Synthesis, reactivity and DFT investigation of a cationic zirconocene benzyl compound with an appended phenyl group

Article abstract of DOI:10.1002/ejic.200700002

The reaction of [η⁵-C₅H₅- (η⁵-C₅H₄CMe₂C₆H ₄Me)Zr(CH₂Ph)₂] (1) with the cation generating agent B(C₆F₅)₃ was studied by means of multinuclear NMR and density functional theory (DFT) methods. The clean reaction in CD₂Cl₂ at -60°C yielded the cationic compound [η⁵-C₅H₅-(η⁵: η¹-C₅H₄-CR₂C₆H ₄R)Zr(η²-CH₂Ph)] (R = Me: 2, R = H: 3), with a tolyl moiety coordinated to the cationic zirconium centre, in addition to the expected η²-coordination of the benzyl moiety. Both coordinations were unambiguously assigned by multi-nuclear one- and two-dimensional NMR spectroscopy. Detailed DFT calculations of congener 3 at the B3LYP level of theory explain the unusual chemical shift of the coordinated atom of the tolyl moiety. Furthermore, detailed electronic analysis (Bader and NBO analysis) were undertaken to ascertain the type of coordination (agostic versus electrostatic) that the tolyl moiety adopts. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200700002

FULL PAPER
DOI: 10.1002/ejic.200700002
Synthesis, Reactivity and DFT Investigation of a Cationic Zirconocene Benzyl
Compound with an Appended Phenyl Group
Jörg Saßmannshausen,*[a] Anna Track,[a] and Tiago A. D. S. Dias[b]
Dedicated to M. L. H. Green
Keywords: Density functional calculations / NMR spectroscopy / Polymerisation
The reaction of [η5-C5H5-(η5-C5H4CMe2C6H4Me)Zr(CH2Ph)2] nuclear one- and two-dimensional NMR spectroscopy. De-
(1) with the cation generating agent B(C6F5)3 was studied by
means of multinuclear NMR and density functional theory
(DFT) methods. The clean reaction in CD2Cl2 at –60 °C
yielded the cationic compound [η5-C5H5-(η5:η1-C5H4-
CR2C6H4R)Zr(η2-CH2Ph)] (R = Me: 2, R = H: 3), with a tolyl
moiety coordinated to the cationic zirconium centre, in ad-
dition to the expected η2-coordination of the benzyl moiety.
Both coordinations were unambiguously assigned by multi-
tailed DFT calculations of congener 3 at the B3LYP level of
theory explain the unusual chemical shift of the coordinated
atom of the tolyl moiety. Furthermore, detailed electronic
analysis (Bader and NBO analysis) were undertaken to ascer-
tain the type of coordination (agostic versus electrostatic) that
the tolyl moiety adopts.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
Introduction
molecular phenyl coordination (Scheme 1).[18] Recently, we
extended this model and used silicon, instead of carbon,
as a bridging atom. Here we noticed the formation of two
different compounds: the expected formation of zir-
conocene compound 6, which is in equilibrium with inner
sphere ion pair 7.[19] Furthermore, we obtained evidence for
the formation of dichloromethane adducts in the case of
cationic zirconocene benzyl compounds 8a,b and explored
the electronic properties by DFT calculations.[20]
As mentioned above, group 4 compounds are also used
as catalysts for the polymerisation of styrene.[21–23] Recently,
Jo et al. demonstrated that in the case of ansa-titanocene
compounds, secondary insertion of styrene, albeit slower
than primary insertion, is actually the process that leads to
the formation of polystyrene.[24] One of the identified in-
terim products was a metallocene benzyl compound. With
this background, we decided to prepare compound 1 as a
precursor to cation 2 to address the following: (1) the pos-
sible coordination of the pendant tolyl group, and, if this
happens, (2) the nature of the coordination mode of the
tolyl group (agostic versus electrostatic). To demonstrate
the usability of our model, we firstly report the DFT calcu-
lations of 3, and secondly we discuss the experimentally ob-
tained NMR spectroscopic data of 2 (Scheme 2). Although
this might be seen as an unusual way to present the ob-
tained results, we believe that this way not only emphasises
the validation of our model systems, but also allows the
NMR results to be more easily understood.
