Uranyl Schiff base complexes as new heterogeneous catalysts for halogen exchange reactions between alkyl halides and elemental halogens

Article abstract of DOI:10.1007/s11172-015-1076-2

Mild and effective procedure for the halogen exchange reaction of alkyl halides with elemental iodine and bromine catalyzed with uranyl Schiff base complexes in various aprotic solvents was developed. Corresponding alkyl bromides and iodides were obtained with high yields within 20—70 min. The structures of the target products were confirmed by physical and spectroscopic data.

Full text of DOI:10.1007/s11172-015-1076-2

1
814
Russian Chemical Bulletin, International Edition, Vol. 64, No. 8, pp. 1814—1818, August, 2015
Uranyl Schiff base complexes as new heterogeneous catalysts for
halogen exchange reactions between alkyl halides and elemental halogens
H. Naeimi and Z. S. Nazifi
Department of Organic Chemistry, Faculty of Chemistry, University of Kashan,
Kashan, 87317, Islamic Republic of Iran.
Fax: +9 (8361) 591 2397. Eꢀmail: naeimi@kashanu.ac.ir
Mild and effective procedure for the halogen exchange reaction of alkyl halides with elemenꢀ
tal iodine and bromine catalyzed with uranyl Schiff base complexes in various aprotic solvents
was developed. Corresponding alkyl bromides and iodides were obtained with high yields
within 20—70 min. The structures of the target products were confirmed by physical and
spectroscopic data.
Key words: uranium(VI) complexes, halogen exchange reaction, benzyl halides, bromine,
iodine, halogens.
Organic halides play a key role in a number of organic
synthesized by the reaction of the corresponding Schiff
base with uranyl acetate in methanol.
1
syntheses. Therefore, synthesis of alkyl halides is a very
important transformation in organic chemistry. Alkyl haꢀ
lides are generally accessed from alcohols, whose converꢀ
sion into halides is one of the most frequently used funcꢀ
tional group transformations. Alkyl iodides are less stable
than the corresponding chlorides and bromides, more reꢀ
active than other halides, being in some cases the only
reactive halides.2
The results of halogen exchange reactions of benzyl
chloride 2a with bromine and iodine (Scheme 1) in the
presence of uranyl complexes 1a—f are given in Table 1.
As it can be seen, halogen exchange of benzyl chloride 2a
catalyzed by complexes 1a—f is relatively fast even at room
temperature and affords the corresponding benzyl halides
3a,b in high yields. Thus, halogen exchange catalyzed by
complex 1c is completed within 40 (3a) and 20 min (3b) to
give the corresponding products in the yields of 85 (3a)
and 90% (3b) (see Table 1, entry 3). Note that catalystꢀ
free halogen exchange of benzyl chloride 2a with the haloꢀ
gen excess (entry 7) either does not proceed (in the case of
iodine) or proceeds with very low conversion (in the case
of bromine). Both prolongation of the reaction time (up to
several days) and reflux have no effect on the reaction rate
and unreacted benzyl chloride 2a was completely recovered.
Effect of transition metal nature on catalytic perforꢀ
mance of the metal Schiff base complexes was examined
on a series of experiments involving halogen exchange of
benzyl chloride 2a in the presence of Mn (1g), Co (1h),
and Cu (1i) complexes (see Scheme 1, Table 1, entries 8—10).
Catalysts 1g—i show lower efficiency compared with
uranyl complexes. These results are in agreement with our
previous observations on catalytic activity of the complexꢀ
Recently, the selective conversion of allylic, benzylic
and other alcohols into the corresponding halides has been
described.3 Although various methods to access alkyl
4
—8
halides from alcohols have been reported,
they are ofꢀ
ten time consuming, require expensive reagents and tedious
workup. The other method towards alkyl halides is haloꢀ
gen exchange either between alkyl halides and sodium
9
halides (the Finkelstein reaction) or involving a pair of
different alkyl halides.1
0
Metal Schiff base complexes are the most versatile catꢀ
1
1,12
alysts for halohydrin synthesis,
conversion of epoxides
1
3,14
to ꢀhydroxy nitriles,
oxidation of cyclooctene and
styrene,1 reduction of benzene, oxidation of sulfides,
5
16
17,18
and olefin cyclopropanation.1 In the present work, we
used metal Schiff base complexes 1a—i as catalysts for
halogen exchange of some organohalides with elemental
bromine and iodine.
