Alkynyl-linked poly(cobaltacarboranes). Directed synthesis, structures, and electrochemistry of linear complexes and benzene-centered pinwheels

Article abstract of DOI:10.1021/om0301379

A series of B(5)- and B(7)-alkynyl-substituted derivatives of CoC₂B₃, CoC₂B₄, and Co₂C₂B₃ cobaltacarboranes has been prepared and linked via metal-promoted cross-coupling reactions to generate several types of polynuclear molecular complexes, which were structurally characterized and studied via electrochemical techniques. The target compounds prepared include linear dicobalt species containing BC≡CC≡CB linkages, e.g., [Cp*Co(2,3-Et₂C₂B₄H₃-7- C≡C)]₂ (8) and [Cp*Co(2,3-Et₂C₂ B₄H₃-5-C≡C)]₂ (17), trigonally symmetrical 1,3,5-triethynylbenzene-anchored tricobalt and hexacobalt complexes, e.g., {Cp*Co(2,3-Et₂C₂B₄H₃-5- C≡C)}₃C₆H₃ (19), {Cp*Co(2,3-Et₂C₂B₄H₃-7- C≡C)}₃C₆H₃ (22), and 1,3,5-[Cp*₂Co₂(2,3-Et₂C₂ B₃H₂-5-C≡C)]₃C₆H₃ (21), and novel cobaltacarborane-Co₂C₂ mixed-cluster systems, e.g., Cp*Co(2,3-Et₂C₂B₄ H₃)-7-C₂HCo₂(CO)₆ (5) and {Cp*Co[2,3-Et₂C₂B₄H₃-7- (C₂Co₂CO)₆]}₃C₆ H₃ (23), a nanocobalt complex. The new compounds were obtained in all cases as air-stable crystalline solids and were characterized by multinuclear NMR and mass spectra, supplemented by X-ray diffraction data for 8, 19, and 21. Electrochemical data on the alkynyl-linked compounds indicate that metal-metal communication in oxidized and reduced species occurs to a limited extent in most cases and to a considerable degree (Robin-Day class III) in the C₂B₃-bridged triple-decker systems.

Full text of DOI:10.1021/om0301379

Organometallics 2003, 22, 2581-2593
2581
Alk yn yl-Lin k ed P oly(coba lta ca r bor a n es). Dir ected
Syn th esis, Str u ctu r es, a n d Electr och em istr y of Lin ea r
Com p lexes a n d Ben zen e-Cen ter ed P in w h eels1
Haijun Yao, Michal Sabat, and Russell N. Grimes*
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901
Piero Zanello and Fabrizia Fabrizi de Biani
Dipartimento di Chimica dell’Universita` di Siena, Via Aldo Moro, 53100 Siena, Italy
Received February 27, 2003
A series of B(5)- and B(7)-alkynyl-substituted derivatives of CoC2B3, CoC2B4, and Co2C2B3
cobaltacarboranes has been prepared and linked via metal-promoted cross-coupling reactions
to generate several types of polynuclear molecular complexes, which were structurally
characterized and studied via electrochemical techniques. The target compounds prepared
include linear dicobalt species containing BCtCCtCB linkages, e.g., [Cp*Co(2,3-Et2C2B4H3-
7-CtC)]2 (8) and [Cp*Co(2,3-Et2C2B4H3-5-CtC)]2 (17), trigonally symmetrical 1,3,5-trieth-
ynylbenzene-anchored tricobalt and hexacobalt complexes, e.g., {Cp*Co(2,3-Et2C2B4H3-5-
CtC)}3C6H3 (19), {Cp*Co(2,3-Et2C2B4H3-7-CtC)}3C6H3 (22), and 1,3,5-[Cp*2Co2(2,3-Et2C2B3H2-
5-CtC)]3C6H3 (21), and novel cobaltacarborane-Co2C2 mixed-cluster systems, e.g., Cp*Co-
(2,3-Et2C2B4H3)-7-C2HCo2(CO)6 (5) and {Cp*Co[2,3-Et2C2B4H3-7-(C2Co2CO)6]}3C6H3 (23), a
nonacobalt complex. The new compounds were obtained in all cases as air-stable crystalline
solids and were characterized by multinuclear NMR and mass spectra, supplemented by
X-ray diffraction data for 8, 19, and 21. Electrochemical data on the alkynyl-linked
compounds indicate that metal-metal communication in oxidized and reduced species occurs
to a limited extent in most cases and to a considerable degree (Robin-Day class III) in the
C2B3-bridged triple-decker systems.
In tr od u ction
connected by acetylenic chains (so-called “carbon wires”)
or other linkers and have developed general synthetic
methods for achieving organosubsitution and linkage at
boron vertexes.4
In the search for new molecule-based synthetic ap-
proaches to electronically tailorable nanostructured
materials, conjugated polyynes are attracting increasing
interest as conductive linkers between metal-containing
electrophores.2 At the same time, the special properties
of small metallacarborane clusters make them attractive
as building blocks for such systems as described below.3
We are currently interested in combining these struc-
tural elements to create molecular complexes of speci-
fied design in which small metallacarborane units are
Using this approach, we have prepared and charac-
terized a variety of iron- and cobalt-based systems
featuring linear, branched, or macrocyclic geometries.1,4
We have also examined the electrochemistry of selected
poly(ferracarborane) systems in detail and interpreted
these findings in light of DFT calculations.5 Here we
report the designed synthesis and properties of some
new alkynyl-linked cobaltacarborane species having
linear or branched architectures. In general, the small
cobaltacarboranes have proved to be less reactive to-
ward metal-catalyzed cross-coupling reactions than
their ferracarborane analogues, an observation that we
ascribe to the greater basicity of the Cp*CoIII vs (arene)-
FeII metal centers, which lowers the polarity of B-X
bonds in the cobalt clusters relative to the iron com-
pounds.
(1) Organotransition-Metal Metallacarboranes. 64. Part 63: Yao, H.;
Sabat, M.; Grimes, R. N.; Fabrizi de Biani, F.; Zanello, P. Angew.
Chem., Int. Ed. 2003, 42, 1002.
(2) Selected publications: (a) Werz, D. B.; Gleiter, R.; Rominger, F.
Organometallics 2003, 22, 843. (b) Rigaut, S.; Perruchon, J .; Le Pichon,
L.; Touchard, D.; Dixneuf, P. H. J . Organomet. Chem. 2003, 670, 37.
(c) Bruce, M. I.; Costuas, K.; Halet, J .-F.; Hall, B. C.; Low, P. J .;
Nicholson, B. K.; Skelton, B. W.; White, A. H. J . Chem. Soc., Dalton
Trans. 2002, 383. (d) Adams, R. D.; Qu, B.; Smith, M. D. Inorg. Chem.
2001, 40, 2932. (e) Yam, V. W.-W.; Zhang, L.; Tao, C.-H.; Wong, K.
M.-C.; Cheung, K.-K. J . Chem. Soc., Dalton Trans. 2001, 1111. (f) Paul,
F.; Lapinte, C. Coord. Chem. Rev. 1998, 178-180, 431. (g) Siemsen,
P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int. Ed. 2000, 39,
2632. (h) Bunz, U. H. F. Top. Curr. Chem. 1999, 201, 131. (i) Bunz, U.
H. F.; Roidl, G.; Altmann, M.; Enkelmann, V.; Shimizu, K. D. J . Am.
Chem. Soc. 1999, 121, 10719. (j) Haley, M. M.; Bell, M. L.; English, J .
J .; J ohnson, C. A.; Weakley, T. J . R. J . Am. Chem. Soc. 1997, 119,
2956. (k) Guo, L.; Bradshaw, J . D., III; Tessier, C. A.; Youngs, W. J . J .
Chem. Soc., Chem. Commun. 1994, 243. (l) Dembinski, R.; Bartik, T.;
J aeger, M.; Gladysz, J . A., J . Am. Chem. Soc. 2000, 122, 810.
(3) Grimes, R. N. Collect. Czech. Chem. Commun. 2002, 67, 728.
(4) (a) Yao, H.; Sabat, M.; Grimes, R. N. Organometallics 2002, 21,
2833. (b) Russell, J . M.; Sabat, M.; Grimes, R. N. Organometallics 2002,
21, 4113. (c) Russell, J . M.; Sabat, M.; Grimes, R. N. Organometallics
2002, 21, 5613. (d) Malaba, D.; Sabat, M.; Grimes, R. N. Eur. J . Inorg.
Chem. 2001, 2557. (e) Bluhm, M.; Pritzkow, H.; Siebert, W.; Grimes,
R. N. Angew. Chem., Int. Ed. 2000, 39, 4562; Angew. Chem. 2000, 112,
4736.
(5) Fabrizi de Biani, F.; Fontani, M.; Ruiz, E.; Zanello, P.; Russell,
J . M.; Grimes, R. N. Organometallics 2002, 21, 4129.
10.1021/om0301379 CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/17/2003

