Models for solvation of zirconocene cations: Synthesis, reactivity, and computational studies of cationic zirconocene benzyl compounds

Article abstract of DOI:10.1021/om060538z

The reactions of the zirconocene compounds [(η⁵-C ₅H₅)₂-Zr(CH₂C₆H ₄R)₂] (R = F (1), CMe₃ (2), Me (3)) with either B(C₆F₅)₃ or the trityl salt [Ph ₃C]⁺[B(C₆F₅)₄] ^- in CD₂Cl₂ were monitored by NMR spectroscopy. In all cases, the cationic compound [(η⁵-C₅H ₅)₂-Zr(η²-CH₂C₆H ₄R)]⁺ was obtained, irrespective of the activator used (B(C₆F₅)₃ or the trityl salt). Whereas NMR studies suggest a η²-coordination of the benzyl ligand to the cationic zirconium metal, detailed DFT studies revealed that in CD ₂Cl₂ this is only the case if one solvent molecule is coordinated via the lone pair of one chlorine to the metal. Without this coordination, a η³-coordination is more likely to occur. Computed NMR shifts at the B3LYP/IGLO II level corroborate this observation, which is in concert with a detailed NBO analysis of the cationic zirconocene compounds.

Full text of DOI:10.1021/om060538z

Organometallics 2006, 25, 4427-4432
4427
Models for Solvation of Zirconocene Cations: Synthesis, Reactivity,
and Computational Studies of Cationic Zirconocene Benzyl
Compounds
Jo¨rg Sassmannshausen,* Anna Track, and Franz Stelzer
Institut for Chemistry and Technology of Organic Materials, TU-Graz, Stremayrgasse 16/I,
A-8010 Graz, Austria
ReceiVed June 20, 2006
The reactions of the zirconocene compounds [(η5-C5H5)2-Zr(CH2C6H4R)2] (R ) F (1), CMe3 (2), Me
(3)) with either B(C6F5)3 or the trityl salt [Ph3C]+[B(C6F5)4]- in CD2Cl2 were monitored by NMR
spectroscopy. In all cases, the cationic compound [(η5-C5H5)2-Zr(η2-CH2C6H4R)]+ was obtained,
irrespective of the activator used (B(C6F5)3 or the trityl salt). Whereas NMR studies suggest a
η2-coordination of the benzyl ligand to the cationic zirconium metal, detailed DFT studies revealed that
in CD2Cl2 this is only the case if one solvent molecule is coordinated via the lone pair of one chlorine
to the metal. Without this coordination, a η3-coordination is more likely to occur. Computed NMR shifts
at the B3LYP/IGLO II level corroborate this observation, which is in concert with a detailed NBO analysis
of the cationic zirconocene compounds.
the cationic metal center. As metallocene-based catalysts are
also known to polymerize styrene to syndiotactic polystyrene,20
we wanted to extend our investigations of solvent adducts to
cationic zirconocene compounds in this direction. Recent
investigations in the mechanism of styrene polymerization
suggest that secondary insertion into the metal-polymer bond
is favored over primary insertion.21 Concequently, we decided
to use cationic zirconocene benzyl compounds, first reported
by Jordan et al.,22,23 as a model compound. To investigate any
possible electronic effects, we introduced various substituents
(F, Me, and CMe3) in the para-position of the benzyl ligand.
These prepared compounds were subjected to detailed low-
temperature NMR studies and DFT investigations. A complete
overview of the discussed zirconocene compounds and their
synthesis is given in Scheme 1.
The paper is organized as follows: in part I of the Results
and Discussion, the synthesis and the low-temperature multi-
nuclear NMR studies of the zirconocene compounds [(η5-
C5H5)2-Zr(CH2C6H4R)2] (R ) F (1), CMe3 (2), Me (3)) with
either B(C6F5)3 or the trityl salt [Ph3C]+[B(C6F5)4]- in CD2Cl2
are discussed. Part II reports the DFT investigations of the
cationic compounds [(η5-C5H5)2-Zr(CH2C6H4R)]+ (R ) F (1c),
CMe3 (2c), Me (3c)) and their corresponding dichloromethane
adducts [(η5-C5H5)2-Zr(CH2C6H4R)ClCH2Cl]+ (R ) F (1c-sol),
CMe3 (2c-sol), Me (3c-sol)).
