Isolation and X-ray crystal structure of an unusual biscarbene metal complex and its reactivity toward cyclopropanation and allylic C-H insertion of unfunctionalized alkenes [1]

Full text of DOI:10.1021/ja003184q

J. Am. Chem. Soc. 2001, 123, 4843-4844
4843
ruthenium/osmium biscarbene analogues. Herein we describe the
isolation and structure characterization of an intriguing biscarbene
osmium porphyrin. This biscarbene species represents the first
structurally characterized trans-biscarbene metal complex whose
carbene groups are not stabilized by heteroatom(s), has an
unprecedentedly long MdC(carbene) bond for such a class of
carbene group, allows a direct comparison among the structure
features of XdMdX (X ) CPh2, NTs, O) functional groups, and
can react with unfunctionalized alkenes to form cyclopropanation
products. Of particular interest is that this biscarbene species is
also reactive toward allylic C-H insertion of unfunctionalized
alkenes, constituting the first isolated metal-carbene complex
exhibiting such reactivity.9,10
Isolation and X-ray Crystal Structure of an Unusual
Biscarbene Metal Complex and Its Reactivity toward
Cyclopropanation and Allylic C-H Insertion of
Unfunctionalized Alkenes
Yan Li,† Jie-Sheng Huang,† Zhong-Yuan Zhou,‡ and
Chi-Ming Che*,†
Department of Chemistry, The UniVersity of Hong Kong
Pokfulam Road, Hong Kong
Department of Applied Biology and Chemical Technology
The Hong Kong Polytechnic UniVersity
Hung Hom, Kowloon, Hong Kong
Several years ago, Woo and co-workers2a demonstrated that a
simple osmium porphyrin, [Os(TTP)(CO)],11a can catalyze the
cyclopropanation of alkenes with ethyl diazoacetate (N2CHCO2-
Et), and that an isolated monocarbene complex, [Os(TTP)(CHCO2-
Et)], can undergo stoichiometric cyclopropanation with styrene.
In our efforts to extend the “N2CHCO2Et + [Os(TTP)(CO)]”
system to diphenyldiazomethane (N2CPh2) in conjunction with a
highly fluorinated osmium porphyrin, [Os(TPFPP)(CO)] (1),11b
we found that complex 1 can catalyze the cyclopropanation of
styrene with N2CPh2 in dichloromethane at 40 °C to form 1,1,2-
triphenylcyclopropane in 85% isolated yield (reaction 1), which
ReceiVed August 28, 2000
The cyclopropanation of alkenes with diazo compounds
catalyzed by metal complexes, a carbon analogue of metal-
catalyzed epoxidation or aziridination of alkenes, has attracted a
myriad of attention.1 It is widely believed that these cyclopro-
panation reactions proceed via metal-carbene intermediates,
which is supported by the isolation of a few monocarbene metal
complexes that can undergo stoichiometric cyclopropanation with
alkenes.2 Strikingly, while there are a considerable number of
isolated biscarbene metal complexes in the literature,3-5 along
with several tetra- up to hexacarbene species,6 none of them have
been reported to be reactive toward alkene cyclopropanations. In
view of the alkene epoxidation/aziridination reactivities observed
for dioxo7/bisimido8 ruthenium(VI) porphyrins, we conceive that
an alkene cyclopropanation reactivity may be observable for their
† The University of Hong Kong.
‡ The Hong Kong Polytechnic University.
(1) For recent reviews, see: (a) Doyle, M. P.; Forbes, D. C. Chem. ReV.
1998, 98, 911. (b) Doyle, M. P.; Protopopova, M. N. Tetrahedron 1998, 54,
7919. (c) Doyle, M. P. In ComprehensiVe Organometallic Chemistry II;
Hegedus, L. S., Ed.; Pergamon: Oxford, 1995; Vol. 12, pp 387-420. (d)
Togni, A.; Venanzi, L. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 497.
