Synthesis of (s-trans-η4-butadiene)tantalocene cation and its CC-coupling reactions with ketones, nitriles, and alkynes

Article abstract of DOI:10.1021/om980576l

(η⁴-Butadiene)(η⁵-cyclopentadienyl)tantalu m dichloride (6), synthesized by treatment of CpTaCl₄ (5) with (butadiene)magnesium (7), was treated with 2 molar equiv of sodium cyclopentadienide to yield Cp₃Ta(butadiene) (9). The spectroscopic analysis revealed the (η⁴-Cp)₂(η¹-Cp) (η²-C₄H₆)Ta structure of 9. Treatment of 9 with 1 molar equiv of the salt [(Cp₂Zr-CH₃) ⁺(CH₃B(C₆F₅)₃) ^-] (11) resulted in the clean transfer of a cyclopentadienide ligand from tantalum to zirconium with formation of the neutral zirconium compound Cp₃-Zr-CH₃ (12) and the cation Cp₂Ta(butadiene) ⁺ (10; with CH₃B(C₆F₅) ₃^- counteranion). The spectroscopic characterization and an X-ray crystal structure analysis has revealed that 10 is a cationic (s-trans-η⁴-butadiene)bis(η⁵-cyclopentadienyl) tantalum complex. It reacts cleanly with a variety of ketones at 60°C to form the respective 7,7-disubstituted tetrahydrotantalaoxepines 13. These cationic seven-membered metallacyclic σ-allyl complexes undergo a rapid topomerization process on the NMR time scale (ΔG?_top ≈ 12 kcal/mol^-1). Organic nitriles add similarly at 60°C to the (s-trans-η⁴-butadiene)tantalocene cation (10) to yield the respective 7-substituted 3,4-dihydrotantala-6H-azepines (14) that exhibit a similar dynamic NMR behavior due to conformational equilibration. Two examples of the seven-membered σ-allyl metallacyclic cation complexes 14 were characterized by X-ray crystal structure analyses (14a, R = CH₃, and 14d, R = CH₂-p-C₆H₄CH₃). In contrast, 2-butyne adds to the (s-trans-η⁴-butadiene)tantalocene cation in a 1:1 ratio to yield the corresponding metallacyclic (π-allyl)metallocene cation complex 15a (characterized by X-ray diffraction). The addition of 1-pentyne gave a 60:40 mixture of the respective regioisomers 15b and 15c, exhibiting the n-C₃H₇ substituent at the ring position C5 and C6, respectively.

Full text of DOI:10.1021/om980576l

5746
Organometallics 1998, 17, 5746-5757
Syn th esis of (s-tr a n s-η4-Bu ta d ien e)ta n ta locen e Ca tion
a n d Its CC-Cou p lin g Rea ction s w ith Keton es, Nitr iles,
a n d Alk yn es†
Hans Christian Strauch, Gerhard Erker,* and Roland Fro¨hlich
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received J uly 8, 1998
(η4-Butadiene)(η5-cyclopentadienyl)tantalum dichloride (6), synthesized by treatment of
CpTaCl4 (5) with (butadiene)magnesium (7), was treated with 2 molar equiv of sodium
cyclopentadienide to yield Cp3Ta(butadiene) (9). The spectroscopic analysis revealed the
(η5-Cp)2(η1-Cp)(η2-C4H6)Ta structure of 9. Treatment of 9 with 1 molar equiv of the salt
[(Cp2Zr-CH3)+(CH3B(C6F5)3)-] (11) resulted in the clean transfer of a cyclopentadienide
ligand from tantalum to zirconium with formation of the neutral zirconium compound Cp3-
Zr-CH3 (12) and the cation Cp2Ta(butadiene)+ (10; with CH3B(C6F5)3- counteranion). The
spectroscopic characterization and an X-ray crystal structure analysis has revealed that 10
is a cationic (s-trans-η4-butadiene)bis(η5-cyclopentadienyl)tantalum complex. It reacts cleanly
with a variety of ketones at 60 °C to form the respective 7,7-disubstituted tetrahydrotan-
talaoxepines 13. These cationic seven-membered metallacyclic σ-allyl complexes undergo a
rapid topomerization process on the NMR time scale (∆Gqtop ≈ 12 kcal/mol-1). Organic nitriles
add similarly at 60 °C to the (s-trans-η4-butadiene)tantalocene cation (10) to yield the
respective 7-substituted 3,4-dihydrotantala-6H-azepines (14) that exhibit a similar dynamic
NMR behavior due to conformational equilibration. Two examples of the seven-membered
σ-allyl metallacyclic cation complexes 14 were characterized by X-ray crystal structure
analyses (14a , R ) CH3, and 14d , R ) CH2-p-C6H4CH3). In contrast, 2-butyne adds to the
(s-trans-η4-butadiene)tantalocene cation in a 1:1 ratio to yield the corresponding metallacyclic
(π-allyl)metallocene cation complex 15a (characterized by X-ray diffraction). The addition
of 1-pentyne gave a 60:40 mixture of the respective regioisomers 15b and 15c, exhibiting
the n-C3H7 substituent at the ring position C5 and C6, respectively.
In tr od u ction
diene) framework. Theoretical work has shown that the
very special bonding features of the bent metallocenes
result in the ability to form stable s-trans-η4-conjugated
diene complexes so easily at their frameworks.3 All
three valence orbitals of, for example, the Cp2Zr unit
are oriented in the major plane bisecting the Cp-Zr-
Cp angle. The more linearly expanded π-system of the
s-trans-butadiene ligand binds quite favorably to the
central metal center using these orbitals. In fact, the
s-cis-butadiene ligand also coordinates strongly to Cp2-
Zr and gives rise to the formation of the respective (s-
cis-C4H6)ZrCp2 isomer, found in a 1:1 ratio with its (s-
trans-C4H6)ZrCp2 congener under equilibrium conditions
at ambient temperature, but cis-1 exhibits a σ2,π-type
metallacyclic structure.1
(Butadiene)zirconocene was the first system where a
η4-coordination mode of an s-trans-conjugated diene was
shown to be present in a stable mononuclear organo-
metallic complex.1 Bonding of all four carbon atoms of
the C4H6 ligand to a single transition metal center
requires some distortion of the butadiene framework
from planarity, but interaction of the conjugated diene
π-system with the group 4 bent metallocene valence
orbitals2 has provided a more than ample compensation
for the strain introduced by constructing the Cp2M(1,3-
* Corresponding author. E-mail: erker@uni-muenster.de. Tel: +49
251 83 33221. Fax: +49 251 83 36503.
† Dedicated to Professor Carl Kru¨ger on the occasion of his 65th
birthday.
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10.1021/om980576l CCC: $15.00 © 1998 American Chemical Society
Publication on Web 11/25/1998

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5747
(Butadiene)zirconocene has been used extensively as
an organometallic butadiene-dianion equivalent. It
undergoes a variety of template reactions in the course
of which organic or organometallic reagents are CC-
coupled with the terminal atoms of the C4 chain.4
Metallacyclic allyl complexes (2-4) are the primary
products of these synthetically useful template cou-
plings. Many specific examples were isolated. In some
cases the mutual interconversion of the (allyl)metal-
locene isomers was followed experimentally when syn-
thetic pathways to the thermodynamically favored final
products were mechanistically investigated.5 Also, the
(conjugated diene) group 4 metallocene complexes have
successfully been used as precursors for very active
single component metallocene Ziegler catalysts.6
of cases, although this bonding mode still has to be
regarded as not frequently encountered.7 The best
chances of observing such species appear to be with
metal complex frameworks that resemble the unique
Cp2M bent metallocene situation electronically. This
is mostly achieved by selecting a specific d-block element
and then attaching to it ligand systems that in their
combination introduce a similar situation as found at
the group 4 metallocenes.8 Nakamura et al. have
successfully used the neutral CpM(5)(η4-butadiene) unit
for this purpose to which an additional (s-trans-η4-
butadiene) ligand has been coordinated.9
We thought of a different way of effecting a close
group 4 metallocene analogy, which simply involves
substitution of the group 4 metal by a group 5 metal
atom in the center of the metallocene. If care is taken
that a resulting stable system is cationic, then a Cp2M-
+
(5)X2 system is obtained that should be very closely
related to the neutral Cp2M(4)X2 bent metallocene
systems. We have developed synthetic pathways to
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5748 Organometallics, Vol. 17, No. 26, 1998
Strauch et al.
such Cp2M(5)(butadiene)+ complexes. Here we describe
as a first example the corresponding tantalum sys-
tem,10,11 which should be isolobal to (butadiene)zir-
conocene or -hafnocene12 and should exhibit a related
structural chemistry and undergo CC-coupling reactions
similar to these systems, except that the typical bent
metallocene chemistry would be carried out at a mono-
cation stage.13
Resu lts a n d Discu ssion
Syn th esis of Cp 2Ta (bu ta d ien e) Ca tion . We chose
CpTaCl2(butadiene) (6) as the starting material of our
synthesis. Complex 6 was prepared by treatment of
CpTaCl4 (5)14 with the oligomeric (butadiene)magne-
sium reagent 7,15 as previously described by A. Naka-
mura et al.9,16 Complex 6 contains an s-cis-η4-butadiene
ligand. We first tried to substitute one of the chloride
ligands in 6 selectively by cyclopentadienide. In a NMR
experiment this was actually achieved, but in experi-
ments on a preparative scale this reaction was hard to
control in our hands to yield Cp2TaCl(butadiene) (8)
sufficiently pure. We, therefore, treated CpTaCl2-
(butadiene) with two molar equivalents of sodium
cyclopentadienide. This resulted in the formation of
tris(cyclopentadienyl)Ta(butadiene) (9), which was iso-
lated in ca. 45% yield as a red-brown amorphous solid.
A thorough NMR analysis, including TOCSY-NMR
of the separated spin systems, has revealed that com-
plex 9 contains a η2-coordinated butadiene ligand
(Figure 1).17 The C4H6 ligand shows four 13C NMR
resonances at δ 24.0 (C1), 36.1 (C2), 149.0 (C3), and
F igu r e 1. 1H NMR TOCSY spectra of 9: (top) η1-C5H5
ligand (signal at δ 3.74 (5-H) was irradiated); (center) η2-
butadiene ligand (signal at δ 1.11 (1-H) was irradiated);
(bottom) complete 1H NMR spectrum (600 MHz, 298 K,
THF-d8).
1-H′), 2.31 (2-H), 6.06 (3-H), 4.21 and 4.54 (4-H, 4-H′).
In 9 the three cyclopentadienides are not equal. Two
of them are η5-coordinated, and they are diastereotopic
(1H NMR in THF-d8: δ 5.30 (s, 5H) and 4.51 (s, 5H)).
The remaining cyclopentadienide is σ-bonded. It ex-
1
hibits five separate H/13C NMR methine resonances (δ
6.89, 6.67, 6.21, 6.13, 3.74/145.5, 145.4, 121.1, 120.8,
43.3 ppm). Thus, complex 9 is to be characterized as
bis(η5-cyclopentadienyl)(η1-cyclopentadienyl)(η2-butadi-
ene)tantalum.19
1
104.9 (C4),18 and it features a H NMR six-spin system
The presence of a σ-cyclopentadienyl ligand in 9 was
fortunate because this should facilitate the Cp-anion
abstraction that was necessary to convert 9 to the Cp2-
Ta(butadiene)+ cation (10). Actually, treatment of 9
with butadiene hydrogen signals at δ 1.11, 1.51 (1-H,
(10) For another electronically equivalent approach see: Sperry, C.
K.; Rodriguez, G.; Bazan, G. C. J . Organomet. Chem. 1997, 548, 1.
(11) Thiele, K.-H.; Kubak, W.; Sieler, J .; Borrmann, H.; Simon, A.
Z. Anorg. Allg. Chem. 1990, 587, 80.
20,21
with the strong organometallic Lewis acid B(C6F5)3
eventually resulted in the formation of (η4-butadiene)-
bis(η-cyclopentadienyl)Ta+, but the reaction was never
clean enough to isolate the pure product, and the exact
nature of the counteranion remained unclear. We tried
a variety of other metallocene cation generating meth-
ods22 on the 9 f 10 conversion, and eventually the
following new procedure was successful.
We had recently developed the chemistry of the Cp3-
Zr-CH3/Cp3Zr+ pair of complexes.23 From this chem-
istry it was known that Cp3Zr-CH3 (12) is readily
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F. A.; Mena, M.; Royo, P.; Antin˜olo, A. J . Organomet. Chem. 1984, 276,
185. Arnold, J .; Tilley, T. D.; Rheingold, A. L.; Geib, S. J . Organome-
tallics 1987, 6, 473. Tueting, D. R.; Olmstead, M. M.; Schore, N. E.
Organometallics 1992, 11, 2235. Antin˜olo, A.; Fajardo, M.; Gil-Sanz,
R.; Lo´pez-Mardomingo, C.; Otero, A. Organometallics 1994, 13, 1200.