Group 4 metallocenes are still a point of research interest
as they can serve not only as the catalyst in hydrosilylation
and hydration reactions, but they are also well known for
their ability to polymerise monomers such as ethene, pro-
pene and styrene. In the last decades, much effort, both ex-
perimentally and theoretically,[1–5] was undertaken to eluci-
date the role and the nature of the active species in these
polymerisation reactions; thus, we have obtained a reason-
ably good picture of the catalytic process.[6–15] The interac-
tion of the cationic group 4 metallocene, which is accepted
as the active species in the catalytic process, with both the
neutral catalytic precursor and the anion has been exten-
sively studied.[6,7,9,14] The role of the solvent has been, by
comparison, less investigated. Some time ago, we started to
develop suitable models for the role of the solvent and
showed by low-temperature NMR studies that arenes can
coordinate to the cationic metal centre (compound 4).[16,17]
We were also the first to report the formation of a zir-
conocene dication, such as 5, which is stabilised by intra-
[a] TU Graz, Institute for Chemistry and Technology of Organic
Materials,
Stremayrgasse 16/I, 8010 Graz, Austria
E-mail: sassmannshausen@tugraz.at
[b] Universidade do Minho, Department of Chemistry, Campus de
Gualtar
4710-057 Braga, Portugal
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2007, 2327–2333
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J. Saßmannshausen, A. Track, T. A. D. S. Dias
FULL PAPER
We explored the possibility of different coordination
modes of both the benzyl and the phenyl moiety to the
cationic zirconium centre, and hence, calculated various
conformers of 3. A thorough scan of the potential energy
surface revealed that 3a is the global minimum of all con-
sidered coordination modes and that it is in rapid equilib-
rium with 3b as confirmed by low-temperature NMR spec-
troscopy (Figure 1). Significant bond lengths, angles and di-
hedral angels are summarised in Table 1; the remaining en-
ergetically-higher-lying conformers are summarised in
Table 2.
Figure 1. Scan of the potential energy surface of 3. Values in paren-
thesis are calculated energies with the PCM solvent model (see
text).
Table 1. Significant bond lengths, angles and dihedral angles of 3a
and 3b.
3a
TS-AB
3b
d(Zr–C7)
2.33 Å
2.71 Å
2.92 Å
–
87.7°
95.5°
2.32 Å
2.71 Å
4.60 Å
3.02 Å
88.2°
2.34 Å
2.71 Å
d(Zr–C8)
d(Zr–C2)
Scheme 1.
d(Zr–C6)
3.16 Å
87.5°
61.2°
Є(Zr–C7–C8)
Є(Zr–C7–C8–C9)
93.74°
Here, the benzyl-moiety is bonded in an η2 fashion to
the zirconium centre and the phenyl moiety is coordinated
in the previously described η1 mode to the metal.[16,17,25]
The Zr–C7–C8–C9 dihedral angle of 95.5° indicates sym-
metric coordination, with only a small distortion that is
probably caused by the coordinated phenyl moiety. As pre-
viously reported,[16,19] the hydrogen attached to the coordi-
nated carbon of the phenyl moiety is bent out of the phenyl
plane by 9.62°, away from the zirconium metal. A second
minimum, 3b, which is 4.72 kcal/mol higher in energy than
3a, was obtained by coordination of the second ortho car-
bon of the phenyl moiety to the zirconium centre. Here, the
Scheme 2.
