Structure - Reactivity relationships in rare-earth metal carboxylate-based binary Ziegler-type catalysts

1626

Organometallics 2006, 25, 1626-1642

Structure-Reactivity Relationships in Rare-Earth Metal

Carboxylate-Based Binary Ziegler-Type Catalysts

Andreas Fischbach,^†Franc Perdih,^†Eberhardt Herdtweck,^†and Reiner Anwander*^,‡

Department Chemie, Lehrstuhl Fu¨r Anorganische Chemie, Technische UniVersita¨t Mu¨nchen,

Lichtenbergstrasse 4, D-85747 Garching, Germany, and Department of Chemistry, UniVersity of Bergen,

Alle´gaten 41, N-5007, Bergen, Norway

ReceiVed January 18, 2006

The organoaluminum-mediated alkylation of tailor-made rare-earth metal carboxylate complexes was

studied, and implications of the degree of Ln alkylation and organoaluminum-chloride-mediated cation

formation for 1,3-diene polymerization were investigated. Highly substituted rare-earth metal benzoate

complexes {Ln(O₂CC₆H₂Me₃-2,4,6)₃}_n(Ln ) Y, La, Nd), {Ln(O₂CC₆H₂iPr₃-2,4,6)₃}_n(Ln ) Y, La, Nd,

Gd, Lu), {Ln(O₂CC₆H₂tBu₃-2,4,6)₃(THF)}_n(Ln ) Y, La), {Ln(O₂CC₆H₃Ph₂-2,6)₃(THF)}_n(Ln ) Y, La),

and {Ln(O₂CC₆H₃Mes₂-2,6)₃(THF)}_n(Ln ) Y, La) were obtained quantitatively according to the silylamide

route from Ln[N(SiMe₃)₂]₃and alkyl(aryl)-substituted benzoic acids. Such oligomeric carboxylate

complexes are insoluble in aliphatic and aromatic solvents, but could be crystallized from donor solvents

such as THF, DMSO, and pyridine. X-ray crystallographic analyses indicated the formation of monomeric

[Nd(O₂CC₆H₂Me₃-2,4,6)₃(DMSO)₃] and dimeric [La(O₂CC₆H₂Me₃-2,4,6)₂(µ-O₂CC₆H₂Me₃-2,4,6)-

(DMSO)₂]₂depending on the metal ion size. Depending on the steric demand of the benzoate ligands,

mono- and bis(tetraalkylaluminate) complexes [Me₂Al(O₂CC₆H₂iPr₃-2,4,6)₂]₂Ln[(µ-Me)₂AlMe₂] and

{Ln(O₂CC₆H₂tBu₃-2,4,6)[(µ-Me)₂AlMe₂]₂}₂, respectively, could be identified as major product components

from the reaction with excess AlR₃(R ) Me, Et), by means of ¹H NMR spectroscopy and X-ray structure

analysis. When activated with Et₂AlCl, the resulting binary Ziegler-type catalysts efficiently polymerized

isoprene (>99% cis-1,4), the polymerization performance depending on the metal center (Nd > Gd >

La) and the degree of alkylation (“Ln(AlMe₄)₂” > “Ln(AlMe₄)”). Equimolar reaction of [Me₂Al(O₂-

CC₆H₂iPr₃-2,4,6)₂]₂Ln[(µ-Me)₂AlMe₂] with R₂AlCl (R ) Me, Et) quantitatively produced [Me₂Al(O₂-

CC₆H₂iPr₃-2,4,6)]₂, proposing “Me₂LnCl” as the polymerization-initiating species. Homoleptic Ln(AlMe₄)₃

was spotted as a crucial reaction intermediate and was used for the high-yield synthesis of the various

alkylated carboxylate complexes according to a novel “tetraalkylaluminate” route.

dienes (butadiene and isoprene) in aliphatic or aromatic

hydrocarbons by a number of Ziegler-Natta-type catalysts based

on the transition metals titanium, cobalt, and nickel and the

lanthanide element neodymium.^2-9The formation of polymers

with the highest cis-1,4 contents (>98%) makes neodymium-

based butadiene rubbers superior with respect to abrasion and

cracking resistance, tack (the ability of the polymer to stick to

itself), and raw polymer strength.^10,11Therefore, these polymers

are particularly useful for the production of high-performance

tires. Numerous binary and ternary neodymium catalytic systems

have been designed empirically and investigated since the early

discoveries in the 1960s. Commonly used neodymium-based

Introduction

Multicomponent Ziegler-Natta catalysts implicating 3d and

4f transition metal inorganics and organoaluminum compounds

display efficient polymerization initiators for the industrial

manufacture of polyolefins such as polypropylene, polybutadi-

ene, and polystyrene.¹Although these “first-generation” catalysts

are often superior to more sophisticated metallocene and

postmetallocene congeners, details of the polymerization mech-

anisms and the formation of catalytically active centers have

remained scarce, and hence improvement and optimization of

the catalytic system have been achieved only empirically.¹

Cationic metal alkyl or hydrido sites are often proposed to

display the active species promoting monomer insertion and

chain elongation.¹In organolanthanide catalysis, Ziegler-Natta-

type multicomponent systems represent the only class of

homogeneous catalysts of considerable commercial relevance.^2-6

High cis-1,4-polydienes are industrially produced from 1,3-

(3) Taube, R.; Sylvester, G. In Applied Homogeneous Catalysis with

Organometallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH:

Weinheim, 2002; p 280.

(4) Thiele, K.-H.; Wilson, D. R. J. Macromol. Sci., Polym. ReV. 2003,

C43, 581.

(5) Ullmann’s Encyclopedia of Industrial Chemistry, 5th ed.; VCH:

Weinheim, 1993; Vol. A4, pp 221, 261.

* To whom correspondence should be addressed. Fax: +47 555 8949.

E-mail: reiner.anwander@kj.uib.no.

(6) Porri, L.; Giarusso, A. In ComprehensiVe Polymer Science; Eastmond,

G. C., Ledwith, A., Russo, S., Sigwalt, P., Eds.; Pergamon Press: Oxford,

U.K., 1989; Vol. 4, Part II, p 53.

(7) Boor, J. Ziegler-Natta Catalysts and Polymerizations; Academic

Press: New York, 1979; Vol. 17, p 130.

(8) Anwander, R. In Applied Homogeneous Catalysis with Organo-

metallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH: Weinheim,

2002; p 974.

^†Technische Universita¨t Mu¨nchen.

^‡University of Bergen.

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Phys. 2003, 204, 289. (c) Bo¨hm, L. L. Angew. Chem., Int. Ed. 2003, 42,

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(11) Lauretti, E.; Miani, B.; Mistrali, F. Rubber World 1994, 210, 34.

Publication on Web 03/01/2006

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1627

Scheme 1. Proposed Activation Sequence of Oligomeric Ln(III) Carboxylates via Different Organoaluminum Cocatalysts

According to the Literature;^15-20Also Shown Are Commercially Employed “O₂XR” (X ) C, P) Ligands

catalysts comprise Nd(III) carboxylates (also alkoxides or

halides), aluminum alkyl halides, and aluminum alkyls or

aluminum alkyl hydrides.^6,10,12-14Typically, the carboxylic

acids, which are provided as mixtures of isomers from petro-

chemical plants (octanoic, versatic, naphthenoic acids), carry

solubilizing aliphatic substituents R. They are treated with the

alkylaluminum reagents to generate the active catalysts in situ

(Scheme 1).

Although heterobimetallic complexes with alkylated rare-earth

metal centers have been proposed to promote 1,3-diene polym-

erization via an allyl insertion mechanism, details of the

polymerization mechanism and of the structure of the catalyti-

cally active center(s) are still elusive.^15-20Moreover, until now,

the interaction of the “cationizing” chloride-donating reagent

with alkylated rare-earth metal centers is not well-under-

stood.^21,22Noteworthy, similar binary and ternary Ln(III)-based

Ziegler catalysts also exhibit good initiation activity toward

alkylene oxides (oxiranes), styrene, and acetylene.^2,4,8,9Recently,

we and others found that rare-earth metal centers provide a

unique stereoelectronic environment for studying structure-

activity relationships in Ziegler-type catalysts. For example, the

interaction of simple aluminum alkyls (AlMe₃[TMA], AlEt₃

[TEA], AliBu₃) with industrially relevant O-only-bonded rare-

earth metal components such as alkoxide, aryloxide, and

carboxylate complexes revealed a fundamental reactivity pattern

and bonding features.^20,23-29In the course of the examination

of the binary system {Ln(O₂CC₆H₂iPr₃-2,4,6)₃}_n/AlMe₃we

discovered an unprecedented alkylation of the Ln center, i.e., a

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Organometallics 2005, 24, 570. (b) Evans, W. J.; Champagne, T. M.; Ziller,

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W.; Michalczyk, R.; Scott, B. L.; Watkin, J. G. Eur. J. Inorg. Chem. 2002,

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327, and references therein.

(16) (a) Kaita, S.; Hou, Z.; Wakatsuki, Y. Macromolecules 1999, 32,

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Soedin., Ser. B 1990, 11, 803. (c) Porri, L.; Ricci, G.; Giarrusso, A.; Shubin,

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Polym. Sci.: Polym. Chem. Ed. 1980, 18, 3345. (b) Rafikov, S. R.;

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Phys. 2002, 203, 1055.

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W. Organometallics 2003, 22, 499.

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2001, 20, 5751. (b) Evans, W. J.; Giarikos, D. G. Macromolecules 2004,

37, 5130.

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36, 4256.

1628 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

Chart 1. Carboxylic Acids Used in This Study

Figure 1. Molecular structure of [Nd(O₂CC₆H₂Me-2,4,6)₃-

(DMSO)₃] (1c′), with atomic displacement parameters at the 50%

probability level. The disorder over two positions at one of the

DMSO molecules (S3a, S3b) and all of the hydrogen atoms were

omitted for clarity.

Scheme 2. Synthesis of Lanthanide Carboxylates via

Silylamine Elimination

[O₂CAr^iPr] f [AlMe₄] transformation, and the formation of Me₂-

Al-bridged bis(carboxylate) chelating ligands.³⁰

Here we wish to present a full account of a detailed

investigation of the structure-reactivity relationships of the

neodymium carboxylate-based polymerization of isoprene.

Tailor-made lanthanide carboxylates were synthesized and

reacted with alkylaluminum reagents in order to isolate alkylated

bimetallic complexes as possible intermediates in the formation

of the active species.

Results and Discussion

pyridine. Carboxylates {Ln(O₂CAr^tBu)₃(THF)}_x(3), {Ln(O₂-

CAr^Ph)₃(THF)}_x(4), and {Ln(O₂CAr^Mes)₃(THF)}_x(5) formed

mono-THF adducts, as indicated by elemental analysis and ¹H

and ¹³C NMR spectroscopy.

Structural Aspects of Carboxylate Complexes 1b and 1c.

Crystallization of complexes 1b and 1c from saturated DMSO

solutions by slow evaporation of the solvent at ambient

temperature yielded X-ray suitable single crystals of mono- (Ln

) Nd (1c′)) and dinuclear carboxylate complexes (Ln ) La

(1b′)) within several weeks.

The molecular structure of the neodymium derivative [Nd-

(O₂CC₆H₂Me₃-2,4,6)₃(DMSO)₃] (1c′) is shown in Figure 1, and

selected bond distances and angles are listed in Table 1. The

nine-coordinate neodymium cation is surrounded by three η²-

coordinated carboxylate ligands and three DMSO molecules in

a facial coordination geometry. To the best of our knowledge,

1c′ represents the first mononuclear rare-earth metal carboxylate

complex.³³The carboxylic oxygens of the bidentate benzoate

ligands form relatively long and nearly equal Nd-O bond

lengths in the range of 2.488(2)-2.551(2) Å. For comparison,

the Nd-O bond distances of the terminally coordinated car-

boxylate ligands in dinuclear {Nd[O₂CCH(Ph)Et]₃[HO₂CCH-

(Ph)Et]₂}₂and Nd₂[O₂CC(CH₃)₂CH₂CH₃]₆(pyridine)₄range

from 2.538(2) to 2.549(2) Å and from 2.494(3) to 2.545(3) Å,

respectively.²⁸On the other hand, the three DMSO molecules

show shorter Nd-O bond distances of 2.452(2)-2.480(1) Å.

Driven by the increased steric unsaturation of the larger metal

center, the corresponding lanthanum derivative crystallized from

DMSO as a dinuclear complex featuring two terminal and one

bridging carboxylate ligand per lanthanum atom. Both lantha-

Tailor-made Lanthanide Carboxylates with Bulky Ben-

zoate Ligands. Lanthanide carboxylate complexes, which are

used in the industrial-scale polymerization of butadiene and

isoprene, are generally derived from octanoic, versatic, and

naphthenonic acids (Scheme 1). Due to their large “aliphatic

tails”, they impart enhanced solubility of the corresponding

complexes in hexane or heptane solutions. Addition of alkylating

reagents, such as trialkylaluminum reagents AlR₃, produces even

more soluble components; however, such oily products exhibit

a low crystallization tendency and NMR spectra that are

extremely difficult to interpret. Therefore, we decided to

investigate the alkylation behavior of tailor-made carboxylates

derived from sterically demanding, symmetrically substituted

aromatic benzoic acids (Chart 1).

All of the lanthanide carboxylates were synthesized according

to silylamine elimination reactions from bis(trimethylsilyl)amide

complexes Ln[N(SiMe₃)₂]₃(Ln ) Y, La, Nd, Gd, Lu)³¹and 3

equiv of the corresponding benzoic acid (Scheme 2).³²The

carboxylate complexes formed in THF solutions at ambient

temperature overnight and were isolated by evaporating the

solvent in vacuo. After several hexane washings homoleptic

carboxylates {Ln(O₂CAr^Me)₃}_x(1) and {Ln(O₂CAr^iPr)₃}_x(2)

were isolated in quantitative yields. Complexes 1 and 2 are

insoluble in aliphatic and aromatic solvents, but can be

crystallized from donor solvents such as THF, DMSO, and

(30) (a) Fischbach, A.; Perdih, F.; Sirsch, P.; Scherer, W.; Anwander,

R. Organometallics 2002, 21, 4569. (b) Fischbach, A. Ph.D. Thesis,

Technische Universita¨t Mu¨nchen, 2003.

(31) Bradley, D. C.; Ghotra, J. S.; Hart, F. A. J. Chem. Soc., Dalton

Trans. 1973, 1021.

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1047.

(33) Ouchi, A.; Suzuki, Y.; Ohki, Y.; Koizumi, Y. Coord. Chem. ReV.

1988, 92, 29.

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1629

Table 1. Selected Bond Lengths and Angles for

[La₂(O₂CC₆H₂Me₃-2,4,6)₆](DMSO)₄(1b′) and

[Nd(O₂CC₆H₂Me₃-2,4,6)₃](DMSO)₃(1c′)

1b′ (Ln ) La)

1c′ (Ln ) Nd)

Bond Lengths (Å)

2.605(1)

2.609(1)

2.568(2)

2.521(1)

2.710(2)

2.508(2)

2.622(2)

2.459(2)

Ln-O1

2.511(2)

2.526(1)

2.488(2)

2.532(2)

Ln-O2

Ln-O3

Ln-O4

Ln-O4′

Ln-O5

2.551(2)

2.524(2)

2.452(2)

2.468(2)

2.480(1)

1.264(3)

1.262(3)

1.260(3)

1.262(2)

Ln-O6

Ln-O1_DMSO

Ln-O2_DMSO

Ln-O3_DMSO

O1-C1

2.502(2)

1.257(3)

1.265(3)

1.250(3)

O2-C1

O3-C11

O4-C11

O4-C11′

O5-C21

O6-C21

Figure 2. Molecular structure of [La(O₂CC₆H₂Me₃-2,4,6)₂(µ-O₂-

CC₆H₂Me₃-2,4,6)(DMSO)₂]₂(1b′), with atomic displacement pa-

rameters at the 50% probability level. The disorder over two

positions at one of the two DMSO molecules (S2a, S2b) and all of

the hydrogen atoms were omitted for clarity.

