A study on the deoxygenation of trialkyl-, dialkyl-phenyl- and alkyl-diphenyl phosphine oxides by hydrosilanes

Article abstract of DOI:10.1002/hc.21376

The deoxygenation of 1-alkyl-3-methyl-3-phospholene 1-oxides, which may be regarded as trialkyl phosphine oxides (R₃PO), and the reduction of dialkyl-phenylphosphine oxides (R₂PhPO) and methyl-diphenylphosphine oxide (MePh₂PO) have been elaborated by applying user-friendly silanes, such as tetramethyldisiloxane (>SiH–O–HSi<) and polymethylhydrosiloxane ((O–SiH)_n) under solvent-free, catalyst-free, and microwave (MW)-assisted conditions. New silanes of type Ar₂SiH₂, alkyl₂SiH₂, and Ar₃SiH were also applied in a few cases. The reactivity of the phosphine oxides and the silanes could be mapped on the basis of our experimental data.

Full text of DOI:10.1002/hc.21376

Received: 7 February 2017
DOI: 10.1002/hc.21376
Revised: 21 April 2017
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R E S E A R C H A R T I C L E
A study on the deoxygenation of trialkyl-, dialkyl-phenyl- and
alkyl-diphenyl phosphine oxides by hydrosilanes
Tamara Kovács
Anita Urbanics
Flóra Csatlós
György Keglevich
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|
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Department of Organic Chemistry and
Technology, Budapest University of
Technology and Economics, Budapest,
Hungary
Abstract
The deoxygenation of 1-alkyl-3-methyl-3-phospholene 1-oxides, which may be re-
garded as trialkyl phosphine oxides (R3PO), and the reduction of dialkyl-
phenylphosphine oxides (R2PhPO) and methyl-diphenylphosphine oxide (MePh2PO)
have been elaborated by applying user-friendly silanes, such as tetramethyldisiloxane
(>SiH–O–HSi<) and polymethylhydrosiloxane ((O–SiH)n) under solvent-free,
catalyst-free, and microwave (MW)-assisted conditions. New silanes of type
Ar2SiH2, alkyl2SiH2, and Ar3SiH were also applied in a few cases. The reactivity of
the phosphine oxides and the silanes could be mapped on the basis of our experimen-
tal data.
Correspondence
György Keglevich, Department of Organic
Chemistry and Technology, Budapest
University of Technology and Economics,
Budapest, Hungary.
Email: gkeglevich@mail.bme.hu
Funding information
Hungarian Research Development and
Innovation Fund, Grant/Award Number:
K119202
Many silanes were described as reducing agents.
Trichlorosilane is the most widespread reagent[18-20]; how-
1
INTRODUCTION
|
These days, the deoxygenation of phosphine oxides is in the
focus due to its high importance.[1-6] The resulting phos-
phines, on the one hand, may be useful intermediates, and
on the other hand, they may serve as P-ligands in transition
metal complexes. Transformations, such as the Wittig, Appel,
and the Mitsunobu reactions, involve the stoichiometric con-
version of triphenylphosphine to triphenylphosphine oxide
causing an environmental burden and meaning cost. These
problems can be eliminated by applying the phosphine in
a catalytic amount, and by insuring the in situ reduction of
the phosphine oxide formed. This was first elaborated for
the Wittig reaction using silanes as the reducing agent by
O’Brien.[7-10] Since then, the catalytic Wittig reaction has be-
come a hot topic and found a number of applications.[11-16] It
is worth mentioning that P-aryl and alkyl phospholanes and
phospholenes are the most suitable phosphines in the cata-
lytic cycles due to the easy reducibility of the related ring
phosphine oxides.[7,8] The ring strain is known to signifi-
cantly aid the deoxygenation of the P=O group.[17]
ever, its volatile (bp: 32°C) and corrosive properties mean
disadvantage. For this, Cl3SiH is, in most cases, applied to-
gether with three equivalents of pyridine or triethylamine that
has also an impact on the stereochemistry.[19] Phenylsilane
may be the choice of the reagent for the deoxygenation of
the P=O function; however, despite the fact that a quantity
of 0.33 equivalents is enough, it is rather expensive.[21-23]
Tetramethyldisiloxane(TMDS)andpolymethylhydrosiloxane
(PMHS) are cheap, but not too reactive reducing agents. For
this, copper-, titanium- and indium-catalyzed methods,[24-28]
along with a phosphoric acid diester-promoted protocol[29]
were developed for the deoxygenation of phosphine oxides.
During our earlier work, we studied the deoxygenation of
1-phenyl-3-methyl-3-phospholene 1-oxide (1) by different
silanes (3-10) in detail.[30,31] The most important results are
summarized in Scheme 1 and Table 1. The expensive phe-
nylsilane (PhSiH3) 3 was found to be the best reagent under
solvent-free and microwave (MW)-assisted conditions that
could be replaced well by TMDS (4) and PMHS (5), al-
though somewhat higher temperatures and longer reaction
times were necessary (Table 1, entries 2 and 3 vs 1).[30] Later
on, other silanes were also tried out.[31] It was found that
1-naphthylsilane (NaphSiH3 6), benzylsilane (BnSiH3 7), and
Contract grant sponsor: Hungarian Research Development and Innovation
Fund.
