Models for solvation of zirconocene cations: Synthesis, reactivity, and computational studies of phenylsilyl-substituted cationic and dicationic zirconocene compounds

Article abstract of DOI:10.1021/om0509488

The reactions of the zirconocene compounds [(η⁵-C ₅H₅)η⁵-C₅H₅SiMe ₅C₆H₅)ZrMe₂] (1) and [η₅C₅H₄SiMe₂C₆H ₄Me)₂ZrMe₂] (2) with either B(C ₆F₅)₃ or the trityl salt [Ph₃C] ⁺[B(C₆F₅)₅]^- in CD ₂C1₂ were monitored by NMR spectroscopy. In the case of the cationic products [(η⁵-C₅H₄SiMe ₂C₆H₅)ZrMe]⁺[MeB(C₆F ₅)₃]^- (4a) and [(η⁵-C ⁵ H₄SiMe₂C₆H₄Me) ₂ZrMe]⁺ X^- (4a) and [(η⁵-C ₅H₄SiMe₂C₆H₄Me) ₂ZrMe)₂ZrMe]⁺ X^- (5x, X = [MeB(C₆F₅)₃]^-; 5b, X = [B(C ₆F₅)₄]^-), coordination of the arene, bonded through Si to the cyclopentadienyl ring, to the cationic zirconium was observed. However, this coordination is rather weak, and stronger Lewis donors such as the anion or the starting material replace the coordinated arene moiety. The solid-state structures of 1 and 2 were determined by X-ray crystallography. Density functional computations (B3LYP/ECP1 and B3LYP/II level) have revealed that the phenyl groups in [η⁵-C₅H₅)(η- C₅H₄SiMe₂C₆H₅)ZrMe ⁺ (10), [(η⁵-C₅H₄SiMe ₂C₆H₄Me)₂Zr]²⁺ (11), and [(η⁵-C₅H₄SiMe₂C ₆H₅Zr]²⁺ (12) are coordinated via one of the arene carbon atoms. The structural assignments are supported by the good agreement between the experimental NMR shifts and the computed (GIAO-B3LYP/II level) shifts in the case of the cationic compound (10). The structure of the dicationic compound 11 differs significantly from that of 12, indicating a strong influence of the para substituent of the arene ring. Compounds 1 and 2 validate previously suggested models for solvent (arene) adducts in Kaminsky-type polymerization.

Full text of DOI:10.1021/om0509488

2796
Organometallics 2006, 25, 2796-2805
Models for Solvation of Zirconocene Cations: Synthesis, Reactivity,
and Computational Studies of Phenylsilyl-Substituted Cationic and
Dicationic Zirconocene Compounds
Jo¨rg Sassmannshausen,*,† Jennifer C. Green,‡ Franz Stelzer,† and Judith Baumgartner§
Institut for Chemistry and Technology of Organic Materials, TU-Graz,
Stremayrgasse 16/I A-8010 Graz, Austria, Department of Chemistry, UniVersity of Oxford,
Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, U.K., and
Inorganic Chemistry, TU-Graz, Stremayrgasse 16/I A-8010 Graz, Austria
ReceiVed NoVember 4, 2005
The reactions of the zirconocene compounds [(η5-C5H5)(η5-C5H4SiMe2C6H5)ZrMe2] (1) and [(η5-
C5H4SiMe2C6H4Me)2ZrMe2] (2) with either B(C6F5)3 or the trityl salt [Ph3C]+[B(C6F5)4]- in CD2Cl2 were
monitored by NMR spectroscopy. In the case of the cationic products [(η5-C5H5)(η5-C5H4SiMe2C6H5)-
ZrMe]+[MeB(C6F5)3]- (4a) and [(η5-C5H4SiMe2C6H4Me)2ZrMe]+ X- (5a, X ) [MeB(C6F5)3]-; 5b, X )
[B(C6F5)4]-), coordination of the arene, bonded through Si to the cyclopentadienyl ring, to the cationic
zirconium was observed. However, this coordination is rather weak, and stronger Lewis donors such as
the anion or the starting material replace the coordinated arene moiety. The solid-state structures of 1
and 2 were determined by X-ray crystallography. Density functional computations (B3LYP/ECP1 and
B3LYP/II level) have revealed that the phenyl groups in [(η5-C5H5)(η-C5H4SiMe2C6H5)ZrMe]+ (10),
[(η5-C5H4SiMe2C6H4Me)2Zr]2+ (11), and [(η5-C5H4SiMe2C6H5)2Zr]2+ (12) are coordinated via one of the
arene carbon atoms. The structural assignments are supported by the good agreement between the
experimental NMR shifts and the computed (GIAO-B3LYP/II level) shifts in the case of the cationic
compound (10). The structure of the dicationic compound 11 differs significantly from that of 12, indicating
a strong influence of the para substituent of the arene ring. Compounds 1 and 2 validate previously
suggested models for solvent (arene) adducts in Kaminsky-type polymerization.
has, to the best of our knowledge, been less actively pursued,
probably due to a lack of suitable model systems. In the case
of monocyclopentadienyltitanium catalysts, the influence of
coordinated arene on ethene trimerization has been studied in
detail by Hessen.17 To this end, we reported some time ago
cationic and dicationic zirconocene compounds with coordinated
phenyl groups.18-20 These compounds can be considered as
models for the influence of solvent on the cationic zirconocene
compound. Earlier studies revealed the dramatic influence of
the bridging CR2 moiety of [(η5-C5H4CR2Ph)2ZrMe]+: Whereas
in the case R ) H we observed the formation of the expected
zwitterionic compound [(η5-C5H4CR2Ph)2ZrMe(µ-Me)B(C6F5)3]
as well as some [(η5-C5H4CR2Ph)2ZrMe]+ using low-temper-
ature NMR studies,21 in the case of R ) Me we obtained clear-
cut evidence for the formation of [(η5-C5H4CR2Ph)2ZrMe]+
under otherwise identical reaction conditions.19,20 Further-
more, the formation of the dicationic compound of [(η5-
C5H4CR2Ph)2Zr]2+ was only observed in the case R ) Me. This
observation led to the conclusion that the coordination of the
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 the
weakly coordinating ligand [(η5-Cp)2MR+‚‚‚D] (D ) X-
(anion), monomer, solvent). Whereas much effort has gone into
elucidating 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
* To whom correspondence should be addressed. E-mail:
sassmannshausen@tugraz.at.
† Institut for Chemistry and Technology of Organic Materials, TU-Graz.
‡ University of Oxford.
§ Inorganic Chemistry, TU-Graz.
(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.
(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.
(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) Hessen, B. J. Mol. Catal. A: Chem. 2004, 213, 129-135.
(18) Bu¨hl, M.; Sassmannshausen, J. Dalton Trans. 2001, 79-84.
