Pd-catalyzed inter- and intramolecular carbene transfer from group 6 metal-carbene complexes

Article abstract of DOI:10.1021/ja002497i

The use of group 6 metal-carbene complexes in inter- and intramolecular carbene transfer reactions has been studied. Thus, pentacarbonyl[(aryl)(methoxy)carbene]chromium(0) and tungsten complexes, 10, efficiently dimerize at room temperature in the presenc

Full text of DOI:10.1021/ja002497i

J. Am. Chem. Soc. 2001, 123, 851-861
851
Pd-Catalyzed Inter- and Intramolecular Carbene Transfer from Group
6 Metal-Carbene Complexes1
Miguel A. Sierra,* Juan C. del Amo, Mar´ıa J. Manchen˜o, and Mar Go´mez-Gallego
Contribution from the Departamento de Qu´ımica Orga´nica I, Facultad de Qu´ımica,
UniVersidad Complutense, 28040-Madrid, Spain
ReceiVed July 10, 2000
Abstract: The use of group 6 metal-carbene complexes in inter- and intramolecular carbene transfer reactions
has been studied. Thus, pentacarbonyl[(aryl)(methoxy)carbene]chromium(0) and tungsten complexes, 10,
efficiently dimerize at room temperature in the presence of diverse Pd(0) and Pd(II)/Et3N catalysts. The effect
of additives (PPh3, AsPh3, or SbPh3) on the nature and the isomeric ratio of the reaction products is negligible.
The nature of the reaction products is more catalyst-dependent for metal carbenes 12 bearing alkyl groups
attached to the carbene carbon. In these cases, either carbene ligand dimerization or â-hydrogen elimination
reactions are observed, depending on the catalyst. The carbene ligand dimerization reaction can be used to
prepare conjugated polyenes, including those having metal moieties at both ends of the polyene system, as
well as enediyne derivatives. The intramolecular carbene ligand dimerization of chromium bis-carbene complexes
28 and 30 allows the preparation of mono- and bicyclic derivatives, with ring sizes from six to nine members.
For bis-carbene derivatives the â-hydrogen elimination reaction is inhibited, provided that both metal centers
are tethered by an o-xylylene group. Other alkyl complexes 32 form new mononuclear carbene complexes 37
or decompose to complex reaction mixtures. The results obtained in these reactions may be explained by
transmetalation from Cr(0) to Pd(0) and the intermediacy of Pd-carbene complexes. Aminocarbene-chromium-
(0) complexes 15, need harsher reaction conditions to transfer the carbene ligand, and this transfer occurs only
in the presence of deactivated olefins. The corresponding insertion/hydrolysis products 48 resulted in these
cases. A catalytic cycle involving transmetalation from a chromacyclobutane to a palladacyclobutane is proposed
to explain these results.
Introduction
group 6 bis-carbene complexes 19 and 210 to yield compounds
3 and 4, respectively, have also been reported (Scheme 1). In
contrast, chelating [(diphenylalkoxy)chromium](0) bis-carbene
mononuclear complexes thermally evolve by R-elimination to
the corresponding dienes, instead of the expected intermolecular
double dimerization products.11
On the other hand, it is well-known that the in situ generation
of highly reactive metallo-carbene species from an organic
precursor and a metal-reagent from groups 8-11 leads to
transient metal-carbene complexes. The reaction of these
complexes and olefins have been extensively exploited in
organic synthesis as a general route to different kind of
cyclopropanes.4a,12 Moreover, the carbene ligand dimerization
of these in situ generated reagents is a topic of continued
(3) (a) Do¨tz, K. H.; Fischer, H.; Hofmann, P.; Kreissel, R.; Schubert,
U.; Weiss, K. Transition Metal Carbene Complexes; Verlag Chemie:
Deerfield Beach, Florida, 1983. (b) Do¨tz, K. H. Angew. Chem., Int. Ed.
Engl. 1984, 23, 587. (c) Wulff, W. D. In ComprehensiVe Organic Synthesis;
Trost, B. M.; Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 5, p 1065.
(d) Schwindt, M. A.; Miller, J. R.; Hegedus, L. S. J. Organomet. Chem.
1991, 413, 143. (e) Rudler, H.; Audouin, M.; Chelain, E.; Denise, B.;
Goumont, R.; Massoud, A.; Parlier, A.; Pacreau, A.; Rudler, M.; Yefsah,
R.; Alvarez, C.; Delgado-Reyes, F. Chem. Soc. ReV. 1991, 20, 503. (f)
Grotjahn, D. B.; Do¨tz, K. H. Synlett. 1991, 381. (g) Wulff, W. D. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G.
A., Wilkinson, G.; Eds.; Pergamon: Oxford, 1995; Vol. 12, p 470. (h)
Hegedus, L. S. In ComprehensiVe Organometallic Chemistry II; Abel, E.
W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995; Vol.
12, p 549. (i) Harvey, D. F.; Sigano, D. M. Chem. ReV. 1996, 96, 271. (j)
Hegedus, L. S. Tetrahedron 1997, 53, 4105. (k) Aumann, R.; Nienaber, H.
AdV. Organomet. Chem. 1997, 41, 163. (l) Alcaide, B.; Casarrubios, L.;
Dom´ınguez, G.; Sierra, M. A. Curr. Org. Chem. 1998, 2, 551. (m)
Barluenga, J.; Fan˜anas, F. J. Tetrahedron 2000, 56, 4597. (n) Sierra, M. A.
Chem. ReV. 2000, 100, 3591.
The ability of group 6 metal-carbene (Fischer) complexes
to act as stable carbene sources was early recognized. In fact
the cyclopropanation of olefins was one of the first reactions
of these complexes ever reported.2 Since those early days, many
other reactions of this class of organometallic reagents have
been discovered, and their applications in organic synthesis are
now far beyond that of a “simple” role as carbene-transferring
reagents.3 Nevertheless, the use of group 6 metal-carbene
complexes as stable reagents for carbene transfer has not yet
encountered its place in modern organic synthesis. Extensive
efforts have been done to study the thermal reactivity of these
complexes and olefins, the main reactions disclosed being
cyclopropanation4 and C-H insertion.5 The thermal decomposi-
tion of heteroatom-stabilized group 6 carbene complexes
occurred at high temperatures (T > 130 °C), leading to carbene
dimers.6 The E/Z ratio of the olefinic products is metal-
dependent, which excludes the participation of free carbenes at
least in some of these processes.7 Additionally, the absence of
cyclobutanone derivatives in the thermolysis of pentacarbonyl-
[(2-oxacyclopentyliden)carbene]chromium(0) in boiling Deca-
line (139 °C), discarded the existence of free carbenes in these
processes.8 The thermal intramolecular dimerization of some
* Author for correspondence. E-mail: sierraor@eucmos.sim.ucm.es.
(1) For a preliminary communication of a part of this work, see: Sierra,
M. A.; Manchen˜o, M. J.; Sa´ez, E.; del Amo, J. C. J. Am. Chem. Soc. 1998,
120, 6812.
(2) (a) Fischer, E. O.; Do¨tz, K. H. Chem. Ber. 1970, 103, 1273. (b) Do¨tz,
K. H.; Fischer, E. O. Chem. Ber. 1972, 105, 1356. (c) Fischer, E. O.; Do¨tz,
K. H. Chem. Ber. 1972, 105, 3966.
10.1021/ja002497i CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/11/2001

852 J. Am. Chem. Soc., Vol. 123, No. 5, 2001
Sierra et al.
interest.13 It seemed attractive to study the viability of making
an analogous reaction using group 6 metal-carbene complexes
as the source of the carbene in a transmetalation reaction. The
goal was to generate a new intermediate metal-carbenoid
complex more reactive than the original to effect the carbene
transfer at temperatures lower than the usual for group 6 carbene
complexes.
Cp(CO)(NO)MCYPh (M ) Cr, Mo, W; Y ) OMe, NMe2)
transfer the carbene ligand to photochemically generated Fe-
(CO)5 to yield the iron carbenes (CO)4FeCYAr in acceptable
yields.14 The thermal equilibrium (140 °C) between alkoxy-
chromium-carbene complexes and W(CO)6 to form alkoxy-
tungsten-carbene complexes and Cr(CO)6 has also been
reported.15 The stoichometric transmetalation of group 6 mono-
nuclear alkoxypentacarbonylmetal-carbene complexes 5 to
group 10 metal centers 6 was reported by Stone. These reactions
yielded trimetallic complexes having µ-carbene ligands 7
together with different triangular clusters 8 and 9 (Scheme 2).16
Several Au(I)- and Au(III)-carbene complexes have been
prepared from the reaction of (CO)5MC(NMe2)Ph and (CO)5-
MC(OMe)Ph (M ) Cr, Mo, W) with chloroauric acid.17,18 The
transition metal-catalyzed carbene transfer from a group 6
alkoxymetal-carbene complex was, to the best of our knowl-
edge, unknown at the beginning of this work. Reported herein
is a full account of the use of group 6 metal-carbene complexes
both in inter- and intramolecular carbene transfer reactions.1
Scheme 1
Scheme 2
The transfer of a carbene ligand from a Fischer-type group 6
carbene complex to another metal center is a rare process. Thus,
(4) For reviews on the use of Fischer carbene complexes as cyclopro-
panating agents, see: (a) Doyle, M. P. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Vol. 12, p 387. (b) Brookhart, M.; Studabaker,
W. B. Chem. ReV. 1987, 87, 411. Selected examples: (c) Barluenga, J.;
Ferna´ndez-Acebes, A.; Trabanco, A. A.; Flo´rez, J. J. Am. Chem. Soc. 1997,
119, 7591. (d) Buchert, M.; Hoffmann; M.; Reissig, H.-U. Chem. Ber. 1995,
128, 605. (e) Merlic, C. A.; Bendorf, H. D. Tetrahedron Lett. 1994, 35,
9529. (f) Harvey, D. F.; Lund, K. P. J. Am. Chem. Soc. 1991, 113, 8916.
(g) Wienand, A.; Reissig, H.-U. Organometallics 1990, 9, 3133. (h)
Wienand, A.; Reissig, H.-U. Tetrahedron Lett. 1988, 29, 2315. (i) Buchert,
M.; Reissig, H.-U. Tetrahedron Lett. 1988, 29, 2319. The intramolecular
cyclopropanation occurred at much lower temperatures. See, among
others: (j) Toledano, C. A.; Rudler, H.; Daran, J.-C.; Jeannin, Y. Chem.
Commun. 1984, 574. (k) Casey, C. P.; Vollendorf, N. W.; Haller, K. J. J.
Am. Chem. Soc. 1984, 106, 3754. (l) So¨derberg, B.; Hegedus, L. S.
Organometallics 1990, 9, 3113. (m) Barluenga, J.; Monserrat, J. M.; Flo´rez,
J. Chem. Commun. 1993, 1068.
(5) Examples: (a) Takeda, K.; Okamoto, Y.; Nakajima, A.; Yoshii, E.;
Koizumi, T. Synlett 1997, 1181. (b) Barluenga, J.; Aznar, F.; Ferna´ndez,
M. Chem. Eur. J. 1997, 3, 1629. (c) Barluenga, J.; Rodr´ıguez, F.; Vadecard,
J.; Bendix, M.; Fan˜anas, F. J. J. Am. Chem. Soc. 1996, 118, 6090. (d)
Takeda, K.; Takeda, M.; Nakajima, A.; Yoshii, E. J. Am. Chem. Soc. 1995,
117, 6400. (e) Wang, S. L. B.; Su, J.; Wulff, W. D. J. Am. Chem. Soc.
1992, 114, 10665. (f) Wienand, A.; Reissig, H.-U. Angew. Chem., Int. Ed.
Engl. 1990, 29, 1129. (g) Fischer, H.; Schmid, J. Chem. Commun. 1985,
572.
Results and Discussion
The first assays to determine the viability of metal-catalyzed
carbene transfer from group 6 stabilized metal-carbene com-
plexes, were carried out by reacting pentacarbonyl[(aryl)-
(methoxy) carbene]chromium(0) complexes 10a and 10b and
catalytic amounts of Rh2(OAc)4 at different temperatures.19 We
observed that carbene ligand dimerization of complex 10a
occurred at temperatures around 100 °C, high enough to not
(6) Group 6 carbene complexes lacking the stabilizing effect of the
heteroatom bonded to the carbene carbon are considerably less stable
thermally. For some examples of the thermal behavior of such complexes
including carbene ligand dimerization, see: (a) Casey, C. P.; Burkhardt, T.
J. J. Am. Chem. Soc. 1973, 95, 5833. (b) Casey, C. P.; Burkhardt, T. J.;
Bunnell, C. A.; Calabrese, J. C. J. Am. Chem. Soc. 1977, 99, 2127. (c)
Casey, C. P.; Polichnowski, S. W. J. Am. Chem. Soc. 1977, 99, 6097. (d)
Fischer, H.; Zeuner, S.; Ackermann, K. Chem. Commun. 1984, 685. (e)
Fischer, H.; Zeuner, S.; Ackermann, K.; Schmid, J. Chem. Ber. 1986, 119,
1546. For other reactivity of these complexes, see: (f) Fischer, H.; Jungklaus,
H. J. Organomet. Chem. 1999, 572, 105 and pertinent references therein.
(7) (a) Fischer, E. O.; Do¨tz, K. H. J. Organomet. Chem. 1972, 36, C4.
