New and versatile routes to zirconium imido dichloride compounds

Article abstract of DOI:10.1039/b500507h

Reactions of zirconium dialkyl- or bis(amido)-dichloride complexes "[Zr(CH₂SiMe₃)₂Cl₂(Et ₂O)₂]" or [Zr(NMe₂)₂Cl ₂(THF)₂] with primary alkyl and aryl amines are described. Reaction of "[Zr(CH₂SiMe₃)₂Cl ₂(Et₂O)₂]" with RNH₂ in THF afforded dimeric [Zr₂(μ-NR)₂Cl₄(THF) ₄] (R = 2,6-C₆H₃ⁱPr₂ (1), 2,6-C₆H₃Me₂ (2) or Ph (3)), [Zr ₂(μ-NR)₂Cl₄(THF)₃] (R = ^tBu (5), ⁱPr (6), CH₂Ph (7)), or the "ate" complex [Zr₂(μ-NC₆F₅) ₂Cl₆(THF)₂ {Li(THF)₃}₂] (4, the LiCl coming from the in situ prepared "[Zr(CH₂SiMe ₃)₂Cl₂(Et₂O)₂]"). With [Zr(NMe₂)₂Cl₂(THF)₂] the compounds [Zr₂(μ-NR)₂Cl₄(L) _x(L′)_y] (R = 2,6-C₆H₃ ⁱPr₂ (8), 2,6-C₆H₃Me₂ (9), Ph (10) or C₆F₅ (11); (L)_X(L′) _y = (NHMe₂)₃(THF), (NHMe₂) ₂(THF)₂ or undefined), [Zr₂(μ-N _tBu)₂Cl₄(NHMe₂)₃] (12) and insoluble [Zr(NR)Cl₂(NHMe₂)]_x (R = ⁱPr (13) or CH₂Ph (14)) were obtained. Attempts to form monomeric terminal imido compounds by reaction of 2 or 5 with an excess of pyridine led, respectively, to the corresponding dimeric adducts [Zr ₂(μ-2,6-C₆H₃ Me₂) ₂Cl₄(py)₄] (15) and [Zr₂(μ-N ^tBu)₂Cl₄(py)₃] (16). The X-ray structures of 1, 2, 4, 8, 12 and 15 have been determined. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b500507h

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F U L L P A P E R
New and versatile routes to zirconium imido dichloride compounds
Stuart R. Dubberley, Simon Evans, Catherine L. Boyd and Philip Mountford*
Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, UK OX1 3TA.
E-mail: philip.mountford@chem.ox.ac.uk; Fax: 01865 285141
Received 12th January 2005, Accepted 14th February 2005
First published as an Advance Article on the web 10th March 2005
Reactions of zirconium dialkyl- or bis(amido)-dichloride complexes “[Zr(CH2SiMe3)2Cl2(Et2O)2]” or
[Zr(NMe2)2Cl2(THF)2] with primary alkyl and aryl amines are described. Reaction of “[Zr(CH2SiMe3)2Cl2(Et2O)2]”
i
with RNH2 in THF afforded dimeric [Zr2(l-NR)2Cl4(THF)4] (R = 2,6-C6H3 Pr2 (1), 2,6-C6H3Me2 (2) or Ph (3)),
t
[Zr2(l-NR)2Cl4(THF)3] (R = Bu (5), iPr (6), CH2Ph (7)), or the “ate” complex [Zr2(l-NC6F5)2Cl6(THF)2
{Li(THF)3}2] (4, the LiCl coming from the in situ prepared “[Zr(CH2SiMe3)2Cl2(Et2O)2]”). With
i
[Zr(NMe2)2Cl2(THF)2] the compounds [Zr2(l-NR)2Cl4(L)x(Lꢀ)y] (R = 2,6-C6H3 Pr2 (8), 2,6-C6H3Me2 (9), Ph (10) or
C6F5 (11); (L)x(Lꢀ)y = (NHMe2)3(THF), (NHMe2)2(THF)2 or undefined), [Zr2(l-NtBu)2Cl4(NHMe2)3] (12) and
i
insoluble [Zr(NR)Cl2(NHMe2)]x (R = Pr (13) or CH2Ph (14)) were obtained. Attempts to form monomeric terminal
imido compounds by reaction of 2 or 5 with an excess of pyridine led, respectively, to the corresponding dimeric
adducts [Zr2(l-2,6-C6H3Me2)2Cl4(py)4] (15) and [Zr2(l-NtBu)2Cl4(py)3] (16). The X-ray structures of 1, 2, 4, 8, 12 and
15 have been determined.
specific imido N-substituent. Nonetheless, compound 1 was
Introduction
shown to be a precursor to other zirconium imido complexes,
Transition metal imido chemistry continues to be a topic of
i
namely [(g-C8H8)Zr(N-2,6-C6H3 Pr2)2Zr(g-C8H8)] and [(g-
considerable interest.1,2 Stoichiometric or catalytic reactions
i
C5H4Me)ClZr(l-N-2,6-C6H3 Pr2)2Zr(g-C5H4Me)Cl], and other
may occur at the metal–ligand multiple bond itself (for ex-
research groups have also used Wigley’s compounds for the
ample, as in Bergman’s zirconocene systems2c), or the imido
synthesis of 2,6-diisopropylphenyl imido complexes.7,9,10,11 Given
group might act as a supporting or ancillary ligand, as in
the versatility and success of the titanium imido systems
Schrock’s Group 6 olefin metathesis catalysts3 and imido-based
[Ti(NR)Cl2(py)3] and [Ti(NR)Cl2(NHMe2)2], and the promising
Ziegler–Natta type olefin polymerisation catalysts.1c We have
i
results reported so far for [Zr(N-2,6-C6H3 Pr2)Cl2(L)n] (L =
THF, n = 2; L = py, n = 3) we decided to develop more general
routes to zirconium imido dichloride compounds and this is the
topic of our present contribution.
been interested in developing Group 4 imido chemistry,2a,b,d
and found that the tris(pyridine) dichlorides4 [Ti(NR)Cl2(py)3]
and the bis(dimethylamine) dichlorides5 [Ti(NR)Cl2(NHMe2)2]
(R = alkyl or aryl) are very useful entry points via chloride
or/and Lewis base substitution reactions. The ease of synthesis
(both yield and scale) of the compounds [Ti(NR)Cl2(py)3]
and [Ti(NR)Cl2(NHMe2)2] and the wide range of accessible
imido N–R substituents are key factors in their usefulness.
In zirconium imido chemistry there is still not yet a general
family of “synthons” of this type which provide a base-stabilised
Zr(NR)Cl2 fragment which may be accessed by a general route.
However, a number of classes of zirconium imido compounds
[(Ln)Zr(NR)]x ((Ln) = supporting ligand or ligand set) have
been prepared from precursors containing a pre-assembled
(Ln)Zr moiety.1a,2c,6,7 Wigley and co-workers have previously
Results and discussion
Synthesis of zirconium imido complexes from
“[Zr(CH2SiMe3)2Cl2(Et2O)2]”
Arnold’s previously-reported12 alkyl-dichloride complex
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” was chosen as a likely entry point
to new zirconium imido compounds as it is readily synthesised,
and the anticipated by-product (SiMe4) of protonolysis
reactions with primary amines would be readily separated. It
has been found previously that “[Zr(CH2SiMe3)2Cl2(Et2O)2]”
is a useful source of the {ZrCl2} fragment by protonolysis
reactions with R2N–H and ArO–H functional groups.13,14 The
reactions of “[Zr(CH2SiMe3)2Cl2(Et2O)2]” with aryl and alkyl
amines are summarised in Scheme 2
reported8 the compounds [Zr(N-2,6-C6H3 Pr2)Cl2(py)3] and
[Zr(N-2,6-C6H3 Pr2)Cl2(THF)2] (1) (Scheme 1) but only for this
i
i
Reaction of “[Zr(CH2SiMe3)2Cl2(Et2O)2]” with one equiva-
i
lent of H2N-2,6-C6H3 Pr2 in THF (rt for 10 h) followed by
simple toluene–THF extraction and evaporation afforded 1
1
as a pure yellow solid in 85% yield. The H and 13C NMR
data for complex 1 are identical to those reported by Wigley
for “[Zr(N-2,6-C6H3 Pr2)Cl2(THF)2]”.8 The previous synthesis
i
of 1 via the two-step route mentioned above (Scheme 1)
also goes in 85% overall yield, but takes three times as long
and includes a low-temperature first-stage addition as well
as a second-stage reflux and a crude separation/extraction
of the proposed imido-bis(amide) intermediate. Corresponding
reactions of “[Zr(CH2SiMe3)2Cl2(Et2O)2]” with one equivalent
of H2NAr (Ar = 2,6-C6H3Me2 or Ph) gave the homologous
compounds 2 and 3 in 74 and 61% isolated yields, respectively.
