Methylene-bridged metallocenes with 2,2′-methylenebis[1H-inden-1-yl] ligands: Synthesis, characterization, and polymerization catalysis of a synthetically simple class of C2- and C2v-symmetric ansa-metallocenes

Article abstract of DOI:10.1002/hlca.200690154

The acid-catalyzed reaction between formaldehyde and 1H-indene, 3-alkyl- and 3-aryl-1H-indenes, and six-membered-ring substituted 1H-indenes, with the 1H-indene/CH₂O ratio of 2:1, at temperatures above 60° in hydrocarbon solvents, yields 2,2′-m

Full text of DOI:10.1002/hlca.200690154

Helvetica Chimica Acta – Vol. 89 (2006)
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Methylene-Bridged Metallocenes with 2,2’-Methylenebis[1H-inden-1-yl]
Ligands: Synthesis, Characterization, and Polymerization Catalysis ofa
Synthetically Simple Class of C2- and C2v-Symmetric ansa-Metallocenes
by Luigi Resconi*a), Isabella Camuratia), Cristina Fioria), Davide Balbonia), Pierluigi Mercandelli*b),
and Angelo Sironib)
a) Basell Polyolefins, Centro Ricerche G. Natta, I-44100 Ferrara
(e-mail: luigi.resconi@basell.com)
b) Dipartimento di Chimica Strutturale, Università di Milano, via Venezian 21, I-20133 Milano
(e-mail: pierluigi.mercandelli@unimi.it)
Dedicated to Professor Giambattista Consiglio on the occasion of his 65th birthday
The acid-catalyzed reaction between formaldehyde and 1H-indene, 3-alkyl- and 3-aryl-1H-indenes,
and six-membered-ring substituted 1H-indenes, with the 1H-indene/CH2O ratio of 2 :1, at temperatures
above 608 in hydrocarbon solvents, yields 2,2’-methylenebis[1H-indenes] 1–8 in 50–100% yield. These
2,2’-methylenebis[1H-indenes] are easily deprotonated by 2 equiv. of BuLi or MeLi to yield the corre-
sponding dilithium salts, which are efficiently converted into ansa-metallocenes of Zr and Hf. The unsub-
stituted dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1H-inden-1-yl]}zirconium ([ZrCl2(1’)])
is the least soluble in organic solvents. Substitution of the 1H-indenyl moieties by hydrocarbyl substitu-
ents increases the hydrocarbon solubility of the complexes, and the presence of a substituent larger than a
Me group at the 1,1’ positions of the ligand imparts a high diastereoselectivity to the metallation step,
since only the racemic isomers are obtained. Methylene-bridged ‘ansa-zirconocenes’ show a noticeable
open arrangement of the bis[1H-inden-1-yl] moiety, as measured by the angle between the planes defined
by the two p-ligands (the ‘bite angle’). In particular, of the ‘zirconocenes’ structurally characterized so
far, the dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[4,7-dimethyl-1H-inden-1-yl]}zirconium
([ZrCl2(5’)] is the most open. The mixture [ZrCl2(1’)]/methylalumoxane (MAO) is inactive in the poly-
merization of both ethylene and propylene, while the metallocenes with substituted indenyl ligands poly-
merize propylene to atactic polypropylene of a molecular mass that depends on the size of the alkyl or
aryl groups at the 1,1’ positions of the ligand. Ethene is polymerized by rac-dichloro-
{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-methyl-1H-inden-1-yl]}zirconium ([ZrCl2(2’)])/MAO
to polyethylene waxes (average degree of polymerization ca. 100), which are terminated almost exclu-
sively by ethenyl end groups. Polyethylene with a high molecular mass could be obtained by increasing
the size of the 1-alkyl substituent.
Introduction. – A large body of literature exists on the chemistry and catalytic prop-
erties of bridged geometrically rigid metallocenes (also referred to as ansa-metallo-
cenes) having ligands based on two (variably substituted) 1H-inden-1-yl moieties,
bridged via the 1,1’ positions of the bis[1H-inden-1-yl] ligands (Fig. 1) [1]. Since the
two indenyl moieties have two enantiotopic faces, these metallocenes are usually
obtained as mixtures of their racemic and meso isomers (Scheme 1), and several proto-
cols have been developed for increasing the diastereoselectivity of the metallation step
[2].
© 2006 Verlag Helvetica Chimica Acta AG, Zürich

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Fig. 1. General structure of a C2-symmetric ansa-metallocene with
a 1,1’-linked bis[1H-inden-1-yl] ligand
Scheme 1
On the other hand, several examples of the synthetically more challenging ansa-
metallocenes with indenyl ligands bridged through their 2,2’ positions have been
reported (Fig. 2) [3–5], and one structurally related system with a substituted tetrahy-
droindenyl system having homotopic faces has also been reported in the literature [6].
Fig. 2. General structure of ansa-metallocenes with a 2,2’-(ethane-1,2-diyl)-
bis[1H-inden-1-yl] ligand

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While ligands of this type can in principle give rise to both racemic and meso ‘zir-
conocene’ isomers when R„H (Scheme 2), both isomers are expected to be aspecific
in propylene polymerization based on local symmetry considerations and non-
bonded-interactions analysis (Corradini’s model for enantioface selectivity in enantio-
morphic-site-controlled chain growth) [7].
Scheme 2
When R=H, the two unsubstituted coordinating indenyl moieties are homotopic
and thus can produce one compound only upon metallation. Such an achiral (thus aspe-
cific) ‘zirconocene’, [ZrCl2{2,2’-CH2CH2(1H-indenyl)2}], if active, would produce atac-
tic polypropylene. This ligand design has been exploited by Nantz, who described the
synthesis of a series of ‘titanocenes’ and ‘zirconocenes’ of this type (Fig. 3) [3–5] but
their catalytic behavior in olefin polymerization was not investigated. Nantz and co-
workers devised two synthetic strategies for the synthesis of the 2,2’-ethanediylb-
is[1H-indene] ligand precursors (Schemes 3 and 4) [3][8].
Scheme 3. From [3].
Schaverien and co-workers have improved the synthesis of the 2,2’-(ethane-1,2-
diyl)bis[1H-inden-1-yl] ligand precursors (Scheme 5), and have shown that the corre-
sponding ethanediyl-bridged ‘zirconocenes’ produce very low molecular mass atactic
polypropylenes (PP), and require H2 for their activation [9].

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Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 4. From [5] and [8].
DSM researchers have reported the synthesis of a series of 2,2’-linked bis[1H-inden-
1-yl] systems, including the S-bridged [ZrCl2{2,2’-S(1H-inden-1-yl)2}] and [ZrCl2{2,2’-
S(1-Bn-1H-inden-1-yl)2}] and the CH2-bridged [ZrCl2{2,2’-CH2(1H-inden-1-yl)2}] com-
plexes [10]. The metallocenes so far described in the above references are shown in
Fig. 3.
While the syntheses of both dimethyldi(1H-inden-2-yl)silane and di(1H-inden-2-yl)
sulfide are relatively simple [10], the synthesis of 2,2’-methylenebis[1H-indene] is quite
laborious. The syntheses of 2,2’-methylenebis[1H-indene] (1) by the DSM group [10]
and Schaverien and co-workers [9] are shown in Schemes 6 and 7, respectively.
Idemitsu described the synthesis of 2,2’-(1-methylethylidene)bis[1H-indene] ligand
precursors (Scheme 8), which were then used in the synthesis of doubly bridged com-
plexes [11]. An alternative synthetic protocol for related ligands has been described
by Herzog and co-workers [12].
All the above methods are multistep and result in low overall yields. We discovered
that the acid-catalyzed reaction between 1H-indenes and formaldehyde (a modified
Prins-type condensation) provides a direct, selective, and atom-economical synthesis
of 2,2’-methylenebis[1H-indenes] (Scheme 9) [13].
Here we describe this simple, one-step synthesis of the symmetric 2,2’-methylene-
ACHTREUNG

Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 5. From [9].
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Scheme 6. Synthesis of 2,2’-Methylenebis[1H-indene] (1) According to [10]

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Fig. 3. Known examples of ansa-metallocenes with 2,2’-linked bis[1H-inden-1-yl] ligands
Scheme 7. Synthesis of 2,2’-Methylenebis[1H-indene] (1) According to [9]
ymerization of the corresponding ‘dichlorozirconocenes’ [ZrCl2(1’)]1) to [ZrCl2(8’)]1),
and the ‘dimethylmetallocenes’ rac-[ZrMe2
(2’)]1) and rac-[HfMe2(4’)]1) (Fig. 4).
A
ACHTREUNG
1
)
For convenience, only one enantiomer of the rac isomer is depicted; for the rac/meso ratios, see
Exper. Part. The ligands 1’–8’ are the dianions of the precursors 1–8.