(b) Fischer, E. O.; Heckl, B.; Do¨tz, K. H.; Muller, J.; Werner, H. J.
Organomet. Chem. 1969, 16, P 29. (c) Unpublished results cited by K. H.
Do¨tz in ref 3a, p 196.
(8) Casey, C. P.; Anderson, R. L. J. Chem. Soc., Chem. Commun. 1975,
895. Free 2-oxacyclopentylidene generated by thermolysis of the corre-
sponding tosylhydrazone yielded 20% of cyclobutanone. See: Foster, A.
M.; Agosta, W. C. J. Am. Chem. Soc. 1972, 94, 5777.
(9) Bao, J.; Wulff, W. D.; Fumo, M. J.; Grant, E. B.; Heller, D. P.;
Whitcomb, M. C.; Yeung, S.-M. J. Am. Chem. Soc. 1996, 118, 2166.
(10) Macomber, D. W.; Hung, M.-H.; Verma, A. G. Organometallics
1988, 7, 2072.
(13) Selected examples: Ru-catalysts: Baratta, W.; Del Zotto, P.; Rigo,
S. Organometallics 1999, 18, 5091. (b) Galardon, E.; Le Maux, P.; Toupet,
L.; Simonneaux, G. Organometallics 1998, 17, 566. (c) Collman, J. P.;
Rose, E.; Venburg, G. D. J. Chem. Soc., Chem. Commun. 1993, 934. Rh-
catalysts: (d) Shankar, B. K. R.; Schechter, H. Tetrahedron Lett. 1980, 21,
1251. Os-catalysts: (e) Woo, L. K.; Smith, D. A. Organometallics 1992,
11, 2344. (f) Demonceau, A.; Lemoine, C. A.; Noels, A. F.; Chizhevsky,
I. T.; Sorokin, P. V. Tetrahedron Lett. 1995, 36, 8419. Cu-catalysts: (g)
Oshina, T.; Hagai, T. Tetrahedron Lett. 1980, 21, 1251.
(14) (a) E. O. Fischer, H.-J. Beck Angew. Chem., Int. Ed. Engl. 1970, 9,
72. (b) E. O. Fischer, H.-J. Beck Chem. Ber. 1971, 104, 3101.
(15) C. P. Casey, R. L. Anderson, J. Chem. Soc., Chem. Commun. 1975,
895.
(16) (a) T. V. Ashworth, M. Berry, J. A. K. Howard, M. Laguna, Stone,
F. G. A. J. Chem. Soc., Dalton Trans. 1980, 1615. (b) T. V. Ashworth, J.
A. K. Howard, M. Laguna, F. G. A. Stone, J. Chem. Soc., Dalton Trans.
1980, 1593. (c) M. Berry, J. A. K. Howard, F. G. A. Stone J. Chem. Soc.,
Dalton Trans. 1980, 1601.
(17) (a) Aumann, R.; Fischer, E. O. Chem. Ber. 1981, 114, 1853. (b)
Fischer, E. O.; Bo¨ck, M.; Aumann, R. Chem. Ber. 1981, 114, 1853. (c)
Fischer, E. O.; Boeck, M. Monastsch. Chem. 1984, 115, 1159.
(18) The transmetalation of diaminocarbene ligands from a group 6 metal
center to late-transition metal centers is much more frequent. See: R.-Z.
Ku, J.-Ch. Huang, J.-Y. Cho, F.-M. Kiang, K. R. Reddy, Y.-Ch. Chen,
K.-J. Lee, J.-H. Lee, G.-H. Lee, S.-M. Peng, S.-T. Liu, Organometallics
1999, 18, 2145 and references therein.
(11) Huy, H. T.; Lefloch, P.; Louis, J. M.; Fetizon, M. J. Organomet.
Chem. 1986, 311, 79.
(12) Zaragoza-Do¨rwald, F. Metal Carbenes in Organic Synthesis; Wiley-
VCH: Weinheim, Germany, 1999; Chapter 4.
(19) Sierra, M. A.; Casarrubios, L.; Dom´ınguez, G. Unpublished results.

Carbene Transfer from Metal-Carbene Complexes
Table 1. Self-dimerization of Complexes 10
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 853
entry
compd
catalyst (load)a/additive
solvent
T
reaction time (h)b
11 E/Zc
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10b
10b
10b
10c
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (2%)/Et3N
THF
THF
THF
THF
THF
THF
hexane
C6H6
Et2O
MeCN
CH2Cl2
THF
THF
THF
THF
THF
THF
THF
THF
rt
rt
rt
rt
rt
0 °C
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
1.0
12.0
0.75
1.5
3.0
2.0
20.0
4.0
8.0
0.25
1.5
21.0
5.0
1.25
0.75
1.0
2.5
18.0
5.0
2:1
4:1
2.5:1
3.6:1
2:1
2.5:1
2.4:1
2.2:1
2.6:1
2:1
2.2:1
5.1:1
2.1:1
2.7:1
2:1
53
58
65
72
52
48
50
63
57
94
68
49
80
64
72
62
55
40
46
Pd(OAc)2 (10%)/Et3N/PPh3 (30%)a
Pd(OAc)2 (10%)/Et3N/AsPh3 (30%)a
Pd(OAc)2 (10%)/Et3N/SbPh3 (30%)a
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(C) (5%)
Pd2(dba)3‚CHCl3 (5%)
PdCl2(PPh3)2 (5%)/Et3N
PdCl2(MeCN)2 (5%)/Et3N
Pd(OAc)2 (10%)/Et3N
Pd(PPh3)4 (3%)
Pd(PPh3)4 (0.6%)
Pd(OAc)2 (10%)/Et3N
2:1
2:1
2:1
1:1
a Referred to the carbene complex. b The reactions were followed by TLC until complete disappearance of the spot corresponding to the starting
c
1
carbene complex. Determined by integration of the signals corresponding to the MeO-groups in the H NMR spectra of the crude reaction
mixtures. Each experiment was repeated at least twice and the value given is the average of both experiments.
Scheme 3
to that experienced by aryl-substituted complexes (Scheme 4,
Table 2). For those reactions forming compounds 14, the
influence of the Pd-catalyst in the reaction selectivity was
negligible, but the reactions were considerably faster for Pd-
(II)/Et3N catalysts (entries 5 and 6 in Table 2) than for Pd(0)
catalysts (entries 2, 3 and 4 in Table 2). Due to the fact that in
group 6 alkyl-carbene complexes the hydrogen â-elimination
induced by bases to form vinyl ethers is a known reaction, it
can be though that enol-ethers 13 are formed without participa-
tion of the Pd-catalyst when Et3N is present. To exclude this
possibility complex 12b was stirred in a THF solution in the
presence of Et3N for 3 h but in the absence of Pd-catalyst. The
complex was recovered unchanged. It is clear that the elimina-
tion reaction has to occur in the presence of the Pd-catalyst.
Phenyltungsten-carbene 10c was also reactive in this kind of
reactions, forming the corresponding dimer 11c in 46% yield
when submitted to treatment with Pd(OAc)2 in the presence
clearly be advantageous over the uncatalyzed process. Thus,
we turned our attention to Pd catalysts. The viability of the
dimerization of the carbene ligand of a group 6 alkoxycarbene
complex promoted by a Pd-catalyst was first studied using
complex 10a as the substrate. Reaction of this compound with
Pd(OAc)2 in the presence of Et3N using THF as solvent led to
a 2:1 E/Z mixture of 1,2-dimethoxydiphenylethene 11a (Scheme
3, Table 1). Lower loads of catalyst (2%) resulted in longer
reaction times and in an increase of the E-selectivity (entry 2,
Table 1). Addition of additives such as PPh3, AsPh3, or SbPh3
had little effect in the overall result of the reaction (entries 3-5,
Table 1). No appreciable variation on the E/Z isomer ratio of
the reaction products was found by changing the nature of the
solvent (entries 7-11, Table 1). Decreasing the temperature
from room temperature (rt) to 0 °C resulted in longer reaction
times, but it has no effect either in the nature of the products or
in the ratio of isomers. The use of (Ph3P)4Pd instead of Pd-
(OAc)2 in the reaction of complex 10b also resulted in a 2:1
mixture of compounds 11b. Again, a decrease of the catalyst
load brought about longer reaction times to consume the starting
carbene complex (entries 16-18, Table 1). Other Pd(II) and
Pd(0) catalysts, including Pd on charcoal, were equally efficient
in promoting the carbene ligand dimerization of complex 10a
(entries 12-15, Table 1).
Scheme 4
Table 2. Reaction of Alkyl-Substituted Carbene Complexes 12
with Different Pd-Catalysts
com-
entry pound
catalyst (10%)a
/additive
reaction
yield
time (h)b 13/14c 14 E/Zd (%)
e
1
2
3
4
5
6
7
12a Pd(OAc)2/Et3N
12a Pd(PPh3)4
12a Pd(C)
12a Pd2(dba)3‚CHCl3
12a PdCl2(PPh3)2/Et3N
12a PdCl2(MeCN)2/Et3N
12b Pd(OAc)2/Et3N
1
20
20
5
3
1
1
100:0
-
-
0:100 1.1:1 87
0:100 1.3:1 70
0:100 1.9:1 76
The catalyst used has a stronger influence on the nature of
the reaction products when the substituents on the carbene
carbon are methyl groups. Thus, alkyl carbene complexes 12a
and 12b gave exclusively vinyl ethers 13a and 13b, respectively,
in the presence of Pd(OAc)2/Et3N. Clearly, for alkyl-substituted
carbene complexes a process of hydrogen â-elimination com-
petes favorably in these conditions with the carbene ligand
dimerization. However, other Pd-catalysts gave the carbene
ligand dimerization products 14 in a process that is analogous
5:95
8:92
100:0
1.3:1 72
1.1:1 78
-
65
a Referred to the carbene complex. b The reaction were followed by
TLC until complete disappearance of the spot corresponding to the
carbene complex. c Determined by 1H NMR analysis of the crude
reaction mixture. d Determined by integration of the signals corre-
sponding to the Me groups. Each experiment was repeated at least twice
and the value given is the average of both experiments. e Compound
13a was unstable. See Experimental Section.

854 J. Am. Chem. Soc., Vol. 123, No. 5, 2001
Sierra et al.
Scheme 5
and enediyne 23 obtained from carbene complex 17a in 51%
yield. In this case PPh3 was added to the reaction as it was
found that better yields were obtained in this way. R,â-
Unsaturated tungsten-carbene complexes 16b and 17b were
again reactive, leading to triene 22 and enediyne 23, respectively,
as in the case of their chromium counterparts (Scheme 5).
The possibility to effect intramolecular carbene ligand dimer-
izations to obtain cyclic compounds was next addressed. Thus,
bis[pentacarbonyl(alkoxy)(phenyl)carbene]chromium(0) com-
plexes 28, differing exclusively in the length of the tether
separating both carbene ligands, were submitted to reaction with
Pd(OAc)2 under the usual conditions. Bicyclic enol ethers 29
were obtained in good to low yields depending on the size of
the ring formed. In fact, yields decreased steadily as the ring
size increased, being maximum for six- and minimum for nine-
membered rings. An equal improvement in the formation of
polymeric materials of unknown structure was also observed
while the ring size increased. Complexes 30 having both metal
nuclei joined by an o-xylylene group formed also the corre-
sponding bicyclic derivatives. It should be noted that complexes
30b and 30c, bear methyl groups but exclusively gave the
dimerization products 31b and 31c. Although Pd(OAc)2/Et3N
was used as the catalyst, none of the expected vinyl ethers
arising from â-elimination processes were formed (Scheme 6).
Scheme 6
of Et3N. In clear contrast, pentacarbonyl[(dimethylamino)-
(phenyl)carbene)]chromium(0), 15a, and pentacarbonyl[(dim-
ethyl-amino)(p-bromophenyl)carbene)]chromium(0), 15b, com-
plexes were unreactive in the conditions used for alkoxycarbene
complexes 10. Their reactivity under harsher reaction conditions
and in the presence of deactivated olefins is discussed below.
The possibility to obtain polyene-conjugated systems using
this methodology was attractive due to increasing interest of
these compounds in material chemistry, especially those com-
pounds incorporating metal ends.20 Complexes 16-21 were
submitted to Pd(OAc)2/Et3N, and the corresponding polyene
derivatives 22-27 were obtained in fair to good yields (Scheme
5). Small amounts of the oxidation products were sometimes
obtained together with the mixture of enol ethers. It is
noteworthy that the presence of additional metallic centers in
the starting material is fully compatible with the dimerization
reaction, allowing the preparation of conjugated polyene systems
with metal moieties at both ends of the conjugated system.
