Reaction of singlet dioxygen with phosphine-borane derivatives: From transient phosphine peroxides to crystalline peroxoboronates

Article abstract of DOI:10.1002/anie.201000520

Singlet dioxygen is readily split by phosphine-boronates under mild conditions. The initially formed phosphine peroxides spontaneously rearrange by B→O migration. The resulting peroxoboronates have been structurally characterized, and their ability to und

Full text of DOI:10.1002/anie.201000520

Communications
DOI: 10.1002/anie.201000520
Singlet Dioxygen Fixation
Reaction of Singlet Dioxygen with Phosphine–Borane Derivatives:
From Transient Phosphine Peroxides to Crystalline Peroxoboronates**
Susana Porcel, Ghenwa Bouhadir, Nathalie Saffon, Laurent Maron, and Didier Bourissou*
Dedicated to Dr. Bernard Meunier
The last two decades has witnessed a spectacular renaissance
in main group chemistry.[1] Of particular interest are ambi-
philic compounds that result from the combination of donor
and acceptor moieties, typically involving Group 13 and 15
elements.[2] Most strikingly, the groups of D. W. Stephan and
G. Erker have shown that phosphine–boranes R2P-spacer-
B(C6F5)2 (R = tBu or Mes (2,4,6-Me3C6H2); spacer= p-C6H4
or CH2CH2) reversibly activate dihydrogen under mild
conditions, opening new avenues in metal-free catalytic
hydrogenation.[3] Recently, reversible binding of carbon
dioxide has also been reported.[4] Moreover, our group has
evidenced versatile coordination properties for mono- and
polyphosphine–boranes featuring o-C6H4 linkers, which pro-
vide a better understanding of unusual interactions between
transition metals and Lewis acids.[5] The borane moiety ortho
to phosphorus was also exploited to stabilize highly reactive
adducts of phosphines. Accordingly, the reaction of R2P-
(o-C6H4)BMes2 with phenyl azide was shown to give a
phosphazide that is dramatically stabilized by intramolecular
a N!B interaction that undergoes an unusual photoisome-
rization process.[6] Furthermore, treatment of the o-phenylene
phosphine–borane system with diethyl azodicarboxylate and
phenyl isocyanate afforded stable versions of the zwitterionic
intermediates involved in the Mitsunobu reaction and cyclo-
oligomerization of isocyanates, respectively.[7]
Our continued interest in phosphine–borane compounds
prompted us to investigate their behavior toward singlet
dioxygen.[8,9] Very little is known about peroxidic adducts
1
between phosphines and O2. Indeed, the phosphadioxirane
deriving from the tris(o-methoxyphenyl)phosphine is the only
such adduct that has been characterized to date, thanks to
low-temperature NMR techniques.[10] Herein we report that
the presence of a Lewis acid in close proximity to the
phosphorus center dramatically influences the fate of the
reaction.[11] In particular, phosphine–boronates are shown to
readily split 1O2. The initially formed phosphine peroxides are
stabilized by intramolecular O!B interactions, but sponta-
neously rearrange by B!O migration to give stable perox-
oboronates.
We began to investigate the behavior of phosphine–
borane compounds towards dioxygen with the previously
described phosphine–borane 1.[12] No sign of oxidation was
observed after several hours when a toluene solution of 1 was
subjected to air bubbling at room temperature.[13] In marked
contrast, compound 1 rapidly reacted with 1O2 (generated by
3
irradiation of O2 in the presence of tetraphenylporphyrin as
photosensitizer) to afford a new compound 2 (Scheme 1). The
[*] Dr. S. Porcel, Dr. G. Bouhadir, Dr. D. Bourissou
Universitꢀ de Toulouse, UPS, LHFA
118 route de Narbonne, 31062 Toulouse (France)
and
CNRS, LHFA UMR 5069
31062 Toulouse (France)
Fax: (+33)5-6155-8204
E-mail: dbouriss@chimie.ups-tlse.fr
1
Scheme 1. Fixation of O2 by the phosphine–borane 1. TPP=tetraphe-
nylporphyrin.