Contract grant number: K119202.
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Heteroatom Chemistry. 2017;28:e21376.
https://doi.org/10.1002/hc.21376
wileyonlinelibrary.com/journal/hc
© 2017 Wiley Periodicals, Inc.
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KOVÁCS et al.
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bis(4-methylphenyl)silane [(4-MePh)2SiH2 8] were more re-
active than PMHS (5) and TMDS (4) (Table 1, entries 4–6),
but tetraphenyl-disilane ([Ph2SiH]2 10) and bis(1-naphthyl)
silane ([1-Naph]2SiH2 9) were less reactive than PMHS (5)
(Table 1, entries 7 and 8). The reactivity of (Ph2SiH)2 (10)
and TMDS (4) seemed to be comparable.
found that under MW irradiation, there is no need for any
catalyst (Table 1, entries 2 and 3).[30,31]
In this article, we wish to make a further profit of our
finding by extending the method to the reduction of a series
of phosphine oxides of type R3-nPArn (where n=0, 1, 2). It
was also our purpose to set the order of reactivity of the phos-
phine oxides and also that of the silanes. For this, we planned
to test a few more new silanes.
The MW-assisted and solvent-free deoxygenation of tri-
arylphosphine oxides (Ar3PO, where Ar=Ph, 4-MePh, 4-
ClPh) requested a higher excess of the silanes (3-5) and more
forcing conditions.[30] Applying PhSiH3 (3) in a quantity of
nine equivalents, the reductions were complete after a 0.5-
hour irradiation at 150°C. Using 10 equivalents of TMDS (4)
or five equivalents of PMHS (5), the deoxygenations were
complete after a treatment of 200°C for 6-8 hour and 175°C
for 7.5 hour, respectively.[30] Steric hindrance is a limiting
factor for P=O deoxygenations.
It is a green chemical approach to substitute catalysts by
MW irradiation. We experienced that in heterogeneous phase
C-alkylations,[32-34] and in Kabachnik-Fields reactions,[35-37]
the catalysts could be omitted under MW conditions. It was
shown above that this approach was utilized in the TMDS- and
PMHS-promoted deoxygenations.[30,31] Due to their lower re-
activity, TMDS and PMHS were advised to be applied to-
gether with metal-containing or metal-free catalysts.[24-29] We
2
RESULTS AND DISCUSSION
|
Our first model compounds were 1-alkyl-3-methyl-
3-phospholene oxides (11a-d) that may be important precur-
sors for phosphines in catalytic Wittig reactions, as it was
mentioned in the Introduction.[7-10] These trialkyl-like phos-
phine oxides (11a-d) were subjected to deoxygenation by
PhSiH3, TMDS, and PMHS under solvent-free conditions
(Scheme 2). The phosphines (12a-d) were analyzed as the
corresponding phospholene sulfides (13a-d). Experimental
data are summarized in Table 2.
As regards the reduction of 1-ethyl-, 1-propyl-, 1-butyl-,
and 1-isopentyl-3-phospholene oxides (11a-d) with PhSiH3
(3), there was practically no observable differences in their
Me
Me
t N
T,
(
)
2
3-10
silane (
)
no solvent
.
P
.
P
Ph
Ph
O
1
2
H
silanes:
H
H
Si
H
H
H
H
Si
Si
Si
Si
H
Si
Si
O
O
O
n
H
3
4
5
6
H
H
H
H
H
Si
Si
H
SCHEME 1 Deoxygenation
of 3-methyl-1-phenyl-3-phospholene
1-oxide (1) by silanes under solvent-free,
microwave-assisted conditions[30,31]
Me
Si
H
Me
Si Si
H
H
7
8
9
10
TABLE 1 Deoxygenation of
3-methyl-1-phenyl-3-phospholene 1-oxide
(1) by different silanes under solvent-free,
microwave-assisted conditions
Entry
Silane
Equiv.
T (°C)
t
Conv. (%)a
Literature
1
2
3
4
5
6
7
8
PhSiH3 (3)
TMDS (4)
PMHS (5)
NaphSiH3 (6)
BnSiH3 (7)
(4-MePh)2SiH2 (8)
(1-Naph)2SiH2 (9)
(Ph2SiH)2 (10)
1
2
2
1
1
1
1
1
80
40 min
3 h
2 h
30 min
50 min
1 h
100
100
100
100
100
100
98
[30]
[30]
[30]
[31]
[31]
[31]
[31]
[31]
110
110
80
80
80
150
150
1 h
45 min
100
aOn the basis of the relative 31P NMR intensities.

KOVÁCS et al.
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Me
Me
Me
25 °C/12 h
T, t (N2)
3-5
no solvent
S8 (1.2 equiv.)
4
3
silane (
)
P
P
5P2
.
CH2Cl2
.
SCHEME 2 Deoxygenation of
1-alkyl-3-methyl-3-phospholene 1-oxides
(11a-d) by silanes (3-5) under solvent-free
conditions
R
11a-d
R
R
O
S
12a-d
13a-d
i
a
b
c
d
R = Et ( ), Pr ( ), Bu ( ), Pe ( )
TABLE 2 Deoxygenation of 1-alkyl-3-methyl-3-phospholene 1-oxides (11a-d) without solvent by different silanes on conventional heating
or microwave irradiation
Entry
Phospholene oxide
Silane
Equiv.