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Siganporia, N. J . Chem. Soc., Dalton Trans. 1980, 2155.
(15) Ramsden, H. E. U.S. Patent, 3, 388, 179, 1968. Nakano, Y.;
Natsukawa, K.; Yasuda, H.; Tani, H. Tetrahedron Lett. 1972, 2833.
Fujita, K.; Ohnuma, Y.; Yasuda, H.; Tani, H. J . Organomet. Chem.
1976, 113, 201. Yasuda, H.; Nakano, Y.; Natsukawa, K.; Tani, H.
Macromolecules 1978, 11, 586. Kai, Y.; Kanehisa, N.; Miki, K.; Kasai,
N.; Mashima, K.; Yasuda, H.; Nakamura, A. Chem. Lett. 1982, 1277.
See also: Datta, S.; Wreford, S. S.; Beatty, R. P.; McNeese, T. J . J .
Am. Chem. Soc. 1979, 101, 1053. Wreford, S. S.; Whitney, J . F. Inorg.
Chem. 1981, 20, 3918.
(18) Horton, A. D.; Orpen, A. G. Organometallics 1992, 11, 8. Wu,
Z.; J ordan, R. F.; Petersen, J . L. J . Am. Chem. Soc. 1995, 117, 5867.
Casey, C. P.; Hallenbeck, S. L.; Pollock, D. W.; Landis, C. R. J . Am.
Chem. Soc. 1995, 117, 9770. Galakhov, M. V.; Heinz, G.; Royo, P. J .
Chem. Soc., Chem. Commun. 1998, 17. Casey, C. P.; Fagan, M. A.;
Hallenbeck, S. L. Organometallics 1998, 17, 287.
(19) See for a comparison: Brainina, E. M.; Dvoryantseva, G. G.
Izv. Akad. Nauk SSSR, Ser. Khim. 1967, 442. Kulishov, V. I.; Brainina,
E. M.; Bokiy, N. G.; Struchkov, Yu. T. J . Chem. Soc. D 1970, 475.
Brainina, E. M.; Gambaryan, N. P.; Lokshin, B. V.; Petrovskii, P. V.;
Struchkov, Y. T.; Kharlamova, E. N. Izv. Akad. Nauk SSSR, Ser. Khim.
1972, 187. Rogers, R. D.; Vann Bynum, R.; Atwood, J . L. J . Am. Chem.
Soc. 1978, 100, 5238.
(20) Massey, A. G.; Park, A. J .; Stone, F. G. A. Proc. Chem. Soc.
1963, 212. Massey, A. G.; Park, A. J . J . Organomet. Chem. 1964, 2,
245. Massey, A. G.; Park, A. J . In Organometallic Synthesis; King, R.
B., Eisch, J . J ., Eds.; Elsevier: New York, 1986; Vol. 3, p 461.
(21) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10015.
(16) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.;
Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1985, 107, 2410.
(17) Thomas, J . L. Inorg. Chem. 1978, 17, 1507. Sen, A.; Halpern,
J . Inorg. Chem. 1980, 19, 1073. Beck, W.; Raab, K.; Nagel, U.; Sacher,
W. Angew. Chem. 1985, 97, 498; Angew. Chem., Int. Ed. Engl. 1985,
24, 505.

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5749
F igu r e 2. A view of the molecular geometry of the (s-trans-
+
η4-butadiene)TaCp2 complex 10 (cation only). Selected
bond lengths (Å) and angles (deg): Ta-C1 2.418(17), Ta-
C2 2.306(15), Ta-C3 2.313(12), Ta-C4 2.297(19), C1-C2
1.32(3), C2-C3 1.53(4), C3-C4 1.33(3) (distances C1-C2
and C3-C4 refined with restraints, also C1-C3 and C2-
C4), Ta-CCp 2.387; C1-C2-C3 102(2), C2-C3-C4 102-
(2), Ta-C1-C2 69.1(10), Ta-C2-C1 78.5(11), Ta-C2-C3
70.9(8), Ta-C3-C2 70.4(10), Ta-C3-C4 72.5(10), Ta-C4-
C3 73.8(11); C1-C2-C3-C4 140(2).
F igu r e 3. A comparison of the characteristic 1H NMR
spectra of (s-trans-η4-butadiene)zirconocene and (s-trans-
η4-butadiene)tantalocene cation in bromobenzene-d5 (600
MHz) at 298 K.
Sch em e 1
formed by treatment of Cp2Zr(Cl)CH3 with a Cp-anion
equivalent. The formation of Cp3Zr-CH3 should be
even more favorable if the cationic Cp2Zr-CH3+ reagent
was employed as a Cp-anion abstracting reagent. In-
deed, (η5-Cp)2(σ-Cp)Ta(η2-butadiene) (9) reacts readily
with the salt [(Cp2ZrCH3)+(CH3B(C6F5)3)-] (11),21 gen-
erated in situ by treatment of dimethylzirconocene with
tris(pentafluorophenyl)borane in an aromatic solvent,
to give a precipitate that turned out to be the Cp2Ta-
-
(butadiene)+ cation (10) (with CH3B(C6F5)3 anion).
Complex 10 contains an s-trans-η4-butadiene ligand.
This follows from the NMR data (see below) and the
results of an X-ray crystal structure analysis. The latter
suffers from some disorder problem that is described in
the Experimental Section, but is sufficient to character-
ize the butadiene ligand as s-trans-η4-coordinated (see
Figure 2). The butadiene ligand C1-C2/C3-C4 bonds
are short (1.32(3)/1.34(3) Å); the C2-C3 linkage is long
(1.53(4) Å). The Ta-C(butadiene) distances are in a
range between 2.42(2) and 2.30(2) Å. The butadiene
framework is, of course, no longer planar (θ C1-C2-
C3-C4 140(2)°). In solution, complex 10 gives only a
single set of NMR signals that are very characteristic
of an (s-trans-η4-butadiene)metallocene system (Figure
3).1 There is only a single 1H NMR Cp resonance (δ
5.40 in dichloromethane-d2; 13C NMR at 97.2) due to
the C2-symmetric structure of the cation. The 13C NMR
signals of the η4-butadiene ligand appear at δ 57.8 (C1/
C4) and 90.1 (C2/C3). The corresponding 1H NMR
resonances are found in the typical s-trans-η4-butadiene
range [δ 3.81 (1-Hsyn, 4-Hsyn), 3.69 (2-H, 3-H), 2.14 (1-
H
anti, 4-Hanti)]. This is very different from the typical
s-cis-η4-butadiene resonances, as they are, for example,
observed in the CpTaCl2(butadiene) starting material
1
5 (13C NMR δ 127.5 (C2/C3), 58.4 (C1/C4); H NMR δ
6.8 (2-H, 3-H), 0.85, 0.10 (1-H, 4-H)).
R ea ct ion s of 10 w it h Ket on es, Nit r iles, a n d
Alk yn es. We have seen that Cp2Ta(butadiene)+ (10)
is readily formed by our novel route (see Scheme 1). The
complex is thermodynamically stable. It contains an
s-trans-η4-butadiene ligand coordinated to the group 5
bent metallocene backbone, and it behaves structurally
very similar to the related neutral group 4 metallocene
butadiene complex (s-trans-η4-butadiene)zirconocene
(trans-1). The latter reacts readily with a great variety
of reagents that contain reactive π-systems.4,5a,b,24 With
equimolar amounts of ketones, nitriles, or alkynes
(butadiene)ZrCp2 reacts cleanly to yield the metallacy-
clic allyl complexes (structural types 2-4, see above),
formed by CC-coupling at a conjugated diene terminus.
To characterize the new cationic Cp2Ta(butadiene)+
complex 10 chemically, we have treated it with a variety
of respective organic reagents and determined the
structures of the obtained products.
(22) (a) Bochmann, M.; J aggar, A. J .; Nicholls, J . C. Angew. Chem.
1990, 102, 830; Angew. Chem., Int. Ed. Engl. 1990, 29, 780. Chien, J .
C. W.; Tsai, W.-M.; Rausch, M. D. J . Am. Chem. Soc. 1991, 113, 8570.
(b) Reviews: Sinn, H.; Kaminsky, W. Adv. Organomet. Chem. 1980,
18, 99. J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325. Bochmann,
M. J . Chem. Soc., Dalton Trans. 1996, 255. Kaminsky, W. J . Chem.
Soc., Dalton Trans. 1998, 1413.
(23) Brackemeyer, T.; Erker, G.; Fro¨hlich, R. Organometallics 1997,
16, 531. Brackemeyer, T.; Erker, G.; Fro¨hlich, R.; Prigge, J .; Peuchert,
U. Chem. Ber. 1997, 130, 899. J acobsen, H.; Berke, H.; Brackemeyer,
T.; Eisenbla¨tter, T.; Erker, G.; Fro¨hlich, R.; Meyer, O.; Bergander, K.
Helv. Chim. Acta 1998, 81, 1692.

5750 Organometallics, Vol. 17, No. 26, 1998
Strauch et al.
Ta ble 1. Activa tion En er gies ∆Gq of th e
Sch em e 2
top
Th er m a lly In d u ced Rin g Top om er iza tion P r ocess
of th e Ca tion ic Seven -Mem ber ed Rin g
Meta lla cycles 13 a n d 14a
compd
heteroatom
R at C7
CH3/CH3
-(CH2-)4
-(CH2-)5-
Ph/Ph
CH3/Ph
CH3
C2H5
∆Gq
Tc (K)
top
13a
13b
13c
13d
13e
14a
14b
14c
14d
14e
O
O
O
O
O
N
N
N
N
N
12.3
11.9
12.5
11.7
12.0
11.4
11.8
11.5
11.8
11.8
258
251
260
245
255
239
248
241
239
251
Ph
CH2-p-C6H4CH3
CHPh2
a
∆Gq ((0.3 kcal/mol-1) determined from the coalescence of
top
the 1H NMR Cp resonances (600 MHz in dichloromethane-d2
solution).
we have obtained a Gibbs activation energy of ∆Gq
)
top
12.3 ( 0.3 kcal/mol-1 for this ring-inverting topomer-
ization process25 of 13a . This is in a range similar to
that observed previously for the analogous topomeriza-
tion process of the neutral seven-membered zircono-
cenacycle 4a .24
(η4-Butadiene)tantalocene cation (10) reacts similarly
to the ketones cyclopentanone, cyclohexanone, or ben-
zophenone to give the seven-membered metallacyclic
cations 13b, 13c, and 13d, respectively. Again, envelope-
shaped metallacyclic conformations must be assumed
to prevail for these molecules, as judged from their
typical NMR features (for details see the Experimental
Section). Conformational equilibration takes place at
elevated temperatures by a thermally induced ring
topomerization process, analogously to that described
above for the acetone coupling product 13a . The Gibbs
activation energies of the ring inversion process of
13b-d are in the same range as observed for 13a
The salt [Cp2Ta(butadiene)+(CH3B(C6F5)3)-] (10) was
dissolved in bromobenzene. A ca. 3-fold excess of acetone
was added. The Cp2Ta(butadiene)+ cation reacts only
slowly with the organic carbonyl compound at ambient
temperature. However, at 60 °C the reaction proceeds
facilely. One molar equivalent of acetone is incorpo-
rated and CC-coupled with the butadiene ligand as
expected to give the seven-membered metallacyclic (σ-
-
allyl)tantalocene cation complex 13a (with CH3B(C6F5)3
anion).
(∆Gq ≈ 12 ( 0.5 kcal/mol-1; see Table 1).
top
Coupling of acetophenone with (butadiene)tantalocene
cation gives rise to the formation of a carbon chirality
center. In combination with the preferred chiral con-
formation of the metallacyclic product this should give
rise to the presence of two diastereoisomers. These are
observed in a 55:45 ratio by NMR under conditions
where the topomerization process, which must in this
case lead to diastereomeric interconversion, is slow on
the NMR time scale. At 213 K in dichloromethane-d2
we observe thus two pairs of Cp singlets of the 13e/13e′
diastereomeric mixture in the 1H/13C NMR spectrum
(600/150 MHz) at δ 6.14, 6.04/112.2, 109.5 and δ 6.38,
6.28/111.9, 109.2 ppm. From the temperature-depend-
ent dynamic NMR spectra a Gibbs activation energy of
the topomerization process, i.e., the 13e h 13e′ diaster-
eomeric interconversion, of ∆Gqtop(255 K) ≈ 12.0 ( 0.3
kcal/mol-1 was obtained.
