Half-sandwich complexes of titanium and zirconium with pendant phenyl substituents. The influence of ansa-aryl coordination on the polymerisation activity of half-sandwich catalysts

Article abstract of DOI:10.1016/S0022-328X(99)00488-X

Benzyl-substituted Group 4 half-sandwich complexes (η⁵-C₅H₄R)TiCl₃ (1a, R = CMe₂Ph; 2a, R = CMe₂CH₂Ph; 4a, R = SiMe₂Ph; 5a, R = CHPh₂) are readily accessible from C₅H₄(R)SiMe₃ and TiCl₄, while the reaction of C₅H₄(CMe₂CH₂Ph)SiMe₃ with ZrCl₄(SMe₂)₂ affords (C₅H₄CMe₂CH₂Ph)ZrCl ₃·dme (3a). The structures of 1a, 4a and 5a have been determined by X-ray diffraction; the compounds are monomeric in the solid state. Alkylation readily affords the corresponding trimethyl and tribenzyl derivatives; the crystal structure of (η⁵-C₅H₄CHPh₂)Ti(CH ₂Ph)₃ (5b) has been determined. Treatment of (η⁵-C₅H₄R)MMe₃ with [Ph₃C]⁺[B(C₆F₅)₄] ^- in dichloromethane at low temperatures generates cationic [(η⁵-C₅H₄R)MMe₂]⁺ complexes; the complexes are stabilised by π-coordination to the phenyl ring to give ansa-arene complexes with one- and two-carbon linkages. The complexes catalyse the polymerisation of propene. Compared to the system Cp*TiMe₃/B(C₆F₅)₃ the ansa complexes show reduced catalytic activity and enhanced chain termination.

Full text of DOI:10.1016/S0022-328X(99)00488-X

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Journal of Organometallic Chemistry 592 (1999) 84–94
Half-sandwich complexes of titanium and zirconium with pendant
phenyl substituents. The influence of ansa-aryl coordination on the
polymerisation activity of half-sandwich catalysts
Jo¨rg Saßmannshausen a, Annie K. Powell b, Christopher E. Anson b, Sigrid Wocadlo b,
Manfred Bochmann a,*
a School of Chemistry, Uni6ersity of Leeds, Leeds LS2 9JT, UK
b School of Chemical Sciences, Uni6ersity of East Anglia, Norwich NR4 7TJ, UK
Received 23 June 1999; accepted 20 July 1999
Abstract
Benzyl-substituted Group 4 half-sandwich complexes (h5-C5H4R)TiCl3 (1a, R=CMe2Ph; 2a, R=CMe2CH2Ph; 4a, R=
SiMe2Ph; 5a, R=CHPh2) are readily accessible from C5H4(R)SiMe3 and TiCl4, while the reaction of C5H4(CMe2CH2Ph)SiMe3
with ZrCl4(SMe2)2 affords (C5H4CMe2CH2Ph)ZrCl3·dme (3a). The structures of 1a, 4a and 5a have been determined by X-ray
diffraction; the compounds are monomeric in the solid state. Alkylation readily affords the corresponding trimethyl and tribenzyl
derivatives; the crystal structure of (h5-C5H4CHPh2)Ti(CH2Ph)3 (5b) has been determined. Treatment of (h5-C5H4R)MMe3 with
[Ph3C]+[B(C6F5)4]− in dichloromethane at low temperatures generates cationic [(h5-C5H4R)MMe2]+ complexes; the complexes
are stabilised by p-coordination to the phenyl ring to give ansa-arene complexes with one- and two-carbon linkages. The
complexes catalyse the polymerisation of propene. Compared to the system Cp*TiMe3/B(C6F5)3 the ansa complexes show reduced
catalytic activity and enhanced chain termination. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Titanium; Zirconium; Ansa; Polymerisation catalysis; Half-sandwich
CH2(h-C6H5)}TiMe2][B(C6F5)4] reported by Flores et
al. [9]. We found recently that Cp*TiMe3/B(C6F5)3
(Cp*=C5Me5) give highly active catalysts for the poly-
merisation of propene to atactic elastomeric poly-
1. Introduction
As part of a study of the factors that affect the
reactivity and catalytic activity of cationic Group 4
cyclopentadienyl complexes [1], we have recently docu-
mented the ability of benzyl substituents to stabilise
electrophilic metal centres through p-coordination of
benzylic aryl substituents [2]. In the case of bis(cy-
clopentadienyl) complexes such interactions presumably
involve h2-coordination [3], similar to the h2-CꢀC coor-
dination detected in zirconocene complexes with
alkenyl-substituted cyclopentadienyl ligands [4]. Half-
sandwich complexes, on the other hand, are capable of
much stronger arene binding. Examples include coordi-
nation to phenyl groups of borate anions [5–7] and
h6-coordination of neutral arenes [8], as well as the
formation of ansa-metallocene complexes [{C5Me4CH2-
(
propene of unusually high molecular weight (Mw:1–
4×106) [10,11] and became interested in the possibility
of using phenyl coordination to control both catalytic
activity and polymer molecular weight. We report here
the synthesis of new titanium and zirconium half-sand-
wich complexes with benzyl substituted cyclopentadi-
enyl ligands and the formation of cationic complexes
with ansa-aryl structure.
2. Results and discussion
Cyclopentadienyl ligands with ꢁCMe2Ph and
ꢁCMe2CH2Ph substituents are readily accessible from
the reaction of dimethylfulvene with phenyllithium and
benzylmagnesium bromide, respectively. Quenching of
* Corresponding author. Fax: +44-113-233-6401.
E-mail address: m.bochmann@chem.leeds.ac.uk (M. Bochmann)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00488-X

;J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
85
the resulting lithium or magnesium cyclopentadienides
with an excess of trimethylchlorosilane gave good yields
of (C5H4SiMe3)CMe2Ph and (C5H4SiMe3)CMe2CH2Ph
as pale-yellow oils, which were used for subsequent
reactions without further purification. The compound
C5H4SiMe2Ph was prepared from sodium cyclopentadi-
enide and dimethylphenylchlorosilane in 82% yield.
The reaction of (C5H4SiMe3)CMe2Ph with TiCl4 in
CH2Cl2 at room temperature (r.t.) readily affords
(C5H4CMe2Ph)TiCl3 (1a) as orange crystals (Scheme 1).
