Di(hydroperoxy)alkane Adducts of Phosphine Oxides: Safe, Solid, Stoichiometric, and Soluble Oxidizing Agents

Article abstract of DOI:10.1002/chem.201703676

The di(hydroperoxy)alkane adducts of phosphine oxides 1–9, Ph₃PO?(HOO)₂CMe₂, Cy₃PO?(HOO)₂CMe₂, Ph₃PO? (HOO)₂CMeEt, Cy₃PO?(HOO)₂CMeEt, Cy₃PO?(HOO)₂CEt₂, Cy₃PO? (HOO)₂C(CH₂)₅, Cy₃PO?(HOO)₂CMePh, (Ph₂P(O)CH₂CH₂P(O)Ph₂)? ((HOO)₂CEt₂)₂, and Ph₂P(O)CH₂P(O)Ph₂?(HOO)₂CMe₂, respectively, are synthesized and fully characterized by ¹H, ¹³C, and ³¹P NMR, and IR spectroscopies. Single crystal X-ray structures are reported for 3–9. Different one-pot synthetic pathways, starting from R₃P, R₃PO, R₃PO?H₂O, and R₃PO?H₂O₂ are explored and discussed and a mechanism for the formation of the di(hydroperoxy)alkane adducts of phosphine oxides is suggested. The longevity of the adducts is tested by monitoring the oxidation of Ph₃P with quantitative NMR. The solubilities of the adducts in organic solvents are presented, and their applicability as stoichiometric oxidizing agents for the selective oxidation of sulfides to sulfoxides is reported.

Full text of DOI:10.1002/chem.201703676

A Journal of
Accepted Article
Title: Di(hydroperoxy)alkane Adducts of Phosphine Oxides: Safe,
Solid, Stoichiometric, and Soluble Oxidizing Agents
Authors: Janet Bluemel, Shin Hye Ahn, and Nattamai Bhuvanesh
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Di(hydroperoxy)alkane Adducts of Phosphine Oxides: Safe, Solid,
Stoichiometric, and Soluble Oxidizing Agents
[a]
[a]
[a]
Shin Hye Ahn, Nattamai Bhuvanesh and Janet Blümel*
Abstract: The di(hydroperoxy)alkane adducts of phosphine oxides
wt%. Its major drawback, however, remains the abundance of
water in the reaction mixture which can lead to unwanted
secondary reactions. Another, in academia less known
Ph
Ph
Cy
Cy
3
3
3
3
PO·(HOO)
PO·(HOO)
PO·(HOO)
PO·(HOO)
2
2
2
2
CMe
CMeEt
CEt
CMePh (7), (Ph
P(O)Ph ·(HOO)
2
(1),
Cy
Cy
PO·(HOO)
P(O)CH CH P(O)Ph
CMe
3
PO·(HOO)
PO·(HOO)
C(CH
2
CMe
2
(2),
(4),
and
(3),
3
2
CMeEt
2
(5),
Cy
3
2
2
)
5
(6),
ingredient of commercial aqueous H
which is used to adjust the pH value to 1 to 2. The nitric acid
serves as stabilizer because within this pH range the H has
the longest life time. Furthermore, in labs with many users
aqueous H decomposes at unpredictable rates, and the
solutions have to be titrated
2 2
O solutions is nitric acid,
2
2
2
2 2 2 2
)·((HOO) CEt )
(8), and Ph
2
P(O)CH
2
2
2
31
2
(9), are synthesized and
2 2
O
1
13
fully characterized by H, C, and P NMR and IR spectroscopy.
Single crystal X-ray structures are reported for 3-9. Different one-pot
2 2
O
[
16]
synthetic pathways, starting from
3
R P,
3
R PO,
R PO·H
3
2
O, and
prior to each application when
R
3
PO·H are explored and discussed and a mechanism for the
2
O
2
exact stoichiometry is needed. Additionally, in case the reagents
are not water soluble, like most unmodified phosphines, the
oxidation reaction has to be performed in a biphasic system,
which entails a phase separation requirement in the workup.
formation of the di(hydroperoxy)alkane adducts of phosphine oxides
is suggested. The longevity of the adducts is tested by monitoring
3
the oxidation of Ph P with quantitative NMR. The solubilities of the
adducts in organic solvents are presented, and their applicability as
stoichiometric oxidizing agents for the selective oxidation of sulfides
to sulfoxides is reported.
Other, water free formulations of H
example, urea hydrogen peroxide (UHP) adducts.
the stoichiometry of this material is not very well defined, it is not
well soluble in organic solvents, and urea and water have to be
removed after the reaction. Other approaches include
2 2
O are also used, for
[17]
However,
[
18]
encapsulated
and immobilized versions of hydrogen
Furthermore, H adducts of metal complexes
Silicon-containing and organic
peroxides are important, too, but they can be difficult to
Introduction
[19,20]
peroxide.
have been characterized.
2 2
O
[21]
Oxidation reactions are crucial for many synthetic
processes, and various inorganic and organic peroxides, either
[22]
synthesize and remove after the reactions.
bishydroperoxides have also received some attention.
Recently,
[1]
solo or in the presence of catalysts play a central role. Recent
[23]
[
2]
examples include the oxidation of amines to amides, alkane
[
3]
[4]
activation,
and epoxidation reactions.
Additionally, the
and the classical
The ideal oxidizing agent is an easy to synthesize peroxide
of reproducible stoichiometry that is soluble in organic solvents.
It should be mechanically and thermally stable at ambient
temperature over prolonged time periods, while retaining its
oxidizing power. Additionally, a solid oxidizing agent would be
preferred due to the ease of handling and application. We
[5-7]
selective oxidation of sulfides to sulfones
Baeyer-Villiger oxidations are important in academia as well as
[
8]
industry.
Many other groups study the practical and theoretical
aspects of the transformation of phosphines to their oxides, and
[
9-11]
vice versa, which do not need any catalyst.
The interest of
recently reported on
a new class of materials, hydrogen
our group in phosphines and phosphine oxides stems from the
application of the former for immobilizing homogeneous
peroxide adducts of phosphine oxides, for example,
[7,15]
(
Cy
points on the above wish list, and additionally, no acid has to be
added to prolong the H life time, since the phosphine oxides
3
PO·H
2
O
2
)
2
.
These adducts already fulfill many of the
[12]
catalysts on solid supports, and the analysis of P(V) surface
species that come into existence under unfavorable
2
O
2
[13]
immobilization conditions. Furthermore, the adsorption of solid
phosphine oxides on silica surfaces leads to interesting mobility
serve as stabilizers. However, our quest for alternative oxidizing
agents with lower phosphine oxide carrier weight led us to yet
another class of adducts. The new di(hydroperoxy)alkane
adducts of phosphine oxides incorporate two active oxygen
atoms per P=O group, while they still come close to the "ideal
oxidizing agent" described above. Two representatives,
[14]
effects that can be probed with solid-state NMR.
For these studies, being able to cleanly oxidize
phosphines to their oxides without overoxidation to phosphinic
[15]
and phosphonic acid esters is crucial.
The best option for
transforming the phosphines into their oxides selectively was the
3 2 2
R PO·(HOO) CMe (R = Cy, Ph), have been communicated
[15]
oxidation with aqueous H
2
O
2
in a biphasic system.
Aqueous
[7]
recently.
2 2
H O
is an enticing oxidizing agent in academic settings
The goal of this contribution is to demonstrate that this new
substance class is of a general nature and that many different
compounds with the general composition R PO·(HOO) CR'R",
3 2
because it is relatively inexpensive and under present safety
regulations available for laboratories in concentrations up to 30
incorporating virtually any combination of alkyl and aryl
substituents R, R', and R", can easily be synthesized and
characterized. Overall, nine representatives of new
di(hydroperoxy)alkane adducts of phosphine oxides will be
presented, their structural and spectroscopic data are discussed,
[a]
S. H. Ahn, Dr. N. Bhuvanesh, Prof. J. Blümel
Department of Chemistry, Texas A&M University
College Station, TX, 77842-3012 (USA)
Fax: (+1) 979-845-5629
E-mail: bluemel@tamu.edu
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and their chemical behavior and oxidizing power will be probed.
For this purpose, first it will be demonstrated that the active
oxygen content and the structural mode stay the same for
different phosphine oxides. This includes the characterization of
the adducts by single crystal X-ray diffraction, and the
quantification of their oxidative strengths, shelf lives under
various conditions, and their solubilities in organic solvents. The
potential of the adducts 1-9 (Schemes 1 and 2) as oxidizing
[5-7]
Scheme 2. Di(hydroperoxy)alkane adducts 8 and 9.
agents for sulfide oxidations
is described.
