CpCo-stabilized cyclopentadienones from cyclobutadiene complexes: Experimental and theoretical investigations

Article abstract of DOI:10.1021/om050048r

The reaction of 1,4,8,11-tetrathiacyclotetradeca-2,9-diyne (7) with C ₅H₄(CO₂Me)Co(CO)₂ (8) and C ₅H₄(SiMe₃)Co(CO)₂ (10) led to the tricyclic cyclopentadienone complexes 9 and 11. In both species the CO was inserted into a former triple bond. This observation led to the preparation of the tetrathiaalkyl- and tetrathiaaryl-substituted C₅H ₄(CO₂Me)Co-capped cyclobutadiene complexes 23 and 27-30. When these compounds were heated under a pressurized CO atmosphere at 170 °C, the corresponding cyclopentadienone complexes 9, 15, and 31-33 were formed. Model calculations at the B3LYP level of theory on tetrasub-stituted (R = CH₃, SH, (CH₂)₃, S-CH₂-S) CpCo-capped cyclobutadiene complexes showed that the substitution, especially by SH and S-CH₂-S, considerably lowered the energy of the assumed intermediate metallacycles 35 and 36, which opens the possibility of reaction.

Full text of DOI:10.1021/om050048r

2106
Organometallics 2005, 24, 2106-2113
CpCo-Stabilized Cyclopentadienones from
Cyclobutadiene Complexes: Experimental and
Theoretical Investigations
Carsten Schaefer, Daniel B. Werz, Tobias H. Staeb, Rolf Gleiter,* and
Frank Rominger
Organisch-Chemisches Institut der Universita¨t Heidelberg, Im Neuenheimer Feld 270,
D-69120 Heidelberg, Germany
Received January 22, 2005
The reaction of 1,4,8,11-tetrathiacyclotetradeca-2,9-diyne (7) with C5H4(CO2Me)Co(CO)2
(8) and C5H4(SiMe3)Co(CO)2 (10) led to the tricyclic cyclopentadienone complexes 9 and 11.
In both species the CO was inserted into a former triple bond. This observation led to the
preparation of the tetrathiaalkyl- and tetrathiaaryl-substituted C5H4(CO2Me)Co-capped
cyclobutadiene complexes 23 and 27-30. When these compounds were heated under a
pressurized CO atmosphere at 170 °C, the corresponding cyclopentadienone complexes 9,
15, and 31-33 were formed. Model calculations at the B3LYP level of theory on tetrasub-
stituted (R ) CH3, SH, (CH2)3, S-CH2-S) CpCo-capped cyclobutadiene complexes showed
that the substitution, especially by SH and S-CH2-S, considerably lowered the energy of
the assumed intermediate metallacycles 35 and 36, which opens the possibility of reaction.
Scheme 1
Introduction
Transition-metal-induced oligomerization reactions of
triple bonds have comprised a pivotal part of organic
synthesis since the seminal work of Reppe.1 The di-, tri-,
and tetramerizations of triple bonds allow short and
efficient syntheses of homo- and heterocyclic ring sys-
tems. A reagent which is frequently used in these
reactions is (η5-cyclopentadienyl)dicarbonylcobalt(I),
[CpCo(CO)2].2 The reaction of this compound with
alkynes leadssdepending on the reaction conditionss
to CpCo-stabilized cyclobutadienes,3 to cyclopentadi-
enone complexes,4 or even to benzene derivatives.5 For
the mechanisms of these reactions there have been two
proposals reported in the literature. Brintzinger sug-
gested the intermediacy of dicobalt complexes, which
could be isolated.6,7 A second mechanism was put
* To whom correspondence should be addressed. Fax: +49 (6221)
544205. Tel: +49 (6221) 548400. E-mail: rolf.gleiter@urz.uni-heidel-
berg.de.
(1) Reppe, W.; Schlichting, O.; Klager, K.; Toepel, T. Liebigs Ann.
Chem. 1948, 560, 1-92.
(2) (a) Piper, T. S.; Cotton, F. A.; Wilkinson, G. J. Inorg. Nucl. Chem.
1955, 1, 165-174. (b) Fischer, E. O.; Jira, R. Z. Naturforsch. 1955,
10B, 355.
(3) (a) Efraty, A. Chem. Rev. 1977, 77, 691-744. (b) Gleiter, R.
Angew. Chem. 1992, 104, 29-46; Angew. Chem., Int. Ed. Engl. 1992,
31, 27-44.
forward by Rausch et al., which assumes intermediates
with only one cobalt nucleus.8 In this latter proposal it
is assumed that both ligands (L) on the metal are
exchanged in a stepwise fashion by one alkyne unit each
(Scheme 1).
This gives rise to the intermediates A and B. From
B the 16e and 18e cobaltols C and D can emerge. From
C the cyclobutadiene complex E, the cyclopentadienone
(4) (a) Hu¨bel, W. I. In Organic Synthesis via Metal Carbonyls;
Wender, I., Pino, P., Eds.; Wiley: New York, 1968; Vol. 1, pp 273-
342. (b) Pino, P.; Braca, G. In Organic Synthesis via Metal Carbonyls;
Wender, I., Pino, P., Eds.; Wiley: New York, 1977; Vol. 2, pp 419-
516. Schore, N. E. Chem. Rev. 1988, 88, 1081-1119.
(5) (a) Vollhardt, K. P. C. Angew. Chem. 1984, 96, 525-541; Angew.
Chem., Int. Ed. Engl. 1984, 23, 539-555. (b) Bo¨nnemann, H.; Brijoux,
W.; Brinkmann, R.; Meurers, W.; Mynott, R.; von Philipsborn, W.;
Egolf, T. J. Organomet. Chem. 1984, 272, 231-249.
(6) Lee, W.-S.; Brintzinger, H. H J. Organomet. Chem. 1977, 127,
93-103.