Dr. N. Saffon
Structure Fꢀdꢀrative Toulousaine en Chimie Molꢀculaire
Toulouse (France)
Dr. L. Maron
mass spectrum (the ion (M+Na)+ was found at m/z 565)
indicated the incorporation of two oxygen atoms, and
1H NMR spectroscopy revealed the desymmetrization of the
two mesityl substituents at boron. Single crystals were
obtained in Et2O at ꢀ208C, and the molecular structure of
2 was unambiguously established by an X-ray diffraction
study (Figure 1, left). Accordingly, the phosphine–borane
compound 1 has split the 1O2 molecule. One oxygen atom sits
at phosphorus (leading to a phosphine oxide moiety), and the
Universitꢀ de Toulouse, INSA, UPS, LPCNO
135 avenue de Rangueil, 31077 Toulouse (France)
and
CNRS, LPCNO UMR 5215
31077 Toulouse (France)
[**] Financial support from the Centre National de la Recherche
Scientifique, the Universitꢀ de Toulouse and the COST action
CM0802 PhoSciNet is gratefully acknowledged. L.M. thanks the
Institut Universitaire de France and S. P. thanks the Ministery of
Ciencia e Innovaciꢁn of Spain for a Postdoctoral Fellowship.
ꢀ
other has been inserted into one of the B Mes bonds. The
boron atom is in a trigonal planar environment, which
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201000520.
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Chemie
performed with a circa 1:1 mixture of (16O)2 and (18O)2, the
three isotopomers (16O)2, (16O18O), and (18O)2 of 5 were
observed by mass spectrometry.[15] The scrambling of the
labeled oxygen atoms suggests a bimolecular process for the
rearrangement of the initially formed 4:1O2 adduct into 5.
Organylperoxides of Group 13 elements (> E-O-O-R,
with E = B, Al, Ga, or In) have attracted a surge of interest in
the last two decades as key intermediates in autoxidation
processes and as potential oxygen transfer reagents. However,
these compounds are usually extremely reactive and rather
unstable,[16] which often prevents their isolation and complete
characterization. The first alkylperoxides of a Group 13
element to be structurally authenticated were the dimeric
[{(tBu)2E(m-OOtBu)}2] (E = Ga, In)[17] and dinuclear
Figure 1. Molecular views of 2 (left) and 5 (right) in the solid state
(ellipsoids set at 50% probability). Phenyl, mesityl, and methyl groups
are simplified and the hydrogen atoms are omitted for clarity. For 5,
only one of the two independent molecules present in the asymmetric
unit is shown. Selected bond lengths [ꢂ] and angles [8]: 2: P1–O1
1.484(1), B1–O2 1.359(2). 5: P1–O1 1.534(3), B1–O1 1.647(6), B1–O2
1.408(6), B1–O3 1.454(6), O3–O4 1.473(4); P1-O1-B1 112.4(3), O2-B1-
O3 115.1(4).
[(tBuOO)(tBuO)Al(m-OtBu)2Al(mesal)2]
(mesal = methyl
salicylate) derivatives.[18] Recently, Uhl et al. took advantage
of the peculiar electronic properties of the CH(SiMe3)2 group
to prepare and crystallographically characterize a monomeric
aluminum peroxide and several original di- and trinuclear
gallium peroxides,[19] all featuring oxidizing peroxo moieties
corresponds with the 11B NMR signal observed at d =
34.7 ppm.
From a mechanistic viewpoint, it is most likely that 1O2 is
first trapped by the ambiphilic phosphine–borane 1, and the
ensuing phosphine peroxide 3 then rearranges by migration of
a mesityl group from boron to oxygen.[14] No intermediate
could be detected by 31P NMR monitoring at ꢀ808C,
suggesting that the rearrangement 3!2 proceeds spontane-
ously. Furthermore, the reaction is totally regioselective, with
ꢀ
(E-O-O) and also reducing E C bonds. Not much is known
either about the related organylperoxides of boron. To date,
only one such compound has been characterized by X-ray
diffraction: in 2009, Piers et al. described an endoperoxide
adduct of a NHC-stabilized 9-boraanthracene.[20]
Compound 5 thus provides a rare example of a structur-
ally authenticated B-O-O skeleton, and the first included in a
ꢀ
the oxygen atom being inserted into one of the B Mes bond
ꢀ
ꢀ
but not into the B C6H4PPh2 bond.
