Mechanistic studies on the reaction of fischer carbene complex with alkynes: Does the alkyne insertion intermediate form irreversibly?

Article abstract of DOI:10.1021/ja983101u

The regioselectivity of the formation of three different products from the reaction of 1-phenylpropyne with (methoxy)(2-methoxyl-1-phenyl)methylene pentacarbonyl chromium 12 was examined in detail. The phenol product is formed with a substantial regioselectivity which is temperature-dependent, but the indene products (obtained as two compounds: indene and indenone) are formed as a nearly equal mixture of regioisomers. The proportion of indene and phenol products is dependent on the concentration with greater amounts of phenol products being formed at higher concentrations. The total regioselectivity of all of the products is also a function of the concentration. This result could be due either to an equilibration of the η¹,η³-vinyl carbene intermediates in this reaction or to a change in mechanisms in the formation of the η¹,η³-vinyl carbene intermediates from one involving a dissociative incorporation of the alkyne to one involving an associative incorporation of the alkyne. Kinetic studies reveal that at 45 °C and at 0.5 M (but not 0.0001 M) the reaction is bimolecular with a first-order dependence on both the carbene complex and the alkyne. However, at 90 °C the reaction is first-order in carbene complex and zero-order in alkyne over the concentration range of 0.05-0.005 M where the total regioselectivity changes from 2.5:1.0 to 1.5:1. This observation constitutes the first experimental evidence for the equilibration of regioisomeric vinyl carbene intermediates during the benzannulation reaction. This equilibration could occur as a result of a deinsertion of the alkyne or via a cyclopropene intermediate. Finally the generality of the unprecedented bimolecular reaction of complex 12 with 1-phenylpropyne at high concentrations was examined for the reaction methoxy(phenyl)methylene pentacarbonyl chromium 28 with diphenylacetylene and phenylacetylene at 0.5 M, and it was found that both reactions are first-order in carbene complex only.

Full text of DOI:10.1021/ja983101u

J. Am. Chem. Soc. 1999, 121, 6403-6413
6403
Mechanistic Studies on the Reaction of Fischer Carbene Complex
with Alkynes: Does the Alkyne Insertion Intermediate Form
Irreversibly?
1
Marcey L. Waters, Mary E. Bos, and William D. Wulff*
Contribution from the Searle Chemistry Laboratory, Department of Chemistry, UniVersity of Chicago,
Chicago, Illinois 60637
ReceiVed August 28, 1998
Abstract: The regioselectivity of the formation of three different products from the reaction of 1-phenylpropyne
with (methoxy)(2-methoxyl-1-phenyl)methylene pentacarbonyl chromium 12 was examined in detail. The phenol
product is formed with a substantial regioselectivity which is temperature-dependent, but the indene products
(obtained as two compounds: indene and indenone) are formed as a nearly equal mixture of regioisomers.
The proportion of indene and phenol products is dependent on the concentration with greater amounts of
phenol products being formed at higher concentrations. The total regioselectivity of all of the products is also
1
3
a function of the concentration. This result could be due either to an equilibration of the η ,η -vinyl carbene
1
3
intermediates in this reaction or to a change in mechanisms in the formation of the η ,η -vinyl carbene
intermediates from one involving a dissociative incorporation of the alkyne to one involving an associative
incorporation of the alkyne. Kinetic studies reveal that at 45 °C and at 0.5 M (but not 0.0001 M) the reaction
is bimolecular with a first-order dependence on both the carbene complex and the alkyne. However, at 90 °C
the reaction is first-order in carbene complex and zero-order in alkyne over the concentration range of 0.05-
0
.005 M where the total regioselectivity changes from 2.5:1.0 to 1.5:1. This observation constitutes the first
experimental evidence for the equilibration of regioisomeric vinyl carbene intermediates during the
benzannulation reaction. This equilibration could occur as a result of a deinsertion of the alkyne or via a
cyclopropene intermediate. Finally the generality of the unprecedented bimolecular reaction of complex 12
with 1-phenylpropyne at high concentrations was examined for the reaction methoxy(phenyl)methylene
pentacarbonyl chromium 28 with diphenylacetylene and phenylacetylene at 0.5 M, and it was found that both
reactions are first-order in carbene complex only.
The reaction of Fischer carbene complexes with alkynes to
give substituted phenols is the most important reactions of this
class of carbene complexes in organic synthesis. The deter-
carbon monoxide dissociation from the starting carbene complex
-
3
to give the 16 e electron unsaturated species 3. Subsequent
reaction with the alkyne was proposed to give the vinyl carbene
complex intermediate 4. Recently, this view has been called
into question by a theoretical study by Sola and co-workers,
which concluded that the first step is an insertion of the alkyne
to give the pentacarbonyl species 2 and then a rate-limiting loss
of CO to give the unsaturated vinyl carbene complex 4.4
However, this inconsistent with the kinetic studies of D o¨ tz et
al., which clearly demonstrated that the first step was CO loss
and that the second step was dependent on the alkyne concen-
2
mination of the mechanism of this reaction thus will be
important in synthetic planning, yet this is by no means the
only driving force for the study of this mechanism. Since the
reaction assembles three different components in a single step
and since a large number of structurally different products can
be formed in the reaction under only slightly modified condi-
tions, the complexity of the reaction manifold is rivaled by few
reactions. The obvious challenges presented in understanding
this reaction have attracted both experimentalists and theorists.
A summary of the current understanding of the reaction of R,â-
unsaturated Fischer carbene complexes with alkynes is presented
in Scheme 1.
3
tration. The vinyl carbene or alkyne insertion product has been
suggested to exist in a number of different forms. It was first
suggested by us in 1987 that the alkyne insertion product 4 may
-
1
3
5
exist as the 18 e η ,η -vinyl carbene complex 5. Subsequently,
extended H u¨ ckel calculations by Hoffman and co-workers found
that 4 and 5 are of comparable energy, and they also ruled out
The first and rate-limiting step of the reaction was long ago
proposed by D o¨ tz et al. on the basis of kinetic studies to be a
6
(
1) ACS Organic Division Fellow 1995-1996 (John Wiley & Organic
a metallacyclobutene intermediate as a precursor to 5. There
Reactions).
have been two recent density functional calculations (DFT)
(2) For reviews on the synthetic applications of Fischer carbene
7
performed, and the one by Hess and co-workers found that 5
complexes, see: (a) D o¨ tz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23,
5
87. (b) Wulff, W. D. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: New York,
995; Vol 12. (c) Hegedus, L. S. In ComprehensiVe Organometallic
is more stable than 4, whereas the one by Sola and co-workers
1
(3) D o¨ tz, K. H.; Fischer, H.; M u¨ hlemeier, J.; M a¨ rkl, R. Chem. Ber. 1982,
115, 1355.
(4) Torrent, M.; Duran, M.; Sola, M. Organometallics 1998, 17, 1492.
(5) Chan, K. S.; Peterson, G. A.; Brandvold, T. A.; Faron, K. L.;
Challener, C. A.; Hyldahl, C.; Wulff, W. D. J. Organomet. Chem. 1987,
334, 9-56.
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon
Press: New York, 1995; Vol 12. (d) Doyle, M. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon Press: New York, 1995; Vol 12. (e) Harvey, D. F.; Sigano,
D. M. Chem. ReV. 1996, 96, 271.
1
0.1021/ja983101u CCC: $18.00 © 1999 American Chemical Society
Published on Web 06/25/1999

6404 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Waters et al.
Scheme 1
Scheme 2
Scheme 3
and co-workers suggests the alkyne insertion should be irrevers-
ible but this information on the CO insertion step was not
8
provided. Energy barriers to reactions are underestimated by
pure density functional calculations, but the relative energy of
the barriers should be more reliable. In previous work we had
experimentally determined that, in the reaction of a 2- furyl
carbene complex with 1-pentyne, at least one of these steps must
12
be irreversible (Scheme 2). This work was initiated in an effort
to determine whether both of the steps are irreversible or, if
not, which of the steps is reversible.
Background
The genesis of the present study was the observation that
the quinone and indene products from the reaction of complex
1
2 with 1-phenylpropyne were formed with different levels of
regioselectivity (Scheme 3). In this reaction, an oxidative workup
with cerium (IV) ammonium nitrate is used to remove the metal
from the product which concurrently oxidizes the naphthol to
the naphthoquinone. The naphthol chromium tricarbonyl prod-
ucts are air sensitive, and thus, precise determination of the yield
by isolation is usually difficult. The o-methoxyl group was used
as a method to preserve the regiochemical information in the
naphthol product. The quinone 13 was isolated in 67% yield
and obtained as a 41:1 mixture of regioisomers with the major
isomer having the phenyl group of the alkyne incorporated
adjacent to the CO derived carbonyl (RL in 10, Scheme 1). The
indene was isolated in 15% yield as a 1.2:1 mixture of isomers
in which the major isomer corresponds to the major isomer of
the quinone. It was quite surprising to find that the regiochem-
istry of the two products would be different despite the fact
8
9
found that 4 is more stable than 5. Barluenga provided spectral
evidence for the structure 6 involving coordination to the distal
double bond, and the recent DFT calculation by Sola finds that
is more stable than either 4 or 5. The insertion of the CO
was originally proposed by D o¨ tz to occur to give the η -vinyl
ketene complex 8 which upon electrocyclic ring closure and
tautomerization gave the observed phenol complexes 10. The
DFT studies reveal that this is the case for aryl complexes,
but for alkenyl carbene complexes there was no local minimum
for the vinyl ketene complex but rather CO insertion and
8
6
4
1
0
7
7
,8
electrocyclic ring closure occurred in the same step.
