Formation, structure, and dynamic behavior of a novel dinuclear cationic μ-2,4-hexadiyne bis(zirconocene) complex

Article abstract of DOI:10.1021/om960918s

Bis(propynyl)zirconocene (1b) reacts with 0.5 molar equiv of trityl tetraphenylborate by a propynyl group transfer to form Ph₃CC≡CCH₃ and Cp₂ZrC≡CCH₃⁺. The in-situ-generated (propynyl)zirconocene cation is not stable under the reaction conditions but instantaneously reacts with the neutral starting material 1b to form the [(μ-C≡CCH₃)(μ-CH₃C≡CC≡CCH ₃)-(ZrCp₂)₂⁺][BPh₄ ^-] salt, 9. Complex 9 was characterized by an X-ray crystal structure analysis. It contains an unsymmetrically bridging hexadiyne ligand and exhibits a planar-tetracoordinate carbon center that is stabilized by a three-center two-electron interaction with the two adjacent zirconocene moieties. In solution, complex 9 exhibits dynamic NMR spectra that indicate a symmetrizing exchange of the bonding situations between the two ends of the μ-hexadiyne ligand. The Gibbs activation energy of the automerization reaction of 9 is ΔG?(190 K) ≈ 9.5 kcal mol^-1.

Full text of DOI:10.1021/om960918s

1440
Organometallics 1997, 16, 1440-1444
F or m a tion , Str u ctu r e, a n d Dyn a m ic Beh a vior of a Novel
Din u clea r Ca tion ic µ-2,4-Hexa d iyn e Bis(zir con ocen e)
Com p lex†
Wolfgang Ahlers, Bodo Temme, Gerhard Erker,* Roland Fro¨hlich, and
Frank Zippel
Organisch-Chemisches Institut der Universita¨t Mu¨nster, Corrensstrasse 40,
D-48149 Mu¨nster, Germany
Received October 31, 1996X
Bis(propynyl)zirconocene (1b) reacts with 0.5 molar equiv of trityl tetraphenylborate by a
propynyl group transfer to form Ph3CCtCCH3 and Cp2ZrCtCCH3+. The in-situ-generated
(propynyl)zirconocene cation is not stable under the reaction conditions but instantaneously
reacts with the neutral starting material 1b to form the [(µ-CtCCH3)(µ-CH3CtCCtCCH3)-
+
(ZrCp2)2 ][BPh4-] salt, 9. Complex 9 was characterized by an X-ray crystal structure analysis.
It contains an unsymmetrically bridging hexadiyne ligand and exhibits a planar-tetracoor-
dinate carbon center that is stabilized by a three-center two-electron interaction with the
two adjacent zirconocene moieties. In solution, complex 9 exhibits dynamic NMR spectra
that indicate a symmetrizing exchange of the bonding situations between the two ends of
the µ-hexadiyne ligand. The Gibbs activation energy of the automerization reaction of 9 is
∆Gq(190 K) ≈ 9.5 kcal mol-1
.
In tr od u ction
The chemistry of alkyl- and hydridozirconocene cat-
ions, Cp2ZrR+ and Cp2ZrH+, respectively, has been of
considerable interest due to their involvement as im-
portant reactive species in alkene polymerization reac-
tions at homogeneous metallocene Ziegler catalysts.1,2
In addition, an interesting stoichiometric organometallic
chemistry of various Cp2ZrR+ cations is evolving that,
among other topics, has led to the disclosure and
development of a variety of novel types of organometallic
compounds.3 The formation of dimetallic systems 3 that
contain a planar-tetracoordinate carbon atom is a
prominent example (eq 1).4
about the organometallic chemistry of the Cp2ZrR+
complexes that contain σ-alkenyl or -alkynyl groups.1,5
There is evidence that such systems may exhibit an
enhanced reactivity, and thus, it might be more diffi-
cult to isolate them. A typical example is depicted
+
in eq 2, where the Cp2ZrCtCCH3 cation is formed
A number of interesting reactions of Cp2ZrR+ systems
containing simple unfunctionalized hydrocarbyl σ-ligands
R have been reported so far, but much less is known
by a σ-ligand abstraction using the strong organome-
tallic Lewis acid B(C6F5)3 but evades its isolation by a
very rapid subsequent insertion reaction of the func-
tionalized borate anion to yield the stable betaine
product 5.6
* Corresponding author. FAX: +49-251-8339772. E-mail: erker@uni-
muenster.de.
