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Cobalt Tetra(hydroquinone)porphyrin An Efficient Electron Transfer Reagent in Aerobic Pd-Catalyzed 1 4-Diacetoxylation of 1 3-Cyclohexadiene.

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l.558gcm-3:p(MoK,) = 9.10cm-') R =0.0536for4942reflectionswith
2 0 < 45 and I 2 3u(/); Rigaku AFC5S diffractometer, graphite
nionochromated Mo,, radiation. The structure was solved using direct
methods with the SHELXTL program package. Further details of the
crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe. Gesellschaft fur wissenschaftlich-technische Information mbH. D-W-7514 Eggenstein-Leopoldshafen 2 (FRG) on quotinp the depository number CSD-56814, the names of the authors. and the
K H Lii. N. S. Wen. C. C. Su. B. R. Chueh, Inorg. Chm?. 1992. 3 / , 439.
and references therein.
P. Amoros. A. LeBail. .
Solid S/(iIe Chenr. 1992. 97. 283.
D. Beltran-Porter. P. Amoros. R. Ibanez. E. Martinez. A. Beltran-Porter.
A LeBail. G. Ferey. G. Villeneuve, SolidSrutp / O N ~ C S1989.32!33. 57, and
rererences therein.
R C Haushalter. Z. Wang, M. E. Thompson, J. Zubieta. C. O'Connor.
/nor,c. Clrcvir., submitted.
LV! G. Kleinperer. T. A. Marquart. 0 . M. Ydghl, Angrw. Chern. 1992. 104.
51 : A r r ~ q r i iC/rm?.
I n / . Ed. En$ 1992. 31. 49.
J. Salta. Q ('hen. J. Zubieta. unpublished.
C;. Huan. .4. J. Jacobson. J. W. Johnson. E. W. Corcoran, Chem. Muler.
1990. 3. Y 1.
M I . Khan. Y. Chang. Q. Chen, H. Hope. S. Parkin. D. P. Goshorn, J.
Zuhieta. , 4 1 1 , q ~ i i ~Cllen?.
1992. 104. 1236, Angew. Clnvn. l n f . Ed. Enxl. 1992.
31. 1197.
C. J. Brinker. G . W. Scherer, Sol-gel Science, Academic Press, San Diego,
port here on the significant increase in the rate of the aerobic
1,4-diacetoxylation of 1,3-cyclohexadiene obtained by the
use of a porphyrin with hydroquinone units.
Cobalt tetra(hydroquin0ne)porphyrin [Co(TQP)] ( 3 ) was
prepared by a Lindsey condensation of 2.5-dimethoxybenzaldehyde and pyrrole. This initially afforded the protected
meso-tetra(2,5-dimethoxyphenyl)porphyrin(TDMPP), which
was then demethylated with BBr, and metalated with
[Co(OAc),] . 4H,0.[47 The new bifunctional catalyst 3 was
used for the aerobic 1,4-diacetoxylation of 1,3-cyclohexadi-
R = O H Co(T0P)
Cobalt Tetra(hydroquinone)prphyrin: An Efficient
Electron Transfer Reagent in Aerobic Pd-Catalyzed
1,4-Diacetoxylation of 1,3-Cyclohexadiene**
By Hclena Grennherg, Sjlvie Fuizon, and Jun-E. Backvall*
The palladium-catalyzed 1,4-diacetoxylation of 1,3-dienes"' was recently developed into an aerobic process by the
use of a one-pot triple catalytic system (Scheme 1).f21 The
triple catalytic system involves selective interactions between
each consecutive catalyst, and the reoxidation of hydroquinone (HQ) to benzoquinone (BQ) is a crucial step. If
a quinone-containing macrocycle is used, an intramolecular
electron transfer between the hydroquinone unit and the
oxidized metal-containing macrocycle may be achieved.I3]
ene.[61The rate of oxygen consumption was measured and
compared to that of the corresponding reaction catalyzed by
free hydroquinone and l."] As can be seen in Figure 1, the
use of 3 results in a faster oxygen consumption, indicating a
more efficient electron transfer. To determine if this rate
enhancement was an effect of the electron-rich phenyl
groups in 3, 3 was also compared to 2 + HQ. The overall
performance of 2 H Q was more similar to that of 1 + H Q
than 3, indicating that the increased reaction rate for the
catalysis with 3 was not an electronic effect from the substituted phenyls.
