Reactivity of the [η2-bis(tert-butylsulfonyl)acetylene] (carbonyl)(η5-cyclopentadienyl)cobalt complex towards electron-rich and -poor acetylenes

Article abstract of DOI:10.1002/ejic.200500308

The electron-rich aminoacetylenes Et₂NC₂R (2a-c, R = SPh, PPh₂, and Ph, respectively) react smoothly with [η²-bis(tert-butylsulfonyl)acetylene](carbonyl) (η⁵-cyclopentadienyl)cobalt (1) to form the do

Full text of DOI:10.1002/ejic.200500308

FULL PAPER
Reactivity of the [η2-Bis(tert-butylsulfonyl)acetylene](carbonyl)(η5-
cyclopentadienyl)cobalt Complex Towards Electron-Rich and -Poor Acetylenes
Avijit Goswami,[a] Tobias H. Staeb,[b] Frank Rominger,[b] Rolf Gleiter,[b] and
Walter Siebert*[a]
Dedicated to Prof. Günter Helmchen on the occasion of his 65th birthday
Keywords: Alkynes / Cobalt / Cyclopentadienyl ligands / N ligands
The electron-rich aminoacetylenes Et2NC2R (2a–c, R = SPh,
PPh2, and Ph, respectively) react smoothly with [η2-bis(tert-
butylsulfonyl)acetylene](carbonyl)(η5-cyclopentadienyl)co-
balt (1) to form the donor–acceptor stabilized (η4-cyclobuta-
diene)cobalt complexes 3a–c in good yields. However, treat-
ment of the electron-poor borylacetylenes 2d–f with the co-
phenylethynyl)sulfide (2g) with two equivalents of 1 gives
rise to the sulfur-bridged bis[η4-(cyclobutadiene)cobalt] com-
plex 3g. The new cobalt complexes were characterized by
NMR spectroscopy, mass spectrometry, and by X-ray struc-
ture analysis for 3a, which reveals almost equal C–C bond
lengths within the cyclobutadiene ring.
balt complex 1 does not lead to the expected (η4-cyclobutadi- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ene)cobalt complexes. Analogously, the reaction of bis(1-
Germany, 2005)
tuted acetylenes as well as alkyl- and aryl-substituted acety-
lenes were allowed to react with 1 to form a new class of
stable (cyclobutadiene)cobalt complexes.[7] They found that
the more electron-rich acetylenes react faster with 1 under
mild conditions, whereas carbon-substituted acetylenes re-
quire heating to initiate the reactions. We have studied elec-
tron-poor borylacetylenes with respect to oligomerization
and therefore tested the possibility whether electron-poor
acetylenes can react with 1 under drastic conditions.
Furthermore, we were interested to find out whether other
heteroatom-substituted acetylenes (such as nitrogen and
phosphorus) are also able to act in the same way as chal-
cogen-substituted alkynes. In this paper, we will address the
scope and limitations of the replacement of the CO group
in 1 by the triple bonds of the electron-rich and -poor acety-
lenes.
Introduction
Di(carbonyl)(η5-cyclopentadienyl)cobalt [CpCo(CO)2] is
a very convenient and efficient reagent for the di- and tri-
merization of alkynes.[1] The CpCo-supported oligomeriza-
tion of unsymmetrical alkynes generally leads to isomers,
which is one of the major disadvantages of that reaction.
This might be overcome if oligomerization could be carried
out in a stepwise fashion. Lee and Brintzinger[2] have been
able to demonstrate by means of IR spectroscopy that, on
irradiation of [CpCo(CO)2] in the presence of diphenylace-
tylene, a new complex with only one CO ligand must be
present. In order to contribute to the clarification of the
mechanism of dimerization and trimerization of alkynes,
Krebs et al.[3,4] reported the first generation of a mono(al-
kyne)cobalt complex by reacting the highly strained alkyne
3,3,6,6-tetramethyl-1-thiacycloheptyne[3] with [CpCo(CO)2].
