MCM-silylamine Pd(II)complex: A heterogeneous catalyst for selective azide reductions

Article abstract of DOI:10.1055/s-1999-2846

Palladium complex immobilized on MCM-41 catalyses the reduction of alkyl, aryl and arylsulfonyl azides to the corresponding amines in excellent yields under mild conditions.

Full text of DOI:10.1055/s-1999-2846

LETTER
MCM-Silylamine Pd(II)Complex: A Heterogeneous Catalyst for Selective Azide Reductions
1413
MCM-Silylamine Pd(II)Complex: A Heterogeneous Catalyst for Selective
Azide Reductions
M. Lakshmi Kantam,* N. Sreenivasa Chowdari, Ateeq Rahman, B.M. Choudary
Indian Institute of Chemical Technology, Hyderabad 500 007, India
Fax: +91 40 7173378; E-mail: mlakshmi@iict.ap.nic.in
Received 8 July 1999
in dry toluene under inert atmosphere for 48h. MCM-si-
lylpropyl amine (1g) was complexed with Bis(benzylcya-
nide)palladium(II) chloride (2 mmol ) in dry benzene
under stirring at room temperature. The bright yellow co-
loured complex thus obtained was filtered, Soxhlet ex-
tracted with benzene for 8 h and dried under vacuum. Pd
content of the catalyst was determined by plasma analysis
Abstract: Palladium complex immobilized on MCM-41 catalyses
the reduction of alkyl, aryl and arylsulfonyl azides to the corre-
sponding amines in excellent yields under mild conditions.
Keywords: reduction, MCM-41, palladium complex, azides,
amines
(
1.99% Pd). The IR spectra of the ligand and the complex
Azides are generally prepared with good regio-, stereo-
and enantio control and subsequent reduction permits a
controlled introduction of amino function. The reduction
showed the silylpropylamine bands. The complex showed
an additional band at 356 cm indicating the presence of
terminal Pd-Cl.
-1
1
15
of azides to amines is an important protocol in organic
synthesis of intermediates applicable in fine chemical in-
dustry. A wide variety of reagents, lithium aluminum hy-
2
3
zinc borohydride,4
dride, sodium borohydride,
borohydride exchange regin (BER), lithium amino boro-
5
6
7
R= aryl, alkyl, arylsulfonyl
hidrides, sodium borohydride/copper(II) sulfate, benzyl
triethyl ammonium tetrathio molybdate, SmI SnCl2,
triphenylphosphine,
8
9
10
Scheme
2
,
1
1
12
iodotrimethylsilane
etc. have
been reported for reduction of azides. These methods gen-
erate an enormous amount of effluents and suffer with te-
dious workup procedures. Stringent environmental laws
and cutting edge competition in fine chemical industry
prompted to opt highly desirable selective ecofriendly cat-
alytic hydrogenation of azides to amines in the presence
of variety functional groups. A catalytic method for azide
reductions using inexpensive and non-polluting reagents
is therefore highly desirable particularly if it can be re-
used.
As shown in Table 1. a number of aryl, alkyl and arylsul-
fonyl azides have been reduced to the corresponding
amines in excellent yields at room temperature indicating
a broader scope of application of our catalytic system un-
like other reagents. The rate of hydrogenation of the
azides is very faster and impressive even at room temper-
ature when compared with NaBH and heterogenised
4
borohydride exchange resin, which requires reflux condi-
tions, stoichiometric quantity of reagent, longer reaction
times (3-18h) and whose application is confined to the re-
The recently discovered family of mesoporous materials
MCM possesses compatible tunable larger pores to large
molecules will find conceivable application in fine chem-
ical industry. Accordingly we designed anchored catalysts
using MCM-41 as a support for nitrogroup reduction and
5,16
duction of aromatic azides. The secondary alkyl azides
are also reduced to the corresponding amines in good
yields (entry10&13). A selective azido reduction in pres-
ence of other functional groups such as carbonyl, sulfonyl,
nitro and benzyl under the conditions employed is a sig-
nificant achievement. However in case of cinnamyl azide
both olefin and azido groups are reduced simultaneously
without any preference. Further, as part of the ongoing
asymmetric catalysis programme this selective reduction
1
3
hydrodehalogenation reactions. We report in this letter
selective azide reductions by a heterogeneous MCM-sil-
ylamine Pd(II) complex for the first time affording excel-
lent yields.
The MCM-silylamine Pd(II) complex was prepared13 as has also been applied for the reduction of 3,4-diazido-1-
described below: The mesoporous material MCM-41 benzylpyrrolidine to the corresponding diamine without
1
4
(
pure silica) was synthesized by stirring a solution of debenzylation and racemization. The catalyst is reused for
tetraethyl ortho silicate (1 mol), ethanol (6 mol), isopro- five cycles with consistent activity, for example 3,4,5- tri-
panol (1 mol) with hexadecylamine (0.3 mol) in water (36 methoxy phenyl azide (entry 1).
ml) at room temperature for 1h. The resultant mixture was
In conclusion we have demonstrated a novel inexpensive
aged for 12 h and the solid was filtered, washed with ex-
and eco-friendly method for selective azide reductions by
cess of distilled water, dried for 24 h at room temperature.
a heterogeneous MCM-silylamine Pd(II) complex for the
1
g of MCM-41 was calcined at 550 °C overnight and re-
first time affording excellent yields. The advantages of
fluxed with 0.686 mmol of 3-aminopropyltriethoxysilane
Synlett 1999, No. 9, 1413–1414 ISSN 0936-5214 © Thieme Stuttgart · New York

1
414
M. L. Kantam et al.
LETTER
Table 1 Reduction of azides to amines catalyzed by MCM-silyl-
amine Pd (II) complex
Acknowledgement
The authors are grateful to the Council of Scientific and Industrial
Research, India and Commission of the European Communities
(Contract No.: CII-CT94-0050 (DG 12 HSMU)) for financial sup-
port.
References and Notes
IICT Communication No.: 4279
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1
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0, 2254.
17) Typical procedure for azide reductions: The catalyst (25 mg,
.0046 mmol of Pd) was suspended in dry methanol (2ml) and
a
1
All products were characterised by H NMR and IR Spectra.
Isolated yield
Yield for fifth cycle.
0
b
c
treated with molecular hydrogen for 20 min and then a
solution of 3,4,5- trimethoxy phenyl azide (209 mg, 1 mmol)
in methanol (2 mL) was added to it dropwise via syringe. A
hydrogen balloon was fitted to the flask and the resultant
solution was stirred at room temperature. On completion of
the reaction (monitored by TLC), the reaction mixture was
filtered (to remove the catalyst), washed with methanol and
evaporated under reduced pressure to give trimethoxy aniline
as a white solid (181 mg, 99% yield).
our methodology are (1) operational simplicity, (2) envi-
ronmental acceptability (3) mild reaction conditions, and
(
4) reusability of the catalyst The present heterogeneous
catalytic system may be a potential candidate to practical
organic synthesis.
Article Identifier:
437-2096,E;1999,0,09,1413,1414,ftx,en;L07499ST.pdf
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Synlett 1999, No. 9, 1413–1414 ISSN 0936-5214 © Thieme Stuttgart · New York