The structural description of 13a as a seven-mem-
bered metallacycle follows from its typical NMR behav-
ior. J ust like its neutral zirconocene analogue [4a (A
) O, B ) CMe2), see above and Scheme 2], the cation
13a exhibits temperature-dependent dynamic NMR
spectra. In the zirconium compound 4a it was shown
by X-ray diffraction and dynamic NMR spectroscopy
that such frameworks are characterized by a pro-
nounced envelope-like ring conformation.24 It consists
of two planar subunits (here: C3, Ta, O, C7, C6, and
C3, C4, C5, C6). This typical nonplanar structure
renders the Cp groups in 10 at tantalum diastereotopic,
and it leads to the generation of diastereotopic hydro-
gens at the former butadiene carbon atoms C3 and C6
as well as a pair of diastereotopic methyl substituents
at the acetone-derived carbon atom C7. This is in fact
observed for 10 in dichloromethane-d2 solution at 198
1
K. In the H NMR spectrum (600 MHz) we observe two
Cp singlets (δ 6.26/6.19), two methyl resonances (δ 1.33/
0.92), and diastereotopic 6-H, 6-H′ hydrogens (δ 2.03/
1.31). Conformational equilibration takes place upon
increasing the monitoring NMR temperature, which
leads to pairwise coalescence of the respective diaste-
reotopic groups. From the Cp coalescence (Tc ) 258 K)
We next treated the (s-trans-η4-butadiene)TaCp2 cat-
ion 10 with acetonitrile. At 60 °C in bromobenzene
(24) Erker, G.; Engel, K.; Atwood, J . L.; Hunter, W. E. Angew. Chem.
1983, 95, 506; Angew. Chem., Int. Ed. Engl. 1983, 22, 494, Angew.
Chem. Suppl. 1983, 675.
(25) Binsch, G.; Eliel, E. L.; Kessler, H. Angew. Chem. 1971, 83,
618; Angew. Chem., Int. Ed. Engl. 1971, 10, 570.

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5751
F igu r e 5. Molecular geometry of 14d (cation only).
F igu r e 4. View of the molecular structure of the (buta-
diene)TaCp2+/acetonitrile addition product 14a (cation
only).
of the respective averaged signals above the coalescence
1
temperature. From the coalescence of the H NMR Cp
signals a Gibbs activation energy of ∆Gqtop(239 K) ) 11.4
( 0.3 kcal/mol-1 was determined for the activation
barrier of the topomerization process of 14a (see Table
1).
solution the [(η4-C4H6)TaCp2+CH3B(C6F5)3-] salt cleanly
adds 1 molar equiv of the organic nitrile. The reaction
requires ca. 5 h to go to completion, and the 1:1 addition
product 14a was isolated as a red-colored solid in ca.
75% yield. Gas-phase diffusion of pentane into a solution
of 14a in dichloromethane led to the formation of single
crystals of 14a that were suited for an X-ray crystal
structure analysis (see Figure 4).
Complex 14a exhibits separated anion and cation
units in the crystal. The cation shows a seven-
membered metallacyclic ring structure. Addition of the
acetonitrile to (butadiene)TaCp2+ has led to the forma-
tion of a 2,3-dihydro-7-methyl-2-tantala-6H-azepine ring
system. The structure shows the presence of the C7-
N1 (1.253(7) Å) and C4-C5 (1.338(10) Å) double bonds
inside the organometallic seven-membered ring system.
There are two σ-bonded ligands at tantalum, namely,
Ta2-C3 (2.264(6) Å) and the rather short Ta2-N1 bond
(1.918(5) Å). The short Ta2-N1 bond lengths in com-
bination with the very large angle at nitrogen (Ta2-
N1-C7: 158.3(5)°) may indicate some metal-nitrogen
π-interaction.26 The pseudo-tetrahedral coordination
around tantalum in 14a is completed by the presence
of the two uniformally η5-bonded cyclopentadienyl
ligands. The corresponding Cp(centroid)-Ta2-Cp(cen-
troid) angle is 134.7°; the C3-Ta2-N1 angle amounts
to 86.7(2)°. The rigid C3-Ta2-N1-C7-C6 part of the
metallacyclic framework shows a coplanar orientation,
as does the remaining C6-C5dC4-C3 moiety. The
metallacyclic framework of 14a exhibits a typical en-
velope-type conformational arrangement. The angle
between the planes P1 (C3-Ta2-N1-C7-C6) and P2
(C6-C5-C4-C3) is 60.9(3)°.
The reaction of (s-trans-η4-butadiene)TaCp2 cation
+
with propionitrile, benzonitrile, p-tolylacetonitrile, or
diphenylacetonitrile proceeds analogously. In the course
of several hours at 60 °C in the polar bromobenzene
solvent, clean addition to yield the respective systems
14b-e is observed. All these systems exhibit structures
similar to 14a . They undergo the intramolecular con-
formational equilibration processes of their respective
envelope-shaped metallacyclic seven-membered ring
frameworks with Gibbs activation energies that are very
similar to the ∆Gq value determined for the parent
top
compound 14a (see above and Table 1).
Single crystals were also obtained from the complex
14d , and its structure was determined by an X-ray
crystal structure analysis (Figure 5). The molecular
structure of the cation 14d is in its essential parameters
very similar to that of the parent compound 14a (see
above). Selected bond lengths and angles of the two
structures are listed in Table 2 for a comparison.
Finally, we have treated the (s-trans-η4-butadiene)-
TaCp2+ cation with the alkynes 2-butyne and 1-pentyne
in this study, respectively. The alkyne addition reaction
is the slowest trapping reaction of (C4H6)TaCp2+ found
in this series so far. It has taken ca. 36 h at 60 °C to
have the reaction between 10 and 2-butyne go to
completion. The metallacyclic 1:1 addition product 15a
was obtained and isolated in ca. 70% yield. It was
characterized spectroscopically (for details see the Ex-
perimental Section) and by an X-ray crystal structure
analysis. Although the structure determination was
complicated due to a disorder problem of the C1-C4
moiety of the ring, it has revealed a pronounced
structural difference between the complex types 15 and
13/14. In the acetonitrile coupling product 14a (see
above) only one of the former butadiene carbon atoms
In solution, complex 14a exhibits an analogous struc-
ture, as evidenced by NMR. At low temperature (198
K, 600 MHz, CD2Cl2) the 1H NMR spectrum of 14a
shows the resonances of two diastereotopic Cp ligands
at δ 5.99 and 5.92 ppm and diastereotopic pairs of 6-H/
2
H′ (δ 3.11, 2.09 ppm, J ) 13.7 Hz) and 3-H/H′ (δ 2.04,
1.38 ppm, 2J ) 10.0 Hz) methylene hydrogen atoms. The
seven-membered metallacycle 14a shows dynamic NMR
spectra due to a ring topomerization process at elevated
temperature that results in a pairwise exchange of the
diastereotopic Cp ligands, as well as the diastereotopic
C6H2 and C3H2 hydrogens, leading to the observation
(26) Erker, G.; Fro¨mberg, W.; Atwood, J . L.; Hunter, W. E. Angew.
Chem. 1984, 96, 72; Angew. Chem., Int. Ed. Engl. 1984, 23, 68.
Fro¨mberg, W.; Erker, G. J . Organomet. Chem. 1985, 280, 343. Erker,
G.; Fro¨mberg, W.; Kru¨ger, C.; Raabe, E. J . Am. Chem. Soc. 1988, 110,
2400.

5752 Organometallics, Vol. 17, No. 26, 1998
Strauch et al.
Ta ble 2. Com p a r ison of Selected Str u ctu r a l
P a r a m eter s of th e Ca tion System s 14a (R ) CH3)
a n d 14d (R-CH2-p-C6H4CH3)
bond lengths (Å)/
angles (deg)
14a
14d
Ta2-N1
1.918(5)
2.264(6)
86.7(2)
1.903(5)
2.278(7)
85.0(2)
Ta2-C3
N1-Ta2-C3
Ta2-N1-C7
N1-C7
158.3(5)
1.253(7)
1.536(9)
116.5(5)
1.484(9)
1.338(10)
1.499(9)
126.5(6)
126.2(6)
1.478(8)
124.3(6)
116.5(5)
111.1(4)
115.1(5)
50.2(5)
159.9(5)
1.270(8)
1.520(10)
116.7(6)
1.426(11)
1.354(11)
1.472(11)
128.7(8)
124.8(7)
1.497(9)
123.1(6)
116.7(6)
112.6(5)
114.9(6)
49.3(6)
C6-C7
N1-C7-C6
C3-C4
C4-C5
C5-C6
C3-C4-C5
C4-C5-C6
C7-C71
F igu r e 6. Projection of the metallacyclic π-allyl metal-
locene framework of 15a (only the cation is depicted) with
selected bond lengths (Å) and angles (deg); the substituted
(π-allyl)tantalocene subunit is enantiomerically disordered.
Ta-C6 2.283(4), C5-C6 1.351(7), Ta-C6-C5 124.1(3), Ta-
C6-C7 118.9(3), C6-C5-C4 119.3(4), C6-C5-C8 125.2-
(5), C4-C5-C8 115.5(5), C4-C5 1.489(8), Cp(centroid)-
Ta-Cp(centroid) 129.1, C1-C2 1.329(9), C2-C3A 1.295(14),
C3A-C4-C5 109.2(5), C3B-C4-C5 106.3(6), C3A-C4
1.449(10), C2-C3B 1.261(15), C3B-C4 1.464(14).
N1-C7-C71
N1-C7-C6
Ta2-C3-C4
C5-C6-C7
N1-Ta2-C3-C4
C7-N1-Ta2-C3
Ta2-N1-C7-C6
N1-C7-C6-C5
C3-C4-C5-C6
8.1(12)
1.7(15)
164.9(9)
-43.6(9)
2.0(12)
-3.6(19)
-46.6(10)
2.4(14)
shows a close contact to tantalumsthe Ta‚‚‚C3 to C6
separations in 14a are 2.264(6), 3.134(8), 3.685(7), and
3.767(7) Åswhereas the analogous Ta...C1 to C4 separa-
tions in 15a are quite different at 2.365(5), 2.421(5),
2.523(10) (averaged value of the disordered C3A and
C3B centers), and 3.411(5) Å. Thus, complex 15a has
to be regarded as a distorted metallacyclic π-allyl
system5,27 with only one typical tantalum-carbon σ-bond
present (Ta-C6 2.283(4) Å), in contrast to the seven-
membered metallacyclic σ-allyl complexes 14. A view
of the structure of 15a is shown in Figure 6, together
regioisomeric metallacyclic (π-allyl)metallocene com-
plexes 15b and 15c. The isomers could clearly be
distinguished by selective 1H NMR TOCSY experi-
ments. This has revealed that the hydrogen atom 5-H
in 15c is connected with the coupled 1-4-H spin system,
whereas in 15b it is separated by the quaternary center
at C5 and thus does not respond to, for example, TOCSY
irradiation at 1-H.
Con clu sion s
The bent metallocene complexes of the d-block metals
exhibit unique stereoelectronic features. Proposed on
the grounds of theoretical calculations and verified by
means of a variety of experiments, it is now clear that
the Cp2M moieties are distinguished by having their
valence orbitals arranged such that additional ligands
bind almost exclusively in the Cp-M-Cp bisecting
plane at the front of the bent metallocene. This specific
arrangement of the available metallocene coordination
sites in a singular plane leads to a number of coordi-
native situations that are very specifically favored at
the Cp2M bent metallocene framework.28 Binding buta-
diene (and other conjugated diene ligands, as well)
preferably in an s-trans-η4-C4H6 bonding mode is one
of the consequences of the specific Cp2M stereoelectronic
situation.
with a list of typical bond lengths and angles.
A
discussion of structural details is omitted because of the
disorder problem at the π-allyl structural subunit that
has complicated the X-ray crystal structure analysis of
the specific example 15a .
(s-trans-η4-Butadiene)zirconocene to our knowledge
was the very first example in this series, prepared and
described by us and independently by A. Nakamura
and H. Yasuda and their co-workers and structurally
characterized by C. Kru¨ger et al.1 The (butadiene)ZrCp2
system still exists as an (s-cis/s-trans-η4-C4H6)zirconocene
equilibrium mixture. Going to the Cp2Hf system shifts
the equilibrium considerably to the side of the σ,π-
structured (s-cis-η4-diene)hafnocene. This is quite dif-
ferent upon going to the group 5 system that is isoelec-
tronic to neutral bis(cyclopentadienyl)hafnium, namely,
the singly positively charged bis(cyclopentadienyl)tan-
talum+ cation framework.2 The Cp2Ta+ template binds
The addition of 1-pentyne to the (butadiene)tanta-
locene cation was carried out under similar conditions
(40 h at 60 °C in bromobenzene, ca. 75% yield of isolated
product). We have obtained a 60:40 mixture of the
(27) Brauer, D. J .; Kru¨ger, C. Organometallics 1982, 1, 204, 207.
Highcock, W. J .; Mills, R. M.; Spencer, J . L.; Woodward, P. J . Chem.
Soc., Chem. Commun. 1987, 128. Larson, E. J .; Van Dort, P. C.; Dailey,
J . S.; Lakanen, J . R.; Pederson, L. M.; Silver, M. E.; Huffman, J . C.;
Russo, S. O. Organometallics 1987, 6, 2141. Larson, E. J .; Van Dort,
P. C.; Lakanen, J . R.; O’Neill, D. W.; Pederson, L. M.; McCandless, J .
J .; Silver, M. E.; Russo, S. O.; Huffman, J . C. Organometallics 1988,
7, 1183. Yasuda, H.; Arai, T.; Okamoto, T.; Nakamura, J . Organomet.