Fig. 1 . Aerobic 1.4-oxidation of 1 mmol of 1.3-cyclohexadiene by addition of
2.5 m o l % of [Pd(OAc),].
Scheme 1 . The triple catalytic system and the overall reaction of the diacetoxylation of 1 .3-cyciohexddiene. ML = metal-containing macrocycle.
This was expected to lead to a more efficient overall reaction
than that observed for the system with the hydroquinone and
metal-containing macrocycle as separate molecules. We re[*] Prof Dr. J.-E. Biickvall, Dr. H. Grennberg. S. Faizon
Department of Organic Chemistry. University of Uppsala
Box 531. S-751 21 Uppsala (Sweden)
This work was supported by the Swedish Natural Science Research Council and the Swedish Research Council for Engineering Science. The Region
PACA (France) is acknowledged for financially supporting the student
exchange between University of Aix-Marseille IiI (S. F.) and University of
Angaw. (%em Inr. Ed. EngI. 1993, 32. N o . 2
Under standard conditions". ( 5 mol YO[Pd(OAc),]), the
reaction catalyzed by 3 was complete in 10 h ; all substrate
was oxidized to give 1,4-diacetoxy-2-cycIohexene4 and benzene.12b1The reaction catalyzed by 1 + HQ ceased after
18 h.lS1The yields of 4 are about the same for both reactions
(ca. 7.5%). However, when a smaller amount of [Pd(OAc),]
(2.5 mol %) was used, the reaction catalyzed by 3 was unaffected, whereas the rate of that catalyzed by 1 + H Q decreased, yielding 65 % of 4 after 28 h (Table
In addition
the reaction catalyzed by 2 + H Q was slow under these conditions, and gave 60% 4 together with benzene after
24 h.[*. 91 The relative stereochemistry of 4,previously shown
to be dependent on both the type and amount of lithium salt
:P? VCH V e r l a ~ s ~ e s e l / . ~ cmhH,
h u f ~ W-6940 Wernherm, 1993
0570-0R33193/020,7-0263$ I 0 00t 2S:O
Table 1. Aerobic 1.4-oxidation of 1,3-cyclohexadiene [a]
LiOAc [moll
Product [b]/Selectivity
r r m s -4i60
truns-4i > 90
Yield [c]/Time
[a] Conditions: 2.5 mol% of [Pd(OAc),], 2-2.5 mol% of [Cofporphyrin)],
10 mol% H Q (for 1 and 2) in 2 mL HOAc at room temperature and 1 atm 0,.
[b] The relative stereochemistry of 4 was determined by 'H NMR spectroscopy. [c] Isolated yield.
present[" and the structure of the quinone,".
was also
found to be dependent on whether the reaction was catalyzed
by 3 or 1 + HQ. With 1 + HQ,['] trans-4 was obtained with
a stereoselectivity of >90% whereas with the catalyst 3 only
a moderate stereoselectivity (70% trans) was achieved.
At least two pathways for the electron transfer in the bifunctional Co(porphyrin-hydroquinone) molecule are possible. The observed efficiency of the quinone-containing porphyrin 3 is best explained by an intramolecular electron
transfer from the hydroquinone unit to the oxidized cobalt
atom via the x-electron system of the porphyrin. An alternative mechanism would involve intermolecular interactions
via a "liquid polymer"[' 'I coordination of the hydroquinone
unit of one porphyrin molecule to the metal center of a
second molecule.
Thus the bifunctional catalyst 3 not only accelerates the
eIectron transfer but also acts as an efficient oxygen activating agent in the aerobic palladium-catalyzed trans-I ,4-diacetoxylation of 1,3-cyclohexadiene.