(19) Doerrer, L. H.; Green, M. L. H.; Ha¨ussinger, D.; Sassmannshausen,
J. J. Chem. Soc., Dalton Trans. 1999, 2111-2118.
(20) Green, M. L. H.; Sassmannshausen, J. Chem. Commun. 1999, 115-
116.
(21) Bochmann, M.; Green, M. L. H.; Powell, A. K.; Sassmannshausen,
J.; Triller, M. U.; Wocadlo, S. J. Chem. Soc., Dalton Trans. 1999, 43-49.
(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.
(7) Britovsek, G. J. P.; Gibson, V. C.; Wass, D. F. Angew. Chem., Int.
Ed. 1999, 38, 428-447.
(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.
10.1021/om0509488 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/22/2006

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 11, 2006 2797
Chart 1. Diagrams of Compounds Discussed in This Paper
arene moiety is very susceptible to its steric environment: a
more crowded environment (R ) Me) enhances the coordina-
tion, whereas a more open environment (R ) H) shows less
propensity for arene coordination. Here we extend our studies
on these solvent model systems and report the outcome of
detailed NMR and DFT investigations of mono- and disubsti-
tuted zirconocene compounds of the general type [(η5-Cp)-
(η-C5H4SiMe2Ph)ZrX]+ and [(η5-C5H4SiMe2C6H4R′)2Zr]2+ (R
) H, Me; X ) Cl, Me). This combination of NMR and
DFT investigations has proven to be very successful in the
past18 and enables investigation of otherwise unobservable re-
active intermediates. The paper is organized as following: in
part I of the Results and Discussion, the reactions of the
compounds [(η5-Cp)(η5-C5H4SiMe2Ph)ZrMe2] (1) and [(η5-
C5H4SiMe2C6H4Me)2ZrMe2] (2) with either B(C6F5)3 or the
trityl salt [Ph3C]+[B(C6F5)4]- in CD2Cl2, investigated by
NMR spectroscopy, are discussed. Part II reports the DFT
investigations of [(η5-Cp)(η5-C5H4SiMe2Ph)ZrX]+, [(η5-
C5H4SiMe2C6H4Me)2Zr]2+, and [(η5-C5H4SiMe2Ph)2Zr]2+ (X )
Cl, Me), respectively. An overview of all discussed cationic
and dicationic zirconocenes is given in Chart 1.
Results and Discussion
I. Experimental Investigations. (a) Preparation of the
Metallocenes 1 and 2. The compounds 1 and 2 were synthe-
sized according to a modified literature procedure.22 Thus,
phenyllithum, freshly prepared from iodobenzene and butyl-
lithium, was reacted with excess dichlorodimethylsilane (cf.
Scheme 1). The resulting crude product was further reacted with
cyclopentadienyllithium to obtain the ligand 3a (R ) H) in good
yields. The ligand 3b was prepared in a similar manner,
phenyllithium being replaced with the Grignard reagent
MeC4H5MgBr. Both ligands were used as obtained; no attempts
of further purification were made, because the NMR spectra
(22) Sassmannshausen, J.; Powell, A. K.; Anson, C. E.; Wocadlo, S.;
Bochmann, M. J. Organomet. Chem. 1999, 592, 84-94.

2798 Organometallics, Vol. 25, No. 11, 2006
Sassmannshausen et al.
Scheme 1a
Table 1. Selected Angles (deg) and Distances (Å) of 1 and 2
1
2
Cpcentr-Zr-Cpcentr
C(11)-Zr-C(12)
Cpcentr-C(10)-Si(1)
Cpcentr-Zr
131.93
96.02(14)
173.74
2.226
Cpcentr-Zr-Cpcentr
C(1)-Zr-C(2)
Cpcentr-C(4)-Si(1)
Cpcentr-C(17)-Si(2)
Cpcentr-Zr
131.49
95.8(2)
168.66
170.34
2.226
Cpcentr-Zr
2.214
C(11)-Zr
2.276(4)
2.276(4)
1.862(4)
Cpcentr-Zr
2.224
C(12)-Zr
C(1)-Zr
C(2)-Zr
C(17)-Si(2)
C(4)-Si(1)
2.296(6)
2.282(5)
1.870(5)
1.854(5)
C(10)-Si(1)
Table 2. Crystallographic Data for 1
empirical formula
formula wt
C20H26SiZr
385.72
temp
100(2) K
wavelength
cryst syst, space group
0.71073 Å
monoclinic, P21/n
unit cell dimens
a
b
c
7.6987(15) Å
19.594(4) Å
12.156(2) Å
90
a Legend: (i) PhLi or Me2C6H4MgBr; (ii) LiCp; (iii) CpZrCl3‚dme;
(iv) LiMe; (v) ZrCl4(thf)2.
R
â
92.04(3)
90
γ
V
1832.5(6) Å3
4, 1.398 Mg/m3
0.661 mm-1
800
Z, calcd density
abs coeff
F(000)
crystal size
θ range for data collection
limiting indices
0.55 × 0.35 × 0.18 mm
1.97-26.37°
-9 e h e 9, -24 e k e 23,
-14 e l e 15
no. of rflns collected/unique
completeness to θ ) 26.37°
abs cor
14 429/3728 (R(int) ) 0.0692)
99.6%
SADABS
max and min transmissn
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
0.8904 and 0.7127
full-matrix least squares on F2
3728/0/203
1.039
R1 ) 0.0467, wR2 ) 0.1118
R1 ) 0.0667, wR2 ) 0.1200
1.280 and -1.360 e Å-3
largest diff peak and hole
C(2)-Zr-C(2) angle (95.83°) and C(1)-Zr/C(2)-Zr distances
(2.296, 2.282 Å) are in good agreement with those of the
reported compound [(η5-C5H4CMe2Ph)2ZrMe2] (9).19 Selected
bond distances (Å) and angles (deg) are given in Table 1. Full
details are given in the Supporting Information (Table S2).
(b) Low-Temperature NMR Spectroscopy Reaction Stud-
ies. All spectroscopic data for these studies are summarized in
Table 4, together with detailed assignments. An overview of
all discussed cationic and dicationic compounds is given in
Chart 1.
