(Alkyliminomethyl)phenylamido and related complexes of zirconium and titanium

Article abstract of DOI:10.1039/b202471c

A range of trialkylsilylamido complexes of zirconium in which the silylamido functional group is attached to an o-(alkyliminomethyl)- or an o-(alkyliminoethyl)-substituted aromatic ring have been synthesised by salt elimination or aminolysis reactions and characterised by spectroscopic and diffraction methods. The monoanionic ligands (L), formally isoelectronic to the cyclopentadienyl ligand, can be introduced to zirconium by reaction of LLi with ZrCl₄ under a variety of conditions giving rise to complexes of type LZrCl₃ and L₂ZrCl₂, by reaction of LLi with Zr(NMe₂)₂Cl₂(THF)₂, and Zr(NEt₂)₂Cl₂(THF)₂ giving rise to LZrCl(NMe₂)₂Cl and LZrCl(NEt₂)₂Cl, respectively, or by reaction of LH with Zr(NMe₂)₄ giving rise to LZr(NMe₂)₃. LZr(NMe₂)₂Cl and LZr(NEt₂)₂Cl can be transformed to LZrCl₃ by reaction with Me₃SiCl, while LZr(NMe₂)₃ on heating rearranges to dimeric imido complexes by elimination of amidosilanes. Aminolysis of Zr(NMe₂)₂Cl₂(THF)₂ with LH results in a formal insertion of the imino C=N into the Zr-amido bond. The combination of enolisable imine and a bulky silyl amide gave rise to a new mixed donor ligand system comprising of one silylamido and one eneamido group. Finally aminolysis of Ti(NMe₂)Cl₂ with LH resulted in the isolation of a C₃ symmetric triamido titanium complex.

Full text of DOI:10.1039/b202471c

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(Alkyliminomethyl)phenylamido and related complexes of
zirconium and titanium†
Robin M. Porter, Scott Winston, Andreas A. Danopoulos* and Michael B. Hursthouse
Department of Chemistry, University of Southampton, Highfield, Southampton, UK SO17 1BJ.
E-mail: ad1@soton.ac.uk
Received 11th March 2002, Accepted 19th June 2002
First published as an Advance Article on the web 29th July 2002
A range of trialkylsilylamido complexes of zirconium in which the silylamido functional group is attached to an
o-(alkyliminomethyl)- or an o-(alkyliminoethyl)-substituted aromatic ring have been synthesised by salt elimination
or aminolysis reactions and characterised by spectroscopic and diffraction methods. The monoanionic ligands (L),
formally isoelectronic to the cyclopentadienyl ligand, can be introduced to zirconium by reaction of LLi with
ZrCl4 under a variety of conditions giving rise to complexes of type LZrCl3 and L2ZrCl2, by reaction of LLi with
Zr(NMe2)2Cl2(THF)2, and Zr(NEt2)2Cl2(THF)2 giving rise to LZrCl(NMe2)2Cl and LZrCl(NEt2)2Cl, respectively, or
by reaction of LH with Zr(NMe2)4 giving rise to LZr(NMe2)3. LZr(NMe2)2Cl and LZr(NEt2)2Cl can be transformed
to LZrCl3 by reaction with Me3SiCl, while LZr(NMe2)3 on heating rearranges to dimeric imido complexes by
elimination of amidosilanes. Aminolysis of Zr(NMe2)2Cl2(THF)2 with LH results in a formal insertion of the imino
C᎐N into the Zr-amido bond. The combination of enolisable imine and a bulky silyl amide gave rise to a new mixed
᎐
donor ligand system comprising of one silylamido and one eneamido group. Finally aminolysis of Ti(NMe2)Cl2 with
LH resulted in the isolation of a C3 symmetric triamido titanium complex.
This is possibly due to the synthetic difficulties associated
Introduction
with the synthesis of this ligand system. We initiated a study in
There is currently great interest in the study of ligand
this area using the ligand backbones shown in Scheme 1. In the
architectures incorporating amido functional groups as non-
metallocene spectators, especially in organometallic complexes
first of a series of papers we report on zirconium and titanium
complexes with the N-silyl (R1 = SiMe3, SiMe2But) substituted
of the early transition metals.1 The well-known electronic char-
analogues of L. As previously noted,5 L is related to a wide
acteristics of the amido group and its facile incorporation into
family of β-diketiminato ligands.6
tunable ligand backbones provides unique opportunities for the
design of complexes with catalytic activity.1c,2 Seminal contribu-
tions in this area have shown the viability of single site polymer-
isation catalysts based on chelating or functionalised amido
ligands. The area has been recently reviewed.2 Furthermore,
organometallic complexes with Schiff bases, mainly salicylal-
Results and discussion
Syntheses of ligands and ligand precursors
The o-[(tert-butyl)iminomethyl]aniline was synthesised by the
literature method.5 Following this method, condensation of
ButNH2 with the commercially available o-aminoaceto-
phenone did not proceed even under forcing conditions
and prolonged reaction times. However, reaction with
cyclohexylamine in toluene in the presence of 4 Å molecular
sieves afforded multigram quantities of the Schiff base in
excellent yields. L1H, L2H and L3H were prepared by lithiation
of the free anilines with BunLi in petrol, followed by quench-
ing of the resulting lithium amides with SiMe3Cl and SiMe2-
ButCl respectively. Deprotonation of the silylanilines with
BunLi in petrol gave the lithium salts L1Li–L3Li as yellow,
crystalline, extremely air sensitive materials. The structure
of L2Li (2) in the solid state was determined by single crystal
X-ray diffraction methods. The molecular structure of L2Li
is given in Fig. 1. with selected bond lengths and angles in
Table 1.
dimines [6-RN᎐C(H)C H OϪ, R = alkyl or aryl] and their
᎐
6
4
derivatives have been extensively explored. Some exhibit high
activity or living behaviour in polymerisation reactions.3 The
attractive features of these ligands are easy synthetic accessi-
bility and steric and electronic tuning by substitution of the
aromatic ring or the imine carbon.3,4 In contrast, the coordin-
ation chemistry of the anionic ligands that formally originate
from salicylaldiminato by replacement of the PhOϪ group with
the isoelectronic PhNRϪ have received less attention,5 even
though the tuning opportunities in this case are even broader
(Scheme 1).
The molecule is a centrosymmetric dimer with bridging
amido nitrogens. The coordination number around each lith-
ium atom is three. The Li2N2 ring is almost planar. The bridging
amido group is tetrahedral. The lithium amido bond lengths
[1.982(8), 2.000(7) Å] are in the range reported for bridging
amido nitrogens.7 The lithium–imino nitrogen bond length
([1.972(8), 1.977(8) Å] is almost equal to the Li–amido bond
length, possibly due to the bridging nature of the amido
ligands.
Scheme 1
† Electronic supplementary information (ESI) available: ORTEP plots
of 6 and 9. See http://www.rsc.org/suppdata/dt/b2/b202471c/
3290
J. Chem. Soc., Dalton Trans., 2002, 3290–3299
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b202471c

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Table 1 Selected bond lengths (Å) and angles (Њ) for 2
Table 2 Selected bond lengths (Å) and angles (Њ) for 4
C(1)–N(1)
C(1)–C(6)
C(6)–C(7)
C(7)–N(2)
1.407(5)
1.419(5)
1.491(5)
1.287(5)
N(1)–Li(1)
N(1)–Li(2)
N(2)–Li(1)
Li(1)–Li(2)
1.989(8)
1.982(8)
1.970(8)
2.415(9)
C(1)–N(1)
C(1)–C(6)
C(6)–C(7)
N(2)–C(7)
Zr(1)–N(1)
1.402(10)
1.420(10)
1.477(10)
1.273(9)
2.029(7)
Zr(1)–N(2)
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–Cl(3)
2.336(9)
2.434(6)
2.386(6)
2.415(8)
N(1)–C(1)–C(6)
C(1)–C(6)–C(7)
N(2)–C(7)–C(6)
C(1)–N(1)–Li(1)
123.7(4)
124.3(4)
119.2(4)
102.5(3)
C(1)–N(1)–Li(2)
Li(1)–N(1)–Li(2)
C(7)–N(2)–Li(1)
N(2)–Li(1)–N(1)
120.3(4)
74.9(3)
117.1(3)
99.6(4)
N(1)–C(1)–C(6)
C(1)–C(6)–C(7)
N(2)–C(7)–C(6)
C(1)–N(1)–Zr(1)
C(7)–N(2)–Zr(1)
120.8(7)
122.5(8)
124.81(8)
101.03(5)
108.12(5)
N(1)–Zr(1)–N(2)
Cl(2)–Zr(1)–Cl(3)
Cl(2)–Zr(1)–Cl(1)
Cl(3)–Zr(1)–Cl(1)
81.19(2)
112.9(2)
95.49(2)
91.13(14)
Fig. 2 ORTEP representation of the crystal structure of 4 (50%
probability thermal ellipsoids).
