Synthesis of Novel Group 4 Complexes Bearing the Tropidinyl Ligand: Investigations of Dynamic Behavior, Reactivity, and Catalytic Olefin Polymerization

1406

Organometallics 2000, 19, 1406-1421

Syn th esis of Novel Gr ou p 4 Com p lexes Bea r in g th e

Tr op id in yl Liga n d : In vestiga tion s of Dyn a m ic Beh a vior ,

Rea ctivity, a n d Ca ta lytic Olefin P olym er iza tion

Steven J . Skoog, Cristina Mateo, Gino G. Lavoie, Frederick J . Hollander, and

Robert G. Bergman*

Department of Chemistry, University of California, Berkeley, California 94720

Received J anuary 18, 2000

A new class of group 4 complexes bearing the tropidinyl (Trop) ligand were synthesized.

This novel anionic ligand, easily derived from the natural product tropine, is regarded as

an analogue of the well-studied Cp ligand (Cp ) cyclopentadienyl) and features a bicyclic

ring system in which an allyl function donates 4π electrons and an amine function donates

2σ electrons to the metal center. The synthesis of the group 4 complexes involved

transmetalation of a stannylated allyl functionality with a group 4 metal halide with

concomitant elimination of Me₃SnCl. Reaction of endo-stannylated tropidine (1) and ZrCl₄,

CpZrCl₃, or CpTiCl₃afforded the complexes (Trop)₂ZrCl₂(2), (Cp)(Trop)ZrCl₂(3), and (Cp)-

(Trop)TiCl₂(4), respectively. These dihalide complexes were alkylated using methyllithium

to generate (Trop)₂ZrMe₂(5), (Cp)(Trop)ZrMe₂(6), (Cp)(Trop)TiMe₂(7), or benzylmagnesium

chloride to give (Trop)₂ZrBn₂(8) and (Cp)(Trop)ZrBn₂(9). Complexes 2, 3, 5, and 8 were

characterized by X-ray crystallography. Complexes 5 and 6 were observed to undergo

protonolysis with various acids (HA) to give mixed [Zr]MeA complexes. Reaction of complex

6 with isonitriles (ArNC) gave the η²-iminoacyl complex (Cp)(Trop)ZrMe[N(Ar)CMe] (13),

whose structure was confirmed by X-ray crystallography. All the complexes displayed

dynamic behavior, and the various exchange processes were investigated by variable-

temperature NMR spectroscopy. The dihalide complexes 2, 3, and 4 in the presence of

modified methylaluminoxane (MMAO) were active catalysts for the polymerization of

ethylene. The catalyst system 3/MMAO displayed a very high ethylene polymerization activity

and was similar to that observed for Cp₂ZrCl₂/MMAO. High molecular weight polypropylene

was generated using 4/MMAO, and polypropylene oligomer was obtained using 3/MMAO.

The cationic complex [(Cp)(Trop)ZrMe][MeB(C₆F₅)₃] (14) was formed upon reaction of the

dimethyl complex 6 with B(C₆F₅)₃and was shown to be an active ethylene polymerization

catalyst.

In tr od u ction

referred to as the “wedge”. The shape of the wedge is

thought to influence the selectivity of the olefin in-

sertion.^6-8A wide variety of structural modifications

have been carried out on this stable framework in order

to enhance the polymerization activity and/or selectivity

of these catalysts.⁹These include use of so-called

“constrained geometry” catalysts to generate isotactic¹⁰

or syndiotactic¹¹polypropylene (PP) and nonbridged

oscillating metallocene catalysts to make elastomeric

stereoblock PP.^12,13

When metallocene-based group 4 complexes of type

A (shown below) are activated with appropriate cocata-

lysts, they form extremely active olefin polymerization

catalysts.^1-3These are thought to act as “single-site”

(5) Albright, T. A.; Burdett, J . K.; Whangbo, M.-H. Orbital Interac-

tions in Chemistry; J ohn Wiley & Sons: New York, 1985.

(6) Pino, P.; Cioni, P.; Wei, J . J . Am. Chem. Soc. 1987, 109, 6189.

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

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

catalysts that generate well-defined polymers from

ethylene and other R-olefins. One attractive feature of

metallocene catalysts is that they are structurally well

defined, with two bent Cp ligands⁴and the L groups

forced to lie in a common plane⁵that is commonly

(11) 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.

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Soc. 1995, 117, 11586.

(1) Kaminski, W. J . Chem. Soc., Dalton Trans. 1998, 1413.

(2) Brintzinger, H. H.; Fischer, D.; Mu¨lhaupt, R.; Reiger, B.;

Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1443.

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Publication on Web 03/09/2000

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1407

Sch em e 1

More recently, attention has been drawn to isoelec-

tronic “nonmetallocene”-based catalysts.¹⁴In particular,

ansa-monocyclopentadienylamido group 4 catalysts were

found to be highly active polymerization catalysts and

are being commercially developed.¹⁵These new com-

plexes contain metal-nitrogen or metal-oxygen bonds

and allow for the generation of polymers with novel

microstructures or lead to more robust catalyst systems.

Examples of these nonmetallocene group 4 complexes

include monoanionic allyl,¹⁶amidinate,^17-19amide,^20-26

alkoxy,^27-29phosphinimide,^30,31and boratabenzene frame-

works,^32-36macrocyclic,^37,38tris(pyrazolyl)borate,³⁹and

oxazoline⁴⁰ligand systems, in addition to dianionic car-

borane,⁴¹dienyl,^42,43and trimethylenemethane⁴⁴ligands.

In a previous communication, we reported the syn-

thesis, reactivity, and olefin polymerization catalysis of

zirconium complexes shown above, bearing two tropidi-

nyl (Trop) ligands (B where L′ ) Trop).⁴⁵This new

ligand is isoelectronic to but less symmetric than the

Sch em e 2^a

a

(a) H₂SO₄/AcOH, 160 °C; (b) t-BuLi, pentane, < -100 °C;

(c) Me₃SnCl, -100 to RT.

Cp ligand and features a split 4π + 2σ electron donor

set.⁴⁶The presence of a two-carbon bridge helps to

localize the allyl functionality in a specific part of the

molecule, and loss of the ligand by â-hydride elimination

to form a bridgehead olefin is energetically unfavorable

(Bredt’s rule).^47-49In this contribution, we present the

synthesis, characterization, reactivity, and catalytic

properties of group 4 complexes bearing both one and

two Trop ligands.

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1995, 14, 2106.

Syn th esis a n d Ch a r a cter iza tion of Tr op id in yl-

Su bstitu ted Meta l Ha lid es. The preparation of all

dichloride complexes prepared in this study utilized the

methodology outlined in Scheme 1. Treatment of the

appropriate group 4 metal chloride with the stannylated

compound 1 affords the coordinated tropidinyl complex

and Me₃SnCl. The tin reagent 1 can be accessed from

tropine via tropidine⁵⁰in two steps as previously

reported and is illustrated in Scheme 2.⁴⁵

Addition of 2 equiv of 1 to a suspension of ZrCl₄in

CH₂Cl₂at room temperature immediately gave an

orange solution of (Trop)₂ZrCl₂(2); the complex was

isolated in 46% yield (eq 1). Orange crystals were grown

(19) Volkis, V.; Shmulinson, M.; Averbuj, C.; Lisovoskii, A.; Edel-

mann, F. T.; Eisen, M. S. Organometallics 1998, 17, 3155.

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H. Organometallics 1996, 15, 2672.

(24) Warren, T. H.; Schrock, R. R.; Davis, W. M. Organometallics

1998, 17, 308.

(25) Baumann, R.; Davis, W. M.; Schrock, R. R. J . Am. Chem. Soc.

1997, 119, 3830.

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J .; Howard, P. Chem. Commun. 1998, 313.

(27) van der Linden, A.; Schaverien, C. J .; Meijboom, N.; Ganter,

C.; Orpen, A. G. J . Am. Chem. Soc. 1995, 117, 3008.

(28) Mitani, M.; Oouchi, K.; Hayakawa, M.; Yamada, T.; Mu-

kaiyama, T. Polym. Bull. 1995, 34, 199.

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Organometallics 1996, 15, 5069.

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X.; Brown, S. J .; Swabey, J . W.; Wang, Q.; Xu, W.; Zoricac, P.; Harrison,

D. G. Organometallics 1999, 18, 2046.

(31) Stephan, D. W.; Stewart, J . C.; Guerin, F.; Spence, R. E. v. H.;

Xu, W.; Harrison, D. G. Organometallics 1999, 18, 1116.

(32) Rogers, J . S.; Lachicotte, R. J .; Bazan, G. C. J . Am. Chem. Soc.

1999, 121, 1288.

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1998, 120, 6037.

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1997, 119, 9305.

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Organometallics 1998, 17, 382.

by slow cooling of a saturated toluene solution, and the

solid-state structure was determined by X-ray crystal-

lography. The ORTEP diagram of this complex is shown

in Figure 1. Crystal data and selected bond lengths and

angles are provided in Tables 1 and 2, respectively. In

the solid state 2 has a C₁-symmetric structure in which

one Trop ligand is rotated 76.86° with respect to the

second. Two different orientations of the Trop ligand

with respect to the Cl ligands are observed in this

structure. One Trop ligand is bound symmetrically and

(39) Nakazawa, H.; Irai, S.; Imaoka, K.; Kai, Y.; Yano, T. J . Mol.

Catal. 1998, 132, 33.

(40) Cozzi, P. G.; Gallo, E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.

Organometallics 1995, 14, 4994.

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Soc. 1991, 113, 1455.

(42) J ime´nez-Pindado, G.; Thorton-Pett, M.; Bochmann, M. J . Chem.

Soc., Dalton Trans. 1997, 3115.

(43) Hessen, B.; van der Heijden, H. J . Am. Chem. Soc. 1996, 118,

11670.

(45) Lavoie, G. G.; Bergman, R. G. Angew. Chem., Int. Ed. Engl.

1997, 36, 2450.

(46) Blu¨mel, J .; Hertkorn, N.; Kanellakopulos, B.; Ko¨hler, F. H.;

Lachmann, J .; Mu¨ller, G.; Wagner, F. E. Organometallics 1993, 12,

3896.

(47) Shea, K. J . Tetrahedron 1980, 30, 1683.

(48) Buchanan, G. L. Chem. Soc. Rev. 1974, 3, 41.

(49) Ko¨brich, G. Angew. Chem., Int. Ed. Engl. 1973, 12, 4.

(50) Ladenburg, A. Liebigs Ann. Chem. 1888, 217, 118.

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1408 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

is oriented symmetrically with respect to the Cl ligands.

The molecules in the crystal are located on a crystal-

lographic mirror plane that passes through the zirco-

nium center and bisects both the Cp and Trop ligands.

The average Zr-C bond distance for the allyl group is

2.499(8) Å and is similar to the average Zr-C bond

distance in zirconocene dichloride (2.49 Å).⁵⁴The Zr-

Cp centroid distance was 2.2123(6) Å and is similar to

that observed in Cp₂ZrCl₂(2.20 Å).⁵⁴The Cl-Zr-Cl

bond angle is more obtuse (104.45(6)°) than that ob-

served for Cp₂ZrCl₂(97.1°).⁵⁴

Titanium complex 4 was also synthesized (97% yield)

using the methodology illustrated in eq 2 (M ) Ti). The

¹H NMR spectra in CD₂Cl₂at 20 °C exhibited two Cp

signals indicating the presence of two isomers 4a and

4b in a 5:3 ratio.

F igu r e 1. ORTEP diagram of (Trop)₂ZrCl₂(2).

Syn th esis a n d Ch a r a cter iza tion of Dia lk yl Com -

p lexes. Preparation of the dialkyl complexes was per-

formed by adding 2 equiv of the appropriate organolith-

ium or benzylmagnesium chloride reagent to a suspen-

sion of the dichloride complex in Et₂O as shown in eq

3. The products could be isolated by repeated extraction

bisects the two chlorine atoms in the wedge, while the

second Trop ligand is oriented unsymmetrically. The

symmetrically bound Trop ligand has similar terminal

allyl Zr-C bond distances (Zr-C1 ) 2.537(3) Å, Zr-C3

) 2.523(3) Å). The allylic C-C bond distances are nearly

identical (C1-C2 ) 1.392(4) Å and C2-C3 ) 1.400(5)

Å). Similar observations were made in structures of

metal complexes containing symmetric π-allyl ligands⁵¹

and other types of bicyclic split 4π + 2π electron ligands

in late metal systems.^46,52,53The allylic functionality of

the unsymmetrically oriented Trop ligand was more

distorted, with the terminal Zr-C and allylic C-C bond

distances unequal: Zr-C9 ) 2.493(3) Å, Zr-C11 )

2.595(3) Å, C9-C10 ) 1.411(4) Å, and C10-C11 )

1.374(4) Å. Similar deviations have been observed in

π-allyl complexes in which the chemical environment

at one terminal carbon is different from that of the

other, due to differing trans-influences.⁵¹The bond

lengths for Zr-Cl(1) and Zr-Cl(2) were found to be

2.5051(8) and 2.5089(8) Å, respectively. These distances

are somewhat longer than those reported for zirconocene

dichloride (2.44 Å).⁵⁴

with hydrocarbon solvents and subsequent crystalliza-

tion at -30 °C. The dimethylzirconium complexes were

observed to decompose under prolonged dynamic vacuum,

so care was taken to avoid extended exposure of these

materials to vacuum in the solid state. Similar observa-

tions were made with (Cp)₂TiMe₂.^55-57

The dimethyl complex (Trop)₂ZrMe₂(5) was charac-

terized by X-ray crystallography and shown to have a

structure similar to that of (Trop)₂ZrCl₂(2); the crystal

data and selected bond distances and angles are given

in Tables 1 and 4, respectively using the same number-

ing scheme as for 2.⁵⁸The Trop ligands feature two

different orientations (symmetric and unsymmetric with

respect to the CH₃ligands) and are rotated with respect

to one another by 87.71°, more than 10° greater than

in 2. The average Zr-C bond distance (2.562(5) Å) and

the average Zr-N distance (2.384(3) Å) are longer than

those observed in complexes 2 or 3. The average Zr-

Me bond length is 2.315(3) Å and is longer than the

average Zr-Me distance measured for Cp₂ZrMe₂(2.276-

(7) Å).⁵⁹The corresponding Me-Zr-Me bond angle is

98.75(9)°, which is larger than that reported for di-

methylzirconocene (95.6(12)°).⁵⁹

The mixed Cp/Trop complex (Cp)(Trop)ZrCl₂(3) was

synthesized in 81% isolated yield as a mixture of two

isomers by adding 1 equiv of 1 to a suspension of

CpZrCl₃in CH₂Cl₂(eq 2 where M ) Zr). One of the two

isomers (3a ) was isolated as an orange crystalline solid

by slow cooling (-30 °C) of a concentrated CH₂Cl₂

solution. The solid-state structure was solved by single-

crystal X-ray diffraction. An ORTEP diagram is shown

in Figure 2, the crystal data are given in Table 1, and

representative bond lengths and angles are given in

Table 3. As can be seen from Figure 2, the Trop ligand

The dibenzyl complex (Trop)₂ZrBn₂(8) was character-

ized by X-ray crystallography. An ORTEP diagram is

(55) Herrmann, W. A.; Salzer, A. Synthetic Methods of Organome-

tallic and Inorganic Chemistry; Theim Medical Publishers: New York,

1996; pp 92-93.