We have now generated the reactive Cp2ZrCtCR+
cation system in a different way, starting from the bis-
(alkynyl)metallocene 1,7 and have found yet another
mode of stabilization by a subsequent CC-coupling
† Dedicated to Professor Peter Welzel on the occasion of his 60th
birthday.
X Abstract published in Advance ACS Abstracts, March 1, 1997.
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S0276-7333(96)00918-1 CCC: $14.00 © 1997 American Chemical Society

Cationic µ-2,4-Hexadiyne Bis(zirconocene)
Organometallics, Vol. 16, No. 7, 1997 1441
-
complex [Cp2Ti(THF)2+]BPh4 (7).9ac The blue bis-
(cyclopentadienyl)bis(tetrahydrofuran)titanium(III) tet-
raphenylborate salt was isolated and identified by an
X-ray crystal structure analysis. The molecular struc-
ture of the Cp2Ti(THF)2+ cation in the crystal structure
of 7 is analogous to the structures recently observed for
reaction that led to a novel dinuclear µ-2,4-hexadiyne
bis(zirconocene) complex exhibiting interesting struc-
tural features and a dynamic behavior.
Resu lts a n d Discu ssion
several closely related examples ([Cp2Ti(THF)-
- 9a
(acetonitrile)+]BPh4
,
[Cp2Ti(THF)2+]Co(CO)4- 9b and
,
Gen er a tin g Liga n d -Sta bilized σ-P r op yn yl Gr ou p
4 Meta llocen e Ca tion s. We have reacted the bis-
(propynyl)metallocenes 1a -c (M ) Ti, Zr, Hf) with N,N-
dimethylanilinium tetraphenylborate8 in THF solution
at low temperature. In a typical experiment Cp2Zr-
(CtCCH3)2 (1b) was dissolved in THF-d8 and charged
[Cp2Ti(pyridine)2+]BPh4- 9c). In 7, the (THF-oxygen)-
Ti-(THF-oxygen) angle is 77.49(7)°; the corresponding
Ti-O distances are 2.208(2) and 2.239(2) Å (further
details about the structure of 7 are provided with the
Supporting Information).
-
with PhNMe2H+BPh4 at -78 °C. Under direct 1H
We, thus, have concluded that ligand-stabilized (σ-
alkynyl)metallocene cations can be generated by means
of protonation reactions, employing a suitable non-
nucleophilic counteranion, of course. Then we tried to
use a similar technique to generate the corresponding
donor ligand free Cp2MCtCCH3+ cations. This was not
successful using the protonation reaction, but an inter-
esting reaction sequence was found when the Cp2Zr-
(CtCCH3)2 starting material (1b) was treated with
trityl tetraphenylborate10 in a noncoordinating solvent.
Syn t h esis of a Din u clea r µ-2,4-Hexa d iyn e Bis-
(zir con ocen e) Ca t ion Syst em . Bis(propynyl)zir-
conocene (1b) was treated with trityl tetraphenylborate
in toluene solution at 0 °C. A product (9) is formed that
precipitates from the aromatic solvent and, thus, is
isolated in close to quantitative yield. Recrystallization
from dichloromethane at -20 °C furnished single crys-
tals of 9 that were suitable for an X-ray crystal structure
analysis.
The X-ray crystal structure analysis of 9 shows the
presence of an organometallic salt with a well-separated
cation and tetraphenylborate anion. The organometallic
monocation of 9 contains two zirconocene units that are
connected by means of two different hydrocarbyl units.
