Oligoalkyne-bridged (η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt fragments - Syntheses and properties

Article abstract of DOI:10.1002/1099-0682(200208)2002:8<2040::AID-EJIC2040>3.0.CO;2-W

The syntheses of (η⁵-cyclopentadienyl)(η⁴ -tetraphenylcyclobutadiene)cobalt units bridged by buta-1,3-diyne, octa-1,3,5,7-tetrayne, and dodeca-1,3,5,7,9,11-hexayne units (15, 18, 21) are reported. All three species could be obtained by Hay coupling of the corresponding mono-, di-, and triyne units 14, 17, and 20. In the case of 14-17 and 21, the molecular structures were confirmed on the basis of X-ray studies on single crystals. Cyclic voltammetry revealed a weak interaction between the metal centers of 15 and no interaction between the metal centers of 18 and of 21. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200208)2002:8<2040::AID-EJIC2040>3.0.CO;2-W

FULL PAPER
Oligoalkyne-Bridged (η4-Cyclobutadiene)(η5-cyclopentadienyl)cobalt Fragments
؊ Syntheses and Properties
Joerg Classen,[a] Rolf Gleiter,*[a] and Frank Rominger[a]
Dedicated to Professor Dwaine O. Cowan
Keywords: Alkynes / Conjugation / Electron transfer / Rod-like molecules / Cobalt
The syntheses of (η5-cyclopentadienyl)(η4-tetraphenylcyclo- structures were confirmed on the basis of X-ray studies on
butadiene)cobalt units bridged by buta-1,3-diyne, octa-
single crystals. Cyclic voltammetry revealed a weak interac-
1,3,5,7-tetrayne, and dodeca-1,3,5,7,9,11-hexayne units (15, tion between the metal centers of 15 and no interaction be-
18, 21) are reported. All three species could be obtained by
Hay coupling of the corresponding mono-, di-, and triyne un-
its 14, 17, and 20. In the case of 14−17 and 21, the molecular
tween the metal centers of 18 and of 21.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
2002)
Introduction
Transition metal complexes with two redox centers are of
current interest in basic and applied research.[1] Since the
first investigation of biferrocene,[1,2] biferrocenylene,[3,4] and
diferrocenylacetylene[5,6] almost 30 years ago, the interest
in dinuclear complexes has increased considerably.[7Ϫ20] Of
current interest are species with rigid alkyne units between
the metal units. The metal centers can be connected
through the ligands as in 1Ϫ3, or they can be connected
directly to the alkyne bridges as in 4 and 5.[13Ϫ20] In both
types, voluminous termini are connected with a rigid car-
bon rod. The most frequent metal species to mark the end
of the rod are iron- and rhenium-based fragments. In this
paper we report on the synthesis, structural and spectro-
scopic properties of molecular wires consisting of C4 to C12
chains bridging two (η5-cyclopentadienyl)(η4-tetra-
phenylcyclobutadiene)cobalt units.
cyclooctadiene unit in 6 by a tricyclo[7.5.0.01,7]tetradeca-
1,8-diene group could only be achieved in 22% yield.[11]
Furthermore, the conversion of the acetyl group in 7[11] to
the alkyne unit according to a protocol described by
Negishi, furnished 8 in only 28% yield.[11] In order to
obtain higher yields of the starting material we replaced
1,8-cyclotetradecadiyne by the less expensive tolan and
chose a different route to generate the alkyne unit. Our syn-
thesis of the monoalkyne complex 14 is summarized in
Scheme 2. The dicarbonyl(η5-methoxycarbonylcyclopenta-
dienyl)cobalt complex 9[21] was converted into the metallo-
cene 10,[22,23] and subsequently reduced to the alcohol 11[24]
according to known procedures. The conversion into the
aldehyde 12[25] was accomplished with BaMnO4 oxida-
tion,[26] followed by a Wittig reaction with (chloromethyl)-
triphenylphosphonium chloride, giving a 1:1 mixture of (E)/
(Z)-alkenes 13.[24] Treatment of the mixture with potassium
Syntheses of 14؊20
Initiated by electrochemical studies on species with (η4-
cyclobutadiene)(η5-cyclopentadienyl)cobalt fragments, we
synthesized 3 and compared its electrochemical properties
with related species. The synthesis of 3 is briefly outlined in
Scheme 1 and has been described in the literature.[11] The
further extension of the length of the alkyne bridges was
hampered by the two low yielding steps for obtaining the
starting material 8 (Scheme 1).[11] The replacement of the
[a]
Organisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
2040
 WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0808Ϫ2040 $ 20.00ϩ.50/0 Eur. J. Inorg. Chem. 2002, 2040Ϫ2046

Oligoalkyne-Bridged (η4-Cyclobutadiene)(η5-cyclopentadienyl)cobalt Fragments
FULL PAPER
tert-butoxide yielded a mixture of the (E) diastereomer and
In order to obtain longer chains we had to find a reason-
the alkyne 14.[24] After separation of 14, the (E) diastere- able path to elongate 14 by one ethynyl unit. This could be
omer was treated with phenyllithium at room temperature, achieved
by
a
modified
CadiotϪChodkiewicz
giving 14 again. The overall yield of the five steps shown in reaction[13,14,30Ϫ33] involving 14 and (triethylsilyl)ethynyl
Scheme 2 was 10%. The structure of 14 could be confirmed bromide,[32,33] as shown in Scheme 3 in 90% yield. The par-
by a diffraction analysis on single crystals.
ent compound 17 could be obtained by solvolysis of 19 with
5  NaOH[10,34] in DMF.
Coupling of 17 to the dimer with four alkyne units could
be achieved with CuI in the presence of tetramethylethylene-
diamine (TMEDA) (Scheme 3) and oxygen. The moderate
yield of this product 18 can be attributed to the instability
of 17 under the coupling conditions. The yield of 18 could
be increased to 95% when 17 was produced in situ and
Scheme 1. Preparation of 3: a) 1,8-cyclododecadiyne; b) LDA/ not isolated.