(56) Erskine, G. J .; Hartgerink, J .; Weinberg, E. L.; McCowan, J .

D. J . Organomet. Chem. 1979, 170, 51.

(57) Alt, H. G.; Di Sanzo, F. P.; Rausch, M. D.; Uden, P. C. J .

Organomet. Chem. 1976, 107, 257.

(58) The details of the structure determination, an ORTEP diagram,

and complete tables containing the crystal data, bond distances, bond

angles, and positional and thermal displacement parameters are given

in the Supporting Information.

(51) Clarke, H. L. J . Organomet. Chem. 1974, 80, 155.

(52) Blu¨mel, J .; Ko¨hler, F. H.; Mu¨ller, G. J . Am. Chem. Soc. 1988,

110, 4846.

(53) Blu¨mel, J .; Ko¨hler, F. H.; Mu¨ller, G.; Wilkenson, D. L. Angew.

Chem., Int. Ed. Engl. 1988, 27, 977.

(54) Prout, K.; Cameron, T. S.; Forder, R. A.; Critchley, S. R.;

Denton, B.; Rees, G. V. Acta Crystallogr., Sect. B 1974, 30, 2290.

(59) Hunter, W. E.; Hrncir, D. C.; Bynum, R. V.; Penttila, R. A.;

Atwood, J . L. Organometallics 1983, 2, 750.

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1409

Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta for 2, 3, 5, 8, a n d 13

2

3

5

8

13

cryst syst

cryst color, habit

space group

formula

MW, g mol^-1

a, Å

monoclinic

orange, plate

P2₁/n (#14)

orthorhombic

orange, column

Pnma (#62)

C₁₃H₁₇Cl₂NZr

349.41

13.0007(7)

10.8353(6)

9.6386(5)

monoclinic

yellow, tabular

P2₁/c(#14)

C₁₈H₂₆N₂Zr

361.64

7.1659(1)

15.1415(1)

15.8990(2)

90.998(1)

1724.82(3)

4

1.393

-124

0.023

0.035

0.029

1.47

monoclinic

yellow, tabular

P2₁/c (#14)

C₃₀H₃₆N₂Zr

517.86

7.6088(1)

16.5441(2)

20.1281(2)

99.943(1)

2495.68(5)

4

1.378

-127

0.026

0.035

0.037

1.43

monoclinic

colorless, prismatic

P2₁/c (#14)

C₂₄H₃₂N₂Zr

439.75

7.8640(3)

21.9650(7)

12.6845(4)

106.124(1)

2104.84(11)

4

1.388

-101

0.028

0.036

0.037

1.68

C

₁₆H₂₄Cl₂N₂Zr

406.51

7.0931(2)

18.2744.2

12.8139(3)

95.777(1)

1652.53(5)

4

1.634

-120

0.028

b, Å

c, Å

â, deg

V, Å³

1357.76(11)

4

Z

F(calcd), g cm^-3

temp, °C

R

1.709

-107

0.029

0.030

0.061

1.20

R_w

R_all

0.035

0.042

1.33

goodness of fit

Ta ble 3. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) of (Cp )(Tr op )Zr Cl₂(3)

Zr-C1

Zr-C2

Zr-C3

Zr-Cp

2.504(7)

2.528(5)

2.497(4)

2.2123(6)

Zr-C6

Zr-C7

Zr-N1

Zr-Cl1

C6-C7

2.493(5)

2.506(7)

2.333(5)

2.4705(11)

1.392(5)

Cl1-Zr-Cl1*

Cp-Zr-Cl1

Cl1-Zr-C7

C1-C2-C3

C2-C1-C2*

C2-C3-C3*

104.45(6)

Zr-N1-C4

C4-N1-C5

C5-N1-C5*

C5-C6-C7

C6-C7-C6*

128.0(4)

113.7(5)

100.7(5)

115.4(5)

120.1(6)

105.51(3)

119.84(7)

107.7(5)

108.8(7)

107.8(3)

Ta ble 4. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) of (Tr op )₂Zr Me₂(5)

Zr-C17

Zr-C18

Zr-C1

Zr-C2

Zr-C3

N1-C8

2.316(2)

2.315(2)

2.685(2)

2.553(2)

2.437(2)

1.472(3)

Zr-N1

Zr-N2

Zr-C9

Zr-C10

Zr-C11

N2-C16

2.389(2)

2.379(2)

2.504(2)

2.549(2)

2.647(2)

1.465(3)

C17-Zr-C18

C7-C1-C2

C4-C3-C2

C1-C2-C3

C4-N1-C7

Zr-N1-C8

98.75(9)

117.0(2)

114.2(2)

120.8(2)

100.3(2)

128.7(1)

N1-Zr-N2

129.45(6)

115.5(2)

116.4(2)

120.8(2)

100.8(2)

126.3(1)

C15-C9-C10

C12-C11-C10

C9-C10-C11

C12-N2-C15

Zr-N2-C16

the bulky aryl groups. The ¹H NMR spectra of 8 in C₆D₆

at room temperature were consistent with an averaged

structure of C_2vsymmetry (Table 6), and a single

resonance was observed for the benzylic protons.

The ¹H NMR spectrum of the dibenzylzirconium

complex (Cp)(Trop)ZrBn₂(9) at 25 °C was consistent

with a complex exhibiting C_ssymmetry (Table 6). The

benzylic protons were observed to be diastereotopic, and

two sharp doublets were observed at 2.07 and 1.83 ppm

F igu r e 2. ORTEP diagram of (Cp)(Trop)ZrCl₂(3).

Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) of (Tr op )₂Zr Cl₂(2)

Zr-Cl1

Zr-Cl2

Zr-C1

Zr-C2

Zr-C3

C1-C2

C2-C3

2.5051(8)

2.5089(8)

2.537(3)

2.518(3)

2.523(3)

1.392(4)

1.400(5)

Zr-N1

2.352(3)

2.369(3)

2.493(3)

2.532(3)

2.595(3)

1.411(4)

1.374(4)

Zr-N2

Zr-C9

Zr-C10

Zr-C11

C9-C10

C10-C11

1

with J _Ha-Hb) 10.5 Hz at ambient temperature and

consistent with the structure shown below.

Cl1-Zr-Cl2

C7-C1-C2

C4-C3-C2

C1-C2-C3

100.89(3)

116.2(3)

116.4(3)

119.8(3)

N1-Zr-N2

133.01(9)

115.6(3)

117.1(3)

120.2(3)

C15-C9-C10

C12-C11-C10

C9-C10-C11

shown in Figure 3, the crystal data are presented in

Table 1, and selected bond distances and angles are

given in Table 5. The C17-Zr-C24 bond angle is 87.91-

(8)° and is smaller than the Me-Zr-Me angle in 5. One

Trop ligand has the allyl function directed toward C24,

while the other Trop ligand has a nitrogen directed

toward C17. This could be due to a steric effect in which

the Trop ligands are directed away from the wedge by

Dyn a m ic Beh a vior of Gr ou p 4 Com p lexes. Analy-

sis of the ¹H NMR spectrum of 2 in CD₂Cl₂at room

temperature reveals a simple pattern consistent with

1410 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

3b. The cross-peaks between resonances corresponding

to 4a (where the allylic and bridgehead resonances were

known) and 4b were used to make the assignments. The

1

2D EXSY H NMR spectrum of 4 using a mixing time

of 7 s, along with the relevant assignments, is given in

the Supporting Information.

The rate of exchange between 3a and 3b was calcu-

lated from the line width at half-height of the Cp

resonance (W ) 12 Hz) at 20 °C (the fast exchange

region) using eq 5^60,62where p_aand p_bare the popula-

k₁) 4πp_ap_bδν²/(W - W_o)

(5)

2

tions of 3a and 3b, respectively, W_ois the line width at

half-height in the absence of exchange (3 Hz), and δν )

120 Hz. The rate and the corresponding activation

barrier are given in Table 7. For 4a and 4b, upon

heating in C₂D₂Cl₄, the two Cp resonances broadened

and coalesced at 70 °C. At 100 °C a broadened spectrum

exhibiting apparent C_ssymmetry was finally observed

(Table 6). The rate of interconversion was calculated

using eq 5 and the two different Cp resonances (W )

42 Hz at 70 °C, δν ) 99 Hz).⁶⁰The rate and activation

barrier⁶¹for this process are given in Table 7.

F igu r e 3. ORTEP diagram of (Trop)₂ZrBn₂(8).

Ta ble 5. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) of (Tr op )₂Zr Bn ₂(8)

Zr-C17

Zr-C24

Zr-C2

2.356(2)

2.378(2)

2.470(2)

2.535(2)

2.588(2)

1.476(3)

Zr-N1

2.396(2)

2.375(2)

2.570(2)

2.521(2)

2.530(2)

1.475(3)

At room temperature the ¹H NMR spectrum of the

dialkyl complexes 5, 6, 7, and 9 was consistent with a

symmetric complex (Table 6). No extensive broadening

of any resonance was observed for complexes 6 and

9 upon cooling in CD₂Cl₂. However, upon cooling a

CD₂Cl₂solution of 5, the resonances in the allylic and

bridgehead region of the ¹H NMR spectrum began to

broaden at -60 °C, and decoalesence of the central allyl

signal was observed at -95 °C. A spectrum at the slow

exchange limit for this complex was not observed,

prohibiting calculation of the activation barrier for this

process. Upon cooling a CD₂Cl₂sample of 7, the single

TiMe resonance began to broaden, and decoalesence was

observed at -40 °C. Two separate TiMe resonances were

finally observed at -80 °C (Figure 6). The low-temper-

ature ¹H NMR spectrum was consistent with a complex

of C₁symmetry. The rate for this exchange process

(averaging of the different Trop and TiMe resonances)

was calculated at the coalescence temperature of the two

TiMe resonances based on the separation observed at

the slow exchange limit (δν ) 414 Hz at -90 °C) using

eq 4.⁶⁰The rate is reported in Table 7 along with the

corresponding activation barrier.⁶¹

Zr-N2

Zr-C10

Zr-C11

Zr-C12

C24-C25

Zr-C3

Zr-C4

C17-C18

C17-Zr-C24

C1-C2-C3

C5-C4-C3

C2-C3-C4

C1-N1-C5

Zr-N1-C8

Zr-C17-C18

87.91(8)

115.1(2)

117.1(2)

119.6(2)

100.4(2)

135.5(1)

128.9(2)

N1-Zr-N2

124.3(7)

115.7(2)

116.9(2)

120.3(2)

101.0(2)

126.6(1)

132.5(2)

C9-C10-C11

C13-C12-C11

C10-C11-C12

C9-N2-C13

Zr-N2-C16

Zr-C24-C25

C_2vsymmetry (Table 6). Upon cooling a CD₂Cl₂solution

of 2, the three allylic and two bridgehead resonances

broadened and separated into 10 signals, all integrating

to the same area at -90 °C (Figure 4). The coalescence

temperature for the central allylic resonances was -48

°C, and the peak separation (δν) of these two resonances

at -90 °C was 168 Hz. The rate, calculated using eq 4,

x

2

k ) πδν/

(4)

at the coalescence temperature for an equally populated

two-site exchange⁶⁰is given in Table 7 along with the

corresponding activation barrier.⁶¹

R ea ct ivit y of Tr op id in yl(d im et h yl)zir con iu m

Com p lexes w ith P r oton Don or s. Protonolysis of

complex 5 with tert-butyl alcohol at room temperature

gave (Trop)₂Zr(Me)(O-t-Bu), 10 (88% yield), and 1 equiv

of methane (Scheme 3). Protonolysis of complex 5 with

1 equiv of trifluoromethanesulfonic acid formed (Trop)₂Zr-

(Me)(OSO₂CF₃) (11) and 1 equiv of methane. This

compound could be easily generated but was found to

undergo slight decomposition during the purification

process, prohibiting satisfactory elemental analysis.