(2) Selected examples: (a) Smith, D. A.; Reynolds, D. N.; Woo, L. K. J.
Am. Chem. Soc. 1993, 115, 2511. (b) Park, S.-B.; Sakata, N.; Nishiyama, H.
Chem. Eur. J. 1996, 2, 303. (c) Lee, H. M.; Bianchini, C.; Jia, G.; Barbaro,
P. Organometallics 1999, 18, 1961.
(3) For structurally characterized Fischer-type biscarbene complexes whose
carbene groups are stabilized by heteroatoms, see: (a) Lappert, M. F.; Pye,
P. L.; Rogers, A. J.; McLaughlin, G. M. J. Chem. Soc., Dalton Trans. 1981,
701. (b) Anderson, D. M.; Bristow, G. S.; Hitchcock, P. B.; Jasim, H. A.;
Lappert, M. F.; Skelton, B. W. J. Chem. Soc., Dalton Trans. 1987, 2843. (c)
Arduengo, A. J., III; Dias, H. V. R.; Calabrese, J. C.; Davidson, F.
Organometallics 1993, 12, 3405. (d) Raubenheimer, H. G.; Toerien, J. G.;
Kruger, G. J.; Otte, R.; van Zyl, W.; Olivier, P. J. Organomet. Chem. 1994,
466, 291. (e) Zhang, S.-W.; Kaharu, T.; Pirio, N.; Ishii, R.; Uno, M.; Takahashi,
S. J. Organomet. Chem. 1995, 489, C62. (f) Raubenheimer, H. G.; Olivier,
P. J.; Lindeque, L.; Desmet, M.; Hrusak, J.; Kruger, G. J. J. Organomet. Chem.
1997, 544, 91. (g) Wang, H. M. J.; Lin, I. J. B. Organometallics 1998, 17,
972. (h) Weskamp, T.; Schattenmann, W. C.; Spiegler, M.; Herrmann, W. A.
Angew. Chem., Int. Ed. Engl. 1998, 37, 2490. (i) Zhang, S.-W.; Takahashi, S.
Organometallics 1998, 17, 4757. (j) Lee, C. K.; Chen, J. C. C.; Lee, K. M.;
Liu, C. W.; Lin, I. J. B. Chem. Mater. 1999, 11, 1237. (k) Calo, V.; Sole, R.
D.; Nacci, A.; Schingaro, E.; Scordari, F. Eur. J. Org. Chem. 2000, 869. (l)
Clyne, D. S.; Jin, J.; Genest, E.; Gallucci, J. C.; RajanBabu, T. V. Org. Lett.
2000, 2, 1125.
(4) For Schrock-type biscarbene complexes, see: (a) Fellmann, J. D.;
Rupprecht, G. A.; Wood, C. D.; Schrock, R. R. J. Am. Chem. Soc. 1978, 100,
5964. (b) Churchill, M. R.; Youngs, W. J. J. Chem. Soc., Chem. Commun.
1978, 1048. (c) Churchill, M. R.; Youngs, W. J. Inorg. Chem. 1979, 18, 1930.
(d) LaPointe, A. M.; Schrock, R. R.; Davis, W. M. J. Am. Chem. Soc. 1995,
117, 4802. (e) Diminnie, J. B.; Hall, H. D.; Xue, Z. Chem. Commun. 1996,
2383.
(5) For a bis(diarylcarbene) metalloporphyrin, see: Woo, L. K.; Smith, D.
A. Organometallics 1992, 11, 2344.
(6) (a) Goldberg, S. Z.; Eisenberg, R.; Miller, J. S. Inorg. Chem. 1977, 16,
1502. (b) Hitchcock, P. B.; Lappert, M. F.; Pye, P. L. J. Chem. Soc., Dalton
Trans. 1978, 826. (c) Plaia, U.; Stolzenberg, H.; Fehlhammer, W. P. J. Am.