1.282(3)

1.266(3)

1.268(3)

1.259(3)

1.263(2)

Bond Angles (deg)

50.15(5)

117.80(5)

49.41(5)

O1-Ln-O2

O3-Ln-O4

O3-Ln-O4′

O4-La-O4′

O5-Ln-O6

O1-C1-O2

O3-C11-O4

O3-C11-O4′

O5-C21-O6

52.09(5)

52.11(5)

68.66(5)

51.09(6)

122.4(2)

51.49(5)

122.2(2)

122.0(2)

121.6(3)

121.9(2)

num centers are nine-coordinated, involving seven carboxylate

oxygen atoms and two DMSO oxygen atoms each. The ORTEP

plot of [La(O₂CC₆H₂Me₃-2,4,6)₂(µ-O₂CC₆H₂Me₃-2,4,6)-

(DMSO)₂]₂(1b′) is shown in Figure 2. Selected intramolecular

bond distances and angles are presented in Table 1.

Figure 3. Molecular structure of [Me₂Al(µ-O₂CAr^iPr)]₂(7), with

atomic displacement parameters at the 50% probability level.

Hydrogen atoms were omitted for clarity.

Compared to the neodymium complex 1c′, the La-O bond

distances of 2.508(2)-2.622(2) Å of the η²-coordinated terminal

carboxylate ligands are slightly elongated. The bond lengths

match the corresponding values in La₂[O₂CC(CH₃)₂CH₂CH₃]₆-

(pyridine)₄(2.517(2)-2.625(2) Å).²⁸A µ₂,η¹:η²-coordination

mode is realized by both bridging carboxylate ligands, with two

short (2.521(1)-2.568(2) Å, η²) and one long La-O distance

(2.710(2) Å, η¹). Similar structural features were previously

reported for the dinuclear carboxylate complexes [La(C₅H₃O₃)₃-

butylaluminum carboxylates as model compounds for carboxy-

late alumoxanes [Al(O)_x(OH)_y(O₂CR)_z]_n.³⁷

In the course of our studies we reacted trimethyl- and

triethylaluminum with all of the aromatic carboxylic acids shown

in Chart 1. Equimolar 1:1 reaction mixtures gave crystalline

products 6-11 of composition “R′₂Al(µ-O₂CAr^R)” (R′ ) Me,

Et) in quantitative yields after 2 h (eqs 1, 2).

AlMe₃+ Ar^RCO₂H f 1/2 [Me₂Al(µ-O₂CAr^R)]₂(6-10) +

(H₂O)₂]₂and [La₂(O₂CC₆H₅)₆(C₁₂H₈N₂)₂].^34b

34a

CH₄(1)

Dialkylaluminum Carboxylate Complexes [R′₂Al(µ-O₂-

CAr^R)]₂. To identify any Ln f Al carboxylate ligand transfer

by NMR spectroscopy, we initially examined the reaction of

AlR₃with substituted benzoic acids. Dialkylaluminum carboxy-

lates have been reported as major products from the reaction of

trialkylaluminum reagents with carboxylic acids.³⁵These prod-

ucts are liquids or oily compounds at ambient temperature and

were characterized without X-ray crystallographic methods.³⁶

In 1997 Bethley et al. synthesized a variety of di-tert-

R ) Me (6), iPr (7), tBu (8), Ph (9), Mes (10)

AlEt₃+ Ar^iPrCO₂H f 1/2 [Et₂Al(µ-O₂CAr^iPr)]₂(11) +

C₂H₆(2)

Compounds 6-11 were fully characterized by elemental

analysis and IR and NMR spectroscopy. The ambient-temper-

1

ature H NMR spectra of 6-10 exhibit only one signal in the

alkylaluminum region for the dimethylaluminum units (-0.23

to -1.05 ppm). Recrystallization of 7 from saturated hexane

solutions yielded colorless single crystals suitable for an X-ray

structure analysis. The solid-state structure of 7 is shown in

Figure 3, and relevant bond lengths and angles are presented in

Table 2.

As predicted previously for other alkylaluminum carboxylates

from IR and Raman spectroscopy, mass spectrometry, and

molecular weight measurements³⁶and as proven for [tBu₂Al-

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1988; Vol. 1, Chapter 6.

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Chem. 1966, 18, 651. (c) Kolesnikov, G. S.; Davidova, S. L.; Yampolskaya,

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1630 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

Table 2. Selected Bond Lengths and Angles for

[Me₂Al(µ-O₂CC₆H₂iPr₃-2,4,6)]₂(7)

Bond Lengths (Å)

Al-C1

Al-C2

Al-O1

1.941(2)

1.935(2)

1.810(1)

Al-O2′

O1-C3

O2-C3

1.840(1)

1.261(2)

1.256(2)

Bond Angles (deg)

O1-Al-C1

O1-Al-C2

O1-Al-O2′

C1-Al-C2

108.21(7)

107.47(7)

104.71(5)

123.02(9)

O2′-Al-C1

O2′-Al-C2

O1-C3-O2

107.35(7)

104.65(7)

122.4(1)

Scheme 3. Synthesis of Heterobimetallic Lanthanide

Carboxylates 12a-e via Alkylation with TMA

Figure 4. Region of the variable-temperature ¹H NMR spectra of

12b measured in toluene-d₈(cf. Scheme 3).

analysis and IR and NMR spectroscopy. At ambient temperature

the proton NMR spectra of 12a showed one set of signals for

the carboxylate ligands and two peaks in the aluminum alkyl

region with an integral ratio of 12:12 (-0.08 (a, Scheme 3)

and -0.41 ppm (b/c, Scheme 3)). At lower temperature, the

higher-field-shifted aluminate resonance separated into two well-

resolved signals at -0.17 (c) and -0.80 (b) ppm (193 K,

toluene-d₈), attributable to bridging and terminal methyl groups.

Due to broad signals, no ⁸⁹Y coupling was observable. A

decoalescence temperature of 263 K was determined for the

yttrium derivative.

Under similar reaction conditions the larger metal centers

lanthanum, neodymium, and gadolinium formed readily hexane-

soluble heterobimetallic complexes within minutes (La (12b),

Nd (12c)) to hours (Gd (12d)). After TMA addition the

carboxylate hexane suspensions turned clear and the products

had to be separated by repeated crystallization from saturated

hexane solutions at -45 °C. Elemental analysis and proton and

carbon NMR spectra revealed the formation of products of net

composition [LnAl₃Me₈(O₂CC₆H₂iPr₃-2,4,6)₄(hexane)]. One

molecule of hexane entrapped in the crystal lattice could not

be removed under reduced pressure (∼10^-2mbar). Also, the

proton NMR spectrum of 12b shows only one set of signals at

298 K for the carboxylate ligands and a 12:12 ratio of the two

alkylaluminum resonances (0.13 (a, Scheme 3) and -0.62 ppm

(b/c, Scheme 3)). A decoalescence temperature of 213 K, as

obtained from variable-temperature NMR experiments in toluene-

d₈(Figure 4), is consistent with an increased steric unsaturation

and more rapid alkyl exchange at the larger lanthanum center

compared to the smaller yttrium derivative 12a.

(µ-O₂CR)]₂by X-ray structural investigations,³⁷7 crystallized

as a centrosymmetric dimer with two Me₂Al units bridged by

two bidentate carboxylate groups. The aluminum atoms of the

central eight-membered ring are four-coordinated by two carbon

and two oxygen atoms in a tetrahedral fashion with Al-O bond

lengths (1.810(1), 1.840(1) Å) consistent with this coordination

number.³⁸On the other hand Al-C bond lengths of 1.935(2)-

1.941(2) Å are in agreement with similar dimethylaluminum

alkoxides (e.g., [Me₂Al(µ-OCMe₂Ph)]₂:³⁹1.9415(9)-1.9456-

(9) Å) and aryloxides (e.g., Me₂Al(OC₆H₂tBu₂-2,6-Me-4(pyri-

dine):⁴⁰1.964(6)-1.956(6) Å).

Carboxylate-Alkyl Exchange in {Ln(O₂CAr^iPr)₃}_x. All of

the synthesized homoleptic lanthanide carboxylates were reacted

with trimethyl- and triethylaluminum. For the isopropyl-

substituted {Ln(O₂CAr^iPr)₃}_x(2a-e) slow addition of a slight

excess of trimethylaluminum (TMA, 3-4 equiv) to a hexane

suspension yielded hexane-insoluble (Ln ) Y, Lu) or hexane-

soluble (Ln ) La, Nd, Gd) Ln-Al heterobimetallic complexes

12a-e in moderate isolated yields of 35-45% (Scheme 3). Up

to now a detailed investigation of the byproducts failed due to

their similar solubilities in aliphatic and aromatic solvents.

According to the ¹H NMR spectra of the crude reaction mixtures,

at least three different alkylated byproducts formed; however,

homoleptic tetramethylaluminate complexes Ln[(µ-Me)₂AlMe₂]₃

were not observed.⁴¹

The results of the dynamic NMR experiments of complexes

12a and 12b are presented in Figures 4 and 5 and Table 3. For

the yttrium derivative 12a, the aluminate methyl group exchange

proceeds with activation parameters ∆H^q) 73(4) kJ mol^-1and

∆S^q) 66(3) J K^-1mol^-1, consistent with a strongly bonded

aluminate ligand and a dissociatiVe methyl group exchange

(Figure 5) reported earlier for Al₂Me₆.⁴²

In contrast, an associatiVe methyl group exchange is indicated

by ∆S^q) -58(3) J K^-1mol^-1for the lanthanum derivative

12b, as proposed previously for half-metallocene bis(tetra-

The hexane-insoluble yttrium (12a) and lutetium derivatives

(12e) have been isolated from the reaction mixture after 24 h

via centrifugation. After several washings with hexane and

drying under vacuum a net composition of the products of

[LnAl₃Me₈(O₂CC₆H₂iPr₃-2,4,6)₄] was indicated by elemental

(38) Haaland, A. Coordination Chemistry of Aluminum; Robinson, G.

H., Ed.; VCH: New York, 1993; Chapter 1.

(39) Allan, J. F.; Clegg, W.; Elsegood, M. R. J.; Henderson, K. W.;

McKeown, A. E.; Moran, P. H.; Rakov, I. M. J. Organomet. Chem. 2000,

602, 15.

(40) Healy, M. D.; Ziller, J. W.; Barron, A. R. J. Am. Chem. Soc. 1990,

112, 2949.

(41) Evans, W. J.; Anwander, R.; Ziller, J. W. Organometallics 1995,

14, 1107.

(42) O’Neill, M. E.; Wade, K. In ComprehensiVe Organometallic

Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon

Press: New York, 1982; p 593.

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1631

Table 3. Thermodynamic Data for the Exchange of Bridging and Terminal Methyl Groups in Ln-Al Heterobimetallic

Complexes 12a and 12b

a

T_c

∆G^{q b}

∆H^{q b}

∆S^{q b}

complex

[K]

[kJ mol^-1

]

[kJ mol^-1

]

[J K^-1mol^-1

]

12a (Ln ) Y)

12b (Ln ) La)

263

213

53(3)

45(2)

44.8

73(4)

28(2)

81.5

66(3)

-58(3)

123.1

c

Me₂Al(µ-Me)₂AlMe₂

Me₂Si(2-MeBenzInd)₂Y[(µ-Me)₂AlMe₂]^c

63.0

24.3

-130

^aDecoalescence temperature. ^bExtracted by line shape analysis. Uncertainities mainly based on temperature errors. ^cProvided for comparison (from refs

42, 43).

Figure 6. Ball-and-stick diagram showing the central core of 13b.

(Ln ) Nd) were isolated in yields of 34 and 17% by

crystallization at -45 °C for several days. In the case of the

smaller metal centers Y and Lu no alkylated products were

isolated.

Figure 5. Arrhenius plot and proposed exchange mechanism for

the exchange of bridging and terminal methyl groups in Ln-Al

heterobimetallic complexes 12a and 12b.

Scheme 4. Synthesis of Heterobimetallic Lanthanide

Carboxylates 13 via Alkylation with TEA

Also for the TEA-alkylation products, elemental analysis and

NMR spectroscopic data confirmed the formation of complexes

13 with a net composition [LnAl₃Et₈(O₂CC₆H₂iPr₃-2,4,6)₄-

(hexane)]. The proton NMR spectrum of 13b showed two

different aluminum ethyl groups in a 1:1 ratio at ambient

temperature, consistent with two bridging diethylaluminum

groups and one highly fluctuating tetraethylaluminate unit.

Despite the different coordination modes of the carboxylate

ligands (η¹, η²), only one set of signals is realized for the

isopropyl-substituted benzoate ligands in the ¹H and ¹³C NMR

spectra.

Recrystallization of complex 13b from a saturated hexane

solution yielded single crystals suitable for an X-ray structure

analysis. Due to severe disordering of the highly mobile

isopropyl groups, even at low temperatures, the connectivity

of the central core of 13b is presented as a ball-and-stick model

(Figure 6). The solid-state structure, which is related to the

previously reported TMA-alkylated neodymium derivative 12c

(triclinic, space group P1h),^30ashows an eight-coordinated

lanthanum atom. One η²-coordinating tetraethylaluminate unit

and six oxygen atoms of two AlMe₂-linked bis(carboxylate)

ligands accomplish an inner coordination sphere of local C₂

symmetry.

In the course of our investigations we developed three

alternative routes to synthesize the heterobimetallic carboxylates

12a-e, all of them starting with homoleptic tetramethylalumi-

nates Ln[(µ-Me)₂AlMe₂]₃. As presented for the yttrium deriva-

tive in eqs 3-6, the hexane-insoluble alkylated isopropyl

carboxylate 12a was isolated from the reaction of Y(AlMe₄)₃

with either the dimethylaluminum carboxylate [Me₂Al(µ-O₂-

CAr^iPr)]₂(7) (eq 4), the carboxylic acid HO₂CAr^iPr(eq 5), or

the homoleptic carboxylate {Y(O₂CAr^iPr)₃}_x(2a) (eq 6). Yields

and product distributions can be directly compared with the

alkylation of the donor-free carboxylate 2a (eq 3, Scheme 3).

methylaluminate) complexes and C₂-symmetric ansa-yttrocene

complex Me₂Si(2-MeBenzInd)₂Y[(µ-Me)₂AlMe₂].⁴³Moreover,

a relatively weak aluminate bonding is proposed by ∆H^q) 28-

(2) kJ mol^-1for the large rare-earth metal center lanthanum.

Note that the larger rare-earth metal centers, and in particular

neodymium, are known to display enhanced catalytic activity

in Ziegler-type catalysts. The comparatively increased activation

enthalpy ∆(∆G^q) of ca. 8 kJ mol^-1for the smaller metal center

yttrium corresponds to a slowing of the methyl group exchange

by a factor of 5 × 10^-2at ambient temperature.