THF; c) ClPO(OEt)2; d) LDA, HCl; e) Cu(OAc)2, pyridine
Compound 21 was prepared by the elongation of the al-
kyne chain of 17 by one unit using the homocoupling pro-
tocol as shown in Scheme 3. As a side reaction, 18 could be
isolated, therefore the yield of 19 was lower (74%) relative
to the coupling reaction which led to 16. In order to obtain
21, the triethylsilyl group of 19 was removed by NaOH in
DMF in situ, followed by a CadiotϪChodkiewicz reaction
(Scheme 3). In this case the product was obtained in 47%
yield. The single crystals obtained of 21 were of poor qual-
ity. Therefore, the X-ray data can only be used as proof of
the constitution and conformation of the end groups.
Structural Investigations
Scheme 2. Preparation of 14: a) tolan, xylene, 120 °C; b) LiAlH4/
ether; c) BaMnO4; d) ClCH2P(C6H5)3ϩClϪ; e) KOtBu; f) C6H5Li
We were able to isolate single crystals for 14Ϫ17 and 21.
In Figures 1 and 2 we display as examples the molecular
structures of 15 and 17. Selected bond lengths of 14Ϫ17 are
summarized in Table 1. The asymmetric unit of 14 contains
two independent molecules, one of them is disordered with
respect to the position of the alkyne unit attached to the
Cp ring. The alkyne unit can be located at two adjacent
Cp carbon atoms with nearly the same occupancies. In the
discussion only the results of the non-disordered molecule
are considered.
To transform 14 into its dimer 15, we tested the protocols
of Eglinton[27,28] and Hay.[29] The reaction of 14 with dry
copper(II) acetate and dry pyridine at 90 °C was not suc-
cessful, only decomposition of the starting material was ob-
served. We were able to isolate 93% of the dimer 15 using
the coupling reported by Hay[29] (Scheme 3). The structure
of 15 could be confirmed by X-ray investigations on single
crystals (see below).
Figure 1. ORTEP plot (50% probability) of the molecular structure
of 17
The mean distances between the cobalt atom and the
˚
cyclopentadienyl (Cp) ring (1.68 A for all structures) are
slightly shorter than between the cobalt atom and the cyclo-
Scheme 3. Synthesis of 15, 16, 18, 19, 21: a) CuCl/pyridine ϩ O2;
b) CuCl/TMEDA ϩ O2 c) nBuLi; d) CuCl; e) BrϪCϵCϪSiMe3,
EtNH2
˚
butadiene (Cb) unit (1.69 A for all structures). These values
are close to those reported for (η4-cyclobutadiene)(η5-
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046
2041

J. Classen, R. Gleiter, F. Rominger
FULL PAPER
with a hexayne unit between two Cp ligands. It can be com-
pared with (CO)2Cp*FeϪ(CϵC)6ϪFeCp*(CO)2, in which
the C12 chain is bound directly to the metal centers.[36]
Figure 3. Molecular structure of 21 (ball-and-stick model)
Spectroscopic and Cyclovoltammetric Data
The NMR spectroscopic data of the new alkynes are
listed in the Exp. Sect. The assignment of all 13C signals
was possible by carrying out a DEPT experiment. In Fig-
ure 4 the superimposed UV/Vis spectra of 15, 18, and 21
are shown. It demonstrates a shift to longer wavelengths
of the absorbance bands with increasing chain length, as
reported for related species.[10,13Ϫ17,36]
Figure 2. ORTEP plot (50% probability) of the molecular structure
of 15
˚
Table 1. Selected bond lengths [A] and bond angles [°] of 14Ϫ17;
for the numbering see Scheme 3
14
15
16
17
CpϪCo (mean values) 1.675(3) 1.675(2) 1.679(2) 1.682(4)
CbϪCo (mean values) 1.691(3) 1.693(2) 1.692(2) 1.693(3)
C1ϪC10
C10ϪC11
C11ϪC12
C12ϪC13
1.443(6) 1.418(3) 1.422(3) 1.425(6)
1.143(7) 1.197(3) 1.204(3) 1.247(7)
1.378(4) 1.387(3) 1.319(7)
1.192(3) 1.275(9)
C1ϪC10ϪC11
C10ϪC11ϪC12
C11ϪC12ϪC13
175.6(7) 175.7(2) 178.4(2) 177.7(5)
178.7(3) 179.4(2) 178.9(7)
179.4(2) 176.3(8)
cyclopentadienyl)cobalt,[35] where the mean distance be-
˚
tween the Cp ring and the cobalt atom is 1.66 A, and the
distance between the cobalt atom and the Cb ring is 1.68
Figure 4. UV/Vis spectra of 15, 18, and 21
[34]
˚
A. The distances between the Cp ring and the sp carbon
˚
centers (C1ϪC10, Scheme 3) vary between 1.44 A (14) and
˚
1.42 A (15Ϫ17). The bond length of the terminal triple
In order to investigate the extent of metalϪmetal interac-
˚
bond in 14 [1.143(7) A] is unrealistically short. This can be tion in 15, 18, and 21, cyclic voltammetric (CV) measure-
attributed to the librational shortening caused by the strong ments were carried out. The uncertainty of the signals is
anisotropic motion of this molecular tail, which cannot be somewhat larger (Ϯ25 mV) than usual (Ϯ15 mV), because
modeled correctly by an ellipsoid-shaped description. The of the low solubility of the samples in dichloromethane. As
distances found for the other triple bonds (C10ϪC11 and a reference, compound 14 was used, which is the simplest
˚
˚
C12ϪC13) vary between 1.20 A (15, 16) and 1.28 A (17). common building block of all three oligomers. The CV
The angles at the triple bonds deviate slightly from 180°, as measurement of 14 shows a reversible oxidation at 540 mV
reported for other long alkyne chains.[32,33] The CϪC bond (Figure 5). The CV of 15 reveals two oxidations, one at 490
lengths within the Cb and Cp rings are found to be equal. mV, the second at 720 mV. The former is reversible, the
The phenyl rings are twisted out of the plane of the Cp ring latter is irreversible at different scan rates of up to 2 V/s.
