Synthesis of zirconocene amides and ketimides and an investigation into their ethylene polymerization activity

Article abstract of DOI:10.1016/S0022-328X(02)01559-0

The zirconocene amide [Cp₂Zr(Cl)N(CH₂Ph)₂] (5), and the zirconocene ketimides [Cp₂Zr(Cl)N=C(Bu^t)Ph] (7), and [Cp₂Zr(Cl)N=C(NMe₂)₂] (9), have been prepared by the trans

Full text of DOI:10.1016/S0022-328X(02)01559-0

Journal of Organometallic Chemistry 656 (2002) 63ꢀ70
/
www.elsevier.com/locate/jorganchem
Synthesis of zirconocene amides and ketimides and an investigation
into their ethylene polymerization activity
Kenneth W. Henderson *, Amanda Hind, Alan R. Kennedy, Arlene E. McKeown,
Robert E. Mulvey
Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK
Received 5 April 2002; received in revised form 30 April 2002; accepted 30 April 2002
Abstract
The zirconocene amide [Cp2Zr(Cl)N(CH2Ph)2] (5), and the zirconocene ketimides [Cp2Zr(Cl)NÄ
[Cp2Zr(Cl)NÄC(NMe2)2] (9), have been prepared by the transmetallation reactions between the appropriate lithiated organonitro-
gen compounds and zirconocene dichloride (2). In addition, their methylated derivatives [Cp2Zr(Me)N(CH2Ph)2] (6),
[Cp2Zr(Me)NÄ C(NMe2)2] (10), have been prepared by the reaction of each of the complexes
C(But )Ph] (8), and [Cp2Zr(Me)NÄ
5, 7 and 9 with MeLi. Compounds 5 and 7 have been characterized by X-ray crystallography and the structure of the cocrystalline
complex [Cp2Zr(Cl)NÄ 10 are
C(But)Ph]0.4[Cp2Zr(Me)NÄC(But )Ph]0.6 (14), has similarly been determined. All of the complexes 5ꢀ
active catalysts for the polymerization of ethylene in the presence of a MAO cocatalyst. In contrast, no polymer was produced using
/
C(But )Ph] (7), and
/
/
/
/
/
/
B(C6F5)3 as an activator, indicating that direct alkene insertion into the ZrÃ
/N bonds does not occur. # 2002 Elsevier Science B.V.
All rights reserved.
Keywords: Zirconium; Amides; Ketimides; Catalysis; Polymerization
1. Introduction
mido variant through a 1,3 sigmatropic rearrangement
(Scheme 2) [9]. Computational studies on this system
suggest that the isomerization process is energetically
favoured due to the formation of strong heteroallenic
Over the past decade there has been enormous
academic and industrial interest in the design and use
of Group 4 compounds for use in polyolefin catalysis
[1,2]. Within this area complexes containing nitrogen-
based ligands are currently receiving increasing atten-
tion [3]. Amide units may be used as alternatives to the
more conventional cyclopentadienyl ligand, allowing the
(ZrÃ
/
NÃ/C) bonding [10].
Complex 1 was found to polymerize ethylene in the
presence of a MAO cocatalyst. Furthermore, the
methylated analogue of 1, [Cp2Zr(Me)NÄ
/
C(But)CH3]
(4), was also found to be an active ethylene polymeriza-
tion catalyst in the presence of either MAO or a mixed
B(C6F5)3=Bui3Al cocatalyst. Solution NMR spectro-
scopic studies indicated that addition of the Lewis acid
B(C6F5)3 to 4 results in methide abstraction, and
use of di- or tridentate ligand configurations [4ꢀ6].
/
Furthermore, zirconocene complexes bearing chelating
diamido ligands have been prepared (Scheme 1) [7].
For our part, we recently reported the synthesis of the
formation of a [Cp2ZrNÄ
/
C(But)CH3]ꢁ[MeB(C6F5)3]ꢂ
zirconocene
ketimide
complex
[Cp2Zr(Cl)NÄ
/
ion pair. However, the resulting zirconocene ketimide
cation was found to be inactive towards ethylene
polymerization unless Bui3Al was also present.
C(But)CH3] (1), via the metathetical reaction between
zirconocene dichloride (2), and the 1-azaallyl compound
[CH2(But)CN(H)Li×
esis reaction the 1-azaallyl unit isomerizes to its keti-
/
HMPA] (3) [8]. During the metath-
This paper extends our studies into the use of
ketimide ligands in these systems, and for comparison
details the effects of using an amide ligand as an
alternative source of a ZrÃ
the synthesis and characterization of the zirconocene
amides [Cp2Zr(Cl)N(CH2Ph)2] (5), and [Cp2Zr(Me)N-
/
N linkage. Herein, we report
* Corresponding author. Tel.: ꢁ
5520876
E-mail address: k.w.henderson@strath.ac.uk (K.W. Henderson).
/
44-141-5482351; fax: ꢁ44-141-
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 5 5 9 - 0

64
K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ70
/
2.2. Syntheses
2.2.1. [Cp2Zr(Cl)N(CH2Ph)2] (5)
Zirconocene dichloride (1.46 g, 5 mmol) and 40 ml of
C6H5CH3 were added to a Schlenk tube and the
Scheme 1. Various structural arrangements of zirconium amides.
resultant suspension was then cooled to ꢂ78 8C.
/
Dibenzylamidolithium (1.02 g, 5 mmol) was added via
a solids addition tube and the mixture was then stirred
at ꢂ78 8C for 30 min, before it was allowed to warm to
/
ambient temperature. The suspension was stirred at
ambient temperature for 16 h, and then filtered through
a pad of Celite to afford a clear solution. Cooling of the
solution to ꢂ
/
20 8C yielded 5 as yellow crystalline
needles. Yield: 1.02 g, 47%. M.p. 178ꢀ
/
180 8C. Anal.
