Reactivity of zirconium complexes incorporating asymmetrically substituted ansa ligands and their use as catalysts in olefin polymerization. X-ray crystal structures of [Me2Si(η5-C5Me4)(η5 -C5</s

Article abstract of DOI:10.1021/om0110639

The synthesis and use of the ansa-zirconocene complexes [Me₂Si(η⁵-C₅Me₄)(η⁵ -C₅H₃R)]-ZrCl₂ (R = H (5), Me (6), Et (7), ⁱPr (8), ^tBu (9), SiMe

Full text of DOI:10.1021/om0110639

2460
Organometallics 2002, 21, 2460-2467
Rea ctivity of Zir con iu m Com p lexes In cor p or a tin g
Asym m etr ica lly Su bstitu ted a n sa Liga n d s a n d Th eir Use
a s Ca ta lysts in Olefin P olym er iza tion . X-r a y Cr ysta l
Str u ctu r es of [Me2Si(η5-C5Me4)(η5-C5H3R)]Zr Cl2
i
(R ) Et, P r )
Antonio Antin˜olo,† Isabel Lo´pez-Solera,† Antonio Otero,*,† Sanjiv Prashar,†,‡
Ana M. Rodr´ıguez,§ and Elena Villasen˜or†
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioqu´ımica, Universidad de Castilla-La
Mancha, Facultad de Quı´micas, Campus Universitario, 13071-Ciudad Real, Spain,
ETS Ingenieros Industriales, Avd. Camilo J ose´ Cela, 3, 13071-Ciudad Real, Spain, and
Departamento de Ciencias Experimentales e Ingenierı´a, ESCET,
Universidad Rey J uan Carlos, 28933 Mo´stoles (Madrid), Spain
Received December 17, 2001
The synthesis and use of the ansa-zirconocene complexes [Me2Si(η5-C5Me4)(η5-C5H3R)]-
ZrCl2 (R ) H (5), Me (6), Et (7), iPr (8), tBu (9), SiMe3 (10)) as catalysts in the polymerization
of ethylene and propylene has been studied. The alkyl complexes [Me2Si(η5-C5Me4)(η5-C5H3R)]-
i
t
ZrMe2 (R ) H (11), Me (12), Et (13), Pr (14), Bu (15), SiMe3 (16)) have also been prepared.
The reaction of 11-16 with B(C6F5)3 gave the cationic species [{Me2Si(η5-C5Me4)(η5-C5H3R)}-
i
t
ZrMe]+ (R ) H (17), Me (18), Et (19), Pr (20), Bu (21), SiMe3 (22)). In the absence of
cocatalyst, 17-22 have been shown to act as catalysts in the polymerization of ethylene.
The molecular structures of 7 and 8 have been determined by single-crystal X-ray diffraction
studies.
In tr od u ction
ansa-zirconocene complexes have been described,6 al-
though the great majority contain indenyl or fluorenyl
systems.7
It has been shown that steric effects in the transition-
metal catalyst greatly effect the polymerization of olefins
and that bulky ligands, such as substituted ansa
ligands, would therefore aid stereospecific olefin coor-
The use of ansa-cyclopentadienyl ligands has received
wide attention in the chemistry of group 4 metals,1 due
mainly to their ability to impart to their complexes a
selective degree of catalytic activity.2 Recent studies
have demonstrated that the incorporation of the ansa
bridge may have a profound influence on the behavior
of the metallocene system.3 Furthermore, the use of
substituted ansa-cyclopentadienyl ligands in the ste-
reoselective synthesis of group 4 metal complexes and
their importance in catalysis is receiving special atten-
tion.4 Simple ligand design, as in Me2Si(C5H3Me-3)2, has
been shown to lead to stereoselective catalysts, e.g. rac-
[Me2Si(C5H3Me)2]ZrCl2.5 Some examples of asymmetric
(6) (a) Obora, Y.; Stern, C. L.; Marks, T. J .; Nickias, P. N. Organo-
metallics 1997, 16, 2503. (b) Giardello, M. A.; Eisen, M. S.; Stern, C.
L.; Marks, T. J . J . Am. Chem. Soc. 1993, 115, 3326. (c) Giardello, M.
A.; Eisen, M. S.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1995,
117, 12114. (d) Schumann, H.; Zietzke, K.; Weimann, R.; Demtschuk,
J .; Kaminsky, W.; Schauwienold, A.-M. J . Organomet. Chem. 1999,
574, 228. (e) Mu¨ller, C.; Lilge, D.; Kristen, M. O.; J utzi, P. Angew.
Chem., Int. Ed. 2000, 39, 789. (f) Suzuki, N.; Mise, T.; Yamaguchi, Y.;
Chihara, T.; Ikegami, Y.; Ohmori, H.; Matsumoto, A.; Wakatsuki, Y.
J . Organomet. Chem. 1998, 560, 47. (g) Herzog, T. A.; Zubris, D. L.;
Bercaw, J . E. J . Am. Chem. Soc. 1996, 118, 11988.
(7) (a) Baker, R. W.; Foulkes, M. A.; Turner, P. J . Chem. Soc., Dalton
Trans. 2000, 431. (b) Razavi, A.; Ferrara, J . J . Organomet. Chem. 1992,
435, 299. (c) Razavi, A.; Atwood, J . L. J . Organomet. Chem. 1993, 459,
117. (c) Ewen, J . A.; J ones, J . L.; Razavi, A.; Ferrara, J . J . Am. Chem.
Soc. 1988, 110, 6255. (d) Llinas, G. H.; Day, R. O.; Rausch, M. D.;
Chien, J . C. W. Organometallics 1993, 12, 1283. (e) Rieger, B.; J any,
G.; Fawzi, R.; Steimann, M. Organometallics 1994, 13, 647. (f) Green,
M. L. H.; Ishihara, N. J . Chem. Soc., Dalton Trans. 1994, 657. (g)
Razavi, A.; Atwood, J . L. J . Organomet. Chem. 1995, 497, 105. (h) Chen,
Y.-X.; Rausch, M. D.; Chien, J . C. W. J . Organomet. Chem. 1995, 497,
1. (i) Bu¨rgi, T.; Berke, H.; Wingbermu¨hle, D.; Psiorz, C.; Noe, R.; Fox,
T.; Knickmeier, M.; Berlekamp, M.; Fro¨hlich, R.; Erker, G. J . Orga-
nomet. Chem. 1995, 497, 149. (j) Kaminsky, W.; Rabe, O.; Schau-
wienold, A.-M.; Schupfner, G. U.; Hanss, J .; Kopf, J .; Veghini, D.;
Henling, L. M.; Burkhardt, T. J .; Bercaw, J . E. J . Am. Chem. Soc. 1999,
121, 564. (k) Ewen, J . A.; J ones, R. L.; Elder, M. J . J . Am. Chem. Soc.
1998, 120, 10786. (l) Patsidis, K.; Alt, H. G.; Milius, W.; Palackal, S.
J . J . Organomet. Chem. 1996, 509, 63. (m) Dietrich, U.; Hackmann,
M.; Rieger, B.; Klinga, M.; Leskela¨, M. J . Am. Chem. Soc. 1999, 121,
4348. (n) Thomas, E. J .; Chien, J . C. W.; Rausch, M. D. Organometallics
1999, 18, 1439. (o) Yoon, S. C.; Han, T. K.; Woo, B. W.; Song, H.; Woo,
S. I.; Park, J . T. J . Organomet. Chem. 1997, 534, 81.
* To whom correspondence should be addressed. E-mail:
antonio.otero@uclm.es.