in a propeller-like fashion (see Figure 2).
The first oxidation of 15 was observed at a lower poten-
The molecular structure of 21 in the solid state is shown tial (by 50 mV) than that of the reference compound 14.
in Figure 3. In this molecule both tetraphenylcyclobutadi- This result can be rationalized by assuming a lower HOMO
ene units are far removed from each other, therefore they energy due to the interaction of both metal fragments. The
can adopt the syn conformation (Figure 3). The crystal data positive charge of the resulting radical cation is delocalized
of 21 reveal R values that are too large to be used for a over both Co atoms through the alkyne backbone, resulting
quantitative evaluation (cf. Table 2). This shortcoming is in a higher second oxidation potential. The potential sep-
mainly due to three disordered dichloromethane molecules aration of 230 mV suggests that the electronic interaction
in the asymmetric unit. Nevertheless, 21 is the first example is relatively weak,[38] therefore, we assign 15 to class II in
2042
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046

Oligoalkyne-Bridged (η4-Cyclobutadiene)(η5-cyclopentadienyl)cobalt Fragments
FULL PAPER
Figure 5. Comparison of the CV data of 14, 15, 18, and 21
the Robin and Day classification of mixed-valent com- overall yield of 10%. With 14 as the key intermediate, we
pounds.[37]
were able to synthesize 15, 18, and 21. The key steps were
A different situation is observed for 18 and 21, where the the Hay coupling reaction of the corresponding mono-,
first reversible oxidation potential is shifted towards a di-, and triyne units 14, 17, and 20, respectively. The yields
higher potential (by 50 mV) with respect to 14. The second of 18 and 21 could be improved by preparing 17 and 20 in
oxidation of 18 and 21 is irreversible at different scan rates situ by deprotection of the protected diyne 16 and triyne
of up to 2 V/s. The larger potential separation of 270 (18) 19, respectively. By means of X-ray studies of the single
and 290 mV (21) seems to indicate an increase in the elec- crystals of 14Ϫ17 and 21 we could confirm the structure
tronic interaction with increasing alkyne chain length. and conformation of the alkynes. For the polyyne part of
However, a larger π-system is expected to result in a de- all the studied samples, clear shortϪlong CϵCϪC bond
crease in the HOMO energy, which in turn should cause a alternation is observed. Our CV studies do not indicate a
more facile oxidation. This contradiction can be explained metalϪmetal interaction through the alkyne rod for 18 and
by a reversible two-electron oxidation, where both Co 21, whereas in 15, where the distance between the metal
atoms are oxidized to CoII at similar potentials. At the se- centers is shorter, a slight shift with respect to 14 is ob-
cond irreversible potential, an oxidation of one or both CoII served.
atoms to CoIII may occur. Another explanation is an ECE
mechanism, where the first oxidation is followed by a chem-
ical transformation, which renders the second oxidation ir-
reversible. The latter complexes show no electronic interac-
Experimental Section
tion, so they can be assigned to class I in the Robin and
General Remarks: All melting points are uncorrected. The NMR
spectra were measured with a Bruker Avance 500 spectrometer (1H
NMR at 500 MHz and 13C NMR at 125.77 MHz) using the solvent
as internal standard (δ). The mass spectra refer to data recorded
with a JEOL JMS-700 instrument. IR spectra were recorded with
a Bruker Vector 22. All reactions with CpCo(COD) were carried
out in dried glassware under argon, using dried and oxygen-free
solvents.
Day classification of mixed-valent compounds.[37]
Concluding Remarks
Our goal was to find a reasonable path to prepare polyal-
kynes with (η5-cyclopentadienyl)(η4-tetraphenylcyclobutadi-
enyl)cobalt fragments at both ends of the carbon rod. This
could be achieved using 14 as a starting material. This com-
(η5-Formylcyclopentadienyl)(η4-tetraphenylcyclobutadienyl)cobalt(I)
(12):[25] BaMnO4 (2.0 g, 7.8 mmol) was added to a solution of 11
pound was made available in five steps from 10, with an (200 mg, 0.4 mmol) in 100 mL of dichloromethane.[26] The suspen-
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046
2043

J. Classen, R. Gleiter, F. Rominger
FULL PAPER
sion was stirred for 24 h under argon. After filtration, the solvent
(η4-Tetraphenylcyclobutadienyl)[η5-(triethylsilylbutadiynyl)-
cyclopentadienyl]cobalt(I) (16): n-Butyllithium (645 mg, 1.5 mmol,
was removed to give 198 mg (99%) of 12 as an orange solid. 1H
NMR (CD2Cl2): δ ϭ 4.91 (pt, 2 H, CpH), 5.23 (pt, 2 H, CpH), 1.6  solution) was slowly added to a solution of 14 (695 mg,
7.21Ϫ7.34 (m, 12 H, o,p-ArH), 7.41Ϫ7.47 (m, 8 H, m-ArH), 9.31
1.4 mmol) in 100 mL of THF, at Ϫ35 °C. Subsequently, CuCl
(s, 1 H, CHO) ppm. 13C NMR (CD2Cl2): δ ϭ 77.5, 92.9 (s), 83.4, (263 mg, 1.4 mmol) was added and the mixture was stirred for
88.9 (d, Cp), 127.3 (d, p-Ar), 128.5 (d, o-Ar), 129.1 (d, m-Ar), 135.2 30 min at Ϫ15 °C. After stirring at room temperature for 10 min,
(s, Ar), 190.9 (d, CHO) ppm.
