Mono-anionic acetophenone imine ligands: Synthesis, ortho-lithiation and first examples of group (v) metal complexes

Article abstract of DOI:10.1039/b903836a

A series of niobium and tantalum imido complexes with mono-anionic ortho-metallated acetophenone imine ligands have been prepared and characterized using NMR spectroscopy, mass spectrometry and elemental analysis. These low symmetry complexes are produced

Full text of DOI:10.1039/b903836a

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www.rsc.org/dalton | Dalton Transactions
Mono-anionic acetophenone imine ligands: synthesis, ortho-lithiation and first
examples of group (V) metal complexes†
Abdollah Neshat, Cheryl L. Seambos, John F. Beck and Joseph A. R. Schmidt*
Received 27th February 2009, Accepted 1st April 2009
First published as an Advance Article on the web 5th May 2009
DOI: 10.1039/b903836a
A series of niobium and tantalum imido complexes with mono-anionic ortho-metallated acetophenone
imine ligands have been prepared and characterized using NMR spectroscopy, mass spectrometry and
elemental analysis. These low symmetry complexes are produced with only one or two structural
isomers in all cases and display interesting correlations between the steric bulk of the ligands employed
and the isomers formed. Crystal structures of several new niobium and tantalum complexes are
presented as confirmation of the connectivity in these structural isomers.
can lead to unique reactivity. Ortho-metallation is commonly
effected by the direct activation of an aryl C–H bond, through
either oxidative addition or direct deprotonation by a strong
Introduction
Among nitrogen donor ligand systems, imido groups (RN2-;
base.16–18 With late transition metals, oxidative addition of the
ortho C–H bond proves to be a very effective pathway to
ortho-metallated complexes and to catalytically functionalize aryl
groups in this position.19–22 In recent work, Crabtree has utilized
this methodology to produce iridium complexes by the ortho-
metallation of a,b-unsaturated ketones, esters and acetophenone,
which have served as useful catalyst precursors for hydroamination
and alkyne hydroalkoxylation reactions.23,24 Given this useful
reactivity, many ligand systems based on a,b-unsaturated ketones,
esters and acetophenones have been explored in recent years.24–38
Our research group has been interested in the reactivity of re-
lated ortho-metallated imines. Ortho-metallation of acetophenone
imines with late metals is readily accessible by C–H activation
of the aryl moiety, and this type of reaction allows for the
synthesis of metal hydrides with potential applications in C–C
bond coupling reactions. Unfortunately, this route has proven to be
generally inaccessible for early transition metals. Many common
early metal starting materials are in their maximum oxidation
state, making ortho-metallation through oxidative addition of
C–H bonds impossible. Alternate routes utilizing lower oxidation
state metal centers have been shown to suffer from deleterious
side reactions attributed to redox processes linked to ligand
reduction, rather than the desired C–H activation.39,40 Due to
these limitations, reports regarding the use of ortho-metallated
acetophenone imine ligands with early metals are rare. We recently
published an effective synthetic route to group (IV) transition metal
complexes of mono-anionic ortho-metallated acetophenone imine
ligands.30 Prior methods for the synthesis of early-metal complexes
of ortho-metallated acetophenone imines had been limited to the
insertion of cyano groups into metal–benzyne bonds, a reaction
that yields dianionic versions of these ligands with very little
substitutional flexibility.41–51 Herein, we report the synthesis of
acetophenone imines with a variety of alkyl and aryl substituents
R = aryl, alkyl) have proven to be extremely important in early
transition metal chemistry.1 The strong bonding observed between
the doubly anionic nitrogen donor atom and a highly charged
early metal lends excellent stability, while broad tuning of the
alkyl or aryl substituent provides for control of steric bulk.1 In
addition to supporting a range of interesting reaction chemistry,
early work on imido complexes of group (V) metals was driven
by their useful luminescence properties.2–4 The first niobium and
tantalum imido complexes, reported by Finn and co-workers in
1980, were synthesized by the reduction of acetonitrile with zinc
or through the metathesis reaction of tantalum neopentylidenes
with imines.5 Later, a more economical route to tantalum and
niobium imido complexes was reported, utilizing the reaction of
silylated alkylamines with MCl5.6–8 A similar reaction of metal
halides with silylanilines in the presence of 1,2-dimethoxyethane
(DME) afforded a more stable series of metal imido precursors
with the general formula of M(NAr)Cl3(DME) (M = Nb, Ta).3,9–11
The lability of DME and halide ligands in these imido complexes
has provided for a variety of intriguing niobium and tantalum
metal complexes.12–15 Herein, we describe their use as precursors
in the synthesis of mono-anionic acetophenone imine group (V)
complexes.
The broad use of bidentate ligands in transition metal chemistry
derives from the stability garnered from the chelate effect, with the
option of using two chemically different donor groups available
as a means to more rigidly control the reactivity at the metal
center. One way to generate a bidentate ligand system is through
the regioselective ortho-metallation of an aryl group covalently
attached to a second donor moiety.16–18 This process leads to
an anionic ligand framework with two dissimilar donor atoms,
yielding electronic asymmetry in the resulting complexes that
Department of Chemistry, The University of Toledo, 2801 W. Bancroft
St. MS 602, Toledo, OH 43606-3390, USA. E-mail: joseph.schmidt@
utoledo.edu
n
that undergo site-specific lithiation upon treatment with BuLi.
These activated ligands have been reacted with niobium and
tantalum imido precursors to generate a series of twelve new metal
imido complexes. The structure and bonding in these complexes
was determined by NMR and X-ray analyses. We believe that
1
† Electronic supplementary information (ESI) available: 13C{ H} NMR
spectra of compounds 10 and 11. CCDC reference numbers 722163–
722168. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b903836a
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through the combination of the imido moiety and the new mono-
anionic ortho-metallated acetophenone imine ligand system, a
series of niobium and tantalum complexes with exceptional
stoichiometric and catalytic reactivity will be uncovered.
Results and discussion
Scheme 3 Ortho-lithiation of the acetophenone imines.
Imine synthesis and ortho-lithiation
Additionally, the electron pair on the nitrogen atom coordinatively
directs the lithiating agent to deprotonate the aromatic ring in
an ortho position. The combination of these effects allows for
regiospecific lithiation of these imines by nBuLi at the carbon atom
ortho to both groups. For most of these imines (1H–3H, 5H), the
product lithiated species were produced by straightforward room
temperature ortho-lithiation using nBuLi; however, in the case
of 4H, these reaction conditions led to substantial formation of
byproducts. The observed unwanted products included lithiation
at other positions on the aryl ring and addition products resulting
from attack at the carbon of the imine moiety. In order to
circumvent this problem, lithiation of 4H was accomplished by
using lower reaction temperatures (-78 ◦C) for longer periods, in
addition to more dilute reaction concentrations.
In our initial communication, we showed that the acetophenone
imine (2H) produced by the Schiff-base condensation reaction
between 3,4-methylenedioxyacetophenone and 2,6-diethylaniline
could be regioselectively deprotonated to produce a new mono-
anionic bidentate ligand (2Li).30 This new ligand was then
successfully utilized in the synthesis of a series of titanium
and zirconium complexes.30 In an effort to lend steric and
electronic diversity to this new ligand class, we have expanded
the synthesis of these imines to include a much broader array
of substituents (Scheme 1). Two new ketimines were formed by
the Schiff-base condensation of 3,4-methylenedioxyacetophenone
with 2,6-diisopropylaniline (1H) and 2,6-dimethylaniline (3H).
Additionally, a related aldimine was produced by the Schiff-
base condensation of piperonal with 2,6-diisopropylaniline (5H).
Each of these imines was readily synthesized in refluxing toluene
using a Dean–Stark trap to drive the reaction to high yield, and
purification was effected by vacuum distillation.
The full range of lithiated products (1Li–5Li) has been charac-
1
terized by H NMR and 13C NMR spectroscopy. One notable
feature of these materials is that the hydrogen atoms of the
–OCH2O– moiety display very large changes in their chemical
shifts upon lithiation. For each of the aryl imines (1Li–3Li, 5Li),
the two protons of this group remained equivalent and shifted
to higher field, while the 1H NMR spectrum of 4Li (derived
from an alkyl imine) showed that these two protons had become
inequivalent, with one shifting to higher field and one to lower
1
field. The H NMR spectra of both 4H and 4Li are shown in
Fig. 1 to demonstrate this effect. Note that in the spectrum of
4H the –OCH2O– protons are equivalent, appearing at 5.28 ppm.
After lithiation, the two protons are no longer equivalent and now
appear as two resonances at d 5.48 and 4.51 ppm. The 1H NMR
signals derived from the methylenedioxy moiety prove to be quite
diagnostic in this ligand set. In fact, these protons are indicative
of the ligand’s environment in its transition metal complexes, as
discussed below for the group (V) metal complexes. It is postulated
that upon lithiation, the acetophenone imine ligands form either
large clusters or polymerized species in which the ligands gather
around groups of lithium ions.53–56 The formation of aggregates of
this type can result in superstructures with lower overall symmetry,
explaining the inequivalence of the two 1H NMR resonances
for the –OCH2O– moiety. This lack of symmetry can result in
one or both of the methylene protons falling in the shielded
region due to the ring current of aryl groups from the imines
or other acetophenone moieties.57,58 This shielding causes a high
field chemical shift in the 1H NMR spectrum. In the cases where
one proton is shifted to lower field, it is possible that one or more
of the oxygen atoms of the –OCH2O– moiety are involved in the
lithium coordination sphere, leading to the observed deshielding.57
Scheme 1 Imine synthesis proceeds through a Schiff-base condensa-
tion reaction (R = Me; R¢ = 2,6-iPr2C6H3 (1H), 2,6-Et2C6H3 (2H),
2,6-Me2C6H3 (3H), or R = H; R¢ = 2,6-iPr2C6H3 (5H)).
In contrast, the Schiff-base condensation of 3,4-methylene-
dioxyacetophenone with tert-butylamine was not successful under
any of the conditions tested. In order to overcome these synthetic
challenges, the desired imine was produced by an alternative
synthetic pathway involving the use of an imido titanium complex
as the imine source. Thus, 4H was synthesized in moderate
yield by the reaction of 3,4-methylenedioxyacetophenone with
one equivalent of (py)3Cl2Ti(NtBu),52 with the poorly soluble
titanium oxo byproduct readily removed by filtration (Scheme 2).
The strong driving force of metal oxide formation promotes this
reaction, yielding the desired imine.
Scheme 2 Synthesis of imine 4H utilizes an imido titanium reagent.
Formation of niobium and tantalum complexes
n
The imines (1H–5H) were lithiated with BuLi to produce a
series of mono-anionic bidentate ligands (Scheme 3). The electron-
withdrawing methylenedioxy moiety (–OCH2O–) helps to activate
the adjacent aryl protons toward deprotonation by strong bases.
Direct metallation of the lithiated ligands through salt metathesis
with group (V) metal halides (MCl5) was problematic, resulting in
intractable mixtures which rapidly decomposed to give insoluble
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Fig. 1 1H NMR spectra of 4H (top) and 4Li (bottom); methyl groups omitted for clarity.
brown materials. Because of these difficulties, attention was turned
to the synthesis of niobium and tantalum complexes containing
the imido moiety. Various aryl and alkyl imido complexes of the
form L2MCl3(NR) (L = neutral donor ligand; M = Nb, Ta; R =
aryl, alkyl) are known and thus function as excellent starting
materials.3,8–10,59–61 Use of the imido group allowed access to high-
valent (M5+) tantalum and niobium centers that were more stable
than the native pentahalides; the strong metal–imido bond gives
these species good thermal stability.1 Furthermore, the substituent
on the imido group helped to solubilize the metal precursors, such
that low polarity solvents could be used.