In terms of carbon-carbon bond formation, the two main
events in the reaction are the alkyne insertion and the CO
insertion. Information about the rates and reversibility of these
processes have been hard to come by due to a rate-limiting CO
dissociation followed by rapid conversion to product, which is
consistent with the difficulty in detection of reaction intermedi-
that the regiochemistry of indene formation has never been
carefully examined for alkoxy chromium complexes.1
3-16
From
the mechanism proposed for the formation of these two products
Scheme 4), it seemed reasonable that both products would be
(
formed with the same level of regioselectivity and perhaps this
is why an investigation of the regioselectivty of indene formation
has never been carried out.
1
1
ates. The DFT study by Hess and co-workers suggests that
7
both steps should be irreversible, and the DFT study by Sola
(
6) (a) Hofmann, P.; H a¨ mmerle, M.; Unfried, G. New J. Chem. 1991,
5, 769. (b) Hofmann, P.; H a¨ mmerle, M. Angew. Chem., Int. Ed. Engl.
989, 28, 908. For citations to metallcyclobutenes, see: (c) Katz, T. J.;
Sivavec, T. M. J. Am. Chem. Soc. 1985, 107, 737. (d) Doxsee, K. M.;
Juliette, J. J. J.; Mouser, J. K. M.; Zientara, K. Organometallics 1993, 12,
The branch point between indene and phenol products is most
often proposed to be the alkyne insertion intermediate which is
1
1
1
3
15,17
drawn as the η ,η -vinyl carbene complex 5 in Scheme 4.
4
1
1
742.
(12) McCallum, J. S.; Kunng, F.-A.; Gilbertson, S. R.; Wulff, W. D.
Organometallics 1988, 7, 2346.
(7) Gleichmann, M. M.; D o¨ tz, K. H.; Hess, B. A. J. Am. Chem. Soc.
996, 118, 10551.
(13) The reaction of an aryl complex with 1-pentyne has been reported
(
8) Torrent, M.; Duran, M.; Sola, M. J. Chem. Soc., Chem. Commun.
998, 999.
9) Barluenga, J.; Aznar, F.; Martin, A.; Garcia-Granada, M. S.; Perez-
Carreno, E. J. Am. Chem. Soc. 1994, 116, 11191.
to give a 3.3:1 mixture of indene isomers.14
(14) Bos, M. E.; Wulff, W. D.; Miller, R. A.; Chamberlin, S.; Brandvold,
T. A. J. Am. Chem. Soc. 1991, 113, 9293.
(15) Indene formation with 1-phenylpropyne has been reported to give
a single regioisomer with an amino carbene complex: Yamashita, A.
Tetrahedron Lett. 1986, 27, 5915.
(
(
10) D o¨ tz, K. H.; Fugen-Koster, B. Chem. Ber. 1980, 113, 1449.
(11) (a) Foley, H. C.; Strubinger, L. M.; Targos, T. S.; Geoffroy, G. L.
J. Am. Chem. Soc. 1983, 105, 3064. (b) Knorr, J. R.; Brown, T. L.
Organometallics 1994, 13, 2178.
(16) Indene formation with 1-phenylpropyne has been reported to give
a single regioisomer with a tungsten complex.1
1a

Reaction of Fischer Carbene Complex with Alkynes
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6405
Scheme 4
Scheme 5
that is not the same for the major isomer 5A as it is for the
minor isomer 5B (Scheme 4). One possibility for this is that
the rate for CO insertion is the same for each intermediate while
the rate for cyclization is slower for 5A than it is for 5B due to
the more severe close contacts experienced by the large
substituent (RL ) phenyl) in 5A than for the small substituent
(
RS ) methyl) in 5B. The fact that 11B is not a predominate
product could be due to a greater proportion of 5A relative to
5
B in solution.
Further complicating the mechanistic picture is our previous
observation that the ratio of indene and naphthol products can
be controlled by variations in the concentration of the alkyne.14
This is illustrated by the example in Scheme 5, where the
reaction of the carbene complex 16 with 3-hexyne can give
either quinone 17 or indene 18 as the major product by simply
changing the concentration. This effect was found to be
dependent on the concentration of the alkyne and not on the
concentration of the carbene complex. This effect was termed
the allochemical effect and was intended to mean a reaction
for which the product distribution is affected by a process that
involves the interaction of a molecule of one of the substrates
with a chemical intermediate of the reaction that has already
had a molecule of that substrate covalently incorporated and
that this interaction leads to a change in the distribution of
products all of which have the first, but not the second, molecule
of substrate covalently incorporated.
For reasons of brevity, alternative schemes with structures 4
and 6 will not be presented but are of course possible.
Cyclization of 5 produces the isoindene 15 which upon 1,5-
hydrogen shift and loss of the metal gives the indene product
which is different in molecular weight from the naphthol product
by the 28 mass units of a carbon monoxide molecule. In addition
to the direct cyclization of 5 shown here, it is also possible that
the formation of 15 occurs in a two-step process involving a
chromacyclohexadiene intermediate.17
All of this suggested to us that regioselectivity could be used
1
3
as a label to determine if the η ,η -vinyl carbene-complexed
intermediate is formed reversibly or not. If the regioisomeric
vinyl carbene intermediates 5A and 5B are formed irreversibly,
then the total regiochemistry of the reaction would be fixed.
Variation of the concentration to produce different amounts of
indene and naphthol products would result in an invariant ratio
of the A isomers to the B isomers. On the other hand, if 5A
and 5B are formed reversibly or can otherwise equilibrate, then
the total regiochemistry of the reaction, calculated from the
amounts of the major and minor isomers of the indene and
naphthol products, could change as the ratio of the indene and
naphthol products changes. The ability to conclude that an
observation of a change in concentration leading-to-different
ratios of indene and naphthol products and thus to a change in
total regiochemistry means that the vinyl carbene-complexed
intermediates are formed reversibly or are otherwise in equi-
librium requires that there is no change in mechanism as the
concentration is changed. For example, the bimolecular reaction
of 1 with alkyne to give 2 may occur with a different regio-
chemistry than the reaction of the alkyne with the intermediate
3 generated from 1 by a rate-limiting loss of CO. Thus kinetic
studies will be required over the concentration ranges examined
to determine if a change in mechanism occurs. The previous
kinetic study that has been performed on this reaction indicates
that the reaction is first-order in carbene complex and zero-
order in alkyne; however, this study was only done at one
The regioselectivity difference for the indene and quinone
products from the reaction of complex 12 was unexpected and
has not been previously studied. The regiochemistry of naphthol
formation is known18 to be mainly a function of the steric
difference between the two substituents on the alkyne, although
1
9
electronic effects can be significant in certain cases. One
explanation for the direction of the regioselectivity of naphthol
1
3
formation that has been put forth involves the η ,η -vinyl
carbene-complexed intermediate 5. From a calculated structure
of 5, it was found that the C-2 substituent is about 1 Å closer
6a
to it’s nearest CO ligand than is the C-1 substituent. The largest
substituent on the alkyne (RL) thus can be more easily
accommodated at the C-1 position in 5A than the C-2 position
in 5B. This results in a preference for the intermediate 5A over
5
B and in a preference for the formation of the isomer 10A.
The unexpected regioselectivity in the formation of the indenes
1A and 11B (Scheme 3) could be accounted for by a difference
in rate for the CO insertion and the electrocyclic ring closure
1
(
17) Casey, C. P. In ReactiVe Intermediates; Jones, M., Jr., Moss, R. A.,
Eds.; Wiley: New York, 1981; Vol. 2, p 155.
18) (a) Wulff, W. D.; Tang, P. C.; McCallum, J. J. Am. Chem. Soc.
981, 103, 7677. (b) D o¨ tz, K. H.; M u¨ hlemeier, J.; Schubert, U.; Orama, O.
(
1
J. Organomet. Chem. 1983, 247, 187. (c) Yamashita, A.; Toy, A.
Tetrahedron Lett. 1986, 27, 3471.
(
19) (a) Chamberlin, S.; Waters, M. L.; Wulff, W. D. J. Am. Chem. Soc.
1
994, 116, 3113. (b) Brandvold, T. A.; Wulff, W. D.; Rheingold, A. L. J.
Am. Chem. Soc. 1991, 113, 5459. (c) Brandvold, T. A.; Wulff, W. D.;
Rheingold, A. L. J. Am. Chem. Soc. 1990, 112, 1645.
3
concentration.

6406 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Waters et al.
Table 1. Regioselectivity of the Reaction of Complex 12 with 1-Phenylpropynea
temp
entry run (°C)
[12]
(M)
[alkyne]
(M)
PPh
(equiv)
3
% yield
13
% yield
14
% yield
19
% yield
Σ %
yield Σ A/Bd
(A/B)b
(A/B)c
(A/B)c
20Ac
e
e
1
2
3
4
5
6
7
8
9
0
1
2
1
2
1
2
1
1
1
2
1
2
1
1
45
45
45
45
45
45
90
90
90
90
90
90
0.5
0.5
1.0
1.0
0.01
0.01
1.0
0.01
0.1
73
67
25
21
29
13
35.5
32.7
4.6
5.3
16.6
7.9
g35:1.0
41:1.0
g48:1.0
49:1.0
11
15
43
62
24
67
56.7
62.0
76.1
71.7
68.5
81.2
1.0:1.0
1.2:1.0
1.1:1.0
1.0:1.0
1.0:1.5
1.2:1.0
1.3:1.0
1.3:1.0
1.4:1.0
1.4:1.0
1.3:1.0
1.3:1.0
∼3
1.0:1.0
∼7
∼94
9.4:1.0
9.6:1.0
2.1:1.0
1.5:1.0
3.3:1.0
1.7:1.0
0
9
7
0
89
0.005
0.005
0.5
0.005
0.05
0.05
0.05
0.005
0.05
0.005
1.5:1.0
1.0:1.3
1.6:1.0
1.2:1.0
1.0:1.1
1.0:1.0
77
96
72
88
13
4
6
0
15
2
2
2
g27:1.0
g35:1.0
18.6:1.0
17.6:1.0
17.2:1.0
19.9:1.0
3.9
1.8
9.0
9.4
2.4
4.9
96.1 2.4:1.0
96.5 2.3:1.0
89.7 1.4:1.0
86.4 1.5:1.0
87.5 1.7:1.0
94.0 1.4:1.0
0.1
f
f
f
0.01
0.01
0.1
1.0:1.2
1.0:1.0
f
1
1
1
2
2
15.8:1.0e
18.7:1.0e
1.0:1.1e
1.0:1.6e
0.01
a
Unless otherwise specified, all yields are for isolated products by column chromatography on silica gel. The solvent at 45 °C is THF and at 90
b
1
d
°
C it is 2,5-dimethyltetrahydrofuran (DMTHF). Ratio determined by GC (average of 3 determinations). c Ratio determined by H NMR. Ratio
of the sum of the yields of the A isomers of products 13, 14, 19, and 20 to that of the sum of the B isomers. For those entries where the ratio of
1
in 80-90% purity from these reactions. Yields determined by H NMR integration using Ph CH as an internal standard.
