Highly efficient reduction of tertiary phosphine oxides and sulfides with amine-assisted aluminum hydrides under mild conditions

Article abstract of DOI:10.1134/S1070363215050266

Reduction of tertiary phosphine oxides and sulfides into the corresponding phosphines with amine-assisted aluminum hydrides has been studied. The method is characterized by mild conditions, short reaction time, high efficiency, and expanded substrate scope. The new method is an alternative to the currently used methods of reducing phosphine oxides or recycling phosphines engaged in organic reactions.

Full text of DOI:10.1134/S1070363215050266

ISSN 1070-3632, Russian Journal of General Chemistry, 2015, Vol. 85, No. 5, pp. 1156–1160. © Pleiades Publishing, Ltd., 2015.
Highly Efficient Reduction of Tertiary Phosphine Oxides
and Sulfides with Amine-assisted Aluminum Hydrides
under Mild Conditions1
Shuyan Yang, Xinxin Han, Minmin Luo, Jing Gao,
Wenxiang Chu, and Yuqiang Ding
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education,
School of Chemical and Material Engineering, Jiangnan University,
Wuxi 214122, Jiangsu Province, China
e-mail: yding@jiangnan.edu.cn
Received December 5, 2014
Abstract—Reduction of tertiary phosphine oxides and sulfides into the corresponding phosphines with amine-
assisted aluminum hydrides has been studied. The method is characterized by mild conditions, short reaction
time, high efficiency, and expanded substrate scope. The new method is an alternative to the currently used
methods of reducing phosphine oxides or recycling phosphines engaged in organic reactions.
Keywords: reduction reaction, amine-assisted, phosphides, aluminum hydrides
DOI: 10.1134/S1070363215050266
INTRODUCTION
sidered as the model substrate. All tests were
performed with 1 equiv. of aluminum hydrides at room
temperature under the atmosphere of nitrogen with
reaction time 10 min (Table 1). Amine-assisted alumi-
num hydrides in THF media gave excellent yields of
products (Table 1, entries 1–3). Further optimization of
the process was performed with the compound Ic used
as the source of hydride in various solvents. According
to the accumulated data the reaction was strongly
solvent-dependent (Table 1, entries 4–10) and could
not occur without the aluminum complex (Table 1,
entry 11).
Phosphines and their derivatives represent an
important class of compounds for life science and
chemical industry [1–6] (Scheme 1). Reduction of
phosphine chalcogenides has been a significant
challenge in phosphorus chemistry.
Currently reduction of phosphine oxides [13–16],
versus substitution reactions of carbon nucleophiles
with P–Cl derivatives or of carbon electrophiles with
alkali metal phosphides [7–9], and phosphination of
alkenes, alkynes, or aromatic halids [10–12], is the
major method of synthesis of phosphines. Among
many reducing agents silanes and aluminum hydrides
remain the reagents of choice for reduction of
phosphine oxides [17–25].
The process under study (Table 2) led to different
phosphines with moderate to high yields upon the
action of aluminum complex Ic. Generally, the
reaction had high substituent tolerance. The aryl ring
substituents with different electronic properties had
little influence on the reaction yields. Similar
conditions of the reaction were applied to bisphosphine
Herein we present reduction of phosphine oxides
and sulfides by amine-assisted aluminum hydrides that
needs no auxiliary catalysts and its advantages (Scheme 2).
Scheme 1. Some important phosphine ligands.
RESULTS AND DISUSSION
The first step of the study was testing various
sources of amine-assisted aluminum hydrides as
hydride sources. Triphenyl phosphine oxide was con-
PPh2
PPh2
PPh2
PPh2
PPh2
Fe
PPh3
PPh2
1 The text was submitted by the authors in English.
1156

