Alkyne Dicobalt Carbonyl Complexes with Sulfide Ligands. Synthesis, Crystal Structure, and Dynamic Behavior

Article abstract of DOI:10.1021/om9903036

Hexacarbonyl dicobalt complex of bis(tert-butylsulfonylethyne) [Co₂(μ-Bu^tSO₂C)₂(CO) ₂6, 3] experiences a thermally induced ligand exchange process with methyl p-tolyl sulfide, dibenzyl sulfide, and diethyl sulfide to give the corresponding stable sulfide complexes [Co₂(μ-Bu^t-S0₂C)₂(CO) ₅SR₂] 4, 5, and 6, respectively, in good yield (59-65%). The reaction with tetrahydrothiophene gives a disubstituted complex 7 in 74% yield. Oxathiane 9, derived from (+)-(2R)-10-mercaptoisoborneol, also reacts with 3 to generate a chiral sulfide complex 8 (58%). The solid-state structures of 5 and 8 have been established by X-ray crystallography and reveal the preference of the incoming sulfur ligand to occupy an equatorial coordination site. Further structural studies on 5 have been performed by low-temperature ¹H NMR analysis and by theoretical procedures at the PM3(tm) level of theory. Analysis of the low-temperature ¹H NMR spectrum of 5 shows a signal splitting consistent with the freezing of an equilibrium between two equatorially coordinated sulfides, and the computational study of the different isomers of 5 shows that the equatorially coordinated complex is 3.9 kcal mol^-1 lower in energy than the most stable axially coordinated one, in agreement with solid-state and solution studies. Finally, ligand exchange experiments have been performed in order to provide an explanation for the Pauson - Khand reactivity of alkynes containing ancillary sulfide ligands and were found to support the experimentally observed rate enhancements.

Full text of DOI:10.1021/om9903036

Organometallics 1999, 18, 4275-4285
4275
Alk yn e Dicoba lt Ca r bon yl Com p lexes w ith Su lfid e
Liga n d s. Syn th esis, Cr ysta l Str u ctu r e, a n d Dyn a m ic
Beh a vior
Xavier Verdaguer,§ Albert Moyano,§ Miquel A. Perica`s,*,§ Antoni Riera,*,§
Angel Alvarez-Larena,† and J oan-F. Piniella†
Unitat de Recerca en Sı´ntesi Asime`trica, Departament de Quı´mica Orga`nica, Universitat de
Barcelona, c/ Martı´ i Franque`s, 1-11, 08028 Barcelona, Spain, and Unitat de Cristal‚lografia,
Facultat de Cie`ncies, Universitat Auto`noma de Barcelona, 08193 Barcelona, Spain
Received April 26, 1999
Hexacarbonyl dicobalt complex of bis(tert-butylsulfonylethyne) [Co2(µ-ButSO2C)2(CO)6, 3]
experiences a thermally induced ligand exchange process with methyl p-tolyl sulfide, dibenzyl
sulfide, and diethyl sulfide to give the corresponding stable sulfide complexes [Co2(µ-But-
SO2C)2(CO)5SR2] 4, 5, and 6, respectively, in good yield (59-65%). The reaction with
tetrahydrothiophene gives a disubstituted complex 7 in 74% yield. Oxathiane 9, derived
from (+)-(2R)-10-mercaptoisoborneol, also reacts with 3 to generate a chiral sulfide complex
8 (58%). The solid-state structures of 5 and 8 have been established by X-ray crystallography
and reveal the preference of the incoming sulfur ligand to occupy an equatorial coordination
1
site. Further structural studies on 5 have been performed by low-temperature H NMR
analysis and by theoretical procedures at the PM3(tm) level of theory. Analysis of the low-
1
temperature H NMR spectrum of 5 shows a signal splitting consistent with the freezing of
an equilibrium between two equatorially coordinated sulfides, and the computational study
of the different isomers of 5 shows that the equatorially coordinated complex is 3.9 kcal
mol-1 lower in energy than the most stable axially coordinated one, in agreement with solid-
state and solution studies. Finally, ligand exchange experiments have been performed in
order to provide an explanation for the Pauson-Khand reactivity of alkynes containing
ancillary sulfide ligands and were found to support the experimentally observed rate
enhancements.
In tr od u ction
chiral auxiliaries in the asymmetric Pauson-Khand
reaction,4,5 and it has been applied to the enantioselec-
tive synthesis of complex molecules.6 While we first
investigated conventional auxiliaries, whose effective-
ness is based on a pronounced conformational bias,4 a
second generation of chelating chiral controllers also
Since its discovery in 1973, the Pauson-Khand reac-
tion has gained a major role in the synthetic chemist
toolbox.1 This reaction consists of the carbonylative
cycloaddition between an alkene and an alkyne to yield
a cyclopentenone. In the noncatalytic versions of this
reaction the first step is the formation of the dicobal-
thexacarbonyl complex of the alkyne, which can be
either isolated or generated in situ. From the very
beginning, the development of an asymmetric version
of this process became of great interest to chemists. Up
to date, to turn this reaction enantioselective several
approaches have been tested.2-5 One of such methodolo-
gies, developed by our group, is based on the use of
(3) For other approaches see, inter alia: (a) Hicks, F. A.; Buchwald,
S. L. J . Am. Chem. Soc. 1996, 118, 11688-11689. (b) Park, H. J .; Lee,
B. Y.; Kang, Y. K.; Chung, Y. K. Organometallics 1995, 14, 3104-
3107. (c) Kerr, W. J .; Kirk, G. G.; Middlemiss, D. Synlett 1995, 1085-
1086. (d) Stolle, A.; Becker, H.; Salau¨n, J .; de Meijere, A. Tetrahedron
Lett. 1994, 35, 3521-3524.
(4) (a) Poch, M.; Valent´ı, E.; Moyano, A.; Perica`s, M. A.; Castro
Tetrahedron Lett. 1990, 31, 7505-8. (b) Castro, J .; So¨rensen, H.; Riera,
A.; Morin, C.; Moyano, A.; Perica`s, M. A.; Greene, A. E. J . Am. Chem.
Soc. 1990, 112, 9388-9389. (c) Verdaguer, X.; Moyano, A.; Perica`s,
M. A.; Riera, A.; Greene, A. E.; Piniella, J . F.; Alvarez-Larena, A. J .
Organomet. Chem. 1992, 433, 305-310. (d) Castro, J .; Moyano, A.;
Perica`s, M. A.; Riera, A.; Greene, A. E. Tetrahedron: Asymmetry 1994,
5, 307-310. (e) Bernardes, V.; Verdaguer, X.; Kardos, N.; Riera, A.;
Moyano, A.; Perica`s, M. A.; Greene, A. E. Tetrahedron Lett. 1994, 35,
575-578. (f) Fonquerna, S.; Moyano, A.; Perica`s, M. A.; Riera, A.
Tetrahedron 1995, 51, 4239-4254. (g) Balsells, J .; Moyano, A.; Perica`s,
M. A.; Riera, A. Tetrahedron: Asymmetry 1997, 8, 1575-1580. (h)
Montenegro, E.; Poch, M.; Moyano, A.; Perica`s, M. A.; Riera, A.
Tetrahedron 1997, 53, 8651-8664. (i) Fonquerna, S.; Moyano, A.;
Perica`s, M. A.; Riera, A. J . Am. Chem. Soc. 1997, 119, 10225-10226.
(5) (a) Verdaguer, X.; Moyano, A.; Perica`s, M. A.; Riera, A.; Ber-
nardes, V.; Greene, A. E.; Alvarez-Larena, A.; Piniella, J . F. J . Am.
Chem. Soc. 1994, 116, 2153-2154. (b) Montenegro, E.; Poch, M.;
Moyano, A.; Perica`s, M. A.; Riera, A. Tetrahedron Lett. 1998, 39, 335-
338. (c) Verdaguer, X.; Va´zquez, J .; Fuster, G.; Bernardes-Ge´nisson,
V.; Greene, A. E.; Moyano, A.; Perica`s, M. A.; Riera, A. J . Org. Chem.
1998, 63, 7037-7052.
§ Universitat de Barcelona.
† Universitat Auto`noma de Barcelona.
(1) Reviews on the Pauson-Khand reaction: (a) Pauson, P. L.;
Khand, I. U. Ann. N. Y. Acad. Sci. 1977, 295, 2-14. (b) Pauson, P. L.
Tetrahedron 1985, 41, 5855-5860. (c) Pauson, P. L. In Organometallics
in Organic Synthesis. Aspects of a Modern Interdisciplinary Field; de
Meijere, A., tom Dieck, H., Eds.; Springer: Berlin, 1988; pp 233-246.
