Reactivity of Cp Rh 16e half-sandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolato ligand. Intermediates in the catalyzed trimerization of methyl acetylene carboxylate and phenylacetylene

Article abstract of DOI:10.1021/om0003077

Reactions of the 16-electron (16e) half-sandwich complexes Cp*Rh[E₂C₂(B₁₀H₁₀)] [E = S (1S), Se (1Se)] with methyl acetylene carboxylate and phenylacetylene were studied in order to obtain information on both the primary addition products and the potential catalyzed oligomerization of the alkynes as a function of reaction conditions.

Full text of DOI:10.1021/om0003077

Organometallics 2000, 19, 4289-4294
4289
Rea ctivity of Cp *Rh 16e Ha lf-Sa n d w ich Com p lexes
Con ta in in g a Ch ela tin g
1,2-Dica r ba -closo-d od eca bor a n e-1,2-d ich a lcogen ola to
Liga n d . In ter m ed ia tes in th e Ca ta lyzed Tr im er iza tion of
Meth yl Acetylen e Ca r boxyla te a n d P h en yla cetylen e
Max Herberhold,* Hong Yan, Wolfgang Milius, and Bernd Wrackmeyer*
Laboratorium fu¨r Anorganische Chemie der Universita¨t Bayreuth,
D-95440 Bayreuth, Germany
Received April 11, 2000
Reactions of the 16-electron (16e) half-sandwich complexes Cp*Rh[E2C2(B10H10)] [E ) S
(1S), Se (1Se)] with methyl acetylene carboxylate and phenylacetylene were studied in order
to obtain information on both the primary addition products and the potential catalyzed
oligomerization of the alkynes as a function of reaction conditions. Both rhodium complexes
1S and 1Se reacted with HCtC-CO2Me under mild conditions to give in low yield the dimers
2S and 2Se, of which 2Se could be characterized by X-ray structural analysis. Both 1S and
1Se act as catalysts for the cyclotrimerization of HCtC-CO2Me and HCtC-Ph to give the
respective 1,3,5- and 1,2,4-trisubstituted benzenes in a 1:1 ratio, if the reaction is carried
out at 70 °C in toluene. In boiling chloroform or at room temperature in dichloromethane,
trimerization is of minor importance. In the case of 1Se and methyl acetylene carboxylate,
an intermediate 3Se, formed in the course of the trimerization process, could be characterized
by X-ray structural analysis. The dimer 2Se catalyzes trimerization in the same way as
1Se. In the absence of HCtC-CO2Me, 2Se rearranges upon heating in toluene at 70 °C
completely into the known carborane-substituted complex 8Se. One of the final products of
the reaction of 1S with HCtC-CO2Me, the 16e complex 4S, also catalyzes the trimerization
of HCtCCO2Me.
In tr od u ction
activation.7 Thus, the complexes 4S-7S, 8Se, and 9S
(Scheme 1) have been isolated and structurally charac-
Although numerous transition metal complexes con-
taining chalcogenolato ligands have been prepared by
various routes, only a few aspects of their chemistry
have been explored so far.1 The reactivity of the 16e half-
sandwich complexes Cp*Rh[E2C2(B10H10)] 1S and 1Se,
and of related compounds of iridium, ruthenium, and
osmium, deserve particular attention considering the
accumulation of reactive sites around the metal center.2
We have already shown that reactions take place with
methyl acetylene carboxylates3-5 and phenylacetylene6
leading to new complexes as the result of consecutive
steps, in which the metal center and the metal-
chalcogen bonds are involved as well as the B(3,6)-H
bonds of the o-carborane cage by metal-induced B-H
terized.3-6
In the cases of the reactions of both 1S and 1Se with
methyl acetylene carboxylate (HCtC-CO2Me), carried
out under mild conditions in dichloromethane at room
temperature, we have noted that small amounts of
rather insoluble complexes 2S and 2Se were formed in
addition to other well-defined products. It had been
assumed that these complexes are dimers of the initial
addition products.4,5 Furthermore, it had been found
that the reactions of 1S or 1Se with both HCtC-CO2-
Me and HCtC-Ph, under mild conditions, produce
small amounts of organic compounds that do not contain
rhodium and are most likely oligomers of the alkynes.
In the present work, we report the hitherto unknown
molecular structure of the rhodium complexes 2, and
we have changed the reaction conditions in order to find
out about the potential catalytic activity of 1S and 1Se
in the oligomerization of the alkynes HCtC-CO2Me
and HCtC-Ph.
* Corresponding authors. Fax: (internat.) +49(0)921/552157. E-
mail: Max.Herberhold@uni-bayreuth.de; B.Wrack@uni-bayreuth.de.