† Universidad de Castilla-La Mancha.
‡ Universidad Rey J uan Carlos.
§ ETS Ingenieros Industriales.
(1) Comprehensive Organometallic Chemistry II; Abel, E. W., Stone,
F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, U.K., 1995;
Vol. 4.
(2) See: Rieger, B.; J any, G.; Fawzi, R.; Steimann, M. Organo-
metallics 1994, 13, 647.
(3) (a) Conway, S. L. J .; Dijkstra, T.; Doerrer, L. H.; Green, J . C.;
Green, M. L. H.; Stephens, A. H. H. J . Chem. Soc., Dalton Trans. 1998,
2689. (b) Shin, J . H.; Parkin, G. Chem. Commun. 1999, 887. (c) Lee,
H.; Bridgewater, B. M.; Parkin, G. J . Chem. Soc., Dalton Trans. 2000,
4490.
(4) Huttenloch, M. E.; Dorer, B.; Rief, U.; Prosenc, M.-H.; Schmidt,
K.; Brintzinger, H. H. J . Organomet. Chem. 1997, 541, 219.
(5) (a) Mise, T.; Miya, S.; Yamazaki, H. Chem. Lett. 1989, 1853. (b)
Ro¨ll, W.; Brintzinger, H. H.; Rieger, B.; Zolk, R. Angew. Chem., Int.
Ed. Engl. 1990, 29, 279. (c) Rieger, B.; Reinmuth, A.; Ro¨ll, W.;
Brintzinger, H. H. J . Mol. Catal. 1993, 82, 67. (d) Wiesenfeldt, H.;
Reinmuth, A.; Barsties, E.; Evertz, K.; Brintzinger, H. H. J . Organomet.
Chem. 1989, 369, 359.
10.1021/om0110639 CCC: $22.00 © 2002 American Chemical Society
Publication on Web 05/14/2002

Zirconium Complexes with ansa Ligands
Organometallics, Vol. 21, No. 12, 2002 2461
F igu r e 1. Molecular structure and atom-labeling scheme
for [Me2Si(η5-C5Me4)(η5-C5H3Et)]ZrCl2 (7), with thermal
ellipsoids at the 20% probability level.
F igu r e 2. Molecular structure and atom-labeling scheme
for [Me2Si(η5-C5Me4)(η5-C5H3iPr)]ZrCl2 (8), with thermal
ellipsoids at the 50% probability level.
dination and the stereoregularity of the polymers ob-
tained using these metallocene catalysts.8 In addition,
the chiral nature of these ligands would also strongly
influence stereoselectivity.9 An extensive review regard-
ing selectivity in propylene polymerization with metal-
locene catalysts has recently been published.10
We have previously described the preparation of
niobocene complexes containing ansa ligands11,12 and,
following from this, the synthesis of niobium and
zirconium systems with symmetrically and asymmetri-
cally substituted ansa ligands.12,13 As an extension of
this work we report here, first, the synthesis, structure,
and reactivity of other zirconocene complexes which
incorporate ansa ligands with two distinctly substituted
cyclopentadienyl rings and, second, the role as catalysts
of these zirconocene species in the polymerization of
ethylene and stereoselective polymerization of pro-
pylene.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 7 a n d 8
7a
8b
Zr(1)-Cent(1)
Zr(1)-Cent(2)
av Zr(1)-C(Cent(1))c
av Zr(1)-C(Cent(2))c
Zr(1)-Cl(1)
2.214
2.207
2.504
2.514
2.223
2.230
2.529
2.531
2.431(2)
2.426(2)
2.429(4)
Zr(1)-Cl(2)
Cent(1)-Zr(1)-Cent(2)
Si(1)-C(1)-Cent(1)
Si(1)-C(11)-Cent(2)
C(1)-Si(1)-C(11)
Cl(1)-Zr(1)-Cent(1)
Cl(1)-Zr(1)-Cent(2)
Cl(2)-Zr(1)-Cent(1)
Cl(2)-Zr(1)-Cent(2)
Cl(1)-Zr(1)-Cl(1A)
126.5
162.7
165.1
93.3(7)
106.1
107.4
126.9
162.8
163.3
94.2(2)
105.6
107.2
107.9
107.3
98.2(1)
100.4(2)
a
For 7, Cent(1) and Cent(2) are the centroids of C(1)-C(3) and
b
C(11)-C(13), respectively. For 8, Cent(1) and Cent(2) are the
centroids of C(1)-C(5) and C(11)-C(15), respectively. c Refers to
the average bond distance between Zr(1) and the carbon atoms of
the C5 ring of the corresponding cyclopentadienyl moiety.
Resu lts a n d Discu ssion
The synthesis and characterization of [Me2Si(η5-C5-
i
Me4)(η5-C5H3R)]ZrCl2 (R ) H (5), Me (6), Pr (8), SiMe3
(10)) have previously been described by us.13 In addition
we have prepared, in a similar manner, the ansa ligands
(C5Me4H)SiMe2(C5H4R) (R ) Et (1), tBu (2)), their
dilithium derivatives [Me2Si(C5Me4)(C5H3R)]Li2 (R ) Et
atomic numbering schemes are shown in Figures 1 and
2, respectively. Selected bond lengths and angles for 7
and 8 are given in Table 1.
The structures of 7 and 8 show the typical bent-
metallocene conformation observed in zirconocene dichlo-
rides. The ansa ligand chelates the zirconium atom, and
both cyclopentadienyl rings are bound to the metal in
an η5 mode. A comparison of 7 and 8 with related
zirconocene and ansa-zirconocene complexes is given in
Table 2 and shows that the molecular structures of all
these complexes are essentially the same. The Cent-
Zr-Cent angles of 7 and 8 are of values between those
of [Me2Si(η5-C5H4)2]ZrCl2 and [Me2Si(η5-C5Me4)2]ZrCl2
and less than that observed for the non-ansa complexes
(η5-C5H5)(η5-C5Me5)ZrCl2 and (η5-C5H5)2ZrCl2 (see Table
2).
t
(3), Bu (4)), and the ansa-zirconocene complexes [Me2-
t
Si(η5-C5Me4)(η5-C5H3R)]ZrCl2 (R ) Et (7), Bu (9)) (see
Experimental Section for further details).
The molecular structures of 7 and 8 were established
by X-ray crystal studies. The molecular structures and
(8) Mo¨hring, P. C.; Coville, N. J . J . Organomet. Chem. 1994, 479, 1
and references therein.
(9) J affart, J .; Nayral, C.; Mathieu, R.; Etienne, M. Eur. J . Inorg.
Chem. 1998, 425 and references therein.
(10) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi, F. Chem. Rev.
2000, 100, 1253.
(11) Antin˜olo, A.; Mart´ınez-Ripoll, M.; Mugnier, Y.; Otero, A.;
Prashar, S.; Rodriguez, A. M. Organometallics 1996, 15, 3241.
(12) Antin˜olo, A.; Otero, A.; Prashar, S.; Rodriguez, A. M. Organo-
metallics 1998, 17, 5454.
We have previously reported that 5, 6, 8, and 10 are
catalytically active in the polymerization of ethylene.13
(13) Antin˜olo, A.; Lo´pez-Solera, I.; Orive, I.; Otero, A.; Prashar, S.;
Rodr´ıguez, A. M.; Villasen˜or, E. Organometallics 2001, 20, 71.

2462 Organometallics, Vol. 21, No. 12, 2002
Ta ble 2. Selected Str u ctu r a l Da ta of Zir con ocen e Com p lexes
Antin˜olo et al.
