Chapter 15

Reagents with Carbon-Metal Reagents with Carbon-Metal BondsBonds

Organometalic Synthesis of Organometalic Synthesis of AlcoholsAlcohols

Section and Problem Assignments

SKIP: Section 15.6 and 15.9SKIP: Section 15.6 and 15.9

In-Text Problems: 15.2 - 15.7 In-Text Problems: 15.2 - 15.7 15.10 - 15.13 15.10 - 15.13

End of Chapter Problems: 1 - 3 End of Chapter Problems: 1 - 3

Sect. 15.1: structure and properties of organometallic

compounds

Organometallic compounds are prepared by the reaction of halides with metals such as sodium, lithium and magnesium.

These reactions involve reduction!!

Organolithium compounds

+ +

R = 1°, 2°, 3°, aryl

X = I > Br > Cl

2 Li Li XR LiR X

Formation of Organolithium ReagentsFormation of Organolithium Reagents

CH3CH2CH2CH2CH2 Br Li

CH3CH2CH2CH2CH2 Li LiBr

Li LiBrBr 2 Li

Examples

+2ether

+

butyllithium

+

phenyllithium

+

Organomagnesium compounds: Grignard Reagents

+ Mgether

X

R = 1°, 2°, 3°, aryl

R X R Mg

Victor Grignard

Source: Michigan State University, Department of Chemistryhttp://www.chemistry.msu.edu/Portraits/PortraitsHH_collection.shtml

Nobel Prize 1912

CH3CH2 O CH2CH3

O

CH3CH2CH2CH2CH3

O

O

SOLVENTS THAT ARE FREQUENTLY USEDSOLVENTS THAT ARE FREQUENTLY USED

diethyl ether

THFtetrahydrofuran

pentane

benzene

1,4-dioxane

..

..

..

..

..

..

..

..

Ethers work especiallywell since they can make complexes withGrignard reagents and solvate them.

O

Mg BrCH3

O

..

..

..

..

Properties of organometallic compounds

• polar covalent bond

• partial negative charge on carbon

• carbon is basic!

• don’t memorize Table 15-1!

All of these reagents react as nucleophiles or bases:

C -

Which are bonded, to various degrees, to the accompanying metal.

M+

BASES AND NUCLEOPHILESBASES AND NUCLEOPHILES

Sect. 15.2: Reaction of Organometallic compounds with

water and acid

Organolithium and organomagnesium compounds give alkanes when reacted with water and acid

R-Mg-Br + H2O R-H + Br-Mg-OH

+:-C Li C Li

43% ionic57% covalent

REACTIONS OF ORGANOLITHIUM COMPOUNDS

strong base

good nucleophile

CH3 Br Li CH3 Li+ or CH3: Li- +

strong bases react with acids (even water and alcohols)

ether

- +

CH3:- + H+

strongbase acid

Any -O-H, -S-H, or -N-H bonds are sufficiently acidic to react.

CH3: COH

O

RCH4 RCOO+ +

- -

- ..

..-

++CH3: CH4H OH :O H

.. --CH3: CH4H O R :O R..++

The reaction with H2O also means that you must rigorously exclude water ( and water vapor = air ) from your reactions.

The reaction with water is a way of reducing an alkyl halide( converting C-X to C-H ).

Br

CH3

Li

CH3

H

CH3

Li H2O

ether

REMOVING A HALOGENREMOVING A HALOGEN

This reaction of an alkyllithium compound with water is generally not useful unless you use D2O, which is a way of placing a deuterium atom in your compound.

CH3: D OD :O DDCH3- -..

..+ +

CH3 Br Li CH3 Li+

Li+ Li+

Br Li D

ether

Li D2O

ether

phenyllithium

MAKING DEUTERIUM COMPOUNDSMAKING DEUTERIUM COMPOUNDS

Sect. 15.3: Reaction of Organometallic Reagents with

epoxides

+ether ..

:.. MgX

+_

H2O

R CH2 CH2 O

R CH2 CH2 OH

CH2CH2

O

R MgX

a terminal alcohol

Grignard reagent

CH3 Li + CH2 CH2

O

ether H2OCH3 CH2 CH2 OH

60% yield

Li

CH2CH

O+

CH2 CH

OHether H2O

Organolithium Organolithium

got the nucleophile.Notice which carbon

Sect. 15.4: Synthesis of Alcohols using Grignard reagents

+ether ..

:.. MgX

+_ H2O

R MgX R C

R

R

O R C OH

R

R

O

CR R

ketone tertiaryalcohol

O

C

..:+

- O

C

..::-

+

THE CARBONYL GROUPTHE CARBONYL GROUP

electrophilic at carbon

nucleophilicat oxygen

Nu:

nucleophiles attack here

H+ or E+

electrophiles attack here

_

C

O:C

REACTIONS WITH THE CARBONYL (C=O) GROUPREACTIONS WITH THE CARBONYL (C=O) GROUP

O

C

..:+

-

+

-

Since oxygen is more electronegative than carbon, the carbonyl group is electron-deficient at carbon, that isan electrophile.

The organometallic compound(R-MgBr) behaves as a nucleophilewith an unshared pair on thecarbon.

C

..:: MgBr+-

new C-Cbond

NUCLEOPHILIC ADDITION TO CARBONYL

BrMg

SYNTHESIS OF ALCOHOLSSYNTHESIS OF ALCOHOLS

The type of alcohol depends on whether you use formaledhyde,another aldehyde, or a ketone.

formaldehyde

other aldehydes

ketones

primary alcohol

tertiary alcohol

secondary alcohol

RMgX +

RMgX +

RMgX +

Reaction of RMgBr with aldehydes and ketones yields alcohols

SYNTHESIS PROBLEM

CH3 O

from

Sect. 15.5: Synthesis of Alkanes; the Wurtz reaction

2 R-X + 2 Na R-R + 2 NaX

Skip Section 15.6

Sect. 15.7: Preparation of lithium dialkyl cuprates

Li

2 + CuI0°C

etherLi

2R Li +

Cu

R

R

LiXR X

R Li + LiI

ALKYLATION WITH RALKYLATION WITH R22CuLiCuLi

R-X + R2CuLi R-R + R-Cu + LiX0o C

ether

X = Cl, Br, I

(CH3)2CuLi + CH3(CH2)4-I CH3-(CH2)4-CH3

EXAMPLES

H

Br

C8H17

H(CH3CH2CH2CH2)2CuLi

H

C4H9

C8H17

H+

Corey-House Reaction

(CH3CH2)2CuLi

:CBr2

Br

Br

H

H

CH2CH3

CH2CH3

H

H

+

CHBr3

MORE LITHIUM DIALKYLCUPRATE COUPLINGMORE LITHIUM DIALKYLCUPRATE COUPLING

Reaction of cuprates with acid chlorides

Cuprates react with acid chloridesto give ketones

Sect. 15.8: Formation of organometallic reagents from

alkynes

+ + M+

:

_

R HC CH RR M C C R

These reagents add to carbonyl groups!! Good stuff!!

Sect. 15.9: Organoboron Compounds revisited

Been there, done that!! See Chapter 14.