Reactivity of carboranylacetylenes towards cobalt complexes

Article abstract of DOI:10.1002/ejic.200500787

The reaction of 1,6-diiodo-C₄B₂ nido-carborane derivative 1 with RC₂Li (R = Me, SPh) yields the corresponding carboranylacetylenes 2b,c. Treatment of the PPh₂-substituted nido-carborane 3a with PhC₂Zn

Full text of DOI:10.1002/ejic.200500787

FULL PAPER
DOI: 10.1002/ejic.200500787
Reactivity of Carboranylacetylenes towards Cobalt Complexes
Avijit Goswami,[a] Yong Nie,[a] Thomas Oeser,[b] and Walter Siebert*[a]
Dedicated to Professor Herbert Schumann on the occasion of his 70th birthday
Keywords: Carboranes / Carboranylacetylenes / Cobalt / (Cyclobutadiene)cobalt complexes / (Cyclopentadienone)cobalt
complexes
The reaction of 1,6-diiodo-C4B2 nido-carborane derivative 1
ric amounts of CpCo(C2H4)2. The 1,6-dialkynyl carborane 6
with RC2Li (R = Me, SPh) yields the corresponding carboran- reacts regioselectively at the basal acetylene group with a
ylacetylenes 2b,c. Treatment of the PPh2-substituted nido-
carborane 3a with PhC2ZnCl in the presence of a catalytic
amount of Pd(PPh3)4 leads to the known basal-substituted
nido-carboranylacetylene 2a. The synthesis of apical-substi-
tuted compound 4b is achieved by the substitution of 3b by a
Pd0-catalyzed Nigishi-type cross-coupling reaction; the basal
boron atom is blocked by the n-butyl group. The 1,3-dicar-
boranyl-substituted (η4-cyclobutadiene)cobalt complexes
5a,c are obtained from the reactions of 2a,c with stoichiomet-
stoichiometric amount of CpCo(CO)2 to give 1,3-dicarbor-
anyl-substituted (cyclobutadiene)cobalt complex 7. The di-
carboranyl-substituted (cyclopentadienone)cobalt complex 8
is formed by the reaction of compound 4b with CpCo(CO)2.
The new compounds are characterized by NMR spec-
troscopy, mass spectrometry, and by X-ray crystal structure
analyses for 5a and 8.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
ated dimerization reactions of apically alkynyl-substituted
closo-C2B5 carboranes with cobalt complexes.[9] While the
inherent scope and reaction efficiencies are found to be lim-
ited, the study introduces the attractive prospect that small
alkynyl-substituted carboranes might be utilized for metal-
mediated dimerization reactions. Here we report the synthe-
sis of functionalized nido-C4B2 carboranes and the reac-
tions of some of the alkynyl-substituted derivatives with co-
balt complexes.
Introduction
Over the past decades numerous functionalized carbor-
anes were synthesized,[1] and their properties have been ex-
tensively investigated by both theoretical[2] and experimen-
tal analyses.[3] A large number of carborane derivatives are
used in medicinal and pharmaceutical applications.[4] The
reactivity of carboranylacetylenes towards transition-metal
complexes has received relatively little attention. In 1973,
Hawthorne et al.[5] reported the first generation of 1,2,4-
tris(closo-1,2-C2B10H11-1-yl)benzene by the reaction of 1-
ethynyl-1,2-carborane with a catalytic amount of bis(acry-
lonitrile)nickel(0). Michl et al.[6] presented a convenient
route to synthesize tris(1,12-carboranyl)-substituted ben-
zene derivatives by a palladium-catalyzed cross-coupling of
three 1,12-dicarba-closo-dodecaboranyl units to a 1,3,5-tri-
halobenzene. In 1982, a series of σ-1-ortho- and σ-1-meta-
carboranylacetylenides of copper, silver, palladium, plati-
num, and iron were synthesized by Zakharkin and his co-
workers.[7] In 2003, Grimes[8] published an account on clus-
ter formation between a 1,3,5-tris(carboranylacetylene)ben-
zene and Co2(CO)8. Very recently, we reported cobalt-medi-
Results and Discussion
Preparation and Characterization of C4B2 nido-
Carboranylacetylenes 2b,c
Because of the easy accessibility and high stability of the
peralkylated 2,3,4,5-tetracarba-nido-hexaboranes(6)[10] (in
comparison with the parent C4B2H6[11]), their reactivity has
drawn special attention.[12,13] To investigate substitution re-
actions of C4B2 nido-carboranes, functional groups other
than alkyl or aryl groups are needed at the boron atom(s).