(7) Sakurai, H.; Hayashi, J. J. Organomet. Chem. 1972, 39, 365-
370.
(8) Rausch, M. D.; Westover, G. F.; Mintz, E.; Reisner, G. M.; Bernal,
I.; Clearfield, A.; Troup, J. M. Inorg. Chem. 1979, 18, 2605-2615.
10.1021/om050048r CCC: $30.25 © 2005 American Chemical Society
Publication on Web 03/23/2005

CpCo-Stabilized Cyclopentadienones
Organometallics, Vol. 24, No. 9, 2005 2107
Scheme 2
Scheme 3
Scheme 4
complex F, and the benzene derivative G can be formed.
This mechanism is supported by the observations that
intermediates of types A and D could be isolated.9-11
Although B and C could not be isolated, there is
experimental evidence for their intermediacy. Studies
on the pyrolysis of cyclobutadiene complexes in the gas
phase by Vollhardt et al. excluded a Cs-symmetrical
intermediate but favored a bis(alkyne) complex of type
B.12 On the basis of isomerization reactions an activa-
tion energy of 51.7 kcal/mol was reported.12 This result
was supported by quantum-mechanical calculations by
Albright et al., which revealed that a direct rearrange-
ment of the cyclobutadiene complex E into C is a
symmetry-forbidden process and, therefore, a high
activation energy is required.13 This led to the conclu-
sion that cyclobutadiene complexes are unreactive spe-
cies which are involved neither in the cyclopentadienone
nor in the benzene formation (Scheme 1).
However, the view that metal-stabilized cyclobutadi-
ene complexes are rather unreactive has to be altered.
Already in 1964 it was shown by Hu¨bel14 and also by
Santarella15 that the cyclobutadiene complexes 1 and
2 lead to tetraphenylcyclopentadienone 3 (Scheme 2).
Furthermore, we could transform the CpCo-stabilized
cyclobutadiene complexes 4a and 4b into the aromatic
species 5 and 6 by heating with benzonitrile and
dimethyl acetylenedicarboxylate (DMAD), respectively
(Scheme 3).16
clobutadiene complexes. We report on the results of an
experimental and quantum-chemical study of one part
of the mechanism shown in Scheme 1: namely, the reac-
tion of cyclobutadiene complexes E with carbon mon-
oxide, leading to the cyclopentadienone complexes F.
Results and Discussion
In our investigation of the reaction between cyclic
tetrathia-substituted diynes and CpCo(CO)2 derivatives
we found that the reaction of 717 and C5H4(CO2Me)-
Co(CO)2 (8) in toluene affords the cyclopentadienone
complex 9 in 6% yield (Scheme 4).
When the solvent is changed to decalin and higher
temperature is applied, the yield can be increased up
to 33% for 9. The same holds for the reaction of 7 and
C5H4(SiMe3)Co(CO)2 (10) (Scheme 4). The cyclopenta-
dienone complex 11 is formed in 36% yield in this
reaction.
Interestingly the CO is inserted into one of the former
triple bonds of the diyne 7, which was proven by means
of X-ray crystallography (Figure 1). Otherwise, one
would expect the CO to be inserted between the two
former triple bonds.
To find out whether the cyclopentadienone formation
summarized in Scheme 4 is limited to cyclic tetrathia-
diynes only or is dependent on substituents at the Cp
ring, we reacted bis(methylthio)acetylene (12)18 with the
CpRCo(CO)2 species 8, 10, and 13 under the same
conditions (Scheme 5). It was found that the ester group
provides the highest yields of the corresponding cyclo-
With this paper we intend to contribute further to an
understanding of the reactivity of CpCo-stabilized cy-
(9) Krebs, A.; Wilke, J. Top. Curr. Chem. 1983, 109, 189-233.
(10) (a) Wakatsuki, Y.; Nomura, O.; Kitaura, K.; Morokuma, K.;
Yamazaki, H. J. Am. Chem. Soc. 1983, 105, 1907-1912. (b) Diercks,
R.; Eaton, B. E.; Gu¨rtzgen, S.; Jalisatgi, S.; Matzger, A. J.; Radde, R.
H.; Vollhardt, K. P. C. J. Am. Chem. Soc. 1998, 120, 8247-8248. (c)
Dosa, P. J.; Whitener, G. D.; Vollhardt, K. P. C.; Bond, A. D.; Teat, S.
I. Org. Lett. 2002, 4, 2075-2078.
(11) Benisch, C.; Cha´vez, J.; Gleiter, R.; Nuber, B.; Irngartinger,
H.; Oeser, T.; Pritzkow, H.; Rominger, F. Eur. J. Inorg. Chem. 1998,
629-632.
(12) (a) Ville, G.; Vollhardt, K. P. C.; Winter, M. J. J. Am. Chem.
Soc. 1981, 103, 5267-5269. (b) Ville, G. A.; Vollhardt, K. P. C.; Winter,
M. J. Organometallics 1984, 3, 1177-1187.
(13) Hardesty, J. H.; Koerner, J. B.; Albright, T. A.; Lee, G.-Y. J.
Am. Chem. Soc. 1999, 121, 6055-6067. See also: Veiros, L. F.;
Dazinger, G.; Kirchner, K.; Calhorda, M. J.; Schmid, R. Chem. Eur. J.
2004, 10, 5860-5870.
(14) Hu¨bel, W.; Mere´nyi, R. J. Organomet. Chem. 1964, 2, 213-
221.
(15) Vallarino, L. M.; Santarella, G. Gazz. Chim. Ital. 1964, 94, 252-
286.
(17) Benisch, C.; Bethke, S.; Gleiter, R.; Oeser, T.; Pritzkow, H.;
Rominger, F. Eur. J. Org. Chem. 2000, 2479-2488.
(18) Verkruijsse, H. D.; Brandsma, L. Synthesis 1991, 818.