9
1
2
es of different metals with Schiff bases.
Results and Discussion
The developed conditions were applied for halogen
exchange of other benzylic halides 2b—f and related
4ꢀbromophenacyl bromide (2g) using uranium(VI) comꢀ
plex 1c as a catalyst (Scheme 2, Table 2).
Our attempts to use sterically hindered aromatic
halides, triphenylmethyl chloride and triphenylmethyl
In the present work, we used complexes of U, Mn, Co,
and Cu with Schiff bases. The Schiff bases were syntheꢀ
sized by the reaction of 2ꢀhydroxyꢀ1ꢀnaphthaldehyde with
the various amines. The uranium(VI) complexes 1a—f were
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1814—1818, August, 2015.
066ꢀ5285/15/6408ꢀ1814 © 2015 Springer Science+Business Media, Inc.
1

Halogen exchange
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
1815
Scheme 1
Scheme 2
3
: Hal = I (a), Br (b)
Conditions: catalyst 1a—i, CH Cl , 20 C.
2
2
Y = (CH2)2 (a), (CH2)8 (b),
(c),
(d),
(f)
2
a
b
c
d
e
f
a—f Hal1 R1 R2
R3
H
H
3a—i Hal2 R1 R2 R3
Cl
Cl
Cl
Br
Br
Br
H
Cl
H
H
H
H
H
H
H
H
Cl
a
b
c
d
e
f
I
Br
I
I
I
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
Cl
Br
NO2
H
(
e),
Cl
Br
NO2
H
H
I
g
h
i
Br
Br
I
Cl
H
H
Cl
H
bromide, into halogen exchange reaction failed: even 6 h
after the reaction onset no halogen exchange products
were detected.
The effect of the solvent on the halogen exchange reꢀ
action was studied on the example of the transformation
M = Mn (g), Co (h), Cu (i)
2
a  3a catalyzed by complex 1c (Table 3). This reaction
proceeds more cleanly in dichloromethane (yield of 85%);
while in chloroform, DMF, DMSO, and acetonitrile the
yields of 3a are noticeably lower.
In our opinion, the following factors can exert a conꢀ
trolling influence on halogen exchange reaction: i) the
nature of the metal ion; ii) the steric hindrance in the
a
Table 1. Halogen exchange reaction between benzyl chloꢀ
ride 2a and elemental bromine and iodine catalyzed by tranꢀ
sition metal complexes 1a—i
b
Entry Catalyst
t/min
Yield 3 (%)
2
а + I2
2а + Br2
3a
3b
Table 2. Halogen exchange reaction between halides 2b—g and
elemental bromine and iodine catalyzed by complex 1ca
1
2
3
4
5
6
7
8
9
1
1a
1b
1c
1d
1e
1f
—
1g
1h
1i
40
45
40
55
75
60
30
35
20
45
60
55
5 days
30
40
25
90
86
85
78
72
70
90
88
90
77
75
72
20
75
55
35
b
Entry Substrate Halogen
t/min
Product Yield (%)
1
2
3
4
5
6
7
8
2b
2c
2d
2e
2f
2g
2b
2c
I2
I2
I2
I2
I2
I2
Br2
Br2
40
35
25
45
50
45
35
25
3c
3d
3e
3f
3i
3j
80
84
90
80
87
82
82
92
c
d
5 days
40
—
72
55
36
50
35
0
3g
3h
a
b
c
Reaction conditions: CH Cl , 20 C.
2
2
Isolated yield.
a
b
Catalystꢀfree conditions.
No product found.
Reaction conditions: CH Cl , 20 C.
2 2
Isolated yield.
d

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816
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
Naeimi and Nazifi
Table 3. Reaction of benzyl chloride 2a with iodine in
different solvents catalyzed by complex 1c
Y (%)
00
1
Entry
Solvent
t/min
Yield 3a (%)
80
60
1
2
3
4
5
CHCl3
DMSO
MeCN
DMF
35
45
55
40
40
82
80
77
70
85
4
2
0
0
CH Cl2
2
1
2
3
4
5
N
substrate; iii) the solvent nature; iv) rate and the order of
the reagent mixing.