the suspension was cooled to Ϫ25 °C and freshly distilled
ethylamine (5 mL) and bromo(triethylsilyl)acetylene (330 mg,
1.5 mmol) were added. After further stirring for 18 h, the hydrolysis
was carried out with 50 mL of saturated NH4Cl solution. The
workup was completed by extraction of the aqueous layer with di-
ethyl ether and drying of the combined organic layers with MgSO4.
Removal of the solvent gave a crude product. Further purification
by column chromatography on silica with light petroleum ether/
dichloromethane (7:1) yielded 804 mg (91%) of 16 as a yellow solid,
m.p. 146 °C. 1H NMR (C6D6): δ ϭ 0.56 (q, CH2, 6 H), 1.01 (t,
CH3, 9 H), 4.31 (pt, CpH, 2 H), 4.61 (pt, CpH, 2 H), 7.04Ϫ7.12
(m, 12 H, ArH), 7.54Ϫ7.59 (m, 8 H, ArH) ppm. 13C NMR (C6D6):
δ ϭ 4.7 (t, CH2), 7.7 (q, CH3), 73.5, 74.5, 77.0, 77.7, 86.0, 91.1 (s,
Cp, CAlkyne, cbd-C,), 85.1 (d, Cp), 87.4 (d, Cp), 126.9 (d, p-Ar),
128.4 (d, o-Ar), 129.2 (d, m-Ar), 135.6 (s, Ar) ppm. IR (KBr): ν˜ ϭ
2955, 2874, 2206, 1630, 1499, 1460 cmϪ1. HRMS (EI): calcd.
642.2153; found 642.2159. C43H39CoSi (642.2): calcd. C 80.35, H
6.12; found C 80.10, H 6.32.
[η5-(E)-1-Chloroethenylcyclopentadienyl](η4-tetraphenylcyclo-
butadienyl)cobalt(I) [(E)-13] and (η5-Ethynylcyclopentadienyl)(η4-
tetraphenylcyclobutadienyl)cobalt(I) (14): Potassium tert-butoxide
(106 mg, 1.0 mmol) was added to a solution of (chloromethyl)tri-
phenylphosphonium chloride (350 mg, 1.0 mmol) in 20 mL of
THF. At Ϫ70 °C, a cooled (Ϫ65 °C) solution of 12 (342 mg,
0.7 mmol) in 20 mL of THF was added to this solution. The re-
sulting mixture was stirred for 30 min at Ϫ65 °C and then 30 min
at room temperature. Subsequently, a solution of potassium tert-
butoxide (106 mg, 1.0 mmol) in 20 mL of THF was added and the
mixture refluxed for 17 h. After cooling and addition of 20 mL of
distilled water, the layers were separated, and the aqueous layer was
washed four times with diethyl ether. After drying (MgSO4) of the
combined organic layers, the solvent was removed and the crude
mixture was purified by column chromatography on alumina (light
petroleum ether to light petroleum ether/diethyl ether, 10:1). This
procedure yielded 166 mg (46%) of (E)-13 as a yellow solid. Follow-
ing the isolation of (E)-13, 134 mg (39%) of the alkyne complex 14
(η5 -Butadiynylcyclopentadienyl)(η4 -tetraphenylcyclo-
butadienyl)cobalt(I) (17): NaOH (0.3 mL of an aqueous 5  solu-
tion) was added to a solution of 16 (337 mg, 0.5 mmol) in 30 mL
of DMF. After 5 min, 2  HCl was added until pH Ͻ 4 (ca. 2 mL).
The resulting precipitate was filtered, washed extensively with
water, dissolved in diethyl ether, and dried with MgSO4. Removal
of the solvent yielded 264 mg (95%) of 17 as a gold-colored, oxy-
gen-sensitive solid. 1H NMR (CDCl3): δ ϭ 2.32 (s, 1 H, CCH),
4.68 (pt, 2 H, CpH), 4.82 (pt, 2 H, CpH), 7.22Ϫ7.33 (m, 12 H,
ArH), 7.43Ϫ7.49 (m, 2 H, ArH) ppm. 13C NMR (C6D6): δ ϭ 69.3,
69.7, 72.4, 73.4, 77.1, 77.2 (s, CAlkyne, cbd-C, Cp), 85.2 (d, Cp), 87.3
(d, Cp), 126.9 (d, p-Ar), 128.4 (d, o-Ar), 129.2 (d, m-Ar), 135.6 (s,
Ar) ppm. IR (KBr): ν˜ ϭ 3060, 2209, 1609, 1499 cmϪ1. HRMS
(FAB): calcd. 528.1289; found 528.1312.