(1) (a) Arnold, J . Progr. Inorg. Chem. 1995, 43, 353-417. (b)
Dilworth, J . R.; Hu, J . Adv. Inorg. Chem. 1993, 40, 411-459.
(2) (a) Herberhold, M.; J in, G.-X.; Yan, H.; Milius, W.; Wrackmeyer,
B. Eur. J . Inorg. Chem. 1999, 873-875. (b) Herberhold, M.; J in, G.-
X.; Yan, H.; Milius, W.; Wrackmeyer, B. J . Organomet. Chem. 1999,
587, 252-257.
Resu lts a n d Discu ssion
(3) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Angew.
Chem. 1999, 111, 3888-3890; Angew. Chem., Int. Ed. Engl. 1999, 38,
3689-3691.
Rea ction of Cp *Rh [S2C2(B10H10)] (1S) w ith Meth -
yl Acetylen e Ca r boxyla te. The results of this reaction
(4) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Chem. Eur.
J . 2000, 6, 3026-3032.
(5) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. Z. Anorg.
Allg. Chem. 2000, 626, 1627-1633.
(7) (a) Kalinin, V. N.; Usatov, A. V.; Zakharkin, L. I. Proc. Indian
Sci. Acad. 1989, 55, 293-317. (b) Zakharkin, L. I.; Kobak, V. V.;
Zhigareva, G. G. Russ. Chem. Rev. 1986, 55, 531-545. (c) Hoel, E. L.;
Hawthorne, M. F. J . Am. Chem. Soc. 1974, 96, 6770-6771.
(6) Herberhold, M.; Yan, H.; Milius, W.; Wrackmeyer, B. J . Orga-
nomet. Chem. 2000, 604, 170-177.
10.1021/om0003077 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/20/2000

4290 Organometallics, Vol. 19, No. 21, 2000
Herberhold et al.
Sch em e 1
carried out in dichloromethane at room temperature
have been described,3,4 and the products 4S, 5S, and
6S have been fully characterized. A dimer 2S (vide infra)
of a first addition product had been proposed on the
basis of the field desorption (FD) MS spectra, but there
had been insufficient other data for a reliable structural
assignment. The formation of 4S requires metal-induced
B-H activation7 and ortho-metalation (see also the
reaction of CpCo[S2C2(B10H10)] with alkynes8) in order
to arrive finally at the B(3/6)-disubstituted carborane
cage.3,4 The complexes 5S and 6S could be considered
as intermediates in the trimerization of HCtC-CO2-
Me. When the reaction of 1S with an excess of HCtC-
CO2Me was performed in toluene at 70 °C, none of these
products could be isolated. Instead, the alkyne was
converted into the isomeric trimers, the 1,3,5- and 1,2,4-
trisubstituted benzenes in a 1:1 ratio, and 1S was left
unchanged. Under the same conditions, the 16e complex
4S reacted with HCtC-CO2Me to give the benzene
derivatives. It is likely that the dimer 2S (vide infra)
as well as the complexes 5S and 6S are intermediates,
which can be isolated only under mild conditions. When
2S was isolated and then heated in toluene at 70°, the
major product was 1S along with traces of organic
material. Under the same conditions, in the presence
of an excess of HCtC-CO2Me, trimerization of the
alkyne took place, and the formation of 1S was observed
as well. Similarly, the reaction of 5S4 with an excess of
HCtC-CO2Me leads cleanly to the 1,3,5- and 1,2,4-
trisubstituted benzenes (ratio 1:1). The influence of the
solvent is remarkable, since the reaction of 1S with an
excess of HCtC-CO2Me in boiling chloroform leads in
high yield to the complex 4S,3 and benzene derivatives
are formed only in a small amount.
F igu r e 1. Molecular geometry of the dinuclear rhodium
complex 2Se. Selected bond lengths [pm] and angles
[deg]: Rh-ring centroid 190.8, Rh-C(4) 205.7(4), Rh-Se-
(1) 248.48(5), Rh-Se(2) 247.13(5), Se(1)-C(3) 192.2(3), Se-
(1)-C(1) 196.5(3), Se(2)-C(2) 193.8(4), C(1)-C(2) 165.5(5),
C(3)-C(4) 133.2(5), C(4)RhSe(1) 90.44(10), Se(1)Rh-
Se(2) 90.749(16), C(3)Se(1)Rh 104.38(10), C(1)Se(1)Rh
103.78(11), C(2)Se(2)Rh 103.12(11), C(3)C(4)Rh 120.2(3),
Se(1)C(3)C(4) 123.2(2), C(3)C(4)C(5) 119.0(3), C(5)C(4)Rh
120.5(2), Se(1)RhSe(2)/Se(1)C(1)C(2)Se(2) 159.2.
