Cyclopentadienyl titanium imido compounds and their ethylene polymerization capability: Control of molecular weight distributions by imido N-substituents

Article abstract of DOI:10.1021/om0608556

Reaction of the previously reported Cp*Ti(N^tBu)Cl(py) (1) with bulky ortfzo-substituted anilines ArNH₂ afforded the corresponding aryl imido derivatives Cp*Ti(NAr)Cl(py) (Ar = 2,6-C ₆H₃ⁱPr₂ (2), 2,6-C₆H ₃Br₂ (3), 2-C₆H₄¹Bu (4), and 2-C₆H₄ⁱPr (5)). Reaction of 2 with B(C ₆F₅)₃ in C₆D₆ or heating in vacuo at 200 °C afforded the imido-bridged dimer Cp* ₂Ti₂(μ-N-2,6-C₆H₃ ⁱPr₂)₂Cl₂ (8). Activation of 1-5 with MAO gave moderately active catalyst systems for the polymerization of ethylene in contrast to the previously reported, highly active titanium imido systems Ti(Me₂[9]aneN₃)(NR)Cl₂/MAO and Ti{HC(Me₂pz)₃}(NR)Cl₂/MAO, which are isolobal and isoelectronic with 1-5. The Cp*-supported precatalyst productivities were sensitive to both the imido N-substituents and initial precatalyst/ cocatalyst concentrations. Depending upon the imido N-substituents and initial precatalyst/cocatalyst concentrations, polyethylene with unimodal (either rather low or very high molecular weight) or bimodal molecular weight distributions can be obtained. Excess AlMe₃ suppresses catalyst productivity but does not affect the overall molecular weight distribution in the system evaluated (1/MAO). Both chain transfer to aluminum and β-hydrogen transfer appear to be active pathways for formation of the low molecular weight fractions of the polymers formed with 1-5/MAO. Under otherwise identical polymerization conditions the catalyst systems 2/MAO and 8/MAO had comparable productivities and gave polyethylene with very similar molecular weight and molecular weight distributions, suggesting a potential role for binuclear species in the catalyst systems 1-5/MAO.

Full text of DOI:10.1021/om0608556

Organometallics 2007, 26, 83-92
83
Cyclopentadienyl Titanium Imido Compounds and Their Ethylene
Polymerization Capability: Control of Molecular Weight
Distributions by Imido N-Substituents
Christopher T. Owen, Paul D. Bolton, Andrew R. Cowley, and Philip Mountford*
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
ReceiVed September 18, 2006
Reaction of the previously reported Cp*Ti(NtBu)Cl(py) (1) with bulky ortho-substituted anilines ArNH2
i
afforded the corresponding aryl imido derivatives Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3-
t
i
Br2 (3), 2-C6H4 Bu (4), and 2-C6H4 Pr (5)). Reaction of 2 with B(C6F5)3 in C6D6 or heating in vacuo at
i
200 °C afforded the imido-bridged dimer Cp*2Ti2(µ-N-2,6-C6H3 Pr2)2Cl2 (8). Activation of 1-5 with
MAO gave moderately active catalyst systems for the polymerization of ethylene in contrast to the
previously reported, highly active titanium imido systems Ti(Me3[9]aneN3)(NR)Cl2/MAO and Ti{HC(Me2-
pz)3}(NR)Cl2/MAO, which are isolobal and isoelectronic with 1-5. The Cp*-supported precatalyst
productivities were sensitive to both the imido N-substituents and initial precatalyst/cocatalyst concentra-
tions. Depending upon the imido N-substituents and initial precatalyst/cocatalyst concentrations,
polyethylene with unimodal (either rather low or very high molecular weight) or bimodal molecular
weight distributions can be obtained. Excess AlMe3 suppresses catalyst productivity but does not affect
the overall molecular weight distribution in the system evaluated (1/MAO). Both chain transfer to aluminum
and â-hydrogen transfer appear to be active pathways for formation of the low molecular weight fractions
of the polymers formed with 1-5/MAO. Under otherwise identical polymerization conditions the catalyst
systems 2/MAO and 8/MAO had comparable productivities and gave polyethylene with very similar
molecular weight and molecular weight distributions, suggesting a potential role for binuclear species in
the catalyst systems 1-5/MAO.
imido compounds (general formula LnMdNR) also have an
established track record in Ziegler-Natta catalysis,11 including
non-cyclopentadienyl compounds of titanium27-33 and cyclo-
Introduction
Olefin polymerization catalysis continues to be an area of
considerable importance to both the academic and industrial
communities, and a wide range of cyclopentadienyl- and non-
cyclopentadienyl-based systems have been described.1-12 Of
particular relevance to this contribution are half-sandwich
compounds of titanium, which in general have a strong track
record in this area. The most notable of these are the constrained
geometry catalysts (CGC)5 and aryloxide, ketimide, guanidinate,
and phosphinimide compounds of the type CpRTi(X)R2 (CpR
) η-C5H5 or substituted cyclopentadienyl, X ) monoanionic
O- or N-donor, R ) Cl or alkyl).12-26 Early transition metal
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* Corresponding author. E-mail: philip.mountford@chem.ox.ac.uk.
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10.1021/om0608556 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/29/2006

84 Organometallics, Vol. 26, No. 1, 2007
Owen et al.
pentadienyl-supported group 5 compounds.34-38
Results and Discussion
Synthesis and Characterization of New Cyclopentadienyl
Titanium Imido Compounds. Mono(cyclopentadienyl) tita-
nium imido compounds have been known for over 20 years,49,50
the first examples being Teuben’s imido-bridged dimers Cp2-
i
t
Ti2(µ-NR)2Cl2 (R ) Et, Pr, Bu, Ph), prepared from CpTi-
(NHR)Cl2 and MeLi.51 Roesky showed that the corresponding
dehydrohalogenation reactions of CpRTi(NHtBu)Cl2 in the
presence of pyridine gave monomeric terminal imido derivatives
CpRTi(NtBu)Cl(py) (CpR ) C5Me5 (1) or C5H4SiMe3).52 We
subsequently prepared a number of monomeric and dimeric
mono(cyclopentadienyl) tert-butyl imido compounds, including
1, from the useful synthons Ti(NtBu)Cl2(L)n (L ) py or 4-tert-
butyl pyridine; n ) 2 or 3).53,54 Bulky cyclopentadienyl ring
substituents are necessary to reduce the likelihood of the
formation of imido-bridged dimers. For example, CpTi(NtBu)-
Cl(py) loses pyridine to form Cp2Ti2(µ-NtBu)2Cl2 on heating
in vacuo, whereas 1 is stable in this regard.54 To explore the
ethylene polymerization capability of cyclopentadienyl titanium
terminal imido compounds, we therefore focused on systems
containing η-C5Me5 (Cp*) ligands. The TACN- and TPM-
supported titanium imido catalyst systems I-R and II-R) require
bulky aryl imido ortho-substituents for higher productivities and
good control of molecular weight distributions. In addition to
determining the ethylene polymerization capability of 1, we
therefore targeted aryl imido compounds of the type Cp*Ti-
(NAr)Cl(py), where Ar is a successful substituent from our
previous studies of I-R and II-R.
The most productive transition metal imido precatalysts so
far reported are of the type Ti(TACN)(NR)Cl2 (I-R, TACN )
1,4,7-trimethyltriazacyclononane)29,33 and Ti(TPM)(NR)Cl2 (II-
R, TPM ) tris(3,5-dimethylpyrazolyl)methane).32 Compounds
t
i
with a bulky imido R-group (e.g., Bu, 2,6-C6H3 Pr2, 2-C6H4-
tBu) provided the best catalyst systems. As described else-
where,39-42 the compounds I-R and II-R are isolobal analogues
of the group 4 metallocenes CpR MCl2. By analogy with the
2
metallocene systems,2,7,43 the active species in ethylene polym-
erization catalysis by I-R and II-R upon activation with MAO
(methyl aluminoxanes) cocatalyst44 are likely to be cations of
the type “[Ti(fac-N3)(NR)R′]+” (fac-N3 ) TACN or TPM).
