An efficient methyltrioxorhenium(VII)-catalyzed transformation of hydrotrioxides (ROOOH) into dihydrogen trioxide (HOOOH)

Article abstract of DOI:10.1021/ja806411a

Dihydrogen trioxide (HOOOH) is formed nearly quantitatively in the low-temperature (-70 °C) methyltrioxorhenium(VII) (MTO)-catalyzed transformation of silyl hydrotrioxides (R₃SiOOOH), and some acetal hydrotrioxides, in various solvents, as confirmed by ¹H, and ¹⁷O NMR spectroscopy. The calculated energetics (B3LYP) for the catalytic cycle, using H₃SiOOOH as a model system, is consistent with the experimentally observed activation energy (9.5 ± 2.0 kcal/mol) and a small kinetic solvent isotope effect (k_H2O/k_D2O = 1.1 ± 0.1), indicating an initial concerted reaction between the silyl hydrotrioxide and MTO in the rate-determining step. With the addition of water in the next step, the intermediate undergoes a σ-bond metathesis reaction to break the Re-OOOH bond and form HOOOH, together with the second dihydroxy intermediate. The final step in the catalytic cycle involves a second, catalytic water that lowers the barrier to form H₃SiOH and MTO. Copyright

Full text of DOI:10.1021/ja806411a

Published on Web 10/04/2008
An Efficient Methyltrioxorhenium(VII)-Catalyzed Transformation of
Hydrotrioxides (ROOOH) into Dihydrogen Trioxide (HOOOH)
†
,†
†
,‡
Ana Bergant, Janez Cerkovnik,* Bo zˇ o Plesni cˇ ar, and Tell Tuttle*
Department of Chemistry, Faculty of Chemistry and Chemical Technology, UniVersity of Ljubljana, P.O. Box 537,
000 Ljubljana, SloVenia, and WestCHEM, Department of Pure and Applied Chemistry, UniVersity of Strathclyde,
95 Cathedral Street, Glasgow G1 1XL, U.K.
1
2
Received August 13, 2008; E-mail: janez.cerkovnik@fkkt.uni-lj.si; tell.tuttle@strath.ac.uk
Hydrotrioxides, ROOOH, have already been found to be key
intermediates in the reaction of ozone with alcohols, ethers, acetals,
hydrocarbons, and organometallic hydrides.
Scheme 1. MTO-Catalyzed Transformation of Various
Hydrotrioxides into Dihydrogen Trioxide
1
Corey et al. have presented evidence that triethylsilyl hydrotri-
oxide, Et
3
SiOOOH, generated by the low-temperature ozonation
1
2,3
of triethylsilane, is an excellent source of singlet oxygen (O
2 g
( ∆ )).
In an extension of this work, we found that, under certain conditions,
HOOOH is also formed (albeit in only relatively modest yields) in
the decomposition of some silyl hydrotrioxides in organic oxygen
Table 1. MTO-Catalyzed Transformation of Hydrotrioxides
(
ROOOH) into Dihydrogen Trioxide (HOOOH) at -70 °C in
a
Acetone-d6
1b
bases as solvents. All the hydrotrioxides and HOOOH have been
1
29
17
1
4
well characterized by NMR ( H, Si, O) and IR spectroscopy.
Recently, the structure of HOOOH has finally also been determined
5
by microwave spectroscopy.
We report here that, surprisingly, HOOOH is formed nearly
6
quantitatively in the low-temperature methyltrioxorhenium(VII)
(
MTO)-catalyzed transformation of dimethylphenylsilyl hydrotri-
oxide in various solvents (acetone-d , methyl acetate, tert-butyl
6
1
17
methyl ether), as confirmed by H, and O NMR spectroscopy.
We found that other silyl hydrotrioxides, as well as some acetal
hydrotrioxides investigated so far, react similarly (see Scheme 1,
Table 1, and Figures S1-S3 in the Supporting Information (SI)).