(16) Gleiter, R.; Kratz, D. Angew. Chem. 1990, 102, 304-307; Angew.
Chem., Int. Ed. Engl. 1990, 29, 276-279.

2108 Organometallics, Vol. 24, No. 9, 2005
Schaefer et al.
Scheme 7
cyclic diyne. From this bis(alkyne) complex only the
cobaltol 18 can be formed directly. Now an isomerization
step has to occur, which could proceed via the interme-
diate cyclobutadiene complex 19. From there both
cobaltols 18 and 20 can be reached. For the formation
of the cyclopentadienone complex 22 the cobaltol 20 has
to be an intermediate in the reaction pathway. In
complex 20 one former triple bond is broken and the
CpCo fragment is inserted. This 16e complex is able to
react with CO to afford the 18e cobaltol 21. A rear-
rangement of 21 would lead to the final product 22. To
prove that a cyclobutadiene complex such as 19 is an
active intermediate in the formation of the cyclopenta-
dienone complexes, we dissolved complex 2319 in decalin
and heated the solution to 170 °C under an atmosphere
of 20 bar of CO (Scheme 7). We obtained cyclopentadi-
enone complex 9 in 42% yield as the only product.
As in the previous reactions (cf. Scheme 4), the CO is
inserted in the same position with respect to the substi-
tuents. This leads to the assumption that a cobaltol inter-
mediate analogous to 20 is formed during the reaction.
To find out whether the reaction sequence 17 f 22
(Scheme 6) depends on electronic and/or steric effects,
we have prepared a variety of tetrathia-substituted
cyclobutadiene complexes 27-3019 by reacting the
dithia-substituted alkynes 1218 and 24-2620 with 8
(Scheme 8).
Figure 1. ORTEP representation of complex 11 (50%
ellipsoid probability). Hydrogen atoms are omitted for the
sake of clarity. Color scheme: red, O; blue, Si; orange, S;
purple, Co.
Scheme 5
pentadienone complexes 14-16 (Scheme 5). Therefore,
we continued our investigations with this substituent
at the Cp ring.
Scheme 8
To rationalize the unexpected experimental result
summarized in Scheme 4, we assume that this reaction
proceeds via the mechanism shown in Scheme 6.
Scheme 6
In analogy to Rausch’s mechanism (Scheme 1) the bis-
(alkyne) complex 17 is formed first, starting from a

CpCo-Stabilized Cyclopentadienones
Organometallics, Vol. 24, No. 9, 2005 2109
Figure 3. Calculated energies relative to the correspond-
ing cyclobutadiene complex [34 + CO].
Table 1. Calculated Relative Energies (kcal/mol)
of [34 + CO], [35 + CO], 36, and 37
[34 + CO]
[35 + CO]
36
37
R ) CH3
0
0
0
0
45.7
18.7
-3.0
-13.8
-34.0
-35.7
-44.5
-44.1
-63.6
-55.6
R ) SH
R∩R ) (CH2)3
11.9
R∩R ) S-CH2-S
-10.1
releasing substituents as well as ring strain, we have
chosen neutral methyl groups (R ) Me), electron-rich
thiol groups (R ) SH), bridging trimethylene chains
(R∩R ) (CH2)3), and, as a combination of ring strain
and electron-donating character, S-CH2-S chains (R∩R
) S-CH2-S).
Figure 2. ORTEP representation of complexes 15 (bottom)
and 30 (top) (50% ellipsoid probability). Hydrogen atoms
are omitted for the sake of clarity. Color scheme: red, O;
orange, S; purple, Co.
The resulting energies relative to the corresponding
cyclobutadiene complexes [34 + CO] are listed in Table
1 and depicted in Figure 3. The energy of the cyclo-
butadiene complexes [34 + CO] is set to 0 kcal/mol. The
influence of the substituents R is reflected in the change
of energy in comparison to that for the methyl-
substituted complexes (R ) Me) which were chosen as
reference compounds. It is apparent that the influence
of the substituents R ) SH, R∩R ) (CH2)3, and R∩R )
S-CH2-S is stabilizing compared to that of R ) Me.
The largest influence results for the substituted cobaltol
intermediates [35 + CO]. Here the stabilization energies
with regard to the methyl-substituted derivative are as
follows: for R ) SH, -27.0 kcal/mol; for the trimethyl-
ene-bridged derivative R ) (CH2)3, -33.8 kcal/mol; for
the derivative with bridging S-CH2-S tethers R∩R )
S-CH2-S, -55.8 kcal/mol. In contrast to this observa-
tion the same substituents have significantly less effect
on the relative energy of the cyclopentadienone com-
plexes 37.
The complexes 27-30 were treated with 40 bar of CO
in decalin and heated to 170 °C. As in the case of 23,
the corresponding cyclopentadienone complexes 15 and
31-33 were formed (Scheme 8). The obtained yields led
us to conclude that the cyclopentadienone formation is
easier with small substituents (Me in 15) rather than
with the bulky tert-butyl groups in 32. In the latter case
we could isolate 3 mg of the product; therefore, the
identification is based on the high-resolution mass
spectrometric data only.
Structural Investigations. Single crystals were
available of the cyclobutadiene complexes of 2719 and
30 as well as of the cyclopentadienone complexes of 11
and 14-16. The molecular structures of 15 and 30 are
shown in Figure 2. For the cyclobutadiene complexes
we find that the substituents at the sulfur centers are
turned away from the CpCo moiety. In contrast, in the
case of the cyclopentadienone complexes at least two
groups are oriented parallel to the π plane of the
cyclopentadienone ring. This allows a good interaction
between the 3p lone pairs at the sulfur atom and the π
system. The molecular parameters such as distances
and angles recorded for 27 and 30 as well as for 9 and
14-16 parallel those reported for related systems.