Wrackmeyer et al.[12] and more recently our group[14] no-
ticed that nucleophilic substitutions proceeded smoothly at
the basal boron atom to give the corresponding carboranes
with organyl, stannyl, diphenylphosphanyl, N-bonded (μ-
NS)Fe2(CO)6 groups, as well as with the [CpFe(CO)2]
group. However, even the presence of an excess of nucleo-
[a] Anorganisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
Fax: +49-6221-54-5609
E-mail: walter.siebert@urz.uni-heidelberg.de
[b] Organisch-Chemisches Institut der Universität Heidelberg,
Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
E-mail: oeser@uni-hd.de
566
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Reactivity of Carboranylacetylenes towards Cobalt Complexes
FULL PAPER
phile was not enough to achieve substitution at the apical
boron atom.[12,14]
Analogously, nucleophilic substitution reactions of
2,3,4,5-tetraethyl-1,6-diiodo-2,3,4,5-tetracarba-nido-hexa-
borane(6) (1) with RC2Li (R = Me, SPh) led to the corre-
sponding basal-substituted carborane derivatives 2b,c in
high yields (Scheme 1). In agreement with the findings of
Wrackmeyer et al.[12] and our recent results,[14] an excess of
lithium acetylides did not effect additional substitution at
the apical boron atom. Compounds 2b,c (light yellow oils)
were characterized by 1H-, 13C-, and 11B NMR spec-
troscopy, as well as by mass spectrometry. The nido-C4B2
framework is retained, and little difference is found in the
1H- and 13C NMR spectra in comparison to that of com-
pound 1. In the 11B NMR spectra of 2b,c the basal boron
atoms give signals at δ = 10–12 ppm, which are only slightly
shifted downfield from that of 1 (δ = 5.5 ppm), while the
shifts of the signals for the apical boron atoms are the same
as that of the starting carborane 1 (δ = –52.7 ppm).
Scheme 2.
On the other hand, treatment of compound 3b with
PhC2ZnCl in the presence of a catalytic amount of
Pd(PPh3)4 led to the expected carborane 4b in moderate
yield (Scheme 3). Compound 4b (yellow oil) was charac-
terized by 1H-, 13C-, and 11B NMR spectroscopy, as well as
by mass spectrometry. The 11B NMR signal of the substi-
tuted apical boron atom is shifted only slightly downfield
to δ = –50.5 ppm, whereas the chemical shift for the basal
boron atom remains the same as that for 3b (δ = 19 ppm).
In the EI mass spectrum of 4b, the molecular ion peak ap-
pears at m/z = 344 with the expected isotopic distribution.
Scheme 1.
1
The H NMR spectrum of 2b exhibits the signals (δ =
1.2–2.4 ppm) for the ethyl groups, in addition to the methyl
resonance (δ = 1.98 ppm). In the 13C NMR spectrum, a
signal (δ = 112.4 ppm) is found for the skeletal carbon
atoms nonadjacent to the basal boron atom, whereas the
signals for the boron-bound carbon atoms and for the acet-
ylene carbon atoms are not observed. Similarly, the 1H
NMR spectrum of 2c shows the signals (δ = 1.3–2.4 ppm)
for the ethyl groups along with the multiplets (δ = 7.2–
7.6 ppm) for the aryl protons. The 13C NMR spectrum fea-
tures a signal at δ = 113.0 ppm for the skeletal carbon
atoms nonadjacent to the basal boron atom; however, the
signals for the boron-bound carbon atoms and the acety-
lene carbon atoms are not detected. EI-MS data confirm
the identity of carboranes 2b,c through the appearance of
the molecular ion peaks with the correct isotopic pattern.
Scheme 3.