More recently, Gleiter et al.[5] have synthesized the
mono(alkyne)cobalt complex 1 by the replacement of one
of the carbonyl groups in di(carbonyl)(η5-cyclopentadienyl)
cobalt with bis(tert-butylsulfonyl)acetylene,[6] which was
found to be a strong electrophile. In the course of their
study, a large number of electron-rich, chalcogen-substi-
Results and Discussion
Treatment of Cobalt Complex 1 with Electron-Rich and
-Poor Acetylenes
The reactions between the cobalt complex 1 and the elec-
tron-rich aminoacetylenes 2a–c were carried out in toluene
at room temperature to afford the (η4-cyclobutadiene)co-
balt complexes 3a–c, respectively, in good yields
(Scheme 1). On the other hand, reactions of the cobalt com-
plex 1 with the “push-pull” 1-boryl-2-aminoacetylene 2d as
well as electron-poor borylacetylenes 2e and 2f in refluxing
[a] Anorganisch-Chemisches Institut der Universität,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-545-609
E-mail: walter.siebert@urz.uni-heidelberg.de
[b] Organisch-Chemisches Institut der Universität,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-544-205
E-mail: rolf.gleiter@urz.uni-heidelberg.de
4086
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejic.200500308
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Reactivity of the a Cobalt Complex Towards Acetylenes
FULL PAPER
toluene were unsuccessful, and only the starting materials
were recovered from the reaction mixtures. This indicates
that electron-poor borylacetylenes have no tendency to re-
act with the powerful electrophile 1, even when applying
drastic reaction conditions.
Scheme 1.
The cobalt complexes were isolated by column
1
Figure 1. Molecular structure of 3a in the solid state; hydrogen
atoms have been omitted for the sake of clarity. Selected bond
lengths [Å] and bond angles [°]: C6–S1 1.769(5), C7–S2 1.755(5),
C6–C7 1.494(6), C7–C8 1.484(7), C8–C9 1.459(7), C6–C9 1.476(7),
C8–N1 1.360(6), C9–S3 1.741(5); C9–C6–C7 88.8(4), C8–C7–C6
chromatography on silica gel and characterized by H and
13C NMR spectroscopy, mass spectrometry, and by X-ray
structure analysis for 3a. The 1H NMR spectra of 3a–c
show two singlets in the region δ = 1.2–1.5 ppm for the
tert-butyl groups in addition to the Cp resonance (δ = 5.0– 89.8(4), C9–C8–C7 89.9(4), C8–C9–C6 91.5(4).
5.3 ppm). In general, the characteristic feature of the 13C
NMR spectra is the chemical shift of the cyclobutadiene
ring atoms, which have values of between δ = 75 and
85 ppm.[7a–7c] However, compounds 3a,b exhibit low-field
resonances (δ = 55–75 ppm) for the cyclobutadiene ring
atoms. In the 13C NMR spectra of 3a–c, the signals for
C5H5 (δ = 82–84 ppm) were detected along with the aryl
carbon atoms (δ = 125.0–138.9 ppm). EI-MS data con-
firmed the formation of complexes 3a–c by the appearance
of the molecular-ion peaks with the expected isotopic
pattern.
The molecular structure of the mononuclear (cyclobuta-
diene)cobalt complex 3a is shown in Figure 1. In the solid-
state, 3a crystallizes with toluene. The conformation is
highly influenced by the bulky tert-butylsulfonyl groups,
which point away from the metal center, as does the phenyl
group bound to the sulfur atom. This behavior allows an
Scheme 2.
almost parallel orientation of the C5 and C4 rings. The
space group (P21/c) of complex 3a clearly indicates the pres-
ence of a racemic mixture.
from the reaction of two equivalents of (Me3SiC2)2S with
[CpCo(CO)2].
Sulfur-Bridged Dinuclear Cobalt Complex 3g
The brown oil 3g was purified by column chromatog-
1
The sulfur-bridged bis[(η4-cyclobutadiene)cobalt] com- raphy on silica gel and characterized by H and 13C NMR
plex 3g was prepared in moderate yield by treating (PhC2)2- spectroscopy as well as by mass spectrometry. The 1H
S (2g) with two equivalents of 1 (Scheme 2). No evidence NMR spectrum of 3g shows the expected multiplets (δ =
for the mononuclear cobalt complex was found.