Theoretical Investigations. To rationalize our ex-
perimental findings, we have carried out density func-
tional theory (DFT) calculations21 on the mechanism
shown in Figure 3. To study the influence of electron-
Provided that the compounds 34 and 35 are in
thermodynamic equilibrium, the stabilizing effect should
(19) Werz, D. B.; Schulte, J. H.; Gleiter, R.; Rominger, F. J.
Organomet. Chem. 2004, 689, 3132-3142.
(20) Riera, A.; Cabre´, F.; Moyano, A.; Perica`s, M. A.; Santamar´ıa,
J. Tetrahedron Lett. 1990, 31, 2169-2172.
(21) (a) Kohn, W.; Sham, L. J. Phys. Rev. A 1965, 140, 1133-1138.
(b) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, U.K., 1989. (c) Koch, W.;
Holthausen, M. C. In A Chemists Guide to Density Functional Theory;
Wiley-VCH: Weinheim, Germany, 2000.

2110 Organometallics, Vol. 24, No. 9, 2005
Schaefer et al.
with the metallacycle and the occupied 3p orbitals at
the SH groups is optimal. Similarly, the conjugation
between the SH groups and the adjacent π system of
36 is better than in 34. In 37 the SH groups in positions
R to the CO group of the cyclopentadienone ring show
a conformation which allows 3p-π interaction, whereas
the SH groups at the â-position adopt the same confor-
mation as in 34. The conformations of the SH groups
in 37 are very close to those crystallographically found
in 14-16.
Conclusions
Our investigations on tetrathia-substituted CpCo-
capped cyclobutadiene complexes revealed an enhanced
reactivity of these complexes toward CO insertion. This
observation can be rationalized by assuming an equi-
librium between the cyclobutadiene complex and a
metallacyclopentadiene species. This assumption is
supported by DFT calculations on assumed intermedi-
ates. These calculations furthermore suggest that the
metallacyclopentadiene complexes substituted with
S-CH2-S bridges should be stable enough to be iso-
lated.
Experimental Section
General Remarks. All melting points are uncorrected.
Elemental analyses were carried out by the Mikroanalytisches
Laboratorium der Universita¨t Heidelberg. UV light absorption
data were recorded using a Hewlett-Packard 8452A spectro-
meter. IR spectra were recorded with a Bruker Vector 22. The
NMR spectra were measured with a Bruker WH 300 or Avance
500 spectrometer (1H NMR at 300 or 500 MHz and 13C NMR
at 75 or 125 MHz), using the solvent as an internal standard
(δ). FAB mass spectra refer to data from a JEOL JMS-700
instrument. As matrix for the FAB experiments, m-nitrobenzyl
alcohol was used. All reactions were carried out in dried
glassware under an argon atmosphere using dried and oxygen-
free solvents. The reactions with carbon monoxide were
performed in high-pressure vessels (Roth). Starting materials
were prepared according to literature methods.17,18,20,22
General Procedure for the Synthesis of the Cyclo-
butadiene Complexes. C5H4(CO2Me)Co(CO)2 (8) and the
alkyne were dissolved in toluene. The mixture was stirred at
120 °C for 3 days. After it was cooled to room temperature,
the reaction mixture was separated by column chromatogra-
phy (silica gel) using a gradient of n-hexane f diethyl ether
as eluant.
Figure 4. DFT (B3LYP) optimized structures 34-37 for
R ) SH.
lead to a shift of the equilibrium toward 35. As cobaltol
35 is the reactive 16-electron species required for the
reaction with a CO molecule, the reactivity toward CO
should be enhanced by substituents that stabilize the
transition state between 34 and 35. Though we were
not able to localize this transition state, we assume that
substituents leading to a substantial stabilization of 35
are likely to stabilize the transition state as well. This
assumption is in agreement with the strong endother-
mic reaction path and, therefore, a product-like transi-
tion state receptive to similar substituent effects such
as 35. The proposed large stabilizing effects of SH
groups on 35 is in line with the experimentally found
enhanced reactivity for the SR-substituted derivative
of 34. In the case of the 2-fold trimethylene-bridged
derivative of 34, the reactivity toward CO could be
expected to be increased as well, and therefore a CO
insertion leading to a cyclopentadienone complex should
be possible. When ring strain and electron-donating
sulfur atoms are combined, the most dramatic effect is
to be expected. For this derivative (R∩R ) S-CH2-S)
the cobaltol intermediate [35 + CO] is located energeti-
cally lower than the respective cyclobutadiene complex
[34 + CO]. Therefore, we suspect that the attempted
synthesis of the cyclobutadiene complex should finally
yield the isolable cobaltol 35 instead. As until now there
has existed no isolated, structurally investigated ex-
ample of this reactive intermediate, the synthesis of this
compound still remains a challenging goal.
(a) (η5-(Methoxycarbonyl)cyclopentadienyl)(η4-tetra-
kis(n-propylthio)cyclobutadiene)cobalt(I) (28). This com-
pound was prepared from C5H4(CO2Me)Co(CO)2 (8; 476 mg,
2.00 mmol) and alkyne 24 (697 mg, 4.00 mmol) in toluene (125
mL). Yield: 552 mg (52%) of a yellow-orange oil. 1H NMR (500
3
MHz, C6D6; δ): 0.89 (t, J ) 7.4 Hz, 12H, CH3), 1.59 (m, 8H,
CH2CH3), 2.80 (t, 3J ) 7.4 Hz, 8H, SCH2), 3.65 (s, 3H, OCH3),
4.86 (ps, 2H, Cp H), 5.62 (ps, 2H, Cp H). 13C NMR (125 MHz,
C6D6; δ): 13.5 (CH3), 23.7 (CH2CH3), 37.5 (SCH2), 51.3 (OCH3),
82.3 (Cbd C), 84.0 (Cp CH), 85.7 (Cp CH), 88.4 (Cp C-CO2Me),
166.4 (CO2Me). IR (KBr; cm-1): 2961, 2931, 2872, 1717, 1467,
1281, 1143. UV-vis (CH2Cl2; λmax/nm (log ꢀ): 238 (4.37), 316
(4.16), 356 (3.33). HR-MS (FAB+; m/z): calcd for C23H35O2S4Co
(M+), 530.0852; found, 530.0827. Anal. Calcd for
C23H35O2S4Co: C, 52.05; H, 6.65; S, 24.17. Found: C, 52.17;
H, 6.65; S, 24.00.