In summary, it
will be demonstrated
that
The applicable ketones are not limited to acetone, but so
far include butanone, 3-pentanone, cyclohexanone, and
acetophenone (Schemes 1 and 2). All adducts are obtained
cleanly in the displayed 1 : 1 ratio of di(hydroperoxy)alkane and
phosphine oxide. The large number of adducts with the same
composition and structural motif, irrespective of their different
substituents at phosphorus and the quaternary carbon atoms,
corroborates the assumption that the two strong hydrogen
bridges lead to a favorable geometry that stabilizes the adducts.
In fact 1-9 are safe oxidizing agents which melt smoothly without
sudden release of oxygen or other violent outbursts. The
adducts are also robust towards sudden mechanical impact and
grinding with a mortar and pestle. It should also be mentioned
that phosphine oxides are flame retardants and they are
di(hydroperoxy)alkane adducts of phosphine oxides are of a
general nature and that they can be fine-tuned and obtained in a
large number of easily synthesized and purified representatives.
This new class of solid, safe, stoichiometric, and soluble
oxidizing agents should have important future applications in
academic and industrial settings, especially in cases where
abundant water or the nitric acid stabilizer are problematic.
Results and Discussion
Since the discovery that phosphine oxides form stable
adducts with di(hydroperoxy)alkanes at room temperature and in
the absence of metal catalysts, only two representatives, 1 and
[24]
basically non-toxic.
[7]
2
(Scheme 1), have been communicated. Therefore, our
Syntheses of the New Adducts
primary goal in this contribution is to demonstrate that this type
of adduct is of a general nature and can be synthesized using a
wide variety of different phosphine oxide carriers and ketones.
Adducts 1-7 which are based on monophosphine oxides, are
displayed in Scheme 1.
Di(hydroperoxy)alkane adducts of phosphine oxides can
be synthesized in a variety of different ways (Scheme 3). One
option is starting from the phosphines R
with a ketone in the presence of aqueous H
excess of H is needed because one oxygen atom of the
3
P and treating them
2
O
2
. In this case, an
2
O
2
oxidant is consumed to generate the phosphine oxide first.
Furthermore, it has to be taken into account that starting from
alkylphosphines entails the risk of formation of other unwanted
products from oxygen insertion into the P-C bonds as described
[15]
earlier. Therefore, oxygen from the atmosphere needs to be
excluded in this approach.
Scheme 1. Di(hydroperoxy)alkane adducts of phosphine oxides 1-7.
Scheme 3. General synthesis routes for di(hydroperoxy)alkane adducts of
The adducts 8 and 9 (Scheme 2) represent a first step
towards reducing the relative weight of the carrier by using
diphosphine dioxides. For their synthesis the mixed
phosphine oxides.
alkyldiarylphosphine oxides [Ph
Ph P(O)CH P(O)Ph (dppmO , 11) are used as educts to give
the corresponding adducts (Scheme 2).
2 2 2 2
P(O)CH ] (dppeO , 10) and
When phosphine oxides are the educts for synthesizing
di(hydroperoxy)alkane adducts, air does not have to be
excluded, and it is not critical, whether they are used in pure
2
2
2
2
form as R
any case, when combined with a ketone and aqueous H
desired adducts shown in Scheme will be generated.
Phosphine oxides readily form water adducts with one hydrogen
3
PO, or as the corresponding H
2
O or H
2
O
2
adducts. In
2
O
2
, the
3
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[
14]
31
bridge, as demonstrated earl
i
i
er, and some phosphine oxides
det
e
rminations or forceful grinding of the pure powders. The
P
[15]
like Me
strongly bound by twofold h
water molecule at the P=O gr oo up.
3
PO are even hygro
s
copic.
However, H
2
O
2
is more
NMR spectra before and after the procedures only indicated the
pre ence of the starting materials. With respect to the safety
ect of future applications it should be noted that phosphine
yy
drogen bonding and replaces the
ss
[7,15]
as
pp
[24a,b]
oxi
d
es are efficient flame retardants
and that they are not
[24c]
The general mechanism for the reaction of phosphine
oxides with ketones and aqu ous H is displayed in Scheme 4.
is more acidic than water (pK
4.0). However, the nitric aa cid contained in the commercial
aqueous H (see above) is most probably responsible for
protonating and activating t hh e ketones, for example, acetone
toxic.
e
e
2 2
O
[
25a]
H
2
O
2
with a pK
a
of 11.8
a
=
1
2
O
2
[25b]
(
pK
a
= 19.2)
in the first st
ee p of the proposed mechanism. In
the next step, H
2
O
2
perfo rr ms a nucleophilic attack at the
carbonyl carbon. This process is repeated with the
hydroperoxy(hydroxy)alkane tt o yield the di(hydroperoxy)alkane,
which is immediately scaven gg ed and stabilized by forming two
hydrogen bonds with the ph oo sphine oxide carrier (Scheme 4).
The viability of this last step has been proven by synthesizing
[
26]
the free di(hydroperoxy)alkane (HOO)
to Cy PO to generate the aa dduct 6 (Scheme 1 and Exper.
Section). The di(hydroperoxy)alkane (HOO) C(CH is bound
more strongly to phosphine oxide carriers than H O or H , and
2
C(CH
2
)
5
and binding it
3
3 2
Fig uu re 1. Single crystals of Cy PO·(HOO) CMeEt (4).
2
2 5
)
2
2 2
O
therefore, the water and hydrogen peroxide adducts of
phosphine oxides can also f uu nction as educts for the synthesis
C hh aracterization of the Adducts
of the di(hydroperoxy)alka nn e adducts. Again, in case a
phosphine is used as startin gg material, one oxygen atom of the
di(hydroperoxy)alkane is sacr ii ficed in the process of forming the
phosphine oxide first.
All dd i(hydroperoxy)alkane adducts 1-9 (Scheme 1) are amenable
to t
h
h
e most powerful analytical methods. These confirm that the
ad dd ucts possess unique characteristics that are distinctly
diff
erent from those of the pure phosphine oxides. In the
foll
owing IR and NMR spectroscopy of the adducts 1-9, as well
as X-ray crystallographic data will be discussed in detail.
IR SS pectroscopy
IR Spectrocopy confirms that the di(hydroperoxy)alkane adducts
are very different from the pure phosphine oxides.
Scheme 4. Suggested mechanism ff or the formation of di(hydroperoxy)alkane
adducts of phosphine oxides.
The adducts 1-9 are o bb tained in nearly quantitative yields
by all procedures discussed
section). In order to obtain dr yy compounds without decomposing
the peroxide groups, the wat r can be conveniently removed as
an azeotropic mixture with thanol in a mild vacuum at room
aa bove (Scheme 3 and Experimental
e
e
3 2
Fig uu re 2. IR spectrum of polycrystalline Ph PO·(HOO) CMeEt (3).
temperature. All adducts are ee asy to purify by crystallization and
often form giant single cry ss tals (Figure 1). Importantly, the
Regarding the IR spectra of the di(hydroperoxy)alkane
di(hydroperoxy)alkane addu
temperature and in the abse
conditions prevent the forma tt ion of potentially dangerous cyclic
peroxide trimers. Additionall , no explosive cyclic trimers or
cc ts are generated at ambient
ad
thatt
and
d
ucts 1-9 there are in general three strong stretching bands
are characteristic and valuable analytically, v(O−H), v(C−O),
v(P=O). All these IR data are summarized in Table 1.
The ν(O-H) band of the di(hydroperoxy)alkane moiety
[21]
nn ce of any metal catalyst. These
y
other oligomers are formed during forced decomposition of 1-9.
hy
and appears between 3200 and 3300 cm . Fortunately, this
val e is distinctly different from the position of the (O-H)
str tching band of PO-adsorbed water at around 3400 cm .
Comparing, for example, the spectra of pure Ph PO with the
cor esponding di(hydroperoxy)butane adduct 3, one can
co clude that the IR spectrum of 3 (Figure 2) stems from a
dd rogen-bonded to the PO groups is rather broad and intensive
-1
The adducts 1-9 hav ee been tested by applying high
u
e
ν
temperatures and mechani
c
al stress. In fact, none of the
-1 [14,15]
adducts displayed any violent decomposition during grinding and
hammering, or being stored over months, or heated up. No
sudden release of oxyge nn occurred during melting point
3
rr
n
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water-free adduct. Additionally, a rather prominent overtone
X-Ray Crystallography
-1
band that would be expected at about 1647 cm from water
[15,27]
bound to the phosphine oxide is absent.