Formation of Bis(carboranyl)cyclobutadiene Cobalt
Complexes 5 and 7
No reaction was observed between carboranylacetylene
derivatives 2 with catalytic and stoichiometric amounts of
CpCo(CO)2 in refluxing toluene for several days, as moni-
tored by 11B NMR spectroscopy. However, adding
CpCo(C2H4)2 to the reaction mixture and refluxing for an
additional two days, followed by column chromatography
afforded the 1,3-dicarboranyl-substituted CpCo(η4-cyclo-
butadiene) complexes 5a,c (Scheme 4). No reaction was ob-
served with 2d,e.
The trans-1,3-isomers are sterically favored, as confirmed
by the solid-state structure of 5a. However, several known
complexes have cis-bis(trimethylsilyl)cyclobutadiene li-
Substitution Reactions at the Apical Boron Atom of 3a
In most of the cases, the apical boron–halogen bonds are gands.[16] The stereochemistry problem was resolved une-
found to be inert;[12,14] however, substitution reactions can quivocally by the analysis of the major peaks in the mass
be achieved by Pd0-catalyzed Nigishi-type cross-coupling spectra with respect to the degradation of the cyclobutadi-
reactions.[15] Analogously, an attempt to prepare the car- ene ring. In general, three different acetylene molecules are
borane 4a by the reaction of 3a with PhC2ZnCl in the pres- released from the molecular ion of the cis isomer, whereas
ence of a catalytic amount of Pd(PPh3)4 was not successful, only one acetylene molecule is released from the trans iso-
as the known carborane 2a[14] was obtained by the substitu- mer.[17] Here, in both of 5a and 5c, only a single acetylene
tion of PPh2 at the basal boron atom (Scheme 2).
molecule was released from the molecular ion. Therefore,
Eur. J. Inorg. Chem. 2006, 566–572
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567

A. Goswami, Y. Nie, T. Oeser, W. Siebert
FULL PAPER
Scheme 4.
the mass spectra clearly provide evidence for trans isomers.
The 11B NMR signals of 5a,c for the basal boron atoms are
shifted downfield to δ = 18 ppm, while the chemical shifts
for the apical boron atoms remain the same as those for in
1
the starting carboranes (δ = –52 ppm). The H NMR spec-
tra of 5a,c show the multiplets (δ = 7.1–7.6 ppm) for the
aryl hydrogen atoms in addition to the Cp resonances (δ =
4.95 and 5.10 ppm). In the 13C NMR spectra, the signals (δ
= 84–86 ppm) for the Cp–C are observed, but the signals
for the four quaternary carbon atoms of the cyclobutadiene
ring are not found.
The structure of 5a was characterized by performing a
single-crystal X-ray diffraction analysis. Two independent
molecules were found in the asymmetric unit with very sim-
ilar distances and angles; the structure of one molecule is
shown in Figure 1. It reveals almost equal C–C bond
lengths within the cyclobutadiene ring, and none of the
phenyl groups lie in the C4 plane. The conformation is
highly influenced by the bulky C4B2 nido-carboranyl
groups, which are oriented away from the metal center.
Regioselective reactivity of the carboranylacetylene de-
rivative 6[14] towards cobalt complexes CpCoL2 (L = CO,
C2H4) was observed. In the reactions of CpCoL2 with the
C4B2 nido-carborane 6 containing two acetylene moieties at
the boron atoms, only the basal boron-substituted acetylene
unit undergoes cyclobutadiene ring formation to give 7
(Scheme 5). The 11B NMR spectrum of complex 7 exhibits
Figure 1. Molecular structure of 5a in the solid state; hydrogen
atoms are omitted for clarity; selected bond lengths [Å] and bond
angles [°]: C1–B1 1.559(6), C3–B3 1.549(6), C1–C2 1.471(5), C2–
C3 1.480(5), C3–C4 1.465(5), C4–C1 1.466(5), B2–I1 2.131(5), B4–
I2 2.114(5), B1–B2 1.943(6), B3–B4 1.820(6), C1–C2–C3 91.2(3),
C2–C3–C4 88.2(3), C3–C4–C1 92.0(3), C4–C1–C2 88.5(3), B1–B2–
I1 144.5(3), B3–B4–I2 141.6(3). Only one of the two independent
molecules is shown to provide a better overview.