(d) Harrington, P. J . Transition Metals in Total Synthesis; Wiley: New
York, 1990; pp 259-301. (e) Schore, N. E. Org. React. 1991, 40, 1-90.
(f) Schore, N. E. In Comprehensive Organic Synthesis; Trost, B. M.,
Ed.; Pergamon Press: Oxford, 1991; Vol. 5, pp 1037-1064.
(2) Use of chiral phosphines: (a) Bladon, P.; Pauson, P. L.; Brunner,
H.; Eder, R. J . Organomet. Chem. 1988, 355, 449-454. (b) Brunner,
H.; Niedernhuber, A. Tetrahedron: Asymmetry 1990, 1, 711-714. (c)
Hay, A. M.; Kerr, W. J .; Kirk, G. G.; Middlemiss, D. Organometallics
1995, 14, 4986-4988.
10.1021/om9903036 CCC: $18.00 © 1999 American Chemical Society
Publication on Web 09/14/1999

4276 Organometallics, Vol. 18, No. 21, 1999
Verdaguer et al.
Sch em e 1
Sch em e 2
be the effect of the electron-withdrawing trifluoromethyl
groups on the cobalt cluster. Bis(tert-butylsulfonyl)-
ethyne 2,10a a strongly electron-deficient alkyne intro-
duced a few years ago by our group as a general
acetylene synthon in the Diels-Alder reaction,10b-d
could be an excellent probe to study the coordination
chemistry of simple alkyl sufides to alkyne-dicobalt
hexacarbonyl complexes. We describe herein the syn-
thesis and a detailed structural study of the cobalt
carbonyl complexes of bis(tert-butylsulfonyl)ethyne with
sulfide ligands.
Ch a r t 1
Resu lts a n d Discu ssion
(A) Syn th esis of Coba lt Ca r bon yl Com p lexes
w ith Su lfid e Liga n d s, Co2(µ-Bu tSO2C2)2(CO)5SRR′.
Bis(tert-butylsulfonyl)ethyne 2 was prepared in two
steps from ButSH and trichloroethene using the previ-
ously described procedure.10a Although the complexation
of alkynes bearing electron-withdrawing groups has
often proved difficult, after a few trials we found that
formation of the hexacarbonyl complex 3 could be
conveniently performed by treating a freshly crystallized
sample of 2 with Co2(CO)8 in dry ether. In this way 3
was obtained as an air-stable red crystalline solid in
97% yield (Scheme 2).
proved to be very effective.5 In these studies, we have
demonstrated that the occurrence of an intramolecular
sulfide coordination to the Co2-alkyne core results in
an enhanced reactivity and diastereoselectivity in the
intermolecular cycloaddition process (Scheme 1), much
in the same way as the regioselectivity of the reaction
is controlled by a sulfide ligand present in the alkyne.7
Therefore, it would be of great interest to study
dicobalt complexes having sulfide ligands that do not
form a part of the original alkyne molecule, toward
designing new catalysts for an enantioselective version
of the Pauson-Khand reaction.
In clear contrast with group V ligands, there are very
few examples in the literature of sulfide coordination
to alkyne dicobalt complexes.7-9 In fact, there is only
one example of such type of complexes with a mono-
dentate sulfide ligand not covalently bonded to the
alkyne: the bis(trifluoromethyl)acetylene derivative 1
(Chart 1), described by Petillon and co-workers.8
Upon analysis of the structural features of 1, we
concluded that a main contribution to its stability could
With 3 in our hands we proceeded to investigate its
reactions with methyl p-tolyl sulfide as a test ligand. It
is known that amine N-oxides oxidize metal-coordinated
CO ligands, providing in this manner a free coordination
site for the incoming ligand.11 Consequently, we first
checked the N-oxide-induced formation of sulfide com-
plexes, in a fashion similar to what had been success-
fully done for the preparation of the pentacarbonyl
complexes of chelating auxiliaries.5 Addition of a slight
excess of N-methyl morpholine N-oxide (NMO) to a
solution of 3 and of methyl p-tolyl sulfide (2 equiv) in
dichloromethane resulted in rapid color change from
bright red to brown. Simultaneously, a new, brown spot
could be observed on TLC. However, upon solvent
removal, no clean sulfide complex could be isolated. We
reasoned that the N-methyl morpholine formed as a
byproduct hampered the purification of the target
complex. To avoid this, we switched to an N-oxide of a
volatile amine, i.e., trimethylamine N-oxide (TMANO).
On using 2 equiv of TMANO in CH2Cl2, we were able
to isolate the corresponding monosulfide complex 4,
(6) (a) Bernardes, V.; Kann, N.; Riera, A.; Moyano, A.; Perica`s, M.
A.; Greene, A. E. J . Org. Chem. 1995, 60, 6670-6671. (b) Tormo, J .;
Verdaguer, X.; Moyano, A.; Perica`s, M. A.; Riera, A. Tetrahedron 1996,
52, 14021-14040. (c) Castro, J .; Moyano, A.; Perica`s, M. A.; Riera, A.;
Greene, A. E.; Alvarez-Larena, A.; Piniella, J . F. J . Org. Chem. 1996,
61, 9016-9020. (d) Tormo, J .; Moyano, A.; Perica`s, M. A.; Riera, A. J .
Org. Chem. 1997, 62, 4851-4856.
(7) (a) Krafft, M. E.; J uliano, C. A.; Scott, I. L.; Wright, C.; McEachin,
M. D. J . Am. Chem. Soc. 1991, 113, 1693-703. (b) Krafft, M. E.; Scott,
I. L.; Romero, R. H. Tetrahedron Lett. 1992, 33, 3829-3832. (c) Krafft,
M. E.; Scott, I. L.; Romero, R. H.; Feibelmann, S.; Vanpelt, C. E. J .
Am. Chem. Soc. 1993, 115, 7199-7207.
(10) (a) For a convenient preparation of 2 see: Riera, A.; Marti, M.;
Moyano, A.; Perica`s, M. A.; Santamaria, J . Tetrahedron Lett. 1990,
31, 2173-6. (b) Riera, A.; Marti, M.; Moyano, A.; Perica`s, M. A.;
Santamaria, J . Tetrahedron Lett. 1990, 31, 2173-6. (c) Virgili, M.;
Belloc, J .; Moyano, A.; Perica`s, M. A.; Riera, A. Tetrahedron Lett. 1991,
32, 4583-4586. (d) Belloc, J .; Virgili, M.; Moyano, A.; Perica`s, M. A.;
Riera, A. Tetrahedron Lett. 1991, 32, 4579-4582.
(11) (a) Shambayati, S.; Crowe, W. E.; Schreiber, S. L. Tetrahedron
Lett. 1990, 31, 5289-5292. (b) J eong, N.; Chung, Y. K.; Lee, B. Y.;
Lee, S. H.; Yoo, S.-E. Synlett, 1991, 204-206.
(8) Rumin, R.; Manojlovic-Muir, L.; Muir, K. W.; Petillon, F. Y.
Organometallics 1988, 7, 375-383.
(9) There is one example of a sulfide-phosphine bidentate ligand
coordinated to a dicobaltcarbonyl acetylene complex: Edwards, A. J .;
Mack, S. R.; Mays, M. J .; Mo, C.-Y.; Raithby, P. R.; Rennie, M.-A. J .
Organomet. Chem. 1996, 519, 243-252.

Alkyne Dicobalt Carbonyl Complexes
Organometallics, Vol. 18, No. 21, 1999 4277
Ta ble 1. Syn th esis of Dicoba ltp en ta ca r bon yl
Com p lexes w ith Su lfid e Liga n d s u n d er Th er m a l
Con d ition s
excess in the reaction, the initial formation of the brown-
colored monosubstituted sulfide complex was soon fol-
lowed by the appearance of a new complex characterized
by a green spot on TLC. At the end, a green solid
insoluble in hexane was obtained in 74% yield. 1H NMR,
mass spectroscopy, and a ∆νj ) 56 cm-1 shift in the
carbonyl IR spectrum confirmed the green solid was a
bis(tetrahydrothiophene) complex, 7. Analysis of the IR
spectrum in the 1990-2100 cm-1 zone indicated that
this compound is most probably the isomer with both
tetrahydrothiophene ligands in axial position (C2v sym-
metry) since 7 shows only three stretching CO, while
four such signals, due to symmetry considerations,
should be expected for any other isomer.14 Finally, the
reaction of 3 with the chiral oxathiane 9, obtained from
(+)-10-mercaptoisoborneol and p-chlorobenzaldehyde,15
afforded an optically active complex 8 (Table 1). 1H NMR
of 8 (C6D6) showed two different But singlets, consistent
with the new diastereotopic nature of the tert-butylsul-
fonyl groups attached to the carbon-cobalt core, as
expected for the coordination of a chiral ligand.