plexes with a Rh-B bond could be isolated (again in
contrast with the sulfur case), and there are selenium
complexes such as 3Se (similar to 5S), which, however,
differ from the sulfur analogues in the substituent
pattern at the CdC bond.5 A product 2Se, analogous to
2S, had not been well characterized except by a FD MS
spectrum indicating the presence of a dinuclear com-
plex.5 This product 2Se could now be crystallized and
its molecular structure determined (Figure 1). It is
assumed that the structure of 2S is similar to that of
2Se. In contrast, the products of the reactions of 1S or
1Se with dimethyl acetylene dicarboxylate, MeO2C-
CtC-CO2Me, are mononuclear complexes,3-5 for which
the molecular structure has been established in the case
of 9S3 (Scheme 1).
Rea ction of Cp *Rh [Se2C2(B10H10)] (1Se) w ith
Meth yl Acetylen e Ca r boxyla te. The reaction of 1Se
with HCtC-CO2Me under mild conditions leads to
products that differ in their structures considerably
from those that were obtained starting from 1S.5 Thus,
8Se is a final product, whereas 8S was not even detected
in the reaction mixtures. Furthermore, selenium com-
Heating the pure dimer 2Se in toluene solution at 70
(8) Khim, D.-H.; Ko, J .; Park, K.; Cho, S.; Kang, S. O. Organo-
metallics 1999, 18, 2738-2740.
°C led exclusively to the known complex 8Se5 as a result

Reactivity of Cp*Rh 16e Half-Sandwich Complexes
Organometallics, Vol. 19, No. 21, 2000 4291
Sch em e 2
of metal-induced B-H activation followed by a number
of additional steps. Heating of 2Se under the same
conditions in the presence of an excess of HCtC-CO2-
Me afforded the isomeric trisubstituted benzene deriva-
tives in a 1:1 ratio together with the starting complex
1Se. When 1Se was treated with an excess of HCtC-
CO2Me in toluene at 70 °C, again the benzene deriva-
tives were formed, and 8Se or precursors were not
detected. These results are summarized in Scheme 2.
Another product, isolated from the reaction of 1Se
with HCtC-CO2Me under mild conditions, is the
complex 3Se, for which the structure had been proposed
on the basis of NMR data.5 By repeated crystallization
of 3Se suitable crystals for X-ray diffraction analysis
were obtained, and the molecular structure is shown in
Figure 2, confirming the previous NMR spectroscopic
evidence. By heating of 3Se in the presence of an excess
of HCtC-CO2Me in toluene at 70 °C, clean formation
of the trimethyl-1,3,5- and trimethyl-1,2,4-benzene-
tricarboxylates (ratio 1:1) was observed together with
the parent complex 1Se (Scheme 3).
F igu r e 2. Molecular geometry of the rhodium complex
3Se. Selected bond lengths [pm] and angles [deg]:
Rh-ring centroid 186.5, Rh-C(6) 203.6(4), Rh-Se(1)
238.33(5), Rh-Se(2) 247.06(6), Se(1)-C(3) 190.0(4), Se(1)-
C(1) 197.4(4), Se(2).C(2) 194.5(4), C(1)-C(2) 165.3(5), C(3)-
C(4) 134.0(6), C(4)-C(5) 143.8(6), C(5)-C(6) 135.0(5),
C(6)RhSe(1) 93.15(11), C(6)RhSe(2) 86.59(11), Se(1)-
RhSe(2) 93.002(18), C(3)Se(1)C(1) 101.07(16), C(3)Se(1)-
Rh 109.54(12), C(1)Se(1)Rh 106.51(11), C(2)Se(2)Rh
102.68(12), Se(1)EhSe(2)/Se(1)C(1)C(2)Se(2) 172.3, Se(1)-
RhC(6)/C(3)C(4)C(5) 158.3.
When a mixture of 8Se and HCtC-CO2Me (excess)
is heated in toluene at 70 °C, the 1,3,5- and 1,2,4-
trisubstituted benzenes are also formed in a 1:1 ratio.
This is accompanied by decomposition of 8Se into
unidentified products. The molecular structure of 8Se
(Scheme 1) shows that a coordinative SefRh bond is
present as part of a three-membered ring.5 Opening of
this bond would lead to a 16e complex which can be
considered as an active catalyst in the trimerization.