3
e
3A to 13B was determined as a minimum, the minimum value is used to calculate the yields of 13A and 13B. The product could only be isolated
f 1
In our previous studies on the mechanism of the allochemical
effect, we provided evidence that the point at which the alkyne
affected the product distribution was after the first alkyne
1
3
inserted and after the η ,η -vinyl carbene-complexed intermedi-
ate 5 was formed. Specifically, it was proposed that the higher
proportion of quinone product at higher concentration was due
to an interaction of the alkyne with the unsaturated form of the
alkyne insertion product (4), which results in an increase in the
rate of CO insertion relative to the rate of cyclization to a five-
membered ring. This is supported in the present work by kinetic
studies (vide infra) which show that a significant allochemical
effect can be seen under conditions in which the order of the
reaction in alkyne does not change. Moreover, the kinetic studies
to be described in this work reveal that there is no change in
mechanism under conditions where it was found that the total
regiochemistry of the reaction does change.
The total regioselectivity (Σ A/B) of the reaction is expressed
as the ratio of the number of moles of the A isomers of all the
products to the number of moles of the B isomers. The
regioselectivity for each product was not affected by concentra-
tion. The distribution between phenol and indene products was
quite sensitive to concentration, but at the same time, the total
mass balance of the reaction is uniformly high. Thus, as expected
from the data in Schemes 3 and 5, the total regiochemistry of
the reaction is a function of the concentration. The change in
total regiochemistry is much greater at 45 °C than it is at 90
°C, and this is simply because there is not as great a change in
the amount of quinone formed at the higher temperature.14 The
error in the measurement of the total regiochemistry mainly
results from the loss of material in determining the isolated
yields. In most instances of duplicate runs, the yields were found
not to vary by more than (3%. The one exception is entry 3 in
Table 1, and in this instance the mass balance of the indene
product was low and the total regiochemistry increased from
1.5:1.0 to 2.1:1.0. The indene can be lost if oxidation in the
workup does not completely remove the metal, in which case
chromium tricarbonyl complexes may not necessarily coelute
with the indenes and also may decompose during elution. It
was decided not too repeat this reaction since, on the basis of
the other entries, if all of the indene had been isolated it would
most likely have been nearly a 1:1 ratio of regioisomers and
the total regiochemistry would have dropped from 2.1:1.0. More
importantly, it was decided not to repeat this reaction since, as
will be described below, there is a change in mechanism between
the reactions at 0.5 and 0.005 M at 45 °C, thus allowing alternate
explanations for this effect. As discussed above, to conclude
that the vinyl carbene-complexed intermediates 5A and 5B are
formed irreversibly and/or are in equilibration, one must show
that there is not a change in mechanism as the concentration is
Results
The distribution between phenol and indene products is
known to be a function of both concentration and temperature
where lower concentration and higher temperatures favors
5,14
indene formation.
Thus the regioselectivity of product
formation from the reaction of complex 12 with 1-phenylpro-
pyne was examined as a function of concentration at 45 and 90
°
C, and the results are presented in Table 1. The chelated
complex 12 was used rather than the nonchelated complex 16
to simplify the analysis. Either could be used since both
complexes give the same distribution between phenol and indene
products1 due to the fact that complex 16 undergoes conversion
to 12 during the course of the reaction. The assignments of the
regiochemistry of the isomers of 13, 14, 19, and 20 are described
in the Experimental Section. The cyclobutenone is not formed
at 90 °C, and this is presumably because it undergoes a thermal
electrocyclic ring opening and subsequent cyclization to give
the quinone 13. Cyclobutenone 20 is formed as a single
regioisomer, whereas the indene 14 and the indenone 19 are
formed as nearly 1:1 mixtures of isomers. The regioselectivity
of the formation of quinone 13 drops off with temperature from
a 41:1 mixture of isomers at 45 °C to an 18:1 mixture of isomers
at 90 °C. This is the first time that the effect of temperature on
the regioselectivity of the reaction of carbene complex with
alkynes has ever been reported. If it is assumed that the rates
of CO insertion in 5A and 5B are the same, then this temperature
effect suggests a decrease in the proportion of 5A relative to
4
5
B at elevated temperature.

Reaction of Fischer Carbene Complex with Alkynes
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6407
Figure 3. Initial rate plot of quinone formation: 0.5 M 12 and 1.0 or
2
.5 M 1-phenylpropyne at 45 ( 0.5 °C.
-
5
-3
-3
Figure 1. Initial rate plot: 9 × 10 M 12 and 2 × 10 or 5 × 10
M 1-phenylpropyne at 45 ( 0.5 °C.
Figure 4. Initial rate plot: 0.05 M 12 and 0.25 or 0.1 M 1-phenyl-
propyne at 89.5 ( 0.5 °C.
Figure 2. Initial rate plot: 0.5 M 12 and 1.0 or 2.5 M 1-phenylpropyne
at 45 ( 0.5 °C.
-
5
-1
1
.8 × 10 s , whereas the rate constant for the bimolecular
-4 -1
reaction at 0.50 M and 45 °C is approximately 6 × 10
M
-
1
s .
changed. As will be shown below, this was found to be the
case for the reactions at 90 °C.
Although the benzannulation reaction is occurring by two
different mechanisms at high and low concentrations of 12 at
To probe for a change in mechanism, we first determined
the order of the reaction of complex 12 with 1-phenylpropyne
at 45 °C at both 0.5 and 0.00009 M in complex 12. Initial rates
were measured to avoid complications of multiple product
formation. The low concentration regime was measured by UV/
vis spectroscopy, but due to the large extinction coefficient of
the carbene complex, at high concentration the rates were
measured by quenching aliquots of the reaction and analyzing
4
5 °C, this change in mechanism is not necessarily the source
of the change in regioselectivity. To determine if there is a
connection between the these two factors, one must analyze the
regioselectivity at concentrations where only one mechanism
is operating. An increase in the temperature of the reaction
should entropically favor a unimolecular reaction, and thus, the
kinetics at 89.5 °C were examined. This is indeed what was
observed: at 89.5 °C and 0.1 M 12 in dimethyl THF (DMTHF)
both mechanisms are occurring as was ascertained from kinetic
data taken at 0.1 M in 12 and 0.2 and 0.6 M in phenylpropyne
(data not shown). However, when the concentration of carbene
complex is dropped to 0.05 M at 90 °C, the reaction is
unimolecular (Figure 4), as it is at 0.005 M (Figure 5). The
-
5
them by GC. As shown in Figure 1, at 9.0 × 10 M carbene
complex 12 the reaction rate was measured with 0.002 and
0
.0005 M alkyne. The rate of reaction was unaffected by a
change in alkyne concentration. The reaction rate was also
-
5
measured at 4.5 × 10 M 12, and the rate was slower by a
-
5
factor of 2 than at 9.0 × 10 M. Thus, the reaction is first-
order in carbene complex and zero-order in alkyne, just as
Fischer and D o¨ tz observed for the reaction of the phenyl carbene
-
3
-1
observed rate constant is 2.5 × 10
s
at 89.5 °C (Table 2).
Although the magnitude of the effect is significantly smaller
than that at 45 °C, the same trend is seen: the regioselectivity
is dependent on concentration. At 0.05 M carbene complex, the
total regioselectivity is 2.4:1, but at 0.005 M carbene complex,
the selectivity drops to 1.5:1. Therefore, the change in mech-
anism observed at 45 °C cannot account for the concentration
dependence of the regioselectivity. To verify that changing
solvents did not affect the product distributions, we ran the
3
complex 28 with diphenylacetylene. At 0.5 M in carbene
complex 12, the reaction rate was again measured at two
different alkyne concentrations: 1.0 and 2.5 M alkyne. To our
surprise, at 0.5 M in carbene complex there is a first-order
dependence in alkyne (Figure 2). Figure 3 shows the corre-
sponding effect of alkyne concentration on the formation of
-
5
quinone. The unimolecular rate constant at 9 × 10 M 12 is

6408 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Waters et al.
Scheme 6
Scheme 7
Figure 5. Initial rate plot: 0.005 M 12 and 0.1 or 0.01 M 1-phenyl-
propyne at 89.5 ( 0.5 °C.
Table 2. Rates of Reaction of Complex 12 at 90 °C
[12] (M)
[alkyne] (M)
k
obs (s-1)
initial rate (M s-1
)
-
-
-
-
3
3
3
3
-4
-4
-5
-5
0
0
0
0
.05
.05
.005
.005
0.25
0.10
0.10
0.01
2.5 ( 0.2 × 10
2.5 ( 0.2 × 10
2.4 ( 0.2 × 10
2.4 ( 0.2 × 10
1.2 ( 0.1 × 10
1.3 ( 0.1 × 10
1.2 ( 0.1 × 10
1.2 ( 0.1 × 10
tivity. However, the cyclopropene intermediate could provide
a mechanism for the isomerization of 5A and 5B while the
concentration dependence is a function of the allochemical
a
14
Rates were measured by GC analysis at 89.5 ( 0.5 °C in 2,5-
dimethyltetrahydrofuran with hexadecane as internal standard.
effect.