2582 Organometallics, Vol. 22, No. 13, 2003
Yao et al.
Resu lts a n d Discu ssion
can be accomplished either by attack of alkynylzinc
reagents at B(7)-halogen atoms or by insertion of a
B-alkynyl moiety into an open-cage (nido) MC2B3
complex anion (Scheme 1, top). In this work, the most
efficient synthesis of the B(7)-ethynyl(trimethylsilyl)
derivative 2 was achieved via treatment of the B(7)-
iodo complex 3b to afford 2 in nearly quantitative yield.
Desilylation of 2 with fluoride ion gave the very useful
B(7)-ethynyl complex 4, which serves as a precursor
to a variety of apically substituted cobaltacarborane
derivatives, as shown. Thus, reaction of 4 with dicobalt
octacarbonyl in pentane at room temperature afforded
the mixed-cluster species Cp*Co(2,3-Et2C2B4H3)-7-C2-
HCo2(CO)6 (5) in 88% yield. This compound, which we
believe to be the first reported metallacarborane-C2M2
system, was isolated as a dark red air-stable solid and
characterized via multinuclear NMR, UV-visible, and
IR spectroscopy and elemental analysis. An example of
multiple conversion of alkynyl groups in the same
molecule to M2C2 clusters is reported below.
Syn th etic Str a tegies. Several advantages are af-
forded by the seven-vertex MC2B4 clusters as building-
block units.3,6
(a) Monosubstitution at boron is restricted to just
three electronically distinguishable locations (B(4,6),
B(5), and B(7)), which greatly simplifies the synthesis
and isolation of specific isomers compared to larger (e.g.,
icosahedral) cluster systems. By employing appropriate
synthetic methods, substituents may be introduced
either on the mirror plane at equatorial (B(5)) or apical
(B(7)) vertexes to give nonchiral products or at B(4) or
B(6) to generate chiral derivatives; chirality can also be
introduced via use of inequivalent groups on the cage
carbons (R * R′).7
In a multistep sequence (Scheme 1), the ethynyl group
in 4 was deprotonated with tert-butyllithium and coupled
to Me3SiCtC, the product was iodinated at B(5) to
generate 6, and the TMS group was removed to give
the B(7)-diethynyl B(5)-iodo derivative 7.
(b) Substitution at boron can be controlled by adjust-
ment of reaction conditions to generate specific B-
functional target compounds in good yield.
(c) Removal of the apex boron (decapitation) affords
nido-MC2B3 complexes that further extend the range
of synthetic possibilities and reactivities.
Direct alkynyl coupling of 4 via reaction with CuI and
pyridine yielded the dimer 8, and palladium-promoted
cross-coupling with p-iodobenzoic acid gave, on acidifi-
cation with HCl, the B(7)-alkynylbenzoic acid complex
9. Characterization of these species, as with all new
compounds reported herein, is based on spectroscopy
and elemental analysis, supported in three cases by
X-ray crystallography.
(d) In B(5,7) difunctional MC2B4 complexes, the
equatorial and apical substituents are orthogonal, al-
lowing the construction of oligomers and extended
systems having square or rectangular patterns.1 The
7-vertex metallacarboranes thus complement, as struc-
tural modules, the icosahedral boron-based C2B10 car-
boranes and other 12-vertex clusters whose more spheri-
cal cage geometry lends itself to quite different molecular
architectures.8
In this paper we describe the introduction of ethynyl
groups at equatorial (B(5)) and apical (B(7)) vertexes,
selected examples of reactivity of the CtC substituents,
their linkage to create diethynyl-linked dimers for use
in building larger systems, and their incorporation into
benzene-centered pinwheel-type polynuclear complexes.
Alk yn yl Su bstitu tion a n d Lin k a ge a t B(7). As was
shown earlier4b in (arene)FeC2B4 cluster chemistry, the
introduction of alkynyl substituents at the apex boron
The expected B(7),B(7′)-diethynyl-linked molecular
structure of 8 was confirmed by X-ray diffraction (Figure
1 and Tables 1 and 2), and the molecule was found to
adopt a centrosymmetric conformation in the crystal.
The diethynyl chain is linear, with C(4)-C(5)-C(5*) and
C(5)-C(4)-B(7) angles of 179.2 and 176.9°, respectively;
the CoC2B4 cluster bond distances and angles are
normal, and the Cp* and carborane rings bound to
cobalt are nearly parallel with a dihedral angle of 4.8°.
Alkyn yl Su bstitu tion an d Lin kage at B(5). Scheme
2 shows the conversions of B(5)-iodo closo- and nido-
cobaltacarboranes (10 and 13, respectively) to the
corresponding B(5)-ethynyl(trimethylsilyl) derivatives
11 (prepared earlier in lower yield4c from the Co(II)
radical anion 10-) and 14, followed by their desilylation
to give 12 and 15, respectively. The open-cage complex
14 was bridge-deprotonated with butyllithium and
reacted with (Cp*CoCl)2 to afford the B(5)-ethynyl-
(trimethylsilyl)ated triple-decker sandwich 16, which we
had envisioned as a potentially useful reagent for
introducing (Cp*Co)2(Et2C2B3H2)-5-CtC- alkynyl triple-
decker substituents. However, this complex has proved
surprisingly unreactive and resists desilylation, even
with strong reagents such as MeOH/NaOH and CH3-
COOH/Bu4NF.
(6) Grimes, R. N. In Contemporary Boron Chemistry; Davidson, M.,
Hughes, A. K., Marder, T. B., Wade, K., Eds.; Royal Society of
Chemistry: London, 2000; p 283.
(7) (a) Benvenuto, M. A.; Grimes, R. N. Inorg. Chem. 1992, 31, 3897.
(b) Benvenuto, M. A.; Sabat, M.; Grimes, R. N. Inorg. Chem. 1992, 31,
3904.
(8) For recent overviews see: (a) Colquhoun, H. M.; Lewis, D. F.;
Herbertson, P. L.; Wade, K.; Baxter, I.; Williams, D. J . In Contemporary
Boron Chemistry; Davidson, M., Hughes, A. K., Marder, T. B., Wade,
K., Eds.; Royal Society of Chemistry: London, 2000; p 59. (b) Grimes,
R. N. In Organic Synthesis Highlights III; Mulzer, J ., Waldmann, H.,
Eds.; Wiley-VCH: New York, 1998; p 406. Leading references: (c)
Zheng, Z.; Knobler, C. B.; Mortimer, M. D.; Kong, G.; Hawthorne, M.
F. Inorg. Chem. 1996, 35, 1235. (d) J iang, W.; Knobler, C. B.; Mortimer,
M. D.; Hawthorne, M. F. Angew. Chem., Int. Ed. Engl. 1995, 34, 1332.
(e) J iang, W.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem. 1996,
35, 3056. (f) Schoeberl, U.; Magnera, T. F.; Harrison, R. M.; Fleischer,
F.; Pflug, J . L.; Schwab, P. F. H.; Meng, X.; Lipiak, D.; Noll, B. C.;
Allured, V. S.; Rudalevige, T.; Lee, S.; Michl, J ., J . Am. Chem. Soc.
1997, 119, 3907.
Dimerization of 12 by treatment with palladium and
copper(I) gave the desired B(5),B(5′)-diethynyl-linked
product 17 in 66% isolated yield. This compound was
doubly deboronated (decapped) with TMEDA to afford
the nido-cobaltacarborane dimer 18; the latter com-
pound was also obtained from 15 by reaction with

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2583
Sch em e 1. B(7)-Alk yn yl Su bstitu tion a n d Lin k a gea
a
B ) B, BH.
chloroacetone and triethylamine. As in the case of their
B(7)-alkynyl isomers, the equatorially functionalized
B(5)-alkynyl complexes are designed as structural
modules for the assembly of larger systems of specific
design, as will be illustrated here.
benzenoid metallacarborane pinwheels, and a prelimi-
nary communication4a reported a benzene-centered
tris(triple-decker) cobaltacarborane complex. Here we
present a full report including several new cobalt-based
systems of this class.
Con st r u ct ion of Ben zen e-Cen t er ed P in w h eel
Com p lexes. The concept of anchoring multiple metal-
lacarborane units to a central hydrocarbon ring reverses
the paradigm of using boron clusters as scaffolds for
hydrocarbon appendages that has been effectively em-
ployed by several groups.8 Benzene offers several ad-
vantages in this role, including stability, high symmetry,
π-aromaticity (allowing it to function as an electron
conduit), and ready availability of 1,3,5-trifunctional
derivatives. Recent papers from one of our laboratories4b,e
have described the synthesis of several ferracarborane-
Reaction of 1,3,5-triiodobenzene with the B(5)-eth-
ynyl closo-cobaltacarborane 12 in THF generated the
tris(cobaltacarboranyl)benzene complex 19, a yellow
solid, in 60% isolated yield, as shown in Scheme 3. The
trigonally symmetric structure (idealized C3h point
group in the conformation represented in Scheme 3) is
supported by multinuclear NMR spectra, which are
consistent with three equivalent Cp*CoIII(Et2C2B4H3)-
5-CtC- units, and has been confirmed by X-ray dif-
fraction analysis (Figure 2 and Tables 1 and 3). The
complex crystallizes in the rhombohedral space group

2584 Organometallics, Vol. 22, No. 13, 2003
Yao et al.
F igu r e 1. Ortep diagram of [Cp*Co(2,3-Et2C2B4H3-7-CtC)]2 (8) (hydrogens omitted).
Ta ble 1. Exp er im en ta l X-r a y Diffr a ction
P a r a m eter s a n d Cr ysta l Da ta
Ta ble 2. Selected Dista n ces (Å) a n d An gles (d eg)
for 8a
8
19
Co-C(2)
2.0264(16)
2.0275(17)
2.099(2)
2.114(2)
2.081(2)
2.0502(18)
2.0671(19)
2.036(2)
2.014(2)
2.015(2)
1.468(2)
1.562(3)
1.765(3)
1.554(3)
C(3)-B(7)
C(2E)-C(2M)
C(3E)-C(3M)
C(2)-C(2M)
C(3)-C(3M)
C(4)-C(5)
C(4)-B(7)
C(5)-C(5*)
B(4)-B(5)
B(4)-B(7)
B(5)-B(6)
B(5)-B(7)
B(6)-B(7)
1.777(3)
1.523(4)
1.534(3)
1.508(3)
1.517(3)
1.208(2)
1.530(3)
1.373(4)
1.692(5)
1.793(4)
1.681(4)
1.750(3)
1.783(3)
Co-C(3)
empirical formula
fw
cryst dimens (mm)
C
36H56B8Co2
C60H87B12Co3
1114.81
Co-B(4)
693.15
Co-B(5)
0.28 × 0.12 ×
0.25 × 0.14 ×
Co-B(6)
0.12
0.12
Co-C(1R)
Co-C(2R)
Co-C(3R)
Co-C(4R)
Co-C(5R)
C(2)-C(3)
C(2)-B(6)
C(2)-B(7)
C(3)-B(4)
space group
R3h (No. 148,
hexagonal setting)
35.425(1)
35.425(1)
8.3845(4)
90
P21/c (No. 14)
a, Å
b, Å
c, Å
8.6443(6)
23.318(2)
30.425(2)
90
92.748(2)
90
R, deg
â, deg
90
120
9112.3(6)
9
1.137
0.842
153(2)
65
γ, deg
V, Å3
6125.7(8)
4
Z
C(3)-C(2)-B(6) 112.58(17) C(4)-B(7)-C(2)
C(2)-C(3)-B(4) 112.87(18) C(4)-B(7)-C(3)
C(3)-B(4)-B(5) 104.85(19) C(4)-B(7)-B(4)
C(2)-B(6)-B(5) 104.94(19) C(4)-B(7)-B(5)
B(6)-B(5)-B(4) 104.75(17) C(5)-C(4)-B(7)
123.30(17)
124.70(17)
132.30(19)
137.78(16)
176.9(2)
D(calcd), g cm-3
µ(Mo KR), mm-1
temp, K
1.209
0.839
153(2)
65
0.73-0.80
84 352
22 126
733
0.0598
0.1296
0.954
2θmax, deg
transmissn factors
no. of rflns collected
no. of obsd rflns (I > 2θ(I)) 7283
no. of params refined
R
0.59-0.80
C(4)-B(7)-B(6) 130.18(19) C(4)-C(5)-C(5*) 179.2(3)
42 276
a
Symmetry transformations used to generate equivalent at-
oms: (#1) -x + 1/3, -y - 1/3, -z + 5/3.
227
0.0516
0.1651
1.471
1.048
Rw
trianion 203-, which reacted with (Cp*CoCl)2 to afford
the dark red air-stable tris(triple-decker sandwich)
complex 21 in 69% yield. From NMR data on 21 it is
clear that the six Cp* ligands, and hence the six cobalt
centers, are electronically equivalent, consistent with
the structure depicted in Scheme 3; this geometry has
been confirmed crystallographically (Figure 3), as re-
ported in a recent communication4a (details of the
structure determination are available as Supporting
Information for ref 4a). As in 19, the C2B3 rings in the
solid state are significantly rotated away from copla-
narity with the benzene ring and, indeed, are nearly
perpendicular to it, but free rotation around the ethynyl
axes is assumed in solution.
goodness of fit
largest peak in final
diff map, e/Å3
0.926
R3h. Bond distances and angles are normal, and the
parameters of the cobaltacarborane cage are within the
usual range for closo-1,2,3-CoC2B4 pentagonal-bipyra-
midal clusters. The Cp* and C2B3 ring planes are not
quite parallel, with a dihedral angle of 4.8°, and are
tilted with respect to the central benzene ring (see
Figure 2), an observation we attribute to crystal-packing
forces that favor a relatively flattened molecular con-
formation.
Complex 19 is isostructural and isoelectronic with the
tris(ferracarboranyl)benzene compound 1,3,5-[(η6-C6H6)-
FeII(Et2C2B4H3)-5-CtC]3C6H3 (19-F e), which was re-
cently prepared in our laboratory by palladium-pro-
moted coupling of (η6-C6H6)Fe(Et2C2B4H3)-5-CtCH to
1,3,5-triiodobenzene.4b
The apically substituted complex Cp*CoIII(Et2C2B4H3)-
7-CtCH (4) was treated with n-butyllithium and zinc
chloride and finally with 1,3,5-C6H3I3 to generate the
benzene-centered product 1,3,5-[Cp*CoIII(Et2C2B4H3)-7-
CtC]3C6H3 (22), isolated as an orange-yellow solid in
81% yield. In an alternative approach, the reaction of a
mixture of 4, Pd(PPh3)2Cl2, CuI, C6H3I3, and Et3N in
THF over 2 days gave 22 in 66% yield. The structural
characterization of 22 is based on multinuclear NMR
and other spectroscopic data, which showed trigonal
symmetry having equivalent cobaltacarborane cluster
Reaction of the nido-cobaltacarborane 15, obtained by
decapping of 12 in aqueous TMEDA, with 1,3,5-C6H3I3
afforded the yellow-orange pinwheel complex 20 (Scheme
3), which was isolated via column chromatography in
87% yield and characterized spectroscopically. Triple
face-deprotonation of this complex with NaH gave the

