Photochemical carbonylation of ethane under snpercritical conditions

Article abstract of DOI:10.1002/1521-3773(20010716)40:14<2692::AID-ANIE2692>3.0.CO;2-P

Feasible photocatalysis: The rhodium catalyst [Rh(CO)(PMe₃)₂Cl] photochemically transforms ethane to propionaldehyde in single-phase mixtures of ethane and in carbon dioxide/ethane single phases [Eq. (1)]. A side reaction of carbon dioxide with the catalyst to give OPMe₃ and [Rh(CO)₂(PMe₃)Cl] or [Rh₂(CO)₂-(PMe₃)₂(μ-Cl) ₂] has also been observed.

Full text of DOI:10.1002/1521-3773(20010716)40:14<2692::AID-ANIE2692>3.0.CO;2-P

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Midland, MI. DMSO was dried over 4-Š molecular sieves. Exact FAB mass
spectra were obtained on an Extrel 4000 instrument in the positive-ion
detection mode. Elemental analyses were performed by Galbraith Labo-
ratories, Inc., Knoxville, TN. The MALDI mass spectra were acquired
using a PerSeptive Biosystems Voyager RP time-of-flight mass spectrom-
eter. Positive-ion mass spectra were acquired in the linear mode, and the
ions were generated by using a nitrogen laser (337 nm) pulsed at 3 Hz with
a pulse width of 3 ns. Ions were accelerated at 30000 Vand amplified using
a multichannel plate. Spectra (70 to 180) were summed into a 500-MHz
Techtronix digital storage oscilloscope and downloaded to a computer for
data processing. All data processing was performed using GRAMS
(Gallactic Industries, Salem, NH). Spectra of TEMPO-labeled dendrimers
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b) P. Kuppusamy, P. Wang, R. A. Shankar, L. Ma, C. E. Trimble, C. J. C.
Hsia, J. L. Zweier, Magn. Reson. Med. 1998, 40, 806 ± 811.
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Bulte), Kluwer, Dordrecht, in press; d) L. H. Bryant, M. W. Brechbiel,
C. C. Wu, J. W. M. Bulte, V. Herynek, J. A. Frank, JMRI J. Magn.
Reson. Imaging 1999, 9, 348 ± 352; e) E. C. Wiener, M. W. Brechbiel, H.
Brothers, R. L. Magin, O. A. Gansow, D. A. Tomalia, P. C. Lauterbur,
Magn. Reson. Med. 1994, 31, 1 ± 8.
were obtained using a trans-3-indoleacrylic acid matrix with a matrix:-
1
analyte ratio of 8000:1. Bovine serum albumin (BSA, MWˆ 66431 gmol
)
was used as an external standard. An aliquot corresponding to 12 pmol of
the analyte was deposited on the laser target.[9] The MALS analyses were
performed by Wyatt Technology Corporation, Santa Barbara, CA, using a
DAWN EOS detector with
a solid-state laser operating at 690 nm.
Nanopure water (G-6-TEMPO-80) or 17 mm acetic acid (G-6-TEMPO-
198) were used as solvents. The EPR spectra were recorded on a Varian E9
X-band spectrometer with a field of 3368 G, a modulation frequency of
100 kHz, a modulation amplitude of 1 G, and a microwave power of
10 mW.
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943, 477 ± 484; b) K. Chen, H. M. Swartz, Biochim. Biophys. Acta 1988,
970, 270 ± 277; c) H. M. Swartz, M. Sentjurc, P. D. Morse II, Biochim.
Biophys. Acta 1986, 888, 82 ± 90.
[7] a) E. Walter, E. K. Woller, K. Sebby, D. Singel, M. J. Cloninger,
presented at the 49th Natural Products Gordon Conference, Plymouth,
New Hampshire, August 2000; b) A. W. Bosman, R. A. J. Janssen,
E. W. Meijer, Macromolecules 1997, 30, 3606 ± 3611.
2: 4-Amino-TEMPO (1) was first purified by gradient elution flash
chromatography (CH2Cl2 !CH2Cl2/MeOH 4/1). Succinic anhydride (1.6 g)
was added to the purified 4-amino-TEMPO (2.8 g) in THF (150 mL), and
the reaction mixture was stirred at ambient temperature for 18 h. The
solvent was evaporated to near dryness, and the residue subjected to
gradient elution flash chromatography (CH2Cl2 !CH2Cl2/MeOH 9/1). The
hygroscopic solid was immediately used in the next step. Yield 2.1 g (47%).