Fig. 1. Reusability of catalyst 1c in bromination of benzyl chloꢀ
ride 2a (CH Cl ). N is the number of a catalytic cycle, Y is the
2
2
A plausible reaction mechanism is given on Scheme 3.
yield of product 3b.
The step (1) involves interaction of halogen (Hal ) and
2
catalyst (BSꢀM) to form a molecular complex as a contact
pair. In the step (2), the molecular complex decomposes
of alkyl halides with elemental halogens. The advantages
of the suggested method is the possibility of catalyst reuse,
the low cost of the catalyst, the versatility and simplicity
of the procedure, short reaction times, and high yields of
the target products.
–
releasing the Hal ion (cf. data from Refs 8 and 11). The
3
–
Hal3 ion is a nucleophile and is able to react with the
substrate molecule (step (3)). The mechanism of the step
(
3) closely resembles the mechanism of the bimolecular
nucleophilic substitution S 2. The final step (4) is the
N
Experimental
regeneration of the catalyst to resume the next catalytic
cycle. These steps continuously occur until either alkyl
halides or halogens are completely consumed. The low
reaction rate of the catalystꢀfree reaction can be satisfacꢀ
torily rationalized in terms of the suggested mechanism.
All commercially available reagents purchased from Merck
in high purity grade were used without further purification. Alkyl
halides and solvents were purified by standard procedures.
IR spectra were recorded on a Perkin—Elmer 781 spectroꢀ
photometer and on an Impact 400 Nicolet FTꢀIR spectrophotoꢀ
1
meter for the KBr pellets. H NMR spectra were recorded on
Scheme 3
a Bruker DRXꢀ400 spectrometer in DMSOꢀd and CDCl using
6
3
Me Si as an internal standard. Melting points were measured
4
with a Yanagimoto micro melting point apparatus and given
uncorrected. The purity determination of the products and the
reaction course monitoring were accomplished by TLC on silica
gel PolyGram SILG/UV 254 plates.
Synthesis of Schiff bases (general procedure). All tetradenꢀ
tate Schiff bases were prepared by the condensation of diamines
(
1 mmol) with 2ꢀhydroxyꢀ1ꢀnaphtaldehyde (2 mmol) in methaꢀ
nol under stirring. After the completion of the reaction (TLC
monitoring), the obtained colored substances were collected by
filtration and washed with cold MeOH. The crude products were
purified by recrystallization from ethanol. The physical and
spectroscopic data for the synthesized Schiff bases were in good
2
0,21
agreement with the published data.
Synthesis of metal Schiff base complexes (general procedure).
To a solution of tetradentate ligand (Schiff base) (1 mmol) in
MeOH, a filtered solution of M(OAc) (1 mmol) in MeOH was
2
added with stirring. After completion of the reaction (TLC monꢀ
itoring), the obtained colored substances were collected by filꢀ
tration and washed with MeOH. Pure metal Schiff base comꢀ
plexes were obtained by recrystallization of the crude products
from EtOH.
After completion of the reaction, the catalyst can be
easily recovered and reused (Fig. 1).
1
,1´ꢀ[Ethaneꢀ1,2ꢀdiylbis(nitrilomethylylidene)dinaphthalenꢀ
Structures of the synthesized products were confirmed
–
1
2
3
1
ꢀolato]uranyl(VI) (1a). Yellow solid, m.p. 330 C. IR, /cm :
1
13
by IR spectroscopy, H and C NMR spectroscopy, and
mass spectrometry.