Addition of KO-t-Bu to 11 gave (Trop)₂Zr(Me)(O-t-Bu)

(10) that was substantially more stable (89% yield).

Addition of 1 equiv of LiNH-t-Bu to 11 gave (Trop)₂Zr-

(Me)(NH-t-Bu) (12). This complex was also spectroscopi-

cally characterized, but lacked sufficient stability to

allow adequate purification for microanalysis. These

Complexes 3 and 4 were isolated as a mixture of two

isomers; the major isomer exhibits apparent C_ssym-

metry (3a and 4a ), and the minor isomer exhibits C₁

symmetry (3b and 4b) (Table 6). The relative concentra-

tion of the different isomers was observed to change as

a function of temperature (Table 8). A van’t Hoff plot is

shown in Figure 5; for complex 3 ∆H° ) 0.8 ( 0.1 kcal

mol^-1, and ∆S° ) 1.2 ( 0.4 cal mol^-1K^-1; for complex

4 ∆H° ) -0.75 ( 0.06 kcal mol^-1, and ∆S° ) 3.5 ( 0.2

cal mol^-1K^-1

.

The assignments of the allyl and bridgehead reso-

nances for 4b given in Table 6 were made with the aid

of 2D EXSY ¹H NMR spectroscopy and extrapolated to

(60) Binsch, G. In Band-Shape Analysis; J ackman, L. M., Cotton,

F. A., Eds.; Academic Press: New York, 1975; pp 45-81.

(61) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:

London, 1982; pp 77-92.

(62) Petit, L. H.; Anderson, W. A. J . Chem. Phys. 1959, 30, 899.

Group 4 Tropidinyl Complexes

Ta ble 6. ¹H NMR Sp ectr oscop ic Da ta for Tr op -Bea r in g Com p lexes^a

elevated-temperature spectrum low-temperature spectrum

Organometallics, Vol. 19, No. 7, 2000 1411

compd

δ(ppm)

mult

J (Hz)

int

assgnt

δ(ppm)

mult

J (Hz) int

assgnt

b

(Trop)₂ZrCl₂(2)

5.72

4.29

3.73

2.48

2.23

t

7

7, 2

2

4

6

8

central allylic

terminal allylic

bridgehead

NMe

6.04

5.47

4.55

4.30

4.28

4.11

4.02

3.88

3.72

2.89

2.51

2.18

2.2-1.98

6.20

5.65

4.37

t

7

1

3

8

5

1

2

3

4

central allyl

terminal allylic

c

q

br

s

br

s

m

s

t

q

s

CH₂

c

bridgehead

NMe

CH₂

(Cp)(Trop)ZrCl₂^d(3)

Cp

7

central allylic

terminal allylic

bridgehead

NMe

7, 4.5

3.77

2.12

2.2-2.09

br

s

m

6.21

5.64

4.37

3.81

2.59

2.20

s

5

1

2

3

4

Cp

br

s

central allylic

terminal allylic

bridgehead

NMe

CH₂

6.60

5.90

5.07

3.09

3.28

2.76

2.5

2.2-2.09

6.32

5.08

4.77

4.16

2.88

2.22-1.79

s

t

5

1

3

4

5

1

2

3

4

Cp

7

central allylic

terminal allylic

bridgehead

NMe

CH₂

Cp

central allylic

terminal allylic

bridgehead

NMe

br

CH₂

m

br

s

m

s

t

(Cp)(Trop)TiCl₂^e(4)

7.2

7, 4.9

q

br

s

5.8

4.6

4.1

3.6

2.1

1.6

1.4

br

5

1

2

3

2

Cp

central allylic

terminal allylic

bridgehead

NMe

CH₂

m

CH₂

6.65

5.89

5.62

4.44

4.32

3.17

2.88

2.22-1.79

s

t

br

s

5

1

3

4

Cp

5.9

7.5

4.8

terminal allylic

central allylic

terminal allylic

bridgehead

NMe

m

CH₂

(Trop)₂ZrMe₂^f(5)

4.86

3.87

3.31

2.12

2.02

1.90

0.22

5.77

4.34

3.84

3.18

1.99

1.86

1.78-1.72

0.08

6.24

5.08

4.60

3.24

2.23

2.11

1.65

t

q

7.4

7.3

2

4

3

4

6

5

1

2

3

2

6

5

1

2

6

central allylic

terminal allylic

bridgehead

CH₂

NMe

CH₂

ZrMe

Cp

central allylic

terminal allylic

bridgehead

CH₂

NMe

CH₂

ZrMe

Cp

central allylic

terminal allylic

bridgehead

CH₂

NMe

g

br

m

s

t

q

br

q

s

m

s

t

br

q

m

s

(Cp)(Trop)ZrMe₂^h(6)

i

7.5

7.2, 4.5

10.2, 4.5

(Cp)(Trop)TiMe₂^j(7)

6.25

5.46

5.04

3.94

3.75

2.31

2.18

1.90

1.53

0.07

s

br

t

br

m

s

5

1

2

3

Cp

10

terminal allylic

central allylic

terminal allylic

bridgehead

CH₂

NMe

TiMe

7.5

15, 5

-0.2

TiMe

s

-1.31

(Trop)₂ZrBn₂^k(8)

5.14

3.79

2.85

2.05

t

7.4

7.5, 4.5

2

4

6

central allylic

terminal allylic

bridgehead

NMe

q

br

s

1412 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

Ta ble 6 (Con tin u ed )

elevated-temperature spectrum

low-temperature spectrum

compd

δ(ppm)

mult

J (Hz)

int

assgnt

δ(ppm)

mult

J (Hz)

int

assgnt

(Trop)₂ZrBn₂^k(8)

1.95

1.72

7.27

7.12

6.90

5.77

4.54

3.76

2.96

2.07

1.88

1.83

1.65

s

t

s

t

br

d

m

4

8

4

2

5

1

2

5

ZrCH₂

CH₂

Ar

Cp

central allylic

terminal allylic

bridgehead

ZrCH₂

CH₂

ZrCH₂

7.7

(Cp)(Trop)ZrBn₂^l(9)

m

7.5

5.7

10.4

7.4

10.4

NMe, CH₂

Spectrum collected at 300 MHz. In CD₂Cl₂at 20 and -90 °C. ^cBridgehead or allyl resonance. In CD₂Cl₂at 20 and -70 °C. ^eIn

a

b

d

C₂D₂Cl₄at 100 °C and CDCl₃at 20 °C. ^fIn CD₂Cl₂at 20 °C. Only exchange-broadened peaks observed at -95 °C. In CD₂Cl₂at 20 °C.

g

h

i

j

k

l

m

No appreciable broadening observed at -95 °C in CD₂Cl₂. In CD₂Cl₂at 20 and -90 °C. In C₆D₆at 20 °C. In C₆D₆at 20 °C. No

appreciable broadening observed at -78 °C in CD₂Cl₂.

Ta ble 8. Equ ilibr iu m Da ta for Gr ou p 4 Com p lexes

Bea r in g th e Tr op Liga n d ^a

complex

T (°C)

K

(Cp)(Trop)TiCl₂(4)

48

36

27

19

13

0.55 ( 0.01

0.57 ( 0.01

0.59 ( 0.02

0.60 ( 0.02

0.61 ( 0.02

0.11 ( 0.01

0.099 ( 0.01

0.088 ( 0.008

0.065 ( 0.006

(Cp)(Trop)ZrCl₂(3)

0

-30

-50

-70

a

Equilibrium for the conversion of a to b (eq 11).

F igu r e 4. Variable-temperature ¹H NMR spectra of

(Trop)₂ZrCl₂(2) in CD₂Cl₂.

Ta ble 7. Ra tes a n d F r ee En er gies of Activa tion for

th e Solu tion Dyn a m ic P r ocesses of Gr ou p 4

Com p lexes Bea r in g th e Tr op Liga n d

T

(°C)

k₁

∆G^q

complex

(s^-1

)

(kcal mol^-1

)

K

a

(Cp)(Trop)Ti(CH₃) ₂-40^b1191 ( 6^c

10.2 ( 0.1

10.9 ( 0.1

1

a

(Trop)₂ZrCl₂

-48^b373 ( 5^c

a

(Cp)(Trop)ZrCl₂

20 324 ( 180^d13.8 ( 0.3 0.13 ( 0.06^e

70 592 ( 150^d15.8 ( 0.2 0.50 ( 0.07^e

f

(Cp)(Trop)TiCl₂

a

b

Spectrum collected in CD₂Cl₂. Coalescence temperature.

^cRate calculated for degenerate exchange using eq 4. Rate for

d

eq 11 calculated using eq 5. ^eValue extrapolated from van’t Hoff

plot. ^fSpectrum collected in C₂D₂Cl₄.

F igu r e 5. A van’t Hoff plot for the equilibration between

the symmetric (a ) and nonsymmetric (b) isomers (eq 11)

of (Cp)(Trop)MCl₂3 and 4 where M ) Ti (2) and Zr ([),

respectively.

mixed complexes each exhibited five-signal patterns in

the bridgehead and allylic region of the ¹H NMR spectra

that are characteristic of Trop complexes with apparent

C₁symmetry. Treatment of the dimethylzirconium

complex 6 in C₆D₆with 10 equiv of the trialkylammo-

nium hydrochloride salt (n-Bu)₃NHCl led to the im-

mediate formation of 3 in an 87% yield by NMR relative

to an internal standard (eq 6).

behavior of tropidinyl complexes, the reactions of 6 with

isonitriles and CO were investigated. Reaction of 2,6-

Me₂C₆H₃NC with complex 6 was found to readily form

the η²-iminoacyl 13 (eq 7). Insertion products were also

In ser tion Ch em istr y of Ison itr iles w ith (Cp )-

(Tr op )Zr Me₂(5). To explore the migratory insertion

observed using t-BuNC, but treatment with CO led only

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1413

Ta ble 9. Selected Bon d Dista n ces (Å) a n d Bon d

An gles (d eg) of

(Cp )(Tr op )Zr (CH₃)[N(2,6-(CH₃)₂C₆H₂)C(CH₃)] (13)

Zr-C1

Zr-C2

Zr-C3

Zr-C4

Zr-C5

Zr-Cp

Zr-N2

Zr-N1

2.559(3)

2.574(3)

2.554(3)

2.551(3)

2.550(3)

2.2612(2)

2.402(2)

2.277(2)

Zr-C17

Zr-C18

Zr-C19

Zr-C6

2.485(3)

2.529(3)

2.6512(3)

2.346(3)

2.238(3)

1.498(4)

1.275(3)

1.452(3)

Zr-C7

C7-C8

C7-N1

N1-C9

Cp-Zr-C6

106.57(6)

N1-Zr-C7

Zr-C7-N1

Zr-N1-C7

Zr-N1-C9

Zr-C7-C8

C6-Zr-C7

32.79(8)

75.32(17)

71.89(15)

162.54(17)

159.7(2)

Cp-Zr-C7

104.35(6)

111.00(5)

83.44(8)

121.5(3)

114.0(3)

116.6(3)

Cp-Zr-N1

C6-Zr-N1

C17-C18-C19

C18-C17-C23

C18-C19-C20

1

F igu r e 6. Variable-temperature H NMR spectra of (Cp)-

(Trop)Ti(CH₃)₂(7) in CD₂Cl₂.

115.78(9)

Sch em e 3

angles of the triangle defined by Zr-C7-N1 are similar

to those of other structurally characterized η²-iminoacyl

complexes^63,64as well as the η²-silaacyl complex Cp₂Zr-

(η²-C(O)SiMe₃)Cl.^65,68The Trop ligand adopts a non-

symmetrical orientation with respect to the wedge. The

coordination of the allyl group was also irregular, where

the Zr-C19 bond distance (2.6512(3) Å) is much larger

than that of the Zr-C17 bond distance (2.485(3) Å),

possibly due to steric crowding with the methyl (C16)

of the 2,6-dimethylphenyl ring.

Eth ylen e P olym er iza tion . The ethylene polymer-

ization activities for the group 4 complexes used in this

study were measured at 25 °C in toluene using 1000

equiv of modified methylaluminoxane (MMAO) under

1 atm of ethylene (Table 10).⁶⁹Polyethylene (PE)

molecular weights were determined by gel permeation

chromatography (GPC), and melting points were deter-

mined by differential scanning calorimetry (DSC). The

3/MMAO system is very active¹⁴(9.86 × 10⁶g PE mol

[M]^-1h^-1atm^-1), exhibiting a rate and polydispersity

of PE similar to that observed with Cp₂ZrCl₂/MMAO

(control experiments run using Cp₂ZrCl₂/MMAO were

consistent with previous reports in the literature).^70-72

The use of the borane cocatalyst tris(pentafluorophenyl)-

borane (B(C₆F₅)₃) with 6 resulted in slightly lower

activity relative to 3/MMAO (Table 10). The other Trop-

bearing complexes (2 and 4) displayed only moderate

polymerization activity under these conditions.

High-density PE was produced from all the catalyst

systems with the exception of 4/MMAO and CpZrCl₃/

MMAO, as evidenced by the high melting points of the

produced PE.⁷³Polymerizations carried out with CpZrCl₃/

MMAO, CpTiCl₃/MMAO, and ZrCl₄/MMAO gave very

low activities. Two distinct melting endotherms were

detected by DSC for polymers produced using the

CpTiCl₃/MMAO and ZrCl₄/MMAO systems.