The phenyl imido compound 3 has been reported previously15
and was made by the in situ lithiation of N-allylaniline
Scheme 1
1 4 4 8
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Scheme 2
(2 equiv.) followed by reaction with ZrCl4 under reflux. Other
than the crystal structure, no experimental yield or NMR or
other characterising data were disclosed and so we provide all
these data in the Experimental section. The compound 3 is in
fact dimeric in the solid state having the imido-bridged structure
represented in Scheme 2. Given the possibility that the ortho-
substituted homologues 1 and 2 could also be dimeric, their
X-ray crystal structures have been determined. The molecular
structures are shown in Fig. 1 and selected distances and angles
at zirconium are given in Table 1
there are some differences which are important to note. In
particular the arrangement of the THF and Cl ligands in 3
differs from the two new structures in that only two Zr–Cl
bonds are perpendicular to the Zr2(l-N)2 plane whereas in 1
and 2 all four are perpendicular to this plane (conversely all four
THF O atoms lie in the Zr2(l-N)2 plane in 1 and 2). This is
attributed to the presence of the sterically more demanding (in
comparison with H atoms) ortho substituents in the aryl imido
ligand in 1 and 2. The second point of interest is the somewhat
pronounced asymmetry in the Zr–Nimide bond distances in 1 (Zr–
˚
Like 3, the compounds 1 and 2 are both dimeric in the solid
state. Molecules of 1 lie on crystallographic inversion centres
and those of 2 on 2/m symmetry sites. The disorder in the
THF molecules (see Experimental section) was satisfactorily
modelled. In general terms the distances and angles associated
with the compounds are within the normal limits.16,17 Apart from
3, a number of other imido bridged dizirconium compounds
have been reported previously, including [(Me4taa)Zr(l-
NR)2Zr(NHR)2] (R = tBu or 2,6-C6H3Me2; H2Me4taa =
Nimid = 2.115(5) and 2.018(5) A) which is absent in 2 (all Zr–Nimide
˚
distances (2.082(2) A) are equivalent by crystallographically
imposed symmetry) and negligible in 3 (Zr–Nimide = 2.062(2)
and 2.051(2) A).15 Asymmetrically bonded M2(l-NR)2 moieties
˚
are not without literature precedent,8,21 although the distortions
can be energetically rather “soft”.21 In the present instance,
the greatest asymmetry is associated with the more sterically
i
demanding imido N-substituent (2,6-C6H3 Pr2) which might
indicate that this dimeric structure is slightly less stable (with
respect to the five-coordinate monomer) than those of 2 and 3.
The solution 1H and 13C NMR data of 1 and 2 are consistent
with the solid-state structures featuring a single set of resonances
for the coordinated THF ligands and resonances attributable to
tetramethyldibenzotetraaza[14]annulene),18
[Cp2Zr(l-N-4-
i
C6H4 Bu)2ZrCp2],19 [(g-C5H4Me)ClZr(l-N-2,6-C6H3 Pr2)2Zr(g-
t
C5H4Me)Cl],8 and [(Me2N)2Zr(l-NtBu)2Zr(NMe2)2].20
While the overall structures and distances and angles for 1
and 2 are broadly comparable to the equivalent ones in 3,
i
2,6-C6H3R2 (R = Pr or Me) substituents. The spectra for 3
also feature the one set of THF resonances, whereas the solid-
state structure shows the presence of two chemically distinct
THF ligands. This implies that the THF ligands of 3 are in
rapid exchange on the NMR timescale. The resonances for the
THF ligands in all three compounds are rather broad at room
temperature suggestive of one or more dynamic processes. The
solution dynamic processes of other imido-bridged dizirconium
complexes are discussed later on in this contribution.
◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for [Zr2(l-N-2,6-
i
C6H3 Pr2)2Cl4(THF)4] (1) and [Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2)
1
2
Zr–Nimide
Zr–Cl
Zr–OTHF
Zr–Npy
2.115(5), 2.018(5)
2.471(2), 2.468(2)
2.329(4), 2.372(4)
—
2.082(2)
2.4643(4)
2.387(2)
—
Surprisingly, reaction of “[Zr(CH2SiMe3)2Cl2(Et2O)2]” with
one equivalent of H2NC6F5 (Scheme 2) consistently produced
the crystallographically characterised “ate” complex [Zr2(l-
NC6F5)2Cl6(THF)2{Li(THF)3}2] (4) rather than the anticipated
complex [Zr2(l-NC6F5)2Cl4(THF)4] analogous to 1–3. The com-
pound 4 was obtained in 63% isolated yield on a preparative
N
imide–Zr–Nimide
81.8(2)
82.7(2)
—
80.49(9)
100.65(7)
—
OTHF–Zr–OTHF
Npy–Zr–Npy
Cl–Zr–Cl
154.79(6)
150.49(2)
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8
1 4 4 9

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Fig. 2 Molecular structure of [Zr2(l-NC6F5)2Cl6(THF)2{Li(THF)3}2]
(4). Displacement ellipsoids drawn at the 25% probability level. H atoms
omitted. Atoms carrying the suffix ‘A’ are related to their counterparts
by the operator [−x, −y, −z].
Table 2 Selected bond lengths (A) and angles (◦) for [Zr2(l-
˚
NC6F5)2Cl6(THF)2{Li(THF)3}2] (4)
Zr(1)–N(1)
Zr(1)–N(1A)
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–Cl(3)
Zr(1)–O(1)
2.089(2)
2.123(2)
2.5497(5) Li(1) · · · F(5A)
2.4871(6) Li(1)–O(2)
2.4674(6) Li(1)–O(3)
Li(1)–Cl(1)
Li(1)–Cl(3)
2.570(4)
2.785(4)
2.843(5)
1.996(4)
1.963(5)
2.007(4)
2.278(2)
Li(1)–O(4)
N(1)–Zr(1)–N(1A) 79.48(7)
Cl(1)–Zr(1)–Cl(2) 96.07(2)
O(1)–Zr(1)–Cl(3) 165.79(4)
i
Fig. 1 Molecular structures of [Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1)
Zr–OTHF bonds perpendicular to the Zr2(l-N)2 plane (cf. 3).
(top) and [Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2) (bottom). Displace-
ment ellipsoids drawn at the 25% probability level. H atoms omitted.
Atoms carrying the suffix ‘A’ are related to their counterparts by the
operators [2 − x, −y, 2 − z] (for 1) and [x + 1/2, y + 1/2, z] (for 2).
There is some asymmetry in the Zr–Nimide bond distances
˚
(2.089(2) and 2.123(3) A) which could easily be attributable to
the rather asymmetric coordination environment about the Zr
˚
atoms. The Zr(1)–Cl(1) bond is 0.0626(8) A longer than Zr(1)–
scale and formed quantitatively in NMR-tube scale experiments.
Attempts to prepare a LiCl-free complex by treatment of 4 with
hot (100 ◦C) toluene were unsuccessful.
Cl(2) and is attributed to the coordination of Li(1) to Cl(1). Each
lithium cation in 4 is six-coordinate and ligated by three THF
molecules, two Zr-bound Cl atoms and the ortho F atom of a
C6F5 substituent. The coordination of solvated lithium cations to
anionic metal complexes is very well precedented.16,17 The ortho
C–F bond assisted coordination of Li has also been reported
previously.22
It is believed that “ate” complex formation only occurs
because of the highly electron-withdrawing C6F5 imido N-
substituent which renders the zirconium centre more elec-
tron deficient (Lewis acidic) and also provides an addi-
tional site of attachment of the Li+ cation (see below).
The source of LiCl is thought to be from the starting ma-
terial “[Zr(CH2SiMe3)2Cl2(Et2O)2]”12 prepared according to
the literature method of reacting LiCH2SiMe3 (2 equiv.)
with ZrCl4 in Et2O followed by a hexane–Et2O extraction
and evaporation of all volatiles. As described by Arnold,12
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” is fairly thermally sensitive and
is not amenable to further work-up or purification. Our own
analysis (Li and Cl elemental composition and 7Li NMR) of “as
prepared” [Zr(CH2SiMe3)2Cl2(Et2O)2]” suggests that it probably
has the composition “Zr(CH2SiMe3)2Cl2(Et2O)2·LiCl”, at least
in our hands. Throughout this present contribution we will
refer to the material as “[Zr(CH2SiMe3)2Cl2(Et2O)2]”, although
for the purposes of the molar calculations in the Experimen-
tal section we have assumed a molar mass appropriate for
“Zr(CH2SiMe3)2Cl2(Et2O)2·LiCl” which is ca. 10% greater than
for the salt-free composition.
The low-temperature (203 K) 500 MHz 1H NMR spectrum of
4 in toluene-d8 is consistent with the solid state structure (Fig. 2).
In total, three sets of THF resonances are observed in a 2 : 1 : 1
ratio (i.e, those bound to the Li+ cations are observed in a 2 : 1
“equatorial” : ”axial” ratio). As the temperature is increased
from 203 to 333 K all three sets of THF resonances broaden
and coalesce to form a single set of resonances indicating that at
high temperature all of the THF molecules are involved in rapid
site-exchange. The low temperature 19F NMR spectrum exhibits
equivalent ortho F atoms indicating that rotation about the N–
Cipso bond (ortho C–F bond exchange) is still rapid at 203 K on
the NMR timescale.
We have also carried out reactions between the alkyl
amines tBuNH2, iPrNH2 and PhCH2NH2 and “[Zr(CH2SiMe3)2-
Cl2(Et2O)2]” (Scheme 2). These yield the imido-bridged com-
t
i
pounds [Zr2(l-NR)2Cl4(THF)3] (R = Bu (5), Pr (6), Bz (7))
in somewhat lower (20–44%) isolated yields than for the aryl
imido complexes 1–4. According to the spectroscopic and
analytical data these compounds possess only three THF ligands
per dizirconium molecule, with one Zr being six-coordinate
and the other five-coordinate. A structurally characterised
tris(dimethylamine) analogue, namely [Zr2Cl4(l-NtBu)2(HN-
Me2)3] (12), is discussed later on.