1
was obtained as a yellow solid. H NMR (CD2Cl2): δ ϭ 4.63 (pt,
2 H, CpH), 4.67 (pt, 2 H, CpH), 5.84 (d, 1 H, CϭCH), 5.93 (d, 1
H, CϭCH), 7.19Ϫ7.30 (m, 12 H, o,p-ArH), 7.37Ϫ7.45 (m, 8 H, m-
ArH) ppm. 13C NMR (CD2Cl2): δ ϭ 76.2 (s), 81.1 (d, Cp), 84.8
(d, Cp), 93.1 (s), 115.8 (d, CϭC), 126.7 (d, p-Ar), 127.2 (d, CϭC),
128.4 (d, o-Ar), 129.1 (d, m-Ar), 136.1 (s, Ar).
Transformation of (E)-13 to 14: Phenyllithium (0.6 mL, 1.1 mmol,
1.8 ) was added to a solution of (E)-13 (500 mg, 0.9 mmol) in
20 mL of THF. After stirring for 20 h, the mixture was hydrolyzed
with 25 mL of brine. The aqueous layer was extracted four times
with diethyl ether, the combined organic layers were dried (MgSO4)
and the solvent was removed. After purification by column chro-
matography on alumina (neutral, grade III, light petroleum ether),
275 mg (59%) of the alkyne 14 was obtained as a yellow solid, m.p.
{µ-[Octatetraynediylbis(η5-cyclopentadienyl)]}bis(η4-tetraphenyl-
cyclobutadienyl)dicobalt(I) (18): NaOH (0.15 mL of 1  solution)
was added to a solution of 16 (145 mg, 0.23 mmol) in 15 mL of
DMF. After 5 min, HCl (1.5 mL of 2  solution) was added. The
organic layer was washed three times with water and brine. The
aqueous layer was extracted twice with diethyl ether, the combined
organic layers were dried with MgSO4 and concentrated to 20 mL.
The solution was poured into a mixture of acetone (20 mL),
N,N,NЈ,NЈ-tetramethylethylenediamine (14 mg) and CuCl (12 mg).
After 4 h of passing oxygen through the mixture, hydrolysis with
30 mL of saturated NH4Cl solution was carried out. After extrac-
tion of the aqueous layer with dichloromethane, the combined
layers were adsorbed on silica. The purification by column chroma-
tography on silica with light petroleum ether/dichloromethane (4:1)
yielded 113 mg (95%) of 18 as an orange-red solid, m.p. 218 °C.
1H NMR (CDCl3/CD2Cl2, 2:1): δ ϭ 4.74 (pt, 4 H, CpH), 4.89 (pt,
4 H, CpH), 7.23Ϫ7.36 (m, 24 H, ArH), 7.42Ϫ7.49 (m, 16 H, ArH)
ppm. 13C NMR (CDCl3/CD2Cl2, 2:1): δ ϭ 63.9, 66.1, 73.6, 74.9,
75.9, 77.2 (s, CAlkyne, cbd-C, Cp), 85.3 (d, Cp), 87.5 (d, Cp), 126.7
(d, p-Ar), 128.1 (d, o-Ar), 128.7 (d, m-Ar), 134.8 (s, Ar) ppm. IR
(KBr): ν˜ ϭ 3061, 2925, 2194, 1630, 1498, 1449 cmϪ1. HRMS
(FAB): calcd. 1055.2498; found 1055.2483.
1
148 °C. H NMR (CD2Cl2): δ ϭ 2.51 (s, 1 H, CCH), 4.62 (pt, 2
H, CpH), 4.79 (pt, 2 H, CpH), 7.23Ϫ7.28 (m, 12 H, ArH),
7.45Ϫ7.49 (m, 8 H, ArH) ppm. 13C NMR (CD2Cl2): δ ϭ 76.4,
76.7, 78.2, 79.5 (s, cbd-C, Cp, CAlkyne), 84.9 (d, Cp), 86.6 (d, Cp),
126.9 (d, p-Ar), 128.4 (d, o-Ar), 129.3 (d, m-Ar), 135.8 (s, Ar) ppm.
IR (KBr): ν˜ ϭ 3056, 2924, 2109, 1628, 1600, 1498, 1445 cmϪ1
.
HRMS (FAB): calcd. 504.1288; found 504.1273.
{µ-[Butadiynediylbis(η5-cyclopentadienyl)]}bis(η4-tetraphenylcyclo-
butadienyl)dicobalt(I) (15): A solution of CuCl (16 mg, 0.16 mmol)
in 15 mL of dry pyridine, saturated with oxygen was added to a
Schlenk flask. To this mixture 14 (209 mg, 0.4 mmol) was added,
and oxygen was passed through the mixture for 46 h. After removal
of the pyridine under vacuum, the crude product was purified by
column chromatography on alumina (neutral, grade III) with light
petroleum ether/diethyl ether (60:1), giving 192 mg (93%) of 15 as
1
a yellow-orange solid, m.p. 240 °C. H NMR (CD2Cl2): δ ϭ 4.69
(pt, 4 H, CpH), 4.81 (pt, 4 H, CpH), 7.16Ϫ7.25 (m, 24 H, ArH),
7.39Ϫ7.47 (m, 16 H, ArH) ppm. 13C NMR (CD2Cl2): δ ϭ 74.1,
76.4, 77.1, 78.5 (s, CAlkyne, cbd-C, Cp), 84.9 (d, Cp), 87.3 (d, Cp),
126.9 (d, p-Ar), 128.5 (d, o-Ar), 129.2 (d, m-Ar), 135.5 (s, Ar) ppm.