Helvetica Chimica Acta – Vol. 89 (2006)
Scheme 8. From [11].
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t
Scheme 9. One-Step Synthesis of 2,2’-Methylenebis[1H-indenes]. R=H, Me, Ph, Bu, etc.
Fig. 4. Ligands and metallocenes described in the present work
Results and Discussion. – 1. Surprises from an Old Reaction, the Prins Condensation
of 1H-Indene with Formaldehyde Reinvestigated: Synthesis of the 2,2’-Methylenebis[1H-
inden-1-yl) Ligand Precursors. The acid-catalyzed dimerization of 1H-indenes (tolu-
ene, TsOH, 808) is known to give 2-(indan-1-yl)-1H-indene, likely due to the stability
of the intermediate benzylic cation (Scheme 10). The acid-catalyzed condensation of
aldehydes and olefins, the Prins reaction (Scheme 11), produces allylic alcohols and
1,3-dioxanes [14].
When applied to 1H-indene and excess formaldehyde, the Prins reaction was shown
to produce 4,4a,5,9b-tetrahydroindeno[1,2-d]-1,3-dioxane (9) [15], and it would be
expected to produce also 1H-indene-2-methanol (10). We discovered that the structure
of the formed product is highly dependent on the reactant ratio (Scheme 12) [13]. Path

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Scheme 10
Scheme 11
Scheme 12. The Prins Condensation of CH2O with 1H-Indene: Influence of the 1H-Indene/CH2O
Ratio
B provides the first direct protocol for 2,2’-methylenebis[1H-indene] (1) and related
2,2’-linked bis[1H-indene] ligand precursors.
The mechanisms for the two reactions A and B are supposed to be strictly related
(Scheme 13). The intermediate 1H-indene-2-methanol (10) [8] was observed as a
minor product by gas chromatography of the reaction mixtures but could not be iso-
lated in pure form.
The experimental results of this modified Prins condensation of 1H-indene and sev-
eral substituted 1H-indenes are shown in Table 1. Remarkably, no product was
observed on condensation of 1-methyl-1H-indene and 1-(tert-butyl)-1H-indene [16],
which needed to be isomerized (under basic conditions) to their respective 3-alkyl-
1H-indene isomers prior to coupling.

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Scheme 13
Virtually any source of CH2O can be used in the modified Prins condensation
although formaline gave better results compared to trioxane and paraformaldehyde.
Given the toxicity of CH2O, we found the use of 1,3-dioxolane as a source of mono-
meric formaldehyde particularly convenient. This reagent is nontoxic and readily avail-
able, and is more conveniently used in excess with respect to the 1H-indene substrate.
In addition, we found that 1,3-dioxolane gives similar yields of the final 2,2’-methyl-
A
Scheme 14. Synthesis of 2,2’-Methylenebis[1H-indenes] from 1H-Indenes and 1,3-Dioxolane. R=H,
50% of 1; R=tBu, 84% of 4.

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Although 3,3’-dialkyl-substituted 2,2’-methylenebis[1H-indenes] can be prepared in
two ways (Scheme 15), the condensation reaction is more efficient when starting from
the 3-substituted indene. Nevertheless, by reaction of 1 with two equiv. of BuLi, fol-
lowed by excess RCl, we obtained in good to high yield 2,2’-methylenebis[3-methyl-
1H-indene] (2), 2,2’-methylenebis[3-benzyl-1H-indene] (6), and 2,2’-methylenebis[1-
(trimethylsilyl)-1H-indene] (7), while 2,2’-methylenebis[1-(trimethylsilyl)-3-methyl-
1H-indene] (8) was obtained from the dilithium salt of 2 and excess Me3SiCl.
G
Scheme 15. Two Alternative Syntheses of 2,2’-Methylenebis[3-methyl-1H-indene] (2)
This modified Prins condensation reaction is highly regioselective, and the regio-
chemistry can not be reversed, as shown by the reaction with 2-methyl-1H-indene,
which gives only the 1,3-dioxane 11 (Scheme 16).
Scheme 16
The scope of the modified Prins condensation seems to be limited to formaldehyde.
Benzaldehyde gives a complicated mixture of products containing only 10% of the
product with the correct mass for 2,2’-benzylidenebis[1H-indene], and ketones (Me2-
A
N

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2. Synthesis of the ‘Zirconocenes’. The 2,2’-methylenebis[1H-indenes] 1–8 are easily
and efficiently converted into the corresponding methylene-bridged metallocenes
(yields 60–100%) by reacting the dilithium salt of the bis[1H-indene] with MtCl4 in
Et2O/toluene. The rac/meso selectivity is a function of the size of the hydrocarbyl sub-
G
stituent at the indene moieties. For example, [ZrCl2(2’)] (R1 =Me) was obtained as a
rac/meso 2 :1 mixture (from which the pure rac isomer was separated by extraction
in CH2Cl2), while only the rac isomer of [ZrCl2(4’)] (R1 =tBu) was formed (Scheme
17). Also for this class of ligands, the dimethyl metallocenes [MtMe2(L)] (Mt=Zr,
U
L=2’; Mt=Hf, L=4’) can be efficiently obtained by direct synthesis [17]. The metal-
locenes prepared are shown in Fig. 5.
Scheme 17. Synthesis of Dichloro{1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-methyl-1H-inden-1-
yl]}zirconium [ZrCl2(2’)]
3. Crystal and Molecular Structures. The molecular structures of the 1,1’-di(tert-
butyl), 1,1’-bis(trimethylsilyl), and 4,4’,7,7’-tetramethyl derivatives [ZrCl2(4’)],
[ZrCl2(7’)], and [ZrCl2(5’)], respectively, were determined by X-ray diffraction analysis.
Fig. 6 shows frontal ORTEP views of the three molecules, with a partial labeling
Scheme. Table 2 contains the most relevant bonding parameters for the three com-
pounds. Table 3 contains the angles between some relevant least-squares planes, a
few slip-fold indicators, and the values of the geometric parameters described in Fig. 7.
The three compounds are isostructural and crystallize in the monoclinic space group
C2/c with a crystallographically imposed two-fold symmetry, the molecules lying about
the Wycoff position 4e. Differences in cell parameters and volumes can easily be
explained by taking into account the growing intrinsic volume demands made by the
t
Me, the Bu, and the Me3
A
respectively. In these compounds the metal atom is pseudotetrahedrally coordinated
by the two cyclopentadienyl groups of the bis[1H-indenyl] moiety and the two chloro
ligands. As usual for bent metallocenes, the overall coordination environment is best
described by the set of parameters depicted in Fig. 7, which can be related to the acces-
sibility of the Zr-atom. In particular, the smaller the ‘bite angle’ b and the bigger the
cpꢀZrꢀcp’ angle a, the more the metal is tucked into the ligand envelope. As previ-
ously stated [18], these parameters are very sensitive to differences in the number
and type of the ansa atoms, while the presence of substituents on the ligand leads to
only minor changes in the local geometry around the metal atom.
Only two (2,2’-ansa-bis[1H-indenyl])dichlorozirconium complexes have been struc-
turally characterized so far, namely the cis-1,2-dicyclohexylcyclobutane-1,2-diyl [19]