Calc. for C24H24ClNZr: C, 63.6; H, 5.3; N, 3.1. Found:
C, 63.6; H, 5.9; N, 2.6%. FTIR (Nujol mull, cmꢂ1):
1600w, 1343sh, 1312sh, 1157w, 1087m, 1022m, 927w,
811w. Upon exposure to air the characteristic signal for
Scheme 2.
(CH2Ph)2] (6), and the zirconocene ketimides
C(But)Ph] (7), [Cp2Zr(Me)NÄ
[Cp2Zr(Cl)NÄ
/
/
C(But)Ph]
the free amine at 3334 cmꢂ1, n(NÃ
/
H), was produced.
7.14 (10H,
(8), [Cp2Zr(Cl)NÄ
/
C(NMe2)2] (9), and [Cp2Zr(Me)NÄ
/
1H-NMR (400.13 MHz, d6-C6H6): d 7.20ꢀ
/
C(NMe2)2] (10) (9 and 10 can also be described as
guanidides) and investigate their utility as catalysts for
ethylene polymerization.
series of overlapping signals, o-, m-, p-Ph), 5.81 (10H, s,
h5-C5H5), 4.24 (4H, s, PhCH2). 13C-NMR (100.63 MHz,
d6-C6H6): d 140.24 (i-C), 129.28ꢀ129.15 (series of
/
overlapping signals, o-, m-Ph), 127.69 (p-Ph), 113.47
(h5-C5H5), 60.69 (PhCH2).
2. Experimental
2.2.2. [Cp2Zr(Me)N(CH2Ph)2] (6)
Compound 5 (4.53 g, 10 mmol) and 30 ml of
C6H5CH3 were added to a Schlenk tube and the mixture
2.1. General
All manipulations were carried out under a protective
Ar atmosphere using standard Schlenk techniques [11].
˚
Argon was purified by passage over 4 A molecular sieves
was then cooled to ꢂ
solution in ether, 10 mmol) was added to afford a yellow
suspension. The mixture was then stirred at ꢂ78 8C for
/
78 8C. MeLi (6.85 ml of a 1.46 M
/
and BTS catalyst. All solvents were distilled over Naꢀ
/
30 min before it was allowed to warm to ambient
temperature. The suspension was stirred at ambient
temperature for 2 h, after which 20 ml of C6H5CH3 was
added as diluent. The mixture was then filtered through
a pad of Celite to afford a yellow solution. All solvent
was removed under reduced pressure to yield the title
compound as a yellow powder. Yield: 3.32 g, 77%. M.p.
˚
benzophenone until blue, degassed and stored over 4 A
molecular sieves prior to use. All glassware was flame-
dried under vacuum before use. MeLi was standardized
by titration with diphenylacetic acid before use [12].
Zirconocene dichloride was purchased from Lancaster
and used as received. Bui3Al was purchased from Aldrich
as a 1 M solution in C6H5CH3 and used as received. The
lithium amide and ketimide complexes were prepared by
168ꢀ170 8C. Anal. Calc. for C25H27NZr: C, 69.4; H,
/
6.3; N, 3.2. Found: C, 68.8; H, 6.3; N, 3.9%. FTIR
(Nujol mull, cmꢂ1): 1620w, 1382w, 1150m, 1064s,
literature methods [13ꢀ
/
15]. Deuteriated solvents for
1
˚
NMR studies were stored over 4 A molecular sieves
under an Ar atmosphere. Ethylene was purchased from
Air Products. MAO was purchased from Witco as a 10
wt.% solution in C6H5CH3 and used as received.
B(C6F5)3 was purchased from Boulder Scientific and
used without further purification. The molecular weight
of polyethylene was determined by gel permeation
chromatography (GPC) using a Waters 150CV GPC
system with C6H3Cl3 diluent. The NMR spectra were
recorded on a Bruker AMX 400 spectrometer at 25 8C.
The IR spectra were recorded on a Mattson Galaxy
Series FTIR 3000 spectrometer and elemental analyses
941m. H-NMR (d6-C6H6): d 7.35ꢀ
/
7.01 (10H, series of
overlapping signals, o-, m-, p-Ph), 5.71 (10H, s, h5-
C5H5), 4.17 (4H, s, PhCH2), 0.31 (3H, s, ZrÃ
/
CH3). 13C-
NMR (100.63 MHz, d6-C6H6): d 142.50 (i-Ph), 130.05
(o-Ph), 128.89 (m-Ph), 127.39 (p-Ph), 110.98 (h5-
C5H5), 56.04 (PhCH2), 14.89 (ZrÃ
/
CH3).
2.2.3. [Cp2Zr(Cl)NÄ
/
C(But)Ph] (7)
Zirconocene dichloride (2.92 g, 10 mmol) and 40 ml of
C6H5CH3 were added to a Schlenk tube. The lithium
NLi] (1.67 g, 10 mmol) was added
ketimide [Ph(But)CÄ
/
to the mixture via a solids addition tube. The resultant
orange suspension was stirred at ambient temperature
for 4 h, and then filtered through a pad of Celite to
were carried out on a Perkinꢀ
/
Elmer 2400 elemental
analyzer.

K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ
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65
1
afford a clear orange solution. The filtrate was concen-
trated under reduced pressure to ca. 15 ml. Cooling of
cmꢂ1, n(NÃ
d6-C6H6): d 5.98 (10H, s, h5-C5H5), 2.43 (12H, s, NÃ
CH3). 13C-NMR (100.63 MHz, d6-C6H6): d 163.45 (NÄ
C), 112.24 (h5-C5H5), 40.62 (NÃ
CH3).