Unlike the preceding examples, reaction attempts
with diphenyl sulfide and di(tert-butyl) sulfide under
either thermal or oxidative conditions were not success-
ful. The two tert-butylsulfonyl groups probably impose
large steric requirements too difficult to meet for a
a
b
∆νj ) νj(3) - νj(X), νj ) mean IR carbonyl frequency. 1 equiv
sterically encumbered sulfide such as But S. In the case
of oxathiane 9 was employed.
2
of Ph2S the problem is probably of electronic nature;
conjugation with two phenyl groups lowers significantly
the Lewis basicity of sulfur, thus preventing coordina-
tion.
albeit in a moderate 24% yield.12 Complex 4 showed a
1H NMR spectra consistent with the complexation of a
methyl p-tolyl sulfide unit. The -SCH3 group, initially
at δ 2.04 ppm (C6D6) in the free ligand, underwent a
downfield shift and appeared at δ 2.39 ppm in 4. Along
with that, the average carbonyl frequencies (νj) in the
IR spectrum of 4 shifted 31 cm-1 with respect to the
parent hexacarbonyl complex, in accordance with the
exchange from a carbonyl to a more electron-releasing
ligand. Similar values of ∆νj are found in the literature
for monophosphine-substituted pentacarbonyldicobalt
complexes.13
To improve the chemical yield obtained when employ-
ing N-oxides, thermal activation was also investigated.
Thus, hexacarbonyl complex 3 and methyl p-tolyl sulfide
in excess were heated at 65 °C in toluene under
nitrogen. To facilitate ligand exchange, CO was periodi-
cally removed through evacuation and refilling with
nitrogen. After 36 h, this treatment produced a brown
solution of 4, which, upon solvent evaporation, extrac-
tion with hexane, and crystallization, afforded 4 as an
analytically pure, brown microcrystalline solid in 59%
yield. Following this general procedure, a series of
sulfide-substituted cobalt complexes 4-8 were synthe-
sized and characterized (Table 1).
(B) Cr ysta l Str u ctu r e of Co2(µ-Bu tSO2C2)2(CO)5-
SBn 2 (5). Dibenzyl sufide complex 5 could be isolated
in two different crystalline forms. This behavior, how-
ever, does not seem to involve any structural change at
the molecular level since both types of crystals display
in solution the same 1H NMR spectra. When 5 was
crystallized from cold hexane, red fragile needles, not
suitable for X-ray diffraction, were obtained (mp 125 °C).
Crystallization from hot hexane, however, yielded dark
red crystals (mp 129 °C), suitable this time for X-ray
analysis. The relevant crystal and structure refinement
data are shown in Table 2. Selected atomic distances
and angles are provided in Table 3, and the correspond-
ing ORTEP drawing is shown in Figure 1.
The interatomic cluster distances found in 5 are
similar to those found in other alkyne-dicobalt com-
plexes.16 The metal-metal bond length found (2.488 Å)
is among the longest for this class of compounds, and
(14) There are six possible isomers for compound 7: one diaxially
substituted, belonging to the C2v symmetry group, three diequatorially
substituted (C2, Cs with both ligands in the same cobalt and Cs with
one ligand in each cobalt), and two axial-equatorially susbtituted (both
belonging to the C1 group). For all of them, except for the diaxial one,
four CO stretchings are expected. It is worth noting than in the other
cobalt complexes prepared in this article the number of carbonyl signals
is in good agreement with the theoretical prediction based on their
symmetry. For a detailed explanation of the procedure see: Cotton,
F. A. Chemical Applications of Group Theory; J ohn Wiley & Sons: New
York, 1990.
Reaction with dibenzyl sulfide and diethyl sulfide led
to the corresponding monosubstituted sulfide complexes
5 and 6, respectively, in 65% and 63% yield. When the
highly nucleophilic tetrahydrothiophene was used in
(12) The possibility of sulfide oxidation by the amine N-oxide has
been ruled out. Treatment of methyl p-tolyl sufide with an excess of
TMANO in DCCl3 at room temperature for 2 h did not yield any
oxidized sulfur compound, as monitored by 1H NMR.
(13) (a) Chia, L. S.; Cullen, W. R.; Franklin, M.; Manning, A. R.
Inorg. Chem. 1975, 14, 2521-2525. (b) Varadi, G.; Vizi-Orosz, A.;
Vastag, S.; Palyi, G. J . Organomet. Chem. 1976, 108, 225-233. (c)
Bradley, D. H.; Khand, M. A.; Nicholas, K. M. Organometallics 1992,
11, 2598-2607.
(15) Aggarwal, V. R.; Ford, J . G.; Fonquerna, S.; Adams, H.; J ones,
R. V. H.; Fieldhouse, R. J . Am. Chem. Soc. 1998, 120, 8328-8339.
(16) (a) J effery, J . C.; Pereira, R. M. S.; Vargas, M. D.; Went, M. J .
J . Chem. Soc., Dalton Trans. 1995, 1805-1811. (b) Bonnet, J . J .;
Mathieu, R. Inorg. Chem. 1978, 17, 1973-1976. (c) Bradley, D. H.;
Khand, M. A.; Nicholas, K. M. Organometallics 1989, 8, 554-556. (d)
D’Agostino, M. F.; Frampton, C. S.; McGlinchey, M. J . Organometallics
1990, 9, 2745-2753. (e) Gelling, A.; Went, M. J .; Povey, D. C. J .
Organomet. Chem. 1993, 455, 203-210.

4278 Organometallics, Vol. 18, No. 21, 1999
Verdaguer et al.
Ta ble 2. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
P a r a m eter s for 5 a n d 8
parmeter
5
8
empirical formula
fw
C
29H32Co2O9S3
C32H39ClCo2O10S3
833.12
293(2)
0.71069
orthorhombic
P 21 21 21
11.098(5)
14.210(6)
24.271(4)
90
90
90
3828(2)
4
1.446
738.59
293(2)
0.71069
monoclinic
C1 2/c 1
28.52(2)
10.364(4)
24.658(13)
90
114.99(6)
90
6607(7)
8
temperature (K)
wavelength (Å)
crystal system
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
volume (Å3)
Z
density (calc) (Mg/m3)
absorption coeff (mm-1
F(000)
1.485
1.243
3040
)
1.151
1720
crystal size (mm)
θ range (deg)
index ranges
0.22 × 0.18 × 0.07 0.43 × 0.32 × 0.20
1.58 to 24.99
-33 e he 30
0 e k e 12
0 e l e 29
5786
1.68 to 24.97
0 e h e 13
0 e k e 16
0 e l e 28
3357
F igu r e 1. ORTEP drawing of 5 showing 30% probability
ellipsoids. H atoms have been omitted for clarity.
no. of unique reflns
absorption correction
empirical
empirical
max. and min. transmn 0.992 and 0.713
1.000 and 0.953
refinement method
no. of data/restrains/
params
full-matrix least-squares on F2
5786/15/388
3357/27/433
goodness of fit on F2
final R indices
[I > 2σ(I)]
0.718
R(F) ) 0.0550
0.891
R(F) ) 0.0433
Rw(F2) ) 0.0830
R(F)) 0.1899
Rw(F2) ) 0.0994
R(F) ) 0.0781
Rw(F2) ) 0.1083
0.04(3)
R indices (all data)
Rw(F2) ) 0.0936
absolute struct param
∆Fmax and ∆Fmin (e A-3
)
0.304/-0.314
0.408/-0.413
modate the bulky sulfide, the torsion angle S(1)-C(1)-
C(2)-S(2) ) 48° deviates also from planarity. In such a
twisted conformation of the bis-tert-butylsulfonylethyne
backbone, the ligand is placed at one of the two
equatorial sites free of the steric repulsion exerted by
the tert-butyl groups. The pseudoequatorial position of
the sulfide group can be clearly apreciated in the
eclipsing of this group with one of the carbonyl groups
[C(22)-O(22)] in the cobalt tricarbonyl fragment,
the corresponding torsion angle being nearly zero (see
Table 3).
F igu r e 2. ORTEP drawing of 8 showing 30% probability
ellipsoids. H atoms have been omitted for clarity.
(C) Cr ysta l Str u ctu r e of Ch ir a l Com p lex 8. The
X-ray diffraction of a single crystal of 8, obtained by slow
cooling of a warm hexane solution, showed the existence
in the unit cell of four molecules of a single enantiomer,
which is depicted in Figure 2. The most relevant
crystallographic and geometrical parameters of the
X-ray structure can be found in Tables 2 and 3.