Helvetica Chimica Acta – Vol. 89 (2006)
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Fig. 5. Metallocenes synthesized and tested in this work
and the 1,1’-[biphenyl]-2,2’-diyl [20] derivatives. The bite angles found in these com-
pounds (61.4 and 55.88, resp.) are noticeably smaller than the angles found in the
CH2-bridged complexes [ZrCl2(4’)], [ZrCl2(7’)], and [ZrCl2(5’)], in agreement with
the presence of longer ansa bridges (two- and four-atoms long, resp.).
As far as ‘ansa-zirconocenes’ with single-atom linkers are concerned, a survey of the
Cambridge Structural Database [21] shows that the widespread dimethylsilylene (Me2-
ACHTREUNG
AHCTREUNG
AHCTREUNG
CH2-bridged derivatives show the largest bite angle values (up to 76.48). Data reported
in Table 3 for the three CH2-bridged complexes [ZrCl2(4’)], [ZrCl2(7’)], and [ZrCl2(5’)]
confirm this behavior. Indeed, the 4,4’,7,7’-tetramethyl derivative [ZrCl2(5’)] is the most
open ‘zirconocene’ structurally characterized so far. The great accessibility of the Zr-
atom in this complex is highlighted in Fig. 8, in which [ZrCl2(5’)] (‘bite angle’ 76.98)
is compared to its 1H-inden-1-yl analog [ZrCl2{rac-1,1’-CH2(4,7-Me2-1H-inden-1-

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Fig. 6. ORTEP Views of the methylene-bridged ‘zirconocenes’ [ZrCl2(4’)], [ZrCl2(7’)], and
[ZrCl2(5’)]. Displacement ellipsoids are drawn at the 30% probability level. H-Atoms have arbitrary
radii. The atom numbering of the side chains is arbitrary, the linking methylene being CH2(8).
yl)2}] (bite angle 71.58) [17] and to the (ethane-1,2-diyl)-bridged complex [ZnCl2{rac-
1,1’-C2H4(4,7-Me2-1H-inden-1-yl)2}] (bite angle 59.98) [22].
The limited sensitivity of the geometric descriptors to indenyl substitution is further
confirmed by the observation that the only noticeable difference between the three
CH2-bridged species is the slightly more open b angle of the 4,4’,7,7’-tetramethyl sub-
stituted compound [ZrCl2(5’)] with respect to the 1,1’-disubstituted compounds
[ZrCl2(4’)] and [ZrCl2(7’)]. This small difference appears even more negligible taking
into account that the bite angle measured for an individual species can vary by as
much as 1.58 depending on which polymorph or particular independent molecule in
the asymmetric unit is considered [21]. This considerable dependence of the bite

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Table 2. Selected Bond Lengths [Å] and Angles [8] of [ZrCl2(4’)], [ZrCl2(7’)], and [ZrCl2(5’)]a)
[ZrCl2(4’)]
[ZrCl2(7’)]
[ZrCl2(5’)]
Zr(1)ꢀcp(1)
2.250(3)
2.412(2)
2.636(6)
2.477(6)
2.399(6)
2.574(5)
2.682(6)
1.412(8)
1.461(8)
1.412(8)
1.540(8)
1.432(8)
1.428(8)
1.409(8)
1.351(9)
1.376(9)
1.369(9)
1.413(8)
1.526(8)
2.2277(16)
2.4187(10)
2.523(2)
2.458(2)
2.457(2)
2.615(3)
2.634(2)
1.438(3)
1.450(3)
1.404(3)
1.518(3)
1.428(3)
1.424(3)
1.434(3)
1.355(4)
1.417(4)
1.360(4)
1.421(3)
2.2316(10)
2.4248(6)
2.4767(19)
2.454(2)
2.4639(19)
2.6401(19)
2.6502(18)
1.407(3)
1.434(3)
1.410(3)
1.514(3)
1.434(3)
1.426(3)
1.430(3)
1.354(3)
1.420(3)
1.356(3)
1.423(3)
Zr(1)ꢀCl(1)
Zr(1)ꢀC(1)
Zr(1)ꢀC(2)
Zr(1)ꢀC(3)
Zr(1)ꢀC(3a)
Zr(1)ꢀC(7a)
C(1)ꢀC(2)
C(1)ꢀC(7a)
C(2)ꢀC(3)
C(2)ꢀC(8)
C(3)ꢀC(3a)
C(3a)ꢀC(4)
C(3a)ꢀC(7a)
C(4)ꢀC(5)
C(5)ꢀC(6)
C(6)ꢀC(7)
C(7)ꢀC(7a)
C(1)ꢀC(9)
C(1)ꢀSi(1)
1.899(2)
C(4)ꢀC(9)
1.500(3)
1.502(3)
115.60(3)
109.07(3)
111.54(3)
98.76(3)
108.60(19)
107.96(18)
123.73(19)
124.82(19)
108.61(19)
132.3(2)
107.10(18)
120.57(18)
116.55(19)
122.75(19)
122.7(2)
C(7)ꢀC(10)
cp(1)ꢀZr(1)ꢀcp(1’)
cp(1)ꢀZr(1)ꢀCl(1)
cp(1)ꢀZr(1)ꢀCl(1’)
Cl(1)ꢀZr(1)ꢀCl(1’)
C(2)ꢀC(1)ꢀC(7a)
C(1)ꢀC(2)ꢀC(3)
C(1)ꢀC(2)ꢀC(8)
C(3)ꢀC(2)ꢀC(8)
C(2)ꢀC(3)ꢀC(3a)
C(3)ꢀC(3a)ꢀC(4)
C(3)ꢀC(3a)ꢀC(7a)
C(4)ꢀC(3a)ꢀC(7a)
C(3a)ꢀC(4)ꢀC(5)
C(4)ꢀC(5)ꢀC(6)
C(5)ꢀC(6)ꢀC(7)
C(6)ꢀC(7)ꢀC(7a)
C(1)ꢀC(7a)ꢀC(3a)
C(1)ꢀC(7a)ꢀC(7)
C(3a)ꢀC(7a)ꢀC(7)
C(2)ꢀC(8)ꢀC(2’)
C(2)ꢀC(1)ꢀC(9)
C(7a)ꢀC(1)ꢀC(9)
C(2)ꢀC(1)ꢀSi(1)
C(7a)ꢀC(1)ꢀSi(1)
C(3a)ꢀC(4)ꢀC(9)
C(5)ꢀC(4)ꢀC(9)
C(6)ꢀC(7)ꢀC(10)
C(7a)ꢀC(7)ꢀC(10)
115.2(2)
107.34(15)
114.74(15)
96.15(11)
105.4(5)
110.1(5)
129.7(5)
117.3(5)
108.0(5)
131.7(6)
107.2(5)
121.1(6)
117.9(6)
121.4(6)
122.4(7)
118.9(6)
109.3(5)
132.6(6)
118.1(5)
101.8(6)
130.2(6)
123.1(5)
115.56(7)
109.93(6)
111.55(6)
96.77(5)
105.55(18)
109.37(19)
125.17(18)
122.12(18)
109.01(19)
133.5(2)
106.69(19)
119.8(2)
119.3(2)
121.1(2)
121.4(2)
119.6(2)
109.15(19)
132.1(2)
118.8(2)
101.3(2)
116.49(19)
107.29(18)
131.8(2)
120.85(18)
100.9(2)
129.43(17)
122.68(16)
120.5(2)
122.9(2)
123.4(2)
120.1(2)
a) cp refers to the centroid of the five-membered ring of the organic ligand. Primes refer to symmetry-
equivalent atoms (ꢀx, y, 12 ꢀz). For atom numbering, see Fig. 6.

