Addition of arenes to ethylene and propene catalyzed by ruthenium

Article abstract of DOI:10.1021/ja035076k

TpRu^II(CO)(Me)(NCMe) (Tp = hydridotris(pyrazolyl)borate) serves as a catalyst precursor for the conversion of benzene and ethylene or propene to alkylaromatic products. The reaction proceeds via the formation of the active catalyst TpRu(CO)(Ph)(NCMe) and is mildly selective for linear propylbenzene over isopropylbenzene. Copyright

Full text of DOI:10.1021/ja035076k

Published on Web 05/28/2003
Addition of Arenes to Ethylene and Propene Catalyzed by Ruthenium
Marty Lail, Benjamin N. Arrowood, and T. Brent Gunnoe*
Department of Chemistry, North Carolina State UniVersity, Raleigh, North Carolina 27695-8204
Received March 10, 2003; E-mail: brent_gunnoe@ncsu.edu
Due to the potential synthetic utility of hydrocarbon function-
alization reactions, transition-metal-mediated C-H activation se-
quences have attracted considerable attention.1 Although many
transition metal complexes that initiate C-H oxidative addition have
been reported,3 efficient chemical synthesis via catalytic C-H
bond activation and subsequent C-C bond formation remains a
challenging goal.6 Significant recent advancements in the arena
of catalytic C-H activation have been reported for aromatic
Scheme 1. Plausible Reaction Pathway for the Conversion of
Complex 1 and Benzene to Methane and Paramagnetic Product
,2
-5
-8
9
systems; however, such reactions are primarily limited to aromatic
systems with heteroatomic functionality. For example, ruthenium-
or rhodium-catalyzed C-H activations of aromatic ketones and
subsequent C-C bond formation with alkenes or alkynes have been
reported.1
0-15
Low-valent ruthenium systems have been demon-
strated to catalyze carbonylation reactions of pyridylbenzenes and
16-18
other heteroaromatics.
Analogous transformations of nonfunc-
tionalized aromatics are more difficult to achieve. Rhodium,
palladium, and ruthenium catalysts that convert aromatics and
olefins to styrenes in the presence of a sacrificial hydrogen reservoir
aromatic C-H activation reactions.32 The reaction of complex 1
in a 1.4:1.0 molar mixture of benzene and acetonitrile at 90 °C
or via oxidative coupling have been reported.1
9-23
Pd or Pt systems
can catalyze electrophilic metalation of aromatic C-H bonds
allows isolation of TpRu(CO)(NCMe)(Ph) (2) (eq 2). Complex 2
followed by C-C coupling with alkynes.24 Another strategy for
1
13
has been characterized by H and C NMR and IR spectroscopy
as well as elemental analysis.
aromatic C-H functionalization involves the formation of B-C
coupled products.2
5-28
Most germane here are recent reports of Ir-
29,30
catalyzed olefin arylation reactions that occur at 180 °C.
Heating a benzene solution (90 °C) of TpRu(CO)(Me)(NCMe)
1) (Tp ) hydridotris(pyrazolyl)borate) results in the conversion
(
of the TpRu system to NMR-silent ruthenium products, and Evans
NMR experiments reveal that the reaction product is paramagnetic.
Although the identity of the product has not been determined,
performing the reaction in C
6 6
D indicates that the transformation
Under a dinitrogen atmosphere, the combination of 0.1 mol %
TpRu (CO)(NCMe)(Ph) (2) in dry benzene under 25 psi of ethylene
at 90 °C results in the formation of ethylbenzene (eq 3). In addition
involves benzene C-H activation and methane elimination. The
II
1
H NMR spectrum of the reaction in C
D
6 6
reveals an upfield 1:1:1
D (eq 1).
triplet (2 Hz) at 0.16 ppm due to the formation of CH
3
to the formation of ethylbenzene, small amounts of 1,3- and 1,4-
diethylbenzene are produced. After 4 h of reaction, approximately
51 catalytic turnovers are observed per mole of catalyst, with
There is no evidence of deuterium incorporation into the methyl,
Tp, or NCMe ligands of complex 1. Thus, the arene C-H activation
is apparently irreversible under the reaction conditions. Free
acetonitrile is observed in the final reaction solution. A plausible
reaction pathway involves initial CH CN/C H ligand exchange
3 6 6
followed by C-H activation and methane elimination (Scheme 1).
-
3
-1 -1
TOF ) 3.5 × 10 mol
s . Catalyst decomposition after 4 h is
evident by a decrease in reaction turnover. Approximately one
turnover of 1,3-diethylbenzene production is observed, and a
negligible amount of 1,4-diethylbenzene is produced. No evidence
of 1,2-diethylbenzene or higher alkyl substitution (e.g., trisubstituted
benzenes) has been found. Setting up the reaction in air using
benzene that has not been predried results in approximately 23
catalytic turnovers after 4 h. Placing the benzene/catalyst solution
under 25 psi of propene results in the addition of benzene to propene
within 30 min at 90 °C. Analysis by gas chromatography reveals
a 1.6:1.0 ratio of n-propyl to isopropylbenzene, with 14 catalytic
Consistent with this notion, the addition of 10 equiv of acetonitrile
suppresses the rate of disappearance of complex 1 in C
C (t1/2 ≈ 80 min versus t1/2 ≈ 15 min in the absence of added
acetonitrile). The closely related Ru(II) complex TpRu(PPh )-
NCMe)(H) has recently been reported to activate C-H bonds,31
and a ruthenium-neopentyl complex has been reported to undergo
6 6
D at 90
°
3
(
7506
9
J. AM. CHEM. SOC. 2003, 125, 7506-7507
10.1021/ja035076k CCC: $25.00 © 2003 American Chemical Society