Rea ction of Cp *Rh [E2C2(B10H10)] (1S, 1Se) w ith
P h en yla cetylen e. The reaction of 1S with an excess
of HCtC-Ph under mild conditions has been de-
scribed.6 In addition to complexes with rhodium-boron
bonds, the rhodium complex 7S (analogous to 8Se) is
one of the final products (Scheme 1). None of these
products was obtained when the reaction of 1S with an
excess of HCtC-Ph was carried out in toluene at 70
°C. The products were the 1,3,5- and 1,2,4-triphenyl-
benzenes, and 1S remained in the mixture. The same
result was obtained by heating of a mixture of 7S and
HCtC-Ph (excess) in toluene at 70 °C; this reaction
was accompanied by decomposition of 7S. Cyclotrimer-
It appears that complexes such as 3Se, 5S, and 6S
must be regarded as intermediates in the process of
alkyne cyclotrimerization, and the same is true for 2S
and 2Se. The catalyst in each case is the 16e complex
1S or 1Se, which is formed once the intermediates react
with the alkyne. Again, in the case of 1Se, the influence
of the solvent is noteworthy: in boiling chloroform, the
reaction of 1Se with an excess of HCtC-CO2Me affords
mainly 8Se and 3Se.

4292 Organometallics, Vol. 19, No. 21, 2000
Herberhold et al.
Sch em e 3
ization of HCtC-Ph proved to be already prominent
in the reaction of 1Se with an excess of HCtC-Ph
under mild conditions. In toluene at 70 °C, the trimer-
ization of the alkyne was the only active process.
Mech a n istic Im p lica tion s. The mechanism pro-
posed previously for the reactions of some half-sandwich
16e metal o-carboranedichalcogenolato complexes with
methyl acetylene carboxylates3-5 or phenylacetylene6 is
confirmed and complemented by the present results.
The alternative to metal-induced B-H activation turns
out to be the catalytic cyclotrimerization of the alkynes,
a well-known process homogeneously or heteroge-
neously catalyzed by many transition metal com-
plexes.9-15 In the present cases, for both alternatives,
the primary step of the reactions is the addition of the
alkyne to the 16e metal center,13-15 followed by inser-
tion16 into one of the Rh-E bonds. In contrast with the
mononuclear complexes 9 obtained with MeO2C-CtC-
CO2Me (see Scheme 1 for the structure of 9S), it proved
possible, in the case of HCtC-CO2Me under mild
conditions, to isolate dinuclear complexes of type 2, of
which 2Se could be characterized both by X-ray analysis
in the solid state and by 77Se NMR in solution. The
effective catalysts for trimerization of the alkynes are
16e complexes such as 1S or 1Se. Catalytic effectivity
appears to be a general function of these 16e complexes
since 4S (Scheme 1) is also active. The dinuclear
complexes 2, in which already two alkene units bridge
the rhodium and one of the chalcogen atoms, are
intermediates in the trimerization of the alkynes.
NMR Sp ectr oscop ic Resu lts. The NMR data of the
complexes shown in Scheme 1 have been reported
previously3-6 and served efficiently to establish the
presence or absence of these species in the reactions of
1S or 1Se with HCtC-CO2Me and HCtC-Ph under
different conditions (boiling CHCl3 or toluene at 70 °C).
It was important to obtain the 77Se NMR spectrum17 of
the sparingly soluble 2Se in solution in order to prove
its dimeric nature or to find evidence for monomer-
dimer equilibria. The 77Se NMR spectrum shows decep-
tively simple splittings into a doublet (δ77Se 469.3) and
a triplet (δ77Se 695.7), respectively. The “doublet” is
assigned to Se(2) as the A-part of an AXX′ spin-system
1
with J (103Rh(X),77Se(2)) ≈ 46.0 Hz and negligibly small
coupling constants J (103Rh(X′),Se(2)) and J (103Rh(X),-
103Rh(X′)). The “triplet” belongs to Se(1), again as the
A-part of an AXX′ spin-system with 1J (103Rh(X),-
77Se(1)), nonnegligible magnitude of 3J (103Rh(X′),-
77Se(1))trans [∑(1J ) + (3J ) ) 29.0 Hz], and a negligibly
small coupling constant J (103Rh(X),103Rh(X′)). Thus, the
dimeric structure of 2Se, determined for the solid state,
is retained in solution.