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2585
Sch em e 2. B(5)-Alk yn yl Su bstitu tion a n d Lin k a gea
a
B ) B, BH.
units, as in the case of 19, discussed above. Although
19 and its isomer 22 are spectroscopically similar, any
possible ambiguity concerning their identities is elimi-
nated by the crystallographically established structure
on 19; hence, the apically bound geometry for 22 shown
in Scheme 3, which is the only other structure consistent
with the NMR data, is clear.
Reaction of 22 with dicobalt octacarbonyl at room
temperature in dichloromethane afforded in 55% yield
the red-brown nonacobalt complex 23. Although appar-
ently high-quality crystals were obtained, repeated
attempts to obtain X-ray data on this compound have
been unsuccessful, owing to loss of solvent from the
crystals. However, the 11B, 1H, and 13C NMR, UV-
visible, and IR spectroscopic data combined with el-
emental analysis are consistent with the structure
depicted in Scheme 3. The close similarity of these
spectra to those of 22 strongly supports the proposed
trigonally symmetric structure.
Electr och em istr y. Several of the compounds de-
scribed above were selected for detailed examination,
and the potentials for the observed redox changes are
compiled in Table 4.
Figure 4 compares the cyclic voltammetric behavior
of the binuclear complex 17 (bottom) with that of the
mononuclear precursor Cp*CoIII(Et2C2B4H4) (top), in
CH2Cl2 solution. Cp*CoIII(Et2C2B4H4) undergoes a re-
versible one-electron oxidation,9 ascribed to the redox
change CoIII/CoIV. The corresponding process for the
dimer 17 seems to occur as a single two-electron step
complicated by following chemical reactions, although
the rapid increase in the solvent discharge may mask
the second process. In this case, however, two very close
one-electron reductions appear, which imply a small
degree of electronic communication between the two
cobalt centers. Given that the observation of separate
redox processes in molecules containing multiple redox-
active centers allows easy determination of the compro-
10
portionation constant Kcom
,
one may attempt to cor-
relate this value with the nature of the electrogenerated
mixed-valent species. In fact, it is commonly accepted11
that the value of the comproportionation constant is
linked to the extent of charge delocalization in mixed-
valent species according to the Robin-Day classifica-
tion.12 However, it must be kept in mind that the value
of Kcom is affected by a number of factors, including
electrostatic repulsion, statistical effects, inductive ef-
fects, and magnetic exchanges.13 On this basis, the 0.05
V separation between the redox potentials of the two
(9) Stephan, M.; Hauss, J .; Zenneck, U.; Siebert, W., Grimes, R. N.
Inorg. Chem. 1994, 33, 4211.
(10) Richardson, D. E.; Taube, H. Inorg. Chem. 1981, 20, 1278.
(11) Bott, A. W. Curr. Sep. 1997, 16, 61 and references therein.
(12) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1967, 10,
247.

2586 Organometallics, Vol. 22, No. 13, 2003
Sch em e 3. Con str u ction of P in w h eel Com p lexesa
Yao et al.
a
B ) B, BH.
electron additions suggests that the mixed-valence
species 17- could be tentatively assigned to the localized
Robin-Day class I (Kcom ≈ 10). Similar results were
obtained using tetrahydrofuran as solvent.
The B(7)-B(7′)-connected dimer 8 exhibits electro-
chemical behavior that qualitatively resembles that of
its B(5)-B-(5′) isomer 17, but the separation between
the two cathodic processes is larger (Kcom ≈ 102),
suggesting that Co-Co communication is greater in 8
than in 17.
the anodic pathway was followed using the weakly
coordinating [NBu4][B(C6F5)4] supporting electrolyte.14
As seen, 22 undergoes three sequential reductions and
three sequential oxidations, each having features of
chemical reversibility on the cyclic voltammetric time
scale. For the sake of simplicity, and taking into account
the number of cobaltacarborane subunits, we assume
that each step involves a one-electron process. The
results are consistent with the presence of electronic
communication to a small extent between the three
cobaltacarborane subunits. This finding again demon-
strates that the intramolecular interaction in multicen-
tered molecules depends on the nature of both the
metal-containing units and the interposed spacers. It
was shown earlier by Zanello and co-workers15 that tris-
(ferrocenylethynyl)benzene exhibits only a single three-
electron, ferrocene-centered oxidation; in tris(cyclopen-
Turning to the trinuclear complexes, Figure 5 il-
lustrates the redox behavior of complex 22 under
experimental conditions (see the figure caption) that
were chosen to highlight its main features. In particular,
(13) (a) Palaniappan, V.; Singru, R. M.; Agarwala, U. C. Inorg. Chem.
1988, 27, 181. (b) Astruc, D. Electron Transfer and Radical Processes
in Transition-Metal Chemistry; Wiley-VCH: New York, 1995. (c)
Brunschwig, B. S.; Sutin, N. Coord. Chem. Rev. 1999, 187, 233. (d)
Demadis, K. D.; Hartshorn, C. M.; Meyer, T. J . Chem. Rev. 2001, 101,
2655. (e) Barriere, F.; Camire, N.; Geiger, N. E.; Mueller-Westerhoff,
T. U.; Sanders, R. J . Am. Chem. Soc. 2002, 124, 7262.
(14) LeSuer, R. J .; Geiger, W. Angew. Chem., Int. Ed. 2000, 39, 248.
(15) Fink, A. H.; Long, N. J .; Martin, A. J .; Opromolla, G.; White,
A. J . P.; Williams, D. J .; Zanello, P. Organometallics 1997, 16, 2646.

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2587
F igu r e 2. Ortep diagram of {Cp*Co(2,3-Et2C2B4H3-5-CtC)}3C6H3 (19) (hydrogens omitted).
tadienylruthenium diphosphine ethynyl)benzene16 three
slightly separated one-electron oxidations occur, as
observed by Weyland et al. in the tris(cyclopentadienyl-
iron diphosphine ethynyl)benzene.17
It is also noteworthy that, in both the cathodic and
the anodic scans, the separation between the first and
the second step is 0.2 V, while that between the second
and the third steps is only 0.1 V. Since such behavior is
in contrast to that expected on the basis of Coulombic
effects, it can be interpreted as arising from the attenu-
ation of the electronic interaction on passing from the
monocharged [22]+ or [22]- species to the corresponding
bicharged [22]2+ or [22]2-species.
In contrast to 22, for complex 19 we were able to
resolve the three-electron oxidation into only two sepa-
rate steps, while the three-electron reduction remained
completely unresolved. These data suggest that any
mixed-valent species [19]n+/n- (n ) 1, 2) will belong to
localized Robin-Day class I.
Let us now discuss the triple-decker complex 16 and
its trimeric counterpart 21, whose voltammetric pat-
terns are shown in Figure 6.
Complex 16 undergoes two separate oxidations and
two separate reductions. Controlled-potential coulom-
etry corresponding to the first anodic process (Ew ) +0.4
V) shows the consumption of one electron per molecule.
Cyclic voltammetric tests on the resulting solution
indicate that the electrogenerated cation 16+ undergoes
minor decomposition. Both the second one-electron
addition and the second one-electron removal appear to
be chemically irreversible. Accordingly, the mixed-valent
congeners 16+ and 16- can be assigned to the completely
delocalized Robin-Day class III (Kcom ) 6.5 × 1021 and
5.4 × 1016, respectively). In this light, the redox behavior
of 16 is quite reminiscent of that of the related com-
plexes (p-MeC6H4CHMe2)2Ru2(Et2C2B3H3) and CpCo-
(Et2C2B3H3)Ru(p-MeC6H4CHMe2),18 the cations of which
are also classified as fully delocalized mixed-valent
species. These results underline the ability of bridging
(R2C2B3H3)4- ligands to allow very strong electronic
interactions between two η5-coordinated metallic centers
in multidecker sandwich systems, as originally shown
by Geiger.19
The redox behavior of the related trimer 21 resembles
that of 16, in that it undergoes oxidation and reduction
processes at similar potential values. Nevertheless, as
shown in Figure 6, the use of [NBu4][B(C6F5)4] as
electrolyte allowed us to resolve the first oxidation in
three very close sequential processes. In support of this
observation, controlled-potential coulometry (Ew ) +0.4
V) showed the involvement of three electrons per
molecule. Upon oxidation the original orange solution
turned brown, and, as was also the case for 16+, cyclic
voltammetry indicated that the electrogenerated tri-
cation 213+ undergoes some minor decomposition.
Finally, complex 20 exhibited only a quasi-reversible
electron reduction accompanied by chemical complica-
tions. The relative square-wave voltammogram can be
simulated by three subsequent processes. Actually, the
solution resulting from exhaustive cathodic reduction
(Ew ) -1.2 V) gave a voltammetric pattern quite close
to that of the monomeric precursor Cp*CoIII(Et2C2B3H5),
which in contrast to Cp*CoIII(Et2C2B4H4) undergoes an
irreversible oxidation process.
(16) Long, N. J .; Martin, A. J .; Fabrizi de Biani, F.; Zanello, P. J .
Chem. Soc., Dalton Trans. 1998, 2017.
(17) Weyland, T.; Lapinte, C.; Frapper, G.; Calhorda, M. J .; Halet,
J .-F.; Toupet, L. Organometallics 1997, 16, 2024.
(18) Merkert, J . W.; Davis, J . H.; Geiger, W. E.; Grimes, R. N. J .
Am. Chem. Soc. 1992, 114, 9846.
(19) Brennan, D. E.; Geiger, W. E., J r. J . Am. Chem. Soc. 1979, 101,
3399.