Support for the intermediacy of a cyclopropene in these
reactions comes from the fact that Semmelhack has shown that
in the presence of M(CO)6 cyclopropenes will open up to give
typical benzannulation products, such as naphthols and in-
reaction at 45 °C in DMTHF. The same product distribution
was obtained as in THF.
Mechanism for the Interconversion of 5A and 5B. The
data above are not consistent with the irreversible formation of
the alkyne inserted intermediate 5 as probed through the ratio
of 5A and 5B, the two regioisomers of 5. Under conditions
where the reaction is first-order in carbene complex and zero-
order in alkyne, the two isomers of 5 must have some
mechanism for interconversion to explain the variation in total
regiochemistry of the reaction with alkyne. One possibility is
that alkyne insertion is reversible and that 5A and 5B undergo
deinsertion to the alkyne and the unsaturated carbene complex
2
0
denes. For example, he found that, when 3-methoxy-1,2,3-
triphenylcyclopropene 22 was heated to 100-145 °C in the
presence of one equivalent of Cr(CO)6, a 40% yield of the
quinone 14 was obtained which is the same product seen from
the reaction of carbene complex 28 and diphenylacetylene
(Scheme 7). Another case which implicates the intermediacy
of a cyclopropene complex is the reaction of the unstabilized
tungsten carbene complex 24 with phenylacetylene (Scheme
2
1
7
). H. Fischer found that, at -80 °C, an intermediate was
observable and that, upon warming to -40 °C, this intermediate
transformed into a new carbene complex 26. This intermediate
was characterized as the cyclopropene metal complex 25 by
3
(the possibility of isomerization via an alkyne complex of 3
cannot be distinguished in the present study). Another possibility
is that the isomerizations of 5A and 5B occur via the cyclo-
propene complex 21 which would maintain a covalent bond
between the two carbon fragments at all times.
If the isomerization involved the cyclopropene, the concentra-
tion effect could be accounted for by the following. The
cyclopropene metal complex is coordinatively unsaturated, so
the equilibration may only occur when a ligand (such as the
alkyne) can coordinate and stabilize this intermediate (Scheme
1
13
1
IR, H NMR, and C NMR and by the H NMR of the
deuterated intermediate formed from phenylacetylene-d. This
reaction occurs without the loss of CO, which has been shown
3
to be the rate-limiting step in the benzannulation reaction but
which has recently been called into question by recent theroetical
4
studies. In either case, this complex is highly reactive, which
may make direct mechanistic comparisons between these two
systems a bit precarious. This is confirmed by the fact that
complex 25 opens up stereoselectively to the regioisomer 26
6
). Thus, at higher alkyne concentrations the equilibration occurs
and the product distribution reflects the competition between
CO insertion and non-CO insertion, but at low concentration,
equilibrium is not reached and the product distribution reflects
the kinetic ratio of 5A and 5B. Ligand-induced isomerization
was investigated by adding two equivalents of PPh3 to the
reaction (Table 1, entries 6 and 7 and entries 12 and 13). If this
mechanism were responsible for the observed regioselectivities,
then adding phosphines should give results similar to those at
1
3
that is less favored in the η ,η -vinylcarbene intermediate 5.
Whether the equilibration occurs via the cyclopropene complex
2
1 cannot be determined at this time. Nonetheless, this does
not affect the conclusion from the above data that the regio-
isomeric vinyl carbene-complexed intermediates 5A and 5B
must be undergoing isomerization faster than CO insertion.
(20) (a) Semmelhack, M. F.; Ho, S.; Steigerwald, M.; Lee, M. C. J. Am.
0
.5 M, where the alkyne concentration is high. However, added
Chem. Soc. 1987, 109, 4397. (b) Semmelhack, M. F.; Ho, S.; Cohen, D.;
Steigerwald, M.; Lee, M. C.; Lee, G.; Gilbert, A. M.; Wulff, W. D.; Ball,
R. G. J. Am. Chem. Soc. 1994, 116, 7108.
phosphine resulted in low total regioselectivity, just as at low
concentration. Thus, this mechanism (Scheme 6) cannot account
for the observed concentration dependence of the regioselec-
(21) Fischer, H.; Hofmann, J.; Mauz, E. Angew. Chem., Int. Ed. Engl.
1991, 30, 998.

Reaction of Fischer Carbene Complex with Alkynes
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6409
constant for the reaction of 12 is an order of magnitude smaller
at the same temperature in the unimolecular regime (kobs(12) )
-
5
-1
1
.8 × 10 s ). If the rate constants for the bimolecular
reactions of 12 and 28 are of similar magnitude, then more
extreme conditions would be required to make the bimolecular
pathway of 28 competitive with the unimolecular pathway. For
example, if one assumes that the bimolecular rate constant for
2
8 would be equal to the one measured for complex 12, then in
order for the bimolecular mechanism to be 100 times faster than
the unimolecular reaction, the alkyne concentration must be on
the order of 40 M. Thus, it is not surprising that no bimolecular
reaction was observed for complex 28. The reason for the slower
unimolecular reaction for complex 12 versus complex 28 is
thought to be due to the intramolecularity of the chelation of
the methoxyl group and not to a chromium-methoxyl bond
that is stronger than a chromium-carbon monoxide bond.
Figure 6. Initial rate plot: 0.4 M 28 and 0.6 or 1.2 M diphenylacetylene
at 45.0 ( 0.5 °C.
Conclusion
The data presented in this work provides the first evidence
that isomers of the alkyne insertion intermediate in the reaction
of Fischer carbene complexes with alkynes are in equilibrium.
It was found that the total regiochemistry of the indene and
phenol products is a function of concentration. Since it was
found that this occurs over a concentration range in which the
reaction is zero-order in alkyne, this means that the ratio of
regioisomers of the alkyne insertion product 5A and 5B cannot
be affected by the alkyne. Thus the change in regiochemistry
must be a consequence of the interconversion of 5A and 5B
and a change in the distrbution between indene and phenol
products that is affected by the alkyne in a second step. The
data are consistent with the formation of the alkyne insertion
product 5 by a process that is first-order in carbene complex
and zero-order in alkyne with a rate-limiting formation of an
open coordination site on the metal. This could involve the
intermediacy of 3 as originally proposed by D o¨ tz (or an alkyne
Figure 7. Initial rate plot: 0.45 M 28 and 1.0 or 2.0 M phenylacetylene
at 45.0 ( 0.5 °C.
3
coordination complex of 3). However, at this point the data
Scheme 8
cannot distinguish whether the isomerization of the regioisomers
of the alkyne insertion intermediate occurs by a deinsertion or
the intermediacy of a cyclopropene complex. The present work
also provides the first example of a bimolecular reaction of a
heteroatom-stablized carbene complex with an alkyne in the
absence of CO pressure, thus supporting Sola’s recent results.4
The fact that the isomers of the alkyne insertion intermediate
do equilibrate rapidly with respect to subsequent CO insertion
Generality of the Bimolecular Mechanism. The unprec-
edented bimolecular mechanism observed for the reaction of
o-methoxyphenyl chromium carbene complex 12 with 1-phenyl-
2
2
may play a role in the determination of the stereochemistry
2
and product distributions from the benzannulation reaction.
1-propyne impelled us to investigate whether this was a general
phenomenon. Although Fischer and D o¨ tz had investigated the
kinetics of phenylmethoxy chromium carbene complex 28 with
various substituted diphenylacetylenes, all of their studies were
Experimental Section
General Procedure for the Reaction of Carbene Complex 12 with
-
3
3
done at 5 × 10 M carbene complex. The most typical
23
1
-Phenyl-1-propyne at 45 °C. Carbene complex 12 (160 mg, 0.51
concentrations for running a benzannulation reaction are at 0.1-
mmol), 0.13 mL of 1-phenylpropyne (1.02 mmol), and THF (0.89 mL
to give 0.5 M 12 or 98.2 mL to give 0.005 M 12) were combined in
a flame-dried flask with a threaded Teflon stopcock and a sidearm under
argon. In some cases, 2 equiv of triphenylphosphine was added. The
flask was sealed, the sidearm was placed under vacuum, and the solution
was frozen in liquid nitrogen. It was then opened to vacuum for 1-2
min, resealed, and warmed to room temperature. This degassing process
was repeated three times. The solution was then placed under argon
and warmed to 45 °C. The reaction was heated for 12-24 h, then cooled
to room temperature and transferred to a round-bottom flask. The
0
.5 M carbene complex, significantly more concentrated than
Fischer’s kinetic studies. Thus, we reinvestigated the reactions
of 28 with diphenylacetylene (Figure 6) and with phenyl
acetylene (Figure 7), at 0.4-0.5 M carbene complex and 0.6-
2
7
.0 M alkyne at 45 °C. The product analysis was performed at
0 °C as indicated in Scheme 8, but the kinetics were performed
at 45 °C to compare with the previous kinetics studies at lower
3
concentrations. We found that, under these typical reaction
conditions, the rates of both reactions are independent of alkyne
concentration. This is not surprising, given the first-order rate
constants for the reaction of 12 versus 28. Fischer and D o¨ tz
(22) (a) Hsung, R. P.; Wulff, W. D.; Rheingold, A. L. J. Am. Chem.
Soc. 1994, 116, 6449. (b) Hsung, R. P.; Wulff, W. D.; Challener, C. A.
Synthesis 1996, 773. (c) Hsung, R. P.; Quinn, J. F.; Weisenberg, B. A.;
Wulff, W. D.; Yap, G. P. A.; Rheingold, A. L. J. Chem. Soc., Chem.
Commun. 1997, 615.
