X-ray crystallographic and NMR spectroscopic study of (η2- Alkene) (μ-alkyne)pentacarbonyldicobalt complexes: Arrested pauson - khand reaction intermediates

Article abstract of DOI:10.1021/om900615m

The hexacarbonyldicobalt complexes of a range of 5-alkynyl-5H-dibenzo[a,d] cycloheptenes, 11a - e, readily undergo loss of a carbonyl ligand with concomitant formation of pentacarbonyldicobalt clusters, 12a-e, in which the vacant coordination site on coba

Full text of DOI:10.1021/om900615m

6308 Organometallics 2009, 28, 6308–6319
DOI: 10.1021/om900615m
X-ray Crystallographic and NMR Spectroscopic Study of (η2-Alkene)
(μ-alkyne)pentacarbonyldicobalt Complexes: Arrested Pauson-Khand
Reaction Intermediates
†
Sarah A. Brusey, Emilie V. Banide, Steffen Dorrich, Paul O’Donohue, Yannick Ortin,
†
†
†
†
€
Helge Muller-Bunz, Conor Long, Paul Evans,* and Michael J. McGlinchey*
†
‡
,†
,†
€
†School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland, and
‡School of Chemical Sciences, Dublin City University, Dublin 9, Ireland
Received July 14, 2009
The hexacarbonyldicobalt complexes of a range of 5-alkynyl-5H-dibenzo[a,d]cycloheptenes,
11a-e, readily undergo loss of a carbonyl ligand with concomitant formation of pentacarbonyldi-
cobalt clusters, 12a-e, in which the vacant coordination site on cobalt is now occupied by the
C(10)-C(11) double bond of the central seven-membered ring. These (η2-alkene)(μ-alkyne)-
pentacarbonyldicobalt complexes provide structural models of the first step of the proposed
mechanism of the Pauson-Khand process for the formation of cyclopentenones via the coupling
of an alkene, an alkyne, and a source of carbon monoxide. X-ray crystallographic data reveal that the
˚
distance between the alkene carbons and the nearest alkyne carbon is approximately 2.85 A, slightly
˚
shorter than the theoretically predicted value of ∼2.95 A. VT NMR data for the interconversion of
11b and 12b yielded activation energies for the forward and reverse processes, 29 and 15 kcal mol-1
,
respectively, and the enthalpy change for the endothermic process (14 kcal mol-1); these match very
well the earlier predictions from DFT calculations. Although the ethynyl-hexacarbonyldicobalt
complex, 11f, does not suffer facile elimination of CO, it does participate in an intermolecular PKR
with norbornadiene. Likewise, attempts to extend the reach of the alkynyl moiety through
incorporation of an additional methylene group yield only an intermolecular PKR product. It is
suggested that the pentacarbonyl complexes, 12a-e, do not continue along the PKR pathway
because of the unfavorable relative orientation of the cobalt-coordinated alkyne and alkene.
Introduction
monoxide, is a highly convergent method for the preparation
of the cyclopentenone ring, 3 (see Scheme 1).1 The process
was initially reported in 1973,2 and early examples focused
on the use of dicobalt octacarbonyl as both the reaction
mediator and the source of the carbonyl functional group.
Since that time, several variants of the original thermal
protocol have been introduced that have enhanced the scope
and utility of the process.3 However, the mechanism con-
tinues to attract discussion.4 The chemically reasonable
reaction pathway first proposed in 1985 by Magnus5a-c
and by Schore5d invokes initial formation of the well-
characterized (μ-alkyne)hexacarbonyldicobalt tetrahedral
cluster, 4, which loses a carbonyl ligand to generate the
pentacarbonyl cluster, 5, thus allowing incorporation of
the alkene moiety as in 6. Subsequent coupling of the alkyne
and alkene to form the metallocycle, 7, alkyl migration to
incorporate the carbonyl group, as in 8, and reductive
elimination of the cyclopentenone from the final intermedi-
ate, 9, completes the process. In the first step, the loss of a
The Pauson-Khand reaction (PKR), the formal [2þ2þ1]
cycloaddition of an alkyne, 1, an alkene, 2, and carbon
*Corresponding authors. Phone: (þ353)-1-716-2880. Fax: (þ353)-1-
716-1185. E-mail: michael.mcglinchey@ucd.ie; paul.evans@ucd.ie.
(1) For review literature see: (a) Pauson, P. L. Tetrahedron 1985, 41,
5855–5860. (b) Schore, N. E. Chem. Rev. 1988, 88, 1081–1119. (c) Schore,
N. E. Org. React. 1991, 40, 1–90. (d) Schore, N. E. In Comparative Organic
Syntheses; Trost, B. M.; Fleming, I., Eds.; Pergamon Press: Oxford, 1991;
Vol. 5, pp 1037-1062. (e) Schore, N. E. In Comprehensive Organometallic
Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Elsevier:
New York, 1995; Vol. 12, pp 703-739. (f ) Fr€uhauf, H.-W. Chem. Rev. 1997,
97, 523–596. (g) Geis, O.; Schmalz, H. G. Angew. Chem., Int. Ed. 1998, 37,
911–914. (h) Chung, Y. K. Coord. Chem. Rev. 1999, 188, 297–340. (i)
Fletcher, A. J.; Christie, S. D. R. J. Chem. Soc., Perkin Trans. 1 2000, 1657–
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(k) Sugihara, T.; Yamaguchi, M.; Nishizawa, M. Chem.;Eur. J. 2001, 7,
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Laschat, S.; Becheanu, A.; Bell, T.; Baro, A. Synlett 2005, 2547–2570. (n)
Rodriguez Rivero, M.; Adrio, J.; Carretero, J. C. Synlett 2005, 26–41. (o)
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Berlin, 1999; Vol 2, pp 491-510. (q) Gibson, S. E.; Stevenazzi, A. Angew.
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pubs.acs.org/Organometallics
Published on Web 09/30/2009
2009 American Chemical Society

Article
Organometallics, Vol. 28, No. 21, 2009 6309
Scheme 1. Proposed Mechanism of the Pauson-Khand
Reactiona
antiaromatic carbocations.11 We chose to prepare (5-phenyl-
ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol)hexacarbonyl dico-
balt, 11a, with the aim of investigating the extent of the
interaction between the 14π aromatic dibenzosuberenyl cation
and the cobalt vertices.12 However, when a solution of the
alkynol ligand in THF was allowed to react with Co2(CO)8 at
room temperature for 15 h, two products were isolated: the
major product (73%) was the anticipated hexacarbonyl clus-
ter, 11a, and the minor product (15%), separable by flash
column chromatography, proved to be the pentacarbonyl-
dicobalt complex 12a, whereby the third ligand site on one of
the cobalt centers was now occupied by the C(10)-C(11)
double bond of the seven-membered ring (Scheme 2). More-
over, further investigation of this previously unprecedented
decarbonylation/alkene-coordination process demonstrated it
to be rather facile. Typically, a mixture of 11a and 12a (85:15)
in deuterated chloroform gradually metamorphosed into a
mixture containing equal amounts of 11a and 12a after 24 h at
room temperature.
a eq = equatorial; ax = axial.
carbonyl ligand is typically achieved thermally or upon
treatment with a mild oxidant such as an amine N-oxide.3
Since 1985 several reports concerning this mechanism have
appeared; for example 5 has been detected using IR spectro-
scopy6 and is isolable when the alkyne contains an S atom
capable of coordinating to the vacant site.7 Similarly, photo-
lysis of 4 at 532 nm brings about loss of a carbonyl ligand,
and the resulting pentacarbonyl can be trapped by pyridine
or a phosphine.8 More recently, electrospray ionization mass
spectrometry has been employed to detect, in one example,
an alkene association complex of the type 6.9 However, apart
from the initially formed (μ-alkyne)hexacarbonyldicobalt
complex, 4, none of the proposed intermediates along this
pathway have previously been isolated and characterized as
stable entities, although Fox has identified side-products
from unproductive pathways in the PKR involving cyclo-
propenes.4b We here report the syntheses, X-ray crystal-
lographic structural characterizations, and a variable-
temperature NMR investigation of a series of (η2-alkene)-
(μ-alkyne)pentacarbonyldicobalt complexes, of the type
6a/6b, which represent the first isolated examples of the first
step in the proposed mechanism of the PKR.10
The IR spectrum of the hexacarbonyl cluster 11a exhibits
ν(CO) peaks at 2090, 2056, and 2029 cm-1, whereas, in the
pentacarbonyl complex, 12a, the ν(CO) absorptions are
found at 2075, 2023, and 1978 cm-1. These data com-
pare well with those reported for the photolysis of
(PhCtCH)Co2(CO)6 in an argon matrix that revealed
strong infrared peaks at 2099, 2062, 2036, and 2031 cm-1
for the hexacarbonyl cluster and at 2081, 2035, 2016, and
1981 cm-1 after loss of a CO ligand.6
The molecular structures of 11a and 12a, determined by
X-ray crystallography, appear in Figures 1 and 2, respec-
tively. The (phenylethynyl)Co2(CO)6 moiety adopts a pseu-
doaxial position and is oriented such that the phenyl ring lies
directly below the C(10)-C(11) double bond, thus shielding
the attached protons, which resonate at 6.27 ppm (7.23 ppm
in the free ligand). The carbonyl ligands in the Co2(CO)6
fragment in 11a are close to the normally observed eclipsed
sawhorse conformation. In the pentacarbonyl complex, 12a,
it is evident that rotation of the dicobalt-alkyne cluster about
the C(5)-C(12) bond has occurred, thus placing one metal
proximate to the C(10)-C(11) linkage. The boat conforma-
tion is now more pronounced, thus generating a distinctly
avian-type structure. The alkyne carbon-carbon linkage
Results and Discussion
˚
(1.340 A) and the C-CtC-C “bend-back” angles (142.6°
and 144.7°) in 12a lie within the usual ranges; as is normal,
Hexa- and Pentacarbonyl Dicobalt Complexes of (5-Alky-
nyl-5H-dibenzo[a,d]cyclohepten-5-ols). Our involvement in
this area arose somewhat serendipitously as a continuation
of earlier studies on metal-cluster-stabilized nonclassical or
complexation to cobalt increases the C(10)-C(11) double
˚
˚
bond distance (from 1.336(3) A in 11a to 1.403(7) A in 12a).
This reaction has now been generalized to include a range
of alkynyl substituents. Thus, the (μ-alkyne)hexacarbo-
nyldicobalt complexes in which R = SiMe3 (11b), p-
C6H4CN (11c), m-C6H4F (11d), p-C6H4CF3 (11e), and H
(11f) have also been prepared. Of these, all except 11f (R=H)
gradually undergo decarbonylation at ambient temperature
(5) (a) Magnus, P.; Principe, L.-M. Tetrahedron Lett. 1985, 26, 4851–
4854. (b) Magnus, P.; Exon, C.; Albaugh-Robertson, P. Tetrahedron 1985,
41, 5861–5869. (c) Magnus, P.; Principe, L.-M.; Slater, M. J. J. Org. Chem.