Synthesis of the niobium and tantalum imido starting materials
was based on previous literature reports. We primarily investigated
niobium complexes utilizing (DME)NbCl3(NR) where R = 2,6-
iPr2C6H3 (9), 2,6-Et2C6H3 (10), 2,6-Me2C6H3 (11), Ph (12), or tBu
(13).3,59 To show the applicability of these reactions with tantalum,
we also explored complexes derived from (DME)TaCl3(N-2,6-
iPr2C6H3) (14).9 In general, a series of twelve niobium and
tantalum imido complexes (15–26) were synthesized by reacting
the group (V) starting materials (9–14) with 2 equiv. of the lithiated
ligand (1Li–5Li; Scheme 4). The best results were observed when
using pentane as solvent, in which case the reaction occurs as a
slurry throughout. In all cases, products of the form (L)2MCl(NR)
(L = ortho-metallated acetophenone imine) were produced. With
Scheme 4 Synthesis of niobium and tantalum complexes (see Table 1 for
definitions of M, R, R¢, and R¢¢).
the bidentate anionic acetophenone imine ligands present, these
species were characterized as six-coordinate, pseudo-octahedral
complexes.
An analysis of the ligands utilized to produce the L2MCl(NR)
complexes (15–26) indicates that a number of possible structural
isomers exist. The acetophenone imine ligand does not have a
large enough bite angle to span trans positions around the metal
center. Thus, there are only two structural isomers possible where
the imido group is oriented trans to the chloride ligand. These
isomers would necessitate either a two-fold rotation axis (trans
acetophenone imine ligands) or a mirror plane (cis acetophenone
imine ligands). In all cases, NMR spectroscopy revealed that no
such symmetry operation existed within the observed complexes—
that is, in each of these metal complexes, C1 symmetry was
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Table 1 Metal complexes and selected physical properties
Complex
M
R
R¢
R¢¢
–OCH2O– resonances d/ppm
Number of isomers
Yield (%)
15
23
16
Nb
Ta
Nb
CH3
CH3
CH3
2,6-iPr2C6H3
2,6-iPr2C6H3
2,6-Et2C6H3
2,6-iPr2C6H3
2,6-iPr2C6H3
2,6-iPr2C6H3
5.141, 5.079, 5.033, 4.950
5.143, 5.103, 5.056, 4.921
1
1
2
93
85
83
5.226, 5.211, 5.133, 5.038 (16)
5.580, 5.248, 5.083, 4.953 (16a)
5.246, 5.218, 5.162, 5.051 (24)
5.638, 5.270, 5.145, 5.019 (24a)
5.391, 5.137, 4.812, 4.728 (17)
5.365, 5.107, 5.017, 4.843 (17a)
5.250, 5.240, 5.147, 5.077 (25)
5.658, 5.293, 5.217, 5.060 (25a)
5.223, 5.210, 5.009, 4.856
5.132, 5.100, 4.980, 4.957
5.133, 5.108, 5.018, 4.845
5.387, 5.351, 5.208, 5.169 (21)
5.295, 5.093, 4.775, 4.743 (21a)
5.481, 4.832, 4.668, 4.581 (22)
5.356, 5.252, 4.730, 4.665 (22a)
5.161, 5.078, 5.058, 4.953
24
17
25
Ta
Nb
Ta
CH3
CH3
CH3
2,6-Et2C6H3
2,6-Me2C6H3
2,6-Me2C6H3
2,6-iPr2C6H3
2,6-iPr2C6H3
2,6-iPr2C6H3
2
2
2
80
75
80
2
18
19
20
21
Nb
Nb
Nb
Nb
CH3
CH3
CH3
CH3
CMe3(tBu)
2,6-iPr2C6H3
2,6-Et2C6H3
2,6-Me2C6H3
Ph
1
1
1
2
62
75
66
33
2,6-iPr2C6H3
2,6-iPr2C6H3
2,6-iPr2C6H3
22
26
Nb
Ta
CH3
H
2,6-iPr2C6H3
2,6-iPr2C6H3
CMe3(tBu)
2
1
20
75
2,6-iPr2C6H3
observed. This was best indicated by the methylenedioxy res-
onances of the ligand backbone, where the presence of four
inequivalent signals from the four protons (on the two ligands)
confirmed the C1 symmetry of these molecules. Thus, we deduced
that the imido ligand was oriented cis to the chloride ligand in all
complexes formed, while noting that this still left four possible
structural isomers (present as racemates). The final important
consideration in the analysis of the L2MCl(NR) complexes
involved electronic parameters. Because of the very strong metal–
imido bonding, the imido group exerts a significant trans influence
on the metal center. Thus, very weak bonding trans to the imido
ligand is expected, favouring dative bonding of the neutral imine
donor, rather than the more strongly bound anionic aryl moiety
of the acetophenone imine ligand. Thus, by constraining the
complexes to those containing a chloride cis to the imido group
and a neutral imine donor trans to the imido group, only two
structural isomers are possible (Scheme 4). This was confirmed by
the resonances observed in the 1H NMR for the –OCH2O– groups,
as each of the twelve new metal complexes exist as either one or
two structural isomers.
In an effort to understand the factors controlling product
distribution in the salt metathesis reactions, we investigated two
steric aspects in relation to the isomers formed. In complexes
15–18 (Nb) and 23–26 (Ta), the bulkiest imido group (N-2,6-
iPr2C6H3) was used and the size of the ligand substituents was
varied. Only one structural isomer was formed when the steric
bulk of the ligand was very large (15, 23, 26) or quite small (18).
Somewhat surprisingly, based on the X-ray crystal structures of
complexes 17, 18 and 23, we found that the same isomer was
present in both cases (Fig. 2–4). Specifically, this is the structural
isomer with an acetophenone imine carbon donor atom oriented
trans to the chloride ligand. The X-ray structure corresponded
well with the solution NMR data. For example, in complex 23,
the only equivalent proton resonances observed by 1H NMR
spectroscopy are those resulting from freely spinning methyl
groups. The isopropyl groups show diastereotopic methyls and
the methylenedioxy moieties yield a total of four inequivalent
resonances. Moreover, through analysis of the methylenedioxy
chemical shifts while considering the relevant spatial locations
Fig.
2 ORTEP diagram (50% thermal ellipsoids) of (3)2Nb(N-2,
6-iPr2C6H3)Cl (17). Hydrogen atoms omitted for clarity. Bond lengths
˚
(A): Nb1–Cl1 = 2.3881(6), Nb1–N1 = 1.767(2), Nb1–N2 = 2.351(2),
Nb1–N3
=
2.486(2), Nb1–C13
=
2.260(2), Nb1–C30
=
2.202(2).
Bond angles (◦): Nb1–N1–C1 = 174.8(2), N2–Nb1–C13 = 70.51(7),
N3–Nb1–C30 = 70.18(7).
in the solid-state structure, it is clear that the significant shielding
of these protons is the effect of their location 3.7–4.2 A above
the aryl rings of the imido and acetophenone imine groups.57,58
The shielding of these protons can be readily attributed to ring
current effects from these aromatic systems and their approximate
distances parallel their chemical shifts.57,58
In contrast, complexes formed from the intermediate sized
ligands (Nb: 16, 17; Ta: 24, 25) yielded a mixture of two structural
isomers. Given the preference for the same isomer with both
sterically large and sterically small ligands described previously,
we were surprised by this result. By carrying out the syntheses of
these complexes at various reaction temperatures, we found that
different ratios of the two isomers were produced as kinetic prod-
ucts that did not equilibrate in solution. That is, when examining
˚
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quality crystals and determine the solid-state structure of these
complexes (Fig. 5 and 6). Subsequent NMR of these crystals
revealed the presence of only a single isomer (no equilibration
observed), confirming that the major isomer in 16 and 24 is the
same structural isomer that we observed in the previous cases. We
postulate that the second isomer was observed because of the steric
congestion at the metal center in the case of intermediate steric
Fig.
3 ORTEP diagram (50% thermal ellipsoids) of (4)2Nb(N-2,
6-iPr2C6H3)Cl (18). Hydrogen atoms omitted for clarity. Bond lengths
˚
(A): Nb1–Cl1 = 2.4489(7), Nb1–N1 = 1.777(2), Nb1–N2 = 2.464(2),
Nb1–N3
=
2.358(2), Nb1–C13
=
2.170(3), Nb1–C26
=
2.278(3).
Bond angles (◦): Nb1–N1–C1 = 177.8(2), N2–Nb1–C13 = 72.82(9),
N3–Nb1–C26 = 71.68(9).
Fig.
5 ORTEP diagram (50% thermal ellipsoids) of (2)2Nb(N-2,
6-iPr2-C6H3)Cl (16). Hydrogen atoms, disordered methyl group, and
˚
diethyl ether molecule have been omitted for clarity. Bond lengths (A):
Nb1–Cl1 = 2.390(1), Nb1–N1 = 1.760(4), Nb1–N2 = 2.330(3), Nb1–N3 =
2.528(4), Nb1–C13 = 2.261(4), Nb1–C32 = 2.196(4). Bond angles (◦):
Nb1–N1–C1 = 173.3(3), N2–Nb1–C13 = 70.5(2), N3–Nb1–C32 = 70.1(2).
Fig.
4
ORTEP diagram (50% thermal ellipsoids) of (1)2Ta(N-2,
6-iPr2C6H3)Cl (23). Hydrogen atoms, disordered methyl group and toluene
˚
solvate molecules are omitted for clarity. Bond lengths (A): Ta1–Cl1 =
2.3627(9), Ta1–N1 = 1.786(3), Ta1–N2 = 2.360(3), Ta1–N3 = 2.519(3),
Ta1–C13 = 2.245(3), Ta1–C34 = 2.195(4). Bond angles (◦): Ta1–N1–C1 =
172.7(3), N2–Ta1–C13 = 71.1(1), N3–Ta1–C34 = 70.4(1).
the room temperature NMR spectra of complexes produced under
different reaction temperatures, substantially differing product
ratios were observed. Variable-temperature NMR showed no
change in isomeric ratios upon cooling, although the onset of
some equilibration between the isomers was commonly observed
near 60 ◦C for most isomers. The high temperature coalescence
point was not reached at 100 ◦C for any of these four complexes.
In the case of complexes 16 and 24, we were able to grow X-ray
Fig.
6 ORTEP diagram (50% thermal ellipsoids) of (2)2Ta(N-2,
6-iPr2C6H3)Cl (24). Hydrogen atoms and ether solvate molecule omitted
˚
for clarity. Bond lengths (A): Ta1–Cl1 = 2.377(1), Ta1–N1 = 1.783(4),
Ta1–N2 = 2.513(4), Ta1–N3 = 2.315(3), Ta1–C13 = 2.191(4), Ta1–C32 =
2.243(4). Bond angles (◦): Ta1–N1–C1 = 173.4(3), N2–Ta1–C13 = 70.1(2),
N3–Ta1–C32 = 71.0(2).
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bulk. With the reduced steric bulk, we suggest that isomerization
pathways in the reaction intermediates are lower in energy and
under the reaction conditions employed, small amounts of the
minor product are formed that are unable to thermally equilibrate
at room temperature. Our current investigations involve alkylation
of these complexes, which may shed further insight into the
production of two isomers using these intermediate sized ligands.
In a second series of experiments, the bulkiest ligand was used
and the imido group on the niobium was varied in size (15, 19–22).