HIGHLY EFFICIENT REDUCTION OF TERTIARY PHOSPHINE OXIDES
Scheme 2. Amine-assisted aluminum hydrides.
1157
hexane, 98%. Tris(4-chlorophenyl)phosphine (IIIk)
[16], hexane, 92%. Tris[4-(trifluoromethyl)phenyl]phos-
phine (IIIl) [16], hexane, 88%. Tri-p-tolylphosphine
(IIIm) [25], hexane, 96%. Tris(4-methoxyphenyl)-
phosphine (IIIn) [25], hexane, 98%. 3,5-
Difluorophenylmethylphenylphosphine (IIIo) [16],
hexane, 94%. 1,2-Bis(diphenylphosphino)ethane (IIIp)
[16], hexane, 92%. 1,1'-Bis(di-phenylphosphino)ferro-
cene (IIIq) [26], hexane, 93%. 2,2'-Bis(diphenyl-
phosphino)-1,1'-binaphthalene (IIIr) [16], hexane,
96%.
H
H
H
H Al N
H
N
Al N
H
H
Al
H
H
Ia
Ic
Ib
oxides. The corresponding bisphosphines were ob-
tained with high yields (Table 2, compounds IIIo–IIIr).
The above method was efficient with phosphine
sulfides leading to high yields of the corresponding
products of reduction (Table 3, compounds IIIa–IIIq).
CONCLUSIONS
Reduction of tertiary phosphine oxides and sulfides
into the corresponding phosphines supported by
amine-assisted aluminum hydrides was determined to
be efficient. The method is characterized by mild
conditions, short reaction time, high efficiency, and
significantly expanded substrate scope. This new
method is the alternative to current methods of
EXPERIMENTAL
The reagents were purchased from commercial
sources (J&KChemic, TCI, Fluka, Acros, SCRC) and
used with dehydration purification.
The products were elucidated with 1H and 31P NMR
spectrometry. NMR spectra were registered on Bruker
Advance 400 and 300. TLC of the reaction mixtures
and products was performed with commercial 100–400
mesh silica gel plates (GF254).
Table 1. Screening of reduction conditions of TPPO (IIa)
with amine-assisted aluminum hydridesa,b
O
Ph
Ph
[Al] 1 equiv. (Al−H = 3)
Compound IIIa (general procedure). Triphenyl-
phosphine oxide or sulfide (1 mmol), dry hexane
(1 mL), and Ic (1 mmol) were added to a Schlenk tube
under the atmosphere of nitrogen. The reaction was
carried out at room temperature for 10 min and
monitored by TLC. Upon completion of the process
the reaction mixture was filtered by silica gel and
washed several times with ethyl acetate. Ethyl acetate
was evaporated and the residue purified by flash
chromatography on silica gel with pure cyclohexane to
afford the desired phosphine. The yield was
determined by GC without additional purification.
Names of products, solvents used, and their yields are
listed below.
Ph
Ph
P
P
solvent, room temperature, N2
Ph
Ph
IIIa
IIa
Entry no.
Comp. no.
Solvent
THF
Yield, %
93
1
2
Ia
Ib
Ic
THF
92
3
THF
95
4
Ic
Toluene
Hexane
Ethyl ether
CH2Cl2
MeCN
DMSO
DMF
91
5
Ic
97
6
Ic
93
7
Ic
89
Triphenylphosphine (IIIa) [20], hexane, 95%.
Diphenylphosphine (IIIb) [20], hexane, 93%.
Methyldiphenylphosphine (IIIc) [20], hexane, 97%.
Methoxymethyldiphenylphosphine (IIId) [20], hexane,
96%. Ethyldiphenylphosphine (IIIe) [28], hexane,
