PALLADIUM–TRIETHYLAMINE–FORMIC ACID

1

Palladium–Triethylamine–Formic Acid

Pd—Et

3

N—HCO

2

H

(Pd)
[7440-05-3]

Pd

(MW 106.42)

InChI = 1/Pd
InChIKey = KDLHZDBZIXYQEI-UHFFFAOYAH
(Et

3

N)

[64-18-6]

C

6

H

15

N

(MW 101.22)

InChI = 1/C6H15N/c1-4-7(5-2)6-3/h4-6H2,1-3H3
InChIKey = ZMANZCXQSJIPKH-UHFFFAOYAU
(HCO

2

H)

[121-44-8]

CH

2

O

2

(MW 46.03)

InChI = 1/CH2O2/c2-1-3/h1H,(H,2,3)/f/h2H
InChIKey = BDAGIHXWWSANSR-QEZKKOIZCL

(transfer hydrogenation system used with a variety of palladium
catalysts for hydrogenation and hydrogenolysis reactions; hydro-
genation of alkynes, alkenes, nitro compounds; hydrogenolysis
of N-benzyl and O-benzyl groups; hydrogenolysis of allyic esters

and allylic carbonates)

Alternate Name:

triethylammonium formate (TEAF).

Physical Data:

see Palladium on Carbon, Triethylamine, and

Formic Acid.

Solubility:

heterogeneous catalyst system.

Hydrogenation and Hydrogenolysis.

Triethylammonium

formate, prepared most frequently in situ from triethylamine and
formic acid, has been used in conjunction with both heterogeneous
and homogeneous palladium catalysts for a variety of chemical
transformations. With heterogeneous palladium catalysts, such as
palladium on charcoal, both hydrogenation and hydrogenolysis
are observed. When used in combination with homogeneous cat-
alysts, hydrogenolysis is mainly observed. Many of these reactions
can also be carried out by replacing triethylammonium formate
with Ammonium Formate or hydrogen. The use of a hydrogen
transfer agent, such as triethylammonium formate, enables the
use of ordinary laboratory glassware and no special hydrogena-
tion equipment is required.

The following reactions have been carried out with heteroge-

neous palladium catalysts. The reduction of alkynes and conju-
gated enynes with Pd/C or Pd/CaCO

3

catalyst was not stereose-

lective and gave mixtures of (E)- and (Z)-dienyl esters along with
substantial amounts of over-reduced byproducts. The yields of the
dienyl esters ranged from 59 to 84%.

1

A combination of tri-

ethylammonium formate and Pd/C was used to reduce alkynes
to alkenes or alkanes. Reduction of 3-hexyne was not selective,
giving a mixture of 3-hexenes (70%) and hexanes (18%). Dipheny-
lacetylene, on the other hand, gave cis-stilbene (93%) with only
2% of bibenzyl. Selective reduction of the double bond in α,β-
unsaturated carbonyl compounds, such as citral (91%), cro-
tonaldehyde (81%), 2-cyclopentenone (83%), methyl crotonate
(83%), and methyl cinnamate (86%), provided good yields of the
carbonyl compounds.

2

The facile reduction of aromatic nitro compounds to anilines

has been reported and oxindole and benzolactam can be formed

directly from o-nitrophenylacetic acid and o-nitrocinnamic acid,
respectively, in 72–75% yields.

3

Some selectivity was observed in

the reduction of one nitro group in dinitro aromatic compounds.
The best results were observed with 2,4-dinitrotoluene, in which
2-nitro-4-aminotoluene was obtained in 92% yield. The yields of
other dinitro compounds ranged from 24 to 77%.

4

Hydrogenolyses of aryl benzyl ethers and allylic acetates or

amines have been reported to give phenols and alkenes, res-
pectively.

5

Hydrogenolysis of aryl halides with triethylammo-

nium formate in the presence of heterogeneous catalysts is an-
other useful synthetic method. Some interesting selectivity was
observed when the heterogeneous catalysts were replaced with
homogeneous catalysts. For example, reduction of 1-nitro-3-
bromobenzene in the presence of 5% Pd/C gave a mixture of ni-
trobenzene (46%) and aniline (15%). Replacement of the 5% Pd/C
with Palladium(II) Acetate and 2 equiv of tri-o-tolylphosphine
gave nitrobenzene (81%) and only 2% of aniline. Similarly, the
yield of benzonitrile from 4-bromobenzonitrile was improved
from 53 to 83% with the homogeneous catalyst.