6.9–7.1 ppm) for the aryl hydrogens in addition to two sing-
This reaction reveals an interesting route to a sulfur- lets (δ = 1.19 and 1.27 ppm) for the tert-butyl groups and
bridged bis[(η4-cyclobutadiene)cobalt] complex, which is the Cp resonance (δ = 5.01 ppm). In the 13C NMR spec-
important especially because the introduction of a hetero- trum, the signals (δ = 58.6–75.2 ppm) for the cyclobutadi-
atom between two metal-stabilized cyclobutadiene rings is ene ring are found along with the Cp resonance at δ =
still difficult. The method used by Wadepohl et al.[8] leads 83.5 ppm. The molecular-ion peak of 3g was detected with
to the mononuclear (η4-cyclobutadiene)cobalt complex the correct isotopic distribution in the mass spectrum.
Eur. J. Inorg. Chem. 2005, 4086–4089
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A. Goswami, T. H. Staeb, F. Rominger, R. Gleiter, W. Siebert
FULL PAPER
124 (15) [CpCo]. MS (70 eV, HR-EI): m/z (%) = 595.1277 (95) [M+;
Conclusions
12
C
27
1H3814N16O432S359Co: 595.1295]; ∆mmu = –1.8.
[η4-1,2-Bis(tert-butylsulfonyl)-4-diethylamino-3-diphenylphospanyl-
cyclobutadiene](η5-cyclopentadienyl)cobalt (3b): Starting material:
0.34 g (1.21 mmol) of 2b, 0.50 g (1.21 mmol) of 1. Yield: 0.48 g
We have shown that the electron-rich aminoacetylenes
2a–c react smoothly (as do the chalcogen-substituted acety-
lenes) with complex 1 to form CpCo-stabilized η4-cyclobu-
tadiene complexes 3a–c, respectively However, the CO
group in the mono(alkyne)cobalt complex 1 cannot be re-
placed by the “push-pull” borylacetylene 2d or by the elec-
tron-poor borylacetylenes 2e and 2f. This result may be ex-
plained by considering the electronic nature of complex 1.
The electron-poor bis(tert-butylsulfonyl)acetylene in 1 re-
duces the back bonding between the Co atom and the CO
ligand, which means that CO is easily replaced by the elec-
tron-rich acetylenes 2a–c; the electron-poor monoborylace-
tylenes 2d–f have weaker donor capabilities and thus do not
react with 1. Interestingly, the sulfur-bridged bis[(η4-cyclo-
butadiene)cobalt] complex 3g can be prepared by treating
complex 1 with (PhC2)2S (2g). The cobalt complexes 3a–c
and 3g are stable at room temperature and resistant to light,
oxygen, and moisture.
1
(0.71 mmol; 58%), orange oil. H NMR (200.1 MHz, CDCl3): δ =
0.85 (t, 6 H, CH2CH3), 1.45, 1.49 [2s, 2×9 H, C(CH3)3], 3.0, 3.3
(2m, 2×2 H, CH2CH3), 5.03 (s, 5 H, Cp), 7.2–7.7 (m, 10 H, PPh2)
ppm. 13C NMR (50.3 MHz, CDCl3): δ = 11.87 (CH2CH3), 24.32,
24.89 [C(CH3)3], 44.02 (CH2CH3), 61.77, 62.64 [C(CH3)3], 65.84,
67.24, 69.79, 72.85 (C4ring), 84.03 (Cp-C), 125.0, 128.1, 129.3, 135.2
(PPh2) ppm. MS (70 eV, EI): m/z (%) = 671 (5) [M+], 550 (60) [M+ –
SO2tBu], 429 (50) [M+ – 2SO2tBu], 124 (5) [CpCo]. MS (70 eV,
12
HR-EI): m/z (%) = 671.1688 (51) [M+;
S259Co: 671.1704]; ∆mmu = –1.6.
