Reaction of (1-azabuta-1,3-diene)tricarbonyliron(0) complexes with sodium borohydride under microwave conditions

Article abstract of DOI:10.1016/S0022-328X(00)00194-7

Reaction of (1-azabuta-1,3-diene)tricarbonyliron(0) complexes with sodium borohydride under microwave irradiation leads to formation of saturated secondary amines. When sodium borodeuteride is used for the reaction the products are 1,2,3-trideutero second

Full text of DOI:10.1016/S0022-328X(00)00194-7

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Journal of Organometallic Chemistry 603 (2000) 240–243
Reaction of (1-azabuta-1,3-diene)tricarbonyliron(0) complexes with
sodium borohydride under microwave conditions
Joseph Akisanya, Timothy N. Danks *, Russell N. Garman
Department of Chemistry, Uni6ersity of Surrey, Guildford, Surrey, GU2 5XH, UK
Received 20 January 2000; received in revised form 11 March 2000
Abstract
Reaction of (1-azabuta-1,3-diene)tricarbonyliron(0) complexes with sodium borohydride under microwave irradiation leads to
formation of saturated secondary amines. When sodium borodeuteride is used for the reaction the products are 1,2,3-trideutero
secondary amines. When this reaction is performed under thermal conditions the complexes are inert to reduction by sodium
borohydride. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: (1-Azabuta-1,3-diene)tricarbonyliron(0); Reduction; Sodium borohydride; Microwave
1
. Introduction
reactions has been shown to significantly enhance the
rate of these processes and in some cases has been used
to promote reactions previously not observed under
conventional thermal activation [7]. Our interest in the
application of microwaves for the promotion of chemi-
cal reactions led us to investigate whether it was possi-
ble to replace the highly reactive reagent lithium
aluminiumhydride with the less reactive sodium boro-
hydride for reductions in which the latter reagent is
ineffective.
In past papers we described how tricarbonyliron(0)
complexes of 1-azabuta-1,3-dienes and 1-oxabuta-1,3-
dienes react with lithium aluminiumhydride to yield
saturated amines and alcohols, respectively [8]. In these
studies we demonstrated that the complexes were inert
to reaction with sodium borohydride even when the
reactions were performed at high temperatures for sev-
eral hours [8]. We also illustrated that when lithium
aluminiumdeuteride was used the reaction products
contained three deuterium atoms in a 1,2,3-relationship
In recent years, the application of microwave irradia-
tion for the promotion of organic reactions has received
increasing attention. The technique has been used to
assist in transfer hydrogenations [1] oxidations [2], aro-
matic substitutions [3], pericyclic reactions [4] and many
other processes of significance to organic chemistry [5].
In addition, the technique has also found applications
in the areas of inorganic and solid state synthesis [6].
The application of microwave irradiation to chemical
Scheme 1.
[8]. In our search to find an alternative procedure to
effect these reductions where it may be possible to
use reagents other than lithium aluminiumhydride we
decided to investigate the effect of microwave
irradiation on the reaction between (1-azabuta-1,3-di-
Scheme 2.
ene)tricarbonyliron(0)
borohydride.
complexes
and
sodium
*
Corresponding author. Fax: +44-01483-876851.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00194-7