The similarity between structures 5 and 8 is striking.
The geometries of both metal clusters are almost
coincident, and the two most important features of 5
are also present in 8: the synclinal conformation of both
tert-butyl groups and the coordination of the sulfide
ligand to an equatorial coordination site on cobalt. With
respect to the ligand itself, the oxathiane ring adopts
the expected chairlike conformation and the sulfur atom
is coordinated through the equatorial lone pair to the
metal center.
the C-C distance of the formerly acetylenic bond is 1.35-
(1) Å. Interestingly, the cluster bond Co(1)-C(2) )
1.900(5) is slightly shorter than Co(1)-C(1) ) 1.964(5),
probably due to the trans effect that the sulfide ligand
exerts. The cobalt-sulfur distance in 5 (Co(1)-S(3) )
2.279(2) Å) is remarkably similar to that found in 1
(2.270 Å). Upon coordination, the alkyl-alkyl angle in
the thioether ligand (C(3)-S(3)-C(4) ) 100.2°) remains
practically untouched and matches exactly the free
sulfide mean angle17 of 100.8°.
Besides this, two significant features present in the
crystal structure of 5 should be stressed: (a) the
coordination of Bn2S to a pseudoequatorial site and (b)
the synclinal conformation of both tert-butyl groups with
respect to the C-C bond of the cluster, the torsion
angles being C(1)-C(2)-S(2)-C(60) ) -94.8° and C(2)-
C(1)-S(1)-C(50) ) 76.2°. In addition, to further accom-
The coordination of the sulfide to an equatorial
position in both cases is somewhat surprising since it
is commonly accepted for this class of compounds that
(17) Obtained from a Cambridge Data Base search.

Alkyne Dicobalt Carbonyl Complexes
Organometallics, Vol. 18, No. 21, 1999 4279
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d An gles (d eg) for X-r a y Str u ctu r es 5 a n d 8
complex 5 complex 8
Co(1)-Co(2)
Co(1)-C(1)
Co(1)-C(2)
Co(2)-C(1)
Co(2)-C(2)
C(1)-C(2)
Co(1)-S(3)
Co(1)-C(11)
Co(1)-C(12)
2.488(1)
1.964(5)
1.900(5)
1.935(6)
1.957(7)
1.35(1)
2.279(2)
1.796(6)
1.811(7)
Co(1)-Co(2)
Co(2)-C(2)
Co(2)-C(1)
Co(1)-C(2)
Co(1)-C(1)
C(1)-C(2)
Co(2)-S(31)
Co(2)-C(21)
Co(2)-C(22)
2.479(2)
1.948(7)
1.926(8)
1.937(7)
1.953(7)
1.37(1)
2.281(2)
1.84(1)
1.80(1)
C(12)-Co(1)-S(3)
C(11)-Co(1)-S(3)
C(11)-Co(1)-C(12)
S(3)-Co(1)-Co(2)
Co(1)-S(3)-C(3)
Co(1)-S(3)-C(4)
C(3)-S(3)-C(4)
C(2)-C(1)-S(1)
C(1)-C(2)-S(2)
96.1(2)
105.7(2)
99.0(3)
C(22)-Co(2)-S(31)
C(21)-Co(2)-S(31)
C(21)-Co(2)-C(22)
Co(1)-Co(2)-S(31)
Co(2)-S(31)-C(32)
Co(2)-S(31)-C(40)
C(32)-S(31)-C(40)
C(1)-C(2)-S(2)
95.1(3)
107.8(4)
96.4(5)
96.71(7)
114.4(3)
110.8(3)
94.6(4)
96.6(1)
110.6(2)
110.4(2)
100.2(3)
146.8(5)
145.6(5)
146.8(6)
145.8(6)
S(1)-C(1)-C(2)
C(11)-Co(1)-Co(2)-C(21)
S(3)-Co(1)-Co(2)-C(22)
C(12)-Co(1)-Co(2)-C(23)
C(11)-Co(1)-S(3)-C(3)
C(12)-Co(1)-S(3)-C(4)
S(1)-C(1)-C(2)-S(2)
-12.3(3)
-8.0(2)
-40.2(7)
-5.8(3)
-14.6(3)
48(1)
C(11)-Co(1)-Co(2)-C(21)
C(12)-Co(1)-Co(2)-S(31)
C(13)-Co(1)-Co(2)-C(22)
C(21)-Co(2)-S(31)-C(32)
C(22)-Co(2)-S(31)-C(40)
S(1)-C(1)-C(2)-S(2)
11.0(5)
6.2(3)
33(1)
9.6(5)
16.6(5)
-38(2)
C(2)-C(1)-S(1)-C(50)
C(1)-C(2)-S(2)-C(60)
-76.2(1)
-94.8(1)
C(1)-C(2)-S(2)-C(7)
78.8(1)
81.8(1)
C(3)-S(1)-C(1)-C(2)
poor π-acceptor ligands prefer coordination to pseudo-
axial sites. There are many examples of axially coordi-
nated monodentate phosphine ligands. Regarding the
sulfide ligands, in the only monodentate case decribed
so far of a sulfide not covalently bonded to the alkyne,
Petillon and co-workers8 have reported that it is axially
coordinated to the metal. Only in the case of bidentate
ligands,9 for obvious structural restrictions, do these
occupy two equatorial sites. It has been suggested that
steric factors also favor axial coordination.18 In our
systems however, this is clearly not the case, and
consequently, to our knowledge, 5 and 8 represent the
first examples of σ-donor, poor π-acceptor monodentate
ligands equatorially coordinated to alkyne-dicobalt
complexes.
(D) F lu xion a l Beh a vior a n d Solu tion Str u ctu r e
of 4 a n d 5. Cobalt complex 5 was submitted to a
1
variable-temperature H NMR study in CD2Cl2 (Figure
3). Whereas at room temperature the four benzylic
protons gave a sole broad resonance at δ 3.91, when the
temperature was lowered (-10 °C) this signal split into
two broad resonances (δ 4.21 and 3.69) in a 1:1 ratio.
Upon further cooling the NMR probe, these resonances
emerged as an AB system (J ) 13 Hz) at -30 °C.
Eventually, before a well-defined doublet forms, the
resonance at δ 4.21 smears and at -80 °C separates
into three signals, a doublet (J ) 13 Hz) and two broad
singlets. At the same time, approximately at -60 °C,
the But resonance has split into two different singlets
at δ 1.49 and 1.39 in an aproximate 1:1 ratio.
The dynamic behavior visible on 1H NMR for 5 is
consistent with two different processes: (1) slow ex-
change between two enantiomeric complexes showing
the nonequivalence of the diastereotopic benzylic pro-
(18) Simpson and co-workers have found that in complex Co2-
(CF3)2C2(CO)5(CH3CN) the acetonitrile replaces an equatorial CO. To
explain this, they have argued that it is due to the small size of CH3-
CN, which is isolobal to CO. Arewgoda, M.; Robinson, B. H.; Simpson,
J . J . Am. Chem. Soc. 1983, 105, 1893-1903.
F igu r e 3. Variable-temperature 1H NMR spectrum of
the benzyl region of 5 in CD2Cl2. Temperatures are given
in °C.

4280 Organometallics, Vol. 18, No. 21, 1999
Verdaguer et al.
Sch em e 3. P ostu la ted Equ ilibr iu m In volved in
th e F lu xion a l P r ocess of 5a
a
Rotation signs are given arbitrarily.
tons and (2) hindered rotation around the Co-S axis.
The coordination of Bn2S to one of the cobalt centers
can lead to two different isomers: one in which Bn2S is
axially coordinated and one equatorially coordinated
complex. There is, however, a degenerate process in-
terconverting two enantiomeric equatorially coordinated
species. The observed splitting of the methylene protons
of the benzyl groups into an AB system at -30 °C
(Figure 3) is in agreement with a slow interchange
between the two enantiomeric complexes 5-eq(+) and
5-qe(-) (Scheme 3). In such a situation, the benzylic
protons -CHAHB- in the ligand are no longer magneti-
cally equivalent and the corresponding AB system
shows up in the spectrum. The coalescence temperature
of +13 °C was used to calculate the activation free
energy for the this equilibrium: ∆G‡ ) 14.4 ( 0.2 kcal
mol-1. This value falls in the same range as the one
found by Vollhardt for a similar equilibrium in an
(alkyne)Mo2(CO)4(fulvalene) complex.19,20 The appear-
ance of two singlets for the But groups at low temper-
atures can also be explained by this model. In 5-eq(+)
and 5-eq(-) the sulfide ligand is always closer to one
of the two tert-butyl groups, providing different chemical
environments, which finally results in two separate
chemical shifts. No other signals are observed in the
benzyl region, suggesting that abundance of the axial
coordinated complexes 5-a x in solution is less than 10%.