[8] P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, J. F. Stoddart,
Angew. Chem. 1997, 109, 756 ± 759; Angew. Chem. Int. Ed. Engl. 1997,
36, 732 ± 735.
‡
Exact FAB mass spectrum: 273.1797 [M ], calcd: 273.1814.
3: Compound 2 (8.0 g) was dissolved in THF (300 mL), after which first
NHS (3.45 g) and then EDAC (5.8 g) were added. The mixture was stirred
at ambient temperature for 18 h. The solvent was evaporated, the residue
redissolved in CHCl3 (300 mL), and the mixture extracted with water (2 Â
100 mL). The organic phase was then separated and dried over MgSO4, and
its volume reduced to about 10 mL. The product was isolated by gradient
elution flash chromatography (CH2Cl2 !CH2Cl2/MeOH 9/1). Yield 8.5 g
[9] E. K. Woller, M. J. Cloninger, unpublished results.
‡
(78%). Exact FAB mass spectrum: 370.1972 [M ], calcd: 370.1978.
General procedure for the preparation of G-6-TEMPO-198 and G-6-
TEMPO-80: A 10% stock solution of G-6 PAMAMTM dendrimer (15 mL)
was lyophilized and the resultant solid heated to 808C in DMSO (200 mL)
to affect complete dissolution. A solution of active ester 3 (6.0 g or 0.98 g,
respectively) in DMSO (100 mL) was then added, followed by triethyl-
amine (100 mL). The reaction mixture was then stirred at 908C for 72 h.
After cooling, the triethylamine was removed by evaporation and the
solution diluted with 10% aqueous acetic acid (300 mL) and methanol
(200 mL). Unchanged active ester and N-hydroxysuccinimide were re-
moved by ultrafiltration with deionized water by using a stirred cell
(Amicon, MA) fitted with a 30-K membrane (Filtron, MA). Occasional
precipitation of a solid material in the cell occurred. In such cases, the
precipitate was brought back into solution by the addition of small portions
of methanol and 10% aqueous acetic acid, after which the diafiltration was
continued until no low molecular weight species were detected inside the
cell (size-exclusion HPLC). The resulting solute was lyophilized to obtain
the products as light orange powders. G-6-TEMPO-198: C 53.72, H 8.56, N
16.10. MALDI-TOF mass spectra: number average MW 101000; weight
average MW 102000. G-6-TEMPO-80: C 49.56, H 8.13, N 16.75. MALDI-
TOF mass spectra: number average MW 71000; weight average MW
72000.
Photochemical Carbonylation of Ethane under
Supercritical Conditions**
Thomas E. Bitterwolf,* Dinara Lukmanova Kline,
John C. Linehan, Clement R. Yonker, and
R. Shane Addleman
The photochemical carbonylation of hydrocarbons and
aromatic compounds [Eq. (1)] by rhodium catalysts of the
general formula [Rh(CO)L2Cl] (where L ˆ PMe3, PPh3) is
[*] Prof. T. E. Bitterwolf, D. Lukmanova Kline
Department of Chemistry, University of Idaho
Moscow, ID 83844-2343 (USA)
Reoxidation of TEMPOL-H by spin-labeled dendrimers: The oxidation of
TEMPOL-H (1 mm) to TEMPOL by TEMPO-conjugated dendrimer in
the presence of 50 mm dendrimer was performed in Ar-saturated water (G-
6-TEMPO-198) or Ar-saturated PBS (G-6-TEMPO-80 and G-6), and
measured as a function of time. The plotted signal intensity due to the
reoxidized TEMPOL-H (divided by gain, see Figure 1) was adjusted by
subtracting the signal intensities of blank solutions of G-6-TEMPO-198 or
G-6-TEMPO-80.