Introduction
Group 4 metallocene compounds play an important role as
catalyst precursors for the hydrogenation,1 hydrosilylation, and
polymerization of olefins.2-11 In particular for alkene polym-
erization, these precursors need to be activated by a cationic
generating compound (CGA) to form what is believed to be
the active species [η5-Cp2MR]+ (Cp ) (substituted) cyclopen-
tadienyl, M ) Ti, Zr, Hf). Obviously, this rather “naked” ion
does not exist by itself in solution; rather it is paired with a
weakly coordinating ligand [η5-Cp2MR+‚‚‚D] (D ) X- (anion),
monomer, solvent). Whereas much effort has gone into elucidat-
ing the role of the anion and the coordination of the
monomer,2,3,5,8,10,12-16 the role of the solvent acting as a ligand
has, to the best of our knowledge, been less actively pursued,
probably due to a lack of suitable model systems. We have
recently developed such models for the polymerization of
monomers such as ethene and propene.17-19 We have noted a
strong propensity of the attached arene ligand to coordinate to
* Corresponding author. E-mail: sassmannshausen@tugraz.at.
(1) Qian, Y.; Li, G.; Huang, Y. J. Mol. Catal. 1989, 54, L 19.
(2) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255-270.
(3) Bochmann, M. Top. Catal. 1999, 7, 9-22.
(4) Bochmann, M.; Pindado, G. J.; Lancaster, S. J. J. Mol. Catal. A:
Chem. 1999, 146, 179-190.
(5) Bochmann, M. J. Organomet. Chem. 2004, 689, 3982-3998.
(6) Brintzinger, H.-H.; Fischer, D.; Mu¨hlhaupt, R.; Rieger, B.; Waymouth,
R. Angew. Chem. 1995, 107, 1255-1383.
Results and Discussions
(7) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428-447.
I. Experimental Investigations: (a) Preparation of the
(8) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434.
(9) Kaminsky, W.; Arndt, M. AdV. Polym. Sci. 1995, 127, 144-187.
(10) Piers, W. E.; Chivers, T. Chem. Soc. ReV. 1997, 26, 345-354.
(11) Rempel, G. L.; Huang, J. Prog. Polym. Sci. 1995, 20, 459-526.
(12) Silanes, I.; Ugalde, J. M. Organometallics 2005, 24, 3233-3246.
(13) Vanka, K.; Ziegler, T. Organometallics 2001, 20, 905-913.
(14) Maccioni, A. Chem. ReV. 2005, 105, 2039-2073.
(15) Song, F.; Lancaster, S. J.; Cannon, R. D.; Schormann, M.;
Humphrey, S. M.; Zuccacia, C.; Macchioni, A.; Bochmann, M. Organo-
metallics 2005, 24, 1315-1328.
Metallocenes 1-3. The zirconocene benzyl compounds 1-3
(18) Doerrer, L. H.; Green, M. L. H.; Ha¨ussinger, D.; Sassmannshausen,
J. J. Chem. Soc., Dalton Trans. 1999, 2111-2118.
(19) Bu¨hl, M.; Sassmannshausen, J. J. Chem. Soc., Dalton Trans. 2001,
79-84.
(20) Ishihara, N.; Seimiya, T.; Kuramono, M.; Uoi, M. Polym. Prepr.
Jpn. 1986, 35, 240.
(21) Yang, J. H.; Huh, J.; Jo, W. H. Organometallics 2006, 25, 1144-
1150.
(22) Jordan, R. F.; LaPointe, R. E.; Baenzinger, N. C.; Hinch, G. D.
Organometallics 1990, 9, 1539-1545.
(23) Jordan, R. F.; LaPointe, R. E.; Bajgur, C. S.; Echols, S. F.; Willet,
R. J. Am. Chem. Soc. 1987, 109, 4111-4113.
(16) Zuccaccia, C.; Stahl, N. G.; Macchioni, A.; Chen, M.-C.; Roberts,
J. A.; Marks, T. J. J. Am. Chem. Soc. 2004, 126, 1448-1464.
(17) Sassmannshausen, J.; Green, J. C.; Stelzer, F.; Baumgartner, J.
