Reactivity of CpCo 16e half-sandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligand toward phenylacetylene

Article abstract of DOI:10.1021/om700454p

The reaction of the 16e half-sandwich complex CpCo[S₂C ₂B₁₀H₁₀] (1S) with phenylacetylene at ambient temperature led to 2S, 3S, and 4S. In 3S the alkyne is twofold inserted into one of the Co-S bonds. In 4S B-substitution occurs at the ortho-carborane cage in the position B(3)/B(6) with the formation of a C-B bond. Upon heating, 3S catalyzed the cyclotrimerization of alkyne to give rise to 1,3,5- and 1,2,4-triphenylbenzenes. In comparison, CpCo[Se₂C₂B ₁₀H₁₀] (1Se) did not react with the alkyne at ambient temperature. However, if heated to 80°C, 2Se and 4Se (an analogue to 4S) were generated. Mechanistic implications on metal-induced B-H bond activation and catalytic cyclotrimerization of alkynes were elucidated. The solid-state structures of 2Se, 3S, and 4S have been determined by X-ray crystallography.

Full text of DOI:10.1021/om700454p

4344
Organometallics 2007, 26, 4344-4349
Reactivity of CpCo 16e Half-Sandwich Complexes Containing a
Chelating 1,2-Dicarba-closo-dodecaborane-1,2-dichalcogenolate
Ligand toward Phenylacetylene
Bao-Hua Xu, De-Hong Wu, Yi-Zhi Li, and Hong Yan*
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, The
Joint Laboratory of Metal Chemistry, Nanjing UniVersity-Jin Chuan Group Ltd., Nanjing UniVersity,
Nanjing, JiangSu 210093, People’s Republic of China
ReceiVed May 7, 2007
The reaction of the 16e half-sandwich complex CpCo[S2C2B10H10] (1S) with phenylacetylene at ambient
temperature led to 2S, 3S, and 4S. In 3S the alkyne is twofold inserted into one of the Co-S bonds. In
4S B-substitution occurs at the ortho-carborane cage in the position B(3)/B(6) with the formation of a
C-B bond. Upon heating, 3S catalyzed the cyclotrimerization of alkyne to give rise to 1,3,5- and 1,2,4-
triphenylbenzenes. In comparison, CpCo[Se2C2B10H10] (1Se) did not react with the alkyne at ambient
temperature. However, if heated to 80 °C, 2Se and 4Se (an analogue to 4S) were generated. Mechanistic
implications on metal-induced B-H bond activation and catalytic cyclotrimerization of alkynes were
elucidated. The solid-state structures of 2Se, 3S, and 4S have been determined by X-ray crystallography.
Introduction
The transition metal complexes containing chelating
1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolate ligands,
[E2C2B10H10]2- (E ) S, Se) have been extensively investigated,
and in some cases their reaction chemistries with metal
fragments and organic substrates have been reported.1-9 Re-
cently, a novel carboranyl-thiol-appended cyclopentadiene
ligand, 1-SH-2-[HCpCH(Ph)]-closo-1,2-C2B10H10, was prepared,
and its reaction with Ti(NMe2)4 generated the corresponding
titanium complex [1-(σ-S)-2-(η5-C5H4CH(Ph))-1,2-C2B10H10)]-
Ti(NMe2)2.10 A type of 16e half-sandwich complexes Cp*M-
[E2C2B10H10] (M ) Co, Rh, Ir; E ) S, Se), for instance, could
serve as promising precursors for synthesis of mixed-metal
* To whom correspondence should be addressed. E-mail: hyan1965@
nju.edu.cn. Fax: (+86)-25-83314502.
(1) (a) Kim, D. H.; Ko, J.; Park, K.; Cho, S.; Kang, S. O. Organometallics
1999, 18, 2738. (b) Won, J. H.; Kim, D. H.; Kim, B. Y.; Kim, S. J.; Lee,
C.; Cho, S.; Ko, J.; Kang, S. O. Organometallics 2002, 21, 1443.
(2) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Z. Anorg. Allg.
Chem. 2000, 626, 1627.
(3) (a) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Angew.
Chem. 1999, 111, 3888. (b) Herberhold, M.; Yan, H.; Milius, W.;
Wrackmeyer, B. Angew. Chem., Int. Ed. 1999, 38, 3689.
(4) (a) Herberhold, M.; Jin, G. X.; Yan, H.; Milius, W.; Wrackmeyer,
B. Eur. J. Inorg. Chem. 1999, 5, 873. (b) Herberhold, M.; Jin, G. X.; Yan,
H.; Milius, W.; Wrackmeyer, B. J. Organomet. Chem. 1999, 587, 252.
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Chim. Acta 1999, 289, 141. (b) Bae, J. Y.; Lee, Y. J.; Kim, S. J.; Ko, J.;
Cho, S.; Kang, S. O. Organometallics 2000, 19, 1514.