2588 Organometallics, Vol. 22, No. 13, 2003
Yao et al.
Ta ble 3. Selected Dista n ces (Å) a n d An gles (d eg)
for 19
NMR spectra were recorded on GN-300/44 and Varian Unity/
Inova 500/51 and 300/51 instruments. 1H and 13C shifts are
referenced to residual 1H and 13C signals in the deuterated
solvent. 11B NMR resonances are referenced to the external
standard BF3‚OEt2. Unit-resolution mass spectra were ac-
quired on a Finnigan (Model LCQ Classic) quadrupole ion trap
mass spectrometer using an atmospheric pressure chemical
ionization interface. Infrared spectra were obtained on a
Nicolet Impact-400 spectrophotometer. Ultraviolet-visible
spectra were recorded on an HP 8452A diode array spectro-
photometer or a Cary 5E UV-vis-near-IR spectrophotometer.
Elemental analyses were performed by Atlantic Microlabs in
Norcross, GA, for new compounds reported, excluding some
synthetic intermediates.
Co(1)-C(3)
Co(1)-C(2)
Co(1)-B(4)
Co(1)-B(6)
Co(1)-B(5)
Co(2)-C(17)
Co(2)-C(16)
Co(2)-B(10)
Co(2)-B(8)
Co(2)-B(9)
Co(3)-C(18)
Co(3)-C(19)
Co(3)-B(14)
Co(3)-B(12)
Co(3)-B(13)
C(2)-C(3)
2.034(3)
2.042(3)
2.091(3)
2.095(3)
2.107(3)
2.030(3)
2.033(3)
2.080(4)
2.091(3)
2.115(3)
2.030(3)
2.021(3)
2.083(3)
2.091(3)
2.123(3)
1.477(4)
1.510(4)
1.552(4)
1.777(4)
1.502(4)
1.514(4)
1.563(4)
1.772(4)
1.527(4)
1.205(3)
1.522(4)
1.436(3)
1.206(4)
1.516(4)
1.435(4)
1.200(4)
1.528(4)
1.439(4)
1.392(3)
1.402(3)
1.396(3)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(16)-C(17)
C(16)-C(16M)
C(16)-B(10)
C(16)-B(11)
C(16E)-C(16M)
C(17)-C(17M)
C(17)-B(8)
1.392(4)
1.395(4)
1.395(3)
1.473(4)
1.513(4)
1.524(5)
1.770(4)
1.511(4)
1.514(4)
1.558(4)
1.761(4)
1.506(4)
1.479(4)
1.510(4)
1.544(4)
1.759(4)
1.459(5)
1.505(4)
1.547(4)
1.770(4)
1.517(4)
1.680(4)
1.790(4)
1.680(4)
1.744(4)
1.789(5)
1.672(5)
1.783(5)
1.684(4)
1.751(4)
1.775(5)
1.679(4)
1.786(5)
1.682(5)
1.747(4)
1.790(5)
C(17)-B(11)
C(17E)-C(17M)
C(18)-C(19)
C(18)-C(18M)
C(18)-B(14)
C(18)-B(15)
C(18E)-C(18M)
C(19)-C(19M)
C(19)-B(12)
C(19)-B(15)
C(19E)-C(19M)
B(4)-B(5)
Ma ter ia ls a n d P r oced u r es. All reactions were carried out
in oven glassware under
a dinitrogen atmosphere using
conventional glovebox or Schlenk techniques, and the products
were worked up in air. All commercial reagents were used as
received without further purification. THF, diethyl ether, and
toluene were distilled from sodium benzophenone ketyl prior
to use. Triethylamine was distilled from CaH2 under an inert
atmosphere. When anhydrous dichloromethane was required,
the solvent was distilled from P2O5 under N2. Cp*Co(2,3-
Et2C2B4H3-7-Br) (3a),20 Cp*Co(2,3-Et2C2B4H3-7-I) (3b),20 Cp*Co-
(2,3-Et2C2B4H3-5-I) (10),21 nido-Cp*Co(2,3-Et2C2B3H4-5-I (13),22
1,3,5-triiodobenzene,8f (Cp*CoCl)2,23 and Me3SiCtCI24 were
prepared according to published procedures.
C(2)-C(2M)
C(2)-B(6)
C(2)-B(7)
C(2E)-C(2M)
C(3)-C(3M)
C(3)-B(4)
C(3)-B(7)
B(4)-B(7)
C(3E)-C(3M)
C(4)-C(5)
B(5)-B(6)
B(5)-B(7)
C(4)-B(5)
B(6)-B(7)
C(5)-C(10)
C(6)-C(7)
B(8)-B(9)
B(8)-B(11)
C(6)-B(9)
B(9)-B(10)
C6H4O2BCtCSi(CH 3)3
(2-((Tr im et h ylsilyl)et h yn yl)-
C(7)-C(12)
C(8)-C(9)
B(9)-B(11)
1,3,2-ben zod ioxa bor ole). To a solution of 5.50 g of (CH3)3-
SiCtCSnMe3 (21.1 mmol)25 in 40 mL of toluene was added
3.3 g of C6H4O2BCl (21.4 mmol) in 80 mL of toluene at -78
°C. The mixture was warmed to room temperature over 7 h
and stirred for an additional 12 h. The solvent was removed
in vacuo to give a light yellow liquid which was purified by
distillation (62 °C, 0.12 mmHg) to give a colorless liquid (3.9
g, 86%). 1H NMR (CDCl3): δ 0.28 (s, 9H, SiMe3), 7.11-7.14
(m, 2H, C6H4), 7.23-7.26 (m, 2H, C6H4). 13C{1H} NMR (125.75
MHz, CDCl3): δ -0.7 (Si(CH3)3), 65.9 (CtC), 112.5 (C6H4),
123.1 (C6H4), 147.5 (C6H4). 11B NMR (CDCl3): δ 23.1 (s). CI+-
mass: m/z (%) 216.0 ([M+], 100).
Cp *Co[2,3-Et2C2B4H3-7-CtCSi(CH3)3] (2). Meth od A. 1
(632 mg, 2.01 mmol) in 40 mL of toluene at 0 °C was treated
with tert-butyllithium (2.5 mL of a 1.65 M solution in hexane,
4.02 mmol). The solution turned dark red-orange as it was
warmed to room temperature; the stirring was continued for
over 6 h. Then the mixture was cooled to 0 °C, and C6H4O2-
BCtCSi(CH3)3 (0.97 g, 4.49 mmol) in 10 mL of toluene was
added at 0 °C. The mixture was warmed to room temperature
and stirred for an additional 24 h, after which the toluene was
removed in vacuo. The residue was taken up in CH2Cl2 and
washed through 3 cm of silica with CH2Cl2. The CH2Cl2 wash
was column-chromatographed on silica in hexane to recover
62 mg of starting material and was then flash-chromato-
graphed in 1:1 CH2Cl2/hexane to afford 615 mg of pure product
as an orange red, air-stable crystalline solid (72.9% yield,
80.7% based on the starting complex consumed).
B(10)-B(11)
B(12)-B(13)
B(12)-B(15)
B(13)-B(14)
B(13)-B(15)
B(14)-B(15)
C(8)-B(13)
C(9)-C(14)
C(10)-C(11)
C(10)-C(15)
C(11)-C(12)
C(3)-C(2)-B(6)
C(2)-C(3)-B(4)
C(5)-C(4)-B(5)
C(4)-C(5)-C(10)
C(7)-C(6)-B(9)
C(6)-C(7)-C(12)
C(9)-C(8)-B(13)
C(8)-C(9)-C(14)
112.4(2) C(17)-C(16)-B(10) 112.2(2)
112.6(2)
176.0(3) C(19)-C(18)-B(14) 112.6(2)
179.1(3) C(18)-C(19)-B(12) 112.4(2)
112.7(2) C(16)-C(17)-B(8)
173.8(3) C(3)-B(4)-B(5)
173.3(3) B(6)-B(5)-B(4)
175.1(3) C(4)-B(5)-B(6)
177.0(3) C(4)-B(5)-B(4)
104.5(2)
105.3(2)
129.2(3)
125.5(2)
105.1(2)
104.9(2)
130.0(3)
125.9(3)
104.1(2)
106.2(3)
C(11)-C(10)-C(15) 119.6(2) C(2)-B(6)-B(5)
C(11)-C(10)-C(5)
C(15)-C(10)-C(5)
120.1(2) C(17)-B(8)-B(9)
120.2(2) C(6)-B(9)-B(8)
C(10)-C(11)-C(12) 120.3(2) C(6)-B(9)-B(10)
C(13)-C(12)-C(11) 119.3(2) B(8)-B(9)-B(10)
C(13)-C(12)-C(7)
C(11)-C(12)-C(7)
119.1(2) C(16)-B(10)-B(9)
121.6(2) C(19)-B(12)-B(13) 105.2(3)
C(12)-C(13)-C(14) 121.4(2) C(8)-B(13)-B(12)
C(15)-C(14)-C(13) 118.7(2) C(8)-B(13)-B(14)
127.9(3)
127.4(3)
C(15)-C(14)-C(9)
C(13)-C(14)-C(9)
C(14)-C(15)-C(10) 120.7(2)
121.5(2) B(12)-B(13)-B(14) 104.7(2)
119.8(2) C(18)-B(14)-B(13) 105.1(3)
In summary, the electrochemical data demonstrate
that in polycobaltacarboranes containing seven-vertex
CoC2B4 units linked via conjugated carbon chains at-
tached to B(5) or B(7), small but measurable electronic
communication between the cobalt centers is observed.
Not surprisingly, this effect is particularly enhanced in
the triple-decker species 16 and 21, which incorporate
the planar C2B3 bridging ring. As previously discussed
for the iron analogues and supported by calculations,5
the C2B3 unit appears to make a major contribution to
the frontier orbitals of its η5-coordinated metal com-
plexes.
Meth od B. To (trimethylsilyl)acetylene (73 mg, 0.75 mmol)
in 4 mL of THF was added n-BuLi (0.5 mL of a 1.51 M solution
in hexane, 0.75 mmol) at 0 °C. After the mixture was stirred
for 0.5 h, anhydrous ZnCl2 (102 mg, 0.75 mmol) in 2 mL of
(20) Curtis, M. A.; Sabat, M.; Grimes, R. N. Inorg. Chem. 1996, 35,
6703.
(21) Stockman, K. E.; Garrett, D. L.; Grimes, R. N. Organometallics
1995, 14, 4661.
(22) Piepgrass, K. W.; Stockman, K. E.; Sabat, M.; Grimes, R. N.
Organometallics 1992, 11, 2404.
(23) Koelle, U.; Fuss, B.; Belting, M.; Raabe, E. Organometallics
1986, 5, 980.
(24) Amatore, C.; Blart, E.; Genet, J . P.; J utand, A.; Lemaire-
Audoire, S.; Savignac, M. J . Org. Chem. 1995, 60, 6829.
(25) Prepared according to the procedure given for (CH3)3SiCt
CSnBu3 in: Logue. M. W.; Teng. K. J . Org. Chem. 1982, 47, 2549.
Exp er im en ta l Section
In str u m en ta tion . 1H (500 MHz (where noted), 300 MHz),
13C (125.8 MHz (where noted), 75.4 MHz), and 11B (96.4 MHz)