The compound (C5H4CMe2CH2Ph)TiCl3 (2a) was made
similarly as a dark-red oil, which could not be induced
to crystallise. The reaction of (C5H4SiMe3)CMe2CH2Ph
with ZrCl4·2SMe2 in dichloromethane followed by
precipitation with dimethoxyethane (dme) gave
(C5H4CMe2CH2Ph)ZrCl3·dme (3a) as an off-white
solid. On the other hand, the reaction of
(C5H4SiMe3)CMe2Ph with ZrCl4·2SMe2 was slow and
did not lead to the desired product, even after pro-
longed reaction times.
The silylcyclopentadienyl complex (C5H4SiMe2-
Ph)TiCl3 (4a) was made by a different route, by treating
a suspension of Li[C5H4SiMe2Ph] with TiCl4 in light
petroleum at −78°C. The complex was obtained as
long yellow needles in 49% yield.
The influence of sterically more hindered cyclopenta-
dienyl substituents was explored by preparing the
diphenylmethyl derivative (C5H4CHPh2)TiCl3 (5a)
which is accessible in an analogous manner from TiCl4
and (C5H4CHPh2)SiMe3 (Scheme 2). The complex
forms orange crystals. Treatment of the trichlorides
Scheme 2.
1a–4a with methylmagnesium chloride in diethyl ether
at −78°C affords the trimethyl derivatives 1b–4b, re-
spectively. All four compounds form dark yellow (Ti)
to red–brown (Zr) oils, which could not be induced to
crystallise. All compounds were spectroscopically pure
according to NMR and were unequivocally character-
ised, although 2b and 4b proved very sensitive and did
not give satisfactory elemental analyses. By contrast,
the reaction of 5a with benzylmagnesium chloride gave
the tribenzyl complex (C5H4CHPh2)Ti(CH2Ph)3 (5b) as
red crystals in 50% yield. The spectroscopic data of the
neutral complexes are collected in Table 1.
Complexes 1a, 4a and 5a gave crystals suitable for
X-ray diffraction; the structures are shown in Figs.
1–3. Selected bond lengths and angles are listed in
Table 2. All three chlorides are monomeric, with unex-
ceptional geometric parameters. The complexes show
the familiar piano-stool geometry. The phenyl sub-
stituents adopt a conformation roughly perpendicular
to the plane of the cyclopentadienyl ring; there is no
indication of either intra- or inter-molecular interaction
between the aryl ring and the metal centre. The
diphenylmethylcyclopentadienyl ligand in 5a adopts a
propeller arrangement; the structure resembles the re-
cently reported rhodium complexes LRh(PF3)(PPri3)
and LRhCl2(PPri3) [12].
The structure of the tribenzyl complex 5b is shown in
Fig. 4. The ꢁCHPh2 substituent adopts a conformation
that minimises interaction with the benzyl ligands. The
three benzyl ligands are h1-bonded, with normal Ti—
CH2ꢁPh angles of 119.7–125.0°, unlike the related ful-
valene complex (h5:h5-C10H8){Ti(CH2Ph)3}2 which
contains differently coordinated benzyl ligands with
TiꢁCꢁC(Ph) angles ranging from 90.9 to 128°, one of
which is h2-bonded, while another shows an a-agostic
interaction [13]. Although in 5b one of the Ti···H
,
distances, TiꢁH(411), is relatively short (2.35(4) A) and
Scheme 1.
falls within the range observed for agostic interactions,

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J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
this is not borne out by the unremarkable TiꢁCꢁC(Ph)
the para-H is low-field shifted by 1.14 ppm, from l 7.36
in the neutral precursor 1b to l 8.50 in 6 (Table 3). Similar
trends can be observed for the ortho and meta protons
of the phenyl ring. Equally indicative is the separation
of the 1H-NMR signals of the monosubstituted cyclopen-
tadienyl rings. In the case of the ansa-metallocenes
{X(C5H4)2}TiCl2 the separation of the two triplets in-
creases with decreasing angle between the Cp planes,
from X=(CH2)3 (Dl=0.04 ppm), Me2Ge (Dl=1.21),
Me2Si (Dl=1.25) to X=H2C (Dl=1.35), a good
indication for increasing chelate ring strain [14]. The
same picture emerges in the transformation of 1b into 6:
while the Cp protons are superimposed in the neutral
complex (l 6.39), they are separated into two sets of
triplets (Dl=1.46 ppm) in the cationic complex.
angle of 120.0(3)°. The other Ti···H distances vary from
,
2.44(4) to 2.55(4) A.
2.1. Cationic complexes
The reaction of 1b–5b with [Ph3C]+[B(C6F5)4]− or
B(C6F5)3 in dichloromethane was studied by NMR
spectroscopy. The reaction of 1b with a slight excess of
[Ph3C]+[B(C6F5)4]− in CD2Cl2 in a NMR tube at −78°C
proceeded slowly but was quantitative on warming to
−40°C. The spectra are recorded at this temperature.
The data indicate that phenyl coordination has occurred
to give the ansa-complex [(h5-C5H4CMe2ꢁhn-
C6H5)TiMe2]+[B(C6F5)4]− (6) (Scheme 3). The signal for
Table 1
NMR data of neutral titanium and zirconium half-sandwich complexes a
Compound
Data (l/ppm, J/Hz)
(C5H4CMe2Ph)TiCl3 (1a)
1H-NMR: l 2.20 (s, 6H, Me), 7.22 (t, 2H, JHH=2.7, Cp), 7.39 (t, 2H, JHH=2.7, Cp), 7.54–7.69
(m, 5H, Ph).
13C-NMR: l 28.80 (Me), 41.00 (CMe2Ph), 121.81 (Cp), 123.55 (Cp), 125.89 (m-C of Ph), 126.67
(p-C of Ph), 128.54 (o-C of Ph), 147.63 (ipso-C of Cp), 154.66 (ipso-C of Ph).
1H-NMR: l 1.33 (s, 9H, TiꢁCH3), 1.75 (s, 6H, CCH3), 6.39 (m, 4H, Cp), 7.36 (m, 1H, p-Ph), 7.47
(s, 2H, m-Ph), 7.48 (s, 2H, o-Ph).
(C5H4CmePh)TiMe3 (1b)
13C-NMR: l 29.42 (CMe2), 39.74 (CMe), 62.79 (TiꢁMe), 109.21 (Cp), 113.68 (Cp), 125.86 (p-C of Ph),
126.01 (m-C of Ph), 128.06 (o-C of Ph), 143.84 (ipso-C, Cp), 150.19 (ipso-C of Ph).