The most important feature of the di(hydroperoxy)alkane
adducts 1-9 is their formation of multiple hydrogen bonds
between the (HOO−) and the P=O groups. We have previously
described the tendency of P=O groups to form hydrogen bonds
The IR stretching bands
general lower values (1113-1163 cm ) than those of the adduct-
free phosphine oxides (1157-1188 cm ).
diminished values of the adducts is that the hydrogen bonding in
-9 weakens the P=O double bonds of the pure phosphine
ν(P=O) of the adducts have in
-1
-1
[7,15]
[7,15]
[14]
[14]
The reason for the
to H
2
O
2
molecules,
H
2
O,
and silanols.
Two X-ray
structures of the di(hydroperoxy)propane adducts 1 and 2,
incorporating hydrogen bonds, have been communicated.
[7]
1
oxides and therefore decreases the frequencies of the stretching
bands. The differences ∆ν(P=O) between the stretching band
wavenumbers of the free phosphine oxides versus the
corresponding adducts cover a rather narrow range of values
Recently, hydrogen bonding between P=O and the OH groups of
a phenol moiety has successfully been applied to create novel
dimeric motifs.
[29]
-1
from 22 to 44 cm (Table 1). Within this limited range there is no
obvious trend for the wavenumbers depending on aryl versus
alkyl substitution at phosphorus or at the quaternary carbon of
the di(hydroperoxy)alkane moiety. As it is the case for the pure
The main interest in the following structural
characterization of the new adducts is to probe whether the
same arrangements of hydrogen bonds to the P=O groups will
be established, and whether the packing motif of the adducts
displays similar trends.
phosphine oxides, the
ν
(P=O) stretching bands of all adducts 1-
9
are very narrow, as the example of 3 in Figure 2 shows.
In addition to the
097 to 1118 cm in all IR spectra of the adducts 1-9 an
ν
(P=O) bands, in the narrow region from
-1
1
additional strong absorption is found. This band can be assigned
to the (C−O) band of the di(hydroperoxy)carbon moiety. For
example, acetals and ketals display IR absorptions between
ν
-
1 [28]
1
035 and 1190 cm .
The related structural element of
-
secondary alcohols show IR bands between 1090 and 1120 cm
1
[28]
.
2 2 5
Furthermore, neat (HOO) C(CH ) displays a strong sharp
-1
peak at 1113 cm . Overall, these narrow and characteristic
bands in IR spectroscopy show that all adducts are well-defined
and of a molecular and crystalline nature throughout the bulk
material.
3 2
Figure 3. Single crystal X-ray structure of Cy PO·(HOO) CMeEt 4 (two
independent molecules). Thermal ellipsoids are shown at the 50% probability
[
31]
level. Only the hydrogen-bonded H atoms are shown for clarity.
Table 1. Stretching bands
IR stretching band values of the pure phosphine oxides Ph
ν
(O-H) and v(C-O), and comparison of the
PO, Cy
(11) with those of the
ν
(P=O)
3
PO,
3
All di(hydroperoxy)alkane adducts of phosphine oxides
crystallize easily in the form of large colorless single crystals,
one representative specimen being shown in Figure 1. Therefore,
Ph
2
P(O)CH
2
CH
2
P(O)Ph
2
(10), and Ph
2 2 2
P(O)CH P(O)Ph
adducts 1-9, given as ∆ν(P=O).
[7,30-36]
-
1
-1
-1
-1
the single crystal X-ray structures of all adducts 1-9
Figures 3-8) could be obtained in high quality. The structures of
-8 confirm that each P=O group forms two hydrogen bridges to
Species
ν
(O−H) (cm
3256
3192
3250
3196
3194
3252
3176
3275
3291
-
)
ν
(C−O) (cm
1118
1099
1118
1101
1103
1103
1101
1097
1099
-
)
ν
(P=O) (cm
1152
1125
1142
1124
1126
1113
)
∆ν(P=O) (cm )
(
1
1
2
3
4
5
6
7
8
9
30
32
40
33
31
44
34
22
25
-
one di(hydroperoxy)alkane moiety. This means that there are
two active oxygen atoms per P=O group, and thus the oxidative
2 2
power (see below) is twice as high as for the H O adducts of
[
7]
phosphine oxides presented previously.
1123
1150
1163
1182
Ph PO
3
[
15]
Cy
3
PO
-
-
1157
-
1
0
-
-
1172
1188
-
11
-
-
-
[
30]
Figure 4. Single crystal X-ray structures of Ph
and Ph PO·(HOO) CEt
3 2 2
3
PO·(HOO)
(5, right). Thermal ellipsoids are shown at the 50%
probability level. Only the hydrogen-bonded H atoms are shown for clarity.
2
CMeEt (3, left)
[
32]
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The recurring and characteristic packing motif consists of
In order to increase the number of active oxygen atoms
per phosphine oxide carrier mass, and to further probe the
general nature of the di(hydroperoxy)alkane adducts, 1,2-
bisdiphenylphosphinoethane (dppe) has been treated with 3-
two adduct assemblies being arranged in a manner so that the
P=O groups point in opposite directions, as seen, for example,
for the adducts 4, 5, 6, and 7 in Figures 3, 4, 5, and 6,
respectively. Even in the case of the adduct 10 (Figure 7), where
the two P=O groups are connected by an ethylene bridge, this
structural packing motif is preferred. The only exception to this
rule so far is adduct 3 which does not form this dimer assembly
pentanone
di(hydroperoxy)pentane adduct [CH
was obtained.
structural characterization
and
aqueous
H
2
O
Ph
2
.
The
(HOO)
expected
CEt (8)
2
2
PO
·
2
2 2
]
[
35]
Again, the large single crystals allowed for
(Figure 7). The two
di(hydroperoxy)pentane moieties are bound to the P=O groups
pointing in opposite directions.
(
Figure 4). The reason for this might be that the phenyl rings of
the Ph PO carriers do not form an arrangement that would be
free of strain when they stack. This can be seen, for example, in
3
[7]
the structure of 1, where the di(hydroperoxy)propane units are
pushed away from the area of the aligned phenyl rings, in order
to accommodate this stacking. In contrast to this, the cyclohexyl
rings
allow
for
unstrained
stacking,
with
the
di(hydroperoxy)alkane moieties being more centered on top of
the P=O groups for 4-7.
Figure 7. Single 35c]rystal X-ray structure of (Ph
2
P(O)CH
2 2 2
CH P(O)Ph )·
[
((HOO)
2
CEt
2
)
2
(8).
Thermal ellipsoids are shown at the 50% probability
level. Only the hydrogen-bonded H atoms are shown for clarity.
Next, we investigated whether offering two P=O groups in
closer proximity as in dppeO
bonding pattern. Interestingly, when dppmO
acetone and aqueous H using the same procedure as for
dppeO only one P=O group per molecule carries the
di(hydroperoxy)propane moiety (Figure 8).
2
would lead to a different hydrogen
2
is reacted with
2
O
2
2
,
Figure 5. Single crystal X-ray structure of Cy
independent molecules).
3
PO·(HOO)
Thermal ellipsoids are shown at the 50%
probability level. Only the hydrogen-bonded H atoms are shown for clarity.
2
C(CH
2
)
5
(6, two
[36]
[
33]
The distances
between the two P=O oxygen atoms and the terminal oxygen
atom of one OOH group are practically identical with 2.816 and
2.817 Å. Therefore, one could imagine that the hydrogen atom
interacts with both P=O oxygen atoms equally. However, the
P=O bond lengths differ. The P=O bond of the group carrying
the adduct is lengthened to 1.495 Å, while the free P=O bond
remains in the typical range of P=O bond lengths with 1.488
So far,
5
is the only representative of the
di(hydroperoxy)alkane adducts of phosphine oxides found that
[32a]
displays polymorphism. It has been obtained in orthorhombic
[32b]
and columnar
adduct assemblies still follow the general composition
Cy PO (HOO) CEt Therefore, the polymorphism will not
impede any later application as stoichiometric oxidizing agent.
crystals. However, in both polymorphs of 5 the
[14]
Å.
The IR spectrum indicates that there is only one HO
absorption present, which differs in its wavenumber from the
3
·
2
2
.
-1 [15]
water band at 3408 cm .
In solution only an averaged
chemical shift is obtained for both P=O groups of 9, therefore it
is possible that the hydrogen bond formation of the
di(hydroperoxy)propane moieties with only one P=O group per
diphosphine dioxide molecule is enforced by the favored packing
of the assemblies in the crystal lattice.