95%. Cyclohexyldiphenylphosphine (IIIf) [20],
hexane, 92%. Tricyclohexylphosphine (IIIg) [20],
hexane, 95%. Tributylphosphine (IIIh) [20], hexane,
96%. tert-Butylmethylphenyl phosphine (IIIi) [16],
hexane, 97%. Dimethylphenylphosphine (IIIj) [16],
8
Ic
64
9
Ic
54
10
11
Ic
57
None
Hexane
Trace
a
Reagents and conditions: nitrogen atmosphere, triphenyl-
phosphine oxide (1 mmol), Cat [Al] loading (1 mmol), solvent
(1 mL), room temperature, 10 min.
b
Yield (%) as determined by GC.
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1158
SHUYAN YANG et al.
Table 2. Reduction of phosphine oxidesa,b
O
R1
R3
R1
R3
Ic, 1 equiv. (Al−H = 3)
P
P
R2
hexane, room temperature, N2, 10 min
R2
II
Yield, Comp.
III
Comp.
no.
Yield,
%
Substrates
O
Product
Substrates
Product
%
no.
Ph
Ph
Ph
P
O
P
n-Bu
n-Bu
IIIa
IIIb
IIIc
95
IIIh
96
97
98
Ph
Ph
n-Bu
n-Bu
P
P
Ph
n-Bu
Ph
O
n-Bu
H
P
O
Ph
Me
93
97
IIIi
IIIj
Ph
H
Ph
Ph
Me
P
P
P
t-Bu
Ph
Ph
O
t-Bu
Ph
Me
P
O
Ph
Cl
Me
Me
Ph Me
P
P
P
Me
Ph
Me
Ph
O
Cl
Cl
Cl
Ph
IIId
96
IIIk
92
Ph
O
P
P
O
P
O
P
Ph
Ph
Cl
P
Cl
CF3
CF3
F3C
F3C
Ph
O
P
IIIe
95
IIIl
88
Ph
O
P
P
Me
Me
Ph
Ph
CF3
CF3
Me
Me
Me
O
Me
Ph
IIIf
Cy
92
95
IIIm
96
Ph
Cy
O
P
P
P
P
Cy
Cy
Me
Me
Cy
Cy
OMe
O
OMe
IIIg
IIIn
98
MeO
MeO
Cy
Cy
P
P
O
Cy
Cy
P
P
OMe
OMe
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HIGHLY EFFICIENT REDUCTION OF TERTIARY PHOSPHINE OXIDES
Yield, Comp.
1159
Table 2. (Contd.)
Comp.
Yield,
%
Substrates
Product
Substrates
Product
no.
%
no.
IIIo
94
IIIq
93
F
F
O
PPh2
PPh2
Fe
PPh2
Fe
O
P
Me
Me
PPh2
O
F
F
P
Ph
PPh2
Ph
IIIpc
92
IIIr
96
O
O
Ph2P
O
PPh2
Ph2P
PPh2
PPh2
PPh2
PPh2
O
a
b
c
Reagents and conditions: nitrogen atmosphere, phosphine oxides (1 mmol), Ic (1 mmol), hexane (1 mL), room temperature, 10 min.
Yield (%) as determined by GC.
Ic (2 mmol).
Table 3. Reduction of phosphine sulfidesa,b
S
R1
R1
R3
Ic 1 equiv. (Al−H = 3)
R3
P
P
hexane, room temperature, N2, 10 min
R2
R2
IV
III
Comp.
no.
Comp.
no.
Substrates
Product
Yield, %
92
Substrates
Cy
Product
Cy
Yield, %
91
S
S
P
Cy
Ph
Ph
IIIa
IIIf
Ph
Ph
Cy
P
P
P
Cy
Ph
Ph
Cy
n-Bu
n
-Bu
S
Ph
Me
S
P
IIIb
IIId
89
93
IIIh
92
88
Ph
Ph
Me
n-Bu
n-Bu
P
P
P
n
-Bu
Ph
Ph
S
n-Bu
IIIqc
Ph
S
P
Me
P
Me
PPh2
PPh2
S
Ph
PPh2
PPh2
Ph
a
b
c
Reagents and conditions: nitrogen atmosphere, phosphine sulfides (1 mmol), Ic (1 mmol), hexane (1 mL), room temperature, 10 min.
Yield (%) as determined by GC.
Ic (2 mmol).
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SHUYAN YANG et al.
12. Huang, Y., Chew, R.J., Li, Y., Pullarkat, S.A., and
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ACKNOWLEDGMENTS
14. Tani, K., Behenna, D.C., McFadden, R.M., and Stoltz, B.M.,
We gratefully acknowledge financial support of this
study by the National Natural Science Foundation of
China (21371080), 333 Talent Project of Jiangsu
Province (BRA2012165) and MOE & SAFEA for the
111 Project (B13025).
Org. Lett., 2007, vol. 9, p. 2529.
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