Fig. 1 ORTEP representation of the crystal structure of 2 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
Zr(1)–N(2) bond length of 2.336(9) Å is much longer; N(2) is
also planar. The bite angle of the chelating ligand is 81.2Њ and
the six-membered chelate ring is puckered. It is interesting to
compare the metrical parameters of 4 with those observed for
the isoelectronic β-diketiminato complexes;6 the former features
an asymmetrical chelate ring with unequal metal–nitrogen
bond lengths, the shortest silylamido–Zr being almost 0.2 Å
shorter and the longest Zr–N imino being 0.2 Å longer than the
equal Zr–N lengths of the β-diketiminato chelate. In both cases
Zirconium complexes
The transformations leading to the zirconium complexes
described in this paper are shown in Scheme 2.
The nature of the zirconium complexes obtained by
metathetical reactions involving lithium amido species and
zirconium halide starting materials is strongly dependent on
the reaction conditions, mainly, the reagents ratio, solvent,
temperature of addition and the nature of the zirconium start-
ing material used. Many products show reduced tendency to
crystallise. This, in combination with their extreme sensitivity to
moisture, reactivity with non-ethereal polar solvents and their
the chelate rings are puckered. In 4 the C᎐N double bond char-
᎐
acter of the imino carbon is maintained after complexation and
is shorter than the Cipso–N(Si). This supports the fact that the
presence of the aromatic ring inhibits delocalisation of electron
density over the chelate. The aromatic carbon–carbon bonds
are not strictly equal lying in the range 1.36 to 1.42 Å.
1
complicated H NMR spectra in solution rendered their full
characterisation painstaking. Attempts to increase the crystal-
linity by using the bulkier and more lipophilic SiMe2But were
successful in some cases (see below). Furthermore, it became
obvious that all three ligands i.e. L1, L2 and L3 were not com-
pletely inert, even under careful exclusion of moisture, under-
going insertion, elimination or deprotonation reactions as
described below.
Reaction of ZrCl4(THT)2, THT = tetrahydrothiophene, in
ethereal solvents with two equivalents of L1Li or L3Li resulted
in the formation of L1 ZrCl2, 6, and L3 ZrCl2, 7, respectively.
2
2
Both compounds can be crystallised from petroleum as yellow,
1
very air sensitive crystals in moderate yields. Their H NMR
spectra show the presence of two inequivalent ligands in a 1 : 1
ratio. This observation supports the presence in solution of a
non-symmetric isomer. In 7 the ketimino methyl protons
appear as a relatively broad singlet at 2.05 ppm. The non-
symmetric nature of the complexes was established by single
crystal X-ray diffraction studies of 6 and 7. A schematic
diagram of 7 is shown in Fig. 3 with selected bond lengths and
angles in Table 3. (The structure of 6 is identical to 7, the
ORTEP plot is included as ESI, CCDC reference number
181537).
Reaction of ZrCl4 with one equivalent of L1Li or L2Li in
toluene results in the isolation of 4 and 5 in moderate yields as
extremely moisture sensitive, microcrystalline yellow powders.
These show limited solubility in toluene, from dilute solutions
of which 4 can be crystallised. The stoichiometry of 4 and 5 was
1
established by analytical methods. The H NMR spectra show
the presence of one type of resonance associated with the lig-
and backbone supporting the presence of a five-cooordinate
zirconium centre. A single crystal X-ray diffraction study of 4
supports the conclusions from the analytical and spectroscopic
methods. A schematic diagram of the molecule is shown in
Fig. 2, with selected bond lengths and angles in Table 2.
Compound 4 is monomeric, comprising of a five-coordinate
zirconium centre in a distorted trigonal bipyramidal geometry
with the imine and chloride functions occupying the axial posi-
tions. The equatorial positions are occupied by the silylamide
and the remaining chlorides. The Zr(1)–N(1) bond length of
2.029(7) Å is in the range for a planar amido nitrogen, while the
The zirconium centre has
a six-coordinate distorted
octahedral geometry with cis chlorides, while the arrangement
of the chelates is such that the amido function of one is trans to
a chloride and the amido function of the second is trans to the
imino function of the first. This gives rise to a low symmetry C1
complex. The bond lengths observed reflect the relative trans
influence of the functional groups involved i.e. Zr(1)–Cl(2)
[trans to silylamide, 2.490(3) Å] is longer than Zr(1)–Cl(1) [trans
to the imine, 2.414(3) Å] and Zr(1)–N(1) [trans to silylamide,
J. Chem. Soc., Dalton Trans., 2002, 3290–3299
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Scheme 2 Compounds in bold have been structurally characterised. Reagents and conditions: (i) L1H, L2H or L3H, BunLi in petroleum (Ϫ78 ЊC
to RT); (ii) L1Li or L2Li and ZrCl4 in toluene (Ϫ78 ЊC to RT); (iii) L1Li or L3Li and ZrCl4(THT)2 in diethyl ether (Ϫ78 ЊC to RT); (iv) L2Li
and Zr(NMe2)2Cl2(THF)2 in THF (Ϫ78 ЊC to RT); (v) Zr(NEt2)2Cl2(THF)2 in THF (Ϫ78 ЊC to RT); (vi) L3Li and Zr(NEt2)2Cl2(THF)2 in THF
(Ϫ78 ЊC to RT); (vii) L2H and Zr(NMe2)4 in toluene 50 ЊC; (viii) heating at 100 ЊC for 24 h; (ix) Zr(NMe2)2Cl2(THF)2 and L1H in toluene at 100 ЊC for
72 h.
Table 3 Selected bond lengths (Å) and angles (Њ) for 7
C(1)–C(6)
C(1)–N(2)
C(6)–C(7)
C(7)–N(1)
N(1)–Zr(1)
1.405(7)
1.419(6)
1.495(7)
1.272(6)
2.366(4)
N(2)–Zr(1)
N(3)–Zr(1)
N(4)–Zr(1)
Cl(1)–Zr(1)
Cl(2)–Zr(1)
2.111(4)
2.459(4)
2.090(4)
2.4417(13)
2.4938(13)
C(6)–C(1)–N(2)
C(1)–C(6)–C(7)
N(1)–C(7)–C(6)
C(7)–N(1)–Zr(1)
C(1)–N(2)–Zr(1)
C(27)–N(3)–Zr(1)
C(21)–N(4)–Zr(1)
123.0(5)
123.9(5)
119.9(4)
123.0(3)
112.0(3)
123.8(3)
115.6(3)
N(2)–Zr(1)–N(1)
N(4)–Zr(1)–Cl(1)
N(1)–Zr(1)–Cl(1)
N(4)–Zr(1)–N(3)
N(2)–Zr(1)–N(3)
Cl(1)–Zr(1)–Cl(2)
81.06(14)
99.47(11)
171.78(10)
78.06(15)
174.70(13)
90.23(5)
dialkylamido halide complexes with LH or LLi, by trans-
amination or salt elimination reactions, respectively.
Reaction of Zr(NMe2)2Cl2(THF)2 with one equivalent of
L2Li or L3Li in THF or reaction of Zr(NEt2)2Cl2(THF)2 with
L2Li in THF gave, after crystallisation from petroleum, pale
yellow moisture sensitive crystals of 8, 9 and 10 respectively in
Fig. 3 ORTEP representation of the crystal structure of 7 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
1
reasonable yields. The H NMR spectra of these compounds
2.486(7) Å)] is slightly longer than Zr(1)–N(4) [trans to chloride,
2.456(6) Å]. As found in complex 4, the localised bonding of
the chelate ring in complexes 6 and 7 is maintained after com-
plexation. The bite angle of the puckered chelate rings lies in
the range 78–81Њ. There is no obvious reason why both 6 and
7 adopt the same geometry. The different size of the silyl
substituents in the two complexes supports the fact that the
observed geometry is sterically favoured.