The reaction of 1 with B(C6F5)3 in CD2Cl2 was monitored
by NMR spectroscopy. Unlike the reported compound [(η5-Cp)-
(η5-C5H4CMe2Ph)ZrMe2], which reacted cleanly at -60 °C to
form the ion pair14-16 [(η5-Cp)(η5-C5H4CMe2Ph)ZrMe]+[MeB-
(C6F5)3]- as the sole product,19 the observed reaction between
1 and B(C6F5)3 yields a mixture of two products: the anticipated
ion pair [(η5-Cp)(η5-C5H4SiMe2Ph)ZrMe]+[MeB(C6F5)3]- (4a)
as well as the zwitterionic species [(η5-Cp)(η5-C5H4SiMe2Ph)-
Zr(Me)(µ-Me)B(C6F5)3] (4b). Evidence for the formation of 4a
could be obtained by the downfield shifts of three protons, a
significant high-field shift of the proton in close proximity to
the metal, and a marginal high-field shift of the remaining proton
of the coordinated28 phenyl group. These results have been
Figure 1. Solid-state structure of 1.
indicated a pure product. Deprotonation of 3a and 3b with
butyllithium and quenching with [(η5-Cp)ZrCl3(dme)] and
[ZrCl4(thf)2], respectively, yielded compounds 1a and 2a.
Compounds 1a and 1b were considered as interim products and
used as obtained, the NMR spectra being satisfactory. Methy-
lation with methyllithium furnished the compounds 1 and 2 in
good yields.
Crystals suitable for X-ray analysis were obtained by
slow cooling of saturated solutions of 1 and 2 in pentane to
-30 °C, respectively. Compound 1 crystallizes with two
independent molecules in the unit cell; only one is shown in
Figure 1. The phenyl group is pointing away from the zirconium
in an arrangement similar to the previously published solid-
state structure of [(η5-Cp)(η5-C5H4CMe2tol)ZrMe2] (8).19 The
Cpcentr-Zr-Cpcentr angle of 131.93° is close to the reported value
of 131.87° for 8. The C(11)-Zr-C(12) angle of 96.0° is
more open, compared to 93.6° for 8, and the Cpcentr-Zr distances
of 2.226 and 2.214 Å are comparable to 2.239 and 2.230 Å for
8, indicating a similar structure. Selected bond distances and
angles are given in Table 1; full details are given in the
Supporting Information (Table S1). The tolyl groups of 2 (Figure
2) are pointing away from the zirconium, and there is no
evidence for intramolecular interactions. The Cpcentr-Zr-Cpcentr
angle (131.49°), Cpcentr-Zr distances (2.226, 2.224 Å),
(23) Horton, A. D.; de With, J.; Linden, J. v. d.; Weg, H. v. d.
Organometallics 1996, 15, 2672-2674.
(24) Selected spectra are available in the Supporting Information.

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 11, 2006 2799
19F NMR data. Both species are interchanging with each other,
rendering the NMR spectrum rather complicated. Complete
assignment of the spectra was possible due to use of 2D
(mulitnuclear) NMR spectroscopy, in particular NOESY/EXSY
spectroscopy.24 Lowering the temperature from -60 to -80 °C
sharpens the peaks assigned to 4a, slowing down the exchange
process between 4a and 4b and furthermore slowing down site
exchange in 4a. The site exchange of various zirconocene
compounds has been studied in detail by Marks.25-27 Evidence
for the exchange between 4a and 4b can be readily obtained
by EXSY spectroscopy: exchange peaks are clearly visible
between the coordinated and free phenyl moieties (Figure 3),
and thus the anion can reversibly replace the coordinated phenyl
moiety. Obviously, due to the larger atomic radius of silicon
(1.17 Å vs 0.77 Å for carbon), the environment around the metal
is less crowded and the phenyl moiety is therefore less prone
to bind to the cationic zirconium center, rendering the coor-
dination more labile. Similar observations were made before
in the case of the [(η5-C5H4CR2Ph)2ZrMe]+ cation (R ) H).21
In that case the main product was the zwitterionic [(η5-
C5H4CH2Ph)2ZrMe(µ-Me)B(C6F5)3], clear-cut evidence for the
formation of the ion pair product [(η5-C5H4CR2Ph)2ZrMe]+-
[MeB(C6F5)3]- could not be obtained.
Figure 2. Solid-state structure of 2.
Table 3. Crystallographic Data for 2
empirical formula
formula wt
C30H40Si2Zr
548.02
temp
100(2) K
The reaction of 2 with 1 equiv of B(C6F5)3 in CD2Cl2 was
monitored by NMR spectroscopy. At -60 °C, evidence for the
formation of the expected ion pair compound [(η5-C5H4SiMe2-
tol)2ZrMe]+[MeB(C6F5)3]- (5a) was obtained. As in the case
of 1, the zwitterionic compound [(η5-C5H4SiMe2tol)2Zr(Me)-
(µ-Me)B(C6F5)3] (5b) was observed as a byproduct. Again, this
is in contrast with the previously investigated reaction of
[(η5-C5H4CMe2tol)2ZrMe2], which gave the ion pair compound
[(η5-C5H4CMe2tol)2ZrMe]+[MeB(C6F5)3]- as the sole product.19
Assignment of the NMR spectra was possible due to NOESY/
EXSY spectroscopy. Similar to the reaction of 1, the two
products are evidently in equilibrium with each other, as
lowering the temperature to -80 °C significantly sharpens the
peaks for 5a and enabled complete assignment.
The reaction of 2 with 1 equiv of the trityl salt [Ph3C]+-
[B(C6F5)4]- in CD2Cl2 was monitored by NMR spectroscopy.
At -60 °C, evidence for the formation of the expected ion
pair [(η5-C5H4SiMe2tol)2ZrMe]+[B(C6F5)4]- (6a) and the ho-
modinuclear compound [((η5-C5H4SiMe2tol)2ZrMe)2(µ-Me)]+-
[B(C6F5)4]- (6b) was obtained. This is in contrast to the
previously investigated reaction of [(η5-C5H4CMe2tol)2ZrMe2]
with trityl salt, which exclusively yielded the ion pair product.19
Again, lowering the temperature to -80 °C sharpened the peaks
assigned to 6a significantly.
The cation [((η5-C5H4SiMe2tol)2ZrMe)2(µ-Me)]+ has been
independently synthesized by reacting 2 equiv of 2 with 1 equiv
of B(C6F5)3 in CD2Cl2 at -60 °C. The sole product of this
reaction was [((η5-C5H4SiMe2tol)2ZrMe)2(µ-Me)]+[MeB(C6F5)3]-
(7), as monitored by NMR spectroscopy. Similar observations
have been made before by Brintzinger29 using B(C6F5)3 and by
Bochmann30 using trityl salt as an activator. Both authors
reported the formation of homodinuclear cationic zirconocene
compounds in the presence of excess starting material.
