Catalytic hydrogenolysis of carbon-fluoride bonds: π bond participation mechanism

Journal of Fluorine Chemistry, 44 (1989)

345-359

345

A REVIEW ARTICLE CATALYTIC HYDROGENOLYSIS OF CARBON-FLUORINE II BOND PARTICIPATION MECHANISM

BONDS:

M. HUDLICKY Department of Chemistry, Virginia Polytechnic Blacksburg, Virginia 24061 (U.S.A.)

Institute

and State University

SUMMARY

A new mechanism for

a

relatively

hydrogenation cyclic

easy

of

can

hydrogenolysis

also

underlie

of

some

is proposed

carbon-fluorine

benzylic

by hydrogen

of carbon-halogen

12-81.

Bromine

readily

than

chlorine

vinylic,

of halogen

but occurs

saturation

hydrogenolysis

of II bonds

and

unusual

bonds

aromatic results

to account

in catalytic

fluorides.

This

of hydrogenation

of

compounds.

Replacement

[l-41

the participation

allylic,

mechanism

other halogen

with

frequently is replaced

fluorine

[lo]

can

in allylic,

be

in saturated

halides

vinylic,

benzylic

and aromatic

halides

than chlorine,

accomplished

of allylic

Hydrogenolysis

141.

- catalytic

scarce

Hydrogenolysis

bond

hydrogenation

- is very

more readily

[S-B].

of the double

bond

in catalytic

without

the

and this in turn more chlorine

of vinylic

hydrogenation

precedes

the

bromine

[gl or

of

double

the

bond. HzPdd(BaS03

CH,CBr=C(CH,)CO&H,

CCIF = CF,

tlqJ5%Pd(C)

Et3N,RT. L atm

-

130.13S",10sec Conspicuously

139/89/%3.50

CHF=CF,+CH,FCHF, 85% 15%

easy hydrogenolysis

that some cooperation 0032-l

- CH,CH=C(CH,)CO,CIH, 71%

of the double

[91

[IO] in allylic

and vinylic

bond at the surface

systems

suggests

of a catalyst

may be

OElsrvier Sequoia/Printedin The Netherlands

346 responsible

for the ready replacement

[21 and Conroy

[ill hinted at "a multicenter

Homer

by hydrogen.

of halogens

et.

but did not elaborate

process"

on

this idea any further. A

direct

scheme

is

However,

of

proof

not

easy

double

X:H

thermodynamically a six-center

N'

bond

according very

is

of such a mechanism

-\

to

readily

the

following

hydrogenated.

can be quoted.

’

H

of

14_bromocodeinone,

by hydrogen

conditions, from

double

in support

hydrogenation

bond

participation

C

/

very gentle

the

/ >c-c I\

\

the

TI bond

since

a few examples

In

a

a,B-

to

transition

with the simultaneous

B,y-position

unfavorable

shift

bromine

to

can hardly

the

was

replaced,

under

shift of the allylic

carbonyl

Such

1111.

be understood

without

a

assuming

state in which the double bond participates.

CH,

HL/lO% Pd(C)

[Ill

CHCI,, McOH 25”. I arm

Neoplnone 81%

14.Bromocodeinone

Similar easy

participation

hydrogenolysis

chloranil

of

of a TI system two

and 1,3-butadiene

bridgehead

can be visualized chlorine

[121.

OH Cl

Cl tlfllo~OrPd(C)

c’

H\F

AcOH. RT c3.5 am IO-15 IIll”

Cl21 Cl OH

atoms

in a surprisingly in

the

adduct

of

347 Also chloride

an unexpected which gives,

accounted

outcome

bond

reduction

dichloroacetyl

instead of chloral,

for by a six-center

carbonyl

of a Rosenmund

transition

state with

of trichloroacetyl

chloride,

can be best

the participation

of the

[131.

Cl H?/Pd(BaS04)

CCL-C Cd-2 _

50-60% H’

H-H

Catalytic to

[I31

CH&COCl

S-q"lnollne I.lV.1 am!

