Chiral ansa metallocenes with Cp ring-fused to thiophenes and pyrroles: Syntheses, crystal structures, and isotactic polypropylene catalysts

DOI: 10.1021/ja004266h

Source and publish data:

Journal of the American Chemical Society p. 4763 - 4773 (2001)

Update date:2022-08-03

Topics:

Authors:

Ewen Ewen

Elder Elder

Jones Jones

Rheingold

Liable-Sands

Sommer Sommer

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Article abstract of DOI:10.1021/ja004266h

Syntheses, crystal structures, and polymerization data for new isospecific metallocenes (heterocenes) having cyclopentenyl ligands b-fused to substituted thiophenes (Tp) and pyrroles (Pyr) are reported. The C₂and C₁-symmetric heterocenes are dimethylsilyl bridged, have methyl groups adjacent to the bridgehead carbon atoms, and have aryl substituents protruding in the front. rac-Me₂Si(2,5-Me₂-3-Ph-6-Cp [b]Tp)₂ZrCl₂/MAO (MAO = methyl alumoxanes) is the most active metallocene catalyst for polypropylene reported to date. rac-Me₂Si (2,5-Me₂-3-Ph-6-Cp[b]Tp)₂ZrCl₂ and rac-Me₂Si (2,5-Me₂-1-Ph-4-Cp[b]Pyr)₂ZrCl₂ have the same structure, and the former is 6 times more active, produces half the total enantiofacial errors, and is 3.5 times less regiospecific in propylene polymerizations at the same conditions. rac-Me₂Si(2-Me-4-Ph-1-Ind)₂ZrCl₂/ MAO is 3.5 times lower in activity than rac-Me₂Si(2,5-Me₂-3-Ph-6-Cp[b] Tp)₂ZrCl₂ catalyst, and while the former is the more stereospecific and the less regiospecific, the sum of these two enantioface errors is the same for both species. Fine-tuning the heterocene sterics by changing selected hydrogen atoms on the ligands to methyl groups influenced their catalyst activities, stereospecificites, regiospecificites, and isotactic polypropylene (IPP) M_w. Thus, both substituting a hydrogen atom adjacent to the phenyl ring with a methyl group on an azapentalenyl ligand system and replacing one and then two hydrogens on the phenyl ring with methyls on thiopentalenyl ligands provided increased polymer T_m and M_w with increasing ligand bulk. Polymer molecular weights are sensitive to and inversely proportional to MAO concentration, and the catalyst activities increase when hydrogen is added for molecular weight control. The polymer T_m values with the thiopentalenyls as TIBAL/[Ph₃C][B(C₆F₅)₄] systems were higher than with MAO as catalyst activator. A racemic C₁, pseudomeso complex with a hybrid dimethylsilyl-bridged 2-Me-4-Ph-1 1-Ind/2,5-Me₂-4-Ph-1-Cp[b]Pyr ligand produced the first sample of IPP with all the steric pentad intensities fitting the enantiomorphic site control model. Speculative mechanistic considerations are offered regarding electronic effects of the heteroatoms and steric effects of the ligand structures, the preferred phenyl torsion angles, and anion effects.

Full text of DOI:10.1021/ja004266h

J. Am. Chem. Soc. 2001, 123, 4763-4773

4763

Chiral Ansa Metallocenes with Cp Ring-Fused to Thiophenes and

Pyrroles: Syntheses, Crystal Structures, and Isotactic Polypropylene

Catalysts

John A. Ewen,*^,†Michael J. Elder,^‡Robert L. Jones,^‡Arnold L. Rheingold,^§

Louise M. Liable-Sands,^§and Roger D. Sommer^§

Contribution from the Catalyst Research Corporation, 14311 Golf View Trail, Houston, Texas 77059,

Basell Polyolefins, North American R & D Center, 912 Appleton Road, Elkton, Maryland 21921, and

Department of Chemistry, UniVersity of Delaware, Newark, Delaware 19716

ReceiVed December 15, 2000

Abstract: Syntheses, crystal structures, and polymerization data for new isospecific metallocenes (heterocenes)

having cyclopentenyl ligands b-fused to substituted thiophenes (Tp) and pyrroles (Pyr) are reported. The C₂-

and C₁-symmetric heterocenes are dimethylsilyl bridged, have methyl groups adjacent to the bridgehead carbon

atoms, and have aryl substituents protruding in the front. rac-Me₂Si(2,5-Me₂-3-Ph-6-Cp[b]Tp)₂ZrCl₂/MAO

(MAO ) methyl alumoxanes) is the most active metallocene catalyst for polypropylene reported to date.

rac-Me₂Si(2,5-Me₂-3-Ph-6-Cp[b]Tp)₂ZrCl₂and rac-Me₂Si(2,5-Me₂-1-Ph-4-Cp[b]Pyr)₂ZrCl₂have the same

structure, and the former is 6 times more active, produces half the total enantiofacial errors, and is 3.5 times

less regiospecific in propylene polymerizations at the same conditions. rac-Me₂Si(2-Me-4-Ph-1-Ind)₂ZrCl₂/

MAO is 3.5 times lower in activity than rac-Me₂Si(2,5-Me₂-3-Ph-6-Cp[b]Tp)₂ZrCl₂catalyst, and while the

former is the more stereospecific and the less regiospecific, the sum of these two enantioface errors is the

same for both species. Fine-tuning the heterocene sterics by changing selected hydrogen atoms on the ligands

to methyl groups influenced their catalyst activities, stereospecificites, regiospecificites, and isotactic

polypropylene (IPP) M_w. Thus, both substituting a hydrogen atom adjacent to the phenyl ring with a methyl

group on an azapentalenyl ligand system and replacing one and then two hydrogens on the phenyl ring with

methyls on thiopentalenyl ligands provided increased polymer T_mand M_wwith increasing ligand bulk. Polymer

molecular weights are sensitive to and inversely proportional to MAO concentration, and the catalyst activities

increase when hydrogen is added for molecular weight control. The polymer T_mvalues with the thiopentalenyls

as TIBAL/[Ph₃C][B(C₆F₅)₄] systems were higher than with MAO as catalyst activator. A racemic C₁, pseudo-

meso complex with a hybrid dimethylsilyl-bridged 2-Me-4-Ph-1-Ind/2,5-Me₂-4-Ph-1-Cp[b]Pyr ligand produced

the first sample of IPP with all the steric pentad intensities fitting the enantiomorphic site control model.

Speculative mechanistic considerations are offered regarding electronic effects of the heteroatoms and steric

effects of the ligand structures, the preferred phenyl torsion angles, and anion effects.

Introduction

regiospecificities.^6,7This quest for a “rational design” of catalysts

has focused on the trends seen from comparison of polymeri-

zation results to catalyst structural parameters that affect the

nonbonded energies in preinsertion and termination assemblies.⁸

The discovery that group 4 metallocenes catalyze stereospe-

cific polymerization to isotactic polypropylene (IPP)^1,2according

to the enantiomorphic site-controlled model³resulted in a lot

of research targeting better catalyst activities, improved stereo-

and regioselectivities, and higher polypropylene molecular

weights.⁴Structural modifications to a prototype rac-Me₂Si-

[indenyl]₂ZrCl₂(1)⁵led to promising catalysts with higher

efficiencies, higher molecular weight polymers, stereospecifici-

ties approaching those of commercial catalysts, and higher

(4) For recent reviews, see: (a) Jordan, R. F. AdV. Organomet. Chem.

1991, 32, 325. (b) Brintzinger, H. H.; Fischer, D.; Mulhaupt, R.; Rieger,

B.; Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143. (c)

Ewen, J. A. Sci. Am. 1997, 276 (5), 60. (d) Metallocene-Based Polyolefins.

Preparation, Properties and Technology; Scheirs, J., Kaminsky, W., Eds.;

Wiley: New York, 1999. (e) Resconi, L.; Cavallo, L.; Fait, A.; Piemontesi,

F.; Chem. ReV. 2000, 100, 1253.

(5) Ewen, J. A.; Haspeslagh, L.; Elder, M. J.; Atwood, J. L.; Zhang, H.;

Cheng, H. N. In Transition Metals and Organometallics as Catalysts for

Olefin Polymerization; Kaminsky W., Sinn, H., Eds.; Springer-Verlag: New

York, 1988; p 281.

(6) Spaleck, W.; Ku¨ber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.;

Antberg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954.