Results and Discussion
DFT Calculations
Structural Investigation
benzyl moiety is slanted significantly (Zr–C7–C8–C9
=
To save computational time, we substituted the para 61.2°) towards the metal and adopts an η3 coordination to
methyl group of the tolyl moiety in 2 with hydrogen, thus the metal centre. The phenyl moiety, which now points
converting the tolyl moiety into a phenyl moiety to give 3 towards the “back” of the metallocene wedge, presumably
(Scheme 2).
leaves more space on the “front”; hence, the benzyl moiety
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Cationic Zirconocene Benzyl Compound with an Appended Phenyl-Group
FULL PAPER
Table 2. Energetically higher lying conformers of 3.
3c
3d
3e
3f
Energy relative to 3a
6.65
7.18
7.38
[kcal/mol]
can adopt a coordination mode more suitable to satisfy the Electronic Structure Investigations
electron-deficient cationic metal centre. A similar coordina- To ascertain the coordination mode (agostic versus elec-
tion of cationic zirconocene benzyl compounds has been trostatic) of the phenyl moiety to the zirconium centre, we
observed before.[20] In the absence of coordinating solvents performed detailed Bader analysis[26] of compounds 3a,b.
such as dichloromethane, we recently reported the forma- Scherer and McGrady recently reported a very detailed in-
tion of an η3-coordinated benzyl moiety to the cationic me- vestigation into the agostic bonding criteria of titanium
tallocene centre, compound 8a (Zr–C7–C8–C9 = 51.8°). The ethyl compounds and we are using their criteria here to as-
addition of one molecule of dichloromethane furnished sign the bonding mode of the phenyl group.[27–29] They ex-
compound 8b (cf. Scheme 1). Although in 3b the electron tended the original definition of agostic bond (“used to dis-
deficiency of the metal is somehow compensated as a result cuss the various manifestations of covalent interactions
of the coordination of the phenyl moiety, it is still strong between carbon–hydrogen groups and transition-metal
enough to force the benzyl moiety into an η3 coordination, centres in organometallic compounds, in which a hydrogen
albeit the slanting angle is about 10° smaller than that in atom is covalently bonded simultaneously to both a carbon
8a. Further exploration of the potential energy surface fur- and to a transition-metal atom”[30,31]) to a broader context
nished compounds 3c–e. The last considered structure, 3f, (“agostic interactions are characterized by the distortion of
with no coordination of the benzyl or tolyl moiety, could an organometallic moiety which brings an appended C–H
not be obtained without restricted rotation of the Zr–CH2 bond into close proximity with the metal centre”[29]), and
bond. In all calculations performed, the benzyl moiety had included heteroatoms such as silicon. Their main criterion
a strong tendency to move towards the metal centre to yield for the definition of an agostic bond was the relationship
structures similar to 3c. To investigate any possible solvent of the electron density distribution ρ(r) and the Laplacian
effects, we computed single-point calculations for the op- of the charge density ٌ2ρ(r) in connection with Bader AIM
timised energy structures, including the polarisable contin- analysis.[26] To support these so-obtained results, we under-
uum model (PCM) solvent model implemented in took a detailed NBO analysis to investigate the relevant or-
GAUSSIAN03, with dichloromethane as a solvent. In gene- bitals that were involved in the coordination of the phenyl
ral, the calculated single-point energies are somewhat lower moiety.[32]
than the solvent-free calculations, and the largest difference
was 0.82 kcal/mol (Figure 1, values in parenthesis).
For 3a, we found a bonding path and a bond critical
point between the zirconium centre and the ortho carbon of
The small energy difference between 3a and 3b is impor- the phenyl group (BCP1). We did not observe a bonding
tant for styrene polymerisation: the incoming monomer path or a bond critical point between the zirconium centre
(the tolyl group in our model) is attracted by the cationic and the hydrogen atom bonded to the ortho carbon (Fig-
metal centre and can coordinate to the free coordination ure 2). The electron density at the bond critical point was
site. This coordination can be envisaged for any of the con- determined to be ρ(r) = 0.0171 and the Laplacian of the
formers of 3. However, as the energy barrier of rearrange- charge density ٌ2ρ(r) = –0.0136. For comparison, the bond
ment between any of the conformers is sufficiently small, critical point between the zirconium centre and the CH2
the styrene monomer can move into a position so that the group (BCP2) was ρ(r) = 0.0812 and a Laplacian of ٌ2ρ(r)
C–C double bond adopts a suitable position for insertion = –0.0165 found. Obviously, as the electron density of
to occur.
