C O M M U N I C A T I O N S
Table 2. Results from Isotope Labeling Experiments with 18OH2a
Ar
+
[
Re(O)(hoz) ] + 2Et SiH
9
8H +
2
3
2
+
(
Et Si) O + [Re(hoz) (CH CN) ]
3 2 2 3 x
hoz ) 2 - (2′-hydroxyphenyl) - 2 - oxazoline(-) (2)
To ascertain the source of oxygen in the silicon product, we
conducted the catalytic reaction in open air with OH (eq S5).
2
% 18
Ob
18
entry
substrate added last
(Ph
2
MeSi)
2
O
1
Quantitative 18O-enrichment was observed in the product, confirm-
ing water as the oxidant. To investigate whether silane adds across
a RedO multiple bond, we conducted two experiments.9 The first
was an isotope labeling experiment under stoichiometric conditions
1
2
3
Re cat. 1
86
80
69
∼2
4
5
Ph2MeSiH
,10
18
c
H2
O
a
18
18
1
8
Conditions: [Ph2MeSiH] ) [1] ) [H2 O] (∼95% O) ) 0.053 M in
(
Re/Ph
2
MeSiH/H
2
O ) 1:1:1) using a different order of substrate
CH3CN at ambient temperature. Two substrates were incubated for 30 min
18
addition (Table 2). The slightly reduced O-enrichment in the silyl
b 18
prior to addition of the third.
determined by GC-MS and into complex 1 by ESI-MS. [Re(hoz)2] (m/z
509, 511) was detected in addition to 1.
O-Incorporation into (Ph2MeSi)2O was
18
c
+
ether product is due to oxo exchange between H
and Figure S3) and the minor side reduction of 1 by Ph
is notable that adding the silane last after incubation of 1 and H
afforded less enrichment (entry 1 versus 2). Addition of water last
entry 3) gave the least enrichment because incubation of 1 and
Ph MeSiH prior to water addition resulted in reduction of some of
2
O and 1 (eq S6
)
2
MeSiH. It
1
8
2
O
use of high-valent metal complexes in dehydrogenative oxidation
with water has no precedence. The reaction proceeds via a novel
mechanistic paradigm in which organosilane adds selectively to
is composed of one hydrogen atom
O. The mechanistic details
for each of the steps in the proposed reaction of Scheme 1 are under
investigation.
(
2
water, and the produced H
from organosilane and the other from H
2
the rhenium catalyst (vide supra and Figure S4).
2
In the second experiment, we tested base catalysis by employing
a hindered noncoordinating base, 2,6-lutidene, which shifts the acid/
base equilibria in favor of dioxorhenium (eq 3). Thus, if 4 is the
active form, 2,6-lutidene would promote catalysis. On the contrary,
we found that addition of base shuts down the catalytic reaction
completely. Therefore, we concluded that 4 is not the active catalyst,
and a second multiply bonded ligand is not needed, contrary to a
previous report.9
Acknowledgment. Acknowledgment is made to Purdue Uni-
versity for financial support and to Prof. Roy Periana and Mr. Oleg
Mironov for their help with the hydrogen gas analyses.
Supporting Information Available: Experimental details, eqs S1-
S6, and Figures S1-S5. This material is available free of charge via
the Internet at http://pubs.acs.org.
,11
References
(
(
1) Special issue “Toward a Hydrogen Economy”, Science 2004, 305, 958.
2) (a) Dybtsev, D. N.; Chun, H.; Yoon, S.-H.; Kim, D.; Kim, K. J. Am.
Chem. Soc. 2004, 126, 32. (b) Rowsell, J. L. C.; Millward, A. R.; Park,
K. S.; Yaghi, O. M. J. Am. Chem. Soc. 2004, 126, 5666. (c) Zhao, X.;
Xiao, B.; Fletcher, A. J.; Thomas, K. M.; Bradshaw, D.; Rosseinsky, M.
J. Science 2004, 306, 1012. (d) Amendola, S. C.; Sharp-Goldman, S. L.;
Tanjua, M. S.; Spencer, N. C.; Kelly, M. T.; Petillo, P. J.; Binder, M. Int.
J. Hydrogen Energy 2000, 25, 969. (e) Grochala, W.; Edwards, P. P. Chem.
ReV. 2004, 104, 1283.
The source of each hydrogen atom in the dihydrogen product
was discerned by employing Et
O (eqs 4 and 5). The produced hydrogen gas was analyzed by
mass spectrometry and found to be exclusively HD.