Similar products were obtained in the reaction of 2b and 2c

with 3-4 equiv of triethylaluminum (TEA) in hexane at ambient

temperature (Scheme 4). After 6 h the mixtures were filtrated

and the supernatants dried in vacuo. The highly soluble

heterobimetallic lanthanide carboxylates 13b (Ln ) La) and 13c

(43) (a) Eppinger, J. Ph.D. Thesis, Technische Universita¨t Mu¨nchen,

1999. (b) Anwander, R.; Klimpel, M. G.; Dietrich, H. M.; Shorokhov, D.

J.; Scherer, W. Chem. Commun. 2003, 1008.

1632 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

Scheme 5. Synthesis of

Due to an efficient precipitation of the hexane-insoluble product

from the reaction of readily soluble educts, pathway 4 was used

to synthesize larger amounts of analytically pure 12a within

2-4 h.

Mono(carboxylate)-Bis(tetramethylaluminate) Complexes 15

via the Alkylation of tert-Butyl-Substituted Lanthanide

Benzoates 3

{Y(O₂CAr^iPr)₃}_x(2a) + 4 AlMe₃f

12a + other products (3)

Y(AlMe₄)₃+ 2 [Me₂Al(µ-O₂CAr^iPr)]₂(7) f

12a + other products (4)

Y(AlMe₄)₃+ 4 HO₂CAr^iPrf 12a + other products (5)

Y(AlMe₄)₃+ {Y(O₂CAr^iPr)₃}_x(2a) f

12a + other products (6)

Alkylation of {Ln(O₂CAr^Me)₃}_xand {Ln(O₂CAr^tBu)₃}_x

with TMA. The formation of complexes Ln[(O₂CAr^iPr)₂(µ-

AlR₂)]₂[(µ-R)₂AlR₂] (12, R ) Me; 13, R ) Et) as alkylation

products seems to be intrinsically associated with isopropyl-

substituted benzoate ligands. Several attempts to synthesize

similar, alkylated, heterobimetallic lanthanide carboxylates

bearing methyl, tert-butyl, phenyl, or mesityl derivatives

produced lower or higher alkylated products instead. In the case

of the sterically less crowded methyl derivatives {Ln(O₂-

CAr^Me)₃}_x(1) the reaction with excess TMA did not produce

any larger amounts of alkylated products overnight. Neverthe-

less, one of the above-mentioned alternative syntheses using

Ln(AlMe₄)₃as a precursor succeeded in the formation of a new

type of homoleptic mixed-metal carboxylate. According to eq

7 slow addition of 3 equiv of dimethylaluminum carboxylate 6

to a toluene solution of homoleptic tetramethylaluminate yielded

a white suspension, which was stirred at ambient temperature

for 18 h. Centrifugation and repeated extraction of the solid

into toluene yielded two soluble compounds, as indicated by

proton NMR spectroscopy. Unfortunately, separation of the

alkylated products 14a and 14b from the nonreacted 6 failed

due to similar solubility in aromatic solvents. However, ¹H and

¹³C NMR spectra suggest the formation of a lanthanide center

that is surrounded by three dimethylaluminum-bridged bis-

(carboxylate) ligands. Note that two of such in situ formed

ancillary ligands were observed in complexes 12 and 13 in the

presence of isopropyl-substituted benzoates.

Ln(AlMe₄)₃were reacted with 1 equiv of the carboxylic acid,

added as a toluene suspension (eq 8). Instantaneous evolution

of methane occurred, and the clear mixture was stirred at

ambient temperature for 4 h. After filtration and evaporation of

the solvent the alkylated carboxylates 15 were isolated in almost

quantitative yields.

2 Ln[(µ-Me)₂AlMe₂]₃+ 2 HO₂CAr^tBu

{Ln(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15) +

2 CH₄+ 2 AlMe₃(8)

f

Ln ) Y (15a), La (15b), Nd (15c)

All of the spectroscopic data were in good agreement with

the formation of mono(carboxylate)-bis(tetramethylaluminate)

complexes {Ln(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂15a (Ln ) Y),

15b (Ln ) La), and 15c (Ln ) Nd). The ambient-temperature

proton NMR spectra of complex 15 showed only one set of

signals for the carboxylate ligands and broad resonances for

the fluctuating tetramethylaluminate units at -0.12, -0.03, and

9.7 ppm, respectively. The distinct low-field shift for the

paramagnetic Nd derivative is in accordance with the 10.5 ppm

observed for homoleptic Nd(AlMe₄)₃.⁴¹For the smallest metal

center (15a: Ln ) Y), three well-resolved signals with an

integral ratio of 24:12:12 were observed at 183 K, indicating

three different types of aluminum-bonded methyl groups. A

region of the variable-temperature NMR spectra is presented

in Figure 7.

At 268 K the resonance of the initially uniform (interchang-

ing) aluminate methyl groups started to separate into two signals

attributable to terminal Al-Me (high-field shifted) and bridging

Y-Me-Al methyl groups (low-field shifted). A second de-

coalescence of the former signal was observed at 228 K,

resulting in two well-separated slightly broadened peaks at

-0.25 and -0.60 ppm (183 K, 1:1 ratio). Although significant

broadening of the low-field shifted signal of the bridging methyl

groups was observed at lower temperatures, as indicated by the

disappearance of the ²J_HYcoupling (observable only from 223

to 213 K), a further separation did not occur until 183 K.

Recrystallization of complexes 15 from warm hexane/toluene

mixtures yielded single crystals of 15b and 15c suitable for an

X-ray structure analysis. The ORTEP plot of the neodymium

Ln(AlMe₄)₃+ 3 [Me₂Al(µ-O₂CAr^Me)]₂(6) f

Ln[(O₂CAr^Me)(µ-AlMe₂)(Ar^MeCO₂)]₃(14) (7)

Ln ) Y (14a), La (14b)

In contrast, alkylation of complexes {Ln(O₂CAr^tBu)₃(THF)}_x

(3), bearing the sterically more crowded tert-butyl-substituted

carboxylate ligands, with TMA exclusively produced hexane-

soluble products overnight (Scheme 5). Filtration and evapora-

tion of the solvent gave sticky residues, which were washed

with small amounts of cold hexane. The purified residues were

dried under reduced pressure and identified as “bis-alkylated”

complexes 15a,b with net composition [LnAl₂Me₈(O₂CC₆H₂tBu₃-

2,4,6)] by elemental analysis and NMR and IR spectroscopy.

The soluble byproducts were investigated by proton NMR

spectroscopy, revealing the mere formation of two alkylated

products.

To synthesize larger amounts of complexes 15a,b and the

neodymium derivative 15c in the absence of any byproduct,

the “tetramethylaluminate route” was employed. Accordingly,

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1633

Table 4. Selected Bond Lengths, Intramolecular Contacts,

and Angles for {La(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15b) and

{Nd(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15c)

15b (Ln ) La)

15c (Ln ) Nd)

Bond Lengths (Å)

3.255(1)

7.700(1)

9.804(1)

2.370(2)

2.434(2)

2.681(3)

2.679(3)

2.693(3)

2.693(4)

2.070(3)

2.063(3)

1.962(4)

1.969(5)

2.072(3)

2.066(4)

1.971(4)

1.971(3)

1.282(3)

1.249(3)

Ln‚‚‚Al1

Ln‚‚‚Al2

Al1‚‚‚Al1′

Al2‚‚‚Al2′

Ln-O1

Ln-O2′

Ln-C1

3.189(1)

3.178(1)

7.787(1)

9.922(1)

2.282(1)

2.365(1)

2.615(2)

2.620(2)

2.614(2)

2.626(2)

2.071(2)

2.076(2)

1.966(3)

1.969(3)

2.081(3)

2.073(2)

1.966(3)

1.978(2)

1.276(2)

1.260(2)

Ln-C2

Ln-C5

Ln-C6

Al1-C1

Al1-C2

Al1-C3

Al1-C4

Al2-C5

Al2-C6

Al2-C7

Al2-C8

C9-O1

C9-O2

Bond Angles (deg)

102.93(7)

77.28(9)

O1-Ln-O2′

C1-Ln-C2

C5-Ln-C6

C1-Al1-C2

C3-Al1-C4

C5-Al2-C6

C7-Al2-C8

O1-C9-O2

94.79(5)

79.29(7)

80.64(7)

107.32(9)

117.5(1)

109.44(9)

120.3(1)

121.1(2)

78.1(1)

108.2(1)

117.8(2)

110.1(1)

119.6(2)

120.2(3)

Figure 7. Region of the variable-temperature ¹H NMR spectra of

15a measured in toluene-d₈.

Slightly shorter Nd-C(µ) bond lengths were observed in

homoleptic Nd[(µ-Me)₂AlMe₂]₃(av 2.598 Å).^41,45Due to the

bulky carboxylate ligands, the central eight-membered ring is

bent, resulting in two different Al-Al′ distances of 7.787(1)

and 9.922(1) Å (see Figure 9). The Nd-O bond distances of

2.282(1) and 2.365(1) Å are only slightly shorter than those in

other η¹-coordinated (bridged) carboxylate ligands, e.g., in

higher coordinated Nd₂[O₂CC(CH₃)₂CH₂CH₃]₆(pyridine)₄(2.360-

(3)-2.434(3) Å)²⁸or [Nd₂(L-R-alanine)₄(H₂O)₈](ClO₄)₆(2.343-

(7)-2.464(5) Å).⁴⁶

Due to the larger metal center, all of the La-C and La-O

distances in 15b appear slightly elongated compared to the

neodymium derivative 15c. For comparison, the La-C(µ) bond

lengths in six-coordinate La(NMe₂)₂(GaMe₃)₂(GaMe₄)⁴⁷and

seven-coordinate La[OSi(OtBu)₃](AlMe₄)₂(AlMe₃)^48a,bare in the

range 2.742(2)-2.992(5) Å and 2.668(5)-2.798(3) Å, respec-

tively. The La-O bond lengths of 2.370(2) and 2.434(2) Å lie

in the range of similar heteroleptic carboxylate complexes, e.g.,

La₂[O₂CC(CH₃)₂CH₂CH₃]₆(pyridine)₄(av 2.513 Å).²⁸

Figure 8. Molecular structure of {Nd(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂

(15c) with atomic displacement parameters at the 50% probability

level. Hydrogen atoms were omitted for clarity.

Alkylation of {Ln(O₂CAr^Ph)₃(THF)}_xand {Ln(O₂CAr^Mes)₃-

(THF)}_xwith TMA. Finally, the alkylation behavior of {Ln-

(O₂CAr^Ph)₃(THF)}_x(4) and {Ln(O₂CAr^Mes)₃(THF)}_x(5), bearing

diphenyl- and dimesityl-substituted carboxylate ligands, was

investigated. Addition of an excess of TMA (>7 equiv) to a

hexane suspension of the homoleptic lanthanide carboxylates 4

derivative is shown in Figure 8, and selected intramolecular

distances and bond angles of 15b and 15c are presented in Table

4.

The solid-state structures of 15b and 15c confirm the

formation of dimeric molecules with a central eight-membered

{LnOCO}₂ring involving two bridging carboxylate ligands.

Both of the lanthanide cations are six-coordinated by two oxygen

atoms of different carboxylate ligands and four methyl groups

of the tetramethylaluminate units. The Nd-C(µ) distances of

15c ranging from 2.614(2) to 2.626(2) Å can be directly

compared with the formally five-coordinate heteroleptic amido-

substituted neodymium tetramethylaluminate Nd[NiPr₂][(µ-

NiPr₂)(µ-Me)AlMe₂][(µ-Me)₂AlMe₂] (2.639(3), 2.659(3) Å).⁴⁴

(45) Klooster, W. T.; Lu, R. S.; Anwander, R.; Evans, W. J.; Koetzle,

T. F.; Bau, R. Angew. Chem., Int. Ed. 1998, 37, 1268.

(46) Glowiak, T.; Legendziewicz, J.; Huskowska, E.; Gawryszenwska,

P. Polyhedron 1996, 15, 2939.

(47) Evans, W. J.; Anwander, R.; Doedens, R. J.; Ziller, J. W. Angew.

Chem., Int. Ed. Engl. 1994, 33, 1641.

(48) (a) Fischbach, A.; Klimpel, M. G.; Widenmeyer, M.; Herdtweck,

E.; Scherer, W.; Anwander, R. Angew. Chem., Int. Ed. 2004, 43, 2234. (b)

Fischbach, A.; Eickerling, G.; Scherer, W.; Herdtweck, E.; Anwander, R.

Z. Naturforsch. 2004, 59b, 1353. (c) Dietrich, H. M.; Zapilko C.; Herdtweck,

E.; Anwander, R. Organometallics 2005, 24, 5767.

(44) Evans, W. J.; Anwander, R.; Ziller, J. W. Inorg. Chem. 1995, 34,

5927.

1634 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

Scheme 6. Synthesis of

Mono(carboxylate)-Bis(tetramethylaluminate) Complexes 16

via the “Tetramethylaluminate Route”⁴⁸

Figure 9. Partial view of {Nd(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15c).

did not produce any clear solutions overnight. After 18 h the

hexane-insoluble solids were separated via centrifugation from

the reaction mixtures, washed several times with hexane,

extracted into toluene, and dried in vacuo. The collected hexane

solutions were evaporated under reduced pressure, yielding

sticky solids. Several attempts to isolate a well-defined alkylated

product from both the hexane-insoluble and the hexane-soluble

part, via crystallization from saturated toluene or hexane

solutions, failed due to the similar solubility of the alkylated

species. Nevertheless, the formation of the dimethylalumium-

bridged cleavage product [Me₂Al(µ-O₂CAr^Ph)]₂(9) was un-

equivocally proven by means of NMR spectroscopy. Addition-

ally, two or three further signals in the alkylaluminum region

of the proton NMR spectra of the hexane-insoluble parts were

observed for yttrium and lanthanum. In agreement with the

identification of 9 the observation of a characteristic doublet at

-0.39 ppm (²J_YH) 2.6 Hz) for the yttrium derivative points to

the formation of lanthanide tetramethylaluminate complexes.

tetramethylaluminate units. In the case of the smaller metal

center (Ln ) Y; 16a) four separated signals with an integral

ratio of 12:12:12:12 were observed at -80 °C, attributable to

two different Y-(µ-Me)-Al (broad signals at 0.15 and -0.53

ppm) and two different Al-Me units (sharp signals at -0.27

and -0.74 ppm).