In Figure 4 we show the optimized structures of 34-
37 for R ) SH. For 34 calculations predict a conforma-
tion in which the 3p orbital at each SH group is oriented
perpendicular to the plane of the cyclobutadiene ring.
This result mirrors the X-ray data of 27 and 30. For
the 16-valence-electron species 35 three of the four SH
groups are oriented in such a way that the conjugation
(22) CpRCo(CO)2: (a) Hart, W. P.; Dong, S.; Rausch, M. D. J.
Organomet. Chem. 1985, 282, 111-121. (b) Rausch, M. D.; Genetti, R.
A. J. Org. Chem. 1970, 35, 3888-3897. (c) Abel, E. W.; Moorhouse, S.
J. Organomet. Chem. 1971, 28, 211-215.

CpCo-Stabilized Cyclopentadienones
Organometallics, Vol. 24, No. 9, 2005 2111
(b) (η5-(Methoxycarbonyl)cyclopentadienyl)(η4-tetrakis-
(tert-butylthio)cyclobutadiene)cobalt(I) (29). This com-
pound was prepared from C5H4(CO2Me)Co(CO)2 (8; 476 mg,
2.00 mmol) and alkyne 25 (810 mg, 4.00 mmol) in toluene (125
mL). Yield: 117 mg (10%) of a yellow solid (mp 69 °C). 1H NMR
(500 MHz, C6D6; δ): 1.42 (s, 36H, C(CH3)3), 3.91 (s, 3H, OCH3),
5.08 (ps, 2H, Cp H), 5.49 (ps, 2H, Cp H). 13C NMR (125 MHz,
C6D6; δ): 17.2 (C(CH3)3), 29.5 (C(CH3)3), 50.8 (OCH3), 81.9 (Cbd
C), 83.2 (Cp CH), 84.6 (Cp CH), 88.0 (Cp C-CO2Me), 166.1
(CO2Me). IR (KBr; cm-1): 2960, 2920, 2860, 1721, 1469, 1364,
1144. UV-vis (CH2Cl2; λmax/nm (log ꢀ)): 252 (4.45), 326 (4.11),
374 (2.95). HR-MS (FAB+; m/z): calcd for C27H43O2S4Co (M+),
586.1478; found, 586.1436. Anal. Calcd for C27H43O2S4Co: C,
55.26; H, 7.39; S, 21.86. Found: C, 55.66; H, 7.24; S, 21.43.
(c) (η5-(Methoxycarbonyl)cyclopentadienyl)(η4-tetra-
kis(phenylthio)cyclobutadiene)cobalt(I) (30). This com-
pound was prepared from C5H4(CO2Me)Co(CO)2 (8; 476 mg,
2.00 mmol) and alkyne 26 (969 mg, 4.00 mmol) in toluene (125
12 (400 mg, 3.38 mmol) in decalin (50 mL). Yield: 158 mg
1
(24%) of a red solid (mp 106 °C). H NMR (300 MHz, CDCl3;
δ): 2.37 (s, 6H, SCH3), 2.64 (s, 6H, SCH3), 4.93 (s, 5H, Cp H).
13C NMR (75 MHz, C6D6; δ): 15.7 (SCH3), 19.1 (SCH3), 84.2
(Cp CH), 86.8 (Cpd C), 93.2 (Cpd C), 157.0 (CO). IR (KBr;
cm-1): 2987, 1688, 1612, 1415, 1302. UV-vis (CH2Cl2; λmax
/
nm (log ꢀ)): 258 (4.14), 350 (4.19), 438 (3.32). HR-MS (FAB+;
m/z): calcd for C14H18OS4Co (M+ + H), 388.9543; found,
388.9573. Anal. Calcd for C14H17OS4Co: C, 43.28; H, 4.41; S,
33.02. Found: C, 43.57; H, 4.49; S, 32.81.
(d) (η5-Methoxycyclopentadienyl)(η4-tetrakis(meth-
ylthio)cyclopentadienone)cobalt(I) (15). This compound
was prepared from C5H4(CO2Me)Co(CO)2 (8; 180 mg, 0.76
mmol) and alkyne 12 (178 mg, 1.51 mmol) in decalin (50 mL).
Yield: 172 mg (51%) of a red solid (mp 124 °C). 1H NMR (300
MHz, C6D6; δ): 2.03 (s, 6H, SCH3), 2.35 (s, 6H, SCH3), 3.52 (s,
3H, OCH3), 4.71 (ps, 2H, Cp H), 5.02 (ps, 2H, Cp H). 13C NMR
(75 MHz, C6D6; δ): 14.4 (SCH3), 18.1 (SCH3), 52.0 (OCH3), 85.1
(Cp CH), 86.4 (Cp CH), 87.8 (Cpd C), 88.5 (Cp C-CO2Me), 92.8
(Cpd C), 156.1 (Cpd CO), 164.5 (CO2Me). IR (KBr; cm-1): 3095,
2979, 1715, 1601, 1461, 1369, 1141. UV-vis (CH2Cl2; λmax/nm
(log ꢀ)): 241 (4.35), 362 (4.29), 428 (3.43). HR-MS (FAB+;
m/z): calcd for C16H20O3S4Co (M+ + H), 446.9628; found,
446.9609. Anal. Calcd for C16H19O3S4Co × 0.1 C6H14: C, 43.81;
H, 4.52; S, 28.18. Found: C, 43.73; H, 4.43; S, 27.99.