The molecular structure of 4 is shown in Fig. 2 and selected
bond distances and angles are listed in Table 2. Molecules
of 4 formally contain a dianionic [Zr2(l-NC6F5)2Cl6(THF)2]2−
unit ligated by two [Li(THF)3]+ cations. The [Zr2(l-
NC6F5)2Cl6(THF)2]2− fragment is broadly comparable to the
neutral [Zr2(l-NAr)2Cl4(THF)4] complexes 1–3 and has its two
1 4 5 0
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8

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The 1H NMR spectrum (and variable-temperature behaviour)
of complexes 5–7 in C2D2Cl4 are similar and only the details
relating to 5 will be discussed. At 298 K the spectrum is rather
complex, possibly suggesting the presence of structural isomers
(e.g., interchange of axial and equatorial coordination sites).
The resonances are broad, indicating possible interconversion
between isomers. As the temperature is raised above 298 K the
spectrum becomes less complex and some of the resonances
sharpen. At 363 K (the high temperature limit) a single sharp
resonance is observed at 1.56 ppm (relative intensity 18H)
assigned to the imido tert-butyl substituent, together with broad
resonances at 4.89 (12H) and 1.93 (12H) ppm for three THF
ligands. This high temperature spectrum is consistent with the
structure proposed, but with all three THF ligands being labile
and in rapid site-exchange. Cooling the sample down from 298
to 183 K in an attempt to observe a static structure afforded only
a very complex spectrum consistent with the presence of several
isomeric species.
Synthesis of zirconium imido complexes from
[ZrCl2(NMe2)2(THF)2]
The use of “[Zr(CH2SiMe3)2Cl2(Et2O)2]” as a starting mate-
rial allowed the general synthesis of a range of zirconium
imido-dichloride complexes of the type [Zr2(l-NR)2Cl4(THF)x]
(R = alkyl or aryl, x = 3 or 4). Nonetheless, this synthetic
route has certain drawbacks in that the starting dialkyl is
of limited stability and cannot be stored for long periods
of time, and that the desired products are often formed as
waxy oils which require a time-consuming trituration step to
produce crystalline samples. Bearing in mind that reaction of
RNH2 with [Ti(NMe2)2Cl2] affords excellent conversions to
the imido complexes [Ti(NR)Cl2(NHMe2)2] for a wide range
of alkyl and aryl amines,5 an alternative synthetic route to
zirconium imido compounds starting from the readily available
and thermally stable [ZrCl2(NMe2)2(THF)2]23 was investigated.
Although [ZrCl2(NMe2)2(THF)2] has not been used in the
preparation of imido complexes, its use as a source of the {ZrCl2}
fragment through R2N–H bond protonolysis reactions has been
reported previously.24
Fig. 3 Molecular structures of [Zr2(l-N-2,6-C6H3Me2)2Cl4(NHMe2)2
(THF)2] (9) (top), [Zr2(l-N-2,6-C6H3Me2)2Cl4(py)4] (15) (bottom; atoms
carrying the suffix ‘A’ are related to their counterparts by the operator
[−x, −y, −z]). Displacement ellipsoids drawn at the 20% probability
level. H atoms bound to carbon omitted. H atoms bonded to N drawn
as spheres of arbitrary radius.
The reactions of four different aryl amines with
[ZrCl2(NMe2)2(THF)2] in pentane for 1–2 h afforded the
i
imido-bridged complexes [Zr2(l-N-2,6-C6H3 Pr2)2Cl4(NHMe2)x
◦
˚
Table 3 Selected bond lengths (A) and angles ( ) for [Zr2(l-N-2,6-
C6H3Me2)2Cl4(NHMe2)2(THF)2] (9)
(THF)y] (8, x and y are ill-defined, see below), [Zr2(l-
N-2,6-C6H3Me2)2Cl4(NHMe2)2(THF)2] (9) and [Zr2(l-
NAr)2Cl4(NHMe2)3(THF)] (Ar = Ph (10) or C6F5 (11)).
The products separate from solution under these conditions
as yellow to off-white solids in ca. 70 to 80% isolated yields.
The X-ray structure of 9 has been determined and confirms
the dimeric structures proposed in Scheme 3. The molecular
structure of 9 is shown in Fig. 3 and selected bond distances
and angles are listed in Table 3.
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–N(3)
Zr(1)–O(1)
2.4931(6) Zr(2)–Cl(3)
2.4596(7) Zr(2)–Cl(4)
2.4615(6)
2.5014(6)
2.133(2)
1.996(2)
2.466(2)
2.381(2)
2.017(2)
2.156(2)
2.455(2)
2.407(2)
Zr(2)–N(1)
Zr(2)–N(2)
Zr(2)–N(4)
Zr(2)–O(2)
N(1)–Zr(1)–N(2)
N(3)–Zr(1)–O(1)
Cl(1)–Zr(1)–Cl(2) 150.45(2) Cl(3)–Zr(2)–Cl(4)
81.14(8) N(1)–Zr(2)–N(2)
92.11(7) N(4)–Zr(2)–O(2)
82.20(8)
89.91(8)
151.62(2)
The coordination geometry and average distances and angles
for 9 are comparable to those of the tetrakis(THF) analogue
[Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2), to which it is formally
related by the replacement of two THF by two NHMe2 ligands.
However, unlike 2 which is constrained by 2/m crystallographic
symmetry, molecules of 9 lie on general positions in the crystal
lattice. There is quite a large variation in bond distances for
chemically equivalent linkages, and in particular the Zr–Cl
and Zr–Nimide bond lengths, although the latter might be a
consequence of the different donor atoms trans to the two Zr–
Nimide bonds. There are some intramolecular NH · · · Cl hydrogen
˚
bonds (NH · · · Cl = 2.79 and 2.89 A; angles subtended at H =
126 and 138◦; sum of the van der Waals radii for Cl and H =
25
˚
2.95 A (H atoms placed in estimated positions, see Experi-
mental section)) but these are at the long end of the range of
Scheme 3
such contacts that are deemed to be significant.26 The solid state
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8
1 4 5 1

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m(N–H) stretching frequency of 3278 cm−1 for 9 is also indicative
of a weak NH · · · Cl interaction according to our recent work on
certain extensively NH · · · Cl hydrogen bonded five-coordinate
titanium imido complexes [Ti(NR)Cl2(NHMe2)2].5 Here m(N–
H) values as low as 3220 cm−1 (associated NH · · · Cl distance
The molecular structure of [Zr2Cl4(l-NtBu)2(HNMe2)3] (12)
is shown in Fig. 4 and selected distances and angles are
summarised in Table 4. Molecules of 12 possess approximately
trigonal bipyramidal (Zr(1)) and octahedral (Zr(2)) metals
linked by bridging tert-butyl imido ligands. The Zr–Cl and
Zr–Nimide distances for Zr(2) are longer that those for Zr(1),
consistent with the higher coordination number of Zr(2) (and
for the Zr(2)–Cl bonds it should also be noted that these are
trans to the labilising l-imido nitrogens). In contrast the Zr(1)–
N(3) (NHMe2 ligand) distance is significantly longer than the
Zr(2)–N(4) and Zr(2)–N(5) distances, even though the latter
NHMe2 ligands are associated with the more sterically crowded
metal centre. The longer Zr–Namine distance for Zr(1) is in fact
attributable to N(3) being more trans to the strongly labilising
l-NR donors whereas the two NHMe2 ligands are only mutually
trans to each other. A structurally characterised precedent for
12 (i.e., containing a Zr2(l-NR)2 unit with different ligand sets
˚
2.45 A) were found. Note, however, that the presence of lower
energy solid state m(N–H) stretches in the other products 8, 10
and 11 (e.g. 3264 cm−1 in 11) indicates that in these cases more
significant NH · · · Cl hydrogen bonding is present.5
It can be seen from Scheme 3 that the exact numbers of THF
and NHMe2 ligands associated with the aryl imido products
8–11 formed from [Zr(NMe2)2Cl2(THF)2] depend critically on
the identity of the aniline aromatic ring substituents (and may be
associated with NH · · · Cl hydrogen bonding possibilities as the
products precipitate from the pentane solvent). Furthermore, the
lability of these donor ligands on the NMR timescale differed,
and in the case of 8 this even prevented the exact stoichiometry
of the donor ligand set from being determined. In principle,
however, it may be possible to convert the compounds 8–11
to the tetrakis(THF) analogues and we have shown this to
be feasible for compound 9. Thus a solution of [Zr2(l-N-2,6-
C6H3Me2)2(HNMe2)2(THF)2] (9) in THF was heated in an NMR
tube at 50 ◦C for 16 h. Removal of all volatiles and redissolving in
C6D6 showed that no dimethylamine remained and that [Zr2(l-
N-2,6-C6H3Me2)2(THF)4] (2) had been formed in quantitative
yield.
t
at each Zr) is [(Me4taa)Zr(l-NR)2Zr(NHR)2] (R = Bu or 2,6-
C6H3Me2),18 which feature six- and four-coordinate zirconium
centres within the same imido-bridged dizirconium molecules.
The ambient temperature solution 1H NMR spectrum of com-
plex 9 was consistent with the solid state structure determined
by X-ray diffraction and contained sharp resonances assigned
to the 2,6-C6H3Me2 substituents and to the dimethylamine and
THF ligands. The sharp nature of the resonances indicated
that the structure was static on the NMR timescale at this
temperature. The two complexes 10 and 11 displayed similar
1
variable-temperature H NMR behaviour and only 10 will be
1
discussed. The H NMR spectrum of 10 at 293 K showed two
equivalent N-phenyl groups. The THF ligand appeared as broad
resonances at 3.63 and 1.18 ppm and the NMe groups of the
three dimethylamine ligands gave rise to a single very broad
resonance at 2.44 ppm indicating rapid exchange. Upon heating
the sample to 363 K this resonance sharpened as expected (fast
exchange limit). Cooling to 223 K afforded the slow exchange
limiting spectrum which was more complex and revealed the
presence of two inequivalent phenyl imido groups, three distinct
dimethylamine ligands and a THF ligand. Therefore the actual
structure of 10 (and 11) appears be completely non-symmetric.