One of the bridges is made up by a µ-η1:η1-propynyl
ligand (Zr1-C30, 2.259(6) Å; Zr2-C30, 2.446(5) Å;
C30-C31, 1.215(8) Å; Zr1-C30-Zr2, 103.0(2)°). These
bonding features are typical of a σ-bridging acetylide
ligand; a closely related molecular arrangement and
NMR monitoring, it was observed that the system
started to react at -40 °C with the formation of propyne
(1H NMR: δ 2.02 (q, 1H), 1.73 (d, 3H)) and the THF-
d8-stabilized (σ-propynyl)zirconocene cation (6b). The
latter is characterized by typical 1H/13C NMR reso-
nances at δ 6.45 (10H, Cp)/115.7 and 1.94 (3H, CH3)/
5.8. The cation 6b is only moderately stable in THF-
d8 solution. Even at -10 °C it is unspecifically decom-
posed during several hours. We tried to isolate the
[Cp2Zr(CtCCH3)(THF)+]BPh4- salt from THF solutions
but have been unsuccessful so far.
The corresponding Cp2Hf(CtCCH3)(THF)+ and Cp2-
Ti(CtCCH3)(THF)+ systems 6c and 6a are slightly
more stable than the zirconium system 6b, but their
isolation has also evaded us so far. Both were, however,
characterized spectroscopically after being generated by
treatment of the respective Cp2M(CtCCH3)2 starting
-
materials (1c, 1a ) with PhNMe2H+BPh4 in THF-d8.
+
1
The (σ-propynyl)TiCp2 cation, thus, exhibits H NMR
signals at δ 6.47 (Cp) and 2.15 (CH3) in a 10:3 intensity
ratio and 13C NMR resonances at δ 119.7 (Cp), 148.0
(R-CtC), 77.0 (â-CtC), and 6.5 (CH3).
Above room temperature, the [Cp2Hf(CtCCH3)-
-
(THF)+]BPh4 system, 6c, decomposes unspecifically.
+
In contrast, the (σ-propynyl)(tetrahydrofuran)TiCp2
cation is decomposed in ca. 3 days at ambient temper-
ature to yield the known paramagnetic titanium(III)
(7) (a) Erker, G.; Fro¨mberg, W.; Mynott, R.; Gabor, B.; Kru¨ger, C.
Angew. Chem. 1986, 98, 456; Angew. Chem., Int. Ed. Engl. 1986, 25,
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metallics 1993, 12, 486. (b) Merola, J . S.; Campo, K. S.; Gentile, R. A.
Inorg. Chem. 1989, 28, 2950. Merola, J . S.; Campo, K. S.; Modrick, M.
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102, 830; Angew. Chem., Int. Ed. Engl. 1990, 29, 780.

1442 Organometallics, Vol. 16, No. 7, 1997
Ahlers et al.
Sch em e 1
similar bonding values have been observed for many
dinuclear µ-acetylide complexes having a group 4 tran-
sition metal involved.4,11,12
electron-deficient zirconium atom Zr1 (Zr1-C35, 2.453-
(5) Å; Zr1-C34, 2.763(6) Å). This rather unsymmetric
“π-agostic” interaction14 leads to some distortion of this
alkynyl group: the C35-C34 triple bond (1.203(8) Å)
is bent toward zirconium (C36-C35-C34, 164.2(6)°),
whereas the terminal methyl group is oriented away
from the metal center (C35-C34-C33, 169.2(7)°)
(Scheme 1).