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2589
F igu r e 3. Ortep diagram of 1,3,5-[Cp*2Co2(2,3-Et2C2B3H2-5-CtC)]3C6H3 (21) (hydrogens omitted).4a
Ta ble 4. F or m a l Electr od e P oten tia ls (in V, vs SCE) a n d P ea k -to-P ea k Sep a r a tion s (in P a r en th eses, in m V;
Mea su r ed a t 0.2 V s-1) for Com p lexes 8, 16, 17, a n d 19-22
compd
E°′3+/2+
E°′2+/+
E°′+/0
E′’
0/-
E°′-/2-
E°′2-/3-
solvent
Mononuclear Complexes
+0.98a
nido-Cp*Co(Et2C2B3H5)
Cp*Co(Et2C2B4H4)
CH2Cl2
CH2Cl2
+1.16 (100)
Binuclear Complexes
8
17
+1.37a,b
-1.82 (120)
-1.69b
-1.77 (50)
-1.81 (70)
-1.94 (120)
-1.74b
THF
THF
CH2Cl2
THF
CH2Cl2
+1.50a,b
+1.48a,b
+1.18b,c
+1.15c (100)
+0.36 (80)
+0.12 (100)
-1.83 (70)
16
-2.80a,b
+1.38a,b
Trinuclear Complexes
+1.36a,b,d
22
19
21
-1.95 (100)
-1.80d (100)
-1.82 (70)
-0.80c,g,d
-2.10 (100)
-2.80a,b
-2.20 (100)
THF
CH2Cl2
THF
CH2Cl2
THF
CH2Cl2
THF
+1.32 (70)
+1.20 (70)
+1.15c,e (80)
+1.40a,b
+1.04 (70)
+1.34a,b,d
+1.05c (80)
+0.32 (120)
+0.17d,f (230)
20
FcH
+0.53 (100)
+0.39 (70)
THF
CH2Cl2
a
b
Peak potential values for irreversible processes. Value estimated by differential pulse voltammetry. c Complicated by following
reactions. Three-electron process. e Two-electron process. f Square wave measurement can be simulated with three sequential peaks at
+0.26, +0.18, and +0.09 V: see text. Square wave measurement can be simulated with three peaks at +0.7, +0.8, and +1.0 V: see text.
d
g
THF was added at 0 °C, the mixture was stirred at room
temperature for 2 h, and 3a (100 mg, 0.25 mmol) and
Pd(PPh3)4 (14 mg, 0.013 mmol) were added. The mixture was
refluxed for 4.5 days, after which the solvent was removed in
vacuo and the residue was flash chromatographed through 3
cm of silica gel in 1:1 hexane/CH2Cl2 to give one orange band.
Removal of solvent gave 85 mg (81%) of orange-red product.
Meth od C. Using a procedure analogous to that described
for method B, (trimethylsilyl)acetylene (570 mg, 5.73 mmol)
was deprotonated with 5.73 mmol of n-BuLi (3.8 mL of a 1.51
M hexane solution) in 20 mL of THF. After the mixture was
stirred for 0.5 h, anhydrous ZnCl2 (781 mg, 5.73 mmol) in 20
mL of THF was added at 0 °C. The mixture was stirred at
room temperature for 2 h, and 3b (860 mg, 1.91 mmol) and
Pd(PPh3)4 (110 mg, 0.1 mmol) were added. The mixture was
refluxed for 4.5 days, after which the solvent was removed in
vacuo and the residue was flash-chromatographed through 5
cm of silica gel in 1:1 hexane/CH2Cl2 to give one orange band.
Removal of solvent gave 755 mg (94%) of the orange-red
product. 1H NMR (CDCl3): δ -0.04 (s, 9H, SiMe3), 1.35 (t, 6H,

2590 Organometallics, Vol. 22, No. 13, 2003
Yao et al.
F igu r e 6. Comparison between the voltammetric behav-
iors of 16 and 21 (inset). (a) Anodic processes: cyclic (s)
and Osteryoung square wave (- - -) voltammetric responses
recorded at a gold electrode on a thf solution of 16 (0.4 ×
10-3 mol dm-3). [NBu4][PF6] (0.2 mol dm-3) was used as
F igu r e 4. Cyclic (s) and differential pulse (- - -) voltam-
metric responses recorded at a platinum electrode on CH2-
Cl2 solutions of (a) Cp*CoIII(Et2C2B4H4) (1.5 × 10-3 mol
dm-3) and (b) 17 (0.9 × 10-4 mol dm-3). [NBu4][PF6] (0.2
mol dm-3) was used as supporting electrolyte; scan rates
were 0.2 and 0.02 V s-1, respectively.
supporting electrolyte; scan rates were 0.2 and 0.1 V s-1
,
respectively. Cathodic processes: cyclic (s) and Osteryoung
square wave (- - -) voltammetric responses recorded at a
platinum electrode on a CH2Cl2 solution of 16 (0.4 × 10-3
mol dm-3). [NBu4][PF6] (0.2 mol dm-3) was used as sup-
porting electrolyte; scan rates were 0.2 and 0.1 V s-1
,
respectively. (b) Cyclic (top) and Osteryoung square wave
(bottom) voltammetric responses recorded at a platinum
electrode on a CH2Cl2 solution of 21 (0.7 × 10-3 mol dm-3
)
(- - -, simulated Gaussian curve). [NBu4][B(C6F5)4] (0.1 mol
dm-3) was used as supporting electrolyte; the scan rate was
0.2 V s-1
.
as an orange-red solid (510 mg, 98%). 1H NMR (CDCl3): δ 1.36
(t, 6H, J ) 7.5 Hz, ethyl CH3), 1.62 (s, 1H, CtCH), 1.78 (s,
15H, C5Me5), 2.27, 2.46 (sestet, 2H, J ) 7.5 Hz, ethyl CH2).
13C{1H} NMR (CDCl3): δ 10.0 (C5Me5), 14.5 (ethyl CH3), 21.9
(ethyl, CH2), 76.6 (CtCH), 91.0 (C5Me5), 93.1 (C2B4). 11B NMR
(CDCl3): δ -4.5 (s, 1B), 3.4 (d, 2B, J BH ) 152 Hz), 11.8 (d, 1B,
J BH ) 151 Hz). IR (KBr pellet, cm-1): ν 3288.0 (vs, CtCH),
2971.7 (s), 2962.2 (s), 2932.1 (m), 2964.3 (s), 2875.4(m), 2561.0
(vs, B-H), 2522.8 (vs, B-H), 2059.1 (w, CtC), 1476.2 (s),
1453.2 (s), 1376.6 (s), 1325.0 (w), 1098.2 (w), 1024.5 (s), 914.5
(w), 815.0 (s), 789.7 (s), 671.8 (vs), 633.7 (s), 648.8 (vs), 430.9
(m). CI+-mass: m/z (%) ) 347.4 ([M+ - 1], 100).
Cp *Co[2,3-Et2C2B4H3-7-(C2HCo2(CO)6] (5). Compound 4
(30 mg, 0.09 mmol) in 4 mL of pentane was slowly added to a
5 mL solution of Co2(CO)8 (30 mg, 0.09 mmol) in pentane. After
the mixture was stirred for 3 days at room temperature, the
solvent was removed and the reaction mixture was separated
on silica TLC plates to afford a red-brown solid (48 mg, 88%).
1H NMR (CDCl3): δ 1.36 (t, 6H, J ) 7.5 Hz, ethyl CH3), 5.70
(s, 1H, C-CH), 1.79 (s, 15H, C5Me5), 2.11, 2.43 (sextet, 2H, J
) 7.8 Hz, ethyl CH2). 13C{1H} NMR (CDCl3): δ 10.2 (C5Me5),
14.5 (ethyl CH3), 21.8 (ethyl CH2), 91.0 (C5Me5), 94.0 (C2B4),
199.9 (C-O). 11B NMR (CDCl3): δ 4.6 (unresolved, BH, 3B),
12.6 (s, 1B). IR (KBr pellet, cm-1): ν 2964.7 (m), 2914.0 (s),
2873.5 (m), 2545.3 (m, B-H), 2534.1 (s, B-H), 2515.4 (s, B-H),
2087.81 (vs, C-C), 2005.4 (vs, C-O), 1496.6 (s), 1446.3 (m),
1433.1 (m), 1059.6 (w), 1020.5 (m), 812.8 (s), 618.0 (w), 562.1
(s), 515.6 (vs), 498.3 (s), 480.0 (m). UV-vis (CH2Cl2, nm (%)):
308 (100), 428 (5) ꢀmax ) 34 493 cm-1 M-1. Anal. Calcd for
B4C24Co3H29O6: C, 45.50; H, 4.61. Found: C, 45.80; H, 4.69.
Cp *Co(2,3-Et2C2B4H2-5-I-7-CtCCtCSiMe3) (6). To com-
pound 4 (139 mg, 0.4 mmol) in 15 mL of THF was added t-BuLi
(0.2 mL of a 2.05 M solution in hexane, 0.4 mmol) at 0 °C.
After 0.5 h of stirring at 0 °C, anhydrous ZnCl2 (54.5 mg, 0.4
mmol) in 5 mL of THF was added at 0 °C. The mixture was
F igu r e 5. Cyclic (top) and differential pulse (bottom)
voltammetric responses of complex 22 recorded under the
following experimental conditions: (a) concentration 0.9 ×
10-4 mol dm-3, mercury working electrode, thf solution,
[NBu4][PF6] (0.2 mol dm-3) supporting electrolyte, scan
rates 0.2 and 0.02 V s-1, respectively; (b) concentration 0.2
× 10-4 mol dm-3, platinum working electrode, CH2Cl2
solution, [NBu4][B(C6F5)4] (0.05 mol dm-3) supporting
electrolyte, scan rate 0.02 V s-1
.
J ) 7.5 Hz, ethyl CH3), 1.77 (s, 15H, C5Me5), 2.30, 2.46 (sextet,
2H, J ) 7.5 Hz, ethyl CH2). 13C{1H} NMR (CDCl3): δ -0.4
(SiMe3), 10.0 (C5Me5), 14.3 (ethyl CH3), 22.0 (ethyl CH2), 90.9
(C5Me5), 92.0 (CtCSiMe3), 93.4 (C2B4). 11B NMR (CDCl3): δ
-3.9 (s, 1B), 3.7 (d, 2B, unresolved), 11.9 (d, 1B, unresolved).
IR (KBr pellet, cm-1): ν 2969.4 (vs), 2931.8 (s), 2872.4 (m),
2522.1 (vs, B-H), 2126.1 (w, CtC), 1472.0 (m), 1452.2 (m),
1377.2 (s), 1247.4 (s), 1168.4 (w), 1140.9 (s), 1111.3 (m), 1062.8
(m), 1026.7 (m), 857.8 (vs), 814.0 (vs), 760.1 (m), 696.8 (w).
CI+-mass: m/z (%) 420.4 ([M+], 100).
Cp *Co(2,3-Et2C2B4H3-7-CtCH) (4). Compound 2 (630 mg,
1.5 mmol) was dissolved in 30 mL of dry THF, and to this
solution was added dropwise 1.5 mL (1.5 mmol of a 1.0 M
solution) of tetrabutylammonium fluoride in THF at 0 °C. The
reaction mixture was stirred at 0 °C for 40 min, after which
the THF was removed and the residue was flash-chromato-
graphed through 3 cm of silica gel in CH2Cl2 to give the product