Unfortunately, the 1H NMR spectrum of complex 8 was
extremely broad even at all temperatures and a full assignment
of the spectrum was not possible.
Fig. 4 Molecular structure of [Zr2(l-NtBu)2Cl4(NHMe2)3] (12). Dis-
placement ellipsoids drawn at the 25% probablility level. H atoms
bonded to C omitted; H atoms bonded to N drawn as spheres of arbitrary
radius.
The solution dynamics of the complex [Zr2Cl4(l-
1
NtBu)2(HNMe2)3] (12) are discussed with reference to the H
NMR spectra at 243, 293, 343 and 383 K (in toluene-d8) shown
in Fig. 5. The 293 K spectrum features a septet at 3.42 ppm
assigned to the N–H protons of the dimethylamine groups
bound to the six-coordinate zirconium centre, and a doublet
at 2.75 ppm assigned to the corresponding methyl groups.
The third dimethylamine group (bound to the five-coordinate
zirconium) affords a broad resonance at 1.95 ppm indicating
that it is labile at this temperature (consistent with the longer
Zr(1)–N(3) distance mentioned above). On cooling to 243 K
this broad resonance sharpens to afford a doublet at 1.82 ppm
We have also examined reactions of [ZrCl2(NMe2)2(THF)2]
with alkyl amines (Scheme 3). Addition of one equiva-
lent of H2NtBu in pentane afforded the complex [Zr2Cl4(l-
NtBu)2(HNMe2)3] (12) as white powder which was isolated
in 64% yield. The imido bridged dimeric structure (anal-
ogous to those proposed for [Zr2Cl4(l-NR)2(THF)3] (5–7,
Scheme 2) consisting of one five- and one six-coordinate zirco-
nium centre was confirmed by single crystal X-ray diffraction
analysis. The molecular structure and variable-temperature
NMR behaviour are discussed below. The related complexes
◦
t
i
˚
Table 4 Selected bond lengths (A) and angles ( ) for [Zr2(l-N Bu)2-
[Zr(NR)Cl2(NHMe2)]x (R = Pr (13) or CH2Ph (14)) were
Cl4(NHMe2)3] (12)
prepared in comparable yields using an analogous synthetic
procedure but were totally insoluble in all non-donor solvents.
The presence of only one NHMe2 ligand per zirconium centre
(according to elemental analysis) suggests the possible presence
of vacant coordination sites, and the very insoluble nature of the
compounds could be indicative of polymer formation. However,
in the absence of structural data it is not possible to speculate
further. The presence of low frequency m(N–H) bands at 3180
(13) and 3194 cm−1 (14) suggest that NH · · · Cl intermolecular
hydrogen bonding may also be a significant factor with regards
to the insolubility of the compounds.
Zr(1)–Cl(1)
Zr(1)–Cl(2)
Zr(1)–N(1)
Zr(1)–N(2)
Zr(1)–N(3)
2.4981(4)
2.4934(4)
2.0111(11)
2.0210(11)
2.4894(12)
Zr(2)–Cl(3)
Zr(2)–Cl(4)
Zr(2)–N(1)
Zr(2)–N(2)
Zr(2)–N(4)
Zr(2)–N(5)
2.5166(3)
2.5382(3)
2.0877(11)
2.0735(11)
2.3971(12)
2.3809(12)
N(1)–Zr(1)–N(2)
Cl(1)–Zr (1)–Cl(2) 156.107(13) Cl(3)–Zr(2)–Cl(4)
N(4)–Zr(2)–N(5)
83.20(4)
N(1)–Zr(2)–N(2)
80.08(4)
91.816(12)
166.76(4)
1 4 5 2
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8

View Article Online
Fig. 5 Variable-temperature 500.1 MHz 1H NMR spectra of [Zr2Cl4(l-NtBu)2(HNMe2)3] (12) in toluene-d8. The multiplet at 2.10 ppm is attributed
residual CHD2C6D5.
with an associated septet (NHMe2) at 1.99 ppm indicating that
at this temperature the ligand is now firmly bound on the NMR
timescale. These resonances are rather upfield in comparison
with those of the other NHMe2 ligands. Heating the sample
to 343 K leads to a broadening of the resonances assigned to
the two NHMe2 ligands bound to the six-coordinate zirconium
centre, indicating that these ligands are labile at this temperature.
Finally, increasing the temperature to 383 K leads to total
coalescence of all NHMe2 methyl group resonances indicating
that at this temperature rapid site-exchange is occurring. The
additional minor peaks in the 243 and 293 K spectra are
probably due to minor conformational isomers of the dimer
which undergo exchange with the major isomer on heating.
of interest to see if some of the new zirconium imido complexes
could also be converted to (monomeric) pyridine adducts.
(1)
Pyridine adducts
Wigley8 has previously reported that the six-coordinate
Reaction of the THF adducts [Zr2(l-N-2,6-C6H3Me2)2-
Cl4(THF)4] (2) and [Zr2(l-NtBu)2Cl4(THF)3] (5) in dichloro-
methane with a very large excess of pyridine afforded the
corresponding dimeric products [Zr2(l-N-2,6-C6H3Me2)2-
Cl4(py)4] (15) and [Zr2(l-NtBu)2Cl4(py)3] (16) as yellow solids
in 35 and 60% isolated yields, respectively (Equation 1). It
therefore appears that these particular imido N-substituents
are insufficient with regards to forming monomeric pyridine
adducts.
The NMR spectra of the new compounds are consistent with
the proposed structures. In particular, the NMR spectra of 16
clearly show the presence of two different pyridine ligands in the
ratio 2 : 1. Compound 15 has been crystallographically charac-
terised. The molecular structure is shown in Fig. 3 and confirms
the dimeric structure. Selected bond distances and angles are
i
tris(pyridine) compound [Zr(N-2,6-C6H3 Pr2)Cl2(py)3] is
i
monomeric (synthesised from [Zr(N-2,6-C6H3 Pr2)(NH-2,6-
i
C6H3 Pr2)2(py)2] and SiMe3Cl and pyridine in THF). We have
shown10 that [Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1) can be con-
i
i
verted to [Zr(N-2,6-C6H3 Pr2)Cl2(py)3] by addition of pyridine,
and also to crystallographically characterised, monomeric six-
i
coordinate [Zr(N-2,6-C6H3 Pr2)Cl2(Me3[9]aneN3)] by addition
of 1,4,7-trimethyltriazacyclononane (Me3[9]aneN3).11 In related
titanium imido chemistry,4 the dimeric (chloride-bridged)
titanium imido compounds [Ti2(NR)2(l-Cl)2Cl2(py)4] (R =
tBu or aryl) can be converted to the monomeric tris(pyridine)
homologues [Ti(NR)Cl2(py)3]. Reaction of certain complexes
[Ti(NR)Cl2(NHMe2)2] with an excess of pyridine also forms the
corresponding [Ti(NR)Cl2(py)3] homologues.5a It was therefore
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8
1 4 5 3

View Article Online
◦
˚
methods. The actual structure of the complex previously re-
ported as “[Zr(CH2SiMe3)2Cl2(Et2O)2]” is believed to be the
“ate” complex “Zr(CH2SiMe3)2Cl2(Et2O)2·LiCl”. This assign-
ment was supported by 7Li NMR spectroscopy (d = −0.2 ppm)
and elemental analysis of a sample quenched with water [found
(calc. for C16H42Cl3LiO2Si2Zr): Li 1.4 (1.3), Cl 22.4 (20.2)%]. All
substances used in air- and moisture-sensitive manipulations
were purified by standard techniques.27 All other compounds
and reagents were purchased from commercial chemical suppli-
ers and used without further purification.
Table 5 Selected bond lengths (A) and angles ( ) for [Zr2(l-N-2,6-
C6H3Me2)2Cl4(py)4] (15)
Zr(1)–Cl(1)
Zr(1)–N(1)
Zr(1)–N(2)
2.4768(3)
2.0229(11)
2.5004(12)
Zr(1)–Cl(2)
Zr(1)–N(1A)
Zr(1)–N(3)
2.4805(3)
2.1227(11)
2.4822(12)
N(1)–Zr(1)–N(1A)
81.24(5)
N(2)–Zr(1)–N(3)
88.94(4)
Cl(1)–Zr (1)–Cl(2) 151.177(12)
listed in Table 5 and these are rather similar to those discussed
above for [Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2) and [Zr2(l-
N-2,6-C6H3Me2)2Cl4(NHMe2)2(THF)4] (9). The Zr–Nimide dis-
tances are slightly different (2.1231(13) and 2.0239(12) A) but
the average value is close to that in 2 and 9, and the extent of
asymmetry is less than in 9. The Zr–Cl distances (av. 2.4787(4)
i
[Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1). To a solution of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.865 g, 1.64 mmol) in THF
˚
(25 cm3) was added H2N-2,6-C6H3 Pr2 (0.30 cm3, 1.64 mmol)
i
at rt. The pale yellow mixture was stirred at rt for 10 h to give
a yellow solution. Removal of volatiles under reduced pressure
gave a waxy yellow solid which was triturated with pentane
(25 cm3) and filtered to give a yellow powder. Extraction into
toluene–THF (3 : 1, 40 cm3) and removal of volatiles under
reduced pressure afforded 1 as a yellow solid. 0.675 g, 85%.