These cations are themselves isolobal analogues of the group 4
metallocenium species “CpR MR+”, and we have reported on
2
this aspect very recently.42
Conical six-electron donors such as TACN and TPM are
isolobal with the [C5R5]- anion.45 Replacing the fac-N3 donors
in [Ti(fac-N3)(NR)X]+ (X ) alkyl or halide) by cyclopentadi-
enide therefore gives CpRTi(NR)X, analogues of the rare earth
metallocenes CpR MR, themselves a rich source of reactivity
2
including polymerization catalysis.46 Jordan has previously
described a similar approach in which one of the cyclopenta-
dienide ligands of [CpR MMe]+ (M ) Ti, Zr, Hf) was replaced
2
by a dianionic dicarbollide ligand to give CpRM(η5-C2B9H11)-
Me, again analogues of the neutral rare earth metallocenes.47,48
In this contribution we describe the synthesis and ethylene
polymerization capability of a series of titanium cyclopentadi-
enyl-imido compounds Cp*Ti(NR)Cl(py) and some related
compounds.
Aryl imido titanium compounds are usually conveniently
accessed by tert-butyl imide/aniline exchange reactions.50,55,56
Since Cp*Ti(NtBu)Cl(py) is conveniently prepared in multigram
quantities,54 this was the route of choice. The syntheses of the
(33) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley, S.
R.; Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang,
B.; Wilson, P. J.; Zuideveld, M. A.; Blake, A. J.; Schro¨der, M.; Mountford,
P. Organometallics 2006, 25, 3888.
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16, 2500.
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Kohlmann, A.; Little, I. R.; Reed, W. Chem. Commun. 1998, 1673.
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L.; Ribeiro da Costa, M. H.; Mastroianni, S. J. Organomet. Chem. 1999,
591, 78.
(37) Feng, S.; Roof, G. R.; Chen, E. Y.-X. Organometallics 2002, 21,
832.
i
new compounds Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-
t
i
C6H3Br2 (3), 2-C6H4 Bu (4), and 2-C6H4 Pr (5)) are summarized
in eq 1. Thus heating solutions of 1 with 1 equiv of the desired
ArNH2 for 4 days at 80 °C in benzene gave the target
compounds in 30-65% isolated yields after recrystallization.
All four have been crystallographically characterized (see
below), and the solid-state structures are consistent with those
proposed in eq 1.
(38) Sato, Y.; Nakayama, Y.; Yasuda, H. J. Appl. Polym. Sci. 2005, 97,
1008.
(39) Williams, D. S.; Schofield, M. H.; Anhaus, J. T.; Schrock, R. R. J.
Am. Chem. Soc. 1990, 112, 6728.
The solution 1H and 13C NMR and other data are also
consistent with the proposed structures (see Experimental
(40) Glueck, D. S.; Green, J. C.; Michelman, R. I.; Wright, I. N.
Organometallics 1992, 11, 4221.
(49) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239.
(50) Mountford, P. Chem. Commun. 1997, 2127.
(51) Vroegop, C. T.; Teuben, J. H.; van Bolhuis, F.; van der Linden, J.
G. M. J. Chem. Soc., Chem. Commun. 1983, 550.
(52) Bai, Y.; Noltemeyer, M.; Roesky, H. W. Z. Naturforsch. 1991, 46b,
1357.
(41) Gibson, V. C. J. Chem. Soc., Dalton Trans. 1994, 1607.
(42) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley, A.
R.; Mountford, P. Organometallics 2006, 25, 2806.
(43) Jordan, R. F. AdV. Organomet. Chem. 1991, 32, 325.
(44) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391.
(45) Elian, M.; Chen, M. M. L.; Mingos, D. M. P.; Hoffmann, R. Inorg.
Chem. 1976, 15, 1148.
(53) Dunn, S. C.; Batsanov, A. S.; Mountford, P. J. Chem. Soc., Chem.
Commun. 1994, 2007.
(46) Hou, Z.; Wakatsuki, Y. Coord. Chem. ReV. 2002, 231, 1.
(47) Crowther, D. J.; Baenziger, N. C.; Jordan, R. F. J. Am. Chem. Soc.
1991, 113, 1455.
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2993.
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Trans. 1997, 293.
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Shishkin., O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
(56) Hazari, N.; Mountford, P. Acc. Chem. Res. 2005, 38, 839.

Cyclopentadienyl Titanium Imido Compounds
Organometallics, Vol. 26, No. 1, 2007 85
i
t
i
Figure 1. Molecular structures of Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3), 2-C6H4 Bu (4), and 2-C6H4 Pr (5)). Displacement
ellipsoids are drawn at the 25% probablility level. H atoms are omitted.
characterized, namely, Cp*Ti(NtBu)Cl(L) (L ) py (1, two
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
i
molecules in the asymmetric unit)52 and MeC(O)NMe2).57 The
general features of 2-5 are similar and comparable to that of
1. Each compound is one of a pair of enantiomers in the
centrosymmetric unit cell, and the metal centers achieve a 16
valence electron count through effectively linear imido ligands
(Ti-N-R > 160°). The Ti-C, Ti-Cl, and Ti-N distances
are all within the previously reported ranges for these types of
ligand.58,59 The aryl substituents adopt a common orientation,
namely, with the normal to the C6 ring plane being effectively
co-incident with the plane containing Ti(1), N(1), and the Cp*
ring centroid. For the monosubstituted aryl imides 4 and 5 the
ortho-substituents are oriented away from the pyridine ligand
on the Ti-Cl side of the molecule.
Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3),
t
i
2-C6H4 Bu (4), and 2-C6H4 Pr (5))a
parameter
Ti(1)-Cl(1)
Ti(1)-N(1)
Ti(1)-N(2)
Ti(1)-Cpcent
Cl(1)-Ti(1)-N(1) 106.58(5)
Cl(1)-Ti(1)-N(2) 94.54(5)
N(1)-Ti(1)-N(2)
2
3
4
5
2.3473(6)
1.7435(16) 1.753(2)
2.1739(17) 2.169(2)
2.3304(8)
2.3381(5)
1.7382(13) 1.7304(19)
2.1793(14) 2.1761(19)
2.3382(7)
2.069
2.056
2.062
2.056
108.03(7)
95.60(6)
103.65(9)
114.9
120.0
111.4
107.53(5)
97.67(4)
98.39(6)
115.3
122.3
111.6
106.86(7)
99.21(6)
98.65(8)
116.1
120.9
111.7
99.61(7)
Cpcent-Ti(1)-Cl(1) 113.8
Cpcent-Ti(1)-N(1) 125.8
Cpcent-Ti(1)-N(2) 111.3
Ti(1)-N(1)-C(1)
174.48(14) 162.38(19) 169.01(11) 170.85(16)
a Cpcent refers to the computed η-C5Me5 ring centroid in each case.
The TidNimide distances in 2-5 (range 1.7304(19)-1.753-
(2) Å) are significantly longer than in Cp*Ti(NtBu)Cl(L) (1.697
Å (av) for 1 and 1.702(2) Å) as is typically the case for aryl
imides in comparison with their tert-butyl imido homologues.
In contrast the Ti-Cl distances in 2-5 are shorter than in
Cp*Ti(NtBu)Cl(L) (2.356 Å (av) for 1 and 2.3697(6) Å), as
are the Ti-Npy (2.192 Å (av) for 1) distances. This is due to
the greater general labilizing effect of tert-butyl compared to
Section). The NMR spectra of each show resonances for η5-
coordinated C5Me5 ligands and an N-bound pyridine donor. The
prochiral isopropyl substituents in 2 give rise to a binomial septet
(integrating as 2 H per Cp* resonance) and two doublets (each
6 H per Cp*) for the methine and methyl groups, respectively.
This indicates free rotation of the N-aryl group on the NMR
time scale. The isopropyl group of 5 also appears as an apparent
septet (1 H per Cp*) and two doublets (each 3 H).
The X-ray structures of 2-5 have all been determined. The
molecular structures are illustrated in Figure 1, and selected bond
distances and angles are listed in Table 1. Two related tert-
butyl imido half-sandwich complexes have been structurally
(57) Kissounko, D. A.; Guzei, I. A.; Gellman, S. H.; Stahl, S. Organo-
metallics 2005, 24, 5208.
(58) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput.
Sci. 1996, 36, 746 (The United Kingdom Chemical Database Service).