Chem. 1989, 361, 161. Hauger, B. E.; Vance, P. J .; Prins, T. J .; Wemple,
M. E.; Kort, D. A.; Silver, M. E. Huffmann, J . C. Inorg. Chim. Acta
1991, 187, 91. Green, M. L. H.; Hughes, A. K. J . Chem. Soc., Dalton
Trans. 1992, 527. Karl, J .; Erker, G.; Fro¨hlich, R. J . Organomet. Chem.
1997, 535, 59.
(28) Erker, G. Acc. Chem. Res. 1984, 17, 103, and references therein.
Tatsumi, K.; Nakamura, A.; Hofmann, P.; Stauffert, P.; Hoffmann, R.
J . Am. Chem. Soc. 1985, 107, 4440.

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5753
using Schlenk-type glassware or in a glovebox. Solvents
(including deuterated solvents) were dried and distilled under
argon prior to use. NMR spectra were recorded on a Varian
Unity Plus (1H, 599.8 MHz; 13C, 150.8 MHz) NMR spectrom-
eter, on a Bruker AC 200 P-FT-NMR spectrometer, or on a
Bruker ARX 300 spectrometer. IR spectroscopy: Nicolet 5
DXC FT-IR spectrometer (KBr). Elemental analyses: Foss
Heraeus CHNO-Rapid. DSC: DuPont 2910 DSC (STA instru-
ments). X-ray crystal structure analyses: Data sets were
collected with Enraf Nonius CAD4 and MACH3 diffractome-
ters, equipped with sealed tube or rotating anode generators.
Programs used: data reduction MolEN, structure solution
SHELXS-86, structure refinement SHELXL-93 and SHELXL-
97, graphics DIAMOND or SCHAKAL. CpTaCl2(butadiene)
(6),16 (butadiene)magnesium (7),15 and [(Cp2ZrCH3)+(CH3-B-
(C6F5)3)-] (11)21 were prepared according to the literature
butadiene strongly through all four carbon atoms as
expected, and in contrast to (C4H6)HfCp2, exclusively
(s-trans-η4-butadiene)TaCp2 has been found and ob-
+
served experimentally so far. It appears that the unique
s-trans-η4-conjugated diene bonding mode is even more
favored, i.e., thermodynamically stabilized, at Cp2Ta+
cation than it was previously found for the neutral bis-
(cyclopentadienyl) group 4 bent metallocene systems.
Our new synthesis has made Cp2Ta(butadiene)+
cationsand probably substituted derivatives as wells
readily available. This has allowed for a first series of
addition reactions to be carried out. The addition of
organic carbonyl compounds proceeded as expected and
gave the corresponding tetrahydrotantalaoxepine cation
systems (13). They probably draw much of their
stabilization from a strong metal oxygen π-back-bonding
interaction,29 similar to that previously observed with
their neutral zirconium and hafnium analogues.24
Nitrogen to tantalum back-bonding is quite pro-
nounced in the seven-membered metallacyclic cations
14, as well. Actually, this stabilizing effect seems to be
even more pronounced in the dihydro-tantala-6H-
azepine cations than in the corresponding neutral
zirconium or hafnium systems. In the latter series we
have only in a singular example seen the seven-
membered metallacyclic σ-complex to be present at all;
usually their five-membered σ-allyl isomers (and tau-
tomers) were more stable.4a In the case of the cationic
(butadiene)TaCp2+/NtC-R addition products we have
exclusively observed the seven-membered σ-allyl met-
allocene systems. Nevertheless, there is evidence that
the Cp2Ta+ complexes are able to respond to variations
of the electronic features around tantalum. Binding an
sp2 carbon center instead of O or N heteroatoms to the
metal center results in an increased local electronic
unsaturation at the metal that is consequently compen-
procedures. For
a compilation of the 1D and 2D NMR
experiments used, see ref 30.
Bis(η5-cyclop en ta dien yl)(η1-cyclop en ta dien yl)(η2-bu ta -
d ien e)ta n ta lu m (9). A 1.00 g (2.70 mmol) sample of 5 and
474 mg (5.39 mmol) of sodium cyclopentadienide were sus-
pended in 40 mL of toluene and stirred for 12 h at room
temperature. The reaction mixture was filtered, and the
solvent was evaporated. The residue was taken up in 30 mL
of pentane and stirred for 12 h. Afterward the product was
collected on a Schlenk frit, washed with two 10 mL portions
of pentane, and dried in vacuo. Yield: 540 mg (47%), mp 101
°C. Anal. Calcd for C19H21Ta (430.32): C, 53.07; H, 4.92.
Found: C, 52.79; H, 5.09. IR (KBr): ν˜ ) 3100, 2961, 1595,
1436, 1383, 1193, 1159, 1010, 833, 774, 721, 668 cm-1
.
1H
NMR (THF-d8, 599.8 MHz, 298 K): δ ) 6.89/6.67 (each br s,
1H, 6-H, 9-H), 6.21/6.13 (each br s, 1H, 7-H, 8-H), 6.06 (ddd,
3
3
3J ) 8.1 Hz, J ) 16.9 Hz, J ) 10.2 Hz, 1H, 3-H), 5.30/4.51
2
3
4
(each s, 5H, Cp-H), 4.54 (ddd, J ) 2.3 Hz, J ) 16.9 Hz, J
) 1.3 Hz, 1H, 4-H′), 4.21 (ddd, J ) 2.3 Hz, J ) 10.2 Hz, J
) 1.1 Hz, 1H, 4-H), 3.74 (br s, 1H, 5-H), 2.31 (m, 1H, 2-H),
1.51 (dd, J ) 6.5 Hz, J ) 10.3 Hz, 1H, 1-H′), 1.11 (dd, J )
6.5 Hz, J ) 11.7 Hz, 1H, 1-H). TOCSY NMR (THF-d8, 599.8
2
3
4
2
3
2
3
MHz, 298 K) experiment 1: Irradiation at δ ) 3.74 (5-H) gave
resonances at δ ) 6.89/6.67 (6-H, 9-H), 6.21/6.13 (7-H, 8-H).
Experiment 2: Irradiation at δ ) 1.11 (1-H) gave resonances
at δ ) 6.06 (3-H), 4.54 (4-H′), 4.21 (4-H), 2.31 (2-H), 1.51 (1-
H). 13C NMR (THF-d8, 150.8 MHz, 298 K): δ ) 149.0 (C3),
145.5/145.4 (C6/C9), 121.1/120.8 (C7/C8), 104.9 (C4), 102.2/
101.6 (C-Cp), 43.3 (C5), 36.1 (C2), 24.0 (C1).
sated by shifting the remaining allyl moiety inside the
+
framework of the corresponding (butadiene)TaCp2
/
alkyne addition (15) in the direction of an η3-coordina-
tion mode. Overall, the (butadiene)tantalocene+ cation
system appears to behave electronically, structurally,
and chemically similar to the well-studied neutral
(conjugated diene) bent metallocene systems described
in the literature. It may be that the very characteristic
features that make (η4-butadiene)MCp2 systems so
unique are even slightly more pronounced in the (s-
trans-η4-butadiene)TaCp2+ cation complex 10 than they
are for the other members of this general complex
family. Whether this may lead to the disclosure of novel
reaction types and novel applications of such systems
in stoichiometric chemistry and in catalysis will be
investigated in our laboratory.
(s-tr a n s-η4-Bu t a d ien e)b is(η5-cyclop en t a d ien yl)t a n t a -
lu m (V) Meth yltr is(p en ta flu or op h en yl)bor a te (10). To
generate [(Cp2ZrCH3)+(CH3B(C6F5)3)-] (11) in situ, 2.00 g (3.91
mmol) of B(C6F5)3 and 1.08 g (4.29 mmol) of dimethylzir-
conocene were mixed and then dissolved in 20 mL of toluene.
This solution was transferred at room temperature to a stirred
solution of 1.90 g (4.41 mmol) of 9 in 20 mL of toluene. An
oily product precipitated, and the supernatant solution was
decanted. The oily residue was washed with three portions
of 20 mL of toluene and dried in vacuo. The crude product
was suspended in 20 mL of pentane, filtered, washed with two
portions of 20 mL of pentane, and dried in vacuo. Yield: 3.13
g (90%), mp 201 °C. Anal. Calcd for C33H19F15BTa (892.21):
C, 44.43; H, 2.15. Found: C, 44.78; H, 2.58. IR (KBr): ν˜ )
3126, 2944, 2933, 1641, 1511, 1457, 1380, 1265, 1088, 1012-
Exp er im en ta l Section
All compounds described are air and moisture sensitive:
They were prepared and handled in an argon atmosphere
942, 847, 802, 756, 659 cm-1 1H NMR (dichloromethane-d2,
.
599.8 MHz, 298 K): δ ) 5.40 (s, 10H, Cp-H), 3.81 (m, 2H,
H-syn), 3.69 (m, 2H, H-meso), 2.14 (m, 2H, H-anti), 0.52 (br s,
3H, Me-B(C6F5)3). TOCSY NMR (dichloromethane-d2, 599.8
MHz, 298 K): Irradiation at δ ) 3.31 (H-syn) gave resonances
at δ ) 3.69 (H-meso), 2.14 (H-anti). GCOSY NMR (dichlo-
romethane-d2, 599.8 MHz, 298 K): δ ) 3.81/3.64, 2.14 (H-syn/
H-meso, H-anti), 3.69/3.81, 2.14 (H-meso/H-syn, H-anti), 2.14/
(29) Katsuki, T.; Sharpless, K. B. J . Am. Chem. Soc. 1980, 102, 5974.
Williams, I. D.; Pedersen, S. F.; Sharpless, K. B.; Lippard, S. J . J . Am.
Chem. Soc. 1984, 106, 6430. Finn, M. G.; Sharpless, K. B. In
Asymmetric Synthesis; Morrison, J . D., Ed.; Academic Press: New
York, 1985; Vol. 5, p 247. Potvin, P. G.; Kwong, P. C. C.; Gau, R.;
Bianchet, S. Can. J . Chem. 1989, 67, 1523. Woodard, S. S.; Finn, M.
G.; Sharpless, K. B. J . Am. Chem. Soc. 1991, 113, 3, 106. Finn, M. G.;
Sharpless, K. B. J . Am. Chem. Soc. 1991, 113, 113. Erker, G.; Dehnicke,
S.; Rump, M.; Kru¨ger, C.; Werner, S.; Nolte, M. Angew. Chem. 1991,
103, 1371; Angew. Chem., Int. Ed. Engl. 1991, 30, 1349. Erker, G.;
Noe, R. J . Chem. Soc., Dalton Trans. 1991, 685.
(30) Braun, S.; Kalinowski, H.; Berger, S. 100 and More Basic
NMR Experiments; VCH: Weinheim, 1996, and references therein.

5754 Organometallics, Vol. 17, No. 26, 1998
Strauch et al.
3.81, 3.69 (H-anti/H-syn, H-meso). 13C NMR (dichloromethane-
1028-950, 847-802 cm-1
.
1H NMR (dichloromethane-d2,
1
d2, 150.8 MHz, 298 K): δ ) 148.3 (pd, J CF ) 236 Hz,
599.8 MHz, 298 K): δ ) 6.43 (pq, J ) 8.2 Hz, 1H, 4-H), 6.26
(s, 10H, Cp-H), 5.39 (pq, J ) 8.5 Hz, 1H, 5-H), 2.58 (pd, J )
8.3 Hz, 2H, 3-H), 1.85 (br s, 2H, 6-H), 1.75-1.56 (m, 8H, 8-H,
9-H, 10-H, 11-H), 0.51 (br s, 3H, Me-B(C6F5)3). Result of the
dynamic 1H NMR spectroscopy (dichloromethane-d2, 599.8
MHz): ∆ν of the Cp resonances without exchange (T ) 213
K) ) 51.4 Hz; coalescence temperature Tc ) 251 K; activation
1
o-B(C6F5)3), 136.9 (pd, J CF ) 233 Hz, p-B(C6F5)3), 136.9 (pd,
1J CF ) 236 Hz, m-B(C6F5)3), 128.8 (br m, ipso-B(C6F5)3), 97.2
(C-Cp), 90.1 (C2/C3), 57.8 (C1/C4), 10.8 (br s, Me-B(C6F5)3).
GHSQC NMR (dichloromethane-d2, 150.8/599.8 MHz): δ )
97.2/5.40 (C-Cp /Cp-H), 90.1/3.69 (C2, C3/H-meso), 57.8/3.81
(C1, C4/H-syn), 57.8/2.14 (C1, C4/H-anti), 10.8/0.52 (Me-
B(C6F5)3). 11B NMR (dichloromethane-d2, 200 MHz): δ )
-15.0. 19F NMR (dichloromethane-d2, 360 MHz): δ ) -130
(br s, 6F, o-C6F5); -136 (br s, 3F, p-C6F5); -166 (br s, 6F,
m-C6F5).
energy: ∆Gq(251 K) ) 11.9 ( 0.3 kcal mol-1
.