Compound 25 was obtained in 73% yield and easily isomerizes
from a starting isomer ratio of 12:1 to a final 1:2 ratio after
column chromatography. Triene 26 was formed in essentially
quantitative yield but decomposed during purification, leading
to an isolated yield of 25%. The method was also applicable to
the synthesis of higher conjugated polyenes such as 27 that was
obtained in 85% yield from chromium-carbene complex 21,
A different process may still occur in these intramolecular
reactions. According to the results obtained at the moment, bis-
carbene complexes 32 should evolve in the presence of Pd-
(OAc)2/Et3N, either by â-elimination to yield the corresponding
bis-enolethers 33 or by carbene ligand dimerization to form
dioxacycles 34. The â-elimination product was observed for
complex 35 which would have led to a large ring had the
dimerization process occurred. Complex 32 (n ) 0) formed a
new carbene complex 37 almost instantaneously. Other com-
plexes 32 (n ) 1, 2, 3) reacted with Pd(OAc)2/Et3N or Pd-
(PPh3)4 forming transient, unidentified, highly colored inter-
mediates to yield finally complex reaction mixtures, from which
we were unable to separate any identifiable product (Scheme
7).
To explain the results obtained in these reactions it is
necessary to propose the transmetalation of the carbene ligand
from complex 38 to the Pd-catalyst to form a new Pd-carbene
complex like 39, probably through a heterobimetallic cyclo-
propane intermediate 40 that evolves to 39 by extrusion of the
M(CO)5 (M ) Cr, W) moiety. Evidence of formation of
transient Pd-carbene complexes was initially shown by Busac-
ca21 to explain the anomalous Stille reactions of methyl
(20) (a) Mu¨ller, T. J. J.; Netz, A.; Ansorge, M.; Schma¨lzlin, E.; Bra¨uchle,
C.; Meerholz, K. Organometallics 1999, 18, 5066 and pertinent references
therein. For a review, see: (b) Long, N. J. Angew. Chem, Int. Ed. Engl.
1995, 34, 6.

Carbene Transfer from Metal-Carbene Complexes
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 855
Scheme 7
Scheme 8
R-(tributylstannyl)acrylate, and the likeliness of the intermediacy
of Pd-carbenes in processes involving cine-substitution during
Stille reactions is now recognized.22 Assuming the initial
formation of a Pd-carbene complex 39, the subsequent trans-
metalation from a new molecule of the carbene complex would
form the Pd-bis-carbene complexes 41. The nature of the
reaction products is defined from the evolution of these Pd-
carbene intermediates 39 and 41 (Scheme 8). Thus, for aryl- or
vinyl-carbene complexes lacking R-hydrogens the evolution of
complex 39 to Pd-bis-carbene 41 occurred. Elimination of Pd
led to the observed products 42. The evolution of Pd-carbene
complexes having R-hydrogens follows a different pathway by
hydride transfer to the metal center to form a new Pd-hydrido
complex 43. This process competes favorably with the incor-
poration of a second carbene ligand, depending on the nature
of the catalyst. The Pd-hydrido intermediate 43 evolves by
reductive elimination forming the observed vinyl ethers, and
regenerating the catalyst (Scheme 8).
An analogous process should occur with bis-carbene com-
plexes 44. In these cases, the second transmetalation to form
the Pd-bis-carbene complex is intramolecular, forming com-
plexes 46 having both carbene ligands tethered by a methylene
or an o-xylylene chain. Complex 32 (n ) 0) form first
heterobimetallic Cr-Pd-bis-carbene complexes 45, but instead
of evolving through a second intramolecular transmetalation
from Cr to Pd, complex 45 (R1 ) R2 ) Me, n ) 0) experiments
an intermolecular C-H insertion, to form complex 37 by Pd
reductive elimination. The reasons why complexes 32 (n ) 1,
2, 3) yield complex reaction mixtures are not yet fully
understood. The clear bias of complexes 30b-c by the intramo-
lecular dimerization reaction in detriment of the hydrogen
â-elimination and the intermolecular dimerization reactions, may
be conformational in origin. In these cases the double trans-
metalation to form bimetallic Pd-carbene 46 should be favored
by the chelating effect of the o-xylylene moiety.23 The resulting
complex has both carbene ligands attached to the Pd-center,
and the metalla-ring may be unable to adopt the required syn-
disposition to experiment the â-elimination process. Evidently,
the double metalation should be disfavored for larger rings and
the â-elimination is competing favorably with the intramolecular
carbene ligand dimerization. This hypothesis is supported by
the behavior of complex 35 that formed exclusively the double
â-elimination product 36 in high yield. The macrocycle resulting
from a dimerization has not been detected in the reaction
mixtures. The simultaneous presence of the two carbene ligands
in the Pd-center should be entropically disfavored in this case.
Hence, the double elimination product should arise from
elimination in different Pd-centers (Scheme 9).
As stated earlier amino-substituted chromium-carbene com-
plexes did not react at rt in the presence of Pd(OAc)2 in the
conditions used to dimerize alkoxychromium(0)-carbenes.
Thus, pentacarbonyl[(N,N-dimethylamino)(p-bromophenyl)car-
bene]chromium(0), 15b, remained unaltered after 78 h of
reaction at rt. Increasing the temperature resulted in the
formation of N,N-dimethyl-p-bromobenzamide and p-bromo-
benzaldehyde after prolonged reaction times. We thought that
in these cases the carbene ligand dimerization should be
precluded, and thence, the possibility to effect the carbene
transfer to olefins in the presence of Pd-catalysts would be
opened using aminocarbene complexes. Thus, complex 15b was
then reacted with methyl acrylate and acrylonitrile in the
presence of Pd(OAc)2 (10% and 2% molar ratio)/Et3N in boiling
THF. γ-Keto-ester 48b (75%) and γ-ketonitrile 48c (40%) were
respectively obtained, together with small amounts of N,N-
dimethyl-p-bromobenzamide and p-bromobenzaldehyde. The
analogous reaction of complex 15a with methyl acrylate and
Pd(OAc)2 (2%)/ Et3N or Pd(PPh3)4 (10% molar ratio) as the
catalyst gave γ-ketoester 48a (80%). It is known that compounds
analogous to 48 are formed by heating pentacarbonyl[(N,N-
dimethylamino)methylene]chromium(0) and different olefins.24
This fact raises the question of whether the reaction products
are formed without transmetalation to the catalyst or if this
transmetalation really occurs. Complex 15b was reacted with
methyl acrylate in boiling THF and in the absence of catalyst.
A mixture of N,N-dimethyl-p-bromobenzamide, formed by
oxidation of the complex during the prolonged heating, and
γ-ketoester 48b (4:1 ratio) was obtained after 48 h of reaction.
The distribution of products is clearly different from the
catalyzed process as the reaction time is considerably shorter
(21) Busacca, C. A.; Swestock, J.; Johnson, R. E.; Bailey, T. R.; Musza,
L.; Rodger, C. A. J. Org. Chem. 1994, 59, 7553.
(22) (a) Farina, V.; Hossain, M. A. Tetrahedron Lett. 1996, 37, 6997.
(b) Quayle, P.; Wang, J.; Xu, J.; Urch, C. J. Tetrahedron Lett. 1998, 39,
489.
(23) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, California, 1987.
(24) Sierra, M. A.; Soderberg, B.; Lander, P. A.; Hegedus, L. S.
Organometallics 1993, 12, 3769.

856 J. Am. Chem. Soc., Vol. 123, No. 5, 2001
Sierra et al.
Scheme 9
(8 h) for the catalytic reaction. These results point to the
participation of Pd intermediates in the reactions of aminocar-
bene complexes and deactivated olefins (Scheme 10). It should
be noted that products derived from the Heck’s coupling on
the aryl bromide were not observed, although it has been
described that organic substrates related to complexes 15
produced high yields of coupling products25 under reaction
conditions analogous to those employed by us.26
ates in the thermal reaction of group 6 metal-carbene complexes
and olefins.4a-b This pathway may account for the observed
inertia of aminochromium(0)-carbenes in the absence of a
carbene acceptor (Scheme 11).
Scheme 11
Scheme 10
It is intriguing that for aminocarbenes the transmetalation to
Pd seems to be productive only when a carbene acceptor is
present. The observed products 48 would result from cyclization
of the Pd carbene and the carbene acceptor followed by transfer
of a â-hydrogen to the metal center of intermediate 49 and
reductive elimination on 50 to form enamine 51. Hydrolysis of
51 during workup would account for the obtained â-ketoderiva-
tives 48.27,28 However, this reaction pathway does not explain
the absence of transmetalation when the carbene acceptor is not
present. A more likely reaction pathway may involve trans-
metalation to Pd from the chroma-cyclobutane 52 initially
formed by cyclization of the chromium-carbene and the carbene
acceptor. Chroma-cyclobutanes are the accepted first intermedi-
To conclude, group 6 metal-carbene complexes can be used
as carbene sources in the presence of Pd-catalysts. Inter- and
intramolecular carbene ligand dimerization processes of the
metal-carbene complexes lead to linear or cyclic derivatives,
in reactions that in most cases are effected with low catalyst
loads and that occurred without the formation of side products.
In fact, although the isolated yields listed throughout this paper
are in some cases low, this is not due to byproduct formation
but to the unstability of the final products. For complexes having
acidic hydrogens in groups attached to the carbene carbon,
elimination competes favorably with carbene ligand dimerization
in some cases, and enol ethers are thus formed. Nevertheless,
the process of â-elimination may be almost inhibited by
changing the catalyst. In clear contrast bis-carbene complexes,
having the metal nuclei tethered by an aliphatic chain and alkyl
groups in both carbene carbons, either decompose to mixtures
of unknown products or evolve to new mononuclear carbene
complexes through an intramolecular C-H insertion. To explain
the observed results the transmetalation of Cr(0) to Pd(0) and
the intermediacy of Pd-carbene complexes in the catalytic cycle
is proposed. The structure of these intermediate complexes and
hence the structure of the starting group 6 metal-carbene
complex define the fate of the reaction, especially the possibility
(25) Heck, R. F. Org. React. 1982, 27, 345.
(26) The Stille’s coupling of diverse ethynyl chromium(0)- and tungsten-
(0)-carbene complexes and organometallic iodides, has been reported by
Fischer: (a) Hartbaum, C.; Roth, G.; Fischer, H. Chem. Ber. 1997, 130,
479. (b) Hartbaum, C.; Mauz, E.; Roth, G.; Weissenbach, K.; Fischer, H.
Organometallics 1999, 18, 2619.
(27) Compounds 51 have been detected sometimes as minor products
1
in the H NMR of crude reaction mixtures.
(28) An alternative to the mechanism written in Scheme 11 would be to
consider that the formation of an intermediate Pd-aminocarbene occurs,
followed by cyclopropanation of the olefin. Thus, compounds 51 would be
then formed by cyclopropane ring opening. The formation in low yields of
products analogous to 51 in the reaction of pentacarbonyl[(pyrrolydinyl)-
(phenyl)carbene]chromium(0) and acrylonitrile in boiling cyclooctane (140
°C) have been explained by Reissig by the ring opening of a transient
aminocyclopropane (see ref 4h). However, taking into account that the
aminocarbene complexes tested are stable in boiling THF for hours and
that there is complete absence of dimerization products in these reactions
makes this alternative mechanism, albeit attractive, little believable in our
case.

Carbene Transfer from Metal-Carbene Complexes
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 857
and the residue was dissolved in 10 mL of degassed water. Me3OBF4
(2.20 g, 14.8 mmol) was added slowly to the solution at 0 °C and stirred
for 10 min. The mixture was extracted with EtOAc and dried over
MgSO4. The solvent was removed in vacuo to yield 2.6 g (79%) of a
of hydrogen â-elimination. Finally, aminocarbene complexes
need harsher reaction conditions to effect the transfer of the
carbene ligand, and even then this only occurs in the presence
of electron-poor olefins. The corresponding insertion/hydrolysis
products resulted in these cases. Efforts to effect the transfer of
the carbene ligand to double bonds to form cyclopropanes in
very mild conditions by employing catalysts based on metals
other than Pd, as well as to elucidate the nature of the
Pd-intermediates, are ongoing in our group.
1
red solid identified as 10b. H NMR (300 MHz): δ 7.34 (d, J ) 8.3
Hz, 2H, ArH), 7.19 (d, J ) 8.3 Hz, 2H, ArH), 4.64 (s, 3H, OCH3). 13
C
NMR (75 MHz): δ 348.3 (CrdC), 223.7 (CO trans), 215.9 (CO cis),
152.0 (C ipso), 136.9 (C ipso), 131.4, 125.3 (aromatic CH), 67.4
(OCH3). IR (KBr): ν 2100, 1960, 1925 cm-1. C13H7BrCrO6: Calcd C
39.92, H 1.80, Br 20.43. Found C 40.12, H 1.97, Br 20.65.