IR (KBr): ν˜ ϭ 3056, 2924, 2148, 1604, 1497, 1446 cmϪ1. HRMS (η4-Tetraphenylcyclobutadienyl)[η5-(triethylsilylhexatriynyl)-
(EI): calcd. 1006.2420; found 1006.2432.
cyclopentadienyl]cobalt(I) (19): n-Butyllithium (73 mg, 0.17 mmol
2044
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046

Oligoalkyne-Bridged (η4-Cyclobutadiene)(η5-cyclopentadienyl)cobalt Fragments
FULL PAPER
of a 1.6  solution) in n-hexane was slowly added to a cooled solu-
tion (Ϫ40 °C) of 17 (81 mg, 0.15 mmol) in 10 mL of THF. Sub-
sequently, CuCl (30 mg, 0.16 mmol) was added. After stirring the
mixture for a further 5 min at Ϫ30 °C, the stirring was continued
at room temperature for 10 min. Subsequently, freshly distilled
ethylamine (1 mL) and bromo(triethylsilyl)acetylene (70 mg,
fied by adding HCl (35 mL of a 2  aqueous solution). The re-
sulting precipitate was filtered, washed extensively with water, and
dissolved in diethyl ether. The aqueous layer was extracted twice
with diethyl ether, the combined organic layers were dried with
MgSO4 and concentrated to 20 mL. The solution was poured into
a solution of acetone (36 mL), N,N,NЈ,NЈ-tetramethylethylenedia-
0.25 mmol) were added at Ϫ25 °C. Stirring was continued for mine (0.053 mL) and CuCl (18 mg). After 80 min of passing oxygen
50 min at that temperature and the mixture was then hydrolyzed through the mixture, 60 mL of diethyl ether and 50 mL of saturated
with 15 mL of a saturated NH4Cl solution. The extraction of the NH4Cl solution were added. The organic layer was washed twice
aqueous layer with diethyl ether and the removal of the solvent
gave a crude product, which was further purified by column chro-
matography on silica with light petroleum ether/dichloromethane
(5:1) gave 75 mg (74%) of 19 as a yellow-brown solid, m.p. 114 °C.
1H NMR (CDCl3): δ ϭ 0.68 (q, 6 H, CH2), 1.05 (t, 9 H, CH3),
with water. and the combined aqueous layers were washed with
dichloromethane. The combined organic layers were dried with
MgSO4, absorbed on silica and purified by column chromato-
graphy on silica with light petroleum ether/dichloromethane (7:1),
1
yielding 45 mg (47%) of 21 as a red solid, m.p. 210 °C. H NMR
4.69 (pt, 2 H, CpH), 4.84 (pt, 2 H, CpH), 7.22Ϫ7.34 (m, 12 H, (CD2Cl2: δ ϭ 4.74 (pt, 4 H, CpH), 4.90 (pt, 4 H, CpH), 7.21Ϫ7.44
ArH), 7.43Ϫ7.48 (m, 8 H, ArH) ppm. 13C NMR (CDCl3): δ ϭ 4.2 (m, 40 H, ArH) ppm. 13C NMR (CD2Cl2): δ ϭ 64.0, 64.2, 64.3,
(CH2), 7.4 (CH3), 62.1, 65.3, 73.2, 74.2, 76.2, 76.9, 86.0, 89.7 (s,
CAlkyne, cbd-C, Cp), 85.2 (Cp), 87.3 (Cp), 126.7 (d, p-Ar), 128.1 (d, (d, Cp), 127.2 (d, p-Ar), 128.5 (d, o-Ar), 129.1 (d, m-Ar), 135.1 (s,
65.9, 73.4, 75.3, 76.4, 77.8 (s, cbd-C, Cp, CAlkyne), 86.2 (d, Cp), 88.2
Ar) ppm. IR (KBr): ν˜ ϭ 2148, 2041, 1630, 1498, 1261 cmϪ1
o-Ar), 128.8 (d, m-Ar), 134.9 (Ar) ppm. IR (KBr): ν˜ ϭ 2953, 2921,
.
2879, 2176, 2067, 1605, 1497, 1454 cmϪ1. HRMS (FAB): calcd. HRMS (FAB): calcd. 1102.2393; found 1102.2366.
666.2153; found 666.2148. C45H39CoSi (666.2): calcd. C 81.06, H
Cyclovoltammetry: The electrochemical measurements were per-
formed with an Ecochem PGStat 20. A glassy carbon disk elec-
5.89; found C 81.19, H 6.15.
{µ-[Dodecahexaynediylbis(η5-cyclopentadienyl)]}bis(η4-tetraphenyl- trode with a 3 mm diameter was used as the working electrode. The
cyclobutadienyl)dicobalt(I) (21): The removal of the protection
group from 19 was achieved by adding NaOH (0.12 mL of a 5 
Ag/AgCl reference electrode was separated from the solution by a
G4-frit and a HaberϪLuggin capillary. As the electrolyte, a 0.1 
aqueous solution) to a solution of 19 (115 mg, 0.17 mmol) in solution of nBu4NϩPF6Ϫ in anhydrous, degassed CH2Cl2 was used.