Diffraction-quality crystals were grown from a pentane solution
at 0 ◦C. Characterising data were consistent with published
values.8
˚
A) are slightly longer than in 2, consistent with the better r
donor ability of pyridine in comparison to THF.
Summary
Protonolysis methodologies based on the reactions of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” or [Zr(NMe2)2Cl2(THF)2] with
primary alkyl and aryl amines provide general entry points to
dimeric zirconium imido dichloride compounds. The previously
i
[Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2). To a solution of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.865 g, 1.64 mmol) in THF
(25 cm3) was added H2N-2,6-C6H3Me2 (0.20 cm3, 1.64 mmol)
at rt. The pale yellow mixture was stirred at rt for 10 h to give
a yellow solution. Removal of volatiles under reduced pressure
gave a waxy yellow solid which was triturated with pentane
(25 cm3) and filtered to gave a yellow powder. Extraction into
toluene–THF (3 : 1, 40 cm3) and removal of volatiles under
reduced pressure afforded 2 as a yellow solid. Yield: 0.513 g
(74%). Diffraction-quality crystals were grown from a THF–
pentane mixture at 5 ◦C. 1H NMR (CDCl3, 500.1 MHz, 298 K):
reported “[Zr(N-2,6-C6H3 Pr2)Cl2(THF)2]” is dimeric, at least in
the solid state. Two main structural types are formed depending
on whether aryl or alkyl amines are used, namely [Zr2(l-
NAr)2Cl4(L)4] or [Zr2(l-NR)2Cl4(L)3]. The presence of LiCl
in “[Zr(CH2SiMe3)2Cl2(Et2O)2]” is only a complication for the
reaction with H2NC6F5 in which case an “ate” complex is
formed. [Zr(NMe2)2Cl2(THF)2] is more convenient as a starting
material in terms of its thermal stability, but it can give less well
defined (or predictable) products. Attempts to cleave dimeric
[Zr2(l-2,6-C6H3Me2)2Cl4(THF)4] or [Zr2(l-NtBu)2Cl4(THF)3]
with pyridine yields only the corresponding dimeric pyridine
adducts.
3
3
d 6.91 (4H, d, J = 10.5 Hz, m-C6H3Me2), 6.62 (2H, t, J =
10.5 Hz, p-C6H3Me2), 3.70 (16H, br s, C4H8O), 2.75 (12H, s,
C6H3Me2), 1.52 (16H, br s, C4H8O). 13C{ H} NMR (CDCl3,
1
Experimental
125.7 MHz, 298 K): d 151.1 (o-C6H3Me2), 130.7 (i-C6H3Me2),
128.2 (m-C6H3Me2), 122.4 (p-C6H3Me2), 72.3 (C4H8O), 25.0
(C4H8O), 21.3 (C6H3Me2). IR (KBr plates, Nujol): 1402 (w),
1250 (m), 1190 (s), 1102 (m), 1044 (w), 1006 (m), 866 (m), 768
(m), 740 (m), 716 (w), 582 (s), 516 (s). Anal. found (calc. for
C32H50Cl4N2O4Zr2): C 44.8 (45.2), H 5.6 (5.9), N 3.6 (3.3)%.
General methods and instrumentation
All air- and moisture-sensitive manipulations were performed
using standard Schlenk-line (Ar) and dry-box (N2) techniques.
Solvents were pre-dried over 4 A molecular sieves, refluxed over
˚
the appropriate drying agents (CaH2, sodium or potassium)
under N2, distilled at atmospheric pressure and stored in Teflon
valve ampoules. Deuterated solvents were dried over sodium,
potassium or CaH2 as appropriate, distilled under reduced
pressure and stored in Teflon valve ampoules. NMR samples
were prepared in Wilmad 505-PS tubes fitted with J. Young
[Zr2(l-NPh)2Cl4(THF)4]
(3). To
a
solution
of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.865 g, 1.64 mmol) in THF
(25 cm3) was added PhNH2 (0.15 cm3, 1.64 mmol) at rt. The
pale yellow mixture was stirred at rt for 10 h to give a yellow
solution. Removal of volatiles under reduced pressure gave
a yellow solid which was extracted into toluene–THF (3 : 1,
40 cm3) and volatiles removed under reduced pressure to afford
NMR/5 valves. 1H, 13C{ H} and 19F NMR spectra were
1
recorded on Varian Unity Plus 500 and Varian Mercury-VX
300 spectrometers. 1H and 13C spectra are referenced internally
to residual protio-solvent (1H) or solvent (13C) resonances and
are reported relative to tetramethylsilane (d = 0 ppm). 19F
spectra were referenced externally to CFCl3. Chemical shifts
are quoted in d (ppm) and coupling constants in Hertz. IR
spectra were recorded on Perkin Elmer 1600 and Perkin Elmer
1710 spectrometers as Nujol mulls between KBr windows or as
CH2Cl2 solutions in a 0.1 mm pathlength NaCl cell. All data are
quoted in wavenumbers (cm−1). Mass spectra were recorded on
Micromass Autospec 500, AEI MS902, and Finnigan MAT 900
XLT spectrometers. All data are quoted in mass/charge ratio
(m/z). Elemental analyses were carried out by the analytical
laboratory at the Inorganic Chemistry Laboratory Oxford or
Mikroanalytisches Labor Pascher, Germany.
1
3 as a yellow solid. Yield: 0.402 g (61%). H NMR (CDCl3,
3
300.1 MHz, 298 K): d 7.18 (4H, app. t, J = 8.4 Hz, m-C6H5),
3
3
7.09 (4H, d, J = 8.1 Hz, o-C6H5), 6.76 (2H, t, J = 7.5 Hz,
p-C6H5), 3.91 (16H, br s, C4H8O), 1.79 (16H, br s, C4H8O).
13C{ H} NMR (CDCl3, 75.5 MHz, 298 K): d 152.4 (i-C6H5),
1
128.0 (m-C6H5), 121.3 (o-C6H5), 120.6 (p-C6H5), 71.0 (C4H8O),
25.6 (C4H8O). IR (KBr plates, Nujol): 1582 (m), 1342 (w), 1228
(s), 1168 (w), 1042 (m), 868 (m), 754 (m), 694 (w), 622 (w), 578
(m). Anal. found (calc. for C28H42Cl4N2O4Zr2): C 41.8 (42.1), H
5.0 (5.3), N 3.2 (3.5)%.
[Zr2(l-NC6F5)2Cl6(THF)2{Li(THF)3}2] (4). To a solution of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.865 g, 1.64 mmol) in THF
(10 cm3) was added a solution of H2NC6F5 (0300 g, 1.64 mmol)
in THF (10 cm3) at rt. The pale yellow mixture was stirred at
rt for 10 h to give a pale yellow solution and a white solid. The
reaction mixture was filtered to afford 4 as a white solid. Yield:
0.614 g (63%). 1H NMR (C7D8, 500.1 MHz, 203 K): d 4.89 (8H,
Literature preparations
The compounds “[Zr(CH2SiMe3)2Cl2(Et2O)2]”12 and [Zr-
(NMe2)2Cl2(THF)2]23 were prepared according to published
1 4 5 4
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8

View Article Online
br m, C4H8O–Zr), 3.60 (16H, br m, C4H8O–Li), 3.48 (8H, br
m, C4H8O–Li), 1.35 (16H, br m, C4H8O–Li), 1.27 (8H, br m,
at rt for 1 h and filtered to afford 8 as a lemon coloured
powder which was dried under reduced pressure. Yield 0.132 g.
A meaningful percentage yield cannot be calculated since
the formula weight is uncertain. Elemental analysis was not
consistent with a meaningful formula. The 1H NMR spectrum
of isolated 8 was extremely broad and an assignment was not
possible. Therefore, 1H and 13C NMR data are reported for the
complex prepared in situ in an NMR tube without removal
1
C4H8O–Li), 0.80 (8H, br m, C4H8O–Zr). 13C{ H} NMR (C7D8,
75.5 MHz, 203 K): d 68.1 (C4H8O), 25.7 (C4H8O). 19F NMR
(C7D8, 282.5 MHz, 203 K): d 145.5 (4F, d, 3J = 24.2 Hz, o- or
3
m-C6F5N), 161.21 (4F, t, J = 24.2 Hz, o- or m-C6F5N), 164.6
3
7
(2F, t, J = 24.2 Hz, p-C6F5N). Li NMR (C6D6, 116.5 MHz,
298 K): d 0.25 (fwhm = 9.39 Hz). IR (KBr plates, Nujol): 1524
(m), 1260 (m), 1098 (m), 1018 (m), 948 (w), 802 (m). Anal. found
(calc. for C44H64Cl6F10Li2N2O4Zr2): C 39.0 (39.2), H 4.6 (4.8), Cl
16.5 (15.8), Li 1.4 (1.0), N 2.0 (2.3)%.