F igu r e 7. ORTEP diagram of(Cp)(Trop)Zr(CH₃)[N(2,6-

(CH₃)₂C₆H₃)C(CH₃)] (13).

to unidentified decomposition products. The aminoacyl

methyl resonance for 13 was observed at 1.78 ppm, and

the ¹³C{¹H} NMR chemical shift of the aminoacyl carbon

at 247.6 ppm was consistent with those of other ami-

noacyl complexes.^63-66The infrared spectrum revealed

a ν_CNstretch at 1577 cm^-1, consistent with η²-coordina-

tion of the iminoacyl ligand.⁶⁴Complex 13 was crystal-

lized as colorless blocks and characterized by X-ray

crystallography. An ORTEP diagram is given in Figure

7; crystal data and selected bond distances and angles

are given in Tables 1 and 9, respectively. The imino

carbon atom is bound directly to the zirconium atom,

and the Zr-C7 bond length (2.238(3) Å) is similar to

Zr-C(iminoacyl) bond distances observed in other com-

plexes (2.23-2.25 Å).^63,67The Zr-Cp(centroid) distance

(2.2612(2) Å) is similar to that observed in CpCp*Zr-

[C(N-2,6Me₂C₆H₃)Si(SiMe)₃]Cl (2.254(11) Å).⁶⁴The bond

The catalyst activity as a function of time was

investigated by measuring the ethylene uptake of the

(67) Cardin, D. J .; Lappert, M. F.; Raston, C. L. Chemistry of

Organo-Zirconium and -Hafnium Compounds; Wiley: New York, 1986;

p 223.

(63) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,

L.; Latesky, S. L.; McMullen, A. K.; Rothwell, I. P.; Folting, K.;

Huffman, J . C.; Streib, W. E.; Wang, R. J . Am. Chem. Soc. 1997, 109,

3390.

(64) Elsner, F. H.; Tilley, T. D.; Rheingold, A. L.; Geib, S. J . J .

Organomet. Chem. 1987, 358, 169.

(68) Tilley, T. D. J . Am. Chem. Soc. 1985, 107, 4084.

(69) J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. M.;

Schumann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091.

(70) Kaminsky, W.; Ku¨lper, K.; Niedoba, S. Macromol. Chem.,

Macromol. Symp. 1986, 3, 377.

(71) Kaminsky, W.; Steiger, R. Polyhedron 1988, 7, 2375.

(72) Chien, J . C. W.; Wang, B.-P. J . Polym. Sci., Part A: Polym.

Chem. 1990, 28, 15.

(65) Campion, B. K.; Falk, J .; Tilley, T. D. J . Am. Chem. Soc. 1987,

109, 2049.

(66) Wolczanski, P. T.; Bercaw, J . E. J . Am. Chem. Soc. 1979, 101,

6450.

(73) Cowie, J . M. G. Polymers: Chemistry and Physics of Modern

Materials; Chapman and Hall: New York, 1994; p 345.

1414 Organometallics, Vol. 19, No. 7, 2000

Ta ble 10. Eth ylen e P olym er iza tion Activities a n d P olym er P r op er ties^a

Skoog et al.

activity (× 10^-3), g PE

mp,^c

°C

b

precatalyst

cocatalyst wt PE, g time, min

mol [M]^-1h^-1atm^-1

10^-3M_n

10^-3M_w

10^-3M_z

M_w/M_n

(Cp)(Trop)ZrCl₂(3)

(Cp)(Trop)Zr(CH₃)₂(6)^d

(Cp)(Trop)TiCl₂(4)

(Trop)₂ZrCl₂(2)^e

Cp₂ZrCl₂

MMAO

B(C₆F₅)₃

MMAO

1.916

0.17

2.5

0.51

7.2

20.15

0.55

1.5

32.1

60.5

2.25

60.7

9860

3750

10

5.4

43

23

14

68

15

17

78

63

170

28

360

59

2100

300

2.7

3.9

3.3

44

2.6

130

133

124

129

134

135

123

133

134

132

0.0063

0.014

0.383

0.9885

0.0053

0.005

0.583

0.007

8

8030

7540

2

CpCp*ZrCl₂

f

CpZrCl₃

ZrCl₄^e,f(128)

Cp₂TiCl₂f

1

2990

1

CpTiCl₃^f(128)

a

b

Polymerization conditions: 100 mL toluene, 25 °C, 5.1 × 10^-6mol catalyst, 1000 Al/M, 1 atm ethylene. By GPC. ^cBy DSC; the

numbers in parentheses indicate a minor peak in the DCS curve. A 1:1 ratio of cocatalyst to precatalyst was used where 5.1 × 10^-6mol

d

of precatalyst was used. ^eMMAO solution added to ethylene-saturated solution of toluene and the precatalyst. ^fLow detector response

prohibited accurate GPC analysis.

Ta ble 11. Rela tive ¹³C{¹H} NMR Meth yl P en ta d

In ten sity for P P Gen er a ted Usin g 4/MMAO^a

experimental

band intensity

theoretical band intensity

for actactic PP

pentad

mmmm

mmmr

rmmr

mmrr

mmrm + rmrr

mrmr

0.03

0.06

0.12

0.06

0.12

0.25

0.12

0.06

0.12

0.06

0.069

0.058

0.099

0.26

0.129

0.115

0.17

rrrr

rrrm

mrrm

0.07

a

See text for polymerization conditions.

tactic pentads (rrrr and rrrm) and depleted in the

isotactic pentads (mmmm and mmmr). Similar results

were obtained at higher polymerization temperatures

(25 °C). The CpTiCl₃/MMAO catalyst system failed to

give any PP under these experimental conditions.

The 3/MMAO catalyst system in liquid propylene at

0 °C gave 1.4 g (activity ) 59 g (mmol cat)^-1h^-1) of an

oily viscous liquid oligomer. Analysis by GC/MS showed

F igu r e 8. Ethylene uptake versus time during ethylene

polymerization using (Cp)(Trop)ZrCl₂/MMAO at 25 °C (b)

and 0 °C ([).

3/MMAO system (Figure 8). Similar profiles were

obtained using Cp₂ZrCl₂/MMAO. A higher activity was

observed at 0 °C than at 25 °C.

1

a size range of C12 to C27.⁷⁶End group analysis by H

r-Olefin P olym er iza tion . Polymerization of propy-

lene was carried out using (Cp)(Trop)MCl₂/MMAO

catalyst systems in liquid propylene. The chain length

of the resulting polymeric material was found to be

metal dependent. High molecular weight polypropylene

(PP) was generated using the 4/MMAO system, and PP

oligomer was generated using 3/MMAO. The 2/MMAO

catalyst system failed to give any polymer or oligomer

under the conditions employed in this study.

The catalyst 4/MMAO in liquid propylene at 0 °C gave

0.62 g (activity ) 37 g PP (mmol cat)^-1h^-1) of rubbery

PP. Analysis by GPC showed a bimodal distribution

with the larger fraction being high molecular weight PP

and a smaller fraction being lower molecular weight

material in a ratio of 70:30. Analysis⁷⁴of the molecular

weight distribution of the larger fraction gave M_w) 4.6

× 10⁵, M_n) 2.9 × 10⁵, and M_w/M_n) 1.6; for the smaller

fraction, M_w) 1.6 × 10³, M_n) 2.09 × 10³, and M_w/M_n

) 1.4; overall the polydispersity was 49. The PP mixture

was analyzed by ¹³C{¹H} NMR spectroscopy, and the

methyl region was resolved at the pentad level; the

results are given in Table 11.⁷⁵As can be seen by

comparison of the experimental and calculated band

intensities, the PP was mildly enriched in the syndio-

NMR indicated that all unsaturated end groups con-

tained the vinylidene (CH₂C(CH₃)CH₂(R)) functionality.

On the basis of previous assignments, the ¹³C{¹H} NMR

spectrum was used to identify n-propyl, isobutyl, and

vinylidene end groups in a 30:40:30 ratio and was

consistent with a product generated from exclusive

head-to-tail propylene insertion.^77,78

In vestiga tion of Active Ca ta lyst Sp ecies. To gain

further insight into the stability and properties of the

active species involved in the polymerizations (and

establish that the Trop ligands remain attached to the

metal center), we carried out spectroscopic studies of

the activation of precatalysts 3 and 6 using MMAO and

B(C₆F₅)₃, respectively. A toluene solution of 3 was

treated with 1000 equiv of MMAO, and the resulting

mixture was quenched using excess (n-Bu)₃NHCl in

toluene after ca. 2 min. Upon addition of MMAO before

quenching, 3 was observed to be completely consumed

(76) The distribution of different molecular weight components was

too narrow to be fit to a Schultz-Flory (most probable) distribution,

possibly due to the isolated material not being representative of the

actual oligomer distribution during polymerization. The oligomer

distribution was found by GC to be (% composition, # of C atoms): (11,

C12); (16, C15); (18, C18); (20, C21); (20, C24); (15, C27).

(77) Resconi, L.; Piemontesi, F.; Franciscono, G.; Abis, L.; Fiorani,

T. J . Am. Chem. Soc. 1992, 114, 1025.

(78) Tsutsui, T.; Mizuno, A.; Kashiwa, N. Polymer 1989, 30, 428.

(74) Reference 73, pp 8-10.

(75) Ewen, J . J . Am. Chem. Soc. 1984, 106, 6355.

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1415

by UV-vis spectroscopy. After quenching with excess

(n-Bu)₃NHCl, the dichloride 3 was regenerated quan-

titatively within the uncertainty limits of this experi-

ment (ca 15%). Upon addition of 5 equiv of MMAO to a

toluene-d₈solution of 3, a color change from orange to

light red was observed. After quenching the reaction

mixture with excess (n-Bu)₃NHCl the original orange

color was restored and 3 was generated in 88% yield by

¹H NMR spectroscopy in the presence of an inert

internal standard (ferrocene).

In the triarylborane experiments, we employed the

activation methodology developed by Marks and co-

workers.^79,80Treating complex 6 with 1 equiv of the

methide-abstracting agent B(C₆F₅)₃in toluene-d₈or

chlorobenzene-d₅resulted in the immediate formation

of a red solution formulated as the methyltriarylborate

complex [(Cp)(Trop)ZrCH₃][CH₃B(C₆F₅)₃] (14) (eq 8).

The ¹H NMR spectrum exhibited a single Cp resonance,

tion of Cp ligands to group 4 metal centers have relied

heavily on the use of thallium, magnesium, and alkali

metal cyclopentadienide reagents.⁶⁷The use of tri(alkyl)-

tin-mediated transmetalation of Cp rings has not been

used as extensively by comparison. The tin reagent

CpSnR₃has only received modest attention for early

metal systems because other methods are highly

effective.^83-86The silicon reagent CpSiMe₃has been

similarly employed to coordinate Cp ligands to Ti metal

centers where electrophilic attack of the Cp group with

cleavage of the Si-C bond was thought to occur.⁸⁷Use

of the traditional methods was not successful in the Trop

series, but the tin reagent 1 proved to be a convenient

and stable source of the Trop ligand⁸⁸and was shown

to readily undergo transmetalation with group 4 chlo-

rides. When coordinatively more saturated forms of the

group 4 metal halides such as ZrCl₄‚(THF)₂or CpZrCl₃‚

DME were used, undesired byproducts were produced.

This observation suggests that initial coordination of the

nitrogen atom in 1 to the unsaturated group 4 metal

chloride may facilitate transmetalation to form the η³-

allyl functionality.

three resonances in the allyl and bridgehead region in

a 1:2:2 ratio, two resonances corresponding to methylene

protons, and methyl resonances corresponding to NMe,

BMe, and ZrMe in a 1:1:1 ratio. The ¹¹B NMR spectrum

exhibited a single resonance at -15 ppm, consistent

with the presence of a tetrahedral borate anion.⁸¹The

¹⁹F NMR spectrum showed a single three-resonance

pattern and indicated that all of the starting borane was

consumed. A large chemical shift difference (5 ppm)

between the meta and para fluorine resonances of the

borate was observed, indicative of coordination of the

borate anion to a cationic zirconium metal center.^23,82

The complex was only moderately stable in toluene-d₈

at room temperature (t_1/2) 1 h) and less stable in more

polar solvents. Approximate room-temperature half-

lives (t_1/2) for decomposition in chlorobenzene-d₅and

CD₂Cl₂were 0.5 and 0.1 h, respectively; however,

solutions of 14 in chlorobenzene-d₅at < 0 °C were stable

for many hours. Upon cooling a solution of 14 to -20

°C, the resonances corresponding to the allyl and

bridgehead protons began to broaden. The line shape

of two separate resonances for the ZrMe and the BMe

groups remained unchanged relative to other nonex-

changing resonances upon lowering the temperature.

The line shape of the central allyl resonance also

remained unchanged, but the chemical shift was found

to move slightly upfield. These changes were similar to

the spectral changes observed upon cooling a CD₂Cl₂

Syntheses of metallocene dialkyl complexes from the

parent dichlorides proceed readily by treating group 4

metallocene dihalides with lithium or magnesium alkyl

reagents.⁸⁹In contrast to the Trop-attachment reactions,

similar routes were effective for the alkylation of

complexes bearing the Trop ligand. The dialkyl com-

plexes also displayed reactivity similar to that of the

corresponding dialkylmetallocenes.⁹⁰

Determination of several X-ray structures shows the

Trop ligand can be either symmetrically or unsymmetri-

cally orientated with respect to the metal wedge. The

symmetric mode, observed in 2, 3, and 5, can be

described as having the NMe group bisecting the wedge

of the Zr coordination sphere.⁹¹An unsymmetric orien-

tation of the Trop ligand was observed in complexes 2,

5, 8, and 13, where the NMe group is directed away from

one of the ligands in the wedge.