We have previously reported the formation of zirconocene
dications by reaction of either [(η5-C5H4CMe2Ph)2ZrMe2] or
[(η5-C5H4CMe2tol)2ZrMe2] with excess B(C6F5)3 in CD2Cl2 at
-60 °C.20 To ascertain the possibility of a similar reaction, we
wavelength
cryst syst, space group
unit cell dimens
a
b
c
R
â
0.710 73 Å
monoclinic, P21/n
12.581(3) Å
16.726(3) Å
13.714(3) Å
90
99.90(3)
90
γ
V
2842.9(10) Å3
4, 1.280 Mg/m3
0.487 mm-1
Z, calcd density
abs coeff
F(000)
crystal size
θ range for data collection
limiting indices
1152
0.44 × 0.28 × 0.20 mm
1.94-25.00°
-14 e h e 14, -19 e k e 19,
-16 e l e 16
no. of rflns collected/unique
completeness to θ ) 26.37°
abs cor
max and min transmissn
refinement method
no. of data/restraints/params
goodness of fit on F2
final R indices (I > 2σ(I))
R indices (all data)
20 045/4993 (R(int) ) 0.1065)
99.9%
SADABS
0.9089 and 0.8143
full-matrix least squares on F2
4993/0/306
1.258
R1 ) 0.0769, wR2 ) 0.1713
R1 ) 0.0871, wR2 ) 0.1770
1.997 and -0.861 e Å-3
largest diff peak and hole
observed before and clearly indicate the coordination of one
ortho carbon of the phenyl group to the cationic zirconium.19
The existence of a second, distinguished zirconocene compound
is corroborated by the two different anions: the separated anion
[MeB(C6F5)3]- has a chemical shift of δ 0.45 ppm for the CH3B
group and the zwitterionic, bridging µ-CH3-B group has a
chemical shift of δ 0.06 ppm. This finding is further cor-
roborated by 19F NMR spectroscopy. The chemical shift
differences ∆δ(m,p) of the aryl fluorines of 4.8 ppm indicates
a bridging µ-CH3-B moiety, whereas the ∆δ(m,p) value of 2.7
ppm indicates a separated anion. Similar values have been found
before19,23 and are in good agreement with the observed 1H and
(25) Lanza, G.; Fragala, I. L.; Marks, T. J. J. Am. Chem. Soc. 1998,
120, 8257-8258.
(26) Deck, P. A.; Marks, T. J. J. Am. Chem. Soc. 1995, 117, 6128-
6129.
(29) Beck, S.; Prosenc, M.-H.; Brintzinger, H.-H.; Goretzki, R.; Herfert,
N.; Fink, G. J. Mol. Catal. A 1996, 111, 67-79.
(30) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 1634-1637.
(27) Beswick, C. L.; Marks, T. J. Organometallics 1999, 18, 2410-
2412.
(28) See part II for the use of “coordinated” rather than “agostic”.

2800 Organometallics, Vol. 25, No. 11, 2006
Table 4. 1H and 13C NMR Data of the Cationic Complexes 4-7
Sassmannshausen et al.
a 500 MHz. b 125.7 MHz. c 470 MHz. CpHn (n ) 1-4) denotes hydrogens of the C5 ring, coupled to CpCn (connectivity determined by CH correlation).
PhHn (n ) 1-5) denotes hydrogens of the C6 ring, coupled to PhCn (connectivity determined by CH correlation).
treated 2 with excess B(C6F5)3 in CD2Cl2 at -60 °C and
monitored the reaction by NMR spectroscopy. However, no
clean-cut evidence for such a dication could be obtained; the
NMR spectrum is rather crowded and probably consists of a
mixture of 5a, 5b, and some unknown compound. To model
structures for the arene-coordinated cationic products re-
ported here, DFT calculations were performed and are reported
in part II.
II. DFT Calculations. An initial optimization of cation 4
from a starting structure similar to the previously described
cationic compound [(η5-Cp)(η5-C5H4CH2C6H5)ZrMe]+ (13)18
gave structure 10a (Figure 4). Resembling 13, structure 10a
has a close contact between the Zr and one of the ortho car-
bons of the phenyl ring (Figure 4). The Zr-C2 distance of 2.73
Å is somewhat longer than the corresponding distance in 13
(Zr-C2 ) 2.629 Å) but is in excellent agreement with the
recently published values from Ziegler et al.31 They reported
the structure of the solvent-separated ion pair [(η5-1,2-Me2C5H3)2-
ZrMe]+[MeB(C6F5)3]- in toluene and obtained Zr-C distances
of 2.60 and 2.74 Å, respectively, for the η2-bonded toluene.
The hydrogen attached to C2 in 10a is bent away from the Zr,
by 8.5° out of the phenyl plane (13: ca. 15°). Both values
indicate a weaker η1 coordination of the phenyl ring to the
cationic zirconium, in comparison with 13. All other Zr-C(Ph)
distances are significantly larger than 3 Å, corroborating the η1
coordination mode (cf. Figure 4) rather than an agostic bonding
mode.18
Further exploration of the potential energy surface revealed
the presence of at least one other minimum wherein the zir-
conium is in close proximity to an ortho carbon (10b, Zr-C6
) 2.71 Å) with the attached hydrogen bent out of the Ph plane
(31) Vanka, K.; Chan, M. S. W.; Pye, C. C.; Ziegler, T. Organometallics
2000, 19, 1841-1849.

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 11, 2006 2801
Figure 5. Stationary points and schematic potential energy surface
for the phenyl rotation of cation 10-cl, with relative energies at the
B3LYP/ECP1 level.
whereas the barrier for the interconversion of 10a and 10b is
rather low, the barrier for the interconversion between 10a-cl
and 10b-cl is significantly higher, namely 66.65 kJ/mol, and
thus even higher than the barrier for TS13. This may be
explained by the greater electronegativity of chlorine and
consequent increased bond strength between Zr and C2.
Whereas the optimized structures suggest that 10a is probably
the dominant species at low temperature, the energies of the
two species are so close that further evidence was sought by
comparison between the measured and calculated NMR spectra
(Table 5). In general, the IGLO II basis set gives more
comparable data with less deviation between the benzene and
TMS references. These data are also in good agreement with
the calculated shifts using the EPC1 basis set and benzene as a
reference. The largest deviation was found using EPC1 and TMS
as a reference.
Figure 3. EXSY spectrum of the phenyl region of 4a/4b.