35 mL of DMF at room temp. After 5 min, the solution was acidi-
All reported potentials are referred to the Fc/Fcϩ couple, which
Table 2. Crystal data and structure refinement for 14Ϫ17 and 21
14
15
16
17
21
Empirical formula
Formula mass
C35H25Co
504.48
C70H48Co2
1006.94
C43H39CoSi
642.76
C37H25Co
528.50
C78H48Co2·3CH2Cl2
1357.80
Temperature [K]
Wavelength [A]
200(2)
0.71073
200(2)
0.71073
200(2)
0.71073
200(2)
0.71073
150(2)
0.71073
˚
Crystal system
Space group
Z
orthorhombic
Pna21
8
27.5105(2)
19.7683(2)
9.3815(1)
90
5102.00(8)
1.31
monoclinic
P21/n
2
10.5359(3)
20.0926(6)
13.0286(4)
112.88(1)
2540.92(13)
1.32
monoclinic
P21/c
4
16.7032(2)
12.7019(2)
16.7817(1)
106.524(1)
3413.40(7)
1.25
monoclinic
P21/c
4
11.1526(2)
14.2496(2)
117.142(2)
99.652(1)
2685.71(7)
1.31
monoclinic
P21/c
4
11.0730(1)
14.3480(2)
41.4520(5)
94.286(1)
6567.3(1)
1.37
˚
a [A]
˚
b [A]
˚
c [A]
β [°]
Volume [A ]
3
˚
Density (calculated) [g/cm3]
Absorption coefficient [mmϪ1
Crystal shape
]
0.694
0.697
0.567
0.66
lamina
0.80
lamina
polyhedron
0.38 ϫ 0.33 ϫ 0.11
1.27 to 25.66
Ϫ33 Յ h Յ 32
Ϫ23 Յ k Յ 23
Ϫ11 Յ l Յ 11
37314
irregular
0.4 ϫ 0.3 ϫ 0.2
1.98 to 25.62
Ϫ12 Յ h Յ 12
Ϫ23 Յ k Յ 23
Ϫ15 Յ l Յ 15
18723
polyhedron
0.42 ϫ 0.30 ϫ 0.30
2.04 to 27.49
Ϫ21 Յ h Յ 21
Ϫ16 Յ k Յ 16
Ϫ1 Յ l Յ 21
34497
Crystal size [mm]
θ range for data collection [°]
Index ranges
0.46 ϫ 0.28 ϫ 0.03
1.9 to 27.5
Ϫ14 Յ h Յ 14
Ϫ8 Յ k Յ 8
Ϫ22 Յ l Յ 22
27287
0.38 ϫ 0.32 ϫ 0.10
1.7 to 21.5
Ϫ6 Յ h Յ 11
Ϫ8 Յ k Յ 14
Ϫ33 Յ l Յ 42
14892
Reflections collected
Independent reflections
Observed reflections
Absorption correction
8350 [R(int) ϭ 0.0298] 4429 [R(int) ϭ 0.0274] 7828 [R(int) ϭ 0.0319] 6170 [R(int) ϭ 0.0594] 7505 [R(int) ϭ 0.0661]
7413 [I Ͼ 2σ(I)]
semi-empirical
from equivalents
0.94 and 0.83
Full-matrix least
squares on F2
8350/221/672
1.03
3813 [I Ͼ 2σ(I)]
semi-empirical
from equivalents
0.89 and 0.77
Full-matrix least
squares on F2
4429/0/325
6463 [I Ͼ 2σ(I)]
semi-empirical
from equivalents
0.86 and 0.74
Full-matrix least
squares on F2
7828/7/424
4180 [I Ͼ 2σ(I)]
semi-empirical
from equivalents
0.98 and 0.83
Full-matrix least
squares on F2
6170/0/343
6123 [I Ͼ 2σ(I)]
semi-empirical
from equivalents
0.96 and 0.65
Full-matrix least
squares on F2
7505/73/821
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
1.09
1.02
1.03
1.26
Final R indices [I Ͼ 2σ(I)]
R1 ϭ 0.036
R1 ϭ 0.030
R1 ϭ 0.037
R1 ϭ 0.053
R1 ϭ 0.130
wR2 ϭ 0.085
] 0.30 and Ϫ0.38
wR2 ϭ 0.063
0.23 and Ϫ0.28
wR2 ϭ 0.090
0.56 and Ϫ0.39
wR2 ϭ 0.132
0.94 and Ϫ0.46
wR2 ϭ 0.281
1.27 and Ϫ1.48
Ϫ3
˚
Largest diff. peak and hole [e·A
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046
2045

J. Classen, R. Gleiter, F. Rominger
FULL PAPER
was used as an internal calibrant. All measurements were per-
formed at room temperature.
[15]
[16]
F. Coat, C. Lapinte, Organometallics 1996, 15, 477Ϫ479.
F. Paul, C. Lapinte, Coord. Chem. Rev. 1998, 178Ϫ180,
431Ϫ509.
[17]
X-ray Crystallography and Structure Solution: The crystallographic
data were recorded with a Bruker Smart CCD diffractometer at
200 K for 14Ϫ17 and 21. Relevant crystal and data collection para-
meters are given in Table 2. The structures were solved using direct
methods (14Ϫ16, 21) or the Patterson heavy atom method (17),
least-squares refinement, and Fourier techniques. Structure solu-
tion and refinement were performed with SHELXTL.[39] CCDC-
172774 (14), -172775 (15), -172776 (16), -172777 (17), and -172778
(21) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html or from the Cambridge Crystallographic
Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK [Fax:
(internat.) ϩ 44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
F. Paul, W. E. Meyer, L. Toupet, H. Jiao, J. A. Gladysz, C.
Lapinte, J. Am. Chem. Soc. 2000, 122, 9405Ϫ9414.