(η5-Cyclopentadienyl)(η4-2,5-bis-carboranyl)(cyclopenta-
dienone)cobalt Complex 8
To investigate the reactivity of the apical boron-bound
signals at δ = 15 and –50.4 ppm; the latter value for the acetylene group, the carboranylacetylene derivative 4b was
apical boron atom is shifted slightly downfield relative to prepared (see earlier), in which the basal boron atom is
that of the starting carborane 6. The mass spectrum shows blocked by the n-butyl group. Interestingly, the reaction of
the molecular ion peak with the expected isotopic pattern.
compound 4b with a stoichiometric amount of CpCo-
Scheme 5.
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Reactivity of Carboranylacetylenes towards Cobalt Complexes
FULL PAPER
Scheme 6.
(CO)2 led to the 2,5-dicarboranyl-substituted (η4-cyclocy- CO, C2H4) have been studied. Reactions in the presence of
clopentadienone)cobalt complex in good yield catalytic amounts of [CpCoL2] with carboranylacetylenes 2,
8
(Scheme 6). It was characterized by 1H-, 13C-, and 11B 4b, and 6 do not lead to benzene derivatives, which can
NMR spectroscopy, mass spectrometry, and X-ray crystal be explained on steric grounds. The (η4-1,3-dicarboranyl-
structure analysis. As expected, the 11B NMR signal of the cyclobutadiene)cobalt complexes 5a,c are formed by the re-
apical boron atom is shifted downfield to δ = –44.4 ppm. actions of 2a,c with stoichiometric amounts of CpCo-
The 1H NMR spectrum of 8 shows a singlet at δ = 4.95 ppm (C2H4)2. Regioselective reactions occur between CpCoL2
for C5H5, in addition to the phenyl group resonances (δ = and the C4B2 nido-carborane 6. Only the basal-substituted
6.90–7.63 ppm). In the 13C NMR spectrum, the signals for borylacetylene moiety of compound 6 is involved in cyclo-
the Cp–C and carbonyl groups are observed at δ = 81.7 and butadiene ring formation, whereas the apical-substituted
188.1 ppm, respectively, while the signals for the cyclopen- borylacetylene unit remains unreacted. The reaction of car-
tadienone ring are not found. The IR spectrum of 8 shows boranylacetylene 4b, carrying an n-butyl group at the basal
a band at ν = 1593 cm–1, and the appearance of the molecu- boron atom, with CpCo(CO)2 leads to the (cyclopen-
˜
lar ion peak with the correct isotopic distribution in the EI- tadienone)cobalt complex 8. The cobalt complexes 5, 7, and
MS data confirms the identity.
8 are stable at room temperature and are resistant to light,
The solid-state structure of 8 was characterized by per- oxygen, and moisture.
forming a single-crystal X-ray diffraction analysis (Fig-
ure 2). Four molecules of 8 crystallized with one hexane
molecule. As expected,[18] the structure reveals that the
bulky carboranyl groups are bound to α-carbon atoms of
the cyclopentadienone ring to reduce the steric strain.
Experimental Section
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-, 13C- and 11B NMR spec-
tra were recorded with a Bruker AC 200 spectrometer. 1H- and 13
C
NMR spectra were referenced to (CH3)4Si, and 11B NMR spectra
were referenced to F3B·OEt2. IR spectra were recorded with a
Bruker IFS 28 FT spectrometer. Mass spectra were obtained with
Finnigan MAT 8230 plus spectrometers using the EI technique.
Melting points (uncorrected) were obtained with a Büchi appara-
tus, using capillaries that were filled under nitrogen and sealed. The
nido-carboranes 1,[19] 2a,d,e,[14] 3a,[14] 6,[14] and CpCo(C2H4)2
[20]
were prepared according to literature procedures. CpCo(CO)2 was
purchased from Aldrich®.
General Procedure for Basal Boron-Substituted Carboranylacetyl-
enes 2b,c
Figure 2. Molecular structure of 8 in the solid state; hydrogen
atoms are omitted for clarity; selected bond lengths [Å] and bond
angles [°]: C5–B1 1.549(5), C2–B3 1.560(5), C1–C2 1.490(5), C2–
C3 1.427(5), C3–C4 1.452(5), C4–C5 1.447(5), C5–C1 1.488(5), C1–
O1 1.241(4), B1–B2 1.878(6), B3–B4 1.851(6), C1–C2–C3 108.0(3),
C2–C3–C4 108.6(3), C3–C4–C5 109.3(3), C4–C5–C1 106.7(3), C5–
C1–C2 106.3(3), O1–C1–C5 126.5(3), O1–C1–C2 126.9(3).