Similar to the previous set of experiments, each of these complexes
was formed as either one or two structural isomers. The number
of structural isomers produced during each reaction was entirely
dependent upon the size of the imido group used. Complexes 15,
nitrogen atom of an acetophenone imine trans to the chloride.
Overall, the synthesis of complexes 15–26 reveal that the salt
metathesis reactions are controlled by more than just the steric
size of the ligands, including such factors as reaction temperature,
type of imido moiety, and the steric bulk of the ligand system.
Conclusions
Herein, we demonstrate that mono-anionic acetophenone imine
ligands can be produced with a wide diversity of imine substituents.
These ligands have proven to be strong chelating ligands for the
synthesis of niobium and tantalum imido complexes of the form
(L)2MCl(NR) (L = ortho-metallated acetophenone imine; M =
Nb, Ta; R = aryl, alkyl). Primarily, the complexes are synthesized
as only a single structural isomer (out of at least six possible
isomers). Exceptions where two isomers are observed suggest the
formation of kinetic products and careful fractional crystallization
allowed for the isolation of a single major isomer in several cases.
These complexes are quite robust—stable to temperatures of at
least 150 ◦C in all cases. Our ongoing investigations involve
the substitution of the chloride ligand with alkyl and amido
groups. Further, we are pursuing the stoichiometric and catalytic
chemistry of these new complexes.
i
19 and 20 had very bulky arylimido moieties (2,6-R2C6H3; R = Pr,
Et, Me), resulting in the formation of only one structural isomer,
while two isomers were formed when smaller imido moieties were
used, as evidenced by 21 and 22. The preferred isomer had the
same relative configuration as that observed in the earlier cases,
as confirmed by the X-ray crystal structure of complex 20 (Fig. 7)
For reactions where two isomers were observed, the synthesis was
carried out a second time at 0 ◦C, rather than room temperature.
This did not prevent the formation of two isomers, but changed
the ratios of the two isomers present. For example, the room
temperature synthesis of 21 results in a 1 : 1 ratio of the two isomers,
while low temperature synthesis (0 ◦C) of the same complex results
in a 5 : 2 ratio. Thus, again we conclude that the structural isomers
are not interconverting in solution at room temperature. Rather,
their formation reflects the kinetic control of the products of these
reactions at the employed temperatures. The major isomer for
complexes 21 and 22 is the same as that described previously
with the chloride ligand located trans to the anionic carbon of an
acetophenone imine ligand, while the minor isomer contains the
Experimental
General considerations
All moisture and air sensitive manipulations were carried out
under a dry nitrogen atmosphere using standard Schlenk tech-
niques and dried glassware. Diethyl ether was dried by passage
through an activated alumina column. Toluene, dichloromethane
˚
and pentane were dried over 4 A activated molecular sieves. The
dried solvents were sparged with nitrogen. 1,2-Dimethoxyethane
(DME), tert-butylamine, cyclohexylamine, and triethylamine were
vacuum transferred under nitrogen from anhydrous CaH2(s)
and degassed with 3 freeze–evacuate–thaw cycles. Aniline,
2,6-diisopropylaniline, 2,6-diethylaniline and 2,6-dimethylaniline
˚
were distilled and stored over 4 A molecular sieves. NbCl5,
TaCl5, ZnCl2, CDCl3, chlorotrimethylsilane, piperonal, 3,4-
methylenedioxyacetophenone and nBuLi (1.5 M in hexanes) were
used as purchased. Benzene-d6 and toluene-d8 were vacuum
transferred under nitrogen from purple Na/benzophenone ketyl
and degassed with 3 freeze–evacuate–thaw cycles. Me3SiNH(2,6-
iPr2C6H3) (6),9 Me3SiNH(2,6-Et2C6H3) (7),62 Me3SiNH(2,6-
Me2C6H3) (8),63 Nb(N-2,6-iPr2C6H3)Cl3(DME) (9),3 Nb(N-
C6H5)Cl3(DME) (12),59 Nb(NCMe3)Cl3(DME) (13),59 Ta(N-2,6-
iPr2C6H3)Cl3(DME) (14),9 (py)3Cl2Ti(NtBu),52 2H30 and 2Li30 were
1
prepared as previously described. The 1H and 13C{ H} NMR
spectra were recorded in benzene-d6, CDCl3, or toluene-d8 at
ambient temperature on a VXRS 400 or an Inova 600 MHz
spectrometer and referenced internally to residual proton peaks
at d 7.16 ppm (C6D6), 2.09 ppm (C7D8), or 7.27 ppm (CDCl3) and
d 128.0 ppm (C6D6), 20.4 ppm (C7D8), or 77.23 ppm (CDCl3) for
13C. Unless otherwise specified, given coupling constants are for
3JHH. Li{ H} NMR data were obtained on a 400 MHz NMR
spectrometer at ambient temperature and externally referenced to
d 0.00 ppm with LiCl (3.00 M in D2O). IR samples were prepared
as Nujol mulls between KBr plates. Melting points were performed
Fig. 7 ORTEP diagram (50% thermal ellipsoids) of one of the two
independent molecules of (1)2Nb(N-2,6-Me2C6H3)Cl (20) in the asym-
metric unit. Hydrogen atoms and ether solvate molecules are omitted
7
1
˚
for clarity. Bond lengths (A): Nb1–Cl1 = 2.3989(8), Nb1–N1 = 1.764(3),
Nb1–N2 = 2.389(3), Nb1–N3 = 2.538(3), Nb1–C9 = 2.250(3), Nb1–C30 =
2.207(3). Bond angles (◦): Nb1–N1–C1 = 172.7(2), N2–Nb1–C9 = 70.7(1),
N3–Nb1–C30 = 70.4(1).
4992 | Dalton Trans., 2009, 4987–5000
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©

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on a Mel-Temp; those compounds that were air sensitive were
taken in a capillary tube sealed under a nitrogen atmosphere
and are uncorrected. Elemental analysis of a representative series
from each group of compounds was performed by Columbia
Analytics, Tucson, Arizona or Galbraith Laboratories, Knoxville,
Tennessee. X-ray structure determinations were performed at the
Ohio Crystallographic Consortium housed at the University of
Toledo. High resolution mass spectra were obtained using electron
impact ionization by the Mass Spectroscopy Laboratory at the
University of Illinois, Urbana, IL.
(w), 1109 (w), 1094 (w), 1086 (w), 1055 (w), 1037 (m), 981 (w), 933
(w), 923 (w), 873 (w), 836 (w), 800 (w), 788 (w), 778 (w), 773 (w),
721 (w). Anal. calcd for C21H24LiNO2: C 76.58, H 7.34, N 4.25.
Found: C 76.34, H 7.56, N 4.39. Melting point: 130–135 ◦C.
3H. (6.8 g, 84%). 1H NMR (C6D6, 600 MHz): d 7.893 (s, 1 H),
7.246 (d, 1 H, J = 8.0 Hz), 7.050 (d, 2 H, J = 8.0 Hz), 6.953
(t, 1 H, J = 8.0 Hz), 6.638 (d, 1 H, J = 8.0 Hz), 5.300 (s, 2 H),
1
1.985 (s, 6 H), 1.659 (s, 3 H). 13C{ H} NMR (CDCl3, 150 MHz):
d 159.23, 145.32, 143.11, 142.74, 129.31, 128.42, 126.09, 122.84,
122.17, 108.32, 101.65, 98.11, 18.42, 17.21. IR: 3069 (w), 3015 (w),
2941 (m), 2901 (m), 1639 (s), 1607 (s), 1593 (s), 1504 (s), 1488 (s),
1472 (s), 1440 (s), 1365 (s), 1344 (s), 1291 (s), 1251 (s), 1222 (s),
1203 (s), 1156 (w), 1113 (m), 1092 (m), 1039 (s), 936 (m), 899 (m),
881 (m), 858 (w), 820 (m), 810 (m), 778 (m), 764 (m). Anal. calcd
for C17H17NO2: C 76.38, H 6.41, N 5.24. Found: C 76.27, H 6.18,
N 4.90. Melting point: 85–92 ◦C.
Synthesis
I. Ligand synthesis. Imines (1H–3H, 5H) were synthesized
according to the procedure described below:
To a solution of 3,4-methylenedioxyacetophenone (5.00 g,
30.4 mmol) or piperonal (5.00 g, 33.3 mmol) in toluene (300 mL)
was added the appropriate amine (45.6 mmol) along with p-
toluenesulfonic acid monohydrate (1.50 g). After heating the
solution to 110 ◦C in a Dean–Stark trap for 2 d, the solution was
neutralized with saturated NaHCO3(aq), washed with deionized
water (2 ¥ 30 mL) and the organic portion dried over anhydrous
MgSO4(s). Volatiles were distilled under reduced pressure (120 ◦C,
200 mtorr), leaving the desired product behind. Each oil was
recrystallized from methanol at -25 ◦C, yielding a pale yellow
crystalline solid (1H: 8.0 g, 81%; 3H: 6.8 g, 84%; 5H: 8.0 g, 85%).
Lithiation of the imines (1H–5H) was accomplished following
the general procedure:
3Li. (1.8 g, 67%). 1H NMR (C6D6, 600 MHz): d 7.228 (d, 1 H,
J = 8.0 Hz), 7.059 (d, 2 H, J = 7.2 Hz), 6.963 (t, 1 H, J = 7.2 Hz),
6.856 (d, 1 H, J = 8.0 Hz), 4.810 (s, 2 H), 1.801 (s, 6 H), 1.645 (s,
1
3 H). 13C{ H} NMR (C6D6, 150 MHz): d 144.03, 143.52, 129.33,
128.57, 125.92, 125.09, 123.64, 123.01, 122.38, 107.76, 107.73,
7
1
104.89, 101.38, 97.79, 18.20, 17.33, 16.91. Li{ H} NMR (C6D6,
155 MHz): d 3.671. IR: 3150 (m), 2875 (s), 1913 (w), 1837 (w),
1611 (s), 1561 (s), 1381 (s), 1321 (s), 1280 (s), 1236 (s), 1200 (s),
1164 (w), 1131 (m), 1082 (s), 1037 (s), 986 (w), 932 (s), 866 (w),
837 (m), 805 (m), 787 (s), 761 (s), 730 (w). Melting point: 136 ◦C
(decomposition).
To a solution of the imine (10 mmol) in pentane (100 mL) at
4H. 3,4-Methylenedioxyacetophenone (2.0 g, 12 mmol) and
(py)3Cl2Ti(NtBu)52 (5.0 g, 12 mmol) were dissolved separately in
toluene (50 mL). Then, the reactants were mixed at 0 ◦C and stirred
for 1 h. The solution was brought to room temperature and stirred
for 24 h, forming a red slurry. The slurry was filtered and the liquid
portion dried under vacuum. The yellowish oil was dissolved in
pentane (30 mL), filtered and concentrated, yielding a light green
oil (1.7 g, 64%). 1H NMR (C6D6, 400 MHz): d 7.825 (s, 1 H), 7.189
(d, 1 H, J = 8.4 Hz), 6.652 (d, 1 H, J = 8.4 Hz), 5.281 (s, 2 H),
◦
n
0
C, BuLi (7.0 mL, 1.4 M in hexanes, 9.8 mmol) was added
n
dropwise via syringe. Upon addition of the BuLi, the solution
turned red. The solution was stirred for 1 h at -78 ◦C and brought
to room temperature and stirred for 3 h. The solution was filtered
and the solid was dried under vacuum, yielding a dark orange
solid. The solid was washed with copious amounts of pentane to
give analytically pure material.