(6) Herberhold, M., Yan, H.; Milius, W. J. Organomet. Chem. 2000,
598, 142.
Figure 1. Molecular structure of 3S. Ellipsoids are shown at the
30% probability level, and hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Co(1)-ring
centroid 1.705, Co(1)-S(1) 2.187(2), Co(1)-S(2) 2.271(2), Co-
(1)-C(6) 1.962(4), S(1)-C(1) 1.839(4), S(1)-C(3) 1.757(4), C(1)-
C(2) 1.663(5), C(3)-C(4) 1.372(5), C(4)-C(5) 1.451 (5), C(5)-
C(6) 1.363(5), C(6)-C(7) 1.475(5), C(3)-C(13) 1.497(5), S(2)-
C(2) 1.778(4), S(1)Co(1)C(6) 96.36(12), Co(1)C(6)C(5) 124.0(3),
C(3)C(4)C(5) 130.8(3), C(4)C(5)C(6) 130.8(3), Co(1)S(1)C(3)
115.12(13), S(1)C(3)C(4) 117.8(3), S(1)Co(1)S(2) 95.01(6), Co-
(1)S(1)C(1) 107.00(12), S(1)C(1)C(2) 114.2(2), S(2)C(2)C(1) 119.1-
(2), Co(1)S(2)C(2) 104.46(13).
clusters, of which oligonuclear frameworks including hetero-
metallic clusters with metal-metal bonds were built up.11-15
On the other hand, the study of addition and substitution
reactions of such complexes with organic molecules is of great
interest. The metal center, the chalcogen element, and the
(7) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Chem.-Eur.
J. 2000, 6, 3026.
(8) (a) McKinney, J. D.; Chen, H.; Hamor, T. A.; Paxton, K.; Jones, C.
J. J. Chem. Soc., Dalton Trans. 1998, 2163. (b) Base, K.; Grinstaff, M. W.
Inorg. Chem. 1998, 37, 1432.
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Soc., Chem. Commun. 1993, 22, 1696. (b) Crespo, O.; Gimeno, M. C.;
Jones, P. G.; Ahrens, B.; Laguna, A. Inorg. Chem. 1997, 36, 495. (c) Crespo,
O.; Gimeno, M. C.; Jones, P. G.; Laguna, A. J. Chem. Soc., Dalton Trans.
1997, 1099.
(11) (a) Lu, S. X.; Jin, G. X.; Eibl, S.; Herberhold, M.; Xin, Y.
Organometallics 2002, 21, 2533. (b) Yu, X. Y.; Jin, G. X.; Hu, N. H.;
Weng, L. H. Organometallics 2002, 21, 5540. (c) Yu, X. Y.; Lu, S. X.;
Jin, G. X.; Weng, L.H. Inorg. Chim. Acta 2004, 357, 361.
(10) Wang, J, H.; Zheng, C.; Maguire, J. A.; Hosmane, N. S. Organo-
metallics 2003, 22, 4839.
10.1021/om700454p CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/12/2007

ReactiVity of CpCo 16e Half-Sandwich Complexes
Organometallics, Vol. 26, No. 17, 2007 4345
Figure 2. 125.76 MHz 13C{1H} NMR spectrum of 3S in CDCl3 at 22 °C.
Figure 3. Molecular structure of 4S. Ellipsoids are shown at the
Figure 4. Molecular structure of 2Se. Ellipsoids are shown at the
30% probability levels, and hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Co(1)-ring
centroid 1.693, Co(2)-ring centroid 1.681, Co(1)-Co(2) 2.414,
Se(1)-Co(1) 2.3089(12), Se(1)-Co(2) 2.3062(12), Se(1)-C(1)
1.965(5), Se(2)-Co(1) 2.3048(12), Se(2)-Co(2) 2.3090(12), Se-
(2)-C(2) 1.985(6), C(1)-C(2) 1.598(8). Co(1)Se(2)C(2) 100.69-
(16), Co(1)Se(1)C(1) 101.56(15), Co(2)Se(1)C(1) 100.38(14),
Co(2)Se(2)C(2) 99.96(17), Co(1)Se(2)Co(2) 63.09(3), Co(1)Se(1)-
Co(2) 63.07(3), Se(1)C(1)C(2) 113.5(3), Se(2)C(2)C(1) 113.7(3).