C
33
1H4314N16O431P32-
[η4-1,2-Bis(tert-butylsulfonyl)-4-diethylamino-3-phenylcyclobutadi-
ene](η5-cyclopentadienyl)cobalt (3c): Starting material: 0.062 g
(0.035 mmol) of 2c, 0.15 g (0.035 mmol) of 1. Yield: 0.16 g
(0.028 mmol; 80%), orange solid, m.p. 127–128 °C. 1H NMR
(200.1 MHz, CDCl3): δ = 0.95 (t, 6 H, CH2CH3), 1.18, 1.45 [2s,
2×9 H, C(CH3)3], 2.9, 3.2 [2m, 2×2 H, CH2CH3], 5.35 (s, 5 H,
Cp), 7.2, 7.6 (2m, 5 H, Ph) ppm. 13C NMR (50.3 MHz, CDCl3): δ
= 11.33 (CH2CH3), 24.43, 24.85 [C(CH3)3], 43.62 (CH2CH3), 61.57,
62.17 [C(CH3)3], 82.70 (Cp-C), 127.5, 128.2, 129.0, 132.48 (Ph)
ppm; C4ring not found. MS (70 eV, EI): m/z (%) = 563 (10) [M+],
442 (25) [M+ – SO2tBu]. MS (70 eV, HR-EI): m/z (%) = 563.1584
Experimental Section
(68) [M+;
C = 1.0.
1H3816O432S259Co: 563.1574]; ∆mmu
12
27
General: All reactions were performed under nitrogen using stan-
dard Schlenk techniques. Solvents were dried with the appropriate
drying agents and distilled under nitrogen. Glassware was dried
with a heat gun under high vacuum. 1H, 11B, and 13C NMR:
C27H38CoO4S2 (563.66): calcd. C 57.53, H 6.80, N 2.48; found C
57.65, H 6.88, N 2.54.
Bis[(η4-cyclobutadiene)]cobalt Complex 3g: Starting material: 0.25 g
(1.06 mmol) of (PhC2)2S (2g), 0.89 g (2.12 mmol) of 1. Yield: 0.47 g
1
Bruker AC 200 spectrometer; H and 13C spectra were referenced
1
(0.46 mmol; 43%), brown oil. H NMR (200.1 MHz, CDCl3): δ =
to (CH3)4Si. IR spectra were recorded on a Bruker IFS 28 FT spec-
trometer. Mass spectra were obtained on a Finnigan MAT 8230
plus spectrometer using the EI technique. Elemental analyses were
carried out by the Mikroanalytisches Laboratorium der Universität
Heidelberg. Melting points (uncorrected) were obtained on a Büchi
apparatus, using capillaries which were filled under nitrogen and
sealed. Complex (1),[9] 2-(diethylamino)-1-phenylthioacetylene
(2a),[10] 2-(diethylamino)-1-(diphenylphosphanyl)acetylene (2b),[11]
2-(diethylamino)-1-phenylacetylene (2c),[12] 1-(diethylamino)-2-
bis(diethylaminoboryl)acetylene,[13] 1-catecholboryl-2-phenylacety-
lene,[12] 1-dithiocatecholboryl-2-phenylacetylene,[12] and (PhC2)2S
(2g)[14] were prepared according to literature procedures.
1.19, 1.27 [2s, 2×18 H, C(CH3)3], 5.01 (s, 10 H, Cp), 7.0–7.3 (m,
10 H, C6H5) ppm. 13C NMR (50.3 MHz, CDCl3): δ = 24.62, 25.19
[C(CH3)3], 62.07, 62.92 [C(CH3)3], 55.20, 58.64, 66.09, 75.17
Table 1. Crystal data and structure refinement for 3a.
Empirical formula
Formula mass
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C27H38CoNO4S3·C7H8
687.83
monoclinic
P21/c
14.7043(8)
8.9725(5)
26.3058(6)
90
General Procedure for the Synthesis of 3a–c and 3g: The mono(al-
kyne)cobalt complex 1 was dissolved in 30 mL of toluene and the
appropriate acetylene was added. The reaction mixture was stirred
for 2 d at room temperature. After completion of the reaction, the
solvent was removed to dryness and the crude product was purified
by column chromatography on silica gel (THF/toluene, 2:1). Cobalt
complex 3a was recrystallized from a solution of toluene at –20 °C.