(59) Allen, F. H.; Kennard, O. Chem. Des. Automation News 1993, 8, 1
and 31.

86 Organometallics, Vol. 26, No. 1, 2007
Owen et al.
aryl imides.49,55,58,59 Within the homologous series 2-5, there
is little variation in the metric parameters. The most significantly
different compound within the series is Cp*Ti(N-2,6-C6H3Br2)-
Cl(py) (3), which features the longest TidNimide distance and
the least linear TidNimide-Ar angle.
Surprisingly, attempts to prepare Cp*Ti(N-2-C6H4CF3)Cl(py)
(the ortho-CF3 analogue of 4 and 5) from H2N-2-C6H4CF3 and
1 according to the general method in eq 1 led to inseparable
mixtures. Since the TACN and TPM catalyst systems containing
this substituent were among the most productive at ambient
temperature, further efforts were made to prepare the target
cyclopentadienyl analogues.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Ti(N-2-C6H4CF3)Cl2(py)3 (6)a
Ti(1)-Cl(1)
Ti(1)-N(1)
2.3909(5)
1.730(2)
Ti(1)-N(2)
Ti(1)-N(3)
2.380(2)
2.2284(15)
Cl(1)-Ti(1)-Cl(1A) 164.64(3)
Cl(1)-Ti(1)-N(3)
88.27(4)
89.74(4)
97.45(4)
82.55(4)
165.34(15)
Cl(1)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(2)
N(1)-Ti(1)-N(2)
N(3)-Ti(1)-N(3A)
97.681(17) Cl(1)-Ti(1)-N(3A)
82.319(17) N(1)-Ti(1)-N(3)
180.00
165.10(8)
N(2)-Ti(1)-N(3)
Ti(1)-N(1)-C(1)
a Atoms carrying the suffix “A” are related to their counterparts by the
symmetry operator 1-x, y, 1/2-z.
Regrettably, reaction of 6 with LiCp* in THF again gave
inseparable mixtures. Further experiments showed that neither
2 nor 4 could be prepared from the analogous Ti(N-2,6-C6H3-
Compound 1 itself is readily prepared from Ti(NtBu)Cl2(py)3,
and so an analogous route to Cp*Ti(N-2-C6H4CF3)Cl(py) was
attempted. The desired starting material Ti(N-2-C6H4CF3)Cl2-
(py)3 (6) had not been previously reported and so was
synthesized in 67% yield by the stoichiometric reaction of H2N-
2-C6H4CF3 with Ti(NtBu)Cl2(py)3 (eq 2) according to a general
method we have described previously for other compounds of
the type Ti(NAr)Cl2(py)3.55
iPr2)Cl2(py)3 or Ti(N-2-C6H4 Bu)Cl2(py)2.28 Further attempts
to prepare Cp*Ti(N-2-C6H4CF3)Cl(py) were discontinued.
55
t
The NMR spectra of 6 are consistent with the structure shown
in eq 2, which has been confirmed by X-ray crystallography
(Figure 2, Table 2). Molecules of 6 lie across crystallographic
2-fold rotation axes (passing through N(1), Ti(1), N(2), and
C(10)), and because of this, the 2-C6H4CF3 ligand is positionally
disordered (see Experimental Section for further details). The
structure of 6 is analogous to the previously characterized
t
compounds Ti(NR)Cl2(py)3 (R ) Bu, Ph, 4-C6H4Me, and
4-C6H4NO2),55 and its TidNimide and Ti-Cl distances are
comparable to those of the aryl imido homologues. However,
the bending of the imido ligand (Ti(1)-N(1)-C(1) ) 165.10-
(8)°) is more pronounced in 6 than in these other examples,
and this is probably due to the steric demands of the ortho-CF3
substituent.
There is no evidence of pyridine loss from 2-5 (e.g., to form
dimeric species) under normal handling or drying in vacuo at
ambient temperature. However, reaction of 1 with 2-bromo-4-
methyl aniline gave the imido-bridged dimer Cp*2Ti2(µ-N-2-
Br-4-C6H3Me)2Cl2 (7) along with free pyridine and tBuNH2 (as
judged by NMR tube scale reactions in C6D6). The formation
of a dimeric, pyridine-free compound in this case is attributed
to the reduced steric protection at the TidNAr bond. Compound
7 was obtained as a mixture of two isomers, denoted 7A and
7B, in a ca. 2:1 ratio, respectively (eq 3). The exact ratio of 7A
and 7B changed slightly depending on the individual sample,
but did not change in solution on heating. We were not able to
obtain diffraction-quality crystals of 7A or 7B, and their
formulation as imido- rather than chloride-bridged dimers is
based on a number of crystallographically characterized litera-
ture precedents, CpR Ti2(µ-NR)2Cl2 (CpR ) C5H5 or substituted
2
cyclopentadienyl, R ) alkyl, aryl, or related).51,58-60
The 1H NMR spectra of 7 show two sets of 2-Br-4-C6H3Me
aryl ring protons in a ca. 2:1 ratio (for 7A and 7B, respectively).
While two corresponding singlets for the para-methyl groups
Figure 2. Molecular structure of Ti(N-2-C6H4CF3)Cl2(py)3 (6).
Displacement ellipsoids are drawn at the 25% probability level. H
atoms are omitted and only one orientation of the disordered 2-C6H4-
CF3 group is shown. Atoms carrying the suffix “A” are related to
their counterparts by the symmetry operator 1-x, y, 1/2-z.
(60) Abarca, A.; Martin, A.; Mena, M.; Yelamos, C. Angew. Chem., Int.
Ed. 2000, 39, 3460.

Cyclopentadienyl Titanium Imido Compounds
Organometallics, Vol. 26, No. 1, 2007 87
Table 3. Ethylene Polymerization Data for Cp*Ti(NtBu)Cl(py) (1), Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3),
i
t
i
i
2-C6H4 Bu (4), and 2-C6H4 Pr (5)), and Cp*2Ti2(µ-N-2,6-C6H3 Pr2)2Cl2 (8)a
precatalyst
loading
(µmol)
productivity
low molecular wt fraction
higher molecular wt fraction
duration
(min)
PE
yield (g)
(kg(PE) mol(Ti)-1
entry
precatalyst
h-1 bar-1
)
Mw
Mw/Mn
wt %b
Mw
Mw/Mn
wt %b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
1
1
1
60
60
40
20
60
60
60
60
60
60
60
60
60
60
60
60
20
10
10
10
2.5
10
10
2.5
10
2.5
10
2.5
10
2.5
10
5
4.70
1.82
1.18
0.40
1.27
0.22
1.26
0.46
1.02
0.74
1.24
0.96
1.12
1.10
1.73
1.88
39
30
35
24
85
4
21
20
21
50
21
64
19
73
29
30
5640
5930
6600
6650
39 000
3350
2.1
2.1
2.5
2.4
3.6
1.8
3.0
e
2.3
e
3.2
e
92
73
87
71
53
72
61
1 345 000
925 000
593 000
2.8
2.4
2.0
2.4
1.9d
3.6
2.7
2.8
2.6
5.9
2.7
2.9
2.8
3.2
2.0
1.5
8
27
13
29
47
28
39
e
28
e
47
e
711 000
1
2 310 000d
644 000
1c
2
6490
1 430 000
2 010 000
1 520 000
1 830 000
1 380 000
2 200 000
1 300 000
1 800 000
587 000
2
3
3
4
4
5
4390
5840
4550
72
53
82
2.2
e
2.3
2.4
18
e
8
5
2 f
8 f
8530
8990
92
96
298 000
4
b
a Conditions: 6 bar of C2H4, Al:Ti ) 1500, 250 mL of toluene, T0 ) 22-24 °C. For bimodal polymer samples “wt %” refers to relative amounts of the
c
d
e
two fractions. With 1500 equiv of AlMe3 added. Mw and Mw/Mn probably underestimated due to truncation of peaks at high Mw. No clear low molecular
f
weight fraction. The MAO used in these experiments was a more aged sample from the same batch as used in entries 1-14 (i.e., entry 15 is identical to
entry 7 in all other regards).67
are seen (relative integrals 6H and 3H), three Cp* methyl group
resonances are also evident, each integrating as 15 H with
respect to the para-methyl signals. These data suggest that the
dominant isomer (7A) has equivalent N-aryl groups but in-
equivalent Cp* rings, whereas the minor isomer (7B) has both
pairs of groups chemically equivalent. The two proposed
structures are illustrated in eq 3. Cs symmetric 7A has the two
ortho-Br substituents oriented “up” toward one Cp* ring,
whereas 7B (Ci symmetric) has them arranged in a mutually
anti arrangement across the molecular inversion center.