Organometallics 2006.
10.1021/om060538z CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/04/2006

4428 Organometallics, Vol. 25, No. 18, 2006
Sassmannshausen et al.
Scheme 1
Table 1. Observed Chemical Shifts for Cations 1c-3c
were synthesized according to a modified literature procedure.24
Thus, zirconocene dichloride, purchased form Aldrich and used
as received, was treated in diethyl ether with a large excess of
a freshly prepared Grignard reagent, (RC6H4CH2)MgBr (R )
F, CMe3, Me). The large excess was required, as during the
preparation of the Grignard the coupling product (RC6H4CH2)2
was obtained in various yields as a side-product. As the
zirconocene benzyl compounds are known to be light sensitive,
the benzylation was performed under exclusion of light. The
compounds obtained are light organge to yellow microcrystalline
compounds that are soluble in pentane and can be stored for a
prolonged period of time under an inert atmosphere of nitrogen
at -30 °C. Elemental analysis was also performed on the halides
Cl and Br to check for remaining Grignard reagent or zir-
conocene dichloride.
1
The JHC coupling constant of 120 Hz for the CH2 group,
together with a characteristic low-field shift of the ipso-carbon
of 148 ppm, suggests a η1-bonded benzyl group.
(b) Low-Temperature NMR Spectroscopy Reaction Stud-
ies. All spectroscopic data for these studies are summarized in
Table 1. The reaction of 1-3 with either B(C6F5)3 or the trityl
salt [Ph3C]+[B(C6F5)4]- in CD2Cl2 at -60 °C was monitored
by NMR spectroscopy. CD2Cl2 is the solvent of choice in these
experiments, as it provides high solubility of the highly polar
cationic products. Recently, the use of halogenated benzene has
been reported as well. However, to compare our results with
previously published data, we continued to use CD2Cl2,
particularly as we have shown recently that aromatic solvents
can coordinate to cationic zirconocene compounds.17-19 In all
cases the expected cation [(η5-C5H5)2-Zr(η2-CH2C6H4R)]+ was
observed. We did not observe any interaction of either anion
([RC6H4CH2B(C6F5)3]- or [B(C6F5)4]-) with the cation. The
chemical shifts of the benzylic CH2 group of around δ (1H)
3.08 ppm and δ (13C) 47 ppm, together with the observed shift
a In CD2Cl2 at -60 °C. b 270 MHz. c 67.8 MHz. Phn (n ) 1-6) denotes
hydrogens and carbons on the phenyl ring.
meta-carbon atoms were observed. We did not observe any
influence of the para substituent in terms of reactivity.
II. DFT Calculations. (a) Structural and NMR Shift
Calculations. Having established the formation of the expected
cationic benzyl compounds [(η5-C5H5)2-Zr(η2-CH2C6H4R)]+, we
performed detailed DFT calculations on the observed cations
1-3 to gain a deeper insight into the coordination nature of the
η2-bonding mode of the benzyl group. To validate our compu-
tational model, we used Jordan’s solid-state structure of the
cationic acetonitrile compound [(η5-C5H5)2-Zr(η2-CH2C6H5)-
NCCH3]+ (4).23 With the employed level of theory and basis
set, we found a good agreement between the calculated and
observed characteristic bond distances and angles (see Figure
1). An initial optimization of the unsubstituted zirconocene
benzyl cation 5 yieled a structure with a η3-coordinated benzyl
1
of δ (13C) 128 ppm for the ipso-carbon and the large JCH
coupling constant of 147 Hz, fit very well with previous
observations23-25 and indicate a η2-bonding mode of the phenyl
group to the cationic zirconium center. The observered cationic
compounds possess a mirror plane in the zirconium, CH2, and
ipso-carbon of the phenyl group, thus rendering the “top” and
the “bottom” of the molecule identical. Therefore only one signal
for the cyclopentadienyl ring and one signal for the ortho- and
(24) Bochmann, M.; Lancaster, S. J.; Hursthouse, M. B.; Maik, K. M.