Cp-Zr-Cp
Cl-Zr-Cl
(deg)
CCp-Si-CCp
complex
Zr-Cp (Å)a
Zr-Cl (Å)
(deg)
(deg)
ref
(η5-C5H5)2ZrCl2
2.21(1)
2.206(5)
2.209 (Cp)
2.219 (Cp*)
2.197(6)
2.441(5)
2.443(1)
2.442
129
128.9(2)
130.01
97.1(2)
95.10(5)
97.78
14
15
16
(η5-C5H4Me)2ZrCl2
(η5-C5H5)(η5-C5Me5)ZrCl2
[Me2Si(η5-C5H4)2]ZrCl2
2.452
2.4334(7)
2.4336(8)
125.4(3)
128.6
126.70(4)
97.98(4)
92.28
101.17(5)
93.2(2)
95.7(1)
93.82(14)
17
18
6d
[Me2Si(η5-C5Me4)2]ZrCl2
2.329
[EtMeSi(η5-C5Me4)(η5-C5H4)]ZrCl2
2.219(2) (Cp)
2.218(2) (Cp*)
2.198(4) (Cp*)
2.202(3) (Cp)
2.184(6) (Cp*)
2.194(2) (Cp)
2.207 (Cp*)
2.214 (Cp)
2.230 (Cp*)
2.223 (Cp)
[Me2Si(η5-C5Me4)(η5-C5H4)]ZrCl2
2.451(1)
2.414(4)
2.429(4)
128.10(2)
126.25(6)
126.5
104.60(7)
101.1(2)
100.4(2)
98.22(7)
95.2(2)
93.1(8)
93.3(7)
94.2(2)
13
[Me2Si(η5-C5Me4)(η5-C5H3Me)]ZrCl2
[Me2Si(η5-C5Me4)(η5-C5H3Et)]ZrCl2 (7)
[Me2Si(η5-C5Me4)(η5-C5H3iPr)]ZrCl2 (8)
13
this work
this work
2.431(2)
2.426(2)
126.90(6)
a
Cp refers to the C5H4 or C5H3R moiety; Cp* refers to the C5Me4 moiety.
Ta ble 3. Eth ylen e P olym er iza tion Resu lts for
ratio of 500:1 instead of the ratio of 125:1 used in the
previously described experiments.13 This behavior is not
unexpected, as MAO, in addition to its role as an
alkylating agent, acts as a moisture scavenger and thus
an increase in its concentration increases the efficiency
of the metallocene catalyst.
[Me2Si(η5-C5Me4)(η5-C5H3R)]Zr Cl2 (R ) H (5), Me (6),
i
t
Et (7), P r (8), Bu (9), SiMe3 (10)), (η5-C5H5)2Zr Cl2,
a
a n d [Me2Si(η5-C5H4)2]Zr Cl2
activ-
ityb
Mw/
Mn
catalyst
Mw
[Me2Si(η5-C5Me4)(η5-C5H4)]ZrCl2 (5)
4500 174 000 4.8
In general, it was found that the catalytic activities
of 5-10 were slightly lower than that recorded for (η5-
C5H5)2ZrCl2 but comparable to that of the unsubstituted
ansa complex [Me2Si(η5-C5H4)2]ZrCl2. This same trend
was observed for the molecular weights of the polymers
obtained. Molecular weight distributions recorded for
5-10, [Me2Si(η5-C5H4)2]ZrCl2, and (η5-C5H5)2ZrCl2 were
all of a high order (probably due to the experimental
conditions employed in the polymerization process).
The asymmetric nature of the ansa-zirconocene com-
plexes 5-10 (chiral in the cases 6-10) should lead to
the stereoselective polymerization of asymmetric olefins
such as propylene. We have therefore tested 5-10 as
catalysts in the polymerization of propylene. The ex-
periments were carried out at 25 °C in the presence of
the zirconium complex and MAO cocatalyst (ratio
1:1000) and at an olefin pressure of 2 bar during 30 min.
The results of the experiments are given in Table 4.
The catalytic activities for 5-10 were lower than
those recorded for [Me2Si(η5-C5H4)2]ZrCl2 and (η5-C5H5)2-
ZrCl2, although in the case of 8 this value was compa-
rable. Polymer molecular weights obtained were all
similar to those achieved for [Me2Si(η5-C5H4)2]ZrCl2 and
(η5-C5H5)2ZrCl2. In the case of 8 the highest polymer
molecular weight was recorded; however, it also gave
the highest molecular weight distribution. In general
the asymmetric ansa-metallocene catalysts gave poly-
mer molecular weight distribution values comparable
to those recorded for [Me2Si(η5-C5H4)2]ZrCl2 and (η5-
C5H5)2ZrCl2.
[Me2Si(η5-C5Me4)(η5-C5H3Me)]ZrCl2 (6) 4333 178 000 5.2
[Me2Si(η5-C5Me4)(η5-C5H3Et)]ZrCl2 (7)
[Me2Si(η5-C5Me4)(η5-C5H3iPr)]ZrCl2 (8)
3700 248 000 9.6
4300 114 000 3.8
[Me2Si(η5-C5Me4)(η5-C5H3tBu)]ZrCl2 (9) 3460 119 500 7.7
[Me2Si(η5-C5Me4)(η5-C5H3SiMe3)]ZrCl2
(10)
3400 136 000 9.1
(η5-C5H5)2ZrCl2
5000 281 000 8.3
4480 183 200 6.2
[Me2Si(η5-C5H4)2]ZrCl2
a
Conditions: 25 °C, 1.5 bar of monomer pressure, 150 mL of
toluene, [MAO] ) 2 × 10-2 mol L-1, [Zr] ) 4 × 10-5 mol L-1, tpolymer
b
) 30 min. In kg of polymer ((mol of Zr) h)-1
.
This initial study was carried out using a low MAO:Zr
catalyst ratio of 125:1 and gave relatively poor catalytic
activities and low polymer weights.13 To improve these
results, we have carried out the polymerization of
ethylene by increasing the MAO/Zr catalyst ratio to 500:
1, and in addition, we have included as catalysts
compounds 7 and 9, which were absent from the initial
report. The polymerization experiments were carried out
at 25 °C and at an olefin pressure of 1.5 bar over 30
min. The results of the experiments are given in Table
3.
Besides the electronic and steric influence of the
silylene bridge itself, the linkage of the two cyclopen-
tadienyl ligands changes the structure and energy of
the metal orbitals and also the angle between the ring
planes, with the latter factor influencing the space
available for reactions at the metal center.19 Differences
in the relative activities in the process of ethylene
polymerization should therefore be the consequence of
changes in the metallocene complex geometry.
For 5 the Cs symmetry should make the metallocene
catalyst syndiospecific in the polymerization of pro-
pylene. However, Morokuma and co-workers have pre-
dicted, via theoretical studies, that catalytic systems
based on the Cs symmetric H2Si(C5Me4)(C5H4) ligand
will be substantially non enantioselective, due to repul-
sive interactions between the methyl group of the
In all cases very much higher activities and polymer
molecular weights were achieved when the polymeri-
zation of ethylene was carried using a MAO:Zr catalyst
(14) Green, J . C.; Green, M. L. H.; Prout, C. K. J . Chem. Soc., Chem.
Commun. 1972, 421.
(15) Petersen, J . L.; Egan, J . W. Inorg. Chem. 1983, 22, 3571.
(16) Rogers, R. D.; Benning, M. M.; Kurihara, L. K.; Moriarty, K.