(7) (a) Stehling, U.; Disbold, J.; Kirsten, R.; Ro¨ll, W.; Brintzinger, H.

H. Organometallics 1994, 13, 964. (b) Schneider, N.; Huttenloch, M. E.;

Stehling, U.; Kirsten, R.; Schaper, F.; Brintzinger, H. H. Organometallics

1997, 16, 3413. (c) Kashiwa, N.; Kojoh, S.; Imuta, J.; Tsutsui, T. In

Metalorganic Catalysts for Synthesis and Polymerization; Kaminsky, W.,

Ed.; Springer: Berlin, 1999; p 30. (d) Kato, T.; Uchino, H.; Iwama, N.;

Imaeda, M.; Kashimoto, M.; Osano, Y.; Sugano, T. In Metalorganic

Catalysts for Synthesis and Polymerization; Kaminsky, W., Ed.; Springer:

Berlin, 1999; p 192.

^†Catalyst Research Corp.

^‡Basell Polyolefins.

^§University of Delaware.

(1) (a) Ewen, J. A. J. Am. Chem. Soc. 1984, 106, 6355. (b) Ewen, J. A.;

Haspeslagh, L.; Atwood, J. L.; Zhang, H. J. Am. Chem. Soc. 1987, 109,

6544.

(2) Kaminsky, W.; Ku¨lper, K.; Brintzinger, H. H.; Wild, F. R. W. P.

Angew. Chem., Int. Ed. Engl. 1985, 24, 507.

(3) (a) Zambelli, A. NMRsBasic Principles and Progress; Springer-

Verlag: Berlin, Heidelberg, New York, 1971; Vol. 4, p 101. (b) Zambelli,

A.; Zetta, L.; Sacchi, C.; Wolfsgruber, C. Macromolecules 1972, 5, 440.

Chem. 1975, 176, 2765.

Published on Web 04/26/2001

4764 J. Am. Chem. Soc., Vol. 123, No. 20, 2001

Ewen et al.

Chart 1

Chart 2

were interchanged to determine influences of the positions and

sizes of substituents on the heterocycles and which can also

influence the preferred torsion angles between the phenyl group

and the Cp plane.

One of these indenyl-type catalysts, rac-Me₂Si(2-Me-4-Ph-1-

indenyl)₂ZrCl₂(2),⁶was adopted in this contribution as a

benchmark for comparisons with similarly substituted cyclo-

penta[b]thiophenes and cyclopenta[b]pyrroles.

A rare opportunity that is offered by studying heterocenes is

the possibility of better separating ligand steric and electronic

effects since catalysts with ligands that are structurally equivalent

around the non-Cp coordination sites but which are, at the same

time, electronically dissimilar from each other because of the

heteroatoms can be compared.¹²There are no measurements of

electron-donating abilities of the ligands but, by definition, S

is a soft, polarizable atom and nitrogen is hard.¹³The Pauling

electronegativities for C (2.55), S (2.58), and N (3.04)¹⁴reflect

the relative inductive electron-withdrawing power of these

atoms.¹²Carbon and sulfur have the same electronegativity,

while nitrogen is one of the most electronegative elements; only

oxygen and fluorine exceed it in this respect. The azapentalenyl

ligands for 4 are therefore structurally equivalent around the

non-Cp coordination sites and are relatively poor electron donors

compared with the isostructural thiopentalenyl ligands for 5.

Modification of the sterics with heterocenes was done with

selected hydrogen atoms on the parent ligands being changed

to methyl groups and determining the influences of ligand bulk

on catalyst activities, stereospecificities, regiospecificities, and

on the IPP molecular weights. This approach was based on the

findings that bulkier 4-indenyl ring-fused aromatics improve

catalyst performance while aryl substituents in the 5-indenyl

position do not.^6,7The methyl substitutions were selected as a

matter of expediency and because methyl and aromatic CH

substituents typically have equivalent effects on stereoregula-

tion.^5,11The steric effect of methyl substitution adjacent to the

phenyl ring on a heterocene was also investigated, not with-

standing the aforementioned unimportance of the 5-indenyl

position.

The first C₂-symmetric heterocene in this series (4, Chart 1)

had an activity close to that of 2, and C_s- and C₁-symmetric

complexes having isopropylidene-bridged cyclopentadienyl and

cyclopentyl[1,2-b:4,3-b′]dithiophene ligands had activities simi-

lar to those of fluorenyl analogues and obeyed the same

symmetry rules for polypropylene tacticity versus catalyst

symmetry.⁹Ligand effects have now been investigated in more

detail, and the present paper reports our results on the prepara-

tion, characterization, and polymerization behavior of new

heterocene complexes with ligands that are dimethylsilyl-

bridged, have a methyl group adjacent to the bridgehead carbon

atom, and have aryl substituents protruding out in the front of

the catalysts by analogy with 2 (Chart 1).

The chosen mode of ring fusion has one heterocycle double

bond aligned with the methylcyclopentenes of these cyclopen-

tadienoid-like systems since b-fusion results in preferential

metalation with n-BuLi at the desired active methylene group

and also improves anionic delocalization relative to c-fused

heterocyclic nuclei.¹⁰Electronic and steric ligand effects were

investigated for sulfur and nitrogen heteroatoms and with the

interchanging of hydrogen atoms and methyl groups adjacent

to (3, 4) and on the pendant phenyl rings (5-7), respectively

(Chart 1). 8 is C₁symmetrical and has the dimethylsilyl-bridged

azapentalenyl and indenyl ligands in a pseudo-meso arrange-

ment.

The importance of metallocene symmetries, bridges, and

ligand substituents for producing polypropylenes with micro-

tacticity control is well known.^4,11New catalyst structural

variants introduced in this study are illustrated in Chart 2.

There is 10° difference in the ligand mouth angles subtended

between the 5/5 and 5/6 rings in the front of the complexes

(Chart 2, I, II). Structures having differing mouth angles

superimposed on each other are depicted as III, where the

relative dispositions of the pendant phenyl rings are shown. IV

indicates the positions at which H atoms and methyl groups

A goal with metallocenes and polypropylene is the creation

of a stable of catalysts that can be used to tailor polypropylene

microstructures ranging from amorphous or low-melting elas-

tomeric materials to hard, perfectly isotactic polypropylene. A

wide variety of C₁- and C₂-symmetric heterocenes and indenyl-

type and fluorenyl-type metallocenes produce high-molecular-

weight IPP with a wide range of melting points.^4e,15The extreme

high and low ends of stereoregulation have not been reported

before. In an effort to attain a very low end of stereoregulation,

we investigated 8, which produced the first sample of isotactic

(8) For a recent review on molecular mechanics, see: Corradini, P.;

Cavalllo, L.; Guerra, G. In Metallocene-Based Polyolefins. Preparation,

Properties and Technology; Scheirs, J., Kaminsky, W., Eds.; John Wiley

& Sons Ltd.: New York, 1999; Vol. 2, pp 4-36.

(9) For earlier reports on heterocenes, see: (a) Ewen, J. A.; Jones, R.

L.; Elder, M. J.; Rheingold, A. L.; Liable-Sands, L. M. J. Am. Chem. Soc.

1998, 120, 10786. (b) Ewen, J. A.; Jones, R. L.; Elder, M. J. In Metalorganic

Catalysts for Synthesis and Polymerization; Kaminsky, W., Ed.; Springer:

Berlin, 1999; p 150.

(10) (a) Volz, H.; Zirngibl, U.; Messner, B. Tetrahedron Lett. 1970, 3593.

(b) MacDowell, D. W. H.; Jourdenais, R. A.; Naylor, R.; Paulovicks, G. E.

J. Org. Chem. 1971, 36, 2683. (c) Skramstad, J. Chem. Scr. 1973, 4, 81.

(11) Ewen, J. A.; Elder, M. J.; Jones, R. L.; Haspeslagh, L.; Atwood, J.

L.; Bott, S. G.; Robinson, K. Makromol. Chem., Macromol. Symp. 1991,

48/49, 253.

(12) (a) Cook, M. J.; Katritzky, A. R.; Linda, P. Heterocycl. Chem. 1974,

17, 257. (c) Hosmane, R. A.; Liebman, J. F. Tetrahedron Lett. 1991, 32,

3949. (b) Box, V. G. S. Heterocycles 1991, 32, 2023. (c) Katritzky, A. R.;

Karelson, M.; Malhotra, N. Heterocycles 1991, 32, 127. (d) Simkin, B.