Changes in the 1H NMR spectra of 5 from -30 to -80
°C can be attributed to hindered rotation around the
S-Co bond. While at -80 °C the AB doublet at δ 4.21
has separated into three signals, consistent with the
formation of three rotamers, the other AB doublet (δ
3.69) is just starting to broaden, suggesting this process
is still rapid at - 80 °C. Although hindered rotations
around sulfide-metal bonds have not been reported,
this behavior is well documented for M-P bonds pos-
1
F igu r e 4. Variable-temperature H NMR spectrum of 4
in CD2Cl2. Temperatures are given in °C.
sessing bulky phosphine ligands.21 In the present case
the highly crowded environment around the Co core is
presumably responsible for the observation of this
phenomenon at relatively high temperatures.
In an effort to further clarify the existence of axially
coordinated complexes vs equatorial ones we also stud-
ied the dynamic behavior of the cobalt complex 4. The
methyl p-tolyl sulfide ligand in 4 has no -CHAHB-
groups, and therefore the exchange process between
equivalent equatorial complexes should be invisible on
1H NMR. According to our expectations, on cooling a
solution of 4 in CD2Cl2, no splitting was observed around
10 °C. However, the -SCH3 resonance started broaden-
ing at -20 °C and split around -35 °C into two singlets
(Figure 4). At -80 °C two singlets at δ 2.74 and 2.61
with a 1:1.5 ratio could be observed.
Unlike the precedent example, the presence of two
signals with different intensity for -SCH3 protons
indicated that an equilibrium between unequally popu-
lated species (with different energies) was taking place.
We thought, at first, that such behavior could be
characteristic of an equilibrium between the axial
sulfide and the equatorial ones, since the corresponding
species should have different energies. Still, the much
lower coalescence temperature (Tc ) -35 °C) than the
one observed for ligand pseudorotation in 5 pointed to
(19) Drage, J . S.; Vollhardt, K. P. C. Organometallics 1986, 5, 280-
297.
(20) (a) Bailey, W. I.; Chisholm, M. H.; Cotton, F. A.; Renkel, L. A.
J . Am. Chem. Soc. 1978, 100, 5764-5773. (b) Amouri, H. E.; Gruselle,
M. Chem. Rev. 1996, 96, 1077-1103. (c) Griffith, D. L.; Roberts, J . D.
J . Am. Chem. Soc. 1965, 87, 4089-4091.
(21) (a) Bushweller, C. H.; Rithner, C. D.; Butcher, D. J . Inorg.
Chem. 1986, 25, 1610-1616. (b) Mann, B. E.; Masters, C.; Shaw, B.
L.; Stainbank, R. E. J . Chem. Soc., Chem. Commun. 1971, 1103-1104.
(c) Widenhoefer, R. A.; Zhong, A.; Buchwald, S. L. Organometallics
1996, 15, 2745-2754.

Alkyne Dicobalt Carbonyl Complexes
Organometallics, Vol. 18, No. 21, 1999 4281
Sch em e 4. P ostu la ted Equ ilibr iu m In volved in
th e F lu xion a l P r ocess of 4a
a
Rotation signs are given arbitrarily.
a different kind of process. A possible explanation for
this observations comes from the ability of the sulfide
ligand to coordinate through one of the two electron lone
pairs (Scheme 4). Bearing two different substituents (R
) Me, R′ ) Tol), upon coordination, the sulfur atom
becomes stereogenic. Thus, when the ligand is coordi-
nated equatorially, we can expect the formation of as
much as four isomers, i.e., the diastereomeric pairs of
enantiomers 4-eq-1(+), 4-eq-1(-), and 4-eq-2(+), 4-eq-
2(-) (Scheme 4). There are two possible single equilib-
rium processes between all four complexes: inversion
at the sulfur center (A type equilibrum), and ligand
pseudorotation followed by a conformational change of
the tert-butyl groups (B type equilibrium). Transforma-
tion of one complex to its corresponding enantiomer (C
type equilibrium) would involve inversion at sulfur,
pseudorotation on cobalt, and conformational change of
the tert-butyl groups (A and B). In view of this, having
in mind that pseudorotation is a higher energy process
as we have shown for 5, the exchange from one set of
diastereomers to the other through an A type of equi-
librium would account for the observed spectra of 4 in
the low-exchange region (-80 °C). Finally, the 1:1.5
ratio observed for the MeS- resonance at -80 °C is in
accordance with one pair of enantiomers being energeti-
cally more stable than the other.
F igu r e 5. Optimized structures of the most relevant
conformers of compound 3 at the PM3(tm) level. H atoms
a
have been omitted for clarity. Relative Energy without
b
geometrical restrictions. Relative energy with the C-C
bond of the cluster fixed at 1.35 Å.
A systematic exploration of the conformational energy
hypersurface of 3 led to the characterization of several
minima. In the lowest energy conformer (3a ) both tert-
butyl groups were antiperiplanar to the C-C bond of
the cluster, the value of the dihedral angles C-C-S-
C(But) being 160°. This structure has C2 symmetry,
probably to minimize the repulsion between the tert-
butyl groups and the equatorial carbonyls of the complex
(Figure 5). Interestingly, conformer 3g, with both tert-
butyl groups synclinal to the C-C bond of the cluster
and consequently with a disposition analogous to the
one present in the crystal structure of 5, was located
3.4 kcal mol-1 higher in energy (Figure 3). It is worth
noting that the calculated C-C-S-C(But) dihedral
angle (87°) in this conformer (3g) is very close to the
observed dihedral angles in the crystal. With respect
to the C2Co2 cluster, both the Co-Co (2.531 Å) and the
C-Co (1.974 Å) distances were accurately reproduced,
while the C-C bond (1.516 Å) was somewhat overesti-
mated.
(E ) Molecu la r Or b it a l Ca lcu la t ion s of Cob a lt
Com p lexes. To shed light on the main features of the
crystal structures of 5 and 8 described above and to
explain the solution behavior of this family of com-
pounds, we decided to perform a conformational study
of complexes 3 and 5 by computational means. It is
worth mentioning that this semiempirical procedure has
already been shown to be suitable for the description of
related alkyne dicobalt carbonyl complexes.5c The ge-
ometries of all conformers were fully optimized using
the semiempirical procedure PM3(tm) as implemented
in the MacSpartan Plus package of programs.22
A conformational study of the cobalt complex Co2(µ-
ButSO2C)2(CO)4(SCH3)2 (10), in which dimethyl sulfide
replaces a carbon monoxide ligand, was next performed
in order to evaluate the structural and energetic influ-
(22) MacSpartan Plus, version 1.0; Wavefunction, Inc.: 18401 Von
Karman Ave., Suite 370, Irvine, CA, 92612.

4282 Organometallics, Vol. 18, No. 21, 1999
Verdaguer et al.
F igu r e 6. Optimized structures of the most relevant
conformers of compound 10 at the PM3(tm) level. H-atoms
have been omitted for clarity. aRelative energy without
geometrical restrictions. bRelative energy with the C-C
bond of the cluster fixed at 1.35 Å.
ence of a non sterically demanding sulfide. Conformers
with dimethyl sulfide in pseudoequatorial or pseudo-
axial sites were considered. Among the species where
both tert-butyl groups are antiperiplanar to the C-C
bond of the cluster (10a ), the most stable complex was
the axially substituted complex 10a -a x, which was 4.6
kcal mol-1 more stable than the corresponding equato-
rial one, 10a -eq. On the other hand, among the con-
formers with both tert-butyl groups gauche to the C-C
cluster bond (10g) the equatorially substituted complex
was 7.0 kcal mol-1 more stable than the corresponding
axial one. Significantly, the most stable axial complex
10a -a x was 3.1 kcal mol-1 more stable than the lowest
energy equatorial one, 10g-eq (Figure 6).
These results are in good agreement with what is
observed in complex 1 and in most phosphine-substi-
tuted cobalt complexes. However, the most important
features present in the X-ray structure of 5 were not
reproduced in the conformational preferences of com-
plexes 10 with dimethyl sulfide as a ligand. We reasoned
that steric interactions provoked by large benzylic
groups could be responsible for this different conforma-
tional bias. Consequently, the conformational hyper-
surface of the benzyl sulfide complex 5 was screened.