30% probability level, and hydrogen atoms have been omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Co(1)-ring
centroid 1.698, Co(1)-S(1) 2.1694(17), Co(1)-S(2) 2.2330(15),
Co(1)-C(4) 2.008(5), C(4)-C(5) 1.497(7), C(3)-C(4) 1.518(7),
C(1)-C(2) 1.668(8), S(1)-C(1) 1.786(5), S(2)-C(2) 1.750(5),
C(3)-B(3) 1.560(8), C(1)-B(3) 1.726(8), C(2)-B(3) 1.771(8), Co-
(1)S(2)C(2) 103.85(18), S(1)Co(1)S(2) 95.78(5), Co(1)S(1)C(1)
106.6(2), S(2)C(2)C(1) 118.5(3), S(1)C(1)C(2) 114.4(4), C(4)C-
(3)B(3) 112.1(4), C(1)B(3)C(3) 108.4(4), S(1)C(1)B(3) 108.6(3),
C(1)S(1)C(4) 96.6(2), S(1)C(4)C(3) 113.7(4), Co(1)C(4)C(5) 116.0-
(4), S(1)C(4)C(5) 114.8(4), C(3)C(4)C(5) 116.0(4).
and further transformations.17 In the case of phenylacetylene,
one type of ortho-metalation compound with a M-B bond was
isolated at ambient temperature in a cisoid arrangement with
respect to the relative positions of E-η2-(Ph)C-C and C(1)-
B(M) units (see A, Scheme 1). If heated, the cisoid species of
different metal centers behave differently. For instance, the
ruthenium and osmium species converted to a transoid arrange-
ment; the rhodium species with sulfur atoms led to cleavage of
a M-B bond and the formation of a C-B bond (see B, Scheme
1); and the Ir species retained the cisoid skeleton and showed
no transformations.18 Surprisingly, the 16e complex Cp*Rh-
[Se2C2B10H10] did not react with phenylacetylene.
reaction conditions strongly influence the reactivity of the
analogous unsaturated 16e complexes.1-7,16
We have shown that 16e complexes Cp*M[E2C2B10H10] (M
) Rh, Ir; E ) S, Se) and (p-cymene)M[S2C2B10H10] (M ) Ru,
Os) reacted with alkynes to generate numerous novel complexes
that resulted from the insertion of alkyne into one of the M-E
bonds, followed by B-H bond activation, M-B bond formation,
(12) (a) Jin, G. X.; Wang, J. Q.; Zhang, Z.; Weng, L. H.; Herberhold,
M. Angew. Chem., Int. Ed. 2005, 44, 259. (b) Wang, J. Q.; Hou, X. F.;
Weng, L. H.; Jin, G. X. Organometallics 2005, 24, 826. (c) Wang, J. Q.;
Hou, X. F.; Weng, L. H.; Jin, G. X. J. Organomet. Chem. 2005, 690, 249.
(d) Cai, S. Y.; Hou, X. F.; Weng, L. H.; Jin, G. X. J. Organomet. Chem.
2005, 690, 910.
(13) (a) Cai, S. Y.; Jin, G. X. Organometallics 2005, 24, 4226. (b) Cai,
S. Y.; Wang, J. Q.; Jin, G. X. Organometallics 2005, 24, 5280.
(14) Jin, G. X.; Wang, J. Q.; Zhang, C.; Weng, L. H.; Herberhold, M.
Angew. Chem., Int. Ed. 2005, 44, 259.
In our continuous and systematic studies of the roles of metal
in the chemistries in these 16e series Cp*M[E2C2B10H10] (M
(17) (a) Wrackmeyer, B.; Yan, H.; Milius, W.; Herberhold, M. Russ.
Chem. Bull. 2001, 50, 1518. (b) Herberhold, M.; Yan, H.; Milius, W.;
Wrackmeyer, B. J. Chem. Soc., Dalton Trans. 2001, 1782.
(18) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. J. Organomet.
Chem. 2000, 604, 170.
(15) Jin, G. X. Coord. Chem. ReV. 2004, 248, 587.
(16) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Chem.-
Eur. J. 2002, 2, 8.

4346 Organometallics, Vol. 26, No. 17, 2007
Scheme 1. Some Examples of Structurally Characterized Complexes (A,19 B,19 C,1 D,7 E,2 F,2 G,2 H3)
Xu et al.
Scheme 2
Scheme 3
Scheme 4
) Co, Rh, Ir; E ) S, Se) complexes, we now report the
reactivity of CpCo[E2C2B10H10] (E ) S, Se), 1, with HCtCPh
in order to obtain more evidence for transition metal induced
B-H bond activation, ortho-metalation, and B(3,6)-substitution
of the carborane cluster as well as to explore the chemistries of
the cobalt complex. Previously, Kang’s group described one
addition product, C (Scheme 1), from the reaction of 1S with
phenyl acetylene.1a In this paper, we report the isolation of new
complexes 3S, 4S, 2Se, and 4Se and the catalytic cyclotrimer-
ization of alkyne by the 16e complexes 1S and 1Se. The
reactivity of the 18e dicobalt complexes 2S and 2Se with HCt
CPh has also been studied.
mixture from which 2S, 3S, and 4S were isolated. 2S was
obtained as a byproduct in a yield of 11%. Its solid-state
structure has been described.1 In the present paper its 11B and
13C NMR data are first reported for comparison with the
selenium analogue.