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2591
stirred at room temperature for 2 h, and Me3SiCtCI (450 mg,
1.6 mmol) and Pd(PPh3)4 (23 mg, 0.02 mmol) were added. The
mixture was refluxed for 2 days, after which the solvent was
removed in vacuo. The residue was taken up in hexane, and
the residue was flash-chromatographed through 3 cm of silica
gel in hexane followed by CH2Cl2. Column chromatography of
the CH2Cl2 wash in 1:1 hexane/CH2Cl2 afforded 6 as a major
orange-red band (103 mg, 45.2%); chromatography of the above
CH2Cl2 wash in 1:2 hexane/CH2Cl2 afforded the known byprod-
uct Cp*Co(2,3-Et2C2B4H2-5-I-7-C≡CH)1 as an orange-yellow
9 as an orange-red solid (75%). 1H NMR (500 MHz, CDCl3): δ
1.39 (t, 6H, J ) 7.5 Hz, ethyl CH3), 1.80 (s, 45H, C5Me5), 2.35,
2.52 (sextet, 6H, J ) 7.5 Hz, ethyl CH2), 7.28 (d, 2H, J ) 8
Hz, C6H4), 7.88 (d, 2H, J ) 8 Hz, C6H4). 13C{1H} NMR (125.75
MHz, CDCl3): δ 10.1 (C5Me5), 14.6 (ethyl CH3), 22.0 (ethyl
CH2), 87.4 (CtC), 91.1 (C5Me5), 93.6 (C2B4), 129.7 (C6H4), 131.6
(C6H4), 171.3 (C-O). 11B NMR (CDCl3): δ -2.9 (unresolved,
BH, 3B), 3.2 (s, 1B). IR (KBr pellet, cm-1): ν 2970.1 (s), 2930.8
(m), 2909.3 (w), 2535.7 (vs, B-H), 1693.5 (s), 1602.6 (vs),
1538.1 (w), 1452.2 (w), 1404.0 (m), 1382.5 (vs), 1309.2 (m),
1265.6 (s), 1173.0 (m), 1027.2 (w). CI+-mass: m/z (%) 469.4
([M+] + 1, 100). Anal. Calcd for C25H33O2Co: C, 64.20; H, 7.11.
Found: C, 64.17; H, 7.20.
Cp *Co(2,3-Et2C2B4H3-5-CtCSiMe3) (11). To (trimethyl-
silyl)acetylene (340 mg, 3.46 mmol) in 30 mL of THF was
added 3.46 mmol of n-butyllithium (2.3 mL of a 1.51 M solution
in hexane) at 0 °C. After 0.5 h of stirring, anhydrous ZnCl2
(472 mg, 3.46 mmol) in 15 mL of THF was added at 0 °C, the
mixture was stirred at room temperature for 2 h, and 10 (520
mg 1.15 mmol) and Pd(PPh3)4 (66.7 mg, 0.058 mmol) were
added. The mixture was refluxed for 4.5 days, after which the
solvent was removed in vacuo and the residue was flash-
chromatographed through 5 cm of silica gel in 1:1 hexane/CH2-
Cl2 to give one orange band. Removal of solvent gave 11 as an
orange-red solid (472 mg, 97%). This complex was prepared
earlier in 25% yield (see compound 7 in ref 4c) via attack of
lithium (trimethylsilyl)acetylenide at the reduced Cp*CoII(2,3-
Et2C2B4H3-5-I)- anion.
1
band (55 mg, 29%). H NMR (CDCl3): δ 0.11 (s, 9H, SiMe3),
1.32 (t, 6H, J ) 7.5 Hz, ethyl CH3), 1.76 (s, 15H, C5Me5), 2.29,
2.46 (sextet, 2H, J ) 7.5 Hz, ethyl CH2). 13C{1H} NMR
(CDCl3): δ -0.6 (SiMe3), 9.6 (C5Me5), 14.7 (ethyl CH3), 21.6
(ethyl CH2), 91.9 (C5Me5), 95.6 (C2B4), 92.1(CtC), 84.2 (Ct
C), 89.2 (CtC). 11B NMR (CDCl3): δ -6.4 (unresolved, BH,
1B), 4.1(unresolved, BH, 3B). IR (KBr pellet, cm-1): ν 2969.6
(s), 2928.8 (m), 2911.5 (m), 2871.2 (w), 2533.5 (vs, B-H), 2186.6
(w, CtC), 2080.4 (vs, CtC), 1471.7 (m), 1451.1 (m), 1383.5
(m), 1375.8 (s), 1249.7 (s), 1222.4 (w), 1064.3 (w), 1029.8 (m),
933.0 (m), 842.0 (vs), 799.3 (s), 759.8 (m), 653.2 (m). CI+-
mass: m/z (%) 571.3 ([M+] + 1, 100).
Cp *Co(2,3-Et2C2B4H2-5-I-7-CtCCtCH) (7). Compound 6
(160 mg, 0.28 mmol) was desilylated with 0.28 mL of a 1.0 M
TBAF solution (0.28 mmol) in 8 mL of dry THF. The reaction
mixture was stirred at 0 °C for 1 h, after which the THF was
removed and the residue was flash-chromatographed through
3 cm of silica gel in CH2Cl2 to give one orange-red band.
Removal of solvent gave an orange-red solid (126 mg, 90.5%).
1H NMR (CDCl3): δ 1.33 (t, 6H, J ) 7.5 Hz, ethyl CH3), 1.94
(s, 1H, CtCH), 1.77 (s, 15H, C5Me5), 2.31, 2.48 (sextet, 2H, J
) 7.8 Hz, ethyl CH2). 13C{1H} NMR (125.75 MHz, CDCl3): δ
9.6 (C5Me5), 14.7 (ethyl CH3), 21.6 (ethyl CH2), 65.0 (CtC),
69.3 (CtC), 92.0 (C5Me5), 95.5 (C2B4). 11B NMR (CDCl3): δ
-6.3 (s, 1B), 4.1 (unresolved, BH, 3B). IR (KBr pellet, cm-1):
ν 3255.7 (vs, CtCH), 2975.3 (m), 2906.8 (w), 2557.4 (s, B-H),
2196.9 (w, CtC), 2046.2 (m, CtC), 1472.0 (m), 1452.1 (m),
1382.9 (vs), 1195.5 (m), 1018.7 (m), 780.0 (s), 650.4 (s). CI+-
Cp *Co(2,3-Et2C2B4H3-5-CtCH) (12). Using a procedure
analogous to that described above for 7, 380 mg of 11 (380
mg, 0.905 mmol) was desilylated with a 1.0 M solution of
tetrabutylammonium fluoride in THF (0.91 mL of a 1 M
solution in THF, 0.91 mmol). The residue was flash-chromato-
graphed through 3 cm of silica gel in CH2Cl2 to give one orange
band. Removal of solvent gave 12 as an orange-red solid (305
1
mg, 97%). H NMR (CDCl3): δ 1.17 (t, 6H, J ) 7.5 Hz, ethyl
CH3), 1.82 (s, 15H, C5Me5), 2.29, 2.49 (sextet, 2H, J ) 6.9 Hz,
ethyl CH2), 3.252 (s, 1H, CtCH). 13C{1H} NMR (CDCl3): δ
9.4 (C5Me5), 14.8 (Et, CH3), 21.5 (Et, CH2), 91.0 (C5Me5), 92.9
(C2B4), 96.3 (CtCH). 11B NMR (CDCl3): δ 7.4 (s, 1B), 4.3 (d,
2B, J BH ) 187 Hz), 1.9 (d, 1B, unresolved). IR (KBr, pellet,
cm-1): ν 3289.7 (vs, CtCH), 2977.3 (s), 2963.5 (s), 2925.0 (m),
2869.5 (m), 2552.6 (vs, B-H), 2531.9 (vs, B-H), 2519.0 (vs,
B-H), 2042.6 (w, CtC), 1472.0 (m), 1450.1 (s), 1427.2 (w),
1376.9 (s), 1383.7 (s), 1206.3 (w), 1163.4 (m), 1067.0 (m), 1028.0
(m), 873.9 (m), 862.0 (s), 662.2 (vs), 595.8 (vs), 560.8 (w), 503.6
(w), 448.7 (w). CI+-mass: m/z (%) 349.4 ([M+] + 1, 100).
Cp *Co(2,3-Et2C2B3H4-5-CtCSiMe3) (14). In a procedure
analogous to that described above for 11, (trimethylsilyl)-
acetylene (420 mg, 4.1 mmol) was deprotonated with n-
butyllithium (2.7 mL of a 1.51 M solution in hexane, 4.1 mmol)
in 30 mL of THF. The solution was stirred for 0.5 h at 0 °C,
and anhydrous ZnCl2 (559 mg, 4.1 mmol) in 15 mL of THF
was added at 0 °C. The solution was stirred at room temper-
ature for 2 h, and 13 (600 mg, 1.36 mmol) and Pd(PPh3)4 (78.6
mg, 0.07 mmol) were added. The mixture was refluxed for 3.5
days, following which the solvent was removed in vacuo and
the residue was flash-chromatographed through 3 cm of silica
gel in 1:1 hexane/CH2Cl2 to give one orange band. Removal of
solvent gave 14 as an orange-yellow solid (520 mg, 93%).
Cp *Co(2,3-Et2C2B3H4-5-CtCH) (15). Meth od A. In a
procedure analogous to that described above for 7, compound
14 (175 mg, 0.43 mmol) was desilylated with 0.43 mL of a 1.0
M TBAF solution (0.43 mmol). Flash chromatography of the
product in hexane give one orange-yellow band. Removal of
solvent gave 15 as a yellow solid (87 mg, 60%).
mass: m/z (%) 499.2 ([M+] + 1, 100). Anal. Calcd for B4C20
CoH28I: C, 48.28; H, 5.67. Found: C, 48.05; H, 5.58.
-
[Cp *Co(2,3-Et2C2B4H3-7-CtC)]2 (8). A mixture of cupric
chloride (16 mg, 0.16 mmol) and 4 (20 mg, 0.081 mmol) was
dissolved in a mixture of 6 mL of toluene and 1 mL of pyridine.
The solution was stirred in the open air at 100 °C for 20 h,
solvent was removed in vacuo, and the residue was flash-
chromatographed through 3 cm of silica gel in CH2Cl2 to give
one orange band. Removal of solvent gave an orange solid
product, which was purified by thick-layer chromatography
on silica gel in 2:1 CH2Cl2/hexane to afford orange-red crystal-
1
line 8 (14 mg, 70%). H NMR (CDCl3): δ 1.25 (t, 12H, J ) 7.5
Hz, ethyl CH3), 1.73 (s, 30H, C5Me5), 2.17, 2.36 (sextet, 4H, J
) 7.5 Hz, ethyl CH2). 13C{1H} NMR (CDCl3): δ 10.0 (C5Me5),
14.6 (ethyl CH3), 21.8 (ethyl CH2), 73.8 (CtC), 93.7 (CtC),
91.0 (C5Me5), 92.1 (C2B4). 11B NMR (CDCl3): δ -4.1 (s, 2B),
4.6 (unresolved, BH, 4B), 4.3 (unresolved, BH, 2B). IR (KBr
pellet, cm-1): ν 2963.4 (s), 2911.0 (m), 2872.9 (m), 2547.1 (vs,
B-H), 2094.4 (m, CtC), 1476.4 (m), 1452.0 (m), 1377.0 (s),
1130.9 (m), 1103.1 (m), 1072.3 (m), 1061.5 (m), 1025.9 (s), 803.1
(vs), 790.6 (vs), 643.2 (w), 588.5 (w). UV-vis (CH2Cl2, nm
(%)): 312 (100), 231 (55), 251 (31), 421 (3), ꢀmax ) 84 240 cm-1
M-1. CI+-mass: m/z (%) 694.0 ([M+], 100).
Cp *Co(2,3-Et2C2B4H3-7-C6H4COOH) (9). To a mixture of
4 (70 mg, 0.2 mmol), Pd(PPh3)2Cl2 (7 mg, 0.01 mmol), CuI (4
mg, 0.02 mmol), and 1,4-IC6H4COOH (50 mg, 0.2 mmol) were
added 4 mL of THF and 1 mL of Et3N. The mixture was stirred
for 18 h, after which the solvent was removed in vacuo. The
residue was dissolved in 6 mL of CH2Cl2, 1 mL of 10% HCl
was added, and the mixture was stirred for 20 min, after which
it was washed with 5 mL of H2O followed by three 6 mL
portions of saturated NaCl solution and finally was dried over
anhydrous Na2SO4. Removal of the solvent afforded 70 mg of
Meth od B. To compound 11 (408 mg, 1.17 mmol) in an open
flask was added 6 mL of N,N,N′,N′-tetramethylethylene-
diamine (TMEDA) and ca. 10 drops of water, and the mixture
was stirred for 3 h. The TMEDA was removed by vacuum, and
the residue was taken up in hexane and flash-chromato-