M. I. Bruce, Coord. Chem. Rev. 1997, 166, 91Ϫ119.
M. I. Bruce, P. J. Low, K. Costuas, J.-F. Halet, S. P. Best, G.
A. Heath, J. Am. Chem. Soc. 2000, 122, 1949Ϫ1962.
U. H. F. Bunz, Angew. Chem. 1996, 108, 1047Ϫ1049; Angew.
Chem. Int. Ed. Engl. 1996, 35, 968Ϫ971.
W. P. Hart, D. Shihua, M. D. Rausch, J. Organomet. Chem.
1985, 282, 111Ϫ121.
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
S. T. Mabrouk, M. D. Rausch, J. Organomet. Chem. 1996,
523, 111Ϫ117.
A. M. Stevens, C. J. Richards, Organometallics 1999, 18,
1346Ϫ1348.
A. M. Stevens, C. J. Richards, Tetrahedron Lett. 1997, 38,
7805Ϫ7808.
M. D. Rausch, R. A. Genetti, J. Org. Chem. 1970, 35,
3888Ϫ3897.
H. Firouzabadi, E. Ghaderi, Tetrahedron Lett. 1978, 9,
839Ϫ840.
O. M. Behr, G. Eglinton, A. R. Galbraith, R. A. Raphael, J.
Chem. Soc. 1960, 3614Ϫ3625.
G. Eglinton, W. McCrae, Adv. Org. Chem. 1963, 4, 225Ϫ328.
A. S. Hay, J. Org. Chem. 1960, 25, 1275Ϫ1276; A. S. Hay, J.
Org. Chem. 1962, 27, 3320Ϫ3321.
P. Cadiot, W. Chodkiewicz, in: Chemistry of Acetylenes (Ed.:
H. G. Viehe), Marcel Dekker, New York, 1969, pp. 597Ϫ647.
W. Chodkiewicz, Ann. Chim. Paris 1957, 2, 819Ϫ869.
R. Dembinski, T. Lis, S. Szafert, C. L. Mayne, T. Bartik, J. A.
Gladysz, J. Organomet. Chem. 1999, 578, 229Ϫ246.
B. Bartik, R. Dembinski, T. Bartik, A. M. Arif, J. A. Gladysz,
New J. Chem. 1997, 21, 739Ϫ750.
R. Eastmond, D. R. M. Walton, Tetrahedron 1972, 78,
4591Ϫ4599.
P. E. Riley, R. E. Davis, J. Organomet. Chem. 1976, 113,
157Ϫ166.
A. Sakurai, M. Akita, Y. Moro-oka, Organometallics 1999,
18, 3241Ϫ3244.
M. B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 1967, 10,
247Ϫ422.
R. Gleiter, H. Röckel, G. Pflästerer, B. Treptow, D. Kratz, Tet-
[1]
D. Astruc, Electron Transfer and Radical Processes in Trans-
ition Metal Chemistry, VCH, New York, 1995.
D. B. Brown (Ed.), Mixed Valence Compounds, Reidel, Dord-
[2]
recht, Netherlands, 1990.
D. O. Cowan, C. LeVanda, J. Park, F. Kaufman, Acc. Chem.
[3]
Res. 1973, 6, 1Ϫ7.
C. LeVanda, K. Bechgaard, D. O. Cowan, M. D. Rausch, J.
[28]
[29]
[4]
Am. Chem. Soc. 1977, 99, 2964Ϫ2968.
C. LeVanda, D. O. Cowan, C. Leitch, K. Bechgaard, J. Am.
[5]
[30]
Chem. Soc. 1974, 96, 6788Ϫ6789.
[6]
J. A. Kramer, D. N. Hendrickson, Inorg. Chem. 1980, 19,
[31]
[32]
3330Ϫ3337.
[7]
O. Lavastre, J. Plass, P. Bachmann, S. Guesmi, C. Moinet, P.
H. Dixneuf, Organometallics 1997, 16, 184Ϫ189.
Z. Yuan, G. Stringer, I. R. Jobe, D. Kreller, K. Scott, L. Koch,
[33]
[34]
[35]
[36]
[37]
[38]
[39]
[8]
N. J. Taylor, T. B. Marder, J. Organomet. Chem. 1993, 452,
115Ϫ120.
[9]
M. Wildschek, C. Rieker, P. Jaitner, H. Schottenberger, K. E.
Schwarzhans, J. Organomet. Chem. 1990, 396, 355Ϫ361.
[10]
M. Altmann, V. Enkelmann, U. H. F. Bunz, Chem. Ber. 1996,
129, 269Ϫ273.
[11]
H. Schimanke, R. Gleiter, Orgonometallics 1998, 17, 275Ϫ277.
M. I. Bruce, B. D. Kelly, B. W. Skelton, A. H. White, J. Or-
[12]
ganomet. Chem. 2000, 604, 150Ϫ156.
M. Brady, W. Weng, Y. Zhou, J. W. Seyler, A. J. Amoroso, A.
[13]
rahedron Lett. 1993, 34, 8075Ϫ8078.
G. M. Sheldrick, Bruker Analytical X-ray Division, Madison,
WI, 1997.
M. Arif, M. Böhme, G. Frenking, J. A. Gladysz, J. Am. Chem.
Soc. 1997, 119, 775Ϫ788.
T. Bartik, B. Bartik, M. Brady, R. Dembinski, J. A. Gladysz,
[14]
Angew. Chem. 1996, 108, 467Ϫ469; Angew. Chem. Int. Ed.
Engl. 1996, 35, 414Ϫ417.
Received November 7, 2001
[I01442]
2046
Eur. J. Inorg. Chem. 2002, 2040Ϫ2046