In this case, the relative energetic order was completely
reversed with respect to 10. The lowest energy con-
former was 5g-eq (equatorially substituted with both
tert-butyl groups in gauche position), in complete agree-
F igu r e 7. Optimized structures of the most relevant
conformers of compound 5 at the PM3(tm) level. H atoms
have been omitted for clarity. aRelative energy without
geometrical restrictions. bRelative energy with the C-C
bond of the cluster fixed at 1.35 Å.
ment with the crystal structure of this compound. This
conformer was 6.0 kcal mol-1 more stable than the
corresponding axial one, 5g-a x, and 2.2 kcal mol-1 more
stable than the lowest axially substituted complex, 5a -
a x (Figure 7). Since the cluster C-C bond distance is
overestimated by the PM3(tm) calculations, all minima
were reoptimized with this bond distance fixed to the
crystallographic value of 1.35 Å. In doing so, all con-
formers with the tert-butyl groups antiperiplanar to the
C-C cluster bond were destabilized with respect to the
synclinal ones, thus indicating that the steric interac-
tions between tert-butyl sulfonyl groups and the metal
cluster can be alleviated in the synclinal conformers
(Table 4). In the case of complex 5, the energetic
difference between 5a -a x and 5g-eq increased to 3.9
kcal mol-1
.
Thus, the present calculations clearly show that the
most important features found in the crystal structure
of 5 are mainly due to the steric interactions originated
by the benzyl groups, since these structural character-
istics are not present in the dimethyl sulfide complex
10. Whereas in complexes 3 and 10, the minimal energy

Alkyne Dicobalt Carbonyl Complexes
Organometallics, Vol. 18, No. 21, 1999 4283
Ta ble 4. Su lfid e-P h osp h in e Liga n d Exch a n ge
a t 20 °C
increased when complexes with bulkier sulfide ligands
where tested. Thus, with complex 5 the conversion went
to 56% in 2 h using triphenyl phosphine as an incoming
ligand (Table 4, entry 4). Methyl p-tolyl sulfide was the
most labile ligand tested, since the treatment of 4 with
PPh3 and P(OCH3)3 led to almost complete conversion
(93% and 97%) after only 2 h (Table 4, entries 5 and 6).
Along with steric effects, the decreased basicity of sulfur
through conjugation with the aromatic ring in the
methyl p-tolyl sulfide might be reponsible for this fact.
The similar conversion numbers obtained when using
PPh3 and P(OCH3)3 indicate that the reaction rate
depends solely on the nature of the departing ligand.
Such behavior agrees with a two-step mechanism in
which the first event, sulfide dissociation, is the rate-
determining step, as it has been described for several
metal carbonyl substitution reactions,23 and explains the
high reactivity in Pauson-Khand reactions of the cobalt
complexes of alkynes bearing sulfide ligands coordinated
to the cobalt atom.
entry s. mat.
L1
prod.
L2
time conv.
1
2
3
4
5
6
3
6
6
5
4
4
CO
SEt2
SEt2
S(CH2Ph)2
MeSp-tolyl
MeSp-tolyl
11
11
12
12
12
11
P(OCH3)3 1 day
P(OCH3)3 2 h
3%
22%
22%
56%
93%
97%
PPh3
PPh3
PPh3
2 h
2 h
2 h
P(OCH3)3 2 h
conformer has both tert-butyl groups in an antiperipla-
nar arrangement with respect to the C-C bond of the
cluster, in complex 5 the presence of a large sulfide
ligand forces a conformation in which both tert-butyl
groups adopt a synclinal arrangement that permits the
accommodation of the large ligand in one of the equato-
rial sites. Moreover the higher energy of the axial
conformers relative to the equatorial ones in compound
5 is also in complete agreement with the observations
made in the low-temperature 1H NMR studies of 4
and 5.
(F ) Liga n d E xch a n ge E xp er im en t s. The sulfide
complexes sythesized in this study were not good
Pauson-Khand substrates, as could be anticipated from
an inspection of the bulky disubstituted alkyne complex.
Thus, reaction of 4 with norbornadiene, one of the most
reactive alkenes, even at high temperatures did not
yield any cyclopentenone product. However, these com-
plexes constitute an excellent probe for testing the
lability of the sulfide ligand compared to a carbonyl in
connection with the mechanism of the Pauson-Khand
reaction. The generation of a vacant cordination site at
cobalt as a preliminary step to the coordination of the
incoming olefin has been postulated to be the rate-
determining step in the Pauson-Khand reaction. As has
been already mentioned, we have developed a sulfur
chelating auxiliary with rate-enhancing properties5
(Scheme 1), and we have proposed5c that this effect was
due to a decreased strength of the sulfide-cobalt bond
vs the original carbonyl-cobalt bond. The lability of the
sulfide ligand would facilitate the coordination of the
olefin to the open site left by the sulfide. To further
verify this hypothesis, we decided to study the reaction
between cobalt complexes 3-6 and phosphorus deriva-
tives. In this way we would be able to easily monitor
the interchange between the carbonyl or sulfide ligands
and a phosphorus ligand. The results of this study are
depicted in Table 4.
Con clu sion s
Thermal reaction of the hexacarbonyl cobalt complex
of bis(tert-butylsulfonylethyne) (Co2(µ-ButSO2C)2(CO)6,
3) with a variety of simple organic thioethers in toluene
yields the corresponding sulfide-substituted complexes
in good yield. These cobalt complexes are stable com-
pounds most likely due to the shielding and electron-
withdrawing effect that the two tert-butylsulfonyl groups
exert. Whereas large sulfide ligands give rise to mono-
substituted complexes, small nucleophilic ones, (i.e.,
tetrahydrothiophene) lead to the substitution of two
carbonyl units. X-ray analysis of complexes derived from
dibenzyl sulfide and oxathiane 9 showed the preference
of the sulfide ligand for an equatorial coordination site
rather than the axial one. To accommodate the incoming
ligand, the two ButSO2- groups adopt a synclinal
arrangement with respect to the C-C bond of the
1
cluster. Variable-temperature H NMR indicated that
large sulfide ligands present a dynamic process in which
the ligand switches between both adjacent equatorial
sites and that axially coordinated complexes are not
major species in solution. In further agreement with
solid-state and solution studies, molecular orbital cal-
culations showed that small sulfides prefer axial coor-
dination and that larger ligands (i.e., dibenzyl sulfide)
in the present system prefer equatorial sites. This
represents the first example of a poor π-acceptor ligand
coordinated equatorially in such type of compounds and
demonstrates that steric effects may overcome electronic
ones. Finally, in a series of ligand exchange experi-
ments, we have demonstrated that alkyne dicobalt
carbonyl complexes containing a sulfide ligand exhibit
a greatly facilitated dissociation. This provides an
explanation for the high reactivity in Pauson-Khand
reaction of intramolecularly chelated complexes of
alkynes with an adequately positioned thioether func-
tion. We are currently investigating the application of
sulfide ligands not bonded to the alkyne as readily
First, hexacarbonyl complex 3 was treated with
trimethyl phosphite in C6D6 at 20 °C, and the formation
of complex Co2(µ-ButSO2C)2(CO)4P(OCH3)3 (11) was
monitored by NMR. After 1 day, only 3% conversion was
observed, clearly indicating the difficulty of the substi-
tution of a carbonyl ligand at this temperature (Table
4, entry 1). Conversely, the reaction of triphenyl phos-
phite or triphenylphosphine with complex 6 (L1 ) Et2S)
at room temperature produced 22% of the corresponding
complexes 11 (L2 ) P(OCH3)3) and 12 (L2 ) PPh3) after
2 h (Table 4, entries 2 and 3). Conversion numbers
(23) (a) Atwood, J . D. Inorganic and Organometallic Reaction
Mechanisms; Brooks/Cole Publishing Co.: Monterey, CA, 1985. (b)
Cetini, G.; Gambino, O.; Stanghellini, P. L.; Vaglio, G. A. Inorg. Chem.
1967, 6, 1225-1228.

4284 Organometallics, Vol. 18, No. 21, 1999
Verdaguer et al.
in vacuo. The residue was solved in hexane, filtered, and
crystallized at -20 °C, yielding 35 mg (59%) of 4 as a dark
brown microcrystalline solid.
removable chiral auxiliaries in the asymmetric Pauson-
Khand reaction.
Mp: 110 °C (DSC). IR (KBr): νmax ) 2010, 2031, 2044, 2049,
2095 cm-1. 1H NMR (300 MHz, C6D6): δ 1.52 (s, 18H), 1.90 (s,
3H), 2.39 (s, 3H), 6.75 (d, J ) 8 Hz, 2H), 7.10 (d, J ) 8 Hz,
2H) ppm. 13C NMR (75 MHz, C6D6): δ 20.9, 24.6, 26.0, 62.3,
129.1, 130.5, 134.0, 139.5 ppm. MS (FAB+, NBA): m/e ) 663
(M+ + 1, 54), 635 (M+ - CO, 46), 550 (M+ - 4CO, 100), 522
(M+ - 5CO, 62). Anal. Calcd for C23H28Co2O9S3: C, 41.69; H,
4.26; S, 14.52. Found: C, 41.68; H, 4.20; S, 14.83.