X-r a y Str u ctu r a l An a lyses of th e Rh od iu m Com -
p lexes 2Se a n d 3Se. The molecular structures of the
rhodium complexes 2Se and 3Se are shown in Figures
1 and 2, respectively. The eight-membered ring in 2Se
adopts a steplike structure, in which the four atoms
C(3), Se(1), Rh, C(4A) [and because of symmetry also
C(4), Rh(A), Se(1A), C(3A)] form a plane within experi-
mental error. According to the bond angles at the CdC
bonds, the E-configuration does not induce significant
strain. In 3Se, the five-membered ring Se(1)RhSe(2)C-
(2)C(1) is less folded than in 2Se. The six-membered
ring Se(1)RhC(6)C(5)C(4)C(3) in 3Se deviates markedly
from a planar arrangement. In both complexes 2Se and
3Se, the carborane cage appears to be hardly distorted,
as shown by the bond lengths dC(1)C(2) 165.5(5) and 165.3-
(5) Å, which are in the range typical of o-carborane
derivatives.18 The prominent structural features of 3Se
are very similar to those of the related sulfur complexes
5S and 6S.4
(9) Reppe, W.; Schweckendiek, W. J . Liebigs Ann. Chem. 1948, 560,
104-116.
(10) (a) Qu, J .-P.; Masui, D.; Ishi, Y.; Hidai, M. Chem. Lett. 1998,
1003-1004. (b) Hashizume, K.; Mizobe, Y.; Hidai, M. Organometallics
1995, 14, 5367-5376. (c) Bohanna, C.; Esteruelas, M. A.; Herrero, J .;
Lopez, A. M.; Oro, L. A. J . Organomet. Chem. 1995, 498, 199-206. (d)
Amer, I.; Bernstein, M. E.; Blum, J .; Vollhardt, K. P. C. J . Mol. Catal.
1990, 60, 313-321. (e) Borrini, A.; Diversi, P.; Ingrosso, G.; Lucherini,
A.; Serra, G. J . Mol. Catal. 1985, 30, 181-195.
(11) (a) Sigman, M. S.; Fatland, A. W.; Eaton, B. E. J . Am. Chem.
Soc. 1998, 120, 5130-5131. (b) Baidossi, W.; Goren, N.; Blum, J .;
Schumann, H.; Hemling, H. J . Mol. Catal. 1993, 85, 153-162.
(12) (a) Choi, K. S.; Park, M. K.; Han, B. H. Bull. Korean Chem.
Soc. 1998, 19, 1257-1261. (b) Kumar, V. G.; Shoba, T. S.; Rao, K. V.
C. Tetrahedron Lett. 1985, 6245-6248. (b) Schumann, H.; Rodewald,
G. J . Chem. Res., Synop. 1982, 210-211.
(13) (a) Grotjahn, D. B. In Comprehensive Organometallic Chemistry
II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L. E., Eds.;
Pergamon: Tarrytown, NY, 1995; Vol. 12, pp 741-770. (b) Schore, N.
E. In Comprehensive Organic Synthesis; Trost, B. M., Fleming, I.,
Paquette, L. A., Eds.; Pergamon: Elmsford, NY, 1991; Vol. 5, pp 1129-
1162. (c) Kochi, J . K. Organometallic Mechanism and Catalysis;
Academic Press: New York, 1978; pp 428-432. (d) Collman, J . P. Acc.
Chem. Res. 1968, 1, 136-143.
(14) (a) Werner, H.; Zolk, R. Chem. Ber. 1987, 120, 1003-1010. (b)
McAlister, D. R.; Bercaw, J . E.; Bergman, R. G. J . Am. Chem. Soc.
1977, 99, 6-1668. (c) Moseley, K.; Maitlis, P. M. J . Chem. Soc., Dalton
Trans. 1974, 169-175. (d) Wakatsuki, Y.; Kuramitsu, T.; Yamazaki,
H. Tetrahedron Lett. 1974, 4549-4552. (e) Eisch, J . J .; Galle, J . E. J .
Organomet. Chem. 1975, 96, C23-C26.
(15) Colborn, R. E.; Vollhardt, K. P. C. J . Am. Chem. Soc. 1981, 103,
6259-6261.
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Exp er im en ta l P a r t
Gen er a l a n d Sta r tin g Ma ter ia ls. The starting complex
19
[Cp*RhCl2]2 and the 16e complexes Cp*Rh[E2C2(B10H10)] [E
(17) For reviews on 77Se NMR see: (a) Klapo¨tke, T. M.; Broschag,
M. Compilation of Reported 77Se NMR Chemical Shifts; Wiley: Chich-
ester, 1996. (b) Duddeck, H. Prog. NMR Spectrosc. 1995, 27, 1-323.
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234.

Reactivity of Cp*Rh 16e Half-Sandwich Complexes
Organometallics, Vol. 19, No. 21, 2000 4293
) S (1S), Se (1Se)] were obtained as described.2 Methyl
acetylene carboxylate and phenylacetylene were used as
commercial products without further purification. NMR mea-
surements: Bruker ARX 250 and DRX 500 spectrometers;
chemical shifts are given with respect to CHCl3/CDCl3 (δ1H )
7.24; δ13C ) 77.0) or CDHCl2 (δ1H ) 5.33, δ13C ) 53.8),
external Et2O-BF3 (δ11B ) 0 for ¥(11B) ) 32.083971 MHz),
external Me2Se (δ77Se ) 0 for ¥(77Se) ) 19.071523 MHz).