J .; Raush, M. D. J . Organomet. Chem. 1985, 293, 51.
(17) Bajgur, C. S.; Tikkanen, W. R.; Petersen, J . L. Inorg. Chem.
1985, 24, 2539.
(18) Koch, T.; Blaurock, S.; Somoza, F. B.; Voigt, A.; Kirmse, R.; Hey-
Hawkins, E. Organometallics 2000, 19, 2556.
(19) Lauher, J . W.; Hofmann, R. J . Am. Chem. Soc. 1976, 98, 1729.

Zirconium Complexes with ansa Ligands
Organometallics, Vol. 21, No. 12, 2002 2463
Ta ble 4. P r op ylen e P olym er iza tion Resu lts for [Me2Si(η5-C5Me4)(η5-C5H3R)]Zr Cl2 (R ) H (5), Me (6), Et (7),
t
a
iP r (8), Bu (9), SiMe3 (10)), (η5-C5H5)2Zr Cl2, a n d [Me2Si(η5-C5H4)2]Zr Cl2
catalyst
activityb
Mw
Mw/Mn
[mmmm] (%)
mp (°C)
[Me2Si(η5-C5Me4)(η5-C5H4)]ZrCl2 (5)
[Me2Si(η5-C5Me4)(η5-C5H3Me)]ZrCl2 (6)
[Me2Si(η5-C5Me4)(η5-C5H3Et)]ZrCl2 (7)
[Me2Si(η5-C5Me4)(η5-C5H3iPr)]ZrCl2 (8)
[Me2Si(η5-C5Me4)(η5-C5H3tBu)]ZrCl2 (9)
[Me2Si(η5-C5Me4)(η5-C5H3SiMe3)]ZrCl2 (10)
(η5-C5H5)2ZrCl2
3100
4120
3333
4812
2333
4323
4920
4915
201 300
188 300
215 000
238 000
191 100
171 100
205 200
183 000
13.9
10.8
12.6
20.3
14.1
15.0
13.1
12.2
c
c
107
110
153
145
155
143
30
85
88
87
84
c
[Me2Si(η5-C5H4)2]ZrCl2
c
30
a
Conditions: 25 °C, 2.0 bar of monomer pressure, 150 mL of toluene, [MAO] ) 4 × 10-2 mol L-1, [Zr] ) 4 × 10-5 mol L-1, tpolymer
)
30 min. In kg of polymer ((mol of Zr) h)-1
.
c 13C NMR spectra showed essentially atactic polymers.
b
F igu r e 3. Steric conditions in the metallocene catalyst.
propylene and the methyl groups of the C5Me4 ligand.20
Our results concur with this affirmation, with the
polypropylene obtained using 5 as catalyst being of low
stereospecificity (as observed by 13C NMR spectroscopy
of the polymer). This is in agreement with a previous
study conducted on this metallocene complex, where this
phenomenon was explained by the assumption that the
polymer chain experiences counterbalanced steric forces
exerted by the monomer methyl group on one hand and
from the â-methyl cyclopentadienyl (C5Me4) substituents
on the other.21
The zirconocene complexes 6-10 exhibit C1 sym-
metry. The stereospecificity of the polypropylene ob-
tained when using 6-10 as catalysts is directly related
to the â-alkyl cyclopentadienyl (C5H3R) substituent. In
C1 symmetric catalysts the two available coordination
positions are nonequivalent. In this case, the stereose-
lectivity of the catalytic systems depends on the energy
difference between structures corresponding to propy-
lene coordination on the two nonequivalent, more and
less crowded, coordination sites (see Figure 3).
If we assume that a chain migratory insertion mech-
anism is taking place and that the two coordination
positions are of similar energy, then these catalysts will
be isospecific or syndiospecific if propylene coordination
at the two coordination positions are enantioselective
in favor of the same or opposite propylene enantiofaces,
respectively. If propylene coordination is enantioselec-
tive in only one of the coordination positions, then the
corresponding catalytic system will be hemi-isospecific.
If the two coordination positions have distinct ener-
gies, a different scenario can be proposed. According to
Morokuma, the presence of a bulky alkyl cyclopentadi-
enyl â-substituent forbids the growing polymer chain
to be located in the more crowded position. In particular,
F igu r e 4. Proposed polymer chain back skip mechanism
in the ansa-zirconocene complexes 7-10.
in the absence of monomer molecule, as probably occurs
at the end of each insertion step, the steric pressure of
the ligand skeleton may force the growing chain to skip
back to the less crowded position. Hence, insertion
always occurs with the same relative disposition of the
monomer and the growing polymer chain and thus leads
to an isospecific polymer (see Figure 4).20 An example
of this back-skip mechanism in the polymerization of
propylene has recently been reported.22
In the case of [Me2Si(η5-C5Me4)(η5-C5H3Me)]ZrCl2 (6)
the catalyst is only enantioselective in one of the two
coordination positions, due to the fact that the â-alkyl
(20) Kawamura-Kuribayashi, H.; Koga, N.; Morokuma, K. J . Am.
Chem. Soc. 1992, 114, 8687.
(21) Ewen, J . A.; Elder, M. J .; J ones, R. L.; Haspeslagh, L.; Atwood,
J . L.; Bott, S. G.; Robinson, K. Makromol. Chem., Macromol. Symp.
1991, 48/49, 253.
(22) Kukral, J .; Lehmus, P.; Feifel, T.; Troll, C.; Rieger, B. Orga-
nometallics 2000, 19, 3767.

2464 Organometallics, Vol. 21, No. 12, 2002
Antin˜olo et al.
cyclopentadienyl substituents oriented toward the more
crowded position are both identically sized methyl
groups. 6 should therefore produce hemi-isotactic polypro-
pylene. However, we were unable to verify this, as the
13C NMR spectrum of the polymer was complicated by
the high atactic nature of these types of plastics. When
the alkyl group of the monosubstituted cyclopentadienyl
moiety is larger than methyl, as in the case of 7-10,
the catalysts produce isotactic polymers. This was
confirmed by characterizing the polymers formed by 13
C
NMR spectroscopy. This technique also permitted us to
measure the level of isotacticty (% mmmm) of the plastic
(see Table 4).
The alkyl derivatives [Me2Si(η5-C5Me4)(η5-C5H3R)]-
i
t
ZrMe2 (R ) H (11), Me (12), Et (13), Pr (14), Bu (15),
SiMe3 (16)) were prepared via the reaction of 2 equiv of
the Grignard reagent MeMgCl with the corresponding
dihalide ansa-zirconocene complexes 5-10. 11-16 were
characterized by spectroscopic methods (see Experimen-
tal Section). The difference in symmetry of 11 (Cs) with
regard to 12-16 (C1) is clearly observed in NMR
spectroscopy. In 11 only one signal was recorded for the
two metal-methyl groups in both 1H and 13C NMR
spectroscopy. However, for 12-16 two signals were
recorded, confirming the inequivalency of the two alkyl
groups.
F igu r e 5. Two possible isomers for [{Me2Si(η5-C5Me4)(η5-
C5H3R)}ZrMe][MeB(C6F5)3] (R ) Me (18), Et (19), iPr (20),
tBu (21), SiMe3 (22)).