Co2(µ-Bu t SO2C)2(CO)5S(CH 2P h )2, 5. According to the
general procedure described above, dicobalt complex 3 (100
mg, 0.18 mmol), dibenzyl sulfide (77 mg, 0.36 mmol), and
toluene (1 mL) were used. The reaction mixture was heated
at 70 °C for 20 h. Crystallization from hexane afforded 87 mg
(65%) of 5 as red needles. Dark red crystals suitable for X-ray
diffraction were obtained when 5 was recrystallized from hot
hexane.
Exp er im en ta l Section
Gen er a l. All reactions were conducted under nitrogen or
argon atmosphere using standard Schlenk techniques. Nuclear
magnetic resonance (NMR) spectra were recorded on a Varian
1
Unity-300 spectrometer. H and 13C NMR spectra were refer-
enced relative to residual solvent peaks. In most akyne dicobalt
complexes the signals corresponding to the cluster carbons do
not appear in the 13C NMR spectrum and the CO signals have
been omitted. Infrared (IR) spectra were recorded on a Nicolet
510 FT spectrometer. Melting points of cobalt complexes were
determined by differential scanning calorimetry (DSC) on a
Mettler DSC-30 under nitrogen. Elemental analyses were
performed at “Serveis cient´ıfico te`cnics de la Universitat de
Barcelona”. High-resolution mass spectra (HRMS) were con-
ducted at “Laboratori d’espectrometria de masses del CSIC de
Barcelona”. Dichloromethane was distilled from CaH2. Toluene
and ether were distilled from sodium benzophenone ketyl.
Hexane was dried with Na wire and degassed by bubbling
argon. Commercially available sulfides (methyl p-tolyl sulfide,
dibenzyl sulfide, diethyl sulfide, tetrahydrothiophene, di(tert-
butyl) sulfide, and diphenyl sulfide) were purchased from
Aldrich and were used as received. Bis(tert-butylsulfonyl)-
ethyne10a and (+)-(2R)-10-mercaptoisoborneol24 were prepared
according to published literature procedures.
Co2(µ-Bu tSO2C)2(CO)6, 3. To a slurry of freshly recrystal-
lyzed (AcOEt) bis(tert-butylsulfonyl)ethyne (260 mg, 1.0 mmol)
in ether (30 mL) was added solid dicobaltoctacarbonyl (375
mg, 1.1 mmol). The reaction mixture was stirred at room
temperature until CO evolution had ceased (1 h). Solvent
removal in vacuo and filtration through a pad of silica (hexane/
AcOEt, 20%) afforded 525 mg (97%) of 3 as a red crystalline
solid.
Mp: 125.9 °C (red needles), 129.5 °C (dark red cryst.) (DSC).
IR (KBr): νmax ) 2012, 2029, 2037, 2054, 2091 (red needles);
1
2004, 2035, 2041, 2053, 2093 (dark red cryst.) cm-1. H NMR
(300 MHz, C6D6): δ 1.49 (s, 18H), 2.90-4.50 (coalescing s, 4H),
6.95-7.10 (m, 6H), 7.12-7.21 (m, 4H) ppm. 13C NMR (75 MHz,
C6D6): δ 24.5, 44.7, 62.0, 127.9, 128.8, 129.8, 135.1 ppm. MS
(FAB+, NBA): m/e ) 739 (M+ + 1, 30), 598 (M+ - 5CO, 100).
Anal. Calcd for C29H32Co2O9S3: C, 47.15; H, 4.36; S, 13.02.
Found: C, 47.19; H, 4.41; S, 13.14.
Co2(µ-Bu tSO2C)2(CO)5S(C2H5)2, 6. According to the gen-
eral procedure described above, dicobalt complex 3 (100 mg,
0.18 mmol), diethyl sulfide (97 µL, 0.9 mmol), and toluene (1
mL) were used. The reaction mixture was heated at 60 °C for
24 h. This yielded a brownish solution. Removal of solvent and
the excess sulfide was effected under vacuum. The residue was
washed with hexane and dried under vacuum. This afforded
70 mg (63%) of 6 as an air-stable brown solid.
Mp: 120 °C (DSC). IR (KBr): νmax ) 2010, 2027, 2037, 2052
Mp: 172 °C (DSC). IR (KBr): νmax ) 2045, 2055, 2062, 2083,
(sh), 2089 cm-1 1H NMR (300 MHz, C6D6): δ 0.78 (t, J ) 7
.
2118 cm-1. H NMR (300 MHz, CDCl3): δ 1.59 (s, 18H) ppm.
1
Hz, 6H), 1.50 (s, 18H), 2.21 (broad s, 4H) ppm. 13C NMR (75
MHz, C6D6): δ 12.7, 24.6, 31.8, 62.2 ppm. MS (FAB+, NBA):
m/e ) 615 (M+ + 1, 60), 587 (M+ - CO, 75%), 474 (M+ - 5CO,
100). HRMS (FAB+): calcd for C19H29Co2O9S3 614.9637, found
614.9647.
13C NMR (75 MHz, CDCl3): δ 24.4 (C(CH3)3), 62.6 (C(CH3)3),
88.7 (C-cluster), 195.5 (CO) ppm. MS (DIP-CI-NH3): m/e )
569 (M+ + 18, 100), 558 (M+ - CO + 35, 32), 530 (M+ - 2CO
+ 35, 11). Anal. Calcd for C16H18Co2O10S2: C, 34.79; H, 3.28;
S, 11.61. Found: C, 35.03; H, 3.18; S, 11.75.
Co2(µ-Bu tSO2C)2(CO)4(SC4H8)2, 7. According to the gen-
eral procedure described above, dicobalt complex 3 (100 mg,
0.18 mmol), tetrahydrothiophene (80 µL, 0.9 mmol), and
toluene (1 mL) were used. The reaction mixture was heated
at 70 °C for 5 h. The original bright red solution turned brown
and finally changed to a green color. Removal of the solvent
and the excess of sulfide under vacuum afforded a solid, which
was washed with hexane and dried under vacuum, yielding
89 mg (74%) of 7 as an air-stable green solid.
Co2(µ-Bu tSO2C)2(CO)5S(p-C6H4CH3)(CH3), 4. (A) N-Oxide-
P r om oted Rea ction . Complex 3 (150 mg, 0.27 mmol), methyl
p-tolylsulfide (44 mg, 0.32 mmol), and CH2Cl2 (5 mL) were
charged in a Schlenk flask under nitrogen. To this mixture,
at room temperature, a solution of trimethylamine N-oxide
(TMANO) (22 mg, 0.29 mmol) in CH2Cl2 (2 mL) was added
dropwise via cannula. This resulted in a rapid color change of
the reaction mixture from bright red to dark brown. After
stirring the reaction for 1 h at room temperature another
equivalent of TMANO was added (20 mg, 0.27 mmol, 2 mL of
CH2Cl2) via cannula. Upon further stirring the reaction
mixture at room temperature for 30 min, the solvent was
removed in vacuo. The remaining solid residue was extracted
with hexane, filtered through Celite under nitrogen, and
crystallyzed at -20 °C overnight. This afforded 43 mg (24%)
of 4 as a dark brown microcrystalline solid.
(B) Th er m a l Rea ction . Gen er a l P r oced u r e for th e
P r ep a r a t ion of Com p lexes Co2(µ-Bu t SO2C)2(CO)5SR 2.
Complex 3 (50 mg, 0.09 mmol), methyl p-tolyl sulfide (50 mg,
0.36 mmol), and toluene (1 mL) were charged in a Schlenk
flask under nitrogen. The reaction mixture was heated at 65
°C for 36 h, removing periodically the CO with vacuum and
refilling with nitrogen. Upon reaction completion the color had
changed from bright red to brown. The solvent was removed
Mp: 153 °C (DSC). IR (KBr): νmax ) 1991, 2020, 2054 cm-1
.
1H NMR (300 MHz, C6D6): δ 1.16 (broad s, 8H), 1.70 (s, 18H),
2.59 (broad s, 8H) ppm. 13C NMR (75 MHz, C6D6): δ 24.8, 29.8,
41.9, 62.0 ppm. MS (FAB+, NBA): m/e ) 673 (M+ + 1, 30),
472 (M+ - 5CO - C4H8S, 100). HRMS (FAB+): calcd for
C
22H35Co2O8S4 672.9878, found 672.9875.