1
mL). Yield: 200 mg (15%) of a yellow solid (mp 128 °C). H
NMR (500 MHz, C6D6; δ): 3.94 (s, 3H, OCH3), 5.01 (ps, 2H, Cp
H), 5.48 (ps, 2H, Cp H), 6.91 (m, 8H, C(Ph) H), 7.15 (m, 8H,
C(Ph) H), 7.21 (m, 4H, C(Ph) H). 13C NMR (125 MHz, C6D6;
δ): 52.0 (OCH3), 82.5 (Cbd C), 84.7 (Cp CH), 86.2 (Cp CH),
87.9 (Cp C-CO2Me), 126.7 (Ph CHpara), 128.4 and 130.2 (Ph
CHortho/meta), 165.9 (CO2Me). IR (KBr; cm-1): 2961, 2931, 2872,
1723, 1622, 1470, 1278, 1145. UV-vis (CH2Cl2; λmax/nm (log
ꢀ)): 262 (4.16), 366 (4.18), 434 (3.40). HR-MS (FAB+; m/z):
calcd for C35H27O2S4Co (M+), 666.0226; found, 666.0225. Anal.
Calcd for C35H27O2S4Co: C, 63.05; H, 4.08; S, 19.23. Found:
C, 63.47; H, 4.16; S, 18.84.
(e) (η5-(Trimethylsilyl)cyclopentadienyl)(η4-tetrakis-
(methylthio)cyclopentadienone)cobalt(I) (16). This com-
pound was prepared from C5H4(SiMe3)Co(CO)2 (10; 192 mg,
0.76 mmol) and alkyne 12 (178 mg, 1.51 mmol) in decalin (50
1
mL). Yield: 133 mg (38%) of an orange solid (mp 103 °C). H
NMR (300 MHz, CDCl3; δ): 0.32 (s, 9H, Si(CH3)3), 2.37 (s, 6H,
SCH3), 2.65 (s, 6H, SCH3), 4.77 (ps, 2H, Cp H), 5.07 (ps, 2H,
Cp H). 13C NMR (75 MHz, CDCl3; δ): -0.6 (SiC), 15.5 (SCH3),
19.1 (SCH3), 85.6 (Cpd C), 87.9 (Cp CH), 88.7 (Cp CH), 92.8
(C), 93.3 (C), 157.9 (CO). IR (KBr; cm-1): 3087, 2951, 1610,
1601, 1423, 1303, 1159. UV-vis (CH2Cl2; λmax/nm (log ꢀ)): 256
(4.05), 354 (4.11), 414 (3.31), 424 (3.25), 440 (3.16). HR-MS
(FAB+): calcd for C17H26OSiS4Co (M+ + H), 460.9968; found,
460.9987. Anal. Calcd for C17H25OSiS4Co: C, 44.32; H, 5.47.
Found: C, 44.83; H, 5.58.
General Procedure for the Synthesis of Cyclopenta-
dienone Complexes via CO Insertion. A solution of the
cyclobutadiene complex in decalin (80 mL) was stirred at 170
°C under a CO atmosphere in a high-pressure vessel for 15 h.
After it was cooled to room temperature, the reaction mixture
was separated by column chromatography (Alox III) using a
gradient of n-hexane f dichloromethane f methanol as
eluant.
General Procedure for the Synthesis of the Cyclopen-
tadienone Complexes via Cyclization. C5H4(CO2Me)Co-
(CO)2 (8), C5H4(SiMe3)Co(CO)2 (10), or CpCo(CO)2 (13) and the
alkyne were dissolved in decalin (60 mL) and stirred at 170
°C for 2 days. After it was cooled to room temperature, the
reaction mixture was separated by column chromatography
(Alox III) using a gradient of n-hexane f dichloromethane f
methanol as eluant.
(a) Cyclopentadienone Complex 9. This compound was
prepared from C5H4(CO2Me)Co(CO)2 (8; 358 mg, 1.50 mmol)
and tetrathiacyclodiyne 7 (390 mg, 1.50 mmol) in decalin (60
mL). Yield: 233 mg (33%) of a deep red oil. 1H NMR (500 MHz,
CDCl3; δ): 2.22 (m, 4H, CH2CHHCH2), 3.12 (m, 2H, SCHH),
3.24-3.33 (m, 6H, CHHCH2CHH), 3.90 (s, 3H, OCH3), 5.07
(ps, 2H, Cp H), 5.31 (ps, 2H, Cp H). 13C NMR (125 MHz, CDCl3;
δ): 31.1 (CH2), 32.1 (CH2), 32.4 (CH2), 52.3 (OCH3), 84.5 (Cpd
C), 85.6 (Cp CH), 88.6 (Cpd C), 89.6 (Cp CH), 93.9 (Cp
C-CO2Me), 151.5 (Cpd CO), 164.5 (CO2Me). IR (KBr; cm-1):
2925, 2223, 1719, 1603, 1470, 1369, 1280, 1193, 1146. UV-
vis (CH2Cl2; λmax/nm (log ꢀ)): 246 (3.93), 360 (4.10), 408 (3.14).
HR-MS (FAB+; m/z): calcd for C18H20O3S4Co (M+ + H),
470.9627; found, 470.9635.
(a) Cyclopentadiene Complex 9. This compound was
prepared from the cyclobutadiene complex 16 (90 mg, 0.20
mmol) and CO (20 bar) in decalin (80 mL). Yield: 40 mg (42%).
For analytical data, see above.