1H-NMR: l 1.51 (s, 6H, Me), 2.87 (s, 2H, CH2), 6.81–6.85 (m, 4H, Cp), 7.20–7.30 (m, 5H, Ph).
13C-NMR: l 26.91 (Me), 38.75 (CMe2), 52.03 (CH2), 121.53 (Cp), 123.45 (Cp), 125.31 (p-C of Ph),
127.87 (o-C of Ph), 130.53 (m-C of Ph), 136.91 (ipso-C of Cp), 154.07 (ipso-C of Ph).
1H-NMR: l 1.35 (s, 9H, TiꢁCH3), 1.36 (s, 6H, CCH3), 3.00 (s, 2H, CH2), 6.31 (t, 2H, JHH=2.6, Cp), 6.38
(t, 2H, JHH=2.6, Cp), 7.10–7.14 (m, 2H, Ph), 7.41–7.46 (m, 2H, Ph).
(C5H4CMe2CH2Ph)TiCl3 (2a)
C5H4CMe2CH2Ph)TiMe3 (2b)
13C-NMR: l 27.09 (CCH3), 36.84 (CCH3), 52.44 (CH2), 62.86 (TiꢁCH3), 108.94 (Cp), 113.47 (Cp),
126.03 (p-C, Ph), 127.45 (o-C, Ph), 130.68 (m-C, Ph), 138.26 (ipso-C, Cp), 143.24 (ipso-C, Ph).
1H-NMR: l 1.51 (s, 6H, Me), 2.82 (s, 2H, CH2), 3.80 (s, br, 6H, OMe), 4.02 (s, br, 4H, OCH2), 6.43
(t, 2H, JHH=2.5, Cp), 6.45 (t, 2H, JHH=2.5, Cp), 6.78 (2H, m-Ph), 7.16 (m, 3H, o-, p-Ph).
13C-NMR: l 26.17 (Me), 38.56 (CMe2), 53.13 (CH2), 63.77 (OMe), 72.78 (OCH2), 117.78 (Cp), 117.98 (Cp),
125.99 (p-C of Ph), 127.40 (m-C of Ph), 130.71 (o-C of Ph), 123.11 (ipso-C of Cp), 146.00
(ipso-C of Ph).
(C5H4CMe2CH2Ph)ZrCl3·
dme (3a)
(C5H4CMe2CH2Ph)ZrMe3 (3b)
1H-NMR: l 0.32 (s, 9H, ZrꢁCH3), 1.27 (s, 6H, CCH3), 2.84 (s, 2H, CH2), 6.18 (t, 2H, JHH=2.6, Cp), 6.22
(t, 2H, JHH=2.6, Cp), 6.93–6.98 (m, 2H, Ph), 7.22–7.27 (m, 3H, Ph).
13C-NMR: l 27.43 (ZrꢁCH3), 35.39 (CCH3), 45.28 (CCH3), 52.24 (CH2), 106.62 (Cp), 110.64 (Cp),
126.06 (p-C, Ph), 127.48 (m-C, Ph), 130.63 (o-C, Ph), 138.28 (ipso-C, Cp), 141.83 (ipso-C, Ph).
1H-NMR: l 0.68 (SiMe2), 7.05 (t, 2H, JHH=2.4, Cp), 7.25 (t, 2H, JHH=2.4, Cp), 7.33–7.53 (m, 5H).
13C-NMR: l −2.27 (SiMe2), 126.49 (Cp), 128.17 (Cp), 129.86 (m-C of Ph), 129.94 (p-C of Ph), 133.95 (o-C
of Ph), 135.81 (ipso-C of Cp), 140.27 (ipso-C of Ph).
(C5H4SiMe2Ph)TiCl3 (4a)
(C5H4SiMe2Ph)TiMe3 (4b)
1H-NMR: l 0.45 (s, 6H, SiꢁCH3), 1.09 (s, 9H, TiꢁCH3), 6.44 (m, 4H, Cp), 7.34–7.38 (m, 3H, Ph),
7.51–7.54 (m, 2H, Ph).
13C-NMR: l 1.88 (SiꢁCH3), 63.19 (TiꢁCH3), 117.58 (Cp), 117.94 (Cp), 124.92 (ipso-C, Cp), 127.92
(p-C, Ph), 129.26 (m-C, Ph), 133.98 (o-C, Ph), 138.43 (ipso-C, Ph).
(C5H4CHPh2)TiCl3 (5a)
1H-NMR: l 5.82 (s, 1H, CHPh2), 6.74 (t, 2H, Cp), 6.96 (t, 2H, Cp), 7.17–7.36 (m, 10H, Ph).
13C-NMR: l 53.21 (CHPh2), 123.32, 123.70, 141.71 (Cp), 127.33, 128.84, 128.91, 147.10 (Ph).
1H-NMR: l 2.93 (s, 6H, CH2Ph), 4.64 (s, 1H, CHPh2), 5.63 (t, 2H, Cp), 5.82 (t, 2H, Cp), 6.64
(d, 6H, o-benzyl), 6.88 (t, 3H, p-benzyl), 7.08–7.34 (m, 16H, m-benzyl and CHPh2).
13C-NMR: l 51.78 (CHPh2), 92.73 (CH2Ph), 115.52 (Cp), 118.11 (Cp), 122.52 (p-C, Bz), 126.24
(m-C, Bz), 126.70 (p-C, Ph), 128.50 (o-C, Bz), 128.58, 128.84 (Ph), 138.52 (ipso-C, Cp), 143.97 (ipso-C, Ph,
148.05 (ipso-C, Bz).
C5H4CHPh2)Ti(CH2Ph)3 (5b)
a CDCl3, 25°C.

J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
87
Fig. 3. Molecular structure of (C5H4CHPh2)TiCl3 (5a).
Fig. 1. Molecular structure of (C5H4CMe2Ph)TiCl3 (1a), showing the
atomic numbering scheme. The atoms are represented by thermal
ellipsoids at 40% probability level.
The chemical shift difference for the Cp protons is less
pronounced, indicating the reduced strain of the
ꢁCMe2CH2ꢁ bridge.