3S was isolated in a yield of 40%. Its X-ray structure as
shown in Figure 1 shows that the alkyne is twofold inserted
into one of the Co-S bonds in a head-head mode. The
generated six-membered ring S(1)Co(1)C(6)C(5)C(4)C(3) is
fused at one Co-S bond with the five-membered ring S(1)Co-
(1)S(2)C(2)C(1). The five-membered ring is no longer planar
as in 1S due to the alkyne insertion. The coordinative SfCo
bond length (2.187 Å) is significantly shorter than the other
covalent S-Co bond (2.271 Å). This probably determines the
presence of the six-membered ring from the double insertion
of the alkyne. In 3S the bond length of C(1)-C(2) (1.663 Å)
of the carborane cage falls in the typical range (1.62-1.70 Å)
Results and Discussion
The reactions of CpCo[E2C2B10H10], 1, with phenylacetylene
were explored at three different temperatures (25, 80, and 110
°C). The products were isolated by chromatography and
characterized with NMR spectroscopic data and X-ray crystal
structure analysis.
Reaction of CpCo[S2C2B10H10] (1S) with Phenylacetylene
at 25 °C. The reaction of 1S with HCtCPh at 25 °C led to a

ReactiVity of CpCo 16e Half-Sandwich Complexes
Organometallics, Vol. 26, No. 17, 2007 4347
Scheme 5. Proposed Mechanisms for Products 3 and 4 and Cyclotrimerization of Alkyne
of o-carborane derivatives.20 The configuration in 3S does not
induce significant strain. A couple of analogous examples have
been isolated from the reactions of Cp*Rh[E2C2B10H10] with
HCtCCO2Me (see D-F, Scheme 1);2,7 however, no such
structure was isolated with HCtCPh in the Rh and Ir systems.
The NMR data of 3S are in agreement with its solid-state
substituted carboranes. In the 13C NMR spectrum, the low, broad
peak at 33.93 ppm shows that the CH2 group is linked to a
boron atom.
Reaction of 1S with Phenylacetylene at Higher Temper-
ature. The reaction of 1S with HCtCPh at 80 °C in toluene
led to 2S, 4S, and 1,2,4- and 1,3,5-triphenylbenzenes (Scheme
3). 3S was not isolated at 80 °C. In a separate experiment,
heating 3S at 80 °C led to decomposition. At 80 °C the
competitive catalytic cyclotrimerization of alkyne becomes
significant, in contrast to that at ambient temperature. If the
temperature was raised to 110 °C, 2S was isolated with a large
amount of triphenylbenzenes and 4S decomposed at 110 °C. It
needs to be mentioned that the species C, shown in Scheme 1,
was not isolated at both ambient and higher temperatures with
the same reaction conditions as described in the literature.1
3S as Catalytic Intermediate. As discussed above, 3S
decomposes at 80 °C. However, in the presence of phenylacety-
lene, 3S acts as a catalyst to generate triphenylbenzenes. 3S
was isolated as the predominant product in the mixture with
traces of 2S and 4S (Scheme 4).
Reaction of CpCo[Se2C2B10H10] (1Se) with Phenylacety-
lene. 1Se did not react with HCtCPh at ambient temperature.
If heated at 80 °C in toluene for 2 h, 2Se and 4Se were isolated
together with 1,3,5- and 1,2,4-triphenylbenzenes in about 1:1
ratio (Scheme 3). 3Se (analogue of 3S) was not isolated at 80
°C. If the reaction was carried out in boiling toluene, 2Se was
the only complex isolated, accompanied by triphenylbenzenes.
4Se decomposed at 110 °C.
2Se was isolated in a yield of 73% at 80 °C and showed
high thermal stability (mp ) 245 °C, dec). The X-ray analysis
displays (Figure 4) a symmetric dinuclear molecular structure
analogous to 2S. The addition of a CpCo moiety to the Se-
Co-Se unit in 1Se generates 2Se with Co-Co bonding. Two
similar dinuclear structures, [(tert-Bu)2(C5H3)Rh]2[E2C2B10H10]
(E ) S, Se), were reported by Jin’s group.13a However, in the
rhodium and iridium series with a larger pentamethylcyclopen-
tadienyl (Cp*) unit such a species was never isolated. It appears
that the generation of 2S and 2Se depends on the size of the
auxiliary ligand. Its 1H NMR spectrum consists of a single sharp
signal of Cp, consistent with the symmetric structure. The 13C
data of the carborane (66.7 ppm) shifts to a high field of about
20 ppm relative to 2S (87.1 ppm) owing to the typical heavy
atom effect exerted by Se versus S. This was observed in Rh
and Ir complexes as well.2,18
1
structure. The H chemical shifts of the CHdCH unit of the
six-membered ring appear at 6.17 and 7.51 ppm, as confirmed
by a homonuclear decoupling experiment. The magnitude of
1
3JH-H (8 Hz) is characteristic of H nuclei in a cis position of
an alkene group. Figure 2 shows the 13C NMR spectrum.