/
H), was produced. H-NMR (400.13 MHz,
/
the solution to ꢂ
large orange crystalline needles. Yield: 3.08 g, 74%. M.p.
150ꢀ152 8C. Anal. Calc. for C21H24ClNZr: C, 60.5; H,
/
20 8C yielded the title compound as
/
/
/
5.7; N, 3.4. Found: C, 60.5; H, 6.0; N, 3.5%. FTIR
(Nujol mull, cmꢂ1): 2059s, 1741w, 1598m, 1495w,
2.2.6. [Cp2Zr(Me)NÄ
/
C(NMe2)2] (10)
Compound 9 (3.71 g, 10 mmol) and 40 ml of
C6H5CH3 were added to a Schlenk tube and the mixture
1311m, 971m, 804m, 1675s n(CÄ
/
N). Upon exposure to
air the characteristic signal for the free amine at 3340
was then cooled to ꢂ
solution in ether, 10 mmol) was added and the resultant
suspension was then stirred at ꢂ78 8C for 30 min,
/
78 8C. MeLi (6.25 ml of a 1.60 M
1
H), was produced. H-NMR (400.13 MHz,
cmꢂ1, n(NÃ
/
d8-C6H5CH3): d 7.11 (2H, t, m-Ph), 7.05 (1H, t, p-Ph),
6.97 (2H, d, o-Ph), 5.75 (10H, s, h5-C5H5), 1.15 (9H, s,
/
before it was allowed to warm to ambient temperature.
The resultant brown suspension was stirred at ambient
temperature for 6 h, after which 10 ml of C6H5CH3 was
added as diluent. The mixture was then filtered through
a pad of Celite to afford a brown solution. All solvent
was removed under reduced pressure to yield the title
compound as a brown powder. Yield: 2.19 g, 59%. M.p.
NCÃ
d 159.78 (NÄ
(p-Ph), 127.94 (o-Ph), 110.66 (h5-C5H5), 43.27 (NCÃ
C(CH3)3), 29.09 (NCÃC(CH3)3).
/
C(CH3)3). 13C-NMR (100.63 MHz, d8-C6H5CH3):
/
C), 137.46 (i-Ph), 128.84 (m-Ph), 128.17
/
/
2.2.4. [Cp2Zr(Me)NÄ
/
C(But)Ph] (8)
Compound 7 (4.17 g, 10 mmol) and 40 ml of
C6H5CH3 were added to a Schlenk tube and the mixture
108ꢀ
/
110 8C. Anal. Calc. for C16H25N3Zr: C, 54.8; H,
7.2; N, 12.0. Found: C, 54.8; H, 5.8; N, 11.0%. FTIR
1
was then cooled to ꢂ
solution in ether, 10 mmol) was added and the mixture
was then stirred at ꢂ78 8C for 30 min, before it was
/
78 8C. MeLi (6.25 ml of a 1.60 M
(Nujol mull, cmꢂ1): 1608s n(CÄ
MHz, d6-C6H6): d 5.76 (10H, s, h5-C5H5), 2.42 (12H, s,
NÃCH3), 0.20 (3H, s, ZrÃ
CH3). 13C-NMR (100.63
MHz, d6-C6H6): d 161.96 (NÄ
C), 109.49 (h5-C5H5),
40.61 (NÃCH3), 15.77 (ZrÃCH3).
/
N). H-NMR (400.13
/
/
/
allowed to warm to ambient temperature. The resultant
orange suspension was stirred at ambient temperature
for 20 h, after which 10 ml of C6H5CH3 was added as
diluent. The mixture was then filtered through a pad of
Celite to afford an orange solution. All the solvent was
removed under reduced pressure to yield the title
compound as an orange powder. Yield: 3.08 g, 81%.
/
/
/
2.2.7. [Cp2Zr(Cl)NÄ
/
C(But)Ph]0.4[Cp2Zr(Me)NÄ
/
C(But)Ph]0.6 (14)
Procedure in Section 2.2.4 was followed but with the
exception of 1 h stirring at ambient temperature cf 20 h.
1H-NMR spectroscopy revealed the product to be a
M.p. 123ꢀ
/
125 8C. Anal. Calc. for C22H27NZr: C, 66.7;
H, 6.8; N, 3.5. Found: C, 67.8; H, 6.1; N, 3.2%. FTIR
40:60
[Cp2Zr(Me)NÄ
reaction was crystallographically characterized and
found to be a cocrystal of [Cp2Zr(Cl)NÄ
C(But)Ph]
and [Cp2Zr(Me)NÄ
C(But)Ph] in a 40:60 ratio. 1H-
NMR (400.13 MHz, d6-C6H6): d 7.17ꢀ6.96 (8H, series
mixture
of
[Cp2Zr(Cl)NÄ
/
C(But)Ph]ꢀ
/
(Nujol mull, cmꢂ1): 1680s n(CÄ
MHz, d6-C6H6): d 7.12ꢀ7.09 (5H, series of overlapping
signals, o-, m-, p-Ph), 5.67 (10H, s, h5-C5H5), 1.16 (9H,
s, NCÃC(CH3)3), 0.14 (3H, s, ZrÃ
CH3). 13C-NMR
(100.63 MHz, d6-C6H6): d 161.14 (NÄC), 138.51 (i-
Ph), 127.61 (m-Ph), 126.56 (p-Ph), 124.47 (o-Ph),
108.70 (h5-C5H5), 40.13 (NCÃ
C(CH3)3), 29.69 (NCÃ
C(CH3)3), 15.74 (ZrÃCH3).