F lu xion a l Beh a vior of Com p lexes Bea r in g th e

Tr op Liga n d . The solid-state structures of the com-

plexes bearing the Trop ligand, with the exception of 3,

were less symmetric than would be predicted on the

basis of their NMR spectra obtained at room tempera-

ture. Variable-temperature NMR studies revealed dy-

namic processes occurring in solution. Two exchange

processes accounted for the increased complexity of the

(83) Lund, E. C.; Livinghouse, T. Organometallics 1990, 9, 2426.

(84) Spetseris, N.; Hadida, S.; Curran, D. P.; Meyer, T. Y. Organo-

metallics 1998, 17, 1458.

(85) Nifant’ev, I. E.; Ivchenko, P. V. Organometallics 1997, 16, 713.

(86) Lisowsky, R. Eur. Pat. Appl. 669340 A 1, 1995.

(87) Cardoso, A. M.; Clarke, R. J . H.; Moorhouse, S. J . Chem. Soc.,

Dalton Trans. 1980, 1156.

(88) The lithiated anion (TropLi) was found to be unstable at

temperatures above -78 °C, and preparations using this species were

cumbersome. See ref 45 for the details of using Li salts directly for

the synthesis of metal complexes.

1

solution of (Cp)(Trop)TiMe₂(7) (see Figure 6). The H

NMR spectrum of complex 14 could not be obtained in

the slow-exchange regime due to the limited liquid

range of the solvent; this precluded estimation of the

energetic barrier for this exchange process.

Discu ssion

(89) J effery, J .; Lappert, M. F.; Luong-Thi, M. F.; Webb, N. T. A., J .

L.; Hunter, W. E. J . Chem. Soc., Dalton Trans. 1981, 1593.

(90) Lappert, M. F., Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.

Comprehensive Organometallic Chemistry; Pergamon Press: Oxford,

1982; Vol. 3, p 580.

(91) Neither of the NMe groups bisects the C17-Zr-C24 angle of

complex 8 and would not be considered to be in a symmetric orientation

as described in the text; however, one Trop ligand adopts an unsym-

metric orientation. It is possible that the distortion of the Trop ligand

from the symmetric orientation is brought about by steric repulsion

between the NMe and the large benzyl groups.

Syn t h esis a n d St r u ct u r e of Tr op id in yl Met a l

Com p lexes. Traditional synthetic routes for coordina-

(79) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1991,

113, 3623.

(80) Yang, X.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,

116, 10015.

(81) Kidd, R. G. Boron-11; Academic Press: New York, 1983; Vol.

2, pp 49-50.

(82) Horton, A. D.; de With, J . Chem. Commun. 1996, 1375.

1416 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

NMR spectra upon lowering the temperature. One

process involves interconversion of enantiomers (com-

plexes 2 and 7). The other involves interconversion of

diastereomers (complexes 3 and 4). The fluxionality of

group 4 metallocene complexes has been found to be im-

portant in determining the selectivity of olefin insertions

into a growing polymer chain.^92-95The implications for

improving the selectivity of olefin insertion based on the

fluxional properties of the Trop ligand prompted us to

study the dynamic behavior of these complexes.

much lower barrier was found for the interconversion

of its isomers and the population differences between

3a and 3b were more pronounced. We suggest that the

large difference in the interconversion free energy bar-

riers of complexes 3 and 4 is predominantly steric and

results from the size difference between zirconium and

titanium. The smaller titanium atomic radius forces the

Trop ligand to lie closer to the metal center relative to

zirconium, resulting in a higher isomerization barrier.

P olym er iza tion Ca ta lysis. Several qualitative com-

parisons can be made from the data in Table 10. The

activity of 3/MMAO is similar to that of Cp₂ZrCl₂/

MMAO. The less hindered mixed Cp/Trop complex

3/MMAO is more active than the more hindered (bis)-

Trop complex 2/MMAO. The broad polydispersity and

bimodal nature (by GPC) of the PE generated from the

2/MMAO catalyst suggests that more than one active

species may be generated in this system. The titanium

complex 4/MMAO also displayed a lower activity than

3/MMAO and generated more highly branched PE, as

evidenced by the lower melting temperature. The

6/B(C₆F₅)₃catalyst system exhibited activity comparable

to that of the 3/MMAO system, but the resulting PE

had a much higher molecular weight and broader

polydispersity. The M_wof the polymer generated from

3/MMAO was much lower than that observed for Cp₂-

ZrCl₂/MMAO, indicating that chain transfer was more

facile for the Trop-bearing complex. The activities of

2/MMAO, 3/MMAO, and 4/MMAO were all higher than

the activities of the parent metal chlorides ZrCl₄,

CpZrCl₃, and CpTiCl₃run under identical conditions.

These observations indicate that at least to some degree

the Trop ligand enhances the reactivity of the metal

centers under our polymerization conditions relative to

the metal chloride precursors.

Complex 7 exists as a single diastereomer that under-

goes interconversion of enantiomers, giving rise to an

1

averaged C_ssymmetric structure by H NMR spectros-

copy at ambient temperature. Similar enantiomer ex-

change processes have been observed with other met-

allocene⁹⁶and π-allyl⁹⁷complexes. A fluxional process

that accounts for the spectral changes observed in Fig-

ure 6 is shown in eq 9. The Trop ligand binds to the

metal in an unsymmetric fashion, giving rise to two

TiMe resonances and five allyl and bridgehead reso-

nances in the low-temperature (-90 °C) ¹H NMR

spectrum.

The solid-state structure of 2 shows that the Trop

1

ligands are inequivalent (Figure 1). The H NMR spec-

trum of complex 2 exhibited time-averaged C_2vsym-

metry and was consistent with rapid rotation of the Trop

ligands.⁹⁶A fluxional process similar to that postulated

for 7, which results in interconversion of enantiomers,

is illustrated in eq 10 and accounts for the temperature

The ethylene uptake experiments indicate that for

3/MMAO an active catalyst system was present in

solution over the course of hours. The results obtained

in this study were similar to the ethylene uptake profile

observed for Cr catalyst systems.^98,99Analogous uptake

profiles were observed for Cp₂ZrCl₂/MMAO under iden-

tical conditions.

1

dependence of the H NMR spectrum (Figure 4).

Both the zirconium and titanium (Cp)(Trop)MCl₂/

MMAO catalyst systems polymerized propylene. The

titanium system produced much higher molecular weight

PP than the zirconium system. This is likely due to

differing chain transfer rates for these two systems. The

more sterically encumbered Ti system exhibits an

apparently higher barrier for chain transfer.⁷⁷Similarly,

Ewen has observed that higher molecular weight PP

was generated from CpCp*ZrCl₂/MAO in comparison to

the less sterically bulky Cp₂ZrCl₂/MAO system. Kamin-

ski et al. have also demonstrated that methyl substitu-

The dichloride complex (Cp)(Trop)TiCl₂(4) at room

temperature in CD₂Cl₂solution was found to exist as a

mixture of two diasteromers in unequal populations. At

room temperature the symmetric isomer is more heavily

populated than the unsymmetric isomer. Once again

rotation of the Trop ligand relative to the metal wedge

accounts for these observations (eq 11). Complex 3

(93) Bruce, M. D.; Coates, G. W.; Hauptman, E.; Waymouth, R. M.;

Ziller, J . W. J . Am. Chem. Soc. 1997, 119, 11174.

(94) Knickmeier, M.; Erker, G.; Fox, T. J . Am. Chem. Soc. 1996,

118, 9623.

(95) Erker, G.; Aulbach, M.; Knickmeier, M.; Wingbermu¨hle, D.;

Kru¨ger, C.; Nolte, M.; Werner, S. J . Am. Chem. Soc. 1993, 115, 4590.

(96) Luke, W. D.; Streitwiser, A., J r. J . Am. Chem. Soc. 1981, 103,

3241.

(97) Buchmann, B.; Piantini, U.; von Philipsborn, W.; Salzer, A.

Helv. Chim. Acta 1987, 70, 1487.

exhibited similar behavior, with the exception that a

(98) Thomas, B. J .; Noh, S. K.; Schulte, G. K.; Sendlinger, S. C.;

Theopold, K. H. J . Am. Chem. Soc. 1991, 113, 893.

(99) Bhandari, G.; Kim, Y.; McFarland, J . M.; Rhingold, A. L.;

Theopold, K. H. Organometallics 1995, 14, 738.

(92) Maciejewski-Petoff, J . L.; Bruce, M. D.; Waymouth, R. M.;

Masood, A. M.; Lal, T. K.; Quan, R. W.; Behred, S. J . Organometallics

1997, 16, 5909.

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1417

Sch em e 4

tion on cyclopentadienyl rings slows down the chain

transfer step relative to the ethylene insertion. This

resulted in higher molecular weight PE for the CpCp*ZrCl₂/

MAO and Cp*₂ZrCl₂/MAO systems relative to that for

Cp₂ZrCl₂/MAO.⁷⁰

ethylene (Table 10). Spectroscopic investigation revealed

the presence of the cationic zirconium complex [(Cp)-

(Trop)ZrMe][MeB(C₆F₅)₃] (14).^79,80Both sides of the Trop

ligand in 14 were equivalent at 20 °C in a C₆D₅Cl

solution, indicating that an exchange process permutes

both sides of the diastereotopic Trop ligand.

Resconi et al.⁷⁷have analyzed the end groups of

propylene oligomers by ¹³C{¹H} NMR. They noted that

the presence of n-propyl and isobutyl end groups are

indicative of a â-H elimination mechanism¹⁰⁰for chain

transfer, and the presence of isobutyl end groups is

consistent with an aluminum chain transfer mecha-

nism.¹⁰¹For the 3/MMAO catalyst system, based on

the end groups present in the isolated oligomer, the

predominant chain transfer mechanism involves â-H

elimination. For this catalyst system no evidence was

found for a â-Me elimination chain transfer path-

way.¹⁰²

Na tu r e of th e Active Ca ta lyst Sp ecies. Mack and

Eisen have shown that amide ligands can be abstracted

by strong Lewis acids such as MAO.¹⁰³Attack upon the

Trop ligand by a strong Lewis acid like MMAO could

convert the complex to a non-Trop-bearing catalyst

during the polymerization or deactivate the catalyst

system. Experiments were carried out to determine

whether the Trop ligand remained intact for precatalyst

3 upon treatment with MMAO. As described above, 3

is regenerated in good yield after activation using

MMAO by adding excess (n-Bu)₃NHCl as a quenching

reagent. These results suggest that that for complex 3

the Trop ligand remains at least substantially intact

during the time of the polymerizations used in this

study.¹⁰⁴

From the data in Table 10, it can be seen that the

complexes bearing the Trop ligand exhibited higher

activities than their corresponding parent metal halides.

These observations reinforce our judgment that the Trop

ligand remains coordinated during the polymerization

catalysis. However, the increase in catalytic activity, for

the generation of PE using complexes 2 and 4, imparted

by coordination of the Trop ligand was modest at best.

Furthermore, the 4/MMAO catalyst system generated

PP, while the CpTiCl₃/MMAO system failed to generate

any PP, indicating that the Trop ligand also imparts

enhanced catalytic reactivity to this complex for the

polymerization of propylene.

Two general mechanisms have been proposed for ex-

change of diastereotopic groups on the ancillary ligands

in group 4 metallocinium ions generated by methide

abstraction using B(C₆F₅)₃.^80,105,106These mechanisms

as applied to complex 14 are shown in Scheme 4. One

exchange pathway involves dissociation of B(C₆F₅)₃to

form two neutral species, followed by reabstraction of

the unique ZrMe group; this is denoted as the borane

dissociation mechanism (mechanism a). The other mech-

anism involves ion-pair separation to form a solvent-

separated cation/anion pair followed by reassociation;

this is denoted as the ion pair dissociation-recombina-

tion mechanism (mechanism b). The former mechanism

exchanges both the ZrMe/BMe groups and the diaste-

reotopic groups on the ligand, while the latter mecha-

nism only exchanges diastereotopic groups on the

ligands. At low temperature in C₆D₅Cl the borane

disassociation mechanism (a) is apparently much slower

than the ion-pair separation mechanism (b) since the

ZrMe and BMe resonances were clearly separated and

no broadening was observed relative to the line shapes

of nonexchanging resonances. Similar results were

observed for [(1,2-(CH₃)₂C₅H₃)₂ZrMe][CH₃B(C₆F₅)₃],

where the rate for ion-pair dissociation was observed

to be 10³times faster than the rate of borane dissocia-

tion at 25 °C in C₆D₅Cl.¹⁰⁶The instability of 14

precluded heating the sample to measure the barrier

for borane dissociation. Qualitatively, we can say from

the current set of experiments that as observed in

Marks’ system, ion-pair dissociation (mechanism b) is

more facile than that of borane dissociation (mechanism

a) at the temperatures employed in this study.

(100) Kaminsky, W.; Ahlers, A.; Mo¨ller-Lindenhof, N. Angew. Chem.,

Int. Ed. Engl. 1989, 28, 1216.

(101) Resconi, L.; Bossi, S.; Abis, L. Macromolecules 1990, 23, 4489.

(102) Eshuis, J . J . W.; Tan, Y. Y.; Teuben, J . H.; Renkema, J . J .

Mol. Catal. 1990, 62, 277.

(103) Mack, H.; Eisen, M. S. J . Organomet. Chem. 1996, 525, 81.

(104) It is of course difficult to rule out the possibility that only a

small concentration of an extremely active “unknown” catalyst is

responsible for the majority of the polymer produced.

(105) Deck, P. A.; Marks, T. J . J . Am. Chem. Soc. 1995, 117, 6128.