Straightforward assignments were made by using 2D 13C/1H
HETCOR (HMQC and HMBC) experiments based on coupling
1
1
n
1
constants J(13C, H) and long-range couplings J(13C, H) (n
) 2, 3). As a result, the CHdCH unit was identified at 127.68
and 141.15 ppm. The carbon atom adjacent to the metal center
(C-M) and the one close to sulfur (C-S) were assigned at
170.45 and 109.65 ppm, respectively. The signals for C(1) and
C(2) of the carborane were readily recognized owing to
broadening by partially relaxed scalar 13C-11B coupling.
4S was isolated in a yield of 35%. The X-ray structure as
shown in Figure 3 displays a B-C bond, and the hydrogen atom
of the B-H bond of the carborane has been transferred to the
terminal carbon of the alkyne. Moreover, the CtC triple bond
of the alkyne has been extended to the range of a C-C single
bond (1.518 Å). The newly generated five-membered ring
C(3)B(3)C(1)S(1)C(4) is nearly planar, whereas the five-
membered ring S(1)Co(1)S(2)C(2)C(1) is nonplanar, in contrast
to the 16e starting complex. Note that A rearranged to B upon
heating in boiling CHCl3, as shown in Scheme 1. In contrast,
4S was synthesized and isolated as a final product at 25 °C. An
analogous species of A with a M-B bond was not seen in the
cobalt case, indicating the 16e cobalt starting material is more
reactive.
The 1H NMR data of 4S support its solid-state structure. The
broader doublets at 1.98 and 2.32 ppm were assigned to the
alkyl group of the B-CH2 unit. The large value (16 Hz) of the
2
geminal coupling constants JH-H is typical for diastereotopic
1H nuclei of the B-CH2 group. The 11B NMR spectrum shows
the pattern of overlapping signals as expected for unsymmetri-
cally substituted o-carborane derivatives; however, a low-field
shift for the substituted boron atom was observed at 1.5 ppm
relative to negative values for the other boron signals. A similar
chemical shift appeared in B18 and G2 (Scheme 1) for B-
4Se was isolated in a yield of 4% from the reaction at 80 °C.
It was identified on the basis of spectral data and elemental
analysis. The NMR spectroscopic properties of 4Se correspond
(19) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Organome-
tallics 2000, 19, 4289.
(20) Bregadze, V. I. Chem. ReV. 1992, 92, 209.

4348 Organometallics, Vol. 26, No. 17, 2007
Xu et al.
Table 1. Crystallographic Data and Structure Refinement Information for 3S, 4S, and 2Se
3S
4S
2Se
formula
fw
C23H27B10CoS2
534.62
C15H21B10CoS2
432.49
C12H20B10Co2Se2
548.16
color
yellow
purple
green
size, mm
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.24 × 0.26 × 0.30
monoclinic
P21/c
11.152 (10)
12.074(10)
20.855(16)
90
105.51(4)
90
2706(4)
0.24 × 0.26 × 0.30
0.24 × 0.26 × 0.30
monoclinic
P21/n
12.250(3)
9.259(3)
17.685(5)
90
99.682(4)
90
1977.3(10)
4
triclinic
P1h
11.962(3)
13.029(3)
15.174(4)
115.007(3)
103.298(5)
98.994(4)
1997.7(9)
4
z
2
θ range (deg)
1.9-26.0
1.8-26.0
1.9-26.0
D(calc) [g/cm3]
1.334
1.438
1.841
µ (mm-1
)
0.804
1.066
5.352
min., max. transmn
no. of data/restraints/params
F(000)
0.7945, 0.8305
5314/0/334
1116
0.7403, 0.7839
7662/0/505
880
0.22, 0.28
3882/0/235
1056
no. of reflns collected
14 286
10 816
10 451
no. of unique reflns (Rint
GOF
)
5314 (0.038)
1.03
7662 (0.035)
1.01
3882 (0.040)
1.10
R indices (I > 2σ(I))
R1 ) 0.0546
wR2 ) 0.1272
R1 ) 0.0712
wR2 ) 0.1320
0.526, -0.515
R1 ) 0.0676
wR2 ) 0.1529
R1 ) 0.0902
wR2 ) 0.1589
0.500, -0.928
R1 ) 0.0510
wR2 ) 0.1257
R1 ) 0.0624
wR2 ) 0.1293
0.564, -0.728
R indices (all data)
largest diff peak and hole (e/Å3)
closely to those of 4S. The mass spectrum displayed a molecular
ion peak, together with microanalysis data, further verifying the
proposed structure for 4Se in Scheme 3.