1H. (8.0 g, 81%). 1H NMR (CDCl3, 400 MHz): d 7.691 (d, 1 H,
4JHH = 2.0 Hz), 7.482 (dd, 1 H, J = 8.0 Hz, 4JHH = 2.0 Hz), 7.21–
7.00 (m, 3 H), 6.891 (d, 1 H, J = 8.0 Hz), 6.042 (s, 2 H), 2.732
(sept, 2 H, J = 7.0 Hz), 2.051 (s, 3 H), 1.145 (d, 6 H, J = 7.0 Hz),
1
1.899 (s, 3 H), 1.328 (s, 9 H). 13C{ H} NMR (C6D6, 150 MHz):
d 159.77, 149.34, 148.57, 138.10, 121.40, 108.06, 107.64, 101.45,
55.27, 31.20, 18.64. IR: 3078 (s), 2965 (m), 2780 (m), 2359 (m),
2050 (w), 1963 (w), 1845 (m), 1640 (s), 1609 (s), 1491 (s), 1434 (s),
1362 (s), 1275 (s), 1111 (m), 1039 (s), 936 (m), 884 (m), 813 (m).
HRMScalcd: 219.1259 for C13H17NO2. HRMSmeasd: 219.1263.
1
1.135 (d, 6 H, J = 7.0 Hz). 13C{ H} NMR (CDCl3, 100 MHz):
d 149.61, 148.12, 136.65, 133.77, 129.12, 128.62, 124.16, 123.73,
122.72, 108.17, 107.94, 101.72, 29.09, 23.76, 23.28, 17.95. IR: 2952
(s), 2924 (s), 2854 (s), 2722 (w), 1859 (w), 1625 (m), 1604 (s), 1590
(m), 1506 (m), 1488 (s), 1460 (s), 1459 (s), 1438 (s), 1378 (s), 1363
(s), 1328 (w), 1288 (s), 1254 (s), 1221 (m), 1188 (m), 1039 (s), 933
(m), 898 (m), 881 (m), 817 (m), 808 (m), 775 (m), 726 (w), 690
(w), 635 (m). Anal. calcd for C21H25NO2: C 77.98, H 7.79, N 4.33.
Found: C 77.41, H 8.05, N 4.14. Melting point: 82–85 ◦C.
4Li. (0.9 g, 40%). 1H NMR (C6D6, 400 MHz): d 6.744 (d, 1 H,
2
J = 7.8 Hz), 6.591 (d, 1 H, J = 7.8 Hz), 5.485 (d, 1 H, JHH
=
2
1.8 Hz), 4.520 (d, 1 H, JHH = 1.8 Hz), 2.185 (s, 3 H), 1.001 (s,
9 H). 13C{ H} NMR (C6D6, 150 MHz): d 178.21, 157.18, 151.80,
1
142.47, 120.82, 107.96, 97.28, 55.57, 33.49, 30.66, 22.86. 7Li{ H}
1
NMR (C6D6, 155 MHz): d 2.820. IR: 2924 (s), 2855 (s), 2723 (w),
2361 (m), 1618 (m), 1559 (m), 1460 (s), 1375 (s), 1302 (s), 1268
(m), 1042 (s), 942 (m), 799 (w), 721 (w). Melting point: 125 ◦C
(decomposition).
1Li. (2.6 g, 80%). 1H NMR (C6D6, 400 MHz): d 7.257 (d, 1 H,
J = 8.4 Hz), 7.030–6.984 (m, 3 H), 6.652 (d, 1 H, J = 8.4 Hz),
4.799 (s, 2 H), 2.753 (sept, 2 H, J = 6.6 Hz), 1.900 (s, 3 H), 0.978
1
(d, 6 H, J = 6.6 Hz), 0.882 (d, 6 H, J = 6.6 Hz). 13C{ H} NMR
5H. (8.0 g, 85%). 1H NMR (C6D6, 600 MHz): d 7.901 (s,
1 H), 7.741 (s, 1 H), 7.191-7.154 (m, 3 H), 6.942 (d, 1 H, J =
7.2 Hz), 6.570 (d, 1 H, J = 7.2 Hz), 5.201 (s, 2 H), 3.15 (sept,
(C6D6, 100 MHz): d 177.41, 155.65, 146.32, 144.11, 143.67, 138.30,
125.12, 124.56, 123.54, 105.50, 97.73, 28.54, 23.52, 23.25, 18.37.
1
1
7Li{ H} NMR (C6D6, 155 MHz): d 4.121. IR: 2955 (s), 2921 (s),
2 H, J = 8.0 Hz), 1.18 (d, 12 H, J = 8.0 Hz). 13C{ H} NMR
2854 (s), 1614 (m), 1588 (w), 1558 (m), 1464 (s), 1459 (s), 1380 (s),
1320 (m), 1283 (m), 1278 (m), 1242 (s), 1186 (w), 1140 (w), 1129
(C6D6, 150 MHz): d 161.21, 151.10, 150.31, 149.23, 138.11, 131.83,
125.82, 124.74, 123.62, 108.53, 107.12, 101.75, 28.64, 23.82; IR:
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2904 (s), 2729 (w), 1845 (w), 1765 (w), 1625 (m), 1597 (m), 1452
(s), 1375 (s), 1251 (s), 1194 (m), 1173 (m), 1091 (m), 1039 (s), 933
(m), 887 (w), 853 (w), 807 (m), 783 (m), 750 (m), 722 (m). Anal.
calcd for C20H23NO2: C 77.64, H 7.50, N 4.53. Found: C 77.40, H
7.59, N 4.52. Melting point: 88–94 ◦C.
J = 8.0 Hz), 6.819 (d, 1 H, J = 8.0 Hz), 6.607 (d, 1 H, J = 8.0 Hz),
6.498 (d, 1 H, J = 8.0 Hz), 5.141 (s, 1 H), 5.079 (s, 1 H), 5.033
(s, 1 H), 4.950 (s, 1 H), 4.731 (sept, 1 H, J = 7.2 Hz), 3.951 (sept,
1 H, J = 6.6 Hz), 3.330 (sept, 1 H, J = 6.6 Hz), 3.280 (sept, 1 H,
J = 6.6 Hz), 2.816 (sept, 1 H, J = 6.6 Hz), 2.452 (sept, 1 H, J =
6.6 Hz), 1.783 (s, 3 H), 1.690 (s, 3 H), 1.427 (d, 3 H, J = 6.6 Hz),
1.339 (d, 3 H, J = 6.6 Hz), 1.185 (d, 3 H, J = 6.6 Hz), 1.073 (d, 3 H,
J = 6.6 Hz), 1.038 (d, 3 H, J = 7.2 Hz), 0.930 (d, 3 H, J = 6.6 Hz),
0.844–0.804 (m, 12 H), 0.703 (d, 3 H, J = 6.6 Hz), 0.631 (d, 3 H,
5Li. (2.1 g, 68%). 1H NMR (C6D6, 600 MHz): d 8.036 (s, 1 H),
7.045 (m, 3 H), 6.899 (d, 1 H, J = 7.2 Hz), 6.616 (d, 1 H, J =
7.2 Hz), 4.975 (s, 2 H), 2.953 (sept, 2 H, J = 8.0 Hz), 0.990 (d, 12 H,
1
J = 8.0 Hz). 13C{ H} NMR (C6D6, 150 MHz): d 175.22, 161.21,
1
J = 6.6 Hz). 13C{ H} NMR (C6D6, 150 MHz): d 183.12, 180.20,
155.53, 149.34, 139.12, 129.53, 126.01, 124.32, 123.53, 105.91,
156.76, 152.44, 150.10, 149.23, 148.36, 148.07, 148.05, 146.78,
143.60, 143.59, 143.41, 143.40, 142.25, 142.24, 141.69, 141.68,
140.81, 140.59, 127.32, 126.89, 126.80, 125.48, 125.00, 124.76,
123.64, 123.07, 122.36, 122.11, 108.38, 106.15, 99.82, 99.62, 29.90,
29.28, 28.92, 28.46, 28.37, 27.95, 26.98, 26.74, 26.21, 25.49, 25.41,
25.25, 25.15, 25.11, 25.08, 24.53, 23.78, 23.29, 22.11, 21.51. IR:
3403 (m), 2854 (s), 2726 (w), 1635 (w), 1549 (w), 1463 (s), 1406
(m), 1367 (s), 1298 (m), 1250 (m), 1243 (m), 1172 (w), 1150 (w),
1122 (w), 1092 (w), 1052 (w), 985 (w), 952 (w), 860 (w). Anal. calcd
for C54H65ClN3NbO4: C 65.85,66 H 6.91, N 4.43. Found: C 66.21,
H 6.51, N 4.22. Melting point: >250 ◦C.
7
1
102.01, 98.84, 28.94, 24.14; Li{ H} NMR (C6D6, 155 MHz): d
3.897; IR: 3061 (w), 2854 (s), 2725 (w), 2361 (w), 1622 (s), 1588 (m),
1553 (s), 1504 (w), 1486 (m), 1460 (s), 1382 (s), 1369 (s), 1323 (s),
1254 (s), 1174 (s), 1134 (w), 1114 (w), 1094 (s), 1046 (s), 934 (m),
861 (m), 788 (s). Anal. calcd for C20H22LiNO2: C 76.18, H 7.03,
◦
N 4.44. Found: C 76.64, H 7.06, N 4.73. Melting point: 143 C
(decomposition).
II. Metal precursor synthesis.
Nb(N-2,6-Et2C6H3)Cl3(DME) (10) (ref. 64). Toluene
(40 mL) was added to NbCl5 (5.0 g, 19 mmol) and the solution was
cooled to 0 ◦C. Dimethoxyethane (2.0 mL) was added to 7 (8.40 g,
37.4 mmol). The 7/DME solution was slowly added to the
NbCl5/toluene forming a purple solution and stirred for 1 h
at 0 ◦C. After stirring overnight at room temperature, the
solution was filtered, concentrated to half volume, and cooled
to -30 ◦C. The purple precipitate was washed with pentane to
yield a purple powder (5.7 g, 69%). 1H NMR (C6D6, 600 MHz): d
7.031 (d, 2 H, J = 8 Hz), 6.952 (t, 1 H, J = 8 Hz), 4.164–4.092 (m,
4 H), 3.493 (s, 3 H), 3.162 (s, 3 H), 2.655 (q, 4 H, J = 8 Hz), 1.354
(2)2Nb(N-2,6-iPr2C6H3)Cl (16). To a flask containing both
9 (0.500 g, 1.07 mmol) and 2Li (0.736 g, 2.44 mmol), pentane
(50 mL) was added. The mixture was stirred at room temperature
for 30 h forming an orange slurry. Volatiles were removed under
vacuum, and the resulting solid was washed with pentane (2 ¥
50 mL) and extracted into toluene (50 mL). After filtration, drying
under vacuum yielded a fine orange solid (0.80 g, 83%). 1H NMR
spectroscopic data of this product revealed a non-interconverting
mixture of two isomers in a 1 : 1 ratio. The separation of 1H NMR
and 13C NMR peaks was pos◦sible by variable temperature NMR
spectra of the product at 80 C in toluene-d8, which leads to 3 :
1
(t, 6 H, J = 8 Hz). 13C{ H} NMR (C6D6, 100 MHz):65 145.40,
128.07, 126.98, 75.43, 70.67, 68.37, 62.62, 26.40, 17.60.
