chap 15 organometallic compounds

8/9/2019 Chap 15 Organometallic Compounds

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Organometallic Compounds

Chapter 15


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Carbon Nucleophiles: Critical in making larger organic molecules.Review some of the ones that we have talked about.

C anide ion: CN ! " R# RCN RC$ %N$ %

&cet lide anions:

'nolate anions:

O't

O O base

O't

O O

$ $$

RX

O't

O O

R

RC C$

strong base

RC C:

RXRC CR

(r to see what factors promote the formation of the negative charge on thecarbon atoms: h bridi)ation* resonance.

Synthetic thinking: Disconnect

N$ % + CN-

+r

, nthetic (hinking: (his offers manopportunities provided ou can work with thetwo carbon straight chain segment. -h

-h

-h

-h

#

-h

-h

#or


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e e/amine two t pes of organometallics: R0g#* a rignard reagent* and R2i* an organolithium compound

-reparation " !

! "

,olvated b ether* aprotic solvent


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+asicitRecall that a carbanion* R 3C: !* is a ver strong base.

,o also rignards and alk l lithiums.

+ottom 2ine: rignards are destro ed b 4weak protic acids: amines*alcohols* water* terminal alk nes* phenols* carbo/ lic acids. (he

rignard* R0g#* is converted to a 0g salt eventuall and R$.

(he liberation of R$ can serve as a test for protic h drogens.

'thane* a gas.


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Reactivit patternsRecall the , N% reaction where the alk l group* R* is part of the electrophile.

Nu: - + R-X Nu - R + X -

'lectrophile

Nucleophile

6orming the rignard converts the R fromelectrophile to a potential nucleophile. & widerange of new reactions opens up with R asnucleophile.

R# " 0g R!0g!#! "

Nucleophile

'lectrophile

'lectrostatic potential

maps.

" !


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Recall Reactions of O/iraneswith Nucleophiles

Recall opening of o/irane with a strong* basic nucleophile.

O

C$ 3

$$

$

CH 3O-

C$ 3

$

O$

$ 3 CO

$$

(he ne/t slides recall the diversit of nucleophiles that ma be used.

Observe that there is limited opportunit of creating new C!C bonds* weldingtogether two R groups. We seem to be somewhat lacking in simplecarbon based nucleophiles.


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Recall , nthetic &pplicationsnucleophile

Onl reaction with the acet lideanion offers the means of makinga new C!C bond and a largermolecule. -roblem is that aterminal alk ne is needed.


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& rignard has a reactive* negative carbon. Now e/amine reaction ofrignard and o/irane ring.

Net results

The size of the alkyl group has increased by 2 . 2ook at this alcohol to alcoholse7uence

R!O$ R!# R!0g!# R!C$ %!C$ %!O$ .

(he functionalit 4O$ has remained at the end of the chain. e could make iteven longer b repeating the above se7uence.

Now a substituted o/irane

Note attack on lesshindered carbon

Newl formed bond

Newl formed bond


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, nthesis '/ample

O$

C$ %C$8C$ %

Retros nthesi)e the following

Recall reaction of a nucleophile with an4o/irane epo/ide to give a $O!C!C!Nu pattern. +ack side attack givesanti opening.

Trans geometr suggests tr ing ano/irane. hat should the nucleophile

be9

(he all l group should be thenucleophile. (his is done b using a

rignard 4or ilman .

O

CH 2=CH - CH 2Mg r

O$


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ilman Reagent 42ithiumdiorganocopper Reagents

R-X

!iR-!i

Cu"R 2Cu!i

ilman-reparation of ilman Reagents


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Reactions of ilman ReagentCoupling Reaction

sed to create new C ; Cbonds..

Overall result. R!# " R

Necessar details

R-X!i

R-!iCu"

R 2Cu!i &s before:

Ne/t step: R 2Cu!iR#-X

R - R#

Restrictions on the process. Caution.

R group which goesinto ilman ma be

meth l* 1 o 4best not % o or 3 o * all lic*vinylic

4unusual * ar l

&lk l 4not 3o * vin lic

nucleophile

electrophile


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-articularl useful* reaction withvin l halides to make an alkene.

Note that the stereochemistr of the alkene isretained.

trans


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ilman and o/iranes

R of the ilman reagent is the nucleophile* t pical of organometallics.

+ecause in basic media 4acid destro s ilman o/ gen of o/irane can notbe protonated. 2ess hindered carbon of o/irane is attacked.

O $% R 2Cu!i $O

R

2% H2O& HC'


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, nthetic &nal sis

O$% R 2Cu!i $O

R

2% H2O& HC'

Newl formed bond.Note its position

relative to the O .

,imilar to rignardanal sis.


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'/ample of Retros nthetic &nal sis

-h

O$

=esign a s nthesis using o/iranes

(he o/irane ring could beon either side of the O$.2ook at both possibilities.

-h

O$

or -h

O$

O

()hCH 2*2Cu!i

On the right* located here.Open o/irane here.Nucleophile makes this bond.

-h

O

!iCu(CH 2CH 3*2

% s nthetic routesavailable

Nucleophile can come in

on onl one position ofo/irane* on the C to whichthe O$ should not beattached

On the left * located here.Open o/irane here.Nucleophile makes this bond.


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, nthesis '/ampleCarr out the following transformation in as man steps as needed.+r O

OC$ 3

O

OC$ 3

O$

OC$ 3

O

+r target

Remembero/idation of asecondaralcohol canproduce aketone.

Note pattern of anucleophile4OC$ 3 then C!Cthen O$. sean epo/ide.

'po/idescan comefrom alkenesvia peracids.

&lkenes cancome fromhalides via'%.


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Carbenes* :C$ %1.

%.

carbene

-reparation of simple carbenes

0echanism of the elimination.


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Reactions of Carbenes* :C$ %4not fors nthesis

&ddition to doublebond.

>nsertion into C!$ bond

6ormation of lide 4later

li7uid


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,immons ,mith Reaction 4 for synthesis *addition to alkenes to ield c clopropanes

C$ %>% " ?n4Cu >C$ %?n>

Carbenoid* propertiessimilar to carbenes.


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'lectronic ,tructure

'lectrons paired* singlet


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(riplet and ,inglet 0eth lene

CH 2 N2

sing'et carbene

stereos+eci,ica--ition

+i e'ectrons

tri+'et carbene

C$%

-ira-ica'

+

non-stereos eci,ic

=ominant form

in solutionas phase

Rotation canoccur around this

bond.

chap 15 organometallic compounds

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