Mode of heating
T (°C)
t
Conv. (%)a
Yield of 13 (%)
1
2
3
4
5
6
7
8
11a
11a
11a
11a
11a
11a
11b
11b
11b
11b
11b
11b
11c
11c
11c
11c
11c
11c
11d
11d
11d
11d
11d
11d
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
1
1
2
2
2
2
1
1
2
2
2
2
1
1
2
2
2
2
1
1
2
2
2
2
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
80
80
1 h
~100
100
99
90 (13a)
91 (13a)
90 (13a)
82 (13a)
90 (13a)
93 (13a)
90 (13b)
89 (13b)
91 (13b)
88 (13b)
91 (13b)
93 (13b)
94 (13c)
89 (13c)
90 (13c)
85 (13c)
91 (13c)
93 (13c)
92 (13d)
90 (13d)
89 (13d)
88 (13d)
90 (13d)
88 (13d)
35 min
5.5 h
3 h
3 h
2 h
70 min
45 min
9 h
5 h
4 h
2 h
1 h
40 min
6 h
4 h
3 h
2 h
1 h
45 min
6 h
110
110
110
110
80
90
100
100
~100
100
~100
~100
~100
~100
100
~100
98
91
99
100
~100
100
94
80
9
110
110
110
110
80
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
80
110
110
110
110
80
80
110
110
110
110
4 h
3 h
2 h
90
97
92
MW
aOn the basis of relative 31P NMR intensities.
reactivity (Table 2, entries 1, 7, 13, and 19). The MW-assisted
accomplishments were significantly faster (Table 2, entries 2,
8, 14, and 20). Using PhSiH3 (3), the reactivity of the alkyl-3-
phospholene oxides (11a-d) was comparable with that of the
phenyl derivative (1) (Table 1, entry 1). Applying TMDS (4)
for the series under discussion (11a-d), the deoxygenations
took somewhat longer than for the 1-phenyl-3-phospholene
oxide 1 (Table 2, entries 3/4, 9/10, 15/16, and 21/22 vs Table 1,
entry 2 in respect of the MW-assisted accomplishments).
Hence, TMDS (4) seems to reveal a somewhat lower reactiv-
ity toward 1-alkyl-3-phospholene oxides (11a-d) than toward
the 1-phenyl derivative (1). Using PMHS (5), it can be said
that the reactivity toward the 1-alkyl-3-phospholene oxides
(11a-d) is more or less the same, as that toward the 1-phenyl
substrate (1) (Table 2, entries 5/6, 11/12, 17/18, and 23/24
Table 1, entry 3 in respect of the MW-assisted variations).
The point is that in the case of 1-alkyl-3-methyl-3-
phospholene 1-oxides (11a-d), PhSiH3 (3) may also be
replaced by the cheap and user-friendly TMDS (4) and PMHS
(5). In both variations, MW assistance is advantageous. The
corresponding phosphine sulfides (13a-d) were prepared in
yields of 82%-93%. The 1-alkyl-3-methyl-3-phospholene
1-sulfides (13a-d) are new compounds that were character-
ized by 31P, 13C, and 1H NMR spectral data, as well as HRMS.

4 of 8
KOVÁCS et al.
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Experimental data on the deoxygenation of dialkyl-
phenylphosphine oxides (14a-d) (Scheme 3) are found in
Table 3. The reducing agents PhSiH3 (3), TMDS (4), and PMHS
(5) were used in a one equivalent, two equivalents, and two
equivalents quantity, respectively, in the range of 110-175°C.
Reduction of dimethyl-phenylphosphine oxide (14a) with
PhSiH3 (3), TMDS (4), and PMHS (5) under MW conditions
required a reaction time of 0.75, 5, and 2.5 hour, respectively
(Table 3, entries 1, 3, and 5), while the thermal variations
were complete after 1.75, 8, and 5 hour, respectively (Table 3,
entries 2, 4, and 6). Dimethyl-phenylphosphine (15a) was
isolated in yields of 90%-95%.
Dipropyl-phenylphosphine oxide (14b) revealed a similar
reactivity toward PhSiH3 (3) (Table 3, entries 7 and 8), but in
respect of TMDS (4) and PMHS (5), its reactivity was some-
what lower (Table 3, entries 9-12). Regarding the MW-assisted
deoxygenations, reaction times of 0.75, 6, and 4 hour were
necessary using PhSiH3 (3), TMDS (4), and PMHS (5), respec-
tively (Table 3, entries 7, 9, and 11). Dipropyl-phenylphosphine
(15b) could be prepared in yields of 85%-88%.
T, t (N2)
silane
O
R P
R
R P
Ph
15
R
no solvent
Ph
14
R = Me ( ), Pr ( ), Bu( ), Pe ( )
i
a
b
c
d
SCHEME 3 Deoxygenation of dialkyl-phenylphosphine oxides
(14a-d) by silanes 3-5
After the deoxygenation of 1-alkyl-3-phospholene oxides
(11a-d) that can be regarded as “trialkyl”-like tertiary phos-
phine oxides, the next model compounds were dialkyl-
phenylphosphine oxides and methyl-diphenylphosphine
oxide. These tertiary phosphine oxides were reduced by user-
friendly silanes PhSiH3 (3), TMDS (4), and PMHS (5) under
solvent-free and MW-assisted conditions. In these cases, the
products were isolated as phosphines. Comparative thermal
experiments were also carried out.