(o

accomplish

replacements

hydrogenolysis

of carbon-fluorine

than

carbon

that

of

of fluorine

and

other

bond

is much

halogens

more

in catalytic

hydrogenations

long and covers

only some two scores

of compounds

114,151.

of them contain

allylic,

few examples known. does

of the catalytic

In unsaturated

not

take

place

striking difference

difference.

kcal/mol

for allylic, saturated [Xl.

is

on the structure

replaced

from

carbon-fluorine hydrogen saturation

in

that

bond

bond

of

bond. unsaturated

while

This

explains

fluorides

of the double bond.

is a

will clarify

such

energy

requires

why is

the

almost

but

much

60-84

compounds

(60

and 79-84

for

kcal/mol

compounds

chlorine

unaffected

[10,17-

at 75 kcal/mol lower

replacement always

is

107-116

remains

of a II bond estimated bond

bond

This

86 for aromatic,

fluorine

bonds are

compounds.

of chlorofluoro

carbon-chlorine

Only a very

bond.

dissociation

rupture

in hydrogenations

energy

double

of hydrogenation

84 for vinylic,

by hydrogen,

fluorine.

of the chlorine-containing

carbon-fluorine

of this,

of the

of

The vast majority

of carbon-fluorine

of other halogen

carbon-chlorine

list

is not very

of sp3 carbon-fluorine

saturation

at the thermochemistry

The bond dissociation far

or aromatic

the hydrogenolysis

from the behavior

chlorides),

Because

not

the

68 for bensylic,

is frequently 241.

fluorides,

While

depending

vinylic

hydrogenolysis

without

A short glance a

bensylic,

A

[S-81.

by hydrogen

difficult

of

than

that

fluorine

accompanied

t251

by

of by the

348

Catalytic

hydrogenolysis

drastic

conditions

methane

and

yields

[26,271.

ethane,

took

temperatures

at

to

higher

deoxyglucoside

190'

and

pressure

extent

than

155'

ethyl

of

palladium

on

Reduction

[271.

B-glucoside

required

converted only

was

fluoride

complete

methyl

of

in

hydrogenation

to 10%

was completely

isopropyl

and

5-lo%,

were

fluoride

of

very

requires

charcoal

Propyl

[271.

only

bond

fluoride

Hydrogenolysis

I271.

the

to methyl

carbon-fluorine

over

respectively,

only

place

sp3

Methyl

at 240" and atmospheric

hydrogenolyzed 110"

of

only

at at

f3-6-fluoro-6-

over Raney

nickel

at 100" and 120 atm [28]. It allylic, mild

comes,

therefore,

vinylic,

conditions,

[14,15,29-321. hydrogen

frequently Also

relatively

cleaved

to

contain

r bonds,

role

bensylic

give

will

be

aromatic

bound

but

of

catalytic

fluorine

atoms

hydrogenolysis takes

to a cyclopropane

ring

probably

only

after

alkene

[33].

Since

all

deduced

was

the

mechanisms

of

at very

replaced

catalytic

by

has been

above

examples

an important

In the following

bonds.

of

pressure

the ring

that this bond plays

of carbon-fluorine putative

place

and atmospheric

most

it can be easily

shown

that

even at room temperature

fluorinated

in the hydrogenolysis

examples

suprise

a

and

fluorine easily,

a

as

survey

carbon-fluorine

hydrogenolyses.

Allylic of

methyl

products, from

fluorine

one resulting

hydrogen.

saturation

‘C=CH / -'co,w, C+CH,)&

the

double

mechanism

bond

accounts

always

and

a

Hydrogenation

mixture

Co2CH’

replacement

of

fluorine

Hfld(C) [30)

1 CH,CH,C&H:COZCH, CH,

of

two

bond, and the other

well for the hydrogenolysis

CH,-CH 2Y 4-5 am

readily.

of the double

‘C-C,Hz //

H>/WC) -

fairly

gave

from the saturation of

The following

. H

by hydrogen

4-fluoro-3-methyl-2-pentenoate

both,

_ k

is replaced

by

[301.

349

When

double

the

methylpentenoate, very energetic

bond

is

inaccessible,

no hydrogenation

conditions

CH@FT=CBrCO,CH,

hydrogenation and occurs

of vinylic

even

under

1301

fluorine

under gentle conditions

double

fluorines

bond

and

by hydrogen

occurs

Clear-cut

addition

[14,15,17-20,341.

hydrogenolysis

mixtures

of

of fluoroalkanes

frequently

of hydrogen

Usually,

fluorine

during

take

the

is rare

both saturation

place

next

with the same or smaller

to each

numbers

of

[14,15,17-201.

66% CHF,CHF,

cHF,cHF,

&;_f-f; F Pd/AIIO,. W, I am, 10% Pdlpumice. 45’ 10% Nilpumu. 25”

F

F

93% 70% 66 8%

Conspicuously fluorinated

is replaced

HO,CCH = CFCOzH

14%

is amino

acids

HZ/PlOz R.T.. Lam

pJ

H

26% 21.5%

hydrogenolysis

by hydrogen

&WC)

F

H 7% 4% 1.4%

easy

unsaturated

= CFCO,H

+ CHF,CH,F

+f-f: +f-f: F

H,NCH,CH

N.R.

of polyfluoroalkenes.

other, affording

fluorine

place

80",80 am

Replacement

96%

took

AcOH *

the

hydrogenolysis

2-bromo-4-fluoro-3-

[301.