The reaction of 2b with B(C6F5)3 cleanly gives [(h5-
C5H4CMe2CH2ꢁhn-C6H5)TiMe2]+[MeB(C6F5)3]− (7b).
The structure of the cation is identical to 7a, with a
non-coordinated counteranion. In an analogous man-
ner, the zirconium complex 3b affords [(h5-
The reaction of 2b with [Ph3C]+[B(C6F5)4]− gave
1
clean H- and 13C-NMR spectra at −60°C which are
consistent with the quantitative formation of
[(h5C5H4CMe2CH2ꢁhn-C6H5)TiMe2]+[B(C6F5)4]− (7a).
This complex appears more stable than 6. The reso-
nances for the para and meta protons of the phenyl ring
are clearly resolved at l 8.73 (p-H) and l 8.43 (m-H).
C5H4CMe2CH2ꢁhn-C6H5)ZrMe2]+[B(C6F5)4]−
(8a),
while the reaction with B(C6F5)3 gives the correspond-
ing [MeB(C6F5)3]− compound 8b, although in this case
unidentified side-products were also in evidence.
Table 2
,
Selected bond lengths (A) and angles (°) of titanium trichloride
complexes
Compound
1a
4a
5a
Bond lengths
TiꢁCl(1)
TiꢁCl(2)
TiꢁCl(3)
TiꢁC(1)
TiꢁC(2)
TiꢁC(3)
TiꢁC(4)
TiꢁC(5)
C(1)ꢁC(6)
C(1)ꢁSi(1)
2.2151(16)
2.2317(15)
2.2368(14)
2.398(3)
2.3342(4)
2.308(4)
2.322(3)
2.358(3)
1.532(5)
2.227(2)
2.213(2)
2.210(2)
2.343(5)
2.327(6)
2.340(6)
2.334(6)
2.344(5)
2.227(2)
2.221(2)
2.2367(13)
2.391(3)
2.344(4)
2.308(4)
2.314(4)
2.340(4)
1.512(5)
1.892(6)
Bond angles
Cl(1)ꢁTiꢁCl(2)
Cl(1)ꢁTiꢁCl(3)
Cl(2)ꢁTiꢁCl(3)
C(1)ꢁC(6)ꢁC(7)
C(1)ꢁSiꢁC(8)
102.43(5)
103.93(5)
102.38(4)
103.5(3)
101.99(9)
102.08(9)
103.39(9)
104.99(6)
101.92(6)
101.90(5)
105.1(3)
Fig. 2. Molecular structure of (C5H4SiMe2Ph)TiCl3 (4a).

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,
Fig. 4. Molecular structure of (C5H4CHPh2)Ti(CH2Ph)3 (5b). Selected bond lengths (A) and angles (°): TiꢁC(21) 2.129(6), TiꢁC(31) 2.111(5),
TiꢁC(41) 2.122(5), TiꢁH(411) 2.35(4), TiꢁH(412) 2.55(4), TiꢁC(21)ꢁC(22) 119.7(4), TiꢁC(31)ꢁC(32) 125.0(3), TiꢁC(41)ꢁC(42) 120.0(3).
In contrast to the reactions with carbon-bridged
compounds, no product could be identified in the
strained chelate ring by p-coordination of one of the
phenyl rings.
The compound exhibits fluxionality. First, the two
CHPh2 phenyl rings can interchange. A second process
that can be envisaged involves a change in the coordi-
nation mode of the benzyl ligands which can displace
the CHPh2 substituent and become h2-bonded. If that
happens, one should expect to see the appearance of
diastereotopic benzyl methylene groups. This is indeed
observed. On lowering the temperature to −90°C a
second isomer of 9 is observed: the broad peak for the
benzylic CH2 groups at l 3.05 splits into two sets of
broadened doublets at l 3.46 and l 2.40, with a gemi-
nal coupling constant of 9 Hz. The difference in Cp
resonances is much smaller than in the major isomer,
Dl=0.86 ppm, in agreement with a less strained struc-
ture. The data are consistent with an equilibrium be-
tween an ansa-complex with h1-benzyl ligands and an
h2-benzyl isomer where the p-phenyl coordination is
weakened or lost (Scheme 4).
reaction
of
(C5H4SiMe2Ph)TiMe3
(4a)
with
[Ph3C]+[B(C6F5)4]−. The spectra indicated extensive de-
composition, even at −60°C. The same result was
obtained when 4a was treated with B(C6F5)3; again
complex spectra were recorded which could not be
assigned.
As is well known, cationic Group 4 benzyl complexes
can be stabilised in several different ways not open to
methyl compounds [15]. For example, one or both of
the benzyl ligands in a cation [CpRM(CH2Ph)2]+ may
be h2-bonded. In [Cp*Zr(CH2Ph)2]+ both h3- and h7-
coordination has been observed [16], while for
[(C5H3But2)Zr(CH2Ph)2]+ h1- and h3-bonding has been
suggested [17]. If the cation was generated by benzyl
abstraction with B(C6F5)3, p-coordination of the
[PhCH2B(C6F5)3]− anion is prevalent [6,7]. On the
other hand, coordination of a neutral arene to a
cationic benzyl complex has to our knowledge not been
observed.
Treatment of a solution of the benzyl complex 5b in
CD2Cl2 at −60°C with [Ph3C+][B(C6F5)4]− gives the
ionic product [h5-C5H4CHPh2)Ti(CH2Ph)2][B(C6F5)4]
(9). The phenyl region of the 1H-NMR spectrum is
difficult to assign because of the superimposition of the
signals for the CHPh2 substituent, the benzyl ligands,
and the Ph3CCH2Ph by-product. Indicative for the
structure of the product are, however, the changes in
the cyclopentadienyl resonances. In 5b these are ob-
served at l 5.63 and 5.82 (Dl=0.19 ppm), whereas in
9 they are found at l 4.92 and l 6.88 (Dl=1.96 ppm),
a clear indication of the formation of a comparatively
Several attempts were made to isolate ionic ansa-aryl
complexes from any of these reactions at a preparative
scale. However, they met with little success, even in the
case of the ꢁCMe2CH2ꢁ compounds which are compar-
atively stable in solution. Orange to brown powders
were obtained which could not be induced to crystallise
and which gave variable elemental analyses.