Attempts to substitute the chlorides in 4, 5, 6 and 7 with
alkyls or amides using lithium or Grignard reagents gave only
intractable mixtures. In order to access these compounds
we reacted simple homoleptic zirconium dialkylamido or
showed inequivalent dialkylamido groups in addition to
peaks assignable to L2 or L3 backbones in a 2 : 1 ratio. This data
supports a trigonal bipyramidal structure in which the
dialkylamido groups are occupying inequivalent positions. The
solution structures were maintained in the solid state as con-
firmed by single crystal X-ray diffraction studies of 9 and 10.
Both molecules adopt identical geometries. Fig. 4 shows the
molecular structure of 10 with selected bond lengths and
angles in Table 4. (The structure of 9 is included as ESI, CCDC
reference number 181539).
The molecules adopt a five-coordinate distorted trigonal
bipyramidal geometry with the imino and chloride groups
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Table 4 Selected bond lengths (Å) and angles (Њ) for 10
Table 5 Selected bond lengths (Å) and angles (Њ) for 11
C(1)–C(6)
C(1)–N(2)
C(6)–C(7)
C(7)–N(1)
N(1)–Zr(1)
1.414(7)
1.426(7)
1.494(8)
1.285(7)
2.460(4)
N(2)–Zr(1)
N(3)–Zr(1)
N(4)–Zr(1)
Cl(1)–Zr(1)
2.112(4)
2.047(4)
2.054(5)
2.5021(13)
C(1)–C(6)
C(1)–N(1)
C(1)–Zr(1)
C(6)–C(7)
C(7)–N(2)
N(1)–Zr(1)
1.416(3)
1.426(3)
2.768(3)
1.499(4)
1.392(3)
2.052(2)
N(2)–Zr(1)
N(3)–Zr(1)
Cl(2)–Zr(1)
Zr(1)–O(1)
C(7)–C(8)
2.1290(19)
2.019(2)
2.4503(7)
2.3625(16)
1.348(3)
C(2)–C(1)–N(2)
C(1)–C(6)–C(7)
N(1)–C(7)–C(6)
C(7)–N(1)–Zr(1)
C(1)–N(2)–Zr(1)
N(3)–Zr(1)–N(4)
121.1(5)
121.0(5)
118.5(4)
116.8(4)
98.5(3)
N(3)–Zr(1)–N(2)
N(4)–Zr(1)–N(2)
N(3)–Zr(1)–Cl(1)
N(4)–Zr(1)–Cl(1)
N(2)–Zr(1)–Cl(1)
N(1)–Zr(1)–Cl(1)
128.42(18)
119.53(17)
96.79(12)
95.20(12)
89.63(12)
162.13(11)
C(6)–C(1)–N(1)
C(1)–C(6)–C(7)
N(2)–C(7)–C(6)
C(1)–N(1)–Zr(1)
C(7)–N(2)–Zr(1)
N(3)–Zr(1)–N(1)
120.5(2)
123.1(2)
115.1(2)
104.00(15)
118.02(16)
115.42(9)
N(3)–Zr(1)–N(2)
N(1)–Zr(1)–N(2)
N(3)–Zr(1)–Cl(2)
N(1)–Zr(1)–Cl(2)
N(2)–Zr(1)–Cl(2)
99.18(8)
89.54(8)
122.11(7)
119.55(6)
98.03(6)
110.78(17)
Fig. 4 ORTEP representation of the crystal structure of 10 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
Fig. 5 ORTEP representation of the crystal structure of 11 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
occupying the axial positions. The stronger π-bonding
amido groups are in the equatorial plane; the two inequivalent
dialkylamido groups are planar, indicating a strong π-bonding
interaction with the metal. The Zr–silylamido and Zr–imino
bond lengths are comparable to those observed in the other
complexes reported in this paper.
We were unable to detect by NMR spectroscopy in C6D6 any
silylamido ene-amido dilithium impurity in the L3Li reagent
used. This, in combination with the fact that the reaction of
Zr(NMe2)2Cl2(THF)2 with L3Li and Zr(NEt2)2Cl2(THF)2 with
L2Li produce the anticipated products, points to a possible
competing intermolecular deprotonation of the enolisable
imine by the excess of bulky lithium silylamide. Lappert has
observed lithium ene-amides in the reaction of LiCH(SiMe3)2
with benzonitrile or isocyanides in the presence of tmed.8 In
this case products are sensitive to the stoichiometry, the nature
of the organic group on the (iso)nitrile and the presence of
tmed.
Attempts to transaminate dimethylamido for silylamido
groups by reaction of L1H with Zr(NMe)2Cl2(THF)2 in toluene
at 100 ЊC resulted in the isolation of low yields of 12 as one
component of a complicated reaction mixture. 12 is formally
formed by insertion of the tert-butylimino group into the
Zr–dimethylamido bond. Insertion reactions, especially of
cumulenes (CO2, CS2, RNCO etc.) are common in early transi-
tion metal amido complexes.9 However, insertion of the imine
into metal–amido bonds is rare. The structure of 12 was deter-
mined by a single crystal X-ray diffraction study. A diagram of
the molecule is shown in Fig. 6 with selected bond lengths and
angles in Table 6.
12 is a dimer with bridging chlorides. The Zr centres are
formally six-coordinate with one face occupied by the ‘tripodal’
ligand. The Zr–nitrogen bond lengths and the bond angles
around the nitrogens support the presence of two mono-
anionic amido groups [Zr(1)–N(1) = 2.0882(18), Zr(1)–N(2) =
2.0122(17) Å] and one dative amine [Zr(1)–N(3) = 2.3582(17) Å]
functional groups. This makes the ligand a ten electron (X2L3)
dianionic donor with one amido and one asymmetrically
trisubstituted amidinato functional group. Functionalised
amidinato complexes have recently appeared in the literature.10
Attempts to substitute the dialkylamido groups with
chlorides by reaction of 8 or 10 with Me3SiCl were carried out
in C6D6 as NMR scale experiments. In the reaction mixture
peaks assignable to L2ZrCl3 and Me3SiNMe2 or Me3SiNEt2 can
be observed. Scaling up of this reaction gave good yields of
isolable L2ZrCl3 only in the case of 10 (see Experimental).
An unexpected result was obtained in an attempt to prepare
L3ZrCl(NEt2)2 by salt elimination reaction between Zr(NEt2)2-
Cl2(THF)2 and L3Li in THF. The only product that could be
isolated reproducibly in good yields was the air sensitive 11 in
which the chelating ligand can be best formulated as the diani-
onic ene-amido silyl amide. The presence of the methylene
group on the carbon α to the nitrogen can be easily established
from the 13C{1H} NMR spectrum (at 88.7 ppm) and DEPT 135
experiment. The structure of 11 was studied by single crystal
X-ray diffraction. A diagram of the molecule is shown in Fig. 5
with selected bond lengths and angles in Table 5.
Here the ligands on the five-coordinate trigonal bipyramidal
Zr are the dianionic ene-iminato silyl amide, one diethylamido,
one chloride and one THF. The axial positions are occupied by
the ene-iminato nitrogen and the THF molecule. The Zr(1)–
N(1)(silylamido) distance is the same as the other complexes
described here; the ene-iminato bond length of 2.1290(19) Å is
much shorter than the C᎐N–Zr bonds in complexes previously
᎐
studied. The chelate ring is puckered and the bite angle of the
new ligand is 89.5Њ.
The reason behind the preferential formation of 11 by reac-
tion of L3Li and Zr(NEt2)2Cl2(THF)2 is not fully understood.