Careful comparison between the calculated values for 10a
and 10b and the experimental values suggest a marginally closer
agreement with structure 10b. It is probable that 10a and 10b
are in rapid exchange. However, exchange between 4a and 4b
has been established experimentally. This exchange is cor-
roborated by the strong EXSY cross-peaks in the phenyl region
of the spectrum (Figure 3). The rapid exchange between 4a and
4b on the NMR time scale is likely to leave the anion in close
proximity to the cation, probably with the methyl group pointing
toward the cationic zirconium and thus fitting nicely in the
pocket of 10b. Such a positioning of the anion may inhibit
rotation of the phenyl ring and the formation of 10a. It is
tempting to speculate that such rapid exchange between 4a and
4b can occur by simply moving the anion to and fro on a
Zr-Me-BX3 axis with a minor rotation of the phenyl ring
(Scheme 2) and that the previously observed “overturning” of
the anion is unlikely.16 This translation would not change much
of the remaining geometry of the molecule and thus results in
observed chemical shifts, which, in consequence, are closer to
structure 10b than to structure 10a.32
Whereas the reaction of [(η5-C5H4CMe2C6H5)2ZrMe2] and
[(η5-C5H4CMe2C6H4Me)2ZrMe2] with 2 equiv of B(C6F5)3 in
CD2Cl2 at -60 °C yields the dicationic compounds [(η5-
C5H4CMe2C6H5)2Zr]2+ (14) and [(η5-C5H4CMe2C6H4Me)2Zr]2+,20
the similar reaction of [(η5-C5H4SiMe2C6H4Me)2ZrMe2] and
B(C6F5)3 did not yield the dicationic compound [(η5-
C5H4SiMe2C6H4Me)2Zr]2+ (11). In light of the above observa-
tions, this is probably not too surprising, given the propensity
Figure 4. Stationary points and schematic potential energy surface
for the phenyl rotation of cation 10, with relative energies at the
B3LYP/ECP1 level.
by 9.6° (Figure 4). This second minimum is slightly higher in
energy (9.31 kJ/mol) than 10a. The transition state TS10, con-
necting these two minima, was located with a loose η3 coor-
dination of the phenyl ring. The distances between zirconium
and C1, C2, and C6 are 2.94, 3.65, and 2.69 Å, respectively
(TS13: 2.840, 2.995, and 3.246 Å, respectively). The smaller
value of Zr-C6 indicates that TS10 is closer to the structure of
10b, rather than to the structure of 10a, which is probably due
to steric reasons. As the resulting barrier is only 13.8 kJ/mol
and is lower than the corresponding barrier for TS13 (19
kJ/mol), rapid scrambling between 10a and 10b can be expected
on the NMR time scale.
To ascertain any possible steric or electronic effects of the
Zr-Me group, we replaced the methyl moiety with a chlorine
atom. The structural features of 10a-cl and of 10b-cl are similar
to those of the parent compounds 10a and 10b (Figure 5). The
Zr-C2 distance of 10a-cl is 2.74 Å; the hydrogen is bent by
10.6° out of the Ph plane. The Zr-C6 distance of 10b-cl is 2.72
Å; the hydrogen is bent by 10.8° out of the Ph plane. In the
transition state TS10-cl, similar to TS10, the corresponding
distances between zirconium and C1, C2, and C6 are 2.90, 3.67,
and 2.81 Å, respectively. Overall, the chloride derivative 10cl
is structurally very similar to the parent compound 10. However,
(32) This exchange is currently under investigation and will be subject
to a separate publication.

2802 Organometallics, Vol. 25, No. 11, 2006
Sassmannshausen et al.
Table 5. GIAO-B3LYP Calculated and Experimental
Chemical Shifts (ppm) of 10a and 10b
the phenyl plane, away from the zirconium by 12.3° (14a:
14.5°). Thus, the structural features of 11a and 14a are very
similar, and this cannot explain the differences in their reactivity.
However, the energy difference between 11a and 11c of 40.5
kJ/mol is substantially higher than the corresponding energy
difference of 14a and 14c (18.9 kJ/mol). Again, the structural
features of both compounds are similar: the Zr-C6 distances
of 2.70 and 2.65 Å in 11c, respectively, are somewhat longer
than the reported distance of 2.57 Å for 14c. It should be noted,
however, that 14c was calculated with symmetry restriction,
whereas 11c was calculated without any restriction. The third
located minimum 11b, which somehow interconnects 11a and
11c, is only 12.5 kJ/mol higher in energy than 11a. It can be
assumed that both 11a and 11b are exchanging rapidly even at
low temperature on the NMR time scale. The most likely
explanation for the failure to obtain the dicationic compound
11 is a weaker bond between the zirconium and the coordinated
carbon of the arene ring, leaving the zirconium more vulnerable
to attack by other Lewis bases such as the anion.
Indeed, DFT calculations of the dicationic compound 12
indicate this. Whereas in the case of 11 the symmetrical
compound 11a was found to be the most stable compound, in
the case of 12 the most stable compound was determined to be
the unsymmetrical compound 12a, which is similar to 11b
(Figure 7). The Zr-C2 distance of 2.67 Å and Zr-C2′ of 2.69
Å for 12a is similar to the corresponding distances of 11b (2.66
and 2.70 Å). Again, the hydrogen bonded to the coordinated
carbon atom is bent out of the arene plane (11.0 and 14.5° for
12a; 10.4 and 14.6° for 12b). Thus, the structural features of
11b and 12a are very similar, but with 12a being lower in energy
than 12b, a situation which is quite unexpected. Furthermore,
the energy difference between 12a and 12b is significantly larger
than the difference between 11a and 11b: 50.48 kJ/mol vs 12.54
kJ/mol. The transition state TS12-1 is, at 74.40 kJ/mol,
significantly higher than the corresponding transition state
TS11-1 (23.97 kJ/mol). Similar observations may be made about
the energy difference between 12b and 12c, compared with 11b
and 11c. It can be assumed that the calculated structure 12a
would be the only observable structure in low-temperature NMR
studies. It can be concluded that the introduction of a methyl
group in the para position disturbs the energy balances between
the different structures significantly enough to render the
stabilization effect of the arene rings weaker. Therefore, the
presence of the anion, although it is claimed to be “noncoor-
dinating”, could perturb this energy balance significantly to
render the observation of 11 very difficult.
ECP1/
TMS
IGLO II/
TMS
ECP1/
C6H6
IGLO II/
C6H6
exptl
Compound 10a
CpC
103.7
107.7
111.1
112.6
103.2
98.3
115.6
105.7
128.0
120.7
127.6
127.4
5.41
117.1
122.4
124.5
125.9
116.0
110.9
130.3
119.5
143.2
134.4
142.4
142.1
116.7
121.0
124.5
126.0
116.6
111.6
129.0
199.1
141.4
134.0
141.0
140.8
5.53
7.05
6.87
6.22
5.99
1.8
6.7
55.7
0.51
115.5
121.1
123.2
126.0
114.7
108.77
129.0
118.2
141.9
133.1
141.1
140.8
5.60
113.8
117.3
120.2
113.6
114.7
118.2
n.d.
n.d.
n.d.
n.d.
n.d.
CpC1
CpC2
CpC3
CpC4
CpC5
PhC1
PhC2
PhC3
PhC4
PhC5
PhC6
CpH
n.d.