Experimental Procedure
TDMPPH, was prepared by a Lindsey condensation [4a]: a solution of trifluoroacetic acid (0.46 g, 4 mmol) in CH,CI, (50 mL) was added over 15 min to
a degassed solution of 2.5-dimethoxybenzaldehyde (1.1 g, 6.6 mmol) and freshly distilled pyrrole (0.51 g, 7.5 mmol) in CH,CI, (250 mL, distilled from CaH,).
The mixture was stirred under an N, atmosphere for about 15 h. A toluene
,4-benzoquinone (I g in 10 mL) was
solution of 2,3-dichloro-5,6-dicyano-l
added and the mixture was heated a t reflux for 1 h, then filtered through basic
alumina and evaporated to dryness. The crude product was dissolved in CHCI,
and precipitated withpentanetoyield0.21 g(15%)TDMPPH,. UV (CH,CI,):
;.[nm] = 398 (sh), 418, 513. 545. 588, 643. 'H N M R ([DJacetone): 6 = 8.80
(brs,8H,fi-pyrrole), 7.64(m,4H.o-Ph), 7.38 (brs. XH,m,p-Ph), 3.95and 3.55
(m. 12H each, OCH,), -2.66 (brs. NH). Correct elemental analysis (C,H,N)
for C,,H,,N,O,
TQPH,: To a cooled (~ 75 -C) solution of TDMPPH, (0.20 g, 0.23 mmol) in
dry CH,CI, (20 mL) under an N, atmosphere was added BBr, [4 b.c] (20 m L of
a 1 M CH,CI, solution) over 30 min. The green mixture was stirred at 75 for
75 min, at room temperature for 1.5 h, and then slowly poured into 300 mL of
a crushed ice-H,O mixture. The biphasic mixture was stirred until the ice had
melted. Subsequently EtOH (200 mL) was added and then solid NaHCO, until
the mixture turned red. The mixture was then extracted with CH,CI, and ether,
washed with H,O, dried over MgSO,, and evaporated to yield 0.15 g (71 %)
TQPH,. UV (acetone): ;.[nm] = 417, 512, 544, 5x9, 645.
2 and 3 were prepared by treating the porphyrin free bases with an excess of
[Co(OAc)] . 4H,O in refluxing, freshly distilled DMF, in accordance with the
literature [4d]. UV (acetone) of3: i.[nm] = 407,53O(unresolved). UV(CH,CI,)
of 2: i.[nm] = 414, 438, 529. 546 (unresolved).
Connolly, J. K. Hurley. M. R. Wdsietewski, J Am. Chem. Sor. 1988, 110,
1733; J. Rodriguez, C. Kirmaier, M. R. Johnson, R. A. Friesner, D.
Holten, J. L. Sessler, ibid. 1991, 113, 1652.
141 a) J. S. Lindsey, I. C. Schreimdn, H. C. Hsu. P. C. Kearney, A. M. Marguerettaz. J Org. Chem. 1987, 52. 827; b) J. F. W. McOmie, D . E. West in
Org. Swirh. Collect. Val V, (Ed: H. E. Baumgarten), Wiley, New York,
1973, p. 412; c) E. H. Vickery, L. F. Pahler. E. J. Eisenbraun, J. Org. Chem.
1979,44.4444; d) A. D. Adler, F. R. Longo. R. Kampas, J. Kim. J. Inorg.
N u d . Chon?. 1970, 32. 2443.
[5] a) J. Dalton, L. R. Milgrom, J. Chenz. Suc. Chem. Commun. 1979. 609:
b) M. A. Bergkamp, J. Dalton, T. L. Netzel, J. Am. Chem. Sor. 1982, 104.
[6] A Co(sa1en-HQ) was recently reported as a catalyst in a Pd-catalyzed
allylic oxidation of cyclohexene [ 5 b]. When this catalyst was tried and
compared to 3 in a 1.4-diacetoxylation, we found that the salene-HQ
complex led to a considerably lower reaction rate and was also less stable
to the reaction conditions than the porphyrin: S. E. Bystrom, E. M.