Ta ble 5. Eth ylen e P olym er iza tion Resu lts for
[{Me2Si(η5-C5Me4)(η5-C5H3R)}Zr Me][MeB(C6F 5)3] (R
i
t
) H (17), Me (18), Et (19), P r (20), Bu (21), SiMe3
(22)), [(η5-C5H5)2Zr Me][MeB(C6F 5)3], a n d
[{Me2Si(η5-C5H4)2}Zr Me][MeB(C6F 5)3]a
The reaction of 11-16 with B(C6F5)3 gave the cationic
species [{Me2Si(η5-C5Me4)(η5-C5H3R)}ZrMe]+ (R ) H
i
t
(17), Me (18), Et (19), Pr (20), Bu (21), SiMe3 (22)),
with MeB(C6F5)3 as the counteranion (see eq 1). 17-22
activ-
ityb
Mw/
Mn
catalyst
Mw
[{Me2Si(η5-C5Me4)(η5-C5H4)}ZrMe]+ (17)
1520 245 100 13.3
1215 183 200 14.2
[{Me2Si(η5-C5Me4)(η5-C5H3Me)}ZrMe]+
(18)
[{Me2Si(η5-C5Me4)(η5-C5H3Et)}ZrMe]+
1613 166 300 9.4
1288 125 000 8.7
1183 171 200 8.5
(19)
[{Me2Si(η5-C5Me4)(η5-C5H3iPr)}ZrMe]+
(20)
[{Me2Si(η5-C5Me4)(η5-C5H3tBu)}ZrMe]+
(21)
[{Me2Si(η5-C5Me4)(η5-C5H3SiMe3)}ZrMe]+ 1172 197 000 8.3
(22)
[(η5-C5H5)2ZrMe]+
2012
89 000 5.2
[{Me2Si(η5-C5H4)2}ZrMe]+
1912 193 000 7.4
a
Conditions: 25 °C, 1.5 bar of monomer pressure, 250 mL of
toluene, [Zr] ) 1.5 × 10-5 mol L-1, [TIBA] ) 8 × 10-3 mol L-1
,
tpolymer ) 30 min. In kg of polymer ((mol of Zr) h)-1
.
b
one of the possible isomers, and it appears likely that
this isomer corresponds to A on the grounds of steric
effects.
The use of the cationic species as a catalyst without
the need of cocatalysts such as MAO has been previously
reported.21 Complexes 17-22 also proved to be catalyti-
cally active in the polymerization of ethylene (see Table
5). The activities obtained were slightly lower than that
for [(η5-C5H5)2ZrMe][MeB(C6F5)3] under the same condi-
tions and overall much lower than those obtained with
the parent dichloro complexes and MAO.
were characterized by 1H NMR spectroscopy. This
revealed the disappearance of one methyl peak and a
shifting of the remaining peak resonances. The Me-B
signal is generally difficult to observe, due to the
relaxation time of the boron nucleus.
In the case of 17 the symmetry of the molecule
changes from Cs to C1 and the lack of symmetry leads
to four multiplets being observed for the cyclopentadi-
1
enyl ring protons in the H NMR spectrum.
Con clu sion s
There are two possible isomers for 18-22 (Figure 5).
For isomer A the metal-methyl group is positioned
below the â-substituent of the monosubstituted cyclo-
pentadienyl moiety. In isomer B the â-substituent of the
monosubstituted cyclopentadienyl ligand situates itself
above the boron-coordinated methyl group. 1H NMR
spectroscopy revealed in all cases the presence of only
We have prepared new ansa-zirconocene complexes,
two of which have been characterized by single-crystal
X-ray diffraction studies. We have tested ansa-zir-
conocene complexes with asymmetrically substituted
cyclopentadienyl rings as catalysts in the polymerization
of olefins. We have found in the case of ethylene that

Zirconium Complexes with ansa Ligands
Organometallics, Vol. 21, No. 12, 2002 2465
mixture was filtered and the filtrate concentrated (10 mL) and
cooled to -30 °C to yield white crystals of the title complex
(0.89 g, 48%). 1H NMR (300 MHz, C6D6): δ 0.33 (3H), 0.36
(3H) (s, SiMe2), 1.14 (m, 3H, CH2CH3), 1.61 (3H), 1.69 (3H),
1.97 (3H), 1.99 (3H) (s, C5Me4), 2.68 (1H), 2.82 (1H) (m, CH2-
CH3), 5.06 (1H), 5.37 (1H), 6.67 (1H) (m, C5H4). 13C{1H} NMR
(300 MHz, C6D6): δ -0.6, -0.5 (SiMe2), 12.3, 12.4, 14.9, 15.0
(C5Me4), 14.1 (CH2CH3), 23.4 (CH2CH3), 96.9 (Cipso), 105.7
(Cipso), 112.0, 113.2, 125.6 (C5H4), 124.9, 125.0, 135.2, 135.3,
143.8 (C5Me4). Anal. Calcd for C18H26Cl2SiZr: C, 49.97; H, 6.06.
Found: C, 49.79; H, 6.00.
the catalytic activities are high, although a little lower
than for (η5-C5H5)2ZrCl2. For propylene it has been
shown that changing the â-substituent of the cyclopen-
tadienyl moiety has a marked influence on the ste-
reospecificity of the polymerization. We have also shown
that the cationic ansa-zirconocene species in the absence
of cocatalyst are catalytically active in the polymeriza-
tion of ethylene.
Exp er im en ta l Section
[Me2Si(η5-C5Me4)(η5-C5H3tBu )]Zr Cl2 (9). The synthesis of
9 was carried out in a manner identical with that for 7, using
ZrCl4 (1.12 g, 4.80 mmol) and [Me2Si(C5Me4)(C5H3tBu)]Li2 (4;
1.50 g, 4.80 mmol). Yield: 1.04 g, 47%. 1H NMR (300 MHz,
C6D6): δ 0.34 (3H), 0.38 (3H) (s, SiMe2), 1.42 (s, 9H, tBu), 1.68
(3H), 1.69 (3H), 1.93 (3H), 1.94 (3H) (s, C5Me4), 5.43 (1H), 5.52
(1H), 6.86 (1H) (m, C5H3). 13C{1H} NMR (300 MHz, C6D6): δ
-1.0, -0.2 (SiMe2), 12.2, 12.4, 15.0, 15.1 (C5Me4), 30.8 (CMe3),
33.7 (CMe3), 97.6 (Cipso), 104.5 (Cipso), 110.2, 113.7, 126.5 (C5H3),
123.8, 125.6, 129.2, 135.0, 151.4 (C5Me4). Anal. Calcd for
Gen er a l P r oced u r es. All reactions were performed using
standard Schlenk tube techniques under an atmosphere of dry
nitrogen. Solvents were distilled from appropriate drying
agents and degassed before use.
[Me2Si(η5-C5Me4)(η5-C5H3R)]ZrCl2 (R ) H (5), Me (6), iPr (8),
SiMe3 (10)) were prepared as described earlier.13 MeMgCl, Mg-
(C5H4Et)2, Li(C5H4tBu), ZrCl4, ClMe2Si(C5Me4H), and B(C6F5)3
were purchased from Aldrich and used directly. 1H and 13C
spectra were recorded on a Varian FT-300 spectrometer and
referenced to the residual deuterated solvent. Microanalyses
were carried out with a Perkin-Elmer 2400 microanalyzer.
Mass spectroscopic analyses were preformed on a VG Autospec
instrument or a Hewlett-Packard 5988A (m/z 50-1000) (elec-
tron impact). Polymer isotacticity was calculated from 13C
NMR spectra of polymer samples dissolved in 1,2,4-trichlo-
robenzene and C6D6 (1:1). Polymer molecular weights were
determined by GPC in o-C6H4Cl2 at 135 °C.
C
20H30Cl2SiZr: C, 52.14; H, 6.56. Found: C, 51.98; H, 6.52.