5.71
6.03
6.76
5.70
6.45
6.20
-3.4
-3.5
46.4
0.36
0.48
0.75
CpH2
CpH3
CpH4
CpH5
SiC1
6.75
6.56
5.91
5.69
6.93
6.70
6.10
5.91
7.00
6.77
6.17
5.98
-11.6
-6.6
42.3
-11.1
-12.4
-6.7
51.0
SiC2
-5.5
ZrCH3
SiCH1
SiCH2
ZrCH3
52.2
0.46
0.45
1.01
0.76
0.75
1.32
0.58
0.52
1.33
0.45
1.26
Compound 10b
CpC
104.0
105.6
118.6
103.6
106.1
102.5
128.9
122.1
130.3
118.3
125.9
107.35
6.06
117.4
117.0
118.9
131.9
116.9
119.4
115.9
142.2
135.5
143.7
131.6
139.2
120.7
115.8
118.6
131.2
115.3
117.1
114.3
143.5
134.7
144.1
131.8
139.6
120.0
6.31
113.8
117.3
120.2
113.6
121.2
118.2
n.d.
n.d.
n.d.
n.d.
n.d.
CpC1
CpC2
CpC3
CpC4
CpC5
PhC1
PhC2
PhC3
PhC4
PhC5
PhC6
CpH
119.9
132.5
116.5
118.4
115.5
144.7
136.0
145.3
131.8
140.8
121.27
6.37
n.d.
6.24
6.03
6.76
5.70
6.45
6.20
-3.4
-3.5
46.4
0.36
0.48
0.76
CpH2
CpH3
CpH4
CpH5
SiC1
6.91
5.53
6.19
5.76
7.09
5.74
6.26
5.94
7.22
5.83
6.50
6.07
5.8
2.4
55.4
0.33
0.77
0.15
7.16
5.81
6.33
6.01
-7.6
-11.0
42.0
0.34
0.69
-0.06
-6.7
-10.4
53.4
-7.9
-11.6
52.1
SiC2
ZrCH3
SiCH1
SiCH2
ZrCH3
0.64
1.00
0.24
0.40
0.84
0.22
Scheme 2. Proposed Exchange Mechanism between 4a and
4b
Conclusion
The reactions of zirconocene compounds bearing one or two
dimethylphenylsilyl substituents on one or two cyclopentadienyl
moieties with either B(C6F5)3 or trityl salt have been studied.
Low-temperature (-60 to -80 °C) multinuclear NMR studies
of 1 provide evidence for the formation of the ion pair product
4a with a Zr-coordinated phenyl group. This product is in
equilibrium with the zwitterionic compound 4b, as observed
by EXSY spectroscopy. This reaction pattern is in strong
contrast to the previously observed reactions of arene-substituted
zirconocene compounds with a carbon bridging atom instead
of a silicon bridging atom, where the ion pair product with
phenyl coordination was the sole product. Similar observations
of the reaction of 2 with either B(C6F5)3 or trityl salt were made.
Again, evidence for the formation of the ion pair product 5a
with a coordinated phenyl group was obtained, which is in
equilibrium with the zwitterionic product 5b. It is apparent that
of the monocation to coordinate the anion. Thus, the propensity
of the hypothetical dication to coordinate the anion would be
much higher. DFT calculations of 11 revealed at least three
minima on the potential energy surface (Figure 6). The lowest
energy was found for structure 11a, which is stabilized by
coordination of the two ortho carbons of the arene ring. The
Zr-C2 distance of 2.68 Å is similar to the previously reported
value of 2.60 Å for 14a.18 Similar values can be found for the
Zr-C1 distances: 3.09 Å for 11a and 3.05 Å for 14a. Again,
the hydrogen bonded to the coordinated carbon is bent out of

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 11, 2006 2803
Figure 6. Stationary points and schematic potential energy surface for the phenyl rotation of dication 11, with relative energies at the
B3LYP/ECP1 level.
Figure 7. Stationary points and schematic potential energy surface for the phenyl rotation of dication 12, with relative energies at the
B3LYP/ECP1 level.
the larger atomic radius of silicon (1.17 vs 0.77 Å for carbon)
moves the arene moiety further away from the cationic metal
center, thus making coordination less likely to occur.
the starting material are more likely to bind to the cationic metal
center, a situation which has been observed and documented
before.
The DFT calculations of the observed cationic compound 4
support the inferences drawn from the experimental results. The
phenyl moiety is further away from the cationic metal center
compared with the carbon-bridged compound 13. Hence, the
stabilization effect of the phenyl moiety is less pronounced.
Similar to the case for 13, the hydrogen attached to the
coordinated carbon is bent out of the phenyl plane, away from
the zirconium. The structural features of 10 are similar to those
of 13, supporting the results. The calculated NMR chemical
shifts, however, indicate a more complex scenario than in 13:
close inspection reveals that 10b is in better agreement with
the experimental values than 10a. This can be explained by
taking into consideration the experimental observed exchange
between 4a and 4b. Indeed, the calculated structure 10b is more
prone to accommodate the methyl group of the anion by simple
rotation of the phenyl group, whereas 10a has to undergo a more
complex rearrangement.
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.
NMR spectra were recorded on a Varian Gemini 200, a Varian
UnityPlus 500, or a Bruker AM300 spectrometer and referenced
to the residual protio 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 coupled pfg-ghsqc spectroscopy. 19F NMR spectra
were referenced to external C6F6 (δ -163.0 ppm).
On the basis of the calculated structures of 11, no clear
explanation for the failure to observe the dicationic compound
in the NMR could be drawn. However, comparison with the
calculated structure of 12 indicates that the stabilization of the
arene is weaker in the case of the silicon-bridged compound in
comparison to the carbon-bridged compound 14. This is in
concert with the results of both experimental and DFT inves-
tigations of 4a. This is strong support for these compounds as
models for arene (solvent) adducts in Kaminsky-type polym-
erization: the likelihood of arene coordination decreases as the
arene moves further away from the cationic metal center, and
thus by comparison stronger Lewis bases such as the anion or
For X-ray structure analyses the crystals were mounted onto the
tip of glass fibers, and data collection was performed with a Bruker-
AXS SMART APEX CCD diffractometer using graphite-mono-
chromated Mo KR radiation (0.710 73 Å). The data were reduced
to Fo and corrected for absorption effects with SAINT33 and
2
SADABS,34,35 respectively. The structures were solved by direct
methods and refined by full-matrix least-squares methods
(SHELXL97).36 If not noted otherwise, all non-hydrogen atoms
(33) SAINTPLUS: Software Reference Manual, Version 6.45; Bruker-
AXS: Madison, WI, 1997-2003.
(34) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51.
(35) SADABS: Version 2.1; Bruker AXS, Madison, WI, 1998.