Figure 8. Single crystal X-ray structure of Ph
2
P(O)CH
2 2 2 2
P(O)Ph ·(HOO) CMe
Figure 6. Single crystal[ X-ray structure of Cy
3
PO·(HOO)
Thermal ellipsoids are shown at the 50%
probability level. Only the hydrogen-bonded H atoms are shown for clarity.
2
CMePh (7, two
[36]
(9, two independent molecules). Thermal ellipsoids are shown at the 50%
34]
independent molecules).
probability level. Only the hydrogen-bonded H atoms and ipso carbon atoms of
the phenyl rings are shown for clarity.
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Chemistry - A European Journal
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Table 3. Hydrogen bond lengths, O···O distances, and O−C−O angles of the
di(hydroperoxy)alkane moieties in the adducts 1 to 9. The values of one of the
two independent molecules are given for 3.
Having obtained all single crystal X-ray structures of 1-9,
their crystallographic data can be compared and evaluated. First,
the change of the P=O bond lengths which was expected from
the shifts of the IR v(P=O) bands to lower frequencies upon
adduct formation (Table 1), was probed by the X-ray data (Table
O−C−O Angle
Adduct
O
···H Distance (
1.777/1.874
1.841/1.873
1.874/1.974
1.838/1.848
1.835/1.846
1.864/1.876
1.825/1.888
1.902/1.981
1.909/1.985
Å
)
O
···H−O Distance (Å)
2.686/2.771
2.677/2.720
2.706/2.733
2.615/2.749
2.679/2.687
2.705/2.723
2.664/2.719
2.751/2.827
2.742/2.816
(°)
2
). According to expectation, in the adducts a qualitative
1
2
3
4
5
6
7
8
9
110.8
lengthening of the P=O bonds, as compared to the respective
pure phosphine oxides, is found. This result corroborates the
weakening of the P=O bond due to the formation of two
hydrogen bonds. The changes of bond lengths are in the range
of those detected for hydrogen peroxide adducts of phosphine
111.5
110.7
108.5
110.5
112.0
111.7
110.7
110.7
oxides. For example, when the adduct [Cy
generated from Cy PO, the two hydrogen bonds per PO group
lead to an increase of the bond length by 0.015 Å.
3
PO
·H
2
O
2
]
2
is
3
[15]
Table 2. Comparison of the P=O bond lengths (Å) of the adducts 1-9 with
those of the pure phosphine oxides Ph PO, Cy PO, Ph P(O)CH CH P(O)Ph
10), and Ph P(O)CH P(O)Ph (11). Averaged bond length values are given
3
3
2
2
2
2
(
2
2
2
for 3, 9 and 10.
Finally, it was considered whether the O−C−O angle in the
di(hydroperoxy)alkane moiety of the adducts could serve as an
indicator for strain in the assemblies due to the formation of the
two hydrogen bonds. In fact, the angles deviate from the ideal
tetrahedral angle of 109.5°, with most of the values being larger
by about 1 to 2.5° (Table 3). Therefore, it seems like the O−C−O
angles increase in order to accommodate the formation of the
two hydrogen bonds per P=O group.
Species
P=O bond lengths (
Å
)
∆
Bond lengths
+0.023
+0.017
+0.016
+0.020
+0.018
+0.022
+0.020
+0.010
+0.002
-
[
7]
1
2
3
4
5
6
7
8
9
1.502
1.507
[
7]
1.506
1.510
1.508
1.512
1.510
1.501
1.492
NMR Spectroscopy
The adducts 1-9 (Schemes 1 and 2) are highly soluble in
organic solvents (see below). Therefore, they can conveniently
be characterized by standard one- and two-dimensional solution
NMR spectroscopy, and using these methods all resonances
[
[
[
[
37]
Ph
3
PO
PO
0
1.479
1.490
1.492
1.491
1
13
have been assigned unequivocally. The H and C NMR
spectra show the signals expected for the phosphine oxide
38]
39]
40]
Cy
3
-
carriers, with characteristic chemical shifts and
J coupling values
1
1
-
that differ only minimally from those of the pure phosphine
[15]
1
-
oxides.
However, the changes of the adduct moieties are
substantial and they follow the expected trends when
[7]
transforming ketones to di(hydroperoxy)alkanes. Most valuable
for the straightforward identification of the adducts is the
appearance of a new resonance in the range of 108 to 115 ppm
for the generated quaternary carbon atoms bound to two oxygen
atoms (Table 4). This chemical shift range is very characteristic
and fortunately it does not overlap with the typical spectral
The formation of hydrogen bonds in 1-9 is corroborated by
the O···H distances (Table 3). Average O···H distances in
[41,42]
hydrogen bonds are in the order of 1.85 to 1.95 Å.
Most
regions of aryl or alkyl carbon signals. As signals of quaternary
values for 1-9 lie well within this range, with only slightly longer
distances for one hydrogen bond each in 8 and 9. In these
cases, most probably the strained geometries in the diphosphine
dioxide carriers diminish the hydrogen bond strengths.
13
carbon nuclei their
C NMR resonances are also easily
1
13
identified by DEPT and H, C COSY NMR spectra.
31
The P NMR signals of all adducts 1-9 are shifted downfield
Another indication for the formation of strong hydrogen
bonds are the comparatively short O···H−O distances between
the oxygen atoms in 1-9 (Table 3). Average distances from 2.75
as compared to those of the corresponding pure phosphine
[15]
[15]
oxides Cy
3
PO (49.91 ppm),
3
Ph PO (29.10 ppm),
[
41,42]
(CH (P(O)Ph ) (32.68 ppm), and CH (P(O)Ph ) (24.86 ppm)
2
2
2
2
2 2
to 2.85 Å indicate hydrogen bond formation,
of all adducts lie well within this range.
and the values
(Table 4). This downfield shift indicates the deshielding of the
phosphorus nuclei by the presence of two strong hydrogen
bonds to the P=O oxygen atom. The ∆δ values cover a relatively
narrow range from 1.4 to 8.9 ppm without visible trend
depending on the substituents at phosphorus or at the
quaternary carbon atoms (Table 4).
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Subsequently, the long term stability of polycrystalline 4 was
[7]
monitored under different conditions (Figure 9). As for 1 and 2,
13
Table 4. C NMR chemical shifts of the quaternary carbon signals of the
3
1
exposure to light did not alter the outcome of the experiments.
However, the temperature had a large impact. While about 10%
of the oxidative power of 4 is lost within 80 days of exposure at
ambient temperature, moderate cooling at 4 °C helps the adduct
to retain about 92% of active oxygen (Figure 9). Storage of
polycrystalline 4 at −20 °C leads to a loss of only about 5% of
oxidative power over the course of 80 days.
di(hydroperoxy)alkane moieties in 1-9, P NMR chemical shifts of the adducts
31
and their corresponding pure phosphine oxides, and the P NMR chemical
shift differences. All values were obtained with CDCl as the solvent.
3
1
3
31
δ
(
C) of C
ppm)
q
31
δ
(
P) of neat
PO (ppm)
∆δ
(ppm)
Adduct
δ( P) (ppm)
(
R
3
1
2
3
4
5
6
7
8
9
109.28
108.91
111.56
111.26
113.76
109.52
110.18
114.13
109.21
34.74
55.59
30.52
58.77
58.35
58.01
58.31
39.42
30.33
29.16
49.91
29.16
49.91
49.91
49.91
49.91
32.68
24.86
5.64
5.68
1.42
8.86
8.44
8.10
8.40
6.74
5.47
When large single crystals of the adducts 1-9 with
3
volumes of about 10 mm are exposed to ambient conditions for
months, practically no decomposition and loss of oxidative
power are detected. Therefore, the exposed surface area of the
crystals is an important factor for the shelf life of the adduts.
Regarding the decomposition process, the two oxygen
atoms per adduct assembly are most likely lost in a consecutive
and not a simultaneous manner. To corroborate this assumption,
we recently identified and characterized the intermediate
hydroperoxy(hydroxy)alkane adduct of tricyclohexylphosphine
[
43]
3 2 5
oxide Cy PO[(HOO)(HO)C(CH ) ].