It is the second hydrocarbyl bridge that makes the
structure of complex 9 so noteworthy. The two zirco-
nium centers are connected by a µ-2,4-hexadiyne ligand
that has been formed by the CC-coupling of two σ-pro-
pynyl ligand at zirconium. The hexadiyne bridges the
two zirconium centers unsymmetrically. The bridging
function is carried out essentially by one of the triple
bonds. It connects them in an η1:η2-fashion. The Zr2-
C37 bond is very short, 2.173(5) Å. The C37-C36
linkage is in the range of a carbon-carbon double bond
(1.317(8) Å). Carbon atom C36 is bonded to both Zr2
and Zr1. This connection is best described as a three-
center two-electron bonding situation (Zr2-C36, 2.530-
(5) Å; Zr1-C36, 2.435(6) Å).4,11 This specific connection
makes carbon atom C36 planar-tetracoordinate.13 It is
bonded to four closely neighboring atoms (C37, Zr2, Zr1,
C35; C36-C35, 1.401(8) Å). The respective bonding
angles around C36 are 130.9(5)° (C35-C36-C37), 59.2-
(3)° (C37-C36-Zr2), 95.8(2)° (Zr2-C36-Zr1), and 74.1-
(3)° (Zr1-C36-C35). The remaining alkynyl group
connected to C36 is only weakly coordinated to the
The global minimum structure of 9 in solution is
equivalent, although complex 9 exhibits dynamic NMR
spectra in solution. The salt 9 is only sparingly soluble
in most noncoordinating solvents. However, its solubil-
ity in CD2Cl2 is just sufficient enough to obtain the
limiting low-temperature 1H NMR spectrum. At 180
K (200 MHz), complex 9 exhibits two sharp Cp singlets
at δ 5.78 and 5.70 (each of relative intensity 10). The
CH3 singlets of the µ-2,4-hexadiyne ligand appear at δ
1
2.84 and 2.55 (each of relative intensity 3), and the H
NMR resonance of the µ-η1:η1-CtC-CH3 ligand appears
at δ 2.41 (relative intensity 3). Upon raising the
monitoring temperature, the Cp signals as well as the
hexadiyne methyl resonances rapidly get broad and
coalesce. At high temperature (269 K), a very simple
1H NMR spectrum of the rapidly equilibrating species
is observed, showing three singlets at δ 5.79 (Cp), 2.75
(CH3), and 2.45 (CtCCH3) in a 20:6:3 ratio. The 13C
NMR spectrum (in THF-d8, 168 K) at the low-temper-
ature limit exhibits signals at δ 219.5, 129.1, 114.1,
110.6, 106.0 and 48.8 (C), 110.4 and 110.0 (Cp), and
33.1, 10.1, 7.9 (CH3).
(11) Erker, G.; Zwettler, R.; Kru¨ger, C.; Noe, R.; Werner, S. J . Am.
Chem. Soc. 1990, 112, 9620. Albrecht, M.; Erker, G.; Nolte, M.; Kru¨ger,
C. J . Organomet. Chem. 1992, 427, C21. Erker, G.; Albrecht, M.;
Werner, S.; Nolte, M.; Kru¨ger, C. Chem. Ber. 1992, 125, 1953. Erker,
G.; Albrecht, M.; Kru¨ger, C.; Werner, S. J . Am. Chem. Soc. 1992, 114,
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R.; Erker, G. Angew. Chem. 1994, 106, 213; Angew. Chem., Int. Ed.
Engl. 1994, 33, 197. Binger, P.; Sandmeyer, F.; Kru¨ger, C.; Erker, G.
Tetrahedron 1995, 51, 4277. Reviews: Erker, G. Comm. Inorg. Chem.
1992, 13, 111. Erker, G. Nachr. Chem., Tech. Lab. 1992, 40, 1099.
Albrecht, M.; Erker, G.; Kru¨ger, C. Synlett 1993, 441.
(12) Nast, R. Coord. Chem. Rev. 1982, 47, 89. Kumar, P. N. V. P.;
J emmis, E. D. J . Am. Chem. Soc. 1988, 110, 125. Erker, G.; Albrecht,
M.; Kru¨ger, C.; Nolte, M.; Werner, S. Organometallics 1993, 12, 4979.
(13) Hoffmann, R.; Alder, R. W.; Wilcox, C. F., J r. J . Am. Chem.
Soc. 1970, 92, 4992. Collins, J . B.; Dill, J . D.; J emmis, E. D.; Apeloig,
Y.; Schleyer, P. v. R.; Seeger, R.; Pople, J . A. J . Am. Chem. Soc. 1976,
98, 5419. Schleyer, P. v. R.; Boldyrev, A. I. J . Chem. Soc., Chem.
Commun. 1991, 1536. Gleiter, R.; Hyla-Kryspin, I.; Niu, S.; Erker, G.
