Catalytic cyanation of aryl halides with NaCN in the presence of crowned phosphine complexes of palladium under solid-liquid two-phase conditions

Article abstract of DOI:10.1055/s-1998-1651

The cyanation of aryl halides with powdered NaCN in dioxane is efficiently catalyzed by crowned phosphine complexes of palladium to give aryl cyanides in good yields. Owing to the proximity effect of the crowned complexes, the catalytic efficiency is superior to those of mixed systems of unmodified phosphine complexes of palladium with the corresponding crown ethers.

Full text of DOI:10.1055/s-1998-1651

SYNLETT
243
LETTERS
Catalytic Cyanation of Aryl Halides with NaCN in the Presence of Crowned Phosphine
Complexes of Palladium under Solid-liquid Two-phase Conditions
*
Tamon Okano, Masahiro Iwahara, and Jitsuo Kiji
Department of Materials Science, Faculty of Engineering, Tottori University, Koyama, Tottori 680, Japan
Received 19 December 1997
Abstract: The cyanation of aryl halides with powdered NaCN in
dioxane is efficiently catalyzed by crowned phosphine complexes of
palladium to give aryl cyanides in good yields. Owing to the proximity
effect of the crowned complexes, the catalytic efficiency is superior to
those of mixed systems of unmodified phosphine complexes of
palladium with the corresponding crown ethers.
The cyanation of aromatic halides with inexpensive alkali metal
cyanides is an important synthetic tool, which is achieved by the use of
1
Ni or Pd phosphine complexes under very mild conditions. However,
alkali metal cyanides are insoluble in common organic solvents,
whereas in such solvents in which the cyanide salts are too soluble, an
2
excess of cyanide anion deactivates these catalysts. In order to keep the
concentration of cyanide anion moderate, the good combination of
2
c,3
2a,4
solvent and cyanide salt,
and the use of phase transfer catalysts
or
5
Al O have been investigated. However, these cyanations require strict
2
3
reaction conditions. Recently, it has been reported that phosphine
complexes modified with crown ethers efficiently react with slightly
6
-8
soluble alkali metal salts.
Therefore we studied the catalytic
cyanation with sodium cyanide using the crowned phosphine complexes
of palladium.
The cyanation of phenyl bromide with powdered NaCN in dioxane
successfully proceeded in the presence of PdCl -{PPh (bc-5)} or
2
2
2
PdCl {PPh (bc-6)}
(PPh (bc-5)=17-diphenylphosphino-2,5,8,11,14-
2
2
2
2
pentaoxa-bicyclo-[13.4.0]-nonadeca-15,17,19-triene, PPh (bc-6)=20-
2
diphenylphosphino-2,5,8,11,14,17-hexaoxa-bicyclo-[16.4.0]-docosa-
1
8,20,22-triene) to give benzonitrile in a considerable turnover number
9
(see Table 1). These catalysts were unfortunately inactive for the
cyanation using an aqueous solution of NaCN in toluene at 100°C.
The addition of benzo-15-crown-5 was effective in increasing the
catalytic activity of PdCl (PPh ) . Though a large amount of the
The turnover number of the solid-liquid cyanation was improved by the
addition of small amounts of Zn powder and free PPh (bc-5). The Zn
2
3 2
2
benzocrown was used, the activity of the mixed system was still inferior
to that of PdCl {PPh (bc-5)} . The crowned phosphine and PPh (dmp)
powder is likely to reduce PdCl {PPh (bc-5)} to the catalytically
2
2
2
2
c
2
2
2
2
active species as reported before. In fact, PhPdBr{PPh (bc-5)} was
2
2
(
PPh (dmp)=1,2-dimethoxy-4-diphenylphosphino-benzene) are almost
1
0
2
active without Zn powder (see Table 2). The addition of the phosphine
mostly contributes to stabilization of the catalytically active species as
described below.
equivalent in both electronic and steric effects. However, the catalytic
activity of PhPdBr{PPh (dmp)} was very poor as compared with that
2
2
of PhPdBr{PPh (bc-5)} . The addition of benzo-15-crown-5 also
2
2
enhanced the catalytic activity of PhPdBr{PPh (dmp)} , but the yield
2
2
was still below the level of PhPdBr{PPh (bc-5)} . The crowned
2
2
phosphine itself is known to be upon the same extractability level with
benzo-15-crown-5.6b Therefore, the high reactivity of the crowned
complexes is likely attributed to a proximity effect as in enzyme