In order to further support this assumption, 4 has been
dissolved in two different solvents (5 wt%) and the solutions
were heated to 105 °C. At regular intervals the oxidizing power
of the solutions was tested (Figure 10). In chlorobenzene the
oxidizing power of 4 is diminished to 50% within 7h, in toluene
within 8 hours. The decomposition curves reach a plateau at
about 50% oxidative power, which means that most probably
one of the two peroxo groups per adduct assembly is
decomposing more easily at higher temperatures. The
Shelflives of the Adducts
Next, the shelf life of the representative adduct 4 has been
monitored. For this purpose, a straightforward standardized in
3
1
[7]
situ P NMR test was applied to determine the number of
active oxygen atoms per adduct in the starting material and in
the course of exposure to different conditions. Hereby, the
oxidative power of 4 was determined at regular time intervals by
hydroperoxy(hydroxy)alkane
CMeEt] is more stable than the starting material 4, and much
adduct
3
Cy PO[(HOO)(HO)-
[43]
higher temperatures are needed to decompose it in solution in a
[43]
timely manner.
adding a slight excess of Ph
was selected as the probe because it is not oxidized readily in
air in the absence of a catalyst. However, di(hydroperoxy)alkane
3
P to a weighed amount of 4. PPh
3
Interestingly, the decomposition of 4 proceeds much faster
in chlorobenzene than in toluene, which suggests that a radical
process is dominant. This result, together with the fact that the
adducts 1-9 incorporate two peroxo groups with different
reactivities, points to a bright potential future of this class of
materials not only as selective oxidizing agents, but also as
hitherto unexplored radical initiators for polymerizations.
[7]
3 3
adducts transform Ph P into Ph PO selectively within minutes.
Therefore, the number of active oxygen atoms can be deduced
3
1
from the intensity ratio of the quantitatively recorded P NMR
resonances of residual Ph P and Ph PO. As anticipated, the
3
3
number of active oxygen atoms in 4 is two, and this number was
used to define 100% oxidative power.
3 2
Figure 10. Oxidative power of Cy PO·(HOO) CMeEt (4), dissolved in toluene
and chlorobenzene (5 wt%), while being heated to 105 °C. 100% oxidative
power is equivalent to 2 moles of active oxygen per mole of 4.
Figure 9. Oxidative power of polycrystalline Cy
3
PO·(HOO)
2
CMeEt (4) after
being stored at the indicated temperatures. 100% oxidative power is
equivalent to 2 moles of active oxygen per mole of 4.
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1
3
After complete loss of oxidizing power C NMR spectra of
the exposed materials indicate that the starting ketones are
regenerated. No alcohols or other products have been found
after complete decomposition of the adducts.
only other reaction products were the corresponding phosphine
oxide carriers and the ketones. The water molecules remained
[14]
attached to the phosphine oxides via hydrogen bonds. No
traces of the overoxidation product sulfone was detected,
demonstrating how easily the solid adducts can be administered
precisely with the proper stoichiometry. The fast and selective
oxidation of THT in one organic phase compares favorably to
studies performed previously with biphasic mixtures and added
Solubilities of the Adducts
[5a]
All di(hydroperoxy)alkane adducts of phosphine oxides are
extremely soluble in organic solvents (Figure 11). This feature
represents one of the most important advantages of these
adducts with respect to their applications as oxidizing agents,
because it allows oxidation reactions to be performed in one
organic phase rendering a second aqueous phase obsolete.
Therefore, transformations that would suffer from the presence
of an excess of water can be undertaken in an organic phase.
The one mole of water generated by using the two active oxygen
atoms of the di(hydroperoxy)alkane moiety for oxidation
processes will be retained by strong hydrogen bonding to the
phosphine oxide and thus will not form a second aqueous
catalysts.
The time requirements of the oxidation reactions decreased
for all adducts at the higher reaction temperatures of 50 °C and
60 °C (Table 5). For example, the adducts 1 and 2 oxidized the
sulfide to the sulfoxide in less than half and hour, and even for
the mildest oxidizing agent 5 the monoxidation was completed
within 6 hours. Again, no overoxidation was found in any case,
even at these elevated temperatures.
Table 5. Selective oxidation of THT (tetrahydrothiophene) to the sulfoxides (2
mol THT : 1 mol adduct). The time (h) required for the complete monoxidation
at the given temperatures is reported.
[14]
layer.
The solubilities in representative organic solvents have
been quantified for four representative di(hydroperoxy)alkane
adducts (Figure 11). All adducts are remarkably soluble in
chloroform and dichloromethane. For example, more than 600
mg of 3 and nearly 400 mg of 4 can be dissolved in 1 mL of
CH Cl . Even in the aromatic solvents toluene and benzene all
2 2
solubilities are substantial and certainly allow oxidation reactions
in these solvents.
Adduct
PO·(HOO) CMe
PO·(HOO) CMe
2
25 °C
50 °C
60 °C
0.4
0.4
1
Ph
3
2
2
(1)
(2)
2
2
5
8
8
6
0.5
0.5
2
Cy
3
2
Ph PO·(HOO) CMeEt (3)
3
2
Cy
3
3
PO·(HOO)
2
2
CMeEt (4)
3
1
Cy
PO·(HOO)
CEt (5)
2
7
6
Cy PO·(HOO) CMePh (7)
3
2
1
0.5
Conclusions
In
this
contribution,
we
widened
the
scope
of
di(hydroperoxy)alkane adducts of phosphine oxides and
described new insights on this new class of materials. It could be
demonstrated that (a) the substituents R in the phosphine oxides
3
R PO can be aryl, alkyl, or mixed substituents, while adducts
Figure 11. Solubilities of Ph
Cy PO·(HOO) CEt (5), and Cy
solvents.
3
PO·(HOO)
2
CMeEt (3), Cy
3
PO·(HOO)
2
CMeEt (4),
with di(hydroperoxy)alkanes are formed in each case. (b) The
stoichiometry of the adducts is well-defined for all phosphine
oxides, including those derived from the chelating phosphine
dppe, with one di(hydroperoxy)alkane moiety per P=O group.
Only in case the P=O groups are too close, just being separated
3
2
2
3
PO·(HOO)
2
C(CH
2 5
) (6) in the indicated
Oxidation Reactions
from each other by
a methylene group, they share one
The di(hydroperoxy)alkane adducts 1-9 are amenable to
the classical H based organic syntheses mentioned above.
di(hydroperoxy)alkane unit. (c) The range of applicable starting
ketones for the formation of the di(hydroperoxy)alkane moieties
has been broadened to include butanone, 3-pentanone,
cyclohexanone, and acetophenone. (d) Several different
synthetic routes have been presented for generating all
di(hydroperoxy)alkane adducts of phosphine oxides without
addition of metal catalysts. (e) All adducts crystallize readily and
reproducibly in large specimens which facilitates purification and
single crystal X-ray analysis. The structures of the adducts and
their packing motifs follow the same theme. (f) In general, there
are two hydrogen bonds formed between the two hydroperoxy
groups in the adduct and one P=O group. (g) Besides structural
analysis in the solid state, NMR and IR spectroscopic studies
2
O
2
Another important application targets the oxidation of sulfides for
academic purposes, but also for the energy saving and efficient
[44]
oxidative desulfurization of petroleum batches.
Once the
fundamental insights about sulfide oxidation with 1-9 are gained,
[10]
adducts of
the enantioselective synthesis of sulfoxides.
In first step towards this direction, selected
P-chiral phosphine oxides could also be applied for
[6]
a
di(hydroperoxy)alkane adducts (Table 5) were combined with
THT (tetrahydrothiophene) in a molar ratio of 1 : 2 in benzene. In
all cases, THT was selectively and quantitatively oxidized to the
sulfoxide at ambient temperature within two to eight hours. The
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Chemistry - A European Journal
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confirm
the
nature
of
the
adducts.
(h)
One
reactions were carried out using standard Schlenk techniques, if not
stated otherwise, although none of the materials described here is air-
sensitive. Reagents purchased from Sigma Aldrich or VWR were used
di(hydroperoxy)alkane moiety releases two active oxygen atoms
in a consecutive manner. (i) All pure or dissolved adducts are
safe and robust towards high temperatures and mechanical
stress. At ambient temperatures shelf lifetimes of months have
been determined. In solution 50% of the oxidative power is lost
within about 8 hours for one representative adduct. (j) The high
solubility of all adducts in the usual organic solvents allow
oxidation reactions in one organic phase. (k) All solid,
stoichiometric adducts can easily be administered and
2 2
without further purification. Aqueous H O solution (35%) was obtained
from Acros Organics and used as received. Solvents were dried by
boiling them over sodium, then they were distilled and stored under
purified nitrogen. Acetone (Aldrich, ACS reagent grade) and ethanol (200
proof) were dried over 3 Å molecular sieves (EMD Chemical Inc.).
Butanone, 3-pentanone, cyclohexanone and methylphenylketone were
used as purchased.