(b) Cyclopentadienone Complex 11. This compound was
prepared from C5H4(SiMe3)Co(CO)2 (10; 290 mg, 1.13 mmol)
and tetrathiacyclodiyne 7 (295 mg, 1.13 mmol) in decalin (60
mL). Yield: 192 mg (36%) of a deep red solid (mp 212 °C). 1H
NMR (300 MHz, CDCl3; δ): 0.28 (s, 9H, Si(CH3)3), 2.13 (m,
2H, CH2CHHCH2), 2.27 (m, 2H, CH2CHHCH2), 2.99-3.11 (m,
8H, CHHCH2CHH), 4.76 (ps, 2H, Cp H), 4.94 (ps, 2H, Cp H)
ppm. 13C NMR (75 MHz, CDCl3; δ): -0.9 (Si(CH3)3), 31.1
(CH2), 32.9 (SCH2), 33.6 (SCH2), 81.9 (Cpd C), 88.5 (Cp CH),
90.2 (Cp CH), 90.5 (Cp C-TMS), 94.3 (Cpd C), 153.2 (Cpd CO).
IR (KBr; cm-1): 2919, 1603, 1412, 1298, 1248, 839. UV-vis
(CH2Cl2; λmax/nm (log ꢀ)): 248 (4.10), 320 (3.84), 356 (4.23),
426 (3.24). HR-MS (FAB+; m/z): calcd for C19H26OS4SiCo (M+
+ H), 484.9968; found, 484.9939. Anal. Calcd for C19H25-
OS4SiCo: C, 47.08; H, 5.20; S, 26.46. Found: C, 47.25, H, 5.23;
S, 26.48.
(b) (η5-Methoxycyclopentadienyl)(η4-tetrakis(meth-
ylthio)cyclopentadienone)cobalt(I) (15). This compound
was prepared from the cyclobutadiene complex 27 (280 mg,
0.67 mmol) and CO (40 bar) in decalin (80 mL). Yield: 162
mg (54%). For analytical data, see above.
(c) (η5-Methoxycyclopentadienyl)(η4-tetrakis(n-propyl-
thio)cyclopentadienone)cobalt(I) (31). This compound was
prepared from the cyclobutadiene complex 28 (159 mg, 0.30
mmol) and CO (40 bar) in decalin (80 mL). Yield: 28 mg (17%)
1
of a red solid (mp 143 °C). H NMR (500 MHz, C6D6; δ): 0.86
(t, 3J ) 7.4 Hz, 6H, CH3), 0.98 (t, 3J ) 7.4 Hz, 6H, CH3), 1.47
(m, 4H, CH2CH3), 1.71 (m, 4H, CH2CH3), 2.73 (m, 2H, SCH2),
2.86 (m, 2H, SCH2), 3.18 (m, 2H, SCH2), 3.68 (s, 3H, OCH3),
3.95 (m, 2H, SCH2), 4.62 (ps, 2H, Cp H), 5.28 (ps, 2H, Cp H).
13C NMR (125 MHz, C6D6; δ): 13.5 (CH3), 13.7 (CH3), 23.6 (CH2-
CH3), 24.1 (CH2CH3), 33.2 (SCH2), 37.4 (SCH2), 51.7 (OCH3),
86.4 (Cp CH), 87.3 (Cp CH), 88.7 (Cp C-CO2Me), 89.0 (Cpd
C), 92.0 (Cpd C), 156.6 (Cpd CO), 164.7 (CO2Me). IR (KBr;
cm-1): 3091, 2975, 1605, 1430, 1354, 1134. UV-vis (CH2Cl2;
(c) (η5-Cyclopentadienyl)(η4-tetrakis(methylthio)cy-
clopentadienone)cobalt(I) (14). This compound was pre-
pared from CpCo(CO)2 (13; 304 mg, 1.69 mmol) and alkyne

2112 Organometallics, Vol. 24, No. 9, 2005
Schaefer et al.
Table 2. Crystallographic Data and Details of the Refinement Procedure of 11, 14-16, and 30
11
14
15
16
30
empirical formula
formula wt
cryst syst
space group
Z
C
19H25OS4SiCo
C14H17OS4Co
C16H19O3S4Co
446.48
monoclinic
P21/c
4
C17H25OS4SiCo
460.66
monoclinic
P21/n
4
C35H27O2S4Co
484.65
triclinic
P1h
388.48
triclinic
P1h
666.74
triclinic
P1h
2
6
2
unit cell dimens
a (Å)
8.8194(1)
8.8964(1)
14.4346(2)
76.275(1)
86.030(1)
84.964(1)
1094.59(2)
1.47
9.1494(3)
12.4455(5)
22.3392(8)
79.022(1)
83.800(1)
79.226(1)
2446.3(2)
1.58
16.4714(6)
8.3209(3)
15.0158(5)
90
114.331(1)
90
1875.23(11)
1.58
1.37
polyhedron
7.9711(1)
14.6145(2)
17.7756(1)
90
95.805(1)
90
2060.13(4)
1.49
1.30
needle
10.3437(6)
10.4068(6)
14.8969(9)
93.530(1)
93.912(1)
102.042(1)
1559.9(2)
1.42
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Dcalcd (g/cm3)
abs coeff (mm-1
cryst shape
)
1.23
1.56
0.85
polyhedron
polyhedron
prism
cryst size (mm3)
0.42 × 0.34 × 0.10 0.21 × 0.10 × 0.02 0.41 × 0.10 × 0.07 0.50 × 0.12 × 0.10 0.31 × 0.20 × 0.15
θ range for data collecn (deg) 2.3-27.5
index ranges
0.9-25.6
-11 e h e 11
-15 e k e 15
-27 e l e 27
23 034
9560
5088
0.97/0.74
9560/0/553
0.95
1.4-27.5
-21 e h e 21
-10 e k e 10
-19 e l e 19
18 886
4300
3175
0.91/0.60
4300/0/222
1.04
1.8-27.5
-10 e h e 10
-18 e k e 18
-23 e l e 23
21 109
4731
3843
0.88/0.56
4731/0/224
1.04
2.0-28.3
-13 e h e 13
-13 e k e 13
-19 e l e 19
16 316
7629
6124
0.88/0.78
7629/0/380
1.02
-11 e h e 11
-11 e k e 11
-18 e l e 18
11 392
no. of rflns collected
no. of indep rflns
no. of obsd rflns
4985
4434
0.89/0.63
max/min transmissn
no. of data/restraints/params 4985/11/251
goodness of fit on F2
R(F)
1.06
0.026
0.049
0.067
0.49, -0.44
0.032
0.061
0.31, -0.33
0.027
0.057
0.32, -0.27
0.038
0.097
0.48, -0.26
Rw(F2)
0.065
(∆F)max, (∆F)min (e Å-3
)
0.48, -0.39
λmax/nm (log ꢀ)): 239 (4.31), 360 (4.01), 431 (3.27). HR-MS
(FAB+; m/z): calcd for C24H36O3S4Co (M+ + H), 559.0879;
found, 559.0859. Anal. Calcd for C24H35O3S4Co: C, 51.59; H,
6.31; S 22.96. Found: C, 51.61; H, 6.40; S, 22.89.