Ya.; Minkin, V. I.; Glukhovtsev, M. N. AdV. Heterocycl. Chem. 1993, 56,

303. (d) Joule, J. A.; Mills, K.; Smith, G. F. Heterocyclic Chemistry, 3rd

ed.; Chapman and Hall: London, 1995.

(13) Pearson, R. G. Hard and Soft Acids and Bases; Dowden, Hutchinson

and Ross: Stroudsburg, PA, 1973.

(14) Allred, A. L. J. Inorg. Nucl. Chem. 1961, 17, 215.

(15) Rieger, B.; Jany, G.; Fawzi, R.; Steinman, M. Organometallics 1994,

13, 647.

Chiral Ansa Metallocenes

J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4765

Table 1. Crystallographic Data for 3, 5, 6, and 8

compound

6‚CH₂Cl₂

8‚0.5CH₂Cl₂

formula

C₃₀H₂₈Cl₂N₂SiZr

606.75

P4₁2₁2

12.7198(2)

34.1068(2)

C₃₂H₃₀Cl₂S₂SiZr

668.89

P2₁/c

9.5183(2)

35.7383(3)

8.8314(2)

91.6932(11)

3002.85(7)

C₃₅H₃₆Cl₄S₂SiZr

781.87

P1h

C_33.5H₃₂Cl₃NSiZr

674.26

I2/a

13.7403(2)

17.3226(2)

26.3308(3)

91.6470(2)

6264.61(8)

formula weight

space group

a, Å

b, Å

c, Å

11.7096(2)

12.6751(2)

12.7721(2)

96.9974(7)

106.8513(5)

100.2661(3)

1754.65(3)

A, deg

â, deg

γ, deg

V, Å³

5518.25(6)

Z, Z^/

cryst color, habit

D(calc), g cm^-3

µ(Mo KR), cm^-1

temp, K

diffractometer

radiation

R(F), %^a

R(wF²), %^a

orange block

1.461

65.8

yellow plate

1.480

74.4

yellow block

1.480

79.6

yellow blade

1.430

66.9

173(2)

243(2)

173(2)

Siemens P4/CCD

Mo KR (λ ) 0.71073 Å)

4.10

3.74

12.80

9.85

4.55

14.08

24.86

19.26

Quantity minimized ) R(wF²) ) ∑[w(F_o- F_c²)²]/∑[(wF_o)²]^1/2; R ) ∑∆/∑(F_o), ∆ ) |(F_o- F_c)|. w ) 1/[σ²(F_o) + (aP)²+ bP], P )

[2F_c²+ max(F_o,0)]/3.

Table 2. Comparison of Structural Parameters for 2, 3, 5, and 6

parameter

Zr-Cl (Å)^a

2.419(1) 2.443(4) 2.437(3)

96.8(1)

2.243(4) 2.230(4) 2.251(6)

2.421(5)

97.86(3) 98.00(11) 99.44(3)

2.256(5)

Cl-Zr-Cl (deg)

Zr-CR^b(Å)

Zr-C(Cp) min (Å) 2.478(3) 2.463(3) 2.484(10) 2.466(2)

Zr-C(Cp) max (Å) 2.640(4) 2.650(3) 2.663(9)

CR-Zr-CR′ (deg) 128.5(3) 128.7(4) 128.4(6)

2.665(2)

127.5

61.3

PL-PL′ (deg)^c

θ^d

59.2

131.4

59.9

59.8

141.2(8) 139.3(9)

139.4

Φ^e(calcd)^f

44.4 (50) 35.5 (34) 30.7 (55) 55.9 (67)

44.8 46.7 41.3 73.0

^aAverages. ^bCR, centroids of the Zr-bound C₅rings. ^cPL and PL′,

mean planes of the C₅rings. ^dAverage ligand mouth angles. ^eMeasured

torsion angle between aryl and Cp plane. ^fEstimated with Molecular

Simulations Inc. Cerius²Version 4.2 software on a Silicon Graphics

Indigo²work station.

polypropylene with sufficiently low stereoregularity for all of

the steric pentad intensities to be measured and fit to the

enantiomorphic site control model.¹⁶

Figure 1. Thermal ellipsoid plot of 3. H atoms omitted for clarity.

Ellipsoids at 30% probability.

Results and Discussion

X-ray Analyses of 3, 5, 6, and 8. The coordination

geometries at Zr determined by X-ray diffraction for 2, 3, 5,

and 6 are very similar to each other, with no deviations greater

than 2° nor 0.02 Å (rows 1-7 in Table 2, Figures 1-3).

Significant structural differences are, however, found in the

vicinity of the non-Cp coordination sites, with the ligand mouth

angles (θ) subtended between the 5/5 and 5/6 rings in the front

of the complexes (Chart 2, I, II) being about 10° larger for the

heterocenes than for 2 and the dihedral angles (Φ) between the

phenyl rings and the Cp planes differing from one another (Table

2, entries 8, 9). The measured torsion disagrees considerably

even within each otherwise C₂-symmetric heterocene and also

rarely agrees with theoretical values. The dihedral angles are

therefore consistent with low rotational barriers and with the

preferred conformations being influenced by either crystal

packing forces or cocrystallized solvent molecules rather than

simply following the theoretical trends for R-substituted biphen-

yls, as discussed by Spaleck and co-workers earlier.⁶Nonbonded

Figure 2. Thermal ellipsoid plot of 5. H atoms omitted for clarity.

Ellipsoids at 30% probability.

contacts between ion pairs and catalyst supports can therefore

affect this sensitive structural parameter and possibly influence

catalyst performance under different scenarios (vide infra).

(16) (a) Sheldon, R. A.; Fueno, T.; Tsunetsugu, T.; Furukawa, J. J. Polym.

Sci. 1965, 3, 23. (b) Furukawa, J. Polym. Prepr. 1967, 8, 39.

4766 J. Am. Chem. Soc., Vol. 123, No. 20, 2001

Ewen et al.

Table 3. Liquid Propylene Polymerization Test Results with 2-7^a

activity^c

(kg PP/

metallocene^b

(mg)

10^-3M_wAPP^eT_mmrrm 2,1-units^f

mmol Zr.h) (g/mol) (wt %) (°C) (%)

(%)

2 (0.4)

3 (0.4)

4 (0.4)

5 (0.05)

6 (0.1)

7 (0.2)

518

443

324

1953

850

479

1184

145

198

445

604

795

0.6

9.4

7.0

0.1

0.4

0.9

156 0.1₉

146 2.1₀

155 1.4₃

156 0.4₁

160 0.3₅

160 0.2₆

0.4₉

0.1₆

0.1₀

0.3₅

0.2₁

0.2₄

^aConditions: 1-gal autoclave, 2.2 L of propylene, 10 mL of 10%

MAO in toluene, 70 °C, 1 h. ^brac, %: 2, 5, 6, 7 ) 100%; 3, 4 )

50%. ^cActivities of the rac isomers. ^dM_wof isotactic fraction. ^eXylene-

soluble fraction. ^fErythro 2,1-regioerrors determined by ¹³C NMR.

Table 4. Liquid Propylene Polymerization Test Results with

Hydrogen^a

activity^b

metallocene

(mg)

(kg PP/

mmol Zr.h) (g/mol) (wt %) (°C) (%)

10^-3M_wAPP^cT_mmrrm 2,1-units^d

(%)

Figure 3. Thermal ellipsoid plot of 6‚CH₂Cl₂. H atoms omitted for

2 (0.1)

3 (0.4)

5 (0.05)

6 (0.1)

7 (0.2)

2123

886

5004

3318

1363

242

122

182

299

0.4 157 0.1₈

0.4₄

clarity. Ellipsoids at 30% probability.

147

0.2 157 0.4₃

0.1 160 0.3₇

0.1 161 0.2₄

0.2₅

0.2₁

0.2₄

Scheme 1

^aConditions: 1-gal autoclave, 2.2 L of propylene, 55 mmol of H₂

(total added), 5 mL of 10% MAO in toluene, 70 °C, 1 h. ^brac isomer.

^cXylene-soluble fraction. ^dErythro 2,1-regioerrors determined by ¹³

NMR.

ketone 16 was obtained in 98% yield by reaction of the 2,3-

disubstituted thiophene 15 with methacrylic acid in 87% super

polyphosphoric acid.¹⁹2,3-Disubstituted thiophenes are therefore

attractive targets for studies of C₂-symmetric metallocene ligand

effects. In comparison, a similar Friedel-Crafts alkylation/

acylation reaction using 3-phenylthiophene proceeded in only

44% yield.