(106) Deck, P. A.; Beswick, C. L.; Marks, T. J . J . Am. Chem. Soc.

1998, 120, 1772.

To further our understanding of the active catalyst

species, we generated catalyst system 6/B(C₆F₅)₃and

found it to be highly active for the polymerization of

1418 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

Toluene, pentane, hexanes, methylene chloride, and benzene

(Fisher) were passed through a column of activated alumina

(type A2, size 12 × 32, Purifry Co.) under nitrogen pressure

and sparged with N₂prior to use. Diethyl ether and tetrahy-

drofuran (Fisher) were distilled from purple sodium/benzophe-

none ketyl under N₂prior to use. All deuterated solvents were

purchased from Cambridge Isotope Laboratories. Benzene-d₆,

toluene-d₈, and THF-d₈were vacuum transferred from purple

sodium/benzophenone ketyl solutions, and CD₂Cl₂was vacuum

transferred from CaH₂. Chlorobenzene-d₅and C₂D₂Cl₄were

degassed, stored over 4 Å sieves, and filtered through dry

Celite before use.

NMR Sp ectr oscop y. NMR experiments were performed

on a Bruker AMX spectrometer resonating at 300.13 MHz for

¹H that was equipped with an inverse probe. One-dimensional

¹³C{¹H} spectra and DEPT spectra were recorded on either a

Bruker AMX spectrometer resonating at 400 MHz for ¹H or

100 MHz for ¹³C that was equipped with a QNP probe or a

Bruker DRX spectrometer resonating at 500 MHz for ¹H or

125 MHz for ¹³C that was equipped with a broad band probe.

The 2D EXSY spectrum was acquired in phase-sensitive mode

using the Bruker pulse program noesytp at 298 K. NMR

analyses of the PP samples were carried out in C₂D₂Cl₄at 100

°C using 1% polymer loading for the long-chain PP and 10%

polymer loading for PP oligomer.

Con clu sion

Using a stannyltropidine reagent, a new class of group

4 complexes bearing the tropidinyl ligand have been

synthesized and their properties investigated. The metal

complexes display fluxional behavior, and the exchange

pathways responsible for these observations were in-

vestigated. The dialkyl complexes display reactivity akin

to that of the analogous Cp complexes. Some of the

complexes were shown to be active polymerization

catalysts when combined with an appropriate cocatalyst.

Upon activation with MMAO, the (Cp)(Trop)ZrCl₂(3)

precatalyst system displayed PE activities and lifetimes

similar to those of Cp₂ZrCl₂/MMAO. Two Trop-based

catalyst systems (3/MMAO and 4/MMAO) were shown

to polymerize propylene. The nature of the active

catalyst species was investigated by methide abstraction

from (Cp)(Trop)ZrMe₂(6) using tris(pentafluorophenyl)-

borane. The observed cationic complex was less stable

than, but displayed similar dynamic behavior to, met-

allocene systems. Current efforts are directed toward

developing synthetic routes to ansa-Trop complexes and

adding substituents to the Trop ligand to investigate

and improve the selectivity and/or activity of the

catalyst systems.

Eth ylen e P olym er iza tion Exp er im en ts. The following

adapted procedure was used for the ethylene polymerization

experiments.⁶⁹Reactions were carried out in oven-dried 250

mL Schlenk flasks with a straight bore stopcock capped with

a septum equipped with a large stir bar and a Teflon valve

attached to a ground glass joint. The flask was charged with

100 mL of toluene inside a glovebox and then attached to a

vacuum line. The toluene was degassed, allowed to saturate

under 1 atm of ethylene, and then brought to the reaction

temperature using a Neslab Endocal LT-50DD constant tem-

perature controller. The catalyst solutions were prepared in

the glovebox by adding a known quantity of MMAO (2.2 mL

of a 2.3 M solution) to a weighed sample of the group 4

precatalyst. The catalyst solution was loaded into a syringe,

removed from the glovebox, and quickly added to the reaction

flask through the septum-capped straight bore stopcock. The

polymerization reaction was allowed to proceed with constant

stirring and stopped by venting the monomer and immediately

quenching with 3 mL of 10% aqueous concentrated HCl/

methanol. The resulting polyethylene was filtered, washed

with 10% HCl, water, and methanol, and dried in an oven or

under vacuum to a constant weight. By performing multiple

runs using the same catalysts the precision of the activities

measured using this method was found to fall within a factor

of 2 of each other. Ethylene uptake measurements were

performed using a MKS Baratron pressure gauge to monitor

the pressure drop using a setup described in the literature.⁹⁸

P r op ylen e P olym er iza tion Exp er im en ts. All propylene

polymerizations were carried out in neat propylene in a 3 oz

Lab Crest glass (rated to 200 psig) reactor with a stir bar using

a modification of an established procedure.¹⁰⁸The flask was

charged with 0.322 g of solid MMAO (dried by removing the

toluene under reduced pressure and exposing to high vacuum

for 48 h) in the glovebox. The flask was then sealed and the

entire reactor assembly removed from the glovebox. The

reactor was equipped with an inlet valve, stir bar, pressure

gauge, a septum port (stainless steel ball valve with a silicone

rubber septum) placed in a 1/4 in. compression fitting, and a

pressure relief valve set to 175 psig. The reactor was then

attached to the propylene line, and the inlet valve was purged

with propylene for 2 min at 25 psig. The flask was cooled to

-78 °C, and propylene (∼50 mL) was then condensed into the

cooled reaction flask. The reactor assembly was protected with

Exp er im en ta l Section

Gen er a l Meth od s. All reactions were performed under an

inert atmosphere (Ar or N₂) using standard glovebox or

Schlenk techniques.¹⁰⁷All infrared (IR) spectra were recorded

on a Mattson Galaxy series FT-IR 3000 spectrometer. UV-

vis experiments were preformed using a Hewlett-Packard 8453

UV-vis spectrometer. Gas chromatography was carried out

using a Hewlett-Packard 5890 series II instrument using a

60 m J and W Scientific DB-XLB column equipped with a

flame ionization detector. GC/MS analysis was carried out

using a Hewlett-Packard 6890 series GC system, equipped

with a 30 m DB-XLB column, with a Hewlett-Packard model

5973 mass selector detector using an ionization voltage of 70

eV. Mass spectrometric (MS) analyses were performed at the

University of California, Berkeley Mass Spectrometry facility

on a AEI MS-12 and Kratos MS-50 mass spectrometers.

Elemental analyses were performed by the University of

California, Berkeley Microanalytical facility. X-ray structural

analyses were performed at the University of California,

Berkeley CHEXRAY facility. DSC analysis was performed on

a TA Instruments DSC 2010 differential scanning calorimeter

at a heating rate of one deg min^-1. GPC analyses of the PE

and PP samples were carried out using a Waters 150 C+

instrument at 145 °C in 1,2,4-trichlorobenzene and calibrated

using a standard sample of PE or PP.

Unless otherwise noted, all reagents were purchased from

Aldrich and used without further purification, and 1 was

synthesized as described previously.⁴⁵The metal halides

CpZrCl₃and CpTiCl₃were purchased from Strem Chemicals,

and 2,6-dimethylisocyanate was purchased from Fluka and

dried over 4 Å sieves as an ethereal solution. MMAO was pur-

chased from Akzo-Nobel, and tris(pentafluorophenyl)borane

was obtained from Albemarle. Polymer grade ethylene and

propylene were purified by passage though a Matheson model

6427-46 oxygen/moisture trap. Potassium bromide (Aldrich),

Celite (Aldrich), silica gel (Merck 60, 230-400), and alumina

(Brockman I, Aldrich) were dried in vacuo at 250 °C for 48 h.

(107) Burger, B. J .; Bercaw, J . E. Vacuum Line Techniques for

Handling Air-Sensitive Organometallic Compounds; In Wayda, A. L.,

Darensbourg, M. Y., Eds. Experimental Organometallic Chemistry;

American Chemical Society: Washington D.C., 1987; Vol. 357, pp 79-

98.

(108) Herzog, T. A.; Zubris, D. L.; Bercaw, J . E. J . Am. Chem. Soc.

1996, 118, 11988.

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1419

a safety shield and allowed to warm to 0 °C. The catalyst

solutions were prepared in the glovebox (∼2 mg or 0.0051

mmol precatalyst in 0.5 mL of either dichloromethane or

toluene) and loaded into a 1 mL Hamilton gastight syringe

with a ground glass luer tip and a 5 in. 15 gauge stainless

steel needle attached with ITW Devon 5 Minute epoxy. The

precatalyst solution was removed from the glovebox and then

injected through the septum port to initiate the reaction. The

polymerizations were allowed to proceed with constant stirring

for 4 h, after which time the monomer was slowly vented and

the reaction quenched with 3 mL of 10% aqueous concentrated

HCl/methanol. The high molecular weight polypropylene was

scraped from the walls of the reaction flask and washed with

water and methanol, dried under vacuum, and weighed. After

quenching the reaction liquid oligomer was extracted using

pentane, separated from the aqueous layer, dried over MgSO₄,

filtered, then concentrated using rotary evaporation.

(Tr op )₂Zr Cl₂(2). A Schlenk flask was charged with a

solution of ZrCl₄(0.391 g, 1.68 mmol) in CH₂Cl₂(12 mL). The

tin reagent 1 (0.959 g, 3.35 mmol) was slowly added. The

solution immediately turned orange and was stirred for 4 h

at room temperature. The reaction mixture was filtered and

the solid extracted with CH₂Cl₂(2 × 3 mL). The volatile

materials were removed from the filtrate under reduced

pressure, and the residue was washed thoroughly with pentane

and then extracted with toluene. The solvent was removed

under vacuum to give 0.572 mg (46%) of an analytically pure

fine orange powder. ¹H NMR (300 MHz, CD₂Cl₂, 20 °C and

-90 °C): see Table 6. ¹H NMR (300 MHz, C₆D₆, 20 °C): δ 5.38

(t, J ) 7.3 Hz, 2H, central allylic), 4.26 (br s, 4H, terminal

allylic), 3.54 (br s, 4H, bridgehead), 2.29 (s, 6H, NMe), 1.84

(s, 4H, CH₂), 1.68 (m, 4H, CH₂). ¹³C{¹H} NMR (100 MHz,

CD₂Cl₂, 20 °C): δ 132.0 (central allylic) 87.6 (terminal allylic),

67.0 (bridgehead), 41.2 (NMe), 38.9 (CH₂). Anal. Calcd for

CH₂Cl₂and filtered through glass fiber filter paper, the solvent

removed under reduced pressure, and the mixture left under

vacuum for 12 h to give 0.65 g (97%) of analytically pure 4.

Complex 4 was isolated as a mixture of two isomers (see text).

¹H NMR (300 MHz, CDCl₃, 100 °C and CD₂Cl₂20 °C): see

Table 6. ¹³C{¹H} (125 MHz, CD₂Cl₂, RT): δ (isomer 4a ) 123.58

(central allylic), 118.32 (C₅H₅), 102.90 (terminal allylic), 66.72

(bridgehead), 40.46 (NCH₃), 35.24 (CH₂); (isomer 4b) 132.21

(central allylic), 123.58 (terminal allylic), 119.56 (C₅H₅), 88.93

(terminal allylic), 67.62 (bridgehead), 64.43 (bridgehead), 42.78

(NCH₃), 35.46 (CH₂), 34.25 (CH₂). MS (EI): m/z 305 (M⁺). Anal.

Calcd for C₁₃H₁₇Cl₂NTi: C, 51.01; H, 5.60; N, 4.58. Found: C,

50.69; H, 5.70; N, 4.27.

(Tr op )₂Zr Me₂(5). The zirconium dichloride complex 2 (118

mg, 0.290 mmol) was dissolved in 10 mL of THF and cooled to

-30 °C. Methyllithium (0.41 mL, 1.4 M in Et₂O) was added,

and the reaction mixture was stirred at room temperature for

an additional 3.5 h. The solvent was evaporated under reduced

pressure, and the residue was extracted with pentane. The

combined pentane extracts were filtered through Celite. The

filtrate was recovered, and the volatile materials were removed

under vacuum to yield 94.6 mg (89%) of analytically pure

1

yellow solid. H NMR (300 MHz, CD₂Cl₂, 20 °C): see Table 3.

¹H NMR (C₆D₆): δ 4.86 (dd, J ) 7.4 Hz, 2H, central allylic),

3.87 (q, J ) 7.3 Hz, 4H, terminal allylic), 3.31 (br, 4H,

bridgehead), 2.12 (m, 4H, CH₂), 2.02 (s, 6H, NMe), 1.90 (m,

4H, CH₂), 0.22 (s, 6H, ZrMe₂). ¹³C{¹H} (100 MHz, CD₂Cl₂, 20

°C): δ 149.7 (central allylic), 103.9 (terminal allylic), 90.1

(bridgehead), 63.9 (NMe), 63.2 (CH₂), 47.6 (ZrMe₂). ¹³C{¹H}

NMR (100 MHz, C₆D₆, 20 °C): δ 126.3 (central allylic), 80.4

(terminal allylic), 66.8 (bridgehead), 40.4 (NMe), 39.9 (CH₂),

25.8 (ZrMe₂). Anal. Calcd for C₁₈H₃₀N₂Zr: C, 59.12; H, 8.27;

N, 7.66. Found: C, 59.43; H, 8.38; N 7.60. LRMS (EI), m/z:

calcd 364. Found: 364.