case of 14, we found three crystallographically independent
molecules in the asymmetric unit, which is rather unusual.
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre. Copies of the data can be obtain-
ed free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (internat.) +44-1223/336-033;
e-mail, data_request@ccdc.cam.ac.uk), on quoting the deposi-
tion numbers CCDC-261360 (11), CCDC-261361 (14), CCDC-
261362 (15), CCDC-261363 (16), and CCDC-261364 (30).
Computational Details. All the calculations were per-
formed using the GAUSSIAN98 program package.25 The struc-
tures were fully optimized by Becke’s three-parameter hybrid
functional26 combined with the Lee-Yang-Parr27 correlation
functional (abbreviated as B3LYP) level of density functional
theory, using the 6-311G(d) basis set28 for C, O, S, and H. For
Co we have chosen Wachters’ (14s, 9p, 5d) basis set29 augment-
ed with a 4f polarization function. All stationary points have
been identified as local minima (number of imaginary frequen-
cies, NImag ) 0). For graphical displays we used the MOLEK-
9000 program.30
(d) (η5-Methoxycyclopentadienyl)(η4-tetrakis(phenyl-
thio)cyclopentadienone)cobalt(I) (33). This compound was
prepared from the cyclobutadiene complex 30 (113 mg, 0.17
mmol) and CO (40 bar) in decalin (80 mL). Yield: 43 mg (36%)
of a red solid (mp 139 °C). 1H NMR (300 MHz, CDCl3; δ): 3.99
(s, 3H, OCH3), 4.98 (pt, 2H, Cp H), 5.34 (pt, 2H, Cp H), 6.75-
6.88 (m, 8H, C(Ph) H), 6.89-6.97 (m, 2H, C(Ph) H), 7.04-7.18
(m, 6H, C(Ph) H), 7.41-7.47 (m, 4H, C(Ph) H). 13C NMR (75
MHz, CDCl3; δ): 52.6 (OCH3), 84.0 (Cpd C), 85.7 (Cp CH), 88.2
(Cp CH), 89.0 (Cp C-CO2Me), 97.2 (Cpd C), 127.0 (Ph CHpara),
127.5 (Ph CHpara), 128.5 (Ph CHortho/meta), 128.6 (Ph CHortho/meta),
130.1 (Ph CHortho/meta), 131.9 (Ph CHortho/meta), 159.5 (Cpd CO),
165.9 (CO2Me). IR (KBr; cm-1): 3092, 2975, 1599, 1454, 1365,
1138. UV-vis (CH2Cl2; λmax/nm (log ꢀ)): 237 (4.11), 363 (4.59),
359 (3.18). HR-MS (FAB+; m/z): calcd for C36H27O3S4Co (M+),
694.0175; found, 694.0204. Anal. Calcd for C36H27O3S4Co: C,
62.24; H, 3.91. Found: C, 62.48; H, 4.08.
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft (SFB 623), the Fonds
X-ray Diffraction Analyses. The reflections were collected
with a Bruker Smart CCD diffractometer (Mo KR radiation,
graphite monochromator). The data were collected at 200 K
except for 30 which was recorded at 296 K. Intensities were
corrected for Lorentz and polarization effects, and an empirical
absorption correction was applied using SADABS,23 based on
the Laue symmetry of the reciprocal space. The structures
were solved by direct methods. The structural parameters of
the non-hydrogen atoms were refined anisotropically according
to a full-matrix least-squares technique (F2). The hydrogen
atom locations were calculated according to stereochemical
aspects. Structure solution and refinement were carried out
with the SHELXTL (5.10) software package.23 ORTEP draw-
ings were obtained using the ORTEP-3 for Windows program
by Farrugia.24 Table 2 contains the crystallographic data and
details of the data collection and refinement procedure. In the
(25) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.,
Jr.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;
Head-Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision
A.7; Gaussian, Inc.: Pittsburgh, PA, 1998.
(26) (a) Becke, A. D. J. Chem. Phys. 1992, 96, 2155-2160. (b) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648-5652.
(27) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1998, 37, 785-789.
(28) Krishnan, K.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem.
Phys. 1980, 72, 650-654.
(23) Sheldrick, G. M. Bruker Analytical X-ray-Division, Madison,
WI, 2001.
(24) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(29) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033-1036.
(30) MOLEK-9000: Bischof, P. Personal communication, Universita¨t
Heidelberg.

CpCo-Stabilized Cyclopentadienones
Organometallics, Vol. 24, No. 9, 2005 2113
Supporting Information Available: Crystal data (CIF
files) for compounds 11, 14-16, and 30 and Gaussian archive
entries of all calculated compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
der Chemischen Industrie, and the BASF Aktiengesell-
schaft, Ludwigshafen, Germany. C.S. is grateful to the
Deutsche Forschungsgemeinschaft (Graduiertenkolleg
850: “Molecular Modeling”) for financial support. D.B.W.
thanks the Studienstiftung des deutschen Volkes for a
graduate fellowship.
OM050048R