This type of transformation appears to represent a convenient and
general method for the preparation of HOOOH, without the
1
,7
interfering presence of hydrotrioxides (ROOOH) or HOOH.
a
Concentration of ROOOH: (0.1 ( 0.05) M. Molar ratio ROOOH/
b
We found that water (always present in the reaction mixture) is
consumed as a reaction proceeds and that the reduced amount of
HOH notably diminishes the rate of the transformation. In addition,
we also observed that the corresponding silanol (alcohol), formed
as the byproduct in the MTO-catalyzed transformation of ROOOH,
could also participate in this reaction (although at a somewhat lower
rate), if HOH is not available.
Therefore, we investigated the role of water in these reactions
and found that the kinetic solvent isotope effect was negligible,
that is, kH2O/kD2O ) 1.1 ( 0.1 (Table S1 in SI). All these
observations indicate that water is a crucial reaction component,
but is not involved in the rate-determining step of this transforma-
tion. The reaction rates for the MTO-catalyzed transformation of
hydrotrioxides into HOOOH are considerably faster than those for
MTO/H O ) 1.0:0.05:1.0. Yields determined by integration of OOOH
2
1
absorption of ROOOH and HOOOH in H NMR spectra. Standard
deviation e10%. Values in parenthesis are yields of transformations
c
without added catalyst, MTO.
3
mation of the simplest of silyl hydrotrioxides, that is, H SiOOOH
into HOOOH in the presence of water. Possible starting points for
8
the reaction were investigated using the B3LYP hybrid functional
9
a,b
in conjunction with the 6-311++G(d,p) basis set,
on all
nonmetal atoms, and the SDD quasi-relativistic pseudopotential and
9
c
associated basis set for Re. All calculations were run using the
1
0
Gaussian 03 program.
The simplified H SiOOOH system was selected to efficiently
3
explore the various mechanistic pathways. However, we have
additionally calculated the rate-determining step of the favored
mechanism (vida infra) using the dimethylphenylsilyl hydrotrioxide
substrate (entry 1, Table 1), and observed only a minor influence
on the energetics of the reaction (see SI for details). Therefore, we
believe the mechanism outlined in Figure 1 is qualitatively correct
for all the substrates tested thus far. A complete computational
investigation of all substrates presented in Table 1 will be published
subsequently.
the decomposition of hydrotrioxides into the corresponding silanol
1
(
alcohol) and singlet oxygen, O
2
( ∆
g
) (Table S2 in SI). The
activation parameters for the catalyzed transformation of hydro-
trioxides (E ) 9.5 ( 2.0 kcal/mol, log A ) 6.5 ( 1.5; acetone-d
methyl acetate) are slightly lower than those for the uncatalyzed
a
6
,
1
b
decomposition (Table S3 in SI).
To shed some light on the mechanism of these transformations,
we have undertaken DFT studies on the MTO-catalyzed transfor-
The catalytic cycle begins with a concerted reaction between
the silyl hydrotrioxide and MTO, whereby the Si-OOOH bond is
exchanged for a Si-ORe bond and a new Re-OOOH bond is
†
University of Ljubljana.
University of Strathclyde.
‡
11
formed. Relative to the separated reactants, the barrier to this
1
4086 9 J. AM. CHEM. SOC. 2008, 130, 14086–14087
10.1021/ja806411a CCC: $40.75  2008 American Chemical Society

C O M M U N I C A T I O N S
7b
silane, which will hopefully allow the preparation of concentrated
solutions of pure HOOOH, are currently under investigation. The
suitability of some other catalyst for this purpose is also being
explored.
Acknowledgment. We thank the Slovenian Research Agency
for financial support (J1-9410) and Dr. J. Plavec (Slovenian NMR
Centre, National Institute of Chemistry, Ljubljana) for running the
1
7
O NMR spectra. T. T. thanks the Royal Society of Edinburgh
for support through the RSE-Scottish Executive Personal Research
Fellowship and the EPSRC (EP\F031769\1).
Supporting Information Available: Complete ref 10; additional
experimental and computational details, NMR spectra, figure and tables
of kinetic data, the structures, Cartesian coordinates and energetic data
of all species indicated in the text are provided. This material is available
free of charge via the Internet at http://pubs.acs.org.
