Nickel(o)-mediated [3+2+2] and [2+2+2+1] cyclization reactions of chromium Fischer carbene complexes and alkynes

Article abstract of DOI:10.1002/anie.200351216

Dramatic changes in Fischer carbene reactivity occur in the presence of [Ni(cod)₂]. Thus, instead of Doetz [3+2+1] benzannulation giving substituted phenols, alkenyl carbene complexes incorporate two equivalents of alkyne in a [3+2+2] cyclizati

Full text of DOI:10.1002/anie.200351216

Communications
Fischer Carbene Cyclizations
Nickel(0)-Mediated [3þ2þ2] and [2þ2þ2þ1]
Cyclization Reactions of Chromium Fischer
Carbene Complexes and Alkynes**
JosØ Barluenga,* Pablo Barrio, Luis A. López,
Miguel Tomµs, Santiago García-Granda, and
Carmen Alvarez-Rffla
Although Fischer carbene complexes of Group 6 metals have
demonstrated great potential in synthetic organic chemistry,[1]
such complexes of late transition metals are almost unknown.
Wilke et al.[2] and Pinhas and Simunic[3] reported the com-
¼
¼
plexes [L2Ni C(NR2)Ph] and [(CO)3Ni C(OSiMe3)Bu],
respectively.[4] The feasibility of the transmetalation reaction
[*] Prof. Dr. J. Barluenga, P. Barrio, Dr. L. A. López, Prof. Dr. M. Tomµs
Instituto Universitario de Química Organometµlica “E. Moles”
Unidad Asociada al CSIC, Universidad de Oviedo
Juliµn Clavería 8, 33071 Oviedo (Spain)
Fax: (+34)98-510-3450
E-mail: barluenga@sauron.quimica.uniovi.es
Dr. S. García-Granda,+ Dr. C. Alvarez-Rffla+
Departamento de Química Física y Analítica, Universidad de
Oviedo
Juliµn Clavería 8, 33071 Oviedo (Spain)
[+] X-ray crystal structure analysis.
[**] Financial support for this work is acknowledged (BQU2001-3853
and PR-01-GE-9). P.B. thanks the Principado de Asturias for a
predoctoral fellowship.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author, and includes
experimental procedures, spectral and analytical data for all
products, and X-ray data for compounds 5b and 8e.
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DOI: 10.1002/anie.200351216
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as a route to these carbene complexes has been studied by us[5]
and others.[6–8] Because of our interest in this area, as well as
the importance of nickel carbene complexes as catalysts in
carbon–carbon bond formation,[9] we explored the reactivity
of chromium Fischer carbene complexes toward alkynes in
the presence of Ni0 complexes, which allowed us to discover a
new synthetic potential for chromium carbene complexes.
First, the active role of nickel was seen (Scheme 1) in the
formation of dimer 2 (1:1 Z/E mixture, 90%) from complex
1a and [Ni(cod)2] (cod = 1,5-cyclooctadiene; 10 mol%, THF,
Table 1: [3þ2þ2] cyclization of chromium alkenyl carbene complexes 1
with alkynes 4.
entry
R1
R2
5 [%][b]
6 [%][b]
1
2
3
4
5
6
7
8
Ph
nPr
nPr
nPr
nPr
Me3Si
(CH2)3CN
Ph
5a (86)
5b (73)
5c (76)
5d (62)
5e (80)
5 f (78)
5g (30)
–
–
–
–
–
–
–
ferrocenyl
2-furyl
nPr
Ph
Ph
2-furyl
Ph
6g (40)
6h (75)
CO2Me
[a] MeCN, 1:4:[Ni(cod)2] 1:3:1.1, ꢀ10 to 208C, 2 h. [b] Yields of isolated
products.
Scheme 1. Ni0-catalyzed dimerization and cyclopropanation of chro-
mium carbene complex 1a. Reagents and conditions: a) [Ni(cod)2]
(10 mol%), THF, 258C, 2 h, 90%; b) acrylonitrile, [Ni(cod)2]
(10 mol%), MeCN, 258C, 3 h, 85%.
2 h), and of cyclopropane 3 (1:1 cis/trans mixture, 85%) from
1a, acrylonitrile, and [Ni(cod)2] (10 mol%, MeCN, 258C, 3 h).