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Table 3. Relevant Geometric Parameters of [ZrCl2(4’)], [ZrCl2(7’)], and [ZrCl2(5’)]a)
[ZrCl2(4’)]
[ZrCl2(7’)]
[ZrCl2(5’)]
a
b
f
d
115.2
74.3
101.8
82.4
13.1
37.2
10.7
3.1
115.6
75.1
101.3
84.5
13.1
37.6
4.6
115.6
76.9
100.9
83.7
12.0
38.5
ꢀ1.2
6.5
G
ZrCl2ꢀcp
bhꢀcpꢀcp’ꢀbh’
W
D
4.8
0.21
0.30
0.24
a) All quantities are given in degrees apart from D [Å]. The angles a, b, f, d, and g, are defined in Fig. 7.
cp and ZrCl2 refer to the least-squares planes defined by the five-membered ring and the ZrCl2 atoms,
respectively. bh refers to the centroid of the bridge-head atoms (C(3a) and C(7a)). W is the angle between
the plane defined by the allylic moiety (C(1), C(2), C(3)) and the least-squares plane defined by the
atoms C(1), C(7a), C(3a), and C(3). D is the distance between the perpendicular projection of the heavy
atom on the ring least-squares plane and the ring centroid.
Fig. 7. Schematic representation of an ‘ansa-zirconocene’ molecule describing the angles listed in Table
3. f is the angle C(2)ꢀC(8)ꢀC(2’), d is the angle between the Zrꢀcp vector and the cp least-squares
plane, g is the angle between the C(2)ꢀC(8) vector and the cp least-squares plane, b is the angle
between the least-squares planes of the two cyclopentadienyl ligands (the ‘bite angle’), and a is the
angle cpꢀZrꢀcp’. For atom numbering, see Fig. 6.
angle on packing interactions is in agreement with the expected low energy associated
with the process of ring tilting in metallocenes.
On comparing the 1,1’-di(tert-butyl)-substituted compound [ZrCl2(4’)] to the 1,1’-
bis(trimethylsilyl)-substituted one [ZrCl2(7’)], we notice that the tert-butyl substituent,
being closer to the metal atom, leads to great distortions in the coordination geometry
of the bis[1H-inden-1-yl] moiety. This effect is recognizable by comparing: i) visually
the two frontal views shown in Fig. 6, ii) the ‘equivalent’ bond distances of C(1) and
C(3) from the metal atom (ZrꢀC(1) vs. ZrꢀC(3): 2.64 vs. 2.40 Å in [ZrCl2(4’)], 2.52
vs. 2.46 Å in [ZrCl2(7’)]), iii) the ‘equivalent’ bond angles about the Zr-atom (cpꢀ
ZrꢀCl vs. cpꢀZrꢀCl’: 107.3 vs. 114.78 in [ZrCl2(4’)], 109.9 vs. 111.68 in [ZrCl2(7’)]),
and iv) the dihedral angles between the ZrCl2 and Zr(cp)2 planes (84.58 in

Helvetica Chimica Acta – Vol. 89 (2006)
1513
Fig. 8. Lateral views of the van der Waals surfaces of the 2,2’-mehylenebis[4,7-dimethyl-1H-inden-1-yl]
derivative [ZrCl2(5’)], and of the 1,1-methylenebis[4,7-dimethyl-1H-inden-1-yl], and 1,1’-(ethane-1,2-
diyl)bis[4,7-dimethyl-1H-inden-1-yl)-coordinated ‘dichlorozirconocene’ derivatives. For clarity, the Cl-
atoms are not shown.
[ZrCl2(4’)], 88.88 in [ZrCl2(7’)]). Moreover, unfavorable steric interactions between the
tert-butyl substituent and the ansa atoms lead to a marked difference in the ‘equivalent’
bond angles about the bridgehead atom C(2) (C(1)ꢀC(2)ꢀC(8) vs. C(3)ꢀC(2)ꢀC(8):
129.7 vs. 117.38 in [ZrCl2(4’)], 125.2 vs. 122.18 in [ZrCl2(7’)]) and eventually to a
more open arrangement of the two indenyl moieties (note the bhꢀcpꢀcp’ꢀbh’ values
of 10.7 and 4.68 for [ZrCl2(4’)] and [ZrCl2(7’)], resp.).
In the achiral compound [ZrCl2(5’)], the presence of four methyl substituents in the
region directly in front of the ZrCl2 moiety is associated with an increase in the distance
of the bridgehead atoms C(3a) and C(7a) from the metal atom (mean value 2.645 Å),
leading to a marked ring slippage, as shown by the W value given in Table 3.
According to an adaptation by Schlögl [23] of the Cahn–Ingold–Prelog rules, the
stereoisomer of [ZrCl2(4’)] and [ZrCl2(7’)] represented in Fig. 6 has the (2S,2’S) config-
uration. However, as they crystallize in a centrosymmetric space group, their (2R,2’R)
enantiomers are also present both in solution and in the solid state.
4. Polymerization of Ethylene (=Ethene). MAO-Activated complexes [ZrCl2(L)]
(L=1’–8’) were tested for ethylene polymerization (MAO=methylaluminoxane).
The results are reported in Table 4. The polyethylenes (PE) were analyzed by both
1H- and 13C-NMR to determine the end group and branching structures. Assignments
were made by using spectra of ethylene/but-1-ene copolymers as reference for ethyl
branches and spectra of ethylene/dec-1-ene copolymers as reference for resonances
associated with long-chain branches [24]. The amount of ethyl and long-chain branches
for 100 C-atoms were calculated from the signals at d(C) 39.64 and 38.18, respectively,
over the sum of all the C-atoms. The branches are of two types: Et branches and
branches of 8 or more C-atoms; no branches of intermediate length could be detected.
The Et branches arise from chain transfer to ethylene followed by reinsertion of the

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Helvetica Chimica Acta – Vol. 89 (2006)

Helvetica Chimica Acta – Vol. 89 (2006)
1515
polymeryl chain into the Zrꢀethyl bond, as shown in Scheme 18 [25], while the long-
chain branches must arise from insertion of ethenyl-terminated ethylene macromers
into a growing polyethylene chain, possibly without complete chain desorption from
the metal coordination sphere (see Scheme 19).
Scheme 18. Formation of Ethyl Branches on Polymerization of Ethylene
Scheme 19. Formation of Long-chain Branches on Polymerization of Ethylene
Some of the PE samples are of low molecular mass. 1H-NMR allows the identifica-
tion of three olefinic groups: the largely predominant terminal ethenyl group (CH2=
CHCH2, m at d(H) 4.92–5.07; CH2=CHCH2, m at 5.80–5.90; formed upon b-H trans-
fer to ethylene), the ethenylidene group (CH2=C(R)ꢀCH2ꢀ, s at d(H) 5.73, formed
upon b-H transfer after primary insertion of an a-olefin oligomer), and the ethene-
1,2-diyl group RꢀCH=CHꢀR (m at d(H) 5.44) [18]. The ethene-1,2-diyl group leaves
an ambiguity since it could have either (Z) or (E) configuration, and be either terminal
(but-2-enyl end group) or internal. This problem was solved by 13C-NMR, by compar-
ison with the spectra of (2Z)- and (2E)-hept-2-ene: the absence of Me resonances at
d(C) 12.5 (2Z) or 17.6 (2E) and the presence of a single CH2 resonance at d(C) 32.8,
indicates that the ethane-1,2-diyl group is both (E) configurated and internal, i.e.,
RꢀCH2CH=CHCH2ꢀR ((2E)-hept-2-ene: CH2(4) at d(C) 32.2; (2Z)-hept-2-ene:
CH2(4) at d(C) 26.7). The formation of internal (E)-ethene-1,2-diyl groups in metallo-
cene-catalyzed ethylene polymerization can arise from either allylic activation [26] or
b-H transfer following a secondary insertion of an a-olefin oligomer. This latter mech-
anism would be consistent with a unimolecular chain-release process, as already sug-
gested for the case of propylene polymerization with a highly congested catalyst
[27]. The only detectable saturated end group is the unbranched alkyl chain.
5. Polymerization of Propylene (=Prop-1-ene). Both 2,2’-methylenebis[1H-inden-
1-yl]-coordinated [ZnCl2(1’)] and 2,2’-(ethane-1,2-diyl)bis[1H-inden-1-yl)-coordinated
[ZrCl3(L)] [9] were practically inactive under our conditions for propylene polymeriza-
tion. All tested catalysts substituted at the indenyl moieties gave atactic polypropylene
(a-PP) of low to medium molecular masses. Selected results are shown in Table 5. Both