1987, 52, 1483–1486. (d) La Belle, B. E.; Knudsen, M. J.; Olmstead, M. M.;
Hope, H.; Yanuck, M. D.; Schore, N. E. J. Org. Chem. 1985, 50, 5215–5222.
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Vaissermann, J.; Li, L.; McGlinchey, M. J. Organometallics 1993, 12, 4917–
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pp 685-702. (c) ElAmouri, H.; Gruselle, M. Chem. Rev. 1996, 96, 1077–1104.
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6310 Organometallics, Vol. 28, No. 21, 2009
Scheme 2. Sequential Formation of Hexacarbonyls 11 and Pentacarbonyls 12
Brusey et al.
to yield the corresponding (η2-alkene)(μ-alkyne)pentacarbonyl-
dicobalt complexes, 12b through 12e. Moreover, the identities of
several of these clusters have been unequivocally established by
X-ray crystallography, as shown in Figure 3.
in the widely invoked Magnus mechanism5 of the Pauson-
Khand cyclopentenone synthesis.
High-level density functional theory studies by Yamanaka
and Nakamura,15 by Milet, Gimbert, and co-workers,16 and
17
also by Pericas, Riera, Verdaguer, and co-workers, in
ꢁ
The molecular structures of the (μ-alkyne)dicobalt-hexa-
carbonyls (11a, 11b, 11e, 11f) and (η2-alkene)(μ-alkyne)-
dicobalt-pentacarbonyls (12a, 12b, 12c, 12d) illustrate clearly
the boat conformations of the seven-membered rings, which
are defined by C(4A)-C(5)-C(5A) [plane 1], C(4A)-
C(5A)-C(9A)-C(11A) [plane 2], and C(9A)-C(10)-
C(11)-C(11A) [plane 3]. The interplanar angles [plane
1]/[plane 2] (j1) and [plane 2]/[plane 3] (j2) and also the
angles between the two benzo ring planes (j3), as defined in
Figure 4, are listed in Table 1. These data reveal that, in
each case, replacement of a carbonyl ligand, in 11, by the
C(10)-C(11) double bond, in 12, leads not only to enhanced
bending of the seven-membered ring, i.e., reduced values
of j1 and j2, but also a decrease in the interplanar angle, j3,
between the two benzo “wing-like” moieties.
Although the carbonyls of the Co(CO)3 fragment in
12a-d deviate only slightly from the conventional orienta-
tion whereby one axial ligand is aligned with the midpoint of
the alkyne bond (see, for example, the structure of the
(trimethylsilyl)alkynyl-Co2(CO)6 cluster 11b in Figure 5a),
the ligands of the Co(CO)2(alkene) fragment are staggered
rather than eclipsed with respect to the Co(CO)3 tripod; in
particular, the alkene is clearly in a pseudoequatorial site, as
exemplified by the structure of 12b in Figure 5b. In this respect,
these complexes provide structural models of the proposed
(η2-alkene)(μ-alkyne)Co2(CO)5 intermediate 6a (Scheme 1).
The thermal instability of the hexacarbonyl clusters,
11a-e, is remarkable; even at room temperature decarbo-
nylation and formation of the pentacarbonyl complexes,
12a-e, is a facile process, possibly as a consequence of its
intramolecular character whereby loss of CO is compensated
by formation of the cobalt-alkene complex as a chelate. This
result is important, as the clusters 12a-e represent the first
examples of structurally characterized (η2-alkene)-(alkyne)-
pentacarbonyldicobalt complexes, a crucial structural type
which the relative energies of the proposed Magnus inter-
mediates have been calculated, suggest that the most energe-
tically demanding step is the loss of a carbon monoxide
ligand from 4 to form the pentacarbonyl complex 5. These
studies also indicate that the two pseudoaxial carbonyl
groups are more strongly bound than their four pseudo-
equatorial counterparts, thereby implying that the alkenyl
complex 6a will be preferentially formed.15,16,18 Subse-
quently, irreversible bond migration within 6a generates
metallocycle 7a. Milet and co-workers have considered this
key carbon-carbon bond-forming step, and they proposed
an alternative scenario whereby systems capable of under-
going rotation of the ML3 vertex generate complex 6b, from
which position olefin insertion, forming 7b, is comparatively
facile energetically.19 The calculations of Yamanaka and
Nakamura15 indicated that the carbonyl ligands in
(HCtCH)Co2(CO)5(η2-C2H4) should be only slightly dis-
placed from the eclipsed orientation generally observed in
alkyne-Co2(CO)6 systems; this contrasts with the experimen-
tally observed staggered orientation in the pentacarbonyl
complexes 12a-d, as shown in Figures 2, 3, and 5. However,
one must recall that these experimental data are derived from
an intramolecular rather than an intermolecular process.
In all the calculated geometries it was found that the
incoming ethylene initially favors a pseudoequatorial site
such that the distance between an alkene carbon and the
nearer alkyne carbon is approximately 2.95 A.16 As listed in
˚
Table 1, and exemplified in Figure 6, the crystallographically
determined structures of the η2-alkene-pentacarbonyldico-
balt-alkyne complexes 12a-d reveal cobalt-alkene-carbon
˚
distances of 2.133 to 2.184 A. More importantly, the cobalt-
complexed alkene carbons are sited within the range 2.817 to
˚
2.880 A from the nearer alkyne carbon (average of the 10
˚
values in 12a-d is 2.845 A); that is, they are somewhat
shorter than the calculated value.16 However, despite the
proximity of these carbons, the pentacarbonyl complexes
12a-d are reasonably stable and do not continue along the
PKR pathway toward the corresponding cyclopentenones,
13, the formation of which may be precluded by severe ring
strain. However, this observation may also support the
(13) Mercury 1.4.2, available from http://www.ccdc.cam.ac.uk/mer-
cury/.
(14) (a) Steiner, T.; Starikov, E. B.; Tamm, M. J. Chem. Soc., Perkin
Trans. 2 1996, 67–71. (b) Steiner, T.; Mason, S. A.; Tamm, M. Acta Crystal-
logr. B 1997, B53, 843–848. (c) In the corresponding bis(1,4-dibenzo[a,
d]cyclohepten-5-ol)buta-1,3-diyne, both alkynyl groups are positioned axi-
ally: Jacobs, A.; Masuku, L. N. Z.; Nassimbeni, L. R.; Taljaard, S. L.
CrystEngComm 2008, 10, 322–326.
ꢁ
(17) Pericas, M. A.; Balsells, J.; Castro, J.; Marchueta, I.; Moyano,
(15) Yamanaka, M.; Nakamura, E. J. Am. Chem. Soc. 2001, 123,
1703–1708.
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A.; Riera, V.; Vazquez, J.; Verdaguer, X. Pure Appl. Chem. 2002, 74,
(16) (a) Robert, F.; Milet, A.; Gimbert, Y.; Konya, D.; Greene, A. E.
J. Am. Chem. Soc. 2001, 123, 5396–5400. (b) de Bruin, T. J. M.; Milet, A.;
Robert, F.; Gimbert, Y.; Greene, A. E. J. Am. Chem. Soc. 2001, 123, 7184–
7185. (c) de Bruin, T. J. M.; Milet, A.; Greene, A. E.; Gimbert, Y. J. Org.
Chem. 2004, 69, 1075–1080.
167–174.
(18) Derdau, V.; Laschat, S.; Jones, P. G. Eur. J. Org. Chem. 2000,
681–689.
(19) de Bruin, T. J. M.; Michel, C.; Vekey, K.; Greene, A. E.;
Gimbert, Y.; Milet, A. J. Organomet. Chem. 2006, 691, 4281–4288.

Article
Organometallics, Vol. 28, No. 21, 2009 6311
proposal that alkene insertion in this type of complex occurs
preferentially from an axial position (i.e., 6b f 7b) whereby
the alkene and alkyne are suitably aligned for coupling, and
the existence of 12 as an arrested Pauson-Khand intermedi-
ate is a consequence of the rigidity of this class of compound.
This lack of rotational freedom manifests itself in the 1H
and 13C NMR spectra of 11 and 12. Typically, in the
(trimethylsilyl)alkynyl-hexacarbonyldicobalt cluster, 11b,
the time-averaged Cs symmetry of the system renders the
Figure 1. Molecular structure of the hexacarbonyl cluster 11a
(thermal ellipsoids at 50%).
Figure 2. Molecular structure of the pentacarbonyl cluster 12a
(thermal ellipsoids at 50%).
Figure 3. Mercury13 representations of the molecular structures of 11b, 12b, 11e, 12d, 11f, and 12c (thermal ellipsoids at 50%).

6312 Organometallics, Vol. 28, No. 21, 2009
Brusey et al.
These experimental values correlate very well with the calcula-
tions of Yamanaka and Nakamura,15 who reported Eact and
ΔH as 26.4 and 14.6 kcal mol-1, respectively, and with those of
Pericas and co-workers,17 who calculated corresponding values
ꢁ
of 33.5 and 12 kcal mol-1. We reiterate, however, that their
calculations were based on an intermolecular reaction to form
(HCtCH)Co2(CO)5(η2-C2H4), whereas the experimental data
were obtained from a more heavily substituted intramolecular
process. Nevertheless, the remarkably good agreement between
the calculated and experimental values is gratifying.
As noted above, molecules 11a-e were readily converted
into 12a-e; in contrast, the least substituted complex, 11f
(R = H), was much more stable and only suffered loss of a
carbonyl ligand at elevated temperatures (PhMe, 110 °C) or
when treated with N-methylmorpholine N-oxide monohy-
drate. In this instance the pentacarbonyl complex 12f proved
to be unstable, and we were unable to isolate this species in
pure crystalline form.
However, 12f was detected in a low-temperature matrix
when 11f was deposited in methane at 20 K. In this experi-
ment it was necessary to raise the temperature to 353 K in
vacuo to generate sufficient vapor pressure of 11f and to
promote the deposition process. In addition to the expected
IR peaks of the precursor hexacarbonyl, 11f (2097, 2062, and
2033 cm-1), peaks of the pentacarbonyl, 12f, at 2083, 2026,
2015, 2007, and 1982 cm-1, along with uncoordinated CO
(2143 cm-1) were observed, thus confirming the decarbony-
lation of 11f at elevated temperatures and demonstrating
that the pentacarbonyl 12f is sufficiently stable to survive in
the gas phase until isolated in the frozen gas matrix. Preli-
minary photochemical experiments suggest that 557 nm
irradiation of the hexacarbonyl, 11f, also promotes decar-
bonylation to form 12f.