Neither reaction occurs in the absence of nickel catalyst.On
the basis of previous reports[5,10] we realized that some nickel
alkoxycarbene species I might act as the active nickel
intermediate.[11]
Therefore, we decided to investigate whether the hypo-
thetical alkoxycarbene complex I might display a new type of
carbene reactivity.Among a number of unsaturated sub-
strates, we selected alkynes since their thermal reaction with
chromium carbene complexes to give substituted phenols—
the so-called benzannulation or Dötz reaction—is the most
emblematic reaction of Fischer carbene complexes.[12] Thus,
alkenyl carbene complexes 1 were mixed with terminal
alkynes 4 at ꢀ108C in acetonitrile in the presence of a
stoichiometric amount of [Ni(cod)2].The reaction mixture
was allowed to warm to 208C over 2 h.Removal of the solvent
and column chromatography of the residue afforded cyclo-
heptatriene tricarbonyl chromium(0) complexes 5 in good
yields (Table 1, entries 1–6).In the case of phenylacetylene
(entry 7), a mixture of 5g (30% yield) and decomplexed
cycloheptatriene 6g (40% yield) was formed.This nickel-
mediated [3þ2þ2] cyclization of Fischer carbene complexes
and alkynes takes place with complete regio- and stereo-
selectivity, the endo isomer being solely formed.Electron-
poor alkynes also undergo this cyclization; for example,
methyl propynoate affords the functionalized cyclohepta-
triene 6h (entry 8).Phenol derivatives arising from the Dötz
reaction were usually detected in less than 5% yield, while no
higher oligomerization products were observed in the crude
reaction mixtures.
The endo configuration of compounds 5 is based on the
3JH6,H7 coupling constant (3.3–4.4 Hz),[13] and the unambigu-
ous structure of 5b was determined by an X-ray analysis
(Figure 1).[14]
Figure 1. Top: ORTEP plot (30% ellipsoids) for 5b; bottom: ORTEP
plot (30% ellipsoids) for 8e.
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Scheme 3. Decomplexation of 5a and hydrolysis of 6a. Reagents and
conditions: a) CO (35 bar), MeCN, 258C, 48 h, quantitative; b) 1n
HCl, THF, 258C, 2 h, 95%.
Scheme 2. Proposed mechanism for the formation of 5 and 6.
systems are readily accessible by CO exchange (Scheme 3).
For instance, cycloadduct 5a was demetalated under CO
pressure (35 bar, MeCN, 258C, 48 h) to provide 6a quantita-
tively, which was in turn hydrolyzed (1n HCl, THF, 258C, 2 h)
to give ketone 9 (95% yield).
A possible pathway for the formation of 5 is depicted in
Scheme 2.First, chromium–nickel exchange forms the nickel
species I (where L denotes cod, MeCN, or alkyne).[15]
Formation of the pentacarbonyl(acetonitrile)chromium(0)
complex is expected to facilitate metal exchange.[5] The
nickel complex I undergoes a double regioselective alkyne
insertion[16] to produce the new nickel carbene complex II,
which then cyclizes to give 5 and/or 6.This cyclization
probably proceeds by intramolecular cyclopropanation (see
Scheme 1) to form the norcaradiene species III, which
isomerizes to the cycloheptatriene ring.[17]
We were further intrigued whether 1-nickela-1,3,5,7-
octatetraenes of type II might also be available by assembling
simple chromium carbene complexes 7 and three alkyne units.
This goal was achieved by using terminal alkynes 4 and
[Ni(cod)2] (1.1 equiv), which, under the reaction conditions
given above, gave complexes 8 in high yields (Table 2).In this
In conclusion, we have reported a novel reactivity pattern
for chromium Fischer carbene complexes.Specifically,
[3þ2þ2] and [2þ2þ2þ1] cyclization reactions, which are
rarely found in the literature,[19,20] between these complexes
and alkynes are very efficient in the presence of Ni0.These
reactions are based on a facile chromium–nickel exchange
and on the particular reactivity of the assumed nickel carbene
species.In this context, some points are noteworthy: 1) the
new Fischer alkoxycarbene complexes of nickel(0) readily
undergo consecutive alkyne insertion reactions, 2) the first
cyclopropanation reaction of nickel carbene complexes is
reported here, and 3) no heptannulation reactions mediated
or catalyzed by nickel carbene species have been hitherto
reported.[16a]
Thus, the reactivity of Fischer carbene complexes can be
modified not only in a quantitative way,[8] but also in a
qualitative manner.The synthetic potential of Fischer car-
bene complexes should be expandable by combination with
appropriate transition metals.Further work to develop a
catalytic process[21] and to design an asymmetric version of the
reaction is underway.