J. Akisanya et al. / Journal of Organometallic Chemistry 603 (2000) 240–243
241
of microwaves for the reduction of these compounds
cannot be used for their complete saturation (Scheme
3
).
In order to explore the scope of this reaction a range
Scheme 3.
of complexes bearing different substituents at nitrogen
and C-2 of the coordinated 1-azabuta-1,3-diene were
studied. The results from these experiments are sum-
marised in Table 1 (Scheme 4).
Table 1
Reaction of (1-azabuta-1,3-diene)tricarbonyliron(0) complexes with
NaBH under microwave conditions
4
In all cases when the substituent at nitrogen of the
-azabuta-1,3-diene contains a phenyl group (Table 1
Entry Complex
R
R%
Product Yield (%)
1
entries 1–5) the reaction results in formation of satu-
rated amines. It is of interest however that when the
substituent at nitrogen contained only an alkyl group
(Table 1 entry 6) formation of saturated amines 14 was
not observed and the reaction yields only starting com-
plex 13. In an attempt to promote a reaction between
complex 13 and sodium borohydride the irradiation
time was extended for period of up to 10 min. In each
attempt the reaction resulted in charring and formation
of unidentifiable products. When the reaction was at-
tempted using lithium aluminiumhydride at 0°C for 3 h
in accordance with previously reported conditions [8],
reduction products were also not observed. It can be
concluded therefore, that complex 13 is inert to reac-
tion with hydride transfer reducing agents under ther-
mal and microwave activation.
1
2
3
4
1
5
7
9
Ph
Ph
H
CH3
H
2
6
8
90
90
90
85
Ph(CH )CH
p-CH OC H
3
H
10
3
6
4
5
6
11
13
p-CH OC H CH3 12
70
0
3
6
4
(CH ) CH
CH3 14
3
2
Scheme 4.
2
. Results and discussion
It has been shown that reaction of LiAlH4 or
LiBEt H with (homodiene)tricarbonyliron(0) complexes
leads to formation of anionic (h -allyl)tricarbonyliron
3
Initially the reaction between (1,4-diphenyl-1-aza-
buta-1,3-diene)tricarbonyliron(0) (1) and sodium boro-
hydride in ethanol was studied. A solution of complex
and sodium borohydride in ethanol was irradiated for
min in a domestic microwave oven [9] (500 W) to
yield a dark mixture. Filtration of this mixture through
alumina followed by removal of the solvent under
reduced pressure lead to formation of a yellow oil
identified as saturated amine on the basis of its spectro-
scopic and analytical date (Scheme 1).
3
complexes. This reaction has been shown to proceed via
formation of an iron formyl intermediate. The possibil-
ity of the formation of iron formyl intermediates during
the hydride transfer reduction of complexes 1 and 2
with sodium borohydride under microwave conditions
cannot therefore be ignored [11].
By way of comparison the free 1-azabuta-1,3-dienes
were also reacted with sodium borohydride under iden-
tical microwave conditions. In these cases the only
products observed were allylic amines which resulted
from 1,2-addition. In each example, there was no evi-
dence for formation of the saturated amines even after
prolonged (e.g. 5 min) microwave irradiation.
1
2
When this reaction was carried out using sodium
borodeuteride under identical conditions the reaction
product obtained was confirmed as 1,2,3-trideutero sec-
1
2
ondary amine 3 from its H-, H-NMR and mass
spectra [8]. Clearly, this result shows that the mecha-
nism of the microwave-assisted reduction is likely to
follow a similar reaction path to that carried out using
lithium aluminiumhydride at 0°C (Scheme 2).
In conclusion, it has been shown that by the applica-
tion of microwave irradiation sodium borohydride may
be used in place of lithium aluminiumhydride for the
reduction of tricarbonyliron(0) complexes of 1-azabuta-
When the identical reaction was performed on the
1
,3-dienes. This not only allows a less hazardous
reagent to be used but also considerably simplifies the
work-up’ procedure by allowing the reaction to be
1
free 1-azabuta-1,3-diene 4 examination of the H-NMR
spectrum (300 MHz) of the product mixture indicated
the presence of allylic amine 5 as the sole reaction
product [10]. There was no evidence for the presence of
saturated amine 2 in the product mixture even when the
period of microwave irradiation was extended to 5 min.
When the reaction times were extended to 10 min the
reaction mixtures charred and failed to yield an iden-
tifiable product. Thus, it appears that, the application
‘
performed in the minimum quantity of solvent. It can
also be concluded that the tricarbonyliron(0) moiety
activates the 1-azabuta-1,3-diene to reduction by
sodium borohydride under microwave conditions in a
similar way to that previously reported for lithium
aluminiumhydride at lower temperature [8]. It is of note
however that the temperatures of these microwave reac-