Pentacarbonyl[(methyl)(o-methylbenzyloxy)carbene]chromium-
(0), 12b. Following the general procedure described by Hegedus32 using
2 g (6.5 mmol) of pentacarbonyl[(methyl)[(tetramethylammonio)oxy]-
carbene]chromium(0), 0.48 mL (6.5 mmol) of acetyl bromide and 0.79
g (6.5 mmol) of o-methylbenzyl alcohol was obtained 12b (1.22 g,
56%) as an orange solid.1H NMR (300 MHz): δ 7.33-7.17 (m, 4H,
ArH), 5.83 (br s, 2H, OCH2), 2.91 (s, 3H, CH3), 2.32 (s, 3H, CH3).13C
NMR (75 MHz): δ 358.8 (CrdC), 223.3 (CO trans), 216.5 (CO cis),
137.5 (C ipso), 132.3 (C ipso), 130.9, 130.5, 126.5 (aromatic CH), 81.8
(OCH2), 49.7 (CH3), 19.1 (CH3). IR (KBr): ν 2080, 1990, 1950, 1900,
1240 cm-1. C15H12CrO6: Calcd C 52.95, H 3.55. Found C 53.17, H
3.72.
Experimental Section
General Procedure. 1H NMR and 13C NMR spectra were recorded
at 22 °C in CDCl3, on a Varian XL-300S (300 and 75.4 MHz), Bruker
250-AM (250 and 63 MHz) and Bruker 200-AC (200 and 50 MHz)
spectrometers. Chemical shifts are given in ppm relative to TMS (1H,
0.0 ppm) or CDCl3 (13C, 77.0 ppm). IR spectra were taken on a Perkin-
Elmer 781 spectrometer. Mass spectra were carried out on a GC-MS
HP-5989 (60 eV) mass spectrometer using methanol as solvent. Melting
points were measured on an Electrothermal digital melting point
apparatus (Gallenkamp) and are uncorrected. All solvents used in this
work were purified by distillation and were freshly distilled immediately
before use. Tetrahydrofuran (THF) and diethyl ether (Et2O) were
distilled from sodium benzophenone, CH2Cl2, and Et3N from CaH2.
Flame-dried glassware and standard Schlenck techniques were used
for moisture-sensitive reactions. Merck silica gel (230-400 Mesh) was
used as the stationary phase for purification of crude reaction mixtures
by flash column chromatography. Identification of products was made
by TLC (kiesegel 60F-254). UV light (λ ) 254 nm) and 5%
phosphomolybdic acid solution in 95% EtOH were used to develop
the plates. All commercially available compounds were used without
further purification. The following products were prepared according
to literature methods:
Pentacarbonyl[(ethoxy)(methyl)carbene]chromium(0),29 pentacarbon-
yl[(methoxy)(methyl)carbene]chromium(0),30 pentacarbonyl[(methoxy)-
(phenyl)carbene]chromium(0),30 pentacarbonyl[(ethoxy) (phenyl)car-
bene]tungsten(0),31 pentacarbonyl[(benzyloxy)(methyl)carbene]chromium-
(0),32 pentacarbonyl[(ethoxy)(2-phenylethenyl)carbene]chromium(0),33
pentacarbonyl[(ethoxy)(2-phenylethenyl)carbene]tungsten(0),33 penta-
carbonyl[(ethoxy)(2-furylethenyl)carbene]chromium(0),33 pentacarbon-
yl[(ethoxy)(4-phenylbutadienyl)carbene]chromium(0),33 pentacarbonyl-
[(ethoxy)(2-phenylethynyl)carbene]chromium(0),34 pentacarbonyl[(ethoxy)-
(2-phenylethynyl)carbene]tungsten(0),34 pentacarbonyl[(methyl)(tetra-
methylammonio)oxycarbene]chromium(0),35 pentacarbonyl[(phenyl)-
(tetramethylammonio)oxycarbene]chromium(0),35 decacarbonyl[µ-
(ethylen-1,2-dioxy)bis(phenyl)carbene]dichromium(0),9 decacarbonyl[µ-
(ethylen-1,2-dioxy)bis(methyl) carbene]dichromium(0),36 pentacarbonyl-
[(dimethylamino)(phenyl)carbene)]chromium(0),37 tricarbonylchromium-
(0)benzaldehyde.38
Pentacarbonyl[(p-bromophenyl)(dimethylamino)carbene]chro-
mium(0), 15b. To a solution of the carbene complex 10b (200 mg,
0.5 mmol) in 10 mL of CH2Cl2 was added dimethylamine (liberated in
situ from a slurry of 125 mg (1.5 mmol) of dimethylamine chlorhydrate
and 0.2 mL (1.5 mmol) of Et3N in CH2Cl2) at rt. The red solution
became yellow after 10 min. Then, the mixture was stirred for an
additional 20 min, and the solvent was removed in vacuo to give 195
mg (96%) of a yellow solid identified as 15b. Complex 15b was used
1
without further purification. H NMR (200 MHz): δ 7.48 (d, J ) 8.4
Hz, 2H, ArH), 6.58 (d, J ) 8.4 Hz, 2H, ArH), 3.97 (s, 3H, CH3), 3.00
(s, 3H, CH3). 13C NMR (75 MHz): δ 275.6 (CrdC), 223.4 (CO trans),
217.0 (CO cis), 151.1 (C ipso), 131.8, 120.7 (aromatic CH), 119.5 (C
ipso), 51.4 (CH3), 46.1 (CH3). IR (KBr): ν 2052, 1971, 1897 cm-1
.
C14H10BrCrNO5: Calcd C 41.61, H 2.49, N 3.47, Br 19.77. Found C
41.85, H 2.65, N 3.61, Br 20.03.
Synthesis of R,â-Unsaturated Alkoxychromium(0)-Carbenes,
19-20. All of these compounds were synthesized by the method
described by Aumann.33 To an equimolecular solution of pentacarbonyl-
[(ethoxy)(methyl)carbene]chromium(0) (1 mmol) and the corresponding
aldehyde (1 mmol) in anhydrous Et2O (5 mL) was added Et3N (4 mmol)
at rt. Then, TMSCl (3 mmol) was added dropwise at the same
temperature, and the mixture was stirred until the disappearance of the
starting material (checked by TLC). The solvent was removed in vacuo
and the product purified by flash column chromatography under argon
pressure (SiO2, 9:1 hexane/Et2O).
Pentacarbonyl[(ethoxy)(2-ferrocenylethenyl)carbene]chromium-
(0), 19. The general procedure was followed, using 1.21 g (4.58 mmol)
of pentacarbonyl [(ethoxy)(methyl)carbene]chromium(0), 1.00 g (4.58
mmol) of ferrocenecarbaldehyde, 2.55 mL (18.32 mmol) of Et3N, and
1.78 mL (13.74 mmol) of TMSCl. After 3 days of reaction and further
flash column chromatography, 1.14 g (54%) of 19 as a black crystalline
solid was obtained. 1H NMR (200 MHz): δ 7.39 (d, J ) 15.0 Hz, 1H,
CHdCH-Fc), 7.09 (d, J ) 15.0 Hz, 1H, CHdCH-Fc), 4.90 (q, J )
7.1 Hz, 2H, OCH2), 4.53 (m, 4H, Cp), 4.13 (s, 5H, Cp), 1.58 (t, J )
7.1 Hz, 3H, CH3). 13C NMR (75 MHz): δ 324.1 (CrdC), 224.3 (CO
trans), 217.3 (CO cis), 138.4 (CHdCH-Fc), 137.4 (CHdCH-Fc),
78.4 (Cp), 75.1 (OCH2), 72.5 (Cp), 70.2 (Cp), 69.8 (Cp), 15.1 (CH3).
IR (KBr): ν 2052, 1924, 1591, 1576, 1215, 1138 cm-1. C20H16-
CrFeO6: Calcd C 52.20, H 3.50. Found C 52.44, H 3.68.
Pentacarbonyl[(ethoxy)(2-(tricarbonylchromiumphenyl)ethenyl)-
carbene]chromium(0), 20. The general procedure was followed, using
0.56 g (2.11 mmol) of pentacarbonyl[(ethoxy)(methyl)carbene]chromium-
(0), 0.51 g (2.11 mmol) of tricarbonylchromium(0)benzaldehyde, 1.17
mL (8.45 mmol) of Et3N, and 0.82 mL (6.33 mmol) of TMSCl. After
4 days and flash column chromatography, 140 mg (16%) of 20 as an
unstable deep purple crystalline solid was obtained. 1H NMR (300
MHz): δ 7.62 (d, J ) 15.2 Hz, 1H, CHdCH-Ar), 6.31 (d, J ) 15.2
Hz, 1H, CHdCH-Ar), 5.56 (d, J ) 6.0 Hz, 2H, ArH), 5.45 (t, J )
6.2 Hz, 1H, ArH), 5.27 (t, J ) 6.4 Hz, 2H, ArH), 5.06 (q, J ) 7.1 Hz,
Synthesis of Carbene Complexes. Pentacarbonyl[(p-bromophen-
yl)(methoxy)carbene]chromium(0), 10b. To a solution of dibro-
mobenzene (2 g, 8.5 mmol) in 10 mL of dry Et2O was added 3.4 mL
(8.5 mmol) of n-BuLi (2.5 M in hexane) at -78 °C. After stirring for
30 min, the solution was transferred via cannula at 0 °C to a suspension
of Cr(CO)6 (1.86 g, 8.5 mmol) in 20 mL of Et2O at rt. The mixture
was refluxed for 3 h, the solvent was removed under reduced pressure,
(29) Hegedus, L. S.; McGuire, M. A.; Schultze, L. M. Organic Syntheses;
John Wiley & Sons: New York, 1993; Collect. Vol. VIII, p 21.
(30) Fischer, E. O.; Aumann, R. Chem. Ber. 1968, 101, 963.
(31) Herrmann, W. A. Synthetic Methods of Organometallic and
Inorganic Chemistry; Thieme: Stuttgart, New York, 1997.
(32) Hafner, A.; Hegedus, L. S.; deWeck, G.; Hawkins, B.; Do¨tz, K. H.
J. Am. Chem. Soc. 1988, 110, 8413.
(33) Aumann, R., Heinen, H. Chem. Ber. 1987, 120, 537.
(34) Aumann, R., Hinterding, P. Chem. Ber. 1993, 126, 421.
(35) Fischer, E. O.; Maasbo¨l, A. Chem. Ber. 1967, 100, 2445.
(36) Dumas, S.; Lastra, E.; Hegedus, L. S. J. Am. Chem. Soc. 1995, 117,
3368.
(37) Imwinkelried, I.; Hegedus, L. S. Organometallics 1988, 7, 702.
(38) (a) Pauson, P. L.; Mahaffy, C. A. L. Inorg. Synth. 1979 19. 155.
(b) Solladie´-Cavallo, A.; Solladie´, G.; Tsamo, E. J. Org. Chem. 1979, 44,
4189.

858 J. Am. Chem. Soc., Vol. 123, No. 5, 2001
Sierra et al.
2H, OCH2), 1.63 (t, J ) 7.1 Hz, 3H, CH3). IR (CCl4): ν 2058, 1981,
Pentacarbonyl[(o-hydroxymethylbenzyloxy) (methyl)carbene]chro-
mium(0): 1H NMR (200 MHz): δ 7.41-7.34 (m, 4H, ArH), 5.98 (br
s, 2H, OCH2), 4.75 (s, 2H, CH2OH), 2.95 (s, 3H, CH3). 13C NMR (75
MHz): δ 358.6 (CrdC), 223.1 (CO trans), 216.2 (CO cis), 139.0 (C
ipso), 132.1(C ipso), 129.4, 128.6, 128.2 (aromatic CH), 62.7 (OCH2).
The signals corresponding to carbons CH3 and OCH2 could not be
detected. IR (CCl4): ν 2064, 1983, 1942, 1246 cm-1. C15H12CrO7:
Calcd C 50.57, H 3.40. Found C 50.80, H 3.56.
1946, 1915, 1583, 1549, 1254 cm-1
.
General Procedure for the Synthesis of Bis-carbene Complexes,
28. All of these compounds were synthesized following the general
method described by Wulff.9 To a solution of the corresponding
ammonium salt (1 mmol) in anhydrous CH2Cl2 (10 mL/mmol) at -30
°C was added dropwise (1 mmol) of pivaloyl chloride or acetyl bromide
(as stated in each case). The mixture was stirred for 1 h, and then, the
diol (0.5 mmol) was added at the same temperature. Afterward, the
reaction was allowed to proceed for an additional 16 h at -30 °C, and
slowly allowed to reach rt. The crude reaction was extracted with CH2-
Cl2 and washed with a saturated solution of NaHCO3; the solvent was
removed in vacuo and submitted to flash column chromatography under
argon pressure (SiO2, 9:1 hexane/EtOAc) to yield pure compounds 28.