2.2. Propene polymerisation
One of the incentives for this work was to study the
influence of reversible phenyl coordination on the activ-
ity of polymerisation catalysts and on polymer molecu-

J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
89
lar weights. As noted earlier, the system Cp*TiMe3/
B(C6F5)3, without a pendant ligand, gives high molecu-
lar weight elastomeric polypropene in either toluene or
light petroleum [10,11]. On the other hand, methylalu-
minoxane activated (h-C5H4CH2CH2Ph)TiCl3 shows
comparatively modest activity for ethene polymerisa-
tion, whereas pendant amino groups ꢁCH2CH2NR2
have an enhancing effect [18].
The effect of a comparatively weakly coordinated
pendant ligand such as phenyl on the behaviour of a
polymerisation catalyst is difficult to predict. A re-
versibly coordinated phenyl ligand might either act to
protect the growing polymer chain from b-H elimina-
tion by stabilising a 16-electron resting state, thus giv-
ing longer polymer chains and narrower molecular
weight distributions, or it might compete with
monomer take-up to such an extent that the rate of
chain termination becomes competitive, possibly result-
ing in oligomers rather than polymers.
Activation of a propene-saturated toluene solution of
2b with an equimolar amount of B(C6F5)3 leads to the
formation of atactic polypropene (Table 4). Except for
the polymerisation carried out at 0°C, the polymer did
not precipitate upon methanol addition. In sharp con-
trast to the system Cp*TiMe3/B(C6F5)3 which gives
molecular weights of the order of 0.5–2×106 at high
productivities (Table 4, entries 9 and 10), the polymer
formed with 2b/B(C6F5)3 is of low molecular weight,
and the polydispersities are comparatively broad.
Broad polydispersities might arise either from partial
decomposition of the catalyst, or be the result of a
comparatively slow equilibrium between dormant (pre-
cursor) and active states.
characterisable cations from 4b were not successful,
mixtures of 4b and showed higher catalytic activity than
2b. On the other hand, polymer molecular weights were
even lower, even at −20°C, while the molecular weight
distributions were narrower. The lowest activity was
observed for the benzyl complex 5b. It appears to be
thermally unstable under catalytic conditions; activity
decreased from −20°C to 0°C, while only trace
amounts of polymer were obtained at 20°C.
2.3. Conclusions
Pendant phenyl moieties coordinate to cationic
Group 4 metal centres to give comparatively stable
ansa-arene complexes of the type [(Cp—X—
Ph)MR2]+. This type of arene coordination is preferred
over coordination to anions such as [MeB(C6F5)3]−,
even in the case of titanium where the formation of
Tiꢁm-MeB(C6F5)3 zwitterions is well documented
[8,11,19]. Low-temperature NMR studies suggest that
in the case of the benzyl complexes at low temperature
there is competition between the ansa structure and
h2-coordination of benzyl ligands. Assuming h6-arene
coordination, the [(Cp—X—Ph)MR2]+ cations repre-
sent 16-electron resting states of active polymerisation
catalysts. Presumably as the result of preferential arene
coordination, mixtures of (Cp—X—Ph)MR3 and
B(C6F5)3 are less active in propene polymerisations
than systems with non-chelating ligands, and chain
termination is enhanced. On the other hand, chain
termination is not as frequent as with Cp2ZrCl2/methyl-
aluminoxane catalysts which give low-molecular-weight
propene oligomers [20].
Although in NMR reactions attempts to generate
Scheme 3. Reagents and conditions: (i) [CPh3][B(C6F5)4]; (ii) a=[CPh3][B(C6F5)4], b=B(C6F5)3.

90
J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
Table 3
NMR data of cationic titanium and zirconium complexes a
Compound
Data (l/ppm, J/Hz)
[(C5H4CMe2Ph)TiMe2][B(C6F5)4](6)
1H-NMR: l 0.97 (s, 6H, TiꢁMe), 1.65 (s, 6H, CMe), 5.91 (t, 2H, Cp),
7.04 (d, 2H, o-Ph), 7.37 (t, 2H, Cp), 8.50 (m, 3H, Ph). 13C-NMR: l 30.04
(CMe), 41.15 (CMe), 68.14 (TiꢁMe), 113.11 (Cp), 124.92 (Cp), 126.12
(o-C of Ph), 128.45 (p-C of Ph), 140.12 (m-C of Ph).
1H-NMR: l 0.42 (br, 3H, BꢁMe), 0.64 (s, 6H, TiꢁMe), 1.30
[(C5H4CMe2CH2Ph)TiMe2]-
[MeB(C6F5)3] (7b)
(s, 6H, CMe2), 2.80 (s, 2H, CH2), 6.18 (s, 2H, Cp), 7.15 (s, 2H, Cp), 7.21
(d, 2H, o-Ph), 8.41 (t, 2H, m-Ph), 8.71 (t, 1H, p-Ph). 13C-NMR: l 9.47
(BꢁMe), 30.30 (CMe), 41.04 (CMe), 47.80 (CH2), 64.62 (TiꢁMe), 114.00
(Cp), 123.47 (Cp), 129.00 (o-C of Ph), 131.45 (p-C of Ph), 137.75
(m-C of Ph), 141.24 (ipso-C of Cp), 142.68 (ipso-C of Ph).
1H-NMR: l 0.18 (s, 6H, ZrꢁCH3), 0.46 (br, 3H, BꢁCH3), 1.40
(s, 6H, CCH3), 3.21 (s, 2H, CH2), 6.27 (t, 2H, Cp), 6.65 (t, 2H, Cp), 7.60
(d, 2H, o-Ph), 8.19 (t, 1H, p-Ph), 8.33 (t, 2H, m-Ph). 13C-NMR: l 9.55
(BꢁCH3), 31.63 (CCH3), 40.89 (CCH3), 42.96 (ZrꢁCH3), 48.70 (CH2),
109.94 (Cp), 117.64 (Cp), 129.13 (p-C of Ph), 130.15 (o-C of Ph), 135.82
(m-C of Ph), 137.76 (ipso-C of Cp), 144.17 (ipso-C of Ph).
[(C5H4CMe2CH2Ph)ZrMe2][MeB-
(C6F5)3] (8b)
a CD2Cl2, −60°C, 300 MHz. The data for 7a and 8a are omitted since they are essentially identical to those given for 7b and 8b.