Representative procedure to determine in general the oxidative power of
adducts, described for the di(hydroperoxy)butane adduct of
tricyclohexylphosphine oxide (4): 11 mg of 4 (0.026 mmol) and 43 mg of
selectively oxidize phosphines
to phosphine oxides
instantaneously at ambient temperature. THT is transformed into
the sulfoxide in organic phases at room temperature without
overoxidation to the sulfone. Higher reaction temperatures lead
to quantitative conversion of THT in most cases within one hour,
without loss of selectivity. (l) The co-products of the oxidation
PPh
under air (PPh
conditions, in the absence of a catalyst). The oxidation is monitored in
3
(0.164 mmol) are dissolved in 0.35 mL of CDCl
3
in an NMR tube
3
is not oxidized by oxygen from the air under these
31
situ via P NMR spectroscopy and is complete within 20 min. The
integral ratio between the signals of OPPh and the remaining PPh is
used to calculate the oxidative power of 4. For this particular reaction, 31%
of the initial PPh (0.051 mmol) is oxidized, which amounts to 2 molar
equivalents of active oxygen per mole of 4.
[24a,b]
reactions, ketones and phosphine oxides, are unreactive
and non-toxic.
3
3
[
24c]
3
One option for the removal of the phosphine oxides from
the reaction mixtures is the strong, but reversible adsorption on
[14,15]
Ph
Schlenk flask and dissolved in acetone (100 mL) under nitrogen. Then
aqueous H (1.0 mL, 10 mmol) was added and the reaction mixture
was stirred for 3 h. The solution was concentrated to 5 mL in vacuo, then
the product was allowed to crystallize at room temperature.
3 2 2 3
PO·(HOO) CMe (1): Ph P (200 mg, 0.762 mmol) was weighed into a
solids like molecular sieves or silica.
Once the phosphine
oxides are retrieved from the support by washing with polar
[15]
2 2
O
solvents, they can be reused after being "recharged" with the
desired ketone and aqueous
di(hydroperoxy)alkane adducts.
H
2
O
2
to form the
Alternatively, one can
(
3 2 2
Ph PO)·(HOO) CMe (1) was obtained in the form of colorless
immobilize the adducts on silica by covalent tethering, like
rectangular crystals (243 mg, 0.629 mmol, 83% yield).
[12,13]
31
1
catalysts and linkers
carriers easily removable and recyclable by recharging them
with a ketone and H . We will further expand the scope of
adduct molecules to include tripodal phosphines
in order to render the phosphine oxide
NMR (δ, CDCl
7.61 (m, 6H, H ), 7.60-7.55 (m, 3H, H
); C 132.57 (s, C ), 132.10 (d, J( P- C) = 10.7 Hz, C
o
3
), P 34.74 (s); H 11.29-10.90 (br. s, OOH), 7.68-
), 7.51-7.46 (m, 6H, H ), 1.47 (m,
),
130.56 (d, J( P- C) = 106.1 Hz, C), 128.77 (d, J( P- C) = 12.6 Hz,
o
p
m
13
2
31
13
6H, CH
3
p
2
O
2
1
31 13
3
31
13
[45]
i
and
as oxide carriers to further increase their
[46]
C
m
), 109.28 (s, CH
NMR (δ, (CD
.68 (m, 6H, H ), 7.67-7.62 (m, 3H, H
3
C), 20.64 (s, CH
)
3 2
3
).
CO), P 31.21 (s); H 10.97 (br. s, OOH), 7.76-
), 7.60-7.53 (m, 6H, H ), 1.35 (s,
tetraphosphines
3
1
1
loading with peroxo groups. Additionally, diketones will be
explored as educts. Finally, new applications for these stable,
stoichiometric, and soluble di(hydroperoxy)alkane adducts of
phosphine oxides will be explored. These will include the use of
7
o
p
m
13
4
31
13
2
31 13
CH
0.2 Hz, C
= 12.1 Hz, C
3 p
); C 133.14 (d, J( P- C) = 2.3 Hz, C ), 132.58 (d, J( P- C) =
1
31
13
3
31
13
1
o
), 132.51 (d, J( P- C) = 104.7 Hz, C
), 109.03 (s, CH C), 20.97 (s, CH ). IR: ν(PO) = 1151.5 cm
. mp (decomp.) 75 °C.
i
), 129.52 (d, J( P- C)
-
m
3
3
[
10]
1
P-chiral phosphine oxides and the enantioselective synthesis
[6]
of sulfoxides.
3 2 2 3
Cy PO·(HOO) CMe (2): Cy P (100 mg, 0.357 mmol) was weighed into a
In conclusion, this contribution describes the general
nature of an important new class of materials that has the
potential to make a significant impact in diverse fields of
synthetic chemistry. The ease of handling, transport, and
storage of the described di(hydroperoxy)alkane adducts render
them attractive oxidizing agents that can be applied as an
alternative to aqueous hydrogen peroxide.
Schlenk flask inside a glove box. The flask was then sealed, brought
outside, and the phosphine was dissolved in acetone (60 mL) under a
nitrogen flow. After addition of aqueous H
reaction mixture was stirred for 1 h. Then a large amount of EtOH (100
mL) was added to the flask, and the azeotropic mixture of EtOH and H
was removed in vacuo at ambient temperature. (Cy PO)·(HOO) CMe (2)
crystallized in the form of large colorless hexagonal specimens (126 mg,
2 2
O (0.5 mL, 5.1 mmol) the
2
O
3
2
2
0
.311 mmol, 87% yield).
31
1
NMR (δ, CDCl
3
), P 55.59 (s); H 1.97-1.80 (m, 15H, PCHaxCHeqCHeq),
CHeq), 1.49-1.36 (s, 12H, PCHCHax, CH ),
C), 34.79 (d,
CH ),
1.77-1.70 (s, 3H, PCH(CH
2
)
2
3
1
3
1
.36-1.21 (m, 9H, PCHCH CHaxCHax); C 108.91 (s, CH
2
3
Experimental Section
1
31
13
3
31 13
J( P- C) = 60.9 Hz, PC), 26.74 (d, J( P- C) = 12.7 Hz, PCHCH
2
2
2
31
13
4
31
13
2
5.98 (d, J( P- C) = 3.6 Hz, PCHCH
PCH(CH CH ), 20.63 (s, CH ).
NMR (δ, (CD
2
), 25.92 (d, J( P- C) = 1.8 Hz,
General Remarks
2
)
2
2
3
3
1
1
3
)
2
CO), P 56.44 (s); H 11.45 (br. s, OOH), 2.02-
1
13
31
The H, C, and P NMR spectra were recorded at 499.70, 125.66, and
1.89 (m, 9H, PCHaxCHeq), 1.86-1.76 (m, 6H, PCHCH
2
CHeq), 1.74-1.66 (m,
1
3
31
1
2
02.28 MHz on a 500 MHz Varian spectrometer. The C and P{ H}
3
H, PCH(CH CHeq), 1.52-1.38 (m, 6H, PCHCHax), 1.37-1.19 (m, 9H,
2 2
)
1
NMR spectra were measured with H decoupling if not stated otherwise.
PCl (δ( P) = +81.92 ppm) in a capillary centered in the 5 mm
NMR tubes was used for referencing the P chemical shifts of the
compounds. For referencing the H and C chemical shifts the residual
proton signals of the solvent CDCl and the carbon signal have been
used (δ( H) = 7.26 ppm, δ( C) = 77.00 ppm). All signal assignments
were based on comparisons with analogous phosphine oxides
two-dimensional H, H and H, C correlation NMR spectroscopy. Virtual
13
1
31
PCHCH
2
CHaxCHax), 1.30 (s, CH
3
); C 108.61 (s, CH
3
C), 35.53 (d, J( P-
CH ), 26.74
). IR: ν(PO) =
31
Neat Ph
2
13
3
31
13
C) = 61.0 Hz, PC), 27.36 (d, J( P- C) = 12.1 Hz, PCHCH
2
2
31
2
31
13
(s, PCH(CH
2
)
2
CH
2
), 26.73 (d, J( P- C) = 2.8 Hz, PCHCH
2
1
13
-1
1124.5 cm . mp (decomp.) 70 °C.
3
1
13
3 2 3
Ph PO·(HOO) CMeEt (3): Ph P (300 mg, 1.14 mmol) was placed in a
[
7,14,15]
and
round bottom flask and dissolved in toluene (40 mL). 2-Butanone (0.12
mL, 1.3 mmol) and aqueous H (0.5 mL, 5 mmol) were added, and the
1
1
1
13
2 2
O
[
47]
couplings are indicated in the data sections of the compounds. The IR
spectra of the neat powders were recorded on a Shimadzu IRAffinity-1
FTIR instrument using a Pike Technologies MIRacle ATR plate. All
reaction mixture was stirred overnight. The solution was concentrated to
about 3 mL in vacuum and the product was allowed to crystallize. Adduct
3
was obtained in the form of colorless crystals (294 mg, 65% yield).