An appropriate solution of lithium acetylide in hexane (30 mL) was
cooled to –40 °C and added by syringe to a solution of the nido-
carborane 1 in hexane (20 mL) at –78 °C. The mixture was warmed
to room temp. and stirred for 2 d. After filtration, the light yellow
solution was dried in vacuo to give a yellow oil.
2,3,4,5-Tetraethyl-1-iodo-6-methylethynyl-2,3,4,5-tetracarba-nido-
hexaborane(6) (2b): Starting materials: compound 1 (0.9 g,
2.05 mmol) and MeC2Li (0.23 g, 5.0 mmol). Yield: 0.5 g (69%), yel-
low oil. 1H NMR (200.1 MHz, CDCl3): δ = 1.25 (t, 3JH,H = 7.6 Hz,
12 H, CH2CH3), 1.98 (s, 3 H, Me), 2.22 (m, 8 H, CH2CH3) ppm.
Conclusions
The reactions of carboranylacetylenes with catalytic and
stoichiometric amounts of cobalt complexes CpCoL2 (L = 13C NMR (50.3 MHz, CDCl3): δ = 13.4, 14.3 (CH2CH3), 18.2
Eur. J. Inorg. Chem. 2006, 566–572
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A. Goswami, Y. Nie, T. Oeser, W. Siebert
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(Me), 18.1, 19.6 (CH2CH3), 112.4 (skeletal carbon atoms nonadja- General Procedure for Cobalt Complexes 5a,c
cent to the basal boron) ppm; skeletal carbon atoms adjacent to
To an appropriate solution of carboranylacetylene in toluene was
the basal boron and alkynyl carbon atoms were not observed. 11B
NMR (64.2 MHz, CDCl3): δ = 10 (br., Bbasal), 52.7 (s, Bapical) ppm.
MS (EI, 70 eV): m/z (%) = 352 (100) [M+], 225 (20) [M+ – I]. MS
added a portion of CpCo(CO)2 at room temp. The deep-red mix-
ture was heated at reflux and monitored by 11B NMR spectroscopy,
indicating that no reaction took place. After 4 d, one portion of
CpCo(C2H4)2 was added, and the resulting mixture was again
heated at 120 °C for another 2 d. After completion of the reaction,
the solvent was removed to dryness, and the crude product was
purified by column chromatography on silica gel to give two frac-
tions. Using hexane as the eluant, unreacted CpCo(CO)2 and
CpCo(C2H4)2 were obtained. The second fraction (toluene) con-
tained the corresponding (cyclobutadiene)cobalt complex.
(HR-EI, 70 eV): m/z (%) = 352.1031 (100) [M+], 12C15 H2311B2127I:
1
352.1030; Δmmu = 0.1.