045 ((C—H), Ar); 2848, 2923 ((C—H), alkyl); 1622 ((C=N));
455—1510 (C=C, Ar); 1195 ((C—O)). H NMR (400 MHz,
1
In summary, we introduced uranium(VI) complex 1c
as an efficient catalyst for the halogen exchange of a series
CDCl ), : 8.41 (s, 2 CH, imine); 7.77 (d, 2 H, Ar); 7.31 (d, 2 H,
3
Ar); 7.13 (d, 2 H); 7.50 (t, 2 H, Ar); 6.93 (t, 2 H); 6.74 (t, 2 H);

Halogen exchange
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
1817
3
1
1
.46 (s, 4 H, 2 CH ). 13C NMR (100 MHz, CDCl ), : 159.24,
38.05, 136.46, 128.26, 127.76, 126.26, 125.88, 123.32, 118.14,
06.73, 76.45, 51.98. Found (%): C, 44.02; H, 2.63; N, 4.18.
Benzyl bromide (3b). Yellow liquid, b.p. 201—202 C (see
2
3
–
1
Ref. 1). IR, /cm : 3064, 2958, 1663, 1452, 1265, 1164, 1072,
1
831, 697. H NMR (400 MHz, CDCl ), : 7.07—7.39 (m, 5 H);
3
13
C H N O U. Calculated (%): C, 45.29; H, 2.85; N, 4.40.
4.411 (s, 2 H). C NMR (100 MHz, CDCl ), : 131.05, 129.76,
2
4
18
2
4
3
1
,1´ꢀ[Octaneꢀ1,8ꢀdiylbis(nitrilomethylylidene)dinaphthalenꢀ
126.94, 127.55, 34.51.
–
1
2
3
1
ꢀolato]uranyl(VI) (1b). Yellow solid, m.p. >300 C. IR, /cm
048 ((C—H), Ar); 2851, 2926 ((C—H), alkyl); 1620 ((C=N));
457—1543 (C=C, Ar); 1179 ((C—O)). H NMR (400 MHz,
:
2ꢀChlorobenzyl iodide (3c). Yellow liquid, b.p. 104—107 C
–
1
(cf. Ref. 1: 109—111 C). IR, /cm : 3035, 2926, 1473, 1443,
1
1
1275, 1052, 823, 674. H NMR (400 MHz, CDCl ), : 7.41 (d, 1 H,
3
CDCl ), : 8.51 (c, 2 CH, imine); 7.67 (d, 2 H, Ar); 7.53 (d, 2 H);
J = 9.3 Hz); 7.29 (d, 1 H, J = 9.3 Hz); 7.19 (m, 2 H); 4.52 (s, 2 H).
3
13
7
.39 (d, 2 H); 7.28 (t, 2 H); 7.08 (m, 2 H); 6.77 (d, 2 H);
C NMR (100 MHz, CDCl ), : 145.78, 138.23, 134.13, 133.04,
3
1
.22—1.61 (t, 4 H, 2 CH ); 3.53 (m, 12 H, 6 CH ).
127.22, 126.19, 33.17.
2
2
1
,1´ꢀ[1,2ꢀPhenylenebis(nitrilomethylylidene)dinaphthalenꢀ2ꢀ
4ꢀChlorobenzyl iodide (3d).1 Oil. IR, /cm–1: 3037, 2929,
–
1
1
olato]uranyl(VI) (1c). Orange solid, m.p. >300 C. IR, /cm
1
:
1597, 1491, 1267, 1093, 825, 682. H NMR (400 MHz, CDCl ),
3
1
600 ((C=N)); 1447—1530 (C=C, Ar); 1168 ((C—O)). H NMR
: 7.34 (d, 2 H, J = 8.5 Hz); 7.31 (d, 2 H, J = 8.5 Hz); 4.37 (s, 2 H).
1
3
(
400 MHz, CDCl ), : 9.71 (s, 2 CH, imine); 8.35 (d, 2 H);
C NMR (100 MHz, CDCl ), : 141.22, 140.18, 135.15,
3
3
7
.91—7.72 (dd, 4 H, Ar, J = 8.0 Hz); 7.45 (t, 2 H); 7.42 (d, 2 H,
Ar); 7.30 (t, 2 H, Ar); 6.89 (t, 2 H, Ar); 6.81 (d, 2 H). MS, m/z
Irel (%)): 685 [M + 1]+ (6); 684 [M]+ (15); 115 (20), 416 (35),
43 (40), 170 (50), 76 (55), 273 (100).