Figure 4. Definition of the interplanar angles j1, j2, and j3.
two benzo rings equivalent, and the protons at C(10) and
C(11) appear as a singlet at 7.01 ppm. In contrast, in the
pentacarbonyl complex 12b, the mirror symmetry is broken,
the benzo rings are now inequivalent, and the protons at
C(10) and C(11) give rise to two 9.5 Hz doublets at 5.34 and
5.19 ppm. By monitoring the intensities of these resonances
as a function of time over a range of temperatures, the
gradual conversion of 11b into 12b was conveniently
followed by NMR spectroscopy and prompted a kinetic
study that allowed the determination of the energetics of
the process. In all cases (except for 11f, R=H), the hexa-
carbonyls, 11a-e, eventually reached an equilibrium with
their alkene-complexed counterparts, 12a-e, at ambient
temperature. In no case did the reaction go to completion
even when the carbon monoxide was free to escape. How-
ever, when a sample of hexacarbonyl 11f (R = H) was
thermolyzed in refluxing toluene, the corresponding penta-
1
carbonyl, 12f, was detected by H NMR spectroscopy, but
Nevertheless, under standard thermal conditions 11f
smoothly underwent an intermolecular Pauson-Khand re-
action with norbornadiene to furnish the expected cyclopen-
tenone, 14, which was fully characterized spectroscopically
and by high-resolution mass spectrometry. The structure of
was not isolable chromatographically; the products were the
free alkynol 10f, the hexacarbonyl 11f, and cobalt-contain-
ing decomposition products. Interestingly, in Gordon’s
matrix infrared study6 of the 254 nm photolysis of
(phenylacetylene)Co2(CO)6 to give (phenylacetylene)Co2-
(CO)5, it was noted that further irradiation at 390 nm
resulted in regeneration of the original hexacarbonyl, pre-
sumably accompanied by decomposition products.
Assuming that the loss of CO is irreversible, one can now
evaluate the activation energies for the interconversion of the
hexacarbonyl and pentacarbonyl species, 11b and 12b, by
intermolecular migration of a carbonyl ligand. As precedent
for such an exchange process we note Seyferth’s observation
that the reaction of chlorocarbynyltricobalt nonacarbonyl,
(OC)9Co3CCl, with AlCl3 to form the acylium salt [(OC)9-
Co3CCO][AlCl4] proceeds readily in the absence of CO,
presumably by ligand transfer from the original cobalt
carbonyl cluster.20
1
14 was elucidated from its H and 13C NMR data, which
indicated formation of the anticipated exo-diastereoiso-
mer.2,22 The conformation of 14 was probed by NOE
measurements, which indicated the proximity of the single
proton in the cyclopentenone ring to the alkene protons at
C(10) and C(11).
Cobalt Carbonyl Complexes of (5-Propynyl-5H-dibenzo-
[a,d]cyclohepten-5-ols). With the aim of synthesizing a more
flexible system to probe whether it is possible to complete
the intramolecular Pauson-Khand reaction in this case,
we chose to prepare [5-(3-propynyl)-5H-dibenzo[a,d]cyclo-
hepten-5-ol], 15, which possesses an additional methylene
group between the seven-membered ring and the alkyne unit.
Propargyl bromide was treated with 2 equiv of butyllithium,
and the resulting dianion23 was allowed to react with diben-
zosuberenone, thus forming 15 after hydrolysis. The X-ray
crystal structures of 15 and of its hexacarbonyldicobalt
complex, 16, reveal that the alkyne moiety (free or com-
plexed) adopts a position such that it is oriented maxi-
mally distant from the C(10)-C(11) double bond in the
seven-membered ring (see Figure 8). Moreover, there was
A standard kinetic treatment21 yielded kforward and kreverse
at each temperature (Table 2), and the van’t Hoff plot of the
temperature dependence of the Keq values gave the overall
enthalpy change for the conversion of the (μ-alkyne)dicobalt
hexacarbonyl, 11b, into the (η2-alkene)(μ-alkyne)dicobalt
pentacarbonyl, 12b. As shown in Figure 7, the activation energy
for the decarbonylation process was found to be ∼29 kcal mol-1
,
.
and the overall reaction was endothermic by ∼14 kcal mol-1
(20) Seyferth, D. Adv. Organomet. Chem. 1975, 14, 97–144.
(21) Engel, T.; Drobny, G.; Reid, P. Physical Chemistry for the Life
Sciences; Pearson-Prentice Hall: Upper Saddle River, NJ, 2008;
pp 682-684.
(22) It is widely reported that this type of intermolecular PKR process
delivers high levels of exo-diastereoselectivity.
(23) Cabezas, J. A.; Pereira, A. R; Amey, A. Tetrahedron Lett. 2001,
42, 6819–6822.

Article
Organometallics, Vol. 28, No. 21, 2009 6313
2
˚
Table 1. Interplanar Angles (deg) and Bond Distances (A) for Free Alkynes 10, (μ-Alkyne)Co2(CO)6 Complexes 11, and (η -Alkene)-
(μ-alkyne)Co2(CO)5 Complexes 12
compound
j1
j2
j3
Co1-C10
Co1-C11
C10 C12
C11 C12
3 3 3
3 3 3
10b (R = TMS)
10f (R = H)a
126.9
123.2
130.2
129.6
135.3
131.7
131.3
129.0
122.4
122.8
123.5
122.3
121.6
153.1
157.9
157.8
156.5
161.3
155.5
155.1
155.6
150.8
152.4
152.8
152.9
151.6
125.8
126.0
132.5
129.7
142.1
133.6
130.3
127.2
120.6
127.3
127.2
123.4
119.9
11a (R = C6H5)b
11b (R = TMS)
11e (R = p-C6H4CF3)
11f (R = H)b
12a (R = C6H5)
12b (R = TMS)b
2.184(5)
2.169(3)
2.178(4)
2.160(2)
2.165(1)
2.139(6)
2.145(3)
2.152(4)
2.146(2)
2.133(1)
2.858
2.877
2.880
2.863
2.830
2.817
2.829
2.840
2.831
2.827
12c R = p-C6H4CN)
12d (R = m-C6H4F)
a Data from ref 14. b Two independent molecules in the unit cell.
Table 2. Kinetic Data for the Conversion of 11b into 12b
temperature (K)
kforward (min-1
)
kreverse (min-1
)
Keq
293
298
303
313
5.18 ꢀ 10-4
1.15 ꢀ 10-3
2.24 ꢀ 10-3
1.27 ꢀ 10-2
1.11 ꢀ 10-3
1.50 ꢀ 10-3
2.20 ꢀ 10-3
6.05 ꢀ 10-3
0.46
0.69
1.02
2.10
Figure 5. View along the cobalt-cobalt bond (a) illustrating the
eclipsed conformations of the Co(CO)3 vertices in 11b and (b)
emphasizing the staggered conformation of the Co(CO)3 and
Co(CO)2(alkene) moieties in the core of the pentacarbonyl
complex 12b.
Figure 7. Energy profile for the conversion of 11b to 12b.
directly above a benzo ring; the 1H NMR resonance of this
proton is readily identified since it is shielded by the ring
current of the proximate benzo moiety and is found at δ 0.10,
while its partner, H(22a), is found at its normal chemical shift
of 0.97 ppm. Although the crystal quality is such as to
preclude unambiguous location of the hydrogens, the oxy-
gens O(1) and O(2) are well positioned to support intramo-
lecular hydrogen bonding between the ketone and the
alcohol; this may hinder rotation about the C(12)-C(13)
bond and help stabilize the observed conformation. Like-
wise, the conformation of 14, the PKR product from 11f and
norbornadiene, may also be favored by hydrogen bonding
between the ketone and the alcohol.
In light of the previous failure of (5-ethynyl-5H-dibenzo[a,
d]cyclohepten-5-ol)hexacarbonyldicobalt, 11f, to suffer loss
of a carbonyl, the propynol 15 was doubly deprotonated and
allowed to react with chlorotrimethylsilane, thus forming
5-[3-(1-trimethylsilylpropynyl)]-5-trimethylsiloxy-5H-di-
benzo[a,d]cycloheptene, 20, whose structure appears in
Figure 10; the monosilylated analogues 21 and 22 were also
formed. Treatment of 20 and 21 with Co2(CO)8 furnished the
hexacarbonyl clusters 23 and 24, respectively; however,
formation of the corresponding Co2(CO)5 derivatives was
not observed, and work in this area is continuing.
Figure 6. Cobalt-carbon bond lengths (- - -) and nonbonded
carbon-carbon distances (- - -) within the core of the pentacar-
bonyl complex 12a; values given in A.
˚
no evidence of facile decarbonylation of 16 to the corre-
sponding alkene-pentacarbonyldicobalt 17, nor to the PKR
product(s) 18 (Scheme 4). In contrast, as indicated in Scheme 5,
an intermolecular PKR with norbornadiene proceeded
smoothly, and the anticipated cyclopentenone product, 19,
was isolated and characterized by X-ray crystallography.
The Pauson-Khand product, 19, is shown in Figure 9 and
clearly illustrates that the cyclopentenone ring adopts an
exo position adjacent to the bridgehead methylene group.
Moreover, one of the bridgehead hydrogens, H(22b), lies
To conclude, the hexacarbonyldicobalt complexes of
a range of 5-alkynyl-5H-dibenzo[a,d]cycloheptenes readily
undergo loss of a carbonyl ligand with concomitant

6314 Organometallics, Vol. 28, No. 21, 2009
Brusey et al.