Chem. Soc. 1985, 107, 2171.
represents an efficient metal complex-catalyzed cyclopropanation
of an aromatic alkene with diaryldiazomethane.12 Although
treatment of complex 1 with 1 equiv of N2CPh2 afforded a
monocarbene complex [Os(TPFPP)(CPh2)] (2) in 92% yield, this
isolated monocarbene species underwent no stoichiometric cy-
clopropanation reaction with styrene even at 80 °C under solvent
free conditions.
Interestingly, treatment of complex 2 with excess N2CPh2 in
dichloromethane gave a biscarbene complex, [Os(TPFPP)-
(CPh2)2] (3), in 61% isolated yield (reaction 2 in Scheme 1).13
(8) (a) Au, S.-M.; Fung, W.-H.; Cheng, M.-C.; Che, C.-M.; Peng, S.-M.
Chem. Commun. 1997, 1655. (b) Au, S.-M.; Huang, J.-S.; Yu, W.-Y.; Fung,
W.-H.; Che, C.-M. J. Am. Chem. Soc. 1999, 121, 9120.
(9) For metal-catalyzed carbene group transfer into unactivated saturated
C-H bonds that is proposed to involve a metal-carbene intermediate, see:
(a) Demonceau, A.; Noels, A. F.; Hubert, A. J.; Teyssie´, P. J. Chem. Soc.,
Chem. Commun. 1981, 688. (b) Callot, H. J.; Metz, F. Tetrahedron Lett. 1982,
23, 4321. (c) Davis, H. M. L.; Hansen, T. J. Am. Chem. Soc. 1997, 119, 9075.
(d) Davis, H. M. L.; Hansen, T.; Churchill, M. R. J. Am. Chem. Soc. 2000,
122, 3063.
(10) For intermolecular carbene group transfer from an isolated metal-
carbene complex into unsaturated C-H bonds, see: (a) Mclain, S. J.; Wood,
C. D.; Schrock, R. R. J. Am. Chem. Soc. 1977, 99, 3519. (b) Semmelhack,
M. F.; Tamura, R. J. Am. Chem. Soc. 1983, 105, 6750. (c) Wienand, A.;
Reissig, H.-U. Angew. Chem., Int. Ed. Engl. 1990, 29, 1129.
(11) (a) TTP ) meso-tetrakis(p-tolyl)porphyrinato dianion. (b) TPFPP )
meso-tetrakis(pentafluorophenyl)porphyrinato dianion.
(12) Metal complex-catalyzed cyclopropanations with diaryldiazomethanes
are extremely rare and in no such cases are aromatic alkenes (such as styrenes)
cyclopropanated in good yields, see: (a) Crumrine, D. S.; Haberkamp, T. J.;
Suther, D. J. J. Org. Chem. 1975, 40, 2274. (b) Doyle, M. P.; Wang, L. C.;
Loh, K.-L. Tetrahedron Lett. 1984, 25, 4087. (c) Pfeiffer, J.; Nieger, M.; Do¨tz,
K. H. Eur. J. Org. Chem. 1998, 1011. (d) Werner, H.; Schneider, M. E.; Bosch,
M.; Wolf, J.; Teuben, J. H.; Meetsma, A.; Troyanov, S. I. Chem. Eur. J. 2000,
6, 3052.
(13) The formation of a biscarbene osmium porphyrin from the reaction
of a monocarbene complex with a diazo compound was first observed by
Woo and co-workers by 1H and 13C NMR spectroscopy (see ref 5); however,
in their case the biscarbene complex, [Os(TTP)(C(p-C6H4Me)2)2], always
coexists with the corresponding monocarbene complex and has not been
isolated in pure form.
(7) (a) Groves, J. T.; Quinn, R. J. Am. Chem. Soc. 1985, 107, 5790. (b)
Leung, W.-H.; Che, C.-M. J. Am. Chem. Soc. 1989, 111, 8812. (c) Ho, C.;
Leung, W.-H.; Che, C.-M. J. Chem. Soc., Dalton Trans. 1991, 2933. (d) Lai,
T.-S.; Zhang, R.; Cheung, K.-K.; Kwong, H.-L.; Che, C.-M. Chem. Commun.