Nb(N-2,6-Me2C6H3)Cl3(DME) (11) (ref. 64). Toluene
(40 mL) was added to NbCl5 (5.0 g, 19 mmol) and the solution
was cooled to 0 ◦C. Dimethoxyethane (2.0 mL) was added to
8 (7.3 g, 38 mmol). The 8/DME solution was slowly added
to the NbCl5/toluene forming a red solution and stirred for
1 h at 0 ◦C. After stirring overnight at room temperature, the
solution was filtered, concentrated to half volume, and cooled to
1
1 peak ratios assignable as major and minor isomers. H NMR
(C7D8, 400 MHz): major isomer (16): d 7.193 (d, 2 H, J = 7.8 Hz),
7.123 (s, 2 H), 7.045 (d, 2 H, J = 7.8 Hz), 6.991–6.940 (m, 5 H),
6.523 (d, 1 H, J = 7.8 Hz), 6.490 (d, 1 H, J = 7.8 Hz), 5.226 (s,
1 H), 5.211 (s, 1 H), 5.133 (s, 1 H), 5.038 (s, 1 H), 4.586 (sept, 1 H,
J = 6.8 Hz), 4.217 (sept, 1 H, J = 6.8 Hz), 2.179 (dq, 2 H, 2JHH
=
15 Hz, J = 7.0 Hz), 2.105 (s, 3 H), 2.083 (d, 6 H, J = 6.8 Hz),
1.815 (dq, 2 H, 2JHH = 15 Hz, J = 7.0 Hz), 1.738 (s, 3 H), 1.731 (d,
3 H, J = 7.0 Hz), 1.699 (dq, 2 H, 2JHH = 15 Hz, J = 7.0 Hz), 1.577
(dq, 2 H, 2JHH= 15 Hz, J = 7.0 Hz), 1.238 (d, 3 H, J = 7.0 Hz),
1.201 (d, 3 H, 7.0 Hz), 1.107 (d, 3 H, J = 7.0 Hz), 1.092 (d, 6 H,
J = 6.8 Hz); minor isomer (16a): 6.930–6.872 (m, 8 H), 6.836 (d,
1 H, J = 7.6 Hz), 6.785 (d, 1 H, J = 7.6 Hz), 6.545 (d, 1 H, J =
7.6 Hz), 6.417 (d, 1 H, J = 7.6 Hz), 6.278 (d, 1 H, J = 7.6 Hz),
5.580 (s, 1 H), 5.248 (s, 1 H), 5.083 (s, 1 H), 4.953 (s, 1 H), 4.493
(sept, 1 H, J = 6.4 Hz), 3.816 (sept, 1 H, J = 6.4 Hz), 3.166 (dq,
◦
-30 C. The red precipitate was washed with pentane to yield a
red powder (5.4 g, 72%). 1H NMR (C6D6, 600 MHz): d 6.730 (d,
2 H, J = 7 Hz), 6.595 (t, 1 H, J = 7 Hz), 3.430 (s, 3 H), 3.090 (s,
1
3 H), 3.019-2.996 (m, 4 H), 2.941 (s, 6 H). 13C{ H} NMR (C6D6,
100 MHz):65 138.75, 128.25, 127.29, 75.20, 70.55, 68.40, 62.40,
20.08.
III. Metal complex synthesis.
(1)2Nb(N-2,6-iPr2C6H3)Cl (15). To a flask containing both 9
(2.0 g, 4.3 mmol) and 1Li (2.8 g, 8.6 mmol), pentane (100 mL) was
added. The mixture was stirred overnight at ambient temperature.
Then, the orange precipitate was filtered and remaining ligand
was removed by washing with pentane (3 ¥ 30 mL). Lithium
chloride was readily removed by extracting the product into
toluene (100 mL) and filtering. The solution was then dried under
vacuum. The resulting oil was recrystallized from ether at -25 ◦C,
yielding an orange crystalline solid (3.8 g, 93%). 1H NMR (C6D6,
600 MHz): d 7.208 (dd, 1 H, J = 7.8 Hz, 4JHH = 1.2 Hz), 7.145 (d,
1 H, J = 7.8 Hz), 7.069–7.049 (m, 4 H), 7.017 (d, 1 H, J = 7.8 Hz),
7.005 (d, 1 H, J = 7.8 Hz), 6.931 (t, 1 H, J = 7.8 Hz), 6.883 (d, 1 H,
2
2
2 H, JHH= 15 Hz, J = 7.0 Hz), 2.547 (dq, 2 H, JHH= 15 Hz,
2
J = 7.0 Hz), 2.430 (dq, 2 H, JHH= 15 Hz, J = 7.0 Hz), 2.374
(dq, 2 H, 2JHH= 15 Hz, J = 7.0 Hz), 2.101 (s, 3 H), 1.897 (s, 3 H),
1.405 (d, 3 H, J = 7.0 Hz), 1.261 (d, 3 H, J = 6.4 Hz), 1.141 (d,
3 H, J = 7.0 Hz), 1.040 (d, 3 H, J = 7.0 Hz), 0.839 (d, 3 H, J =
7.0 Hz), 0.730 (d, 3 H, J = 6.4 Hz), 0.683–0.646 (m, 6 H). 13C{ H}
1
NMR (C7D8, 100 MHz): major isomer (16): d 195.15, 182.70,
182.46, 180.36, 179.59, 156.21, 152.40, 150.07, 149.87, 148.23,
147.60, 143.15, 140.00, 138.04, 137.35, 135.89, 135.55, 129.15,
126.86, 126.45, 126.18, 126.00, 124.99, 124.69, 122.33, 121.93,
4994 | Dalton Trans., 2009, 4987–5000
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©

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121.76, 107.97, 105.79, 99.81, 28.36, 27.58, 25.30, 24.62, 24.45,
24.30, 24.25, 24.08, 23.79, 23.64, 23.52, 19.18, 18.82, 18.52, 15.55,
15.35, 14.79, 12.85; minor isomer (16a): 200.40, 152.27, 151.71,
149.69, 149.30, 149.25, 149.14, 148.58, 148.41, 147.45, 142.63,
138.90, 137.84, 137.25, 136.97, 136.88, 135.14, 126.31, 125.54,
124.82, 124.57, 124.25, 123.91, 123.75, 123.26, 123.08, 121.67,
106.83, 105.59, 100.99, 29.53, 28.73, 28.53, 26.30, 25.83, 24.16,
23.19, 21.58, 20.69, 20.48, 19.23, 18.05, 15.52, 14.55, 13.84, 12.19.
IR: 1915 (s), 1549 (w), 1459 (s), 1375 (m), 1302 (w), 1244 (m), 1176
(w), 1147 (w), 1115 (w), 1046 (m), 941 (m), 860 (w), 804 (w), 778
(w), 725 (w). Anal. calcd for C50H57ClN3NbO4: C 67.30, H 6.44,
(w), 792 (w), 764 (w). Anal. calcd for C46H49ClN3NbO4: C 66.07,
H 5.91, N 5.02. Found: C 66.43, H 6.82, N 5.49. Melting point:
195–200 ◦C.
(4)2Nb(N-2,6-iPr2C6H3)Cl (18). A flask containing both 9
(0.32◦1 g, 0.684 mmol) and 4Li (0.315 g, 1.38 mmol) was cooled
to 0 C. Then, pentane (50 mL) was added and the mixture was
stirred cold for 30 min. After warming to room temperature and
stirring for 24 h, a pale yellow slurry formed. The mixture was dried
under vacuum and washed with pentane (3 ¥ 50 mL), leaving a
brown solid. Lithium chloride was readily removed by extracting
the product into toluene (50 mL) and filtering. The product was
then dried under vacuum. The resultant oil was recrystallized from
ether at -25 ◦C, yielding a dark brown crystalline solid (0.32, 62%).
1H NMR (C6D6, 600 MHz): d 7.134 (d, 1 H, J = 7.6 Hz), 7.064
(d, 1 H, J = 7.6 Hz), 7.024 (d, 1 H, J = 7.6 Hz), 6.920 (t, 1 H, J =
7.6 Hz), 6.801 (d, 1 H, J = 7.6 Hz), 6.629 (d, 1 H, J = 7.6 Hz),
◦
N 4.71. Found: C 66.58, H 6.76, N 4.33. Melting point: 205 C
(decomposition).
(3)2Nb(N-2,6-iPr2C6H3)Cl (17). To a flask containing both
9 (0.500 g, 1.07 mmol) and 3Li (0.638 g, 2.44 mmol), pentane
(50 mL) was added, forming a pale yellow slurry. The mixture
was stirred at room temperature for 30 h forming a brown slurry.
Volatiles were removed under vacuum, and the resulting solid
was washed with pentane (3 ¥ 50 mL) and dried under vacuum
leaving a fine orange solid. Lithium chloride was readily removed
by extracting the product into toluene (50 mL) and filtering.
The product was dried under vacuum. The resulting oil was
recrystallized from ether at -25 ◦C, yielding an orange crystalline
solid (0.67, 75%). 1H NMR showed a non-interconverting mixture
of two isomers with a 1 : 1 ratio of peak heights. 1H NMR signals
assignable to each isomer was achieved by repetition of the above
synthetic procedure at 0 ◦C, which leads to a 3 : 1 ratio of the
2
6.543 (d, 1 H, J = 7.6 Hz), 5.223 (d, 1 H, JHH= 1.2 Hz), 5.210
(d, 1 H, 2JHH = 1.2 Hz), 5.009 (d, 1 H, 2JHH = 1.2 Hz), 4.856 (d,
2
1 H, JHH = 1.2 Hz), 4.069 (sept, 1 H, J = 7.2 Hz), 2.646 (sept,
1 H, J = 7.2 Hz), 2.088 (s, 3 H), 2.021 (s, 3 H), 1.585 (d, 3 H, J =
7.2 Hz), 1.519 (s, 9 H), 1.390 (d, 3 H, J = 7.2 Hz), 1.335 (s, 9 H),
1
1.035 (d, 3 H, J = 7.2 Hz), 1.018 (d, 3 H, J = 7.2 Hz). 13C{ H}
NMR (C6D6, 150 MHz): d 179.80, 173.15, 149.63, 148.14, 147.87,
147.15, 141.49, 125.23, 123.75, 123.46, 122.97, 122.21, 120.13,
119.26, 107.27, 105.76, 101.95, 99.87, 99.20, 59.72, 58.07, 32.66,
32.15, 31.18, 28.49, 28.42, 27.94, 25.30, 25.07, 24.66, 23.67, 22.92,
22.56, 21.32. IR: 1683 (w), 1459 (s), 1375 (s), 1301 (w), 1256 (w),
1152 (w), 1043 (w), 941 (w), 804 (w), 724 (w). Anal. calcd for
C38H49ClN3NbO4: C 61.66, H 6.67, N 5.68. Found: C 61.98, H
6.66, N 5.62. Melting point: 150 ◦C (decomposition).