2,3,4,5-Tetraethyl-1-iodo-6-phenylthioethynyl-2,3,4,5-tetracarba-
nido-hexaborane(6) (2c): Starting materials: compound 1 (0.9 g,
2.05 mmol) and PhSC2Li (0.7 g, 5.0 mmol). Yield: 0.65 g (71%),
1
3
yellow oil. H NMR (200.1 MHz, CDCl3): δ = 1.29, 1.31 (t, JH,H
= 7.5 Hz, 2×6 H, CH3), 2.05, 2.38 (m, 2×4 H, CH2), 7.22–7.61
(m, 5 H, SPh) ppm. 13C NMR (50.3 MHz, CDCl3): δ = 13.5, 14.6
(CH3), 18.5, 19.9 (CH2), 113.0 (skeletal carbon atoms nonadjacent
to the basal boron), 127.6, 128.1, 131.7 (SPh) ppm; skeletal carbon
atoms adjacent to the basal boron and alkynyl carbon atoms were
not observed. 11B NMR (64.2 MHz, CDCl3): δ = 12 (br., Bbasal),
–52.7 (s, Bapical) ppm. MS (EI, 70 eV): m/z (%) = 446 (100) [M+],
{η4-Bis[2,3,4,5-tetraethyl-1-iodo-2,3,4,5-tetracarba-nido-hexaboran-
yl]diphenyl(cyclobutadiene)}(η5-cyclopentadienyl)cobalt(
I) (5a):
Starting materials: compound 2a (0.50 g, 1.2 mmol), CpCo(CO)2
(0.10 g, 0.6 mmol), and CpCo(C2H4)2 (0.10 g, 0.6 mmol). Yield:
0.40 g (76%), yellow crystals, m.p. 124–125 °C. Compound 5a was
recrystallized from a solution of toluene at –20 °C. 1H NMR
(200.1 MHz, CDCl3): δ = 1.3 (m, 24 H, CH3), 2.3 (m, 16 H, CH2),
5.10 (s, 5 H, Cp–H), 7.25, 7.55 (m, 10 H, Ph) ppm. 13C NMR
(50.3 MHz, CDCl3): δ = 13.4, 14.3 (CH3), 18.4, 19.8 (CH2), 84.5
(Cp–C), 113.0 (skeletal carbon atoms nonadjacent to the basal bo-
ron), 127.6, 128.0, 131.7 (Ph) ppm; quaternary carbon atoms were
not found. 11BNMR (64.2 MHz, CDCl3): δ = 18 (br., Bbasal), –52.0
(s, Bapical) ppm. MS (EI, 70 eV): m/z (%) = 952 (100) [M+], 538 (10)
319 (10) [M+ – I]. MS (HR-EI, 70 eV): m/z (%) = 446.0922 (58)
[M+],
C
20
1H2511B2127I32S: 446.0908; Δmmu = 1.4.
12
6-Butyl-2,3,4,5-tetraethyl-1-iodo-2,3,4,5-tetracarba-nido-hexa-
borane(6) (3b): A solution of nBuLi (1.7 mL, 4.2 mmol) was very
slowly added to a solution of nido-carborane 1 (0.92 g, 2.1 mmol)
in hexane (50 mL) at –78 °C. The mixture was warmed to room
temp. and was stirred for 20 h. After filtration, the slightly yellow
filtrate was dried in vacuo and distilled at 43 °C/0.04 mbar to give
[M+ – Et4C4B2I(C2Ph)]. MS (HR-EI, 70 eV): m/z = 952.2087 [M+],
12
1
C
45
1H5511B459Co127I2: 952.2097; Δmmu = –1.0.
a yellow oil. Yield: 0.70 g (90%). H NMR (200.1 MHz, CDCl3):
{η4-Bis[2,3,4,5-tetraethyl-1-iodo-2,3,4,5-tetracarba-nido-hexaboran-
δ = 0.89, 1.45, 1.95 (m, 9 H, nBu), 1.19, 1.40 (t, 2×6 H, CH2CH3),
2.08, 2.36 (m, 2 × 4 H, CH2CH3) ppm. 13C NMR (50.3 MHz,
CDCl3): δ = 13.7, 14.2 (CH3), 18.5, 19.0 (CH2), 16.0, 17.6, 25.9,
26.6 (nBu), 112.9 (skeletal carbon atoms nonadjacent to the basal
boron) ppm. 11B NMR (64.2 MHz, CDCl3): δ = 19 (br., Bbasal),
–52.6 (s, Bapical) ppm. MS (EI, 70 eV): m/z (%) = 370 (100) [M+],
243 (10) [M+ – I].