[Me2Si(η5-C5Me4)(η5-C5H4)]Zr Me2 (11). A 3 M solution of
ClMgMe in THF (0.66 mL, 1.98 mmol) was added to a stirred
solution of [Me2Si(η5-C5Me4)(η5-C5H4)]ZrCl2 (5; 0.40 g, 0.99
mmol) in THF (25 mL) at -78 °C. The solution was warmed
to room temperature and stirred for 4 h. Solvent was removed
in vacuo and the remaining solid extracted in hexane (30 mL).
A white crystalline solid was obtained by concentrating (5 mL)
1
(C5Me4H)SiMe2(C5H4Et) (1). ClMe2Si(C5Me4H) (2.50 g,
11.64 mmol) in THF (50 mL) was added to a solution of Mg-
(C5H4Et)2 (1.23 g, 5.82 mmol) in THF (50 mL) at -78 °C. The
reaction mixture was warmed to room temperature and stirred
for 15 h. Solvent was removed in vacuo, and hexane (150 mL)
was added to the resulting orange oil. The mixture was filtered
and solvent removed from the filtrate under reduced pressure
to yield the title compound as a dark orange oil (3.01 g, 95%).
and cooling (-30 °C) the solution (0.27 g, 75%). H NMR (300
MHz, C6D6): δ -0.32 (s, 6H, CH3), 0.31 (6H, s, SiMe2), 1.58
(6H), 1.89 (6H) (s, C5Me4), 5.27 (2H), 6.77 (2H) (m, C5H4). 13C-
{1H} NMR (300 MHz, C6D6): δ -0.4 (SiMe2), 11.6, 14.4 (C5Me4),
31.8 (CH3), 100.0 (Cipso), 111.7, 120.2 (C5H3), 121.9, 122.4, 126.7
(C5Me4). Anal. Calcd for C18H28ZrSi: C, 59.44; H, 7.76.
Found: C, 59.27; H, 7.73.
[Me2Si(η5-C5Me4)(η5-C5H3Me)]Zr Me2 (12). The synthesis
of 12 was carried out in a manner identical with that for 11,
using a 3 M solution of MgMeCl in THF (0.67 mL, 2.00 mmol)
and [Me2Si(η5-C5Me4)(η5-C5H3Me)]ZrCl2 (6; 0.42 g, 1.00 mmol).
1H NMR (300 MHz, C6D6; for the predominant isomer):
δ
-0.20 (s, 6H, SiMe2), 1.12 (m, 3H, CH2CH3), 1.78 (6H), 1.90
(6H) (s, C5Me4), 2.37 (m, 2H, CH2CH3), 2.74 (1H), 3.30 (1H)
(m, HC5), 6.02 (1H), 6.36 (1H), 6.51 (1H) (m, C5H3). MS electron
impact (m/e (relative intensity)): 272 (85) (M+, (C5Me4H)-
SiMe2(C5H4Et)+), 257 (100) (M+ - Me), 179 (75) (M+ - C5H4-
Et), 151 (72) (M+ - C5Me4H).
1
Yield: 0.22 g, 76%. H NMR (300 MHz, C6D6): δ -0.44 (3H),
-0.34 (3H) (s, CH3), 0.32 (3H), 0.33 (3H) (s, SiMe2), 1.55 (3H),
1.64 (3H), 1.91 (3H), 1.92 (3H) (s, C5Me4), 2.20 (s, 3H, C5H3Me),
4.97 (1H), 5.25 (1H), 6.47 (1H) (m, C5H3). 13C{1H} NMR (300
MHz, C6D6): δ -0.3, -0.2 (SiMe2), 11.6, 11.7, 14.3, 14.5, 15.0
(C5Me4, C5H3Me), 31.0, 35.5 (CH3), 99.1 (Cipso), 111.1 (Cipso),
112.3, 112.5, 120.9 (C5H3), 122.4, 124.5, 125.2, 126.5, 129.6 (C5-
Me4). Anal. Calcd for C19H30SiZr: C, 60.41; H, 8.00. Found:
C, 60.19; H, 7.90.
(C5Me4H)SiMe2(C5H4tBu ) (2). The preparation of 2 was
carried out in a manner identical with that for 1, using ClMe2-
t
Si(C5Me4H) (2.50 g, 11.64 mmol) and Li(C5H4 Bu) (1.49 g, 11.64
1
mmol). Yield: 3.35 g, 96%. H NMR (300 MHz, C6D6; for the
predominant isomer): δ -0.20 (s, 6H, SiMe2), 1.20 (s, 9H,
t
[Me2Si(η5-C5Me4)(η5-C5H3Et)]Zr Me2 (13). The synthesis
of 13 was carried out in a manner identical with that for 11,
using a 3 M solution of MgMeCl in THF (0.59 mL, 1.76 mmol)
and [Me2Si(η5-C5Me4)(η5-C5H3Et)]ZrCl2 (7; 0.38 g, 0.88 mmol).
C5H3 Bu), 1.79 (6H), 1.90 (6H) (s, C5Me4), 2.86 (1H), 3.26 (1H)
(m, HC5), 6.00 (1H), 6.36 (1H), 6.64 (1H) (m, C5H3). MS electron
impact (m/e (relative intensity)): 300 (13) (M+, (C5Me4H)SiMe2-
(C5H4 Bu)+), 285 (15) (M+ - Me), 179 (100) (M+ - C5H4Me).
t
[Me2Si(C5Me4)(C5H3Et)]Li2 (3). nBuLi (1.6 M in hexane)
(13.8 mL, 22.10 mmol) was added via syringe to a solution of
1 (3.01 g, 11.05 mmol) in Et2O (50 mL) at -78 °C. The mixture
was warmed to 25 °C and stirred for 15 h. Solvent was removed
in vacuo to give a white solid, which was washed with hexane
(2 × 50 mL) and dried under vacuum to yield a free-flowing
white solid of the title complex (2.76 g, 88%). Anal. Calcd for
C18H26Li2Si: C, 76.03; H, 9.22. Found: C, 75.76; H, 9.11.
[Me2Si(C5Me4)(C5H3tBu )]Li2 (4). The preparation of 4 was
carried out in a manner identical with that for 3, using 2 (3.35
g, 11.14 mmol) and nBuLi (1.6 M in hexane) (13.9 mL, 22.28
mmol). Yield: 2.82 g, 81%. Anal. Calcd for C20H30Li2Si: C,
76.89; H, 9.68. Found: C, 76.71; H, 9.66.
1
Yield: 0.28 g, 79%. H NMR (300 MHz, C6D6): δ -0.44 (3H),
-0.33 (3H) (s, CH3), 0.33 (3H), 0.35 (3H) (s, SiMe2), 1.20 (m,
3H, CH2CH3), 1.58 (3H), 1.65 (3H), 1.92 (3H), 1.93 (3H) (s,
C5Me4), 2.63 (m, 2H, CH2CH3), 5.06 (1H), 5.27 (1H), 6.56 (1H)
(m, C5H4). 13C{1H} NMR (300 MHz, C6D6): δ -0.3, -0.2
(SiMe2), 11.6, 11.7, 14.4, 14.5 (C5Me4), 15.4 (CH2CH3), 23.2
(CH2CH3), 31.3, 34.9 (CH3), 99.1 (Cipso), 106.5 (Cipso), 111.1,
112.2, 119.4 (C5H4), 122.2, 126.8, 128.8, 136.4, 143.1 (C5Me4).
Anal. Calcd for C20H32SiZr: C, 61.31; H, 8.23. Found: C, 61.22;
H, 8.24.