Silyl Bridges. The dimethylsilyl bridges were introduced in

3-7 by deprotonation of the methylcyclopentene methylene

carbons with n-BuLi and reacting the resulting anions with

dichlorodimethylsilane in THF. The dimethylsilyl-bridged mixed

ligand for 8 was obtained by reacting the azapentalene anion

with dimethylchloro(2-methyl-4-phenyl-1-indene)silane.

Metallocene Syntheses. 3-7 were prepared from ZrCl₄and

their ligand dianions in ether and pentane solvents using standard

procedures, and detailed descriptions of these and the other

synthetic methods are given in the Experimental Section. In all

cases, except for 4, it was possible to isolate the pure racemic

forms by fractional crystallization from different solvents. The

pseudo-meso form of 8 was isolated by fractional crystallization

from dichloromethane. Complexes 5-7 with silicon-bridged

cyclopenta[b]thiopene ligands were unusually stable toward

moisture. The zirconocenes could be isolated on open filter

funnels, and addition of small amounts of water to NMR

solutions of 5 did not decompose the complex.

Scheme 2

Preparation of Cyclopenta[b]heterocycles. 5-Methyl-1-

phenyl-cyclopenteno[b]pyrrole (13) was prepared as outlined

in Scheme 1, analogous to the previously described procedure⁹

for its 2,5-dimethyl analogue but absent the initial methylation.

The selectivity of the POCl₃/DMF acylation to 9 improved by

30% in the absence of the 2-methyl group. Cyclization of

intermediate 11 with PPA proceeded in nearly quantitative yield,

and 13 was also isolated in higher yield than for the dimethyl

analogue.

The syntheses of the cyclopenta[b]thiophenes followed the

outline in Scheme 2. 14 was obtained by regioselective

2-lithiation of 3-bromothiophene at -78 °C with lithium

diisopropylamide (LDA), followed by methylation with iodo-

methane.¹⁷The coupling of PhMgBr and 14 proceeded smoothly

in ether at 25 °C with Ni(dppp)Cl₂as a catalyst.¹⁸The cyclic

Propylene Polymerization Catalysis with 2-7. The po-

lymerization data and polymer analyses with 2-7 activated with

methyl alumoxanes (MAO) at 70°C are summarized in Table

3. Polymerization test results on the influences of hydrogen

(Table 4), MAO concentration (Table 5), and B(C₆F₅)₄with

and without hydrogen (Table 6) are also provided.

Catalyst Activities. The activities for 2-4 and the most

crowded Tp complex (7) are on the same order of magnitude,

whereas the polymerization rates for 5 and 6 are significantly

(18) Monteheard, J. P.; Delzant, J. F.; Gazard, M. Synth. Commun. 1984,

14, 289.

(17) Hallberg, A.; Gronowitz, S. Chem. Scr. 1980, 16, 42.

(19) Meth-Chon, O.; Gronowitz, S. Acta Chem. Scand. 1966, 20, 9.

Chiral Ansa Metallocenes

J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4767

Table 5. Polymerization Results with 5 versus MAO^a

Chart 4

activity

(kg/mmol

cat.h)

(mL)

yield

(g)

10^-3M_w

(g/mol)

T_m

(°C)

Al/Zr

10.0

5.0

2.5

146

215 000

107 749

53 875

32 325

1953

1204

856

447

545

707

786

155

154

1.5

763

^aPolymerization conditions: 0.05 mg of 5, 10 wt % MAO in toluene,

2.2 L of propylene, 70 °C, 1 h, bulk.

Table 6. Results of Liquid Propylene Polymerizations with

[Ph₃C][B(C₆F₅)₄]-Activated Catalysts^a

activity

metallocene

(mg)

(kg PP/

mmol Zr.h) (g/mol) (wt %) (°C) (%)

10^-3M_wAPP^dT_mmrrm 2,1-units^e

(%)

5 (0.2)

687

2101

553

648

1422

564

465

1165

473

358

555

0.1

0.3

0.2

0.1

157

160 0.3₉

162

164 0.0₆

164

166

5 (0.1)^b

6 (0.2)

0.1₅

0.0₉

6 (0.1)^b

6 (0.58)^c

7 (0.5)^b

^aConditions: 1-gal autoclave, 2.2 L of propylene, 1.4 mg of

[Ph₃C][B(C₆F₅)₄], 1.0 mmol of Al(i-Bu)₃, 70 °C, 1 h. ^b15 mmol of H₂

added to the reactor. ^c10-gal autoclave, 22 L of propylene, 3.5 mg of

[Ph₃C][B(C₆F₅)₄], 12 mmol of Al(i-Bu)₃, 55 mmol of H₂, 70 °C, 1 h.

^dXylene-soluble fraction. ^eerythro-2,1-regioerrors determined by ¹³C

NMR.

activity decreases (Table 5) that transfer to Al is an important

termination mechanism with 5. It is logical that less sterically

hindered structures have faster bimolecular transfer to Al and

transfer to monomer terminations.

The M_wdata in Table 3 for the 5/5 systems are consistent

with steric inhibition of termination reactions affecting M_wsince

the heterocene-produced IPP M_wincreases in every case as the

ligands become more bulky and since this trend occurs

regardless of the catalyst activity. M_wfor 5 is double that of 4

for these sterically equivalent species and is consistent again

with an electronic difference between pyrrole and thiophene

resulting in 5 having the higher propagation rate.

Chart 3

Activities and IPP M_wvalues tend to vary hand-in-hand with

metallocenes.⁵The more unusual low activity-high IPP M_w

relationship for the Pyr catalyst 4 relative to 3 (Table 3) arises

from Me versus H substitutions at the ligands’ 5-positions (Chart

1, 3 and 4). The bulkier 5-Me apparently results in 4 having

both lower termination rates and, to a lesser extent, a lower

propagation rate. Steric considerations might likewise account

for the similar, albeit more extreme, trend for 2 versus 5.

The effect of hydrogen with five catalysts shows catalyst

activation by 2-4-fold with large decreases in M_wbut no

significant changes in T_m, mrrm, nor 2,1-units (Table 4). An

electronic effect on hydrogen response for 3 versus 5 is not

obvious with the limited data.

Microstructures. The molecular assembly 5a for a 1,2-

insertion with the “wrong” π-face coordinated results in a steric

inversion or “error”, as depicted in Chart 4 (R,R,si: ent )

S,S,re). There is a steric driving force for 5a to convert to the

2,1-erythro preinsertion intermediate 5b via a 180° propylene

rotation.²¹These are the only microstructural defects in the

polymers, and accordingly catalyst stereo- and regiospecificities

share a common origin with the “wrong” face coordinated. The

total of a catalyst’s “errors” in stereospecific (enantioselective)

IPP polymerizations can therefore be taken as the sum of its

polymer’s mrrm units and 2,1-units, and the ratio of (mrrm/

2,1-units) is presumably determined by the relative activation

energies for the competing reactions in Chart 4 and monomer

dissociations. The total enantiofacial “errors” with MAO

increase in the order 7 (0.5%) < 6 (0.6%) < 2 (0.7%) < 5

(0.8%) , 4 (1.5%) < 3 (2.3%), and the (mrrm/2,1-unit) ratios

higher (Table 3). The similarity in the activities for 2 and 3 is

consistent with earlier results for 2 versus 4.⁹It is possible that

opposing steric and electronic effects are at work, with N

electronically deactivating 3 and 4 and the larger mouth angle

for the 5/5 systems reactivating them.

5 has the highest activity known for metallocenes, and its

5-fold increase over the Pyr analogue 4 is attributed to greater

electron donation by the Tp ligand to Zr and the effect this has

on the propagation rate. This is in accord with the electroneg-

ativities of S and N, the two catalysts being isostructural, and

the Tp complex more than doubling M_wunder the same

polymerization conditions. Faster insertion reactions with

increased ligand electron donation is a consequence of the alkyl

ligand being rendered more anionic, which should enhance

nucleophilic migration to the olefin already polarized by the Zr

cation, i.e., should promote insertion (Chart 3).²⁰

A comparison of the electronic contribution to the relative

activities of Tp versus Ind catalysts is not possible since they

are not structural analogues, their relative basicities are un-

known, and the 3.5-fold improvement in activity for 5 versus 2

may be partially steric in origin. An unusual trend for the 5/5

catalysts in Table 3 not found for Ind catalysts is the decreasing

activities with increasing ligand bulk.