HfltOz.

CH3

of

nor

as in methyl

of

carbon-fluorine

[29] and dicarboxylic

acids

under very mild conditions.

H2NCH,CH,CH,C0,H

HO,CCH,CHFCO,H

[291

+ HOZCCH,CH2C02H

209. 1 Pun k

N.R. 20”. I aim

[311

bond

in

some

[31,32] where

350 The proposed the

hydrogenation

Hydrogenation

varying

ratios

[311.

acid

and over

pressure Since

of fluorine

that succinic

hydrogenolysis

fluorofumaric

and atmospheric

hydrogenolysis

involving

of

or conjugate

of fluorofumaric

room temperture in

mechanism

under

acids

difluoromaleic

palladium

on activated

gave fluorosuccinic

fluorosuccinic

does

charcoal

not

on

[31,321.

and succinic

acid

the same conditions

acid was formed directly

the participation

will be illustrated

at acid

suffer

[311, it must be assumed

from fluorofumaric

acid by a mechanism

of the double bond:

H-H H0,C3L H'

HO&y

F

ccc4

H'

'CO,H

intermediate acid,

/c--c.

of

which

difluoromaleic

HW,C=C,W’ 'F

hydrogen

inserts

sequence acid

a,a'-difluorosuccinic

F'

H'

'CO,H

Similar

H

HO&I

_

.

Elimination

HZ

RT

[31,321

'CO,H

H

H H-H HO&,&_~)~ H'

HZ -

c-d.

I/H 'CO,H

fluoride

gives

into another

of reactions

which

gives,

in addition

F/J L'F /Ti'-H

I

and succinic

,CO,H

I

H2

H2

HO2C,

H02C,C_C,C4H

(.;-i;y b

H-H

I

HW,C_C,W’ F'i I'F HH

I CO,H c-c' H'i I'F HH

HO2C,

‘H

F

C

H'H

H-c

HO,C,C=C,CO,H H'

'H

HZ I HO&

carbene-like

to form succinic

addition

acid [31].

..c-c I'F H

-

a

in the hydrogenation

to a regular

HOzC,

or

of hydrogen

can be visualized

HW,C=C,CW

H,,-78'

carbene

molecule

acid, fluorosuccinic

I

a

,COzH c-c H'I I'H HH

1311

of

product,

351 Experiments

mixtures

aimed

of hydrogen

difluorobutenoic

most

prior

during

extensive

palladium

since

or

esters

study

oxide

assumed reactive

by Birkofer oxide

gave

in the presence

the expectations,

as

results

and is expected

[321.

or

amines,

fast

has been

[35-371.

hydrogenation

acid

is not

to undergo

of a carbene

that, whereas

of hydrochloric

of elemental

and

in the two above examples,

hydrazones

using

by

of fluoro-

of some diazo compounds

I371 shows

alone

mechanism

hydrogenations

Such a behavior

hydrogenation

took place with elimination

carbene

and did not give conclusive

it is very

catalytic

the

did not fulfill

to other reactions.

platinum

over palladium

of

in catalytic

the intermediate

to intercept

observed

support

and their

overlapped

The carbenoid,

hydrogenation

the

and deuterium

acids

1R and 1D spectra

easy

at

The over

hydrogenation

or of cupric

oxide

nitrogen.

[371

C,H,COCHN, \e

C,H,COC",

30%

Hz/pdO,CuO -

C,H,COCH,CH,COC,H,

30%

PhMe&lux

hydrochloric

Both, decomposition (called molecule

diaso

ketones

"freie Radikale" of hydrogen

unsaturated bond

of

acid

y-diketone

[391.

Depending

methyl ketones

and

cupric

to

carbenes

at that time)

to give

a methyl

[381 which on the

and y-diketones

[371.

result

or

are

or

undergoes of the

else

carbene,

from different

c C&J&IX

to

RCOCHN2

dimerize

RCOCH:

into the

to an a,B-

of the double

different

diaso ketones

(CH,),CHCOCH,+[(CH,),CHCOCH,], t371 5% 90%

catalyze +

can insert

saturation

H-JPdO,CuO

(CH,),CHCOCHN,

known

carbenoids

The carbene

ketone,

readily

stability

oxide

yields [371.

of

352 The

carbene

carbon-fluorine

mechanism

can

be

also

operating

bond in p,!3,6-trifluorostyrene

bond but also the aromatic

in

[401.

the

Here

hyarogenolysis

of

not only the double

ring may participate:

H2/hOz

F

-F

[401

RT, overnIght

CH=CHF

F

Participation hydrogenolysis

of the

of benrylic

T system fluorine

of

-

the

CH,CH,F

F

aromatic

ring

for

easy

[41-441.