Figure 8. Mercury representations of the structure of [5-(3-propynyl)-5H-dibenzo[a,d]cyclohepten-5-ol], 15, and of its dicobalt
hexacarbonyl complex, 16 (thermal ellipsoids at 50%).
performed on a Micromass Quattro Micro instrument. Infrared
spectra were recorded on a Perkin-Elmer Paragon 1000 FT-IR
spectrometer and were calibrated with polystyrene. Merck silica
gel 60 (230-400 mesh) or alumina was used for flash chroma-
tography. Melting points were determined on an Electrothermal
Eng. instrument and are uncorrected. Elemental analyses were
carried out by the Microanalytical Laboratory at University
College Dublin. 5-Trimethylsilylethynyl-5H-dibenzo[a,d]cyclo-
hepten-5-ol (10b) and 5-ethynyl-5H-dibenzo[a,d]cyclohepten-
5-ol (10f) were prepared according to literature procedures.14
Synthesis of 5-Phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol
(10a). In a typical reaction, n-BuLi (17.15 mL, 27.5 mmol) was
added dropwise to a solution of phenylacetylene (3.45 mL,
30 mmol) in dry THF (250 mL) at -78 °C. After stirring the
solution for 30 min at -78 °C, it was allowed to warm to room
temperature and stirred for a further 30 min. The reaction
mixture was cooled to -78 °C, and a solution of dibenzosuber-
enone (5.15 g, 25 mmol) in dry THF (20 mL) was added
dropwise. The mixture was stirred for 1 h, then quenched with
distilled water (150 mL) and extracted using diethyl ether, and
the organic layers were combined. These were washed with brine
and dried over magnesium sulfate, the solvent was removed,
and the crude product was chromatographed on an alumina
column using pentane/dichloromethane (80:20) as eluent to give
5-phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol (10a) (6.0 g,
Scheme 3. Intermolecular PKR of Hexacarbonyl 11f with
Norbornadiene
formation of pentacarbonyldicobalt clusters, 12a-e, in
which the vacant coordination site on cobalt is now occupied
by the C(10)-C(11) double bond of the central seven-
membered ring. One can surmise that the rigidity of the
pentacarbonyl complexes, such that the complexed alkene
cannot rotate into a pseudoaxial site, together with potential
steric strain in the product, prevents continuation along the
Pauson-Khand reaction pathway. Consequently, these
complexes provide structural models of the first step of the
proposed mechanism of the PKR process for the formation
of cyclopentenones via the coupling of an alkene, an alkyne,
and a source of carbon monoxide. X-ray crystallographic
data reveal that the distance between the alkene carbons and
1
19.5 mmol; 77%) as a pale yellow solid. H NMR (500 MHz,
˚
the nearest alkyne carbon is approximately 2.85 A, some-
˚
CDCl3): δ 8.16 (d, 2H, J=8.0 Hz, H4, H6), 7.48-7.43 (m, 6H,
H1, H3, H7, H9, phenyl-H), 7.37-7.32 (m, 5H, H3, H8, phenyl-
H), 7.23 (s, 2H, H10, H11), 3.14 (s, 1H, OH). 13C NMR (125
MHz, CDCl3): δ 140.5 (C4a, C5a), 132.9 (C9a, C11a), 131.8
(phenyl o-CH), 131.6 (C10, C11), 129.3 (C1, C9), 128.7 (phenyl
p-CH), 128.6 (C3, C7), 128.4 (phenyl m-CH, phenyl ipso-C),
127.3 (C2, C8), 123.9 (C4, C6), 122.6 (C13), 90.5 (C12). IR
(CHCl3): 3598 (OH), 2227 (CtC) cm-1. Anal. Calcd for
C23H16O: C, 89.58; H, 5.23. Found: C, 89.19; H, 5.33.
Analogously, (5-(4-cyanophenyl)ethynyl)-5H-dibenzo[a,d]-
cyclohepten-5-ol), 10c, 5-(3-fluorophenyl)ethynyl)-5H-diben-
zo[a,d]cyclohepten-5-ol, 10d, and 5-(R,R,R-trifluorotolyl)-
ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol, 10e, were pre-
pared by reaction of dibenzosuberene with the appropriate
lithio-alkynes.
(5-(3-Fluorophenyl)ethynyl)-5H-dibenzo[a,d]cyclohepten-5-ol (10d).
1HNMR(400MHz,CDCl3):δ8.07 (d, J=8.00 Hz, H4,H6), 7.42 (td,
2H, J=7.2Hz, J=1.6 Hz, H3, H7), 7.40 (d, 2H, J=6.8Hz, H1,H9),
7.31 (td, J=7.6 Hz, J=1.2 Hz, H2,H8), 7.28-7.14 (m, 3H, phenyl-H),
7.18 (s, 2H, H10, H11), 7.07 (d, 1H, J=8.4 Hz, phenyl-H), 6.99 (tdd,
1H, J = 7.6 Hz, J=2.4 Hz, J=0.8 Hz, phenyl-H). 13C NMR (100
MHz, CDCl3): δ 162.4 (d, J = 245.2 Hz, CF), 140.5 (C4a, C5a), 132.9
(C9a, C11a), 131.6 (C10, C11), 130.0 (d, J = 8.6 Hz, C13a), 129.9 (d, J=
8.6 Hz, C15), 129.5 (C1, C9),128.5 (C3, C7), 127.6 (d, J = 2.8
Hz, C14), 127.2 (C2, C8), 123.5 (C4, C6), 118.5 (d, J=22.6 Hz),
what shorter than the theoretically predicted value of ∼2.95 A.
However, the activation energies for the forward and reverse
processes, 29 and 15 kcal mol-1, respectively, and the
enthalpy change for the endothermic process (14 kcal mol-1
)
match very well the earlier predictions from DFT calcula-
tions. Although the ethynyl-hexacarbonyldicobalt complex,
11f, does not suffer facile elimination of CO, it does partici-
pate in an intermolecular PKR with norbornadiene. At-
tempts to bring about an intramolecular PKR by extending
the reach of the alkynyl moiety through incorporation of an
additional methylene group were unsuccessful. Future work
will involve the gradual diminution of rigidity and potential
steric strain in these systems so as to probe the viability of
arresting the PKR at subsequent stages of the process.
Experimental Section
General Methods. All reactions were carried under a nitrogen
atmosphere, and solvents were dried by standard procedures. 1H
and 13C NMR spectra were recorded on Varian 300, 400, or 500
MHz spectrometers. Assignments were based on standard two-
dimensional NMR techniques (1H-1H COSY, 1H-13C HSQC,
and HMBC, NOESY). Electrospray mass spectrometry was

Article
Organometallics, Vol. 28, No. 21, 2009 6315
Scheme 4. Unsuccessful Attempts to Carry Out an Intramolecular PKR with 16
Scheme 5. Formation of 19, the Pauson-Khand Product of 16
with Norbornadiene
Figure 9. Mercury representation of the structure of 19, the
Pauson-Khand product from 16 and norbornadiene (thermal
ellipsoids at 50%).
115.8 (d, J=21.1 Hz), (C16, C18), 91.9 (br s, C13), 82.5 (C12), 78.3
(C5a). Anal. Calcd for C23H15OF: C, 84.64; H, 4.63. Found: C,
84.29; H, 4.78.
5-(r,r,r-Trifluorotolyl)-5H-dibenzo[a,d]cyclohepten-5-ol (10e).
1
Yellow solid, 45% yield, mp 79-82 °C. H NMR (500 MHz,
CDCl3): δ 8.10 (d, J=8.0 Hz, 2H, H4, H6), 7.56 (d, J = 8.0 Hz, 2H,
phenyl m-H), 7.51 (d, J = 8.0 Hz, 2H, phenyl o-H), 7.47 (td, J=7.0
Hz, J = 1.5 Hz, 2H, H3, H7), 7.44 (d, J = 8.0 Hz, 2H, H1, H9), 7.35
(td, J=7.0 Hz, J = 1.5 Hz, 2H, H2, H8), 7.22 (s, 2H, H10, H11), 3.23
(s, 1H, OH). 13C NMR (125 MHz, CDCl3): δ 140.2 (C4a, C5a),
132.9 (C9a, C11a), 132.1 (phenyl o-C), 131.7 (C10, C11), 130.4 (q, J=
32.9 Hz, phenyl p-C), 129.4 (C1, C9), 128.7 (C3, C7), 127.4 (C2, C8),
126.5 (phenyl ipso-C), 125.3 (q, J = 3.9 Hz, phenyl m-C), 124.0 (q,
J = 271 Hz, CF3), 123.5 (C4, C6), 93.3 (C12), 83.5 (C13), 72.5
(C-OH). Anal. Calcd for C24H15OF3: C, 76.59; H 4.02. Found: C,
76.23; H 4.03.
Syntheses of (5-Phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-
ol)hexacarbonyldicobalt (11a) and (5-Phenylethynyl-5H-di-
benzo[a,d]cyclohepten-5-ol)pentacarbonyldicobalt (12a). A solu-
tion of 10a (720 mg, 2.34 mmol) and Co2(CO)8 (1.60 g, 4.67
mmol) in THF (25 mL) was stirred at room temperature for 15 h.
The solvent was removed at low temperature, and the crude
product was purified by chromatography on a silica gel column
using pentane/dichloromethane as eluent, to give (5-phenylethy-
nyl-5H-dibenzo[a,d]cyclohepten-5-ol)hexacarbonyldicobalt, 11a
(73%), and (5-phenylethynyl-5H-dibenzo[a,d]cyclohepten-5-
ol)pentacarbonyldicobalt, 12a (15%), as brown solids, which
were subsequently recrystallized from pentane/dichloro-
Figure 10. Mercury representation of the structure of 5-[3-(1-
trimethylsilylpropynyl)]-5-trimethylsiloxy-5H-dibenzo[a,d]cyclo-
heptene, 20 (thermal ellipsoids at 50%).
13C NMR (125 MHz, CDCl3): δ 197.6 (CO), 142.6 (C5a), 142.3
(C4a), 136.4 (C13a), 135.3 (C9a), 134.4 (C11a), 129.8 (C14, C18),
129.7 (C1), 128.8 (C9), 128.5 (C15, C17), 128.1, 128.0 (C3, C16),
128.0 (C7), 127.4 (C2), 127.1 (C8), 123.6 (C12), 122.0 (C4), 91.3
(C13), 76.4 (C5), 74.2 (C11), 70.9 (C10). IR (CHCl3): ν(CO) 2075,
2023, 1978 cm-1. The hexacarbonyl clusters, 11b-f, and the
pentacarbonyl complexes, 12b-e, were prepared analogously.