Fax : (‡1)208-885-6173
E-mail: bitterte@uidaho.edu
J. C. Linehan, C. R. Yonker, R. S. Addleman
Chemical Sciences Department
Pacific Northwest National Laboratory
PO Box 999, Richland, WA 99352 (USA)
[**] This work is supported by the Research Corporation and the Director,
Office of Science, Office of Basic Energy Sciences, Chemical Sciences
Division of the US Department of Energy under contract DE-ACO6-
76RLO 1830.
Received: December 13, 2000 [Z16270]
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well known,[1] and the mechanism of these reactions has been
examined by several groups.[2] This reaction has been ex-
tended to liquid propane[3] and recently the carbonylation of
benzene to benzaldehyde and benzyl alcohol in supercritical
CO2 (scCO2), has been reported in the patent literature.[4]
Methane and ethane are the major constituents of natural
gas and are attractive C1 and C2 synthons for organic synthesis.
Direct conversion to their alcohols would be particularly
attractive, but carbonylation to the n‡1 aldehydes would also
open up a significant hydrocarbon reservoir to nonfuel
applications. A wide range of catalytic reactions have been
examined in supercritical media[5, 6] although to the best of our
knowledge only the patent noted above has utilized the
[Rh(CO)(PMe3)2Cl] photochemical catalyst. The research
presented herein was undertaken to establish whether photo-
catalytic carbonylation could be extended to methane and
ethane, and to provide a preliminary understanding of the
behavior of the catalyst under supercritical conditions.
Supercritical ethane, sc-ethane, (Tc ˆ 32.18C, Pc ˆ 48.8 atm)
is an excellent solvent for organometallic catalysts. As the
introduction of solutes and gases such as CO alters the phase
behavior of supercritical fluids, photochemical studies in these
single-phase mixtures were carried out at ethane pressures
and temperatures well above the critical point.
catalyst at 408C for 12 h resulted in the decrease in the band
1
for the catalyst (1966 cm ) and the appearance of a new band
1
at 1743 cm . After photolysis the reaction mixture was
vented into CDCl3, and an NMR spectrum confirmed the
presence of propionaldehyde. Yields are less than 5% based
on initial loading of ethane under these conditions.
Attempts to carry out analogous reactions with methane in
single-phase CO2 mixtures were unsuccessful in that no new
bands were observed in the region where one might expect the
carbonyl stretching band of acetaldehyde, nor was any
aldehyde detected by NMR spectroscopy of the vented
reaction mixtures. Neither increasing the photolysis times
nor the pressure of methane altered these results.
To our surprise we have found that the rhodium catalyst
reacts slowly thermally and more rapidly photochemically
with CO (10 atm) in single-phase CO2 mixtures to give a
1
product with IR bands at 2102 and 2006 cm . In contrast,
high-pressure IR studies established that [Rh(CO)(PMe3)2Cl]
did not thermally react with CO (34 atm) in petroleum ether
over two days. [Rh(CO)2(PMe3)Cl] has been found to display
IR bands at 2093 and 2001 cm 1 in petroleum ether,[9] and we
tentatively assign the new bands in the CO2 mixtures to this
species.
When the rhodium catalyst was photolyzed in single-phase
CO2 mixtures without other reactants a band at 1984 cm 1 was
found to grow in as the catalyst band diminished. This mixture
was vented into a Schlenk flask in a dry box, and the
nonvolatile products were taken up into air-free CDCl3.
13P NMR spectroscopy established the presence of OPMe3 in
the photolyzed sample, as well at a new doublet at d ˆ 27.0
Single-phase mixtures of ethane (100 atm), CO (13.6 atm),
and [Rh(CO)(PMe3)2Cl] (5.0 mg) were photolyzed at 608C
with a high-pressure mercury lamp for 12 h. A quartz-
windowed water filter was used to remove IR radiation from
the source beam, but otherwise the light was unfiltered.
1
During this time bands of the catalyst (1969 cm ) were found
1
1
to decrease slightly, while a new band grew in at 1734 cm .
(JRh,P ˆ 116 Hz). Bands at 1983 cm have been observed in
After photolysis the reaction mixture was vented into a cooled
Schlenk flask and the recovered product was analyzed by
mass spectrometry, which confirmed the presence of propio-
naldehyde. No effort has been made to optimize the yields
from these photolyses.
petroleum ether solutions of [Rh2(CO)4(m-Cl)] and PMe3
(1:2) and are attributed to the formation of cis- and trans-
[Rh2(CO)2(PMe3)2(m-Cl)2]. The reactions of the rhodium
catalyst in CO2 with and without excess CO are presented in
Scheme 1.