Table 2: [2þ2þ2þ1] cyclization of chromium carbene complexes 7 with
alkynes 4.
Received: February 18, 2003 [Z51216]
entry
R1
R2
8 [%][b]
syn:anti[c]
Keywords: alkynes · carbene ligands · chromium · cyclization ·
nickel
1
2
3
4
5
6
7
Me
Me
Me
c-C3H5
p-MeOC6H4
2-furyl
Ph
nPr
8a (92)
8b (65)
8c (96)
8d (75)
8e (83)
8 f (86)
8g (68)
>98:2
>98:2
>98:2
>98:2
>98:2
90:10
.
Me3Si
(CH2)3CN
nPr
nPr
nPr
[1] W.D. Wulff in Comprehensive Organometallic Chemistry II,
Vol. 12 (Eds.: E. W. Abel, F. G. A., Stone, G. Wilkinson),
Pergamon, New York, 1995, p.469.
[2] B.Gabor, C.Krüger, B.Marczinke, R.Mynott, G.Wilke, Angew.
Chem. 1991, 103, 1711; Angew. Chem. Int. Ed. Engl. 1991, 30,
1666.
nPr
60:40
[a] MeCN, 7:4:[Ni(cod)2] 1:4:1.1, ꢀ10 to 208C, 2 h. [b] Yields of isolated
products. [c] 1H NMR spectroscopy (300 MHz) on the crude reaction
mixture.
[3] a) L.Simunic, A.R.Pinhas, Organometallics 1987, 6, 1358; b) L.
Simunic, A.R.Pinhas, Inorg. Chem. 1989, 28, 2400.
[4] For a PdII aminocarbene complex, see A.C.AlbØniz, P.Espinet,
R.Manrique, A.PØrez-Mateo, Angew. Chem. 2002, 114, 2469;
Angew. Chem. Int. Ed. 2002, 41, 2363.
[5] J.Barluenga, LA. .López, O.Löber, M.Tomµs, S.García-
Granda, C.Alvarez-Rffla, J.Borge, Angew. Chem. 2001, 113,
3495; Angew. Chem. Int. Ed. 2001, 40, 3392.
[6] a) T.Liu, K.R.Reddy, Chem. Soc. Rev. 1999, 28, 315; b) R.-Z.
Ku, J.-C. Huang, J.-Y. Cho, F.-M. Kiang, K. R. Reddy, Y.-C.
Chen, K.-J. Lee, J.-H. Lee, G.-H. Lee, S.-M. Peng, S.-T. Liu,
Organometallics 1999, 18, 2145.
novel [2þ2þ2þ1] cyclization three consecutive alkyne inser-
tion reactions are efficiently accomplished in a regioselective
manner.The syn isomer was found to be the sole (entries 1–5)
or the major isomer (entries 6 and 7).The structural assign-
ment of syn-8a–d was based on NMR spectroscopic data.
Moreover, an X-ray analysis was performed on compound 8e
(Figure 1).[14]
Apart from the synthetic importance of the cyclohepta-
triene chromium complexes,[18] the corresponding metal-free
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Chemie
¼
[7] a) For [Mo{ CPh(OMe)}(CO)(Cp)(NO)] with [Fe(CO)5], see
[20] The [2þ2þ1þ1] cyclization of simple Fischer carbene complexes
and alkynes has been reported: W.D.Wulf, R.W.Kaesler, G.A.
Peterson, P.-C. Tang, J. Am. Chem. Soc. 1985, 107, 1060.
[21] Significantly, we found that the cyclization of the carbene
complex 1 (R1 = Ph) and methyl propiolate to produce 6g
(Table 1, entry 8) also takes place in the presence of 10 mol% of
[Ni(cod)2], albeit in somewhat lower yield than with 1.1 equiv-
alents (55 versus 75%).
E.O.Fischer, H-.J.Beck, C.G.Kreiter, J.Lynch, J.Müller, E.
¼
Winkler, Chem. Ber. 1972, 105, 162; b) For [W{ CPh(O-
Me)}(CO)5] with H[AuCl4], see R.Aumann, EO. .Fischer,
Chem. Ber. 1981, 114, 1853; c) For [W{ CPh(OMe)}(CO)5] and
[W{ CPh(NEt2)}(CO)5] with [PdBr(C6F5)(MeCN)2], see ref.[4].