(5-Trimethylsilylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol)he-
xacarbonyldicobalt (11b). Yield: 64%. 1H NMR (500 MHz,
CDCl3): δ 8.20 (d, 2H, J=8 Hz, H4, H6), 7.50-7.46 (m, 2H,
H3, H7), 7.38 (d, 4H, J=4 Hz, H1, H2, H8, H9), 7.01 (s, 2H, H10,
H11), 2.93 (s, 1H, OH), 0.28 (s, 9H, TMS). 13C NMR (125 MHz,
CDCl3): δ 198.5 (CO), 142.5 (C4a, C5a), 132.9 (C9a, C11a), 132.2
(C10, C11), 130.3 (C1, C9), 128.9 (C3, C7), 127.8 (C2, C8), 125.3
(C4, C6), 78.7 (C13), 77.3 (C12), 76.2 (C5), 1.6 (Me3Si). IR
1
methane. 11a: H NMR (400 MHz, CDCl3): δ 8.19 (dd, 2H,
3J = 8.0, 4J=1.2 Hz, H4, H6), 7.42 (ddd, 2H, 3J = 8.0 Hz, 3J =
7.2 Hz, 4J = 1.6 Hz, H3, H7), 7.29 (td, 2H, 3J=7.6 Hz, 4J=1.2
Hz, H2, H8), 7.27-7.19 (m, 3H, phenyl H’s), 7.17 (dd, 2H, 3J =
7.6 Hz, 4J=1.6 Hz, H1, H9), 6.80-6.76 (m, 2H, phenyl H’s), 6.27
(s, 2H, H10, H11), 2.84 (s, 1H, OH). 13C NMR (125 MHz,
CDCl3): δ 198.7 (CO), 141.2 (C4a, C5a), 138.0 (C13a), 132.2
(C9a, C11a), 130.2 (C10, C11), 128.8 (C1, C9), 128.7 (Cphenyl),
127.6 (C3, C7), 126.9 (Cphenyl), 126.5 (C2, C8), 126.1 (Cphenyl),
123.7 (C4, C6), 109.1, 93.0 (C12, C13), 75.2 (C5a). IR (liquid,
CDCl3): ν(CO) 2090, 2056, 2029 cm-1. 12a: 1H NMR (500
MHz, CDCl3): δ 7.95 (d, 1H, 3J = 8.0 Hz, H6), 7.89 (d, 1H, 3J=
8.0 Hz, H4), 7.58 (d, 1H, 3J = 7.5 Hz, H1), 7.44 (td, 1H, 3J = 7.5
Hz, 4J = 1.0 Hz, H3), 7.37 (d, 1H, 3J = 7.5 Hz, H9), 7.33 (t, 1H,
3J = 7.5 Hz, H7), 7.32 (t, 1H, 3J = 7.5 Hz, H2), 7.20 (t, 1H, 3J =
7.5 Hz, H16), 7.18 (t, 1H, 3J=7.5 Hz, H8), 7.14 (t, 2H, 3J=7.5 Hz,
H15, H17), 6.90 (d, 2H, 3J=7.5 Hz, H14, H18), 5.40 (d, 1H, 3J =
9.5 Hz, H11), 5.37 (d, 1H, 3J = 9.5 Hz, H10), 2.54 (s, 1H, OH).
(CH2Cl2): ν(CO) 2090, 2055, 2026 cm-1
.
[5-(4-Cyanophenyl)ethynyl)-5H-dibenzo[a,d]cyclohepten-5-ol]he-
xacarbonyldicobalt (11c). Yield: 57%. 1H NMR (400 MHz,
CDCl3): δ 8.19 (d, 2H, J = 8 Hz, H4, H6), 7.53 (d, 2H, H14,
H18), 7.47 (t, 2H, H3, H7), 7.34 (t, 2H, H2, H8), 7.2 (d, 2H, H1, H9),
6.87 (d, 2H, H15, H17), 6.28 (s, 2H, H10, H11), 2.89 (s, 1H, OH). 13
C
NMR (100 MHz CDCl3): δ 198.0 (CO), 145.6 (C13a), 142.0 (C4a,

6316 Organometallics, Vol. 28, No. 21, 2009
Brusey et al.
C5a), 132.9 (C9a, C11a), 131.6 (C14, C18), 131.3 (C10, C11), 130.0
(C15, C17), 129.9 (C1, C9), 128.9 (C3, C7), 127.8 (C2, C8), 124.7 (C4,
C6), 118.8 (CdN), 110.2 (C16), 90.6 (C12), 76.4 (C13), 76.0 (C5).
[5-(3-Fluorophenyl)ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol]he-
xacarbonyldicobalt (11d). Yield: 84%. 1H NMR (500 MHz,
CDCl3): δ 8.18 (dd, 2H, J = 8.5 Hz, J = 1 Hz, H4, H6), 7.42
(td, 2H, J = 7.5 Hz, J = 1.5 Hz, H3, H7), 7.32 (td, 2H, J = 7.5 Hz,
J=1.5 Hz, H2, H8), 7.20 (d, 2H, J=7.5Hz, H1, H9), 7.20 (q, 1H, J
=7.5 Hz, H16), 6.99 (tdd, 1H, J=8.5 Hz, J = 2.5 Hz, J = 1 Hz,
H15), 6.57 (dq, 1H, J = 8 Hz, J = 1 Hz, H18), 6.47 (dt, 1H, J = 9.5
Hz,
(C8), 125.4 (C14), 121.89 (C4), 121.85 (C6), 115.9 (C18), 114.8 (C16),
105.0 (C12), 88.98 (C13), 76.01 (C5), 74.3 (C10), 70.9 (C11). IR
(CH2Cl2): ν(CO) 2076, 2022, 1980 cm-1
.
[(5-(r,r,r-Trifluorotolyl)ethynyl)-5H-dibenzo[a,d]cyclohepten-5-
ol)]pentacarbonyldicobalt (12e). Yield: 12%. 1H NMR (400 MHz,
CDCl3): δ 7.92 (d, 1H, J = 8 Hz), 7.86 (d, 1H, J = 8 Hz, H4, H6),
7.58 (d, 1H, J = 8 Hz,), 7.50 (d, 1H, J = 8 Hz, H1, H9), 7.44 (br t,
J = 8 Hz, H3 or H7), 7.38-7.30 (m, phenyl-H’s), 7.2-7.17 (m,
phenyl-H’s), 6.90 (d, 1H, J = 8 Hz, H2 or H8), 6.89 (t, J = 8 Hz, H2
or H8), 5.42 (d, 1H, J = 9.6 Hz, H10 or H11), 5.37 (d, 1H, J=9.6 Hz,
H10 or H11). IR (CH2Cl2): ν(CO) 2078, 2022, 1982 cm-1. Anal.
J = 2 Hz, H14), 6.33 (s, 2H, H10, H11), 2.85 (s, 1H, OH). 13C NMR
(125 MHz, CDCl3): δ 193.3 (CO), 162.2 (d, J = 245.2, CF), 142.0
(C4a, C5a), 133.2 (C9a, C11a), 131.2 (C10, C11), 129.9 (C1, C9), 129.8
(d, J = 8.5 Hz, C13a), 129.4 (d, J = 103 Hz), 128.8 (C3, C7), 127.6
(C2, C8), 125.4 (d, J = 2.8 Hz, C18), 124.7 (C4, C6), 116.4 (d, J =
22.7 Hz, C14), 113.9 (d, J = 21.2 Hz, C15), 109.1 (C12), 92.06 (C13),
76.3 (C5).
[5-(r,r,r-Trifluorotolyl)ethynyl-5H-dibenzo[a,d]cyclohepten-
5-ol]hexacarbonyldicobalt (11e). Yield: 88%. 1H NMR (500
MHz, CDCl3): δ 8.19 (d, 2H, J = 8.5 Hz, H4, H6), 7.50 (d,
2H, J = 8.5 Hz, phenyl m-H), 7.45 (td, 2H, J = 8.5 Hz, J =1.5
Hz, H3, H7), 7.32 (td, 2H, J = 7.5 Hz, J = 1.5 Hz, H2, H8), 7.19
(d, 2H, J = 7.5 Hz, J = 1.5 Hz, H1, H9), 6.88 (d, 2H, J = 8.0 Hz,
phenyl o-H), 6.30 (s, 2H, H10, H11), 2.84 (s, 1H, OH). 13C NMR
(125 MHz, CDCl3): δ 198.2 (CO), 141.9 (C4a, C5a), 133.1 (C9a,
Calcd for C29H15O6F3Co2 0.25CH2Cl2: C, 53.59; H, 2.38; F, 8.69;
3
Co, 17.98. Found: C, 53.63; H, 2.58; F, 9.14; Co, 17.63.
Synthesis of exo-2-(5-Hydroxy-5H-dibenzo[a,d]cyclohepten-5-
yl)-3a,4,7,7a-tetrahydro-4,7-methanoinden-1-one (14). A solu-
tion of the cobalt complex 11f (54 mg, 0.104 mmol, 1 equiv) in
toluene (5 mL) was degassed for 10 min with nitrogen. Norbor-
nadiene (0.11 mL, 1.02 mmol, 10 equiv) was added, and the
mixture was heated to reflux for 1 h. On cooling, the title
compound, 14 (35 mg, 96%) was isolated as a yellow oil by
preparative TLC (cyclohexane/EtOAc, 9:1). Rf =0.25 (cyclo-
hexane/EtOAc, 9:1). IR (neat): 3467, 3065, 3022, 2976, 2947,
1681, 1484, 1436, 1311, 1021 cm-1 1H NMR (400 MHz,
.
CDCl3): δ 8.07 (1H, d, J = 7.5 Hz, ArH), 8.05 (1H, d, J=7.0
Hz, ArH), 7.50-7.46 (2H, m, ArH), 7.34-7.25 (4H, m, ArH),
6.92 (1H, d, J=12.0 Hz, CH), 6.86 (1H, d, J=12.0 Hz, CH), 6.74
(1H, d, J = 3.0 Hz, CH), 6.21 (1H, dd, J = 3.0, 5.5 Hz, CH), 6.09
(1H, dd, J = 2.0, 5.5 Hz, CH), 5.02 (1H, s, OH), 2.72-2.70 (1H,
m, CH), 2.60-2.58 (1H, m, CH), 2.54-2.52 (1H, m, CH), 2.13
(1H, d, J=5.0 Hz, CH), 1.25 (1H, d, J = 9.0 Hz, CH2), 0.97 (1H,
d, J = 9.0 Hz, CH2). 13C NMR (100 MHz, CDCl3): δ 210.4
(CO), 160.7 (CH), 145.0 (C), 139.6 (C), 139.2 (C), 138.6 (CH),
137.0 (CH), 132.5 (C), 132.3 (C), 131.5 (CH), 130.9 (CH), 129.1
(CH), 129.0 (2 ꢀ CH), 128.9 (CH), 126.9 (CH), 126.8 (CH),
124.35 (CH), 124.3 (CH), 74.4 (C), 53.1 (CH), 46.7 (CH),
43.8 (CH), 43.1 (CH), 41.2 (CH2). MS m/z (ESþ): 353 (MH)þ,
40%, 335 (M - OH)þ, 100%. HRMS: m/z 353.1554; calcd for
C25H21O2 353.1542.
C
11a), 131.3 (C10, C11), 129.7 (C1, C9), 129.6 (q, J = 28 Hz,
phenyl p-C), 129.5 (phenyl o-C), 128.9 (C3, C7), 127.7 (C1, C9),
124.9 (q, J = 3.75 Hz, phenyl m-C), 124.7 (C4, C6), 124.1 (q, J =
270 Hz, CF3), 110.0 (C-alkyne), 91.4 (C-alkyne), 76.4 (C5).
Microanalytical data on the hexacarbonyls 11a-e are vari-
able because of ready conversion to the corresponding penta-
carbonyl species.