IPP Molecular Weights. M_wis proportional to the ratio of

propagation and termination rates. M_win Table 3 is lower for

all of the heterocenes than for 2, even in cases where the

activities are higher for the former, suggesting faster termination

rates for the heterocenes. It can be inferred from the inverse

dependence of M_won MAO and from M_wincreasing even as

(20) Ewen, J. A.; Elder, M. J. Makromol. Chem., Macromol. Symp. 1991,

66, 179.

(21) Guerra, G.; Longo, P.; Cavallo, L.; Corradini, P.; Resconi, L. J.

Am. Chem. Soc. 1997, 119, 4394.

4768 J. Am. Chem. Soc., Vol. 123, No. 20, 2001

Ewen et al.

are roughly Pyr ) 15, Tp )1.5, and Ind ) 0.4. The two Pyr

catalysts are about 3 times lower in enantiofacial selectivity and

3 times higher in regiospecificity than the more closely

equivalent Ind and Tp catalysts. A stronger effect of 2,1-units

than mrrm on T_mis seen when comparing the data for 2 (T_m)

156 °C, mrrm ) 0.2%, 2,1-units ) 0.5%) and 4 (T_m) 155 °C,

mrrm ) 1.4%, 2,1-units ) 0.1%). This effect on T_mwith

carbocene catalysts has been noted before.²²

The difference in steresopecificity between 3 and 4 is

attributed to a steric effect on stereoregulation. There is no

precedent for an effect on stereoregulation due to methyl

substitution at an analogously remote Cp position. However, φ

is predicted to be 20° higher for 4 compared to 3 due to the

5-methyl group, and the polymerization data show 4 with T_m

increased by 9 °C and mrrm decreased by 0.7% (Table 3). It

can be tentatively argued that with a larger φ an ortho-carbon

of the Ph ring is closer in proximity to the propylene methyl

group for the “wrong” preinsertion intermediates such as 5a

(Chart 4), making 4 more stereospecific than 3, with the caveat

that unknown ion-pairing effects on the preferred conformations

of the pendant phenyl groups are also likely (vide supra).

The stereospecificities for the Tp series are similar to those

of 2, follow the trend for increasingly large aryl groups at the

4-indenyl position,⁶and are in the order p-Xyl (99.5%) ≈ o-Tol

(99.4%) > Ph (99.2%), with the slightly higher stereospecificity

of 6 and 7 relative to 5 in accord once again with the 12° lower

φ for 5 than for 6 and 7 and the preferred conformation proposal

of Spaleck et al.⁶On the other hand, the higher stereospecifcity

for 5 as compared with that for 4 suggests an unprecedented

electronic effect because there are no structural differences

between the two to account for this. The differences in

regioregulation between the Pyr and Tp series may also be an

electronic effect. It has been suggested that the higher mrrm

placements and the lower 2,1-erythro (E) units in the Pyr

catalysts may reflect a more highly unsymmetrical metal-

propylene bonding since olefins coordinate to d⁰metal com-

plexes in an unsymmetrical fashion with buildup of positive

charge at C2. As this effect is enhanced, as might be the case

with stronger metal-olefin adducts, then there should be a

stronger electronic preference for 1,2-insertion and hence a lower

2,1-insertion tendency.^23,24

Figure 4. Thermal ellipsoid plot of 8‚0.5CH₂Cl₂. H atoms omitted

for clarity. Ellipsoids at 30% probability.

Chart 5

to test the theory that an ortho-carbon of the pendant Ph makes

contact with the propylene methyl and influences stereoselec-

tivity.

There is a strong steric driving force for the chain to return

to the uncrowded side of meso structures, where it has no

preferred chiral chain orientation and has no influence on

stereoselectivity.⁸Insertions are infrequent or do not occur at

all while the chain is at the highly crowded sides of C₁species,

even in bulk propylene.^9bThe complete regiospecificity of 8 is

consistent with the chain being on the less crowded side of the

catalyst during insertion since propylene rotation (Chart 4) is

inhibited for this arrangement.⁸Further, it is unlikely that

stereoregulation occurs with the chain-orientated mechanism

while the chain resides at the crowded side of 8 since this would

lead to hemi-isotactic (hit-PP) or an atactic/hemi-isotactic mixed

microstructure in the event of some intervening back-skip

reactions. It is reasoned that if 8 obeys the site-controlled model

rather than the hit-PP models,^11,26this would be evidence for

stereocontrol from the differences in the energies of the contacts

between the propylene methyl and the two phenyl rings

sandwiching the monomer. The proposed stereoselective 1,2-

insertion assembly for 8 and the enantiomorphic site control

microstructure for IPP are displayed in Chart 5 with the selection

of an S,si assembly on the basis that 2 is about 1% more

stereospecific than 4.

The slightly higher IPP T_mand enantioface selectivities

obtained with thiophene catalysts using Ph₃CB(C₆F₅)₄/TIBAL

as an activator (Table 6) compared with MAO (Table 3) are

consistent with anions having an influence on stereoregulation

despite their being present as olefin-separated ion pairs required

for chain growth.²⁵The IPP melting points increased to as high

as 166 °C with 6 under commercial polymerization conditions.

The reason for this effect is unproven, but the results are

consistent with cation/anion contacts with MAO^-and B(C₆F₅)₄

influencing φ differently and hence affecting the catalyst’s

stereospecificities and activities. The same phenomenon has

been previously noted for rac-Me₂Si(2-Me-4-(1-naphthyl)-

Ind)₂ZrCl₂at very low polymerization temperatures.^7c

Low Site Control Stereoregulation. Propylene polymeriza-

tions were conducted with pseudo-meso-8 (Figure 4) in order

(22) Haylock, J. C.; Phillips, R. A.; Wolkowitz, M. D. In Metallocene-

Based Polyolefins; Scheirs, J., Kamisnky, W., Eds.; John Wiley and Sons

Ltd.: Chichester, 2000; Vol. 2, p 333.

(23) We thank an anonymous reviewer for pointing this out.

(24) (a) Carpentier, J. F.; Wu, Z.; Chul, W. L.; Stro¨mberg, S.; Christopher,

J. N.; Jordan, R. F. J. Am. Chem. Soc. 2000, 122, 7750. (b) Carpentier, J.

F.; Maryin, V. P.; Lucy, J.; Jordan, R. F. J. Am. Chem. Soc. 2001, 123,

898.

The polymerization data with 8, the ¹³C NMR spectrum for

the 68% m polymer methyl region, and the fit of the pentads to

the enantiomorphic site pentad intensity equations²⁷are dis-

played in Figure 5. This is the first time all steric pentads have

been fit to the enantiomorphic site model. It is also the first

(25) Eisch, J. J.; Pombrik, S. L.; Zhang, G. X. Makromol. Chem.,

Macromol. Symp. 1993, 66, 109; Organometallics 1993, 12, 3856.

(26) Farina, M.; Di Silvestro, G.; Sozzani, P. Macromolecules 1982, 15,

1451.

Chiral Ansa Metallocenes

J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4769

1-Phenylpyrrole-2-carbaldehyde (9). POCl₃(107.3 g, 0.70 mol)

was added dropwise to 76 mL of DMF (71.7 g, 0.98 mol) and stirred

for 10 min. The temperature was lowered to 0 °C, and a solution of

1-phenylpyrrole (100 g, 0.70 mol) in 100 mL of dichloromethane was

added slowly. The viscous solution was slowly warmed to 50 °C and

stirring continued for 1 h. After being cooled to room temperature, the

flask was opened to the air and charged with 750 g of crushed ice. A

20 wt % solution of NaOH (885 mL) was added cautiously, and the

mixture was immediately heated to 85-90 °C and stirred for 10 min.

The solvent was distilled off in the process. The flask was placed in

an ice bath and cooled to room temperature, and the reaction mixture

was extracted with dichloromethane (2 × 200 mL). The combined

organic fractions were washed with water and dried (MgSO₄). Evapora-

tion of the solvent yielded 114 g of product as an orange oil containing

ca. 10% of the 1-phenylpyrrole-3-carbaldehyde isomer. The product

was used without further purification. ¹H NMR (CDCl₃): δ 9.5 (s, 1H),

7.4 (m, 3H), 7.3 (m, 2H), 7.1 (dd, 1H), 7.0 (t, 1H), 6.35 (dd, 1H). ¹³

NMR (CDCl₃): δ 178.1, 138.1, 131.9, 130.4, 128.4, 127.5, 125.4, 121.3,

110.3. EIMS: m/z (relative intensity) 171 (M⁺, 100), 154 (7), 142 (8),

115 (50), 93 (42), 77 (16).