1
isomers. H NMR (C6D6, 400 MHz): major isomer (17): d 7.194
(d, 1 H, J = 7.6 Hz), 7.185 (d, 1 H, J = 7.6 Hz), 6.998 (t, 1 H, J =
7.6 Hz), 6.951 (t, 1 H, J = 7.6 Hz), 6.814–6.775 (m, 6 H), 6.673 (d,
1 H, J = 7.6 Hz), 6.636 (d, 1 H, J = 7.6 Hz), 6.441 (d, 1 H, J =
7.6 Hz), 5.391 (d, 1 H, 2JHH= 1.2 Hz), 5.137 (d, 1 H, 2JHH= 1.2 Hz),
4.812 (d, 1 H, 2JHH= 1.2 Hz), 4.728 (d, 1 H, 2JHH = 1.2 Hz), 3.814
(sept, 1 H, J = 6.8 Hz), 3.683 (sept, 1 H, J = 6.8 Hz), 2.894 (s,
3 H), 2.135 (s, 3 H), 2.028 (s, 3 H), 1.794 (s, 3 H), 1.712 (d, 3 H,
J = 6.8 Hz), 1.172 (d, 3 H, J = 6.8 Hz), 1.139 (s, 3 H), 1.122 (s,
3 H), 1.007 (d, 3 H, J = 6.8 Hz), 0.741 (d, 3 H, J = 6.8 Hz); minor
isomer (17a): 7.274 (d, 1 H, J = 7.6 Hz), 7.079–7.051 (m, 3 H),
6.966–6.941 (m, 5 H), 6.746 (d, 1 H, J = 7.6 Hz), 6.703 (d, 1 H, J =
7.6 Hz), 6.595 (d, 1 H, J = 7.6 Hz), 6.520 (d, 1 H, J = 7.6 Hz), 5.365
(s, 1 H), 5.107 (s, 1 H), 5.017 (s, 1 H), 4.843 (s, 1 H), 3.376 (sept,
1 H, J = 6.8 Hz), 2.952 (sept, 1 H, J = 6.8 Hz), 2.802 (s, 3 H), 2.236
(s, 3 H), 1.885 (s, 3 H), 1.760 (s, 3 H), 1.614 (d, 3 H, J = 6.8 Hz),
1.104 (s, 3 H), 0.880 (s, 3 H), 0.850 (d, 3 H, J = 6.8 Hz), 0.587
(1)2Nb(N-2,6-Et2C6H3)Cl (19). To a flask containing both
10 (0.40 g, 0.99 mmol) and 1Li (0.744 g, 1.82 mmol), pentane
(50 mL) was added, forming an orange slurry. The mixture was
stirred at room temperature for 30 h, forming a brown slurry.
The mixture was dried under vacuum and washed with pentane
(3 ¥ 50 mL), leaving a fine orange solid. Lithium chloride was
readily removed by extracting the product into toluene (50 mL)
and filtering. The product was dried under vacuum. The resultant
oil was recrystallized from ether at -25 ◦C, yielding an orange
1
crystalline solid (0.65 g, 75%). H NMR (C6D6, 600 MHz): d
7.208 (d, 1 H, J = 8.0 Hz), 7.157 (t, 1 H, J = 8.0 Hz), 7.065 (d,
1 H, J = 8.0 Hz), 7.08–7.04 (m, 3 H), 6.932 (d, 1 H, J = 7.0 Hz),
6.909 (d, 1 H, J = 7.0 Hz), 6.885 (d, 1 H, J = 8.0 Hz), 6.855
(t, 1 H, J = 7.0 Hz), 6.829 (d, 1 H, J = 8.0 Hz), 6.610 (d, 1 H,
1
2
(d, 3 H, J = 6.8 Hz), 0.476 (d, 3 H, J = 6.8 Hz). 13C{ H} NMR
J = 8.0 Hz), 6.518 (d, 1 H, J = 8.0 Hz), 5.132 (d, 1 H, JHH
=
=
2
2
(C6D6, 150 MHz): major isomer (17): d 182.90, 179.60, 156.35,
152.58, 150.32, 150.15, 150.07, 149.55, 149.36, 148.12, 147.67,
143.15, 140.03, 133.11, 132.09, 130.70, 130.50, 129.93, 129.52,
128.86, 128.02, 126.24, 125.67, 125.28, 125.09, 122.58, 122.19,
108.32, 106.23, 100.23, 99.90, 28.68, 27.91, 25.22, 24.38, 24.31,
24.09, 20.49, 18.75, 18.27, 18.02, 17.81, 17.25; minor isomer (17a):
183.23, 181.12, 152.90, 151.93, 150.25, 149.91, 149.63, 149.53,
147.31, 142.84, 138.86, 132.75, 132.16, 131.28, 129.76, 127.58,
125.38, 124.78, 124.32, 123.90, 123.64, 123.32, 122.72, 122.29,
108.07, 108.00, 107.29, 106.06, 101.70, 100.83, 29.91, 29.10, 29.01,
26.18, 24.74, 22.25, 21.09, 20.09, 19.67, 19.53, 18.86, 18.53. IR:
1923 (s), 1552 (m), 1459 (s), 1403 (m), 1377 (w), 1306 (m), 1242
(s), 1190 (w), 1147 (w), 1117 (w), 1091 (w), 1049 (m), 942 (w), 861
1.0 Hz), 5.100 (d, 1 H, JHH = 1.0 Hz), 4.980 (d, 1 H, JHH
2
1.0 Hz), 4.957 (d, 1 H, JHH = 1.0 Hz), 3.588 (sept, 1 H, J =
7.0 Hz), 3.520 (dt, 1 H, 2JHH = 23 Hz, J = 8.0 Hz), 3.441 (dt, 1 H,
2JHH = 23 Hz, J = 8.0 Hz), 3.361 (sept, 1 H, J = 7.0 Hz), 3.066
(dt, 1 H, 2JHH = 23 Hz, J = 8.0 Hz), 2.853 (sept, 1 H, J = 7.0 Hz),
2.461 (dt, 1 H, 2JHH = 23 Hz, J = 8.0 Hz), 2.430 (sept, 1 H, J =
7.0 Hz), 1.731 (s, 3 H), 1.703 (s, 3 H), 1.418 (d, 3 H, J = 7.0 Hz),
1.190 (t, 3 H, J = 8.0 Hz), 1.009 (t, 3 H, J = 8.0 Hz), 0.893 (d,
3 H, J = 7.0 Hz), 0.881 (d, 3 H, J = 7.0 Hz), 0.869 (d, 3 H, J =
7.0 Hz), 0.802 (d, 3 H, J = 7.0 Hz), 0.791 (d, 3 H, J = 7.0 Hz),
1
0.668 (d, 3 H, J = 7.0 Hz), 0.656 (d, 3 H, J = 7.0 Hz). 13C{ H}
NMR (C6D6, 150 MHz): d 183.30, 180.36, 156.97, 152.28, 150.02,
149.22, 148.55, 148.17 (¥2), 146.02, 143.66 (¥2), 143.39, 142.14,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 4987–5000 | 4995
©

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141.99, 141.78 (¥2), 140.89, 140.27, 127.20, 126.95, 126.75, 125.75,
125.32, 124.96, 124.80, 124.45 (¥2), 123.65, 122.35, 108.42, 106.18,
99.90, 99.59, 29.72, 29.25, 28.50, 28.04, 26.75, 26.68, 26.09, 25.89,
25.50, 25.22 (¥2), 24.69 (¥2), 23.28, 21.93, 21.21, 15.62, 14.97. IR:
2854 (s), 1655 (m), 1635 (m), 1549 (m), 1462 (s), 1406 (m), 1377 (s),
1351 (w), 1298 (w), 1250 (w), 1172 (w), 1150 (w), 1092 (w), 1052
(w), 942 (w), 860 (w). Anal. calcd for C52H61ClN3NbO4: C 67.86,
H 6.68, N 4.57. Found: C 67.28, H 7.19, N 4.26. Melting point:
180–187 ◦C.
1 H, J = 7.0 Hz), 3.442 (sept, 1 H, J = 7.0 Hz), 3.281 (sept, 1 H,
J = 7.0 Hz), 3.187 (sept, 1 H, J = 7.0 Hz), 1.828 (s, 3 H), 1.796
(s, 3 H), 1.444 (d, 3 H, J = 7.0 Hz), 1.241 (d, 3 H, J = 7.0 Hz),
1.139 (d, 3 H, J = 7.0 Hz), 1.058 (d, 3 H, J = 7.0 Hz), 1.004 (d,
3 H, J = 7.0 Hz), 0.819 (d, 3 H, J = 7.0 Hz), 0.783 (d, 3 H, J =
7.0 Hz), 0.588 (d, 3 H, J = 7.0 Hz); minor isomer (21a): 7.277 (d,
1 H, J = 8.0 Hz), 7.241 (d, 1 H, J = 8.0 Hz), 7.191 (d, 1 H, J =
8.0 Hz), 7.003 (d, 1 H, J = 8.0 Hz), 6.981 (d, 1 H, J = 8.0 Hz),
6.963 (t, 1 H, J = 8.0 Hz), 6.960 (t, 1 H, J = 8.0 Hz), 6.937 (t,
1 H, J = 8.0 Hz), 6.896 (d, 1 H, J = 8.0 Hz), 6.866 (d, 1 H, J =
8.0 Hz), 6.845 (t, 1 H, J = 8.0 Hz), 6.784 (d, 1 H, J = 8.0 Hz),
6.711 (t, 1 H, J = 8.0 Hz), 6.479 (d, 1 H, J = 8.0 Hz), 6.451 (d,
(1)2Nb(N-2,6-Me2C6H3)Cl (20). To a flask containing both
11 (0.40 g, 0.98 mmol) and 1Li (0.796 g, 2.44 mmol), pentane
(50 mL) was added, forming a pale yellow slurry. The mixture
was stirred at room temperature for 30 h, forming a brown slurry.
The mixture was dried under vacuum and washed with pentane
(3 ¥ 50 mL), leaving a fine orange solid. Lithium chloride was
readily removed by extracting the product into toluene (50 mL)