TABLE 3 Deoxygenation of dialkyl-phenylphosphine oxides (14a-d) by different silanes under solvent-free conditions on conventional
heating or microwave irradiation
Entry
Phosphine oxide
Silane
Equiv.
Mode of heating
T (°C)
t (h)
Conv. (%)a
Yield (%)
1
2
3
4
5
6
7
8
14a
14a
14a
14a
14a
14a
14b
14b
14b
14b
14b
14b
14c
14c
14c
14c
14c
14c
14d
14d
14d
14d
14d
14d
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
1b
1
2
2
2
2
1
1
2
2
2
2
1
1
2
2
2
2
1
1
2
2
2
2
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
MW
Δ
110
110
175
175
175
175
110
110
175
175
175
175
110
110
175
175
175
175
0.75
1.75
5
8
2.5
5
0.75
1.75
6
10
4
6
1
2
7
10
4
6
1.25
2.5
7
10
4
~100
~100
95
98
92
96
96
96
88
90
98
95
95
99
98
90
92
97
95
97
94
85
90
83
92
95
90
83
85
87
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
88
88
90
84
87
89
82
110
175
175
175
175
6
aOn the basis of relative 31P NMR intensities.
bNine equivalents of PhSiH3 were used in an unoptimized experiment.[30]

KOVÁCS et al.
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H
Si
H
H
Si
H
H
Si
H
H
Si
Ph
Ph
FIGURE 1 New silanes applied by us
17
16
18
19
in deoxygenations
TABLE 4 Deoxygenation of 3-methyl-1-phenyl-3-phospholene 1-oxide (1) by silanes 16-19 under solvent-free conditions
Entry
Silane
Equiv.
Mode of heating
T (°C)
t (h)
Conv. (%)a
1
2
3
4
5
6
7
8
Anth2SiH2 (17)
Anth2SiH2 (17)
1
1
1
1
1
1
1
1
Δb
180
180
150
150
150
150
200
200
3
1.5
2
1
3
1.5
3
3
98
96
100
100
97
99
0
MWb
Δb
Fluorenyl2SiH2 (18)
Fluorenyl2SiH2 (18)
(4-PhPh)2SiH2 (16)
(4-PhPh)2SiH2 (16)
1-Naph3SiH (19)
1-Naph3SiH (19)
MWb
Δb
MWb
Δb
MW
0
aOn the basis of relative 31P NMR intensities.
bIn the presence of 0.05 mL of PhMe to avoid heterogeneity.
Dibutyl-phenylphosphineoxide(14c)behavedrathersimilarly
to the dipropyl analog 14b. Regarding the MW accomplishments,
using PhSiH3 (3), TMDS (4), and PMHS (5), there was a need
for a 1-, 7-, and 4-hour reaction time, respectively, to reach al-
most quantitative conversions (Table 3, entries 13, 15, and 17).
Completion of the thermal variations required 2, 10, and 6 hour,
respectively (Table 3, entries 14, 16, and 18).
The deoxygenating experiments with diisopentyl-
phenylphosphine oxide (14d) also matched into the series
including the reductions of the propyl and butyl derivatives
(Table 3, entries 19-24).
To broaden the scope of the reductive agents, other silanes,
suchasbis(4-phenylphenyl)silane([4-PhPh]2SiH2 16), bis(anthra-
nyl)silane (Anth2SiH2 17), bis(fluorenyl)silane (Fluorenyl2SiH2
18), and tri(1-naphthyl)silane (1-Naph3SiH 19), were also
tested (Figure 1). The model reaction was the reduction of
3-methyl-1-phenyl-3-phospholene 1-oxide (1) that is an dialkyl-
aryl-like phosphine oxide. The results are found in Table 4.
It was found that the fluorenyl and the 4-PhPh bis-silanes
(18 and 16) could be used in the deoxygenation of phospholene
oxide 1at 150°C (Table 4, entries3 and5), and the reactions were
faster on MW irradiation (Table 4, entries 4 and 6). However, the
application of Anth2SiH2 (17) required a higher temperature of
180°C (Table 4, entries 1 and 2). Trinaphthylsilane 19 remained
unreactive even at 200°C (Table 4, entries 7 and 8).
Taking into account also the earlier experiences sum-
marized in Scheme 1,[30,31] the order of reactivity shown in
Figure 2 can be set for the silanes (3-10, 16-19) applied in
our study.