CH=CHC,H5 H-H

accounts

L421

H -

\ o-

,

C%C%C&

Q-n

-

\

,

LCF

[43]

H-H

H CH,CH,C,H5 c \/ o-

H

The participation concomitant bensylidene

complete fluoride

of the

II bond

hydrogenation [441 which gives,

in the benzene of

the

benzene

in addition

ring may ring

facilitate

in

to toluene,

the

case

the of

a small amount

353

H

of methylcyclohexane, gives bensylidene

and

in the

fluoride,

case

toluene

of

a-chloro-a,a-difluorotoluene

and methylcyclohexane

[44].

o\

On the other cyclohexane

hand, bensotrifluoride

without

ring

also

[44-481.

acid

acid

in ethanol,

fluoroacetophenone

afforded

probably

hydrogen

adsorbed

responsible

in

gave

over Raney nickel

alloys,

when

R-Fluorobensoic

cyclohexanecarboxylic fluorophenylacetic

occurs

[4$1

to trifluoromethyl-

1441.

the

fluorine

acid

gave

hydrogenation ethyl

cm2

was hydrogenated

the loss of fluorine

Hydrogenolysis

,

over

is

linked

at 180-200°

at the surface

and

platinum

black

160-180

of Raney nickel L451.

the

and

1-phenylethanol

for the hydrogenolysis

to

bensoic

cyclohexylphenylacetate

ultimately

which

atm

aromatic

ultimately [441,

R-

in hydrogenation [481,

on heating

and

E-

with Raney

or Raney copper being

354

[481

o-

CH,CO,C,H,

CH,CO,H

r HH

80%

H

93%

Ni-Al alloy, 5% NaOH. SO” Cu-AI alloy, 5% NaOH. 50”

In

the

fluorine to

the

fluorine

was

of

bond

catalytic

phosphonic

2-fluoro-4'-acetylbiphenyl,

saturated

participation

Similar by

case

[451

after of

the

hydrogenolysis benzene

ring

only

the

of fluorine. in

the

ring

This

hydrogenolysis

containing

result of

points carbon-

[47].

replacement

of single

hydrogenation

of

aromatic

fluorine

fluoronitroaromatics

acid 1501, and of 5-fluorouracil

[511.

atoms was also t491,

achieved

o-fluorobenzene-

355 Even although

On fluorine

fluorine usually

the

in poly-

perfluoroaromatics

hand,

only

perfluorotoluene

partly,

and

at very

is replaced

(280-320°C)

only at high temperatures

other

bond

and

[52-541.

suffered energetic

by hydrogen,

hydrogenolysis conditions

of carbon-

(450',

100 atm)

t551.

The cyclic fluorine these

-\ Ii? o-

0)

also explains

in a-flaoroketones

cases,

oxygen,

mechanism

the

II bonds

respectively,

[56,571

between

participate

the relatively

and

carbon

a-fluoronitro and oxygen

easy hydrogenolysis coqouads

and between

of

[581.

In

nitrogen

and

in the mechanism.

[561 r

H-H

356

Hfld

-

CF&H=N\

MeOH

/O

80%

CF,CH=NOH

-!?+

[58]

OH

0

0

H1-

CF$F=N'

51%

CF,CF=NOH

[58]

'OH

Finally, hydrogenation explained and

the

an of

using

interesting two

isomeric

cyclic

intermediate

case

of

replacement

fluorine

during

2-bromo-2-fluoro-1-phenylcyclopropanes

transitions

states

between

2-fluoro-1-phenylpropene

formed by hydrogenolytic

of

opening

and

of the cyclopropane

the molecules

the

can

be

of hydrogen

2-fluoro-3-phenylpropene, ring 1331.

[331 THtBr

,q cH=c II Ph

-

\ ; CH,-CH,-CH,

F Ph

li_"(Br

HZ

,ql CHY-c -

*,CH,/ CH=C\

I Ph

Ph

I F

Ph

F

/ HZ

F

,

\ -

All four asterisked over

palladium

necessary

oxide

products

in

for hydrogenolysis

!?’

were isolated.

methanol,

at

much

H-H

The hydrogenation

lower

of a non-substituted

CH3

temperatures

cyclopropane

took place than

ring.

those

357

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