1H NMR
(dichloromethane-d2, 599.8 MHz, 198 K): δ ) 6.36 (pq, J )
8.7 Hz, 1H, 4-H), 6.27/6.18 (each s, 5H, Cp-H), 5.34 (m, 1H,
5-H), 2.49 (m, 2H, 3-H), 2.01 (m, 1H, 6-H′), 1.55 (m, 1H, 6-H),
1.76-1.21 (m, 8H, 8-H, 9-H, 10-H, 11-H), 0.40 (br s, 3H, Me-
B(C6F5)3). TOCSY NMR (dichloromethane-d2, 599.8 MHz, 198
K): Irradiation at δ ) 2.49 (3-H) gave resonances at δ ) 6.36
(4-H), 5.34 (5-H), 2.01 (6-H′), 1.55 (6-H). 13C NMR (dichlo-
X-ray crystal structure analysis of 10: formula C33H19BF15
-
Ta‚CH2Cl2, M ) 977.17, yellow crystal, 0.20 × 0.15 × 0.10 mm,
a ) 12.714(3) Å, b ) 14.821(3) Å, c ) 17.367(3) Å, V ) 3272.5-
(12) Å3, Fcalc ) 1.983 g cm-3, F(000) ) 1888 e, µ ) 36.35 cm-1
,
1
romethane-d2, 150.8 MHz, 198 K): δ ) 147.6 (d, J CF ) 234.8
empirical absorption correction via æ scan data (0.729 e C e
0.998), Z ) 4, orthorhombic, space group P212121 (No. 19), λ )
0.710 73 Å, T ) 173 K, ω/2θ scans, 3693 reflections collected
(+h, +k, +l), [(sin θ)/λ] ) 0.62 Å-1, 3693 independent and 3108
observed reflections [I g 2 σ(I)], 461 refined parameters, R )
0.038, wR2 ) 0.092, max. residual electron density 1.07 (-0.96)
e Å-3, butadiene unit refined with restraints (SADI 0.01 C1-
C2 and C3-C4, SADI 0.01 C1-C3 and C2-C4), hydrogens
calculated and refined as riding atoms.
1
Hz, o-B(C6F5)3), 136.9 (d, J CF ) 244.1 Hz, p-B(C6F5)3), 135.6
(C4), 135.4 (d, 1J CF) 247.8 Hz, m-B(C6F5)3), 127.7 (br m, ipso-
B(C6F5)3), 124.7 (C5), 112.0 (C-Cp), 109.1 (C-Cp), 110.3 (C7),
39.3 (C3), 36.1 (C6), 38.5, 35.0, 23.2, 22.4 (C8, C9, C10, C11),
9.35 (br m, Me-B(C6F5)3). 11B NMR (dichloromethane-d2, 200
MHz, 298 K): δ ) -15. 19F NMR (dichloromethane-d2, 360
MHz, 298 K): -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F,
p-(CH3)B(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
2,2-Bis(η5-cyclopen tadien yl)-7,7-pen tam eth ylen e-2,3,6,7-
tetr ah ydr o-2-tan talaoxepin e Meth yltr is(pen taflu or oph e-
n yl)bor a te (13c). The reaction of 350 mg (0.392 mmol) of 10
with 0.1 mL (0.965 mmol) of cyclohexanone according to the
procedure of 13a gives 13c. Yield: 264 mg (69%), mp 139 °C
(dec). Anal. Calcd for C38H27BF15OTa (976.33): C, 47.30; H,
2.95. Found: C, 46.57; H, 3.14. IR (KBr): ν˜ ) 3126, 2940,
2858, 1642, 1511, 1459, 1287, 1264, 1088, 997-936, 848, 840,
2,2-Bis(η5-cyclop en t a d ien yl)-7,7-d im et h yl-2,3,6,7-t et -
r a h yd r o-2-ta n ta la oxep in e Meth yltr is(p en ta flu or op h e-
n yl)bor a te (13a ). A 350 mg (0.39 mmol) sample of 10 was
dissolved in 20 mL of bromobenzene; 0.1 mL (1.36 mmol) of
acetone was added, and the solution was stirred for 12 h at
60 °C. Then the solvent was evaporated, and the residue was
taken up in 20 mL of pentane and stirred for 5 h at -20 °C.
The product was collected on a Schlenk frit, washed with three
portions of 20 mL of pentane, and dried in vacuo. Yield: 222
mg (70%), mp 135 °C. Anal. Calcd for C36H25BF15OTa
(950.19): C, 45.51; H, 2.65. Found: C, 44.71; H, 3.01. IR
(KBr): ν˜ ) 3126, 2963, 2934, 1641, 1511, 1458, 1383, 1368,
801 cm-1 1H NMR (dichloromethane-d2, 599.8 MHz, 298 K):
.
δ ) 6.44 (pq, J ) 7.5 Hz, 1H, 4-H), 6.25 (s, 10H, Cp-H), 5.33
(pq, J ) 8.5 Hz, 1H, 5-H), 2.56 (pd, J ) 8.3 Hz, 2H, 3-H), 1.85-
1.20 (m, 12H, 6-H, 8-H, 9-H, 10-H, 11-H, 12-H), 0.50 (br s,
1
1265, 1087, 1028-934, 841-802 cm-1
.
1H NMR (dichlo-
3H, Me-B(C6F5)3). Result of the dynamic H NMR spectros-
copy (dichloromethane-d2, 599.8 MHz): ∆ν of the Cp reso-
nances without exchange (T ) 213 K) ) 37.5 Hz; coalescence
temperature Tc ) 260 K; activation energy ∆Gq(260 K) ) 12.5
romethane-d2, 599.8 MHz): δ ) 6.44 (pq, J ) 10.6 Hz, 1H,
4-H), 6.27 (s, 10H, Cp-H), 5.39 (pq, J ) 10.3 Hz, 1H, 5-H),
2.56 (pd, J ) 8.3 Hz, 2H, 3-H), 1.75 (br s, 2H, 6-H), 1.27-1.20
(br s, 6H, 8-H), 0.52 (br s, 3H, Me-B(C6F5)3). 1H NMR
(dichloromethane-d2, 599.8 MHz, 198 K): δ ) 6.38 (pq, J )
9.0 Hz, 1H, 4-H), 6.26/6.19 (each s, 5H, Cp-H), 5.31 (pq, J )
( 0.3 kcal mol-1 1H NMR (dichloromethane-d2, 599.8 MHz,
.
213 K): δ ) 6.38 (pq, J ) 9.0 Hz, 1H, 4-H), 6.26/6.20 (each s,
5H, Cp-H), 5.30 (m, 1H, 5-H), 2.48 (m, 2H, 3-H), 1.98 (m, 1H,
6-H′), 1.24 (m, 1H, 6-H), 1.81-1.10 (m, 10H, 8-H, 9-H, 10-H,
11-H, 12-H), 0.41 (br s, 3H, Me-B(C6F5)3). TOCSY NMR
(dichloromethane-d2, 599.8 MHz, 198 K): Irradiation at δ )
2.48 (3-H) gave resonances at δ ) 6.38 (4-H), 5.30 (5-H), 1.98
(6-H′), 1.24 (6-H). 13C NMR (dichloromethane-d2, 150.8 MHz,
198 K): δ ) 147.5 (pd, 1J CF ) 235.8 Hz, o-B(C6F5)3); 136.9 (pd,
1J CF ) 244.2 Hz, p-B(C6F5)3), 135.8 (C4), 135.7 (pd, 1J CF ) 244.8
Hz, m-B(C6F5)3); 127.6 (br m, ipso-B(C6F5)3), 124.3 (C5), 112.2
(C-Cp), 109.6 (C-Cp), 102.5 (C7), 39.5 (C3), 39.3 (C6), 36.6,
33.8, 24.6, 22.2, 21.5 (C8, C9, C10, C11, C12), 9.36 (br m, Me-
B(C6F5)3). 11B NMR (dichloromethane-d2, 200 MHz, 298 K):
δ ) -15 ppm. 19F NMR (dichloromethane-d2, 360 MHz, 298
K): δ ) -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B-
(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
2,2-Bis(η5-cyclop en t a d ien yl)-7,7-d ip h en yl-2,3,6,7-t et -
r a h yd r o-2-ta n ta la oxep in e Meth yltr is(p en ta flu or op h e-
n yl)bor a te (13d ). A 400 mg (0.448 mmol) sample of 10 and
163 mg (0.897 mmol) of benzophenone were dissolved in 20
mL of bromobenzene and stirred for 48 h at 60 °C. Afterward
the solvent was removed, and the residue was taken up in 5
mL of dichloromethane. Addition of 10 mL of pentane led to
the precipitation of an oily product. The solvent was decanted
and the crude product stirred for 8 h at -20 °C in 20 mL of
pentane. Subsequently the product was collected on a Schlenk
frit, washed with two portions of 20 mL of pentane (cooled to
-20 °C), and dried in vacuo. Yield: 373 mg (77%), mp 136 °C
(dec). Anal. Calcd for C46H29BF15OTa (1074.33): C, 51.43; H,
3
2
8.9 Hz, 1H, 5-H), 2.45 (m, 2H, 3-H), 2.03 (dd, J ) 13.0 Hz, J
) 8.2 Hz, 1H, 6-H′), 1.33 (s, 3H, CH3), 1.31 (m, 1H, 6-H), 0.92
(s, 3H, CH3), 0.39 (br s, 3H, Me-B(C6F5)3). Result of the
dynamic 1H NMR spectroscopy (dichloromethane-d2, 599.8
MHz): ∆ν of the Cp resonances without exchange (T ) 198
K) ) 43.2 Hz; coalescence temperature Tc ) 258 K; activation
energy: ∆Gq(258 K) ) 12.3 ( 0.3 kcal mol-1; with ∆Gq ) RTc
ln((RTc21/2)/(2πNAh∆ν)). TOCSY NMR (dichloromethane-d2,
599.8 MHz, 198 K): Irradiation at δ ) 2.45 (3-H) gave
resonances at δ ) 6.38 (4-H), 5.31 (5-H), 2.03 (6-H′), 1.31 (6-
H). 13C NMR (dichloromethane-d2, 150.8 MHz, 198 K): δ )
1
1
147.3 (pd, J CF ) 235 Hz, o-B(C6F5)3), 136.8 (pd, J CF ) 235
1
Hz, p-B(C6F5)3), 136.0 (C4), 135.6 (pd, J CF ) 235 Hz,
m-B(C6F5)3), 127.5 (br m, ipso-B(C6F5)3), 124.5 (C5), 111.9 (C-
Cp), 109.0 (C-Cp), 99.3 (C7), 38.8 (C3), 38.4 (C6), 28.3 (CH3),
24.4 (CH3), 9.19 (br m, Me-B(C6F5)3). 11B NMR (dichlo-
romethane-d2, 200 MHz, 298 K): δ ) -15. 19F NMR (dichlo-
romethane-d2, 360 MHz, 298 K): δ ) -131 (br s, 6F, o-C6F5);
-163 (br s, 3F, p-C6F5); -166 (br s, 6F, m-C6F5).
2,2-Bis(η5-cyclopen tadien yl)-7,7-tetr am eth ylen e-2,3,6,7-
tetr ah ydr o-2-tan talaoxepin e Meth yltr is(pen taflu or oph e-
n yl)bor a te (13b). In a procedure similar to that for 13a the
cationic compound 13b was obtained starting from 300 mg
(0.336 mmol) of 10 and 0.1 mL (1.13 mmol) of cyclopentanone.
Yield: 221 mg (67%), mp 130 °C (dec). Anal. Calcd for C38H27
-
BF15OTa (976.33): C, 46.75; H, 2.79. Found: C, 46.19; H, 2.97.
IR (KBr): ν˜ ) 3125, 2958, 1641, 1511, 1458, 1381, 1265, 1087,

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5755
2.72. Found: C, 49.71; H, 3.06. IR (KBr): ν˜ ) 3123, 2960,
124.5 (o-Ph), 111.9 (C-Cp), 109.2 (C-Cp), 101.1 (C7), 39.4
(C3), 34.6 (C6), 25.8 (C14). 11B NMR (dichloromethane-d2, 200
MHz, 298 K): δ ) -15. 19F NMR (dichloromethane-d2, 360
MHz, 298 K): -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F,
p-(CH3)B(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
1645, 1510, 1458, 1382, 1267, 1087, 1032-945, 842-786 cm-1
.