Experimental data on the deoxygenation of methyl-
diphenylphosphine oxide (20) (Scheme 4) are shown in
Table 5. It is recalled that triphenylphosphine oxide was re-
duced by PhSiH3 (3) at 150°C.[30] The reactivity of diphenyl
derivative 20 allowed a lower temperature of 110°C. Under
MW conditions and after an irradiation of 1 hour, phosphine
21 was obtained in a complete conversion and in a yield of
90% (Table 5, entry 1). The comparative thermal exper-
iment required a 2-hour heating (Table 5, entry 2). TMDS
(4) and PMHS (5) were of lower reactivity requesting a reac-
tion temperature of 175°C. Using TMDS (4), an irradiation
of 7 hour was necessary to obtain phosphine 21 in a yield
of 87% (Table 5, entry 3). Measuring in PMHS (5), similar
results could be obtained after a somewhat shorter (5 hour)
reaction time (Table 5, entry 5). In the last two cases, the
thermal control experiments required a reaction time of 15
and 9 hour, respectively (Table 5, entries 4 and 6).
~
~
>
>
>>
>
>
(1-Napht)2SiH2
PhSiH3
NaphSiH3
BnSiH3
(4-MePh)2SiH2
PMHS
TMDS
(Ph2SiH)2
10
~
3
6
( )
7
8
( )
5
4
( )
9
( )
( )
Fluorenyl2SiH2
18
( )
(4-PhPh)2SiH2
16
( )
1-Naph3SiH
19
(
)
>
>
>>>
Anth2SiH2
17
(
)
(
)
(
)
(
)
FIGURE 2 The order of reactivity of different types of silanes in deoxygenation

6 of 8
KOVÁCS et al.
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T, t (N2)
silane
The spectra used for estimation of the percentage quan-
tity of the components were obtained applying a 30°
pulse, d1=2.2 seconds, AQ=0.9 seconds, number of data
points=65 536, number of scans: ca. 32. High-resolution
molecular weights were obtained using a Q-TOF Premier
mass spectrometer in positive electrospray mode. PMHS
with an average molecular weight 1700-3200 was used.
The reactions were carried out in a 300-W CEM Discover
focused microwave reactor equipped with a pressure
controller applying 50-80 W under isothermal condi-
tions. Silanes 3-5 and 7 are available commercially, while
silanes 6, 8-10, and 16-19 were prepared by LiAlH4
reduction of the corresponding chlorosilanes in accord
with literature procedures.[38-41] Compound 9 may also
be synthesized by a known procedure.[42] PMHS with an
average molecular weight of 1700-3200 was purchased
from Sigma-Aldrich.
O
Ph P Me
Ph P Me
no solvent
Ph
20
Ph
21
SCHEME 4 Deoxygenation of diphenyl-methylphosphine oxide
(20) by silanes 3-5
It can be seen that methyl-diphenylphosphine oxide 20 is
significantly less reactive than the dialkyl-phenyl derivatives
(14a-d) are. This may be due to steric factors.
Dialkyl-phenylphosphines
15a-c
and
methyl-
diphenylphosphine (21) are known compounds that were
identified by comparison of their δP chemical shifts with
literature data and by HRMS. New phosphine 15d was iden-
tified in a similar way.
The order of reactivity of the phosphine oxides investi-
gated in the present study and earlier[30] is shown in Figure 3.
In summary, a MW-assisted solvent- and catalyst-
free method using TMDS and PMHS as user-friendly
and cheap silanes was elaborated for the deoxygenation
of 1-alkyl-3-methyl-3-phospholene 1-oxides, dialkyl-
phenylphosphine oxides, and methyl-diphenylphosphine
oxide. The reactivity of the different phosphine oxides and
silanes was mapped, and a few new phosphine sulfides were
prepared during our work.
3.2
General procedure
|
for the deoxygenation of 1-alkyl-3-methyl-
3-phospholene 1-oxides (11) and for the
trapping of the phosphines (12) so obtained
Amixtureof0.55 mmolof1-alkyl-3-methyl-3-phospholene
1-oxides (11a-d) (11a: 0.08 g, 11b: 0.09 g, 11c: 0.10 g,
11d: 0.10 g) and 0.068 mL (0.55 mmol) of PhSiH3 (3), or
0.19 mL (1.1 mmol) of TMDS (4), or 0.042 mL (1.1 mmol)
of PMHS (5), or 0.55 mmol of silanes 6-10 and 16-19 (6:
0.087 mL, 7: 0.075 mL, 8: 0.12 mL, 9: 0.20 g, 10: 0.19 g,
16: 0.16 g, 17: 0.21 g, 18: 0.20 g, 19: 0.23 g) was heated
under nitrogen atmosphere at the appropriate temperature
for the appropriate time in a glass bomb immersed to an
oil bath or in a commercial MW vial in the MW reactor
3
EXPERIMENTAL
General
|
3.1
|
31P NMR spectra were registrated in CDCl3 solution on
a Bruker AV-300 spectrometer operating at 121.5 MHz.
Chemical shifts are downfield relative to 85% H3PO4.
TABLE 5 Deoxygenation of methyl-diphenylphosphine oxide (20) by different silanes under solvent-free conditions on conventional heating
or microwave irradiation
Entry
Silane
Equiv.
Mode of heating
T (°C)
t (h)
Conv. (%)a
Yield of 21 (%)
1
2
3
4
5
6
PhSiH3 (3)
PhSiH3 (3)
TMDS (4)
TMDS (4)
PMHS (5)
PMHS (5)
1
1
2
2
2
2
MW
Δ
MW
Δ
MW
Δ
110
110
175
175
175
175
1
2
7
15
5
98
99
90
90
93
89
90
90
87
87
89
~84
9
aOn the basis of relative 31P NMR intensities.