and filtering. The product was then dried under vacuum. The
2
1 H, J = 8.0 Hz), 5.295 (d, 1 H, JHH = 2.0 Hz), 5.093 (d, 1 H,
2
2JHH = 2.0 Hz), 4.775 (d, 1 H, JHH = 2.0 Hz), 4.743 (d, 1 H,
2JHH = 2.0 Hz), 3.761 (sept, 1 H, J = 7.0 Hz), 3.645 (sept, 1 H,
J = 7.0 Hz), 2.932 (sept, 1 H, J = 7.0 Hz), 2.804 (sept, 1 H, J =
7.0 Hz), 2.054 (s, 3 H), 1.919 (s, 3 H), 1.597 (d, 3 H, J = 7.0 Hz),
1.077 (d, 3 H, J = 7.0 Hz), 1.029 (d, 3 H, J = 7.0 Hz), 0.895 (d,
3 H, J = 7.0 Hz), 0.878 (d, 3 H, J = 7.0 Hz), 0.798 (d, 3 H, J =
7.0 Hz), 0.599 (d, 3 H, J = 7.0 Hz), 0.563 (d, 3 H, J = 7.0 Hz).
◦
resultant oil was recrystallized from ether at -25 C, yielding an
orange crystalline solid (0.58 g, 66%). 1H NMR (C6D6, 600 MHz):
4
d 7.208 (dd, 1 H, J = 8.0 Hz, JHH = 1 Hz), 7.162 (t, 1 H, J =
1
13C{ H} NMR (C6D6, 150 MHz): major isomer (21): d 185.12,
8.0 Hz), 7.08–7.04 (m, 4 H), 6.868 (d, 1 H, J = 8.0 Hz), 6.820 (d,
1 H, J = 7.0 Hz), 6.819 (d, 1 H, J = 8.0 Hz), 6.800 (d, 1 H, J =
7.0 Hz), 6.695 (t, 1 H, J = 7.0 Hz), 6.595 (d, 1 H, J = 8.0 Hz),
6.521 (d, 1 H, J = 8.0 Hz), 5.133 (d, 1 H, 2JHH = 1.0 Hz), 5.108 (d,
1 H, 2JHH = 1.0 Hz), 5.018 (d, 1 H, 2JHH = 1.0 Hz), 4.845 (d, 1 H,
2JHH = 1.0 Hz), 3.668 (sept, 1 H, J = 7.0 Hz), 3.373 (sept, 1 H,
J = 7.0 Hz), 2.938 (sept, 1 H, J = 7.0 Hz), 2.799 (s, 3 H), 2.434
(sept, 1 H, J = 7.0 Hz), 2.233 (s, 3 H), 1.721 (s, 3 H), 1.706 (s, 3 H),
1.411 (d, 3 H, J = 7.0 Hz), 0.923 (d, 3 H, J = 7.0 Hz), 0.914 (d,
3 H, J = 7.0 Hz), 0.874 (d, 3 H, J = 7.0 Hz), 0.800 (d, 3 H, J =
7.0 Hz), 0.788 (d, 3 H, J = 7.0 Hz), 0.754 (d, 3 H, J = 7.0 Hz),
184.48, 159.09, 152.14, 150.48, 149.33, 149.24 (x 2), 148.94, 142.13,
141.95, 141.79, 141.74, 141.02, 139.51, 127.90, 127.55, 127.28,
127.14, 125.18, 124.98, 124.61, 124.53, 124.48, 124.19, 123.86,
122.83, 122.74, 106.94, 105.67, 100.51, 100.39, 28.86, 28.67, 28.66,
26.96, 25.77, 25.35, 25.15, 24.79, 24.69, 24.65, 23.77, 23.32, 20.51,
20.11; minor isomer (21a): 182.27, 180.46, 176.75, 169.34, 153.06,
151.40, 150.14, 149.94, 149.57, 147.17, 144.95, 143.43, 142.03,
141.74, 141.70, 138.76, 128.92, 128.68, 127.28, 126.67, 126.44,
125.55, 124.74, 124.63, 124.40, 124.23, 122.62, 122.06, 107.56,
106.23, 100.68, 100.09, 30.75, 29.90, 29.04, 28.20, 27.36, 26.78,
26.71, 25.59, 25.51 (x 2), 23.07, 22.72, 22.07, 21.73. IR: 1543 (m),
1460 (s), 1408 (m), 1377 (m), 1312 (m), 1245 (m), 1145 (w), 1095
(w), 1047 (m), 937 (w), 860 (w), 802 (m), 778 (w), 688 (w). Anal.
calcd for C48H53ClN3NbO4: C 66.70, H 6.18, N 4.86. Found: C
65.28, H 6.23, N 4.70. Melting point: 195 ◦C (decomposition).
1
0.677 (d, 3 H, J = 7.0 Hz). 13C{ H} NMR (C6D6, 150 MHz): d
151.85, 149.90, 149.36 (¥2), 148.64 (¥2), 147.96, 143.68, 143.22,
142.03 (¥2), 141.70 (¥2), 141.00, 140.70, 139.85 (¥2), 136.23 (¥2),
127.48, 127.22, 127.11, 127.02, 126.70, 125.71, 124.85, 124.40,
123.89, 123.68, 122.39, 108.40, 106.27, 99.91, 99.64, 29.75, 29.26,
28.53, 28.02, 26.78, 26.60, 25.49, 25.29, 25.01, 24.77, 24.57, 23.20,
21.80, 21.08, 21.03, 19.63. IR: 2905 (s), 1650 (m), 1635 (m), 1509
(m), 1444 (s), 1401 (w), 1357 (m), 1345 (w), 1280 (m), 1238 (w),
1154 (w), 1144 (w), 1087 (w), 1052 (w), 938 (w), 802 (w). Anal.
calcd for C50H57ClN3NbO4: C 67.30, H 6.44, N 4.71. Found: C
67.05, H 6.69, N 4.36. Melting point: 149 ◦C (decomposition).
(1)2Nb(N-CMe3)Cl (22). A flask containing both 13 (1.0 g,
3.9 mmol) and 1Li (2.6 g, 7.8 mmol) was cooled to 0 ◦C,
followed by the addition of cooled◦pentane (50 mL). A yellow
slurry formed and was stirred at 0 C for 1 h. The mixture was
warmed to room temperature and stirred for an additional 3 h.
The mixture was filtered and washed with pentane (3 ¥ 20 mL).
Lithium chloride was readily removed by extracting the product
into toluene (50 mL) and filtering. The resulting solution was then
dried under vacuum to yield a fine dark green solid (0.6 g, 20%).
The 1H NMR shows a mixture of two isomers in a 3 : 1 ratio. 1H
NMR (C6D6, 600 MHz): major isomer (22): d 7.290 (d, 1 H, J =
7.8 Hz), 7.203 (d, 1 H, J = 7.8 Hz), 7.086 (t, 2 H, J = 7.8 Hz), 7.016
(d, 2 H, J = 7.8 Hz), 6.691 (d, 1 H, J = 7.8 Hz), 6.549 (d, 1 H, J =
7.8 Hz), 6.489 (d, 1 H, J = 7.8 Hz), 6.365 (d, 1 H, J = 7.8 Hz),
5.481 (d, 1 H, 2JHH = 1.2 Hz), 4.832 (d, 1 H, 2JHH = 1.2 Hz), 4.668
(s, 1 H), 4.581 (s, 1 H), 4.250 (sept, 2 H, J = 7.2 Hz), 4.087 (sept,
2 H, J = 7.2 Hz), 3.314 (s, 3 H), 3.118 (s, 9 H), 1.900 (s, 3 H),
1.670 (d, 6 H, J = 7.2 Hz), 1.615 (d, 6 H, J = 7.2 Hz), 1.510 (d,
6 H, J = 7.2 Hz), 0.932 (d, 6 H, J = 7.2 Hz); minor isomer (22a):
7.338 (d, 1 H, J = 7.8 Hz), 7.257 (d, 1 H, J = 7.8 Hz), 7.191 (d,
1 H, J = 7.8 Hz), 7.092 (d, 2 H, J = 7.8 Hz), 6.977 (t, 2 H, J =
7.8 Hz), 6.921 (d, 1 H, J = 7.8 Hz), 6.849 (d, 1 H, J = 7.8 Hz),
(1)2Nb(N-C6H5)Cl (21). To a flask containing both 12 (2.0 g,
7.2 mmol) and 1Li (2.4 g, 14 mmol), which had been cooled (0 ◦C),
cold pentane (100 mL) was added, forming a yellow slurry. The
mixture was kept at 0 ◦C for 1 h, brought to room temperature and
stirred for 3 h. The mixture was filtered and washed with pentane
(3 ¥ 30 mL). Lithium chloride was readily removed by extracting
the product into toluene (50 mL) and filtering. The product was
concentrated under vacuum to precipitate a fine brown solid with a
5 : 2 ratio of the products (1.8 g, 33%). 1H NMR (C6D6, 600 MHz):
major isomer (21): d 7.261 (d, 1 H, J = 8.0 Hz), 7.175 (t, 1 H, J =
8.0 Hz), 7.09–7.02 (m, 3 H), 7.042 (d, 1 H, J = 8.0 Hz), 6.947 (d,
1 H, J = 8.0 Hz), 6.837 (t, 2 H, J = 7.0 Hz), 6.763 (d, 1 H, J =
8.0 Hz), 6.697 (d, 1 H, J = 8.0 Hz), 6.609 (t, 1 H, J = 7.0 Hz),
6.476 (d, 1 H, J = 7.0 Hz), 6.204 (d, 2 H, J = 7.0 Hz), 5.387
(d, 1 H, 2JHH = 1.0 Hz), 5.351 (d, 1 H, 2JHH = 1.0 Hz), 5.208 (d,
2
2
1 H, JHH = 1.0 Hz), 5.169 (d, 1 H, JHH = 1.0 Hz), 3.726 (sept,
4996 | Dalton Trans., 2009, 4987–5000
This journal is
The Royal Society of Chemistry 2009
©

View Article Online
6.646 (d, 1 H, J = 7.8 Hz), 5.356 (d, 1 H, 2JHH = 1.2 Hz), 5.252 (d,
1 H, 2JHH = 1.2 Hz), 4.730 (s, 1 H), 4.665 (s, 1 H), 3.959 (sept, 2 H,
J = 6.6 Hz), 3.519 (sept, 2 H, J = 6.6 Hz), 3.380 (s, 3 H), 3.263 (s,
9 H), 2.110 (s, 3 H), 1.430 (d, 3 H, J = 6.6 Hz), 1.405 (d, 3 H, J =
6.6 Hz), 1.365 (d, 3 H, J = 6.6 Hz), 1.301 (d, 3 H, J = 6.6 Hz),
1.172 (d, 3 H, J = 6.6 Hz), 1.002 (d, 3 H, J = 6.6 Hz), 0.691
vacuum leaving a fine orange solid. Lithium chloride was readily
removed by extracting the product into toluene (30 mL) and
filtering. H NMR spectroscopic data of this product revealed
1
a non-interconverting mixture of two isomers in a 2 : 1 ratio.
1
The separation of H NMR and 13C NMR peaks was possible
by variable temperature NMR studies of the product at 42 ◦C in
C6D6 which leads to 3 : 1 peak ratios assignable as major and minor
isomers. Crystals suitable for X-ray diffraction were recrystallized
1
(d, 3 H, J = 6.6 Hz), 0.510 (d, 3 H, J = 6.6 Hz). 13C{ H} NMR
(C6D6, 150 MHz): major isomer (22): d 156.12, 151.65, 150.18,
139.39, 137.83, 130.08, 129.84, 128.39, 127.90, 127.20, 126.89,
126.35, 125.94, 125.34, 125.33, 125.30, 125.13, 124.90, 123.90,
109.33, 109.10, 107.37, 101.15, 34.54, 31.96, 30.30, 30.26, 29.95,
29.74, 29.31, 27.10, 26.86, 26.40, 26.29, 25.46, 24.93, 24.45, 22.93,
22.19, 22.09, 19.56; minor isomer (22a): 153.41, 146.65, 142.93,
142.44, 140.79, 140.73, 135.61, 128.73, 128.30, 126.01, 125.07,
124.85, 124.55, 119.18, 108.71, 108.45, 106.90, 102.87, 102.61,
101.46, 101.40, 100.24, 85.45, 35.15, 32.70, 32.51, 32.42, 31.73,
29.86, 29.08, 28.34, 27.03, 26.96, 26.57, 26.21, 25.61, 24.75, 24.34,
24.23, 22.48, 19.11. IR: 2926 (s), 2853 (s), 2355 (s), 1555 (w), 1492
(m), 1456 (s), 1373 (m), 1243 (m), 1046 (m), 823 (w). Melting Point:
175 ◦C (decomposition).