[Me2Si(η5-C5Me4)(η5-C5H3iP r )]Zr Me2 (14). The synthesis
of 14 was carried out in a manner identical with that for 11,
using a 3 M solution of MgMeCl in THF (0.60 mL, 1.80 mmol)
and [Me2Si(η5-C5Me4)(η5-C5H3iPr)]ZrCl2 (8; 0.40 g, 0.90 mmol).
[Me2Si(η5-C5Me4)(η5-C5H3Et)]Zr Cl2 (7). THF (50 mL) was
added to a solid mixture of ZrCl4 (1.00 g, 4.29 mmol) and [Me2-
Si(C5Me4)(C5H3Et)]Li2 (3; 1.22 g, 4.29 mmol). The resulting
pale yellow solution was stirred for 15 h. Solvent was removed
in vacuo and toluene added (75 mL) to the resulting solid. The
1
Yield: 0.26 g, 72%. H NMR (300 MHz, C6D6): δ -0.40 (3H),
-0.31 (3H) (s, CH3), 0.32 (3H), 0.36 (3H) (s, SiMe2), 1.21 (3H),
1.31 (3H) (d, HCMe2) (3J (1H-1H) 6.8 Hz), 1.60 (3H), 1.65 (3H),
1.92 (3H), 1.94 (3H), (s, C5Me4), 3.06 (sep, 1H, HCMe2), 5.16

2466 Organometallics, Vol. 21, No. 12, 2002
Antin˜olo et al.
(1H), 5.25 (1H), 6.65 (1H) (m, C5H3). 13C{1H} NMR (300 MHz,
C6D6): δ -0.4, -0.1 (SiMe2), 11.6, 11.7, 14.4, 14.5 (C5Me4), 22.4,
25.5 (HCMe2), 28.6 (HCMe2), 31.4, 34.6 (CH3), 91.4 (Cipso), 98.9
(Cipso), 110.2, 111.6, 117.9 (C5H3), 121.9, 122.5, 126.8, 129.0,
141.5 (C5Me4). Anal. Calcd for C21H34SiZr: C, 62.15; H, 8.44.
Found: C, 62.00; H, 8.38.
Ta ble 6. Cr ysta l Da ta a n d Str u ctu r e Refin em en t
Deta ils for 7 a n d 8
7
8
formula
fw
C
18H28Cl2SiZr
C19H28Cl2SiZr
446.62
218.79
T (K)
293(2)
250(2)
[Me2Si(η5-C5Me4)(η5-C5H3tBu )]Zr Me2 (15). The synthesis
of 15 was carried out in a manner identical with that for 11,
using a 3 M solution of MgMeCl in THF (0.54 mL, 1.60 mmol)
and [Me2Si(η5-C5Me4)(η5-C5H3tBu)]ZrCl2 (9; 0.38 g, 0.80 mmol).
cryst syst
space group
a (Å)
b (Å)
c (Å)
orthorhombic
Pnma
10.997(2)
13.416(2)
13.218(1)
monoclinic
P21/n
9.799(6)
13.677(1)
15.625(3)
102.244(9)
2046.4(13)
4
1.450
0.855
920
1
Yield: 0.24 g, 72%. H NMR (300 MHz, C6D6): δ -0.28 (3H),
â (deg)
V (Å3)
Z
-0.27 (3H) (s, CH3), 0.34 (3H), 0.37 (3H) (s, SiMe2), 1.38 (s,
1950.1(3)
8
1.470
0.894
884
t
9H, Bu), 1.64 (3H), 1.65 (3H), 1.87 (3H), 1.89 (3H) (s, C5Me4),
5.27 (1H), 5.46 (1H), 6.72 (1H) (m, C5H3). 13C{1H} NMR (300
MHz, C6D6): δ -0.6, 0.2 (SiMe2), 11.6, 11.7, 14.5, 14.6 (C5Me4),
31.3 (CMe3), 33.5 (CMe3), 31.8, 33.4 (CH3), 92.0 (Cipso), 98.4
(Cipso), 108.7, 112.6, 118.9 (C5H3), 121.5, 123.1, 127.0, 145.7,
148.6 (C5Me4). Anal. Calcd for C22H36SiZr: C, 62.94; H, 8.64.
Found: C, 62.69; H, 8.55.
Dc (g cm-3
)
µ (mm-1
F(000)
)
cryst dimens (mm)
θ range (deg)
hkl ranges
0.4 × 0.3 × 0.2
2.16-24.97
0 e h e 13,
0 e k e 5,
0 e l e 15
1793/112
1.191
0.3 × 0.3 × 0.2
2.26-28.00
-12 e h e 12,
0 e k e 18,
0 e l e 20
4918/208
1.109
[Me2Si(η5-C5Me4)(η5-C5H3SiMe3)]Zr Me2 (16). The syn-
thesis of 16 was carried out in a manner identical with that
for 11, using a 3 M solution of MgMeCl in THF (0.56 mL, 1.68
mmol) and [Me2Si(η5-C5Me4)(η5-C5H3SiMe3)]ZrCl2 (10; 0.40 g,
no. of data/params
goodness of fit on F2
final R indices
R1 ) 0.0960
R1 ) 0.0549
1
0.84 mmol). Yield: 0.30 g, 81%. H NMR (300 MHz, C6D6): δ
(I > 2σ(I))a
-0.31 (s, 6H, CH3), 0.35 (3H), 0.38 (3H) (s, SiMe2), 0.36 (s,
9H, SiMe3), 1.62 (3H), 1.63 (3H), 1.85 (3H), 1.87 (3H) (s, C5Me4),
5.46 (1H), 5.66 (1H), 6.96 (1H) (m, C5H3). 13C{1H} NMR (300
MHz, C6D6): δ -0.6, 0.2 (SiMe2), 0.0 (SiMe3), 11.6, 11.7, 14.5,
14.6 (C5Me4), 32.0, 32.6 (CH3), 92.1 (Cipso), 103.8 (Cipso), 115.7,
117.5, 127.3 (C5H3), 121.4, 123.0, 127.0, 127.1, 127.2 (C5Me4).
Anal. Calcd for C21H36Si2Zr: C, 57.86; H, 8.32. Found: C,
57.61; H, 8.21.
wR2 ) 0.2981
1.798/-1.295
wR2 ) 0.1429
1.661/-1.01
largest diff peak (e Å-3
)
a
R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]0.5
.
[{Me2Si(η5-C5Me4)(η5-C5H 3SiMe3)}Zr Me][MeB(C6F 5)3]
(22). The synthesis of 22 was carried out in a manner identical
with that for 17, using B(C6F5)3 (0.23 g, 0.46 mmol) and 16
1
(0.20 g, 0.46 mmol). H NMR (300 MHz, C6D5CD3): δ 0.09 (s,
[{Me2Si(η5-C5Me4)(η5-C5H4)}Zr Me][MeB(C6F 5)3] (17). A
solution of B(C6F5)3 (0.28 g, 0.55 mmol) in toluene (25 mL) was
added to a stirred solution of 11 (0.20 g, 0.55 mmol) in toluene
(25 mL) at -78 °C. The mixture was warmed to room
temperature and stirred for 30 min. Solvent was removed in
vacuo to give a red oil, which was identified as the title
3H, CH3), 0.10 (s, 9H, SiMe3), 0.25 (3H), 0.29 (3H) (s, SiMe2),
1.20 (3H), 1.45 (3H), 1.57 (3H), 1.71 (3H) (s, C5Me4), 5.17 (1H),
5.61 (1H), 6.42 (1H) (m, C5H3).