3. Experimental
lowed to warm to r.t. and stirred for 20 min. The
resulting white suspension was slowly added to a mix-
ture of 23.2 g (214 mmol) of trimethylchlorosilane in
120 cm3 THF. The reaction mixture was stirred
overnight, poured onto ice water and extracted with
light petroleum. The organic phase was dried over
magnesium sulphate, the volatiles were removed under
vacuum to yield a yellow oil which was distilled at
reduced pressure. Yield: 32.6 g (124.8 mmol, 58.3%),
b.p. 82–100°C/0.1 torr. 1H-NMR (300 MHz, 22°C,
CDCl3): l 0.29 (s, 9 H, SiMe3), 1.87 (s, 6 H, CMe2),
6.70–6.47 (m, 4 H, C5H4), 7.64–7.43 (m, 5 H, Ph).
3.1. General procedures
All experiments were carried out under nitrogen at-
mosphere by using standard Schlenk techniques. Sol-
vents were dried over sodium (toluene, low in sulphur),
sodium–potassium alloy (diethyl ether, light petroleum,
b.p. 40–60°C) sodium–benzophenone (THF) and cal-
cium hydride (dichloromethane). NMR solvents were
,
dried over activated 4 A molecular sieves and degassed
by several freeze–thaw cycles. NMR spectra were
recorded using Bruker ARX250, DPX300 or Jeol
EX270 spectrometers and referenced to residual solvent
peaks. Chemical shifts are quoted in ppm relative to
TMS. Propene (BOC) was passed through P2O5 and
activated molecular sieves and condensed onto
Et2AlOHex prior to use.
3.3. Preparation of C5H4(SiMe3)CMe2CH2Ph
To a solution of benzylmagnesium chloride (220
mmol) in 350 cm3 THF was added 22.7 g (214 mmol) of
dimethylfulvene over a period of 1 h at r.t. The reaction
mixture was stirred overnight and added to a solution
of 23.2 g (214 mmol) of trimethylchlorosilane in 100
cm3 THF at r.t. The colour changed to orange and a
precipitation formed. After stirring for 1 h the mixture
was poured onto ice water and extracted with light
petroleum. The organic phases was dried over magne-
3.2. Preparation of C5H4(SiMe3)CMe2Ph
To a solution of phenyllithium (214 mmol) in 200
cm3 diethyl ether at −78°C was added dropwise 22.7 g
(214 mmol) of dimethylfulvene. The mixture was al-

J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
91
sium sulphate and the volatiles were removed in vacuo
to yield a yellow oil which was distilled under reduced
pressure, b.p. 92–93°C/0.01 torr. H-NMR (250 MHz,
1H-NMR (250 MHz, CDCl3, 20°C): l 0.02 (s, 9H,
SiMe3); 5.29 (s, 1H, CHPh2); 5.8 (m, 2H, Cp); 6.5 (m,
2H, Cp); 7.21–7.38 (m, 10H, Ph).
1
22°C, CDCl3): l 0.05 (s, 9 H, SiMe3), 1.24 (s, 6 H,
CMe2), 2.84 (s, 2 H, CH2), 6.77–6.08 (m, 4 H, C5H4),
7.27–7.11 (m, 5 H, Ph).
3.7. Preparation of (C5H4CMe2Ph)TiCl3 (1a)
A solution of 7.69 g (30 mmol) of C5H4(SiMe3)-
CMe2Ph in 10 cm3 CH2Cl2 was added to a solution of
5.69 g (30 mmol) of TiCl4. The colour changed to dark
red. The mixture was stirred overnight and the solvent
removed to yield a dark-red oil which solidified after 1
day. The product was recrystallised from 10 cm3 CH2Cl2
at −16°C to give orange crystals suitable for X-ray
diffraction. A second batch of crystals was obtained
from the mother liquor. Combined yield: 5.63 g (17.4
mmol, 57.8%). Anal.: C14H15Cl3Ti found (calc.): C, 50.0
(49.8); H, 4.5 (4.5); Cl, 31.3 (31.5)%.
3.4. Preparation of C5H5SiMe2Ph
The compound was made by a modification of a
literature procedure [21]. A solution of sodium cy-
clopentadienide (146 mmol) in 200 cm3 THF was added
to
a solution of 25 g (146 mmol) of chloro-
dimethylphenylsilane in 180 cm3 THF at 0°C. The
reaction mixture was stirred for 20 min at r.t., poured
onto ice water and extracted with petroleum. Colourless
oil, yield: 24.2 g (120.8 mmol, 82.7%), b.p. 60–80°C/0.1
torr.
3.8. Preparation of (C5H4CMe2Ph)TiMe3 (1b)
3.5. Preparation of diphenylmethylcyclopentadiene
To a solution of 12.9 g (38.1 mmol) of (C5H4-
CMe2Ph)TiCl3 in 250 cm3 diethyl ether at −78°C was
added dropwise 38.1 cm3 (114.3 mmol) of 3 M MeMgCl
in Et2O. The colour changed from red to yellow. The
reaction mixture was warmed to 0°C and the solvent
removed in vacuo. The residue was extracted with light
petroleum and centrifuged. Evaporation of the solvent
yielded a dark-yellow oil which could not be crys-
tallised, yield: 3.22 g (11.7 mmol, 39%). For subsequent
reactions a 1.17 M stock solution of 1b in light
petroleum was used. Anal.: C17H24Ti found (calc.): C,
73.2 (73.9); H, 8.9 (8.8)%.
To a solution of 100 g (0.5 mol) of chlorodiphenyl-
methane in 200 cm3 THF at −78°C was added NaCp
(0.5 mol) in 200 cm3 THF. The reaction mixture was
warmed to r.t., stirred for 30 min, poured onto ice
water–NH4Cl and worked up as described above. Or-
ange oil, yield: 30 g (129 mmol, 25.8%), b.p. 125–145°C/
0.01 torr. 1H-NMR (89 MHz, 28.8°C, CDCl3): l 1.29 (s,
1 H, CHPh2), 5.17 (m, 1 H, CpꢁH), 6.4–5.79 (m, 4 H,
C5H4), 7.49–6.90 (m, 10 H, Ph).
3.6. Preparation of C5H4(SiMe3)CHPh2
To 10.95 g (47.2 mmol) C5H4CHPh2 in 200 cm3 THF
was added at −78°C 18.9 cm3 (47.2 mmol) of 2.5 M
butyllithium. The colour changed to red. The reaction
mixture was warmed to r.t., stirred for 1 h and added
slowly to a mixture of 5.13 g (47.2 mmol) of chloro-
trimethylsilane in 100 cm3 THF at −78°C. The blue
mixture turned yellow on warming to r.t. and was
worked up as above. Removal of the solvent in vacuo
yielded a waxy solid, yield: 11.0 g (36.1 mmol, 76%).