/
N). H-NMR (400.13
/
C(But)Ph]. A single crystal from this
1
/
/
/
/
/
/
/
of overlapping signals, o-, m-, p-Ph, 7; o-, m-, p-Ph, 8),
5.79 (6.5H, s, h5-C5H5, 7), 5.63 (10H, h5-C5H5, 8), 1.17
/
/
/
(6H, s, NCÃ
/
C(CH3)3, 7), 1.11 (9H, s, NCÃ
/
C(CH3)3, 8),
0.09 (3H, s, ZrÃ
/CH3).
2.2.5. [Cp2Zr(Cl)NÄ
/
C(NMe2)2] (9)
Zirconocene dichloride (2.92 g, 10 mmol) and 50 ml of
C6H5CH3 were added to a Schlenk tube. The lithium
2.3. X-ray crystallography
ketimide [(Me2N)2CÄ
/
NLi] (1.21 g, 10 mmol) was added
Data for compounds 5, 7 and 14 were recorded on a
to the mixture via a solids addition tube. The resultant
suspension was stirred at ambient temperature for 6 h,
and then filtered through a pad of Celite to afford a
brown solution. The brown filtrate was concentrated
under reduced pressure to ca. 20 ml. Cooling of the
Rigaku AFC7S diffractometer with graphite monochro-
˚
Ka radiation (lꢃ0.71069 A). Absorption
mated Moꢀ
/
/
corrections were applied based on azimuthal scans of
several reflections and data were corrected for Lp
effects. All structures were refined to convergence
against F2 using the SHELXL-97 program. In 7 one Cp
ring was modelled as disordered over two sites.
Although the displacement parameters of several other
of the Cp rings indicated considerable motion this was
not modelled. Full details of refinement parameters and
crystal data are given in Table 1.
solution to ꢂ20 8C yielded the title compound as large
/
brown crystalline blocks. Yield: 2.19 g, 59%. M.p.
154 8C. Anal. Calc. for C15H22ClN3Zr: C, 48.6; H,
6.0; N, 11.3. Found: C, 48.3; H, 6.0; 11.1%. FTIR
(Nujol mull, cmꢂ1): 1587s n(CÄ
/N). Upon exposure to
air the characteristic signal for the free amine at 3217

66
K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ70
/
Table 1
Crystallographic parameters for 5, 7 and 14
3. Results and discussion
Compound
5
7
14
3.1. Syntheses
Chemical formula
C
24H24ClNZr C21H24ClNZr C21.56H25.69N-
Cl0.44Zr
Complexes 5, 7 and 9 were prepared in a similar
manner via the transmetallation reaction of 2 with one
molar equivalent of the appropriate lithiated amide or
ketimide. Regarding the synthesis of metal amide 5, this
was prepared by the equimolar reaction of lithium
dibenzylamide, [(PhCH2)2NLi] (11), with 2. Attempts
to perform a second amination using two molar
equivalents of 11 proved unsuccessful, with only 5
isolated as product. However, we have recently reported
that two dibenzylamido units may be transferred onto a
zirconium center using the less sterically hindered ZrCl4
Formula weight
Crystal system
Space group
453.11
Monoclinic
P21/c
417.08
Monoclinic
P21/c
405.60
Monoclinic
P21/c
˚
a (A)
16.013(3)
8.093(2)
16.317(3)
100.12(2)
2081.7(8)
4
7.962(5)
11.412(4)
21.040(6)
92.02(4)
1911(1)
4
8.005(1)
11.420(2)
21.068(8)
92.204(6)
1924.5(4)
4
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
Z
Dcalc (g cmꢂ3
)
1.446
0.665
1.450
0.717
1.400
0.634
m (mmꢂ1
Crystal size (mm)
)
0.40ꢄ0.25
ꢄ0.15
4959
0.45ꢄ0.25
ꢄ0.20
4710
0.70ꢄ0.48
ꢄ0.28
6511
as
a
reagent, to yield the bis-solvated complex
2THF] (12) [16]. This reaction
Reflections collected
Independent reflec-
[{(CH2Ph)2N}2ZrCl2×
/
4791
4396
6125
was completed using the magnesium bisamide
[Mg(N(CH2Ph)2)2] (13), as the amide transfer reagent,
Eq. (1) [17].
tions
Rint
R
0.0502
0.0396
0.1020
0.0614
0.0651
0.1869
0.0254
0.0280
0.0755
wR2
ð1Þ
2.4. Polymerization of ethylene
Polymerization experiments were carried out on a
Buchi miniclave rig, consisting of three 200 ml glass
reactors (max Pꢃ10 atm at 200 8C) each fitted with
/
However, reaction of 13 with 2 again only resulted in the
preparation of the monosubstituted product 5, regard-
less of the stoichiometry of the amide used. In compar-
ison, Otero reported that the equimolar reaction of 2
with the lithium amide [LiN(H)C6H4-o-SMe] consis-
tently resulted in the formation of a mixture of the
mono- and disubstituted zirconocenes [Cp2Zr(Cl)-
N(H)C6H4-o-SMe] and [Cp2Zr{N(H)C6H4-o-SMe}2],
respectively [18]. In this instance the reduced steric
encumbrance of the primary amide unit clearly influ-
ences the outcome of the reaction. Nevertheless, the
chloride of 5 was readily replaced by the small and
highly nucleophilic methyl unit, on reaction with one
molar equivalent of MeLi, to form 6.