Me
Me
O
O
O
~
>>
>
Ph P Ph >>
R P R
Ar P Ar
P
P
FIGURE 3 The order of reactivity
of different tertiary phosphine oxides in
deoxygenations by silanes
Ph
14
Me
20
Ar
Ph
R
11a d
O
O
1
-
[
]
30

KOVÁCS et al.
7 of 8
|
(Table 2). Then, the reaction mixture containing phos-
phine 12 was cooled to 26°C, and the crude product was
reacted further immediately to form the corresponding
sulfide (13).
J=30.3, 1H, CH=); [M+H]+found=203.1029, C10H20PS re-
quires [M+H]+=203.1023.
3.3
General procedure for the
|
To ~0.55 mmol of the corresponding phosphine (12) in
2 mL of dichloromethane, 20.7 mg (0.65 mmol) of powdered
sulfur was added under nitrogen. The mixture was stirred
at 25°C for overnight, and then the solvent was evaporated.
Column chromatography of the residue using hexane-ethyl
acetate 9:1 as the eluent afforded the sulfide (13) as a dense
oil. For the details, see Table 2.
deoxygenation of the phosphine oxides 14a-d
and 20 using phenylsilane, TMDS, and PMHS
A mixture of 0.50 mmol of phosphine oxide (14a: 0.08 g,
14b: 0.11 g, 14c: 0.12 g, 14d: 0.12 g, 20: 0.12 g), 0.50 mmol
(0.062 mL) of phenylsilane or 1.0 mmol (0.18 mL) of TMDS
or 1.0 mmol (0.040 mL) of PMHS was heated under nitro-
gen atmosphere using an oil bath or a microwave oven at the
appropriate temperature in a glass bomb (a thick-wall glass
tube that can be closed) or in a commercial MW vial, re-
spectively, for the appropriate time. Then, the reaction mix-
ture was cooled to room temperature, and after taking up the
oily mixture in some ethyl acetate, it was absorbed on a 2-cm
layer of silica gel. Then, the phosphine was washed off using
hexane-ethyl acetate, 9:1 to afford the corresponding phos-
phine 14a-d and 20 (as colorless oils). As a matter of fact, the
main fraction was collected after a smaller pre-fraction. For
the details, see Tables 3 and 5.
The following phospholene sulfides were prepared:
1-Ethyl-3-methyl-3-phospholene 1-sulfide (13a). 31P
NMR (CDCl3) δ: 65.1; 13C NMR (CDCl3) δ: 6.7 (2JP-
C=4.6, C2′), 19.6 (3JP-C=10.3, C3-Me), 26.0 (1JP-C=48.7,
C1′), 37.8 (1JP-C=50.1, C2*), 41.0 (1JP-C=52.6, C5*),
121.2 (2JP-C=5.2, C4), 137.2 (2JP-C=9.6, C3), *may be re-
versed; 1H NMR (CDCl3) δ: 1.24 (dt, J1=7.6, J2=19.5,
3H, CH2CH3), 1.81 (bs, 3H, C3-CH3), 1.88-2.08 (m, 2H,
CH2CH3), 2.54-2.91 (m, 4H, CH2PCH2), 5.49 (d, J=30.5,
1H, CH=); [M+H]+found=161.0551, C7H14PS requires
[M+H]+=161.0548.
3-Methyl-1-propyl-3-phospholene 1-sulfide (13b). 31P
NMR (CDCl3) δ: 62.4; 13C NMR (CDCl3) δ: 15.1 (3JP-C=15.9,
C3′), 16.2(2JP-C=3.6, C2′), 19.4(3JP-C=10.3, C3-Me), 34.7(1JP-
C=47.5, C1′), 38.4 (1JP-C=50.0, C2*), 41.6 (1JP-C=52.5, C5*),
121.0 (2JP-C=5.2 C4), 137.1 (2JP-C=9.6, C3), *may be reversed;
1H NMR (CDCl3) δ: 1.07 (t, J=7.3, 3H, CH2CH3), 1.63-1.77
(m, CH2CH3) overlapped by 1.80 (bs, C3-CH3), total int. 5H,
1.89-2.02 (m, CH2Et, 2H), 2.60-2.92 (m, 4H, CH2PCH2), 5.48
(d, J=31.2, 1H, CH=); [M+H]+found=175.0711, C8H16PS re-
quires [M+H]+=175.0705.
The following phosphines were prepared:
Dimethyl-phenylphosphine (15a). From the experi-
ment marked in Table 3, entry 5. Yield: 83%, colorless
oil; 31P NMR (CDCl3) δ: −43.2, δ (CDCl3)[43]: −42.4;
[M+H]+found=139.0682, C8H12P requires: 139.0677.
Dipropyl-phenylphosphine (15b). From the experi-
ment marked in Table 3, entry 11. Yield: 88%, colorless
oil; 31P NMR (CDCl3) δ: −26.3, δ (CDCl3)[44]: −27.7;
[M+H]+found=195.1316, C12H20P requires: 195.1297.
Dibutyl-phenylphosphine (15c). From the experi-
ment marked in Table 3, entry 17. Yield: 84%, colorless
oil; 31P NMR (CDCl3) δ: −24.2, δ (CDCl3)[45]: −24.6;
[M+H]+found=223.1618, C14H24P requires: 223.1610.