Angew. Chem. 1993, 105, 753; Angew. Chem., Int. Ed. Engl. 1993, 32,
754. Gleiter, R.; Silverio, S. J .; Binger, P.; Sandmeyer, F.; Erker, G.
Chem. Ber. 1995, 128, 775. Poumbga, C. N.; Be´nard, M.; Hyla-Kryspin,
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Fleischer, R.; Stalke, D. J . Am. Chem. Soc. 1996, 118, 6924, and
references cited in these articles.
It must be assumed that the reaction of Cp2Zr-
(CtCCH3)2 (1b) with the trityl cation is initiated by a
σ-propynyl abstraction from zirconium and transfer to
carbon to give CH3CtCCPh3 (which is observed as a
reaction product by 1H NMR spectroscopy) and the Cp2-
+
ZrCtCCH3 cation (8). In the absence of a suitable
donor ligand, the 14e- cation 8 seems to be extremely
reactive, too reactive to be observed directly under the
reaction conditions and certainly too reactive to allow
its isolation from the reaction mixture. Instead, the
(14) Erker, G.; Noe, R.; Kru¨ger, C.; Werner, S. Organometallics 1992,
11, 4174.

Cationic µ-2,4-Hexadiyne Bis(zirconocene)
Organometallics, Vol. 16, No. 7, 1997 1443
intermediate 8 reacts instantaneously with the neutral
bis(propynyl)zirconocene starting material present in
solution. The associative coupling of the organometallic
reagents is probably facilitated by the high propensity
of connecting the two electrophilic metal centers by
means of a thermodynamically favorable Zr2(µ-η1:η1-
alkynyl) linkagessuch acetylide bridges seem to be
among the strongest means of connecting two zirconium
centers by a hydrocarbyl bridging ligand.4,11,12 The
system is then further stabilized by the subsequent
carbon-carbon coupling of two of the propynyl groups
present at the dinuclear zirconocene systems to form
the 2,4-hexadiyne ligand, which is then stabilized by
forming the unsymmetrically bridged Zr2[µ-(η1-C:η2-C,C]
dinuclear metallocene cation system (9), exhibiting a
planar-tetracoordinate carbon atom. We had recently
shown that the formation of (µ-RCCR)Zr2 type cations
containing a planar-tetracoordinate carbon center is in
general very favorable. The formation of the dimetal-
labicyclic structure with this unusual carbon coordina-
tion geometry was found to be favored by ca. 10-12 kcal
mol-1 over the dimetallacyclopentene.4a Therefore, it
is not surprising to observe the analogous structural
type here.
Often the alkyl substituents at C2 of the planar-
tetracoordinate carbon complexes 3 form an agostic
interaction with their adjacent metal center (i.e., Zr2
in 3, see eq 1).4,15 In the new complex 9, such a σ-agostic
interaction cannot be formed straightforwardly, since
the favored regioisomer (9) has a -CtCCH3+ substitu-
ent attached at its planar-tetracoordinate bridgehead
carbon. Instead, the π-system of this substituent is used
to diminish the electron-deficiency of the nearby zir-
conocene group by forming a weak π-agostic interac-
tion.14
It may be that this coordinative acetylide to metal
interaction facilitates the novel type of dynamic process
observed to take place within the cation 9. The parent
planar-tetracoordinate carbon complexes 3 (see eq 1) are
known to rapidly exchange the three-center two-electron
bonding situation between the zirconium centers Zr1/
Zr2 and C1/C2.4a This type of degenerate rearrange-
ment (which reversibly interchanges the planar-tetra-
coordinate carbon bonding situation between carbon
atoms C2 and C1) is prohibited in 9 because of the
unsymmetrical substitution pattern. However, we ob-
serve an alternative low-energy automerization path-
way (∆Gq(190 K) ≈ 9.5 ( 0.5 kcal mol-1 from the
dynamic 1H NMR experiment at the Cp coalescence
temperature) that leads to a mutual exchange of the
propynyl moieties of the µ-2,4-hexadiyne ligand (and
hence an intramolecular equilibration of the metallocene
units).16
Our study has again shown that planar-tetracoordi-
nate carbon is enormously stabilized by two zirconium
centers in the environment of the dimetallabicyclic
framework encountered here. At the same time, it
appears that the dimetallic (Cp2Zr)2(µ-CtCR)+ cation
fragment is formed very easily and may allow for the
formation of novel types of dinuclear metallocene π-com-
plexes that may show interesting properties when used
as stoichiometric organometallic reagents or in catalysis.