1998, 1583.
10.1021/ja003184q CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/25/2001

4844 J. Am. Chem. Soc., Vol. 123, No. 20, 2001
Communications to the Editor
Scheme 1
alkene. Reaction 4 also occurred in dichloromethane at 40 °C
but proceeded more slowly under these conditions. A striking
feature of the cyclopropanation by 3 lies in the high yield achieved
for trans-â-methylstyrene (92%), which has not been reported to
be a good substrate for the cyclopropanations mediated by other
metalloporphyrins.2a,17 Competitive cyclopropanation of styrene
and para-substituted styrenes p-X-C6H4CHdCH2 (X ) MeO, Me,
Cl, CF3) by 3 revealed that the cyclopropanation process is
promoted by the electron-donating but retarded by the electron-
withdrawing substituents, and the log(kX/kH) vs σ+ plot exhibits
a linearity with F+ ) -1.28 ( 0.08 and R ) 0.99 (see Figure
S1).
Remarkably, the reaction between complex 3 and cyclopentene
(8a) or cyclohexene (8b) resulted in transfer of the carbene group
selectively into the allylic C-H bonds, affording respective
diphenylmethyl-substituted cyclic alkenes (9) in ∼80% yields
(reaction 5).
Complex 3 can also be prepared in a similar yield from a direct
reaction of complex 1 with excess N2CPh2 (reaction 3 in Scheme
1). The 13C NMR spectra of 2 and 3 show a low-field signal at
273.60 and 313.79 ppm, respectively, which are typical for metal-
carbene complexes.5
Both complexes 2 and 3 have been characterized by X-ray
structure determinations. The structure of the biscarbene complex
3 shows several unusual features. First, compared with the Osd
C(carbene) bond lengths in monocarbene complexes 2 (1.870(2)
Å) and [Os(TTP)(C(p-C6H4Me)2)] (1.856(8) Å),14 the correspond-
ing bond lengths in 3 (2.035(2) and 2.027(3) Å) are rather long.15
Such a large difference in the Os-C(carbene) distance between
mono- and biscarbene complexes 2 and 3 can be attributed to
the trans effect of the CPh2 group and could account for the
dramatic difference in their reactivity (see below). Second, the
Ph2CdOsdCPh2 moiety in 3 adopts a roughly perpendicular
arrangement of the two carbene groups (similar to allenes R2Cd
CdCR2), unlike the parallel arrangement of the heteroatom-
stabilized carbene groups in an octahedral trans-biscarbene
molybdenum complex.3a Third, the porphyrin ring in 3 exhibits
a large ruffling distortion with a mean deviation of 0.197 Å from
its least-squares plane, in contrast to the basically planar porphyrin
ring in the monocarbene complex 2 with a mean deviation of
0.0382 Å.
The formation of 3 from reaction of 1 with excess N2CPh2
formally resembles the reaction between 1 and excess PhIdNTs
or m-CPBA to form [Os(TPFPP)(NTs)2] (4) or [Os(TPFPP)O2]
(5), respectively, both of which have been isolated and character-
ized by X-ray structural determinations (OsdNTs 1.803(3), 1.799-
(3) Å; OsdO 1.741(2) Å). Direct comparison of the spectral and
structural features among the biscarbene, bisimido, and dioxo
metal complexes (Table S1) reveals a substantially smaller Hâ
chemical shift16 and a much longer M-L axial bond for the
biscarbene complex 3 than for the bisimido and dioxo complexes
4 and 5.
It should be noted that reactions 4 and 5 are unlikely to proceed
via free CPh2 species in solution. Upon preparation of [Os-
(TPFPP)(CPh2-d10)2] (3-d20) from 1 and excess N2CPh2-d10, we
conducted a crossover experiment, which showed that no cross-
over product, [Os(TPFPP)(CPh2)(CPh2-d10)], is formed in an
equimolar mixture of 3 and 3-d20 in dichloromethane at 40 °C.