1
of volatiles. H NMR (C6D6, 500.1 MHz, 293 K): d 7.21 (4H,
3
i
3
d, J = 7.6 Hz, m-NC6H3 Pr2), 6.95 (2H, t, J = 7.6 Hz, p-
NC6H3 Pr2), 4.78 (4H, sept., 3J = 7.1 Hz, ArCHMe2), 3.61
i
(16H, m, OCH2CH2) 2.11 (24H, br s, HNMe2), 1.53 (24H, d,
3J = 7.1 Hz, ArCHMe2), 1.30 (16H, m, OCH2CH2). Resonance
[Zr2Cl4(l-NtBu)2(THF)3]
(5). To
a
solution
of
1
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.327 g, 0.62 mmol) in THF
(20 cm3) was added tBuNH2 (65 ll, 0.62 mmol) at rt. The pale
yellow mixture was stirred at rt for 10 h. Removal of volatiles
under reduced pressure gave a waxy pale yellow solid which
was triturated with pentane (15 cm3) and filtered to give a pale
yellow powder. Extraction into toluene–THF (3 : 1, 40 cm3)
and removal of volatiles under reduced pressure afforded 5 as
for HNMe2 not observed. 13C{ H} NMR (C6D6, 125.7 MHz,
i
i
293 K): d 151.9 (i-NC6H3 Pr2), 143.4 (o-NC6H3 Pr2), 122.4
i
i
(m-NC6H3 Pr2), 120.3 (p-NC6H3 Pr2), 68.8 (OCH2CH2), 40.2
(HNMe2), 27.8 (ArCHMe2), 25.5 (OCH2CH2) 24.6 (ArCHMe2).
IR (KBr plates, Nujol): 3254 (w), 3230 (w), 3148 (w), 1422 (m),
1356 (w), 1334 (m), 1282 (w), 1102 (w), 1016 (w), 992 (w), 944
(w), 756 (w). Anal. found C 48.3 H 7.0, N 5.1%.
1
a pale yellow solid. Yield: 0.091 g (43%). H NMR (C2D2Cl4,
500.1 MHz, 363 K): d 4.89 (12H, br s, C4H8O), 1.93 (12H, br s,
C4H8O), 1.56 (18H, s, NtBu). IR (KBr plates, Nujol): 1362 (m),
1218 (m), 1176 (s), 1042 (s), 972 (s), 916 (w), 894 (m), 858 (m).
Anal. found (calc. for C20H42Cl4N2O3Zr2): C 34.9 (35.2), H 6.2
(6.2), N 4.0 (4.1)%. This complex decomposes slowly at high
temperatures in C2D2Cl4 so 13C NMR data were not recorded.
[Zr2(l-N-2,6-C6H3Me2)2Cl4(NHMe2)2(THF)2] (9). To
a
stirred suspension of [ZrCl2(NMe2)2(THF)2] (0.224 g,
0.57 mmol) in pentane (20 cm3) was added H2N-2,6-C6H3Me2
(70 ll, 0.57 mmol) at rt. The pale yellow–green suspension
became deep yellow almost instantly. The suspension was
stirred at rt for 1 h and filtered to afford 9 as a dark yellow
powder which was dried under reduced pressure. Yield:
0.178 g (79%). Diffraction-quality crystals were grown by
slow diffusion of pentane into a toluene solution of 9 at
rt. 1H NMR (C6D6, 300.1 MHz, 293 K): d 6.98 (4H, d,
3J = 7.9 Hz, meta-NC6H3Me2), 6.73 (2H, t, 3J = 7.9 Hz,
[Zr2Cl4(l-NiPr)2(THF)3]
(6). To
a
solution
of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.474 g, 0.90 mmol) in THF
i
(20 cm3) was added PrNH2 (77 ll, 0.90 mmol) at rt. The pale
yellow mixture was stirred at rt for 16 h to give an orange
solution. Removal of volatiles under reduced pressure gave a
waxy orange solid which was triturated with pentane (30 cm3)
and filtered to give a sandy coloured powder. Extraction into
toluene–THF (3 : 1, 40 cm3) and removal of volatiles under
reduced pressure afforded 6 as a sandy coloured solid. Yield:
0.058 g (20%). 1H NMR (C2D2Cl4, 500.1 MHz, 393 K): d 4.19
(12H, br s, C4H8O), 1.99 (12H, br s, C4H8O), 1.37 (12H, br
m, CHMe2), CHMe2 resonance not observed. IR (KBr plates,
Nujol): 1261 (m), 1161 (w), 1114 (w), 1042 (m), 917 (w), 848
(m), 722 (w). Anal.: found (calc. for C18H38Cl4N2O3Zr2): C 32.6
(33.0), H 5.4 (5.8), N 4.0 (4.3)%. This complex decomposes
slowly at high temperatures in C2D2Cl4 so 13C NMR data were
not recorded.
3
para-NC6H3Me2), 3.70 (8H, app. t, app. J = 6.6 Hz, C4H8O),
3.18 (12H, s, NC6H3Me2), 1.76 (12H, s, HNMe2), 0.96 (8H, m,
1
C4H8O), resonance for HNMe2 not observed. 13C{ H} NMR
(C6D6, 75.5 MHz, 293 K): d 151.8 (ipso-NC6H3Me2), 130.1
(meta-NC6H3Me2), 128.6 (ortho-NC6H3Me2), 122.1 (para-
NC6H3Me2), 73.4 (C4H8O) 38.9 (HNMe2), 25.2 (C4H8O), 22.3
(NC6H3Me2). Mass spectrum (EI+, m/z): 561 [M − 2THF −
2HNMe2]+ 5%. IR (KBr plates, Nujol): 3278 (w), 1580 (w),
1402 (w), 1252 (m), 1196 (s), 1102 (m), 996 (m), 888 (m), 570
(m), 496 (m) cm−1. Anal. found (calc. for C28H48Cl4N4O2Zr2):
C 39.8 (42.2), H 6.1 (6.1), N 7.6 (7.0)%. Recrystallisations did
not lead to an improved %C figure for this crystallographically
characterised compound.
[Zr2Cl4(l-NCH2Ph)2(THF)3] (7). To
a
solution of
“[Zr(CH2SiMe3)2Cl2(Et2O)2]” (0.474 g, 0.90 mmol) in THF
(20 cm3) was added PhCH2NH2 (98 ll, 0.90 mmol) at rt.
The pale yellow mixture was stirred at rt for 20 h to give a
dark red/brown solution. Removal of volatiles under reduced
pressure gave a dark red–brown waxy solid which was triturated
with pentane (30 cm3) and filtered to give a brown powder.
Extraction into toluene–THF (3 : 1, 40 cm3) and removal of
volatiles under reduced pressure afforded 7 as a brown solid.
[Zr2Cl4(l-NPh)2(HNMe2)3(THF)] (10). To a stirred suspen-
sion of [ZrCl2(NMe2)2(THF)2] (0.217 g 0.55 mmol) in pentane
(20 cm3) was added H2NPh (50 ll, 0.55 mmol) at rt. Shortly after
addition, the pale yellow–green suspension became pale yellow.
The suspension was stirred at rt for 2 h and filtered to afford 10 as
a pale yellow powder which was dried under reduced pressure.
1
Yield: 0.162 g (83%). H NMR (C6D6, 300.1 MHz, 293 K): d
7.24 (8H, app. d, app. 3J = 4.1 Hz, overlapping ortho and meta-
NC6H5), 6.80 (2H, app. quin., app. 3J = 4.1 Hz, para-NC6H5),
1
Yield: 0.150 g (44%). H NMR (C2D2Cl4, 500.1 MHz, 353 K):
3
d 7.38 (10H, br m, overlapping o-, m-, p-C6H5), 3.91 (12H, br s,
C4H8O), 1.92 (12H, br s, C4H8O), CH2C6H5 resonance not
observed. IR (KBr plates, Nujol): 1588 (w), 1299 (w), 1261 (m),
1094 (w), 1071 (w), 1041 (m), 916 (w), 850 (w), 801 (m), 699
(m). Anal. found (calc. for C26H38Cl4N2O3Zr2): C 41.1 (41.6),
H 5.3 (5.1), N 3.7 (3.7)%. This complex decomposes slowly
at high temperatures in C2D2Cl4 so 13C NMR data were not
recorded.
3.63 (4H, app. t, app. J = 6.3 Hz, C4H8O), 2.44 (18H, br s,
HNMe2), 1.18 (4H, br s, C4H8O), resonance for HNMe2 not
observed. 1H NMR (toluene-d8, 300.1 MHz, 223 K): d 7.4 − 7.2
(8H, m, ortho and meta-NC6H5), 6.9–6.7 (2H, m, para-NC6H5),
3
3.58 (4H, m, C4H8O), 3.37 (1H, sept., J = 5.9 Hz, HNMe2),
2.70 (6H, d, 3J = 5.9 Hz, HNMe2), 2.48 (1H, sept., 3J = 5.9 Hz,
3
HNMe2), 2.17 (6H, d, J = 5.9 Hz, HNMe2) 1.90 (1H, sept.,
3J = 5.9 Hz, HNMe2), 1.61 (6H, d, 3J = 5.9 Hz, HNMe2), 1.38
(2H, m, C4H8O), 0.69 (2H, m, C4H8O). IR (KBr plates, Nujol):
3250 (w), 1582 (s), 1470 (s), 1228 (s), 1170 (m), 1068 (w), 1000
(m), 888 (s), 832 (m), 756 (s), 698 (m), 612 (w), 578 (s), 500 (m),
472 (w), 448 (w). Anal. found (calc. for C22H39Cl4N5OZr2): C
36.0 (37.0), H 5.5 (5.5), N 9.8 (9.8)%. Recrystallisations did not
lead to an improved %C figure.
i
“[Zr2Cl4(l-N-2,6-C6H3 Pr2)2(NHMe2)x(THF)y]” (8). To a
stirred suspension of [ZrCl2(NMe2)2(THF)2] (0.209 g,
0.53 mmol) in pentane (20 cm3) was added H2N-2,6-C6H3 Pr2
i
(100 ll, 0.53 mmol) at rt. The pale yellow–green suspension
became deep yellow almost instantly. The suspension was stirred
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8
1 4 5 5

View Article Online
[Zr2Cl4(l-NC6F5)2(HNMe2)3(THF)] (11). To a stirred sus-
pension of [ZrCl2(NMe2)2(THF)2] (0.209 g, 0.53 mmol) in
pentane (20 cm3) was added a solution of H2NC6F5 (0.097 g,
0.53 mmol) in pentane (10 cm3) at rt. Following addition, the
mixture became slightly darker. The suspension was stirred at rt
for 2 h and filtered to afford 11 as an off-white powder which was
was stirred for 5 h at rt and filtered to afford 14 as a white powder
which was dried under reduced pressure. Yield: 0.103 g (52%).