Decacarbonyl[µ-(propylene-1,3-dioxy)bis(phenylcarbene)]dichro-
mium(0), 28b. The general procedure was followed, using 0.94 g (2.45
mmol) of pentacarbonyl[(phenyl)(tetramethylammonio) oxycarbene]-
chromium(0), 0.30 mL (2.45 mmol) of pivaloyl chloride, and 90 µL
(1.22 mmol) of freshly distilled propanediol. 28b (0.28 g, 36%) was
obtained as a red solid. 1H NMR (200 MHz): δ 7.32 (br s, 6H, ArH),
7.09 (br s, 4H, ArH), 4.94 (m, 4H, OCH2), 2.64 (qt, J ) 5.9 Hz, 2H,
CH2).13C NMR (75 MHz): δ 351.2 (CrdC), 224.1 (CO trans), 215.9
(CO cis), 153.9 (C ipso), 130.1, 128.3, 122.2 (aromatic CH), 75.9
(OCH2), 29.2 (CH2). IR (CCl4): ν 2062, 1982, 1950, 1109 cm-1. C27H16-
Cr2O12: Calcd C 50.96, H 2.53. Found C 51.14, H 2.76.
Decacarbonyl[µ-(o-xylylenedioxy)(methyl)(phenyl)biscarbene]-
dichromium(0), 30c. The general procedure was followed, using 0.31
g (0.84 mmol) of pentacarbonyl[(phenyl)(tetramethylammonio)-
oxycarbene]chromium(0), 100 µL (0.84 mmol) of pivaloyl chloride,
and 0.30 g (0.84 mmol) of pentacarbonyl[(o-hydroxymethyl- benzyl-
oxy)(methyl)carbene]chromium. 30c (270 mg, 51%) was obtained as
1
a dark red solid. H NMR (300 MHz): δ 7.49 (br s, 4H, ArH), 7.33
(br s, 3H, ArH), 7.15 (br s, 2H, ArH), 5.92 (s, 2H, OCH2), 5.88 (s, 2H,
OCH2), 2.80 (s, 3H, CH3). 13C NMR (75 MHz): δ 359.8 and 350.6
(CrdC), 223.9 and 223.0 (CO trans), 216.2 and 216.0 (CO cis), 153.5
(C ipso), 133.6 (C ipso), 132.9 (C ipso), 130.5, 130.2, 130.0, 128.3,
122.7 (aromatic CH), 79.8 (OCH2), 79.4 (OCH2), 49.7 (CH3). IR
(KBr): ν 2064, 1986, 1948, 1220 cm-1. C27H16Cr2O12: Calcd C 50.96,
H 2.53. Found C 51.20, H 2.68.
Decacarbonyl[µ-(1,16-pentaethyleneglycoxy)bis(methyl)carbene)]-
dichromium(0), 35. The general procedure was followed, using 1.5 g
(4.85 mmol) of pentacarbonyl[(methyl)(tetramethylammonio)oxycarbene]-
chromium(0), 0.36 mL (4.85 mmol) of freshly distilled acetyl bromide,
and 0.61 g (2.42 mmol) of pentaethyleneglycol. 35 (0.74 g, 45%) was
Decacarbonyl[µ-(butylene-1,4-dioxy)bis(phenylcarbene)]dichro-
mium(0), 28c. The general procedure was followed, using 1.25 g (3.37
mmol) of pentacarbonyl[(phenyl)(tetramethylammonio) oxycarbene]-
chromium(0), 0.41 mL (3.37 mmol) of pivaloyl chloride, and 0.15 mL
(1.68 mmol) of freshly distilled 1,4-butanediol. 28c (0.48 g, 44%) was
1
obtained as an orange oil. H NMR (200 MHz): δ 4.95 (br s, 4H,
OCH2), 3.96 (m, 4H, OCH2), 3.65 (m, 6H, OCH2), 3.60 (s, 6H, OCH2),
2.91 (s, 6H, CH3). 13C NMR (75 MHz): δ 359.3 (CrdC), 223.2 (CO
trans), 216.3 (CO cis), 79.8 (OCH2), 70.9 (OCH2), 70.5 (OCH2), 69.1
(OCH2), 48.8 (CH3). IR (CCl4): ν 2064, 1983, 1942, 1252 cm-1. C24H26-
Cr2O16: Calcd C 42.74, H 3.89. Found C 42.99, H 4.02.
General Procedure for the Pd Catalyzed Reactions of Alkoxy-
chromiun(0) and Alkoxytungsten(0) Carbene Complexes. A THF
solution (4 mL/mmol) of the carbene was placed in a flame-dried airless
flask containing a magnetic stirring bar, degassed by evacuation/back-
fill with argon (3 times). Pd(OAc)2 (0.1 mmol, 10%) and Et3N (1.1
mmol) were added at rt, and the mixture was stirred until the
disappearance of the starting material (checked by TLC). The solvent
was distilled under reduced pressure, and the residue was dissolved in
ethyl acetate and filtered through Celite. The solvent was removed in
vacuo, and the residue was purified by flash column chromatography
(SiO2, 10:1 hexane:EtOAc) or molecular distillation.
1
obtained as a dark red solid. H NMR (200 MHz): δ 7.32 (m, 6H,
ArH), 7.16 (m, 4H, ArH), 4.83 (br s, 4H, OCH2), 2.22 (br s, 4H,
CH2).13C NMR (75 MHz): δ 350.1 (CrdC), 224.1 (CO trans), 216.1
(CO cis), 153.5 (C ipso), 130.1, 128.3, 122.5 (aromatic CH), 79.7
(OCH2), 27.1 (CH2). IR (CCl4): ν 2062, 1982, 1946, 1215 cm-1. C28H18-
Cr2O12: Calcd C 51.70, H 2.79. Found C 51.95, H 2.97.
Decacarbonyl[µ-(pentylene-1,5-dioxy)bis(phenylcarbene)]dichro-
mium(0), 28d. The general procedure was followed, using 1.27 g (3.43
mmol) of pentacarbonyl[(phenyl)(tetramethylammonio) oxycarbene]-
chromium(0), 0.42 mL (3.43 mmol) of pivaloyl chloride, and 0.18 mL
(1.71 mmol) of 1,5-pentanediol. 28d (0.62 g, 55%) was obtained as a
dark red oil. 1H NMR (300 MHz): δ 7.32 (m, 6H, ArH), 7.15 (m, 4H,
ArH), 4.79 (br s, 4H, OCH2), 2.06 (qt, J ) 6.7 Hz, 4H, CH2), 1.75 (qt,
J ) 6.9 Hz, 2H, CH2).13C NMR (75 MHz): δ 349.8 (CrdC), 224.1
(CO trans), 216.0 (CO cis), 153.6 (C ipso), 130.1, 128.2, 122.5
(aromatic CH), 80.4 (OCH2), 29.2 (CH2), 22.7 (CH2). IR (CCl4): ν
2062, 1982, 1948, 1215 cm-1. C29H20Cr2O12: Calcd C 52.42, H 3.03.
Found C 52.68, H 2.90.
Decacarbonyl[µ-(o-xylylenedioxy)bis(phenylcarbene)]dichromium-
(0), 30a. The general procedure was followed, using 1.38 g (3.7 mmol)
of pentacarbonyl [(phenyl)(tetramethylammonio) oxycarbene]chro-
mium(0), 0.45 mL (3.7 mmol) of pivaloyl chloride, and 265 mg (1.85
mmol) of o-hydroxymethylbenzyl alcohol. 30a (0.47 g, 36%) was
obtained as a dark-red oil.1H NMR (200 MHz): δ 7.46 (br s, 4H, ArH),
7.29 (m, 6H, ArH), 7.04 (m, 4H, ArH), 5.78 (s, 4H, OCH2).13C NMR
(75 MHz): δ 350.8 (CrdC), 224.1 (CO trans), 215.9 (CO cis), 153.3
(C ipso), 133.3 (C ipso), 130.2, 130.0, 128.3, 122.3 (aromatic CH),
79.3 (OCH2). IR (CCl4): ν 2064, 1982, 1952, 1195 cm-1. C32H18-
Cr2O12: Calcd C 55.03, H 2.60. Found C 55.25, H 2.78.
1,2-Dimethoxy-1,2-diphenylethene, 11a.39 From carbene complex
10a (312 mg, 1 mmol), Pd(OAc)2 (22 mg, 0.1 mmol) and 0.15 mL
(1.1 mmol) of Et3N after 1 h was obtained 11a as a mixture of isomers
E/Z (2:1), that were separated by flash column chromatography to give
1
22 mg (18%, Z-isomer) and 42 mg (35%, E-isomer). Z-isomer: H
NMR (300 MHz): δ 7.61 (d, J ) 7.3 Hz, 4H, ArH), 7.34 (t, J ) 7.3
Hz, 4H, ArH), 7.25 (t, J ) 7.3 Hz, 2H, ArH), 3.33 (s, 6H, OCH3). 13
C
NMR (75 MHz) δ 145.1 (Cq), 134.0 (C ipso), 128.2, 128.1, 127.7
(aromatic CH), 58.5 (OCH3). IR (CHCl3): ν 1640, 1265 cm-1
.
1
E-isomer: H NMR (300 MHz): δ 7.07 (s, 10H, ArH), 3.52 (s, 6H,
OCH3). 13C NMR (75 MHz): δ 143.2 (Cq), 134.6 (C ipso), 129.9,
128.0, 127.6 (aromatic CH), 58.2 (OCH3). IR (CHCl3): ν 1600, 1250
cm-1. C16H16O2: Calcd C 79.97, H 6.71. Found: C 80.25, H 6.95.
The same experiment was carried out using 4.5 mg (0.02 mmol, 2%)
of Pd(OAc)2 to give, after 12 h, 70 mg (58%) of 11a as an E/Z mixture
(4:1).
Decacarbonyl[µ-(o-xylylenedioxy)bis(methylcarbene)]dichromium-
(0), 30b. The general procedure was followed, using 3.0 g (9.71 mmol)
of pentacarbonyl [(methyl)(tetramethylammonio) oxycarbene]chro-
mium(0), 0.72 mL (9.71 mmol) of acetyl bromide, and 0.69 g (4.85
mmol) of o-hydroxymethylbenzyl alcohol. 30b (850 mg, 31%) as an
orange solid and pentacarbonyl[(o-hydroxymethylbenzyloxy)(methyl)-
carbene]chromium(0) as an orange oil (0.74 g, 42%) were obtained.
1H NMR (200 MHz): δ 7.52 (br s, 4H, ArH), 5.98 (br s, 4H, OCH2),
2.93 (s, 6H, CH3). 13C NMR (50 MHz): δ 360.2 (CrdC), 222.9 (CO
trans), 216.3 (CO cis), 133.2 (C ipso), 130.5, 130.2 (aromatic CH),
Carbene Ligand Dimerization of Complex 10a Using Different
Solvents. (Hexane). From carbene complex 10a (50 mg, 0.16 mmol),
Pd(OAc)2 (3.6 mg, 0.016 mmol) and 17 mg (0.17 mmol) of Et3N in 1
mL of hexane after 20 h was obtained 9.6 mg (50%) of 11a as a mixture
of isomers E/Z (2.4:1). (CH2Cl2). From carbene complex 10a (50 mg,
0.16 mmol), Pd(OAc)2 (3.6 mg, 0.016 mmol) and 17 mg (0.17 mmol)
of Et3N in 1 mL of CH2Cl2 after 1.5 h was obtained 13.0 mg (68%) of
11a as a mixture of isomers E/Z (2.2:1). (MeCN). From carbene
complex 10a (50 mg, 0.16 mmol), Pd(OAc)2 (3.6 mg, 0.016 mmol)
80.0 (OCH2), 50.2 (CH3). IR (KBr): ν 2064, 1988, 1909, 1252 cm-1
C22H14Cr2O12: Calcd C 46.01, H 2.46. Found C 46.27, H 2.58.
.
(39) Bachmann, W. E. J. Am. Chem. Soc. 1934, 56, 963.

Carbene Transfer from Metal-Carbene Complexes
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 859
and 17 mg (0.17 mmol) of Et3N in 1 mL of acetonitrile after 15 min
was obtained 18.0 mg (94%) of 11a as a mixture of isomers E/Z (2:1).
(Benzene). From carbene complex 10a (50 mg, 0.16 mmol), Pd(OAc)2
(3.6 mg, 0.016 mmol) and 17 mg (0.17 mmol) of Et3N in 1 mL of
benzene after 4 h was obtained 12.0 mg (63%) of 11a as a mixture of
isomers E/Z (2.2:1). (Et2O). From carbene complex 10a (50 mg, 0.16
mmol), Pd(OAc)2 (3.6 mg, 0.016 mmol) and 17 mg (0.17 mmol) of
Et3N in 1 mL of diethyl ether after 8 h was obtained 11 mg (57%) of
11a as a mixture of isomers E/Z (2.6:1).
Carbene Ligand Dimerization of Complex 10a Using Additives.