Ethylene Polymerization Studies. Ethylene polymerization
experiments on the monomeric precatalysts 1-5 were carried
out using MAO cocatalyst under comparable conditions to those
used for the ambient temperature studies of the TACN and TPM
systems I-R and II-R. Precatalyst samples were preactivated
with MAO (Al:Ti ratio ) 1500:1) for 30 min, and then ethylene
was admitted at 6 bar pressure for 1 h (unless otherwise stated)
at ambient temperature (see the Experimental Section for further
details). The results are summarized in Table 3.
Initial studies focused on the tert-butyl imido system Cp*Ti-
(NtBu)Cl(py) (1) (entries 1-6 in Table 3) to determine the
effects of different precatalyst loadings, polymerization time,
and added AlMe3 (TMA). In general, 1 (and the other precata-
lysts listed) has “moderate” productivities (namely, in the range
10-100 kg(PE) mol(Ti)-1 h-1 bar-1).6 Considering first the
productivities of 1/MAO it can be seen that at 20 and 10 µmol
loading of 1 in 250 mL of toluene ([Ti] ) 8 × 10-5 and 4 ×
10-5 M, respectively) the productivities are comparable (4.70
and 1.82 g of isolated PE, giving figures of merit 30 and 39
kg(PE) mol(Ti)-1 h-1 bar-1). The productivities at 10 µmol
loading at 20, 40, and 60 min polymerization times are again
comparable within experimental error and suggest that this
system continues to produce PE during the course of the entire
experiment. These experiments also show that, for PE yields
of up to ca. 4 g under these experimental conditions, mass
transport limitations do not have significant effects on the
productivity figures.
to mass transport limitations in the higher loading experiments.
Instead it may reflect the higher absolute concentrations of both
1 and the MAO cocatalyst (and the TMA that it contains, ca.
20 wt % based on aluminum). To assess the effect of free TMA
on the productivity of 1/MAO, a further experiment at 10 µmol
precatalyst loading was carried out (entry 6) in which 1500 equiv
of TMA was added to the polymerization mixture. This
experiment yielded only 0.22 g of PE (4 kg(PE) mol(Ti)-1 h-1
bar-1) compared to 1.82 g with no added TMA (entry 2, 30
kg(PE) mol(Ti)-1 h-1 bar-1). The decreased productivity is
attributed to binding of AlMe3 to the titanium centers of the
catalytically active species as observed previously.7,61 Addition-
ally, the higher productivities at the lower precatalyst loadings
(higher dilutions) might reflect reduced ion-pairing effects if
the active species are cationic.62
The aryl imido catalyst systems Cp*Ti(NAr)Cl(py)/MAO (Ar
i
t
) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3), 2-C6H4 Bu (4), and 2-C6H4-
iPr (5)) were first evaluated at 10 µmol precatalyst loadings
(Table 3, entries 7, 9, 11, 13). The productivities were all
comparable to that of 1/MAO under these conditions. The aryl
imido systems were also evaluated at 2.5 µmol precatalyst
loadings (Table 3, entries 8, 10, 12, 14) and, with the exception
of 2/MAO, showed an increase in productivity compared to the
10 µmol loading experiments. This is analogous to the results
found for 1/MAO (Table 3, entries 2 and 5). At the 2.5 µmol
loading level the productivities of the aryl imido systems 4/MAO
and 5/MAO were comparable to that of 1/MAO. The produc-
tivities of 2/MAO and 3/MAO were somewhat lower. These
results show that although the imido substituents have some
effect on the productivities of these systems, at least at the lower
concentrations, the differences are rather small in comparison
to the MAO-activated TACN and TPM systems I-R and II-
R.29,32,33 Furthermore, the productivities of the best of these
systems (ca. 1200 kg(PE) mol(Ti)-1 h-1 bar-1) are some 2
orders of magnitude greater than the best of the Cp*Ti(NR)-
Cl(py)/MAO systems under comparable conditions. Analogous
results were reported by Jordan for the carbollide systems
CpRM(η5-C2B9H11)Me (M ) Ti, Zr).47,48
Reducing the precatalyst loading of 1 to 2.5 µmol ([Ti] ) 1
× 10-5 M, all other parameters being the same) gave an increase
in productivity to 85 kg(PE) mol(Ti)-1 h-1 bar-1 (entry 6)
compared to those for the 20 and 10 µmol loading experiments
(entries 1 and 2). As established above, this is not attributable
(61) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 1634.
(62) D’Agnillo, L.; Soares, J. B. P.; Penlidis, A. Macromol. Chem. Phys.
1998, 199, 955.

88 Organometallics, Vol. 26, No. 1, 2007
Owen et al.
transfer processes. The soluble polymer formed with 1/MAO/
TMA (Table 3, entry 6) was almost exclusively terminated by
methyl end groups (ratio of saturated:unsaturated polyethylene
ca. 7:1), consistent with the greater degree of chain transfer to
aluminum expected in this case.
GPC analysis of the polymers formed with the aryl imido
systems 2-5/MAO at 10 µmol precatalyst loading showed
analogous features to that of 1/MAO, as readily seen from the
chromatograms (Figure 4) and entries 7, 9, 11, and 13 in Table
3. The relative proportions of low and high molecular weight
polymer components varied with imido N-substituent from 53
(4/MAO) to 82 wt % (5/MAO). 1H NMR analysis of the soluble
portion of the polymer for 5/MAO again showed a mixture of
saturated and unsaturated end groups (saturated:unsaturated
polyethylene ca. 3:2; PDI ) 3.2). The chromatograms for the
polymer formed with 2/MAO and 4/MAO clearly show that
the low molecular weight components are comprised of two
overlapping bands, consistent with two types of chain transfer
mechanism. As was the case for the 1/MAO catalyst system,
reducing the precatalyst loading for 2-5/MAO to 2.5 µmol gave
a change in molecular weight distributions. Unlike the 1/MAO
system, however, the aryl imido systems formed polymer with
only a well-defined high molecular weight component (Table
3, entries 8, 10, 12, 14) with PDIs in the range 2.8-5.9. In
each of the systems 1-5/MAO, the molecular weight of the
polymer formed with a 2.5 µmol precatalyst loading was
significantly higher than that obtained at the 10 µmol level. The
increased molecular weights at higher dilution (of both the imido
precatalyst and MAO cocatalyst) may tentatively be attributed
to reduced chain transfer to aluminum.
Figure 3. Molecular weight distributions determined by GPC for
the polyethylenes produced by Cp*Ti(NtBu)Cl(py)/MAO (1/MAO)
at the various precatayst loadings indicated.
The polyethylenes produced by the new catalyst systems were
analyzed by GPC. Selected chromatograms are given in Figures
3 and 4, and the data are summarized in Table 3. The molecular
weights and distributions all show a dependence on the imido
N-substituent and catalyst loading. We consider first the Cp*Ti-
(NtBu)Cl(py) (1)/MAO catalyst systems (Table 3, entries 1-6;
Figure 3). At 20 µmol precatalyst loading the polymer has one
dominant low molecular weight fraction (Mw ) 5640 g mol-1
,
92 wt % of total polymer) with a narrow polydispersity index
(PDI, Mw/Mn) of 2.1. The narrow PDI is consistent with a single-
site catalyst undergoing chain transfer processes, for which the
Schultz-Flory distribution predicts a PDI of 2.0.63 The Mn for
this fraction (2690 g mol-1) indicates that ca. 80 polymer chains
per precatalyst metal center are formed. In addition to the low
molecular weight fraction there is a higher molecular weight
one (Mw ) 1 345 000) with a broader PDI of 2.8, which is also
consistent with single-site type behavior. As the precatalyst
loading is decreased (Table 3, entries 2 and 5; Figure 3), the
bimodal nature of the molecular weight distributions become
more pronounced, with the lower molecular weight fraction
composing only 53 wt % of the total polymer at 2.5 µmol
loading of 1.