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201703676
FULL PAPER
31
1
NMR (δ, CDCl
), 7.60-7.55 (m, 3H, H
.6 Hz, 2H, CH CH ), 1.41 (s, 3H, CCH
); C 132.32 (d, J( P- C) = 2.7 Hz, C
3
), P 30.52 (s); H 11.38 (s, 2H, OOH), 7.69-7.64 (m, 6H,
3
1
1
H
o
p
), 7.51-7.46 (m, 6H, H
m
3
), 1.79 (q, J( H- H) =
Cy
3
PO·(HOO)
2
3
CMePh (7): [Cy PO·H
2
O
2
]
2
(425 mg, 1.30 mmol) was
1
1
7
CH
2
3
3
), 1.01 (t, J( H- H) = 7.6 Hz, 3H,
dissolved in 3 mL of acetophenone (25.7 mmol) in a round bottom flask.
After aqueous H (1.3 mL, 130 mmol) was added the mixture was
stirred for 4 h. The solution was concentrated in vacuo to about 3 mL and
allowed to crystallize. Cy PO·(HOO) CMePh (7) was obtained in the form
of colorless crystals (327 mg, 54%).
13
4
31
13
2
31 13
2
CH
3
p
), 132.08 (d, J( P- C)
2 2
O
1
31
13
3
31
=
10.0 Hz, C
o
), 131.29 (d, J( P- C) = 105.4 Hz, C
C) = 12.3 Hz, C ), 111.56 (s, CH C), 26.09 (s, CH
CCH ), 8.38 (s, CH CH ).
NMR (δ, C ), P 31.42 (s); H 11.95 (s, 2H, OOH), 7.62-7.56 (m, 6H,
), 7.03-6.98 (m, 3H, H
.6 Hz, 2H, CH CH ), 1.65 (s, 3H, CCH
); C 132.32 (d, J( P- C) = 10.4 Hz, C
i
), 128.66 (d, J( P-
1
3
m
3
2
CH ), 17.46 (s,
3
3
2
3
2
3
31
1
31
1
6
D
6
NMR (δ, CDCl
2H, H ), 7.38-7.33 (m, 2H, H
PCHaxCHeqCHeq), 1.75-1.71 (m, 3H, PCH(CH
1.47-1.37 (m, 6H, PCHCHax), 1.30-1.20 (m, 9H, PCHCH
140.09 (s, C), 127.98 (s, C ), 127.82 (s, C
CCH
Hz, PCHCH
3
), P 58.31 (s); H 11.89 (br. s, 2H, OOH), 7.59-7.56 (m,
), 7.31-7.27 (m, 1H, H ), 1.94-1.80 (m, 15H,
CHeq), 1.66 (s, 3H, CH
3
1
1
H
o
p
), 6.96-6.91 (m, 6H, H
m
3
), 2.09 (q, J( H- H) =
o
m
p
1
1
7
CH
2
3
3
), 1.11 (t, J( H- H) = 7.6 Hz, 3H,
2
)
2
3
13
),
1
3
2
31
13
31 13
1
31
13
2
CH
3
o
), 132.11 (d, J( P- C)
2
CHaxCHax);
C
4
3
31
=
104.0 Hz, C
i
), 132.10 (d, J( P- C) = 3.2 Hz, C
C) = 12.3 Hz, C ), 111.70 (s, CH C), 26.94 (s, CH
CCH ), 8.78 (s, CH CH ). IR: ν(PO) = 1118.7 cm . mp (decomp.) 54 °C.
p
), 128.72 (d, J( P-
i
o
p
), 125.94 (s, C
m
31
), 110.18, (S,
1
3
1
31 13
3
13
m
3
2
CH ), 18.16 (s,
3
3
), 34.68 (d, J( P- C) = 60.5 Hz, PC), 26.70 (d, J( P- C) = 12.1
-
1
2
31
13
3
2
3
2
CH
2
), 25.95 (d, J( P- C) = 3.3 Hz, PCHCH
2
), 25.89 (d,
4
31
13
J( P- C) = 1.4 Hz, PCH(CH
2
)
2
CH ), 23.40 (CCH ). IR: ν(PO) = 1122.6
2
3
-1
Cy
placed in a round bottom flask and dissolved in 30 mL of butanone (0.33
mol). After addition of aqueous H (0.5 mL, 5 mmol) the solution was
stirred overnight. Excess butanone was removed under vacuum until a
precipitate appeared. Subsequently, 50 mL of EtOH was added to the
3
PO·(HOO)
2
CMeEt (4): [Cy
3
PO·H
2
O
2
]
2
(300 mg, 0.91 mmol) was
cm . mp (decomp.) 100 °C.
2
O
2
(Ph
(20 mg, 0.05 mmol) was dissolved in 0.3 mL of pentanone (2.8 mmol) in
a round bottom flask. Subsequently, aqueous H (0.1 mL, 1 mmol) was
2 2 2 2 2 2 2 2 2 2 2
P(O)CH CH P(O)Ph )·((HOO) CEt ) (8): Ph P(O)CH CH P(O)Ph
2 2
O
flask, and the azeotropic mixture of EtOH and H
vacuo at ambient temperature to give white crystals of 4 (345 mg, 0.82
2
O was removed in
added, the solution was stirred for 1 h and then left to crystallize via slow
evaporation of the solvent. Adduct 8 crystallized in the form of colorless,
needle-like crystals (22 mg, 78% yield).
mmol, 90% yield).
31
1
31
1
31
1
NMR (δ, CDCl
3
), P 58.77 (s); H 11.47 (s, 2H, OOH), 1.97-1.80 (m,
NMR (δ, CDCl
Hz, 2H, OOH), 7.81-7.75 (m, 8H, H
3
), P 39.42 (s); H 10.81 (virtual doublet, J( P- H = 82.2
), 7.58-7.53 (m, 4H, H ), 7.51-7.46
3
1
1
1
1
CCH
5H, PCHCHeqCHeq), 1.73 (q, J( H- H) = 7.6 Hz, 2H, CH
.72 (m, 3H, PCH(CH CHeq), 1.48-1.39 (m, 6H, PCHCHax), 1.38 (s, 3H,
), 1.29-1.23 (m, 9H, PCHCH
2
CH
3
), 1.76-
o
p
3
31
1
3
1
1
2
)
2
(m, 8H, H
7.6 Hz, 8H, CH CH
o
132.74 (s, C ), 130.67 (virtual quintet, J( P- C) = 5.1 Hz, C ), 129.61 (d,
m 2
), 2.66 (d, J( P- H) = 2.7 Hz, 2H, PCH ), 1.75 (q, J( H- H) =
3
1
1
3
1
1
13
3
2
CHaxCHax), 0.97 (t, J( H- H) = 7.6 Hz,
2
CH
3
), 1.00 (t, J( H- H) = 7.6 Hz, 12H, CH
2
3
);
C
13
1
31
13
31
13
3H, CH
2
CH
3
); C 111.26 (s, CH
3
C), 34.72 (d, J( P- C) = 60.5 Hz, PC),
CH ), 26.02 (s, CH CH ), 25.96
), 25.91 (d, J( P- C) = 1.4 Hz,
), 8.36 (s, CH CH ). IR: ν(PO) = 1124.4
p
3
31
13
1
31
13
31
13
26.72 (d, J( P- C) = 12.1 Hz, PCHCH
2
2
2
3
J( P- C) = 102.8 Hz, C
), 114.13 (s, CCH ), 21.81 (s, CH
), 7.99 (s, CH ). IR: ν(PO) = 1149.6 cm . mp (decomp.)
i
), 129.23 (virtual quintet, J( P- C) = 6.1 Hz,
2
31 13
4
31
13
31
13
(
d, J( P- C) = 2.8 Hz, PCHCH
PCH(CH CH ), 17.41 (s, CCH
cm . mp (decomp.) 108 °C.
2
C
m
3
2 3
CH ), 21.05 (virtual triplet, J( P- C)
-
1
2
)
2
2
3
2
3
= 33.0 Hz, PCH
2
3
-1
104-110 °C.
Cy
a round bottom flask and combined with 3-pentanone (0.4 mL, 2 mmol)
and aqueous H (0.2 mL, 2 mmol). The mixture was stirred for 1 h,
then left to crystallize. Cy PO·(HOO) CEt (5) was obtained in the form of
white, rod-shaped crystals (425 mg, 97% yield).