-
4
-1
reported a rate constant of 2.55 × 10
s
for the reaction of
2
8 with diphenylacetylene at 45.4 °C. The first-order rate

6410 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Waters et al.
solvent was removed, and the crude product was dissolved in about 40
mL of ether. The product was oxidized with 5 mL of 0.5 M CAN. The
solution was transferred to a separatory funnel, and the organic layer
was washed twice with water and once with brine. The organic layer
The ratios of regioisomers for the indenes and indenones were
determined by H NMR on the crude reaction mixtures. The ratios of
1
regioisomers of the quinones were determined by GC analysis on a
Varian 3600 GC on the quinones obtained from the chromatography
column for the reactions at 0.05 M, and by GC analysis of the crude
reaction mixture for the reactions at 0.005 M. GC analysis was
performed on a 30 m, 0.32 mm i.d. Alltech SE-54 column with a
split injector under the following conditions: injector temp, 300 °C;
detector temp, 300 °C; head pressure, 12 psig; initial column temp,
150 °C (2 min); final column temp, 300 °C; ramp rate, 20 °C/min;
hold time, 5 min for analysis of reactions at 0.05 M. The retention
time for 13A was 9.5 min and for 13B was 9.3 min. For GC analysis
of the crude reaction mixtures at 0.005 M, the following conditions
4
was dried over MgSO and filtered through Celite, and the solvent was
1
removed under reduced pressure. A crude H NMR was taken prior to
purification. In some cases, one tenth of the crude reaction mixture
was separated and analyzed by GC. The products were then isolated
from the remaining nine tenths by column chromatography on silica
gel using a 10:1:1 mixture of hexane/methylene chloride/ether to give
the indenes 14 and the indenones 19 in separate fractions, and then
upon further elution with a 4:1:1 solvent mixture, the quinones 13.
The ratios of regioisomers for the indenes and indenones were
1
determined by H NMR on the crude reaction mixtures. The ratios of
were used: T
1 min; R of quinone A ) 14.6 min; and R
min. Reported ratios are from the average of 6 runs.
Quinone 13A. R ) 0.27 (4:1:1 hexane/ether/methylene chloride);
) δ 2.06 (s, 3H), 4.03 (s, 3H), 7.20 (d, 2H, J ) 8 Hz),
7.29 (d, 1H, J ) 8 Hz), 7.4-7.45 (M, 3H), 7.66 (t, 1H, J ) 8.3 Hz),
7.73 (d, 1H, J ) 8 Hz); 13C NMR (CDCl
) δ 14.83, 56.41, 117.30,
i
) 200 °C, hold 5 min; T
f
) 250 °C, rate 5 °C/min, hold
regioisomers of the quinones were determined by GC analysis on a
Varian 3600 GC on the quinones obtained from the chromatography
column or by GC analysis of the crude reaction mixture. GC analysis
was performed on a 30 m, 0.32 mm i.d. Alltech SE-54 column with
a split injector under the following conditions: injector temp, 300 °C;
detector temp, 300 °C; head pressure, 12 psig; initial column temp,
T
T
for quinone B ) 14.2
f
1
H NMR (CDCl
3
3
1
50 °C (2 min); final column temp, 300 °C; ramp rate, 20 °C/min; and
119.21, 127.85, 128.06, 128.29, 129.30, 133.51, 134.31, 134.61, 144.05,
145.92, 159.25, 184.22, 184.97; IR (thin film) 2924w, 1657s, 1587s,
hold time, 5 min for analysis of reactions at 0.05 M. For GC analysis
of the crude reaction mixtures, the following conditions were used: T
-1
1471m, 1437m, 1375s, 1331m, 1267s, 1061m, 964m, 705m cm ; mass
+
)
210 °C, hold 25 min; R
T
of quinone A ) 19.6 min; and R
T
for
spectrum m/z (% rel intensity) 278 M (100), 263 (30), 261 (12), 249
quinone B ) 18.4 min. Reported ratios are from the average of 6 runs.
The quinones obtained from this reaction were highly enriched in
isomer 13A, and as result, a pure sample of quinone 13A could be
obtained by crystallization from chloroform/hexanes. The assignment
of the quinone 13A as the major isomer of this reaction is based on
the regioselectivity that has previously been established for the reactions
of carbene complexes with alkynes. The spectral data for the minor
isomer 13B of the quinone product were obtained on a sample that
was prepared by an independent synthesis described below. The spectral
data for the indenes 14 and the indenones 19 were taken on mixtures
of the two regioisomers in each case.
(10), 235 (12), 189 (10), 115 (11), 104 (11), 76 (28). Anal. calcd for
C H O : C, 77.68; H, 5.07. Found: C, 76.73; H, 5.18. Bright yellow
18 14 3
solid, mp 155-7 °C.
Quinone 13B. R ) 0.27 (4:1:1 hexane/ether/methylene chloride);
f
1
H NMR (CDCl ) δ 2.03 (s, 3H), 3.96 (s, 3H), 7.19 (d, 2H, J ) 7.4
3
Hz), 7.27 (d, 1H, J ) 8.5 Hz), 7.36-7.42 (m, 3H), 7.65 (t, 1H, J )
1
8
13
8.1 Hz), 7.78 (d, 1H, J ) 7.6 Hz); C NMR (CDCl ) δ 14.27, 56.36,
3
117.66, 118.93, 119.94, 127.90, 128.22, 129.35, 133.94, 134.34, 134.54,
141.66, 147.74, 129.59, 183.58, 186.08; IR (CHCl ) 1658s, 1588s cm
mass spectrum m/z (% rel intensity) 278 M (100), 263 (30), 249 (12),
-1
3
;
+
235 (14), 219 (13), 134 (23), 115 (18), 104 (23), 76 (60). Anal. calcd
General Procedure for the Reaction of Carbene Complex 12 with
14 3
for C18H O : C, 77.68; H, 5.07. Found: C, 77.05; H, 4.95. Yellow
solid, mp 195-7 °C.
1
0
-Phenyl-1-propyne at 90 °C. The carbene complex 1223 (100 mg,
.32 mmol) was dissolved in 6.3 mL (to give 0.05 M 12) of
Indene 14A. R ) 0.23 (10:1:1 hexane/ether/methylene chloride);
f
1
dimethyltetrahydrofuran (DMTHF) or 63.74 mL of DMTHF (to give
.005 M 12), in a flame-dried single-necked flask equipped with a
threaded Teflon high vacuum stopcock. In some cases, 2 equiv of
triphenylphosphine was added. After 1-phenyl-1-propyne was added
H NMR (CDCl , data from a 1.3:1 mixture of 14A/14B) δ 2.03 (s,
3
0
3H), 3.14 (s, 3H), 3.94 (s, 3H), 5.14 (s, 1H), 6.75 (d, 1H, J ) 8.3 Hz),
1
3
6.77 (d, 1H, J ) 7.4 Hz), 7.21-7.53 (m, 6H, overlap with 14B); C
NMR (CDCl , data from a mixture of 14A/14B; peaks assigned by
3
(
2 equiv, 0.08 mL, 0.64 mmol) and the flask was sealed with the
taking spectra of two samples with different isomer ratios) δ 12.07,
52.05, 55.53, 83.72, 108.64, 112.81, 126.58, 127.36, 128.35, 128.87,
threaded stopcock at 25 °C, the mixture was cooled to -78 °C and the
flask was opened to vacuum for 30 s. The flask was then resealed and
allowed to warm to room temperature. This was repeated three times
130.13, 134.52, 139.42, 140.83, 146.81, 156.28; IR (CHCl , for mixture)
3
2931w, 1601m, 1586m, 1478s, 1439w, 1272m, 1259s, 1088m, 700m
-
1
(the reaction mixture was not frozen in liquid nitrogen due the expansion
cm ; GC mass spectrum (R ) 14.12 min for 14A) m/z (% rel
T
+
of DMTHF upon freezing, which tends to break the flask). After being
warmed to room temperature the third time, the flask was filled with
argon, sealed, and placed in a 90 °C oil bath for 2-4 h (0.05 M 12) or
intensity) 266 M (100), 251 (66), 235 (24), 223 (16), 189 (19), 178
(6), 165 (10), 115 (10). High-resolution mass spectrum (on mixture):
calcd for C H O m/z 266.1307, measd m/z 266.1293. Anal. calcd
18
18
2
6
-12 h (0.005 M 12). The DMTHF was then removed, and the
18 18 2
for C H O : C, 81.17; H, 6.81. Found (for mixture): C, 81.53; H,
remaining yellow-orange mixture was dissolved in approximately 20
mL of ether. Oxidation of the crude products was performed by the
addition of 5 mL 0.5 M cerium ammonium nitrate in water and stirring
for 30 min (0.05 M) or 10-15 min (0.005 M). The mixture was
transferred to a separatory funnel, and the layers were separated. The
aqueous layer was washed twice with ether. The combined organic
layers were washed once with water and once with brine. The solution
was dried over magnesium sulfate, filtered, and concentrated. After
7.18. White crystalline solid.
Indene 14B. R ) 0.23 (10:1:1 hexane/ether/methylene chloride);
f
1
H NMR (CDCl , data from a 1.4:1 mixture of 14A/14B) δ 2.27 (d,
3
3H, J ) 1.3 Hz), 2.96 (s, 3H), 3.95 (s, 3H), 5.67 (d, 1H, J ) 1.5 Hz),
6.81 (d, 1H, J ) 8.2 Hz), 6.93 (d, 1H, J ) 7.4 Hz), 7.21-7.53 (m, 6H,
overlap with 14A); 13C NMR (CDCl , data from a mixture of 14A/
3
14B; peaks assigned by comparison of spectra of samples with different
isomer ratios) δ 12.00, 51.49, 55.58, 82.16, 109.43, 112.26, 126.45,
126.90, 128.30, 128.74, 130.42, 135.25, 136.14, 140.89, 147.55, 156.04;
3
1
taking a crude H NMR spectrum, the products were eluted from a
silica gel column with a 10:1:1 mixture of hexane/ether/methylene
chloride to give the indenes 14 and the indenones 19 in separate
fractions and then, upon further elution with a 4:1:1 solvent mixture,
the quinones 13. For the 0.005 M reaction, one tenth of the crude
reaction mixture was set aside for GC analysis. The yields for indenones
IR (CHCl , for mixture) 2931w, 1601m, 1586m, 1478s, 1439w, 1272m,
1259, 1088m, 700m cm-1; GC mass spectrum (R ) 12.38 min for
T
+
14B) m/z (% rel intensity) 266 M (100), 251 (86), 235 (26), 223 (14),
189 (17), 178 (7), 165 (10), 115 (9). High-resolution mass spectrum
(on mixture): calcd for C H O m/z 266.1307, measd m/z 266.1293.