The polyethylenes produced by the 1-5/MAO catalyst
systems contrast with those formed with MAO-activated TACN
and TPM systems I-R and II-R.29,32,33 In these cases the highly
active systems produced only unimodal polyethylene with
molecular weights 300 000-2 250 000 g mol-1 and polydis-
persities generally in the range 2.4-4.8. The origins of the
differing behavior are not clear at this time, and it is not
appropriate to speculate further.
Monomeric or Dimeric Precatalysts/Active Species? Previ-
ous reports have shown that imido-bridged binuclear titanium
complexes can act as ethylene polymerization precatalysts.30,31
The ready formation of Cp*2Ti2(µ-N-2-Br-4-C6H3Me)2Cl2 (7)
and related dimers in the literature prompted us to determine
under what conditions the monomeric compounds Cp*Ti(NR)-
Cl(py) (1-5) might be induced to form dimeric analogues. It
has been reported before that compound 1 does not lose pyridine
on heating under dynamic vacuum.54 However, MAO contains
numerous Lewis acidic sites that would be expected to abstract
pyridine from Cp*Ti(NR)Cl(py), which could subsequently form
the corresponding Cp*2Ti2(µ-NR)2Cl2 as the “true” catalyst
precursors. The Lewis acid BArF3 (ArF ) C6F5)64 has previously
been used as an effective pyridine-abstracting agent to form
low-coordinate titanium imido compounds65 and so was em-
ployed as a model Lewis acid in studies of 1 and 2.
GPC analysis of the polymer formed (10 µmol loading of 1)
after 20 and 40 min (Table 3, entries 3 and 4) showed no
significant or systematic variation in the proportion of high and
low molecular weight fractions. Interestingly, the proportion of
high and low molecular weight polymer formed with 1/MAO
in the presence of an excess of TMA (Table 3, entry 6) was not
significantly different from that formed with MAO alone (entry
2) under otherwise identical conditions, despite the very different
productivities (4 and 30 kg(PE) mol-1(Ti) h-1 bar-1, respec-
tively). However, the molecular weights of the high and low
molecular fractions were somewhat lower in the presence of
TMA, as would be expected if chain transfer to aluminum is
important in these systems. 1H NMR analysis (1,2-C6D4Cl2, 100
°C) of the soluble part of the polymer formed with 1/MAO (10
µmol loading, Table 3, entry 2) confirmed the product as linear
polyethylene with a mixture of saturated (methyl) and unsatur-
ated (vinyl, -CHdCH2) end groups. The ratio of saturated:
unsaturated polyethylene was ca. 3:1, showing that although
the low molecular weight fraction (73 wt %) has a relatively
narrow PDI (2.1), it contains polymer formed by two chain
Addition of BArF3 (1 equiv) to an NMR tube sample of 1 in
C6D6 formed the adduct py‚BArF 65 and a new compound whose
3
tBu and Cp* resonances were shifted from those of 1. It is not
clear if this compound is the binuclear species Cp*2Ti2(µ-N-
tBu)2Cl2 or monomeric Cp*Ti(NtBu)Cl, analogous to the previ-
ously described42 [Ti(TACN)(NtBu)Cl]+ (which also readily
(64) Piers, W. E. AdV. Organomet. Chem. 2005, 52, 1.
(65) Blake, A. J.; Collier, P. E.; Gade, L. H.; Mountford, P.; Lloyd, J.;
Pugh, S. M.; Schubart, M.; Skinner, M. E. G.; Tro¨sch, J. M. Inorg. Chem.
2001, 40, 870.
(63) Flory, P. J. Principles of Polymer Chemistry; Cornell University
Press: Ithaca, NY, 1992.

Cyclopentadienyl Titanium Imido Compounds
Organometallics, Vol. 26, No. 1, 2007 89
Figure 4. Molecular weight distributions determined by GPC for the polyethylenes produced by MAO-activated Cp*Ti(NtBu)Cl(py) (1)
i
t
i
and Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3), 2-C6H4 Bu (4), and 2-C6H4 Pr (5)) at 10 µmol precatalyst loadings.
forms a crystallographically characterized pyridine adduct).
Attempts to isolate “Cp*Ti(NtBu)Cl” on a preparative scale were
unsuccessful, as was the case for [Ti(TACN)(NtBu)Cl]+.
A similar structure was postulated for the phenyl imido-bridged
dication [Ti2(TACN)2(µ-NPh)2Cl2]2+, which could be isolated
as its [BArF ]- salt (unlike the tert-butyl imido species [Ti-
4
(TACN)(NtBu)Cl]+).66
The ethylene polymerization capabilities of Cp*Ti(N-2,6-
i
i
C6H3 Pr2)Cl(py) (2) and Cp*2Ti2(µ-N-2,6-C6H3 Pr2)2Cl2 (8) were
evaluated at 10 µmol precatalyst loading (based on Ti centers)
with an Al:Ti ratio of 1,500:1. The results given in Table 3
(entries 15 and 16) show that under otherwise identical
experimental conditions the productivities of 2/MAO and
8/MAO are very similar.67 The polymer molecular weights and
their distributions are also highly analogous, therefore indicating
that 2/MAO and 8/MAO both ultimately give rise to the same
catalyst system, each producing ca. 45 polymer chains (low
molecular weight fraction) per titanium center present.
The corresponding reaction of 2 (as a representative aryl
imido compound) with BArF was carried out in C6D6. The
3
adduct py‚BArF was again formed, along with a sparingly
3
soluble brown powder (8). Attempts to obtain pure samples of
8 from the preparative scale reaction of 2 with BArF were
Experimental Section
3
unsuccessful, but heating a sample of 2 at 200 °C under 1 ×
10-5 mbar dynamic vacuum for 2 h gave 8 in 92% yield (eq
4). Attempts to obtain a pyridine-free derivative of 1 by this
method (i.e., “Cp*Ti(NtBu)Cl”) gave a complex mixture of
products by NMR spectroscopy.
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon or of dinitrogen. Protio- and deutero-
solvents were predried over activated 4 Å molecular sieves and
were refluxed over the appropriate drying agent, distilled, and stored
under dinitrogen in Teflon valve ampules. NMR samples were
prepared under dinitrogen in 5 mm Wilmad 507-PP tubes fitted
Although 8 has low solubility in C6D6, it dissolves adequately
1
in CD2Cl2. The H and 13C NMR spectra showed resonances
i
1
with J. Young Teflon valves. H, 13C{1H}, and 19F NMR spectra
for a single Cp* and 2,6-C6H3 Pr2 environment and none for
pyridine. The EI mass spectrum showed a molecular ion
were recorded on Varian Mercury-VX 300 and Varian Unity Plus
1
500 spectrometers. H and 13C assignments were confirmed when
centered at m/z ) 786 with the correct isotope distribution for
i
necessary with the use of DEPT-135, DEPT-90, and two-
a dimeric species Cp*2Ti2(µ-N-2,6-C6H3 Pr2)2Cl2. The relatively
1
1
dimensional H-1H and 13C-1H NMR experiments. H and 13C
spectra were referenced internally to residual protio-solvent (1H)
or solvent (13C) resonances and are reported relative to tetrameth-
ylsilane (δ ) 0 ppm). 19F spectra were referenced externally to
low solubility of 8 is consistent with it possessing a symmetrical,
dimeric structure. The structure proposed for 8 (see eq 4) has
molecular C2h symmetry with mutually trans Cp* ligands. In
accord with this, the chemically equivalent isopropyl substituents
give rise to a single methine resonance (septet, integral 2 H
with respect to that for each Cp*) but two methyl resonances
(doublets, each of relative integral 6 H). Alternative structures
with mutually cis Cp* groups and/or bridging chloride ligands
would be inconsistent with these data. The proposed structure
is also analogous to those determined crystallographically for
Cp2Ti2(µ-NPh)2Cl251 and Cp*2Ti2(µ-N-2,4,6-C6H2Me3)2Me2.60
(66) Bolton, P. D.; Adams, N.; Clot, E.; Cowley, A. R.; Wilson, P. J.;
Schro¨der, M.; Mountford, P. Organometallics 2006, 25, 5549.