BCP1 is lower than the electron density of the BCP2 bond,
Eur. J. Inorg. Chem. 2007, 2327–2333
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J. Saßmannshausen, A. Track, T. A. D. S. Dias
FULL PAPER
we concluded that rather than a typical Lewis-type bond
between the zirconium centre and the ortho carbon of the
phenyl moiety, a more polarised bonding mode as we have
previously described existed.[16]
Figure 3. Contour plot of the electron density ρ(r) of 3b. Plane
through zirconium, ortho-phenyl carbon and hydrogen. Benzyl CH2
is on the left hand side. Default contour lines used.
Figure 2. Contour plot of the electron density ρ(r) of 3a. Plane comparison, the second C–C bond between the ipso and
through zirconium, ortho phenyl carbon and hydrogen. Default
the ortho carbon bond [πCC = 0.716(p)C-ipso +0.699(p)C-ortho
]
contour lines used.
only has an energy of 1.21 kcal/mol. It is tempting to assign
this coordination to agostic coordination; however, unlike in
the cases reported by Scherer and McGrady, we did not
find a bonding path between the zirconium centre and the
hydrogen atom. It is possible that by replacing the benzyl
moiety with a stronger donor this could be shifted towards
agostic bonding. Owing to the curvature of the bonding
path in 3b, we concluded that, in this case, a “transition
state” somewhere in between a covalent bond and an agos-
tic bond must be present.
NBO analysis revealed electron donation between the
CH bonding orbital [σCH = 0.794(sp2.30)C +0.607(s)H] and
the empty Zr orbital of mainly d-character (LP*Zr = sd3.81
)
with a second-order perturbation energy of 5.12 kcal/mol.
For comparison, for the CH bonding orbital in the para
position of the coordinated carbon, similar values were ob-
tained [σCH = 0.794(sp2.34)C +0.608(s)H]. Thus, as the sec-
ond-order perturbation energy for this carbon to zirconium
is zero (i.e. no bond), we concluded that although there is
a bonding path between the ortho carbon and the zirconium
centre, the NHO of the two carbons are very similar, which
indicates that an electrostatic rather than a covalent bond
exists. Coloured plots of the orbitals are available in the
Supporting Information (Figures S1–S3).
For 3b, Bader analysis revealed a bonding path from the
zirconium centre to the coordinated ortho carbon of the
phenyl moiety; however, in this case, a straight line, as in
3a, was not detected, but a more curved line was found (cf.
Figure 3). It appears as if the bonding path first steers
towards the bond critical point of the CH bond and just
before it reaches this point it turns sharply towards the car-
bon atom. A similar kind of “conflict catastrophe struc-
ture” has been observed before, notably with alkyl titanium
chloride cations[33] and for unusual H···π interactions.[34]
The relevant values of the bond critical point (BCP3)
were calculated as ρ(r) = 0.0114 and ٌ2ρ(r) = –0.0086. For
comparison, the values of the bond critical point (BCP4)
between the zirconium centre and the CH2 group were cal-
culated to be ρ(r) = 0.0803 and ٌ2ρ(r) = –0.0160, which
Chemical Shift Computations
To verify our computed structures with experimental re-
sults, we calculated the chemical shifts of 3a and 3b. Be-
cause of the low activation barrier between 3a and 3b
(5.28 kcal/mol), we can assume that both compounds are
in equilibrium even at –60 °C. Furthermore, we predict a
chemical shift of δH = 2.64 ppm for the ortho hydrogen of
the phenyl moiety. This unusual highfield shift for an aro-
matic hydrogen can be explained very easily because of the
magnetic anisotropy cone of the η2-bonded benzyl moiety.