(5-Ethynyl-5H-dibenzo[a,d]cyclohepten-5-ol)hexacarbonyldico-
balt (11f). Yield: 60%. 1H NMR (500 MHz, CDCl3): δ 8.10 (d,
2H, J = 8 Hz, H4, H6), 7.40 (td, 2H, J = 7.0, J = 1.5 Hz, H3, H7),
7.31 (td, 2H, J = 8.0 Hz, J=1.5 Hz, H2, H8), 7.28 (d, 2H, J = 7.0
Hz, H1, H9), 7.06 (s, 2H, H10, H11), 6.05 (s, 1H, OH), 2.66 (s, 1H,
H13). 13C NMR (125 MHz, CDCl3): δ 198.50 (CO), 142.6 (C9a,
C11a), 132.5 (C4a, C5a), 131.5 (C10, C11), 129.6 (C2, C6), 128.5 (C3,
C7), 127.2, (C1, C9), 124.2 (C4, C6), 73.6 (C12), 29.6 (C13). IR
(CH2Cl2): ν(CO) 2092, 2057, 2026 cm-1. Anal. Calcd for
C23H12O7Co2: C, 53.30; H, 2.33; Co, 22.76. Found: C, 53.12; H,
2.39; Co 22.49.
Synthesis of 5-(3-Propynyl)-5H-dibenzo[a,d]cyclohepten-5-ol
(15). To a solution of n-BuLi (75 mL, 120 mmol) in THF at
-78 °C was added freshly dried TMEDA (4.5 mL, 30 mmol),
followed by dropwise addition of propargyl bromide (5.35 mL,
60 mmol), and the resulting mixture was stirred for 30 min. A
solution of dibenzosuberenone (6.19 g, 30 mmol) in THF
(50 mL) was added dropwise over 15 min, and the reaction
mixture was allowed to warm to room temperature over 2 h. The
reaction was quenched with distilled water (150 mL) and
extracted with diethyl ether. The organic layers were combined,
washed with aqueous HCl solution (150 mL), saturated NH4Cl
solution, and then with brine, and dried using MgSO4, and the
solvent was removed. The crude material was purified by
chromatography on an alumina column using pentane/ethyl
acetate (85:15) as eluent, and 5-(3-propynyl)-5H-dibenzo[a,
d]cyclohepten-5-ol, 15 (2.96 g, 12 mmol, 40%), was isolated as
a pale yellow oil. X-ray quality crystals, mp 113-114 °C, were
obtained from dichloromethane. 1H NMR (300 MHz, CDCl3):
δ 8.03 (d, 2H, 3JHH=8.00 Hz, H4, H6), 7.46 (dt, 2H, 3JHH = 7.48
(5-Trimethylsilylethynyl-5H-dibenzo[a,d]cyclohepten-5-ol)pen-
tacarbonyldicobalt (12b). Yield: 6.5%. 1H NMR (500 MHz,
CDCl3): δ 7.82 (d, 1H, J = 7 Hz, H4), 7.78 (d, 1H, J = 8 Hz,
H6), 7.55 (d, 1H, J = 7.5 Hz, H1), 7.40 (td, 1H, J = 7.5 Hz, J = 1
Hz, H3), 7.30 (d, 1H, J = 8 Hz, H9), 7.29 (td, 1H, J = 6.5 Hz, J =
1 Hz, H2), 7.24 (td, 1H, J = 7.5 Hz, J = 1 Hz, H7), 7.11 (td, 1H.
J = 7.5 Hz, J = 1 Hz, H8), 5.34 (d, 1H, J = 9.5 Hz, H11), 5.19 (d,
1H, J = 9.5 Hz, H10), 2.26 (s, 1H, OH), 0.0 (s, 9H, TMS). 13
C
NMR (125 MHz, CDCl3): δ 198.8 (CO), 143.8 (C5a), 142.5 (C4a),
135.7 (C9a), 134.9 (C11a), 129.8 (C1), 129.0 (C9), 128.3 (C3), 128.0
(C7), 127.8 (C2), 127.2 (C8), 122.5 (C4), 121.7 (C6), 83.0 (C13), 76.6
(C5), 70.7 (C10), 0.0 (C-TMS). IR (CH2Cl2): ν(CO) 2073, 2015,
1972 cm-1. Anal. Calcd for C25H20O6SiCo2: C, 53.39; H, 3.58.
Found: C, 53.27; H, 3.61.
4
Hz, JHH=1.02, H3, H7), 7.40-7.30 (m, 4H, H1, H2, H8, H9),
7.06 (s, 2H, H10, H11), 3.38 (s, 1H, OH), 2.98 (s, 2H, H12), 1.91 (s,
1H, H14). 13C NMR (75 MHz, CDCl3): δ 140.8 (C4a, C5a), 132.2
(C9a, C11a), 131.5 (C10, C11), 129.4 (C2, C8), 128.7 (C3, C7), 126.8
(C1, C9), 124.3 (C4, C6), 79.8 (C13), 74.7 (C5), 72.5 (C14), 27.2
(C12). IR (CHCl3): 3553 (OH), 3305 (alkyne CH), 2116 cm-1
(CtC). EI-MS: m/z 246 (M)þ 3%, 207.4 100%. Anal. Calcd for
C18H14O: C, 87.78; H, 5.73. Found: C, 87.82; H, 5.92.
Synthesis of [5-(3-Propynyl)-5H-dibenzo[a,d]cyclohepten-5-
ol]hexacarbonyldicobalt (16). A solution of Co2(CO)8 (1.18 g,
3.45 mmol) in dry THF (15 mL) was added slowly at room
temperature to a solution of 15 (0.85 g, 3.45 mmol) in dry THF
(35 mL). After stirring for 18 h, the solvent was removed and the
[5-(3-Fluorophenyl)ethynyl)-5H-dibenzo[a,d]cyclohepten-5-ol]pen-
tacarbonyldicobalt (12d). Yield: 16%. 1H NMR (500 MHz, CDCl3):
δ 7.93 (d, 1H, J = 7.5 Hz, H6), 7.87 (d, 1H, J = 7.5 Hz, H4), 7.56
(dd, 1H, J = 7 Hz, 1 Hz, H1), 7.45 (dd, 1H, J = 7.5 Hz, 1.5 Hz, H3),
7.37 (dd, 1H, J = 8 Hz, H9), 7.34 (m, 1H, H7), 7.31 (td, J = 7.5 Hz,
J = 1 Hz, H2), 7.19 (td, 1H, J = 7.5 Hz, J = 1 Hz, H8), 7.10-7.06
(m, 1H, H15), 6.87 (td, 1H, J = 8 Hz, J = 2 Hz, H16), 6.62 (d, 1H,
J=8Hz,H14), 6.45 (dt, J=10Hz,J=2Hz,H18), 5.40 (d, 1H, J=
9.5 Hz, H10), 5.35 (d, 1H, J = 9.5 Hz, H11), 2.49 (s, 1H, -OH). 13
C
NMR (125 MHz, CDCl3): δ 197 (CO), 162.2 (d, J = 247 Hz, C17),
142.1 (C5a), 142.09 (C4a), 138.8 (C13a), 134.9 (C9a), 133.9 (C11a),
129.5 (C1), 128.72 (C9), 128.0 (C3), 127.6 (C7), 127.3 (C2), 127.1

Article
Organometallics, Vol. 28, No. 21, 2009 6317
crude material was purified by chromatography on a silica gel
column using pentane/dichloromethane (50:50) as eluent to give
[5-(3-propynyl)-5H-dibenzo[a,d]cyclohepten-5-ol]hexacarbonyl-
dicobalt, 16 (1.47 g, 2.76 mmol, 80%), as a deep red solid, mp
NMR (125 MHz, CDCl3): δ 142.7 (C4a, C5a), 132.1 (C9a, C11a),
132.0 (C10, C11), 129.1 (C2, C8), 128.2 (C3, C7), 126.4 (C1, C9),
125.2 (C4, C6), 104.1 (C13), 88.9 (C14), 81.6 (C5), 27.7 (C12), 3.0
(OTMS), -0.3 (TMS). IR (CH2Cl2): 2176 cm-1 (CtC). EI-MS:
m/z (%) 390 (2) [Mþ], 279.4 (100). Anal. Calcd for C24H30O1Si2:
C, 73.79; H, 7.74. Found: C, 73.57; H, 7.58.
5-[3-(1-Trimethylsilylpropynyl)]-5H-dibenzo[a,d]cyclohepten-
5-ol (21). Yield: 100 mg, 0.31 mmol, 14%, isolated as a colorless
oil during purification. 1H NMR (300 MHz, CDCl3): δ 7.96 (d,
2H, 3JHH = 7.88 Hz, H4, H6), 7.46-7.25 (m, 6H, H1, H2, H3, H7,
H8, H9), 7.01 (s, 2H, H10, H11), 3.42 (s, 1H, OH), 2.92 (s, 2H,
H12), -0.01 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3): δ 141.0
(C4a, C5a), 132.2 (C9a, C11a), 131.5 (C10, C11), 129.4 (C1, C9 or C2,
C8 or C3, C7), 128.6 (C1, C9 or C2, C8 or C3, C7), 126.9 (C1, C9 or
C2, C8 or C3, C7), 124.5 (C4, C6), 102.3 (C5 or C13 or C14), 89.6
(C5 or C13 or C14), 74.8 (C5 or C13 or C14), 28.9 (C12), -0.2
(TMS).
100-101 °C. 1H NMR (500 MHz, CDCl3): δ 7.95 (d, 2H, 3JHH
=
8.0 Hz, H4, H6), 7.47 (dt, 2H, 3JHH=7.53 Hz, 4JHH = 1.6 Hz,
H3, H7), 7.38 (d, 2H, 3JHH = 7.6 Hz, 4JHH = 1.5 Hz, H1, H9),
7.33 (dt, 2H, 3JHH = 7.3 Hz, 4JHH =1.10H2, H8), 7.02 (s, 2H, H10,
H11), 4.90 (s, 1H, H14), 3.66 (s, 2H, H12), 2.61 (s, 1H, OH). 13C
NMR (125 MHz, CDCl3): δ 199.7 (CO), 141.4 (C4a, C5a), 132.5
(C9a, C11a), 131.7 (C10, C11), 129.6 (C1, C9), 128.9 (C3, C7), 127.0
(C2, C8), 124.3 (C4, C6), 89.5 (C13), 77.6 (C5), 73.5 (C14), 41.7 (C12).
IR (CHCl3): 2091, 2052, 2024 cm-1 (CO). MS (ES-): m/z 531 (M -
H). Anal. Calcd for C24H14Co2O7: C, 54.16; H, 2.65. Found: C,
54.09; H, 2.76. Attempts to carry out an intramolecular PKR with
16, either by treatment with NMO at room temperature or by
heating at reflux in toluene, were unsuccessful.