Complexes 7 and 9 were prepared by reaction of the
respective lithium ketimides with 2, and subsequently
transformed into their methylated derivatives 8 and 10
upon reaction with MeLi. Interestingly, conversion of 7
to 8 was only partially completed after a period of 1 h,
when a cocrystalline material, 14, was formed. The ratio
of the two components 7 and 8 was confirmed to be
40:60 by both 1H-NMR spectroscopic studies and X-ray
analysis of the crystalline sample produced. Allowing
the reaction to proceed for 20 h resulted in complete
conversion to the methylated complex 8.
magnetically coupled stirrers. The ethylene feed was
controlled by a Bronkhorst Hi Tec mass flow controller/
pressure controller (max flow rate 500 ml minꢂ1) to
maintain constant pressure. The ethylene flow rate,
vessel pressure and temperature was logged on a PC
using OpTo 22 software. Standard solutions of each
catalyst and cocatalyst were made up in C6H5CH3 to
give concentrations of 3.42ꢄ
M for 5, 9.26ꢄ
10ꢂ3 M for 6, 1.92ꢄ
10ꢂ2 for 8, 2.16ꢄ10ꢂ2 for 9, 2.29ꢄ
M for MAO, 9.78ꢄ
10ꢂ3 M for B(C6F5)3 and 0.01 M
/
10ꢂ2 M for 2, 8.84ꢄ
10ꢂ2 for 7, 2.02ꢄ
10ꢂ2 for 10, 1.50
/
10ꢂ3
/
/
/
/
/
/
for Bui3Al: All polymerization reactions were based on
20 mmol of Zr. A typical polymerization was as follows.
The required aliquots of catalyst and cocatalyst were
transferred via syringe into the glass reactor in a glove-
box and the total reaction volume made up to 50 ml
with C6H5CH3. The reactor was sealed, removed from
the glove-box and attached to the Buchi miniclave rig.
After 1 h the polymerization was vented to the atmo-
sphere and quenched with MeOH. The mixture was
poured into an acidified solution of MeOH and stirred.
The polyethylene produced was filtered off, washed with
MeOH and dried to constant weight under reduced
pressure.

K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ
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67
3.2. X-ray crystallographic studies
Previously, we used X-ray crystallography as a key
tool in determining the mode of bonding within the ZrÃ
NÃC unit for compound 3 [8]. Hence, compounds 5, 7
and 14 were characterized by X-ray crystallography for
a similar purpose. As can be seen from Figs. 1ꢀ3, the
/
/
/
compounds have similar gross structural features. Dis-
cussion of the detailed geometric parameters within 14
will be restricted due to the sample being a cocrystalline
mixture, we note however that it is isostructural and
isomorphous with 7.
Table 2 lists the important bond lengths and angles
associated with 5, 7 and 14. In all of the structures the
cyclopentadienyl rings are h5-bound to the metal, with
Fig. 2. ORTEP view of 7 with disordered Cp ring components and
hydrogen atoms omitted for clarity. Drawn with 50% thermal
ellipsoids.
ZrÃ
/
Cp(centroid) distances in the narrow range 2.216ꢀ
/
˚
2.249 A, which compares well with those of other
Cp2Zr(IV) complexes [19]. Next, regarding the local
bonding environment around the anionic nitrogen
centers, it can be seen that the ZrÃ/N bond distance in
5 (2.068(3)), is similar to those found in the related
˚
dibenzylamide 12 (2.038(3) and 2.049(2) A) but is
somewhat shorter than those found in other Zr(IV)
amides [16]. More specifically, the Cambridge Structural
Database indicates that the mean ZrÃ
/
N bond distance
˚
in complexes of the type Cp2ZrNR2 is ca. 2.16 A [20].
Furthermore, in both 5 and 12 the anionic nitrogens are
essentially planar; with the sum of the angles surround-
ing N being 359.78 for 5, and 359.9 and 360.08 for 12.
However, the individual angles at each N are highly
distorted from the ideal trigonal planar arrangement of
1208 and range between 109.5(3) and 135.3(2)8 for 5 and
between 112.5(3) and 124.4(2)8 for 12. Adopting the
planar geometry may accentuate overlap of the lone pair
on the nitrogen atom with an acceptor orbital on the
zirconium center [21]. Overall, this result in a relatively
Fig. 3. ORTEP view of the methylated component of 14 with hydrogen
atoms omitted for clarity, showing 50% thermal ellipsoids.
as would be expected due to the extra stabilization
inferred by the heteroallenic bonding [10]. In both 7 and
14 the But groups of the ketimide ligands are orientated
syn with respect to the chloride attached to the metal
center. The remaining geometric parameters found in 7,
strong metalꢀ
short ZrÃN distances, found in 5 and 12.
The ZrÃN bond in the ketimide 7 is significantly
/
anion interaction, which rationalizes the
such as the almost linear Zr1Ã
/
N1ÃC7 angle of 174.6(4)8
/
/
˚
C7 bond distance of 1.268(6) A, are similar
and the N1Ã
/
/
to those found in 3 and are in accord with zirconium to
ketimide bonding [8].
˚
shorter than for the amide 5 (2.006(4) versus 2.068(3) A)
3.3. Polymerization studies
With complexes 5ꢀ10 in hand, we then wished to
/
study their ability to catalyze polyethylene production.
These studies were carried out using a MAO, B(C6F5)3,
or a mixed Bui3Al=B(C6F5)3 cocatalyst and the results of
the polymerizations are given in Table 3.