(PPh3). From carbene complex 10a (50 mg, 0.16 mmol), Pd(OAc)2
(3.6 mg, 0.016 mmol), 17 mg (0.17 mmol) of Et3N,and 12.6 mg (0.048
mmol) of PPh3 in 1 mL of THF after 45 min was obtained 12.4 mg
(65%) of 11a as a mixture of isomers E/Z (2.5:1). (AsPh3). From
carbene complex 10a (50 mg, 0.16 mmol), Pd(OAc)2 (3.6 mg, 0.016
mmol), 17 mg (0.17 mmol) of Et3N, and 15.1 mg (0.048 mmol) of
AsPh3 in 1 mL of THF after 1.5 h was obtained 13.9 mg (72%) of 11a
as a mixture of isomers E/Z (3.6:1). (SbPh3). From carbene complex
10a (50 mg, 0.16 mmol), Pd(OAc)2 (3.6 mg, 0.016 mmol), 17 mg (0.17
mmol) of Et3N, and 17.1 mg (0.048 mmol) of SbPh3 in 1 mL of THF
after 3 h was obtained 10 mg (52%) of 11a as a mixture of isomers
E/Z (2:1).
Carbene Ligand Dimerization of Complex 10a Using Other
Catalysts. (Pd on Charcoal, 5%). From carbene complex 10a (50
mg, 0.16 mmol) and Pd(C) (17 mg, 0.008 mmol), in 1 mL of THF
after 21 h was obtained 9.5 mg (49%) of 11a as a mixture of isomers
E/Z (5.1:1). (PdCl2(MeCN)2). From carbene complex 10a (50 mg, 0.16
mmol), PdCl2(MeCN)2 (2.1 mg, 0.008 mmol), and 18 mg (0.18 mmol)
of Et3N in 1 mL of THF after 45 min was obtained 13.9 mg (72%) of
11a as a mixture of isomers E/Z (2:1). (PdCl2(PPh3)2). From carbene
complex 10a (50 mg, 0.16 mmol), PdCl2(PPh3)2 (5.6 mg, 0.008 mmol),
and 18 mg (0.18 mmol) of Et3N in 1 mL of THF after 75 min was
obtained 12.3 mg (64%) of 11a as a mixture of isomers E/Z (2.7:1).
(Pd2(dba)3‚CHCl3). From carbene complex 10a (100 mg, 0.32 mmol)
and Pd2(dba)3‚CHCl3 (16.6 mg, 0.016 mmol) in 2 mL of THF after 5
h was obtained 31 mg (80%) of 11a as a mixture of isomers E/Z
(2.1:1).
1,2-Bis(p-bromophenyl)-1,2-dimethoxyethene, 11b. From carbene
complex 10b (392 mg, 1 mmol), Pd(OAc)2 (22 mg, 0.1 mmol), and
0.15 mL (1.1 mmol) of Et3N after 1.5 h was obtained 170 mg of a
mixture of 11b and Cr(CO)6. Molecular distillation of the mixture
afforded 120 mg (62%) of a white solid identified as an E/Z (2:1)
mixture of isomers of 11b. The isomers could be separated by flash
column chromatography to give 32 mg (16%, Z-isomer) and 72 mg
(37%, E-isomer). Z-isomer: 1H NMR (300 MHz): δ 7.48 (m, 8H,
ArH), 3.29 (s, 6H, OCH3). 13C NMR (75 MHz): δ 144.7 (Cq), 132.6
(C ipso), 131.4, 129.8 (aromatic CH), 121.8 (C ipso), 58.5 (OCH3). IR
(CHCl3): ν 1600, 1259 cm-1. E-isomer: 1H NMR (300 MHz) δ 7.25
(d, J ) 8.5 Hz, 4H, ArH), 6.95 (d, J ) 8.5 Hz, 4H, ArH), 3.51 (s, 6H,
OCH3). 13C NMR (75 MHz): δ 142.7 (Cq), 133.4 (C ipso), 131.4,
131.3 (aromatic CH), 121.9 (C ipso), 58.5 (OCH3). IR (CHCl3): ν 1630,
1260 cm-1. C16H14Br2O2: Calcd C 48.27, H 3.54, Br 40.14. Found C
48.43, H 3.28, Br 39.76. Reaction with Pd(PPh3)4 (3% Molar Ratio).
Following an analogous procedure, from carbene complex 10b (391
mg, 1 mmol) and Pd(PPh3)4 (39 mg, 0.033 mmol) after 2.5 h was
obtained 280 mg of 11b as a mixture of isomers E/Z (2:1) and Cr-
(CO)6. The Cr(CO)6 was eliminated by dissolving the residue in MeOH
and filtering through Celite to give 110 mg (55%) of the pure alkene.
Reaction with Pd(PPh3)4 (0.6% Molar Ratio). Following an analogous
procedure, from carbene complex 10b (391 mg, 1 mmol) and Pd(PPh3)4
(7.8 mg, 0.006 mmol) after 18 h was obtained 160 mg of 11b as a
mixture of isomers E/Z (2:1) and Cr(CO)6. The Cr(CO)6 was eliminated
by dissolving the residue in MeOH and filtering through Celite to give
80 mg (40%) of the pure alkene.
ArH), 3.71 (q, J ) 7.0 Hz, 4H, OCH2), 3.49 (q, J ) 7.0 Hz, 4H, OCH2),
1.25 (t, J ) 7.0 Hz, 6H, CH3), 1.06 (t, J ) 7.0 Hz, 6H, CH3). 13C
NMR (75 MHz): δ 144.1 (Cq), 142.6 (Cq), 135.4 (C ipso), 134.7 (C
ipso), 129.8, 128.3, 127.9, 127.8, 127.5, 127.3 (aromatic CH), 66.4
(OCH2), 65.9 (OCH2), 15.6 (CH3), 15.2 (CH3). IR (CCl4): ν 1665,
1599, 1551, 1259 cm-1. C18H20O2: Calcd C 80.56, H 7.51. Found C
80.41, H 7.65.
1,2-Dibenzyloxy-1,2-dimethyethene, 14a. From carbene complex
12a (100 mg, 0.31 mmol) and Pd on charcoal (5%) (66 mg, 0.031
mmol) in 2 mL of THF after 20 h was obtained 14a (28 mg, 70%) as
a mixture of isomers E/Z (1.3:1). Compound 14a was unstable for
further purification. 1H NMR (300 MHz): δ 7.40-7.23 (m, 20H, ArH),
4.71 (s, 4H, OCH2), 4.56 (s, 4H, OCH2), 1.77 (s, 6H, CH3), 1.71 (s,
6H, CH3). 13C NMR (50 MHz): δ 137.9 (Cq), 137.3 (Cq), 128.3, 128.2,
127.9, 127.8, 127.7, 127.5 (aromatic CH), 71.7 (OCH2), 71.2 (OCH2),
15.1 (CH3), 12.0 (CH3). IR (CCl4): ν 1608, 1587, 1261 cm-1
.
Carbene Ligand Dimerization of Complex 12a Using Other
Catalysts. (Pd(PPh3)4). From carbene complex 12a (50 mg, 0.15 mmol)
and Pd(PPh3)4 (17.3 mg, 0.015 mmol) in 1 mL of THF after 20 h was
obtained 17.5 mg (87%) of 14a as a mixture of isomers E/Z (1.1:1).
(Pd2(dba)3‚CHCl3). From carbene complex 12a (50 mg, 0.15 mmol)
and Pd2(dba)3‚CHCl3 (15.5 mg, 0.015 mmol) in 1 mL of THF after 5
h was obtained 15.2 mg (76%) of 14a as a mixture of isomers E/Z
(1.9:1). (PdCl2(PPh3)2). From carbene complex 12a (50 mg, 0.15
mmol), PdCl2(PPh3)2 (10.7 mg, 0.015 mmol), and 17 mg (0.17 mmol)
of Et3N in 1 mL of THF after 3 h was obtained 14.4 mg (72%) of 14a
as a mixture of isomers E/Z (1.3:1) and 5% of 13a. (PdCl2(MeCN)2).
From carbene complex 12a (50 mg, 0.15 mmol), PdCl2(MeCN)2 (4.0
mg, 0.015 mmol), and 17 mg (0.17 mmol) of Et3N in 1 mL of THF
after 1 h was obtained 15.6 mg (78%) of 14a as a mixture of isomers
E/Z (1.1:1) and 8% of 13a.
E,Z,E- and E,E,E-3,4-Diethoxy-1,6-diphenyl-1,3,5-hexatrienes, 22.
From carbene complex 16a (176 mg, 0.5 mmol), Pd(OAc)2 (11.4 mg,
0.05 mmol), and 80 µL (0.55 mmol) of Et3N after 24 h was obtained
90 mg of a dark brown solid, that after flash column chromatography
yielded 42 mg (53%) of an inseparable mixture of E/Z isomers of 22
(2:1 ratio). 1H NMR (300 MHz): δ 7.42 (d, J ) 7.6 Hz, M + m, 8H,
ArH), 7.31-7.16 (m, M + m, 12H, ArH), 7.07 (d, J ) 16.1 Hz, M,
2H, CHdCH-Ph), 6.99 (d, J ) 15.5 Hz, m, 2H, CHdCH-Ph), 6.81
(d, J ) 15.5 Hz, m, 2H, CHdCH-Ph), 6.72 (d, J ) 16.1 Hz, M, 2H,
CHdCH-Ph), 3.97 (q, J ) 7.0 Hz, M, 4H, OCH2), 3.84 (q, J ) 7.0
Hz, m, 4H, OCH2), 1.36 (t, J ) 7.0 Hz, m, 6H, CH3), 1.34 (t, J ) 7.0
Hz, M, 6H, CH3). 13C NMR (75 MHz): δ 147.9 (Cq), 145.7 (Cq),
137.3 (C ipso), 128.6, 128.3, 128.0, 127.6, 127.5, 126.7, 126.6, 120.4,
119.2 (aromatic and CH), 69.5 (OCH2), 67.9 (OCH2), 15.8 (CH3), 15.7
(CH3). IR (CHCl3): ν 1637, 1597, 1227, 1196 cm-1. C22H24O2: Calcd
C 82.46, H 7.55. Found C 82.63, H 7.81. Following an analogous
procedure, from carbene complex 16b (100 mg, 0.21 mmol), Pd(OAc)2
(4.7 mg, 0.021 mmol), and 23 mg (0.23 mmol) of Et3N after 15 h was
obtained 60 mg of a brown solid, that after flash column chromatog-
raphy yielded 17 mg (50%) of an inseparable mixture of E/Z isomers
of 22 (1:1 ratio).
3,4-Diethoxy-1,6-diphenyl-1,5-hexadiyn-3-ene, 23. From carbene
complex 17a (150 mg, 0.43 mmol), Pd(OAc)2 (9.6 mg, 0.043 mmol),
PPh3 (33.7 mg, 0.13 mmol,) and 48 mg (0.48 mmol) of Et3N after 16
h was obtained 110 mg of a brown oil identified as a mixture of E/Z
isomers (2:1 ratio) of 23. Further purification of the reaction mixture
by flash column chromatography allowed the separation of 35 mg (51%)
of the major isomer. 23 (major isomer): 1H NMR (200 MHz): δ 7.43-
7.36 (m, 4H, ArH), 7.29-7.23 (m, 6H, ArH), 4.12 (q, J ) 7.0 Hz, 4H,
OCH2), 1.31 (t, J ) 7.0 Hz, 6H, CH3). 13C NMR (50 MHz): δ 131.3
(Cq), 131.0, 128.4 (aromatic CH), 122.8 (C ipso), 97.5 (CtC), 82.9
(CtC), 66.1 (OCH2), 15.4 (CH3). IR (KBr): ν 2201 (CtC), 1577,
1256, 1198 cm-1. C22H22O2: Calcd C, 83.51, H 6.37. Found: C 83.41,
1
1,2-Diethoxy-1,2-diphenylethene, 11c. From carbene complex 10c
(150 mg, 0.33 mmol), Pd(OAc)2 (7.4 mg, 0.033 mmol), and 36 mg
(0.36 mmol) of Et3N after 5 h was obtained 120 mg of a mixture of
11c and W(CO)6. Molecular distillation of the mixture afforded 21 mg
(46%) of a white solid identified as an E/Z (1:1) mixture of isomers of
H 6.32. 23 (minor isomer): H NMR (200 MHz): δ 7.43-7.36 (m,
4H, ArH), 7.29-7.23 (m, 6H, ArH), 4.04 (q, J ) 7.0 Hz, 4H, OCH2),
1.30 (t, J ) 7.0 Hz, 6H, CH3). Following an analogous procedure, from
carbene complex 17b (150 mg, 0.31 mmol), Pd(OAc)2 (7.1 mg, 0.031
mmol), and 34 mg (0.34 mmol) of Et3N after 15 h was obtained 150
mg of a black solid, that after flash column chromatography yielded
15.6 mg (32%) of a mixture of E/Z isomers of 23 (1:1 ratio).
1
11c. H NMR (300 MHz): δ 7.74 (d, J ) 7.5 Hz, 4H, ArH), 7.32 (t,
J ) 7.8 Hz, 4H, ArH), 7.21 (t, J ) 7.2 Hz, 2H, ArH), 7.09 (s, 10H,

860 J. Am. Chem. Soc., Vol. 123, No. 5, 2001
Sierra et al.