18
18
2
1
and quinones in the 0.005 M reactions were determined by H NMR
18 18 2
Anal. calcd for C H O : C, 81.17; H, 6.81. Found (for mixture): C,
integration using triphenylmethane as an internal standard.
81.53; H, 7.18. White crystalline solid.
Indenone 19A. R ) 0.15 (10:1:1 hexane/ether/methylene chloride);
, data from a mixture of 19A/19B) δ 1.90 (s, 3H),
f
(23) (a) D o¨ tz, K. H.; Sturms, W.; Popall, M.; Riede, J. J. Organomet.
1
H NMR (CDCl
3
Chem. 1984, 277, 267. (b) Wulff, W. D.; Tang, P.-C.; Chan, K.-S.;
McCallum, J. S.; Yang, D. C.; Gilbertson, S. R. Tetrahedron 1985, 41,
3.96 (s, 3H, overlaps with methoxy peak of 19B), 6.66 (d, 1H, J ) 7.1
Hz), 6.78 (d, 1H, J ) 8.6 Hz), 7.26 (t, 1H, J ) 7.1 Hz), 7.38-7.49 (m,
5
813.

Reaction of Fischer Carbene Complex with Alkynes
H, overlaps with aromatic peaks of 19B); 13C NMR (CDCl
a mixture of 19A/19B; peaks assigned by comparison of spectra of
samples with two different isomer ratios) δ 8.61, 56.01, 113.50, 113.98,
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6411
5
3
, data from
with 14B but not 14A. Thus, the assignment was confirmed by the
following experiment in which a mixture of the indenes 14A and 14b
was hydrogenated to the corresponding indanes. In a nitrogen-flushed
Teflon sealed flask was placed 64 mg of 5% Pd-C (0.03 mm Pd,
Kodak), 10 mL of absolute ethanol, and a 1.4:1 mixture of indenes
14A/14B (79.2 mg, 0.30 mmol) in 2 mL of additional ethanol. The
black slurry was stirred under an atmosphere of hydrogen overnight.
The catalyst was filtered off onto Celite with methanol, and the solvent
was removed. Preparative chromatography (500 µm plate, 10:1:1
hexane/ether/methylene chloride) gave 44.7 mg of a 1.4:1 mixture of
1
1
1
28.17, 128.57, 128.82, 131.48, 132.90, 135.21, 148.10, 152.21, 156.41,
96.17, 1 C not located; IR (thin film, mixture) 1703s, 1596m, 1475m,
-
1
282m, 1261m, 1602w, 699m cm ; GC mass spectrum (R
T
) 14.49
+
min for 19A) m/z (% rel intensity) 250 M (100), 235 (31), 221 (45),
2
07 (19), 189 (24), 179 (10), 165 (10), 152 (8), 125 (5), 115 (11), 95
6), 89 (7), 76 (9), 63 (5). Yellow oil.
Indenone 19B. R ) 0.15 (10:1:1 hexane/ether/methylene chloride);
, data from a mixture of 19A/19B) δ 2.28 (s, 3H),
.96 (s, 3H, overlaps with methoxy peak of 19A), 6.79 (d, 1H, J ) 7
Hz), 6.84 (d, 1H, J ) 8.4 Hz), 7.29-7.41 (m, 6H, overlaps with
(
f
1
1
H NMR (CDCl
3
indanyl ethers 33A and 33B in 56% combined yield. The H NMR
3
experiments summarized below allowed for the unambiguous assign-
ment of the major isomer as 1,7-dimethoxy-2-methyl-3-phenyl-2-indane
33A. The following spectral data were collected on the mixture of
1
3
aromatic peaks of 19A); C NMR (CDCl
9A/19B; peaks assigned by comparison of spectra of samples with
two different isomer ratios) δ 12.45, 56.01, 112.75, 114.33, 127.50,
3
, data from a mixture of
13
1
isomers: R
f
) 0.40 (10:1:1 hexane/ether/methylene chloride); C NMR
(CDCl , partial data for mixture); 33A, δ 12.10, 43.35, 54.75, 55.64,
3
1
1
1
1
1
7
28.12, 129.67, 131.28, 133.42, 135.58, 148.33, 151.32, 156.09, 194.48,
58.84, 83.78, 106.65, 118.65, 126.36, 130.50, 131.12, 143.08, 157.17;
33B, δ 20.00, 44.29, 54.25, - -, 58.13, 83.28, 108.74, 117.15, 126.40,
C not located; IR (thin film, mixture) 1703s, 1596m, 1475m, 1282m,
-
1
261m, 1602w, 699m cm ; GC mass spectrum (R
T
) 17.22 min for
130.05, 132.45, 139.88, 150.44. Mass spectrum m/z (% rel intensity)
+
+
9B) m/z (% rel intensity) 250 M (100), 235 (25), 221 (34), 207 (15),
91 (20), 178 (17), 165 (8), 152 (7), 125 (7), 115 (12), 95 (5), 89 (6),
6 (8), 63 (5). Yellow oil.
268 M (65), 237 (100), 221 (18), 191 (8); calcd for C18
20 2
H O , m/z
268.1463, found m/z 268.1456. White solid.
1
The H NMR spectral data was collected on the 1.4:1 mixture of
Cyclobutenone 20. R
chloride); H NMR (CDCl
.87 (d, 1H, j ) 8.1 Hz), 7.00 (t, 1H, J ) 7.4 Hz), 7.27-7.43 (m, 4H),
.63 (d, 1H, J ) 7.0 Hz), 7.57 (d, 2H, J ) 7.4 Hz); C NMR (CDCl
δ 13.80, 53.41, 55.60, 98.28, 111.61, 120.76, 124.52, 127.46, 128.58,
28.61, 128.97, 129.48, 129.61, 148.24, 157.00, 172.39, 190.56; IR
thin film) 2936m, 1759 vs (nCO), 1640m, 1596m, 1490s, 1462m,
f
) 0.20 (10:1:1 hexane/ether/methylene
) δ 2.34 (s, 3H), 3.47 (s, 3H), 3.72 (s, 3H),
6
33A/33B in d -benzene and is summarized below. Specific assignments
are given where possible below each isomer, and combined assignments
are made following the individual assignments. Irradiation of the
1
3
6
7
13
3
)
multiplet at 2.54 ppm (H
other multiplets into singlets. Conversely, irradiation of the multiplet
corresponding to H in the minor isomer 33B only affected two of the
three remaining multiplets. This pattern can only be obtained for the
given assignments: 33A, H δ ) 0.92 (d, 3H, J ) 7.3 Hz), H δ )
2.54 (m, 1H), H δ ) 3.33 (s, 3H), H δ ) 3.47 (s, 3H), H δ ) 4.05
(d, 1H, J ) 8.5 Hz), H δ ) 4.73 (d, 1H, J ) 6.2 Hz); 33B, H δ )
1.3 (d, 3H, J ) 7.2 Hz), H δ ) 3.14 (m, 1H), H δ ) 3.26 (d, 1H,
J ) 5.6 Hz), H δ ) 3.29 (s, 3H), H δ ) 3.47 (s, 3H), H δ ) 4.98
b
) of the major isomer 33A collapsed the three
1
(
1
b
-
1
253m, 1088s, 758m, 695m cm ; mass spectrum m/z (% relative
a
b
+
intensity) 294 M (41), 279 (40), 251 (42), 235 (25), 135 (100), 115
e
f
c
(
26), 105 (20), 77 (47). Calculated for C19
m/z 294.1206. White solid, mp 85-6 °C.
Assignment of Major and Minor Isomers of the Reaction
Products. (A) Quinones 13. The assignment of the regioselectivity of
the major quinone obtained from the reaction of complex 12 with
H O
18 3
m/z 294.1256. Found
d
a
b
c
d
e
f
(d, 1H, J ) 5.2 Hz); aryl protons, δ ) 6.42 (t, 1H, J ) 8.4 Hz), 6.72
(d, 1H, isomer A, J ) 7.5 Hz), 6.82 (d, 1H, isomer B, J ) 7.4 Hz),
6.96-7.24 (m, 12H), 7.50 (d, 1H, isomer B, J ) 7.6 Hz).
1
-phenyl-1-propyne was made on the basis of the regioselectivity that
1
8
is known for quinone formation from this reaction. A sample of the
minor isomer 13B was obtained from the reaction of the methoxy
m-methoxyphenyl chromium carbene complex 31 with 1-phenyl-1-
propyne and used to obtain spectral data and GC retention times for
1
3B.
(
C) Indenones 19. The regioisomers of the indenones were assigned
by chemical correlation with the indenes 14. A 2:1 mixture of indenes
4A and 14B (44.8 mg, 0.17 mmol) was dissolved in 1 mL of methylene
1
chloride under argon. Upon addition of 0.05 mL of water and 43.4 mg
of DDQ (0.19 mmol), the solution immediately turned dark blue-green.
The solution was stirred at room temperature for 14 h. The final solution
was a yellow-brown slurry. The solution was filtered through Celite
and washed three times with saturated aqueous sodium bicarbonate.