(67) It should be noted that the MAO used in entries 15 and 16 was a
more aged sample (but from the same batch) than that used in entries 1-14
(and in particular entry 7). An even more pronounced beneficial effect of
aging of MAO on catalyst performance has been noted by Jordan and co-
workers: Murtuza, S.; Casagrande, O. L.; Jordan, R. F. Organometallics
2002, 21, 1882.

90 Organometallics, Vol. 26, No. 1, 2007
Owen et al.
t
3
4
CFCl3. Chemical shifts are quoted in δ (ppm) and coupling
constants in hertz. Infrared spectra were prepared as Nujol mulls
between KBr or NaCl plates and were recorded on Perkin-Elmer
1600 and 1710 series FTIR spectrometers. Infrared data are quoted
in wavenumbers (cm-1). Mass spectra were recorded by the mass
spectrometry service of Oxford University’s Department of Chem-
istry. Elemental analyses were carried out by the Elemental Analysis
Service of the Inorganic Chemistry Laboratory, University of
Oxford, or at London Metropolitan University. GPC analyses were
carried out by Rapra Technology Ltd. in 1,2,4-trichlorobenzene
solvent at 160 °C relative to polystyrene calibrants and using the
appropriate Mark Houwink parameters for polyethylene.
6-C6H4 Bu), 7.30 (app td, app J ) 7.8 Hz, J ) 1.3 Hz, 1 H,
t
5-C6H4 Bu), 6.89 (ddd, 3J ) 7.8, 7.8 Hz, 4J ) 2.1 Hz, 1 H, 4-C6H4-
tBu), 6.60 (br app s, 1 H, p-NC5H5), 6.23 (br app s, 1 H, m-NC5H5),
1.94 (s, 15 H, C5Me5), 1.75 (s, 9 H, CMe3). 13C{1H} NMR (C6D6,
t
125.7 MHz, 293K): 159.1 (1-C6H4 Bu), 150.1 (o-NC5H5), 142.0
(2-C6H4 Bu), 139.3 (p-NC5H5), 130.4 (3-C6H4 Bu), 126.4 (6-C6H4-
tBu), 125.8 (5-C6H4 Bu), 124.2 (m-NC5H5), 121.4 (C5Me5), 121.2
t
t
t
t
(4-C6H4 Bu), 35.9 (CMe3), 30.4 (CMe3), 11.8 (C5Me5). IR (KBr
plates, Nujol mull, cm-1): 1608 (w), 1305 (s), 1263 (m), 1100
(br, s), 1018 (br, s), 961 (m), 799 (s), 747 (m), 699 (m), 464 (w).
FIMS: m/z 364.9 [M - py]+ (75%). Anal. Found (calcd for C25H33-
ClN2Ti): C 67.4 (67.5), H 7.6 (7.5), N 6.2 (6.3).
Literature Preparations. The compounds Ti(NtBu)Cl2(py)3 and
Cp*Ti(NtBu)Cl(py) (1) were prepared according to published
methods.54,55 MAO was kindly provided by Albermarle. LiCp* was
prepared by treating Cp*H68 with n-butyllithium in cold hexanes.
All other compounds and reagents were purchased from commercial
chemical suppliers and used without further purification, with the
exception of the variety of substituted anilines, which were dried
over calcium hydride and degassed prior to use.
i
Cp*Ti(N-2-C6H4 Pr)Cl(py) (5). Prepared by analogy to 2.
1
Yield: 0.61 g (52%). H NMR (C6D6, 299.8 MHz, 293 K): 8.45
(br s, 2 H, o-NC5H5), 7.21-7.11 (overlapping m, 3 H, 3-, 5-, and
i
i
6-C6H4 Pr), 6.89 (app t, app 3J ) 7.3 Hz, 1 H, 4-C6H4 Pr), 6.73 (br
app s, 1 H, p-NC5H5), 6.40 (br app s, 2 H, m-NC5H5), 4.20 (sep, 3J
3
) 6.8 Hz, 1 H, CHMe2), 1.92 (s, 15 H, C5Me5), 1.35 (d, J ) 7.1
Hz, 6 H, CHMe2). 13C{1H} NMR (C6D6, 75.4 MHz, 293K): 158.0
i
i
(1-C6H4 Pr), 150.4 (o-NC5H5), 143.7 (2-C6H4 Pr), 137.7 (p-NC5H5),
125.6, 125.4 and 125.2 (3-, 5-, and 6-C6H4 Pr), 124.0 (m-NC5H5),
121.4 (C5Me5), 121.3 (4-C6H4 Pr), 28.1 (CHMe2), 23.9 (CHMe2),
11.8 (C5Me5). IR (KBr plates, Nujol mull, cm-1): 1605 (w), 1311
(s), 1261 (s), 1086 (br, s), 1026 (br, s), 971 (m), 800 (s), 691 (m),
448 (m). FIMS: m/z 387.1 [M - Pr]+ (1%), 79.0 [NC5H5]+
(100%). Anal. Found (calcd for C24H31ClN2Ti): C 64.7 (66.9), H
7.1 (7.3), N 6.3 (6.5). A satisfactory %C analysis could not be
obtained.
Cp*Ti(N-2,6-C6H3 Pr2)Cl(py) (2). A solution of Cp*Ti(NtBu)-
i
i
Cl(py) (1, 1.00 g, 2.71 mmol) in C6H6 (30 mL) was made up and
i
transferred to a thick walled ampule. To this was added H2N-2,6-
i
C6H3 Pr2 (0.511 mL, 2.71 mmol) under an N2 atmosphere in a dry
box. The reaction mixture was stirred, degassed via freeze pump
thawing, and then heated at 80 °C for 4 days. The color of the
solution was observed to deepen from cherry red to dark brown.
The volatiles were then removed under reduced pressure, furnishing
a brown solid. This was subsequently dissolved in the minimum
amount of CH2Cl2/pentane and stored at -80 °C for one week. A
quantity of dark brown powder precipitated, from which the
i
Ti(N-2-C6H4CF3)Cl2(py)3 (6). To a stirred solution of Ti(N-
tBu)Cl2(py)3 (1.00 g, 2.34 mmol) in CH2Cl2 (25 mL) was added
H2N-2-C6H4CF3 (0.291 mL, 2.34 mmol). The reaction mixture was
transferred to a thick walled Rotaflow ampule, degassed via freeze
pump thawing, and heated at 40 °C for 16 h. The solution was
then filtered and concentrated under reduced pressure until saturated.
Hexane (30 mL) was added until the microcrystalline product
precipitated out of solution. The supernatant was then filtered away
and the yellow-brown solid washed with hexane (1 × 20 mL).
Yield: 0.81 g (67%). 1H NMR (CDCl3, 299.9 MHz, 293 K): 9.07
1
supernatant was removed by filtration. Yield: 0.74 g (63%). H
3
NMR (CD2Cl2, 499.9 MHz, 293 K): 8.71 (d, J ) 5.0 Hz, 2 H,
o-NC5H5), 7.95 (t, 3J ) 7.6 Hz, 1 H, p-NC5H5), 7.55 (app t, app 3J
i
) 4.8 Hz, 2 H, m-NC5H5), 6.87 (d, 3J ) 7.5 Hz, 2 H, 3-C6H3 Pr2),
i
6.68 (t, 3J ) 7.5 Hz, 1 H, 4-C6H3 Pr2), 3.51 (app sept, app 3J ) 6.8
3
Hz, 2 H, CHMe2), 1.90 (s, 15 H, C5Me5), 1.21 (d, J ) 6.8 Hz, 6
3
H, CHMe2), 1.08 (d, J ) 6.8 Hz, 6 H, CHMe2). 13C{1H} NMR
i
(CD2Cl2, 125.7 MHz, 293 K): 155.0 (1-C6H3 Pr2), 150.7 (o-NC5H5),
3
(d, J ) 5.6 Hz, 4 H, o-NC5H5 cis to imide), 8.65 (br s, 2 H,
i
143.8 (2-C6H3 Pr2), 140.0 (p-NC5H5), 125.6 (m-NC5H5), 122.3 (C5-
o-NC5H5 trans to imide), 7.77 (t, 3J ) 7.3 Hz, 2 H, p-NC5H5 cis),
7.62 (br s, 1 H, p-NC5H5 trans), 7.32 (app t, app 3J ) 6.5 Hz, 4 H,
m-NC5H5 cis), 7.29-7.11 (overlapping m, 5 H, 3-, 4-, and 6-C6H4-
i
i
Me5), 122.1 (3-C6H3 Pr2), 120.6 (4-C6H3 Pr2), 28.0 (CHMe2), 24.6
(CHMe2), 24.4 (CHMe2), 11.8 (C5Me5). IR (KBr plates, Nujol mull,
cm-1): 1605 (s), 1327 (m), 1273 (s), 1216 (w), 1099 (br, s), 1015
(br, s), 963 (m), 800 (br, s), 757 (s), 697 (s), 641 (m), 460 (w), 441
(m). FIMS: m/z 393.0 [M - py]+ (70%), 135.1 [C5Me5]+ (5%),
79.0 [NC5H5]+ (5%). Anal. Found (calcd for C27H37ClN2Ti): C
68.7 (68.6), H 7.8 (7.9), N 5.8 (5.9).