yl]diphenylthio(cyclobutadiene)}(η5-cyclopentadienyl)cobalt(
I
) (5c):
Starting materials: compound 2c (0.40 g, 1.2 mmol), CpCo(CO)2
(0.10 g, 0.6 mmol), and CpCo(C2H4)2 (0.10 g, 0.6 mmol). Yield:
0.25 g (54%), brown-red oil. 1H NMR (200.1 MHz, CDCl3): δ =
1.26, 1.35 (t, 2×12 H, CH3), 2.10, 2.35 (m, 2×8 H, CH2), 4.95 (s,
5 H, Cp–H), 7.15–7.55 (m, 10 H, SPh) ppm. 13C NMR (50.3 MHz,
CDCl3): δ = 13.6, 15.7 (CH3), 19.1, 19.7 (CH2), 85.4 (Cp–C), 115.5
(skeletal carbon atoms nonadjacent to the basal boron), 125.0,
128.8, 131.0 (SPh) ppm; skeletal carbon atoms adjacent to the basal
boron and quaternary carbon atoms were not found. 11BNMR
(64.2 MHz, CDCl3): δ = 18 (br., Bbasal), –52.1 (s, Bapical) ppm. MS
Attempt to Prepare 2,3,4,5-Tetraethyl-1-phenylethnyl-6-diphenyl-
phosphanyl-nido-carborane (4a): To lithium phenylacetlylide (0.54 g,
5.0 mmol) in THF (15 mL) at room temp. was added ZnCl2 (0.68 g,
5.0 mmol), and the solution was stirred for 3 h. The solution was
then added to a mixture of 3a (1.24 g, 2.5 mmol) and Pd(PPh3)4
(0.04 g, 0.034 mmol), and the resulting yellow mixture was heated
at reflux for 10 d. The solvent was removed under high vacuum,
the black residue was extracted with hexane (2×20 mL) and fil-
tered. The yellow filtrate was dried in vacuo to give a yellow viscous
oil. Yield: 0.51 g (49%) 2a. NMR and mass spectroscopic data were
in agreement with the previously reported result.[19]
( E I , 7 0 e V ) : m/ z ( % ) = 1 0 1 6 ( 7 0) [ M + ] , 5 7 0 ( 5) [M+
–
Et4C4B2I(C2SPh)]. MS (HR-EI, 70 eV): m/z = 1016.1550 [M+],
1H5511B459Co127I232S2: 1016.1538; Δmmu = 1.2.
12
C
45
CpCo[Bis(carboranyl)cyclobutadiene] (7): To a solution of 6
(0.053 g, 0.14 mmol) in toluene (8 mL) was added a portion of
CpCo(CO)2 (0.04 g, 0.22 mmol) at room temp. The deep-red reac-
tion mixture was heated at reflux for 9 d. The brown reaction mix-
ture was cooled and filtered through a pad of sea sand; the yellow-
brown filtrate was dried in vacuo to give a brown oil. Yield: 0.056 g
(89%). 11B NMR (64.2 MHz, CDCl3): δ = 15 (br, Bbasal), –50.4 (s,
Bapical) ppm. MS (EI, 70 eV): m/z (%) = 892 (100) [M+]. MS (HR-
6-Butyl-2,3,4,5-tetraethyl-1-phenylethynyl-2,3,4,5-tetracarba-nido-
hexaborane(6) (4b): To lithium phenylacetlylide (0.54 g, 5.0 mmol)
in THF (30 mL) at room temp. was added ZnCl2 (0.68 g,
5.0 mmol), and the solution was stirred for 3 h. The solution was
then added to a mixture of 3b (0.85 g, 2.3 mmol) and Pd(PPh3)4
(0.04 g, 0.034 mmol) in THF (30 mL). The resulting yellow mixture
was heated at reflux for 6 d. After evaporation of the solvent, the
black residue was extracted with hexane (2×20 mL) and filtered.
The yellow filtrate was dried in vacuo to give a yellow oil. Yield:
0.5 g (63%). 1H NMR (200.1 MHz, CDCl3): δ = 0.95, 1.52, 2.02
(m, 9 H, nBu), 1.19, 1.25 (t, 2×6 H, CH2CH3), 2.10, 2.45 (m, 2×4
H, CH2CH3), 7.22–7.35 (m, 5 H, Ph) ppm. 13C NMR (50.3 MHz,
1
EI, 70 eV): m/z = 892.4999 [M+], 12C55 H7311B459Co28Si2: 892.4955;
Δmmu = 4.4.