A. Organometallics 1994, 13, 2235-2243.
(25) Mintz, E. A.; Moloy, K. G.; Marks, T. J. J. Am. Chem. Soc. 1982,
104, 4692.

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 18, 2006 4429
Figure 1. Comparison between calculated and solid-state structure
of 4.
Figure 3. Calculated structure of 5-sol.
Figure 2. Calculates structure 5 and data taken from ref 26.
1
Table 2. Measured and Calculated H and 13C NMR Data of
5, 1c, and 1c-sol
Figure 4. Density plot of 4.
whereas the observed NMR spectrum suggests a η2-coordinated
benzyl group in solution, we can draw the conclusion that these
calculated structures do not represent the observed structure in
solution. As all our low-temperature NMR studies were
conducted in dichloromethane, we looked into the possibility
of the coordination of one solvent molecule to the cationic metal
center. Indeed, placing one molecule of dichloromethane in close
proximity to the metal leads to a η2-coordinated benzyl group
with a dative chlorine-zirconium bond. The structural features
of 5-sol are in good agreement with those of 4 (Figure 3).
Now the calculated NMR shifts are in much better agreement
with the observed values. For example, in the case of 1c, the
observed values for the CH2 group are δ (1H) 3.08 ppm and δ
(13C) 47.6 ppm, and the calculated values for 1c-sol are 3.25
and 50.9 ppm, respectively (Table 2). We can conclude that in
dichloromethane one solvent molecule is coordinated. A close
inspection of the ortho- and meta-carbons of the aromatic ring
reveal, however, some differences in the calculated values,
indicating a different electronic environment of the correspond-
ing atoms. We therefore investigated the electronic structure of
the cations 1c-3c and 1c-solv-3c-solv.
a In CD2Cl2 at -60 °C, activated with B(C6F5)3. b 270 MHz. c 67.8 MHz.
d Values taken from ref 24. Phn (n ) 1-6) denotes hydrogens and carbons
on the phenyl ring.
(b) Electronic Investigations. To gain a detailed insight in
the electronic structures of the cations 4, 5, and 5-solv, we
performed a Bader analysis on these compounds using the
recommended Hay-Wadt basis set.27 In particular, we wanted
to investigate the nature of the coordinating ligand acetonitrile
and dichloromethane. In the case of 4, the total electron density
plot through the Zr-N-Cipso plane clearly indicates the
coordination of the ipso-carbon to the cationic zirconium (Figure
4). As expected, in the case of 5 the η3-coordination is clearly
visible (Figure 5a). Most remarkable, the plots for 5-sol and 4
are very similar, indicating not only that the coordination of
the chlorine from the solvent to the cationic zirconium is similar
to the coordination of acetonitrile, but also the benzyl group is
coordinated in a similar fashion (Figure 5b). Bader analysis
confirms the observed bonding modes and indicates that this
bonding takes place not because of electrostatic interactions but
due to Lewis-type bonds.
group (Figure 2). This kind of “edge-on” coordination mode of
the benzyl ligand has been observed before by Pellecchia for
the cationic compound [(η5-C5Me5)Zr(η3-CH2C6H5)(η7-CH2C6H5)
(6).26 The structural features of 5 and 6 are very similar; relevant
distances and angles are listed in Figure 2. Like 6, 5 shows the
characteristic bond length alteration of the asymmetric arene
ring. The η3-coordination of 5 is rather weak; only 3.07 kcal/
mol is necessary for bond breaking and inversion of the
configuration. As expected, the calculated chemical shifts of 5
do not fit well with the observed chemical shifts (Table 2). In
particular, the calculated chemical shift for the CH2 group of
64.8 ppm is in strong contrast to the observed chemical shift of
47.5 ppm.24 Similar observations can be made for the para-
substituted zirconocene benzyl compounds. For example, the
calculated shift of the CH2 group of 1c of 64.5 ppm is in strong
contrast to the observed shift of 47.6 ppm. Furthermore, as the
calculated structures suggest a η3-coordinated benzyl group
As Bader analysis does not tell us the orbitals involved in
the bonding, we performed a more detailed NBO (natural bond
(26) Pellecchia, C.; Immirzi, A.; Pappalardo, D.; Peluso, A. Organome-
tallics 1994, 13, 3773-3775.