E, and F (Scheme 1) together with 3S, the coordinative SfCo
bond is about 0.1 Å shorter than the other covalent S-Co bond
in a six-membered ring, whereas the coordinative SfCo bond
is nearly the same as the other S-Co bond in length in the
four-membered-ring complexes H (Scheme 1)3 and [CpCo-
(S2C2B10H10)(MeCO2CdCCO2Me)].1 Addition of one more
alkyne to 3 leads to release of 1 and generation of 1,2,4-
triphenylbenzene, thus completing a catalytic cycle. Here, it is
needed to mention that the similar D and F complexes (Scheme
1) with a phenyl group as a substituent were not isolated in
this reaction; however, they are the intermediates to the catalytic
products of both 1,3,5- and 1,2,4-triphenylbenzenes since the
two substituted benzene derivatives were experimentally ob-
tained. Higher temperature favors the catalytic pathway.
Reactions of (CpCo)2[E2C2B10H10] (2S, 2Se) with Pheny-
lacetylene. In the present report, 2S and 2Se were generated as
byproducts from the reactions of 16e complexes 1S and 1Se,
respectively, and HCtCPh. Alternatively, they were isolated
from the reactions of CpCo(CO)I2 and Li2[E2C2B10H10] for the
preparation of 1S and 1Se, respectively. The 16e complexes
1S and 1Se have demonstrated interesting reactivities with HCt
CPh. In contrast, the corresponding 2S and 2Se did not react
with HCtCPh even at 110 °C.
Mechanism Implications. The two reaction pathways leading
from 1 to 3 and 4, as had been suggested in part previously,3,7
are summarized in Scheme 5. Although some species shown
were never isolated, some were identified and even characterized
by X-ray analysis from other reactions. The complex I was
not isolated in this reaction; however, two analogues generated
from MeCO2CtCCO2Me are stable and characterized by their
solid-state structure.1,3 The 18e structure in I appears to be
fairly rigid, and the cobalt atom cannot get close to the carborane
cage. The equilibrium between I and II is possible if the
coordinative EfM bond is weak enough. The core skeleton in
II is more flexible so that the metal center can approach
the B(3)/B(6) positions of the carborane cage to activate the
B-H bond, as a result, to generate M-H-B bonding as shown
in III. The bridging hydrogen atom is passed stereoselectively
to the olefinic carbon atom, accompanied by formation of a
M-B bond to give rise to IV. IV was not detected even by
monitoring the reaction by NMR spectroscopy at ambient
temperature; however, numerous complexes of such type have
been reported with other alkynes and metal centers by our
group.7,18 The cleavage of a M-B bond leads to a C-B bond
to afford 4.
Conclusion
The reactions of CpCo[E2C2B10H10] (1S, 1Se) with HCtCPh
led to new complexes 2Se, 3S, 4S, and 4Se. The two 16e
complexes display markedly different reactivity toward pheny-
lacetylene: 1S > 1Se. It is conceivable that the selenium atom
instead of sulfur changes the kinetics of some of the reactions
involved owing to the larger covalent radius of selenium and
different strength of the Co-Se bond. This result has been
observed in analogous Rh and Ir systems. On the other hand,
1S and 1Se are more reactive than the analogous 16e rhodium
and iridium complexes, as revealed in the reaction with
phenylacetylene. This is reflected by the generation of a C-B
bond at ambient temperature, rather than a M-B bond as
occurred in Rh and Ir complexes. These 16e cobalt species may
be promising for various transformations with other reagents.
Experimental Section
General Procedures. n-Butyllithium (2.0 M in cyclohexane,
Aldrich), o-carborane (Katchem, Czech), and phenylacetylene (Alfa
Apparently, the insertion of a second alkyne competes with
the pathway from I to 4, and in 3 the strength of the coordinative
SfCo bond may be increased by forming a six-membered ring
relative to a four-membered ring in I. Indeed, as reported in D,
21
Aesar) were used as supplied. CpCo(CO)I2 and CpCo[E2C2-
(21) Frith, S. A.; Spencer, J. L. Inorg. Synth. 1990, 28, 273.

ReactiVity of CpCo 16e Half-Sandwich Complexes
Organometallics, Vol. 26, No. 17, 2007 4349
(B10H10)] (E ) S, Se)1,22 were prepared by slightly modified
literature procedures. All reactions were carried out under argon
using standard Schlenk techniques. All solvents were dried and
deoxygenated prior to use. Diethyl ether, THF, petroleum ether,
and toluene were refluxed and distilled over sodium/benzophenone
ketyl under nitrogen. CH2Cl2 was refluxed and distilled over CaH2
under nitrogen. Silica gel (100-200 mesh) was predried at 180 °C
before use. The NMR measurements were performed on a Bruker
AC 500 spectrometer. Chemical shifts were given with respect to
(70 eV): m/z 526 (M+, 9%). Anal. Calcd for C15H21B10Co1Se2:
C, 34.23; H, 4.02. Found: C, 34.40; H, 4.11.