The aqueous layer was extracted twice with methylene chloride. The
combined organic layers were washed with brine, dried over magnesium
sulfate, and filtered. After removal of solvent, an 82% (34.7 mg; 0.14
mmol) yield of indenones was obtained as a 2:1 mixture of 19A and
19B. The major isomer 19A obtained from this reaction was found by
A deoxygenated solution of 694 mg of methoxy m-methoxyphenyl
chromium carbene complex 31 and 510 µL of 1-phenyl-1-propyne (4.06
mmol) in 4 mL of THF (0.5 M) was heated at 45 °C for 23 h. Oxidative
workup with CAN followed by chromatography on silica gel with a
1
H NMR to be identical with the minor indenone isomer obtained from
1
the reaction of complex 12 with 1-phenyl-1-propyne: H NMR
1
0:1:1 to 4:1:1 mixture hexane/ether/methylene chloride gave two
3
spectrum (CDCl , for major isomer in a 2:1 mixture of 19A and 19B)
yellow bands which were collected, concentrated, and crystallized from
chloroform/hexanes. No attempt to take second crops was made,
although substantial material remained. Recovered were the quinone
δ 1.90 (s, 3H), 3.96 (s, 3H, overlaps with methoxy peak of 19B), 6.66
(d, 1H, J ) 7.1 Hz), 6.78 (d, 1H, J ) 8.6 Hz), 7.26 (t, 1H, J ) 7.1
Hz), 7.38-7.49 (m, 5H, overlaps with aromatic peaks of 19B). The
indenes 14A and 14B could also be oxidized to the indenones 19A
and 19B with ceric ammonium nitrate although the reaction was slow
at room temperature with complete conversion requiring several days
and the yield was not determined.
3
2 (182 mg, 0.65 mmol, 32%) and quinone 13 (82 mg, 0.29 mmol,
1
4%), which was found to be a 14:1 mixture of 13B to 13A. The
regioselectivity for the formation of quinone 32 was not determined.
B) Indenes 14. The initial assignment of the regiochemistry of the
(
indene products was made on the basis of the coupling constant (1.4
Hz) between the methyl group and the allylic hydrogen in the minor
isomer which is due to long-range coupling that would be consistent
(D) Cyclobutenone 20. Cyclobutenone 20 was obtained as a single
diastereomer which was assigned as 20A by chemical correlation. A
sample of 20 was dissolved in benzene under nitrogen and heated

6412 J. Am. Chem. Soc., Vol. 121, No. 27, 1999
Waters et al.
-
3
overnight in a pressure flask at 110 °C. After solvent removal and CAN
oxidation, an NMR spectrum of the crude residue showed a single
quinone product corresponding to the major quinone 13A isolated from
the benzannulation reaction.
1.0 × 10 M 1-phenylpropyne. The same parameters as above were
-10 -1
used to collect the spectra. Rate ) 7.7 × 10
10
Kinetic Measurements of the Reaction of 12 with 1-Phenylpro-
M s ; kobs ) 1.9 ×
-
5
-1
s
.
pyne at 0.5 M 12, 45 °C. (A) At 1.0 M 1-Phenylpropyne. Carbene
Measurement of the Extinction Coefficient for 12. A 5.03 ×
complex 1223 (333.7 mg, 1.06 mmol) and triphenylmethane (259.3 mg,
-
3
23
1
0 M stock solution of 12 was made by dissolving 15.8 mg (0.05
1
.06 mmol) were dissolved in THF to a final volume of 2 mL in a
mmol) of 12 in THF to a final volume of 10 mL in a volumetric flask.
Three samples were made from this stock solution by diluting 0.2 mL
of the stock solution to a final volume of 10 mL, resulting in a 1.0 ×
volumetric flask, giving a stock solution of 0.53 M 12 and 0.53 M
triphenylmethane. To a 25 mL three-neck flask fitted with two glass
stoppers and a vacuum adapter with a stopcock was added 1 mL of
the stock solution. After the flask was sealed, the solution was frozen,
evacuated under high vacuum, and warmed to room temperature again.
This process was repeated three times to deoxygenate the solution. The
flask was then filled with argon and placed in a 44.4 ( 0.3 °C oil bath
monitored with a thermocouple thermometer. Once the temperature had
equilibrated, 0.133 mL of 1-phenylpropyne was added, and 0.05 mL
aliquots of the reaction were taken at 1 min intervals for the first 4
min, followed by 2-3 min intervals for the next 10 min. The reaction
was followed for a total of 3 h. The initial reaction concentrations were
-
4
1
0
M solution. The absorbance at 445.8 nm was measured for each
sample three times, and the background absorbance was subtracted for
each. The average absorbance was used to determine the extinction
coefficient e from Beer’s law: A ) elc, where Aavg ) 1.15, l ) 1 cm,
-
4
-1
-1
and c ) 10 M. Thus, e ∼11 400 M cm
.
Kinetic Measurements of the Reaction of 12 with 1-Phenylpro-
-
5
-5
pyne at 9.8 × 10 M 12, 45 °C. (A) At 9.8 × 10 M 12 and 2 ×
M 1-Phenylpropyne. A stock solution of 12 was made by
dissolving 15.6 mg (0.05 mmol) of 12 in THF to a final volume of 10
-
3
23
1
0
-
3
mL in a volumetric flask, giving a 4.97 × 10 M solution. A 0.99 ×
0
.47 M 12 and 0.94 M 1-phenylpropyne.
-
-
4
3
1
1
0
0
0
M solution of 12 was prepared by diluting 0.2 mL of the 4.97 ×
The progress of the reaction was monitored by the disappearance of
0
M solution to a final volume of 10 mL in a volumetric flask. A
the carbene complex 12 which in turn was monitored by the disap-
pearance of the corresponding ester, methyl 2-methoxy benzoate, from
the crude reaction mixture obtained upon oxidative workup. The aliquots
were quenched with 0.5 M CAN in methanol and diluted with 0.2 mL
of ether. The progress of the reaction was followed by GC, using a
.304 M stock solution of 1-phenylpropyne was prepared by diluting
.038 mL (0.304 mmol) of the alkyne in THF to a final volume of 1
mL in a volumetric flask.
In a quartz cuvette (1 cm path length) modified with a high vacuum
-
5
Teflon stopper and a sidearm was added 3 mL of the 9.9 × 10
M
0.32 mm i.d. SE- (DB-5 equivalent) capillary column with a program-
solution of 12. The solution was deoxygenated by cooling to -78 °C,
opening to vacuum for a period of 1 min, sealing the flask, and warming
to room temperature. This cycle was repeated three times. The flask
was then filled with argon, and 0.02 mL of the 0.304 M solution of
mable on-column injector. GC conditions were as follows: head
pressure ) 7 psi; pressure ) 15.2; velocity ) 21.7; detector, 300 °C;
injector, T
min; column, T
0 °C/min; and T
1
) 80 °C, T
) 90 °C, hold 1 min; T
) 250 °C, ramp rate ) 20 °C/min, hold 12 min.
2
) 250 °C, ramp rate ) 150 °C/min, hold 10
1
2
) 200 °C, ramp rate )
1
-phenylpropyne was added to the sidearm. The solution was placed
5
3
in the cuvette holder in the spectrophotometer, which was connected
to a recirculating bath set at 44.6 °C, and monitored with a thermocouple
thermometer. The solution temperature was allowed to equilibrate for
The retention time for the ester (methyl 2-methoxy benzoate) was 4.7
min, and that for triphenylmethane was 7.9 min. The retention times
for the quinones were 14.8 and 15.3 min. The response factor for the
5
min prior to mixing the alkyne in the sidearm with the carbene
ester relative to triphenylmethane was R
for the quinones relative to triphenylmethane was R
B) At 2.5 M 1-Phenylpropyne. Carbene complex 12 (428.8 mg,
.37 mmol) and triphenylmethane (333.2 mg, 1.37 mmol) were
f
) 0.38. The response factor
complex solution. Upon mixing, the reaction concentrations were
f
) 0.62.
-
5
-3
9
.8 × 10 M 12 and 2.0 × 10 M 1-phenylpropyne. The scanning
(
parameters were as follows: lmax ) 445.8 nm; T ) 44.6 °C; range )
1
6
6
1
00-350 nm; speed ) 300 nm/min; interval ) 2 min; and scans )
0. In all cases the background spectrum was subtracted. Rate )
dissolved in THF to a final volume of 2 mL in a volumetric flask,
giving a stock solution of 0.68 M 12 and 0.68 M triphenylmethane.
Using the same setup as above, 0.69 mL of the stock solution was
transferred to the reaction vessel. The solution was degassed and heated
to 44.6 °C. Once the solution was equilibrated, 0.31 mL of 1-phenyl-
propyne (2.48 mmol) was added and aliquots of the reaction were taken
every minute for the first 12 minutes, and then every 3 min for another
-
9
-1
-5 -1
.7 × 10 M s ; kobs ) 1.8 × 10
s .
-
4
-3
(
B) At 1.0 × 10 M 12 and 5.0 × 10
M 1-Phenylpropyne.
Compound 12 (15.8 mg, 0.05 mmol) was dissolved in THF to a final
-
3
volume of 10 mL to give a 5.03 × 10 M stock solution. A 0.30 M
stock solution of 1-phenylpropyne was prepared by diluting 0.188 mL
of 1-phenylpropyne with THF to a final volume of 5 mL. The reaction
sample was made by combining 0.06 mL of the stock solution of 12
with 2.89 mL of THF in a cuvette fitted with a high vacuum threaded
Teflon stopper and a sidearm. The solution was deoxygenated in the
same manner as above. After being filled with argon, 0.05 mL of the
stock solution of 1-phenylpropyne was put in the sidearm. After
allowing the temperature of the cuvette to equilibrate to 44.6 °C (as
above), we mixed the solutions and collected the UV spectra at 2 min
8
min. The reaction was followed for a total of 3 h. The reaction
concentrations were 0.47 M 12, 0.47 M triphenylmethane, and 2.48 M
-phenylpropyne. The reaction progress was followed by GC as above.