E,Z,E- and E,E,E-3,4-Diethoxy-1,6-bis(2-furyl)-1,3,5-hexatrienes,
24. From carbene complex 17 (150 mg, 0.44 mmol), Pd(OAc)2 (10
mg, 0.04 mmol), and 70 µL (0.48 mmol) of Et3N after 24 h was
obtained 80 mg of a dark brown solid, that after flash column
chromatography yielded 37 mg (54%) of an inseparable mixture of
(CH and aromatic), 69.4 (OCH2), 67.9 (OCH2), 15.8 (CH3), 15.7 (CH3).
IR (KBr): ν 1626, 1599, 1581, 1215 cm-1
.
5,6-Diphenyl-2,3-dihydro-[1,4]dioxine, 29a. From bis-carbene com-
plex 28a (359 mg, 0.58 mmol), Pd(OAc)2 (13.3 mg, 0.058 mmol), and
90 µL (0.63 mmol) of Et3N after 2 h and further flash column
chromatography was obtained 29a (96 mg, 70%) as a white crystalline
1
E/Z isomers of 24 (2:1 ratio). H NMR (200 MHz): δ 7.33 (m, M +
1
m, 4H, Furan), 6.93 (d, J ) 15.3 Hz, m, 2H, CHdCH-Furyl), 6.92
(d, J ) 15.9 Hz, M, 2H, CHdCH-Furyl), 6.57 (d, J ) 15.9 Hz, M,
2H, CHdCH-Furyl), 6.49 (d, J ) 15.3 Hz, m, 2H, CHdCH-Furyl),
6.34 (m, M + m, 4H, Furan), 6.24 (m, M + m, 4H, Furan), 3.92 (q,
J ) 7.1 Hz, M, 4H, OCH2), 3.81 (q, J ) 7.0 Hz, m, 4H, OCH2), 1.34.
(t, J ) 7.0 Hz, m, 6H, CH3), 1.30 (t, J ) 7.1 Hz, M, 6H, CH3). 13C
NMR (75 MHz): δ 153.6 (Cq, Furan), 147.8 (Cq), 145.6 (Cq), 142.4,
142.1, 119.1, 117.9, 115.7, 115.3, 111.8, 109.1, 108.8 (CH and Furan),
69.5 (OCH2), 67.8 (OCH2), 15.7 (CH3). IR (KBr): ν 1599, 1261, 1229
cm-1. C18H20O4: Calcd C 71.98, H 6.71. Found: C 72.15, H 6.82.
E,Z,E- and E,E,E-3,4-Diethoxy-1,6-bis(ferrocenyl)-1,3,5-hexatrienes,
25. From carbene complex 19 (230 mg, 0.5 mmol), Pd(OAc)2 (11.4
mg, 0.05 mmol), and 80 µL (0.55 mmol) of Et3N after 45 min was
obtained 140 mg of a dark brown solid identified as a mixture of Z/E
isomers (12:1 ratio) of 25. Further purification of the reaction mixture
by flash column chromatography led to a partial isomerization of one
of the isomers to yield 31 mg (23%) of the former major isomer and
67 mg (50%) of the former minor isomer, respectively; both compounds
were obtained as dark brown-red solids. Triene 25 (major isomer):
1H NMR (200 MHz): δ 6.53 (d, J ) 15.4 Hz, 2H, CHdCH-Fc),
6.44 (d, J ) 15.4 Hz, 2H, CHdCH-Fc), 4.36 (m, 4H, Cp), 4.21 (m,
4H, Cp), 4.07 (s, 10H, Cp), 3.92 (q, J ) 7.1 Hz, 4H, OCH2), 1.33 (t,
J ) 7.1 Hz, 6H, CH3). 13C NMR (50 MHz): δ 144.2 (Cq), 125.9 (CHd
CH-Fc), 118.3 (CHdCH-Fc), 83.7 (Cp), 69.2 (Cp), 69.0 (Cp), 67.7
solid (mp 93-94 °C). H NMR (300 MHz): δ 7.17-7.15 (m, 4H,
ArH), 7.10-7.08 (m, 6H, ArH), 4.25 (s, 4H, OCH2). 13C NMR (75
MHz): δ 135.3 (Cq), 134.6 (Cq), 128.9, 127.8, 127.4 (aromatic CH),
65.1 (OCH2). IR (KBr): ν 1634, 1597, 1288, 1107 cm-1. Mass-spectra
(EI), m/z (%): 238 (M+, 7), 149 (40), 105 (100), 91 (15), 77 (36).
C16H14O2: Calcd C 80.65, H 5.92. Found C 80.93, H 6.13.
2,3-Diphenyl-6,7-dihydro-5H-[1,4]dioxepine, 29b. From bis-car-
bene complex 28b (197 mg, 0.31 mmol), Pd(OAc)2 (7.0 mg, 0.031
mmol), and 50 µL (0.34 mmol) of Et3N after 45 min and further flash
column chromatography was obtained 29b (50 mg, 64%) as a white
1
crystalline solid (mp 118-119 °C). H NMR (200 MHz): δ 7.18-
7.12 (m, 4H, ArH), 7.09-7.03 (m, 6H, ArH), 4.43 (t, J ) 6.1 Hz, 4H,
OCH2), 2.14 (qt, J ) 6.1 Hz, 2H, CH2). 13C NMR (50 MHz): δ 141.7
(Cq), 136.6 (C ipso), 129.5, 127.7, 127.4 (aromatic CH), 69.9 (OCH2),
30.1 (CH2). IR (KBr): ν 1616, 1261, 1101 cm-1. C17H16O2: Calcd C
80.93, H 6.39. Found C 81.02, H 6.51.
2,3-Diphenyl-5,6,7,8-tetrahydro-[1,4]dioxocine, 29c. From bis-
carbene complex 28c (245 mg, 0.38 mmol), Pd(OAc)2 (8.6 mg, 0.038
mmol), and 60 µL (0.42 mmol) of Et3N after 2 h and further flash
column chromatography was obtained 29c (21 mg, 21%) as a white
1
crystalline solid (mp 102-104 °C). H NMR (200 MHz): δ 7.18-
7.14 (m, 4H, ArH), 7.10-7.05 (m, 6H, ArH), 4.29 (br s, 4H, OCH2),
1.90 (br s, 4H, CH2). 13C NMR (50 MHz): δ 141.7 (Cq), 136.8 (C
ipso), 129.3, 127.8, 127.3 (aromatic CH), 72.0 (OCH2), 27.9 (CH2).
IR (KBr): ν 1616, 1277, 1086, 1068 cm-1. C18H18O2: Calcd C 81.17,
H 6.81. Found C 81.25, H 6.95.
(OCH2), 66.9 (Cp), 15.8 (CH3). IR (KBr): ν 1560, 1265, 1215 cm-1
.
C30H32Fe2O2: Calcd C 67.19, H 6.01. Found: C 67.32, H 6.19. Triene
1
25 (minor isomer): H NMR (200 MHz): δ 6.62 (d, J ) 15.9 Hz,
2,3-Diphenyl-6,7,8,9-tetrahydro-5H-[1,4]dioxonine, 29d. From bis-
carbene complex 28d (245 mg, 0.38 mmol), Pd(OAc)2 (8.6 mg, 0.038
mmol), and 60 µL (0.42 mmol) of Et3N after 2 h and further flash
column chromatography was obtained 29d (14 mg, 14%) as a very
viscous colorless oil. 1H NMR (300 MHz): δ 7.17-7.13 (m, 4H, ArH),
7.10-7.06 (m, 6H, ArH), 4.21 (t, J ) 5.1 Hz, 4H, OCH2), 1.84 (m,
4H, CH2), 1.70 (m, 2H, CH2). 13C NMR (50 MHz): δ 142.1 (Cq),
136.5 (C ipso), 129.5, 127.8, 127.3 (aromatic CH), 72.4 (OCH2), 29.4
2H, CHdCH-Fc), 6.44 (d, J ) 15.9 Hz, 2H, CHdCH-Fc), 4.38 (m,
4H, Cp), 4.22 (m, 4H, Cp), 4.05 (s, 10H, Cp), 3.81 (q, J ) 7.1 Hz, 4H,
OCH2), 1.36 (t, J ) 7.1 Hz, 6H, CH3). 13C NMR (50 MHz): δ 146.1
(Cq), 126.2 (CHdCH-Fc), 117.3 (CHdCH-Fc), 83.6 (Cp), 69.3 (Cp),
69.2 (Cp), 69.1 (OCH2), 67.0 (Cp), 15.8 (CH3). IR (KBr): ν 1622,
1221 cm-1
.
E,Z,E- and E,E,E-3,4-Diethoxy-1,6-bis[(tricarbonylchromium)-
phenyl]-1,3,5-hexatrienes, 26. From carbene complex 20 (105 mg,
0.21 mmol), Pd(OAc)2 (4.6 mg, 0.021 mmol), and 40 µL (0.23 mmol)
of Et3N after 10 min was obtained 80 mg of a dark brown solid that
after flash column chromatography yielded 15.2 mg (25%) of 26 as a
(CH2), 25.9 (CH2). IR (KBr): ν 1549, 1275, 1254, 1084 cm-1
.
C19H20O2: Calcd C 81.40, H 7.19. Found C 81.65, H 7.26.
3,4-Diphenyl-1,6-dihydro-benzo[f][1,4]dioxocine, 31a. From bis-
carbene complex 30a (100 mg, 0.14 mmol), Pd(OAc)2 (3.1 mg, 0.014
mmol), and 20 µL (0.15 mmol) of Et3N after 2 h and further flash
column chromatography was obtained 31a (23.5 mg, 54%) as a white
1
mixture of E/Z isomers (5:1 ratio). H NMR (300 MHz): δ 6.88 (d,
J ) 16.0 Hz, m, 2H, CHdCH-Ar), 6.75 (d, J ) 15.1 Hz, M, 2H,
CHdCH-Ar), 6.35 (d, J ) 15.1 Hz, M, 2H, CHdCH-Ar), 6.26 (d,
J ) 16.0 Hz, m, 2H, CHdCH-Ar), 5.44 (d, J ) 6.0 Hz, M + m, 8H,
ArH), 5.37 (t, J ) 6.0 Hz, M + m, 8H, ArH), 5.22 (t, J ) 5.7 Hz,
M + m, 4H, ArH), 3.93 (q, J ) 6.9 Hz, M, 4H, OCH2), 3.80 (q, J )
6.9 Hz, m, 4H, OCH2), 1.30 (t, J ) 6.9 Hz, M + m, 12H, CH3). 13C
NMR (50 MHz, major isomer): δ 232.9 (CO), 145.6 (Cq), 125.4 (CHd
CH-Ar), 122.9 (CHdCH-Ar), 105.6 (C ipso), 92.8, 91.1, 91.0
(aromatic CH), 68.1 (OCH2), 15.7 (CH3). IR (KBr): ν 1973, 1904,
1551, 1217 cm-1. The mixture of compounds was unstable and correct
analytical data could not be obtained.
E,E,E,E,E- and E,E,Z,E,E-5,6-Diethoxy-1,10-diphenyl-1,3,5,7,9-
decapentaene, 27. Following the general procedure carbene complex
21 (150 mg, 0.40 mmol), Pd(OAc)2 (9 mg, 0.04 mmol) and 44 mg
(0.44 mmol) of Et3N were reacted for 14 h. Then, the crude reaction
was dissolved in hexane and filtered through Celite to give 63 mg of
a mixture of E/Z isomers (1.7:1 ratio) of 27 (85%) as a yellow solid.
Compound 27 was too unstable for further purification, and all
spectroscopic data of the mixture had to be obtained right after the
reaction. Correct analytical data could not be obtained. 1H NMR (300
MHz): δ 7.36-7.11 (m, M + m, 22H, ArH, and CH), 6.93-6.83 (m,
M + m, 4H, CH), 6.79-6.48 (m, M + m, 10H, ArH, and CH), 3.91
(q, J ) 7.2 Hz, M, 4H, OCH2), 3.78 (q, J ) 7.2 Hz, m, 4H, OCH2),
1.33 (t, J ) 7.2 Hz, m, 6H, CH3), 1.30 (t, J ) 7.2 Hz, M, 6H, CH3).
13C NMR (75 MHz): δ 148.1 (Cq), 146.0 (Cq), 137.5, 133.2, 132.8,
129.3, 129.2, 129.0, 128.6, 127.4, 126.4, 126.3, 124.7, 123.6, 118.8
1
crystalline solid (mp 89-90 °C). H NMR (200 MHz): δ 7.27-7.22
(m, 2H, ArH), 7.13-7.10 (m, 2H, ArH), 7.04-7.00 (m, 6H, ArH),
6.96-6.91 (m, 4H, ArH), 5.25 (s, 4H, OCH2). 13C NMR (50 MHz): δ
139.8 (Cq), 136.0 (C ipso), 135.4 (C ipso), 129.5, 129.2, 128.7, 127.7,
127.4 (aromatic CH), 72.4 (OCH2). IR (KBr): ν 1641, 1261, 1063 cm-1
.