C O MMU N I C A T I O N S
turnovers after 19 h. Thus, the catalyst system is mildly selective
for the linear alkylbenzene (eq 4). Similar catalytic reactions are
al. have suggested a catalytic cycle that involves olefin binding to
an Ir(III)-aryl complex, followed by insertion and reaction with
another equivalent of arene.37 We are presently working to further
discern mechanistic details, explore the scope of the reaction, and
improve catalyst activity and selectivity.
Acknowledgment. We thank North Carolina State University
for support of this research.
Supporting Information Available: Details of experimental
procedures and compound characterization data (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
observed when complex 1 is used as the catalyst precursor (see
Supporting Information); however, the rate is faster for complex 2
versus using 1 as the catalyst precursor. Formation of the
paramagnetic complex that results from the reaction of 1 with
benzene (see above and Scheme 1) is not observed for catalysis
with 2, and it is unlikely that the paramagnetic complex is the
catalyst.
References
(
1) Davies, J. A.; Watson, P. L.; Liebman, J. F.; Greenberg, A. SelectiVe
Hydrocarbon ActiVation; VCH: New York, 1990.
(2) Shilov, A. E.; Shul’pin, G. B. Chem. ReV. 1997, 97, 2879-2932.
(
(
3) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91-100.
4) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H. Acc.
Chem. Res. 1995, 28, 154-162.
Lewis acid catalysts are known to initiate olefin arylation
reactions including the coupling of benzenes with ethylene (Friedel-
Crafts reactions).3 However, the ruthenium-catalyzed reactions
reported herein exhibit characteristics that are inconsistent with a
Friedel-Crafts mechanism and that are consistent with a metal-
mediated C-H activation pathway. Friedel-Crafts reactions typi-
cally produce 1,2-dialkyl products in addition to 1,3- and 1,4-
dialkylbenzenes. Presumably, the lack of formation of 1,2-
diethylbenzene with 1 or 2 is due to steric selectivity in the C-H
activation step, similar to that directly observed in stoichiometric
aromatic C-H oxidative addition reactions.35 Heating (90 °C) a
(
5) Jones, W. D. In Topics in Organometallic Chemistry; Murai, S., Ed.;
Springer: Berlin, 1999; Vol. 3, pp 9-46.
3,34
(
6) Kakiuchi, F.; Murai, S. In Topics in Organometallic Chemistry; Murai,
S., Ed.; Springer: Berlin, 1999; Vol. 3, pp 47-79.
(
(
7) Dyker, G. Angew. Chem., Int. Ed. 1999, 38, 1698-1712.
8) Guari, Y.; Sbao-Etienne, S.; Chaudret, B. Eur. J. Inorg. Chem. 1999,
1047-1055.
(
9) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. ReV. 2002, 102, 1731-1769.
(
10) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda,
M.; Chatani, N. Nature 1993, 366, 529-531.
(
11) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.; Sonoda,
M.; Chatani, N. Pure Appl. Chem. 1994, 66, 1527-1534.
(12) Kakiuchi, F.; Yamamoto, Y.; Chatani, N.; Murai, S. Chem. Lett. 1995,
681-682.
(
13) Thalji, R. K.; Ahrendt, K. A.; Bergman, R. G.; Ellman, J. A. J. Am. Chem.
Soc. 2001, 123, 9692-9693.
1
:1 molar mixture of 1,4-diethylbenzene and benzene in the
presence of 1 does not result in the formation of ethylbenzene (after
4 h) as is observed for Friedel-Crafts catalysts. In contrast to
(
14) Tan, K. L.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2001, 123,
2685-2686.
2
(15) Lenges, C. P.; Brookhart, M. J. Am. Chem. Soc. 1999, 121, 6616-6623.
16) Chatani, N.; Ie, Y.; Kakiuchi, F.; Murai, S. J. Org. Chem. 1997, 62, 2604-
610.
(
catalysis with 1 or 2, Lewis acid actiVation of propene in the
2
presence of arenes yields the production of branched alkyl products
(17) Fukuyama, T.; Chatani, N.; Tatsumi, J.; Kakiuchi, F.; Murai, S. J. Am.
Chem. Soc. 1998, 120, 11522-11523.