¼
¼
[8] In several papers Sierra et al.have proposed palladium biscar-
bene complexes as the active intermediates in the palladium-
catalyzed dimerization of chromium(0) alkoxycarbene com-
plexes: a) M.A. Sierra, M.J. Mancheæo, E. Sµez, J.C.
del Amo, J. Am. Chem. Soc. 1998, 120, 6812; b) M.A. Sierra,
J.C. del Amo, M.J. Mancheæo, M. Gómez-Gallego,
J. Am.
Chem. Soc. 2001, 123, 851; c) M.A.Sierra, J.C.del Amo, M.J.
Mancheæo, M.Gómez-Gallego, M.R.Torres, Chem. Commun.
2002, 1842.Other carbene species of Rh, Cu, and Pd have been
proposed as intermediates: d) I.Göttker-Schnetmann, R.
Aumann, Organometallics 2001, 20, 346; e) I.Göttker-Schnet-
mann, R.Aumann, K.Bergander, Organometallics 2001, 20,
3574; f) R.Aumann, I.Göttker-Schnetmann, R.Fröhlich, O.
Meyer, Eur. J. Org. Chem. 1999, 2545; g) H.Sakurai, K.Tanabe,
K.Narasaka, Chem. Lett. 1999, 75.
[9] a) C.P.Kubiak in Comprehensive Organometallic Chemistry II,
Vol. 9 (Eds:. E.W.Abel, F.G.A.Stone, G.Wilkinson), Perga-
mon, New York, 1995, p.1. Selected references: b) V.P.W.
Böhm, C.W.K. Gstöttmayr, T. Weskamp, W.A. Herrmann,
Angew. Chem. 2001, 113, 3500; Angew. Chem. Int. Ed. 2001, 40,
3387; c) Y.Sato, M.Takimoto, M.Mori, J. Am. Chem. Soc. 2000,
122, 1624.
¼
¼
[10] Complexes [Ni{ CBu(OSiMe3)}(CO)3] and [Ni{ CBu(O-
Li)}(CO)3] dimerize rapidly at room temperature and at low
temperature, respectively.See ref.[3b].
[11] a) The preparation of N-heterocyclic carbenes of Ni0 was first
reported by Arduengo et al.: A. J. Arduengo III, S. F. Gamper,
J.C.Calabrese, F.Davidson, J. Am. Chem. Soc. 1994, 116, 4391;
b) For the preparation and X-ray structure of a diphenylcarbene
complex of Ni0, see D.J.Mindiola, G.L.Hillhouse, J. Am. Chem.
Soc. 2002, 124, 9976.
[12] K.H.Dötz, Angew. Chem. 1984, 96, 573; Angew. Chem. Int. Ed.
Engl. 1984, 23, 587.
[13] It was found for related complexes that the coupling constant
between H6 and H7 is about 8 Hz for the exo isomer and about
2 Hz for the endo isomer: S.D. Reynolds, T.A. Albright,
Organometallics 1985, 4, 980.
[14] See Supporting Information for crystal data of 5b and 8e.
[15] The corresponding nickel(0) biscarbene complex is very unlikely
to be formed, because 1) no dimerization occurs, and 2) when
0.5 equiv of [Ni(cod)2] is used the yield of 5a drops to 45% and
about half of the carbene complex 1a is recovered.
[16] a) The insertion of alkynes into nickel carbene complexes was
demonstrated by Eisch et al.in the cross-oligomerization of
alkynes with carbene sources to give substituted cyclopenta-
dienes: J.J. Eisch, A.A. Aradi, M.A. Lucarelli, Y. Qian,
Tetrahedron 1998, 54, 1169; b) The insertion of carbonyl and
sulfur substrates into a diphenylcarbene nickel(0) complex has
been just reported (ref.[11b]).
[17] a) For a related formation of oxepines by alkyne insertion into a
rhodium(i) carbene complex, see A.Padwa, S.L.Xu,
J. Am.
Chem. Soc. 1992, 114, 5881; b) For the norcaradiene–cyclo-
heptatriene equilibrium, see A.A. Jarzecki, J. Gajewski, E.R.
Davidson, J. Am. Chem. Soc. 1999, 121, 6928.
[18] R.H.Rigby, Tetrahedron 1999, 55, 4521.
[19] a) For an elegant allyl/alkyne [3þ2þ2] cycloaddition mediated
by cobalt, see N.Etkin, T.L.Dzwiniel, K.E.Schweibert, J.M.
Stryker, J. Am. Chem. Soc. 1998, 120, 9702; b) For the carbon-
ylative cyclization of enediynes, see I.Ojima, S-.Y.Lee, J. Am.
Chem. Soc. 2000, 122, 2385.
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