The present work provides new insight into the intermediates
in metal-catalyzed cyclopropanation of alkenes. The inertness of
2 toward stoichiometric styrene cyclopropanation and the obser-
vation of reactions 2-4 (Scheme 1) suggest that the biscarbene
species 3 acts as an active intermediate in reaction 1. This is
further supported by an efficient cyclopropanation of styrene with
N2CPh2 in the presence of a catalytic amount of 3, which afforded
the cyclopropane product in 63% isolated yield without an
induction period under the same conditions as for catalyst 1.18
Acknowledgment. This work was supported by The University of
Hong Kong (the Generic Drug Research Program), the Hong Kong
University Foundation, and the Hong Kong Research Grants Council
(HKU 501/96P).
Supporting Information Available: Experimental details (including
the spectral data of all the new compounds reported in this work), Tables
S1 and S2, Figure S1, and the X-ray structure determinations of complexes
2‚2MeOH, 3‚2H2O‚CH2Cl2, 4‚CH2Cl2, and 5‚MeOH (including the
ORTEP drawings, crystal data and structure refinements, tables of final
coordinates, bond lengths, bond angles, and anisotropic displacement
parameters) (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
Treatment of 3 with styrene and its derivatives 6 at 80 °C
afforded the corresponding cyclopropanes 7 in 70-94% yields
(reaction 4 in Scheme 1 and Table S2), accompanied by formation
of the monocarbene complex 2. In contrast, neither 4 nor 5 was
found to undergo imido or oxo group transfer reaction with an
(14) Djukic, J.-P.; Smith, D. A.; Young, V. G., Jr.; Woo, L. K. Organo-
metallics 1994, 13, 3020.
JA003184Q
(15) Although the Os-C(CPh2) distance in 3 is similar to an Os-C(alkyl)
distance (compare with the Os-C(CH2SiMe3) distance of 2.070(6) Å in cis-
[Os(CHBut)2(CH2SiMe3)2] reported in ref 4d), it is unlikely that the CPh2 units
in 3 belong to CHPh2 groups in view of the 13C NMR spectral feature of 3
and the virtually planar arrangement of both the Os-CPh2 moieties in 3 (see
Table S1).
(16) The chemical shift for the pyrrole protons of the porphyrin macrocycle
in the 1H NMR spectrum (δ ) 8.26, 9.06, and 9.22 for the diamagnetic species
3, 4, and 5, respectively). Note that for a diamagnetic metalloporphyrin, the
Hâ chemical shift usually increases with the oxidation state of the metal ion,
see: Antipas, A.; Buchler, J. W.; Gouterman, M.; Smith, P. D. J. Am. Chem.
Soc. 1980, 102, 198.
(17) Other representative examples: (a) Callot, H. J.; Piechocki, C.
Tetrahedron Lett. 1980, 21, 3489. (b) Maxwell, J. L.; O’Malley, S.; Brown,
K. C.; Kodadek, T. Organometallics 1992, 11, 645. (c) Wolf, J. R.; Hamaker,
C. G.; Djukic, J.-P.; Kodadek, T.; Woo, L. K. J. Am. Chem. Soc. 1995, 117,
9194. (d) Galardon, E.; Le Maux, P.; Simonneaux, G. Chem. Commun. 1997,
927. (e) Lo, W.-C.; Che, C.-M.; Cheng, K.-F.; Mak, T. C. W. Chem. Commun.
1997, 1205. (f) Frauenkron, M.; Berkessel, A. Tetrahedron Lett. 1997, 38,
7175.
(18) The lower yield obtained for the cyclopropanation catalyzed by 3 than
by 1 (63 vs 85%) may indicate that 3 is the prevailing but not the sole active
intermediate in the latter system.