Pauson-Khand Reaction of 16 with Norbornadiene. Norbor-
nadiene (0.38 mL, 3.76 mmol) was added under nitrogen to a
solution of 16 (0.20 g, 0.38 mmol) in dry toluene and heated at
reflux for 2 h. The solvent was removed, and the crude material
was purified by chromatography on silica gel column using
cyclohexane/ethyl acetate (80:20) as eluent to give 19 (0.13 g,
0.35 mmol, 94%) as a colorless oil, which was recrystallized
from pentane/chloroform. 1H NMR (300 MHz, CDCl3): δ 8.12
(d, 1H, 3JHH = 8.0 Hz, H4 or H6), 7.94 (d, 1H, 3JHH = 8.0 Hz,
H4 or H6), 7.42 (dt, 1H, 3JHH = 7.6 Hz, 4JHH = 1.45, H3 or H7),
5-(3-Propynyl)-5-trimethylsiloxy-5H-dibenzo[a,d]cyclohep-
tene (22). Yield: 100 mg, 0.31 mmol, 14%, isolated as a colorless
oil during purification. 1H NMR (300 MHz, CDCl3): δ 7.98 (d,
2H, 3JHH = 7.13 Hz, H4, H6), 7.52 (t, 2H, 3JHH = 7.49 Hz, H3,
H7), 7.43 (d,2H, 3JHH = 7.24 Hz, H1, H9), 7.38 (t, 2H, 3JHH
=
7.30 Hz, H2, H8), 7.15 (s, H, H10, H11), 3.12 (s, 2H, H12), 1.85 (s,
1H, H14), 0.56 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3): δ
142.1 (C4a, C5a), 132.2 (C9a, C11a), 131.6 (C10, C11), 129.2 (C2,
C8), 128.4 (C3, C7), 126.5 (C1, C9), 125.1 (C4, C6), 81.2 (C5 or
C13), 81.4 (C5 or C13), 72.3 (C14), 25.9 (C12), 3.0 (OTMS).
Synthesis of {5-[3-(1-Trimethylsilylpropynyl)]-5-trimethylsil-
oxy-5H-dibenzo[a,d]cycloheptene}hexacarbonyldicobalt (23). A
solution of Co2(CO)8 (0.47 g, 1.38 mmol) in dry THF (10 mL)
was added slowly at room temperature under nitrogen to a
solution of 18 (0.54 g, 1.38 mmol) in dry THF (25 mL). After
stirring for 18 h, the solvent was removed and the crude material
was purified by chromatography on silica gel using pentane as
eluent to give {5-[3-(1-trimethylsilylpropynyl)]-5-trimethylsil-
oxy-5H-dibenzo[a,d]cycloheptene}hexacarbonyldicobalt (0.42
3
4
7.32 (dt, 1H, JHH = 7.6 Hz, JHH = 1.2 Hz, H3 or H7),
7.31-7.27 (m, 2H, H1, H9), 7.26-7.24 (m, 1H, H2 or H8), 7.18
(dt, 1H, H2 or H8), 7.04 (s, 1H, H10 or H11), 7.03 (s, 1H, H10 or
H11), 6.80 (d, 1H, 3JHH = 2.2 Hz, H21), 6.15 (dd, 1H, 3JHH = 5.4
Hz, 3JHH = 3.0 Hz, H18), 6.08 (dd, 1H, 3JHH = 5.6 Hz, 3JHH
=
2
2.9 Hz, H17), 5.83 (s, 1H, OH), 3.28 (d, 1H, JHH = 14.7 Hz,
H12), 2.72 (s, 1H, H16), 2.60 (d, 1H, 2JHH=14.7 Hz, H12), 2.45 (s,
1H, H20), 2.32 (s, 1H, H19), 2.15 (d, 1H, 3JHH = 4.9 Hz, H15),
0.97 (d, 1H, 2JHH = 9.6 Hz, H22a), 0.10 (d, 1H, 2JHH = 9.6 Hz,
22b). 13C NMR (75 MHz, CDCl3): δ 213.4 (C14), 165.0 (C21),
1
H
g, 0.62 mmol, 45%) as a deep red solid. H NMR (500 MHz,
147.0 (C13), 143.0 (C4a or C5a), 141.7 (C4a or C5a), 138.3 (C18),
136.7 (C17), 132.6 (C9a or C11a), 132.2 (C9a or C11a), 131.9 (C10 or
C11), 131.5 (C10 or C11), 129.2 (C1 or C9), 128.8 (C2 or C8), 128.7
(C3 or C7), 128.6 (C3 or C7), 126.5 (C1 or C9), 126.4 (C2 or C8),
125.3 (C4 or C6), 124.9 (C4 or C6), 76.0 (C5), 52.4 (C15), 48.2
(C20), 43.4 (C16), 42.4 (C19), 40.7 (C22), 34.0 (C12). IR (CHCl3):
3353 (OH), 1677 (CO) cm-1. A sample suitable for X-ray
crystallography was obtained by recrystallization from pen-
tane/chloroform. However, although the atom connectivity
was readily established, the crystal quality precludes the report-
ing of precise bond lengths and angles.
C6D6): δ 8.17 (m, 2H, H4, H6), 7.51-7.05 (m, 6H, H1, H2, H3,
H7, H8, H9), 6.80 (s, 2H, H10, H11), 4.08 (s, 2H, H12), 0.50 (s, 9H,
OTMS), 0.67 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3): δ
200.7 (CO), 200.1 (CO), 142.6 (C4a, C5a), 137.3 (C9a, C11a), 132.0
(C10, C11), 128.9 (C1, C2, C3, C7, C8, C9), 128.7 (C1, C2, C3, C7,
C8, C9), 127.3 (C4, C6), 105.1 (C5), 85.6 (C13), 82.7 (C14), 46.2
(C12), 3.8 (OTMS), 0.7 (TMS). IR (THF): ν(CO) 2083, 2044,
2015 cm-1
.
Synthesis of {5-[3-(1-Trimethylsilylpropynyl)]-5-trimethylsil-
oxy-5H-dibenzo[a,d]cycloheptene}hexacarbonyldicobalt (24). A
solution of Co2(CO)8 (0.47 g, 1.38 mmol) in dry THF (10 mL)
was added slowly at room temperature under nitrogen to a
solution of 19 (0.54 g, 1.38 mmol) in dry THF (25 mL). After
stirring for 18 h, the solvent was removed and the crude material
was purified by chromatography on silica gel using pentane as
eluent to give {5-[3-(1-trimethylsilylpropynyl)]-5-trimethylsil-
oxy-5H-dibenzo[a,d]cycloheptene}hexacarbonyldicobalt, 24
Synthesis of 5-[3-(1-Trimethylsilylpropynyl)]-5-trimethylsil-
oxy-5H-dibenzo[a,d]cycloheptene (20). n-BuLi (2.85 mL, 4.55
mmol) was added dropwise to a solution of 15 (0.56 g, 2.27
mmol) in dry THF (60 mL) at -78 °C and stirred for 1 h. A
solution of freshly distilled chlorotrimethylsilylane (1.15 mL,
6.82 mmol) in THF (10 mL) was added slowly, and the reaction
was allowed to warm to room temperature over a period of 3 h.
The solution was quenched with distilled water (30 mL) and
extracted with diethyl ether several times, the organic layers
were combined, washed with distilled water and brine, dried
over MgSO4, and filtered, and the solvent was removed. The
crude material was purified by chromatography on silica gel
using pentane/dichloromethane (80:20) as eluent to yield
5-[3-(1-trimethylsilylpropynyl)]-5-trimethylsiloxy-5H-dibenzo-
[a,d]cycloheptene, 20 (0.59 g, 1.51 mmol, 67%), as a colorless oil.
A sample, mp 68-69 °C, suitable for an X-ray crystal structure
determination was obtained by recrystallization from pentane/
dichloromethane. 1H NMR (500 MHz, CDCl3): δ 7.88 (d, 2H,
1
(0.42 g, 0.62 mmol, 45%), as a deep red solid. H NMR (500
MHz, C6D6): δ 8.17 (m, 2H, H4, H6), 7.51-7.05 (m, 6H, H1, H2,
H3, H7, H8, H9), 6.80 (s, 2H, H10, H11), 4.08 (s, 2H, H12), 0.50 (s,
9H, OTMS), 0.67 (s, 9H, TMS). 13C NMR (125 MHz, CDCl3):
δ 200.7 (CO), 200.1 (CO), 142.6 (C4a, C5a), 137.3 (C9a, C11a),
132.0 (C10, C11), 128.9 (C1, C2, C3, C7, C8, C9), 128.7 (C1, C2, C3,
C7, C8, C9), 127.3 (C4, C6), 105.1 (C5), 85.6 (C13), 82.7 (C14), 46.2
(C12), 3.8 (OTMS), 0.7 (TMS). IR (THF): ν(CO) 2083, 2044,
2015 cm-1
.
Kinetic Measurements. A sample of the trimethylsilylethynyl-
dicobalt hexacarbonyl complex, 11b, dissolved in CDCl3, was
monitored by NMR spectroscopy at regular intervals (every
minute for the first hour and every 5 min thereafter) for 12 h. The
decreasing intensity of the singlet attributable to H(10,11) at δ
7.01 was evident, as was the increase in the total intensity of the
corresponding pair of doublets at δ 5.34 and 5.19 in 12b. After
3JHH = 7.7 Hz, H4, H6), 7.41 (dt, 2H, 3JHH = 7.6 Hz, 4JHH
=
1.3, H3, H7), 7.34 (d, 2H, 3JHH = 7.6 Hz, H1, H9), 7.26 (dt, 2H,
3JHH = 7.4 Hz, 4JHH = 1.2 Hz, H2, H8), 7.05 (s, 2H, H10, H11),
3.02 (s, 2H, H12), 0.47 (s, 9H, OTMS), -0.08 (s, 9H, TMS). 13
C

6318 Organometallics, Vol. 28, No. 21, 2009
Brusey et al.