Carboxylate-Alkyl Exchange. A Mechanistic Scenario of

the Formation of Differently Alkylated Ln Carboxylate

Complexes. From the results presented above it can be

rationalized that not only electronic effects control the formation

of differently alkylated products. The steric demand of the

aliphatic and aromatic substituents in 2,6-position of the

benzoate ligands is also a crucial factor governing the reaction

of the homoleptic carboxylates with an excess of alkylaluminum

reagents. We propose a mechanistic alkylation scenario as shown

in Scheme 7. Accordingly, homoleptic tetramethylaluminate Ln-

(AlMe₄)₃is a key intermediate (I₄) for the reassociation reaction

with separated dimethylaluminum carboxylates 6-10. The

active role of Ln(AlMe₄)₃is supported by the novel “tetraalkyl-

aluminate route”, giving access to complexes [Me₂Al(O₂-

CC₆H₂iPr₃-2,4,6)₂]₂Ln[(µ-Me)₂AlMe₂] (12 ) I₆), {Ln(O₂-

CC₆H₂tBu₃-2,4,6)[(µ-Me)₂AlMe₂]₂}₂(15 ) I₃), and Ln-

[(O₂CAr^Me)(µ-AlMe₂)(Ar^MeCO₂)]₃(14). Furthermore, Ln-

(AlMe₄)₃display an extraordinary catalytic activity in the cis-

1,4 stereospecific polymerization of isoprene.^48a,b

Stereospecific Polymerization of Isoprene by Binary

Ziegler-Type Catalysts. Pre-alkylated Ln-Al heterobimetallic

complexes 12, 13, and 15 were used as catalyst components in

isoprene polymerization. A binary Ziegler-type precatalyst

mixture was obtained by addition of various amounts of Et₂-

AlCl as a “cationizing” reagent (cocatalyst, cf. Scheme 1). The

precatalyst mixture was aged for 30 min at ambient temperature

prior to addition of isoprene. A catalyst-to-monomer ratio of

1:1000 was realized in all of the experiments which were carried

out at 40 °C for 24 h in hexane solutions. Conversions,

stereospecificities, and molecular weights are summarized in

Table 5.

{Ln(O₂CAr^Ph)₃(THF)}_x+ >7 AlMe₃f

[Me₂Al(µ-O₂CAr^Ph)]₂(9) + Me₃Al(THF) +

alkylated Ln products (9)

{Ln(O₂CAr^Mes)₃(THF)}_x+ >7 AlMe₃f

[Me₂Al(µ-O₂CAr^Mes)]₂(10) + Me₃Al(THF) +

alkylated Ln products (10)

Similar problems resulted from the alkylation of dimesityl-

substituted carboxylates 5 after an 18 h reaction period. The

NMR spectroscopic investigation of the hexane-soluble residues

showed the formation of 10 as a cleavage product from the

alkylation of the yttrium and lanthanum metal centers. Unfor-

tunately, similar solubility and several signals in the alkylalu-

minum regions prevented the unequivocal identification of

alkylated Ln-containing products.

Attempts to synthesize and isolate one of the alkylation

products via alternative strategies failed. However, the “tetra-

methylaluminate route” using Ln[(µ-Me)₂AlMe₂]₃and 1 equiv

of HO₂CAr^Phgenerated hexane-soluble mono(carboxylate)-bis-

(tetramethylaluminate) complexes 16 similar to complexes 15,

carrying the tert-butyl-substituted benzoate ligands (Scheme 6).

After a 3 h reaction period the hexane-insoluble parts were

separated by centrifugation and the products purified via

crystallization.

To elucidate the influence of the metal centers on the catalytic

activity, the alkylated lanthanide carboxylates 12a-e were used

as precatalyst components at constant n_Cl:n_Lnratios of 1:1 (runs

1, 3, 7, 10, and 11). The yttrium (12a) and lutetium derivatives

(12e) were completely inactive, whereas polymer yields in-

creased for the larger metal centers in the order La < Gd < Nd

(12, 24, 77%). This behavior is in agreement with previously

published activity orders.^18a,49

Elemental analysis and proton and carbon NMR spectroscopy

confirmed the formation of complexes 16. Due to a rapid

exchange of terminal and bridging methyl groups, the ambient-

1

temperature H NMR spectra showed only one signal for the

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1635

Scheme 7. Carboxylate-Alkyl Interchange: A Mechanistic Scenario of the Formation of Differently Alkylated Lanthanide

Carboxylate Complexes^a

^aExcept for I₁, I₂, and I₅all Ln complexes were completely characterized; Ar^R) C₆H₂R′₃-2,4,6 or C₆H₃R′₂-2,6.

Table 5. Effect of Metal Size and Degree of Alkylation

(Steric Bulk of Benzoate Ligands) on Ln-Based

Polymerization of Isoprene after 24 h

This increased catalytic activity can be rationalized on the

enhanced solubility of the tetraethylaluminate versus the tetra-

methylaluminate Ln components (see below). In general, the

stereospecificities and activities could be improved by increasing

the amount of the halide-transferring cocatalyst. For the tetra-

methylaluminate derivatives 12b (Ln ) La) and 12c (Ln ) Nd)

a larger n_Cl:n_Lnratio (2:1, 3:1; runs 4, 5, 8, and 9) increased

both the cis-1,4-polymerization and monomer conversion. This

is in agreement with literature reports on lanthanide carboxylate-

based catalysts showing the highest conversions in diene

polymerization at n_Cl:n_Lnratios of ∼2.⁵⁰After 24 h 12c

quantitatively polymerized isoprene under these conditions (run

8), whereas polymer yields for the lanthanum derivative 12b

increased from 12 to 70% (runs 3 versus 4). At n_Cl:n_Lnratios g

3 polymer yields decreased again, due to the likely formation

of higher halogenated and hence more insoluble lanthanide

species. However, for complexes 12b and 12c maximum cis-

1,4-contents (>99%; only cis-signals in the ¹³C NMR) were

observed only at n_Cl:n_Lnratios of 3 and larger (runs 5 and 9).

The molecular weights of the isolated polymers show

relatively similar values for the tetramethylaluminate derivatives

12b-d; however, the molecular weight distributions (MWD)

strongly depend on the metal center. The lowest polydispersities

of 2.29 and 2.11 were realized for the most active mono-

(tetramethylaluminate) neodymium complex 12c at n_Cl:n_Ln) 2

and 3, respectively (runs 8 and 9). All of the GPC elugrams

show polymodal mass distributions indicating two or three

catalytically active species.

d

M_n

M_w

b

run^aprecat. n_Cl:n_Lnconv/% cis-1,4^c/% (×10³) (×10³) PDI^d

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

12a

12b

12c

12d

12e

13b

13c

15b

15c

1:1

0:1

1:1

2:1

3:1

0:1

1:1

2:1

3:1

1:1

2:1

3:1

1:1

2:1

3:1

1:1

2:1

3:1

1:1

2:1

3:1

0

12

70

21

0

77

>99

98

24

0

97

>99

60

97

>99

83

>99

86

>99

95.1

98.1

> 99

137

180

100

558

816

452

4.08

4.52

93.5

98.6

>99

92.0

165

271

194

112

575

621

410

589

3.48

2.29

2.11

5.27

94.3

96.6

>99

90.7

95.6

98.7

97.5

>99

98.7

78

91

66

94

92

290

454

217

297

266

229

593

564

307

787

705

462

3.73

4.98

3.27

3.16

2.88

2.94

4.76

3.23

5.37

2.84

2.82

2.79

78

125

175

57

277

250

165

>99

^aPolymerization procedure: 0.02 mmol of precatalyst, 8 mL of hexane,

0.02-0.06 mmol of Et₂AlCl (1-3 equiv), 20 mmol of isoprene; 24 h, 40

°C. ^bCatalyst preformation 30 min at room temperature. ^cMeasured by

means of ¹³C NMR spectroscopy in CDCl₃. ^dDetermined by means of size

exclusion chromatography (SEC) against polystyrene standards.

The tetraethylaluminate derivatives 13b (Ln ) La) and 13c

(Ln ) Nd) displayed higher activity and also gave almost

quantitative conversions for the lanthanum derivative (runs 12

and 15). Therefore, a distinct metal effect was not observed for

n_Cl:n_Lnratios of 1:1 and 2:1 within the reaction time of 24 h.

(49) (a) Shen, Z. Inorg. Chim. Acta 1987, 140, 7. (b) Wang, S.; Li, Z.;

Wang, F. Polym. Commun. 1984, 425.

(50) (a) Witte, J. Angew. Macromol. Chem. 1981, 94, 119. (b) Pross,

A.; Marquardt, P.; Reichert, K. H.; Nentwig, W.; Knauf, T. Angew.

Macromol. Chem. 1993, 211, 89. (c) Friebe, L.; Nuyken, O.; Windisch,

H.; Obrecht, W. Macromol. Chem. Phys. 2002, 203, 1055.

1636 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

Scheme 8. Proposed Mechanistic Scenario of the Formation of the Active Species for Mono(tetramethylaluminate)

Complexes 12

Mono(carboxylate) bis(tetramethylaluminates) 15b and 15c

displayed an even higher catalytic activity, producing polyiso-

prene in high to quantitative yields within 24 h (runs 18-23).

Compared with the mono(tetraalkylaluminate) complexes 12 and

13, cis-contents of the polymers were higher (>97.5%), even

in the presence of only 1 equiv of Et₂AlCl. On the other hand,

molecular weights and molecular weight distributions were

similar to those obtained via the mono(tetramethylaluminate)

complexes, showing broader distributions for the less active

lanthanum derivative(s).

Reactivity of 12a and 12b with R₂AlCl. In order get a deeper

insight into the structure-reactivity relationship of the formation

of the catalytically active binary system, we examined the

interaction of the “cationizing” chloride-donating reagent with

the alkylated rare-earth metal centers of complexes 12 (cf.

Scheme 1). Accordingly, complexes 12a and 12b were reacted

with equimolar amounts of Me₂AlCl in hexane solutions.

Immediately after the addition of the Al cocatalyst a white

precipitate formed, which was separated after 2 h via centrifuga-

tion. The supernatant hexane solution was dried in vacuo and

investigated by NMR spectroscopy. Surprisingly, only one

soluble product formed, which could be identified as the dimeric

dimethylaluminum-bridged carboxylate 7. Quantitative yields

of 7 indicated that both chelating bis(carboxylate) ligands in

12a and 12b were cleaved by the addition of only 1 equiv of

Me₂AlCl. Although the elemental analyses of the insoluble

lanthanide-containing products were not satisfactory, the amount

of insoluble products points at the formation of polymeric/ionic

“{Me₂LnCl}_x” (17) as a possible polymerization-inititating

species. A mechanistic scenario for this activation sequence is

presented in Scheme 8.

reactive polymeric “{Me₂LnCl}_x”. On the other hand, initial

cleavage of the tetramethylaluminate unit in 12 has to be taken

into consideration. Correspondingly, the reaction path on the

right-hand side involves the formation of a terminal chloride

ligand in intermediate I₉via addition of Me₂AlCl. Subsequently,

released Al₂Me₆causes the cleavage of both of the bis-

(carboxylate) ligands in a two-step reaction.

Although none of the intermediates I₇-I₁₀could be isolated,

several additional experiments support the reaction sequence

presented in Scheme 8. According to a “AlR₃cross experiment”

(eq 11), addition of 1 equiv of Et₂AlCl instead of Me₂AlCl to

mono(tetramethylaluminate) complex 12b produced a mixture

of several hexane-soluble species, as indicated by proton NMR

spectroscopy. Although crystallization failed due to similar

solubilities, the dimethylaluminum-bridged bis(carboxylate) 7

was formed as one of the products, as expected from the

mechanistic scenario. On the other hand, addition of 1 equiv of

Et₂AlCl to the mono(tetraethylaluminate) complex 13b produced

11 exclusively, as indicated by ¹H NMR spectroscopy (eq 12);

no mixed-alkylated species were generated.

12b + Et₂AlCl f

[Me₂Al(µ-O₂CAr^iPr)]₂(7) + other products (11)

13b + Et₂AlCl f

[Et₂Al(µ-O₂CAr^iPr)]₂(11) + other products (12)

Furthermore, given the thermal stability of “LnMe₃”,⁵²one

can also speculate about a ligand disproportionation reaction

of “monocationic” “{Me₂LnCl}_x” into “{LnMe₃}_x” and

“{LnCl₃}_x”. At n_Cl:n_Lnratios g 2, “dicationic” “{MeLnCl₂}_x”

seems to be a chemically sound and realistic activation product.⁵³

We suggest two possible reaction pathways for the interaction

of Me₂AlCl with complexes 12. As shown on the left-hand side,

addition of 1 equiv of the alkylaluminum reagent causes an Al

f Ln chloride transfer with a simultaneous cleavage of one of

the AlMe₂-bridged bis(carboxylate) ligands, forming intermedi-

ate I₇. Then, the Ln-bonded tetramethylaluminate unit undergoes

a reorientation by breaking one of the Al-C(Me) bonds and

forming an Al-O interaction, which is known from Ln-Al

heterobimetallic alkoxide^23,24,51and aryloxide^26,27chemistry.

From intermediate I₈, featuring a terminal methyl group, the

second biscarboxylate ligand dissociates, finally forming highly

(51) Evans, W. J.; Boyle, T. J.; Ziller, J. W. J. Organomet. Chem. 1993,

462, 141.

(52) Dietrich, H. M.; Raudaschl-Sieber, G.; Anwander, R. Angew. Chem.,

Int. Ed. 2005, 44, 5303.

(53) (a) Maiwald, S.; Weissenborn, H.; Windisch, H.; Sommer, C.;

Mu¨ller, G.; Taube, R. Macromol. Chem. Phys. 1997, 198, 3305. (b)

Maiwald, S.; Taube, R.; Hemling, H.; Schumann, H. J. Organomet. Chem.

1998, 552, 195. (c) Ward, B. D.; Bellemin-Laponnaz, S.; Gade, L. H. Angew.

Chem., Int. Ed. 2005, 44, 1668. (d) Arndt, S.; Beckerle, K.; Zeimentz, P.

M.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2005, 44, 7473.

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1637

Scheme 9. Allyl Insertion Mechanism of 1,3-Diene Polymerization Taking into Account Organoaluminum-Mediated Chain

Transfer

However, given the ready availability of organoaluminum

reagents in the reaction mixtures, equilibria reactions involving

species “{Me₂LnCl}_x(AlR₃)_y” and “{MeLnCl₂}_x(AlR₃)_z” have

to be taken into account as well.

type catalysts, are consistent with pronounced Ln-to-Al polymer

chain transfer.

Experimental Section

General Considerations. All operations were performed with

rigorous exclusion of air and water, using high-vacuum and

glovebox techniques (MBraun MB150B-G-II; <1 ppm O₂, <1 ppm

H₂O). Solvents were predried and distilled from Na/K alloy

(benzophenone ketyl) under argon. Deuterated solvents were

obtained from Merck. C₆D₆and THF-d₈were degassed and dried

over Na/K alloy; DMSO-d₆was used without further purification.

2,4,6-Trimethylbenzoic acid was obtained from Aldrich, and 2,4,6-

triisopropylbenzoic acid from ABCR; both were used without

further purification. 2,4,6-Tri-tert-butylbenzoic acid,⁵⁴2,6-diphe-

nylbenzoic acid,⁵⁵and 2,6-dimesitylbenzoic acid⁵⁵were synthesized

according to literature procedures. The lanthanide silylamide

precursors Ln[N(SiMe₃)₂]₃(Ln ) Y, La, Nd, Gd, Lu) were

synthesized according to the literature.³¹Trimethylaluminum,

triethylaluminum, dimethylaluminum chloride, and diethylaluminum

chloride were purchased from Aldrich and used as received.

CAUTION: Alkylaluminum reagents react violently with moisture.

Isoprene was dried over molecular sieves (3 Å) and distilled prior

to use.

Conclusions

The interaction of tailor-made rare-earth metal benzoate

complexes {Ln(O₂CAr^R)₃}_xwith homoleptic organoaluminum

reagents AlR′₃(R′ ) Me, Et) reveals an unprecedented

alkylation and carboxylate ligand rearrangement sequence

depending on the steric bulk of the carboxylate substituents R.