1H NMR (dichloromethane-d2, 599.8 MHz, 298 K): δ ) 7.40-
7.38 (m, 4H, m-Ph), 7.35-7.33 (m, 2H, p-Ph), 7.16-7.14 (m,
4H, o-Ph), 6.52 (pq, J ) 8.5 Hz, 1H, 4-H), 6.21 (s, 10H, Cp-
H), 5.31 (pq, J ) 8.3 Hz, 1H, 5-H), 2.71 (br pd, 6-H, 3-H), 0.54
(br s, 3H, Me-B(C6F5)3). Result of the dynamic 1H NMR
spectroscopy (dichloromethane-d2, 599.8 MHz): ∆ν of the Cp
resonances without exchange (T ) 213 K) ) 42.9 Hz; coales-
cence temperature Tc ) 245 K; activation energy ∆Gq(245 K)
2,2-Bis(η5-cyclop en t a d ien yl)-2,3-d ih yd r o-7-m et h yl-2-
t a n t a la -6H -a zep in e Met h ylt r is(p en t a flu or op h en yl)b o-
r a te (14a ). A 300 mg (0.34 mmol) sample of 10 was dissolved
in 15 mL of bromobenzene, and 0.1 mL (1.90 mmol) of
acetonitrile was added. Then the solution was stirred for 5 h
at 60 °C. Afterward the reaction mixture was filtered, and
the solvent was removed in vacuo. The crude product was
taken up in 20 mL of pentane and stirred for 5 h at - 20 °C.
Subsequently the product was collected on a Schlenk frit,
washed with two portions of 20 mL of pentane, and dried in
vacuo. Yield: 235 mg (75%). Single crystals suitable for X-ray
diffraction analysis were obtained by slow diffusion of pentane
into a dichloromethane solution of 14a at room temperature;
mp 205 °C (dec). Anal. Calcd for C35H22BF15NTa (933.16): C,
45.05; H, 2.39; N, 1.51. Found: C, 44.19; H, 2.89; N, 1.62. IR
(KBr): ν˜ ) 3125, 2958, 2917, 1699, 1640, 1510, 1457, 1381,
) 11.7 ( 0.3 kcal mol-1 1H NMR (dichloromethane-d2, 599.8
.
MHz, 213 K): δ ) 7.37-7.25 (m, 6-H, m-Ph, p-Ph), 7.15-7.03
(each pd, 7.49 and 7.65 Hz, 2H, o-Ph), 6.47 (pq, J ) 9.2 Hz,
1H, 4-H), 6.20/6.13 (each s, 5H, Cp-H), 5.18 (pq, J ) 9.1 Hz
1H, 5-H), 3.11 (pq, J ) 7.5 Hz, 1H, 6-H′), 2.76 (pt, J ) 10.3
Hz, 1H, 3-H′), 2.49 (pq, J ) 8.1 Hz, 1H, 3-H), 2.07 (pt, J )
10.7 Hz, 1H, 6-H), 0.43 (br s, 3H, Me-B(C6F5)3). TOCSY NMR
(dichloromethane-d2, 599.8 MHz, 213 K): Irradiation at δ )
5.18 (5-H) gave resonances at δ ) 6.47 (4-H), 3.11 (6-H′), 2.76
(3-H′), 2.49 (3-H), 2.07 (6-H). 13C NMR (dichloromethane-d2,
150.8 MHz, 213 K): δ ) 147.3 (pd, 1J CF ) 237.6 Hz, o-B(C6F5)3),
1
1368, 1266, 1087, 965, 951, 845, 841, 757, 725, 659 cm-1 1H
.
143.8, 142.3 (ipso-Ph), 136.9 (C4), 136.7 (pd, J CF ) 243.6 Hz,
1
p-B(C6F5)3), 135.7 (pd, J CF ) 246.3 Hz, m-B(C6F5)3), 128.5,
NMR (dichloromethane-d2, 599.8 MHz, 298 K): δ ) 6.28 (pq,
1H, 4-H), 6.00 (s, 10 H, Cp-H), 4.91 (pq, 1H, 5-H), 2.72 (br s,
2H, 6-H), 2.18 (s, 3H, 8-H), 1.83 (br s, 2H, 3-H), 0.50 (br s,
128.2 (m-Ph), 128.2, 127.4 (p-Ph), 127.7 (br m, ipso-B(C6F5)3),
125.7, 125.4 (o-Ph), 124.4 (C5), 112.0 (C-Cp), 109.9 (C-Cp),
104.8 (C7), 40.9 (C3), 37.4 (C6), 9.2 (br m, Me-B(C6F5)3). 11B
NMR (dichloromethane-d2, 200 MHz, 298 K): δ ) -15. 19F
NMR (dichloromethane-d2, 360 MHz, 298 K): δ ) -131 (m,
6F, o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B(C6F5)3), -166 (m,
6F, m-(CH3)B(C6F5)3).
1
Me-B(C6F5)3). Result of the dynamic H NMR spectroscopy
(dichloromethane-d2, 599.8 MHz): ∆ν of the Cp resonances
without exchange (T ) 198 K) ) 42.7 Hz; coalescence tem-
perature Tc ) 239 K; activation energy ∆Gq(239 K) ) 11.4 (
0.3 kcal mol-1 1H NMR (dichloromethane-d2, 599.8 MHz, 198
.
2,2-Bis(η5-cyclop en ta d ien yl)-7-m eth yl-7-p h en yl-2,3,6,7-
tetr ah ydr o-2-tan talaoxepin e Meth yltr is(pen taflu or oph e-
n yl)bor a te (13e). According to the procedure of 13d reaction
of 500 mg of 10 and 0.2 mL (1.71 mmol) of acetophenone
resulted in the formation of the adduct 13e. Yield: 361 mg
(64%), mp 141 °C (dec). Anal. Calcd for C41H27BF15OTa
(1012.26): C, 48.65; H, 2.68. Found: C, 46.36; H, 2.85. IR
(KBr): ν˜ ) 3122, 2930, 1646, 1510, 1458, 1274, 1095, 992-
K): δ ) 6.20 (pq, 1H, 4-H), 5.99/5.92 (each s, 5H, Cp-H), 4.80
2
3
(pq, 1H, 5-H), 3.11 (dd, J ) 13.7 Hz, J ) 8.3 Hz, 1H, 6-H′),
2
3
2.09 (m, 1H, 6-H), 2.11 (s, 3H, 8-H), 2.04 (dd, J ) 10.0 Hz, J
) 8.1 Hz, 1H, 3-H′), 1.38 (pt, J ) 10.0 Hz, 1H, 3-H). 0.37 (br
s, Me-B(C6F5)3). TOCSY NMR (dichloromethane-d2, 599.8
MHz, 198 K): Irradiation at δ ) 4.76 (5-H) gave resonances
at δ ) 6.20 (4-H), 3.08 (6-H′), 2.09 (6-H), 2.01 (3-H′), 1.36 (3-
H). 13C NMR (dichloromethane-d2, 150.8 MHz, 198 K): δ )
1
951, 850, 776, 767 cm-1 1H NMR (dichloromethane-d2, 599.8
.
181.1 (C7), 147.3 (pd, J CF ) 253 Hz, o-B(C6F5)3), 138.0 (C4),
1
1
136.7 (pd, J CF ) 240 Hz, p-B(C6F5)3), 135.6 (pd, J CF ) 243
Hz, m-B(C6F5)3), 127.3 (br m, ipso-B(C6F5)3), 112.7 (C5), 107.3
(C-Cp), 104.7 (C-Cp), 35.2 (C6), 29.6 (C3), 26.3 (C8), 9.3 (br
m, Me-B(C6F5)3). 11B NMR (dichloromethane-d2, 200 MHz,
298 K): δ ) -15. 19F NMR (dichloromethane-d2, 360 MHz,
298 K): -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B-
(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
MHz, 298 K): δ ) 7.43-7.41 (m, 2H, m-Ph), 7.37-7.35 (m,
1H, p-Ph), 7.25-7.24 (m, 2H, o-Ph), 6.49 (pq, J ) 8.5 Hz, 1H,
4-H), 6.36, 6.09 (each s, 5 H, Cp-H), 5.48 (pq, J ) 8.7 Hz, 1H,
5-H), 2.63 (m, 4H, 3-H, 6-H), 1.51 (br s, 3H, 14-H), 0.53 (br s,
1
3H, Me-B(C6F5)3). Result of the dynamic H NMR spectros-
copy (dichloromethane-d2, 599.8 MHz): ∆ν of the Cp reso-
nances without exchange (T ) 213 K) ) 58.8 Hz; coalescence
temperature Tc ) 255 K; activation energy ∆Gq(255 K) ) 12.0
X-ray crystal structure analysis of 14a : formula C35H22BF15
-
( 0.3 kcal mol-1
.
1H NMR (dichloromethane-d2, 599.8 MHz,
NTa, M ) 933.30, yellow crystal, 0.30 × 0.30 × 0.20 mm, a )
10.020(1) Å, b ) 10.813(1) Å, c ) 15.027(1) Å, R ) 80.38(1)°, â
) 84.55(1)°, γ ) 81.00(1)°, V ) 1581.5(2) Å3, Fcalc ) 1.960 g
cm-3, F(000) ) 904 e, µ ) 35.93 cm-1, empirical absorption
correction via æ scan data (0.831 e C e 0.999), Z ) 2, triclinic,
space group P1h (No. 2), λ ) 0.710 73 Å, T ) 173 K, ω/2θ scans,
1
198 K): The H NMR spectrum showed two isomers in a ratio
of 55:45. δ ) 7.40-7.24 and 7.10-7.08 (m, 10H, Ph-H
isomers A and B). Isomer A: δ ) 6.26 (m, 1H, 4-H), 6.14/
6.04 (each s, 5H, Cp-H), 5.29 (m, 1H, 5-H), 2.93 (m, 1H, 6-H′),
2.64 (m, 2H, 3-H′), 2.45 (m, 1H, 3-H), 1.55 (m, 1H, 6-H), 1.60
(s, 3H, 14-H). Isomer B: δ ) 6.54 (m, 1H, 4-H), 6.38/6.28 (each
s, 5H, Cp-H), 5.47 (m, 1H, 5-H), 2.59 (m, 1H, 6-H′), 2.52 (m,
2H, 3-H), 1.75 (m, 1H, 6-H), 1.25 (s, 3H, 14-H) 0.42 (br s, 3H,
Me-B(C6F5)3, isomers A und B). TOCSY NMR (dichlo-
romethane-d2, 599.8 MHz, 198 K) isomer A: Irradiation at δ
) 5.29 (5-H) gave resonances at δ ) 6.26 (4-H), 2.93 (6-H′),
2.64 (3-H′), 2.45 (3-H), 1.55 (6-H). Isomer B: Irradiation at δ
) 5.47 (5-H) gave resonances at δ ) 6.54 (4-H), 2.59 (6-H′),
2.52 (3-H), 1.75 (6-H). 13C NMR (dichloromethane-d2, 150.8
MHz, 213 K): The resonances of the methyltris(pentafluo-
rophenyl)borate anions were identical for both isomers A and
B: δ ) 147.4 (pd, 1J CF ) 234.0 Hz, o-B(C6F5)3), 136.7 (pd, 1J CF
) 243.2 Hz, p-B(C6F5)3), 135.7 (pd, 1J CF) 243.3 Hz, m-B(C6F5)3),
127.7 (br m, ipso-B(C6F5)3), 9.2 (br m, Me-B(C6F5)3); isomer
A: δ ) 141.8 (ipso-Ph), 135.9 (C4), 128.3 (m-Ph), 127.5 (p-
Ph), 124.6 (C5), 124.2 (o-Ph), 112.2 (C-Cp), 109.5 (C-Cp),
102.8 (C7), 39.8 (C3), 36.1 (C6), 31.2 (C14), isomer B: δ ) 143.5
(ipso-Ph), 136.8 (C4), 128.2 (m-Ph), 127.9 (p-Ph), 124.3 (C5),
6680 reflections collected ((h, (k, +l), [(sin θ)/λ] ) 0.62 Å-1
,
6425 independent and 6036 observed reflections [I g 2 σ(I)],
480 refined parameters, R ) 0.036, wR2 ) 0.103, max.
residual electron density 1.46 (-3.31) e Å-3, hydrogens calcu-
lated and refined as riding atoms.
2,2-Bis(η5-cyclop en ta d ien yl)-2,3-d ih yd r o-7-eth yl-2-ta n -
t a la -6H -a zep in e Met h ylt r is(p en t a flu or op h en yl)b or a t e
(14b). According to the procedure of 14a the reaction of 300
mg (0.34 mmol) of 10 with 0.1 mL (1.40 mmol) of propionitrile
resulted in the formation of 14b. Yield: 181 mg (57%), mp
201 °C (dec). Anal. Calcd for C36H24BF15NTa (947.19): C,
45.56; H, 2.56; N, 1.48. Found: C, 44.77; H, 2.93; N, 1.51. IR
(KBr): ν˜ ) 3127, 2963, 2949, 1694, 1641, 1511, 1458, 1381,
1273, 1087, 968, 951, 846, 803, 756 cm-1
.