2
44
LETTERS
SYNLETT
chemistry. That is to say, the intramolecular substitution of the
palladium complex with the cyanide anion extracted with the side crown
arm is much faster than the corresponding intermolecular reaction in the
mixed catalyst system. Analogous proximity effects are observed in
other reactions of crowned phosphine complexes.6a,7,11
(4) H. Prochazka and M. Siroky, Coll. Czech. Chem. Commun., 1983,
48, 1765; N. Sato and M. Suzuki, J. Heterocycl. Chem., 1987, 24,
1371; E. Piers and F. F. Fleming, Can. J. Chem., 1993, 71, 1867.
(5) J. R. Dalton and S. L. Regen, J. Org. Chem., 1979, 44, 4443.
(
6) (a) T. Okano, M. Iwahara, T. Suzuki, H. Konishi, and J. Kiji,
Chem. Lett., 1986, 1467; (b) T. Okano, M. Iwahara, H. Konishi,
and J. Kiji, J. Organomet. Chem., 1988, 346, 267.
The biphasic cyanation of iodides as well as aryl bromides was also
achieved. As aryl chlorides were inert under these conditions, bromo or
iodo chlorobenzenes gave the corresponding chlorobenzonitriles in
good yields. These biphasic reactions have the advantage in that the
product and the cyanide salt are easily separated from the reaction
mixture.
(7) M. Sawamura, H. Nagata, H. Sakamoto, and S. Ito, J. Am. Chem.
Soc., 1992, 114, 2586 .
(8) G. M. Gary, Comments Inorg. Chem., 1995, 17, 94.
(9) These dichloro compounds were prepared by the previously
reported procedure.6
Acknowledgement. The authors gratefully acknowledge support for
this research by Grant-in-Aid for Scientific Research on Priority Areas
(10) This phenyl compound was prepared as follows. To a mixture of
PdCl (0.05 g) and PPh (bc-5) (0.51 g) in DMSO (4 ml) at 130°C,
2
2
(No. 283 , "Innovative Synthetic Reactions") from Monbusho.
NH NH ·H O (0.07 ml) was added. After addition of benzene (30
2
2
2
ml), the solution was washed with water (10 ml) several times.
After concentration and dryness, the residue was treated with
PhBr (0.3 ml) in benzene (4 ml) under reflux for 20 h to give
References and Notes
(
1) G. P. Ellis and T. M. Romney-Alexander, Chem Rev., 1987, 87,
79; V. V. Grushin and H. Alper, Chem Rev., 1994, 94, 1047.
7
trans-PhPdBr{PPh (bc-5)} as orange crystals (0.21 g, 64 %, mp.
2 2
9
6
7-100 °C). 1H-NMR(270 MHz, CDCl , δ) : 3.7-4.2 (32H, m),
.23 (2H, dd, J=7.3 and 7.8Hz), 6.35 (1H, t, J= 7.3Hz), 6.62 (2H,
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3
d, J=7.8Hz), 6.78 (2H, d, J=8.4Hz), 7.0 (2H, m), 7.1-7.7 (22H, m).
1
30, 1862; (c) Y. Sakakibara, F. Okuda, A. Shimobayashi, K.
13
C-NMR(67.8 MHz, CDCl , δ) : 68.7, 69.0, 69.4, 69.5, 70.5,
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Jpn., 1988, 61, 1985.
3
7
1
0.6, 71.2, 71.3, 113.0, 121.8, 122.5, 125.3, 127.7, 127.8, 128.6,
29.5, 132.3, 134.3, 136.3, 148.4, 150. 8, 156.3. 31P-NMR(109.3
(
3) K. Takagi, K. Sasaki, and Y. Sakakibara, Bull. Chem. Soc. Jpn.,
MHz, CDCl , δ) : 22.7.
3
1991, 64, 1118; Y. Sakakibara, Y. Ido, K. Sasaki, M. Sakai, and
(11) E. M. Hyde, B. L. Show, and I. Shepherd, J. Chem. Soc., Dalton
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Trans., 1978, 1686.