Mass spectra: VARIAN MAT CH7 for EI-MS (70 eV), direct
inlet; VARIAN MAT 311A for FD-MS. IR spectra: Perkin-
Elmer 983 G. Melting or decomposition points are uncor-
rected.
Hea tin g of 2S a n d 2Se in Tolu en e a t 70 °C. Suspensions
of the complexes 2S (10.6 mg, 0.01 mmol) or 2Se (12.4 mg,
0.01 mmol) in toluene (15 mL) were heated at 70 °C for 24 h.
In the case of 2S a green solution was obtained, and the 1H
NMR spectrum indicated the presence of the 16e complex
Cp*Rh[S2C2(B10H10)] (1S) as the main component. In the case
of 2Se, a deep brown solution was obtained, and after removing
the solvent a product was left for which the NMR spectra
showed complete agreement with known data for 8Se.5
Hea tin g of 2S, 2Se w ith Meth yl Acetylen e Ca r boxyla te
in Tolu en e a t 70 °C. The complex 2S (5.3 mg, 5 × 10-3 mmol)
or 2Se (6.2 mg, 5 × 10-3 mmol) was added to a solution of
methyl acetylene carboxylate (0.5 mL, 5.9 mmol) in toluene
(15 mL). Then the mixtures were heated at 70 °C for 24 h.
The resulting deep-brown solutions were evaporated under
reduced pressure until viscous residues were left. 1H NMR
spectra showed these to consist of a mixture of trimethyl-1,2,4-
and trimethyl-1,3,5-benzenetricarboxylates in an approximate
ratio of 1:1, along with a small amount of the corresponding
16e complex 1S or 1Se, respectively.
Rea ction of 4S w ith Meth yl Acetylen e Ca r boxyla te in
Tolu en e a t 70 °C. The complex 4S3 (12.2 mg, 0.02 mmol) was
dissolved in toluene (15 mL), and methyl acetylene carboxylate
(0.5 mL, 5.9 mmol) was added. The mixture was heated for
24 h at 70 °C until it turned to a deep-red solution, which was
evaporated to give a viscous residue. The 1H NMR spectra
showed the presence of a mixture of trimethyl-1,2,4- and
trimethyl-1,3,5-benzenetricarboxylates in an approximate ratio
of 1:1. The 1H(Cp*) NMR signal of 4S was still detectable,
although it was very weak, indicating that decomposition of
4S occurred to some extent in the course of the reaction.
Rea ction s of 3Se a n d 5S w ith Meth yl Acetylen e Ca r -
boxyla te in Tolu en e a t 70 °C. The complex 5S4 (15.3 mg,
0.025 mmol) or 3Se5 (15.6 mg, 0.025 mmol) was added to a
solution of methyl acetylene carboxylate (0.5 mL, 5.9 mmol)
in toluene (15 mL). Then the mixtures were heated at 70 °C
for 24 h. The resulting dark-red solutions were evaporated to
give a viscous residue. The 1H NMR spectra showed the
presence of trimethyl-1,2,4- and trimethyl-1,3,5-benzenetri-
carboxylates in 1:1 ratio and also the complexes 1S and 1Se,
respectively.
Syn th esis of 2S. Methyl acetylene carboxylate (0.38 mL,
4.5 mmol) was added to the green solution of 1S (200 mg, 0.45
mmol) in CH2Cl2 (30 mL), and the mixture was stirred for 3
days at ambient temperature to give a brown solution. After
removing the solvent, chromatography of the residue on silica
gel (Merck, Kieselgel 60) with elution by CH2Cl2 gave 2S as
an orange-red solid (11.9 mg, 5%; mp ) 190 °C (dec)). 1H NMR
(CDCl3): δ 1.71 (s, 15H, Cp*), 3.61 (s, 3H, OMe), 5.11 (s, 1H,
CH). 11B NMR (CDCl3): δ -9.5, -5.4. 13C NMR (CDCl3): δ
9.6 (Cp*), 51.4 (OMe), 91.8 and 94,9 (C2B10H10), 101.3
(1J (103Rh,13C) ) 5.7 Hz, Cp*), 117.1 (C-S), 168.8 (1J (103Rh,13C)-
)37.0 Hz, C-Rh), 171.9 (CdO). IR (KBr) [cm-1]: νB-H ) 2572,
2593, νCOOMe ) 1698. EI-MS (70 eV): 613 (4%, M+ - (Cp*Rh-
1
(S2C2B10H10))), 529 (25%,
10H10)]+.