Figure 1. MTO-catalyzed mechanism for the production of HOOOH from
H3SiOOOH. Values are relative enthalpies (∆H(298 K)) and are given with
respect to the preceding intermediate.
q
reaction is 9.8 kcal/mol (∆H (298 K)), which is consistent with
the experimentally observed value of E
a
) 9.5 ( 2.0 kcal/mol.
References
The reaction is exothermic by 3.8 kcal/mol and results in the first
(
1) (a) Tuttle, T.; Cerkovnik, J.; Plesni cˇ ar, B.; Cremer, D. J. Am. Chem. Soc.
004, 126, 16093. (b) Cerkovnik, J.; Tuttle, T.; Kraka, E.; Lendero, N.;
Plesni cˇ ar, B.; Cremer, D. J. Am. Chem. Soc. 2006, 128, 4090. (c) Plesni cˇ ar,
B.; Cerkovnik, J.; Tekavec, T.; Koller, J. Chem.sEur. J. 2000, 6, 809. (d)
Plesni cˇ ar, B. Acta Chim. SloV. 2005, 52, 1.
1
2
2
intermediate (I-1, Figure 1). A reactant complex, which is 6.2
kcal/mol lower in enthalpy relative to the separated reactants can
be formed. However, the complex is not directly connected to the
TS (i.e., an initial rotation of the reactants from their complex
geometry is required to form the TS), and as such we consider the
separated reactants as the most meaningful reference state. For
further details on the energetics and structures of all calculated
reactants, products, and transition states see the SI.
With the addition of water, I-1 is able to undergo σ-bond
metathesis. The water molecule donates a proton to the hydrotri-
oxide ligand, which breaks the Re-OOOH bond and generates the
observed HOOOH. Concomitantly, a new Re-OH bond is formed,
resulting in the second intermediate (I-2, Figure 1). The barrier to
this reaction is 9.0 kcal/mol, relative to the separated reactants. The
reaction is thermoneutral (∆H ) 0.7 kcal/mol), with respect to the
resulting product complex from this reaction (see SI). However,
the dissociation of HOOOH results in an enthalpic penalty of 4.3
kcal/mol.
(2) Corey, E. J.; Mehrotra, M. M.; Khan, A. U. J. Am. Chem. Soc. 1986, 108,
2
472.
(3) (a) Posner, G. H.; Weitzberg, M.; Nelson, W. M.; Murr, B. L.; Seliger,
H. H. J. Am. Chem. Soc. 1987, 109, 278. (b) Hassner, A.; Stumer, C.
Organic Syntheses Based on Name Reactions, 2nd ed.; Pergamon: Am-
sterdam, The Netherlands, 2002; p 293.
(
4) For IR-matrix studies of HOOOH, see: (a) Engdahl, A.; Nelander, B. Science
002, 295, 482. For studies of HOOOH in solution, see: (b) Kova cˇ i cˇ , S.;
Koller, J.; Cerkovnik, J.; Tuttle, T.; Plesni cˇ ar, B. J. Phys. Chem. A 2008,
12, 8129.
5) Suma, K.; Sumiyoshi, Y.; Endo, Y. J. Am. Chem. Soc. 2005, 127, 14998.
2
1
(
(6) For reviews on MTO-catalyzed oxygen-transfer reactions, see: (a) Rom a˜ o,
C. C.; K u¨ hn, F. E.; Herrmann, W. A. Chem. ReV. 1997, 97, 3197. (b)
Herrmann, W. A.; K u¨ hn, F. E. Acc. Chem. Res. 1997, 30, 169. (c) Espenson,
J. H. Chem. Commun. 1999, 479. (d) Gonzales, J. M.; Distasio, R., Jr.;
Periana, R. A.; Goddard, W. A., III; Oxgaard, J. J. Am. Chem. Soc. 2007,
1
29, 15794.