(η5-Cyclopentadienyl)(η4-2,5-bis-carboranyl-3,4-diphenylcyclo-
pentadienone)cobalt(I) (8): Carboranylacetylene 4b (0.45 g,
1.3 mmol) and (η5-cyclopentadienyl)(dicarbonyl)cobalt(i) (0.11 g,
0.65 mmol) were dissolved in toluene (30 mL). The resulting dark-
red mixture was stirred at 120 °C for 3 d. After cooling, the solvent
CDCl3): δ = 14.1, 15.4, 22.6, 26.3 (nBu), 17.4, 18.5 (CH3), 29.7, was removed under high vacuum, and the black residue was puri-
30.5 (CH2), 112.1 (skeletal carbon atoms nonadjacent to the basal
fied by column chromatography (SiO2, hexane). Cobalt complex 8
was recrystallized from a solution of hexane at –20 °C. Yield: 0.4 g
boron), 127.7, 128.0, 131.9 (Ph) ppm. 11B NMR (64.2 MHz,
CDCl3): δ = 20 (br., Bbasal), –50.5 (s, Bapical) ppm. MS (EI, 70 eV): (73 %), brown solid, m.p. 133–136 °C. 1H NMR (200.1 MHz,
m/z (%) = 344 (100) [M+].
CDCl3): δ = 1.20 (m, 2×12 H, CH2CH3), 0.90, 1.85, 2.12 (m, 2×9
570
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 566–572

Reactivity of Carboranylacetylenes towards Cobalt Complexes
FULL PAPER
Table 1. Crystal data and structure refinement for 5a and 8.
5a
8
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C45H55B4CoI2
951.86
monoclinic
P21/c
18.045(1)
27.847(2)
17.133(1)
90
93.395(2)
90
8594(1)
8
1.47
1.87
C55C54H73B4CoO + ¼ C6H14
861.84
triclinic
¯
P1
11.0954(2)
13.7519(3)
18.9481(4)
108.757(1)
103.617(1)
94.669(1)
2621.6(1)
2
α [°]
β [°]
γ [°]
Volume [Å3]
Z
Calcd. density [g/cm3]
1.09
0.36
μ [mm–1]
F(000)
Crystal size [mm]
Θmax [°]
3824
0.29×0.09×0.08
28.3
929
0.3×0.16×0.06
22.0
Index ranges
Reflections:
Collected
–24/24, –36/37, 22/22
–11/11, –14/14, –19/19
87065
21131(0.051)
18167
953
1.24
17190
6392 (0.042)
4865
574
1.02
Independent (Rint
)
Observed [I Ͼ 2σI]
Parameters
Goodness-of-fit on F2
R1 [I Ͼ 2σI]
0.064
0.048
wR2 [I Ͼ 2σI]
0.101
100(2)
2.42/–2.17
0.129
200(2)
0.76/–0.29
T [K]
Residual electron density [e/A3]
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H, nBu), 2.10, 2.35 (m, 2×8 H, CH2), 4.95 (s, 5 H, Cp–H), 6.90,
7.45, 7.63 (m, 2×5 H, Ph) ppm. 13C NMR (50.3 MHz, CDCl3): δ
= 14.1, 14.9 (CH3), 19.3, 19.9 (CH2), 17.1, 19.5, 21.2, 25.3 (nBu),
81.7 (Cp–C), 113.5 (skeletal carbon atoms nonadjacent to the basal
boron), 126.9, 128.8, 132.0 (Ph), 188.1 (CO) ppm; skeletal carbon
atoms adjacent to the basal boron and quaternary carbon atoms
were not found. 11BNMR (64.2 MHz, CDCl3): δ = 18 (br., Bbasal),
–44.4 (s, Bapical) ppm. IR (hexane): ν = 1593 (s) cm–1. MS (EI,
˜
70 eV): m/z (%) = 840 (50) [M+], 812 (100) [M+ – CO]. MS (HR-
EI, 70 eV): m/z = 840.5334 [M+],
Δmmu = –3.1.
C
54
1H7311B459Co16O: 840.5365;
12
[2]
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X-ray Crystal Structure Determinations of 5a and 8: Crystal data
and details of the structure determinations are listed in Table 1.
Reflections were collected with Bruker SMART APEX (5a) and
Bruker-AXS SMART 1000 (8) diffractometers (Mo-Kα radiation,
λ = 0.71073 Å, graphite monochromator, ω-scan). Empirical ab-
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276981 (8) contain the supplementary crystallographic data for this
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bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
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Received: September 6, 2005
Published Online: December 16, 2005
572
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Eur. J. Inorg. Chem. 2006, 566–572