J. Chem. Soc., Dalton Trans., 2002, 3290–3299
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Table 6 Selected bond lengths (Å) and angles (Њ) for 12
Table 7 Selected bond lengths (Å) and angles (Њ) for 14
N(1)–C(1)
C(7)–N(2)
C(7)–C(6)
C(7)–N(3)
C(6)–C(1)
Zr(1)–N(2)
1.424(3)
1.480(3)
1.500(3)
1.507(3)
1.413(3)
2.0122(17)
Zr(1)–N(1)
Zr(1)–N(3)
Zr(1)–Cl(2)
Zr(1)–Cl(1)
Zr(1)–Cl(1_3)
2.0882(18)
2.3582(17)
2.4395(7)
2.6142(7)
2.7067(8)
C(1)–N(1)
C(1)–C(6)
C(6)–C(7)
C(7)–N(2_3)
N(1)–Zr(1_3)
1.359(4)
1.442(5)
1.465(5)
1.298(4)
2.066(3)
N(1)–Zr(1)
N(2)–Zr(1)
N(3)–Zr(1)
N(4)–Zr(1)
Zr(1)–Zr(1_3)
2.217(3)
2.306(3)
2.065(3)
2.064(3)
3.3262(3)
N(1)–C(1)–C(6)
C(1)–C(6)–C(7)
N(2_3)–C(7)–C(6)
C(1)–N(1)–Zr(1_3)
C(1)–N(1)–Zr(1)
Zr(1_3)–N(1)–Zr(1) 101.84(12)
C(7_3)–N(2)–C(9) 123.6(3)
125.7(3)
123.7(3)
121.0(3)
134.3(2)
122.5(2)
C(7_3)–N(2)–Zr(1) 133.2(2)
N(4)–Zr(1)–N(3) 122.49(13)
N(4)–Zr(1)–N(1_3) 119.78(13)
N(3)–Zr(1)–N(1_3) 117.26(12)
N(1_3)–Zr(1)–N(1)
N(1)–Zr(1)–N(2)
C(1)–N(1)–Zr(1) 120.66(14)
C(7)–N(3)–Zr(1)
N(2)–Zr(1)–N(1)
N(2)–Zr(1)–N(3)
N(1)–Zr(1)–N(3)
N(3)–Zr(1)–Cl(2)
N(2)–Zr(1)–Cl(1)
N(1)–Zr(1)–Cl(1_3)
83.60(11)
92.01(7)
63.07(7)
N(2)–C(7)–C(6)
N(2)–C(7)–N(3)
C(6)–C(7)–N(3)
C(7)–N(2)–Zr(1)
C(1)–C(6)–C(7)
C(6)–C(1)–N(1)
112.59(17)
101.01(16)
113.08(17)
97.72(12)
121.17(19)
120.61(19)
84.70(7)
78.16(12)
158.22(10)
169.92(5)
142.23(5)
172.23(5)
Fig. 7 ORTEP representation of the crystal structure of 14 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
Compound 14 is a centrosymmetric dimer in which L2 acts as
a bridging ligand via an imido function. The coordination
sphere of each Zr centre is completed by one imino and two
dimethylamido groups, giving a total coordination number
of five. The Zr2N2 ring is highly asymmetric [Zr(1)–N(2) =
2.2187(15) Å, Zr(1)–N(2_3) = 2.0652(14) Å]. There is no
evidence of any metal–metal interaction [Zr(1)–Zr(1_3) =
3.3262(3) Å]. Both imido and amido nitrogens are planar with
the Zr imido bond distance almost equal to the Zr dimethyl-
amido distances. An interesting feature of 14 is the planarity of
the chelate ring. This is to be contrasted with the puckered
conformation of the chelate rings described earlier. It could be
ascribed to increased π-interaction of the imido with the metal
centre. The mechanism of formation of 14 probably involves an
initial transamination step followed by intra- or inter-molecular
Me3SiNMe2 elimination resulting in the formation of the imido
group. If the elimination is intramolecular dimerisation gives
rise to 14.
Fig. 6 ORTEP representation of the crystal structure of 12 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
Attempts to independently synthesise this ligand system11 are
under way. The exact mechanism of formation of 12 is unclear.
Although transamination of one dimethylamido functional
group by silylamide followed by insertion of the imine to the
second dimethylamide is plausible, an intermolecular pathway
involving nucleophilic attack of dimethylamide followed by
transamination cannot be eliminated. The observed reactivity
of the imino group in the presence of highly electrophilic early
transition metals has to be taken into account when using salen
type ligands as spectators. It is interesting to notice that a simi-
lar reaction is not observed between Zr(NMe)2Cl2(THF)2 and
the ketimine L2H.
Attempts to introduce L2 by transamination of Zr(NMe2)4
with one equivalent of L2H in toluene resulted in clean form-
ation of 13 as the only detectable product in an NMR scale
reaction (C6D6). This was established by the disappearance of a
peak at 10.4 ppm assignable to the NH of L2H and the simul-
taneous appearance of signals assignable to free dimethylamine
and the product. 13 can be isolated as a very moisture sensitive
oil making its characterisation by analytical methods difficult.
However, the identity of the compound is easily established by
NMR spectroscopy (see Experimental) where a peak at 3 ppm
is assignable to the dimethylamido functions; furthermore
peaks assignable to the ligand framework are also observed.
Introduction of a second L2 by reaction with Zr(NMe2)4
using two equivalents of L2H in toluene at 100 ЊC gave, after
crystallisation, low yields of the dimer 14. We were unable to
record a 1H NMR spectrum of 14 because of its poor solubility
in inert solvents. However, 14 was characterised by a single crys-
tal X-ray diffraction study. A diagram of the molecule is shown
in Fig. 7 with selected bond lengths and angles in Table 7.
Titanium macrocyclic complex
Preliminary attempts to extend the chemistry of L1H to
titanium gave unexpected results. Reaction of Ti(NMe)2Cl2
with o-C H (NH )(CH᎐NBut)] in toluene at 100 ЊC gave
᎐
6
4
2
complex 15 stabilised by a novel face-blocking C3 sym-
metric trianionic macrocyclic amide as shown in Scheme 3. It
1
was the only product detected by H NMR spectroscopy in
solution.
Air stable deep red crystals of 15 were isolated by crystallis-
1
ation from diethyl ether solutions. The H NMR spectrum of
15 showed signals at 2.3 and 2.8 ppm assignable to the dia-
stereotopic dimethylamino methyl groups, and signals due to
azomethine and aromatic protons. There was no evidence for
the formation of more than one diastereomer. The identity of
15 was established by a single crystal X-ray diffraction study.
A diagram of the molecule is given in Fig. 8 with selected
bond lengths and angles in Table 8.
3294
J. Chem. Soc., Dalton Trans., 2002, 3290–3299

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Table 8 Selected bond lengths (Å) and angles (Њ) for 15
the ligand backbone. The pyramidal nitrogen atoms of the
dimethylamino groups [N(12), N(22), N(32)] interact only
weakly with the metal centre [average Ti(1)–N distance 2.37 Å].
Although the mechanism of the formation of 15 is not clear
and still under investigation, there is evidence that it involves a
metal directed condensation. Pre-coordination of the of o-tert-
butyliminomethylaniline is necessary for the reaction to occur.
This is shown by the inertness of the electronically richer
Ti(NMe2)4 which fails to produce 15 by heating at 100 ЊC
with o-tert-butyliminomethylaniline, possibly due to its reduced
nucleophilicity.
The self-condensation of o-aminobenzaldehyde gives cyclic
trimeric and tetrameric products, which were unambiguously
characterised.12 If the condensation is carried out in the pres-
ence of metal templates, macrocyclic complexes with the “face-
blocking” trimer A or the planar “porphyrin-like” tetramer B
(Scheme 3) are obtained; the first compounds of this type were
realised and characterised in 1965 by Busch.12 Furthermore,
complexes with A and B can react with strong nucleophiles (RϪ,
ROϪ, RSϪ etc.) at the azomethine carbons giving derivatives
with functionalised anionic macrocycles. A ruthenium complex
incorporating A has recently been reported.13
Ti(1)–N(11)
Ti(1)–N(31)
Ti(1)–N(21)
Ti(1)–N(32)
Ti(1)–Cl(1)
Ti(1)–N(22)
1.975(2)
1.979(2)
1.981(2)
2.366(2)
2.3722(10)
2.380(2)
Ti(1)–N(12)
N(11)–C(11)
N(12)–C(17)
C(17)–N(21)
C(17)–C(16)
C(11)–C(16)
2.385(2)
1.387(3)
1.498(3)
1.460(4)
1.500(4)
1.416(4)
N(11)–Ti(1)–N(31)
N(11)–Ti(1)–N(21)
N(31)–Ti(1)–N(21)
N(11)–Ti(1)–Cl(1)
N(31)–Ti(1)–Cl(1)
N(21)–Ti(1)–Cl(1)
87.35(9)
87.18(9)
87.75(9)
127.23(7)
126.36(7)
127.60(7)
C(11)–N(11)–Ti(1)
N(21)–C(17)–N(12)
N(21)–C(17)–C(16) 111.5(2)
N(11)–C(11)–C(16) 116.2(2)
130.44(18)
98.3(2)
C(17)–N(21)–Ti(1)
102.67(16)
To the best of our knowledge this is the first time that a
selective cyclotrimerisation of an o-aminobenzaldehyde deriv-
ative has been achieved in non-polar solvents using a transition
metal amide as template. This method could open a new route
to template-directed macrocyclisation reactions. The use
of early transition metals could prove beneficial in the iso-
lation of the demetallated macrocycle under mild conditions.