1H NMR (dichlo-
romethane-d2, 599.8 MHz, 298 K): δ ) 6.27 (pq, 1H, 4-H), 5.96
(s, 10H, Cp-H), 4.87 (pq, 1H, 5-H), 2.66 (br s, 2H, 6-H), 2.43
(q, 3J ) 7.2 Hz, 2H, 8-H), 1.82 (br s, 2H, 3-H), 1.10 (t, 3J ) 7.2
Hz, 3H, 9-H), 0.50 (br s, 3H, Me-B(C6F5)3). Result of the

5756 Organometallics, Vol. 17, No. 26, 1998
Strauch et al.
dynamic 1H NMR spectroscopy (dichloromethane-d2, 599.8
MHz): ∆ν of the Cp resonances without exchange (T ) 213
K) ) 44.4 Hz; coalescence temperature Tc ) 248 K; activation
H, 2.76; N, 1.37. Found: C, 48.03; H, 2.90; N, 1.46. IR
(KBr): ν˜ ) 3123, 2952, 1696, 1642, 1510, 1453, 1383, 1266,
1087, 1005-939, 850 cm-1
.
1H NMR (dichloromethane-d2,
3
energy: ∆Gq(248 K) ) 11.8 ( 0.3 kcal mol-1
.
1H NMR
599.8 MHz, 298 K): δ ) 7.21 (d, J ) 7.7 Hz, 10-H), 7.00 (d,
3J ) 7.7 Hz, 2H, 11-H), 6.26 (pq, 1H, 4-H), 5.83 (s, 5H, Cp-
H), 4.84 (m, 1H, 5-H), 3.65 (s, 2H, 8-H), 2.72 (br s, 2H, 6-H),
2.36 (s, 3H, 13-H), 1.79 (br s, 2H, 3-H), 0.53 (br s, Me-
B(C6F5)3). Result of the dynamic 1H NMR spectroscopy
(dichloromethane-d2, 599.8 MHz): ∆ν of the Cp resonances
without exchange (T ) 198 K) ) 10.4 Hz; coalescence tem-
perature Tc ) 233 K; activation energy ∆Gq(233 K) ) 11.8 (
(dichloromethane-d2, 599.8 MHz, 213 K): δ ) 6.18 (pq, 1H,
4-H), 5.96/5.88 (each s, 5H, Cp-H), 4.79 (pq, 1H, 5-H), 3.05
2
3
(dd, J ) 13.6 Hz, J ) 8.3 Hz, 1H, 6-H′), 2.47 (m, 1H, 8-H′),
2.26 (m, 1H, 8-H), 2.07 (m, 1H, 6-H), 2.05 (m, 1H, 3-H′), 1.38
(pt, J ) 9.4 Hz, 1H, 3-H), 1.00 (pt, J ) 7.1 Hz, 3H, 9-H), 0.40
(br s, 3H, Me-B(C6F5)3). 13C NMR (dichloromethane-d2, 150.8
1
MHz, 213 K): δ ) 184.64 (C7), 147.5 (pd, J CF ) 237.6 Hz,
o-B(C6F5)3), 138.1 (C4), 136.8 (pd, 1J CF ) 243.6 Hz, p-B(C6F5)3),
0.3 kcal mol-1 1H NMR (dichloromethane-d2, 599.8 MHz, 198
.
1
3
3
135.7 (pd, J CF ) 246.3 Hz, m-B(C6F5)3), 127.5 (br m, ipso-
K): δ ) 7.15 (d, J ) 7.8 Hz, 2H, 11-H), 6.96 (d, J ) 7,8 Hz,
2H, 10-H), 6.19 (pq, 3J ) 8.3 Hz, 2J ) 16.8 Hz, 1H, 4-H), 5.77/
5.75 (each s, 5H, Cp-H), 4.77 (pdd, 3J ) 7.4 Hz, 2J ) 16.9 Hz,
B(C6F5)3), 112.5 (C5), 107.4, 104.8 (C-Cp), 35.0 (C6), 33.0 (C8),
29.7 (C3), 9.4 (br m, Me-B(C6F5)3), 9.1 (C9). 11B NMR
(dichloromethane-d2, 200 MHz, 298 K): δ ) -15. 19F NMR
(dichloromethane-d2, 360 MHz, 298 K): -131 (m, 6F, o-(CH3)B-
(C6F5)3), -163 (m, 6F, p-(CH3)B(C6F5)3), -166 (m, 6F, m-(CH3)B-
(C6F5)3).
2
1H, 5-H), 3.72/3.56 (each d, J ) 17.6 Hz, 1H, 8-H′, 8-H), 3.18
3
2
(pdd, J ) 8.2 Hz, J ) 13.7 Hz, 1H, 6-H′), 2.24 (s, 3H, 13-H),
3
2
3
2.20 (pdd, J ) 5.5 Hz, J ) 13.7 Hz,1H, 6-H), 1.98 (pdd, J )
2
8.1 Hz, J ) 10.0 Hz, 1H, 3-H′), 1.38 (pt, J ) 10.0, 1H, 3-H),
2,2-Bis(η5-cyclop en t a d ien yl)-2,3-d ih yd r o-7-p h en yl-2-
t a n t a la -6H -a zep in e Met h ylt r is(p en t a flu or op h en yl)b o-
r a te (14c). A 300 mg (0.34 mmol) sample of 10 and 0.1 mL
(0.98 mmol) of benzonitrile were dissolved in 15 mL of
bromobenzene and stirred for 10 h at 60 °C. The reaction
mixture was filtered, and the solvent was removed. The
residue was taken up in 5 mL of dichloromethane. After
addition of 15 mL of pentane the crude product precipitated.
The solvent was decanted, and the crude product was stirred
for 5 h at - 20 °C in 20 mL of pentane. Subsequently the
product was collected on a Schlenk frit, washed with three
portions of 15 mL of pentane (cooled at -20 °C), and dried in
vacuo. Yield: 231 mg (69%), mp 198 °C (dec). Anal. Calcd
0.41 (br s, 3H, Me-B(C6F5)3). TOCSY NMR (dichloromethane-
d2, 599.8 MHz, 198 K): Irradiation at δ ) 4.77 (5-H) gave
resonances at δ ) 6.19 (4-H), 3.18 (6-H′), 2.20 (6-H), 1.98 (3-
H′), 1.38 (3-H). 13C NMR (dichloromethane-d2, 150.8 MHz, 198
K): δ ) 181.6 (C7), 147.3 (pd, 1J CF ) 244 Hz, o-B(C6F5)3), 138.3
1
(C4), 136.9 (C9), 136.7 (pd, J CF ) 244 Hz, p-B(C6F5)3), 135.7
(pd, 1J CF ) 244 Hz, m-B(C6F5)3), 130.7 (C12), 128.9 (C11), 128.5
(C10), 127.3 (br m, ipso-B(C6F5)3), 112.6 (C5), 107.2/104.7 (C-
Cp), 45.1 (C8), 34.2 (C6), 29.7 (C3), 20.6 (C13), 9.35 (br m, Me-
B(C6F5)3). 11B NMR (dichloromethane-d2, 200 MHz, 298 K):
δ ) -15. 19F NMR (dichloromethane-d2, 360 MHz, 298 K):
-131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B(C6F5)3),
-166 (m, 6F, m-(CH3)B(C6F5)3).
for
Found: C, 46.77; H, 2.68; N, 1.41. IR (KBr): ν˜ ) 3125, 2959,
1652, 1512, 1457, 1266, 1087, 995-935, 849 cm-1 1H NMR
C
40H24BF15NTa (995.23): C, 48.27; H, 2.43; N, 1.41.
X-ray crystal structure analysis of 14d : formula C42H28BF15-
NTa, M ) 1023.41, yellow-orange crystal, 0.30 × 0.20 × 0.20
mm, a ) 14.464(3) Å, b ) 12.282(2) Å, c ) 21.057(3) Å, â )
90.39(2)°, V ) 3771.4(11) Å3, Fcalc ) 1.802 g cm-3, F(000) )
2000 e, µ ) 30.23 cm-1, empirical absorption correction via æ
scan data (0.899 e C e 0.999), Z ) 4, monoclinic, space group
P21/n (No. 14), λ ) 0.710 73 Å, T ) 223 K, ω/2θ scans, 7858
reflections collected ((h, +k, +l), [(sin θ)/λ] ) 0.62 Å-1, 7648
independent and 6242 observed reflections [I g 2 σ(I)], 543
refined parameters, R ) 0.039, wR2 ) 0.105, max. residual
electron density 0.84 (-0.99) e Å-3, hydrogens calculated and
refined as riding atoms.
.
(dichloromethane-d2, 599.8 MHz, 298 K): δ ) 7.79 (m, 2H,
9-H), 7.63 (m, 1H, 11-H), 7.55 (m, 2H, 10-H), 6.43 (pq, 1H,
4-H), 6.08 (s, 10H, Cp-H), 5.63 (pq, 1H, 5-H), 3.20 (v br, 2H,
6-H), 1.99 (br, 2H, 3-H), 0.52 (br s, 3H, Me-B(C6F5)3). Result
of the dynamic 1H NMR spectroscopy (dichloromethane-d2,
599.8 MHz): ∆ν of the Cp resonances without exchange (T )
198 K) ) 40.9 Hz; coalescence temperature Tc ) 241 K;
activation energy ∆Gq(241 K) ) 11.5 ( 0.3 kcal mol-1
.
1H
NMR (dichloromethane-d2, 599.8 MHz, 213 K): δ ) 7.78 (pd,
2H, 9-H), 7.57 (pt, 1H, 11-H), 7.48 (pt, 2H, 10-H), 6.34 (pq,
1H, 4-H), 6.08/6.01 (each s, 5H, Cp-H), 4.93 (pq, 2H, 5-H),
2,2-Bis(η5-cyclop en ta d ien yl)-2,3-d ih yd r o-7-(d ip h en yl-
m eth yl)-2-tan tala-6H-azepin e Meth yltr is(pen taflu or oph e-
n yl)bor a te (14e). According to the procedure of 14c the
reaction of 400 mg (0.45 mmol) of 10 with 0.2 mL (0.897 mmol)
of diphenylacetonitrile led to the formation of 14e. Yield: 321
mg (66%), mp 207 °C (dec). Anal. Calcd for C47H30BF15NTa
(1085.36): C, 52.01; H, 2.79; N, 1.29. Found: C, 51.10; H, 3.14;
N, 1.39. IR (KBr): ν˜ ) 3110, 1695, 1640, 1510, 1457, 1264,
2
3
2
3.99 (dd, J ) 13.5 Hz, J ) 8.4 Hz, 1H, 6-H′), 2.22 (dd, J )
3
2
3
13.5 Hz, J ) 5.8 Hz, 1H, 6-H), 2.15 (dd, J ) 11.2 Hz, J )
3
8.5 Hz, 1H, 3-H′), 1.62 (pt, J ) 8.5 Hz, 1H, 3-H), 0.41 (br s,
3H, Me-B(C6F5)3). TOCSY NMR (dichloromethane-d2, 599.8
MHz, 213 K): Irradiation at δ ) 2.22 (6-H) gave resonances
at δ ) 6.34 (4-H), 4.93 (5-H), 3.99 (6-H′), 2.15 (3-H′), 1.62 (3-
H). 13C NMR (dichloromethane-d2, 150.8 MHz, 213 K): δ )
1087, 994-934, 841, 702 cm-1
.
1H NMR (dichloromethane-
1
175.5 (C7), 147.3 (pd, J CF ) 241 Hz, o-B(C6F5)3), 138.9 (C4),
d2, 599.8 MHz): δ ) 7.42 (m, 4-H, m-Ph), 7.37 (m, 2H, p-Ph),
7.08 (m, 4-H, o-Ph), 6.32 (pq, 1H, 4-H), 5.83 (s, 10, Cp-H),
5.05 (s, 1H, 8-H), 4.86 (pq, 1H, 5-H), 2.76 (br s, 2H, 6-H), 1.84
(br s, 2H, 3-H), 0.53 (br s, 3H, Me-B(C6F5)3). Result of the
dynamic 1H NMR spectroscopy (dichloromethane-d2, 599.8
MHz): ∆ν of the Cp resonances without exchange (T ) 198
K) ) 67.3 Hz; coalescence temperature Tc ) 251 K; activation
1
1
136.72 (pd, J CF ) 244 Hz, p-B(C6F5)3), 135.7(pd, J CF ) 249
Hz, m-B(C6F5)3), 133.0 (C8), 130.7 (C11), 129.0 (C9), 128.5
(C10), 127 (br m, ipso-B(C6F5)3), 113.4 (C5), 107.4/104.9 (each
Cp-H), 30.2 (C6), 29.1 (C3), 9.2 (Me-B(C6F5)3). 11B NMR
(dichloromethane-d2, 200 MHz, 298 K): δ ) -15. 19F NMR
(dichloromethane-d2, 360 MHz, 298 K): -131 (m, 6F, o-(CH3)B-
(C6F5)3), -163 (m, 6F, p-(CH3)B(C6F5)3), -166 (m, 6F, m-(CH3)B-
(C6F5)3).
energy ∆Gq(251 K) ) 11.8 ( 0.3 kcal mol-1
.