3.9. Preparation of (C5H4CMe2CH2Ph)TiCl3 (2a)
To 3.3 cm3 (30 mmol) TiCl4 in 130 cm3 dichloro-
methane was slowly added at r.t. a solution of 8.11 g (30
mmol) of C5H4(SiMe3)CMe2CH2Ph in 20 cm3
dichloromethane. The red mixture was stirred for 2 h.
The volatiles were removed in vacuo to yield a dark red
oil which could not be crystallised. Yield: 9.3 g (26.5
mmol, 88%).
Scheme 4. Reagents and conditions: (i) [CPh3][B(C6F5)4].

92
J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
Table 4
Propene polymerisation with titanium half-sandwich complexes and B(C6F5)3 in toluene
Entry Precursor complex Ti (mmol)
B (mmol) Temp. (°C)
Time (min)
Mass (mg) a
Productivity a
Mw×10−3 Mw/Mn
1
2
3
4
5
6
7
8
9
2b
2b
2b
2b
4b
4b
5b
5b
40
40
40
40
20
20
20
20
20
20
40
40
40
40
20
20
20
20
20
20
0
20
40
60
0
−20
0
−20
0
3
3
3
3
1
1
10
1
1
2
164.3
230.3 b
161.8 b
82.5 b
324
295
150
422
1366
3470
6.4
16.2
18.8
16.0
76
33
3.5
47.6
276
520
406
124.5
54.8
23
28.2
36.6
36.6
129
14.8
5.8
3.5
3.7
2.8
2.7
3.5
3.3
2.9
2.0
Cp*TiMe3
Cp*TiMe3
518
2275
10
−45
a In 104 g PP (mol Ti)−1 [C3H6]−1 h−1 bar−1
b Polymer isolated by solvent evaporation overnight.
.
3.10. Preparation of (C5H4CMe2CH2Ph)TiMe3 (2b)
120 cm3 petroleum and cooled to −78°C. A solution of
3.3 cm3 (30 mmol) TiCl4 in 5 cm3 light petroleum was
added slowly, the mixture was stirred for 3 h, warmed
to −60°C and filtered. Another aliquot of petroleum
was added and the suspension warmed to 40°C and
filtered. The filtrate was stored at −16°C to yield long,
yellow needles which were suitable for X-ray diffrac-
Following the procedure for 1b, methylation of 9.3 g
(26.5 mmol) of 2a with. 26.5 cm3 (79.4 mmol) 3 M
MeMgCl afforded as a dark yellow oil. Yield: 4.4 g
(15.3 mmol, 58%). The compound was pure by NMR
but did not give consistent elemental analyses.
tion. Yield: 5.21
g
(14.6 mmol, 49%). Anal.:
C13H15Cl3SiTi found (calc.): C, 44.3 (44.2); H, 4.0 (4.3);
Cl, 30.2 (30.1)%.
3.11. Preparation of (C5H4CMe2CH2Ph)ZrCl3·dme
(3a)
3.14. Preparation of (C5H4SiMe2Ph)TiMe3 (4b)
A solution of 10.72 g (30 mmol) of ZrCl4·2SMe2 in
120 cm3 dichloromethane was treated with 8.11 g (30
mmol)
C5H4(SiMe3)CMe2CH2Ph
in
20
cm3
Treatment of 4.26 g (12 mmol) of 4a in 180 cm3
diethyl ether at −78°C with 12.0 cm3 (36 mmol)
methylmagnesium chloride in THF led to a colour
change to bright yellow. The reaction mixture was
stirred for 1 h at −78°C and slowly warmed to 0°C.
The volatiles were removed at this temperature, the
residue was extracted with 120 cm3 light petroleum and
centrifuged. Removal of the solvent gave a dark yellow
oil, yield: 2.3 g (7.9 mmol, 65.5%). The compound was
spectroscopically pure, though the analyses were af-
fected by its sensitivity to hydrolysis. Anal.: C16H24SiTi
found (calc.): C, 62.1 (65.7); H, 8.1 (8.3)%.
dichloromethane at 0°C. The mixture was stirred
overnight, 20 cm3 dme were added, the solution was
concentrated and cooled to −30°C. A solid formed
which was filtered off, washed with 4×5 cm3 dme at
−30°C and dried under vacuum. An off-white solid
was obtained, yield: 6.41 g (13 mmol, 43%). Anal.:
C19H27Cl3O2Zr found (calc.): C, 46.1 (47.1); H, 5.8
(5.6); Cl, 22.8 (21.9)%.
3.12. Preparation of (C5H4CMe2CH2Ph)ZrMe3 (3b)
Following the procedure for 1b, compound 3b was
obtained from 6.41 g (13 mmol) of 3a and 13 cm3 (39.7
mmol) of MeMgCl as a dark red–brown oil, yield: 3.6
g (10.7 mmol, 83%). Anal.: C18H26Zr found (calc.): C,
63.9 (64.8); H, 6.9 (7.8)%.
3.15. Preparation of (C5H4CHPh2)TiCl3 (5a)
To 7.0 g (23 mmol) C5H4(SiMe3)CHPh2 in 20 cm3
toluene was added 4.4 g (23 mmol) TiCl4 in 80 cm3
toluene. The colour changed to dark red and the reac-
tion was stirred for 2 h. Removal of yielded a green
solid, which was washed with 2×100 cm3 light
petroleum and extracted with 30 cm3 CH2Cl2. Concen-
tration of the filtrate orange crystals suitable for X-ray
crystallography. Yield: 2.35 g (6.1 mmol, 27%). Anal.:
C18H15Cl3Ti found (calc.): C, 57.4 (56.1); H, 4.1 (3.9);
Cl, 26.3 (27.6)%.