(27) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.

4430 Organometallics, Vol. 25, No. 18, 2006
Sassmannshausen et al.
Figure 5. (a) Density plot of 5. (b) Density plot of 5-solv.
Figure 7. (a) Dative bonding between C2-C3 and empty d orbital
of Zr. (b) Dative bonding between C2-C3 and empty d orbital of
Zr.
Figure 6. (a) Dative bond between lone pair of N and empty d
orbital of Zr. (b) Back-bonding between Zr-C1 bond and C2-C3
antibonding orbital.
orbital) analysis.28 In 4, we found that the lone pair of the
nitrogen donates electron density into an empty orbital of the
zirconium and forms a dative acetonitrile-zirconium bond. The
second-order pertubation energy theory of the donor-acceptor
energy was estimate to be 43.7 kcal/mol, indicating a rather
strong bond. The Zr-Cipso bond back-bonds into the antibonding
orbital between Cipso-Cortho. The engery was estimate to be 17.5
kcal/mol, much weaker than the dative bond of the acetonitrile
bond (Figure 6, see Supporting Information for more detailed,
colored plots).
In the case of 5 this bonding mode contributes 25.1 kcal/
mol, which is significantly stronger than in the case of 4.
Additional bonding contribution is gained by two dative bonds
between of the Cipso-Cortho into an empty d orbital of the
zirconium (14.2 and 5.1 kcal/mol) (Figure 7).
In 5-sol the bonding situation is similar to 4: a dative bond
between a lone pair of the chlorine and an empty orbital of the
zirconium of 39.4 kcal/mol and a back-bonding between the
Zr-Cipso bond and the Cipso-Cortho antibond (14.7 kcal/mol) (see
Supporting Information). These values are similar to those
computed for 4 and indicate that the solvent dichloromethane
is bonded quite strongly to the cationic zirconium.
This back-bonding is particularly strong in the case of 5,
where no solvent molcule is donating electron density into empty
d orbitals of the zirconium and consequently turning the phenyl
ring in such a position to enable η3-bonding rather than the
expected η2-bonding mode of the benzyl ligand.
Figure 8. Reaction profile between 5 and 5-solv.
this can only be achieved with one solvent molecule coordinat-
ing to the cationic zirconium, we did not find any evidence in
the spectra for a coordinated solvent molecule. Therefore we
can safely assume that even at low temperature this coordinated
solvent molecule is rather labile, leading to rapid exchange
between coordinated and noncoordinated solvent molecules.
Indeed, kinetic studies on 5 support this. The small activation
barrier of 2.09 kcal/mol and the very small energy difference
between 5 and 5-solv of 0.77 kcal/mol indicate facile exchange
between both species (Figure 8). Given that in solution the
solvent is in large excess, we can safely assume that 5 only
exists in minute amounts in the NMR tube.
We investigated the possible reaction path between 5-solv
and 5 by moving the solvent in steps of 0.3 Å away from the
zirconium. We located a transition state at a zirconium-chlorine
distance of 3.64 Å. This transition state was confirmed by an
intrinsic reaction coordinate (IRC) calculation.
Conclusion
Low-temperature NMR studies of para-substituted zir-
conocene benzyl compounds indicate the formation of cationic
zirconocene benzyl compounds with the benyzl group bonded
η2 to the zirconium. We did not observe any coordination of
the anion to the cation, as the same cation was obtained
regardless of the activation with either (B(C6F5)3 or the trityl
salt [Ph3C]+[B(C6F5)4]-). From detailed DFT calculations, we
obtained evidence that in solution one molecule of dichlo-
romethane, the solvent, is coordinated to the cationic compound.
This coordination is rather labile, and facial exchange between
coordinated and free solvent molecules can be expected. The
Similar observations are made for the cationic compounds
1c-3c and 1c-solv-3c-solv. We did not observe any significant
influence of the para substituent on the energies of these
bonding modes.
(c) Computational Kinetic Investigations. Although the
low-temperature NMR investigations suggest a η2-coordination
of the benzyl ligand and our computational studies suggest that
(28) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.G; Theoretical
Chemistry Institute, University of Wisconsin: Madison, WI, 2001.