III
exclusiVely. Finally, attempted catalysis using Ru Cl
3
-trihydrate
(
(
(
18) Chatani, N.; Fukuyama, T.; Kakiuchi, F.; Murai, S. J. Am. Chem. Soc.
II
2
or TpRu (CO) (Me) fails to produce ethylbenzene. If the reactions
1996, 118, 493-494.
19) Sasaki, K.; Sakakura, T.; Tokunaga, Y.; Wada, K.; Tanaka, M. Chem.
Lett. 1988, 685-688.
were Lewis acid catalyzed, it might be anticipated that similar (or
enhanced) reactivity would be observed for the Ru(III) chloride
20) Hong, P.; Yamazaki, H. J. Mol. Catal. 1984, 26, 297-311.
II
system. The lack of activity for TpRu (CO)
2
(Me) (the immediate
(21) Weissman, H.; Song, X.; Milstein, D. J. Am. Chem. Soc. 2001, 123, 337-
3
38.
22) Matsumoto, T.; Yoshida, H. Chem. Lett. 2000, 1064-1065.
(23) Jia, C.; Lu, W.; Kitamura, T.; Fujiwara, Y. Org. Lett. 1999, 1, 2097-
100.
precursor to complex 1) indicates that minor amounts of impurities
from commercial starting reagents are not responsible for the
catalysis.
(
2
(
24) Jia, C.; Piao, D.; Oyamada, J.; Lu, W.; Kitamura, T.; Fujiwara, Y. Science
2000, 287, 1992-1995.
Taken together, our studies indicate that TpRu(CO)(Me)(NCMe)
(
25) Cho, J.-Y.; Tse, M. K.; Holmes, D.; Maleczka, R. E.; Smith, M. R., III.
Science 2002, 295, 305-308.
(1) reacts with arenes to initiate C-H activation and loss of methane
via initial arene/acetonitrile ligand exchange (Scheme 1). This
reaction produces the active catalyst TpRu(CO)(NCMe)(Ph) (2),
and a plausible catalytic cycle involves olefin/acetonitrile ligand
exchange followed by olefin insertion into the Ru-aryl bond, which
provides a pathway for C-C bond formation. Subsequent C-H
activation of another equivalent of arene allows elimination of
alkylbenzene and re-formation of the catalyst. Although we have
not yet definitively established the mode of C-H activation, an
electrophilic reaction similar to that reported by Milstein et al. seems
(26) Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc. 1999, 121, 7696-
7697.
(
27) Cho, J.-Y.; Iverson, C. N.; Smith, M. R., III. J. Am. Chem. Soc. 2000,
122, 12868-12869.
(
28) Chen, H.; Schlecht, S.; Semple, T. C.; Hartwig, J. F. Science 2000, 287,
1995-1997.
(29) Matsumoto, T.; Taube, D. J.; Periana, R. A.; Taube, H.; Yoshida, H. J.
Am. Chem. Soc. 2000, 122, 7414-7415.
(
(
(
(
30) Matsumoto, T.; Periana, R. A.; Taube, D. J.; Yoshida, H. J. Mol. Catal.
A.: Chem. 2002, 180, 1-18.
31) Ng, S. M.; Lam, W. H.; Mak, C. C.; Tsang, C. W.; Jia, G.; Lin, Z.; Lau,
C. P. Organometallics 2003, 22, 641-651.
32) Lehmkuhl, H.; Bellenbaum, M.; Grundke, J. J. Organomet. Chem. 1987,
330, C23-C26.
likely.21 Electrophilic attack of Ru on an arene could lead to a
33) Roberts, R. M.; Khalaf, A. A. Friedel-Crafts Alkylation Chemistry: A
Century of DiscoVery; Marcel Dekker: New York, 1984.
III
σ-metathesis type transition state. Closely related Cp*Ir (PMe
3
)-
(R) systems have been suggested to activate CH bonds via oxidative
(34) Patinkin, S. H.; Friedman, B. S. In Friedel-Crafts and Related Reactions;
Olah, G. A., Ed.; John Wiley and Sons: New York, 1964; Vol. 2, pp
addition, and a similar mechanism cannot be definitively eliminated
from consideration.36 In addition, a bis-acac Ir(III) complex has
recently been proposed to be the active species of an Ir system
1-288.
(35) Jones, W. D.; Feher, F. J. J. Am. Chem. Soc. 1982, 104, 4240-4242.
36) Klei, S. R.; Tilley, T. D.; Bergman, R. G. J. Am. Chem. Soc. 2000, 122,
816-1817.
(37) Periana, R. A.; Liu, X. Y.; Bhalla, G. Chem. Commun. 2002, 24,
000-3001.
(
1
29,30,37
that catalyzes the addition of arenes across CdC bonds,
and
3
the comparable selectivities of this Ir catalyst and the Ru systems
reported herein imply potential mechanistic similarities. Periana et
JA035076K
J. AM. CHEM. SOC.
9
VOL. 125, NO. 25, 2003 7507