Syn th esis of 2Se. Methyl acetylene carboxylate (0.32 mL,
/
M+), 444 (100%, [Cp*Rh(S2C2-
2
B
3.7 mmol) was added to the suspension of 1Se (200 mg, 0.37
mmol) in CH2Cl2 (30 mL). Within several hours at ambient
temperature the mixture changed to a red solution. After the
solvent had been removed, the residue was chromatographed
on a column of silica gel. Elution with hexane/CH2Cl2 (4:3) gave
2Se as an orange-red solid (23 mg, 10%; mp ) 182 °C (dec)).
1H NMR (CDCl3): δ 1.76 (s, 15H, Cp*), 3.60 (s, 3H, OMe), 5.46
(s, 1H, CH). 11B NMR (80.1 MHz, CDCl3): δ -7.6, -4.4. 13C
NMR (62.9 MHz, CDCl3): δ 9.7 (Cp*), 51.6 (OMe), 100.4
(1J (103Rh,13C) ) 4.7 Hz, Cp*), 115.1 (C-Se), 172.5 (CdO). IR
(KBr) [cm-1]: νB-H ) 2592, νCOOMe ) 1687. EI-MS (70 eV): 707
(5%, [M - Cp*Rh(Se2C2B10H10)]+, 622 (18%, 1/2 M+), 539 (100%,
[Cp*Rh(Se2C2B10H10)]+).
Rea ction s of 7S w ith P h en yla cetylen e a n d of 8Se w ith
Meth yl Acetylen e Ca r boxyla te in Tolu en e a t 70 °C.
Toluene solutions (15 mL) of 7S6 (10.9 mg, 0.02 mmol) and
phenylacetylene (0.5 mL, 4.6 mmol) or 8Se5 (12.4 mg, 0.02
mmol) and methyl acetylene carboxylate (0.5 mL, 5.9 mmol),
respectively, were heated at 70 °C for 24 h. The resulting dark-
red solutions were evaporated to give viscous residues. 13C
NMR showed in the case of 7S that a mixture of 1,2,4-
triphenylbenzene and 1,3,5-triphenylbenzene was present
(ratio close to 1:1). 13C NMR (62.9 MHz, CDCl3, 22 °C; all 8
signals for quaternary carbon atoms are resolved and 12 of
16 signals for the o-, m, and p-CH carbon atoms): δ13C 142.3,
141,4, 141.0, 141.1, 140.9, 140.5, 140.3, 139.5 (quaternary C);
131.1, 129.82, 129.84, 129.4, 128.6, 128.3, 127.85, 127.89,
127.4, 126.6, 126.5, 126.1 (o-, m, p-CH). In the case of 8Se, a
mixture of trimethyl-1,2,4- and trimethyl-1,3,5-benzenetricar-
boxylates was present in an approximate ratio of 1:1.
Rea ction s of 1S a n d 1Se w ith P h en yla cetylen e in
Tolu en e a t 70 °C. Phenylacetylene (0.5 mL, 4.6 mmol) was
added to 1S (22.2 mg; 0.05 mmol) or 1Se (27 mg, 0.05 mmol)
in toluene (15 mL), and the mixtures were heated at 70 °C for
17 h to give dark-red solutions. After removing the solvent in
vacuo, viscous residues were left. According to the 13C NMR
spectra, the residues contained 1,2,4- and 1,3,5-triphenyl-
benzenes in an approximate ratio of 1:1, a small amount of
unreacted phenylacetylene, and the respective 16e complex.
The EI-MS showed the molecular ion peak at m/e 306 (100%).
Cr ysta l Str u ctu r e An a lyses of 2Se a n d 3Se. The reflec-
tion intensities were collected on a Siemens P4 diffractometer
(Mo KR radiation, λ ) 71.073 pm, graphite monochromated).
Rea ction s of 1S a n d 1Se w ith Meth yl Acetylen e Ca r -
boxyla te in Boilin g CHCl3. Methyl acetylene carboxylate
(0.5 mL, 5.9 mmol) was added to 0.05 mmol of 1S (22.2 mg) or
1Se (27 mg) in CHCl3 (20 mL). Then the mixtures were heated
at reflux for 24 h. After removing the solvent and unreacted
methyl acetylene carboxylate, the compositions of the residues
were checked by 1H NMR. For the reaction with 1S, the
residue contained 4S, trimethyl-1,2,4-benzenetricarboxylate,
and trimethyl-1,3,5-benzenetricarboxylate in
a ratio of
2.5:1:0.8. For the reaction with 1Se, the residue contained 8Se,
3Se, trimethyl-1,2,4-benzenetricarboxylate, and trimethyl-
1,3,5-benzenetricarboxylate in a ratio of 15:5:1:1. 1H NMR (250
MHz, CDCl3): δ1H 8.39 (d, J (H,H) 1.6 Hz, 1H, C(3)-H), 8.17
(dd, J (H,H) 1.6 and 8.0 Hz, 1H, C(5)-H), 7.72 (d, J (H,H) )
8.0 Hz, 1H, C(6).H), 3.93 (s, 3H, OMe), 3.90 (s, 6H, OMe), 1,2,4-
isomer; 8.82 (s, 3H, CH), 3.95 (s, 9H, OMe) 1,3,5-isomer. The
identification of 4S,3 3Se, and 8Se5 was based on the com-
parison of NMR data.