Variable-temperature NMR studies and X-ray crystallographic

analyses give precise insight into the metal-size-dependent

dynamic behavior of the tetraalkylaluminate ligand and the

coordination features of heteroleptic mono- and bis(tetraalkyl-

aluminate) complexes [Me₂Al(O₂CC₆H₂iPr₃-2,4,6)₂]₂Ln[(µ-

Me)₂AlMe₂] and {Ln(O₂CC₆H₂tBu₃-2,4,6)[(µ-Me)₂AlMe₂]₂}₂,

respectively. This intrinsic (ligand-dependent) alkylation ame-

nability certainly hampers a direct comparison with industrially

applied versatate- and naphthenoate-coordinated neodymium

centers; however, the formation of tetraalkylaluminate moieties

seems to be a preferred reaction pathway. The accessibility of

the various alkylated carboxylate complexes via reaction of

homoleptic Ln(AlMe₄)₃with benzoic acids or alkylation byprod-

ucts [R₂AlO₂CAr^R] suggests a crucial role of the tris(tetraalkyl-

aluminate) Ln complexes. The enhanced thermodynamic and

kinetic lability of tetraalkylaluminate ligands bonded to large

rare-earth metal centers and the existence of extensive Al-to-

Ln and Ln-to-Al ligand transfer sequences, including [O₂CAr^iPr]

f [AlMe₄] and [AlMe₃] f [Me₂Al(O₂CAr^iPr)₂] transformations,

underline the ease of polymer chain transfer via Ln-Al

heterobimetallic complexes in Ziegler-type catalysts. This is

realized in a modified allyl insertion mechanism of isoprene

polymerization as shown in Scheme 9.

A comprehensive study of isoprene polymerization revealed

that the alkylated Ln-Al heterobimetallic carboxylate com-

plexes are highly efficient precatalyst components in binary

Ziegler-type catalysts. After activation with Et₂AlCl, the catalyst

systems confirm classic features of rare-earth metal carboxylate-

based catalysts such as high cis-1,4 polymerization (>99%),

neodymium as the most active metal center (“neodymium

effect”), and a favorable n_Cl:n_Lnratio of ∼2. In addition, the

polymerization efficiency depends on the degree of alkylation

(“Ln(AlMe₄)₃” > “Ln(AlMe₄)₂” > “Ln(AlMe₄)”). Finally, the

broad molecular weight distributions, which usually result from

solution polymerizations with such multicomponent Ziegler-

NMR spectra were recorded either on a JEOL-GX-400 (FT,

399.78 MHz ¹H; 100.5 MHz ¹³C) or on a JEOL JNM-GX-270 (FT,

1

270.16 MHz H; 67.93 MHz ¹³C) spectrometer. H and ¹³C shifts

are referenced to internal solvent resonances and reported relative

to TMS. IR spectra were recorded on a Perkin-Elmer 1650-FTIR

spectrometer as Nujol mulls or KBr pellets. Elemental analyses

were performed in the microanalytical laboratory of TUM.

General Procedure for the Synthesis of Rare-Earth Metal

Carboxylates. To a solution of Ln[N(SiMe₃)₂]₃in THF was slowly

added a solution of 3 equiv of the chosen carboxylic acid in THF

at -45 °C, and the resulting mixture was stirred at ambient

temperature overnight. Then, the solvent and the volatile byproducts

were removed in vacuo. The remaining solid was washed several

times with hexane. After drying for several hours the powdery

products were isolated in high yields.

{Y(O₂CC₆H₂Me₃-2,4,6)₃}_n(1a). Following the procedure de-

scribed above, Y[N(SiMe₃)₂]₃(0.855 g, 1.50 mmol) and HO₂CAr^Me

(0.739 g, 4.50 mmol) yielded 1a as a colorless, THF-insoluble solid

(0.850 g, 1.47 mmol, 98%). IR (KBr): 3000 s, 2958 s, 2922 s,

(54) Betts, E. E.; Barclay, L. R. C. Can. J. Chem. 1955, 33, 1768.

(55) (a) Du, C.-J. F.; Hart, H.; Ng, K.-K. D. J. Org. Chem. 1986, 51,

3162. (b) Saednya, A.; Hart, H. Synthesis 1996, 1455. (c) Waller, S. C.;

Mash, E. A. Org. Prep. Proc. Int. 1997, 29, 679. (d) Lu¨ning, U.; Wangnick,

C.; Peters, K.; von Schnering, H. G. Chem. Ber. 1991, 124, 397.

1638 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

2854 m, 2731 w, 1718 w, 1607 s, 1522 s, 1427 s, 1294 m, 1252

m, 1182 s, 1116 s, 1040 m, 844 s, 825 m, 795 m, 747 m, 608 s,

IR (KBr): 2960 s, 2923 s, 2868 s, 1684 m, 1608 s, 1527 s, 1460

s, 1424 s, 1381 m, 1362 s, 1318 m, 1158 m, 1110 m, 1070 m, 940

m, 874 s, 792 m, 616 m cm^-1. ¹H NMR (DMSO-d₆): δ 6.95 (s, 6

H, Ar-H), 3.27 (septet, ³J_HH) 6.6 Hz, 6 H, o-CHMe₂), 2.83 (septet,

1

599 s, 568 w cm^-1. H NMR (DMSO-d₆): δ 6.73 (s, 6 H, Ar-H),

2.25 (s, 18 H, o-Me), 2.18 (s, 9 H, p-Me). ¹³C{¹H} NMR (DMSO-

d₆): δ 180.5 (COO), 137.0, 135.7, 133.4, 127.4, 20.6 (p-Me), 19.7

(o-Me). Anal. Calcd for C₃₀H₃₃O₆Y: C, 62.29; H, 5.75. Found: C,

62.38; H, 5.80.

{La(O₂CC₆H₂Me₃-2,4,6)₃}_n(1b). Following the procedure

described above, La[N(SiMe₃)₂]₃(0.931 g, 1.50 mmol) and HO₂-

CAr^Me(0.739 g, 4.50 mmol) yielded 1b as a colorless, THF-

insoluble solid (0.899 g, 1.43 mmol, 95%). IR (Nujol): 1610 m,

1574 w, 1517 s, 1307 w, 1180 m, 1112 w, 1031 w, 846 w, 834 m,

801 w, 608 m cm^-1. ¹H NMR (DMSO-d₆): δ 6.73 (s, 6 H, Ar-H),

2.27 (s, 18 H, o-Me), 2.18 (s, 9 H, p-Me). ¹³C{¹H} NMR (DMSO-

d₆): δ 181.2 (COO), 137.9, 135.2, 133.2, 127.3, 20.5 (p-Me), 19.7

(o-Me). Anal. Calcd for C₃₀H₃₃LaO₆: C, 57.33; H, 5.29. Found:

C, 57.91; H, 5.41.

3

³J_HH) 6.6 Hz, 3 H, p-CHMe₂), 1.18 (d, J_HH) 6.6 Hz, 18 H,

p-CHMe₂), 1.15 (d, ³J_HH) 6.6 Hz, 36 H, o-CHMe₂). ¹³C{¹H} NMR

(DMSO-d₆): δ 183.3 (COO), 147.4, 143.4, 135.9, 119.8, 33.5 (p-

CHMe₂), 29.9 (o-CHMe₂), 24.2 o-CHMe₂), 23.9 (p-CHMe₂). Anal.

Calcd for C₄₈H₇₂LuO₆: C, 62.87; H, 7.58. Found: C, 62.25; H,

7.33.

{Y(O₂CC₆H₂tBu₃-2,4,6)₃(THF)}_n(3a). Following the procedure

described above, Y[N(SiMe₃)₂]₃(0.855 g, 1.50 mmol) and HO₂-

CAr^tBu(1.307 g, 4.50 mmol) yielded 3a (1.348 g, 87%) as a

colorless solid. IR (KBr): 2965 s, 2912 s, 2868 s, 1700 m, 1604 s,

1552 s, 1527 s, 1495 s, 1457 s, 1394 s, 1356 s, 1267 m, 1244 m,

1217 m, 1091 w, 1010 w, 912 w, 878 m, 846 m, 807 m, 770 m,

1

674 w, 650 w, 603 w cm^-1. H NMR (THF-d₈): δ 7.43 (s, 6 H,

Ar-H), 3.63 (m, 4 H, THF), 1.78 (m, 4 H, THF), 1.52 (s, 54 H,

o-CMe₃), 1.33 (s, 27 H, p-CMe₃). ¹³C{¹H} NMR (THF-d₈): δ 193.3

(COO), 149.9, 147.0, 133.5, 122.5, 68.2 (THF), 37.9 (o-CMe₃),

35.6 (p-CMe₃), 33.3 (o-CMe₃), 31.7 (p-CMe₃), 25.4 (THF). Anal.

Calcd for C₆₁H₉₅O₇Y: C, 71.18; H, 9.30. Found: C, 71.22; H, 9.04.

{Nd(O₂CC₆H₂Me₃-2,4,6)₃}_n(1c). Following the procedure

described above, Nd[N(SiMe₃)₂]₃(0.938 g, 1.50 mmol) and HO₂-

CAr^Me(0.739 g, 4.50 mmol) yielded 1c as a light blue, THF-

insoluble solid (0.878 g, 1.39 mmol, 92%). IR (Nujol): 3000 s

2959 s, 2922 s, 2856 m, 1718 w, 1611 s, 1518 s, br, 1250 m, 1181

s, 1113 s, 1035 m, 933 m, 889 m, 832 s, 802 m, 728 m, 602 s, 566

m cm^-1. Anal. Calcd for C₃₀H₃₃NdO₆: C, 56.85; H, 5.25. Found:

C, 56.58; H, 5.14.

{Y(O₂CC₆H₂iPr₃-2,4,6)₃}_n(2a). Following the procedure de-

scribed above, Y[N(SiMe₃)₂]₃(1.140 g, 2.00 mmol) and HO₂CAr^iPr

(1.490 g, 6.00 mmol) yielded 2a (1.576 g, 95%) as a colorless solid.

IR (KBr): 2964 s, 2926 s, 2869 s, 1683 m, 1607 s, 1520 s, 1461

s, 1416 s, 1362 s, 1318 m, 1157 m, 1109 m, 1070 m, 940 m, 874

s, 791 m, 617 m cm^-1. ¹H NMR (THF-d₈): δ 7.00 (s, 6 H, Ar-H),

{La(O₂CC₆H₂tBu₃-2,4,6)₃(THF)}_n(3b). Following the proce-

dure described above, La[N(SiMe₃)₂]₃(0.868 g, 1.40 mmol) and

HO₂CAr^tBu(1.220 g, 4.20 mmol) yielded 3b (1.252 g, 83%) as a

colorless solid. IR (KBr): 2972 s, br, 2900 s, 2861 s, 1697 s, 1603

s, 1535 s, br, 1461 s, 1399 s, 1363 s, 1267 s, 1244 s, 1218 s, 1174

m, 1136 w, 1093 m, 1027 w, 984 m, 911 m, 876 s, 842 m, 807 s,

1

782 m, 652 m, 590 s, 486 m cm^-1. H NMR (DMSO-d₆): δ 7.21

(s, 6 H, Ar-H), 3.59 (m, 4 H, THF), 1.75 (m, 4 H, THF), 1.45 (s,

1

54 H, o-CMe₃), 1.24 (s, 27 H, p-CMe₃). H NMR (THF-d₈): δ

3

7.36 (s, 6 H, Ar-H), 1.47 (s, 54 H, o-CMe₃), 1.31 (s, 27 H, p-CMe₃).

¹³C{¹H} NMR (THF-d₈): δ 188.5 (COO), 148.3, 146.1, 136.2,

122.1, 37.7 (o-CMe₃), 35.5 (p-CMe₃), 33.2 (br, o-CMe₃), 31.7 (p-

CMe₃). Anal. Calcd for C₆₁H₉₅LaO₇: C, 67.88; H, 8.87. Found:

C, 67.01; H, 9.40.

3.29 (septet, J_HH) 6.7 Hz, 6 H, o-CHMe₂), 2.87 (septet, J_HH

)

6.7 Hz, 3 H, p-CHMe₂), 1.23 (d, ³J_HH) 6.7 Hz, 54 H, o/p-CHMe₂).

¹³C{¹H} NMR (THF-d₈): δ 187.7 (COO), 149.3, 145.0, 136.0,

120.9, 35.4 (p-CHMe₂), 31.8 (o-CHMe₂), 24.8 (o-CHMe₂), 24.4

(p-CHMe₂). Anal. Calcd for C₄₈H₆₉O₆Y: C, 69.38; H, 8.37.

Found: C, 69.41; H, 8.54.

{Y(O₂CC₆H₃Ph₂-2,6)₃(THF)}_n(4a). Following the procedure

described above, Y[N(SiMe₃)₂]₃(0.570 g, 1.00 mmol) and HO₂-

CAr^Ph(0.823 g, 3.00 mmol) yielded 4a (0.832 g, 85%) as a colorless

solid. IR (Nujol): 1583 w, 1571 w, 1535 m, 1523 m, 1494 w, 1438

s, 1304 w, 1283 w, 1182 w, 1148 w, 1072 w, 1028 m, 916 w, 880

{La(O₂CC₆H₂iPr₃-2,4,6)₃}_n(2b). Following the procedure

described above, La[N(SiMe₃)₂]₃(1.240 g, 2.00 mmol) and HO₂-

CAr^iPr(1.490 g, 6.00 mmol) yielded 2b (1.695 g, 96%) as a colorless

solid. IR (KBr): 2954 s, 2924 s, 2868 s, 1671 m, 1608 s, 1518 s,

1461 s, 1410 s, 1361 s, 1317 m, 1156 m, 1108 m, 1070 m, 940 m,

1

w, 856 m, 754 s, 701 s, 616 w, 534 m, 427 w cm^-1. H NMR

1

874 s, 790 m, 616 m cm^-1. H NMR (THF-d₈): δ 6.93 (s, 6 H,

3

(THF-d₈): δ 7.43 (d, J_HH) 7.0 Hz, 12 H, o-Ph), 7.37 (t, J_HH

)

3

7.7 Hz, 3 H, p-Ar-H), 7.22 (d, ³J_HH) 7.7 Hz, 6 H, m-Ar-H), 7.17-

7.08 (m, 18 H, m-Ph, p-Ph), 3.63 (m, 4 H, THF), 1.79 (m, 4 H,

THF). ¹³C{¹H} NMR (THF-d₈): δ 181.9 (COO), 143.0, 140.9,

137.6, 130.1, 128.5, 128.0, 126.9, 68.1 (THF), 26.3 (THF). Anal.

Calcd for C₆₁H₄₇O₇Y: C, 74.69; H, 4.83. Found: C, 72.60; H, 5.71.

Ar-H), 3.43 (septet, J_HH) 7.0 Hz, 6 H, o-CHMe₂), 2.83 (septet,

3

³J_HH) 7.0 Hz, 3 H, p-CHMe₂), 1.22 (d, J_HH) 7.0 Hz, 18 H,

p-CHMe₂), 1.17 (d, ³J_HH) 7.0 Hz, 36 H, o-CHMe₂). ¹³C{¹H} NMR

(THF-d₈): δ 186.1 (COO), 148.4, 145.2, 137.4, 120.8, 35.4 (p-

CHMe₂), 31.4 (o-CHMe₂), 25.0 o-CHMe₂), 24.5 (p-CHMe₂). Anal.

Calcd for C₄₈H₆₉LaO₆: C, 65.44; H, 7.89. Found: C, 64.97; H,

8.16.