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Helvetica Chimica Acta – Vol. 89 (2006)
catalyst activity and a-PP molecular mass increase with the size of the substituent at the
Cp moieties. As expected, catalyst activity decreases and a-PP molecular mass
increases on replacement of Zr by Hf. The 4,7-dimethyl-1H-indenyl derivative
[ZrCl2(5’)] shows a surprisingly high activity.
Table 5. Propylene Homopolymerizationa)
b
c
ꢀ
ꢀ
Mv
)
PN
)
Precatalyst (amount [mg])
Al/Zr [mol/mol]
kgPP/mmolMt/h
[ZrCl2(1’)] (2)
[ZrCl2(2’)] (5)
[ZrCl2(3’)] (1)
[ZrCl2(4’)] (0.2)
1500
1000
3000
5000
1000
3000
1000
1000
–
–
–
26
263
430
2
40
73
14
447
284
63
18700
33500
90200
20600
26900
39300
[HfMe
A
ꢂ1100
[ZrCl2(5’)] (0.25)
[ZrCl2(7’)] (0.5)
[ZrCl2(8’)] (0.5)
255
487
a
b
ꢀ
) 508, 1 h, 300 g of propylene (=prop-1-ene), MAO co-catalyst. ) Mv =average viscosity molecular mass,
1
c
ꢀ
estimated from intrinsic viscosity (THN, 1358). ) PN =average polymerization degree by H-NMR.
Fig. 9 shows the methyl pentad region of the 13C-NMR spectrum of two a-PP sam-
ples, obtained with the catalysts [HfMe2(4’)] and [ZrCl2(8’)]. The spectrum shows the
G
lack of enantiofacial preference in propylene insertion. All other a-PP samples show
the same or very similar pentad distributions. Chain release occurs by b-H transfer,
as shown by the presence of ethenylidene end groups (1H-NMR), which were used
to determine the average polymerization degree, under the assumption that no chain
transfer to Al occurs with these catalyst systems.
Conclusions. – A one-step, highly atom-economical synthesis of 2,2’-methylene-
bis[1H-indenes] from a variety of substituted 1H-indenes was efficiently achieved.
The yields of the condensation step were higher with 3-substituted 1H-indenes. Double
deprotonation with BuLi followed by metallation with ZrCl4 or HfCl4 proceeded in
good to high yields, and the diastereoselectivity of metallation was driven by the bulki-
ness of the substituent at C(1) and C(1’) of the intermediate bis[1H-inden-1-yl] anions.
Methylene-bridged ‘ansa-zirconocenes’ show a noticeable open arrangement of the
bis[1H-inden-1-yl] moiety, as measured by the angle between the planes defined by the
two p-ligands (the ‘bite angle’). In particular, the 2,2’-methylenebis[4,7-dimethyl-1H-
inden-1-yl] derivative [ZrCl2(5’)] is the most open ‘zirconocene’ structurally character-
ized so far. Interestingly, this catalyst shows a very high activity in propylene polymer-
ization.
All the metallocenes tested produced low-molecular-mass, fully atactic polypropy-
lenes. Ethylene could be polymerized with high activities to PE with molecular masses
which strongly depended on the substitution of the ligands. In some cases, ethyl and
long-chain branches were observed. PE waxes were obtained in quite high yields and
a high selectivity for a-olefin end groups.

Helvetica Chimica Acta – Vol. 89 (2006)
1517
Fig. 9. Methyl pentad region of the 13C-NMR (C2
D2Cl4, 1208) spectrum of a-PP obtained with the cata-
G
lyst systems a) rac-[ZrCl2(8’)]/MAO (liquid propylene, Tp 508, mm=17.6%, mr=44.2%, rr=38.2%)
and b) rac-[HfMe2(4’)]/MAO (liquid propylene, Tp 508, mm=22.1%, mr=50.5%, rr=27.4%).
Experimental Part
1
1. General. H-NMR Spectra: d in ppm rel. to CDHCl2 (d 5.377) or C6
G
N
C
ACHTREUNG
fonic acid monohydrate (TSOH·H2O), toluene, and the 1H-indene was heated to 808 under stirring. The
type of indene, amounts of reagents, time of reaction, and yields are specified in Table 1. The reaction was
quenched with H2O/NaHCO3 and the org. layer washed with H2O, and evaporated. The crude product
crystallized upon standing at r.t., and was then further purified by washing with pentane or MeOH. Sim-
ilar results were obtained with 1,3-dioxolane as the source of formaldehyde. For example, 1 was obtained
with 50% conversion with 1 equiv. of 1,3-dioxolane and TsOH, in toluene after 6 h at 808. The reaction
mixture contained also 10% of the 1H-indene dimer.
2,2’-Methylenebis[3-(tert-butyl)-1H-indene] (4). TsOH·H2O (4.1 g, 21.6 mmol), toluene (200 ml), 1,
3-dioxolane (Aldrich; 7.6 ml, 108.8 mmol), and 3-(tert-butyl)-1H-indene (19.0 g, 110 mmol) were mixed
in this order and then heated to 808 within 20 min and stirred at 808 for 6 h. After cooling to r.t., the mix-
ture was poured onto ice/NaHCO3, the aq. layer washed with Et2O (2×150 ml), and the combined org.
A