Attempts to extend this synthetic methodology to other main
group and transition metals, the preparation of organometallic
derivatives of 15 and the use of o-aminobenzaldehyde derived
macrocycles as spectators in catalyst design will be reported in a
forthcoming paper.
Scheme 3
Ethylene polymerisation studies
The activity of 7 and 8 for the polymerisation of ethylene in the
presence of MAO was studied. They show medium polymeris-
ation activity, 3.0 and 8.8 g mmolϪ1 barϪ1 hϪ1 respectively, at
room temperature. This fact is not surprising in view of the
generally inferior activity reported for silylamides (‘silicon
effect’). The synthesis and polymerisation activity of N-aryl
substituted analogues of L1 and L2 will be reported shortly in a
forthcoming paper.
Experimental
Elemental analyses were carried out by the University College
London Microanalytical Laboratory. NMR data were recorded
on Bruker AMX-300 and AM-300 spectrometers, operating at
300 MHz (1H). The spectra were referenced internally using the
signal from the residual protio-solvent (1H) or the signals of the
solvent (13C). All manipulations involving moisture sensitive
materials were carried out under vacuum or N2 using standard
Schlenk techniques. All solvents used were dried by continuous
reflux under N2 and distillation from suitable drying agents
immediately prior to use; the light petroleum had bp 40–60 ЊC.
Commercial chemicals were from Aldrich and Avocado. The
following starting materials were prepared following liter-
ature methods: L1H2,5 ZrCl4(THT)2,14 Zr(NMe2)4,15 Zr(NMe2)-
Cl2(THF)2 and Zr(NEt2)Cl2(THF)2,16 TiCl2(NMe2)2.17
Fig. 8 ORTEP representation of the crystal structure of 15 (50%
probability thermal ellipsoids). Hydrogens are omitted for clarity.
The coordination geometry around the titanium can be best
described as a tricapped trigonal pyramid. The macrocyclic
ligand adopts a cone conformation reminiscent of the cone con-
formation found in calixarenes. The three shorter titanium–
nitrogen distances [Ti(1)–N(11), Ti(1)–N(21) and Ti(1)–N(31),
average 1.978 Å] fall in the long end of the bond range charac-
teristic of titanium() amido bonds. The geometry of these
nitrogens is almost planar (average angle sum 354.4Њ). The
slight deviation from planarity can be ascribed to competition
of N–C and N–Ti π-bonding, or due to constraints imposed by
Synthesis
[o-(tert-Butyl)iminomethyl]-N-(trimethylsilyl)aniline (L1H).
To a cooled (Ϫ78 ЊC), stirred solution of o-(tert-butyl)imino-
aniline (5.0 g, 28.5 mmol) in ether (200 cm3) was added drop-
wise a solution of BunLi (12.8 cm3 of 2.45 M solution in
hexanes, 31.3 mmol). The mixture was stirred for 15 min then
allowed to reach room temperature and stirred for 2 h. The
J. Chem. Soc., Dalton Trans., 2002, 3290–3299
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resulting yellow suspension was cooled again to Ϫ30 ЊC and a
solution of Me3SiCl (3.40 g, 31.3 mmol) in ether (10 cm3) was
added dropwise from a syringe. After stirring at room temper-
ature for 12 h the majority of the ether was removed under
reduced pressure, the resulting residue was extracted with pet-
roleum (2 × 100 cm3), the organic extracts were filtered through
Celite and evaporated to dryness. The remaining oily residue
gave after distillation under vacuum the product as a colourless
oil (bp 68–70 ЊC, 0.05 mmHg). Yield: 4.6 g, 65%. δH (C6D6)
0.25 [9H, s, (CH3)3Si], 1.2 [9H, s, (CH3)3C], 6.6–7.2 (4H, m,
aromatic), 8.2 (1H, s, imino), 9.9 (1H, s, NH).
cyclohexyl) 1.98 (3H, s, imino CH3), 3.27–3.38 (1H, m, H on
cyclohexyl C α to imino N), 6.82–6.88 (2H, m, aromatic), 7.21
(1H, d, aromatic), 7.31 (1H, d, aromatic). δC (C6D6) 1.8 (SiMe3),
19.6 (imino CH3), 25.2, 25.2, 26.1, 34.4 (cyclohexyl), 60.2
(cyclohexyl C α to imino N), 117.2, 129.8, 129.9, 130.7, 132.3,
156.7 (aromatic), 170.1 (C᎐N).
᎐
[o-(Cyclohexyl)iminoethyl]-N-(tert-butyldimethylsilyl)aniline
(L3H). To a cooled (Ϫ78 ЊC), solution of L2H2 (4.00 g, 18.5
mmol) in diethyl ether (150 cm3), was added slowly via cannula
BunLi (8.3 cm3 of 2.45 M solution in hexanes, 20.4 mmol). The
mixture was then stirred at Ϫ78 ЊC for 1 h, allowed to reach
room temperature and stirred for a further 2 h. To this, was
added via cannula a solution of tert-butyldimethylchlorosilane
(3.07 g, 20.4 mmol) in diethyl ether (20 cm3) and stirring was
continued for a further 15 h resulting in the formation of a
brown solution and LiCl precipitate. The mixture was concen-
trated to ca. 50 cm3 and petroleum (150 cm3) was added to
induce complete precipitation of LiCl. Filtration and removal
of the volatiles in vacuo gave the product as a light brown solid.
Yield: 4.71 g, 77%. δH (CDCl3) 0.29 (6H, s, SiMe2), 1.01 (9H, s,
SiBut), 1.2–1.9 (10H, m, cyclohexyl), 2.31 (3H, s, imino CH3),
3.50–3.60 (1H, m, H on cyclohexyl C α to imino N), 6.64 (1H, t,
aromatic), 6.83 (1H, d, aromatic), 7.10 (1H, t, aromatic), 7.50
(1H, d, aromatic), 9.77 (1H, br. s, NH ). δC (CDCl3) Ϫ3.8
(SiMe2), 16.0 (imino CH3), 18.4 (SiBut), 25.3, 26.0 (cyclohexyl),
26.7 (SiBut), 34.5 (cyclohexyl), 60.0 (cyclohexyl C α to imino
N), 115.4, 118.0, 122.7, 129.6, 129.9, 150.1 (aromatic), 166.0
Lithium [o-(tert-butyl)iminomethyl]-N-(trimethylsilyl)anilide,
(L1Li), 1. To a solution of L1H (3 g, 12 mmol) in petroleum
(50 cm3) at Ϫ78 ЊC was added slowly via cannula BunLi (5.4 cm3
of 2.45 M solution in hexanes, 13.2 mmol). The mixture was
stirred at Ϫ78 ЊC for 1 h, allowed to reach room temperature
and stirred for 12 h. This produced a light yellow suspension.
The product precipitate was isolated by filtration as a light
yellow, extremely air sensitive solid. Yield: 2.2 g, ca. 71%.
[o-(Cyclohexyl)iminoethyl]aniline (L2H2). 2-Aminoaceto-
phenone (10.0 g, 74.1 mmol) was dissolved in toluene (100 cm3)
and to the solution were added activated 4 Å molecular sieves
and cyclohexylamine (63 cm3, 552 mmol). The resulting orange
mixture was stirred at 100 ЊC in a closed vessel under reduced
pressure for 4 days. After completion, filtration of the sieves
and removal of the volatiles under reduced pressure gave a light
brown solid, which was crystallised from petroleum as white
solid that was washed with cold petroleum. Yield: 10.12 g, 63%.
δH (CDCl3) 1.25–1.90 (10H, m, cyclohexyl), 2.30 (3H, s, imino
CH3), 3.50–3.70 (1H, m, H on cyclohexyl C α to imino N), 6.55
(2H, br. s, NH2), 6.65 (2H, m, aromatic), 7.10 (1H, t, aromatic),
7.50 (1H, d, aromatic). δC (CDCl3) 15.7 (imino CH3), 24.9, 26.0,
34.3 (cyclohexyl), 59.3 (cyclohexyl C α to imino N), 116.0,
(C᎐N).