The product was insoluble in all standard (non-coordinating)
solvents and NMR data could not be obtained. IR (KBr plates,
Nujol): 3194 (s), 1600 (w), 1344 (w), 1260 (w), 1112 (w), 1046
(s), 1026 (s), 888 (s), 804 (w), 698 (s). Anal. found (calc. for
{C9H14Cl2N2Zr}x): C 33.7 (34.6), H 5.4 (4.5), N 9.4 (9.0)%.
1
dried under reduced pressure. Yield: 0.160 g (68%). H NMR
(C6D6, 300.1 MHz, 293 K): d 3.59 (4H, app. t, C4H8O), 2.8–1.8
(18H, 2 br s, HNMe2), 1.24 (4H, br s, C4H8O), resonance for
HNMe2 not observed. 19F NMR (C6D6, 252.2 MHz, 293 K):
[Zr2(l-N-2,6-C6H3Me2)2Cl4(py)4] (15). [Zr2(l-N-2,6-C6H3-
Me2)2Cl4(THF)4] (2, 1.490 g, 1.75 mmol) was slurried into
CH2Cl2 (40 cm3) and pyridine (30 cm3) was added. The resulting
yellow solution was stirred at rt for 16 h and concentrated
under reduced pressure to a volume of 40 cm3, giving an orange
solution and a bright yellow precipitate. Filtration yielded 15
as a yellow powder which was washed with CH2Cl2 (2 ×
10 cm3) and dried under reduced pressure Yield: 0.562 g (35%).
Diffraction-quality crystals were grown by layering a CH2Cl2
solution of 15 (containing a few drops of pyridine to solubilise
3
4
d −162.45 (4F, dd, J = 16.6 Hz, J = 7.6 Hz, ortho-NC6F5),
3
3
−165.00 (4F, dd, J(ortho-meta) = 16.6 Hz, J(meta-para) =
3
4
22.7 Hz, meta-NC6F5), −173.65 (2F, tt, J = 22.7 Hz, J =
1
7.6 Hz, para-NC6F5). H NMR (C7D8, 300.1 MHz, 203 K):
d 3.73 (2H, br s, (HNMe2)2Zr), 3.44 (4H, br s, C4H8O), 2.61
(12H, app. t, (HNMe2)2Zr), 1.92 (1H, m, (HNMe2)(THF)Zr),
3
1.41 (6H, d, J = 5.9 Hz, (HNMe2)(THF)Zr), 0.56 (4H, br s,
C4H8O). 19F NMR (C7D8, 252.2 MHz, 203 K): d −150.68 (2F,
3
1
app. d, app. J = 22.7 Hz, ortho-NC6F5), −151.43 (2F, app. d,
the compound) with pentane at room temperature. H NMR
app. 3J = 22.7 Hz, ortho-NC6F5), −164.15 (2F, app. t, app. 3J =
22.7 Hz, meta-NC6F5), −164.76 (2F, app. t, app. 3J = 22.7 Hz,
(CDCl3, 500.1 MHz, 298 K): d 8.42 (8 H, br s, o-NC5H5),
7.58 (4 H, br t, 3J = 6.83, p-NC5H5), 7.03 (8 H, br m, m-
NC5H5), 6.69 (4 H, d, 3J = 7.32 m-C6H3Me2), 6.56 (2 H,
3
meta-NC6F5), −167.80 (1F, app. t, app. J = 22.7 Hz, para-
3
3
1
t, J = 7.32, p-C6H3Me2), 2.59 (12 H, s, C6H3Me2). 13C{ H}
NMR (CDCl3, 75.5 MHz, 298 K): d 150.4 (overlapping o-
C6H3Me2 and o-NC5H5), 137.0 (p-NC5H5), 132.5 (i-C6H3Me2),
127.8 (m-C6H3Me2), 123.26 (m-NC5H5), 121.9 (p-C6H3Me2),
21.2 (C6H3Me2). IR (CH2Cl2, cm−1): 3944 (w), 3756 (w), 3728
(w), 3692 (w), 3066 (s), 3048 (s), 2986 (s), 2830 (w), 2686 (m), 2522
(w), 2410 (w), 2304 (s), 2156 (w), 2126 (w), 2054 (w), 1970 (w),
1604 (w), 1550 (w), 1422 (s, br), 1284 (s), 1268 (s), 1250 (s), 1200
(s), 1156 (m), 1100 (w), 1064 (w), 1082 (w), 1008 (w), 986 (w), 822
(s), 788 (s), 754 (s), 744 (s), 742 (s), 682 (s), 576 (m), 538 (m), 526
(m), 508 (s), 498 (s), 478 (s), 416 (s). EIMS: m/z 280 [1/2M −
py − Cl]+. Anal. found (calc. for C36H38Cl4N6Zr2·0.3CH2Cl2): C
48.1 (48.2), H 4.4 (4.3), N 9.5 (9.3)%.
NC6F5), −169.08 (1F, app. t, app. J = 22.7 Hz, para-NC6F5).
IR (KBr plates, Nujol): 3320 (w), 3302 (w), 3264 (w), 2664 (w),
2422 (w), 1644 (w), 1622 (w), 1586 (w), 1494 (s), 1444 (s), 1298
(m), 1248 (w), 1210 (w), 1158 (s), 1124 (w), 1108 (w), 1016 (s),
1000 (s), 978 (s), 928 (w), 850 (w), 780 (w), 676 (w), 652 (m), 532
(w). Anal. found (calc. for C22H29Cl4F10N5OZr2): C 29.2 (29.6),
H, 3.7 (3.3), N 7.8 (7.8)%.
[Zr2Cl4(l-NtBu)2(HNMe2)3] (12). To a stirred suspension of
[ZrCl2(NMe2)2(THF)2] (0.334 g, 0.85 mmol) in pentane (20 cm3)
was added H2NtBu (89 ll, 0.85 mmol) at rt. The suspension
was stirred for 3 d at rt, during which time the mixture became
milky white. The reaction mixture was filtered to afford 12 as
a white powder which was dried under reduced pressure. Yield:
0.162 g (64%). Diffraction-quality crystals were grown from a
[Zr2(l-NtBu)2Cl4(py)3] (16). To
a
slurry of [Zr2(l-
NtBu)2Cl4(THF)3] (5, 1.512 g, 2.21 mmol) in CH2Cl2 (30 cm3)
was added pyridine (40 cm3) to give a yellow solution which
was stirred at rt for 16 h. Volatiles were removed under reduced
pressure and the resulting yellow oil was triturated with pentane
(40 cm3) and filtered to yield 16 as a yellow solid. Yield: 0.928 g
(60%). 1H NMR (CDCl3, 500.1 MHz, 298 K): d 9.67 (2 H, br s, o-
C5H5N), 8.69 (4 H, br s, o-C5H5N), 7.89 (1 H, br m, p-C5H5N),
7.67 (2 H, m, br m, p-C5H5N), 7.50 (2 H, br m, m-C5H5N),
1
pentane solution at rt. H NMR (C7D8, 300.1 MHz, 293 K):
3
d 3.42 (2H, sept., J = 5.9 Hz, (Me2NH)2Zr), 2.75 (12H, d,
3J = 5.9 Hz, (Me2NH)2Zr), 1.95 (6H, br s, (Me2NH)Zr), 1.49
1
(18H, s, NtBu), resonance for (Me2NH)Zr not observed. H
NMR (C7D8, 300.1 MHz, 243 K): d 3.39 (2H, sept., 3J =
5.9 Hz, (Me2NH)2Zr), 2.70 (12H, d, 3J = 5.9 Hz, (Me2NH)2Zr),
3
3
1.99 (1H, sept., J = 5.9 Hz, (Me2NH)Zr), 1.82 (6H, d, J =
5.9 Hz, (Me2NH)Zr), 1.50 (18H, s, NtBu). 13C{ H} NMR (C7D8,
1
1
7.29 (4 H, br m, m-C5H5N), 1.48 (18 H, s, tBu). 13C{ H} NMR
75.5 MHz, 243 K): d 63.1 (NCMe3), 42.2 ((Me2NH)2Zr), 38.5
((Me2NH)Zr), 31.3 (NCMe3). IR (KBr plates, Nujol): 3280 (w),
1466 (s), 1354 (m), 1250 (w), 1220 (w), 1176 (s), 1108 (w), 1016
(m), 992 (s), 956 (s), 884 (s), 778 (w), 644 (s), 498 (w). Anal.:
found (calc. for C14H39Cl4N5Zr2): C 27.1 (27.9), H 6.5 (6.5),
N 11.0 (11.6)%. Recrystallisations did not lead to improved
%C or N figures for this crystallographically characterised
compound.