2592 Organometallics, Vol. 22, No. 13, 2003
Yao et al.
graphed through 3 cm of silica gel in hexane to give one orange-
2.12 (sextet, 4H, J ) 7.5 Hz, ethyl CH2), -5.10 (B-H-B, 4H).
13C{1H} NMR (CDCl3): δ 9.3 (C5Me5), 17.2 (ethyl CH3), 22.4
(ethyl CH2), 85.0 (CtC), 91.5 (C2B3), 92.7 (C5Me5), 111.9 (Ct
C). 11B NMR (CDCl3): δ 1.1 (unresolved, 4B), 6.6 (s, 2B). IR
(KBr pellet, cm-1): ν 2962.8 (vs), 2928.4 (s), 2906.7 (s), 2868.0
(s), 2520.6 (vs, B-H), 2090.0 (m, CtC), 1879.6 (m, B-H-B),
1569.7 (s), 1505.6 (m), 1481.6 (s), 1450.7 (s), 1379.8 (vs), 1075.1
(m), 1029.2 (s), 996.2 (m), 879.7 (s), 772.6 (s), 626.4 (w), 440.0
yellow band. Removal of solvent gave 15 as a yellow solid (360
1
mg, 90%). H NMR (CDCl3): δ -5.15 (2H, B-H-B), 1.09 (t,
6H, J ) 7.2 Hz, ethyl CH3), 1.78 (s, 15H, C5Me5), 2.90, 2.12
(sextet, 2H, J ) 7.5 Hz, ethyl CH2), 2.91 (s, 1H, CtCH). 13C-
{1H} NMR (CDCl3): δ 9.2 (C5Me5), 17.3 (Et, CH3), 22.3 (Et,
CH2), 92.4 (C5Me5), 94.5 (C2B3). 11B NMR (CDCl3): δ 6.6 (s,
1B), 0.9(d, 2B, J BH ) 138 Hz). IR (KBr, pellet, cm-1): ν 2965.2
(s), 2907.7 (s), 2865.4 (m), 2519.2 (s, B-H), 2495.9 (s, B-H),
2120.1 (m, CtC), 1896.2, 1873.3, 1843.3 (B-H-B), 1567.8 (m),
1480.4 (m), 1468.6 (m), 1428.6 (m), 1375.8 (s), 1248.8 (s), 1134.3
(m), 1101.0 (s), 1029.7 (s), 893.8 (vs), 853.1 (vs), 772.5 (s), 754.3
(s), 669.6 (s), 582.0 (w), 526.6 (m), 480.7 (w). CI+-mass: m/z
(%) 339.5 ([M+] + 1, 100).
(w). UV-vis (CH2Cl2, nm (%)): 243 (100), 295 (78), ꢀmax
)
60 751 cm-1 M-1. CI+-mass: m/z (%) 674.5 ([M+], 100). Anal.
Calcd for C36H58B6Co2: C, 64.19; H, 8.68. Found: C, 64.24; H,
8.72.
{Cp *Co(2,3-Et2C2B4H3-5-CtC)}3C6H3 (19). To a mixture
of 12 (70 mg, 0.1 mmol), Pd(PPh3)2Cl2 (7 mg, 0.01 mmol), CuI
(4 mg, 0.02 mmol), and C6H3I3 (27 mg, 0.06 mmol) were added
5 mL of THF and 5 mL of Et3N. The mixture was stirred for
3 days, after which the solvent was removed in vacuo. The
residue was taken up in CH2Cl2 and flash-chromatographed
through 3 cm of silica gel in CH2Cl2. TLC column chromatog-
raphy of the CH2Cl2 wash with 1:3 hexane/CH2Cl2 afforded
19 as a major orange-yellow band (40 mg, 60%). 1H NMR
(CDCl3): δ 1.19 (t, 18H, J ) 7.5 Hz, ethyl CH3), 1.85 (s, 45H,
C5Me5), 2.31, 2.51 (sextet, 6H, J ) 7.2 Hz, ethyl CH2), 7.53 (s,
3H, C6H4). 13C{1H} NMR (125.75 MHz, CDCl3): δ 9.7 (C5Me5),
15.0 (ethyl CH3), 21.7 (ethyl CH2), 91.2 (C5Me5), 93.1 (C2B4),
110.3 (CtC), 125.9 (C6H4), 131.8 (C6H4). 11B NMR (at 50 °C,
CDCl3): δ 8.7 (s, 3B), 4.1 (BH, 9B, unresolved). IR (KBr pellet,
cm-1): ν 2965.3 (s), 2931.0 (m), 2870.6 (w), 2540.7 (vs, B-H),
2161.8 (w, CtC), 1572.5 (s), 1378.1 (m), 1238.4 (m), 1025.8
(m), 869.7 (s), 683.7 (m). UV-vis (CH2Cl2, nm (%)): 299 (100),
271 (89), ꢀmax ) 284 699 cm-1 M-1. CI+-mass: m/z (%) 1116.9
([M+], 100).
Cp *Co(2,3-E t2C2B3H 2-5-CtCSiMe3)CoCp * (16). Com-
pound 14 (220 mg, 0.53 mmol) in 20 mL of THF was
deprotonated with n-BuLi (0.35 mL of a 1.51 M solution in
hexane, 0.53 mmol) at 0 °C. This solution was stirred for 2 h
at room temperature, after which (Cp*CoCl)2 (122.6 mg, 0.27
mmol) in 5 mL of THF was added. The mixture was stirred
overnight, and the solvent was removed in vacuo. The red-
brown residue was washed through 3 cm of silica gel with
dichloromethane. The crude material was then chromato-
graphed on a silica gel column in 1:1 hexane/dichloromethane
to give one major red-brown band. Removal of solvent afforded
1
16 as an air-stable dark red solid (120 mg, 37.3%). H NMR
(CDCl3): δ 0.27 (s, 9H, BCtCSiMe3), 1.54 (t, 6H, J ) 7.5 Hz,
ethyl CH3), 1.60 (s, 30H, C5Me5), 2.54 (m, 4H, J ) 7.5 Hz, ethyl
CH2). 13C{1H} NMR (125.75 MHz, CDCl3): δ 0.6 (BCtCSiMe3),
9.2 (C5Me5), 15.5 (ethyl CH3), 23.7 (ethyl CH2), 87.4 (C5Me5),
88.3 (C2B4), 126.5 (BCtCSiMe3). 11B NMR (CDCl3): δ 9.2 (BH,
2B, unresolved), 40.9 (s, 1B). IR (KBr pellet, cm-1): ν 2964.6
(s), 2907.5 (vs), 2483.7 (s, B-H), 2075.9 (s, CtC), 1476.3 (m),
1447.7 (m), 1376.9 (s), 1241.3 (m), 1153.2 (m), 1100.8 (m),
1021.9 (m), 879.3 (s), 847.2 (vs), 802.0 (vs), 754.7 (m), 690.6
(w), 584.7 (m). UV-vis (CH2Cl2, nm (%)): 312 (100), 231 (55),
251 (31), 421 (3), ꢀmax ) 84 240 cm-1 M-1. CI+-mass: m/z (%)
) 603.6 ([M+], 100). Anal. Calcd for B3C31Co2H51Si: C, 61.84;
H, 8.54. Found: C, 61.72; H, 8.55.
[Cp *Co(2,3-Et2C2B4H3-5-CtC)]2 (17). To a mixture of 12
(347.6 mg, 1 mmol), Pd(PPh3)2Cl2 (18 mg, 0.026 mmol), CuI
(9.5 mg, 0.05 mmol), and I2 (127 mg, 0.5 mmol) were added 5
mL of pyridine and 1 mL of Et3N, and the mixture was stirred
for 15 h. Solvent was removed in vacuo, and the residue was
flash-chromatographed through 5 cm of silica gel in hexane
to give one yellow band, which was Cp*Co(2,3-Et2C2B3H5-5-
CtCH (10 mg), then CH2Cl2 to give one orange-red band.
Removal of solvent gave the orange-red solid 17 (228 mg,
65.8%). 1H NMR (CDCl3): δ 1.17 (t, 12H, J ) 7.5 Hz, ethyl
CH3), 1.82 (s, 30H, C5Me5), 2.28, 2.48 (sextet, 4H, J ) 7.2 Hz,
ethyl CH2). 13C{1H} NMR (125.75 MHz, CDCl3): δ 9.7 (C5Me5),
15.0 (ethyl CH3), 21.7 (ethyl CH2), 92.8 (CtC), 91.2 (C5Me5),
96.3 (C2B4). 11B NMR (CDCl3): δ 4.3 (unresolved, BH, 6B), 8.2
(unresolved, BH, 2B). IR (KBr pellet, cm-1): ν 2973.1 (s),
2909.7 (s), 2870.2 (m), 2552.1 (vs, B-H), 2074.4 (w, CtC),
1472.0 (s), 1448.1 (s), 1383.0 (vs), 1376.7 (vs), 1158.5 (s), 1123.4
(m), 1064.5 (m), 1026.8 (s), 884.8 (m), 861.5 (s), 674.6 (m), 592.5
(w), 446.4 (m). UV-vis (CH2Cl2, nm (%)): 289 (100), 350 (71),
ꢀmax ) 38 666 cm-1 M-1. CI+-mass: m/z (%) 694.7 ([M+], 100).
Anal. Calcd for C36H36B8Co2: C, 62.38; H, 8.14. Found: C,
62.29; H, 8.14.
{Cp *Co(2,3-Et2C2B3H4-5-CtC)}3C6H3 (20). To a mixture
of 15 (318 mg, 0.94 mmol), Pd(PPh3)2Cl2 (33 mg, 0.05 mmol),
CuI (18 mg, 0.1 mmol), and C6H3I3 (137 mg, 0.3 mmol) were
added 5 mL of THF and 1 mL of Et3N. The mixture was stirred
for 4 h, after which the solvent was removed in vacuo and the
residue was taken up in CH2Cl2 and flash-chromatographed
through 3 cm of silica gel in CH2Cl2. Column chromatography
of the residue from the CH2Cl2 wash in hexane gave 20 as a
major orange-yellow band (283 mg, 87%). 1H NMR (CDCl3):
δ 1.11 (t, 18H, J ) 7.8 Hz, ethyl CH3), 1.81 (s, 45H, C5Me5),
1.93, 2.15 (sextet, 6H, J ) 7.5 Hz, ethyl CH2), 7.48 (s, 3H,
C6H4), -4.96 (6H, B-H-B). 13C{1H} NMR (CDCl3): δ 9.3
(C5Me5), 17.3 (ethyl CH3), 22.4 (ethyl CH2), 105.4 (CtC), 92.6
(C5Me5), 111.9 (C2B3), 124.9 (C6H4), 132.9 (C6H4). 11B NMR
(CDCl3): δ 6.5 (s, 3B), 0.6 (BH, 6B, unresolved). IR (KBr pellet,
cm-1): ν 3055.2 (w), 2960.3 (vs), 2962.3 (s), 2866.7 (m), 2509.9
(vs, B-H), 2181.0 (w, CtC), 1576.2 (vs), 1560.2 (m), 1376.5
(s), 1202.8 (s), 1027.8 (m), 932.2 (m), 875.9 (s), 773.8 (m). UV-
vis (CH2Cl2, nm (%)): 274 (100), 328 (17) ꢀmax ) 32 392 cm-1
M-1. CI+-mass: m/z (%) 1085.7 ([M+], 100). Anal. Calcd for
B9C60Co3H90: C, 66.39; H, 8.36. Found: C, 66.63; H, 8.39.
1,3,5-[Cp *2Co2(2,3-Et2C2B3H2-5-CtC)]3C6H3 (21). To an
84 mg (0.077 mmol) sample of 20 in 8 mL of THF was added
11 mg of NaH (0.46 mmol) at room temperature. This solution
11
was stirred for 1 h, 53 mg (0.12 mmol) of (Cp*CoCl)2 in 5
mL of THF was added, and the mixture was stirred overnight,
after which the solvent was removed in vacuo. The red-brown
residue was washed through 3 cm of alumina with dichlo-
romethane, and the crude material was chromatographed on
alumina TLC in 1:1 hexane/dichloromethane to afford 21 as
an air-stable dark red solid (88 mg, 0.053 mmol, 69% yield).
1H NMR (300 MHz, 25 °C, CDCl3): δ 1.57 (t, 6H, J ) 7.2 Hz,
ethyl CH3), 1.67 (s, 30H, C5Me5), 2.53-2.60 (q, 4H, J ) 7.5
Hz, ethyl CH2), 7.61 (s, 3H, C6H4). 13C{1H} NMR (75.5 MHz,
25 °C, CDCl3): δ 9.4 (C5Me5), 15.6 (ethyl CH3), 23.9 (ethyl CH2),
87.6 (C5Me5), 88.1 (C2B4), 122.8 (BCtC), 127.1 (C6H4), 129.1
(C6H4). 11B NMR (96.4 MHz, 25 °C, CDCl3): δ 8.6 (BH, 2B,
unresolved), 41.5 (s, 1B); IR (KBr pellet, cm-1): ν 2974.2 (m),
2903.7 (vs), 2471.7 (s, B-H), 2131.7 (w, CtC), 1569.7 (m),
[Cp *Co(2,3-Et2C2B3H4-5-CtC)]2 (18). Triethylamine (121
mg, 1.2 mmol) was added to a stirred mixture of Pd(PPh3)4
(18 mg, 016 mmol), CuI (8.6 mg, 0.045 mmol), and 15 (203
mg, 0.6 mmol) in 4 mL of pyridine. This mixture was then
sequentially treated with chloroacetone (56 mg, 0.6 mmol) and
stirred for 15 h at room temperature. Following removal of
the solvent in vacuo, the residue was flash-chromatographed
through 5 cm of silica gel in hexane to give one yellow band,
orange-yellow solid 18 (137 mg, 68%). 1H NMR (CDCl3): δ 1.09
(t, 12H, J ) 7.5 Hz, ethyl CH3), 1.79 (s, 30H, C5Me5), 1.90,