Reactions of 1Se with Phenylacetylene at Ambient Temper-
ature. Phenylacetylene (0.22 mL, 2 mmol) was added to 1Se (85.0
mg, 0.2 mmol) in CH2Cl2 or toluene (20 mL), and the resultant
mixture was stirred at ambient temperature for 24 h. After removal
of solvent, the residue contained unreacted 1Se and traces of 1,3,5-
and 1,2,4-triphenylbenzenes.
Reaction of 1S with Phenylacetylene in Toluene at 80 °C.
Phenylacetylene (0.22 mL, 2 mmol) was added to the red solution
of 1S (66.0 mg, 0.2 mmol) in toluene (10 mL). Then the mixture
was heated at 80 °C for 2 h, and the color changed to deep red.
After removal of solvent, the residue was chromatographed to give
rise to 2S, 4S, and triphenylbenzenes (∼1:1).
1
CHCl3/CDCl3 (δ H ) 7.24; δ 13C ) 77.0) and external Et2O-
BF3 (δ 11B ) 0). The IR spectra were recorded on a Bruker Vector
22 spectrophotometer with KBr pellets in the region of 4000-400
cm-1. The C and H microanalyses were carried out with a Perkin-
Elmer 240C elemental analyzer. The mass spectra were recorded
in a Micromass GC-TOF for EI-MS (70 eV).
Reactions of 1S and 1Se with Phenylacetylene in Boiling
Toluene. Phenylacetylene (0.22 mL, 2 mmol) was added to 1S (66.0
mg, 0.2 mmol) or 1Se (85.0 mg, 0.2 mmol) in toluene (10 mL).
Then the mixture was heated at 110 °C for 3 h, and the color
changed from red to deep green. After removal of solvent, the
residue was chromatographed to give 2S (35 mg, 75%) and 2Se
(40 mg, 73%), respectively, and triphenylbenzenes (∼1:1).
Synthesis of 2S, 3S, and 4S. Phenylacetylene (0.22 mL, 2 mmol)
was added to the red solution of 1S (66.0 mg, 0.2 mmol) in CH2-
Cl2 (20 mL), and the resultant mixture was stirred at ambient
temperature for 24 h. The color changed to brown-red within the
first 2 h and then gradually to deep brown. After removal of solvent,
the residue was chromatographed on silica gel eluting with
petroleum ether to give 2S and then with petroleum ether/CH2Cl2
(10:1) to give 3S and 4S.
Reaction of 3S with Phenylacetylene in Toluene at 80 °C.
Phenylacetylene (0.11 mL, 1 mmol) was added to the yellow
solution of 3S (50 mg, 0.1 mmol) in toluene (5 mL). Then the
mixture was heated at 80 °C for 3 h, and the color changed to
brown-yellow. After removal of solvent, the residue contained 3S
and triphenylbenzenes as major products and 2S and 4S as minor
products.
2S: green solid, yield 5.3 mg (11%). 1H NMR (CDCl3): δ 5.02
(s, Cp). 13C NMR (CDCl3): δ 77.73 (Cp), 87.14 (carborane). 11B
NMR (CDCl3): δ -9.1 (2B), -5.4 (2B), -1.6 (2B), 6.6 (4B). EI-
MS (70 eV): m/z 454 (M+, 40%). IR (KBr): 2586 (νB-H).
1
3S: yellow solid, yield 43 mg (40%). Mp ) 165 °C (dec). H
NMR (CDCl3): δ 4.98 (s, 5H, Cp), 6.17 (d, J ) 8 Hz, 1H, CHd
CH), 7.51 (d, J ) 8 Hz, 1H, CHdCH), 7.27 (m, 1H), 7.29 (m,
1H), 7.34 (m, 2H), 7.45 (m, 2H), 7.46 (m, 2H), 7.77 (m, 2H) (phenyl
groups). 11B NMR (CDCl3): δ -9.2 (1B), -7.4 (1B), -4.8 (4B),
-3.0 (2B), -2.4 (2B). 13C NMR (CDCl3): δ 90.63 (Cp), 94.64,
101.40 (carborane), 109.65 (CHdC-S), 126.30, 126.46, 126.75,
127.82, 128.16. 129.10, 137.77, 156.01 (Ph), 127.68 (CHdC-S),
141.15 (Co-CdCH), 170.45 (Co-CdCH). EI-MS (70 eV): m/z
535 (M+, 1%). IR (KBr): 2586 (νB-H). Anal. Calcd for C23H27B10-
Co1S2: C, 51.67; H, 5.09. Found: C, 51.51; H, 5.17.