{La(O₂CC₆H₃Ph₂-2,6)₃(THF)}_n(4b). Following the procedure

described above, La[N(SiMe₃)₂]₃(0.873 g, 1.35 mmol) and HO₂-

CAr^Ph(1.111 g, 4.05 mmol) yielded 4b (1.272 g, 91%) as a colorless

solid. IR (Nujol): 1581 w, 1570 w, 1512 s, br, 1494 s, 1443 s,

1308 m, 1171 w, 1155 w, 1076 w, 1028 w, 973 w, 919 w, 868 m,

847 s, 766 s, 755 s, 700 s, 648 m, 614 m, 521 m, 428 m cm^-1. ¹H

{Nd(O₂CC₆H₂iPr₃-2,4,6)₃}_n(2c). Following the procedure

described above, Nd[N(SiMe₃)₂]₃(0.625 g, 1.00 mmol) and HO₂-

CAr^iPr(0.745 g, 3.00 mmol) yielded 2c (0.843 g, 95%) as a light

blue solid. IR (KBr): 2965 s, 2925 s, 2869 s, 1674 m, 1608 s,

1516 s, 1459 s, 1408 s, 1361 s, 1318 m, 1156 m, 1109 m, 1070 m,

940 m, 874 s, 791 m, 616 m cm^-1. Anal. Calcd for C₄₈H₆₉NdO₆:

C, 65.05; H, 7.85. Found: C, 64.81; H, 7.73.

{Gd(O₂CC₆H₂iPr₃-2,4,6)₃}_n(2d). Following the procedure

described above, Gd[N(SiMe₃)₂]₃(0.638 g, 1.00 mmol) and HO₂-

CAr^iPr(0.745 g, 3.00 mmol) yielded 2d (0.841 g, 93%) as a white

solid. IR (KBr): 2957 s, 2924 s, 2869 s, 1674 m, 1607 s, 1513 s,

br, 1460 s, 1416 s, br, 1382 s, 1361 s, 1318 m, 1243 w, 1156 m,

1109 m, 1070 w, 940 w, 874 s, 791 m, 618 m cm^-1. Anal. Calcd

for C₄₈H₆₉GdO₆: C, 64.11; H, 7.73. Found: C, 63.72; H, 7.79.

3

NMR (THF-d₈): δ 7.44 (d, J_HH) 7.3 Hz, 12 H, o-Ph), 7.34 (t,

³J_HH) 7.7 Hz, 3 H, p-Ar-H), 7.22-7.17 (m, 18 H, m-Ar-H, m-Ph),

3

7.06 (t, J_HH) 7.4 Hz, 6 H, p-Ph), 3.63 (m, 4 H, THF), 1.79 (m,

4 H, THF). ¹³C{¹H} NMR (THF-d₈): δ 182.7 (COO), 143.3, 141.1,

138.6, 129.9, 128.7, 127.8, 126.6, 68.1 (THF), 26.3 (THF). Anal.

Calcd for C₆₁H₄₇LaO₇: C, 71.07; H, 4.60. Found: C, 70.19; H,

5.09.

{Y(O₂CC₆H₃Mes₂-2,6)₃(THF)}_n(5a). Following the procedure

described above, Y[N(SiMe₃)₂]₃(0.570 g, 1.00 mmol) and HO₂-

CAr^Mes(1.075 g, 3.00 mmol) yielded 5a (1.111 g, 90%) as a

colorless solid. ¹H NMR (DMSO-d₆): δ 7.39 (s, br, 3 H, p-Ar-H),

6.83 (s, br, 6 H, m-Ar-H), 6.76 (s, 12 H, m-Ph), 3.59 (m, 4 H,

THF), 2.22 (s, 18 H, p-Me), 1.91 (s, 36 H, o-Me), 1.75 (m, 4 H,

{Lu(O₂CC₆H₂iPr₃-2,4,6)₃}_n(2e). Following the procedure de-

scribed above, Lu[N(SiMe₃)₂]₃(0.656 g, 1.00 mmol) and HO₂CAr^iPr

(0.745 g, 3.00 mmol) yielded 2e (0.891 g, 97%) as a colorless solid.

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1639

3

THF). ¹³C{¹H} NMR (THF-d₈): δ 179.8 (COO), 139.5, 139.1,

136.1, 134.9, 134.2, 128.4, 127.4, 126.8, 67.0 (THF), 25.1 (THF),

20.6 (o-Me), 20.5 (p-Me). Anal. Calcd for C₇₉H₈₃O₇Y: C, 76.93;

H, 6.78. Found: C, 76.54; H, 6.63.

7.06 (s, 8 H, Ar-H), 3.27 (septet, J_HH) 7.0 Hz, 8 H, o-CHMe₂),

3

2.72 (sp, J_HH) 6.6 Hz, 4 H, p-CHMe₂), 1.28 (d, J_HH) 7.0 Hz,

3

48 H, o-CHMe₂), 1.17 (d, J_HH) 6.6 Hz, 24 H, p-CHMe₂), 0.13

(s, 12 H, AlMe₂), -0.62 (s, 12 H, AlMe₄). ¹³C{¹H} NMR (C₆D₆):

δ 183.3 (COO), 151.4, 144.8, 131.8, 121.3, 34.8 (p-CHMe₂), 32.2

(o-CHMe₂) 24.6 (o-CHMe₂), 24.0 (p-CHMe₂), 3.9 (AlMe₂), -10.8

(AlMe₄). Anal. Calcd for C₇₈H₁₃₀Al₃LaO₈: C, 66.17; H, 9.26.

Found: C, 66.14; H, 9.45.

{La(O₂CC₆H₃Mes₂-2,6)₃(THF)}_n(5b). Following the procedure

described above, La[N(SiMe₃)₂]₃(0.701 g, 1.13 mmol) and HO₂-

CAr^Mes(0.930 g, 3.39 mmol) yielded 5b (1.343 g, 93%) as a

colorless solid. IR (KBr): 2953 s, 2916 s, 2854 m, 1741 w, 1610

m, 1579 s, 1524 s, br, 1484 s, 1453 s, 1437 s, 1384 s, 1145 w,

1066 w, 1031 m, 850 s, 771 m, 710 m, 589 m, 575 w, 452 m

cm^-1. ¹H NMR (DMSO-d₆): δ 7.25 (s, br, 3 H, p-Ar-H), 6.8-6.7

(m, 18 H, m-Ar-H, m-Ph), 3.59 (m, 4 H, THF), 2.21 (s, 18 H,

p-Me), 1.94 (s, 36 H, o-Me), 1.75 (m, 4 H, THF). ¹³C{¹H} NMR

(DMSO-d₆): δ 179.9 (COO), 139.4, 138.6, 137.8, 135.5, 135.4,

134.2, 127.7, 127.1, 66.9 (THF), 25.0 (THF), 20.6 (o-Me), 20.5

(p-Me). Anal. Calcd for C₇₉H₈₃LaO₇: C, 73.93; H, 6.52. Found:

C, 73.42; H, 6.39.

General Procedures for the Synthesis and Isolation of

Alkylated Rare-Earth Metal Carboxylates. Procedure A. In a

glovebox, 6 equiv of TMA were added to the homoleptic carboxy-

late complexes suspended in hexane. After stirring the suspension

overnight at ambient temperature, the reaction mixture was

centrifuged, and the insoluble product was washed several times

with hexane. After drying for several hours the heteroleptic

aluminate complexes were obtained as colorless solids in moderate

yields.

Procedure B. In a glovebox, 3 or 4 equiv of TMA (or TEA)

were added to the precursor carboxylate complexes suspended in

hexane. The suspension turned into a clear solution within several

minutes to hours. After additional stirring for 2 h, the reaction

mixture was filtrated through a Celite pad and the solvent removed

in vacuo. After drying for several hours, the solid was dissolved in

hexane and crystallized at -45 °C. The heteroleptic aluminate

complexes were obtained with one molecule of hexane in the crystal

lattice within 16 h to several weeks in moderate yields.

Procedure C. In a glovebox, Ln(AlMe₄)₃was dissolved in

hexane, and a toluene solution of [Me₂Al(µ-O₂CAr^R)]₂(2 or 3

equiv) was slowly added. After stirring overnight at ambient

temperature the solvent was removed in vacuo. The product was

isolated via extraction into toluene, washed several times with

hexane, and dried until constant weight under reduced pressure.

Nd[(O₂CAr^iPr)₂(µ-AlMe₂)]₂[(µ-Me)₂AlMe₂](hexane) (12c). Fol-

lowing procedure B, 2c (0.445 g, 0.50 mmol) and TMA (0.126 g,

1.75 mmol) yielded 12c (0.285 g, 40%) as light blue crystals. IR

(Nujol): 1618 m, 1526 s, 1429 s, 1363 s, 1351 m, 1331 m, 1317

m, 1195 w, 1157 w, 1109 w, 1086 w, 941 w, 887 w, 876 w, 777

w, 698 s, 633 w, 587 w, 486 w, 460 w, 408 w. Anal. Calcd for

C₇₈H₁₃₀Al₃NdO₈: C, 65.93; H, 9.22. Found: C, 66.12; H, 9.36.

Gd[(O₂CAr^iPr)₂(µ-AlMe₂)]₂[(µ-Me)₂AlMe₂](hexane) (12d). Fol-

lowing procedure B, 2d (0.451 g, 0.50 mmol) and TMA (0.126 g,

1.75 mmol) yielded 12d (0.293 g, 41%) as a colorless solid. IR

(Nujol): 1624 s, 1606 m, 1574 w, 1427 s, 1364 s, 1350 s, 1330 m,

1316 s, 1196 m, 1154 m, 1108 m, 1086 w, 940 w, 888 m, 877 m,

778 m, 698 vs, 631 w, 587 m, 490 w, 468 w. Anal. Calcd for

C₇₈H₁₃₀Al₃GdO₈: C, 65.28; H, 9.14. Found: C, 65.14; H, 8.75.

Lu[(O₂CAr^iPr)₂(µ-AlMe₂)]₂[(µ-Me)₂AlMe₂] (12e). Following

procedure A, 2e (0.459 g, 0.50 mmol) and TMA (0.216 g, 3.00

mmol) gave 12e (0.250 g, 37%) as a colorless solid. IR (Nujol):

1596 m, 1573 m, 1542 m, 1513 m, 1423 s, 1364 s, 1317 w, 1302

w, 1190 w, 1160 w, 1110 w, 1072 w, 940 w, 878 m, 767 w, 693

s, 632 w, 617 w, 584 w, 476 w, 456 w, 414 w cm^-1. H NMR

1

3

(C₆D₆): δ 6.98 (s, 8 H, Ar-H), 3.11 (septet, J_HH) 6.6 Hz, 8 H,

3

o-CHMe₂), 2.73 (septet, J_HH) 6.6 Hz, 4 H, p-CHMe₂), 1.20 (d,

³J_HH) 6.6 Hz, 72 H, o/p-CHMe₂), 0.10 (s, 12 H, AlMe₂), -0.33

(s, 12 H, AlMe₄). ¹³C{¹H} NMR (C₆D₆): δ 181.1 (COO), 150.6,

144.4, 132.5, 121.2, 34.8 (p-CHMe₂), 32.1 (o-CHMe₂), 24.7 (o-

CHMe₂), 24.1 (p-CHMe₂), 0.3, -10.3. Anal. Calcd for C₇₂H₁₁₆

Al₃LuO₈: C, 63.33; H, 8.56. Found: C, 62.98; H, 8.49.

-

La[(O₂CAr^iPr)₂(µ-AlEt₂)]₂[(µ-Et)₂AlEt₂](hexane) (13a). Fol-

lowing procedure B, 2b (0.440 g, 0.50 mmol) and TEA (1.75 mL

of a 1.0 M hexane solution, 1.75 mmol) yielded 13a (0.262 g, 34%)

as colorless crystals. IR (Nujol): 1620 s, 1606 m, 1573 w, 1526 s,

1421 s, 1364 m, 1350 m, 1329 m, 1314 m, 1156 w, 1109 w, 1086

w, 988 w, 953 w, 877 m, 766 w, 657 s, 640 m, 604 w cm^-1. H

1

Procedure D. In a glovebox, Ln(AlMe₄)₃was dissolved in

hexane, and a toluene suspension of the carboxylic acid, HO₂CAr^R

(1-4 equiv), was slowly added. The solution was stirred at ambient

temperature for 18 h. The solvent was removed in vacuo, and the

product was isolated via extraction into toluene, washed with

hexane, and dried for several hours.

Y[(O₂CAr^iPr)₂(µ-AlMe₂)]₂[(µ-Me)₂AlMe₂] (12a). Following

procedure A, 2a (0.623 g, 0.75 mmol) and TMA (0.325 g, 4.50

mmol) yielded 12a (0.345 g, 36%) as a colorless solid. IR (Nujol):

1604 s, 1593 s, 1573 s, 1513 s, 1429 s, 1377 s, 1364 s, 1298 m,

1190 m, 1161 m, 1111 m, 1072 w, 940 w, 880 m, 768 w, 692 s,

NMR (C₆D₆): δ 7.05 (s, 8 H, Ar-H), 3.20 (septet, ³J_HH) 6.6 Hz,

8 H, o-CHMe₂), 2.73 (septet, ³J_HH) 7.0 Hz, 4 H, p-CHMe₂), 1.67

3

(t, J_HH) 7.7 Hz, 12 H, AlEt), 1.30 (d, J_HH) 6.6 Hz, 48 H,

o-CHMe₂), 1.17 (d, ³J_HH) 7.0 Hz, 24 H, p-CHMe₂), 1.13 (t, ³J_HH

3

) 8.1 Hz, 12 H, AlEt), 0.59 (q, J_HH) 7.7 Hz, 8 H, AlEt), 0.15

(q, J_HH) 8.1 Hz, 8 H, AlEt). ¹³C{¹H} NMR (C₆D₆): δ 182.6

3

(COO), 151.2, 144.9, 131.8, 121.4, 34.8 (p-CHMe₂), 32.2 (o-

CHMe₂) 24.7 (o-CHMe₂), 24.0 (p-CHMe₂), 14.9 (br, AlEt), 13.1

(AlEt), 8.9 (AlEt), -0.2 (br, AlEt). Anal. Calcd for C₈₆H₁₄₆Al₃-

LaO₈: C, 67.60; H, 9.63. Found: C, 67.72; H, 9.82.

Nd[(O₂CAr^iPr)₂(µ-AlEt₂)]₂[(µ-Et)₂AlEt₂](hexane) (13b). Fol-

lowing procedure B, 2c (0.445 g, 0.50 mmol) and TEA (1.75 mL

of a 1.0 M hexane solution, 1.75 mmol) yielded 13c (0.132 g, 17%)

as light blue crystals. IR (Nujol): 1620 m, 1573 w, 1524 s, 1424

m, 1348 m, 1328 m, 1314 m, 1155 w, 1109 w, 1086 w, 985 w,

954 w, 878 m, 788 w, 658 s, 634 m, 598 w cm^-1. Anal. Calcd for

C₈₆H₁₄₆Al₃NdO₈: C, 67.37; H, 9.60. Found: C, 66.13; H, 9.30.

636 w, 623 w, 585 w, 504 w, 481 w, 456 w cm^-1

.