2804 Organometallics, Vol. 25, No. 11, 2006
Sassmannshausen et al.
were refined with anisotropic displacement parameters. All hydro-
gen atoms were located in calculated positions to correspond to
standard bond lengths and angles. All diagrams were drawn with
30% probability thermal ellipsoids, and all hydrogen atoms were
omitted for clarity. Crystallographic data (excluding structure
factors) for the structures of compounds 1 and 2 reported in this
paper have been deposited with the Cambridge Crystallographic
Data Centre as Supplementary Publication Nos. CCDC-278805 (1)
and CCDC-278806 (2). Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (internat.) +44-1223/336-033;
e-mail, deposit@chemcrys.cam.ac.uk).
Computational Details. Density functional theory calculations
were carried out using the GAUSSIAN0337 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 according
to Becke38 (hybrid) and Lee, Yang, and Parr39 (denoted B3LYP),
with the corresponding valence basis set for Zr (Stuttgart-Dresden,
keyword SDD in GAUSSIAN) and standard 6-31G* basis set40 for
C, H, Cl, and Si (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.
zirconocene dichlorides 1a and 2a were characterized by NMR
spectroscopy and were methylated without further purification due
to the NMR spectra being satisfactory.
(a) Preparation of [(η5-Cp)(η5-C5H4SiMe2Ph)ZrCl2] (1a). The
compound n-butyllithium (20 mL, c ) 2.5 mol/L, 50 mmol) was
added dropwise to a solution of freshly distilled cyclopentadiene
(3.33 g, 50 mmol) in 120 mL of thf at -78 °C. After complete
addition, the reaction mixture was warmed to room temperature
and slowly added to a solution of 10.2 g of chlorodimethylphen-
ylsilane (60 mmol) in 20 mL of thf. After the addition was
completed, the pale yellow solution was stirred for 2 h at room
temperature. The reaction mixture was poured onto ice/water, and
the aqueous phase was extracted two times with 80 mL of pentane.
The combined organic phases were washed with 40 mL of brine,
dried over Na2SO4, and filtered and the volatiles removed under
reduced pressure, yielding a pale yellow oil. The product was used
without further purification. Yield: 6.00 g (30 mmol, 60%).
The ligand obtained above (3.00 g, 15 mmol) was diluted with
80 mL of thf and cooled to -78 °C. The compound n-butyllithium
(6 mL, c ) 2.5 mol/L, 15 mmol) was added via syringe. After the
addition was completed, the reaction mixture was warmed to room
temperature and stirred for 30 min to ensure complete reaction.
After the mixture was recooled to -78 °C, [(η-Cp)ZrCl3(dme)]
(5.29 g, 15 mmol) was added in small portions. The dark yellow
solution was warmed to room temperature and stirred overnight.
The volatiles were removed under reduced pressure, and the
resultant dark solid was extracted into 20 mL of toluene. The extract
was stored at -30 °C to yield the desired compound as a off-white
solid. Yield: 2.45 g (5.9 mmol, 40%). 1H NMR (CDCl3, 200 MHz,
20 °C): δ (ppm) 0.63 (s, 6H, SiCH3); 6.27 (s, 5H, Cp); 6.57 (t,
2H, Cp′); 6.75 (t, 2H, Cp′); 7.38-7.42 (m, 3H, Ph); 7.55 (d, 2H,
Ph). 13C NMR (CDCL3, 50 MHz, 20 °C): δ (ppm) -1.8 (SiCH3);
116.0 (Cp); 118.2 (Cp′); 125.2 (Cp′); 128.0 (m-C, Ph); 129.5 (p-C,
Ph); 134.0 (o-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,41 involving the same B3LYP
level of theory, together with the recommended IGLO-basis II42
on C, H, and Si or with the ECP1 basis set for comparison. 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 complexes.18 1H and 13C chemical
shifts have been calculated relative to benzene as a primary
reference and TMS for comparison, with absolute shieldings for
benzene σ(1H) ) 24.54 and σ(13C) ) 47.83 and for TMS σ(1H) )
31.73 and σ(13C) ) 177.59 with the IGLO II basis set. For the
ECP1 basis set, the absolute shieldings for benzene were calculated
to be σ(1H) ) 24.96 and σ(13C) ) 68.62, and for TMS σ(1H) )
31.92 and σ(13C) ) 183.77, respectively. The values for benzene
were converted into the TMS scale using the experimental δ values
of benzene (7.26 and 128.5, respectively). Tables of Cartesian
coordinates of all calculated structures are available as Supporting
Information in x, y, z format.
(b) Preparation of [(η5-Cp)(η5-C5H4SiMe2Ph)ZrMe2] (1). A
suspension of 1a (2.45 g, 5.7 mmol) in 100 mL of diethyl ether at
-78 °C was treated with 8.4 mL of MeLi (11.8 mmol, c ) 1.6
mol/L in diethyl ether) in a dropwise manner. The reaction mixture
was slowly warmed to room temperature and stirred for 1 h. The
volatiles were removed under reduced pressure to yield a light tan
solid, which was extracted into 150 mL of light petroleum. The
volatiles were removed under reduced pressure to yield a white
solid. Yield: 1.6 g (4.2 mmol, 72.7%). Anal. Found: C, 61.8; H,
6.5. Calcd for C20H26SiZr: C, 62.2; H, 6.7. 1H NMR (CDCl3, 200
MHz, 20 °C): δ (ppm) -0.39 (ZrCH3); 0.49 (s, 6H, SiCH3); 5.94
(s, 5H, Cp); 6.28 (dd, 4H, Cp′); 7.35-7.39 (m, 2H, Ph); 7.48-
7.52 (m, 2H, Ph). 13C NMR (CDCl3, 50 MHz, 20 °C): δ (ppm)
-1.5 (SiCH3); 30.1 (ZrCH3); 110.5 (Cp); 114.6 (Cp′); 117.5 (Cp′);
127.8 (m-C Ph); 129.2 (p-C Ph); 133.8 (o-C Ph); 147.3 (i-C Ph);
178.4 (i-C Ph).
(c) Preparation of [(η5-C5H4SiMe2C6H4Me)2ZrCl2] (2a). The
compound 4-bromotoluene (34.2 g, 200 mmol) was added to a
suspension of 4.9 g of magnesium turnings (210 mmol) in 400 mL
of diethyl ether at 0 °C and stirred at this temperature for 2 h. The
reaction mixture was warmed to room temperature and stirred
overnight. The reaction mixture was slowly filtered into a solution
of dichlorodimethylsilane (29.7 g, 230 mmol) in 100 mL of diethyl
ether at -30 °C and was slowly warmed to room temperature. After
the mixture was stirred overnight, the volatiles were removed under
reduced pressure, yielding a yellow oil and a white precipitate. The
oil was extracted into 90 mL of light petroleum and three times
into 80 mL of dichloromethane. The volatiles of the combined
extracts were removed under reduced pressure, yielding a yellow
oil. Yield: 29.26 g (158.9 mmol, 64.57%). 1H NMR (CDCl3, 500
Preparation of Compounds 1 and 2. The compound [(η5-Cp)-
ZrCl3(dme)] was prepared as described in the literature.43 The
(36) Sheldrick, G. M. SHELX97: Programs for Crystal Structure
Analysis (Release 97-2); Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1998.