Ethyl (2Z)-2-Methyl-3-[1-phenylpyrrol-2-yl]prop-2-enoate (10).

A solution of triethyl 2-phosphonopropionate (153 mL, 0.714 mol) in

75 mL of THF was added slowly to a mixture of sodium hydride (24.3

g, 1.0 mol) in 60 mL of THF at 0 °C. The slurry was warmed to room

temperature and stirred for 1 h. The temperature was lowered to -10

oC, and a solution of 9 (113 g, 0.665 mol) in 200 mL of THF was

added dropwise. The reaction mixture was warmed to room temperature

over 30 min, resulting in a thick precipitate. A saturated aqueous

solution of NH₄Cl (100 mL) was added cautiously, giving a two-phase

solution. THF was distilled off, and the crude product was extracted

with ether (2 × 200 mL). The ether extract was washed with brine

solution and dried (MgSO₄). The solvent was evaporated, and the crude

product was washed with hexane to give the product as a white

Figure 5. ¹³C NMR spectrum of the methyl pentad region of isotactic

polypropylene produced with an activity of 138 kg g-cat^-1h^-1in bulk

for 1 h at 50 °C by pseudo-meso 8, and the fit of the pentad intensities

to the enantiomorphic site model.

instance we are aware of with stereoregulation for a catalyst

with all the stereodirecting groups on the same side. The modest

degree of site control stereoregulation for 8 is consistent with

the small differences in stereoselectivities for 2 and 4. In light

of these results and the failure of both the hit-PP model and a

mixed hit-PP/APP model, the hypothesis of the influence of an

ortho-carbon on the pendant phenyls contacting the monomer

methyl group to give some degree of stereocontrol seems

reasonable.

crystalline solid. Yield: 89% (151 g). H NMR (CDCl₃): δ 7.4 (m,

4H), 7.3 (m, 2H), 7.0 (dd, 1H), 6.7 (dd, 1H), 6.4 (t, 1H), 4.1 (q, 2H),

2.2 (s, 3H), 1.2 (t, 3H). ¹³C NMR (CDCl₃): δ 168.6, 139.0, 129.4,

129.0, 127.3, 126.1, 126.0, 124.8, 122.8, 114.1, 109.9, 60.2, 14.1.

EIMS: m/z (relative intensity) 255 (M⁺, 50), 226 (5), 210 (23), 182

(100), 167 (47), 154 (12), 115 (7), 77 (18). Mp: 73 °C.

Experimental Section

General Procedures. All manipulations with air-sensitive materials

were performed under a nitrogen atmosphere using standard Schlenk

techniques and a Vacuum Atmospheres drybox (except polymerizations,

which were conducted using argon as the inert gas). THF, ether, and

toluene were distilled from sodium/benzophenone, pentane was distilled

from sodium/benzophenone/triglyme, and dichloromethane was distilled

from CaH₂and stored over 4-Å molecular sieves. Mass spectra of

organic intermediates were measured with a Hewlett-Packard 6890

series gas chromatograph equipped with a 5973 mass-selective detector

(EI, 70 eV). Mass spectra of zirconocenes were measured on a Hewlett-

Packard quadrupole 5889B series, using a direct insetion probe (DIP)

in electron impact (EI) mode. Scan parameters were set from mass

100 to 800. Samples were prepared under a nitrogen atmosphere,

inserted in the DIP, and heated from 30 to 300 °C at 20 °C/min. The

source and quadrupole were heated at 300 and 150 °C, respectively.

NMR spectra of organic and organometallic compounds were recorded

on a Varian Unity-300 NMR spectrometer at ambient probe temper-

ature. ¹H and ¹³C NMR chemical shifts are reported relative to SiMe₄.

Melting points are uncorrected. Elemental analyses were performed

by Oneida Research Services, Whitesboro, NY. rac-{(2-Me-4-Ph-1-

indenyl)₂SiMe₂}ZrCl₂(2) was purchased from Boulder Scientific Co.

{(2,5-Me₂-1-Ph-cyclopento[3,2-b]pyrrol-4-yl)₂SiMe₂}ZrCl₂(4) and {(2,5-

Me₂-1-Ph-cyclopento[3,2-b]pyrrol-4-yl)(2-Me-4-Ph-inden-1-yl)SiMe₂}-

ZrCl₂(8) were prepared by literature methods.⁹Super PPA²⁸was

(typically) prepared by stirring 164.3 g of P₂O₅in 975.7 g of commercial

polyphosphoric acid (Aldrich Chemical Co.) at 140 °C until all P₂O₅

dissolved.

Ethyl 2-Methyl-3-[1-phenylpyrrol-2-yl]propanoate (20). A mixture

of 10 (55 g, 0.22 mol) and 10% Pd/C (2.3 g) in 300 mL of

dichloromethane was stirred under 80 psig of hydrogen for 4 h. After

the catalyst was filtered off and washed with dichloromethane, solvent

was removed on a rotary evaporator to give the product. Yield: 54 g

(97%). H NMR (CDCl₃): δ 7.4 (m, 3H), 7.2 (m, 2H), 6.7 (m, 1H),

6.1 (m, 1H), 6.0 (m, 2H), 4.0 (q, 2H), 2.9 (m, 1H), 2.5 (m, 2H), 1.2 (t,

3H), 1.0 (d, 3H). ¹³C NMR (CDCl₃): δ 175.6, 128.9, 127.0, 126.0,

121.8, 107.8, 60.0, 39.3, 30.3, 16.7, 13.9. EIMS: m/z (relative intensity)

257 (M⁺, 9), 216 (7), 184 (6), 146 (100), 77 (16).

2-Methyl-3-[1-phenylpyrrol-2-yl]propanoic Acid (11). The ester

20 (42.1 g, 0.164 mol) was treated with 78 mL of Claisen’s reagent

and heated to 90-95 °C. After being stirred for 1 h, the solution was

poured onto crushed ice and acidified to pH 1-2 with 6 N HCl. The

precipitated free acid was extracted with ether (2 × 200 mL), washed

with brine solution, and dried (MgSO₄). Ether was removed from the

product by rotary evaporation. Yield: 27.9 g (75%). ¹H NMR

(CDCl₃): δ 7.2-7.6 (m, 5H), 6.7 (d, 1H), 6.2 (t, 1H), 6.1 (d, 1H), 3.0

(m, 1H), 2.6 (m, 2H), 1.1 (d, 3H).

5-Methyl-1-phenyl-5,6-dihydrocyclopenta[1,2-b]pyrrol-4-one (12).

A solution of 11 (43 g, 0.188 mol) in 75 mL of dichloroethane was

added dropwise to 1000 g of super PPA at 100 °C. After being stirred

for 5 h, the mixture was cooled to 60 °C and poured slowly onto crushed

ice. The product was extracted with 30% (v/v) dichloromethane in

hexane (2 × 200 mL). The combined organic fractions were washed

with a saturated aqueous solution of NaHCO₃and dried (MgSO₄).

Solvents were removed on a rotary evaporator, leaving the product as

a tan solid. Yield: 37 g (93%). ¹H NMR (CDCl₃): δ 7.5 (m, 2H), 7.4

(m, 3H), 7.1 (d 1H), 6.4 (d, 1H), 3.3 (dd, 1H), 3.0 (m, 1H), 2.6 (dd,

1H), 1.3 (d, 3H). ¹³C NMR (CDCl₃): δ 199.6, 156.6, 138.8, 129.8,

129.2, 127.9, 127.2, 122.0, 104.1, 47.5, 30.8, 17.1. EIMS: m/z (relative

(27) (a) Doi, Y. Makromol. Chem., Rapid Commun. 1982, 3, 635. (b)

Inoue, Y.; Itabashi, Y.; Chujo, R.; Doi, Y. Polymer 1984, 25, 164. (c)

Sheldon, R. A.; Fueno, T.; Tsunetsugu, T.; Furukawa, J. J. Polym. Sci.