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Helvetica Chimica Acta – Vol. 89 (2006)
phase dried (NaSO4) and evaporated: red paste (18.6 g) containing 82% of 4 (77% conversion). This
paste was taken up in pentane (50 ml), the mixture stirred for 30 min and filtered, the filtrate evaporated,
and the residue dried in vacuo: 7.0 g (34.8%, purity 97.5% by GC) of 4. Ochre powder. 1H-NMR: Table 6.
Table 6. 1H-NMR (CDCl3, r.t.) of the Ligand Precursors 1–5. d in ppm.
1
2
3
4
5
7.1–7.5 (m, 8 H); 6.65 (s, 2 H); 3.72 (s, 2 H); 3.40 (s, 4 H)
7.2–7.5 (m, 8 H); 3.73 (s, 2 H); 3.35 (s, 4 H ); 2.29 (s, 6 H)
7.1–7.7 (m, 18 H); 3.76 (s, 2 H); 3.39 (s, 4 H)
7.1–7.4 (m, 6 H); 7.6–7.8 (d, 2 H); 4.23 (s, 2 H); 3.34 (s, 4 H ); 1.58 (s, 18 H)
7.1–6.9 (m, 4 H); 6.78 (s, 2 H); 3.79 (s, 2 H); 3.29 (s, 4 H); 2.45 (s, 6 H); 2.33 (s, 6 H)
2,2’-Methylenebis[3-methyl-1H-indene] (2). A soln. of 2,2’-methylenebis[1H-indene] (1; 5.11 g,
91.1% by GC, 19 mmol) in THF (50 ml) in a Schlenk tube was cooled to ꢀ408, and 1.6M MeLi in Et2
C
with H2O (100 ml), the aq. layer extracted twice with Et2O, and the combined org. phase dried (MgSO4)
E
and evaporated: 5.61 g (84%, purity 85% by GC) of oily 2 which was analyzed by GC/MS and 1H-NMR:
Table 6.
2,2’-Methylenebis[1-(trimethylsilyl)-1H-indene] (7). A soln. of 1 (6.0 g, purity 77% by GC, 18.9
mmol) in Et
The orange suspension was allowed to reach r.t., stirred for 5 h, and then added to a soln. of Me
(5 ml, 39.8 mmol) in Et
ACHTREUNG
AHCTREUNG
2O (30 ml) previously cooled to ꢀ308. The yellow suspension was allowed to
reach r.t., stirred overnight, then quenched with MeOH, and filtered. The filtrate was evaporated: 7
(8.2 g, purity 71.5% by GC; meso/rac 1:1). Clear, thick orange oil which was used as such in the zirco-
1
nation reaction. H-NMR (CDCl3): 0.03 (s, Me3
G
N
CHSi); 3.85 (s, 2 H, CH2 bridge, rac); 3.58, 3.66, 3.87, 3.95 (AB, CH2 bridge, meso); 6.59 (br. m, 2 H,
HꢀC(3,3’)); 6.71 (br. m, 2 H, HꢀC(3,3’)); 7.07–7.42 (m, 8 arom. H).
2,2’-Methylenebis[3-methyl-1-(trimethylsilyl)-1H-indene] (8). A soln. of 2 (8.05 mmol) in Et2O (50
G
ml) was cooled to ꢀ508 and treated with 2.5M BuLi in hexane (6.7 ml, 17 mmol). The red-violet suspen-
sion was allowed to reach r.t. and then added to a soln. of Me3SiCl (2.2 ml) in Et2O (30 ml) previously
A
ACHTREUNG
cooled to ꢀ308. The suspension was allowed to reach r.t. (!color fading) and stirred overnight, then
quenched with MeOH (!yellow), and filtered. The filtrate was evaporated: 8 (3.55 g, 100%; meso/rac
1
1:1). Brown-orange liquid. H-NMR (CDCl3): ꢀ0.12 (s, SiMe3); ꢀ0.05 (s, SiMe3); 1.97 (m, Me); 2.13
(m, Me); 3.31 (br. q, 2 H, CHSi); 3.41 (br. q, 2 H, CHSi); 3.76 (s, 2 H, CH2 bridge, rac); 3.38, 3.46,
3.98, 4.06 (AB, 2 H, CH2 bridge, meso); 7.03–7.32 (m, 8 H, Ar).
3. Synthesis of the ‘Zirconocenes’. All ‘zirconocenes’ were prepared in a Schlenk tube following stan-
dard procedures.
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1H-inden-1-yl]}zirconium ([ZrCl2(1’)]). To
a soln. of 1 (6.9 g, purity 77% by GC, 21.77 mmol) in Et
A
(18.3 ml, 45.7 mmol) was added dropwise (!orange slurry). The mixture turned light brown when
allowed to warm to r.t., and was stirred for 4 h. After cooling to ꢀ308, the mixture was added to a slurry
of ZrCl4 (5.0 g, 21.77 mmol) in toluene (50 ml) at ꢀ308. Then the mixture was warmed to r.t. (!yellow)
and stirred overnight. Et2O was evaporated from the yellow suspension, which was then filtered over a
A
G3 frit. The filtrate was discarded, the yellow residue (11.06 g) dried, analyzed by 1H-NMR (product and
some org. by-products), and extracted with refluxing CH2Cl2 for 12 h, leaving 6.22 g of crude [ZrCl2(1’)]
on the filter, containing LiCl. 1H-NMR (CD2Cl2): 4.30 (s, 2 H, CH2 bridge); 6.12 (s, 4 H, Cp); 7.21–7.31
(m, 4 arom. H); 7.49–7.59 (m, 4 arom. H).
Since [ZrCl2(1’)] has a very low solubility and limited stability in CH2Cl2, it was not possible to fur-
ther purify it. Washing with Et
A
extract contained some product, starting ligand, and polymeric by-products.

Helvetica Chimica Acta – Vol. 89 (2006)
1519
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-methyl-1H-inden-1-yl]}
zirconium
([ZrCl2(2’)]). To a soln. of 2 (6.5 g, purity 90% by GC, 21.5 mmol) in Et2
A
1.6M BuLi in hexane (27 ml, 43.2 mmol) was added dropwise within 15 min. The soln. was allowed to
warm to r.t. and stirred for 5 h. The obtained red suspension was then cooled to ꢀ808 and added to a
slurry of ZrCl4 (5 g, 21.4 mmol) in pentane (160 ml) at ꢀ808. After warming to r.t., the mixture was stir-
red overnight. The yellow suspension was dried to a free-flowing powder, this powder washed with pen-
tane (1H-NMR: rac and meso product), transferred into an extraction apparatus and extracted with
refluxing CH2Cl2, (!yellow precipitate in the collecting flask). After the extraction, CH2Cl2 was concen-
trated to 20 ml and then the mixture filtered. The residue was washed with Et2O, then pentane, and finally
dried: 2.98 g of pure (by 1H-NMR) rac-[ZrCl2(2’)]. Yellow solid. 1H-NMR (CD2Cl2): 2.51 (s, 6 H, Meꢀ
C(1,1’)); 4.35 (s, 2 H, CH2 bridge); 5.95 (br. s, 2 H, Cp); 7.19–7.33 (m, 4 arom. H); 7.45–7.54 (m,
4 arom. H).
Dimethyl{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-methyl-1H-inden-1-yl]}zirconium
([ZrMe
N
N
1.12 mmol) diluted in Et
G
mixture was evaporated, the dark red solid extracted with pentane (100 ml) at 308, the extract concen-
trated to 10 ml and cooled to ꢀ208, and the obtained precipitate filtered, washed once with a small
amount of pentane, and dried in vacuo: 0.2 g of rac-[ZrMe
2.00 (s, 6 H, MeꢀC(1,1’)); 3.27 (s, 2 H, CH2 bridge); 5.39 (s, 2 H, Cp); 6.91–7.04 (m, 4 arom. H);
7.36–7.44 (m, 4 arom. H).
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-phenyl-1H-inden-1-yl]}zirconium
([ZrCl2(3’)]). To a soln. of 3 (3.5 g, purity 97.3% by GC, 8.59 mmol) in Et2
A
BuLi in hexane (7.5 ml, 18.75 mmol) was added dropwise within 15 min. The soln. was allowed to warm
to r.t. and stirred for 6 h. The obtained light brown suspension was then cooled to ꢀ808 and added to a
slurry of ZrCl4 (2 g, 8.58 mmol) in pentane (80 ml) at ꢀ808. After warming to r.t., the mixture was stirred
overnight. The yellow suspension was concentrated to 30 ml and filtered. The solid was dried and then
extracted with refluxing CH2Cl2 until the extract was colorless (!yellow precipitate in the collecting
flask). After the extraction, CH2Cl2 was concentrated to 15 ml, the mixture cooled to ꢀ208 overnight,
and the precipitate filtered, washed with CH2Cl2 until the washing turned from brown to yellow, and
1
finally dried: 2.2 g of pure (by H-NMR) [ZrCl2(3’)]. Yellow solid. Additional [ZrCl2(3’)] (0.25 g) was
recovered from the combined filtrate and washings which were concentrated to 8 ml, cooled to ꢀ208
overnight and worked up similarly. Combined yield 51.3%. 1H-NMR (CD2Cl2): 4.74 (s, 2 H, CH2 bridge);
5.60 (m, 2 H, Cp); 7.23–7.92 (m, 8 arom. H).
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-(1,1-dimethylethyl)-1H-inden-1-yl]}zirco-
nium ([ZrCl2(4’)]). To a soln. of 4 (3 g, purity 93.1% by GC, 7.83 mmol) in Et2
A
1.6M BuLi in hexane (10.6 ml, 16.96 mmol) was added dropwise within 15 min. The soln. was allowed to
warm to r.t. and stirred for 5 h. The obtained red suspension was then cooled to ꢀ808 and added to a
slurry of ZrCl4 (1.96 g, 8.41 mmol) in pentane (63 ml) at ꢀ808. After warming to r.t., the mixture was stir-
red overnight. The yellow suspension was dried to a free-flowing powder (1H-NMR: only rac isomer),
and the powder slurried in CH2Cl2 (100 ml), transferred into an extraction apparatus, and extracted
with refluxing CH2Cl2 for 6 h (!yellow precipitate in the collecting flask). After the extraction,
CH2Cl2 was concentrated to 10 ml and the mixture filtered. The residue was washed with pentane
until the washing was colorless, and finally dried: 1.757 g of pure (by 1H-NMR) rac-[ZrCl2(4’)]. Yellow
solid. Additional rac-[ZrCl2[4’)] (0.4 g) was recovered from the filtrate, by recrystallization from toluene
and washing with Et
2O. Combined yield 55%. 1H-NMR (CD2Cl2): 1.69 (s, 18 H, tBu); 4.90 (s, 2 H, CH2
G
bridge); 6.20 (m, 2 H, Cp); 7.17–7.27 (m, 4 arom. H); 7.39–7.48 (m, 4 arom. H).
Dimethyl{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-(1,1-dimethylethyl)-1H-inden-1-yl]haf-
nium ([HfMe
N
N
Et2O (12.6 ml, 20.16 mmol) was added dropwise within 5 min at r.t. (exothermic reaction). After 10 min,
AHCTREUNG
a white suspension was obtained. Stirring was continued for 2 h. Then the suspension was cooled to ꢀ808,
and a slurry of HfCl4 (Roc-Ric; 1.62 g, 99.99%, 50.6 mmol) in pentane (30 ml), also cooled to ꢀ808, was
added. The mixture was stirred overnight by letting the temp. rise slowly to r.t. in the Dewar. The gray
suspension was evaporated and the obtained free-flowing powder extracted with pentane (100 ml) in a