3

The homogeneous catalytic system, on the other hand, is also

able to deoxygenate phenols via their aryl sulfonates (eq 1).

6

By

varying the phosphine ligands, the phenol starting materials could
be regenerated and thus the sulfonyl group only acts as a protecting
group (eq 2). Similarly, aryl triflates are also hydrogenolyzed in
excellent yields (eq 3).

7

Selective hydrogenolysis of the triflates

was realized in the presence of alkenes.

Allyl esters (eq 4) and carbonates (eq 5) are converted to alkenes

under the homogeneous catalysis reaction conditions.

8

The least

substituted alkene is formed preferentially.

O

O

OSO

2

R

O

O

Pd(OAc)

2

dppp

TEAF

(1)

90%

O

O

OSO

2

R

O

O

Pd(OAc)

2

dppm

TEAF

OH

(2)

95%

O

(3)

TfO

O

O

O

TEAF

82%

(4)

OCHO

OTHP

OTHP

Pd(OAc)

2

Bu

3

P

TEAF

86%

Pd(OAc)

2

Bu

3

P

TEAF

(5)

t

-Bu

OCO

2

Me

t

-Bu

82%

Avoid Skin Contact with All Reagents

2

PALLADIUM–TRIETHYLAMINE–FORMIC ACID

The Pd-catalyzed Carroll rearrangement of allyl β-ketocar-

boxylates to give α-allyl ketones was realized in THF (eq 6).

9

(6)

O

O

O

O

Pd(OAc)

2

Ph

3

P, THF

TEAF

44%

Switching the solvent to MeCN provided α,β-unsaturated

ketones instead (eq 7).

10

(7)

O

O

O

O

Pd(OAc)

2

Ph

3

P, MeCN

TEAF

85%

Allyl β-keto esters can also be hydrogenolyzed to form ketones

without allylation (eq 8).

11

Pd(OAc)

2

Ph

3

P, THF

TEAF

O

C

5

H

11

O

O

O

C

5

H

11

(8)

100%

1.

Weir, J. R.; Patel, B. A.; Heck, R. F., J. Org. Chem. 1980, 45, 4926.

2.

Cortese, N. A.; Heck, R. F., J. Org. Chem. 1978, 43, 3985.

3.

Cortese, N. A.; Heck, R. F., J. Org. Chem. 1977, 42, 3491.

4.

Terpko, M. O.; Heck, R. F., J. Org. Chem. 1980, 45, 4992.

5.

Krishnamurty, H. G.; Ghosh, S.; Sathyanarayana, S., Indian J. Chem.,
Sect. B 1986

, 25B, 1253.

6.

Cabri, W.; Bernardinis, S. D.; Francalanci, F.; Penco, S., J. Org. Chem.
1990, 55, 350.

7.

Cacchi, S.; Ciattini, P. G.; Morera, E.; Ortar, G., Tetrahedron Lett. 1986,
27

, 5541.

8.

(a) Tsuji, J.; Yamakawa, T., Tetrahedron Lett. 1979, 613. (b) Mandai, T.;
Suzuki, S.; Murakami, T.; Fujita, M.; Kawada, M.; Tsuji, J., Tetrahedron
Lett. 1992

, 33, 2987.

9.

(a) Shimizu, I.; Yamada, T.; Tsuji, J., Tetrahedron Lett. 1980, 21, 3199.
(b) Tsuda, T.; Chujo, Y.; Nishi, S.; Tawara, K.; Saegusa, T., J. Am. Chem.
Soc. 1980

, 102, 6381.

10.

Shimizu, I.; Tsuji, J., J. Am. Chem. Soc. 1982, 104, 5844.

11.

Tsuji, J.; Nisar, M.; Shimizu, I., J. Org. Chem. 1985, 50, 3416.

Anthony O. King & Ichiro Shinkai

Merck & Co., Inc., Rahway, NJ, USA

A list of General Abbreviations appears on the front Endpapers