All of the complexes were able to polymerize ethylene
in the presence of a MAO cocatalyst. However, all of the
ZrÃ
/
N containing compounds are less active than
Cp2ZrCl2 (with the singular exception of 6 at 5 atm
pressure of ethylene). This is consistent with our
N linkages in
Fig. 1. ORTEP view of 5 with hydrogen atoms omitted for clarity,
showing 50% thermal ellipsoids.
previous study and suggests that the ZrÃ
/

68
K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ70
/
Table 2
˚
Selected bond lengths (A) and angles (8) for compounds 5, 7 and 14
Compound 5
Compound 7
Compound 14
Bond lengths
Zr1ÃN1
Zr1ÃCl1
Zr1ÃCp1
Zr1ÃCp2
N1ÃC1
N1ÃC8
C8ÃC9
C1ÃC2
2.068(3)
2.493(1)
2.224
Zr1ÃN1
Zr1ÃCl1
Zr1ÃCp1
N1ÃC7
C7ÃC8
C7ÃC4
C8ÃC9
2.006(4)
2.491(2)
2.216
Zr1ÃN1
Zr1ÃCl1
Zr1ÃC9
Zr1ÃCp1
Zr1ÃCp2
N1ÃC1
2.0200(12)
2.500(5)
2.327(13)
2.220
2.249
1.268(6)
1.529(6)
1.509(6)
1.544(7)
1.541(6)
1.529(6)
1.478(4)
1.465(4)
1.521(5)
1.513(5)
2.220
1.262(2)
1.508(2)
1.541(2)
1.537(2)
1.538(2)
1.529(2)
C1ÃC3
C8ÃC10
C8ÃC11
C1ÃC2
C2ÃC10
C2ÃC11
C2ÃC12
Bond angles
Cl1ÃZr1ÃN1
Cp1ÃZr1ÃCp2
Cp1ÃZr1ÃCl1
Cp2ÃZr1ÃCl1
Cp1ÃZr1ÃN1
Cp2ÃZr1ÃN1
Zr1ÃN1ÃC8
Zr1ÃN1ÃC1
C1ÃN1ÃC8
98.15(8)
126.5
107.3
Cl1ÃZr1ÃN1
Cp1ÃZr1ÃCp2
Cp1ÃZr1ÃCl1
Cp1ÃZr1ÃN1
N1ÃC7ÃC4
N1ÃC7ÃC8
C4ÃC7ÃC8
100.20(12)
132.2
106.1
Cl1ÃZr1ÃN1
C9ÃZr1ÃN1
Cp1ÃZr1ÃCp2
Cp1ÃZr1ÃC9
Cp2ÃZr1ÃC9
Cp1ÃZr1ÃCl1
Cp2ÃZr1ÃCl1
Cp1ÃZr1ÃN1
Cp2ÃZr1ÃN1
N1ÃC1ÃC3
99.85(13)
98.6(4)
130.5
104.7
105.6
110.9
106.0
108.9
103.2
119.4(4)
122.2(4)
118.3(4)
174.6(4)
103.3
108.1
135.3(2)
114.9(2)
109.5(3)
Zr1ÃN1ÃC7
107.5
103.8
119.71(12)
122.31(13)
117.97(11)
174.42(11)
N1ÃC1ÃC2
C2ÃC1ÃC3
Zr1ÃN1ÃC1
5ꢀ
/
10 are generally more difficult to cleave than the ZrÃ
/
than the ketimides 7ꢀ
presence of stronger ZrÃ
compounds.
/
10, which again indicates the
Cl bonds in 2 [8]. It is however interesting to note that
/
N bonding in the latter set of
the amides 5 and 6 show significantly greater activity
Table 3
a
Polymerization of ethylene catalyzed by 2 and 5ꢀ10
/
b
c
Catalyst
MAO/Zr molar
equivalent
B(C6F5)3/Zr molar
equivalent
/
Bui3Al=Zr molar
equivalent
Pethylene
Yield (g)
Activity
Mw
Mw/Mn
2
1000
1000
1000
1000
1000
ꢀ
ꢀ/
ꢀ/
ꢀ/
/
ꢀ
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
1
/
1
5
1
1
5
1
5
1
5
1
1
5
5
5
1
1
5
5
8.23
10.80
6.71
2.65
16.99
0
4.06
5.33
3.31
1.31
8.50
0
71 000
49 000
2.3
5.2
2.7
2.3
5.1
2
5
671 000
659 000
321 000
6
6
ꢀ/
6
ꢀ/
ꢀ/
ꢀ/
ꢀ/
1000
1000
1000
1
1
1
1
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
2.3
2.4
2.4
6
0
0
6
0
0
6
1
0
0
7
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
0.64
0.76
4.87
0
0.32
0.37
2.40
0
390 000
387 000
488 000
8
8
ꢀ
1
1
/
8
ꢀ/
ꢀ/
1000
1000
1000
ꢀ/
ꢀ/
ꢀ/
ꢀ/
2.3
2.3
2.3
2.2
8
1
0
0
9
ꢀ/
ꢀ/
ꢀ/
1
ꢀ/
ꢀ/
ꢀ/
1
0.57
0.49
2.21
0.19
0.28
0.24
1.09
0.09
462 000
454 000
517 000
472 000
10
10
10
ꢀ/
a
Zr, 20 mmol, tolueneꢃ50 ml, Tꢃ20 8C, tꢃ1 h.
atm.
b
c
ꢄ105 g molꢂ1 hꢂ1 atmꢂ1
.

K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ
/70
69
Replacing MAO with a B(C6F5)3, or a mixed
Bui3Al=B(C6F5)3 cocatalyst generally resulted in no
polymer being produced, with only compound 10
showing any activity at all. These results are in stark
contrast with the similar experiments carried out using
the ketimide 4, which showed significant activity using a
after replacement of the amide or ketimide component
by an alkyl group from a cocatalyst.
4. Supplementary material
mixed Bui3Al=B(C6F5)3 cocatalyst system (3.27ꢄ105 g
/
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
molꢂ1 hꢂ1 atmꢂ1). Monitoring the reaction of the
methylated compounds 6, 8 and 10 with the activator
1
B(C6F5)3 by H-NMR spectroscopy indicated that the
Data Centre, CCDC no. 183178ꢀ183180 for compound
/
5, 7 and 14. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
methyl group of each complex was indeed abstracted.