(1S,4R,6R,8R)-4-(Ch lor op h en yl)-11,11-d im eth yl-5-oxa -
3-th ia tr icyclo[6.2.1.01,6]u n d eca n e, 9. To a cooled solution
(ice bath) of (+)-10-mercaptoisoborneol (1.0 g, 5.3 mmol) and
p-chlorobenzaldehyde (0.83 g, 5.9 mmol) in CH2Cl2 (10 mL)
under nitrogen was added BF3-OEt2 (0.73 mL, 5.9 mmol). The
reaction mixture was stirred at 0 °C for 0.5 h, and the crude
was filtered through a pad of silica eluting with hexane/AcOEt
(90:10). Solvent removal under vacuum and recrystalization
from hexane afforded 1.18 g (71%) of 9 as colorless needles.
Mp: 134 °C. [R]D ) -86.4 (c 1.0, CHCl3). IR (KBr): νmax
)
740, 1060, 1485, 2950 cm-1 1H NMR (300 MHz, CDCl3): δ
.
(24) (a) Eliel. E. L.; Frazee, W. J . J . Org. Chem. 1979, 44, 3598-
3599. (b) DeLucchi, O.; Lucchini, V.; Marchiorio, C. J . Org. Chem. 1986,
51, 1457-1466.
0.95 (s, 3H), 0.91-1.13 (m, 2H), 1.45 (s, 3H), 1.49-1.59 (m,
1H), 1.67-1.80 (m, 3H), 1.96-2.07 (m, 1H), 2.77-3.29 (AB, J

Alkyne Dicobalt Carbonyl Complexes
Organometallics, Vol. 18, No. 21, 1999 4285
) 14 Hz, 2H), 3.73-3.77 (dd, J ) 3 and 8 Hz, 1H), 5.65 (s,
1H), 7.28-7.40 (m, 4H) ppm. 13C NMR (75 MHz, CDCl3): 20.4,
23.3, 27.2, 29.8, 34.4, 37.9, 41.8, 45.5, 46.7, 82.2, 85.7, 127.7,
128.4, 133.9, 137.9 ppm. MS (DIP-CI-NH3): m/e ) 309 (M+
+ 1, 100), 326 (M+ + 18, 16). Anal. Calcd for C17H21ClOS: C,
66.11; H, 6.85; S, 10.38. Found: C, 66.02; H, 6.85; S, 9.94.
Co2(µ-Bu tSO2C)2(CO)5(SC17H21ClO), 8. According to the
general procedure described above, dicobalt complex 3 (100
mg, 0.18 mmol), oxathiane 9 (61 mg, 0.2 mmol), and toluene
(1 mL) were used. The reaction mixture was heated at 65 °C
for 36 h. Solvent removal under vacuum and crystallization
from hexane afforded 88 mg (58%) of 8 as air-stable red
crystals.
were taken. When using PPh3, upon complete conversion the
reaction mixture showed a H NMR spectrum consistent with
1
formation of Co2(ButSO2C)2(CO)5P(C6H5)3, 12, as verified by
the independent synthesis described above. The following
signals were used in the other cases: for 4 the protons
corresponding to CH3-S and Ar-CH3 (δ 2.39 and 1.40 coord.,
δ 2.04 and 2.02 free); for 5 the benzyl protons (δ 2.40-4.50
-broad- coord., δ 3.34 free); and for 6 the methyl protons of
Et2S (δ 0.79 coord., δ 1.05 free).
Cr ysta l Str u ctu r e Deter m in a tion of 5 a n d 8. Suitable
crystals of 5 and 8 were grown from warm hexane. Relevant
crystal data and structure refinement information are dis-
played in Tables 2 and 3. Cell constants were obtained by least-
squares refinement on diffractometer angles for 25 automati-
cally centered reflections. Data measured on an Enraf-Nonius
CAD4 diffactrometer using graphite-monochromated Mo KR
radiation (λ ) 0.71069 Å) and a ω-2θ scan. Lp and empirical
absorption corrections25 were applied. The structure was solved
by direct methods (SHELXS-86)26 and refined by full-matrix
least-squares procedures on F2 for all reflections (SHELX-
97).27 All non-hydrogen atoms were refined anisotropically, and
hydrogen atoms were placed in calculated positions with
isotropic temperature factors 1.5 (methyl hydrogens) or 1.2 (the
rest) times the Ueq values of the corresponding carbons. Full
details of the structure determination for 5 and 8 are available
as Supporting Information.
Mp: 160 and 177 °C (DSC). [R]D ) -138° (c 0.02, CH2Cl2).
1
IR (KBr): νmax ) 2004, 2033, 2049, 2059, 2095 cm-1. H NMR
(300 MHz, C6D6): δ 0.50-0.59 (m, 1H), 0.67-0.75 (m, 1H),
1.01 (s, 3H), 1.14-1.28 (m, 1H), 1.40-1.50 (m, 3H), 1.42 (s,
9H), 1.51 (s, 9H), 1.58 (s, 3H), 1.80-1.90 (m, 1H), 2.92, 3.97
(AB, J ) 14 Hz, 2H), 3.32-3.36 (dd, J ) 3 and 8 Hz, 1H), 4.92
(s, 1H), 7.15-7.25 (m, 4H) ppm. 13C NMR (75 MHz, C6D6): δ
20.1, 23.1, 24.5, 27.1, 33.6, 37.9, 40.7, 44.9, 45.8, 47.1, 61.9,
62.5, 86.5, 90.1, 129.3, 130.1, 134.7, 136.5 ppm. MS (FAB+,
NBA): m/e ) 833, 835 (M+, 7), 692, 694 (M+ - 5CO, 100). Anal.
Calcd for C32H40ClCo2O10S3: C, 46.07; H, 4.83; S, 11.53.
Found: C, 45.99; H, 4.79; S, 11.52.
Co2(µ-Bu tSO2C)2(CO)5P (C6H5)3,12. According to the gen-
eral procedure described for the preparation of sulfide com-
plexes, dicobalt complex 3 (95 mg, 0.17 mmol), triphenylphos-
phine (49 mg, 0.18 mmol), and toluene (1 mL) were used. The
reaction mixture was heated at 60 °C for 7 h. Solvent removal
was effected under vacuum. The resulting solid was washed
with hexane and dried under vacuum. This afforded 108 mg
(80%) of the target complex as an air-stable dark pink solid.
Mp: Amorphous solid, no sharp fusion peak was detected
Ack n ow led gm en t. Financial support from DGICYT
(PB95-0265) and from CIRIT (1996SGR-00013) is grate-
fully acknowledged. X.V. is an M.E.C. fellow. We thank
Dr. M. Virgili for supplying a sample of 2, Dr. Ll. Sola`
for technical support on differential scanning calorim-
etry (DSC), and Dr. M. Rocamora for her help in IR
interpretation.
by DSC. IR (KBr): νmax ) 2004, 2035, 2051, 2093 cm-1 1H
.
NMR (300 MHz, C6D6): δ 1.52 (s, 18H), 6.94-7.10 (m, 9H),
7.64-7.73 (m, 6H) ppm. 13C NMR (75 MHz, C6D6): δ 24.8, 62.8,
128.7 (J P ) 10 Hz), 130.6, 134.2 (J P ) 11 Hz), 134.7 ppm.
HRMS (FAB+): calcd for C33H33Co2O9PS2Na 808.9865, found
808.9874.
Su p p or tin g In for m a tion Ava ila ble: Tables of complete
X-ray crystal data, ORTEP drawings, refinement parameters,
atomic coordinates, and bond distances and angles for 5 and
8. This material is available free of charge via the Internet at
http://pubs.acs.org.
Con ver sion Deter m in a tion for Liga n d Exch a n ge Re-
a ction s. Complexes 3-6 (0.015 mmol) were dissolved in an
NMR tube in C6D6 (0.7 mL). To this solution a 3-fold excess of
PPh3 or P(OMe)3 was added. The tube was shaken, and its
contents were analyzed by 1H NMR at 20 °C. Exchange
conversions were calculated from the integration of the
coordinated vs free ligand resonances. In the reaction of the
parent hexacarbonyl complex 3 the areas of the But resonances
of 3 (δ 1.35) and the product phosphite complex 11 (δ 1.53)
OM9903036
(25) North, A. C. T.; Philips, P. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(26) Sheldrick, G. M. SHELXS 86. In Crystallographic Computing
3; Sheldrick, G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University
Press: Oxford, U.K., 1985; pp 175-178.
(27) Sheldrick, G. M. SHELX-97, Program for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.