Alkynyl-Linked Poly(cobaltacarboranes)
Organometallics, Vol. 22, No. 13, 2003 2593
1560.2 (m), 1458.6 (m), 1457.0 (m), 1379.4 (s), 1212.3 (w),
1079.5 (w), 1025.7 (m), 960.3 (w), 803.5 (s). UV-vis (CH2Cl2,
nm (%)): 243 (100), 276 (68), 345 (98), 428 (31), 528 (8), 753
(10), ꢀmax ) 74 074 cm-1 M-1. CI+-mass: m/z (%) 1662.7 ([M+],
100). The purity of 21 was established from clean multinuclear
NMR spectra (see the Supporting Information in ref 4a).
{Cp *Co(2,3-Et2C2B4H3-7-CtC)}3C6H3 (22). Meth od A. To
a solution of 4 (348 mg, 1 mmol) in 25 mL of THF was added
t-BuLi (0.63 mL of a 1.6 M solution in hexane, 1 mmol) at 0
°C. After the solution was stirred for 0.5 h at 0 °C, anhydrous
ZnCl2 (136 mg, 1 mmol) in 8 mL of THF was added at 0 °C.
The mixture was stirred at room temperature for 2 h, C6H3I3
(137 mg, 0.3 mmol) and Pd(PPh3)4 (52 mg, 0.045 mmol) were
added, and refluxing was continued for 16 h, after which the
solvent was removed in vacuo. The residue was taken up in
CH2Cl2 and flash-chromatographed through 3 cm of silica gel
in CH2Cl2. Column chromatography of the CH2Cl2 wash in 1:1
hexane/CH2Cl2 yielded 22 as a major orange-yellow band (280
mg, 81.5%).
Meth od B. To a mixture of 4 (35 mg, 0.1 mmol), Pd(PPh3)2-
Cl2 (3.5 mg, 0.005 mmol), CuI (2 mg, 0.01 mmol), and C6H3I3
(13 mg, 0.03 mmol) were added 5 mL of THF and 1 mL of Et3N.
The mixture was stirred for 2 days, the solvent was removed
in vacuo, and the residue was taken up in CH2Cl2 and flash-
chromatographed through 3 cm of silica gel in CH2Cl2. TLC
chromatography of the CH2Cl2 wash in 1:3 hexane/CH2Cl2 gave
22 as a major orange-yellow band (22 mg, 66%). 1H NMR
(CDCl3): δ 1.31 (t, 18H, J ) 7.5 Hz, ethyl CH3), 1.77 (s, 45H,
C5Me5), 2.26, 2.44 (sextet, 6H, J ) 7.5 Hz, ethyl CH2), 6.861
(s, 3H, C6H4). 13C{1H} NMR (CDCl3): δ 10.0 (C5Me5), 14.5
(ethyl CH3), 21.9 (ethyl CH2), 86.6 (CtC), 93.6 (CtC), 91.0
(C5Me5), 92.1 (C2B4), 123.5 (C6H4), 133.8 (C6H4). 11B NMR (75
°C, toluene-d8): δ -2.3 (s, 3B), 3.9 (unresolved, BH, 6B), 7.9
(unresolved, BH, 3B). IR (KBr pellet, cm-1): ν 2964.4 (s),
2931.9 (m), 2910.9 (m), 2873.9 (w), 2533.2 (vs, B-H), 2176.9
(w, CtC), 1717.4 (m), 1715.3 (m), 1576.3 (s), 1476.3 (s), 1383.7
(s), 1219.3 (s), 1027.1 (m), 880.9 (m), 784.2 (vs). CI+-mass: m/z
(%) 1115.8 ([M+], 100). UV-vis (CH2Cl2, nm (%)): 307 (100),
247 (23) ꢀmax 285 961 cm-1 M-1. Anal. Calcd for C60H87B12Co3:
C, 64.64; H, 7.87. Found: C, 64.74; H, 7.83.
diffractometer at -120 °C using graphite-monochromated Mo
KR radiation (λ ) 0.710 73 Å). A total of 1800 frames were
collected for each crystal using ω scans. Empirical absorption
corrections were applied using the Bruker SADABS program,26
with the transmission factors ranging 0.59-0.80 and 0.73-
0.80 for 8 and 19, respectively. The structures were solved by
direct methods within the Bruker SHELXTL program suite.27
2
Full-matrix least-squares refinement on |F| yielded the final
R1 and wR2 values of 0.0516 and 0.1651 for 9 as well as 0.0598
and 0.1296 for 18. Hydrogen atoms were placed in calculated
positions, except those attached to the boron atoms, which
were found in difference maps and refined with isotropic
displacement parameters. The final difference Fourier maps
were essentially featureless. Crystallographic data for both
new structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre, CCDC Nos. 204135
(8) and 204136 (19). Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, +44-1223-336033; e-mail,
deposit@ccdc.cam.ac.uk; web, http://www.ccdc.cam.ac.uk).
Electr och em istr y. Anhydrous 99.9% HPLC grade dichlo-
romethane for electrochemistry was purchased from Aldrich.
Anhydrous 99.9% HPLC grade tetrahydrofuran for electro-
chemistry (purchased from Aldrich) was distilled over sodium
before use. The supporting electrolyte used was either elec-
trochemical grade [NBu4][PF6], obtained from Fluka, or [NBu4]-
[B(C6F5)4], prepared as described in ref 10. Cyclic voltammetry
was performed in a three-electrode cell having a platinum
working electrode surrounded by a platinum-spiral counter
electrode and an aqueous saturated calomel reference electrode
(SCE) mounted with a Luggin capillary. Either a BAS 100A
or a BAS 100W electrochemical analyzer was used as a
polarizing unit. Controlled-potential coulometry was conducted
in an H-shaped cell with anodic and cathodic compartments
separated by a sintered-glass disk. The working macroelec-
trode was platinum gauze; a mercury pool was used as the
counter electrode. All reported potential values are referred
to the saturated calomel electrode (SCE).
Ack n ow led gm en t. Support from the National Sci-
ence Foundation for the synthetic studies (Grant No.
CHE-9980708 to R.N.G.) and for the purchase of a
departmental CCD X-ray diffractometer (Grant No.
CHE-9974875 to the Department of Chemistry) is
gratefully acknowledged. P.Z. gratefully acknowledges
the financial support of the University of Siena (PAR
2001).
{Cp *Co[2,3-E t2C2B4H 3-7-C2Co2(CO)6]}3C6H 3 (23). To a
solution of Co2(CO)8 (34 mg, 0.1 mmol) in 4 mL of CH2Cl2 was
slowly added 22 (33.5 mg, 0.03 mmol) in 6 mL of CH2Cl2 at 0
°C. After the solution was stirred for 3 days at room temper-
ature, the solvent was removed and the residue was separated
on TLC plates in 2:1 CH2Cl2/hexane to afford the red-brown
solid 23 (33 mg, 55.7%). 1H NMR (CDCl3): δ 1.20 (t, 18H, J )
7.5 Hz, ethyl CH3), 1.77 (s, 45H, C5Me5), 2.01, 2.30 (sextet,
6H, J ) 7.8 Hz, ethyl CH2), 7.040 (s, 3H, C6H4). 13C NMR
(CDCl3): δ 10.1 (C5Me5), 14.3 (ethyl CH3), 21.8 (ethyl CH2),
90.8 (C5Me5), 100.0 (C-Co-C), 95.0 (C2B4), 129.0 (C6H4), 139.4
(C6H4), 199.5 (C-O). IR (KBr pellet, cm-1): ν 2972.6 (m),
2934.3 (m), 2909.6 (m), 2542.2 (m, B-H), 2083.2 (vs, C-C),
2053.1 (vs, C-O), 2016.7 (C-O), 1560.2 (m), 11452.3 (m),
1383.3 (s), 1029.2 (m), 788.2 (m), 563.2 (m), 520.6 (s), 466.0
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond distances, bond angles, anisotropic thermal
parameters, and calculated mean planes for 8 and 19. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OM0301379
(s). UV-vis (CH2Cl2, nm (%)): 216 (100), 314 (21) ꢀmax
)
108 836 cm-1 M-1. Anal. Calcd for C78H87B12Co9O18: C, 47.49;
H, 4.45. Found: C, 47.67; H, 4.55.
(26) Sheldrick, G. M. SADABS: Program for Empirical Absorption
of Area Detector Data; University of Gottingen, Gottingen, Germany,
1996.
(27) Sheldrick, G. M. SHELXTL Version 5.1 Reference Manual;
Bruker AXS: Madison, WI, 1997.
X-r a y Str u ctu r e Deter m in a tion s on 8 a n d 19. All
diffraction data were collected on a Bruker SMART APEX CCD