᎐
Lithium
[o-(cyclohexyl)iminoethyl]-N-(tert-butyldimethyl-
silyl)anilide, (L3Li), 3. To a cooled (Ϫ78 ЊC), stirred solution of
L3H (2.74 g, 8.30 mmol) in petroleum (100 cm3) was slowly
added via cannula BunLi (3.6 cm3 of 2.45 M solution in hexanes,
8.7 mmol).The mixture was stirred at Ϫ78 ЊC for 1 h, allowed to
reach room temperature and stirred for 15 h. This produced a
light yellow suspension. From this the product was isolated by
filtration as a white, extremely air sensitive solid (1.7 g), which
was dried in vacuo. The mother liquor was reduced to ca. 30 cm3
and cooled to Ϫ35 ЊC for 12 h giving a second crop (0.5 g).
Yield 2.2 g, 79%. δH (C6D6) Ϫ0.15 (3H, s, SiMe) Ϫ0.08 (3H, s,
SiMe), 0.90 (9H, s, SiBut), 1.15–1.90 (10H, m, cyclohexyl), 1.95
(3H, s, imino CH3), 3.20–3.40 (1H, m, H on cyclohexyl C α to
imino N), 6.75 (1H, t, aromatic), 7.10 (1H, d, aromatic), 7.17
(1H, d, aromatic), 7.24 (1h, t, aromatic).
117.0, 121.7, 129.4, 129.9, 148.3 (aromatic), 165.1 (C᎐N).
᎐
[o-(Cyclohexyl)iminoethyl]-N-(trimethylsilyl)aniline (L2H).
To a cooled (Ϫ78 ЊC), stirred solution of L2H2 (5.90 g, 27.3
mmol) in diethyl ether (150 cm3), was added slowly via cannula
BunLi (12.3 cm3 of 2.45 M solution in hexanes, 30 mmol). After
completion of addition, the bright yellow solution was stirred
at Ϫ78 ЊC for 1 h, allowed to reach room temperature and
stirred for 2 h. Trimethylchlorosilane (3.8 cm3, 30 mmol) was
then added via syringe and the mixture was stirred for 15 h
giving a light yellow suspension. Concentration to ca. 50 cm3,
followed by addition of petroleum (150 cm3), filtration of the
precipitated LiCl and removal of the volatiles under reduced
pressure gave a dark orange oil which was purified by vacuum
distillation. The product was collected as bright yellow oil (bp
140 ЊC, 0.05 mm Hg). Yield: 6.74 g, 86%. δH (CDCl3) 0.35 (9H,
s, SiMe3), 1.10–1.90 (10H, m, cyclohexyl), 2.32 (3H, s, imino
CH3), 3.53–3.70 (1H, H on cyclohexyl C α to imino N), 6.70
(1H, t, aromatic), 6.83 (1H, m, aromatic), 7.17 (1H, t, aro-
matic), 7.54 (1H, d, aromatic), 10.0 (1H, s, NH ). δC (CDCl3) 0.3
(SiMe3), 15.2 (imino CH3), 24.9, 26.2, 35.0 (cyclohexyl), 59.2
(cyclohexyl C α to imino N), 115.7, 117.7, 122.8, 130.0, 130.2,
L1ZrCl3, 4. To a stirred, cooled (Ϫ78 ЊC) suspension of ZrCl4
(0.233 g, 1 mmol) in toluene (50 cm3) was added a solution of
L1Li (0.255 g, 1 mmol) in toluene (50 cm3). The suspension was
allowed to reach room temperature, when it started developing
a yellow colouration, and was stirred at this temperature for
24 h. Filtration through Celite, concentration of the extracts
and cooling (Ϫ20 ЊC) gave the product as light yellow crystals.
Yield: 0.12 g, 26%. δH (C6D6) 0.25 [9H, s, (CH3)3Si], 1.25 [9H, s,
(CH3)3C], 6.7–7.1 (4H, m, aromatic), 7.9 (1H, s, imino). (Found:
C, 37.7; H, 5.4; N, 6.0. C14H23N2SiCl3Zr requires C, 37.8; H, 5.2;
N, 6.3%).
150.6 (aromatic), 165.9 (C᎐N).
᎐
L2ZrCl3, 5. To a stirred, cooled (Ϫ78 ЊC) suspension of ZrCl4
(0.233 g, 1 mmol) in toluene (50 cm3) was added slowly via
cannula a solution of L2Li (0.294 g, 1 mmol) in toluene
(50 cm3). After completion the reaction mixture was stirred at
Ϫ78 ЊC for 1 h, allowed to reach room temperature and the
resulting yellow solution was stirred for 24 h after which period
it turned to an orange suspension. The supernatant was filtered
and the toluene removed in vacuo. The residue was washed with
petroleum (5 × 10 cm3) yielding the product as an orange solid.
Yield: 0.11 g, 23%. δH (CD2Cl2) 0.24 (9H, s, SiMe3), 1.00–2.20
(10H, m, cyclohexyl), 2.26 (3H, s, imino CH3), 3.45–3.60
(1H, m, H on cyclohexyl C α to imino N), 6.50–7.90 (4H, m,
Lithium [o-(cyclohexyl)iminoethyl]-N-(trimethylsilyl)anilide,
(L2Li), 2. To a cooled (Ϫ78 ЊC), stirred solution of L2H (4.58 g,
15.9 mmol) in petroleum (150 cm3) was added slowly via can-
nula BunLi (7.1 cm3 of 2.45 M solution in hexanes, 17.5 mmol).
The mixture was stirred at Ϫ78 ЊC for 1 h, allowed to reach
room temperature and stirred for 15 h. This produced a light
yellow suspension. From this the product was isolated by filtra-
tion as a white, extremely air sensitive solid (3.2 g), which was
dried in vacuo. The mother liquor was reduced to ca. 30 cm3 and
cooled to Ϫ35 ЊC for 12 h giving a second crop (0.8 g). Yield:
4.0 g, 86%. δH (C6D6) 0.06 (9H, s, SiMe3), 1.10–1.90 (10H, m,
3296
J. Chem. Soc., Dalton Trans., 2002, 3290–3299

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aromatic). (Found: C, 42.4; H, 6.0; N, 6.4. C17H27N2SiCl3Zr
requires C, 42.1; H, 5.6; N, 5.8%).
0.5 mmol) in THF. X-Ray diffraction quality crystals were
obtained by cooling petroleum solutions. Yield: 0.05 g, 18%.
δH (C6D6) Ϫ0.05 (3H, s, SiMe) 0.13 (3H, s, SiMe), 0.85 (9H, s,
SiBut), 1.10–1.90 (10H, m, cyclohexyl), 1.85 (3H, s, imino CH3),
2.80 (6H, s, NMe2), 2.96 (6H, s, NMe2), 3.30–3.45 (1H, m, H on
cyclohexyl C α to imino N), 6.90–7.40 (4H, m, aromatic).
δC (C6D6) Ϫ0.7 (SiMe2), 0.5 (SiMe2), 11.6, (SiBut), 20.6 (imino
CH3), 21.9, 25.4, 25.8, (cyclohexyl), 27.2 (SiBut), 32.0, 32.6
(cyclohexyl), 42.9 (NMe2), 43.3 (NMe2), 64.1 (cyclohexyl C α to
imino N), 120.8, 129.6, 131.1, 131.8, 133.7, 145.5 (aromatic),
L12ZrCl2, 6. To a stirred and cooled (Ϫ78 ЊC) solution of
ZrCl4(THT)2 (0.30 g, 0.72 mmol) in diethyl ether (50 cm3) was
added via cannula a solution of L1Li (0.37 g, 1.45 mmol) in
diethyl ether (50 cm3). The reaction was stirred at Ϫ78 ЊC for
1 h, allowed to reach room temperature and stirred for 24 h.
Removal of the diethyl ether under reduced pressure was fol-
lowed by extraction of the residue into petroleum (ca. 150 cm3).
The extracts were filtered, concentrated and the solution cooled
to Ϫ35 ЊC to produce pale yellow crystals. Yield: 0.15 g, 32%.
δH (C6D6) 0.25 (18H, s, SiMe3), 1.25 and 1.35 (18H, s, inequiv-
alent tert-butyl groups), 6.5–7.0 (8H, m, aromatic), 8.0 and 8.2
(two singlets, 1H each, inequivalent imino CHNBut). (Found:
C, 49.5; H, 7.5; N, 7.8. C28H46N4Si2Cl2Zr requires C, 51.1; H,
7.0; N, 8.5%).
168.9 (C᎐N). (Found: C, 53.25; H, 8.57; N, 10.87. C H N Si-
᎐
24 45
4
ClZr requires C, 52.95; H, 8.33; N, 10.29%).