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 18, 2006 4431
combination of functionals and basis sets has proven to be quite
effective for chemical shift computations for transition metal
complexes.19 1H and 13C chemical shifts have been calculated
relative to benzene, with absolute shieldings for benzene σ(1H)
24.54 and σ(13C) 47.83 with the IGLO II basis set. The values for
benzene were converted into the TMS scale using the experimental
δ values of benzene (7.26 and 128.5 ppm, respectively). Tables of
Cartesian coordinates of all calculated structures are available as
electronic Supporting Information in x, y, z format. Bader analysis
was performed using the Hay-Wadt all-electron basis set, and
drawing of the electron charge density plots was performed using
Xaim.35 MOLDEN36 was used for the chemical representation of
the calculated compounds, and NBO-View for the representation
of the orbitals.28
coordination is a dative bond from a lone pair of the chlorine
to an empty orbital of the zirconium and is similar in engery to
the corresponding acetonitrile compound 4. Without the solvent,
our calculations show that the benzyl group bonds η3 to the
zirconium, with strong dative bonds from the Cispo-Cortho bonds
into empty d orbitals of the zirconium. We can conclude that
these solvent adducts may play an important role in the
polymerization chemistry of styrene when dichloromethane is
used as a solvent and the catalyst is a zirconocene compound.
Experimental Section
All experiments were carried out under a nitrogen atmosphere
using standard Schlenk techniques. Solvents were dried over sodium
(toluene, low in sulfur), sodium/potassium alloy (diethyl ether, light
petroleum, bp 40-60 °C, pentane), potassium (thf), and calcium
hydride (dichloromethane). NMR solvents were dried over activated
molecular sieves, freeze-thawed, and stored in Young’s-Tap sealed
ampules. All chemicals were purchased from Aldrich and used as
received.
Preparation of the Grignard Reagent. Magnesium turnings
(0.85 g, 35 mmol) were suspended in 70 mL of diethyl ether, and
30 mmol of the corresponding benzyl bromide was added under
occasional ice-bath cooling. The reaction mixture was stirred for 2
h at room temperature and filtered.
This method was used in all preparations.
NMR spectra were recorded on a JEOL EX90FT or a JEOL
EX270FT spectrometer and referenced to the residual proton solvent
peak for 1H. Chemical shifts are quoted in ppm relative to
tetramethylsilane. 13C NMR spectra were referenced with the solvent
peak relative to TMS and were proton decoupled using a WALTZ
sequence. CH-coupling constants were measured by a modified
INEPT pulse sequence. Low-temperature NMR studies were
conducted as previously reported.17
Computational Details. Density functional theory calculations
were carried out using the GAUSSIAN0329 program package,
running on a Mandrake Linux Dual-Opteron or a Dual-Xeon system,
respectively. Geometries have fully been optimized without sym-
metry constraints, involving the functional combinations accord-
ing to Becke30 (hybrid) and Lee, Yang, and Parr31 (denoted
B3LYP), with the corresponding valence basis set for Zr (Stuttgart-
Dresden, keyword SDD in Gaussian) and standard 6-31G* basis
set32 for C, H, Cl, and F (denoted as ECP1). The stationary points
and transition states were characterized as minima by analytical
harmonic frequency (zero or one imaginary frequency, respectively),
which were used without scaling for zero-point and thermal
corrections.
Preparation of Cp2Zr(CH2C6H4F)2 (1). Zirconocene dichloride
(1.45 g, 5 mmol) was added to the solution of para-fluorobenzyl-
magnesium bromide. The reaction mixture was stirred overnight,
and the color changed from light yellow to orange. The volatiles
were removed under reduced pressure to yield an orange residue.
The residue was extracted into a mixture of 30 mL of PE and 30
mL of toluene. The solvent was removed under reduced pressure
and re-extracted into 12 mL of PE and 16 mL of toluene. The extract
was stored at -20 °C for one week, yielding orange and some white
crystals. The crystals were separated manually. Only the orange
crystals were recrystallized from a mixture of 10 mL of PE and 14
mL of toluene, yielding the desired compound as orange crystals.
Yield: 150 mg (6.8%) Anal. Found: C, 63.26; H, 4.98; F, 8.38.