Poliakoff and co-workers have photolyzed [Cp*Ir(CO)2]
(Cp* ˆ C5Me5) in single-phase mixtures of methane (270 atm,
295 K) and observed the oxidative addition product, [Cp*Ir-
(CO)(H)(CH3)] by IR spectroscopy.[6h] Under similar con-
ditions (300 atm methane, 10 atm CO, 308 K) we detected no
bands attributable to [Rh(CO)(PMe3)2Cl] in the supercritical
phase. The lack of solubility of the catalyst under these
conditions made it impossible to proceed with the photo-
chemical studies.
It is known that [Rh(CO2)(PBu3)2Cl] undergoes slow
thermal decomposition at room temperature to [Rh(CO)-
(OPBu3)(PBu3)Cl],[10] and that [Rh(PR3)3Cl] and excess
Our inability to carry out the photolyses in sc-methane
prompted us to examine the possibility of using a mixed-
solvent system with scCO2 (Tc ˆ 31.18C, Pc ˆ 73 atm) as the
primary medium. The solubility of the rhodium compound in
single-phase mixtures of CO2 (408C, 75 ± 90 atm) was estab-
lished by using the Chrastil relationship.[7] Under the con-
ditions used in our studies the solubility of the rhodium
catalyst was found to be on the order of 8 Â 10 5 m, and the
rhodium catalyst displayed strong bands in the metal carbonyl
region of the IR spectrum. Full details of this methodology for
determining the solubilities in scCO2 will be published
separately.[8]
Photolysis of a mixture of single-phase mixtures of CO2
(110 atm), CO (10 atm), and ethane (34 atm) with 3.4 mg of
Scheme 1. Photochemical reaction of [Rh(CO)(PMe3)2Cl] in scCO2 with
and without excess CO.
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1996, 118, 344 ± 355; c) P. G. Jessop, T. Ikariya, R. Noyori, Nature 1994,
368, 231 ± 233; d) P. G. Jessop, T. Ikariya, R. Noyori, Science 1995, 269,
1065 ± 1069; e) J. A. Banister, P. D. Lee, M. Poliakoff, Organometallics
1995, 14, 3876 ± 3885; M. A. Banister, S. M. Howdle, M. Poliakoff, J.
Chem. Soc. Chem. Commun. 1993, 1814 ± 1815; f) M. Poliakoff, S. M.
Howdle, S. G. Kazarian, Angew. Chem. 1995, 107, 1409 ± 1432; Angew.
Chem. Int. Ed. Engl. 1995, 34, 1275 ± 1295; g) M. J. Banks, S. Feng,
M. F. Gross, W. Tumas, J. Am. Chem. Soc. 1995, 117, 8277 ± 8278;
h) J. A. Banister, A. I. Cooper, S. M. Howdle, M. Jobling, M. Polia-
koff, Organometallics 1996, 15, 1804 ± 1812.
phosphane react catalytically with CO2 in refluxing decalin
(ca. 1858C) to give OPR3 in the rate order PPh3 < PBuPh2 <
PEt3.[11] The rate for the PPh3 derivative is about 20 turnovers
per day. In the current studies, it appears that CO2 undergoes
reaction with the catalyst to give OPMe3. In the presence of
an excess of CO [Rh(CO)2(PMe3)Cl] is formed, while in the
absence of CO [Rh2(CO)2(PMe3)2(m-Cl)2] is formed. We are
presently investigating the mechanism of this reaction.
These studies have established the feasibility of carrying out
photocatalysis of ethane to propionaldehyde in either single-
phase ethane or CO2 mixtures. A competing side reaction
probably involving CO2 cleavage and phosphine oxide
formation may preclude the use of CO2 as a medium for
these rhodium catalysts.
[7] a) J. Chrastil, J. Phys. Chem. 1982, 86, 3016; b) R. S. Addleman, M. J.
Carrott, C. M. Wai, Anal. Chem. 2000, 72, 4015 ± 4022.
[8] R. S. Addleman, C. R. Yonker, J. C. Linehan, T. E. Bitterwolf, D. L.