3 2 3
Si-D with H O, and Et Si-H with
D
2
1
mol% Re Cat. (1)
(3) For oxidation of silane in the presence of water and air by late transition-
metal catalysts (Ru and Ir), see: (a) Lee, M.; Ko, S.; Chang, S. J. Am.
Chem. Soc. 2000, 122, 12011. (b) Lee, Y.; Seomoon, D.; Kim, S.; Han,
H.; Chang, S.; Lee, P. H. J. Org. Chem. 2004, 69, 1741. The authors do
not note gas evolution. The source of oxygen in the product was not
determined, but air/oxygen was required.
Et Si-D (∼97%) + H O
8 HD + Et SiOH
3
2
3
gas analysis: H ) 5.6%, HD ) 94.2%, and D ) 0.2% (4)
2
2
1
mol% Re Cat. (1)
Et Si-H + D O (99% )
8HD + Et SiOH
(4) For production of organosilanes at an industrial scale, see “GE Moves in
3
2
3
Silicon Field”, Chem. Eng. News 2005, 83 (April 18), 14.
gas analysis: H ) 2.0%, HD ) 97.6%, and D ) 0.4% (5)
(5) See Supporting Information for details.
2
2
(
(
(
6) McPherson, L. D.; B e´ reau, V. M.; Abu-Omar, M. M.; Ugrinova, V.; Pu,
1
L.; Taylor, S. D.; Brown, S. N. Inorg. Synth. 2004, 34, 54.
The progress of reaction was investigated by H NMR for Ph
MeSiH (Figure S1). The rate of formation of silanol is first-order
in [Ph MeSiH], [Re] , and [H O]. The rate of silyl ether formation
is first-order in [Ph MeSiOH] and [Re], but inhibited by water. A
2
-
7) (a) Baney, R. H.; Itoh, M.; Sakakibara, A.; Suzuki, T. Chem. ReV. 1995,
95, 1409. (b) Loy, D. A.; Shea, K. J. Chem. ReV. 1995, 95, 1431.
III
+
8) Reduced Re , [Re(hoz)
2
] , was detected by mass spectrometry (m/z )
CN solvent molecules
does not catalyze the
2
T
2
1
87
185
5
11/509, Re/ Re). However, one or two CH
3
2
may be coordinated. (PPh
)
2
(CH
CN)Re Cl
III
3
3
3
mechanism that is consistent with the observed isotope labeling
and kinetic experiments is given in Scheme 1.12,13
hydrolytic oxidation of organosilanes.
(9) Kennedy-Smith, J. J.; Nolin, K. A.; Gunterman, H. P.; Toste, F. D. J.
Am. Chem. Soc. 2003, 125, 4056. The activity of Re(O) I(PPh in
2
3 2
)
hydrosilation was attributed to the presence of two oxo ligands in which
silane adds across one RedO bond [2 + 2].
10) Addition of silane to early transition metal multiple bonds: (a) Sweeney,
Z. K.; Polse, J. L.; Andersen, R. A.; Bergman, R. G.; Kubinec, M. G. J.
Am. Chem. Soc. 1997, 119, 4543. (b) Gountchev, T. I.; Tilley, T. D. J.
Am. Chem. Soc. 1997, 119, 12831.
Scheme 1
(
(
(
(
11) In absence of water, 1 catalyzes the hydrosilation of aldehydes and ketones.
Ison, E. A.; Abu-Omar, M. M. Purdue University, West Lafayette, IN.
Unpublished results.
12) Organosilanes are believed to react via either oxidative addition (late
metals) or σ-bond metathesis (early metals). For additional mechanisms,
see: Glaser, P. B.; Tilley, T. D. J. Am. Chem. Soc. 2003, 125, 13640.
13) Oxidative addition to the five-coordinate cationic complex [Re(O)(hoz)
to give initially a rhenium(VII) silyl hydride complex, [Re(O)(SiR )(H)-
] , followed by nucleophilic attack of water onto the bound silicon
]+
2
3
+
(hoz)
2
is also possible.
We have described a new methodology for storage and produc-
2
tion of pure H via catalytic hydrolytic oxidation of an organic liquid
(organosilanes). This catalytic reaction is remarkable because the
JA053860U
J. AM. CHEM. SOC.
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VOL. 127, NO. 34, 2005 11939