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Helvetica Chimica Acta – Vol. 89 (2006)
Soxhlet apparatus for 4.5 h. The extract was dried to a yellow powder (1.46 g) which was taken up in pen-
tane (10 ml), stirred, and filtered. The residue (0.3 g), a light yellow powder, was rac-[HfMe2(4’)] contain-
ing a small amount of impurities. The pentane-soluble fraction was concentrated, treated with Et2O (2
2(4’)] (50 mg) was recovered by filtration.
AHCTREUNG
AHCTREUNG
ml), and cooled to ꢀ208. After three days, pure rac-[HfMe
ACHTREUNG
t
1H-NMR (C6
G
Hf); 1.47 (s, 18 H, Bu); 3.99 (s, 2 H, CH2 bridge); 5.65 (s, 2 H,
Cp); 6.89–6.96 (m, 4 arom. H); 7.31–7.36 (m, 2 arom. H); 7.74–7.79 (m, 2 H).
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[4,7-dimethyl-1H-inden-1-yl]}zirconium
([ZrCl2(5’)]). To a soln of 5 (2.24 g, purity 89% by GC, 6.66 mmol) in Et2
A
BuLi in hexane (6 ml, 15 mmol) was added dropwise within 10 min. The soln. was allowed to warm to r.t.
and stirred for 6 h. The obtained pink-red suspension was cooled to ꢀ808 and added to a slurry of ZrCl4
(1.6 g, 6.87 mmol) in pentane (63 ml) at ꢀ808. After warming to r.t., the mixture was stirred overnight.
The yellow-brown suspension was dried to a free-flowing powder and this powder slurried in CH2Cl2
(100 ml), transferred into an extraction apparatus, and extracted with refluxing CH2Cl2 for 6 h (!yellow
precipitate in the collecting flask). After the extraction, CH2Cl2 was concentrated to 20 ml, and the mix-
ture cooled to ꢀ208 overnight and finally filtered. The residue was washed with CH2Cl2 until the washing
turned from brown to straw-yellow, and finally dried: 1.215 g of pure (by 1H-NMR) [ZrCl2(5’)]. Yellow
solid. Additional [ZrCl2(5’)] (0.734 g) was recovered from the combined filtrate and washings by drying
and washing with toluene. Combined yield 63%. 1H-NMR (CD2Cl2): 2.42 (s, 12 H, Me); 4.37 (s, 2 H, CH2
bridge); 6.03 (s, 4 H, Cp); 6.95 (s, 4 arom. H).
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-(trimethylsilyl)-1H-inden-1-yl]}zirconium
([ZrCl2(7’)]). To a soln. of 7 (8.0 g, purity 71.5% by GC, 14.6 mmol) in Et2
A
BuLi in hexane (17.3 ml, 43.2 mmol) was added dropwise within 5 min (orange ! red soln.). The soln.
was allowed to warm to r.t. and stirred for 5 h. The obtained brick-red suspension was then cooled to
ꢀ308 and added to a slurry of ZrCl4 (4.8 g, 20.6 mmol) in toluene (50 ml) at ꢀ308. After warming to
r.t., the yellow mixture was stirred overnight. The yellow suspension was concentrated to remove Et2O
and then filtered. The contents of the toluene soln. were discarded following 1H-NMR analysis. The yel-
low residue on the filter (9.12 g of the target product, containing LiCl) was extracted with refluxing
CH2Cl2 (Soxhlet, 7 h). The residue (6.0 g) was pure rac-[ZnCl2(7’)] containing LiCl. 1H-NMR
(CD2Cl2): 0.57 (s, 18 H, Me3Si); 4.56 (s, 2 H, CH2 bridge); 6.39 (s, 2 H, Cp); 7.19–7.33 (m, 4 arom. H);
G
7.48–7.56 (m, 2 arom. H); 7.62–7.71 (m, 2 arom. H).
The extract (2.75 g) contained some impurities and traces of the meso isomer, identified from the
diagnostic q centered at d(H) 4.45 (CH2 bridge).
Dichloro{(1,1’,2,2’,3,3’,3a,3’a,7a,7’a-h)-2,2’-methylenebis[1-methyl-3-(trimethylsilyl)-1H-inden-1-
yl]}zirconium ([(ZrCl2(8’)]). To a soln. of 8 (3.55 g, 8.53 mmol) in Et2
G
BuLi in hexane (7.1 ml, 18 mmol) was added dropwise within 5 min (orange ! red soln.). The soln.
was allowed to warm to r.t. and stirred overnight. The obtained darker red soln. was cooled to ꢀ308
and added to a slurry of ZrCl4 (1.98 g, 8.53 mmol) in toluene (50 ml) at ꢀ308. After warming to r.t.,
the brown-violet mixture was stirred overnight. The brown suspension was concentrated to remove Et2-
O and then filtered. The residue was discarded following 1H-NMR analysis. The toluene soln. was evapo-
rated, the residue washed with Et2O (50 ml), the mixture filtered, the residue discarded, and the filtrate
A
evaporated again to 3.2 g of a brown product which was then washed with pentane. The residue was dried
in vacuo: 1.75 g of pure (by 1H-NMR) rac-[ZrCl2(8’)] as the only isomer. 1H-NMR (CD2Cl2): 0.51 (s, 18 H,
Me3
A
arom. H); 7.61–7.66 (m, 2 arom. H).
4. X-Ray Diffraction Structural Analysis. Suitable crystals of [ZrCl2(4’)], [ZrCl2(5’)], and [ZrCl2(7’)],
obtained by cooling conc. solns. in CH2Cl2, were mounted in air on a glass fiber tip which was subse-
quently fixed onto a goniometer head. Single-crystal X-ray diffraction data were collected at r.t. on a Sie-
mens-SMART-CCD area detector diffractometer for [ZrCl2(7’)] and on an Enraf-Nonius-CAD-4 diffrac-
tometer for [ZrCl2(4’)] and [ZrCl2(5’)], with graphite-monochromatized MoKa radiation (l 0.71073 Å).
For [ZrCl2(7’)], unit-cell parameters were initially obtained from ca. 50 reflections taken from 45 frames
collected in three different w regions, and eventually refined against 7182 reflections, while for [ZrCl2(4’)]
and [ZrCl2(5’)], the setting angles of 25 randomly distributed intense reflections with 108<q<148 were
processed by least-squares fitting. For [ZrCl2(7’)], a full sphere of reciprocal space was scanned by 0.38 w