We are currently trying to develop the chemistry of such
species experimentally.
Exp er im en ta l Section
All reactions were carried out in an inert atmosphere (argon)
using Schlenk-type glassware or in a glovebox. Solvents were
dried and distilled under argon prior to use. For additional
general information, including a list of spectrometers and
equipment used for the physical characterization, see ref 4a.
The following compounds and reagents were prepared accord-
ing to published procedures: bis(propynyl)titanocene, -zir-
conocene, and -hafnocene (1a -c),7 N,N-dimethylanilinium
tetraphenylborate,18 and trityl tetraphenylborate.19
Rea ction of th e Bis(p r op yn yl) Gr ou p 4 Meta llocen es
1a -c w ith N,N-Dim eth yla n ilin iu m Tetr a p h en ylbor a te.
These reactions were carried out in deuterated solvent in a
NMR tube. The products 6a -c plus propyne were not isolated
but only characterized spectroscopically (1H, 13C NMR). Gen-
eral procedure: a sample of ca. 10 mg of the respective complex
6 was mixed with an equimolar quantity of solid N,N-
dimethylanilinium tetraphenylborate in a 5 mm NMR tube.
Then, ca. 0.5 mL of tetrahydrofuran-d8 was added at -50 °C.
Propyne was formed at -40 °C, and the metallocene cation
systems 6 were spectroscopically characterized at tempera-
tures <0 °C to prevent rapid decomposition. Complex 6a
(prepared starting from 10 mg (39 µmol) of 1a ): 1H NMR
(THF-d8) δ 6.47 (s, 10H, Cp), 2.15 (s, 3H, CH3); δ 7.32 (m, 8H),
6.90 (m, 8H), 6.75 (m, 4H) (BPh4-); δ 7.14, 6.65 (m, 5H, Ph),
2.88 (s, 6H, CH3) (N,N-dimethylaniline); δ 2.02 (q, 1H, CH),
1.73 (d, 3H, CH3) (propyne). 13C NMR (THF-d8): δ 148.0, 77.0,
6.5 (CtC-CH3), 119.7 (Cp); δ 165.1 (1J BC ) 50 Hz), 137.1,
125.8, 122.0 (BPh4-); δ 151.6, 132.6, 117.0, 113.2, 40.5 (N,N-
dimethylaniline); δ 80.0, 68.4, 2.8 (propyne). Complex 6b
(prepared starting from 10 mg (33 µmol) of 1b): 1H NMR
(THF-d8) δ 6.45 (s, 10H, Cp), 1.94 (s, 3H, CH3). 13C NMR
(THF-d8): δ 115.7 (Cp), 78.0, 5.8 (1 acetylide C not located).
Complex 6c (prepared starting from 8 mg (21 µmol) of 1c):
1H NMR (THF-d8) δ 6.38 (s, 10H, Cp), 1.96 (s, 3H, CH3). 13C
NMR (THF-d8): δ 114.9 (Cp), 139.6, 54.2, 5.7 (CtCCH3),
signals of BPh4-, N,N-dimethylaniline, and propyne, see above.