1965, 3, 23; 1969, 7, 763. (d) Furukawa, J. Polym. Prepr. 1969, 8, 39.

(28) Bailey, D.; DeGrazia, C.; Lape, H.; Frering, R.; Fort, D.; Skulan,

T. J. Med. Chem. 1973, 16, 151.

4770 J. Am. Chem. Soc., Vol. 123, No. 20, 2001

Ewen et al.

intensity) 211 (M ⁺, 100), 196 (55), 182 (33), 167 (27), 154 (12), 120

(23), 105 (38), 77 (46). Mp: 120 °C.

free-flowing tan powder. ZrCl₄(2.09 g, 9.0 mmol) was added to the

flask, and the contents were stirred overnight in a mixture of pentane

(75 mL) and ether (1.5 mL). The solids were collected on a closed frit

funnel, washed with pentane, and dried under vacuum, giving an orange

solid (5.9 g). A portion of the crude product (5.65 g) was stirred in

dichloromethane (75 mL) and filtered. The filtrate was concentrated

to a small volume, and pentane was added to precipitate the complex.

Yield: 4.1 g (79%, 50/50 rac/meso). Crystals of the rac isomer were

obtained by slow evaporation of a dichloromethane/toluene solution

Tosyl Hydrazone of 5-Methyl-1-phenyl-5,6-dihydrocyclopenta-

[1,2-b]pyrrol-4-one (21). The ketone 12 (36 g, 0.171 mol), p-

toluenesulfonhydrazide (33 g, 0.177 mol), and p-toluenesulfonic acid

monohydrate (6.6 g, 0.035 mol) were stirred in 220 mL of ethanol at

70 °C for 16 h. After the solution was cooled to room temperature and

left to stand for several hours, the precipitated product was collected

on a filter funnel, washed with ether, and dried under vacuum. Solvents

were evaporated from the filtrate, and additional product was obtained

by trituration of the residue with toluene. A tan solid was recovered.

of the rac/meso complex. H NMR (CD₂Cl₂): δ 7.3-7.5 (m, 8H, rac

and meso), 7.38 (d, J ) 3.5 Hz, 2H, rac), 7.15-7.25 (m, 2H, rac and

meso), 7.12 (d, J ) 3.5 Hz, 2H, meso), 6.45 (s, 2H, rac), 6.4 (s, 2H,

meso), 6.32 (d, J ) 3.5 Hz, 2H, rac), 6.2 (d, J ) 3.5 Hz, 2H, meso),

2.4 (s, 6H, meso), 2.2 (s, 6H, rac), 1.125 (s, 3H, meso), 1.118 (s, 3H,

meso), 1.10 (s, 6H, rac). Anal. Calcd for C₃₀H₂₈Cl₂N₂SiZr: C, 59.38;

H, 4.65. Found: C, 59.78; H, 4.74.

Yield: 58.9 g (91%). H NMR (CDCl₃): δ 7.9 (d, 2H), 7.1-7.6 (m,

7H), 7.1 (d, 1H), 6.7 (d, 1H), 3.5 (m, 1H), 3.2 (dd, 1H), 2.6 (dd, 1H)

2.4 (s, 3H), 1.3 (d, 3H). ¹³C NMR (CDCl₃): δ 162.2, 147.0, 143.5,

138.9, 135.5, 129.7, 129.2, 128.1, 126.9, 126.3, 121.8, 121.4, 105.5,

42.8, 32.4, 21.5, 19.7. Mp: 186 °C (dec).

3-Bromo-2-methylthiophene (14). To a solution containing 62.0 g

(610 mmol, 88 mL) of diisopropylamine dissolved in 150 mL of THF

was added 210 mL of n-butyllithium in hexanes (2.5 M, 610 mmol)

while the temperature was maintained at 0 °C. After addition was

complete, stirring continued for an additional 30 min. The flask

containing lithium diisopropylamide (LDA) was cooled to -78 °C,

and then a solution containing 100 g (610 mmol) of 3-bromothiophene

dissolved in THF (60 mL) was added dropwise. After addition was

complete, the solution was warmed to 0 °C (ice bath) and stirred an

additional 30 min. The temperature of the reaction slurry was lowered

to -78 °C, and a solution containing 86.5 g (610 mmol) of iodomethane

dissolved in 40 mL of THF was added in one portion. The reaction

mixture was stirred an additional 30 min at -78 °C and then warmed

to room temperature and stirred for 1 h. The organic layer was collected

with ether, washed with water, dried over magnesium sulfate, and

filtered, and then solvents were removed in vacuo. A light orange oil

was recovered. Yield: 89.8 g (74.8%), 90.7% by GC. ¹H NMR

(CDCl₃): δ 7.1 (d, 1H), 6.9 (d, 1H) 2.4 (s, 3H). ¹³C NMR (CD₂Cl₂):

δ 134.6, 130.3, 123.3, 109.8, 14.8. EIMS: m/z (relative intensity) 176,

178 (M⁺, 57), 97 (100), 81 (4), 69 (12), 53 (14).

5-Methyl-1-phenyl-4-hydrocyclopenta[2,1-b]pyrrole (13). To a

solution of the tosylhydrazone 21 (32.5 g, 0.086 mol) in THF (200

mL) was added 76 mL of n-butyllithium in hexanes (2.5 M, 0.189 mol)

at -78 °C. The reaction mixture was slowly warmed to room

temperature and stirred for 16 h. A saturated aqueous solution of NH₄-

Cl (20 mL) was added dropwise, and the organic solvents were distilled

off. Water (100 mL) was added, and the mixture was extracted with

ether (2 × 100 mL). The combined ether fractions were dried (MgSO₄),

and the solvent was removed on a rotary evaporator. The brown oily

residue was stirred vigorously with hexane (150 mL) for 1 h. The

insoluble products were removed by filtration, and the hexane was

evaporated, giving the product as a light yellow oil. Yield: 12 g (72%).

Two isomers were recovered. H NMR (CDCl₃): δ 7.5 (m, 4H), 7.3

(m, 1H), 7.1 (d, 1H), 7.0 (d, 1H), 6.6 (s, 1H), 6.4 (s, 1H) 6.3 (d, 1H),

6.2 (d, 1H), 3.3 (s, 1H), 3.1 (s, 1H), 2.2 (s, 3H), 2.17 (s, 3H). EIMS:

m/z (relative intensity) 195 (M ⁺, 100), 180 (28), 167 (7), 152 (10),

139 (2), 127 (3), 116 (3), 91 (12), 77 (8).

(5-Me-1-Ph-4-hydrocyclopenta[3,2-b]pyrrol-4-yl)SiMe₂Cl (22). A

solution of 13 (11.2 g, 0.057 mol) in 100 mL of ether was treated with

28 mL of n-butyllithium in hexanes (2.5 M, 0.070 mol) at -10 °C and

stirred at room temperature for 16 h. Pentane (50 mL) was added to

the reaction mixture, the precipitated lithium salt was allowed to settle,

and the liquid was removed with a filter stick. The precipitate was

redissolved in ether (150 mL) and cooled to -78 °C, and dichlorodi-

methylsilane (10.5 mL, 0.086 mol) was added by syringe. The reaction

mixture was warmed to room temperature and then refluxed for 2 h.

After the mixture was cooled and filtered, volatiles were removed from

the filtrate in vacuo (100 mTorr, 40 °C), giving the product as a colorless

2-Methyl-3-phenylthiophene (15). To a slurry containing 14 (89.8

g, 460 mmol) and 1 g of [bis(diphenylphosphino)propane)]dichloronickel

(Ni(dppp)Cl₂) in 200 mL ether was added 152 mL of phenylmagnesium

bromide in ether (3 M, 456 mmol) dropwise. After addition was

complete, the reaction flask was stirred for 1 h, and the reaction was

quenched with water. The organic fraction was extracted with dichlo-

romethane, washed with water, and dried over magnesium sulfate, and

then the solvents were removed in vacuo. A dark orange oil was

recovered. Yield: 77.13 g (84.7%), 87.2% by GC. H NMR (ppm,

oil. Yield: 12.7 g (77%). H NMR (CD₂Cl₂): δ 7.5 (m, 4H), 7.3 (m,

CDHCl₂): δ 7.3-7.6 (m, 5H), 7.1-7.25 (m, 2H), 2.6 (s, 3H). ¹³C NMR

(CD₂Cl₂): δ 139.1, 137.2, 134.6, 129.6, 129.2, 129.1, 128.9, 128.8,

127.7, 127.5, 127.1, 122.0, 14.4. EIMS: m/z (relative intensity) 176

(6), 175 (18), 174 (100), 173 (98), 172 (6), 171 (14), 158 (2), 147 (9),

141 (15), 135 (4), 129 (18) 115 (15).