peroxoboronate moiety.[21–24] The O1 P1 bond distance of 5
To study the influence of the substituents at boron, the
two mesityl groups were replaced by a pinacol unit. The
phosphine–boronate 4[15] was also found to react spontane-
ously with 1O2 (but not with 3O2), leading to a single
compound 5 (Scheme 2). The mass spectrum indicated the
(1.534(3) ꢀ) is significantly longer than that of 2 (1.484(1) ꢀ),
in agreement with the additional interaction of O1 toward B
ꢀ
(O1 B1: 1.647(6) ꢀ). The ensuing five-membered ring is
almost planar, and the six-membered ring linked in a spiro
ꢀ
fashion at boron adopts a chair conformation. The B O bond
is slightly shorter for the boron–alkoxide than for the boron–
ꢀ
ꢀ
peroxide linkage (B1 O2: 1.408(6) ꢀ versus B1 O3:
ꢀ
1.454(6) ꢀ). The O3 O4 distance (1.473(4) ꢀ) falls in the
typical range for alkylperoxides of Group 13 elements,[17–19]
ꢀ
and the torsion angle across the O3 O4 bond (60.88) is similar
to those observed by Uhl et al. in gallium endoperoxides[19b–d]
(values of more than 908 are encountered in acyclic per-
oxides).
1
Scheme 2. Fixation of O2 by the phosphine–boronate 4.
At this stage, it should be noted that the peroxo skeleton
of > E-O-O-R compounds usually comes from a dioxygen
incorporation of two oxygen atoms and the low field shift of
the 31P NMR signal (from d = ꢀ4.1 ppm for 4 to d = +
46.0 ppm for 5) substantiated the oxidation of the phosphorus
atom. Furthermore, the presence of two sets of 1H and
13C NMR signals for the CMe2 groups revealed the desym-
metrization of the pinacol moiety, and the 11B NMR reso-
nance signal observed at d = + 15.9 ppm (compared to
+ 31.1 ppm for 4) suggested a tetracoordinate environment
around boron. Compound 5 was isolated as a white moisture-
sensitive solid by recrystallisation from diethyl ether at
ꢀ208C, and its molecular structure was definitely confirmed
by X-ray crystallography (Figure 1, right). The phosphine–
boronate 4 has thus split the dioxygen molecule in a similar
fashion to that observed with 1. In this case, one oxygen atom
bridges the phosphorus and boron atoms, whilst the other
oxygen atom has been inserted into the B(pin) ring, leading to
a B-O-O skeleton. When the reaction of 4 with 1O2 was
ꢀ
molecule (insertion into E C bonds) or a hydroperoxide
(condensation reaction), whereas for 5, the B-O-O fragment
ꢀ
is obtained by insertion of one oxygen atom into a B O bond.
To gain more insight into the structure and relative
1
stability of the various phosphine–borane: O2 adducts, DFT
calculations were performed at the B3PW91/SDD(P,B),6-
31G**(other atoms) level of theory on the model compound I
featuring an ethylene glycol unit at boron.[15] The optimized
structures of the dioxygen adducts II–IV are shown in
ꢀ
Figure 2. In the cyclic adduct II, the O1 O2 distance is
1.54 ꢀ and the boron atom does not interact with the
phosphadioxirane moiety (the BO1 and BO2 distances
exceed 2.7 ꢀ). The formation of II from I + 1O2 is strongly
favored thermodynamically (DGI!II = ꢀ32.8 kcalmolꢀ1). In
marked contrast with that predicted computationally for
simple phosphines,[25] the corresponding phosphine peroxide
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Communications
membered ring. Oxygen transfer between the peroxoboro-
nate 8 and the starting material 6 readily occurs at room
temperature, as substantiated by the instantaneous and
quantitative formation of the phosphine oxide 7 upon
mixing both reagents in a 1:1 ratio. This result confirms that
7 is formed from 6 and 1O2 at room temperature.