242
J. Akisanya et al. / Journal of Organometallic Chemistry 603 (2000) 240–243
1
3
tions could not be recorded, and it is therefore uncer-
tain whether the activation of sodium borohydride is a
result of rapid heating or a ‘microwave effect’.
CHCH ) and 6.50–7.50 (10H, m, aryl-H). C-NMR
3
(75.4 MHz; CDCl ): 20.69 (CH ), 32.36 (C-2), 36.67
(C-1), 47.70 (C-3), 113.03, 116.79, 125.73, 128.24,
3
3
1
2
28.33, 129.17, 141.67, 147.43 (2×Ph). EIMS: m/z
+
55 [M , 80%], 150 [100, M−105] and 91 [75, C H ].
7
7
3. Experimental
3.3. N-(1-phenylethyl)-3-phenylpropylamine (8)
Complexes 1 [12], 5, 7 [13], 9 [14], 11, and 13 [15]
were synthesised by literature procedures. Melting
B.p. 150–152°C at 1 mmHg; (0.030 g, 90%). Found:
C, 85.3; H, 8.7; N, 6.0. C H N. Calc. C, 85.3; H, 8.8;
points were recorded on a Kofler hot stage micro-
17 21
−
1
1
N, 5.9%. IR (cm ) (liquid film) wmax: 3320m (NH).
melting-point apparatus and are uncorrected. H- and
1
1
3
H-NMR (300 MHz; CDCl ): 1.37 (3H, d, J 7.0 Hz,
C-NMR spectra were recorded on a Bruker AC 300
3
CH CH), 1.58 (1H, broad, NH), 1.81 (2H, m, J 8.0
instrument at 300 and 75.4 MHz, respectively. All
chemical shifts are quoted in ppm relative to a te-
tramethylsilane standard. Chromatography was per-
formed on Merck (40–63 mm) silica. Filtration
through alumina was performed using deactivated
Brockmann (grade iv) alumina. Elemental analyses
was performed on a Leeman Laboratories CE 477
instrument.
3
Hz, CH CH CH ), 2.60 (4H, m, PhCH CH CH ), 3.78
2
2
2
2
2
2
(
2
1H, q, J 7.0 Hz, CHCH ) and 7.10–7.50 (10H, m,
×aryl-H). C-NMR (100.6 MHz CDCl ): 24.16
3
3
13
(
(
1
CH CH), 31.76 (C2), 33.35 (C3), 47.22 (C1), 58.19
3
CHCH ), 125.57, 126.43, 126.70, 128.15, 128.26,
3
+
42.08, and 145.67 (aromatics). EIMS: m/z 239 [M ,
3%], 224 [62, MꢀCH ] and 105 [100, M−134,
2
3
CH(CH )Ph].
3
3
.1. Reaction of
3.4. N-(4-methoxyphenyl)-3-phenylpropylamine (10)
(
1,4-diphenyl-1-azabuta-1,3-diene)tricarbonyliron(0) (1)
with NaBH under microwa6e conditions and the
synthesis of N-phenyl-3-phenylproylamine (2)
4
M.p. 45–46°C; (0.029 g, 85%). Found: C, 79.5; H,
.0; N, 5.7. C H NO. Calc. C, 79.6; H, 7.9; N, 5.8%.
IR (cm ) (Nujol) wmax: 3410 (NH). H-NMR (400
8
16
19
−
1
1
A suspension of complex 1 (0.05 g, 0.14 mmol) and
sodium borohydride (0.025 g, 0.65 mmol) in ethanol
MHz; CDCl ): 1.96 (2H, dt, J 7.0 and 7.5 Hz,
3
CH CH CH ), 2.75 (2H, t, J 7.5 Hz, PhCH CH ), 3.12
2
2
2
2
2
(
5
0.05 ml) was irradiated at full power for 2 min in a