Klein, unpublished results.
[9] a) T. E. Bitterwolf, unpublished results, 1999; b) for L ˆ PPh3 and
PMe2Ph see: A. R. Sanger, Can. J. Chem. 1985, 63, 571 ± 575.
[10] M. Aresta, C. F. Nobile, Inorg. Chim. Acta 1977, 24, L49 ± L50.
[11] K. M. Nicholas, J. Organomet. Chem. 1980, 188, C10 ± C12.
[12] A. J. Deeming, B. L. Shaw, J. Chem. Soc. A 1969, 597 ± 602.
Experimental Section
A thermostated, stainless steel, high-pressure photolysis cell fitted with
CaF2 IR windows and a sapphire photolysis window was used in all high-
pressure studies. The cell volume is about 12 mL and the IR pathlength is
0.1 mm. A small spin bar inside the cell was used for mixing. The cell was
designed with a maximum pressure rating of 700 atm. IR spectra were
recorded on
a Perkin Elmer Spectrum 1000 FT IR Spectrometer.
[Rh(CO)(PMe3)2Cl] was prepared by standard literature methods.[12]
In a typical reaction, the rhodium catalyst was added to the cell as a solid,
then the sealed cell was charged with reactant gases using a high-pressure
line equipped with a syringe pump. Gases such as CO2 and ethane were
condensed into the syringe pump by chilling the pump with ice packs and
then charged into the heated cell.
Rearrangement of a Tricyclic
2,5-Cyclohexadienone: Towards a General
Synthetic Route to the Daphnanes and
(‡)-Resiniferatoxin**
Reaction mixtures were photolyzed by using a 350-W high-pressure Hg
lamp. A 30-mm quartz-windowed, water filter was used to remove IR
wavelengths from the incident beam. Photolysis times of 6 ± 12 h were used,
and IR spectra were recorded at the beginning of each photolysis reaction
and at regular intervals during the photolysis. Samples for mass spectro-
metric and NMR analysis were recovered by venting the sample through a
restrictor tube directly into DCCl3 in a N2-flushed Schlenk flask immersed
in an ice water bath.
Stona R. Jackson, Michael G. Johnson,
Masafumi Mikami, Sojiro Shiokawa, and
Erick M. Carreira*
The daphnane resiniferatoxin[1] (RTX) and structurally
related tiglianes possess complex, densely functionalized
architectures, along with important biological activity, that
have inspired much innovative research in chemistry and
biology. The recent isolation and cloning of the principal
receptor targeted by resiniferatoxin holds great promise for
the development of RTX-related therapeutics.[2, 3] In this
regard, parallel advances in the design and synthesis of
analogues is imperative because these may serve as cellular
probes and useful pharmacologically important compounds.
Received: November 6, 2000
Revised: April 30, 2001 [Z16046]
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[5] ªMetal-Complex-Catalyzed Reactionsº: P. G. Jessop, W. Leitner in
Chemical Synthesis Using Supercritical Fluids (Eds.: P. G. Jessop, W.
Leitner), Wiley-VCH, New York, 1999, and references therein.
[6] a) D. R. Palo, C. Erkey, Ind. Eng. Chem. Res. 1998, 37, 4203 ± 4206;
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[*] Prof. Dr. E. M. Carreira, S. R. Jackson, M. G. Johnson, M. Mikami,
S. Shiokawa
Laboratorium für Organische Chemie
ETH-Zentrum, Universitätsstrasse 16
8092, Zürich (Switzerland)
Fax : (‡41)1-632-1328
E-mail: Carreira@org.chem.ethz.ch
[**] We wish to gratefully acknowledge the support of Daiso Ltd., Japan
(M.M.), and Meiji Seika Kaisha Ltd., Japan (S.S.). M.J. thanks
Pharmacia-UpJohn for a graduate fellowship during his third year at
Caltech. Financial support was provided by the Packard Foundation,
the National Science Foundation (USA), the National Institutes of
Health (USA), and by generous funds from Eli Lilly, Merck, Novartis,
Pfizer, Pharmacia-Upjohn, Zeneca, the Eidgenössische Technische
Hochschule (ETH), the Kontaktgruppe für Forschungsfragen (KGF),
and Hoffmann La Roche.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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