A similar oxygen transfer was also observed between the
phosphine–boronate 4 and the ensuing peroxoboronate 5
(Scheme 4). This comproportionation reaction required 3 h at
room temperature, and cleanly afforded the phosphine oxide
9. Compound 9 was isolated in 64% yield after recrystalliza-
1
Figure 2. Optimized geometries and relative energies of the O2
adducts deriving from the model phosphine–boronate I (free energies
G at 258C relative to I+1O2).
derivative III was also found to be a minimum on the
potential energy surface, located 10.7 kcalmolꢀ1 lower in
energy.[26] Compound III is stabilized by a strong intra-
ꢀ
molecular O!B interaction (B O2 distance: 1.554 ꢀ). Over-
all, the phosphine–borane skeleton bridges the two oxygen
ꢀ
atoms (O1 O2 1.50 ꢀ), leading to a puckered six-membered
Scheme 4. Oxygen transfer reaction from 5 to 4.
ring. Finally, the peroxoboronate form IV (related to 5) is a
further 14.2 kcalmolꢀ1 lower in energy compared to III, and
its optimized geometry reproduced well the structure deter-
tion in Et2O/pentane and fully characterized by NMR and X-
ray diffraction.[15] Finally, the ability of the peroxoboronates 5
and 8 to oxidize simple phosphines was examined using PPh3
as a model substrate. According to 31P NMR, the reaction
proceeds cleanly in both cases, leading to Ph3PO (d = +
25.0 ppm) together with the phosphine oxide 9 or 7. In line
with observations for the comproportionation reactions, the
reaction proceeds faster with 8 than with 5, complete
conversion being achieved within 2 h at room temperature
with 8 but requiring heating overnight at 1008C with 5.
In summary, ortho-phenylene phosphine–borane systems
have been shown to readily react with singlet dioxygen.
Starting from phosphine–boronates 4 and 6, two stable
peroxoboronates 5 and 8 have been isolated and fully
characterized. The ability of these compounds to undergo
oxygen transfer reactions has been substantiated. The poten-
tial application of such peroxoboronates as oxidizing agents
and the extension of the present work to other phosphine–
borane systems is currently under study in our group.
ꢀ
mined crystallographically (O2 O3 1.46 ꢀ).
To substantiate the generality of the reaction observed
1
between 4 and O2, we then investigated the behavior of the
related phosphine–borane compound 6[15] featuring a six-
1
membered-ring boronate. In this case, reaction of 6 with O2
under the same conditions afforded the phosphine oxide–
boronate 7 (Scheme 3), as deduced from mass spectrometry
(incorporation of a single oxygen atom) and NMR spectros-
1
Scheme 3. Fixation of O2 by the phosphine–boronate 6.
Experimental Section
All reactions and manipulations were carried out using standard
Schlenk techniques. The NMR spectra were recorded at 258C.
General procedure for the reactions of the phosphine–borane
compounds with 1O2: A toluene solution of the phosphine–borane
compound (concentrations ranging from 0.02m to 0.09m) containing
5–7 mol% of tetraphenylporphyrin was irradiated with a halogen
lamp under a dried atmosphere of dioxygen until 31P NMR spectros-
copy indicated complete conversion. Toluene was removed under
vacuum, and the residue was purified by crystallization in diethyl
ether (for 2 and 5) or precipitation in dichloromethane/pentane (for
8).
copy (d 31P = + 32.2 ppm and d 11B = + 27.4 ppm). Taking into
account the fact that 6 is reluctant toward oxidization by 3O2,
we speculated that the phosphine oxide 7 was formed by a
1
side reaction between unreacted 6 and a O2 adduct thereof.