(
7) (a) Wentworth, P., Jr.; Jones, L. H.; Wentworth, A. D.; Zhu, X. Y.; Larsen,
N. A.; Wilson, I. A.; Xu, X.; Goddard, W. A., III; Janda, K. D.;
Eschenmoser, A.; Lerner, R. A. Science 2001, 293, 1806. (b) Nyffeler,
P. T.; Boyle, N. A.; Eltepu, L.; Wong, C.-H.; Eschenmoser, A.; Lerner,
R. A.; Wentworth, P., Jr Angew. Chem., Int. Ed. 2004, 43, 4656.
8) (a) Becke, A. D. Phys. ReV. A 1988, 38, 3098. (b) Becke, A. D. J. Chem.
Phys. 1993, 98, 5648. (c) Lee, C. T.; Yang, W. T.; Parr, R. G. Phys. ReV.
B 1988, 37, 785. (d) Vosko, S. H.; Wilk, L.; Nusair, M. Can. J. Phys.
(
The final step in the cycle involves the formation of a reactant
complex with a second water molecule, which partially offsets the
enthalpy loss from the dissociation of HOOOH. The water molecule
forms a H-bond with the hydroxide ligand, to generate this complex,
which is 4.0 kcal/mol lower in enthalpy than the separated reactants
1
980, 58, 1200. (e) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch,
M. J. J. Phys. Chem. 1994, 98, 11623. (f) Hertwig, R. H.; Koch, W. Chem.
Phys. Lett. 1997, 268, 345.
(
9) (a) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639. (b)
Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980,
72, 650. (c) Andrae, D.; H a¨ ussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Theor. Chim. Acta 1990, 77, 123.
(
i.e., I-2 + HOH).
The second water molecule is catalytic, it substantially lowers
(
(
10) Frisch, M. J.; et al. Gaussian 03, version 01, Gaussian, Inc.; Wallingford,
CT, 2004.
the barrier to the hydrogen transfer and is not consumed in the
reaction. The barrier is decreased from 18.8 kcal/mol (intramolecular
proton transfer in I-2) to 1.2 kcal/mol, relative to the separated
reactants. The resulting silanol (H SiOH) and MTO are formed in
3
an exothermic reaction (∆H ) -2.6 kcal/mol).
11) We have investigated the possibility of an initial interaction between MTO
and HOH, resulting in two hydroxide ligands, in a mechanism analogous
to that outlined in ref 6d (Figure 2) for the HOOH substrate. However, the
barrier to forming this complex is 19.5 kcal/mol (23.6 kcal/mol for HOOH)
and is not competitive with the reaction between MTO and the silyl
hydrotrioxide.
1
13
(
12) A splitting of the CH
3
absorption of MTO, observed in the H and
C
The rate-limiting step in the catalytic cycle is the initial addition
of the silyl hydrotrioxide to the catalyst, which is consistent with
the negligible kinetic solvent isotope effect. Furthermore, we have
additionally explored a potential role for water in assisting the initial
Si-ORe bond-forming step, however this led to an increased
barrier, relative to the mechanism presented in Figure 1. Thus, water
is unable to play any role in the rate-limiting step of the reaction.
In summary, HOOOH is formed nearly quantitatively in the low-
temperature MTO-catalyzed transformation of silyl and acetal
NMR spectra of some of the substrates studied (see for example, Figure
S4 in Supporting Information), might be tentatively assigned to the
intermediates of the type I-1.
(
13) A possible side reaction, i.e., the catalyst-assisted formation of HOOOH
1
from singlet oxygen (O
2
( ∆
g
)) and water, as recently suggested for the
7
a
antibody-catalyzed formation of HOOOH, cannot be completely ruled
out. However, our present preliminary evidence, that is, the absence of the
17
17
17
2
O-enrichment of HOOOH (by O NMR), when O enriched (50%) H O
was added to the reaction mixture before the reaction, does not support
this presumption (see Figure S2 in SI).
(
14) (a) Jain, K. R.; K u¨ hn, F. E. J. Organomet. Chem. 2007, 692, 5532. (b)
Saladino, R.; Neri, V.; Pellicia, A. R.; Caminiti, R.; Sadun, C. J. Org. Chem.
2002, 67, 1323.
1
3
hydrotrioxides. Further improvements of the method, that is, the
1
4
use of both the polymer-bound MTO and the polymer-bound
JA806411A
J. AM. CHEM. SOC. 9 VOL. 130, NO. 43, 2008 14087