This cone points straight to the ortho hydrogen of the
phenyl moiety, and thus explains the unusual shift for an
aromatic hydrogen. Similar observations have been made
before.[18] The experimental and calculated shifts are sum-
marised in Table 3.
Low-Temperature VT-NMR Studies
The reaction between 2 and B(C6F5)3 in CD2Cl2 was
are similar to BCP2. The values for BCP1 are somewhat monitored by NMR spectroscopy (Figure 4). The spectrum
higher than the values of BCP3, which indicates a higher recorded at –60 °C indicates the coordination of both the
electron density between the zirconium centre and the ortho tolyl and benzyl moieties. The chemical shift of the benzylic
carbon of the phenyl moiety in the case of 3a. NBO analysis CH2 group at δH = 2.69 ppm and δC{H} = 45.5 ppm to-
of 3b revealed the expected interaction between the CH gether with the coupling constant JC,H = 149.0 Hz clearly
bond [σCH = 0.786(sp2.30)C +0.618(s)H] and the empty or- indicate an η2-coordinated benzyl moiety.[35,36] The chemi-
bital (LP*Zr = sd3.81) with a second-order perturbation en- cal shift of the diastereotopic CMe2 groups at 1.05 and
ergy of 3.09 kcal/mol, but furthermore, an interaction be- 1.62 ppm are indicative of coordination of the tolyl moiety.
tween the C–C bond [πCC = 0.675(p)C-ipso +0.738(p)C-ortho
]
Similar values, albeit with a smaller difference, have been
with an energy of 5.88 kcal/mol (cf. Figures S4–S7). For reported before.[18] As predicted, a peak at δH = 2.33 ppm
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Cationic Zirconocene Benzyl Compound with an Appended Phenyl-Group
FULL PAPER
Table 3. Chemical shifts for 2 (observed) and 3a,b (calculated).
2
3a[c]
3b[c]
1H (δ [ppm])[a]
13C (δ [ppm])[b]
1H (δ [ppm])
12C (δ [ppm])
1H (δ [ppm])
13C (δ [ppm])
Ph1
Ph2
Ph3
Ph4
Ph5
Ph6
CH2
137.7
98.2
136.4
–
130.0
126.5
45.5
140.0
103.2
142.0
128.5
141.6
128.3
48.6
–
124.6
140.5
131.4
133.0
131.6
135.7
–
139.4
128.7
139.8
131.3
134.7
108.8
56.5
–
134.7
104.8
132.7
130.8
136.1
137.4
–
2.33
6.72
–
7.67
7.13
2.96
3.04
–
6.71
6.91
6.84
6.91
6.71
1.05
1.62
–
2.39
5.39
5.22
6.18
5.79
6.66
2.64
6.59
–
7.82
7.04
3.27
3.39
–
7.25
7.65
7.75
7.67
7.16
–
–
–
–
5.34
5.26
6.26
5.88
6.58
7.25
7.91
–
6.71
5.46
3.36
2.98
–
5.38
6.02
7.15
7.67
7.37
–
–
–
–
5.77
5.94
6.10
6.18
6.71
–
Ph8
123.2
128.1
127.9
122.9
127.9
128.1
27.5
26.8
37.3
20.7
109.8
97.7
Ph9
Ph10
Ph11
Ph12
Ph13
CCH3
–
–
–
–
–
–
CCH3
PhCH3
Cp
111.8
99.9
108.6
109.1
117.9
112.5
101.8
114.5
111.3
117.6
CpЈ
103.6
106.4
115.8
[a] –60 °C, CD2Cl2, 500 MHz. [b] –60 °C, CD2Cl2, 125 MHz. [c] B3LYP/IGLOII.
can be assigned to the ortho hydrogen of the coordinated cross peak between δH = 2.33 ppm and δH ≈ 7.2 ppm can
tolyl moiety. The predicted equilibrium between 3a and 3b only be explained by the interconversion between 3a and
could be confirmed by EXSY spectroscopy (Figure 5). The 3b, and fits very well with the predicted values of 2.64 and
1
Figure 4. 500 MHz H NMR spectrum of 2 at –60 °C. Significant peaks of the cation are labelled.