Rea ction s of 1S a n d 1Se w ith Meth yl Acetylen e Ca r -
boxyla te in Tolu en e a t 70 °C. Methyl acetylene carboxylate
(0.5 mL, 5.9 mmol) was added to 0.05 mmol of 1S (22.2 mg) or
of 1Se (27 mg) in toluene (15 mL). Then the mixtures were
heated at 70 °C for 24 h, and the color of the solutions turned
dark red. After removing the solvent the residues were checked
1
by H NMR. The residues contained the trimethyl-1,2,4- and
trimethyl-1,3,5-benzenetricarboxylates in a ratio close to 1:1,
and the respective 16e complex 1S or 1Se, respectively, was
still present (identified by the typical 1H NMR signal of the
Cp* group). EI-MS showed the molecular ion peak at m/e )
252.

4294 Organometallics, Vol. 19, No. 21, 2000
Herberhold et al.
Structure solution and refinements were carried out with the
program package SHELXTL-PLUS V.5.1. The temperature for
all structure determinations was 296 K. All non-hydrogen
atoms were refined with anisotropic temperature factors. The
hydrogen atoms at the boron atoms were located from differ-
ence Fourier syntheses. The remaining hydrogen atoms are
on calculated positions. All hydrogen atoms were refined
applying the riding model with fixed isotropic temperature
factors.
Cr ysta l str u ctu r e of 2Se: C32H58B20O4Se4Rh2, red plate
with dimensions 0.18 × 0.15 × 0.08 mm crystallizes in the
triclinic space group P1h with the lattice parameters a )
1154.19(6), b ) 1162.08(8), c ) 1319.05(8) pm, R ) 104.643-
(5)°, â ) 105.382(4)°, γ ) 113.184(4)°, V ) 1435.06(15) × 106
pm3, Z ) 1, µ ) 3.427 mm-1; 5639 reflections collected in the
range 3° e 2ϑ e 50°, 4850 reflections independent, 4156
assigned to be observed [I > 2σ(I)], full-matrix least-squares
refinement against F2 with 314 parameters converged at R1/
wR2 values of 0.028/0.073; empirical absorption correction
(Ψ-scans) resulted in min./max. transmission factors of 0.7147/
0.9985, the max./min. residual electron density was 0.59/-0.46
10-6 e pm3.
reflections independent, 3958 assigned to be observed [I >
2σ(I)], full-matrix least-squares refinement against F2 with 335
parameters converged at R1/wR2 values of 0.032/0.073, em-
pirical absorption correction (Ψ-scans) resulted in min./max.
transmission factors of 0.2324/0.2721, the max./min. residual
electron density was 0.507/-0.285 10-6 e pm-3
.
Su p p or tin g In for m a tion Ava ila ble: Crystallographic
data (excluding structure factors) for the structures reported
in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publications
no. CCDC-142272 (2Se) and CCDC-142271 (3Se). Copies of
the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax (internat.): +44
(0)1223/336033; e-mail: deposit@ccdc.cam.ac.uk].
Ack n ow led gm en t. Support of this work by the
Deutsche Forschungsgemeinschaft and the Fonds der
Chemischen Industrie is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Details about the
X-ray crystal structures, including tables of crystal data and
structure refinement, atomic coordinates, bond lengths and
angles, and anisotropic displacement parameters for 2Se and
3Se, are available free of charge via the Internet at
http://pubs.acs.org.
Cr ysta l Str u ctu r e of 3Se: C20H33B10O4Se2Rh, dark-red
prism with dimensions 0.18 × 0.13 × 0.10 mm crystallizes in
the monoclinic space group P21/n with the lattice parameters
a ) 960.99(9), b ) 3057.47(14), c ) 991.38(8) pm, â )
91.076(7)°, V ) 2912.4(4) 106 pm3, Z ) 4, µ ) 3.112 mm-1
;
6316 reflections collected in the range 3° e 2ϑ e 50°, 5101
OM0003077