Calcd for C24H22F2Zr: C, 63.57; H, 5.04; F, 8.64. No halides (Cl
or Br) were detected in the sample. 1H NMR (90 MHz, CDCl3, 29
°C) δ (ppm): 1.77 (s, 4 H, CH2-Ph′); 5.93 (s, 10 H, Cp), 6.66-
6.71 (m, 8 H, Ph′). 13C NMR (270 MHz, CD2Cl2, 22 °C) δ (ppm):
58.9 (CH2-Ph′); 112.5 (Cp); 114.9 (d, m-C-Ph′, 2JCF ) 21 Hz); 126.7
3
(d, o-C-Ph′, JCF ) 7 Hz); 148.2 (ipso-C-Ph′); 158.5 (d, p-C-Ph′,
1JCF ) 238 Hz).
Preparation of Cp2Zr(CH2C6H4CMe3)2 (2). Zirconocene dichlo-
ride (1.45 g, 5 mmol) was added to the rapidly stirred solution of
4-tert-butylbenzylmagnesium bromide. The reaction mixture was
stirred overnight, and the color changed from light yellow to light
orange. The volatiles were removed under reduced pressure to yield
a light orange residue, which was extracted into a mixture of 30
mL of toluene and 30 mL of PE. The extract was concentrated and
stored at -30 °C. After 4 weeks crystals were obtained, which were
recrystallized from 12 mL of petroleum ether. Yield: 100 mg
(3.9%). Anal. Found: C, 74.83; H, 7.76. Calcd for C32H40Zr: C,
74.50; H, 7.82. No halides (Cl or Br) were detected in the sample.
1H NMR (270 MHz, CD2Cl2, 21 °C) δ (ppm): 1.29 (s, 18 H, CH3);
1.77 (s, 4 H, CH2-Ph′); 5.91 (s, 10 H, Cp); 6.72 (d, 4 H, o-H-Ph′);
7.17 (d, 4 H, m-H-Ph′). 13C NMR (62.9 MHz, CD2Cl2, 21 °C) δ
(ppm): 31.5 (C-CH3); 34.3 (C-CH3); 48.2 (CH2-Ph′); 112.3 (Cp);
125.2 (m-C-Ph′); 129.0 (o-C-Ph′); 143.8 (ipso-C-Ph′); 150.2 (p-C-
Ph′).
Magnetic shieldings σ have been evaluated for the B3LYP/ECP1
geometries using a recent implementation of the GIAO (gauge-
included atomic orbitals)-DFT method,33 involving the same B3LYP
level of theory, together with the recommended IGLO basis II34
on C, H, and F. The former approach with this particular
(29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Jr., J. A. M.; Vreven, T.; Kudin, K. N.; Burant,
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4432 Organometallics, Vol. 25, No. 18, 2006
Sassmannshausen et al.
yellow to orange. The volatiles were removed under reduced
pressure to yield an orange residue, which was extracted twice into
40 mL of petroleum ether. Fractional crystallization at -30 °C
yielded the byproduct 1,2-(para-methylphenyl)ethane, the Grignard
reagent, and the desired product as orange crystals. Yield: 200 mg
(9.2%). Anal. Found: C, 72.22; H, 6.66. Calcd for C26H28Zr: C,
72.33; H, 6.53. No halides (Br or Cl) were detected in the sample.
1H NMR (270 MHz, CD2Cl2, 23 °C) δ (ppm): 1.69 (s, 4 H, CH2-
Ph′); 2.19 (s, 6 H, Bz-CH3); 5.83 (s, 10 H, Cp); 6.66 (d, 4 H, o-H-
Ph′); 6.88 (d, 4 H, m-H-Ph′). 13C NMR (62.9 MHz, CD2Cl2, 23
°C) δ (ppm): 19.6 (Bz-CH3); 58.8 (CH2-Ph′); 111.2 (Cp); 124.7
(m-C-Ph′); 127.9 (o-C-Ph′); 148.0 (ipso-C-Ph′); 148.0 (p-C-Ph′).
Acknowledgment. A.T. thanks the Technical University of
Graz for a student grant. J.S. thanks M. Bochmann for his
support. Part of this work was supported by BP.
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM060538Z