α [°]
β [°]
γ [°]
99.080(2)
90
3427.1(3)
4
1.33
0.72
Volume [Å3]
Z
Dcalcd. [gcm–3]
µ [mm–1]
F(000)
1456
Crystal size [mm]
Θmax(°)
Index ranges
Reflections collected
Reflections independent (Rint
0.30×0.08×0.04
21.5
–15/15, –9/9, –27/27
20502
3940 (0.1512)
2243
397
0.99
0.048
0.071
200(2)
[η4-1,2-Bis(tert-butylsulfonyl)-4-(diethylamino)-3-phenylthiocyclobu-
tadiene](η5-cyclopentadienyl)cobalt (3a): Starting material: 0.25 g
(1.21 mmol) of 2a, 0.50 g (1.21 mmol) of 1. Yield: 0.55 g
(0.92 mmol; 76%), orange solid, m.p. 132–133 °C. 1H NMR
(200.1 MHz, CDCl3): δ = 1.03 (t, 6 H, CH2CH3), 1.38, 1.47 [2s,
2×9 H, C(CH3)3], 3.1, 3.4 (2m, 2×2 H, CH2CH3), 5.21 (s, 5 H,
Cp), 7.0–7.3 (m, 5 H, SPh) ppm. 13C NMR (50.3 MHz, CDCl3): δ
= 11.05 (CH2CH3), 24.32, 24.89 [C(CH3)3], 42.25 (CH2CH3), 61.77,
62.62 [C(CH3)3], 54.90, 58.34, 65.79, 74.87 (C4ring), 83.24 (Cp-C),
125.1, 125.4, 128.9, 138.9 (SPh) ppm. MS (70 eV, EI): m/z (%) =
595 (30) [M+], 475 (20) [M+ – SO2tBu], 353 (45) [M+ – 2SO2tBu],
)
Reflections observed [I Ͼ 2σ(I)]
Parameters
Goodness-of-fit on F2
R1 [I Ͼ 2σ(I)]
wR2 [I Ͼ 2σ(I)]
T [K]
Residual electron density [eÅ–3]
0.38/–0.35
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Reactivity of the a Cobalt Complex Towards Acetylenes
FULL PAPER
tallic Chemistry (Eds: F. G. A. Stone, E. W. Abel), Pergamon
Press, Oxford, 1982, vol. 5, p. 248.
(C4ring), 83.54 (Cp-C), 125.5, 125.7, 129.3, 135.4 (Ph) ppm. MS
(70 eV, EI): m/z (%) = 1014 (10) [M+], 941 (15) [M+ – tBuO]. MS
[2] W. S. Lee, H. H. Brintzinger, J. Organomet. Chem. 1977, 127,
12
32
(70 eV, HR-EI): m/z (%) = 1014.1307 (100) [M+;
S559Co2: 1014.1243]; ∆mmu = 6.4.
C -
1H5616O8
46
93.
[3] A. Krebs, J. Wilke, Top. Curr. Chem. 1983, 109, 189.
[4] B. Jessel, Dissertation, Universität Hamburg, 1984; see ref.[3]
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Oeser, H. Pritzkow, F. Rominger, Eur. J. Inorg. Chem. 1998,
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[6] A. Riera, M. Marti, A. Moyano, M. A. Pericas, J. Santamaria,
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629–632.
X-ray Crystal Structure Determination of 3a: Crystal data and de-
tails of the structure determination are listed in Table 1. Reflections
were collected with a Bruker-AXS SMART 1000 diffractometer
(Mo-Kα radiation, λ = 0.71073 Å, graphite monochromator, ω-
scan). An empirical absorption correction was applied. The struc-
ture was solved by direct methods and refined by least-squares
methods based on F2 with all measured reflections (SHELXTL
5.1).[15] All non-hydrogen atoms were refined anisotropically.
CCDC-268675 (for 3a) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
[10] T. Nakai, K. Tanaka, N. Ishikawa, Chem. Lett. 1976, 11, 1263.
[11] G. Himbert, M. Regitz, Chem. Ber. 1974, 107 2513.
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[13] A. Goswami, C.-J. Maier, H. Pritzkow, W. Siebert, Eur. J. Inorg.
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Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 623) and the Fonds der Chemischen Industrie.
[14] M. Herres, O. Walter, H. Lang, R. Hosch, J. Hahn, J. Or-
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[1] a) J. P. Collman, L. S. Hegedus, J. R. Norton, R. G. Finke,
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[15] SHELXTL 5.1, Bruker AXS, Madison, WI, USA, 1997.
Received: April 14, 2005
Published Online: August 24, 2005
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