1H NMR
(dichloromethane-d2, 599.8 MHz, 198 K): δ ) 7.36 (m, 4H,
m-Ph), 7.30 (m, 2H, p-Ph), 7.06/6.93 (each d, 3J ) 7.5 Hz, 3J )
7.3 Hz, 2H, o-Ph), 6.25 (pq, 1H, 4-H), 5.81/5.70 (each s, 5H,
Cp-H), 5.12 (s, 1H, 8-H), 4.77 (pq, 1H, 5-H), 3.10 (dd, 2J )
2,2-Bis(η5-cyclop en t a d ien yl)-2,3-d ih yd r o-7-(p -t olyl-
m eth yl)-2-tan tala-6H-azepin e Meth yltr is(pen taflu or oph e-
n yl)bor a te (14d ). According to the procedure of 14c the
reaction of 500 mg (0.56 mmol) of 10 with 0.2 mL (1.52 mmol)
of p-tolylacetonitrile led to the formation of 14d . Yield: 369
mg (65%). Single crystals suitable for X-ray diffraction
analysis were obtained by slow diffusion of pentane into a
dichloromethane solution of 14d at room temperature; mp 188
°C (dec). Anal. Calcd for C42H38BF15NTa (1023.3): C, 49.30;
3
2
3
13.6 Hz, J ) 8.3 Hz, 1H, 6-H′), 2.24 (dd, J ) 13.6 Hz, J )
5.1 Hz, 1H, 6-H), 2.00 (pt, J ) 10.3 Hz, 1H, 3-H′), 1.45 (pt, J
) 10.3 Hz, 1H, 3-H), 0.41 (br s, 3H, Me-B(C6F5)3). TOCSY
NMR (dichloromethane-d2, 599.8 MHz, 198 K): Irradiation at
δ ) 2.24 (6-H′) gave resonances at δ ) 6.25 (4-H), 4.77 (5-H),
3.10 (6-H′), 2.00 (3-H′), 1.45 (3-H). 13C NMR (dichloromethane-

(s-trans-η4-Butadiene)tantalocene Cation
Organometallics, Vol. 17, No. 26, 1998 5757
1
d2, 150.8 MHz, 198 K): δ ) 182.4 (C7), 147.4 (pd, J CF ) 234
Hz, o-B(C6F5)3), 138.5 (C4), 138.0, 136.7 (C9, C13), 136.7 (pd,
(1-3:6-η)-5-P r op ylh exa -2,5-d ien -1,6-ylen ebis(η5-cyclo-
p en ta d ien yl)ta n ta lu m Meth yltr is(p en ta flu or op h en yl)-
b or a t e (15b ) a n d (1-3:6-η)-6-P r op ylh exa -2,5-d ien -1,6-
ylen ebis(cyclop en ta d ien yl)ta n ta lu m Meth yltr is(p en ta -
flu or op h en yl)bor a te (15c). According to the procedure of
15a the reaction of 500 mg (0.56 mmol) of 10 and 0.2 mL of
pentyne led to the formation of a mixture of 15b and 15c.
1J CF ) 243 Hz, p-B(C6F5)3), 135.7 (pd, J CF ) 246 Hz,
1
m-B(C6F5)3), 128.8, 128.5, 128.2, 128.1 (C10, C11, C14, C15),
127.6, 127.5 (C12, C16), 127.4 (br m, ipso-B(C6F5)3), 113.2 (C5),
107.2/104.7 (C-Cp), 59.7 (C8), 34.4 (C6), 30.2 (C3), 9.4 (br m,
Me-B(C6F5)3). 11B NMR (dichloromethane-d2, 200 MHz, 298
K): δ ) -15 ppm. 19F NMR (dichloromethane-d2, 360 MHz,
298 K): -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B-
(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
(1-3:6-η)-5,6-Dim eth ylh exa -2,5-d ien -1,6-ylen ebis(η5-cy-
clopen tadien yl)tan talu m Meth yltr is(pen taflu or oph en yl)-
bor a te (15a ). A 500 mg (0.56 mmol) sample of 10 and 0.2
mL of butyne were dissolved in 25 mL of bromobenzene and
stirred for 48 h at 60 °C. Subsequently the solvent was
removed and the residue was stirred in 20 mL of pentane.
After collecting the product on a Schlenk frit the product was
washed with two portions of 20 mL of pentane and dried in
vacuo. Single crystals suitable for X-ray diffraction analysis
were obtained by slow diffusion of pentane into a dichlo-
romethane solution of 15a at room temperature. Yield: 381
Yield: 412 mg (77%), mp 173 °C. Anal. Calcd for C38H27BF15
-
Ta (960.23): C, 47.53; H, 2.83. Found: C, 47.54; H, 3.25. IR
(KBr): ν˜ ) 3130, 2959, 2933, 2871, 1640, 1510, 1458, 1273,
1089, 1017-934, 854 cm-1 1H NMR (bromobenzene-d5, 599.8
.
MHz, 298 K): The 1H NMR spectrum showed two regioisomers
15b:15c in a ratio of 60:40. Isomer 15b: δ ) 6.64-6.61 (m,
1H, 6-H), 5.12-5.07 (m, 1H, 3-H), 5.03/4.89 (each s, 5H, Cp-
H), 4.84-4.79 (m, 1H, 2-H), 2.86-2.82 (m, 1H, 4-H′), 2.30-
2.24 (m, 1H, 4-H), 2.10-2.08 (m, 1H, 1-H′), 1.72-1.68 (m, 1H,
7-H′), 1.58-1.54 (m, 1H, 7-H), 1.27-1.21 (m, 1H, 8-H′), 1.17-
1.15 (m, 1H, 8-H), 1.05-1.02 (m, 1H, 1-H), 0.87 (t, 3J ) 4.8
Hz, 9-H). Isomer 15c: δ ) 5.81-5.80 (m, 1H, 5-H), 5.04-
4.89 (m, 1H, 3-H), 5.00-4.87 (each s, 5H, Cp-H), 4.61-4.55
(m, 1H, 2-H), 2.81-2.77 (m, 1H, 4-H′), 2.36-2.31 (m, 1H, 4-H),
2.07-2.04 (m, 1H, 1-H′), 1.83-1.78 (m, 1H, 7-H′), 1.75-1.72
(m, 1H, 7-H), 1.27-1.21 (m, 2H, 8-H), 1.01-0.97 (m, 1H, 1-H),
0.78 (t, 3J ) 7.8 Hz, 9-H). The resonance of the methyltris-
(pentafluorophenyl)borate anion was identical for both regioi-
somers at δ ) 1.11. TOCSY NMR (bromobenzene-d5, 599.8
MHz, 298 K) 15b: Irradiation at δ ) 2.09 (1-H′) gave
resonances at δ ) 5.10 (3-H), 4.82 (2-H), 2.84 (4-H′), 2.27 (4-
H), 1.03 (1-H). 15c: Irradiation at δ ) 2.06 (1-H′) gave
resonances at δ ) 5.81 (5-H), 5.00 (3-H), 4.57 (2-H), 2.79 (4-
H′), 2.33 (4-H), 0.99 (1-H). 13C NMR (bromobenzene-d5, 150.8
MHz, 298 K) 15b: δ ) 154.8 (C6), 147.9 (C5), 112.9 (C3), 111.5
(C2), 102.5/101.8 (C-Cp), 47.2 (C7), 37.9 (C4), 35.0 (C1), 23.7
(C8), 14.2 (C9). 15c: δ ) 157.9 (C6), 140.1 (C5), 114.2 (C3),
109.3 (C2), 103.0/102.9 (C-Cp), 43.6 (C7), 39.1 (C4), 33.6 (C1),
21.3 (C8), 13.9 (C9). The resonance signals of the methyltris-
(pentafluorophenyl)borate anion were identical for both re-
mg (72%), mp 158 °C. Anal. Calcd for
C37H25BF15Ta
(946.20): C, 46.97; H, 2.66. Found: C, 46.61; H, 2.92. IR
(KBr): ν˜ ) 3128, 2961, 2910, 2852, 1639, 1511, 1457, 1272,
1088, 1017-934, 861, 839 cm-1 1H NMR (bromobenzene-d5,
.
599.8 MHz, 298 K): δ ) 5.00/4.88 (each s, 5H, Cp-H), 4.87-
4.82 (m, 1H, 3-H), 4.77-4.71 (m, 1H, 2-H), 2.91 (pdd, 2J ) 16.1
Hz, 3J ) 4.6 Hz, 1H, 4-H′), 2.44-2.40 (m, 1H, 4-H), 2.11 (pdd,
2J ) 5.4 Hz, 3J ) 7.7 Hz, 1H, 1-H′), 1.44 (m, 3H, 7-H), 1.37 (s,
3H, 8-H), 1.10 (br s, 3H, Me-B(C6F5)3), 1.03 (pdd, 2J ) 5.43
3
Hz, J ) 13.2 Hz, 1H, 1-H): TOCSY NMR (bromobenzene-d5,
599.8 MHz, 298 K): Irradiation at δ ) 4.87 (3-H) gave
resonances at δ ) 4.75 (2-H), 2.91 (4-H′), 2.42 (4-H), 2.11 (1-
H′), 1.03 (1-H). 13C NMR (bromobenzene-d5, 599.8 MHz, 298
K): δ ) 163.8 (C6), 148.6 (d, 1J CF ) 237 Hz, o-B(C6F5)3), 143.5
(C5), 137.6 (d, 1J CF ) 244 Hz, p-B(C6F5)3), 136.7 (d, 1J CF ) 244
Hz, m-B(C6F5)3), 112.2 (C2), 105.2 (C3), 102.8/101.8 (C-Cp),
43.3 (C4), 36.3 (C1), 28.3 (C7), 20.8 (C8), 11.2 (br m, Me-
B(C6F5)3). The resonance signal of the ipso-carbon atom of the
1
gioisomers: 148.6 (pd, J CF ) 237 Hz, o-B(C6F5)3), 137.6 (pd,
1
1J CF ) 246 Hz, p-B(C6F5)3), 136.5 (pd, J CF ) 246 Hz,
m-B(C6F5)3), 11.2 (br m, Me-B(C6F5)3). The resonance signal
of the ipso-carbon atom of the tris(pentafluorophenyl)borane
fragment was not observed. 11B NMR (dichloromethane-d2,
200 MHz, 298 K): δ ) -15. 19F NMR (dichloromethane-d2,
360 MHz, 298 K): -131 (m, 6F, o-(CH3)B(C6F5)3), -163 (m,
6F, p-(CH3)B(C6F5)3), -166 (m, 6F, m-(CH3)B(C6F5)3).
tris(pentafluorophenyl)borane fragment was not observed. 11
B
NMR (dichloromethane-d2, 200 MHz, 298 K): δ ) -15. 19F
NMR (dichloromethane-d2, 360 MHz, 298 K): -131 (m, 6F,
o-(CH3)B(C6F5)3), -163 (m, 6F, p-(CH3)B(C6F5)3), -166 (m, 6F,
m-(CH3)B(C6F5)3).
X-ray crystal structure analysis of 15a : formula C37H25BF15
-
Ta, M ) 946.33, yellow crystal, 0.50 × 0.50 × 0.25 mm, a )
12.722(1) Å, b ) 14.150(1) Å, c ) 19.317(1) Å, â ) 107.50(1)°,
V ) 3316.4(4) Å3, Fcalc ) 1.895 g cm-3, F(000) ) 1840 e, µ )
34.28 cm-1, empirical absorption correction via æ scan data
(0.945 e C e 0.999), Z ) 4, monoclinic, space group P21/n (No.
14), λ ) 0.710 73 Å, T ) 223 K, ω/2θ scans, 6941 reflections
collected ((h, +k, +l), [(sin θ)/λ] ) 0.62 Å-1, 6739 independent
and 5610 observed reflections [I g 2 σ(I)], 500 refined
parameters, R ) 0.032, wR2 ) 0.089, max. residual electron
density 1.33 (-1.78) e Å-3, atom C3 disordered with ratio 054-
(2):046(2), thermal parameters of C11, C12, C15, and C16
indicate disorder, refinement with split positions leads to no
improvement, hydrogens calculated and refined as riding
atoms.
Ackn owledgm en t. Financial support from the Fonds
der Chemischen Industrie, the Bundesminister fu¨r
Bildung, Wissenschaft, Forschung und Technologie, and
the Deutsche Forschungsgemeinschaft is gratefully
acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Details of the X-ray
crystal structure analyses of complexes 10, 14a , 14d , and 15a ,
including complete listings of bond lengths and angles, thermal
parameters, and atomic positional parameters and listings of
additional NMR data (GCOSY and GHSQC) (43 pages).
Ordering information is given on any current masthead page.
OM980576L