Eur. J. Inorg. Chem. 2007, 2327–2333
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J. Saßmannshausen, A. Track, T. A. D. S. Dias
FULL PAPER
7.25 ppm.[37] As expected, this exchange is rapid, even at observed. Our model clearly indicates that for styrene poly-
–60 °C, and thus some broad peaks in the aromatic region merisation with ansa group 4 metallocenes, the coordina-
of the spectrum can be observed. Lowering the temperature tion of the phenyl ring from the growing chain does not
to –90 °C did not resolve the broad peaks, which hampered hamper the coordination of the free monomer: it is possible
a detailed kinetic investigation. All calculated and observed for the monomer to get caught by the catalyst, rearrange
chemical shifts are summarised in Table 3.
and insert into the polymer chain.
Experimental Section
General: All experiments were carried out under a nitrogen atmo-
sphere by using standard Schlenk techniques. Solvents were dried
with sodium (toluene, low in sulfur), sodium/potassium alloy (di-
ethyl ether, light petroleum, b.p. 40–60 °C, pentane), potassium
(thf) and calcium hydride (dichloromethane). All chemicals were
purchased from Aldrich and used as received. NMR solvents were
dried with activated molecular sieves, freeze thawed and stored in
Young’s Tap sealed ampoules. NMR spectra were recorded with a
VARIAN Unity Plus 500 spectrometer and referenced to the resid-
1
ual proton solvent peak for H. Chemical shifts are quoted in ppm
relative to tetramethylsilane. 13C NMR spectra were referenced
with the solvent peak relative to tetramethylsilane and were proton
decoupled by using a WALTZ sequence. CH coupling constants
were measured with a coupled gHSQC pulse sequence. Low-tem-
perature NMR studies were conducted as previously reported.[19]
Computational Details: Density functional theory calculations were
carried out by using the GAUSSIAN03[38] program package, run-
ning on a Mandrake Linux Dual-Opteron or a Dual-Xeon system,
respectively. Geometries were fully optimised without symmetry
constraints, which involved the functional combinations according
to Becke[39] (hybrid) and Lee, Yang and Parr[40] (denoted B3LYP),
with the corresponding pseudopotential basis set for Zr (Stuttgart-
Dresden, keyword SDD in Gaussian) and the standard 6-31G* ba-
sis set[41] for C, H, Cl and F (denoted as ECP1). The stationary
points and transition states were characterised as minima by ana-
lytical harmonic frequencies (zero or one imaginary frequency,
respectively), which were used without scaling for zero-point and
thermal corrections.
Figure 5. EXSY spectrum of 2 at –60 °C in CD2Cl2. Strong cross
peaks are EXSY, medium ones are NOSY.
Conclusions
Magnetic shieldings σ were evaluated for the B3LYP/ECP1 geome-
tries by using a recent implementation of the GIAO (gauge-includ-
ing atomic orbitals)-DFT method,[42] which involved the same
B3LYP level of theory, together with the recommended IGLO II
basis[43] on C, H and F. The former approach with this particular
combination of functionals and basis sets has proven to be quite
effective for chemical shift computations for transition metal com-
plexes.[16] 1H and 13C NMR chemical shifts were 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 by using the experimental δ
values of benzene (δ =7.26 ppm and 128.5 ppm, respectively).