1
The temperature was 44.6 ( 0.2 °C.
Kinetic Measurements of the Reaction of 12 with 1-phenylpro-
23
pyne at 90 °C. (A) At 0.05 M 12. Carbene complex 12 (62.8 mg,
0
.20 mmol) and hexadecane (29 mL, 0.099 mmol) were dissolved in
dimethyltetrahydrofuran (DMTHF) to a total volume of 2 mL in a
volumetric flask, giving a stock solution of 0.1 M 12 and 0.05 M
hexadecane. A sample of (0.75 mL) of the stock solution was transferred
to a flame-dried two-necked 10 mL Wheaton flask with screw caps
containing Teflon-lined septa under argon. The solution was diluted
with enough DMTHF so that the final volume after addition of
1-phenyl-1-propyne was 1.5 mL. The solution was deoxygenated by
the freeze-pump-thaw method (3 cycles) and then placed in a
preheated (89.7 °C ( 0.7 °C) oil bath. After two minutes, 1-phenyl-
1-propyne was added (19-47 mL), giving a final concentration of 0.05
M 12, 0.025 M hexadecane, and 0.1-0.25 M 1-phenyl-1-propyne.
The progress of the reaction was monitored by the disappearance of
the carbene complex 12 which in turn was monitored by the disap-
pearance of the corresponding ester, methyl 2-methoxy benzoate, from
the crude reaction mixture obtained upon oxidative workup with
hexadecane as the internal standard. Aliquots (0.05 mL) were taken
every 1-10 min and quenched in 0.1 mL of 0.5 M cerium ammonium
nitrate (CAN) in methanol. After oxidation for approximately 5 min,
-
4
intervals. The reaction concentrations were 1.0 × 10 M 12 and
.0 × 10 M 1-phenylpropyne. The same parameters as above were
used to collect the spectra. Rate ) 1.6 × 10 M s ; kobs ) 1.9 ×
-
3
5
-
9
-1
-
5
-1
1
0
s .
-
5
-3
(
C) At 5 × 10 M 12 and 1 × 10 M 1-Phenylpropyne.
Compound 12 (15.8 mg, 0.05 mmol) was dissolved in THF to a final
-
3
volume of 10 mL to give a 5.03 × 10 M stock solution. A 0.15 M
stock solution of 1-phenylpropyne was prepared by diluting 0.094 mL
of 1-phenylpropyne with THF to a final volume of 5 mL. The reaction
sample was made by combining 0.03 mL of the stock solution of 12
with 2.95 mL of THF in a cuvette fitted with a high vacuum threaded
Teflon stopper and a sidearm. The solution was deoxygenated in the
same manner as above. After being filled with argon, 0.02 mL of the
stock solution of 1-phenylpropyne was put in the sidearm. After
allowing the temperature of the cuvette to equilibrate to 44.6 °C (as
above), we mixed the solutions and collected the UV spectra at 2 min
-
5
intervals. The reaction concentrations were 5.0 × 10 M 12 and

Reaction of Fischer Carbene Complex with Alkynes
J. Am. Chem. Soc., Vol. 121, No. 27, 1999 6413
each aliquot was diluted with 0.25 mL of ether and 0.2 mL of water.
The layers were allowed to separate, and the bottom layer was removed
with a pipet before GC analysis. GC analysis was performed on a Varian
Kinetic Measurements. The progress of the reaction was monitored
by the disappearance of the carbene complex which in turned was
monitored by the disappearance of the corresponding ester, methyl
benzoate, from the crude reaction mixture obtained upon oxidative
workup with dodecane as the internal standard. Aliquots (0.025 mL)
were taken every 10 min for the first hour and then every 30 min for
two more hours. The aliquots were quenched in 0.05 mL of 0.5 M
cerium ammonium nitrate (CAN) in methanol. After oxidation for
approximately 5 min, each aliquot was diluted with 0.5 mL of ethyl
acetate and 1 mL of water. The layers were allowed to separate, and
the bottom layer was removed with a pipet before GC analysis.
3
600 with a 30 m Alltech SE-54 0.53 mm i.d. megabore column and
with an on-column injector. The following conditions were used:
injector temp, 250 °C; detector temp, 300 °C; head pressure, 3 psig;
initial column temp, 150 °C (2 min); final column temp, 250 °C; ramp
rate, 10 °C/min; and hold time, 13 min. The retention time for the
ester (methyl 2-methoxy benzoate) was 6.41 min, and that for
hexadecane was 9.5 min. The response factor for the ester relative to
hexadecane was R
f
) 0.65.
(B) At 0.005 M 12. The same concentration of the stock solution
GC analysis was performed on a Varian 3600 with a 30 m Alltech
SE-54 0.53 mm i.d. megabore column and with an on-column injector.
The following conditions were used: injector temp, 250 °C; detector
was used as for the 0.05 M reactions. The reaction solution was made
by diluting 0.075 mL of the stock solution with DMTHF so that the
final volume after addition of the 1-phenyl-1-propyne was 1.5 mL. The
solution was deoxygenated by the freeze-pump-thaw method (6
cycles) and then placed in an (89.5 ( 0.7 °C) oil bath. After two
minutes, 1-phenyl-1-propyne was added (9-19 mL) to give a final
concentration of 0.005 M 12, 0.0025 M hexadecane, and 0.0479-0.1
M 1-phenyl-1-propyne.
Aliquots (0.05 mL) were taken every 1-10 min and were quenched
in 0.05 mL of 0.5 M CAN in methanol. The preparation of aliquots
for GC analysis was the same as for the 0.05 M reactions. GC analysis
of the aliquots was performed under the following conditions: injector
temp, 250 °C; detector temp, 300 °C; head pressure, 3 psig; initial
column temp, 100 °C (8 min); final column temp, 230 °C; ramp rate,
temp, 300 °C; head pressure, 3 psig; T
ramp rate, 10 °C/min; T ) 300 °C; ramp rate, 50 °C/min; and hold
time, 6.4 min. The retention time for the ester (methyl benzoate) is
1
) 80 °C (2 min); T
2
) 120 °C;
3
R
R
T
) 5.72 min. The retention time for dodecane (internal standard) is
) 4.95 min. The response factor of methyl benzoate relative to
T
dodecane is R ) 0.55.
f
Kinetic Measurements of Phenyl Methoxy Chromium Carbene
Complex 28 with Phenylacetylene. A stock solution of carbene
complex was made by combining 400 mg of 28 (1.28 mmol) and 0.291
mL of dodecane (1.28 mmol) with THF in a 2 mL volumetric flask to
give a 0.641 M solution of both 28 and dodecane.
2
0 °C/min; and hold time, 10 min. The retention time was 14.23 min
(A) At 0.5 M Complex 28 and 2.0 M Phenylacetylene. With the
same setup as for diphenylacetylene, 0.78 mL of the stock solution of
carbene complex was combined with 0.22 mL of phenylacetylene (2.00
mmol) for a final volume of 1 mL. The solution was degassed with
three freeze-pump-thaw cycles and placed in a preheated oil bath at
44.4 ( 0.4 °C.
for the ester (methyl 2-methoxy benzoate) and was 16.53 min for
hexadecane. The lengthy hold time was necessary due to the large size
of the solvent peak at these concentrations.
Kinetic Measurements of Phenyl Methoxy Chromium Carbene
Complex 28 with Diphenylacetylene. (A) Stock Solutions. A stock
solution of carbene complex 28 was made by combining 416.1 mg of
CC (1.33 mmol) and 0.303 mL of dodecane (1.33 mmol) with THF in
a 2 mL volumetric flask to give a 0.667 M solution of both CC and
dodecane. A separate stock solution of diphenylacetylene was made
by combining 534.8 mg of alkyne (3.00 mmol) with THF to a total
volume of 1 mL in a volumetric flask, resulting in a 3.00 M solution
of alkyne.
(B) At 0.5 M Complex 28 and 1.0 M Phenylacetylene. With the
same setup as for diphenylacetylene, 0.78 mL of the stock solution of
carbene complex was combined with 0.11 mL of phenylacetylene (1.00
mmol) and 0.11 mL of THF for a final volume of 1 mL. The solution
was degassed with three freeze-pump-thaw cycles and placed in a
preheated oil bath at 44.5 ( 0.5 °C. The progress of the reaction was
monitored by the disappearance of the carbene complex just as for the
reaction with diphenylacetylene. The same GC conditions were also
used.
(B) At 1.2 M Diphenylacetylene and 0.4 M Complex 28. In a
flame-dried three-necked 25 mL flask with two glass stoppers and one
glass stopcock under argon were combined 0.6 mL of the carbene
complex stock solution and 0.4 mL of the alkyne stock solution, giving
a final concentration of 0.40 M 28, 0.40 M dodecane, and 1.2 M alkyne.
The solution was deoxygenated by the freeze-pump-thaw method (3
cycles), and the glass stopcock was then replaced with a septum. The
flask was then placed in a preheated (44.2 ( 0.6 °C) oil bath. The
progress of the reaction was monitored as described below.
Acknowledgment. This work was supported by the National
Science Foundation (CHE-9422517). We thank the Division of
Organic Chemistry of the ACS for a fellowship for M.L.W.
co-sponsored by John Wiley & Sons and Organic Reactions.
The NMR instruments used were funded in part by the NSF
Chemical Instrumentation Program. We thank Professors Ken’ichi
Takeuchi, Koichi Komatsu, and T. Ishihara for an improved
procedure for the preparation of cyclopropenone 22.
(
C) At 0.6 M Diphenylacetylene and 0.4 M Complex 28. With
the same setup as above, 0.4 mL of the carbene complex stock solution,
.2 mL of the alkyne stock solution, and 0.2 mL of THF were combined,
0
deoxygenated as above, and placed in a preheated (44.5 ( 0.5 °C) oil
bath. The progress of the reaction was monitored as described below.
JA983101U