(CDCl3, 75.5 MHz, 298K): d 152.3 (o-C5H5N), 150.1(o-C5H5N),
139.3 (p-C5H5N), 136.5 (p-C5H5N), 124.1 (m-C5H5N), 123.8 (m-
C5H5N), 64.0 (CMe3), 30.6 (CMe3). IR (CH2Cl2, cm−1): 3944
(m), 3758 (w), 3726 (w), 3962 (w), 3060 (s), 3048 (s), 2982 (s),
2830 (w), 2696 (m), 2522 (w), 2410 (w), 2304 (s), 2156 (w), 2126
(w), 2054 (w), 1970 (w), 1608 (w), 1582 (w), 1550 (w), 1426 (s),
1284 (s), 1276 (s), 1250 (s), 1156 (m), 1102 (w), 1104 (w), 1070
(w), 1030 (w), 1012 (w), 1104 (w), 1070 (w), 1030 (w), 1012 (w),
992 (w), 958 (w), 892 (s), 784 (s), 740 (s), 716 (s), 700 (s), 680 (s),
666 (s), 586 (m), 570 (m), 554 (m), 520 (s), 490 (s), 466 (s), 456 (s),
440 (s), 424 (s). Anal. found (calc. for C23H33Cl4N5Zr2·0.5C5H12):
C, 41.5 (41.4); H 4.7 (5.3); N, 9.6 (9.5)%.
[Zr(NiPr)Cl2(NHMe2)]x (13). To a stirred suspension of
[ZrCl2(NMe2)2(THF)2] (0.250 g, 0.63 mmol) in pentane (20 cm3)
was added H2NiPr (54 ll, 0.63 mmol) at rt. The suspension
was stirred for 15 h at rt. The reaction mixture was filtered to
afford 13 as a white powder which was dried under reduced
pressure. Yield: 0.162 g (64%). The product was insoluble in all
standard (non-coordinating) solvents and NMR data could not
be obtained. IR (KBr plates, Nujol): 3180 (s), 1260 (w), 1158
(w), 1112 (m), 1022 (w), 982 (w), 894 (m), 802 (w). Anal.: found
(calc. for {C5H14Cl2N2Zr}x): C 22.6 (22.7), H 6.5 (5.3), N 11.4
(10.6)%.
Crystal structure determinations of
i
[Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1),
[Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2),
[Zr2(l-NC6F5)2Cl6(THF)2{Li(THF)3}2] (4),
[Zr2(l-N-2,6-C6H3Me2)2Cl4(NHMe2)2(THF)2] (9),
[Zr2(l-NtBu)2Cl4(NHMe2)3] (12) and
[Zr2(l-N-2,6-C6H3Me2)2Cl4(py)4] (15)
[ZrCl2(NCH2Ph)(HNMe2)]x (14). To a stirred suspension of
[ZrCl2(NMe2)2(THF)2] (0.250 g, 0.63 mmol) in pentane (25 cm3)
was added H2NCH2Ph (69 ll, 0.63 mmol) at rt. The suspension
Crystal data collection and processing parameters are given
in Table 6. Crystals were immersed in a film of perfluo-
ropolyether oil on a glass fiber and transferred to a Enraf-Nonius
1 4 5 6
D a l t o n T r a n s . , 2 0 0 5 , 1 4 4 8 – 1 4 5 8

View Article Online
i
Table 6 X-ray data collection and processing parameters for [Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1), [Zr2(l-N-2,6-C6H3Me2)2Cl4(THF)4] (2),
[Zr2(l-NC6F5)2Cl6(THF)2{Li(THF)3}2] (4), [Zr2(l-N-2,6-C6H3Me2)2Cl4(NHMe2)2(THF)2] (9), [Zr2(l-NtBu)2Cl4(NHMe2)3] (12) and [Zr2(l-N-2,6-
C6H3Me2)2Cl4(py)4] (15)
1
2
4
9
12
15
Formula
Formula weight 963.22
C40H66Cl4N2O4Zr2 C32H50Cl4N2O4Zr2 C44H64Cl6F10Li2N2O8Zr2 C28H48Cl4N4O2Zr2 C14H39Cl4N5Zr2
C36H38Cl4N6Zr2
878.99
Monoclinic
851.00
Orthorhombic
Cmca
12.7820(3)
17.5806(5)
15.5901(4)
—
—
—
1722.4(1)
4
1348.02
Triclinic
P1
796.97
Orthorhombic
Pca21
9.4672(1)
17.0837(3)
21.1400(3)
—
—
—
3419.1(1)
4
601.75
Triclinic
¯
P1
Crystal system
Space group
Monoclinic
¯
P21/n
11.1206(4)
15.9555(6)
12.6383(5)
—
93.200(2)
—
2239.0(1)
2
P21/n
˚
a/A
10.3615(2)
11.7620(2)
11.9942(2)
93.973(1)
97.234(1)
106.1726(8)
1384.35(4)
1
10.0181(1)
10.0274(1)
14.3986(2)
97.5478(6)
101.1935(6)
110.7356(6)
1295.05(3)
2
12.2186(1)
12.4098(2)
12.2628(2)
—
105.0415(7)
—
1795.70(4)
2
0.914
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
l/mm−1
0.74
0.92
11874
14507
1.23
Total reflections 8483
0.0644
4063
0.0271,
0.0326
0.749
0.0350
0.0278
0.95
0.0231
0.0267
11080
0.0194
0.0093
7336
0.0232
0.0253
Ra
a
Rw [I > 3r(I)]
0.0487
ꢀ
ꢀ
ꢀ
ꢀ
√
a R1 = ꢁFo| − |Fcꢁ/ |Fo|; Rw
=
{
w(|Fo| − |Fc|)2/ (w|Fo|2}.
Kappa-CCD diffractometer equipped with an Oxford Cryosys-
tems low-temperature device. Data were collected at low tempe-
rature using Mo-Ka radiation; equivalent reflections were
merged and the images were processed with the DENZO and
SCALEPACK programs.28 Corrections for Lorentz-polarisation
effects and absorption were performed and the structures were
solved by direct methods using SIR92.29 Subsequent difference
Fourier syntheses revealed the positions of all other non-
hydrogen atoms, and hydrogen atoms were placed geometrically
ed. C. G. Screttas and B. R. Steele, Royal Society of Chemistry,
Cambridge, 2003, pp. 28–47.
3 R. R. Schrock and A. H. Hoveyda, Angew. Chem., Int. Ed., 2003, 42,
4592.
4 P. E. Collier, S. C. Dunn, W.-S. Li, P. Mountford and O. V. Shishkin,
J. Chem. Soc., Dalton Trans., 1997, 1549.
5 (a) N. Adams, H. R. Bigmore, T. L. Blundell, C. L. Boyd, S. R.
Dubberley, A. J. Sealey, A. R. Cowley, M. E. G. Skinner and P.
Mountford, Inorg. Chem, in press; (b) N. Adams, A. R. Cowley, S. R.
Dubberley, A. J. Sealey, M. E. G. Skinner and P. Mountford, Chem.
Commun., 2001, 2738.
6 For other selected examples, see: R. D. Profilet, C. H. Zambrano,
P. E. Fanwick, J. J. Nash and I. P. Rothwell, Inorg. Chem., 1990,
29, 4362; C. H. Zambrano, R. D. Profilet, J. E. Hill, P. E. Fanwick
and I. P. Rothwell, Polyhedron, 1993, 12, 689; C. P. Schaller, C. C.
Cummins and P. T. Wolczanski, J. Am. Chem. Soc., 1996, 118, 591;
J. L. Bennett and P. T. Wolczanski, J. Am. Chem. Soc., 1997, 119,
10696; A. Caselli, L. Giannini, E. Solari, C. Floriani, N. Re, A.
Chiesi-Villa and C. Rizzoli, Organometallics, 1997, 16, 5457; M. D.
Fryzuk, J. B. Love and S. J. Rettig, Organometallics, 1998, 17, 846;
S. R. Dubberley, A. Friedrich, D. A. Willman, P. Mountford and U.
Radius, Chem. Eur. J., 2003, 9, 3634.
7 J. L. Thorman, I. A. Guzei, V. G. Young and L. K. Woo, Inorg. Chem,
1999, 38, 3814.
8 D. J. Arney, M. A. Bruck, S. R. Huber and D. E. Wigley, Inorg.
Chem., 1992, 31, 3749.
9 A. J. Blake, P. Mountford, G. I. Nikonov and D. Swallow, Chem.
Commun., 1996, 1835.
10 L. H. Gade, J. Lloyd, P. Mountford, S. M. Pugh, M. Schubart,
M. E. G. Skinner and D. J. M. Tro¨sch, Inorg. Chem., 2001, 40,
870.
˚
˚
(N–H = 0.87 A; C–H = 1.0 A. Extinction corrections were
applied as required.30 Crystallographic calculations were per-
formed using SIR92 and CRYSTALS.31
i
Molecules of [Zr2(l-N-2,6-C6H3 Pr2)2Cl4(THF)4] (1) lie across
crystallographic inversion centres. Both of the unique THF
molecules were disordered over two sites with equal chemical
occupancies. The disorder was modelled satisfactorily and the
non-H atoms of these ligands were positionally and isotropically
refined subject to vibrational restraints, and similarity restraints
on the O–C and C–C distances and associated internal ring
angles.
Molecules of [Zr(N-2,6-C6H3Me2)2Cl4(THF)4] (2) lie across
crystallographic 2/m symmetry sites with the Zr2N2O4 coordi-
nation cores lying on the mirror planes and perpendicular two-
fold axes bisecting the Zr · · · Zr vectors. The THF molecules
were disordered over two sites with equal chemical occupancies,
and this disorder was modelled satisfactorily.
CCDC reference numbers 260433–260438.
See http://www.rsc.org/suppdata/dt/b5/b500507h/ for cry-
stallographic data in CIF or other electronic format.
11 P. J. Wilson, PhD Thesis, University of Nottingham, 1999.
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Acknowledgements
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