,1´ꢀ[1,4ꢀPhenylenebis(nitrilomethylylidene)dinaphthalenꢀ2ꢀ
132.42, 33.74.
4ꢀBromobenzyl iodide (3e). White solid, m.p. 56—58 C (cf.
Ref. 1: 57—59 C). IR, /cm : 3021, 2900, 2850, 1588, 1490, 1222,
1030, 850, 675. H NMR (400 MHz, CDCl ), : 7.39 (d, 2 H,
J = 8.4 Hz); 7.29 (d, 2 H, J = 8.4 Hz); 4.24 (s, 2 H). C NMR
–1
(
1
1
3
1
3
1
–1
olato]uranyl(VI) (1d). Brown solid, m.p. 295—299 C. IR, /cm
2
1
:
(100 MHz, CDCl ), : 143.55, 140.12, 134.32, 133.02, 33.24. MS
3
+
+
977 (C—H, alkyl); 1607 ((C=N)); 1471—1544 (C=C, Ar);
(EI), m/z (Irel (%)): 298 [M + 2 H] (3), 296 [M] (3), 171 (100),
169 (100), 127 (25), 91 (42), 90 (100), 89 (95), 77 (12), 76 (10),
63 (60), 39 (25).
4ꢀNitrobenzyl iodide (3f). Pale yellow solid, m.p. 95—97 C
(cf. Ref. 1: 94—95 C). IR, /cm : 3059, 2998, 1695, 1581,
1
178 ((C—O)). H NMR (400 MHz, CDCl ), : 9.74 (s, CH,
3
imine); 7.82 (d, 2 H); 7.79, 7.55 (dd, 8 H); 7.54 (t, 2 H); 7.33
t, 2 H); 6.84 (d, 2 H); 6.62 (d, 2 H). Found (%): C, 48.30; H, 2.74;
N, 4.02. C H N O U. Calculated (%): C, 49.13; H, 2.65;
(
–
1
3
0
25
2
4
1
N, 4.09.
,1´ꢀ[Methylenebis(4,1ꢀphenylene)bis(nitrilomethylylidene)ꢀ
1395, 1195, 1069, 991, 807, 71. H NMR (400 MHz, CDCl ), : 8.13
3
3
1
(d, 2 H, J = 8.8 Hz); 7.63 (d, 2 H, J= 8.8 Hz); 4.32 (s, 2 H). 1 C NMR
dinaphthalenꢀ2ꢀolato]uranyl(VI) (1e). Orange solid, m.p.
(100 MHz, CDCl ), : 174.68, 144.81, 129.96, 124.05, 30.99.
3
2
1
74—277 C. IR, /cm–1: 3100 w (C—H, Ar); 1607 ((C=N));
2ꢀChlorobenzyl bromide (3g). Yellow liquid, b.p. 103—105 C.
1
–1
471—1544 (C=C, Ar); 1138 ((C—O)). H NMR (400 MHz,
IR, /cm : 3078, 2966, 1513, 1458, 1279, 1084, 833, 684.
1
CDCl ), : 9.40 (s, 2 CH, imine); 8.47 (d, 2 H); 7.91 (d, 2 H);
H NMR (400 MHz, CDCl ), : 7.49 (d, 1 H, J = 9.4 Hz); 7.42
3
3
13
7.78 (d, 2 H); 7.59, 7.52 (both dd, 8 H); 7.57 (t, 2 H); 7.38 (t, 2 H);
(d, 1 H, J = 9.4 Hz); 7.29 (m, 2 H); 4.72 (s, 2 H). C NMR
7
.33 (d, 2 H); 6.99 (d, 2 H); 4.04 (m, CH ). Found (%): C, 52.86;
(100 MHz, CDCl ), : 146.11, 139.98, 135.13, 133.62, 128.12,
2
3
H, 3.07; N, 3.46. C H N O U. Calculated (%): C, 54.27;
127.32, 34.96.
3
5
24
2
4
H, 3.12; N, 3.62.
,1´ꢀ[Sulfonylbis(4,1ꢀphenylene)bis(nitrilomethylylidene)diꢀ
naphthalenꢀ2ꢀolato]uranyl(VI) (1f). Orange solid, m.p. >300 C.