To prevent this comproportionation process, the reaction
1
between 6 and O2 was carried out at ꢀ608C. Gratifyingly,
31P NMR spectroscopy revealed the exclusive formation of a
new product 8 (d = + 52.9 ppm) that was isolated in 76%
yield by precipitation from a dichloromethane/pentane mix-
ture at ꢀ208C. All the spectroscopic data for 8 support a
peroxoboronate structure analogous to 5, which was unam-
2: 31P{1H} NMR (202.5 MHz, C6D6): d = 37.8 ppm; 11B NMR
(160.5 MHz, CDCl3): d = 34.7. HRMS (ESI+) calcd for [M+Na]+
(C36H37BO2P+): 565.2444, found: 565.2443. 5: 31P NMR (202.5 MHz,
CDCl3): d = 46.0 ppm; 11B NMR (160.5 MHz, CDCl3): d = 15.9 ppm.
HRMS (ESI+) calcd for [M+H]+ (C24H27BO4P+): 421.1740, found:
421.1757. 8: 31P{1H} NMR (202.5 MHz, C6D6): d = 52.9 ppm;
11B NMR (160.5 MHz, C6D6): d = 12.9 ppm. HRMS (CI+) calcd for
[M+H]+ (C23H25BO4P+): 407.1584, found: 407.1578.
biguously confirmed by crystallography.[15] The O O distance
ꢀ
of 8 (1.433(3) ꢀ) is slightly shorter than that of 5, whilst the
ꢀ
torsion angle around the O O bond widens to 98.78 as the
result of the inclusion of the B-O-O-C skeleton in a seven-
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Angew. Chem. Int. Ed. 2010, 49, 6186 –6189

Angewandte
Chemie
Received: January 28, 2010
Revised: April 6, 2010
Published online: June 22, 2010
[10] a) R. Gao, D. G. Ho, T. Dong, D. Khuu, N. Franco, O. Sezer, M.
Selke, Org. Lett. 2001, 3, 3719 – 3722; b) D. G. Ho, R. Gao, J.
Celaje, H.-Y. Chung, M. Selke, Science 2003, 302, 259 – 262; c) D.
Zhang, B. Ye, D. G. Ho, R. Gao, M. Selke, Tetrahedron 2006, 62,
10729 – 10733; d) D. Zhang, R. Gao, S. Afzal, M. Vargas, S.
Sharma, A. McCurdy, M. Yousufuddin, T. Stewart, R. Bau, M.
Selke, Org. Lett. 2006, 8, 5125 – 5128; e) J. J. Wilke, F. Weinhold,
J. Am. Chem. Soc. 2006, 128, 11850 – 11859.
Keywords: ambiphilic compounds · boronates · oxygen transfer ·
.
phosphines · singlet oxygen
[11] For the reaction of boranes with molecular oxygen, see: H. C.
Brown in Boranes in Organic Chemistry, Cornell University
Press, 1972.
[1] For a recent review highlighting unexpected similarities between
main group elements and transition metals, see: P. P. Power,
Nature 2010, 463, 171 – 177. See also the special issue (number
33) of Dalton Transactions published in 2008.
[12] T. W. Hudnall, Y.-M. Kim, M. W. P. Bebbington, D. Bourissou,
F. P. Gabbai, J. Am. Chem. Soc. 2008, 130, 10890 – 10891.
[13] The inertness of 1 toward oxidation by 3O2 is reminiscent of that
reported by Buchwald et al. for biarylphosphines: T. E. Barder,
S. L. Buchwald, J. Am. Chem. Soc. 2007, 129, 5096 – 5101.
[14] 1,2-Shifts of aryl groups from boron to oxygen have already been
observed; see, for example: R. W. Hoffmann, K. Ditrich, Syn-
thesis 1983, 107 – 109.
[2] a) D. W. Stephan, Dalton Trans. 2009, 3129 – 3136; b) D. W.
Stephan, G. Erker, Angew. Chem. 2010, 122, 50 – 81; Angew.
Chem. Int. Ed. 2010, 49, 46 – 76.
[3] a) G. C. Welch, R. R. San Juan, J. D. Masuda, D. W. Stephan,
Science 2006, 314, 1124 – 1126; b) P. A. Chase, G. C. Welch, T.