3
CF3 and p-NC5H5 trans), 6.73 (t, J ) 7.6 Hz, 1 H, 5-C6H4CF3).
13C{1H} NMR (CDCl3, 75.4 MHz, 293 K): 155.4 (1-C6H4CF3),
151.5 (o-NC5H5 cis), 150.3 (br, o-NC5H5 trans), 138.8 (p-NC5H5
cis), 136.7 (p-NC5H5 trans), 131.7 (4-C6H4CF3), 130.1 (6-C6H4-
CF3), 124.8 (q, 3JC-F ) 5.4 Hz, 3-C6H4CF3), 124.2 (m-NC5H5 cis),
123.7 (m-NC5H5 trans), 123.7 (q, 2JC-F ) 272.9 Hz, 2-C6H4CF3),
121.0 (5-C6H4CF3). 13C{19F} NMR data (CDCl3, 75.4 MHz, 293
K): 360.0 (C6H4CF3), other resonances observed between 156 and
120 ppm. 19F NMR (CDCl3, 282.1 MHz, 293 K): -61.2 (CF3). IR
(KBr plates, Nujol mull, cm-1): 1606 (w), 1331 (m), 1304 (w),
1260 (s), 1094 (br, s), 1015 (br, s), 799 (s), 150 (w), 690 (m).
FIMS: m/z 161.1 [H2N-2-C6H4CF3]+ (10%), 79.0 [NC5H5]+
(100%). Anal. Found (calcd for C22H19Cl2F3N4Ti): C 51.0 (51.3),
H 3.8 (3.7), N 10.8 (10.9).
Cp*Ti(N-2,6-C6H3Br2)Cl(py) (3). Prepared by analogy to 2.
1
Yield: 0.46 g (31%). H NMR (C6D6, 499.9 MHz, 293 K): 8.87
(d, 3J ) 5.1 Hz, 2 H, o-NC5H5), 7.27 (d, 3J ) 8.1 Hz, 2 H, 3-C6H3-
3
3
Br2), 6.46 (t, J ) 6.3 Hz, 1 H, p-NC5H5), 6.35 (app t, app J )
3
6.3 Hz, 2 H, m-NC5H5), 5.99 (t, J ) 8.1 Hz, 1 H, 4-C6H3Br2),
1.95 (s, 15 H, C5Me5). 13C{1H} NMR (C6D6, 125.7 MHz, 293 K):
154.0 (1-C6H3Br2), 151.6 (o-NC5H5), 138.7 (p-NC5H5), 131.8 (3-
C6H3Br2), 124.1 (m-NC5H5), 123.5 (C5Me5), 120.8 (4-C6H3Br2),
119.4 (2-C6H3Br2), 12.2 (C5Me5). IR (KBr plates, Nujol mull, cm-1):
1605 (s), 1260 (s), 1218 (w), 1071 (br, s), 953 (s), 800 (br, s),
753 (s), 722 (s), 694 (s), 645 (w), 559 (w), 459 (w). FIMS: m/z
334.7 [M - py - C5Me5]+ (100%), 251.1 [H2N-2,6-C6H3Br2]+
(20%), 135.1 [C5Me5]+ (5%), 79.1 [NC5H5]+ (15%). Anal. Found
(calcd for C21H23Br2ClN2Ti): C 45.9 (46.2), H 4.4 (4.2), N 4.9
(5.1).
Cp*2Ti2(µ-N-2-Br-4-C6H3Me)2Cl2 (7). A solution of Ti(η-C5-
Me5)(NtBu)Cl(py) (1, 1.00 g, 2.71 mmol) in C6H6 (30 mL) was
made up and transferred to a thick walled ampule. To this was
added a solution of H2N-2-Br-4-C6H3Me (0.336 mL, 2.71 mmol)
in C6H6 (15 mL). The reaction mixture was stirred, degassed via
freeze pump thawing, and heated at 80 °C for 4 days. The color of
the solution deepened from cherry red to deep red-brown. The
volatiles were then removed under reduced pressure, yielding an
impure brown solid. This was subsequently dissolved in the
minimum amount of CH2Cl2/hexane and stored at -80 °C for one
week. A quantity of red-brown powder was precipitated, from which
t
Cp*Ti(N-2-C6H4 Bu)Cl(py) (4). Prepared by analogy to 2.
1
Yield: 0.38 g (31%). H NMR (C6D6, 499.9 MHz, 293 K): 8.39
3
3
4
(d, J ) 4.6 Hz, 2 H, o-NC5H5), 7.32 (dd, J ) 7.8 Hz, J ) 1.3
t
3
4
Hz, 1 H, 3-C6H4 Bu), 7.26 (dd, J ) 7.8 Hz, J ) 2.1 Hz, 1 H,
(68) Kohl, F. X.; Jutzi, P. J. Organomet. Chem. 1983, 243, 119.

Cyclopentadienyl Titanium Imido Compounds
Organometallics, Vol. 26, No. 1, 2007 91
i
Table 4. X-ray Data Collection and Processing Parameters for Cp*Ti(NAr)Cl(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3),
t
i
2-C6H4 Bu (4), and 2-C6H4 Pr (5)) and Ti(N-2-C6H4CF3)Cl2(py)3 (6)
2
3
4
5
6
formula
fw
cryst syst
space group
a/Å
C27H37ClN2Ti
472.96
orthorhombic
Pbca
17.7428(2)
13.2892(2)
21.3972(3)
90
C21H23Br2ClN2Ti
546.59
triclinic
C25H33ClN2Ti
444.90
triclinic
P1h
8.4499(2)
11.7126(2)
13.6175(3)
70.3832(9)
81.1385(9)
70.9648(10)
1198.58(4)
2
C24H31ClN2Ti
430.88
triclinic
C22H19Cl2F3N4Ti
515.22
monoclinic
C2/c
12.4719(4)
19.5247(8)
9.6046(3)
90
93.795(2)
90
2333.69(14)
2
0.637
9008
0.0311
P1h
P1h
8.6809(2)
9.7070(3)
13.8311(5)
97.8878(12)
90.4074(12)
111.1461(14)
1074.70(6)
2
8.3636(2)
11.5408(3)
12.7908(4)
75.1960(9)
82.9984(10)
74.2354(12)
1146.89(5)
2
b/Å
c/Å
R/deg
â/deg
90
90
γ/deg
V/Å3
5045.19(12)
8
0.462
11 476
0.0359
0.0410
Z
µ/mm-1
total no. of reflns
4.249
18 043
0.0331
0.0387
0.481
17 408
0.0349
0.0405
0.501
19 884
0.0368
0.0391
a
R indices R1, Rw
[I > 3σ(I)]
R1 )
Rw
)
0.0324
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; Rw ) x{∑w(|Fo| - |Fc|)2/∑(w|Fo| )}.
the supernatant was removed by filtration. The above recrystalli-
zation process was then repeated to obtain clean product. Yield:
0.19 g (17%). H NMR (C6D6, 499.9 MHz, 293 K) isomer 7A:
60 min, the reactor was isolated and the pressure was released.