4ꢀChlorobenzyl bromide (3h). Solid, m.p. 50—53 C (see
–
1
1
Ref. 1). IR, /cm : 3075, 2961, 1513, 1455, 1281, 1083, 839,
1
680. H NMR (400 MHz, CDCl ), : 7.32 (d, 2 H, J = 8.8 Hz);
3
–
1
13
IR, /cm : 3000 w (C—H, Ar); 1612 ((C=N)); 1495—1546
7.17 (d, 2 H, J = 8.8 Hz); 4.37 (s, 2 H). C NMR (100 MHz,
1
(
C=C, Ar); 1095—1133 ((C—O)). H NMR (400 MHz, CDCl ),
CDCl ), : 144.05, 142.16, 135.13, 133.62, 35.81.
3
3

: 9.73 (s, 2 CH, imine); 8.48 (d, 2 H); 7.95 (d, 2 H); 7.75
1ꢀ(4ꢀBromophenyl)ꢀ2ꢀiodoethanꢀ1ꢀone (3i). Pale yellow solꢀ
id, m.p. 111—113 C. IR, /cm– : 3444, 2960, 1487, 1348, 1225,
1
(
d, 2 H); 7.47, 7.60 (both dd, 8 H); 7.52 (t, 2 H); 7.20 (t, 2 H);
1
6
.66 (d, 2 H).
1112, 859, 800, 712, 696, 670. H NMR (400 MHz, CDCl ),
3
Halogen exchange reaction of alkyl halides with elemental haloꢀ
: 7.52 (d, 2 H, J = 8.4 Hz); 7.65 (d, 2 H, J = 8.4 Hz); 4.23 (s, 2 H).
13
gens (general procedure). A solution of alkyl halide (1 mmol) in
dichloromethane (5 mL) was added to a stirred solution of cataꢀ
lyst (0.1 mmol) in CH Cl (5 mL) at room temperature followed
C NMR (100 MHz, CDCl ), : 191.13, 141.12, 138.22, 132.35,
3
131.15, 35.50.
2
2
by dropwise addition of a solution of elemental halogen (Br or
The authors are grateful to University of Kashan for
2
I2) (2 mmol) in dichloromethane (5 mL) over 15 min. After
completion of the reaction (TLC monitoring), the reaction mixꢀ
ture was filtered and the obtained organic solution was washed
with 10% aqueous Na S O (2×10 mL) and water (2×10 mL).
supporting this work by Grant 159148/12.
References
2
2
3
The aqueous layer was extracted with CH Cl (2×10 mL) and the
2
2
combined organic layers were dried with CaCl . Removal of the
1. A. R. Hajipour, A. R. Falahatia, A. E. Ruoho, Tetrahedron
Lett., 2006, 47, 4191.
2. B. Boyer, M. Keramane, S. Arpin, J. L. Montero, J. P.
Roque, Tetrahedron, 1999, 55, 1971.
2
solvent afforded pure target alkyl halides. Structures of the obtained
alkyl halides were confirmed by a comparison with authentic
2
samples prepared in accordance to the literature procedure.
Benzyl iodide (3a). Yellow solid, m.p. 26—27 C (cf. Ref. 1:
3. G. A. Olah, S. C. B. Narang, G. B.Gupta, R. Malhotra,
Angew. Chem., Int. Ed., 1979, 18, 612.
4. H. N. Rydon, B. L. Tong, J. Chem. Soc., 1956, 3043.
5. S. Hanessian, M. M. Ponpinom, P. Lavalle, Carbohydr. Res.,
1972, 24, 45.
–
1
2
7
4
1
5 C). IR, /cm : 3031, 2932, 1572, 1495, 1452, 1072, 811,
1
63, 667. H NMR (400 MHz, CDCl ), : 7.03—7.21 (m, 5 H);
3
.21 (s, 2 H). 13C NMR (100 MHz, CDCl ), : 129.50, 127.96,
3
25.54, 123.55, 33.21.

1
818
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 8, August, 2015
Naeimi and Nazifi
6
7
8
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. P. J. Gregg, B. J. Samuelsson, Chem. Soc., Perkin Trans. 1,
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Received June 5, 2014