Jurca, D. W. Stephan, Angew. Chem. 2007, 119, 8196 – 8199;
Angew. Chem. Int. Ed. 2007, 46, 8050 – 8053; c) P. Spies, G.
Erker, G. Kehr, K. Bergander, R. Frꢁhlich, S. Grimme, D. W.
Stephan, Chem. Commun. 2007, 5072 – 5074; d) P. Spies, S.
Schwendemann, S. Lange, G. Kehr, R. Frꢁhlich, G. Erker,
Angew. Chem. 2008, 120, 7654 – 7657; Angew. Chem. Int. Ed.
2008, 47, 7543 – 7546.
[15] See the Supporting Information for details.
[16] a) Y. A. Alexandrov, N. V. Chikinova, J. Organomet. Chem.
1991, 418, 1 – 59; b) A. R. Barron, Chem. Soc. Rev. 1993, 22, 93 –
99.
[17] a) W. M. Cleaver, A. R. Barron, J. Am. Chem. Soc. 1989, 111,
8966 – 8967; b) M. B. Power, W. M. Cleaver, A. W. Apblet, A. R.
Barron, J. W. Ziller, Polyhedron 1992, 11, 477 – 486.
[4] C. M. Mꢁmming, E. Otten, G. Kehr, R. Frꢁhlich, S. Grimme,
D. W. Stephan, G. Erker, Angew. Chem. 2009, 121, 6770 – 6773;
Angew. Chem. Int. Ed. 2009, 48, 6643 – 6646.
´
[18] a) J. Lewinski, J. Zachara, E. Grabska, J. Am. Chem. Soc. 1996,
´
´
118, 6794 – 6795; b) J. Lewinski, J. Zachara, P. Gos, E. Grabska,
[5] a) S. Bontemps, H. Gornitzka, G. Bouhadir, K. Miqueu, D.
Bourissou, Angew. Chem. 2006, 118, 1641 – 1644; Angew. Chem.
Int. Ed. 2006, 45, 1611 – 1614; b) S. Bontemps, G. Bouhadir, K.
Miqueu, D. Bourissou, J. Am. Chem. Soc. 2006, 128, 12056 –
12057; c) M. Sircoglou, S. Bontemps, M. Mercy, N. Saffon, M.
Takahashi, G. Bouhadir, L. Maron, D. Bourissou, Angew. Chem.
2007, 119, 8737 – 8740; Angew. Chem. Int. Ed. 2007, 46, 8583 –
8586; d) S. Bontemps, M. Sircoglou, G. Bouhadir, H. Pusch-
mann, J. A. K. Howard, P. W. Dyer, K. Miqueu, D. Bourissou,
Chem. Eur. J. 2008, 14, 731 – 740; e) S. Bontemps, G. Bouhadir,
W. Gu, M. Mercy, C.-H. Chen, B. M. Foxman, L. Maron, O. V.
Ozerov, D. Bourissou, Angew. Chem. 2008, 120, 1503 – 1506;
Angew. Chem. Int. Ed. 2008, 47, 1481 – 1484; f) M. Sircoglou, S.
Bontemps, G. Bouhadir, N. Saffon, K. Miqueu, W. Gu, M. Mercy,
C.-H. Chen, B. M. Foxman, L. Maron, O. V. Ozerov, D.
Bourissou, J. Am. Chem. Soc. 2008, 130, 16729 – 16738; g) M.
Sircoglou, M. Mercy, N. Saffon, Y. Coppel, G. Bouhadir, L.
Maron, D. Bourissou, Angew. Chem. 2009, 121, 3506 – 3509;
Angew. Chem. Int. Ed. 2009, 48, 3454 – 3457; h) P. Gualco, T.-P.
Lin, M. Sircoglou, M. Mercy, S. Ladeira, G. Bouhadir, L. M.
Pꢂrez, A. Amgoune, L. Maron, F. P. Gabbaꢃ, D. Bourissou,
Angew. Chem. 2009, 121, 10076 – 10079; Angew. Chem. Int. Ed.
