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+ oxidation state. The Fe3+ is not active for hydrosilylation 10 min in step scan mode. The catalyst was pressed into a 4 mm
self-supporting wafer and placed in a stainless steel holder. The
3
but remains active for hydrogenation and does not get re-
2
+
reactor consisted of a straight quartz tube (1ЈЈ OD, 10ЈЈ length)
with an Ultra-Torr® fitting equipped with shut-off valves. At both
ends of the reactor were Kapton windows sealed with O-rings. The
reactor has an internal thermocouple at the sample, which controls
the clamshell furnace. After treatment with gas flows (3.5% H in
2
He; 50 sccm) at elevated temperature, the catalysts were cooled in
the flowing gas and re-measured at room temperature without ex-
duced back to Fe under dihydrogen at the reaction tem-
perature as determined by in situ X-ray absorption spec-
troscopy. Thus, the activation of hydrogen does not seem to
involve electron transfer from the iron center. Of the several
possible mechanisms for hydrogen activation by Et O-
2
Fe(CAT-POP), we favor heterolytic cleavage into an iron
hydride and protonated catechol ligand. Further studies are posure to air.
on-going.
X-ray Absorption Analysis at the Fe K-Edge: The XANES pre-edge
energy was obtained from the data calibrated with the Fe foil ob-
tained simultaneously with each spectrum. EXAFS fits of the
Fe(CAT-POP) catalysts were modeled from experimental phase
shift and backscattering amplitudes, which were obtained from
Experimental Section
General Considerations: All manipulations were carried out under
inert conditions unless otherwise noted. Et OFe(CAT-POP) was
2
III
Fe acetylacetonate (6 Fe–O at 1.99 Å). Standard procedures
based on WINXAS 3.1 software were used to fit the XAS data.
The EXAFS coordination parameters were obtained by a least-
prepared as previously reported.[ Multiple batches of CAT-POP,
Fe starting material, and Fe(CAT-POP) were prepared and com-
pared for consistency. The iron concentration was determined by
ICP-MS and is reproducible. Batch hydrogenations were conducted
in a pressure vessel with typically 5 mg (0.005 mmol, 5 mol-%) cata-
20]
2
squares fit in r-space of the first shell nearest neighbor, k -weighted
–1
Fourier transform data (Δk = 2.8–10.5 Å and ΔR = 1.1–1.9 Å).
Supporting Information (see footnote on the first page of this arti-
cle): A description of the XAS fitting procedure and a table of
calculated XAS parameters for Fe(CAT-POP) catalysts and stan-
dards.
6
lyst in 0.6 mL [D ]benzene with 40 equiv. of substrate.
Plug-Flow Catalyst Testing Procedures: The catalyst performance
testing was conducted in a vertical quartz tube reactor equipped
with mass flow controllers, and the products were determined by
on-line gas chromatography (J&W scientific #115-3552, GS-Alu-
Acknowledgments
2
mina, 50 mϫ 0.530 mm). Et OFe(CAT-POP) (ca. 0.100 g) was di-
The work at Argonne National Laboratory was supported by the
U.S. Department of Energy, Office of Basic Energy Sciences,
Chemical Science and Engineering Division under Contract DE-
AC-02-06CH11357. B. H. and A. S. H. would like to thank the Illi-
nois Institute of Technology for a Starr-Fieldhouse Fellowship
luted with SiO (ca. 0.800 g) and supported on quartz wool, and
2
an internal thermocouple was placed at the top of the catalyst bed.
Because of its air sensitivity, the sample was packed and sealed in
a Vacuum Atmospheres glovebox under N
was purged with H (UHP Grade, Airgas USA, LLC) at 50 mL/
min at room temperature and then for 15 min at either 150 or
75 °C. The reaction mixture was 4% H /Ar mixture at a flow rate
2
. Initially, the catalyst
2
(
B. H.) and startup funding support. The use of the Advanced Pho-
ton Source (APS) was supported by the U. S. Department of En-
ergy, Office of Science, Office of Basic Energy Sciences, under Con-
tract No. DE-AC02-06CH11357. Materials Research Collaborative
Access Team (MRCAT, Sector 10 ID) operations are supported by
the Department of Energy and the MRCAT member institutions.
1
2
of 30 mL/min and 4% propene/Ar at a flow rate of 15 mL/min.
Generally the conversions were under differential conditions, i.e.,
less than 10%. Air-exposed samples were treated in the same man-
ner as those not exposed to air in order to observe the catalytic
activity of Fe3+(CAT-POP). The catalyst was exposed to air for ca.
5
min, then loaded into the reactor, heated to reaction temperature,
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3+
and tested. Fe (CAT-POP) was also tested after storage in air for
about 1 month, and rates were the same as those with the freshly
oxidized sample. Product composition was determined by using gas
calibration standards and analyzed by a flame ionization detector
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3] N. Menashe, Y. Shvo, Organometallics 1991, 10, 3885.
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(99.999%, Airgas USA, LLC) and air (Ͻ 2 ppm
2
6, 4135.
H
2
O, Airgas USA, LLC). Turnover rates were calculated by as-
[
[
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suming that all Fe sites are active.
In Situ XAFS Measurements at the Fe K-Edge (7.112 keV): X-ray
absorption measurements were conducted with the bending magnet
beamline of the Materials Research Collaborative Access Team
[
[
[
7] C. P. Casey, H. Guan, Organometallics 2012, 31, 2631.
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(MRCAT, 10-BM) at the Advanced Photon Source (APS), Ar-
gonne National Laboratory. Ionization chambers were optimized
at the midpoint of the Fe spectrum for the maximum current with
linear response (ca. 1010 photons detected per second) by using
[10] D. W. Stephan, G. Erker, Angew. Chem. 2010, 122, 50; Angew.
Chem. Int. Ed. 2010, 49, 46.
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3
0% He in N
2
(15% absorption) in the incident X-ray detector and
(70% absorption) in the trans-
[
[
[
12] S. C. Bart, E. Lobkovsky, P. J. Chirik, J. Am. Chem. Soc. 2004,
a mixture of ca. 30% Ar in N
2
126, 13794.
mission X-ray detector. A third detector in the series simulta-
neously collected a Fe foil reference spectrum with each measure-
ment for energy calibration. A cryogenically cooled double-crystal
Si(111) monochromator was used and detuned to 50% in order to
minimize the presence of harmonics. The X-ray beam was
13] S. C. Bart, E. J. Hawrelak, E. Lobkovsky, P. J. Chirik, Organo-
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0
.5ϫ1.5 mm and data was collected in transmission geometry in
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