This was evidenced by the significant downfield shifts in
the respective CH3 resonances (from d 0.31 to 0.84 for 6,
0.09 to 0.99 for 8 and 0.23 to 0.63 for 10) upon addition
of the activator to the compounds in d6-benzene
solutions.
Road, Cambridge CB2 1EZ, UK (Fax: ꢁ44-1223-
/
336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Recently, the ability of monocyclopentadienylꢀ
mide titanium(IV) complexes, for example
[CpTi(Me)2NÄ
C(But)But], to polymerize ethylene in
/
keti-
Acknowledgements
/
We thank BP Amoco for funding (studentship to
A.E.M.) and their representatives Dr Ian Little and Dr
Charles Jenny for useful discussions. We also wish to
thank the Royal Society for a University Research
Fellowship (K.W.H.).
combination with a B(C6F5)3 cocatalyst has been
investigated by Piers and coworkers [22]. These studies
have established that the ketimide moiety remains intact
upon reaction with the boron activator. Indeed, the
stability of such linkages has led to them being proposed
as alternative ancillary ligands to Cp. Additionally,
Stephan has prepared the related phosphinimide com-
PR3)X2], where Rꢃ
Cy, Pri or But and
/
References
plexes [CpTi(NÄ
/
XꢃCl or Me, which utilize phosphinimide ligands [NÄ
/
/
[1] For recent reviews see: (a) G.W. Coates, J. Chem. Soc. Dalton
Trans. (2002) 467;
PR3] as steric mimics to Cp [23]. In combination with a
MAO, B(C6F5)3 or [Ph3C][B(C6F5)4] cocatalyst, some of
these complexes were found to be active catalysts for the
polymerization of ethylene.
Considering the results from these previous studies it
is unsurprising that the ketimide complexes 6, 8 and 10
are inactive for the polymerization of ethylene in
combination with a B(C6F5)3 cocatalyst. It also appears
in all of the systems studied that direct insertion of
(b) H.H. Brintzinger, D. Fischer, R. Mulhaupt, B. Rieger, R.M.
Waymouth, Angew. Chem. Int. Ed. Engl. 34 (1995) 1143;
(c) M.J. Bochmann, J. Chem. Soc. Dalton Trans. (1996) 255;
(d) K. Soga, T. Shiono, Prog. Polym. Sci. 22 (1997) 1503;
(e) W. Kaminsky, M. Arndt, Adv. Polym. Sci. 127 (1997) 143;
(f) W. Kaminsky, J. Chem. Soc. Dalton Trans. (1998) 1413.
[2] (a) P.C. Mohring, N.J. Coville, J. Organomet. Chem. 479 (1994)
1;
(b) N.J. Long, Metallocenes*An Introduction to Sandwich
/
Complexes, Blackwell Science, Oxford, 1998.
[3] (a) M.E.G. Skinner, D.A. Cowhig, P. Mountford, Chem. Com-
mun. (2000) 1167;
ethylene into a ZrÃ/N bond does not occur [24]. There-
fore, activation of the amide and ketimide complexes by
MAO is presumably made possible through replacement
of the organonitrogen anion by an alkyl group from the
cocatalyst. The anomalous activity of 4, and also the
very limited activity exhibited by 10, using a mixed
Bui3Al=B(C6F5)3 cocatalyst system may be caused by
replacement of the ketimide unit by a Bui anion on the
zirconium center. In these instances the possibility of the
aluminium cocatalyst incorporating chelating ligands
may drive the reaction. For 4 this would involve
isomerization of the ketimide to 1-azaallyl ligand upon
transfer to the aluminium, which has precedence in the
literature [25]. For 10 this would simply be chelation of
the ligand through a dimethylamido sidearm [26].
(b) L.H. Gade, Chem. Commun. (2000) 173;
(c) C. Lorber, B. Donnadieu, R. Choukroun, Organometallics 19
(2000) 1963;
(d) C.H. Hoon, Y.-H. La, J.W. Park, Organometallics 19 (2000)
344;
(e) G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem. Int.
Ed. Engl. 38 (1999) 428;
(f) J.D. Scollard, D.H. McConville, N.C. Payne, J.J. Vittal,
Macromolecules 29 (1996) 5241;
(g) R.R. Schrock, R. Baumann, S.M. Reid, J.T. Goodman, R.
Stumpf, W.M. Davis, Organometallics 18 (1999) 3649.
[4] (a) V.C. Gibson, B.S. Kimberley, A.J.P. White, D.J. Williams, P.
Howard, Chem. Commun. (1998) 313;
(b) J.D. Scollard, D.H. McConville, J.J. Vittal, Organometallics
16 (1997) 4415.
[5] (a) Y.-M. Jeon, S.J. Park, J. Heo, K. Kim, Organometallics 17
(1998) 3161;
In summary, we have prepared and characterized a
series of new nitrogen containing zirconocenes which
(b) T.H. Warren, R.R. Schrock, W.M. Davis, Organometallics 17
(1998) 308;
(c) L. Grocholl, V. Huch, L. Stahl, R.J. Staples, P. Steinhart, A.
display strong ZrÃ
/
N bonding. These compounds are
active catalysts for ethylene polymerization but only

70
K.W. Henderson et al. / Journal of Organometallic Chemistry 656 (2002) 63ꢀ70
/
Johnson, Inorg. Chem. 36 (1997) 4457;
(d) J.D. Scollard, D.H. McConville, J. Am. Chem. Soc. 118 (1996)
10008;
[14] D. Barr, W. Clegg, R.E. Mulvey, R. Snaith, K. Wade, J. Chem.