2009, 48, 9892 – 9895; i) M. Sircoglou, S. Bontemps, M. Mercy, K.
Miqueu, S. Ladeira, N. Saffon, L. Maron, G. Bouhadir, D.
Bourissou, Inorg. Chem. 2010, 49, 3983 – 3990.
´
T. Kopec, I. Madura, W. Marciniak, I. Prowotorow, Chem. Eur. J.
2000, 6, 3215 – 3227.
[19] a) W. Uhl, B. Jana, Chem. Eur. J. 2008, 14, 3067 – 3071; b) W. Uhl,
M. R. Halvagar, Angew. Chem. 2008, 120, 1981 – 1983; Angew.
Chem. Int. Ed. 2008, 47, 1955 – 1957; c) W. Uhl, M. R. Halvagar,
F. Roge, W. Massa, Eur. J. Inorg. Chem. 2009, 489 – 492; d) W.
Uhl, M. R. Halvagar, M. Layh, Chem. Commun. 2009, 4269 –
4271.
[20] T. K. Wood, W. E. Piers, B. A. Keay, M. Parvez, Angew. Chem.
2009, 121, 4069 – 4072; Angew. Chem. Int. Ed. 2009, 48, 4009 –
4012.
[21] Sodium perborate, which is commonly used as a bleaching agent
ꢀ
in the detergent industry, features O O bridges: W. P. Griffith,
A. C. Skapski, A. P. West, Chem. Ind. 1984, 185.
[22] The peroxoborate tBuOOB(en)(en=ethylene glycol) was pre-
pared from tBuOOH and ClB(en) and used to oxidize organo-
lithium and Grignard reagents. See Ref. [13] and: R. W. Hoff-
mann, B. Hꢁlzer, O. Knopff, K. Harms, Angew. Chem. 2000, 112,
3206 – 3207; Angew. Chem. Int. Ed. 2000, 39, 3072 – 3074.
[23] For a crystalline peroxoboronic acid that is k2-O,O coordinated
to rhodium, see: M. Ahijado, T. Braun, Angew. Chem. 2008, 120,
2996 – 3000; Angew. Chem. Int. Ed. 2008, 47, 2954 – 2958.
[24] A peroxoborate complex [Rh]OOB(pin) (pin = tetramethyl-
ethylene glycol) has been characterized by NMR at low temper-
ature upon reacting a h2-peroxo rhodium complex with pinacol-
borane HB(pin): M. A. Ahijado Salomon, T. Braun, A. Pener,
Angew. Chem. 2008, 120, 8999 – 9003; Angew. Chem. Int. Ed.
2008, 47, 8867 – 8871.
[6] M. W. P. Bebbington, S. Bontemps, G. Bouhadir, D. Bourissou,
Angew. Chem. 2007, 119, 3397 – 3400; Angew. Chem. Int. Ed.
2007, 46, 3333 – 3336.
[7] S. Moebs-Sanchez, G. Bouhadir, N. Saffon, L. Maron, D.
Bourissou, Chem. Commun. 2008, 3435 – 3437.
[25] a) K. Nahm, Y. Li, J. D. Evanseck, K. N. Houk, C. S. Foote,
J. Am. Chem. Soc. 1993, 115, 4879 – 4884; b) S. Tsuji, M. Kondo,
K. Ishiguro, Y. Sawaki, J. Org. Chem. 1993, 58, 5055 – 5059.
[26] The phosphadioxirane II was predicted to rearrange into the
phosphine peroxide III with a barrier height of only 5.1 kcal
[8] The lowest singlet state, referred to as 1Dg, features one doubly-
occupied p* orbital and one empty p* orbital, so singlet
dioxygen can be considered as an ambiphilic molecule.
[9] The frustrated Lewis pair tBu3P/B(C6F5)3 was recently found to
readily bind nitrous oxide (N2O): E. Otten, R. C. Neu, D. W.
Stephan, J. Am. Chem. Soc. 2009, 131, 9918 – 9919.
molꢀ1
.
Angew. Chem. Int. Ed. 2010, 49, 6186 –6189
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
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