L2Zr(NEt2)2Cl, 10. This was prepared as above from Zr-
(NEt2)2Cl2(THF)2 (0.225 g, 0.5 mmol) and L2Li (0.147 g, 0.5
mmol) in THF. X-Ray diffraction quality crystals were
obtained by cooling petroleum solutions. Yield: 0.150 g, 54%.
δH (C6D6) 0.35 (9H, s, SiMe3), 0.90 (6H, t, NEt2), 1.07 (6H, t,
NEt2), 1.10–1.80 (10H, m, cyclohexyl), 1.78 (3H, s, imino CH3),
3.0–3.75 (9H, m, H on cyclohexyl C α to imino N and two
inequivalent NEt2 groups), 6.75 (1H, t, aromatic), 7.00 (1H, d,
aromatic), 7.04 (1H, t, aromatic), 7.30 (1H, d, aromatic).
δC (C6D6) 2.5 (SiMe3), 13.6, 13.7 (NEt2), 21.1 (imino CH3),
25.5, 25.9, 26.0, 31.6, 32.1 (cyclohexyl), 42.0, 42.4 (NEt2), 63.7
(cyclohexyl C α to imino N), 121.2, 128.8, 131.1, 131.8, 134.0,
L3 ZrCl2, 7. To a stirred and cooled (Ϫ78 ЊC) solution of
2
ZrCl4(THT)2 (0.205 g, 0.5 mmol) in diethyl ether (50 cm3) was
added via cannula a solution of L3Li (0.336 g, 1 mmol) in
diethyl ether (50 cm3). The reaction was stirred at Ϫ78 ЊC for
1 h, allowed to reach room temperature and then stirred for
24 h. From the pale yellow suspension the diethyl ether was
removed in vacuo and the residue was extracted into petroleum
(ca. 150 cm3). The extracts were filtered, concentrated to ca.
25 cm3 and the solution cooled to Ϫ35 ЊC to produce pale
yellow crystals. Yield: 0.11 g, 27%. mp 197–205 ЊC. δH (C6D6)
Ϫ0.45–0.25 (12H, br. s, SiMe2), 0.64 (18H, s, SiBut), 1.10–1.90
(20H, m, cyclohexyl), 2.00–2.20 (6H, br. s, imino CH3), 2.6–2.8
(2H, m, H on cyclohexyl C α to imino N), 6.6–7.5 (8H, m,
aromatic H ). (Found: C, 57.3; H, 8.0; N, 6.7. C40H66N4Si2Cl2Zr
requires C, 58.5; H, 8.1; N, 6.8%).
145.8 (aromatic), 168.8 (C᎐N). (Found: C, 54.05; H, 8.60; N,
᎐
10.15. C25H47N4SiClZr requires C, 53.77; H, 8.48; N, 10.03%).
Conversion of L2Zr(NEt2)2Cl to L2ZrCl3. To a solution of 10
(0.200 g, 0.36 mmol) in benzene at room temperature was added
via syringe trimethylchlorosilane (0.110 g, 1.00 mmol). The
bright yellow solution was stirred for 15 h resulting in a very
pale orange solution. The volatiles were removed in vacuo to
yield the product as a pale orange powder. Yield: 0.165 g, 94%.
δH (C6D6) 0.25 (9H, s, SiMe3), 0.90–1.65 (10H, m, cyclohexyl),
1.58 (3H, s, imino CH3), 3.38–3.52 (1H, m, H on cyclohexyl C
α to imino N), 6.85 (1H, t, aromatic), 6.95–7.05 (2H, m,
aromatic), 7.18 (1H, d, aromatic).
L2Zr(NMe2)2Cl, 8. To a cooled (Ϫ78 ЊC) solution of Zr-
(NMe2)2Cl2(THF)2 (0.790 g, 2 mmol) in THF (80 cm3), was
added slowly a solution of L2Li (0.588 g, 2 mmol) in THF
(40 cm3). The light yellow mixture was stirred at Ϫ78 ЊC for 1 h,
allowed to reach room temperature and stirred for 15 h giving
an orange solution. The THF was removed in vacuo and the
residue extracted into petroleum (3 × 50 cm3). Filtration, con-
centration of the extracts to ca. 25 cm3 and cooling at Ϫ35 ЊC
for 15 h gave an orange solid (0.4 g). Further concentration of
the supernatant and cooling gave further product (0.12 g).
Yield: 0.52 g, 52%. mp 120–127 ЊC. δH (C6D6) 0.33 (9H, s,
SiMe3), 1.05–1.95 (10H, m, cyclohexyl), 1.72 (3H, s, imino
CH3), 2.86 (6H, s, NMe2), 2.97 (6H, s, NMe2), 3.32–3.45 (1H,
m, H on cyclohexyl C α to imino N), 6.70 (1H, t, aromatic), 7.06
(2H, m, aromatic), 7.28 (1H, d, aromatic). δC (C6D6) 2.5
(SiMe3), 11.6 (imino CH3), 20.6, 22.7, 25.5, 25.7, 32.2 (cyclo-
hexyl), 43.0 (NMe2), 43.7 (NMe2), 63.7 (cyclohexyl C α to imino
Silylamido(ene-iminato)zirconium complex, 11. To a cooled
(Ϫ78 ЊC), stirred solution of Zr(NEt2)2Cl2(THF)2 (0.225 g,
0.5 mmol) in THF (20 cm3) was added slowly a solution of L3Li
(0.168 g, 0.5 mmol) in THF (20 cm3). The light yellow mixture
was stirred at Ϫ78 ЊC for 1 h, allowed to reach room temper-
ature and stirred for 15 h giving a yellow solution. Removal of
the THF in vacuo was followed by extraction of the residue into
petroleum (50 cm3), The supernatant solution was then filtered
and concentrated to ca. 20 cm3 before cooling to Ϫ35 ЊC for 15
h gave orange, X-ray diffraction quality crystals. Yield: 0.135 g,
45%. δH (C6D6) 0.29 (3H, s, SiMe), 0.45 (3H, s, SiMe), 0.79 (6H,
t, NEt2), 1.02 (9H, s, SiBut), 1.20–2.40 (10H, m, cyclohexyl),
1.30–1.35 (4H, m, THF), 2.8–3.1 (4H, m, NEt2), 3.27–3.43
(1H, m, H on cyclohexyl C α to ene-iminato N), 3.69 (4H, t,
N), 121.2, 129.1, 131.1, 131.4, 145.5 (aromatic), 168.4 (C᎐N).
᎐
(Found: C, 49.7; H, 7.8; N, 10.0. C21H39N4SiClZr requires C,
50.2; H, 7.8; N, 11.2%).
THF), 4.27 (1H, s, C᎐CH ), 4.44 (1H, s, C᎐CH ), 6.90–
᎐
᎐
2
2
7.02 (2H, m, aromatic), 7.10 (1H, t, aromatic), 7.67 (1H, d,
aromatic). δC (C6D6) Ϫ2.0 (SiMe2), 12.0 (SiBut), 14.1 (NEt2),
25.3 (THF), 25.9, 26.1 (cyclohexyl), 27.0 (SiBut), 32.7, 34.1
(cyclohexyl), 42.5 (NEt2), 62.9 (cyclohexyl C α to ene-iminato
Conversion of L2Zr(NMe2)2Cl to L2ZrCl3. Compound 8
(0.032 g, 0.07 mmol) was dissolved in d6-benzene and placed in
an NMR tube fitted with a Youngs PTFE tap. Trimethylchloro-
silane (8 drops) was added to the solution and the closed NMR
tube was heated at 50 ЊC for 48 h during which period the
N), 69.7 (THF), 88.7 (C᎐CH ), 123.9, 127.9, 128.7, 131.5,
᎐
2
135.0, 142.0, (aromatic), 174.0 (C(N)᎐CH ). (Found: C, 56.36;
᎐
2
1
progress of the reaction was monitored by H NMR. After
H, 8.54; N, 7.15. C28H50N3SiOClZr requires C, 56.10; H, 8.41;
N, 7.01%).
completion the volatiles were removed in vacuo to yield the
product as a yellow oil which was characterised by NMR after
redissolving in d6-benzene. δH (C6D6) 0.25 (9H, s, SiMe3), 0.90–
1.50 (10H, m, cyclohexyl), 1.60 (3H, s, imino CH3), 3.30–3.50
(1H, m, H on cyclohexyl C α to imino N), 6.90 (1H, t,
aromatic), 6.95–7.10 (2H, m, aromatic), 7.18 (1H, d, aromatic).