Reactions of 2S and 2Se with Phenylacetylene in Boiling
Toluene. Phenylacetylene (0.11 mL, 1 mmol) was added to the
green solution of 2S (45 mg, 0.1 mmol) or 2Se (55 mg, 0.1 mmol)
in toluene (5 mL). The mixture was stirred for 6 h at 110 °C, but
no color change occurred. After removal of solvent, the residue
was chromatographed to give 2S (42 mg, 93%) or 2Se (53 mg,
96%).
X-ray Crystallography. Crystals suitable for X-ray analysis were
obtained by slow evaporation of a solution in petroleum ether/
dichloromethene. Diffraction data were collected on a Bruker
SMART Apex II CCD diffractometer using graphite-monochro-
mated Mo KR (λ ) 0.71073 Å) radiation at 273 K. During the
intensity data collection, no significant decay was observed. The
intensities were corrected for Lorentz-polarization effects and
empirical absorption with the SADABS program.23 The structures
were solved by direct methods using the SHELXL-97 program.24
All non-hydrogen atoms were found from the difference Fourier
syntheses. The H atoms were included in calculated positions with
isotropic thermal parameters related to those of the supporting
carbon atoms but were not included in the refinement. All
calculations were performed using the Bruker Smart program.
1
4S: purple solid, yield 35 mg (40%). Mp ) 179 °C (dec). H
NMR (CDCl3): δ 1.98 (br d, J ) 16 Hz, 1H, B-CH2), 2.32 (br d,
J ) 16 Hz, 1H, B-CH2), 4.52 (s, 5H, Cp), 7.31 (s, 5H, Ph). 13C
NMR (CDCl3): δ 33.93 (br, B-CH2), 84.86 (Ph-C), 86.47 (Cp),
94.78, 97.91 (carborane), 124.65 (br), 126.31, 129.08, 152.76 (Ph).
11B NMR (CDCl3): δ -14.1 (1B), -9.9 (1B), -9.1 (1B), -8.2
(5B), -7.6 (1B), 1.5 (B-CH2, 1B). EI-MS (70 eV): m/z 432 (M+,
42%). Anal. Calcd for C15H21B10Co1S2: C, 41.66; H, 4.89. Found:
C, 41.76; H, 4.95.
Syntheses of 2Se and 4Se. Phenylacetylene (0.22 mL, 2 mmol)
was added to the suspension of 1Se (85.0 mg, 0.2 mmol) in toluene
(10 mL), and the mixture was heated at 80 °C for 2 h. The color
changed to deep red. After removal of solvent, the residue was
chromatographed. Elution with petroleum ether gave 2Se and 4Se.
1
Acknowledgment. Financial support by the National Science
Foundation of China (No. 20471017) is gratefully acknowl-
edged.
2Se: green solid, yield 40 mg (73%). Mp ) 245 °C (dec). H
NMR (CDCl3): δ 4.99 (s, Cp). 13C NMR (CDCl3): δ 66.71
(carborane), 76.54 (Cp). 11B NMR (CDCl3): δ -8.6 (2B), -4.1
(2B), -1.5 (2B), 3.2 (4B). EI-MS (70 eV): m/z 548 (M+, 21%).
IR (KBr): 2577 (νB-H). Anal. Calcd for C12H20B10Co2Se2: C, 16.66;
H, 3.68. Found: C, 16.78; H, 3.59.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determination of compounds 2Se,
3S, and 4S are available free of charge via the Internet at
http://pubs.acs.org.
1
4Se: purple solid, yield 4 mg (4%). H NMR (CDCl3): δ 2.09
(br d, J ) 16 Hz, 1H, B-CH2), 2.68 (br d, J ) 16 Hz, 1H, B-CH2),
5.35 (s, 5H, Cp), 7.30 (s, 5H, Ph). 11B NMR (CDCl3): δ -14.2
(1B), -9.4 (1B), -8.1 (5B), -7.2 (2B), 1.7 (B-CH2, 1B). EI-MS
OM700454P
(22) (a) Hou, X. F.; Wang, X.; Wang J. Q.; Jin, G. X. J. Organomet.
Chem. 2004, 689, 2228. (b) Murata, M.; Habe, S.; Araki, S.; Namiki, K.;
Yamada, T.; Nakagawa, N.; Nankawa, T.; Nihei, M.; Mizutani, J.; Kurihara
M.; Nishihara, H. Inorg. Chem. 2006, 45, 1108, and references therein.
(23) Sheldrick, G. M. SADABS, A Program for Empirical Absorption
Correction; University of Go¨ttingen: Go¨ttingen, Germany, 1998.
(24) Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.