Table 3. Crystallographic Data for 11a, 12a, 11b, 11e, 11f, and 12b
11a 12a 11b 11e
11f
12b
empirical formula
fw
cryst syst
C29H16O7Co2 C28H16O6Co2 C26H20O7SiCo2 C30H15O7F3Co2 (C23H12O7Co2)4 CH2Cl2 C25H20O6SiCo2
3
594.28
566.27
monoclinic
Cc (#9)
15.4109(17)
13.1859(14)
12.1179(13)
90
109.525(2)
90
2320.8(4)
4
1.621
590.37
662.28
2157.67
triclinic
P1 (#2)
562.36
triclinica
P1 (#2)
triclinic
P1 (#2)
10.5878(11)
13.3942(13)
18.1754(18)
74.179(2)
81.926(2)
89.863(2)
2453.6(4)
4
1.609
100(2)
1.401
1200
1.58 to 28.00
monoclinic
P21/c (#14)
15.6083(15)
9.8377(10)
17.1024(16)
90
108.570(2)
90
2489.3(4)
4
1.575
monoclinic
P21/n (#14)
9.8271(10)
20.906(2)
13.1398(13)
90
99.147(2)
90
2665.2(5)
4
1.651
100(2)
1.314
1328
1.85 to 26.99
-12 e h e 12
-26 e k e 26
-16 e l e 16
48 743
space group
˚
a, A
9.8943(7)
11.1286(8)
20.5053(15)
75.448(1)
87.776(1)
77.788(1)
2135.7(3)
1
1.678
100(2)
1.660
1082
1.93 to 28.29
-13 e h e 13
-14 e k e 14
-26 e l e 27
21 896
9.8221(15)
9.2641(14)
26.205(4)
90.136(2)
96.267(2)
90.261(2
2370.2(6)
4
1.576
100(2)
1.489
1144
0.78 to 26.00
-12 e h e 12
-11 e k e 11
-32 e l e 32
20 335
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
volume, A
Z
density (calc; g cm-3
temp, K
)
100(2)
1.473
100(2)
1.425
1200
abs coeff, mm-1
F(000)
1144
2.09 to 30.00 2.42 to 30.00
θ range, deg
index ranges
-13 e h e 13 -21 e h e 21 -21 e h e 21
-17 e k e 17 -18 e k e 18 -13 e k e 13
-23 e l e 24
23 995
-17 e l e 16 -23 e l e 24
12 130 27 084
reflns measd
reflns used (Rint
parameters
)
11 701 (0.0231) 6423 (0.0290) 7227 (0.0302)
813 326 369
5818 (0.0362)
439
10 496 (0.0208)
614
9270 (0.0263)
768b
final R values I > 2σ(I)]: R1, wR2 0.0396, 0.1083 0.0547, 0.1496 0.0306, 0.0778 0.0285, 0.0724
0.0361, 0.0850
0.0478, 0.0910
1.022
0.0406, 0.0945
0.0535, 0.1003
1.064
R values (all data): R1, wR2
goodness-of-fit on F2
largest diff peak and hole, e A
0.0474, 0.1142 0.0629, 0.1915 0.0359, 0.0802 0.0310, 0.0740
1.035
1.820, -0.331 1.035, -0.964 0.787, -0.435
1.163
1.043
1.053
0.612, -0.353
-3
˚
0.778, -0.560
0.668, -0.545
a The unit cell is given in the pseudo-monoclinic setting. b The SAME instruction was used to fit the minor disorder to the shape of the major one.
Table 4. Crystallographic Data for 12c, 12d, 15, 16, and 20
12c
12d
15
16
20
empirical formula
fw
cryst syst
C29H15 NO6 Co2 CHCl3
710.65
C28H15O6FCo2
584.26
triclinic
C18H14
246.29
O
C24H14O7Co2
532.21
triclinic
C24H30OSi2
390.66
triclinic
3
monoclinic
P21/c (#14)
10.7596(9)
12.5615(11)
20.7266(17)
90
93.813(2)
90
2795.1(4)
4
1.689
monoclinic
P21/c (#14)
11.5912(14)
13.8714(16)
8.0454(9)
90
101.579(2)
90
1267.3(3)
4
1.291
space group
˚
P1 (#2)
P1 (#2)
P1 (#2)
a, A
7.8288(3)
8.3735(3)
17.7715(7)
84.900(1)
88.034(1)
79.116(1)
1139.35(7)
2
1.703
100(2)
1.509
588
10.6121(15)
14.552(2)
15.424(2)
114.073(2)
90.156(3)
90.025(3)
2174.7(5)
4
1.625
100(2)
1.569
1072
8.3253(7)
15.4506(14)
18.9537(17)
74.760(2)
89.845(2
81.079(2)
2322.0(4)
4
1.118
100(2)
0.163
840
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
volume, A
Z
density (calc; g cm-3
temp, K
)
3
100(2)
1.520
1424
100(2)
0.078
520
abs coeff, mm-1
F(000)
θ range, deg
index ranges
1.90 to 28.33
-14 e h e 14
-16 e k e 16
-27 e l e 27
27 930
2.30 to 35.84
-12 e h e 12
-13 e k e 13
-29 e l e 28
56 397
1.79 to 32.02
-17 e h e 17
-20 e k e 20
-11 e l e 11
30 199
1.45 to 31.83
-15 e h e 15
-21 e k e 21
-22 e l e 22
24 719
1.38 to 30.45
-11 e h e 11
-21 e k e 21
-26 e l e 26
27 101
reflns measd
reflns used (Rint
parameters
)
6935 (0.0284)
443
10 241 (0.0205)
400
4213 (0.0297)
228
13 277 (0.0427)
606
13 645 (0.0205)
716a
final R values I > 2σ(I)]: R1, wR2
R values (all data): R1, wR2
goodness-of-fit on F2
0.0357, 0.0910
0.0410, 0.0937
1.075
0.0239, 0.0657
0.0253, 0.0664
1.061
0.0486, 0.1286
0.0534, 0.1321
1.041
0.0530, 0.1346
0.0584, 0.1371
1.188
0.0463, 0.1168
0.0547, 0.1225
1.032
-3
˚
largest diff peak and hole, e A
1.010, -0.369
0.685, -0.481
0.589, -0.183
0.959, -0.477
0.517, -0.199
a The two disorder parts were restrained to have the same shape using the SAME command.
12 h, no more changes were apparent, and so these values were
used to evaluate the equilibrium constant at the given tempera-
ture. For an equilibrium situation, A a B, a plot of ln([A]t -
[A]eq) versus time yields a straight line graph with a negative
slope equal to the sum of the forward and reverse reaction rate
constants (kf þ kr).21 Using this value and the ratio kf /kr derived
from the measured equilibrium constant, Keq, these two rate
constants can be calculated. The process was subsequently
repeated over a range of temperatures to allow evaluation of
the activation energies for the process.
Matrix IR Spectroscopy. The matrix isolation apparatus
consists of a closed-cycle helium refrigerator, sample window,
shroud, deposition tube, gas mixing chamber, gas inlet, backing
pump, diffusion pump, and temperature control unit. Matrixes
were deposited on a CaF2 window cooled to 20 K, with matching
outer windows on the vacuum shroud. A CS202 closed-cycle
refrigerator was used to cool the sample plate to 20 K, and its
temperature was maintained using a Lakeshore 330 autotuning
temperature controller. Two-stage backing pumps and an oil
diffusion pump fitted with a liquid nitrogen trap reduce the

Article
Organometallics, Vol. 28, No. 21, 2009 6319
shroud pressure to 8 ꢀ 10-4 Torr prior to cooling and achieve
better than 10-6 Torr when the sample window reaches 20 K.
Host gases (Cryo Service) are deposited from the gas mixing
chamber via a needle valve connected to two inlet jets positioned
on either side of the deposition tube. A ratio of sample to host
matrix in the region 1:2000 was achieved. Typically the rate of
gas deposition of 0.3-0.6 Torr/min provides an appropriate
sample-host dilution. Both the sample and isolating gas were
deposited simultaneously. The alkyne dicobalt hexacarbonyl,
11f, was sublimed from a right-angled tube that was electrically
heated to 353 K. The sample deposition was monitored using
infrared spectroscopy and was stopped when the absorbance of
one of the metal carbonyl bands reached approximately 1 AU. A
Perkin-Elmer Spectrum One FTIR spectrophotometer was used
to record IR spectra at 1 cm-1 resolution from 16 interfero-
grams. Matrixes were photolyzed using a 200 W Xe/Hg arc lamp
in combination with a 10 cm water filter to remove the IR
component and appropriate interference filters to select the
desired Hg emission line.
X-ray Crystallography. X-ray crystallographic data were
collected using a Bruker SMART APEX CCD area detector
diffractometer and are listed in Tables 3 and 4. A full sphere of
reciprocal space was scanned by phi-omega scans. Pseudoem-
pirical absorption correction based on redundant reflections
was performed by the program SADABS.24 The structures were
solved by direct methods using SHELXS-9725 and refined by full
matrix least-squares on F2 for all data using SHELXL-97.26
Anisotropic displacement parameters were refined for all non-
hydrogen atoms. Hydrogen atom treatment varied from com-
pound to compound, depending on the crystal quality. All
hydrogen atoms in 11a, 11e, 12c, and 15, alkyne hydrogens in
11f and 16, and ordered hydrogens in 12d and 18 were located in
the difference Fourier map and allowed to refine freely with
isotropic thermal displacement parameters. In 18 C-H bond
˚
lengths were restrained to be their default values (0.99 A for CH2
˚
˚
groups, 0.98 A for methyl groups, 0.95 A for aromatic and
alkene hydrogens) using DFIX. All other hydrogen atoms were
added at calculated positions and refined using a riding model.
Their isotropic thermal displacement parameters were fixed to
1.2 times (1.5 times for methyl and OH groups) the equivalent
isotropic displacement parameters of the atom to which they are
attached. The crystals of 1927 were of insufficient quality to yield
a publishable structure. The connectivity of non-hydrogen
atoms could be established without a doubt, but high R values
led to uncertainties in bond lengths and angles, and hydrogen
atom positions could not be reliably located.
Crystallographic data for the structures reported in this paper
have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publications nos. CCDC 629903 (11a),
CCDC 735735 (11b), CCDC 735738 (11e), CCDC 735737 (11f),
CCDC 629902 (12a), CCDC 735736 (12b), CCDC 735740 (12c),
CCDC 735739 (12d), CCDC 735742 (15), CCDC 735741 (16),
and CCDC 735743 (18).
Acknowledgment. We thank Science Foundation
Ireland and University College Dublin for generous
financial support. S.D. thanks the University of
(24) Sheldrick, G. M. SADABS; Bruker AXS Inc.: Madison, WI, 2000.
€
Wurzburg for an Erasmus exchange fellowship.
€
(25) Sheldrick, G. M. SHELXS-97; University of Gottingen, 1997.
€
(26) Sheldrick, G. M. SHELXL-97-2; University of Gottingen, 1997.
(27) Cell parameters for 19: monoclinic, space group: Cc (#9), a=
Supporting Information Available: Kinetic plots for the con-
version of 11b to 12b. This information is available free of charge
via the Internet at http://pubs.acs.org.
˚
˚
˚
6.682(1) A, b=17.857(2) A, c=31.470(4) A, β=94.873(2)°, V=3742(1)
3
A , Z=8, Dc=1.301 g cm
-1
˚
.