C

₁₆H₂₄N₂Cl₂Zr: C, 47.28; H, 5.95; N, 6.89. Found: C, 46.78;

(Cp )(Tr op )Zr Me₂(6). To a cooled (-30 °C) suspension of

3 (0.467 g, 1.34 mmol) in Et₂O (10 mL) was added methyl-

lithium (1.86 mL, 1.45 M in ether) over a period of 5 min. The

mixture was allowed to react for 1 h at -30 °C and finally

warmed to room temperature. The supernatant was filtered

through a pad of Celite, the filter cake was washed with Et₂O

(3 × 2 mL), and the solvent was removed under reduced

pressure. The crude product was extracted with pentane (3 ×

5 mL), and the combined fractions were filtered through glass

fiber filter paper. The solution was concentrated to 8 mL and

cooled to -30 °C for 12 h, and yellow crystals were isolated to

give 0.253 g of 6. The resulting supernatant was then

concentrated to 5 mL to give a second crop (0.043 g, 72%

combined yield). The product was observed to decompose upon

H, 5.85; N, 6.60. HRMS calcd: 404.0364. Found: 404.0361.

(Cp )(Tr op )Zr Cl₂(3). A solution of 1 (3.03 g, 7.86 mmol)

was added to a suspension of CpZrCl₃(2.03 g, 7.73 mmol) in

CH₂Cl₂(100 mL). Upon addition of the tin reagent the solution

immediately turned orange. The solution became homoge-

neous, and it was allowed to stir for 45 min. The solvent was

removed under reduced pressure. The crude product was

washed with pentane (3 × 60 mL), and the material was placed

under vacuum for 12 h. The crude material was taken up in a

minimum amount of CH₂Cl₂(100 mL) and filtered through

glass fiber filter paper into a 250 mL round-bottom Schlenk

flask. Then 100 mL of pentane was slowly added, and an

orange precipitate immediately formed. The flask was attached

to a swivel frit assembly, cooled to -78 °C, and allowed to stir

for 0.5 h. The orange precipitate was collected by filtration at

-78 °C. The material was then washed with pentane and dried

under vacuum (2.19 g, 81% yield). Analytically pure material

was obtained by slow cooling (-40 °C) of a saturated CH₂Cl₂

solution to afford crystals of 3. ¹H NMR (300 MHz, CD₂Cl₂, 20

1

prolonged exposure to dynamic vacuum. H NMR (300 MHz,

CD₂Cl₂, 20 °C): see Table 6. ¹H NMR (300 MHz, C₆D₆, RT): δ

5.77 (5H, s, C₅H₅), 4.34 (1H, J ) 7.5 Hz, central allylic), 3.84

(2H, q, J ) 7.2, 4.5, terminal allylic), 3.18 (2H, br, bridgehead),

1.99 (2H, q, J ) 10.2, 4.5, CH₂), 1.86 (3H, br, NCH₃), 1.78-

1.72 (2 H, m, CH₂).). ¹³C{¹H} (125.75 MHz, C₆D₆, RT): δ 123.1

(CH, central allylic), 109.6 (CH, C₅H₅), 79.9 (CH, terminal

allylic), 66.3 (CH, bridgehead), 39.8 (CH₃, NMe), 39.5 (CH₂),

27.0 (CH₃, ZrMe). HRMS (EI) m/z M⁺calcd for C₁₅H₂₃NZr:

307.087. Found: 307.088 (a ¹H NMR spectrum of purified

material used to obtain the HRMS is provided in the Support-

ing Information).

1

°C and -70 °C): see Table 6. H NMR (300 MHz, C₆D₆, RT):

δ 5.89 (5H, s, C₅H₅), 4.76 (1 H, br, central allylic), 3.82 (2H,

br, terminal allylic), 3.56 (2H, br, bridgehead), 2.40 (3H, br,

NCH₃), 1.69-1.59 (4H, m, CH₂). ¹³C{¹H} (100 MHz, CD₂Cl₂,

20 °C): δ 129.9 (central allylic), 114.2 (C₅H₅), 88.0 (terminal

allylic), 66.4 (bridgehead), 40.2 (NCH₃), 38.3 (CH₂). UV (tolu-

ene) λ_max, nm (ꢀ): 421 (1,371). MS (EI): m/z 347 (M⁺). Anal.

Calcd for C₁₃H₁₇Cl₂NZr: C, 44.69; H, 4.90; N, 4.01. Found: C,

44.42; H, 4.98; N, 3.75.

(Cp )(Tr op )TiMe₂(7). Methyllithium (0.6 mL, 1.4 M in

Et₂O) was added to a cooled (-30 °C) suspension of (Cp)(Trop)-

TiCl₂(4) (0.128 g, 0.42 mmol) in Et₂O (4 mL). The reaction

was allowed to proceed at -30 °C for 1.5 h. The red/brown

supernatant was separated from the LiCl by filtration through

a pad of Celite while still somewhat cold and the Et₂O removed

under reduced pressure. The resulting red solid was extracted

with pentane (3 × 3 mL), filtered through glass fiber filter

paper, concentrated to 6 mL, and cooled to -30 °C for 12 h.

Red needles were then harvested to give 0.065 g (58% yield)

(Cp )(Tr op )TiCl₂(4). A solution of 1 (0.625 g, 2.18 mmol)

in CH₂Cl₂(3 mL) was added to a suspension of CpTiCl₃(0.471

g, 2.14 mmol) in CH₂Cl₂(3 mL). The color of the solution

immediately changed from orange to yellow to green, and the

reaction was allowed to proceed for 12 h. The solvent was

removed under reduced pressure, and the green residue was

washed with pentane (3 × 5 mL) and left under dynamic

vacuum for 12 h. Finally, the green solid was taken up in

1

of analytically pure material. H NMR (500 MHz, CD₂Cl₂, 20

1420 Organometallics, Vol. 19, No. 7, 2000

Skoog et al.

°C and -80 °C): see Table 6. ¹³C{¹H} (125.75 MHz, CD₂Cl₂,

RT): δ 128.78 (CH, central allylic), 113.61 (CH, C₅H₅), 65.99

(CH, bridgehead), 41.25 (CH₃, NMe), 37.59 (CH₂). ¹³C{¹H}

(125.75 MHz, CD₂Cl₂, -80 °C): δ 127.84 (CH, central allylic),

113.04 (CH, C₅H₅), 100.61 (CH, terminal allylic), 77.26 (CH,

terminal allylic), 66.16 (CH, bridgehead), 62.32 (CH, bridge-

head), 46.39 (CH₃, TiMe), 40.27 (CH₃, NMe), 37.74 (CH₂), 35.72

(CH₂), 27.93 (CH₃, TiMe). Anal. Calcd for C₁₅H₂₃NTi: C, 67.92;

H, 8.74; N, 5.28. Found: C, 67.54; H, 8.95; N, 5.17.

(Tr op )₂Zr Bn ₂(8). Complex 2 (103 mg; 0.254 mmol) was

dissolved in THF (10 mL) and cooled to -30 °C. Benzylmag-

nesium chloride (1 M in ether; 0.48 mL; 0.48 mmol) was added

to the solution and it was stirred at room temperature for 2

h. The solvents were removed in vacuo. Complex 8 was

recovered by extraction of the residue with toluene. The

volatile materials were removed to give 110 mg (88%) of an

orange solid, which was recrystallized by vapor diffusion of

pentane into a toluene solution of 8 at -30 °C to give

analytically pure crystals. ¹H NMR (300 MHz, C₆D₆, RT): see

Table 6. ¹³C{¹H} NMR (100 MHz, C₆D₆, RT): δ 155.8 (C, ipso),

128.9 (CH, central allylic), 128.0 (CH, Ar), 125.7 (CH, Ar),

119.4 (CH, p-Ar), 83.8 (CH, terminal allylic), 66.4 (CH,

bridgehead), 58.6 (CH₂Ar), 40.2 (NMe), 39.5 (CH₂). Anal. Calcd

for C₃₀H₃₈N₂Zr₁: C, 69.58; H, 7.40; N, 5.41. Found: C, 69.56;

H, 7.60; N, 5.21.

(Cp )(Tr op )Zr Bn ₂(9). Benzylmagnesium chloride (0.5 mL,

1.22 M) was added to a cooled (-30 °C) suspension of (Cp)-

(Trop)ZrCl₂(0.106 g, 0.304 mmol) in Et₂O (8 mL). The reaction

mixture was allowed to warm to room temperature and

allowed to stir for 2 h. The orange supernatant was separated

from MgCl₂by filtration through Celite. The Et₂O was then

removed under reduced pressure to leave an orange solid

(0.132 g, 94% yield). Analytically pure material was obtained

by slow cooling (-40 °C) of a saturated toluene solution. ¹H

NMR (300 MHz, C₆D₆, 20 °C): see Table 6. ¹³C{¹H} (125.75

MHz, C₆D₆, RT): δ 154.09 (C, ipso), 128.38 (CH, central allylic),

128.29 (CH, Ar), 128.30 (CH, Ar), 126.04 (CH, Ar), 120.43 (CH,

p-Ar), 112.23 (CH, Cp), 81.72 (CH, terminal allylic), 66.54 (CH,

bridgehead), 58.36 (CH₂), 39.65 (CH₃, NMe), 39.02 (CH₂,

CH₂Ar). Anal. Calcd for C₂₇H₃₁Cl₂NZr: C, 70.38; H, 6.78; N,

3.01. Found: C, 70.02; H, 7.05; N, 3.05.

vacuo. The solid was washed with pentane (4 × 3 mL) until

the filtrate was colorless. The residue was extracted with THF.

The filtrate was collected and the solvent removed under

reduced pressure to give 49.4 mg (89%) of yellow solid.

Attempts to recrystallize 11 were unsuccessful, and substantial

decomposition was observed when 11 was subjected to LRMS

conditions. ¹H NMR (400 MHz, toluene-d₈, 20 °C): δ 5.11 (dd,

J ) 7.4 Hz, 2H, central allylic), 3.99 (m, 4H, terminal allylic),

3.12 (br s, 2H, bridgehead), 3.06 (br s, 2H, bridgehead), 1.92

(m, 4H, CH₂), 1.84 (s, 6H, NMe), 1.69 (m, 4H, CH₂), 0.38 (s,

3H, ZrMe). ¹³C{¹H} NMR (100 MHz, toluene-d₈, 20 °C):

δ

129.5, 128.6 (CH, central allylic), 85.3, 82.9 (CH, terminal

allylic), 66.4, 66.0 (CH, bridgehead), 39.8 (CH₂), 39.1 (CH₃),

39.0 (CH₃) (CF₃was not detected). ¹⁹F{¹H} NMR (400 MHz,

toluene-d₈, 20 °C): δ -77.0. LRMS (EI) m/z on C₁₈H₂₇N₂F₃O₃-

SZr calcd: 498. Found: 499.

(Tr op )₂Zr (Me)(NH-t-Bu ) (12). A solution of complex 11

(44.1 mg, 0.0883 mmol) in THF (10 mL) was cooled to -30 °C,

and LiNH-t-Bu (7.2 mg, 0.091 mmol) was added to it. The

reaction mixture was warmed to room temperature and stirred

for 15 min. The solvents were removed in vacuo and the

residue extracted with toluene. The volatiles were removed

under reduced pressure to give 34.2 mg (92%) of (Trop)₂Zr-

(Me)(NH-t-Bu). Attempts to recrystallize 12 were unsuccessful.

Analysis by electron-impact mass spectrometry did not give

satisfactory results, presumably due to decomposition of 12

under the experimental conditions. ¹H NMR (400 MHz, C₆D₆,

20 °C): δ 5.55 (t, J ) 7.4 Hz, 2H, central allylic), 4.08 (m, 2H,

terminal allylic), 3.81 (m, 2H, terminal allylic), 3.36 (br t, J )

5.3 Hz, 2H, bridgehead), 2.91 (br t, J ) 5.4 Hz, 2H, bridge-

head), 2.18 (m, 4H, CH₂), 1.92 (s, 6H, NMe), 1.88 (m, 4H, CH₂),

1.29 (s, 9H, t-Bu), -0.30 (s, 3H, ZrMe). ¹H NMR (300 MHz,

THF-d₈, 20 °C): δ 5.48 (t, J ) 7.4 Hz, 2 H, central allylic),

3.96 (m, 2H, terminal allylic), 3.88 (m, 2 H, terminal allylic),

3.86 (br s, 1H, NH), 3.22 (br s, 2 H, bridgehead), 3.23 (br s, 2

H, bridgehead), 2.20 (s, 6H, NMe), 2.19 (m, 8 H, CH₂), 1.08 (s,

9H, t-Bu), -0.17 (s, 3 H, ZrMe). ¹³C{¹H} NMR (100 MHz, C₆D₆,

20 °C): δ 127.6 (CH, central allylic), 81.3 (CH, br, terminal

allylic), 80.2 (C, CMe₃), 78.2 (CH, br, terminal allylic), 67.6

(CH, bridgehead), 66.1 (CH, bridgehead), 41.0 (CH₃, NMe), 39.6

(CH₂), 39.5 (CH₂), 34.9 (CH₃, CMe₃), 15.3 (CH₃, ZrMe).

(Cp )(Tr op )Zr (CH ₃)[N(2,6-(CH ₃)₂C₆H₂)C(CH ₃)] (13). A

solution of 2,6-dimethylisocyanate (0.040 g, 0.30 mmol) in C₆H₆

(1 mL) was added to 6 (0.029 g, 0.30 mmol) in C₆H₆(5 mL).