¹H NMR

3

(C₆D₆): δ 7.03 (s, 8 H, Ar-H), 3.20 (septet, J_HH) 6.7 Hz, 8 H,

3

o-CHMe₂), 2.73 (septet, J_HH) 7.0 Hz, 4 H, p-CHMe₂), 1.22 (d,

3

³J_HH) 6.7 Hz, 48 H, o-CHMe₂), 1.19 (d, J_HH) 7.0 Hz, 24 H,

p-CHMe₂), -0.08 (s, 12 H, AlMe₂), -0.41 (s, 12 H, AlMe₄). ¹³C-

{¹H} NMR (C₆D₆): δ 181.7 (COO), 151.0, 144.7, 132.0, 121.3,

34.8 (p-CHMe₂), 32.1 (o-CHMe₂), 24.6 (o-CHMe₂), 24.1 (p-

CHMe₂), 0.0, -10.4. Anal. Calcd for C₇₂H₁₁₆Al₃O₈Y: C, 67.58;

H, 9.14. Found: C, 66.02; H, 9.28.

Y[(O₂CAr^Me)₂(µ-AlMe₂)]₃(14a). Following procedure C,

Y(AlMe₄)₃(0.350 g, 1.00 mmol) and [Me₂Al(µ-O₂CAr^Me)]₂(0.661

g, 1.50 mmol) yielded 14a (∼80%) together with a mixture of

La[(O₂CAr^iPr)₂(µ-AlMe₂)]₂[(µ-Me)₂AlMe₂](hexane) (12b). Fol-

lowing procedure B, 2b (0.440 g, 0.50 mmol) and TMA (0.126 g,

1.75 mmol) gave 12b (0.321 g, 45%) as a colorless solid. IR

(Nujol): 1618 m, 1527 s, 1425 s, 1365 s, 1350 m, 1331 m, 1316

m, 1196 w, 1150 w, 1108 w, 1086 w, 940 w, 877 m, 779 w, 698

s, 632 w, 592 w, 489 w, 459 w, 406 w cm^-1. ¹H NMR (C₆D₆): δ

1

different alkylated byproducts, which could not be separated. H

NMR (C₆D₆): δ 6.58 (s, 12 H, Ar-H), 2.41 (s, 36 H, o-Me), 1.99

(s, 18 H, p-Me), -0.54 (s, 18 H, AlMe₂). ¹³C{¹H} NMR (C₆D₆):

δ 181.6 (COO), 139.4, 134.9, 133.0, 128.6, 21.1 (p-Me), 20.4 (o-

Me), -9.9 (AlMe₂).

1640 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

La[(O₂CAr^Me)₂(µ-AlMe₂)]₃(14b). Following procedure C, La

(AlMe₄)₃(0.400 g, 1.00 mmol) and [Me₂Al(µ-O₂CAr^Me)]₂(0.661

g, 1.50 mmol) gave 14b (∼70%) together with other alkylated

byproducts, which could not be separated. ¹H NMR (C₆D₆): δ 6.57

(s, 12 H, Ar-H), 2.43 (s, 36 H, o-Me), 1.99 (s, 18 H, p-Me), -0.54

(s, 18 H, AlMe₂).

added to a cooled hexane suspension (-35 °C) of the aromatic

carboxylic acid. The solution became clear immediately except for

9, and gas evolution (CH₄, C₂H₆) was observed. After stirring at

ambient temperature for an additional 3 h the solvent was removed

in vacuo, yielding the products as white solids in quantitative yields.

[Me₂Al(µ-O₂CC₆H₂Me₃-2,4,6)]₂(6). Following the procedure

described above, HO₂CAr^Me(0.328 g, 2.00 mmol) and TMA (0.144

g, 2.00 mmol) yielded 6 (0.439 g, >99%) as a colorless solid. IR

(Nujol): 1722 w, 1613 m, 1524 s, 1502 s, 1195 m, 1034 w, 872

{Y(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15a). Following procedure D,

Y(AlMe₄)₃(0.175 g, 0.50 mmol) and HO₂CAr^tBu(0.145 g, 0.50

mmol) yielded 15a (0.253 g, 87%) as a colorless solid. IR (Nujol):

1598 w, 1531 s, 1266 w, 1244 w, 1215 m, 1192 m, 1088 w, 880

w, 797 w, 779 w, 761 w, 721 m, 698 m, 692 s, 662 w, 580 m, 544

1

w, 847 m, 788 w, 701 s, 665 m, 636 m, 582 m, 517 m cm^-1. H

NMR (C₆D₆): δ 6.52 (s, 4 H, Ar-H), 2.34 (s, 12 H, o-Me), 1.95 (s,

6 H, p-Me), -0.25 (s, 12 H, AlMe₂). ¹³C{¹H} NMR (C₆D₆): δ

177.9 (COO), 141.3, 137.4, 130.3, 129.8, 21.0 (o-Me), 20.9 (p-

Me), -10.6 (AlMe₂). Anal. Calcd for C₂₄H₃₄Al₂O₄: C, 65.44; H,

7.78. Found: C, 65.50; H, 7.75.

1

m cm^-1. H NMR (C₆D₆): δ 7.50 (s, 2 H, Ar-H), 1.47 (s, 18 H,

o-CMe₃), 1.31 (s, 9 H, p-CMe₃), -0.12 (s, br, 24 H, AlMe₄). ¹³C-

{¹H} NMR (C₆D₆): δ 184.9 (COO), 150.8, 145.3, 125.2, 123.8,

37.8 (o-CMe₃), 35.0 (p-CMe₃), 33.3 (o-CMe₃), 31.2 (p-CMe₃), 2.2

(br, AlMe₄). Anal. Calcd for C₅₄H₁₀₆Al₄O₄Y₂: C, 58.69; H, 9.67.

Found: C, 58.86; H, 9.72.

[Me₂Al(µ-O₂CC₆H₂iPr₃-2,4,6)]₂(7). Following the procedure

described above, HO₂CAr^iPr(0.497 g, 2.00 mmol) and TMA (0.144

g, 2.00 mmol) gave 7 (0.605 g, >99%) as a colorless solid. IR

(Nujol): 1771 w, 1591 s, 1483 m, sh, 1363 s, 1319 w, 1296 w,

1194 m, 1162 w, 1112 w, 1103 w, 1070 w, 941 w, 880 w, 772 w,

698 s, br, 630 w, 574 w, 496 w, 465 w cm^-1. ¹H NMR (C₆D₆): δ

{La(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15b). Following procedure

D, La(AlMe₄)₃(0.200 g, 0.50 mmol) and HO₂CAr^tBu(0.145 g, 0.50

mmol) yielded 15b (0.281 g, 93%) as a colorless solid. IR (Nujol):

1598 w, 1525 s, 1265 w, 1242 w, 1204 m, 1186 m, 1088 w, 879

w, 799 w, 778 w, 761 w, 719 m, 692 s, 583 m, 573 m, 551 w

3

7.05 (s, 4 H, Ar-H), 3.20 (septet, J_HH) 6.6 Hz, 4 H, o-CHMe₂),

1

3

cm^-1. H NMR (C₆D₆): δ 7.50 (s, 2 H, Ar-H), 1.50 (s, 18 H,

2.70 (septet, J_HH) 7.0 Hz, 2 H, p-CHMe₂), 1.27 (d, J_HH) 6.6

o-CMe₃), 1.26 (s, 9 H, p-CMe₃), -0.03 (s, br, 24 H, AlMe₄). ¹³C-

{¹H} NMR (C₆D₆): δ 185.6 (COO), 151.1, 145.1, 123.3, 122.9,

37.7 (o-CMe₃), 35.0 (p-CMe₃), 33.4 (o-CMe₃), 31.2 (p-CMe₃), 7.1

(AlMe₄). Anal. Calcd for C₅₄H₁₀₆Al₄La₂O₄: C, 53.82; H, 8.87.

Found: C, 53.70; H, 8.91.

Hz, 24 H, o-CHMe₂), 1.15 (d, J_HH) 7.0 Hz, 12 H, p-CHMe₂),

3

-0.23 (s, 12 H, AlMe₂). ¹³C{¹H} NMR (C₆D₆): δ 179.8 (COO),

151.3, 144.8, 131.7, 121.6, 34.8 (p-CHMe₂), 32.3 (o-CHMe₂), 24.3

(o-CHMe₂), 24.0 (p-CHMe₂), -10.9 (AlMe₂). Anal. Calcd for

C₃₆H₅₈Al₂O₄: C, 71.02; H, 9.60. Found: C, 70.81; H, 9.45.

{Nd(O₂CAr^tBu)[(µ-Me)₂AlMe₂]₂}₂(15c). Following procedure

D, Nd(AlMe₄)₃(0.203 g, 0.50 mmol) and HO₂CAr^tBu(0.145 g, 0.50

mmol) gave 15c (0.287 g, 94%) as a bluish solid. IR (Nujol): 1598

w, 1524 s, 1554 s, 1362 s, 1266 w, 1242 w, 1206 m, 1187 m, 1088

[Me₂Al(µ-O₂CC₆H₂tBu₃-2,4,6)]₂(8). Following the procedure

described above, HO₂CAr^tBu(0.363 g, 1.25 mmol) and TMA (0.090

g, 1.25 mmol) yielded 8 (0.340 g, 98%) as a colorless solid. IR

(Nujol): 1593 s, 1416 m, 1364 m, 1266 w, 1243 w, 1196 m, 1104

w, 940 w, 879 w, 786 w, 697 s, 623 w, 585 w, 574 w, 492 w, 447

w, 879 w, 798 w, 778 w, 761 w, 719 s, 691 s, 573 m, 548 w cm^-1

.

¹H NMR (C₆D₆): δ 9.66 (s, br, 48 H, AlMe₄), 8.26 (s, 4 H, Ar-H),

2.04 (s, 18 H, p-CMe₃), -1.66 (s, 36 H, o-CMe₃). Anal. Calcd for

C₅₄H₁₀₆Al₄Nd₂O₄: C, 53.34; H, 8.79. Found: C, 53.25; H, 8.83.

w cm^-1. H NMR (C₆D₆): δ 7.54 (s, 4 H, Ar-H), 1.53 (s, 36 H,

1

o-CMe₃), 1.25 (s, 18 H, p-CMe₃), -0.27 (s, 12 H, AlMe₂). ¹³C-

{¹H} NMR (C₆D₆): δ 181.0 (COO), 151.1, 146.7, 129.8, 122.8,

37.5 (p-CMe₃), 35.1 (o-CMe₃), 33.0 (o-CMe₃), 31.3 (p-CMe₃), -9.6

(AlMe₂). Anal. Calcd for C₄₂H₇₀Al₂O₄: C, 72.80; H, 10.18.

Found: C, 72.93; H, 10.09.

{Y(O₂CAr^Ph)[(µ-Me)₂AlMe₂]₂}₂(16a). Following procedure D,

Y(AlMe₄)₃(0.140 g, 0.40 mmol) and HO₂CAr^Ph(0.110 g, 0.40

mmol) yielded 16a (0.138 g, 64%) as a colorless solid. IR (Nujol):

1944 w, 1876 w, 1684 w, 1584 m, 1561 s, 1496 m, 1402 m, 1303

w, 1214 w, 1195 w, 1158 w, 1072 w, 1029 w, 918 w, 816 w, 780

w, 758 m, 722 m, 698 s, 647 w, 615 w, 595 w, 575 m, 521 w, 483

[Me₂Al(µ-O₂CC₆H₃Ph₂-2,6)]₂(9). Following the procedure

described above, HO₂CAr^Ph(0.262 g, 1.00 mmol) and TMA (0.072

g, 1.00 mmol) yielded 9 (0.330 g, >99%) as a colorless solid. IR

(Nujol): 1619 vs, 1599 s, 1578 s, 1495 s, 1408 s, 1302 w, 1190 m,

1168 w, 1072 m, 1029 w, 917 w, 817 w, 783 m, 758 s, 736 m, 696

1

3

w cm^-1. H NMR (C₆D₆): δ 7.32 (d, J_HH) 7.6 Hz, 8 H, Ph-

H

_ortho), 7.21 (t, ³J_HH) 7.6, 8 H, Ph-H_meta), 7.10 (t, ³J_HH) 7.6 Hz,

4 H, Ph-H_para), 6.92 (s, 6 H, Ar-H), -0.43 (s, br, 48 H, AlMe₄). ¹H

NMR (toluene-d₈, -80 °C): δ 7.3-7.0 (m, 20 H, Ph-H), 6.80 (s,

6 H, Ar-H), 0.14 (s, br, 12 H, Y-Me-Al), -0.27 (s, 12 H, AlMe₂),

-0.53 (s, br, 12 H, Y-Me-Al), -0.72 (s, 12 H, AlMe₂). ¹³C{¹H}

vs, br, 644 m, 575 m, 524 m, 484 m, 475 m cm^-^{1 1}H NMR

.

(C₆D₆): δ 7.30-7.16 (m, 10 H, Ar-H, Ph), 7.04-6.96 (m, 3 H,

Ar-H, Ph), -1.05 (s, 12 H, AlMe₂). ¹³C{¹H} NMR (C₆D₆): δ 175.1

(COO), 141.4, 140.7, 133.4, 130.0, 129.7, 129.0, 128.9, 128.7, -9.6

(AlMe₂). Anal. Calcd for C₄₂H₃₈Al₂O₄: C, 76.35; H, 5.80. Found:

C, 75.96; H, 5.95.

[Me₂Al(µ-O₂CC₆H₃Mes₂-2,6)]₂(10). Following the procedure

described above, HO₂CAr^Mes(0.346 g, 1.00 mmol) and TMA (0.072

g, 1.00 mmol) gave 10 (0.410 g, >99%) as a colorless solid. IR

(Nujol): 1612 s, 1584 m, 1546 w, 1402 m, 1308 w, 1192 m, 1169

w, 1066 w, 1032 w, 1014 w, 848 m, 820 w, 784 m, 735 m, 692 s,

2

NMR (C₆D₆): δ 177.8 (d, J_CY) 3.1 Hz, COO), 141.6, 141.4,

132.4, 130.5, 130.2, 129.2, 128.9, 128.7, 1.5 (br, AlMe₄). Anal.

Calcd for C₅₄H₇₄Al₄O₄Y₂: C, 60.45; H, 6.95. Found: C, 59.86; H,

6.72.

{La(O₂CAr^Ph)[(µ-Me)₂AlMe₂]₂}₂(16b). Following procedure

D, La(AlMe₄)₃(0.184 g, 0.46 mmol) and HO₂CAr^Ph(0.126 g, 0.46

mmol) yielded 16b (0.160 g, 59%) as a colorless solid. IR (Nujol):

1967 w, 1948 w, 1892 w, 1810 w, 1586 m, 1574 m, 1543 s, 1513

m, 1495 m, 1311 w, 1210 m, 1186 s, 1151 m, 1072 w, 1028 w,

914 w, 816 w, 784 w, 758 s, 717 s, 698 s, 648 w, 602 w, 573 m,

1

3

585 m, 570 w, 498 w cm^-1. H NMR (C₆D₆): δ 7.02 (t, J_HH

)

7.7 Hz, 2 H, p-Ar-H), 6.90 (s, 8 H, m-Mes-H), 6.76 (d, ³J_HH) 7.7

Hz, 4 H, m-Ar-H), 2.23 (s, 12 H, p-Mes-Me), 2.02 (s, 24 H, o-Mes-

Me), -1.03 (s, 12 H, AlMe₂). ¹³C{¹H} NMR (C₆D₆): δ 174.5

(COO), 140.7, 137.1, 137.0, 135.6, 133.8, 131.1, 129.3, 128.8, 21.1

(p-Me), 20.6 (o-Me), -11.6 (AlMe₂). Anal. Calcd for C₅₄H₆₂-

Al₂O₄: C, 78.23; H, 7.54. Found: C, 78.09; H, 7.43.

