,
  and the attached alkyl groups are named by a
  prefix.

3
Nomenclature
4
The utility of organometallic compounds is their
carbanionic character
?
?
?
?
organometallics are a source of nucleophilic
carbon
5
Tab. 14.1
6
Organolithium Compounds
normally prepared by reaction of alkyl halides
with lithium
same for ArX
is an oxidation-reduction reaction carbon is
reduced
7
Examples
diethylether
(CH3)3CCl 2Li
(CH3)3CLi LiCl
10C
(75)
diethylether
Br
2Li
Li
LiBr
35C
(95-99)
8
Organomagnesium CompoundsGringnard Reagents
prepared by reaction of alkyl halides with
magnesium
RMgX
same for ArX
Diethyl ether is most often used solvent.
Tetrahydrofuran is also used.
9
Examples
diethylether
Mg
10C
(96)
diethylether
Br
Mg
MgBr
35C
(95)
10
Organolithium and Organomagnesium Compounds as
Bronsted Bases
H2O
CH3CH2CH2CH2Li
CH3CH2CH2CH3

LiOH
(100)
11
Organolithium and Organomagnesium Compounds as
Bronsted Bases

• Organolithium and Organomagnesium compounds are
  strong bases. They easily react with acids.
• Therefore no acidic protons can be present in
  compounds used to form them.

12
Tab. 14.2
13
Synthesis of Alcohols with Organolithium and
Organomagnesium Reagents

• Organolithium and organomagnesium reagents react
  with
• formaldehyde to give primary alcohols
• aldehydes to give secondary alcohols
• ketones to give tertiary alcohols
• esters to give tertiary alcohols

14
Example

1. diethyl ether 2. H3O
(76)
15
Synthesis of Acetylenic Alcohols
NaNH2
NH3
16
Retrosynthetic Analysis

• In retrosynthetic Analysis, we work backwards
  from the target molecule in order to determine
  viable synthetic path.
• In the retrosynthetic analysis of alcohols
• 1. locate the hydroxyl-bearing carbon
• 2. remove one attached group
• 3. what remains is a Grignard reagent and
  carbonyl.

17
Example
There are two other possibilities. Can you see
them?
CH3MgX
18
Tertiary Alcohol Synthesis with Esters and
Grignard Reagents
R'
R'
?
?
C

MgX
O



but species formed is unstable and dissociates
under the reaction conditions to form a ketone
19
R'
R'
?
?
C

MgX
O



CH3OMgX
this ketone then goes on to react with a second
mole of the Grignard reagent to give a tertiary
alcohol


20
Example

2 CH3MgBr
1. diethyl ether 2. H3O
Two of the groups attached to the tertiary
carbon come from the Grignard reagent
OH
(CH3)2CHCCH3
CH3
(73)
21
Alkane Synthesis with Organocopper Reagents
Lithium dialkylcuprates are useful synthetic
reagents. They are prepared from alkyllithiums
and a copper(I) halide.
22
the alkyllithium first reacts with the copper(I)
halide
Li
I
23
Lithium Dialkyl Cuprates are used to form
carbon-carbon bonds.

(CH3)2CuLi
CH3(CH2)8CH2I
diethyl ether
CH3(CH2)8CH2CH3
(90)
primary alkyl halides work best (secondary and
tertiary alkyl halides undergo elimination)
24
Organozinc Reagents
formed by reaction of diiodomethane withzinc
that has been coated with copper(called
zinc-copper couple)
Cu
CH2I2 Zn
ICH2ZnI
reacts with alkenes to form cyclopropanes reaction
with alkenes is called theSimmons-Smith reaction
25
Organozinc Reagents are used for Cylcopropane
Synthesis
CH2CH3
CH2CH3
CH2I2, Zn/Cu
H2C
C
CH3
diethyl ether
CH3
(79)
26
The addition is syn
CH2I2, Zn/Cu
diethyl ether
27
Carbene
name to give to species that contains adivalent
carbon (carbon with two bondsand six electrons)
Carbenes are very reactive normally cannot be
isolated and stored. Are intermediates in
certain reactions.
28
Generation of Dibromocarbene
Br

Br
H
Br
29
Carbenes react with alkenesto give cyclopropanes
Br
KOC(CH3)3
CHBr3
(CH3)3COH
Br
(75)
CBr2 is an intermediate stereospecific syn
addition
30
Transition Metal Organometallic Compounds

• Many organometallic compounds derivedfrom
  transition metals have useful properties.
• Typical transition metals are iron,
  nickel,chromium, platinum, and rhodium.

31
18-Electron Rule

• The number of ligands attached to a metalwill be
  such that the sum of the electronsbrought by the
  ligands plus the valenceelectrons of the metal
  equals 18.
• When the electron-count is less than 18, metal
  is said to be coordinatively unsaturatedand can
  take on additional ligands.
• 18-Electron rule is to transition metals asthe
  octet rule is to second-row elements.

32
Ni has the electron configuration Ar4s23d8 Ni
has 10 valence electrons Each CO uses 2
electrons to bond to Ni 4 CO contribute 8
valence electrons 10 8 18
CO
OC
CO
Ni
CO
Nickel carbonyl
33
Cr has the electron configuration Ar4s23d4 Cr
has 6 valence electrons Each CO uses 2 electrons
to bond to Cr 3 CO contribute 6 valence
electrons benzene uses its 6 ? electrons to bind
to Cr.
34
Fe2 has the electron configuration
Ar3d6 Each cyclopentadienide anion contributes
6 ? electrons Total 6 6 6
18 Organometallic compounds with
cyclopentadienide ligands are called metallocenes.
35
Karl Ziegler
Al(CH2CH3)3
The polyethylene formed under Ziegler's
conditions is called high-density polyethylene
and has, in many ways, more desirable properties
than the polyethylene formed by free-radical
polymerization.
36
Guilio Natta
Al(CH2CH3)3
polypropylene
Natta found that polymerization of propene under
Ziegler's conditions gave mainly isotactic
polypropylene. This discovery made it possible
to produce polypropylene having useful properties.
37
Ziegler-Natta Catalysts
Early Ziegler-Natta catalyst were a combination
of TiCl4 and (CH3CH2)2AlCl, or TiCl3 and
(CH3CH2)3Al. Currently used Ziegler-Natta
catalyst combinations include a metallocene such
as bis(cyclopentadienyl)zirconium dichloride.
38
MAO
The metallocene is used in combination with a
promoter such as methyl alumoxane (MAO)
39
Mechanism of Coordination Polymerization
MAO
This is the activeform of the catalyst.
40
Mechanism of Coordination Polymerization
41
Mechanism of Coordination Polymerization