Dimeric zirconium complex, 12. To a solution of L1H (0.20 g,
0.8 mmol) in toluene (5 cm3) was added a solution of Zr-
(NMe2)2Cl2(THF)2 (0.33 g) in toluene (10 ml) and the reaction
mixture stirred at 95 ЊC under partial vacuum for 3 days. The
solution was then filtered, the solvent removed in vacuo and the
resulting solid crystallised by dissolving in ether (3 cm3) and
standing overnight at room temperature. Two types of crystal
L3Zr(NMe2)2Cl, 9. This was prepared as above from Zr-
(NMe2)2Cl2(THF)2 (0.198 g, 0.5 mmol) and L3Li (0.168 g,
J. Chem. Soc., Dalton Trans., 2002, 3290–3299
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were formed, one yellow and one orange which could not be
separated by chemical means. The crystal structure obtained
was that of the yellow crystal. δH (C6D6) 0.27 [9H, s, Si(CH3)3],
1.14 [9H, s, C(CH3)3], 1.53 [6H, s, N(CH3)2], 3.31 (1H, d,
aromatic), 6.71 (1H, t, aromatic), 6.88 (1H, d, aromatic), 7.01
(1H, t, aromatic), 8.21 (1H, s, N–CH–N).
L2Zr(NMe2)3, 13. Zr(NMe2)4 (0.067 g, 0.25 mmol) and L2H
(0.072 g, 0.25 mmol) dissolved in d6-benzene were placed in an
NMR tube fitted with a Youngs PTFE tap. The tube was heated
at 50 ЊC for 72 h during which period the progress of the reac-
tion was monitored by NMR. After completion the volatiles
were removed in vacuo and the product was obtained as an
orange oil which was characterised by NMR after redissolving
in d6-benzene. δH (C6D6) 0.26 (9H, s, SiMe3), 1.00–1.80 (10H, m,
cyclohexyl), 1.84 (3H, s, imino CH3), 2.99 (18H, t, NMe2), 3.30–
3.45 (1H, m, H on cyclohexyl C α to imino N), 6.72 (1H, t,
aromatic), 7.05–7.12 (2H, m, aromatic), 7.25 (1H, d, aromatic).
Dimeric zirconium complex, 14. Zr(NMe2)4 (0.134 g, 0.5
mmol) was dissolved in toluene (15 cm3) and added via cannula
to L2H (0.288 g, 1.0 mmol). The reaction was heated at 100 ЊC
for 24 hours and the toluene removed in vacuo. X-Ray diffrac-
tion quality crystals were grown from a saturated petroleum
solution. Once the crystals were formed it was not possible to
dissolve them in inert deuterated solvents in order to obtain
spectroscopic data.
Titanium macrocyclic complex, 15. To a solution of TiCl2-
(NMe2)2 (0.074 g, 0.36 mmol) in toluene (10 cm3) was added via
cannula a solution of o-(tert-butyliminomethyl)aniline (0.127 g,
0.72 mmol) in toluene (5 cm3). The mixture was heated at 95 ЊC
overnight before the resulting dark red solution was filtered and
the toluene removed in vacuo. The resulting solid was recrystal-
lised from diethyl ether at room temperature to give dark red,
X-ray diffraction quality crystals. Yield: 0.082 g, 43%. δH (C6D6)
2.3 (9H, s, N–CH3), 2.8 (9H, s, N–CH3), 5.3 (3H, s, Ph–
CHNMe–N), 6.0 (3H, d, aromatic), 6.5 (3H, t, aromatic), 6.7
(3H, t, aromatic), 7.0 (3H, d, aromatic). 13C{1H} δC 41.5, 49.2
(N–CH3), 87.2, 106.4, 118.1, 128.3, 129.4, 130.0 (aromatic C),
174.2 [Ph–CHN(CH3)2].
Ethylene polymerization catalysis.18 8 (0.050 g, 0.09 mmol)
was dissolved in toluene (100 ml) in a glass pressure bottle.
MAO (10% weight in toluene) (66.3 ml, 100 mmol) was added
to the solution of 8. This was stirred for 30 minutes at room
temperature. The toluene solution was then saturated with
ethylene at a pressure of 7 bar for 2 hours. A white solid was
formed in the toluene solution during the catalysis run. After
2 hours the ethylene was blown off the system and the poly-
merization quenched by the addition of ethanol (5 ml). The
polymeric solid that was produced was filtered away from the
toluene solution and stirred overnight in a 20 vol% ethanolic
hydrochloric acid solution, then washed with water and ethanol
and dried in vacuo.
Average yield of polyethylene produced: 9.068 g. This
corresponds to a catalyst activity of ca. 8.8 g mmolϪ1 barϪ1 hϪ1
The melting point of the polyethylene was 210–220 ЊC.
.
This procedure was followed for 7 but on half the scale. The
yield of polyethylene was 2.114 g. This corresponds to a catalyst
activity of 3.02 g mmolϪ1 barϪ1 Ϫ1. The melting point of the
h
polyethylene was 217–230 ЊC.
Crystal structure determinations of compounds 2, 4, 7, 10, 11, 12,
14, 15
A summary of the crystal data, data collection and refinement
for compounds 2, 4, 7, 10, 11, 12, 14, 15 is given in Table 9. All
data sets were collected on an Enraf Nonius Kappa CCD area
detector diffractometer with rotating anode FR591 and an
3298
J. Chem. Soc., Dalton Trans., 2002, 3290–3299

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(c) P. R. Woodman, N. W. Alcock, I. J. Munslow, C. J. Sanders
Oxford Cryosystems low-temperature device, operating in the
omega scanning mode with phi scans to fill the Ewald sphere.
The only exception is compound 4 was collected using a FAST
TV area detector and due to this has a small goodness of fit due
to underestimation of esds by the machine. The crystals were
isolated under dinitrogen, covered with Flombin vacuum oil
and mounted on a glass fibre with silicon grease. All solutions
and refinements were performed using the WinGX,19 Ortep-320
for Windows and Platon21 software packages. Non-hydrogen
atoms were refined with anisotropic thermal parameters.
Hydrogen atoms were included using a riding model. Structure
7 contains a highly disordered molecule of diethyl ether which
has not been completely modelled due to the extent of the dis-
order. Structure 10 has a residual peak which does not represent
an atom and is located within 0.8 Å of the zirconium centre and
is caused by a heavy metal ripple effect.
and P. Scott, J. Chem. Soc., Dalton Trans., 2000, 19, 3340;
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40, 2918.
4 J. Tian, P. D. Hustad and G. W. Coates, J. Am. Chem. Soc., 2001,
123, 5134.
5 C. Weymann, A. A. Danopoulos, G. Wilkinson, T. K. N. Sweet and
M. B. Hursthouse, Polyhedron, 1996, 15, 3605 and references
therein.
6 (a) L. Kakaliou, W. J. Scanlon IV, B. Qian, S. W. Baek, M. R. Smith
III and D. H. Morty, Inorg. Chem., 1999, 38, 5964; (b) B. Qian,
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Organometallics, 1998, 17, 1315.
7 D. K. Kennepohl, S. Brooker, G. M. Sheldrick and H. W. Roesky,
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8 P. B. Hitchcock, M. F. Lappert and M. Layh, Chem. Commun., 1998,
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9 M. F. Lappert, P. P. Power, A. R. Sanger and R. C. Srivastava,
Metal and Metalloid Amides, Ellis Horwood Publishers, Chichester,
1980, p. 567.
10 See for example (a) D. Doyle, Y. K. Gun’ko, P. B. Hitchcock and
M. F. Lappert, J. Chem. Soc., Dalton Trans., 2000, 22, 4093;
(b) J. R. Hagadorn and J. Arnold, Inorg. Chem., 1997, 36, 132;
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11 M. W. Partridge and M. F. G. Stevens, J. Chem. Soc., 1964, 3663.
12 A. G. Kolchinski, Coord. Chem. Rev., 1998, 174, 207.
13 C. Stern, F. Franceschi, E. Solari, C. Floriani, N. Re and
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14 F. M. Chung and A. D. Westland, Can. J. Chem., 1969, 47, 195.
15 D. C. Bradley and I. M. Thomas, J. Chem. Soc., 1960, 3857.
16 S. Brenner, R. Kempe and P. Arndt, Z. Anorg. Allg. Chem., 1995,
621, 2021.
CCDC reference numbers 181535, 181536, 181538 and
181540–181544.
See http://www.rsc.org/suppdata/dt/b2/b202471c/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the EPSRC for support and Dr Sven Kleinhenz for
assistance in solving the crystal structures of 12 and 15.
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