Soc. Chem. Commun. (1986) 295.
[15] W. Clegg, R. Snaith, H.M.M. Shearer, K. Wade, G. Whitehead,
J. Chem. Soc. Dalton Trans. (1983) 1309.
(e) J.D. Scollard, D.H. McConville, S.J. Rettig, Organometallics
16 (1997) 1810;
[16] K.W. Henderson, A.R. Kennedy, A.E. McKeown, R.E. Mulvey,
Acta Crystallogr. Sect. C 57 (2001) 674.
(f) J.D. Scollard, D.H. McConville, J.J. Vittal, N.C. Payne, J.
Mol. Catal. A: Chem. 128 (1998) 201;
[17] (a) W. Clegg, K.W. Henderson, R.E. Mulvey, P.A. O’Neil, J.
Chem. Soc. Chem. Commun. (1994) 769;
(g) P. Mehrkhodavandi, R.R. Schrock, J. Am. Chem. Soc. 123
(2001) 10746;
(b) W. Clegg, F.J. Craig, K.W. Henderson, A.R. Kennedy, R.E.
Mulvey, P.A. O’Neil, D. Reed, Inorg. Chem. 36 (1997) 6238.
[18] R. Fandos, M. Martinez-Ripoll, A. Otero, M.J. Ruiz, A.
Rodriguez, P. Terreros, Organometallics 17 (1998) 1465.
[19] For example: (a) W.E. Hunter, D.C. Hrncir, R. Vann Bynum,
R.A. Penttila, J.L. Atwood, Organometallics 2 (1983) 750;
(b) J. Jeffery, M.F. Lappert, N.T. Luong-Thi, M. Webb, J.L.
Atwood, W.E. Hunter, J. Chem. Soc. Dalton Trans. (1981) 1593.
[20] F.H. Allen, O. Kennard, Chem. Des. Autom. News 8 (1993) 31.
(h) K.C. Jayaratne, R.J. Keaton, D.A. Henningsen, L.R. Sita, J.
Am. Chem. Soc. 122 (2000) 10490;
(i) K.C. Jayaratne, L.R. Sita, J. Am. Chem. Soc. 122 (2000) 958;
(j) R.J. Keaton, K.C. Jayaratne, D.A. Henningsen, L.A. Koter-
was, L.R. Sita, J. Am. Chem. Soc. 123 (2001) 6197.
[6] (a) D.D. Graf, R.R. Schrock, W.M. Davis, R. Stumpf, Organo-
metallics 18 (1999) 843;
(b) R. Baumann, W.M. Davis, R.R. Schrock, J. Am. Chem. Soc.
119 (1997) 3830;
[21] For similar interactions see: (a) H.G. Alt, K. Fottinger, W.
¨
(c) F. Gue´rin, D.H. McConville, N.C. Payne, Organometallics 15
(1996) 5085.
Milius, J. Organomet. Chem. 564 (1998) 115;
(b) D.W. Carpenetti, L. Kloppenburg, J.T. Kupec, J.L. Petersen,
Organometallics 15 (1996) 1572;
[7] H. Mack, M.S. Eisen, J. Organomet. Chem. 525 (1996) 81.
[8] D.R. Armstrong, K.W. Henderson, I. Little, C. Jenny, A.R.
Kennedy, A.E. McKeown, R.E. Mulvey, Organometallics 19
(2000) 4369.
(c) R.M. Pupi, J.N. Coalter, J.L. Petersen, J. Organomet. Chem.
497 (1995) 17;
(d) A.K. Hughes, A. Meetsma, J.H. Teuben, Organometallics 12
(1993) 1936.
[9] For other uses of the 1-azaallyl ligand see: (a) P.B. Hitchcock, M.
Lappert, D.-S. Liu, J. Chem. Soc. Chem. Commun. (1994) 2637;
(b) M.F. Lappert, D.-S. Liu, Neth. Pat. Appl. 9401515, 1994;
(c) M.F. Lappert, D.-S. Liu, J. Organomet. Chem. 500 (1995) 203.
[10] (a) G. Erker, W. Froemberg, J.L. Atwood, W.E. Hunter, Angew.
Chem. Int. Ed. Engl. 23 (1984) 68;
[22] S. Zhang, W.E. Piers, X. Gao, M. Parvez, J. Am. Chem. Soc. 122
(2000) 5499.
[23] D.W. Stephan, J.C. Stewart, F. Gue´rin, R.E.v.H. Spence, W. Xu,
D.G. Harrison, Organometallics 18 (1999) 1116.
[24] F. Benetollo, G. Cavinato, L. Crosara, F. Milani, G. Rossetto, C.
Scelza, P. Zanella, J. Organomet. Chem. 555 (1998) 177.
[25] (a) C. Cui, H.W. Roesky, M. Noltemeyer, M.F. Lappert, H.-G.
Schmidt, H. Hao, Organometallics 18 (1999) 2256;
(b) L. Bourget, P.B. Hitchcock, M.F. Lappert, J. Chem. Soc.
Dalton Trans. (1999) 2645.
(b) G. Erker, W. Froemberg, C. Krueger, E. Raabe, J. Am. Chem.
Soc. 10 (1988) 2400.
[11] D.F. Shriver, M.A. Drezdzon, The Manipulation of Air-Sensitive
Compounds, Wiley, New York, 1986.
[12] W.G. Kofron, L.M. Baclawski, J. Org. Chem. 41 (1976) 1879.
[13] D. Barr, W. Clegg, R.E. Mulvey, R. Snaith, J. Chem. Soc. Chem.
Commun. (1984) 285.
[26] N.D.R. Barnett, R.E. Mulvey, W. Clegg, P.A. O’Neil, Polyhedron
11 (1992) 2809.