1H), 7.0 (d, 1H), 6.6 (s, 1H), 6.3 (d, 1H), 3.3 (s, 1H), 2.3 (s, 3H), 0.5

(s, 3H) 0.1 (s, 3H). ¹³C NMR (CD₂Cl₂): δ 144.9, 129.9, 125.5, 121.1,

120.6, 117.9, 106.2, 45.0, 18.0, 0.95, -1.25.

(5-Me-1-Ph-4-hydrocyclopenta[3,2-b]pyrrol-4-yl)₂SiMe₂(23). A

solution of 13 (4.7 g, 24 mmol) in 60 mL of ether was treated with

11.2 mL of n-butyllithium in hexanes (2.5 M, 28 mmol) and stirred

for 16 h. Pentane (50 mL) was added, and the slurry was filtered through

a closed frit funnel. The tan lithium salt was redissolved in 50 mL of

THF, cooled to -78 °C, and treated with chlorosilane 22 (6.7 g, 24

mmol) dissolved in 50 mL of THF. The dark brown solution was slowly

warmed to 50 °C and stirred for 16 h. Volatiles were removed in vacuo,

and the residue was extracted with dichloromethane to remove LiCl.

Evaporation of the solvent gave the product as a white solid. Yield:

2,5-Dimethyl-3-phenyl-5,6-dihydrocyclopenta[1,2-b]thiophen-4-

one (16). A solution containing 15 (124.7 g, 542 mmol), methacrylic

acid (61.7 g, 715 mmol), and 200 mL of dichloromethane was added

slowly to 1000 g of super PPA with stirring at 70 °C. The flask and

contents were refluxed for 10 h, with an additional 208 g of methacrylic

acid in 250 mL of dichloromethane added in 60- or 75-g portions during

the reaction. After being stirred for 10 h, the reaction mixture was

poured onto ice. The organic layer was collected with 20% (v/v)

dichloromethane in hexane and washed with water, a saturated solution

of sodium hydrogen carbonate, and then water again. The organic layer

was dried over magnesium sulfate and filtered, and then solvents were

removed in vacuo, leaving a dark brown oil. Yield: 202.9 g (81.7%

by GC, 95.6%), used in subsequent steps without additional purification.

8.5 g (81%). Two isomers were recovered. H NMR (CD₂Cl₂): δ 7.5

(m, 8H), 7.25 (m, 2H), 7.05 (d, 1H), 6.95 (d, 1H), 6.6 (s, 2H), 6.5 (d,

1H), 6.3 (d, 1H), 3.45 (s, 2H), 2.3 (s, 3H), 2.2 (s, 3H), -0.20 (s, 3H),

-0.22 (s, 3H). ¹³C NMR (CD₂Cl₂): δ 146.3, 146.2, 141.3, 140.7, 130.3,

129.9, 125.2, 120.9, 120.2, 120.1, 117.0, 106.4, 106.2, 42.8, 42.5, 18.3,

18.25, -6.9, -7.2. EIMS: m/z (relative intensity) 446 (M ⁺, 18), 252

(100), 237 (8), 224 (7), 194 (7), 165 (3).

{Me₂Si(5-Me-1-Ph-cyclopento[3,2-b]pyrrol-4-yl)₂}ZrCl₂(3). A

solution of 23 (4.0 g, 9.0 mmol) in 100 mL of ether was cooled to

-78 °C, treated with 8.0 mL of butyllithium in hexanes (2.5 M, 20

mmol), and warmed to room temperature. After the solution was stirred

overnight, the pressure was reduced to evaporate the solvents. The

residue was washed with pentane (40 mL) and dried in vacuo to a

Note: Two isomers of 16 were recovered in a ratio of 3:1. H NMR

(CD₂Cl₂): δ 7.05-7.4 (m, 5H), 2.6-3.0 (m, 2H), 2.3 (s, 3H), 1.7-

1.85 (m, 1H), 1.1 (d, 3H). ¹³C NMR (CD₂Cl₂): δ 199.9, 167.6, 152.1,

136.5, 134.6, 130.4, 129.6, 139.4-127.1, 46.5, 33.8, 17.1, 17.0, 16.2.

EIMS: m/z (relative intensity) 242 (100), 227 (54), 214 (10), 213 (17),

199 (38), 185 (21), 184 (11), 165 (14), 152 (8), 139 (4), 128 (5), 115

(12).

2,5-Dimethyl-3-phenyl-4,5,6-trihydrocyclopenta[1,2-b]thiophen-

Chiral Ansa Metallocenes

J. Am. Chem. Soc., Vol. 123, No. 20, 2001 4771

4-ol (17). A 1.0 M solution of lithium aluminum hydride in ether (300

mmol, 300 mL) was added dropwise at 0 °C to 202 g of 16 dissolved

in 300 mL of THF. After addition was complete, the temperature of

the reaction flask was raised to room temperature, and then the solution

was stirred an additional 2 h. The reaction was quenched with water,

the organic layer was collected with ether, washed with water, dried

over magnesium sulfate, and filtered, and then the solvents were

removed in vacuo. Multiple isomers of the product were recovered.

An additional 16 g of material was recovered by repeated washing of

the lithium prill. The product was recovered as a yellow solid Yield:

139.1 (75%), 78.5% by GC, used in subsequent steps without additional

{Me₂Si(2,5-Me₂-3-Ph-cyclopento[2,3-b]thiophen-6-yl)₂}ZrCl₂(5).

To a solution containing 1.82 g (3.6 mmol) of 24 slurried in 100 mL

of diethyl ether was added a 2.5 M solution of n-butyllithium in hexane

(2.9 mL, 7.2 mmol) dropwise at room temperature. Stirring was

continued for 5 h, and then 0.83 g (3.6 mmol) of zirconium tetrachloride

was added slowly as a dry powder. The reaction mixture was stirred

an additional 3 h, and then the solution was filtered. The solids collected

in this fashion were washed with ether, and then the solvents were

removed in vacuo, leaving 770 mg of a 3:5 rac/meso mixture. The

solids remaining on the filter were then slurried in dichloromethane

and filtered, and the solvents were removed from the solution in vacuo.

A 350 mg amount of pure rac isomer was recovered. Yield: 1.12 g

purification. H NMR (CD₂Cl₂): δ 7.2-7.8 (m, 4H), 4.9 (0.5H), 4.8

(0.5H), 2.6-3.2 (m, 3H), 2.4-2.6 (m, 3H), 1.1-1.3 (m, 3H). ¹³C NMR

(CD₂Cl₂): δ 146.8, 140.2, 136.4, 129.5, 129-127, 80.8, 74.4, 73.7,

49.0, 43.9, 35.7, 35.4, 35.2, 19.4, 15.3, 15.27, 14.7. EIMS: m/z (relative

intensity) 244 (100), 229 (48), 211 (26), 201 (21), 188 (10) 187 (12),

185 (15), 184 (14), 178 (16), 171 (13), 167 (12), 165 (16), 153 (11),

152 (13), 115 (17).

(47%). H NMR (CD₂Cl₂): δ 7.25-7.6 (m, 10H, rac), 6.58 (s, 2H,

rac), 2.55 (s, 3H, rac), 2.3 (s, 3H, rac), 1.05 (s, 6H, rac). ¹³C NMR

(CD₂Cl₂): δ 168.8, 147.6, 145.3, 135.5, 135.4, 129.95, 129.47, 128.2,

119.0, 85, 19.9, 16.0, 0.0. EIMS: m/z 669 (M^•++ 1 of theo).

2-Methyl-3-(2-methylphenyl)thiophene (25). An ether solution of

o-tolylmagnesium bromide (350 mL, 2.0 M, 0.7 mol) was added slowly

to a mixture of 3-bromo-2-methylthiophene, 14 (123 g, 0.7 mol), and

1.2 g of Ni(dppp)Cl₂in 50 mL of ether. After the mixture was stirred

overnight, water (200 mL) was added slowly to the reaction mixture

at room temperature. The organic layer was separated, washed with

brine solution (100 mL), and dried (MgSO₄). Solvents were removed