3 2 2 3 2 2 2
PO·(HOO) CEt (5): [Cy PO·H O ] (330 mg, 1 mmol) was placed in
Ph
was dissolved in 60 mL of CH
(0.5 mL, 5 mmol) was added, and the solution was stirred for 1 h.
The organic layer was collected in a separation funnel, and the solvent
was removed in vacuo. The resulting white residue of
2
P(O)CH
2
P(O)Ph
2
·(HOO)
2
CMe
2
(9): Ph
2 2 2
PCH PPh (384 mg, 1 mmol)
2
Cl
2
in a round bottom flask. Then aqueous
2 2
O
2 2
H O
3
2
2
3
1
1
NMR (δ, CDCl
3
), P 58.35 (s); H 10.82 (br. s, 2H, OOH), 1.96-1.81 (m,
CHeq), 1.81 (t,
), 1.68 (q, J( H- H) = 7.6 Hz, 4H, CCH ),
.47-1.37 (m, 8H, PCHCHax CCH CH CH ), 1.30-1.22 (m, 9H,
CHaxCHax), 0.94 (t, J( H- H) = 7.6 Hz, 6H, CCH
Ph
addition of 0.5 mL of aqueous
crystallize. Adduct 9 was obtained as white, needle-like crystals (364 mg,
6% yield).
NMR (δ, CDCl
H, H ), 7.47-7.42 (m, 4H, H
14.7 Hz, 2H, PCH ), 1.48 (s, 6H, CCH
J( P- C) = 107.0 Hz, C), 130.86 (virtual quintet, J( P- C) = 5.1 Hz,
3
), 128.64 (virtual quintet, J( P- C) = 6.1 Hz, C ), 109.21 (s, CCH ),
2
P(O)CH
2
P(O)Ph
2
was dissolved in 5 mL of acetone, and after the
1
5H, PCHaxCHeqCHeq), 1.76-1.71 (m, 3H, PCH(CH )
2 2
2 2
H O ,
the product was allowed to
3
1
1
3
1
1
J( H- H) = 6.4 Hz, 4H, CCH
1
PCHCH
2
2
,
2
2
2
7
3
1
1
13
2
CH
3
3
);
C
31
1
2
), P 30.33 (s); H 11.01 (br. s, 2H, OOH), 7.72-7.66 (m,
3
1
31 13
31
1
13.76 (s, CCH
3
), 34.64 (d, J( P- C) = 60.5 Hz, PC), 26.68 (d, J( P-
3
31
1
8
o
p
), 7.38-7.33 (m, 8H, H
m
), 3.62 (t, J( P- H)
1
3
2
31
13
C) = 11.6 Hz, PCHCH
2
CH
2
), 25.93 (d, J( P- C) = 3.3 Hz, PCHCH
CH ), 21.64 (s, CH CH ), 7.91
). IR: ν(PO) = 1126.4 cm . mp (decomp.) 138 °C.
2
),
13
=
2
3
); C 132.21 (s, C ), 131.07 (d,
p
13
4
31
13
2
5.87 (d, J( P- C) = 0.9 Hz, PCH(CH
2
)
2
2
2
3
1
31
13
31
i
-
1
(
s, CH
2
CH
3
31 13
C
3
o
m
1
31
13
3.40 (t, J( P- C) = 59.1 Hz, PCH
2
)20.63 (s, CCH
3
).
Cy
3
PO·(HOO)
2
C(CH )
2 5
(6): 0.3 mL of H
2
SO
4
(5 mmol) and 13.5 mL of
31
1
NMR (δ, (CD
3
)
2
CO), P 26.63 (s); H 10.49 (br. s, OOH), 7.87-7.81 (ddd,
aqueous H
2
O
2
(0.135 mol) were combined with THF (25 mL) in a round
3
31
1
3
1
1
4
1
1
o
J( P- H) = 12.2 Hz, J( H- H) = 8.3 Hz, J( H- H) = 1.2 Hz, H ), 7.52-
bottom flask. Cyclohexanone (1.00 mL, 9.7 mmol) was added dropwise
over a period of 15 min, while stirring vigorously. After stirring for 5 h, 10
3
1
1
4
1
1
3
1
7
p
.47 (dt, J( H- H) = 7.3 Hz, J( H- H) = 1.2 Hz, H ), 7.43-7.38 (dt, J( H-
1
3
1
1
2
31
1
H) = 8.3 Hz, J( H- H) = 7.3 Hz, H
m
), 3.99 (t, J( P- H) = 13.9 Hz, CH
2
),
),
mL of CH
mixture to pH 7. Then the organic layer was collected, washed with H
4 times 3 mL), dried with MgSO , and filtered. All solvents were removed
from the filtrate in vacuo to leave pure (HOO)
2
Cl
2
was added, and NaHCO
3
was used to neutralize the
13
1
31
13
1.36 (s, CH
3 i p
); C 133.46 (d, J( P- C) = 106.2 Hz, C), 131.74 (s, C
O
31
13
2
1
30.89 (virtual quintet, J( P- C) = 29.3 Hz, C
), 128.38 (virtual quintet,
3
C), 33.11 (t, J( P- C) = 60.9
o
(
4
31
13
1
31 13
J( P- C) = 30.5 Hz, C
Hz, PCH ), 20.25 (s, CH
20 °C.
m
), 108.34 (s, CH
). IR: ν(PO) = 1163.1 cm . mp (decomp.)
1
C(CH
matched those reported in the
(297 mg, 0.9 mmol) was dissolved in 1 mL of
toluene and added to the flask. The mixture was stirred for 2 h and
subsequently concentrated in vacuo to about mL at ambient
temperature. Cy PO·(HOO) C(CH (6) was obtained in the form of clear,
hexagonal crystals (235 mg, 0.53 mmol, 59% yield).
2
)
5
behind. The
H
-1
2
2
3
1
3
2 2 5
and C NMR spectra of (HOO) C(CH )
1
[
22]
3 2 2 2
literature. [Cy PO·H O ]
3
Representative procedure for the oxidation of tetrahydrothiophene (THT)
to the sulfoxide: 17.6 mg (0.2 mmol) of THT and 0.1 mmol of the
respective adduct were weighed into a 5 mm NMR tube and dissolved in
3
2
2 5
)
3
1
1
NMR (δ, CDCl
1
3
), P 58.01 (s); H 10.66 (br. s, 2H, OOH), 1.97-1.79 (m,
0
6 6
.5 mL of C D inside a glove box. The tube was then sealed with a glass
3
1
1
5H, PCHaxCHeqCHeq), 1.81 (t, J( H- H) = 6.4 Hz, 4H, CCH
2
), 1.75-1.71
CHeq), 1.58 (quin, J( H- H) = 6.4 Hz, 4H, CCH CH ),
.47-1.37 (m, 8H, PCHCHax CCH CH CH ), 1.31-1.22 (m, 9H,
CHaxCHax); C 109.52 (s, CCH ), 34.67 (d, J( P- C) = 60.5
[48]
1
13
stopper lubricated with silicone grease. H and C NMR spectra of the
sample were recorded at room temperature every 30 min until the
oxidation was complete. In between the measurements, the sample was
kept in an oil bath with the desired reaction temperature. Stirring versus
shaking the NMR tube did not change the pace of the reaction.
3
1
1
(m, 3H, PCH(CH
2
)
2
2
2
1
,
2
2
2
13
1
31
13
PCHCH
Hz, PC), 29.68 (s, CCH
2
PCH(CH CH ), 25.55 (s, CCH CH CH
=
2
3
3
31
13
2
), 26.69 (d, J( P- C) = 12.1 Hz, PCHCH
2
CH
), 25.89 (d, J( P- C) = 0.9 Hz,
), 22.53 (s, CCH CH ). IR: ν(PO)
1103.3 cm . mp (decomp.) 144-150 °C.
2
),
2
31
13
4
31
13
5.94 (d, J( P- C) = 3.3 Hz, PCHCH
2
2
)
2
2
2
2
2
2
2
-
1
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201703676
FULL PAPER
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Acknowledgements
This material is based upon work supported by The Welch
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This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201703676
FULL PAPER
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CCDC 1451014 contains the supplementary crystallographic data of
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Entry for the Table of Contents
Shin Hye Ahn, Nattamai Bhuvanesh,
Janet Blümel*
Page No. – Page No.
FULL PAPER
Di(hydroperoxy)alkane Adducts of
Phosphine Oxides: Safe, Solid,
Stoichiometric, and Soluble Oxidizing
Agents.
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