3.13. Preparation of (C5H4SiMe2Ph)TiCl3 (4a)
To 6.01 g (30 mmol) of C5H4SiMe2Ph in 120 cm3
light petroleum was added 18.75 cm3 (30 mmol) butyl-
lithium. A white precipitated formed. The reaction
mixture was stirred 90 min at r.t., filtered and washed
with light petroleum. The product was suspended in

J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
93
Table 5
Crystal data for compounds 1a, 4a, 5a and 5b
1a
4b
5a
5b
Formula
M
Crystal system
Space group
C14H15Cl3Ti
337.51
Monoclinic
P21/c
12.375(5)
11.632(5)
21.205(5)
90
91.633(5)
90
3051(2)
298(2)
C
13H15Cl3SiTi
C18H15Cl3Ti
385.55
Monoclinic
P21/c
8.979(3)
19.565(5)
10.511(4)
90
110.75(3)
90
1726.7(10)
298(2)
4
C39H16Ti
552.58
Triclinic
353.59
Monoclinic
P21/c
7.972(4)
10.594(3)
19.296(3)
90
97.39(2)
90
1616.1(10)
298(2)
4
(
P1
,
a (A)
11.228(3)
11.299(4)
13.497(4)
75.24(3)
85.54(3)
66.73(2)
1520.6(8)
233(2)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
U (A )
T (K)
Z
8
2
Dcalc (g cm−3
)
1.469
1.066
1.453
1.080
1.483
0.952
1.207
0.307
v(Mo–Ka) (mm−1
)
Reflections collected/unique
5631/5365
0.0256
0.1047
0.0359
2727/2525
0.0528
0.1141
0.0423
3044/3044
–
0.1194
0.0407
5264/4226
0.0445
0.1184
a
Rint
wR2
b
R1 (I\2|(I)) c
0.0490
a Rint=SꢀF2o−Fo2(mean)ꢀ/S[F2o] for those reflections measured more than once.
b wR2={S[w(Fo2−Fc2)2]/S[w(F2o)2]}0.5
.
c R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ. Note: structures refined against F2 using all data; R1 for ‘observed’ data is calculated only for comparison with other
structures refined against F.
3.16. Preparation of (C5H4CHPh2)Ti(CH2Ph)3 (5b)
carried out by equilibrating a given amount of purified
and degassed solvent at the stated temperature with the
monomer at 1 bar. Polymerisation was initiated by
injecting an aliquot of the metal alkyl stock solution
followed by the injection of an equimolar amount of either
B(C6F5)3 or [CPh3][B(C6F5)4] and terminated by injecting
2 cm3 of methanol. The polymer was precipitated with
large amounts of methanol and dried at 60°C for 12 h.
In the case of low-molecular-weight polymers the
toluene–methanol mixture was allowed to evaporate and
the residue recovered for analysis.
The compound was prepared from 2.35 g (6.1 mmol)
(C5H4CHPh2)TiCl3 and 20 mmol benzylmagnesium chlo-
ride. The colour changed to orange. The reaction mixture
was stirred overnight. Removal of volatiles gave a
dark-red solid which was extracted with 230 cm3 hot
petroleum. Cooling the filtrate slowly to −30°C yielded
red crystals. A second crop was obtained from the mother
liquor. Yield: 1.68 g (3 mmol, 50%). Anal.: C39H36Ti
found (calc.): C, 84.6 (84.8); H, 6.9 (6.6)%.
3.17. Generation of cationic complexes
3.19. X-ray crystallography
About 0.1 mmol of the titanium or zirconium trialkyl
complex was dissolved in 0.25 cm3 CD2Cl2, transferred
to a NMR tube and cooled to −78°C. 0.11 mmol of either
B(C6F5)3 or [CPh3][B(C6F5)4] was dissolved in 0.3 cm3
CD2Cl2 and mixed with the metal alkyl solution. The
colour darkened to orange. The sample was immediately
insertedintothepre-cooled(−60°C)spectrometerprobe.
Attempts to isolate the ionic products from analogous
reactions at a preparative scale gave orange to brown
solids, which could not be crystallised.
Data were collected on a Rigaku AFC7R diffractome-
ter using graphite-monochromated Mo–Ka radiation
,
(u=0.71073 A). Structures were solved by direct meth-
ods, and refined against all data by full-matrix least-
squares on F2, with anisotropic displacement parameters
assigned to all non-hydrogen atoms. The SHELXTL suite
of programs [22] was used for all calculations. Crystal
data, and further details of data collection and refinement,
are summarised in Table 5.
3.18. Propene polymerisations
4. Supplementary material
Polymerisations were conducted in a flame-dried all-
glass reactor. Stock solutions (ca. 10−5 M) of metal alkyls
were freshly prepared in toluene. Polymerisations were
The Cambridge Crystallographic Data Centre deposi-
tion numbers for complexes 1a, 4a, 5a and 5b are
CCDC-132427, -132428, -132429 and -133204. Copies of

94
J. Saßmannshausen et al. / Journal of Organometallic Chemistry 592 (1999) 84–94
Horton, J. de With, Organometallics 16 (1997) 5424. (d) M.G.
Thorn, Z.C. Etheridge, P.E. Fanwick, I.P. Rothwell,
Organometallics 17 (1998) 3636.
this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ,
UK (Fax: +44-1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
[8] (a) D.J. Gillis, M.J. Tudoret, M.C. Baird, J. Am. Chem. Soc. 115
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M.B. Hursthouse, S.J. Coles, Organometallics 14 (1995) 2456. (c)
D.J. Gillis, R. Quyoum, M.J. Tudoret, Q. Wang, D. Jeremic,
A.W. Roszak, M.C. Baird, Organometallics 15 (1996) 3600.
[9] J.C. Flores, J.S. Wood, J.C.W. Chien, M.D. Rausch,
Organometallics 15 (1996) 4944.
Acknowledgements
This work was supported by the Engineering and
Physical Sciences Research Council. J.S. thanks BASF
AG for a studentship. We thank RAPRA Technology,
Shawbury, for GPC determinations.
[10] (a) J. Saßmannshausen, M. Bochmann, J. Ro¨sch, D. Lilge, J.
Organomet. Chem. 548 (1997) 23. (b) A. Eckstein, J. Suhm, C.
Friedrich, R.D. Maier, J. Saßmannshausen, M. Bochmann, R.
Mu¨lhaupt, Macromolecules 31 (1998) 1335.
[11] See also: (a) T.L. Tremblay, S.W. Ewart, M.J. Sarsfield, M.C.
Baird, Chem. Commun. (Cambridge) (1997) 831. (b) S.W.
Ewart, M.J. Sarsfield, D. Jeremic, T.L. Tremblay, E.F. Williams,
M.C. Baird, Organometallics 17 (1998) 1502.
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