Larsson. B. iqkermark, J. Org. Chem. 1990, 55, 5674.
[7] The oxygen consumption gives a good estimate of the progress of the
Pd-catalyzed oxidation: 12 mL of 0, corresponds to conversion of 1 mmol
of the substrate [2b].
[U] In the reaction catalyzed by 1 HQ. the free quinone was consumed in a
Diels-Alder reaction with 1,3-cyclohexadiene, and no benzene formation
was observed (by GC o r GC-MS).
[9]a) A control experiment employing 2 without hydroquinone yielded a very
rapid and unexpected [9b] oxygen consumption. I n only 4 hall diene was
converted to 4 and benzene. of which 4 was isolated in 35 O h yield. Interestingly. the relative stereochemistry of the product was reversed from the
70% irans obtained by using 3 to 7 5 % cis with 2. This mechanistically
interesting observation will be the subject of a separate study. b) Employing 1 without a quinone yielded only porphyrin degradation products.
[lo] H. Grennberg, A. Gogoll. J.-E. Bickvall. J. Org. Chem. 1991, 56. 5808.
[ I 11 E. B. Fleischer. A. M. Shachter. Inorg. Chem. 1991, 31. 3763.
Surprising Differences in the Cycloaddition
Reactions of Cumulenes and Heterocumulenes
to Vinylidenetitanocene: Formation of
Four- or Five-Membered Titanacycles**
By Riidiger Beckhaus,* Isabelle Strauj?, Trixie Wagner,
and Paul Kiprof
The stabilization of the vinylidene group H,C=C:, tautomeric to acetylene, by complexation as metallaallene 1 led
to an extensive chemistry, particularly for electron-rich transition metals.''. The methylidene titanacyclobutane 3, acCH
Received: September 11. 1992 [Z 5568 IE]
German version: Angcw. Chem. 1993, 105, 269
[ l ] J:E. BBckvall, S. E. Bystram, R E Nordberg. J. Org. Chem. 1984. 4Y.
[2] a) J:E. Bickvall, A. K. Awasthi, Z. D. Renko, J. Am. Chem. Sor. 1987,
f09.4750; b) J.-E. Biickvall, R. B. Hopkins, H. Grennberg, M. M. Mader,
A. K . Awasthi. ;bid. 1990, 1f2. 5160.
[3] Intramolecular electron transfer has been reported in porphyrin-quinone
photosynthesis model compounds: M. R. Wasielewski. Chem. R a . 1992.
92,435; J. A. Schmidt. A. R. McIntosh, A. C. Weedon, J. R. Bolton. J. S.
$3 VCH
Verlugsgrselkchuft mbH. W-6940 Weinltcini, f993
cessible from the divinyltitanocene 2 in almost quantitative
yield,[3a*h1 is an efficient source for vinylidenetitanocene 4,141
which is formed from 3 by heating to cleave ethylene. Extended Hiickel MO calculations show that the electronic
structure of 4 makes it ideally suited for cycloaddition reactions with multiply bonded systems.[41
Dr. R. Beckhaus. I. StrauD. T. Wagner
Institut fur Anorgdnische Chemie der Technischen Hochschule
Professor-Pirlet-Strdsse1, D-W-5100 Aachen (FRG)
Dr. P. Kiproq+]
Anorgdnisch-chemisches Institut der Technischen Universitiit Munchen
['I Present address:
Department of Chemistry, University of Wisconsin
Madison (USA)
[**I The experimental studies were partly carried out during a visit to the
Anorganisch-chemisches Institut der Technischen Universitit Munchen
(extraordinary research grant of the Alexander von Humboldt Foundation for RB). RB thanks Prof. P. Hofmann for his continued interest.
Financial support from the Fonds der Chemischen Industrie is gratefully
S f0.00f ,2510
Angen. Chrm. Int. Ed. h g l . 1993, 32, No. 2
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efficiency, cyclohexadiene, reagents, transfer, diacetoxylation, porphyrio, aerobics, tetra, electro, cobalt, hydroquinone, catalyzed
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