The yellow color began to fade upon addition, and the reaction

was allowed to proceed for 3 h. The solvent was removed under

reduced pressure to give a yellow oil. The oil was extracted

with pentane, and the combined extracts were cooled to -30

°C. After 2 days colorless blocks formed to give 0.092 g (70%

yield) of analytically pure 13. ¹H NMR (300 MHz, C₆D₆, 20

°C): δ 6.94 (3H, s, ArH), 5.86 (5H, br, CpH), 4.84 (1H, t, J )

7.2 Hz, central allylic), 3.80 (1H, br, terminal allylic), 3.51 (1H,

br, bridgehead), 3.06 (1H, br, terminal allylic), 2.79 (1H, br,

bridgehead), 2.09 (6H, s, Ar-CH₃) 1.96 (3H, s, NMe), 1.78 (3H,

s, NCMe), 1.69 (4H, m, CH₂), 0.22 (3H, s, ZrMe). ¹³C{¹H}

(125.75 MHz, toluene-d₈, -50 °C): δ 247.59 (C, ZrCNAr),

147.50 (C, ipso), 130.46 (C, Ar), 129.72 (C, Ar), 128.37 (CH,

Ar), 128.30 (CH, Ar), 127.11 (CH, br), 124.56 (CH), 106.83 (CH,

Cp), 86.83 (CH, br), 68.04 (CH), 66.36 (CH), 65.09 (CH), 41.37

(CH₃, NMe), 39.63 (CH₂), 39.31 (CH₂), 23.18 (CH₃, CNCH₃),

19.01 (CH₃, ArCH₃), 18.95 (CH₃, CH₃Ar), 3.97 (CH₃, br, ZrMe).

IR (KBr, cm^-1): 1577 (s, ν_NC). Anal. Calcd for C₂₄H₃₂N₂Zr: C,

65.55; H, 7.33; N, 6.37. Found: C, 65.39; H, 7.59; N, 6.04.

Ca ta lyst Recover y Stu d ies. A solution of (Cp)(Trop)ZrCl₂

(3) in toluene was added to a solution of MMAO to yield a

solution 3.8 × 10^-5M in 3 and 0.04 M in MMAO. This solution

was separated into three fractions. The first fraction was

analyzed by UV-vis spectroscopy. The band at 421 nm

(corresponding to 3) was absent, indicating that all of 3 reacted

with the MMAO. After several minutes the second fraction

was quenched with solid (n-Bu)₃NHCl (to give a 0.4 M solution

(Tr op )₂Zr (Me)(O-t-Bu )

(10).

(Method

A)

From

(Trop)₂ZrMe₂: Complex 5 (6.0 mg, 0.016 mmol) was dissolved

in 4 mL of pentane and cooled to -30 °C, and tert-butyl alcohol

(2.5 mg, 0.034 mmol) in pentane (2 mL) was added. The

reaction mixture was stirred for 15 min. The volatile materials

were removed under vacuum to yield (Trop)₂Zr(Me)(O-t-Bu)

as an analytically pure pale yellow solid. (Method B) From

(Trop)₂Zr(Me)(OSO₂CF₃): Potassium tert-butoxide (1.6 mg;

0.014 mmol) in THF (1 mL) was added to a solution of

(Trop)₂Zr(Me)(OSO₂CF₃) (11) (67.0 mg, 0.013 mmol) in THF

(2 mL) cooled to -30 °C. After 10 min at room temperature,

the solvent was removed under reduced pressure, and the

residue was extracted with pentane. The extracts were com-

bined, and the solvent was removed in vacuo to give 5.0 mg

1

(88%) of complex 5. H NMR (300 MHz, C₆D₆, 20 °C): δ 5.38

(t, J ) 7.3 Hz, 2H, central allylic), 4.29 (m, 2H, terminal

allylic), 4.02 (m, 2H, terminal allylic), 3.40 (m, 2H, bridgehead),

2.87 (m, 2H, bridgehead), 2.19 (m, 4H, CH₂), 1.86 (s, 10H, NMe

and CH₂), 1.22 (s, 9H, O-t-Bu), 0.35 (s, 3H, ZrMe). ¹³C{¹H}

NMR (100 MHz, C₆D₆, 20 °C): δ 128.4 (CH, central allylic),

86.8 (CH, br, terminal allylic), 75.9 (C, CMe₃), 72.2 (CH, br,

terminal allylic), 67.6 (CH, bridgehead), 65.5 (CH, bridgehead),

41.2 (CH₃, NMe), 39.8 (CH₂), 39.5 (CH₂), 33.0 (CMe₃), 10.0

(ZrMe). Anal. Calcd for C₂₁H₃₆N₂O₁Zr₁: C, 59.52; H, 8.56; N,

6.61. Found: C, 59.22; H, 8.74; N, 6.45.

(Tr op )₂Zr (Me)(OSO₂CF ₃) (11). Trifluoromethanesulfonic

acid (9.8 µL, 0.11 mmol) was added to a solution of complex 5

(41.3 mg, 0.113 mmol) in pentane (12 mL) at -30 °C. The

reaction mixture was warmed to room temperature and stirred

for an additional 1 h. The volatile materials were removed in

Group 4 Tropidinyl Complexes

Organometallics, Vol. 19, No. 7, 2000 1421

in amine salt) and analyzed by UV-vis spectroscopy. Complex

3 was regenerated as evidenced by the reappearance of the

band at 421 nm. From the absorbance of this band the

concentration of 3 was calculated to be 4.4 × 10^-5M using

the molar absorptivity (ꢀ ) 1.371) obtained from a Beers law

plot of 3 in pure toluene. The third fraction (5 mL) was placed

under an atmosphere of ethylene. From the weight of PE

generated the activity was calculated to be 2632 × 10³g PE/

mol [Zr] h. A similar reaction sequence was performed in which

5 equiv of MMAO was added to 0.5 mL of orange solution (9.0

× 10^-3M) of 3 in toluene-d₈. The resulting red solution was

quenched by adding 50 equiv of solid (n-Bu)₃NHCl, and the

original orange color was restored. Analysis of the quenched

solution by NMR indicated 88% recovery of 3 relative to a

ferrocene internal standard.

McAuley.¹¹²The values for the mass attenuation coefficients

are those of Creagh and Hubble.¹¹³All calculations were

performed using the teXsan crystallographic software package

of the Molecular Structure Corporation. An ORTEP diagram

is given in Figure 1; selected bond lengths and angles are given

in Table 2. A complete listing of experimental details, posi-

tional and anisotropic thermal parameters, and tables of bond

lengths and bond angles are provided as Supporting Informa-

tion for all compounds characterized by X-ray crystallography.

X-r a y Cr ysta l Str u ctu r e of (Cp )(Tr op )Zr Cl₂(3). An

orange columnar crystal of 3, grown from slow cooling of a

saturated CH₂Cl₂solution at -30 °C, was mounted on a glass

fiber using Paratone N hydrocarbon oil.

Cell constants and an orientation matrix, obtained from a

least-squares refinement using the measured positions of 2890

reflections in the range 3.00° < 2θ < 45.00°, corresponded to

a primitive orthorhombic cell with dimensions given in Table

1. On the basis of the systematic absences, packing consider-

ations, a statistical analysis of intensity distribution, and

successful solution and refinement of the structure, the space

group was determined to be Pnma (#62). Data reduction and

structure solution and refinement were performed as described

for 2. An ORTEP diagram is given in Figure 2; selected bond

lengths and angles are given in Table 3.

X-r a y Cr ysta l Str u ctu r e of (Tr op )₂Zr Bn ₂(8). X-ray

quality crystals were obtained by slow cooling of a pentane

solution at -30 °C. The crystal mounting, data collection, data

reduction, and solution and refinement were performed as

described for the X-ray crystallographic analysis of 2 except

the cell constants were determined using 8192 reflections. An

ORTEP diagram is given in Figure 3; selected bond lengths

and angles are given in Table 5.

X-r a y Cr ysta l Str u ctu r e of (Cp )(Tr op )Zr (CH₃)[N(2,6-

(CH₃)₂C₆H₂)C(CH₃)] (13). A single colorless prismatic crystal,

grown from slow cooling of a saturated pentane solution at

-30 °C, was analyzed by X-ray crystallography. The crystal

mounting, data collection, data reduction, and the solution and

refinement were performed as described for the X-ray crystal-

lographic analysis of 2 except the cell constants were deter-

mined using 7082 reflections. An ORTEP diagram is given in

Figure 7; selected bond lengths and angles are given in

Table 9.

Gen er a tion of [(Cp )(Tr op )Zr (CH₃)][CH₃B(C₆F ₅)₃] (14).

Cooled (-30 °C) C₆D₅Cl (0.4 mL) was added to 2.5 mg (0.0081

mmol) of 6 and 4.1 mg (0.0081 mmol) of B(C₆F₅)₃at -30 °C.

The solution was mixed, placed in a NMR tube, sealed with a

Teflon valve, removed from the glovebox, and immediately

cooled to -196 °C. The sample was then placed in a precooled

NMR spectrometer probe, warmed to the desired temperature,

1

and characterized by NMR spectroscopy. H NMR (500 MHz,

C₆D₅Cl, 0 °C): δ 5.95 (5H, br, C₅H₅), 4.89 (1H, br, central

allylic), 4.16 (2H, br, terminal allylic), 2.69 (2H, br, bridge-

head), 1.86 (2H, br, CH₂), 1.64 (2H, br, CH₂), 1.58 (3H, br,

NCH₃), 0.627 (3H, br, BCH₃), 0.18 (3H, br, ZrCH₃). ¹¹B NMR

(160 MHz, C₆D₅Cl, 0 °C): δ -15.1 (s, MeB(C₆F₅)₃). ¹⁹F NMR

(400 MHz, C₆D₅Cl, RT): δ 132.9 (d, J _FF) 40 Hz, 2 F, o-F),

160.4 (br, 1 F, p-F), 154.7 (br, 2 F, m-F).

X-r a y Cr ysta l Str u ctu r e of (Tr op )₂Zr Cl₂(2). An orange

platelike crystal was grown by slow cooling of a saturated

CH₂Cl₂solution and mounted on a glass fiber using Paratone

N hydrocarbon oil. All measurements were made on a Siemens

SMART (Siemens Industrial Automation, Inc.) diffractometer

with a CCD area detector with graphite-monochromated Mo

KR radiation (λ ) 0.71069 Å).

Cell constants and an orientation matrix were obtained from

a least-squares refinement using the measured positions of

4979 reflections in the range 3.00° < 2θ < 45.00° and

corresponded to a primitive orthorhombic cell with dimensions

given in Table 1. On the basis of systematic absences, packing

considerations, a statistical analysis of intensity distribution,

and successful solution and refinement of the structure, the

space group was determined to be P2₁/n (#14). Frames corre-

sponding to an arbitrary hemisphere of data were collected

using ω scans of 0.3° counted for a total of 10.0 s per frame.

Data were integrated by the program SAINT (Siemens

Industrial Automation, Inc.) to a maximum 2θ value given in

Table 1. The data were corrected for Lorentz and polarization

effects. Data were analyzed for agreement and possible

absorption using XPREP (Siemens Industrial Automation,

Inc.). An empirical absorption correction based on comparison

of redundant and equivalent reflections was applied using

XPREP (T_max) 0.91, T_min) 0.80).

Ack n ow led gm en t. We thank the Union Carbide

Corporation, South Charleston, WV, for GPC data,

Albermarle Corporation (Dr. Bruce Berris) for a gift of

tris(pentafluorophenyl)borane, and Kyle Fujdala and

Professor T. Don Tilley for DSC data. We also acknowl-

edge Drs. Dana Caulder and Ryan Powers, University

ofCalifornia,Berkeley,X-raydiffraction facility(CHEXRAY),

for assistance with the X-ray studies. C.M. is grateful

for a postdoctoral fellowship from the Spanish Ministry

of Education and Culture. We are grateful for support

of this work from the National Science Foundation

(Grant No. CHE-9633374).

The structure was solved by direct methods¹⁰⁹and expanded

using Fourier techniques. Non-hydrogen atoms were refined

anisotropically. Hydrogen atoms were refined isotropically. The

final cycle of full-matrix least-squares refinement, based on

the observed reflections and variable parameters given in the

Supporting Information, converged with unweighted and

weighted agreement factors (R and R_w, respectively) given in

Table 1.

Su p p or tin g In for m a tion Ava ila ble: Tables of crystal

data, ORTEP diagrams, bond distances and angles, and

positional and displacement parameters for complexes 2, 3,

5, 8, and 13 and spectroscopic data for 6 and 4a /4b are

provided. This material is available free of charge via the

Internet at http://pubs.acs.org.

Neutral atom scattering factors were taken from Cromer

OM000038K

and Waber.¹¹⁰Anomalous dispersion effects were included in

111

F_calc

;

the values for ∆f ′ and ∆f ′′ were those of Creagh and

(111) Ibers, J . A.; Hamilton, W. C. Acta Crystallogr. 1964, 17, 781.

(112) Creagh, D. C.; McAuley, W. J . International Tables for

Crystallography; Wilson, A. J . C., Ed.; Kluwer Academic Publishers:

Boston, 1992; Vol. C, pp 219-222.

(113) Creagh, D. C.; Hubble, J . H. International Tables for Crystal-

lography; Wilson, A. J . C., Ed.; Kluwer Academic Publishers: Boston,

1992; Vol. C, pp 200-206.

(109) Altomare, A.; Camalli, M.; Cascarano, M.; Giacovazzo, C.;

Guagliardi, A. J . Appl. Crystallogr. 1993, 26, 343.

(110) Cromer, D. T.; Waber, J . T. International Tables for X-ray

Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. IV,

pp 72-94.

Article Doi

Synthesis of Novel Group 4 Complexes Bearing the Tropidinyl Ligand: Investigations of Dynamic Behavior, Reactivity, and Catalytic Olefin Polymerization

DOI: 10.1021/om000038k

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