Diisopentyl-phenylphosphine (15d). From the experiment
marked in Table 3, entry 23. Yield: 82%, colorless oil; 31P
NMR (CDCl3) δ: −22.8, δ (CDCl3); [M+H]+found=251.1929,
C16H28P requires: 251.1923. On oxidation by 30% H2O2, the
starting phosphine oxide (14d) was regenerated; 31P NMR
(CDCl3) δ: 42.5, [M+H]+found=267.1880, C16H28PO re-
quires: 267.1872.
1-Butyl-3-methyl-3-phospholene 1-sulfide (13c). 31P
NMR (CDCl3) δ: 62.9; 13C NMR (CDCl3) δ: 13.4 (C4′),
19.5 (3JP-C=18.2, C3-Me), 23.7 (3JP-C=15.5, C3′), 24.7 (2JP-
C=3.8, C2′), 32.6 (1JP-C=47.7, C1′), 38.4 (1JP-C=50.1, C2*),
41.7 (1JP-C=52.6, C5*), 121.2 (2JP-C=5.2, C4), 137.2 (2JP-
1
C=9.6, C3), *may be reversed; H NMR (CDCl3) δ: 0.95 (t,
J=7.3, 3H, CH2CH3), 1.38-1.52 (m, 2H, CH2), 1.57-1.72
(m, 2H, CH2), 1.80 (bs, 3H, C3-CH3), 1.89-2.04 (m, 2H,
CH2Pr), 1.91-2.04 (m, 4H, CH2PCH2), 5.48 (d, J=31.3,
1H, CH=); [M+H]+found=189.0867, C9H18PS requires
[M+H]+=189.0861.
Diphenyl-methylphosphine (21). From the experi-
ment marked in 5, entry 5. Yield: 89%, colorless oil;
31P NMR (CDCl3) δ: −26.4, δ (CDCl3)[46]: −26.1;
[M+H]+found=201.0840, C13H14P requires: 201.0833.
1-Isopentyl-3-methyl-3-phospholene 1-sulfide (13d).
31P NMR (CDCl3) δ: 63.4; 13C NMR (CDCl3) δ: 19.4 (3JP-
C=10.3, C3-Me), 21.9 (2× CHCH3), 28.5 (3JP-C=15.0, C3′),
30.6 (1JP-C=47.9, C1′), 31.1 (2JP-C=3.8, C2′), 38.1 (1JP-
C=50.1, C2*), 41.4 (1JP-C=52.6, C5*), 130.0 (2JP-C=5.2, C4),
137.0 (2JP-C=9.6, C3), *may be reversed; 1H NMR (CDCl3) δ:
0.71-0.81 (m, 6H, 2× CHCH3), 1.26-1.40 (m, 2H, CH2CH),
1.41-1.53 (m, 1H, CH), 1.62 (bs, 3H, C3-CH3), 1.71-1.84
(m, 2H, PCH2CH2), 2.39-2.69 (m, 4H, CH2PCH2), 5.30 (d,
ACKNOWLEDGMENTS
This project was supported by the Hungarian Research
Development and Innovation Fund (K119202).

8 of 8
KOVÁCS et al.
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REFERENCES
[25] M. Berthod, A. Favre-Réguillon, J. Mohamad, G. Mignani, G.
Docherty, M. Lemaire, Synlett 2007, 10, 1545.
[26] C. Petit, A. Favre-Réguillon, B. Albela, L. Bonneviot, G. Mignani,
M. Lemaire, Organometallics 2009, 28, 6379.
[1] D. Hérault, D. H. Nguyen, D. Nuel, G. Buono, Chem. Soc. Rev.
2015, 44, 2508.
[2] T. Kovács, G. Keglevich, Curr. Org. Chem. 2017, 21, 569.
[3] L. D. Quin, A Guide to Organophosphorus Chemistry, John
Wiley & Sons, New York 2000.
[27] L. Pehlivan, E. Metay, D. Delbrayelle, G. Mignani, M. Lemaire,
Tetrahedron 2012, 68, 3151.
[28] T. Coumbe, N. J. Lawrence, F. Muhammad, Tetrahedron. Lett.
1994, 35, 625.
[4] G. M. Kosolapoff, L. D. Quin, M. L, in Organic Phosphorus
Compounds (Eds: G. M. Kosolapoff, L. Maier), Wiley-
Interscience, New York 1973, Vol. 6, Ch. 18, pp. 1.
[5] R. Engel, in Handbook of Organophosphorus Chemistry (Ed: R.
Engel), Marcel Dekker, New York 1992, Ch. 5, pp. 193.
[6] G. Keglevich, Hung. Chem. J. 1998, 53, 385.
[7] C. J. O’Brien, J. L. Tellez, Z. S. Nixon, L. J. Kang, A. L. Carter,
S. R. Kunkel, K. C. Przeworski, G. A. Chass, Angew. Chem. Int.
Ed. 2009, 48, 6836.
[29] Y. H. Li, L. Q. Lu, S. Das, S. Pisiewicz, K. Junge, M. Beller, J.
Am. Chem. Soc. 2012, 134, 18325.