Bader analysis was performed using the DZVP all-electron basis
set,[44] drawing of the electron charge density plots were performed
with the use of an Aim2000 instrument.[45] MOLDEN[46] was used
for the chemical representation of the calculated compounds and
NBO-View for the representation of the orbitals.[32]
We prepared the benzyl congener [η5-C5H5-(η5-
C5H4CMe2C6H4Me)Zr(CH2Ph)2] (1) of the previously
reported zirconocene compound [η5-C5H5(η5-C5H4-
CMe2C6H4Me)ZrMe2]. The reaction of 1 with B(C6F5)3 in
CD2Cl2 was monitored by low-temperature NMR spec-
troscopy, and we obtained evidence for the coordination of
both the benzyl moiety in the expected and previously re-
ported η2-bonding mode and the tolyl moiety. Our experi-
mentally obtained data were predicted correctly from our
computational studies. Furthermore, our model system pre-
dicted correctly the unusual chemical shift of δH = 2.33 ppm
(observed) and δH = 2.64 ppm (calculated) for the ortho hy-
drogen of the coordinated tolyl (phenyl) moiety. Detailed
AIM and NBO analysis revealed that although it is tempt-
ing to name this coordination “agostic”, strictly spoken it
is not agostic but rather an electrostatic interaction for 3a.
For 3b, this coordination mode can be best described as a
“transition state” between a covalent bond an agostic bond.
These results fit quite well with the reported bonding modes
of Ti(Et)Cl3 and dmpeTi(Et)Cl3: only in the case of the
[η5-C5H5-(η5-C5H4CMe2C6H4Me)Zr(CH2Ph)2] (1): Previously
prepared
[η5-C5H5-(η5-C5H4CMe2C6H4Me)ZrCl2][17]
(2.4 g,
5.65 mmol) was added to a rapidly stirred solution of benzylmagne-
sium chloride in diethyl ether.[20] The colour of the solution
changed to orange. The reaction mixture was stirred overnight. The
volatiles were removed under reduced pressure, and the orange resi-
dmpe adduct could agostic bonding of the Et moiety be due was extracted into pentane. Fractionated crystallisation yielded
2332 Eur. J. Inorg. Chem. 2007, 2327–2333
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Cationic Zirconocene Benzyl Compound with an Appended Phenyl-Group
FULL PAPER
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the desired compound in a moderate yield as orange microcrystals.
Yield: 410 mg (13.5%). 1H NMR (500 MHz, CDCl3, 20 °C): δ =
1.51 (s, 6 H, CCH3), 1.82 (s, 4 H, CH2-Ph), 2.24 (2, 3 H, PhCH3),
5.71 (s, 5 H, Cp), 5.76 (apparent t, J = 5 Hz, 2 H, CpЈ), 5.87 (appar-
ent t, J = 5 Hz, 2 H, CpЈ), 6.76 (t, J = 10 Hz, 2 H, p-H-Ph), 7.05
(d, J = 10 Hz, 4 H, o-H-Ph), 7.06 (d, J = 10 Hz, 4 H, -C4H4-Me),
7.09 (t, J = 10 Hz, 4 H, m-H-Ph) ppm. 12C NMR (125 MHz,
CDCl3, 20 °C): δ = 21.1 (-C4H4-CH3), 30.9 (CCH3), 39.7 (CCH3),
61.4 (CH2-), 111.8 (CpЈ), 112.8 (Cp), 120.9 (p-C-Ph), 125.7 (o-C-
Ph), 126.2 (o-C-tolyl), 128.2 (m-C-Ph), 129.1 (m-C-tolyl), 136.0
(ispo-C), 138.3 (ispo-C), 146.7 (ispo-C), 152.5 (ispo-C) ppm.
C34H36Zr (535.59): calcd. C 76.21, H 6.77; found C 76.10, H 6.65.
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Received: January 2, 2007
Published Online: April 18, 2007
Eur. J. Inorg. Chem. 2007, 2327–2333
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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