F or m a t ion of Bis(cyclop en t a d ien yl)b is(t et r a h yd r o-
fu r a n )tita n iu m (III) Tetr a p h en ylbor a te, 7. Bis(propynyl)-
titanocene (1a , 100 mg, 0.39 mmol) was mixed with 85 mg
(0.195 mmol) of N,N-dimethylanilinium tetraphenylborate;
then, 3 mL of THF was added. The mixture was briefly
homogenized with stirring and then left for 48 h at room
temperature without stirring. During that time, blue crystals
of 7 were formed that were characterized by an X-ray crystal
structure analysis of 7: formula C42H46O2BTi, Mw ) 641.50,
0.6 × 0.2 × 0.1 mm, a ) 13.008(3) Å, b ) 13.482(3) Å, c )
20.330(7) Å, â ) 106.98(2)°, V ) 3410(2) Å3, Fcalcd ) 1.250 g
cm-3, µ ) 2.87 cm-1, no absorption correction, Z ) 4, mono-
clinic, space group P21/c (No. 14), λ ) 0.710 73, ω/2θ scans,
Establishing the reaction pathway of this automer-
ization reaction in detail requires additional experimen-
tal investigations and probably a thorough theoretical
study, but it is likely that a symmetrical intermediate
geometry (transition state or high-lying reactive inter-
mediate) of a bis(π-alkyne)(ZrCp2)2(µ-CtCR) structural
type (10) is readily available starting from 9.6a,17
7224 reflections collected ((h,-k,(l), [(sin θ)/λ]max ) 0.62 Å-1
,
6921 independent and 4330 observed reflections [I > 2σ(I)],
(15) Horton, A. D.; Orpen, A. G. Angew. Chem. 1992, 104, 912;
Angew. Chem., Int. Ed. Engl. 1992, 31, 876.
(16) For a related exchange process of σ-acetylide ligands in di-
nuclear group 4 metallocene complexes, see: e.g. Erker, G.; Fro¨mberg,
W.; Benn, R.; Mynott, R.; Angermund, K.; Kru¨ger, C. Organometallics
1989, 8, 911.
(17) See for a comparison: Burlakov, V. V.; Ohff, A.; Lefeber, C.;
Tillack, A.; Baumann, W.; Kempe, R.; Rosenthal, U. Chem. Ber. 1995,
128, 967.
(18) Crane, F. E., J r. Anal. Chem. 1956, 28, 1794.
(19) Pohlmann, J . L. W.; Brinckmann, F. E. Z. Naturforsch. 1965,
20B, 5.

1444 Organometallics, Vol. 16, No. 7, 1997
Ahlers et al.
(84%) of 9, mp 166 °C (dec). 1H NMR (CDCl3, 300 K): δ 5.62
(s, 20H, Cp), 2.58 (s, 6H, CH3), 2.16 (s, 3H, CH3); δ 7.47 (m,
8H), 7.05 (m, 8H), 6.93 (m, 4H) (BPh4-). 1H NMR (THF-d8,
168 K): δ 6.01 (s, 10H, Cp), 5.94 (s, 10H, Cp), 2.98 (s, 3H,
CH3), 2.53 (s, 3H, CH3), 2.43 (s, 3H, CH3). 13C NMR (THF-d8,
300 K): δ 110.2 (Cp), 129.9, 112.0, 10.0 (µ-CtCCH3), 20.2
(CH3-CtCCtCCH3, acetylide carbons not observed at 300 K).
13C NMR (THF-d8, 168 K): δ 110.4, 110.0 (Cp), 129.1, 110.6,
10.1 (µ-CtCCH3), 219.5, 114.1, 106.0, 48.8, 33.1, 7.9 (µ-CH3-
CtCCtCCH3); δ 164.7 (1J BC ) 49 Hz, ipso-C of Ph), 137.0,
125.9, 122.0 (Ph) (BPh4-). 1H/13C-2D NMR correlation experi-
ments20 (atom numbering used as in Figure 1), GHSQC-NMR
(giving the immediate 13C/1H connection) (THF-d8, 168 K,
150.8/599.8 MHz): δ 110.4/6.01 (Cp), 110.0/5.94 (Cp), 33.1/2.98
(38), 10.1/2.43 (32), 7.9/2.53 (33). GHMBC-NMR (providing
the long-range 13C/1H correlation) (THF-d8, 168 K, 150.8/599.8
MHz): δ 219.5/2.98 (C-37/38-H), 129.1/2.43 (C-30/32-H),
114.1/2.53 (C-34/33-H), 110.6/2.43 (C-31/32-H), 110.4, 110.0,
106.0/2.98 (C-36/38-H), 48.8/2.53 (C-35/33-H), 33.1, 10.1, 7.9.