Methanol (5 mL) was added to the mixture, followed by water (50
mL) with stirring. The mixture was acidified to pH ) 1 using a
solution of 10% HCl(aq) in MeOH and stirred overnight. The
precipitated polymers were filtered, washed with water (total volume
ca. 1000 mL), and dried to constant weight at room temperature.
Crystal Structure Determinations of Cp*Ti(NAr)Cl(py) (Ar
) 2,6-C6H3iPr2 (2), 2,6-C6H3Br2 (3), 2-C6H4tBu (4), and 2-C6H4iPr
(5)) and Ti(N-2-C6H4CF3)Cl2(py)3 (6). Crystal data collection and
processing parameters are given in Table 4. Crystals were immersed
in a film of perfluoropolyether oil on a glass fiber and transferred
to an Enraf-Nonius Kappa-CCD diffractometer equipped with an
Oxford Cryosystems low-temperature device.69 Data were collected
at low temperature using Mo KR radiation; equivalent reflections
were merged, and the images were processed with the DENZO
and SCALEPACK programs.70 Corrections for Lorentz-polariza-
tion effects and absorption were performed, and the structures were
solved by direct methods using SIR92.71 Subsequent difference
Fourier syntheses revealed the positions of all other non-hydrogen
atoms, and hydrogen atoms were placed geometrically. Crystal-
lographic calculations were performed using SIR9271 and CRYS-
TALS.72
For 2 the thermal parameters of the pyridyl C atoms were
unusually large, suggesting that this group has a pronounced
librational motion about an axis perpendicular to the plane of the
ring. For 4 the large thermal parameters of the Cp* and to some
extent the pyridyl ligands suggest that the librational motion of
these groups is also facile.
Molecules of 6 (refined in the space group C2/c) lie across
crystallographic 2-fold axes on which Ti(1), N(1), N(2), and C(10)
are situated. This necessarily results in disorder of the 2-C6H4CF3
group, as this cannot possess internal 2-fold symmetry. Nonetheless,
all non-H atoms of 6 were satisfactorily refined anisotropically.
An attempt was also made to refine the structure in the space group
Cc, in which the 2-fold axis that causes the disorder is not present.
However, the disorder of the C6H4CF3 group was still clearly
apparent in Fourier maps, and attempts to refine the structure failed
to converge, confirming the original assignment of symmetry
Details of the structure solution and refinements are given in
the Supporting Information (CIF data). A full listing of atomic
coordinates, bond lengths and angles, and displacement parameters
1
3
4
7.62 (d, J ) 8.3 Hz, 2 H, 6-C6H3BrMe), 7.28 (d, J ) 1.2 Hz, 2
4
H, 3-C6H3BrMe), 6.72 (dd, J ) 2.2, 8.2 Hz, 2 H, 5-C6H3BrMe),
1.88 (s, 6 H, C6H3Br{CH3}), 1.85 (s, 15 H, C5Me5), 1.82 (s, 15 H,
C5Me5); isomer 7B: 8.16 (d, 3J ) 8.3 Hz, 2 H, 6-C6H3BrMe), 7.33
4
4
(d, J ) 1.2 Hz, 2 H, 3-C6H3BrMe), 6.81 (dd, J ) 1.5, 8.3 Hz, 2
H, 5-C6H3BrMe), 1.89 (s, 6 H, C6H3Br{CH3}), 1.86 (s, 30 H,
C5Me5). 13C{1H} NMR (C6D6, 125.7 MHz, 293 K) isomer A: 153.0
(1-C6H3BrMe), 135.4 (2-C6H3BrMe ipso to bromo), 134.4 (3-C6H3-
BrMe), 129.9 (C5Me5), 127.6 (C5Me5), 127.4 (5-C6H3BrMe), 125.7
(6-C6H3BrMe), 118.4 (4-C6H3BrMe), 20.1 (C6H3Br{CH3}), 12.1
(C5Me5), 12.0 (C5Me5); isomer B: 133.7 (3-C6H3BrMe), 127.9 (5-
C6H3BrMe), 125.5 (6-C6H3BrMe), 128.8 (C5Me5), 20.1 (C6H3Br-
{CH3}), 12.0 (C5Me5). Resonances for three aromatic quaternary
carbons not resolved. IR (KBr plates, Nujol mull, cm-1): 2895
(s), 2281 (w), 1599 (m), 1504 (w), 1270 (s), 1230 (w), 1110 (w),
1069 (w), 1010 (m), 962 (w), 797 (w), 755 (s), 715 (s), 696 (s),
520 (w), 482 (w). Anal. Found (calcd for C34H42Br2Cl2N2Ti2): C
50.2 (50.7), H 5.1 (5.3), N 3.5 (3.5).
i
Cp*2Ti2(µ-N-2,6-C6H3 Pr2)2Cl2 (8). A sublimation tube was
i
loaded with Cp*Ti(N-2,6-C6H3 Pr2)Cl(py) (2, 1.00 g, 2.11 mmol)
and heated at 200 °C under dynamic vacuum (1 × 10-5 mbar) for
1
2 h to yield 8 as a brown powder. Yield: 0.77 g (92%). H NMR
(CD2Cl2, 499.9 MHz, 293 K): 6.92 (d, 3J ) 7.6 Hz, 4 H, 3-C6H3-
3
i
3
iPr2), 6.76 (t, J ) 7.6 Hz, 2 H, 4-C6H3 Pr2), 3.19 (sept, J ) 6.8
Hz, 4 H, CHMe2), 2.05 (s, 30 H, C5Me5), 1.27 (d, 3J ) 6.8 Hz, 12
H, CHMe2), 1.10 (d, J ) 6.8 Hz, 12 H, CHMe2). 13C{1H} NMR
3
i
(CD2Cl2, 125.7 MHz, 293 K): 144.3 (2-C6H3 Pr2), 125.5 (C5Me5),
122.5 (3-C6H3iPr2), 121.6 (4-C6H3iPr2), 28.1 (CHMe2), 25.4 (CHMe2),
i
23.8 (CHMe2), 12.2 (C5Me5), the 1-C6H3 Pr2 resonance was not
resolved. IR (NaCl plates, Nujol mull, cm-1): 1325 (s), 1277 (s),
1100 (m), 1024 (w), 969 (w), 795 (m), 742 (s), 729 (s), 699 (m).
EIMS: m/z ) 786.0 [M]+ (50%), 743.1 [M - Pr]+ (10%), 652.1
i
i
[M - C5Me5]+ (10%), 393.0 [Ti(η-C5Me5)(N-2,6-C6H3 Pr2)Cl]+
(100%). Anal. Found (calcd for C44H64Cl2N2Ti2): C 63.4 (67.1),
H 8.4 (8.2), N 3.2 (3.6). A satisfactory %C analysis could not be
obtained.
Typical Procedure for Ambient Temperature Ethylene Po-
lymerization Studies. To a sealable metal reactor containing a glass
insert was added the appropriate amount of MAO (Albermarle, 10%
in toluene) made up to 200 mL with toluene. The solution was
stirred at 250 rpm for 5 min, and then the precatalyst (20, 10, or
2.5 µmol) in toluene (50 mL) was added to the reactor and the
mixture stirred for a further 30 min. The reaction vessel was placed
under dynamic vacuum for 10 s, the stirring was increased to 750
rpm, and a dynamic pressure of ethylene (6 bar) was admitted. After
(69) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105.
(70) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Academic Press: New York, 1997.
(71) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(72) Betteridge, P. W.; Cooper, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.

92 Organometallics, Vol. 26, No. 1, 2007
Owen et al.
for all the structures has been deposited at the Cambridge
Crystallographic Data Centre. See Notice to Authors, Issue No. 1.
Supporting Information Available: X-ray crystallographic data
in CIF format for the structure determinations of Cp*Ti(NAr)Cl-
i
t
(py) (Ar ) 2,6-C6H3 Pr2 (2), 2,6-C6H3Br2 (3), 2-C6H4 Bu (4), and
i
2-C6H4 Pr (5)) and Ti(N-2-C6H4CF3)Cl2(py)3 (6). This information
Acknowledgment. We thank the EPSRC for support and
Dr. S. R. Dubberley for the 20 µmol loading polymerization
experiment with 1.
is available free of charge via the Internet at http://pubs.acs.org.
OM0608556