(37) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K.
N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A.
D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A.
G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
(38) Becke, A. D. J. Chem. Phys. 1993, 98, 5648-5642.
(39) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-789.
(40) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257-2261.
(42) Kutzelnigg, W.; Fleischer, U.; Schindler, M. NMR Basic Principles
and Progress; Springer-Verlag: Berlin, 1990; Vol. 23, pp 165-262.
(43) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426-2427.
(41) Cheeseman, J. R.; Trucks, G. W.; Keith, T. A.; Frisch, M. J. J.
Chem. Phys. 1996, 104, 5497-5509.

Models for SolVation of Zirconocene Cations
Organometallics, Vol. 25, No. 11, 2006 2805
MHz, 20 °C): δ (ppm) 0.85 (s, 3H, SiCH3); 1.00 (s, 3H, SiCH3);
2.54 (s, 3H, PhCH3); 7.40 (d, 2H, Ph), 7.71 (d, 2H, Ph). 13C NMR
(CDCl3, 125 MHz, 20 °C): δ (ppm) 2.1 (SiCH3); 2.9 (SiCH3); 21.5
(PhCH3); 128.9 (m-C Ph); 132.3 (i-C Ph); 133.1 (o-C Ph); 140.4
(i-C Ph).
The volatiles of the extract were removed under reduced pressure,
yielding a yellow oil, which crystallized after 2 days. Yield: 2.76
g (5.22 mmol, 17.4%). H NMR (CDCl3, 300 MHz, 20 °C): δ
(ppm) 0.57 (s, 12H, SiCH3); 2.36 (s, 6H, PhCH3); 6.28 (t, 4H, Cp′);
6.58 (t, 4H, Cp′); 7.21 (d, 4H, Ph); 7.41 (d, 4H, Ph). 13C NMR
(CDCl3, 75 MHz, 20 °C): δ (ppm) -1.7 (SiCH3); 21.5 (PhCH3);
117.1 (Cp′); 123.9 (i-C Ph); 126.6 (Cp′); 128.7 (m-C Ph); 134.1
(o-C Ph); 139.3 (i-C Ph).
(d) Preparation of [(η5-C5H4SiMe2C6H4Me)2ZrMe2] (2). A
suspension of 2a (2.76 g, 5.22 mmol) in 150 mL of diethyl ether
at -78 °C was treated with 7.0 mL of MeLi (10.4 mmol, c ) 1.5
mol/L in diethyl ether) in a dropwise manner. The reaction mixture
was slowly warmed to room temperature and stirred for 2 h. The
volatiles were removed under reduced pressure to yield an off-
white solid, which was extracted into 150 mL of light petroleum.
The extract was concentrated and cooled to -30 °C to yield light
tan crystals. Crystals suitable for X-ray analysis were grown by
slowly cooling a solution in light petroleum to -30 °C. Yield: 1.63
g (3.3 mmol, 63.2%). Anal. Found: C, 65.0; H, 7.3. Calcd for
C30H40Si2Zr: C, 65.8; H, 7.3. 1H NMR (CDCl3, 300 MHz, 20 °C):
δ (ppm) -0.44 (s, 6H, ZrCH3); 0.44 (s, 12H, SiCH3); 2.36 (s, 6H,
PhCH3); 6.06 (t, 4H, Cp′); 6.15 (t, 4H, Cp′); 7.19 (d, 4H, Ph); 7.38
(d, 4H, Ph). 13C NMR (CDCl3, 125 MHz, 20 °C): δ (ppm) -1.4
(SiCH3); 21.5 (PhCH3); 30.2 (ZrCH3); 114.2 (Cp′); 116.6 (i-C Ph);
118.3 (Cp′); 128.6 (m-C Ph); 133.9 (o-C Ph); 135.1 (i-C-Cp′) 139.0
(i-C Ph).
1
To the compound ClSiMe2C6H4Me thus prepared (29.26 g, 158.9
mmol) in 100 mL of diethyl ether was slowly added a solution of
sodium cyclopentadienyl, freshly prepared from NaH (6.35 g, w )
60% in mineral oil, 158.9 mmol) and freshly distilled cyclopenta-
diene (10.5 g, 158.9 mmol), in 300 mL of thf at 0 °C. After the
addition was completed, the reaction mixture was stirred overnight.
The reaction mixture was quenched by pouring it onto a mixture
of ice and water and ammonium chloride. The phases were
separated, and the aqueous phase was extracted twice into 100 mL
of petroleum ether. The combined organic phases were washed with
brine, dried over magnesium sulfate, and filtered. The volatiles were
removed under reduced pressure, yielding a yellow oil. Yield: 28.07
1
g (130.9 mmol, 82.7%). H NMR (CDCl3, 500 MHz, 20 °C): δ
(ppm) 0.36 (s, 6H, SiCH3); 2.55 (s, 3H, PhCH3); 6.70 (br, 2H, Cp′);
6.81 (br, 2H, Cp′); 7.38 (d, 2H, Ph); 7.65 (d, 2H, Ph). 13C NMR
(CDCl3, 125 MHz, 20 °C): δ (ppm) -4.4 (SiCH3); 21.4 (PhCH3);
128.5 (m-C Ph); 130.5 (Cp′), 133.3 (Cp′); 133.5 (o-C Ph); 133.8
(i-C Ph); 139.1 (i-C Ph).
The ligand obtained above (12.9 g, 60 mmol) was diluted with
250 mL of petroleum ether, and the compound n-butyllithium (24
mL, c ) 2.5 mol/l, 60 mmol) was slowly added. The white
suspension was stirred for 2 h. The supernatant yellow solution
was filtered off, and the white precipitate was washed twice with
80 mL of light petroleum and dried at reduced pressure. The product
was dissolved in 200 mL of thf and the red solution cooled to -78
°C. The compound ZrCl4(thf)2 (11.3 g, 30 mmol) was slowly added,
and the reaction mixture was stirred for 1 h at -78 °C, slowly
warmed to room temperature, and stirred for an additional 3 h. The
volatiles were removed under reduced pressure, yielding a yellow,
sticky solid, which was extracted into 180 mL of dichloromethane.
Supporting Information Available: Tables and figures giving
1
crystal data and additional views of 1 and 2, figures giving H,
13C, 31F, and EXSY NMR spectra for 4a/4b, and tables giving
Cartesian coordinates for all compounds calculated in this paper.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM0509488