P olym er iza tion of Eth ylen e w ith 5-10. The ansa-
zirconocene catalyst (6 µmol), MAO (10% in toluene; 3000
µmol), and toluene (150 mL) were mixed together in a Schlenk
tube. The N2 pressure inside the Schlenk tube was reduced
by applying vacuum. An ethylene pressure of 1.5 bar was then
applied to the Schlenk tube, and stirring of the mixture
commenced. After exactly 30 min, stirring was halted and the
ethylene pressure was released. Excess MAO was then de-
stroyed by adding cautiously a mixture of methanol and HCl
(90:10). The polymer formed was isolated by filtration, washed
with ethanol, and dried under vacuum at 60 °C for 12 h.
P olym er iza tion of P r op ylen e w ith 5-10. The ansa-
zirconocene catalyst (6 µmol), MAO (10% in toluene; 6000
µmol), and toluene (150 mL) were mixed together in a Schlenk
tube. The N2 pressure inside the Schlenk tube was reduced
by applying vacuum. A propylene pressure of 2.0 bar was then
applied to the Schlenk tube, and stirring of the mixture
commenced. After exactly 30 min, stirring was halted and the
propylene pressure was released. Excess MAO was then
destroyed by adding cautiously a mixture of methanol and HCl
(90:10). The polymer formed was isolated by filtration, washed
with ethanol, and dried under vacuum at 60 °C for 12 h.
1
complex. H NMR (300 MHz, C6D5CD3): δ 0.21 (s, 3H, CH3),
0.06 (3H), 0.18 (3H) (s, SiMe2), 1.14 (3H), 1.29 (3H), 1.48 (3H),
1.68 (3H) (s, C5Me4), 4.59 (1H), 5.26 (1H), 6.27 (1H), 6.53 (1H)
(m, C5H4).
[{Me2Si(η5-C5Me4)(η5-C5H3Me)}Zr Me][MeB(C6F 5)3] (18).
The synthesis of 18 was carried out in a manner identical with
that for 17, using B(C6F5)3 (0.27 g, 0.53 mmol) and 12 (0.20 g,
0.53 mmol). 1H NMR (300 MHz, C6D5CD3): δ 0.18 (s, 3H, CH3),
0.08 (3H), 0.12 (3H) (s, SiMe2), 1.11 (3H), 1.30 (3H), 1.50 (3H),
1.72 (3H) (s, C5Me4), 2.09 (s, 3H, C5H3Me), 4.33 (1H), 5.28 (1H),
6.00 (1H) (m, C5H3).
[{Me2Si(η5-C5Me4)(η5-C5H3Et)}Zr Me][MeB(C6F 5)3] (19).
The synthesis of 19 was carried out in a manner identical with
that for 17, using B(C6F5)3 (0.24 g, 0.47 mmol) and 13 (0.20 g,
0.47 mmol). 1H NMR (300 MHz, C6D5CD3): δ 0.22 (s, 3H, CH3),
0.03 (3H), 0.08 (3H) (s, SiMe2), 0.97 (m, 3H, CH2CH3), 1.09
(3H), 1.30 (3H), 1.47 (3H), 1.69 (3H) (s, C5Me4), 2.32 (1H), 2.45
(1H) (m, CH2CH3), 4.40 (1H), 5.29 (1H), 6.02 (1H) (m, C5H4).
[{Me2Si(η5-C5Me4)(η5-C5H3iP r )}Zr Me][MeB(C6F 5)3] (20).
The synthesis of 20 was carried out in a manner identical with
that for 17, using B(C6F5)3 (0.25 g, 0.49 mmol) and 14 (0.20 g,
0.49 mmol). 1H NMR (300 MHz, C6D5CD3): δ 0.23 (s, 3H, CH3),
0.02 (3H), 0.05 (3H) (s, SiMe2), 0.91 (3H), 0.97 (3H) (d, HCMe2)
(3J (1H-1H) ) 6.7 Hz), 1.09 (3H), 1.39 (3H), 1.49 (3H), 1.69 (3H)
(s, C5Me4), 2.70 (sep, 1H, HCMe2), 4.51 (1H), 5.34 (1H), 6.11
(1H) (m, C5H3).
P olym er iza tion of Eth ylen e w ith 17-22. The ansa-
zirconocene cationic catalyst (6 µmol), [TIBA] (scavenger; 16
µmol), and toluene (150 mL) were mixed together in a Schlenk
tube. The N2 pressure inside the Schlenk tube was reduced
by applying vacuum. An ethylene pressure of 1.5 bar was then
applied to the Schlenk tube, and stirring of the mixture
commenced. After exactly 30 min, stirring was halted and the
ethylene pressure was released. The polymer formed was
isolated by filtration, washed with ethanol, and dried under
vacuum at 60 °C for 12 h.
[{Me2Si(η5-C5Me4)(η5-C5H3tBu )}Zr Me][MeB(C6F 5)3] (21).
The synthesis of 21 was carried out in a manner identical with
that for 17, using B(C6F5)3 (0.24 g, 0.48 mmol) and 13 (0.20 g,
0.48 mmol). 1H NMR (300 MHz, C6D5CD3): δ 0.30 (s, 3H, CH3),
t
0.09 (3H), 0.29 (3H) (s, SiMe2), 1.07 (s, 9H, Bu), 1.23 (3H),
X-r a y Str u ctu r e Deter m in a tion s for [Me2Si(η5-C5Me4)-
i
1.47 (3H), 1.59 (3H), 1.74 (3H) (s, C5Me4), 5.01 (1H), 5.44 (1H),
6.15 (1H) (m, C5H3).
(η5-C5H3R)]Zr Cl2 (R ) Et (7), P r (8)). Intensity data were
collected on a NONIUS-MACH3 diffractometer equipped with

Zirconium Complexes with ansa Ligands
Organometallics, Vol. 21, No. 12, 2002 2467
a graphite monochromator (Mo KR radiation; λ ) 0.710 73 Å),
using an ω/2θ scan technique. For 7, the specimen diffracted
weakly. The final unit cell parameters were determined from
25 well-centered reflections and refined by least-squares
methods. Data were corrected for Lorentz and polarization
effects but not for absorption. The space group was determined
from the systematic absences, and this was vindicated by the
success of the subsequent solutions and refinements. The
structures were solved by direct methods using the SHELXS
computer program24 and refined on F2 by full-matrix least
squares (SHELXL-97).25 All non-hydrogen atoms were refined
with anisotropic thermal parameters. The hydrogen atoms
were included in calculated positions and were refined with
an overall isotropic temperature factor using a riding model.
Weights were optimized in the final cycles. In 7, the ethyl
group is in a disordered position. Crystallographic data are
given in Table 6.
Ack n ow led gm en t. We gratefully acknowledge fi-
nancial support from the Direccio´n General de Ensen˜an-
za Superior e Investigacio´n Cient´ıfica of Spain (Grants
No. PB 98-0159-C02-01-02 and No. BQU 2000-0463). We
also thank Dr. M. Laguna for providing mass spectros-
copy data.
Su p p or tin g In for m a tion Ava ila ble: Details of the data
collection and refinement, atom coordinates, anisotropic dis-
placement parameters, and bond lengths and angles for
complexes 7 and 8. This material is available free of charge
via the Internet at http://pubs.acs.org.
(23) Chen, E. Y.-X.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(24) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(25) Sheldrick, G. M. Program for the Refinement of Crystal
Structures from Diffraction Data; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
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