Helvetica Chimica Acta – Vol. 89 (2006)
1521
steps, collecting 2400 frames each at 30-s exposure and keeping the detector at 5.0 cm from the sample.
Intensity decay was monitored by recollecting the initial 100 frames at the end of data collection and ana-
lyzing the duplicate reflections. The collected frames were processed for integration, and an empirical
absorption correction was made on the basis of 8896 symmetry-equivalent reflection intensities
(SADABS [28]; average redundancy: 4.75).
For [ZrCl2(4’)] and [ZrCl2(5’)] data collection was performed by the w scan method with variable
scan speed (maximum time per reflection, 90 and 60 s, resp.) and variable scan range (1.80+0.35tanq
and 1.00+0.35tanq degrees, resp.). Crystal stability under diffraction was checked by monitoring three
standard reflections every 180 min. For [ZrCl2(4’)], due to crystal decay, the fraction of unique reflections
measured out to 238 is only 0.75. The measured intensities were corrected for Lorentz, polarization,
decay, and background effects and reduced to F2o. An empirical absorption correction was applied by
using y scans of three suitable reflections having c values close to 908 [29]. Crystal data and data collec-
tion parameters are summarized in Table 7.
Table 7. Summary of Crystallographic Data of [ZrCl2(4’)],[ZrCl2(5’)], and [ZrCl2(7’)]
[ZrCl2(4’)]
[ZrCl2(5’)]
[ZrCl2(7’)]
Formula
Mr
Crystal system
Space group
a [Å]
C27
516.63
H30
U
N
C23
460.53
G
Cl2
U
C25
548.79
monoclinic
C2/c (No.15)
20.324(11)
10.234(5)
13.166(7)
113.34(1)
2514(2)
4
G
Cl2
N
G
monoclinic
C2/c (No.15)
19.450(11)
10.676(3)
12.505(6)
113.69(5)
2377.8(19)
4
monoclinic
C2/c (No.15)
15.875(3)
9.360(1)
13.870(3)
107.50(1)
1965.6(6)
4
b [Å]
c [Å]
b [8]
V [Å3]
Z
F(000)
1064
1.443
0.70
Enraf-Nonius
CAD-4
3.1ꢃqꢃ23.0
ꢀ21ꢃhꢃ11
0ꢃkꢃ11
ꢀ13ꢃlꢃ13
14
936
1.556
0.83
Enraf-Nonius
CAD-4
3.1ꢃqꢃ26.0
ꢀ13ꢃhꢃ19
0ꢃkꢃ11
ꢀ14ꢃlꢃ17
none
1128
1.450
0.76
Density [g cmꢀ3
]
Absorption coefficient [mmꢀ1
Diffractometer
]
Siemens SMART
q range [8]
Index ranges
2.2ꢃqꢃ27.1
ꢀ25ꢃhꢃ25
ꢀ12ꢃkꢃ12
ꢀ16ꢃlꢃ16
4
Intensity decay [%]
Absorption correction
Min transmission factor
Measured reflections
y scan
0.62
1645
y scan
0.92
1925
SADABS
0.90
12608
Independent reflections
1645
–, 0.050
1240
1240 / 137
0.085, 0
1.07
1925
–, 0.022
1660
1660 / 119
0.028, 0.87
1.12
0.021
0.052
0.22, ꢀ0.26
2584
0.037, 0.036
2086
2584 / 137
0.040, 0
1.00
0.029
0.068
0.35, ꢀ0.42
a
Rint, Rs
)
Reflections with I>2s(I)
Data/parameters
Weights (a, b)b)
Goodness-of-fit S(F2)c)
R(F), I>2s(I)d)
0.045
0.085
wR(F2), all datae)
Largest difference peak and hole [e Åꢀ3] 0.80, ꢀ0.85
2
2
2
2
2
2
2
2
a) Rint =S|Fo2 ꢀF2mean|/S|Fo|; Rs =S|s(Fo)|/S|Fo b) w=1/[s (Fo)+(aP) +bP], where P=(Fo +2Fc )/3. )
c
˙
S=[Sw(F2o ꢀF2c )2/(nꢀp)]1/2, where n is the number of reflections and p is the number of refined param-
2
2
2
2
4 1/2
eters. ) R(F)=S||Fo|ꢀ|Fc||/S|Fo e) wR(F )=[Sw(Fo ꢀFc ) /SwFo]
.
d
˙

1522
Helvetica Chimica Acta – Vol. 89 (2006)
The structures were solved by direct methods [30] and subsequent Fourier synthesis, and they were
refined by full-matrix least-squares on F2 [31] by using all reflections for [ZrCl2(7’)], and reflections with
I>2s(I) for [ZrCl2(4’)] and [ZrCl2(5’)]. Scattering factors for neutral atoms and anomalous dispersion
corrections were taken from the internal library of SHELX97 [31]. Weights were assigned to individual
observations according to the formula w=1/[s2(Fo2 )+(aP)2 +bP], where P=(Fo2 +2F2c )/3; a and b were
chosen to give a flat analysis of variance in terms of F2o. Anisotropic displacement parameters were
assigned to all non-H-atoms. H-Atoms were placed in idealized position and refined riding on their
parent atom with an isotropic displacement parameter 1.2 times that of the parent C-atom (AFIX 23,
43, and 133 in SHELX97 [21]). The final difference electron density maps showed no features of chemical
significance, with the largest peaks lying close to the metal atoms. Final conventional agreement indexes
and other structure refinement parameters are listed in Table 7.
CCDC-290783–290785 contain the supplementary crystallographic data for this paper. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif. from the Cambridge Crys-
tallographic Data Centre.
5. Polymerizations. Polymerization-grade propylene, ethylene, and hexane were received directly
from the Montell Ferrara plant. MAO was a commercial product (Crompton; 10% w/w in toluene)
which was used as received.
Co-catalysts. Methylalumoxane (MAO): the commercial 10% toluene solution (1.7M; Crompton)
was used as such. Alternatively, MAO was dried in vacuo to a free-flowing powder (residual AlMe3,
ca. 3–5 mol-%). The catalyst mixture was prepared by adding the desired amount of the metallocene
to the proper amount of the MAO soln., obtaining a soln. which was stirred for 10 min at r.t. and then
injected into the autoclave at the polymerization temp. in the presence of the monomer.
Ethylene Polymerizations. Under ethylene purge, technical hexane (513 ml) and AliBu3 (1 mmol)
were charged in a 1-l stainless-steel autoclave, previously thermostatted with H2O/steam and purified
by purging with ethylene at 808. The temp. was brought to 808, and the reactor was vented to remove
residual N2 and then pressurized with ethylene up to 9.5 bar-g. The catalyst/co-catalyst mixture was
injected with ethylene overpressure, and the ethylene partial pressure was stabilized to 9.6 bar-a, (Ptot
11 bar-a). The test was carried out at 808, 1 h, by maintaining a constant ethylene partial pressure.
After degassing unreacted ethylene, the polymer was isolated by filtration and dried in a vacuum oven
at 608.
Propylene Polymerizations. Propylene was charged at r.t. in a 1-l or 4.25-l jacketed stainless-steel
autoclave, equipped with a magnetically driven stirrer and a 35-ml stainless-steel vial, connected to a
thermostat for temp. control, previously purified by washing with a AliBu3 soln. in hexanes and dried
at 508 in a stream of propylene. AliBu3 (1 mmol in hexane) was added as scavenger before the monomer.
The autoclave was then thermostatted at 28 below the polymerization temp., and then the toluene soln.
containing the catalyst/co-catalyst mixture was injected in the autoclave by means of N2 pressure through
the stainless-steel vial, the temp. rapidly raised to the polymerization temp., and the polymerization car-
ried out at constant temp. for 1 h. The polymerizations were stopped with CO, the unreacted monomers
vented, and the polymer dried in a vacuum oven at 608.
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Received January 2, 2006