1

3

544 m, 528 m, 484 w cm^-1. H NMR (C₆D₆): δ 7.33 (d, J_HH

)

7.3 Hz, 8 H, Ph-H_ortho), 7.18 (t, ³J_HH) 7.3, 8 H, Ph-H_meta), 7.05 (t,

³J_HH) 7.3 Hz, 4 H, Ph-H_para), 6.90 (s, 6 H, Ar-H), -0.33 (s, 48

H, AlMe₄). ¹³C{¹H} NMR (C₆D₆): δ 180.5 (COO), 140.4, 140.3,

132.2, 130.3, 129.7, 129.3, 129.0, 128.3, 4.3 (br, AlMe₄). Anal.

Calcd for C₅₄H₇₄Al₄La₂O₄: C, 55.30; H, 6.36. Found: C, 55.41;

H, 6.43.

[Et₂Al(µ-O₂CC₆H₂iPr₃-2,4,6)]₂(11). Following the procedure

described above, HO₂CAr^iPr(0.497 g, 2.00 mmol) and TEA (0.228

g, 2.00 mmol) yielded 11 (0.663 g, >99%) as a colorless solid. IR

(Nujol): 1592 vs, 1487 s, 1443 vs, 1364 s, 1320 w, 1195 w, 1163

w, 1111 w, 1071 w, 988 w, 951 w, 920 w, 877 w, 772 w, 721 w,

General Procedure for the Synthesis of Alkylaluminum

Carboxylates. In a glovebox, 1 equiv of TMA or TEA was slowly

Binary Ziegler-Type Catalysts

Organometallics, Vol. 25, No. 7, 2006 1641

Table 6. Crystallographic Data for Compounds 1b′, 1c′, 7, 15b, and 15c

1b′

1c′

7

15b

15c

formula

fw

C₆₈H₉₀La₂O₁₆S₄

1569.50

C₃₆H₅₁NdO₉S₃

868.22

C₃₆H₅₈Al₂O₄

608.78

C₅₄H₁₀₆Al₄La₂O₄

1205.13

C₅₄H₁₀₆Al₄Nd₂O₄

1215.79

color/habit

cryst dimens (mm³)

cryst syst

space group

a, Å

colorless/fragment

0.16 × 0.42 × 0.53

monoclinic

C2/c (no. 15)

26.0737(3)

18.9165(2)

16.9219(2)

90

120.9598(6)

90

7157.16(15)

4

pale blue/fragment

0.50 × 0.64 × 0.64

triclinic

colorless/fragment

0.28 × 0.36 × 0.45

monoclinic

P2₁/n (no. 14)

10.0759(1)

10.0962(1)

19.2370(2)

90

104.2331(3)

90

1896.88(3)

2

colorless/fragment

0.23 × 0.30 × 0.33

monoclinic

C2/c (no. 15)

23.7992(2)

19.6717(1)

15.1649(1)

90

114.6295(3)

90

6453.84(8)

4

pale blue/fragment

0.18 × 0.18 × 0.51

monoclinic

C2/c (no. 15)

23.5611(2)

19.4031(1)

15.2363(1)

90

113.5901(3)

90

6383.32(8)

4

P1h (no. 2)

9.6455(1)

15.2867(2)

15.6504(2)

116.9415(5)

99.3467(7)

94.9344(7)

1996.17(4)

2

b, Å

c, Å

R, deg

â, deg

γ, deg

V, Å³

Z

T, K

123

1.457

1.357

3216

123

1.444

1.506

894

153

1.066

0.109

664

173

1.240

1.397

2512

123

1.265

1.700

2536

D

_calcd, g cm^-3

µ, mm^-1

F(000)

θ range, deg

2.15-25.34

(31, (22, (20

18 159

6433/0.024

5786

6433/0/581

0.0221/0.0498

0.0269/0.0520

1.023

1.50-25.35

(11, (18, (18

39 487

7305/0.038

7191

7305/0/641

0.0196/0.0502

0.0201/0.0504

1.080

2.58-25.33

(12, (12, (23

41 190

3455/0.040

3143

3455/0/318

0.0348/0.0913

0.0388/0.0945

1.028

1.73-25.33

(28, (23, (18

72 245

5898/0.046

4835

5898/0/394

0.0244/0.0564

0.0348/0.0602

1.039

1.41-25.33

(28, (23, (18

75 409

5856/0.041

5152

5856/0 /502

0.0179/0.0397

0.0230/0.0415

1.023

index ranges (h, k, l)

no. of rflns collected

no. of indep rflns/R_int

no. of obsd rflns (I > 2σ(I))

no. of data/restraints/params

R1/wR2 (I > 2σ(I))^a

R1/wR2 (all data)^a

GOF (on F²)^a

largest diff peak and hole (e Å^-3

)

+0.62/-0.44

+1.44/-0.81

+0.33/-0.21

+0.70/-0.87

+0.69/-0.33

2

^aR1 ) ∑(||F_o| - |F_c||)/∑|F_o|; wR2 ) {∑[w(F_o- F_c)²]/∑[w(F_o)²]}^1/2; GOF ) {∑[w(F_o- F_c)²]/(n - p)}^1/2

1

661 m, 634 m, 540 w, 506 w, 494 w, 465 w cm^-1. H NMR

temperature to constant weight. The polymer yield was determined

gravimetrically.

3

(C₆D₆): δ 7.07 (s, 4 H, Ar-H), 3.23 (septet, J_HH) 6.8 Hz, 4 H,

3

o-CHMe₂), 2.70 (septet, J_HH) 6.8 Hz, 2 H, p-CHMe₂), 1.33 (d,

Polymer Characterization. The molar masses M_wand M_nof

the polymers were determined by size exclusion chromatography

(SEC). Sample solutions (1.0 mg polymer per mL CHCl₃) were

filtered through a 0.2 µm syringe filter prior to injection. SEC was

operated with a pump supplied by Waters (type: Waters 510), and

Ultrastyragel columns with pore sizes of 500, 1000, 10 000, and

100 000 Å were used. The signals were detected by a differential

refractometer (Waters 410) and calibrated against polystyrene

standards (M_w/M_n< 1.15). The flow rate was 1.0 mL min^-1. The

microstructure of the polyisoprenes was examined via ¹³C NMR

experiments in CDCl₃.

³J_HH) 6.8 Hz, 24 H, o-CHMe₂), 1.32 (t, J_HH) 8.0 Hz, 12 H,

3

AlCH₂CH₃), 1.14 (d, J_HH) 6.8 Hz, 12 H, p-CHMe₂), 0.38 (q,

³J_HH) 8.0 Hz, 8 H, AlCH₂CH₃). ¹³C{¹H} NMR (C₆D₆): δ 180.0

(COO), 151.3, 144.8, 131.5, 121.6, 34.7 (p-CHMe₂), 32.4 (o-

CHMe₂), 24.5 (o-CHMe₂), 23.9 (p-CHMe₂), 8.8 (AlCH₂CH₃), -1.0

(AlCH₂CH₃). Anal. Calcd for C₄₀H₆₆Al₂O₄: C, 72.25; H, 10.00.

Found: C, 71.81; H, 9.85.

Reaction of 12a with Me₂AlCl. In a glovebox, 12a (0.448 g,

0.35 mmol) was suspended in 8 mL of hexane, and 1 equiv of

Me₂AlCl (0.35 mL of a 1.0 M hexane solution, 0.35 mmol) was

added at ambient temperature. Immediately a white precipitate

formed. After stirring for an additional 2 h the solid was separated

via centrifugation, washed several times with hexane, and dried.

Yield: 0.049 g (0.32 mmol, 91%). Anal. Calcd for C₂H₆ClY

(17a): C, 15.56; H, 3.92. Found: C, 19.11; H, 4.68. The hexane

solution was filtrated through a Celite pad, and the solvent was

removed in vacuo, yielding 0.431 g of a colorless, crystalline

product, which was identified as 7. Anal. Calcd for C₃₆H₅₈Al₂O₄:

C, 71.02; H, 9.60. Found: C, 71.51; H, 9.86.

Reaction of 12b with Me₂AlCl. Following the procedure

described above, 12b (0.354 g, 0.25 mmol) and Me₂AlCl (0.25 mL,

0.25 mmol) yielded 0.044 g (0.22 mmol, 86%) of a white solid

(17b) and 0.314 g of 7. Anal. Calcd for C₂H₆ClLa (17b): C, 11.75;

H, 2.96. Found: C, 17.46; H, 4.39. Anal. Calcd for C₃₆H₅₈Al₂O₄

(7): C, 71.02; H, 9.60. Found: C, 71.33; H, 9.80.

Polymerization of Isoprene. All manipulations were performed

in a glovebox under an argon atmosphere. A detailed polymerization

procedure for run 8 of Table 5 is described as a typical example.

To a solution of 12c (0.018 g, 0.02 mmol) in 8 mL of hexane was

added 2 equiv of Et₂AlCl (5.0 µL, 0.04 mmol), and the mixture

was aged at ambient temperature for 30 min before use. After the

addition of isoprene (2.0 mL, 20 mmol) the polymerization was

carried out at 40 °C for 24 h. The polymerization mixture was

poured into a large quantity of acidified 2-propanol containing 0.1%

(w/w) 2,6-di-tert-butyl-4-methylphenol as a stabilizer. The polymer

was washed with 2-propanol and dried under vacuum at ambient

Single-Crystal X-ray Structure Determination of Compounds

1b′, 1c′, 7, 13b, 15b, and 15c. General Comments. Crystal data

and details of the structure determination are presented in Table 6.

Suitable single-crystals for the X-ray diffraction study were grown

with standard cooling techniques. Except for 1b′ and 1c′ all

preparations were carried out in a glovebox. Crystals were stored

under perfluorinated ether, transferred in a Lindemann capillary,

fixed, and sealed. Preliminary examination and data collection were

carried out on an area detecting system (NONIUS, MACH3,

κ-CCD) at the window of a rotating anode (NONIUS, FR591) and

graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). The

unit cell parameters were obtained by full-matrix least-squares

refinements during the scaling procedure. Data collections were

performed at low temperatures (Oxford Cryosystems), each mea-

sured with a couple of data sets in rotation scan modus with ∆æ/

∆ω ) 1.0. Intensities were integrated, and the raw data were

corrected for Lorentz, polarization, and, arising from the scaling

procedure, latent decay and absorption effects. The structures were

solved by a combination of direct methods and difference Fourier

syntheses. All non-hydrogen atoms were refined with anisotropic

displacement parameters. Full-matrix least-squares refinements were

2

carried out by minimizing ∑w(F_o- F_c²)²with the SHELXL-97

weighting scheme and stopped at shift/err < 0.004. The final

residual electron density maps showed no remarkable features.

Neutral atom scattering factors for all atoms and anomalous

dispersion corrections for the non-hydrogen atoms were taken from

1642 Organometallics, Vol. 25, No. 7, 2006

Fischbach et al.

International Tables for Crystallography. All calculations were

performed on an Intel Pentium II PC, with the STRUX-V system,

including the programs PLATON, SIR92, and SHELXL-97.⁵⁶

Special: 1b′: A disorder over two positions (0.667(4):0.333(4))

of one of the two DMSO ligands could be resolved clearly. Their

methyl hydrogen atoms were refined as part of rigid groups, with

d_C-H) 0.98 Å and U_iso(H)) 1.5U_eq(C). All other hydrogen atoms

were located from difference Fourier syntheses and were allowed

to refine freely. The X-ray results of a single-crystal grown in a

different flask show the same behavior (STOE&Cie. IPDS, T )

173 K, a ) 26.050(2) Å, b ) 19.021(1) Å, c ) 16.954(1) Å, â )

120.576(6)°, V ) 7232.4(9) Å³, disorder 0.671(4):0.329(4)). 1c′:

A disorder over two positions (0.752(3):0.248(3)) of one of the

three DMSO ligands could be resolved clearly. The methyl

laluminate ligands were located from difference Fourier syntheses

and were allowed to refine freely. All other hydrogen atoms were

located from difference Fourier syntheses but either refined as part

of rigid rotating groups, with d_C-H) 0.98 Å and U_iso(H)) 1.5U_eq(C)

or placed in calculated positions and refined using a riding model,

with an aromatic d_C-Hdistance of 0.95 Å and U_iso(H)) 1.2U_eq(C)

,

.

15c: Small extinction effects were corrected with the SHELXL-

97 procedure with ꢀ ) 0.00019(2). All hydrogen atoms were located

from difference Fourier syntheses and were allowed to refine freely.

7: All hydrogen atoms were located from difference Fourier

syntheses and were allowed to refine freely. Crystallographic data

(excluding structure factors) for the structures reported in this paper

have been deposited with the Cambridge Crystallographic Data

Centre as supplementary publication nos. CCDC-289152 (1b′),

CCDC-298151 (1c′), CCDC-298154 (15b), CCDC-298155 (15c),

and CCDC-298153 (7). Copies of the data can be obtained free of

charge on application to CCDC, 12 Union Road, Cambridge CB2

1EZ,UK(fax: (+44)1223-336-033;e-mail: deposit@ccdc.cam.ac.uk).

hydrogen atoms were refined as part of rigid groups, with d_C-H

)

0.98 Å and U_iso(H)) 1.5U_eq(C). All other hydrogen atoms were

located from difference Fourier syntheses and were allowed to refine

freely. 13b: C₈₀H₁₃₂Al₃LaO₈, M_r) 1441.71, colorless fragment

(0.15 × 0.20 × 0.63 mm³), monoclinic, C2/c (No. 15), a ) 25.8264-

(2) Å, b ) 20.4639(2) Å, c ) 18.6338(2) Å, â ) 103.8579(3)°, V

) 9561.5(2) Å³, Z ) 4, d_calc) 1.002 g cm^-3, F₀₀₀) 3088, µ )

0.517 mm^-1, R1/wR2 (I > 2σ(I)) ) 0.0416/0.1193, R1/wR2 (all

data) ) 0.0460/0.1224. The result suffers from a severe disordering

of the highly mobile isopropyl and ethyl groups, even at low

temperatures. Attempts to get better results in the acentric space

group Cc failed. 15b: Methyl hydrogen atoms of the tetramethy-

Acknowledgment. Financial support by the Deutsche For-

schungsgemeinschaft and the Fonds der Chemischen Industrie

is gratefully acknowledged. F.P. thanks the University of

Ljubljana for an “Otto and Karla Likar” student fellowship. We

also thank Dr. Lars Friebe for GPC analysis. E.H. thanks

Stefanie Neumann for her help during the course of the X-ray

measurements of compound 1b′.

(56) (a) Data Collection Software for Nonius k-CCD DeVices; Delft, The

Netherlands, 2001. (b) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997,

276, 307. (c) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;

Burla, M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.

(d) International Tables for Crystallography; Wilson, A. J. C., Ed.; Kluwer

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Supporting Information Available: Text giving tables of

atomic coordinates, atomic displacement parameters, bond distances

and angles, and disorder models for complexes 1b′, 1c′, 7, 13b,

15b, and 15c. This material is available free of charge via the

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

OM060052I

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Structure - Reactivity relationships in rare-earth metal carboxylate-based binary Ziegler-type catalysts

DOI: 10.1021/om060052i

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Article abstract of DOI:10.1021/om060052i

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