IR (KBr): ν˜ ) 3113 cm-1, 3053, 3032, 2982, 2918, 2850, 2065,
1579, 1479, 1427, 1262, 1015, 809, 744, 704. UV-vis
(dichloromethane): λmax ) 256 (ꢀ 14 300), 285 (sh, ꢀ 11 000),
314 (sh, ꢀ 4500). Anal. Calcd for C53H49BZr2 (879.2): C, 72.40;
H, 5.62. Found C, 73.82; H, 5.66%. X-ray crystal structure
analysis of 9: formula C53H49BZr2, Mw ) 879.17, 0.6 × 0.3 ×
0.25 mm, a ) 15.006(2) Å, b ) 15.086(4) Å, c ) 19.741(3) Å, â
) 111.53(1)°, V ) 4157.2(14) Å3, Fcalcd ) 1.405 g cm-3, µ ) 5.38
cm-1, empirical absorption correction via ψ-scan data (0.873
e C e 0.999), Z ) 4, monoclinic, space group P21/n (No. 14),
λ ) 0.710 73, ω/2θ scans, 7607 reflections collected (-h,-k,(l),
[(sin θ)/λ]max ) 0.59 Å-1, 7313 independent and 4400 observed
reflections [I > 2σ(I)], 508 refined parameters, R1 ) 0.053,
F igu r e 1. A view of the molecular geometry of the cation
9; carbon atom C36 is planar-tetracoordinate. Selected bond
lengths (Å) and angles (deg): Zr2-C(Cp) (av), 2.509(7);
Zr1-C(Cp) (av), 2.494(7); Zr2-C30, 2.446(5); Zr1-C30,
2.259(6); C30-C31, 1.215(8); C31-C32, 1.463(8); C30-
C31-C32, 173.4(6); Zr1-C30-Zr2, 103.0(2); Zr2-C30-
C31, 93.6(4); Zr1-C30-C31, 163.4(5); Zr2-C37, 2.173(5);
C37-C38, 1.481(8); C37-C36, 1.317(8); Zr2-C37-C38,
143.7(5); Zr2-C37-C36, 89.4(4); C36-C37-C38, 126.9(6);
C36-C35, 1.401(8); C35-C34, 1.203(8); C34-C33, 1.483-
(9); C35-C36-C37, 130.9(5) (for additional values, see
text).
wR2 ) 0.122, max residual electron density 0.81 (-1.54) e Å-3
,
hydrogens calculated and riding. Data were collected on an
Enraf-Nonius MACH3-diffractometer. Structures were solved
with the program SHELXS-86 and refined with SHELXL-93.
Graphics were done with XP.
Ackn owledgm en t. Financial support from the Fonds
der Chemischen Industrie, the Wissenschaftsministe-
rium des Landes Nordrhein-Westfalen, and the Volks-
wagen-Stiftung is gratefully acknowledged.
415 refined parameters, R1 ) 0.047, wR2 ) 0.113, max
residual electron density 0.38 (-0.35) e Å-3, hydrogens calcu-
lated and riding. For detailed information about the structural
data of 7 see the Supporting Information.
P r ep a r a tion of 9. A mixture of bis(propynyl)zirconocene
(1b, 500 mg, 1.65 mmol) and trityl tetraphenylborate (464 mg,
825 µmol) was suspended in 10 mL of dichloromethane and
stirred for 2 h at room temperature. Solvent was then
removed in vacuo, and the oily residue was stirred with
pentane overnight to solidify. The pentane phase was de-
canted (1,1,1-triphenylbut-2-yne was isolated from the pentane
phase: 1H NMR (CDCl3) δ 7.23 (m, 15H, Ph), 1.92 (s, 3H, CH3).
13C NMR (CDCl3): δ 145.9 (ipso-C of Ph), 129.1, 127.9, 126.6
(Ph), 85.1, 80.8 (CtC), 55.9 (CPh3), 3.9 (CH3)), and the
remaining precipitate was dried in vacuo to give 609 mg
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, atomic coordinates, bond
lengths and angles, anisotropic displacement parameters, and
hydrogen coordinates of 7 and 9 (19 pages). Ordering infor-
mation is given on any current masthead page.
OM960918S
(20) Braun, S.; Kalinowski, H.; Berger, S. 100 and More Basic NMR
Experiments; VCH: Weinheim, Germany, 1996, and references cited
therein.