[30] G. Keglevich, T. Kovács, F. Csatlós, Heteroatom. Chem. 2015,
26, 199.
[31] T. Kovács, A. Urbanics, F. Csatlós, J. Binder, A. Falk, F. Uhlig, G.
Keglevich, Curr. Org. Synth. 2016, 13, 148.
[32] G. Keglevich, T. Novák, L. Vida, I. Greiner, Green. Chem. 2016,
8, pp. 1073.
[8] C. J. O’Brien, Z. S. Nixon, A. J. Holohan, S. R. Kunkel, J. L.
Tellez, B. J. Doonan, E. E. Coyle, F. Lavigne, L. J. Kang, K. C.
Przeworski, Chem. Eur. J. 2013, 19, 15281.
[33] G. Keglevich, A. Grün, Z. Blastik, I. Greiner, Heteroatom. Chem.
2011, 22, 174.
[34] A. Grün, Z. Blastik, L. Drahos, G. Keglevich, Heteroatom. Chem.
2012, 23, 241.
[9] C. J. O’Brien, F. Lavigne, E. E. Coyle, A. J. Holohan, B. J.
Doonan, Chem. Eur. J. 2013, 19, 5854.
[35] G. Keglevich, A. Szekrényi, Lett. Org. Chem. 2008, 5, 616.
[36] E. Bálint, E. Fazekas, L. Drahos, G. Keglevich, Heteroatom.
Chem. 2013, 24, 510.
[10] E. E. Coyle, B. J. Doonan, A. J. Holohan, K. A. Walsh, F. Lavigne,
E. H. Krenske, C. J. O’Brien, Angew. Chem. Int. Ed. 2014, 53,
12907.
[37] E. Bálint, E. Fazekas, J. Kóti, G. Keglevich, Heteroatom. Chem.
2015, 26, 106.
[11] T. Werner, M. Hoffmann, S. Deshmukh, Eur. J. Org. Chem. 2014,
2014, 6873.
[38] A. E. Finholt, A. C. Bond Jr., K. E. Wilzbach, H. I. Schlesinger, J.
Am. Chem. Soc. 1947, 69, 2692.
[12] M. Hoffmann, S. Deshmukh, T. Werner, Eur. J. Org. Chem. 2015,
2015, 4532.
[39] P. D. Prince, M. J. Bearpark, G. S. McGrady, J. W. Steed, Dalton.
Trans. 2008, 2008, 271.
[13] T. Werner, M. Hoffmann, S. Deshmukh, Eur. J. Org. Chem. 2015,
2015, 3286.
[40] J. Binder, R. Fischer, M. Flock, H.-G. Stammler, A. Torvisco, F.
Uhlig, Phosphorus Sulfur Silicon 2016, 191, SI, 478.
[41] J. Binder, PhD thesis, Graz University of Technology 2015.
[42] W. Steudel, H. Gilman, J. Am. Chem. Soc. 1960, 82, 6129.
[43] S. Sayalero, M. A. Pericàs, Synlett 2006, 16, 2585.
[44] J. Tong, S. Liu, S. Zhang, S. Z. Li, Spectrochim. Acta. Mol.
Biomol. Spectrosc. 2007, 67, 837.
[14] T. Werner, M. Hoffmann, S. Deshmukh, Eur. J. Org. Chem. 2014,
2014, 6630.
[15] M.-L. Schirmer, S. Adomeit, A. Spannenberg, T. Werner, Chem.
Eur. J. 2016, 22, 2458.
[16] H. A. Van Kalkeren, A. L. Blom, F. P. J. T. Rutjes, M. A. J.
Huijbregts, Green. Chem. 2013, 15, 1255.
[17] G. Keglevich, M. Fekete, T. Chuluunbaatar, A. Dobó, V. Harmat,
L. Tőke, J. Chem. Soc. Perkin. Trans. 2000, 1, 4451.
[18] H. Fritzsche, U. Hasserodt, F. Korte, Chem. Ber. 1965, 98, 171.
[19] L. D. Quin, K. C. Caster, J. C. Kisalus, K. A. Mesch, J. Am. Chem.
Soc. 1984, 106, 7021.
[45] T. Li, A. J. Lough, R. H. Morris, Chem. Eur. J. 2007, 13, 3796.
[46] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, Eur. J. Inorg.
Chem. 2006, 24, 5138.
[20] E. H. Krenske, J. Org. Chem. 2012, 77, 3969.
[21] H. Fritzsche, U. Hasserodt, F. Korte, Chem. Ber. 1964, 97, 1988.
[22] K. L. Marsi, J. Org. Chem. 1974, 39, 265.
[23] O. M. Demchuk, R. Jasiński, K. M. Pietrusiewicz, Heteroatom.
Chem. 2015, 26, 441.
How to cite this article: Kovács T, Urbanics A,
Csatlós F, Keglevich G. A study on the deoxygenation
of trialkyl-, dialkyl-phenyl- and alkyl-diphenyl
phosphine oxides by hydrosilanes. Heteroatom Chem.
2017;28:e21376. https://doi.org/10.1002/hc.21376
[24] Y. H. Li, S. Das, S. L. Zhou, K. Junge, M. Beller, J. Am. Chem.
Soc. 2012, 134, 9727.