C22H18O2: Calcd C 84.05, H 5.77. Found C 84.30, H 5.94.
3,4-Dimethyl-1,6-dihydro-benzo[f][1,4]dioxocine, 31b. From bis-
carbene complex 30b (150 mg, 0.26 mmol), Pd(OAc)2 (5.9 mg, 0.026
mmol) ,and 40 µL (0.29 mmol) of Et3N after 2 h and further flash
column chromatography was obtained 31b (25.7 mg, 52%) as a white
1
crystalline solid (mp 58-60 °C). H NMR (200 MHz): δ 7.25-7.21
(m, 2H, ArH), 7.16-7.09 (m, 2H, ArH), 5.11 (s, 4H, OCH2), 1.55 (s,
6H, CH3). 13C NMR (50 MHz): δ 136.3 (Cq), 133.7 (C ipso), 128.9,
128.3 (aromatic CH), 72.1 (OCH2), 15.7 (CH3). IR (KBr): ν 1689,
1618, 1236, 1174 cm-1. C12H14O2: Calcd C 75.76, H 7.42. Found C
75.87, H 7.61.
3-Methyl-4-phenyl-1,6-dihydro-benzo[f][1,4]dioxocine, 31c. From
bis-carbene complex 30c (150 mg, 0.24 mmol), Pd(OAc)2 (5.4 mg,
0.024 mmol), and 40 µL (0.26 mmol) of Et3N after 2 h and further
flash column chromatography was obtained 31c (31.5 mg, 53%) as a
1
dense light yellow oil. H NMR (200 MHz): δ 7.26-7.08 (m, 9H,
ArH), 5.34 (s, 2H, OCH2), 4.97 (s, 2H, OCH2), 1.65 (s, 3H, CH3). 13
C
NMR (50 MHz): δ 139.7 (Cq), 137.6 (Cq), 135.6 (Cq), 135.1, 134.5,
131.0, 128.7, 128.2, 127.9, 127.3, 127.1 (aromatic CH), 72.8 (OCH2),

Carbene Transfer from Metal-Carbene Complexes
J. Am. Chem. Soc., Vol. 123, No. 5, 2001 861
71.8 (OCH2), 17.3 (CH3). IR (CCl4): ν 1697, 1269, 1164 cm-1
C17H16O2: Calcd C 80.93, H 6.39. Found C 81.15, H 6.49.
.
Celite. Then the crude reaction was purified by flash column chroma-
tography or molecular distillation.
Methyl 4-Phenyl-4-oxobutanoate, 48a.41 From a mixture of carbene
complex 15a (250 mg, 0.76 mmol), Pd(AcO)2 (3.4 mg, 0.015 mmol),
Et3N (0.21 mL, 1.5 mmol), and methyl acrylate (0.35 mL, 3.8 mmol)
in 12 mL of THF after 4 h was obtained 160 mg of a residue that after
molecular distillation afforded pure 48a (116 mg, 80%). 1H NMR (300
MHz): δ 7.92 (d, J ) 7.2 Hz, 2H, ArH), 7.51-7.35 (m, 3H, ArH),
3.64 (s, 3H, OCH3), 3.26 (t, J ) 6.7 Hz, 2H, CH2), 2.70 (t, J ) 6.7 Hz,
2H, CH2). 13C NMR (75 MHz): δ 198.1 (CO), 173.5 (CO2CH3), 136.6
(C ipso), 133.3, 128.7, 128.1 (aromatic CH), 51.9 (CH2), 33.5 (CH2),
28.1 (CH3). IR (CHCl3): ν 1735, 1685 cm-1. C11H12O3: Calcd C 68.74,
H 6.29. Found C 68.62, H 6.02.
Reactions of â-Elimination in Chromium Carbene Complexes.
Synthesis of Enol Ethers 13a, 13b, and 36. Benzyl vinyl ether, 13a.40
From carbene complex 12a (326 mg, 1 mmol), Pd(OAc)2 (22 mg, 0.1
mmol), and 0.15 mL (1.1 mmol) of Et3N after 1.5 h was obtained 230
mg of a mixture of the enol ether 13a and Cr(CO)6. Compound 12a
1
was very unstable and could not be further purified. H NMR (300
MHz): δ 7.29-7.25 (m, 5H, ArH), 6.48 (dd, J1 ) 14.4 Hz, J2 ) 6.6
Hz, 1H, CHdCH2), 4.71 (s, 2H, OCH2), 4.22 (d, J ) 14.4 Hz, 1H,
CHdCH2), 3.98 (d, J ) 6.6 Hz, 1H, CHdCH2). 13C NMR (75 MHz):
δ 151.5 (CHdCH2), 136.7 (C ipso), 128.4, 127.7, 127.4 (aromatic CH),
87.2 (CHdCH2), 69.9 (OCH2).
Methyl 4-p-Bromophenyl-4-oxobutanoate, 48b.42 From a mixture
of carbene complex 15b (200 mg, 0.5 mmol), Pd(AcO)2 (2.2 mg, 0.009
mmol), Et3N (0.15 mL, 1 mmol), and methyl acrylate (0.23 mL, 2.5
mmol) in 12 mL of THF after 8 h was obtained 120 mg of a residue
that was purified by molecular distillation to afford pure 48b (101 mg,
75%). 1H NMR (300 MHz): δ 7.78 (d, J ) 7.7 Hz, 2H, ArH), 7.54 (d,
J ) 7.7 Hz, 2H, ArH), 3.64 (s, 3H, OCH3), 3.21 (t, J ) 6.6 Hz, 2H,
CH2), 2.70 (t, J ) 6.6 Hz, 2H, CH2). 13C NMR (75 MHz): δ 197.2
(CO), 173.3 (CO2CH3), 135.3 (C ipso), 132.0, 129.6 (aromatic CH),
128.5 (C ipso), 52.0 (CH2), 33.4 (CH2), 28.0 (CH3). IR (CHCl3): ν
1735, 1690 cm-1. C11H11BrO3: Calcd C 48.73, H 4.09, Br 29.47. Found
C 48.44, H 4.34, Br 29.18. Thermal Reaction of Aminocarbene
Complex 15b and Methyl Acrylate. A solution of aminocarbene
complex 15b (150 mg, 0.37 mmol) and methyl acrylate (159 mg, 1.85
mmol) was refluxed in 4 mL of THF for 48 h. Filtration through Celite
and solvent evaporation gave 95 mg of a residue containing N,N-
dimethyl-p-bromobenzamide and 4-p-bromophenyl-4-oxobutanoate,
48b, in a 4:1 ratio. The reaction crude was not further purified.
4-p-Bromophenyl-4-oxobutanenitrile, 48c. From a mixture of
carbene complex 15b (400 mg, 0.9 mmol), Pd(AcO)2 (4.4 mg, 0.02
mmol), Et3N (0.3 mL, 1.98 mmol), and acrylonitrile (262 mg, 4.95
mmol) in 12 mL of THF after 8 h was obtained a residue that after
column chromatography (hexane:EtOAc, 10:1) afforded 48c (94 mg,
40%). 1H NMR (300 MHz): δ 7.76 (d, J ) 8.6 Hz, 2H, ArH), 7.58 (d,
J ) 8.6 Hz, 2H, ArH), 3.29 (t, J ) 7.0 Hz, 2H, CH2), 2.71 (t, J ) 7.0
Hz, 2H, CH2). 13C NMR (75 MHz): δ 194.4 (CO), 134.3 (C ipso),
132.3, 129.5 (aromatic CH), 129.3 (C ipso), 119.1 (CtN), 34.3 (CH2),
11.8 (CH2). IR (KBr): ν 2260 (CtΝ), 1680 cm-1. C10H8BrNO: Calcd
C 50.45, H 3.39, N 5.88, Br 33.56. Found C 50.22, H 3.57, N 6.13, Br
33.22.
(o-Methylbenzyl)vinyl Ether, 13b. From carbene complex 12b (340
mg, 1 mmol), Pd(OAc)2 (22 mg, 0.1 mmol), and 0.15 mL (1.1 mmol)
of Et3N after 45 min was obtained 230 mg of a mixture of 13b and
Cr(CO)6. Compound 13b was purified by molecular distillation to yield
1
96 mg (65%) of a colorless oil. H NMR (300 MHz): δ 7.27-7.12
(m, 4H, ArH), 6.50 (dd, J1 ) 14.0 Hz, J2 ) 7.0 Hz, 1H, CHdCH2),
4.66 (s, 2H, OCH2), 4.25 (d, J ) 14.0 Hz, 1H, CHdCH2), 4.01 (d,
J ) 7.0 Hz, 1H, CHdCH2), 2.26 (s, 3H, CH3). 13C NMR (75 MHz):
δ 151.7 (CHdCH2), 136.7 (C ipso), 134.7 (C ipso), 130.3, 128.6, 128.4,
125.9 (aromatic CH), 87.1 (CHdCH2), 68.5 (OCH2), 18.7 (CH3). IR
(KBr): ν 1645, 1620, 1500, 1250 cm-1. C10H12O: Calcd C 81.04, H
8.16. Found: C 81.32, H 8.38.
(Pentaethylenglycol)divinyl Ether, 36. From carbene complex 35
(150 mg, 0.22 mmol), Pd(OAc)2 (5.1 mg, 0.022 mmol), and 40 µL
(0.24 mmol) of Et3N after 3 h was obtained a mixture of 36 and Cr-
(CO)6. The Cr(CO)6 was removed by filtration after dissolving the
mixture in cold MeOH to yield 54 mg (85%) of 36 as a light yellow
oil. Compound 36 was obtained in pure form and further purification
1
was not required. H NMR (200 MHz): δ 6.42 (dd, J1 ) 14.3 Hz,
J2 ) 6.8 Hz, 2H, CHdCH2), 4.10 (d, J ) 14.3 Hz, 2H, CHdCH2),
3.93 (d, J ) 6.8 Hz, 2H, CHdCH2), 3.77 (m, 4H, OCH2), 3.66 (m,
4H, OCH2), 3.58 (s, 12H, OCH2).13C NMR (50 MHz): δ 151.7 (CHd
CH2), 86.6 (CHdCH2) 70.7 (OCH2), 70.6 (OCH2), 69.2 (OCH2), 67.2
(OCH2). IR (CCl4): ν 1614, 1549, 1244, 1205, 1126 cm-1. C14H26O6:
Calcd C 57.91, H 9.03. Found C 58.02, H 9.20.
Pentacarbonyl[(6-methyl-2,5-dioxa-6-cycloheptenyliden)carbene]-
chromium(0), 37. From carbene complex 32a (n ) 0) (170 mg, 0.34
mmol), Pd(OAc)2 (6.7 mg, 0.03 mmol) and 50 µL (0.33 mmol) of Et3N
after 20 min were obtained 73 mg of a mixture of Cr(CO)6 and 37.
Further purification of 37 by flash column chromatography gave 41
1
mg (40%) of 37 as a deep red solid. H NMR (300 MHz): δ 6.98 (s,
Acknowledgment. This paper is warmly dedicated with our
best wishes to Professor Jose´ Luis Soto on the occasion of his
70th birthday. Support for this work under Grants PB97-0323
and 2FD97-0314-CO2-02 from the Direccio´n General de
Ensen˜anza Superior e Investigacio´n Cient´ıfica y Te´cnica (MEC-
Spain) and the European Commission is acknowledged. J.C.d.A.
acknowledges the MEC for a predoctoral (FPI-MEC) fellowship.
We thank Dr. Carl A. Busacca (Boehringer Ingelheim Phar-
maceuticals, Inc.) for helpful suggestions.
1H, CH), 4.76 (br s, 2H, OCH2), 4.31 (br s, 2H, OCH2), 2.02 (s, 3H,
CH3). 13C NMR (75 MHz): δ 302.4 (CrdC), 224.6 (CO trans), 217.6
(CO cis), 156.4 (Cq), 119.0 (CH), 77.7 (OCH2), 73.4 (OCH2), 23.0
(CH3). IR (CCl4): ν 2080, 1990, 1940, 1560, 1280, 1195 cm-1
.
General Procedure for Pd-Catalyzed Reactions of Aminocarbene
Complexes 15 with Methyl Acrylate and Acrylonitrile. A solution
of the aminocarbene complex was placed in a flame-dried airless flask
containing a magnetic stirring bar, degassed by evacuation/back-fill
with argon (three cycles). Then, the indicated Pd(OAc)2, Et3N, and the
indicated excess of the alkene were added at rt, and the mixture was
refluxed at 70 °C during the stated time. The solvent was removed in
vacuo, and the residue was dissolved in AcOEt, and filtered through
JA002497I
(41) (a) Dauben, W. G.; Tilles, H. J. Org. Chem. 1950, 15, 785. (b)
Kloetzel, M. C. J. Am. Chem. Soc. 1940, 62, 1708.
(40) Mikawa, Y. Bull. Chem. Soc. Jpn. 1956, 29, 110.
(42) Lutz, R. E.; Scott, G. W. J. Org. Chem. 1948, 13, 284.