00 W domestic microwave oven. A saturated solution
(
3
2H, t, J 7.0 Hz, CH CH NH), 3.35 (1H, m, NH),
2 2
.76 (3H, s, OCH ) and 6.50–7.40 (9H, m, 2×aryl-
3
of sodium chloride (1×10 ml) was added and the
organic fraction was extracted into diethyl ether (3×
13
H). C-NMR (75.4 MHz; CDCl ): 31.06 (C2), 33.31
3
(
1
C3), 44.31 (C1), 55.69 (OCH ), 113.94, 114.77,
3
10 ml) and the combined organic layers were dried
23.78, 128.27, 141.61, 142.50 and 151.90 (aromatics).
over magnesium sulphate. The solvent was removed
under reduced pressure to leave yellow oil. This oil
was identified as saturated amine 2 (0.03 g, 90%). B.p.
+
EIMS m/z 241 [M , 45%] and 136 [100,
MꢀPhCH CH CH].
2
2
1
50–152°C at
1 mmHg. Found: m/z 211.1360.
3
.5. N-(4-methoxyphenyl)-4-phenyl-2-butylamine (12)
−
1
C H N requires 211.1361. IR (cm ) (liquid film)
wmax: 3410 broad (NH). H-NMR (300 MHz; CDCl ):
1
1
5
17
1
3
M.p. 140–141°C; (0.025 g, 70%). Found. C, 79.8, H,
.91 (2H, m, CH CH CH ), 2.21 (2H, t, J 9.0 Hz,
2 2 2
8.3, N, 5.5; C H NO. Calc. C, 80.0; H, 8.3; N, 5.5%.
IR (cm ) (Nujol) wmax: 3395m (NH). H-NMR (300
MHz; CDCl ): 1.16 (3H, d, J 6.3 Hz, CHCH ), 1.64–
1.89 (2H, m, PhCH CH CH), 2.69 (2H, t, J 6.3 Hz,
PhCH ), 3.37 (1H, m, CHCH ), 3.70 (3H, s, OCH ),
17 21
PhCH CH ), 3.12 (2H, t, J 9.0 Hz, HNCH CH ), 3.40
−1
1
2
2
2
2
(
1H, broad, NH), and 6.50–7.50 (10H, m, 2×aryl-
3
3
1
3
H). C-NMR: (100.6 MHz; CDCl ), 30.8 (C-2), 33.1
3
2 2
(
C-3), 43.1 (C-1), 112.51, 116.93, 125.70, 128.17,
2
3
13
3
1
2
28.98, 141.45, and 148.13 (aromatics); EIMS m/z:
6
.46–7.28 (9H, m, 2×Ph). C-NMR: (75.4 MHz;
+
11 [M , 27%], 106 [100, M−PhCH CH ], and 91
2
2
CDCl ): 20.75 (CHCH ), 32.39 (PhCH CH CH), 38.72
(PhCH ), 48.77 (CHCH ), 55.66 (OCH ), 114.62,
2 3 3
3
3
2
2
[20, M−120, C H ].
7 7
1
14.81, 125.72, 128.27, 128.34, 141.67, 141.99, 121.72
3.2. N-Phenyl-4-phenyl-2-butylamine (6)
+
(
2×Ph). FABMS: m/z 255 [M , 100%], 150 [70, M−
1
05] and 91 [25, C H ].
7 7
M.p. 140–142°C; (0.028 g, 90%). Found: C, 84.9; H,
.5; N, 6.1. C H N Calc. C, 85.3; H, 8.5; N, 6.2%.
8
1
6
19
−
1
1
IR (cm ) (Nujol) wmax: 3390 (NH). H-NMR (300
MHz; CDCl ): 1.95 (3H, d, J 7.0 Hz, CH CH), 1.89
Acknowledgements
3
3
(
2H, m, CH CH CH), 2.75 (2H, t,
J
8.0 Hz,
We thank the University of Surrey for financial
support.
2
2
PhCH CH ), 3.54 (1H, br, NH), 3.55 (1H, m,
2
2

J. Akisanya et al. / Journal of Organometallic Chemistry 603 (2000) 240–243
243
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