◦
1
from ether after a day at -25 C (0.28 g, 80%). H NMR (C6D6,
400 MHz): major isomer (24): d 7.216 (d, 2 H, J = 8.0 Hz), 7.197
(d, 2 H, J = 8.0 Hz), 7.052 (d, 1 H, J = 8.0 Hz), 7.013–6.868 (m,
4 H), 6.591 (dd, 2 H, J = 8.0 Hz, 4JHH = 1.2 Hz), 6.534 (dd, 2 H,
J = 8.0 Hz, 4JHH = 1.2 Hz), 5.246 (s, 1 H), 5.218 (s, 1 H), 5.162 (s,
1 H), 5.051 (s, 1 H), 4.573 (sept, 1 H, J = 7.2 Hz), 4.219 (sept, 1 H,
J = 7.2 Hz), 3.149 (dq, 2 H, 2JHH = 16 Hz, J = 7.2 Hz), 2.620 (dq,
2 H, 2JHH = 16 Hz, J = 7.2 Hz), 2.170 (dq, 2H, 2JHH = 16 Hz, J =
7.2 Hz), 1.720 (dq, 2 H, 2JHH = 16 Hz, J = 7.2 Hz), 1.622 (s, 3 H),
1.592 (s, 3 H), 1.372 (d, 3 H, J = 7.2 Hz), 1.319 (d, 3 H, J = 7.2 Hz),
1.139 (t, 3 H, J = 7.2 Hz), 1.108 (t, 3 H, J = 7.2 Hz), 0.869 (d, 3 H,
J = 7.2 Hz), 0.813 (d, 3 H, J = 7.2 Hz), 0.784 (t, 3 H, J = 7.2 Hz),
0.753 (t, 3 H, J = 7.2 Hz); minor isomer (24a): 7.258 (d, 2 H, J =
7.6 Hz), 7.094–7.020 (m, 3 H), 6.841 (d, 2 H, J = 7.6 Hz), 6.774 (d,
2 H, J = 8.0 Hz), 6.742 (d, 2 H, J = 8.0 Hz), 6.466 (dd, 1 H, J =
8.0 Hz, 4JHH = 1.2 Hz), 6.353 (dd, 1 H, J = 8.0 Hz, 4JHH = 1.2 Hz),
5.638 (s, 1 H), 5.270 (s, 1 H), 5.145 (s, 1 H), 5.019 (s, 1 H), 3.749
(sept, 1 H, J = 7.2 Hz), 3.412 (dq, 2 H, 2J = 16 Hz, J = 7.2 Hz),
(1)2Ta(N-2,6-iPr2C6H3)Cl (23). To a flask containing both
14 (0.30 g, 0.54 mmol) and 1Li (0.352 g, 1.08 mmol), pentane
(100 mL) was added, and the mixture was stirred at room
temperature for 24 h, forming an orange slurry. The mixture
was filtered, washed with pentane (2 ¥ 50 mL), and dried under
vacuum leaving a fine orange solid. Lithium chloride was readily
removed by extracting the product into toluene (50 mL), filtering
and removing solvent under vacuum (0.51, 85%). Crystals suitable
for X-ray diffraction were recrystallized from a 1 : 1 ratio of
toluene and n-pentane after two days at -18 ◦C. 1H NMR (C6D6,
600 MHz): d 7.195 (d, 1 H, J = 7.2 Hz), 7.131 (d, 1 H, J = 7.2 Hz),
7.114–7.064 (m, 4 H), 7.057 (d, 1 H, J = 7.8 Hz), 7.034 (t, 1 H,
J = 7.2 Hz), 6.913 (d, 1 H, J = 7.8 Hz), 6.888 (d, 1 H, J = 6.0 Hz),
6.875 (d, 1 H, J = 6.0 Hz), 6.621 (d, 1 H, J = 7.8 Hz), 6.497 (d,
1 H, J = 7.8 Hz), 5.143 (s, 1 H), 5.103 (s, 1 H), 5.065 (s, 1 H),
4.921 (s, 1 H), 4.686 (sept, 1 H, J = 6.6 Hz), 3.901 (sept, 1 H,
J = 6.6 Hz), 3.308 (sept, 1 H, J = 6.6 Hz), 3.268 (sept, 1 H, J =
6.6 Hz), 2.640 (sept, 1 H, J = 6.6 Hz), 2.399 (sept, 1 H, J = 6.6 Hz),
1.775 (s, 3 H), 1.658 (s, 3 H), 1.404 (d, 3 H, J = 6.6 Hz), 1.359 (d,
3 H, J = 6.6 Hz), 1.267 (d, 3 H, J = 6.6 Hz), 1.091 (d, 3 H, J =
6.6 Hz), 1.043 (d, 3 H, J = 6.6 Hz), 0.913 (d, 3 H, J = 6.6 Hz),
0.837–0.809 (m, 12 H), 0.679 (d, 3 H, J = 6.6 Hz), 0.578 (d, 3 H,
2
3.335 (sept, 1 H, J = 7.2 Hz), 2.364 (dq, 2 H, J = 16 Hz, J =
7.2 Hz), 1.896 (dq, 2 H, 2J = 16 Hz, J = 7.2 Hz), 1.695 (dq, 2 H,
2J = 16 Hz, J = 7.2 Hz), 1.539 (s, 3 H), 1.530 (d, 3 H, J = 7.2 Hz),
1.522 (s, 3 H), 1.253 (d, 3 H, J = 7.2 Hz), 1.205 (d, 3 H, J = 7.2 Hz),
1.149 (t, 3 H, J = 7.2 Hz), 1.104 (t, 3 H, J = 7.2 Hz), 0.791 (t, 3 H,
J = 7.2 Hz), 0.744 (t, 3 H, J = 7.2 Hz), 0.714 (d, 3 H, J = 7.2 Hz).
1
13C{ H} NMR (C6D6, 150 MHz): major isomer (24): d 183.59,
181.09, 178.95, 178.90, 158.18, 153.35, 150.76, 150.38, 149.62,
148.32, 148.18, 147.95, 143.19, 138.58, 137.94, 136.55, 136.36,
127.30, 126.97, 126.50, 126.30, 125.82, 125.59, 124.45, 123.25,
122.09, 121.58, 108.20, 106.14, 100.30, 100.08, 30.08, 28.33, 27.50,
25.21, 24.83, 24.77, 24.61, 24.33, 24.03, 23.98, 23.73, 19.35, 16.23,
15.30, 14.68, 13.43; minor isomer (24a): 182.22, 178.65, 175.98,
172.56, 150.20, 149.62, 147.82, 144.71, 143.04, 141.44, 140.21,
138.41, 137.72, 135.70, 128.40, 128.16, 126.73, 126.08 (x 2), 125.26,
124.87, 124.62, 124.55, 124.42, 123.83, 122.95, 107.25, 105.88,
100.93, 100.24, 28.88, 28.46, 27.75, 26.74, 26.21, 25.77, 25.60,
23.49, 22.02, 20.03, 18.75, 16.28, 15.92, 15.01, 14.37, 12.82. IR:
2923 (s), 2856 (s), 1459 (s), 1375 (m), 1248 (w), 1122 (w), 1050
(w), 943 (w), 805 (w), 723 (w). Anal. calcd for C50H57ClN3O4Ta:
C 61.25, H 5.86, N 4.29. Found: C 61.58, H 6.19, N 4.17. Melting
point: 190–195 ◦C.
1
J = 6.6 Hz). 13C{ H} NMR (C6D6, 150 MHz): d 183.93, 181.34,
179.63, 178.38, 154.52, 153.26, 150.73, 150.42, 150.09, 148.29,
147.26, 147.13, 143.85, 143.26, 142.61, 142.36, 141.98, 140.91,
127.57, 126.98, 126.92, 126.15, 124.91, 124.46, 124.26, 123.65,
123.36, 122.42, 121.38, 108.24, 106.14, 99.93, 99.78, 29.82, 29.28,
28.65, 28.45, 27.94, 27.10, 26.80, 26.29, 25.71, 25.56, 25.26, 25.22,
25.09, 25.02, 24.80, 23.51, 23.35, 22.64, 22.04. IR: 1547 (m), 1459
(s), 1408 (w), 1376 (w), 1303 (w), 1248 (m), 1150 (w), 1123 (w),
1094 (w), 1050 (w), 943 (w), 863 (w), 800 (w), 777 (w). Anal. calcd
for C54H65ClN3O4Ta: C 62.57, H 6.32, N 4.04. Found: C 62.66, H
6.11, N 4.02. Melting point: 210 ◦C (decomposition).
(3)2Ta(N-2,6-iPr2C6H3)Cl (25). To a flask containing both 14
(0.133 g, 0.240 mmol) and 3Li (0.125 g, 0.482 mmol), pentane
(100 mL) was added, and the mixture was stirred at room
temperature for 24 h, forming an orange slurry. The mixture
was filtered, washed with pentane (2 ¥ 50 mL), and dried
under vacuum, leaving a fine orange solid. The fine powder was
redissolved in toluene and the insoluble LiCl was filtered off.
Removal of volatiles under vacuum leaves behind a brownish oil.
The oil was recrystallized from ether at -25 ◦C, yielding an orange
crystalline solid. 1H NMR shows a mixture of two isomers with a
(2)2Ta(N-2,6-iPr2C6H3)Cl (24). To a flask containing both
14 (0.20 g, 0.36 mmol) and 2Li (0.217 g, 0.723 mmol), pentane
(100 mL) was added, and the mixture was stirred at room
temperature for 24 h, forming an orange slurry. The mixture
was filtered, washed with pentane (2 ¥ 50 mL), and dried under
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 4987–5000 | 4997
©

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1 : 1 ratio. Synthesis of this product at 0 ◦C results in the formation
of major and minor isomers in a 3 : 1 ratio (0.18 g, 80%). 1H NMR
(C6D6, 600 MHz): major isomer (25): 7.258 (d, 1 H, J = 7.2 Hz),
7.038 (d, 1 H, J = 7.2 Hz), 6.990 (d, 1 H, J = 7.2 Hz), 6.930–6.884
(m, 3 H), 6.882 (d, 1 H, J = 7.8 Hz), 6.862 (d, 1 H, J = 7.2 Hz),
6.855 (d, 1 H, J = 7.8 Hz), 6.815 (d, 1 H, J = 7.8 Hz), 6.688 (t,
1 H, J = 7.8 Hz), 6.588 (d, 1 H, J = 7.8 Hz), 6.533 (d, 1 H, J =
7.8 Hz), 5.250 (s, 1 H), 5.240 (s, 1 H), 5.147 (s, 1 H), 5.077 (s,
1 H), 4.616 (sept, 1 H, J = 6.6 Hz), 4.318 (sept, 1 H, J = 6.6 Hz),
2.354 (s, 3 H), 1.869 (s, 3 H), 1.593 (s, 3 H), 1.481 (s, 3 H), 1.466
(s, 3 H), 1.435 (d, 3 H, J = 6.6 Hz), 1.365 (d, 3 H, J = 6.6 Hz),
1.331 (s, 3 H), 1.222 (d, 3 H, J = 6.6 Hz), 0.810 (d, 3 H, J =
6.6 Hz); minor isomer (25a): 7.128 (d, 1 H, J = 7.8 Hz), 7.085 (d,
1 H, J = 7.8 Hz), 7.035 (d, 1 H, J = 7.8 Hz), 6.962–6.930 (m,
6 H), 6.741 (t, 1 H, J = 7.8 Hz), 6.507 (d, 1 H, J = 8.4 Hz), 6.481
(d, 1 H, J = 8.4 Hz), 6.342 (d, 1 H, J = 7.8 Hz), 5.658 (s, 1 H),
5.293 (s, 1 H), 5.217 (s, 1 H), 5.060 (s, 1 H), 3.760 (sept, 1 H, J =
6.6 Hz), 3.576 (sept, 1 H, J = 6.6 Hz), 2.403 (s, 3 H), 2.189 (s,
3 H), 2.139 (s, 3 H), 1.897 (s, 3 H), 1.663 (d, 3 H, J = 6.6 Hz),
1.580 (s, 3 H), 1.292 (d, 3 H, J = 6.6 Hz), 1.199 (s, 3 H), 1.157
142.78, 142.27, 141.26, 141.03, 137.79, 128.93, 127.85, 127.68,
127.45, 126.95, 126.37, 125.94, 125.72, 124.00, 123.93, 123.65,
123.03, 122.86, 122.22, 109.26, 106.66, 100.36, 99.99, 29.88, 29.05,
28.61, 28.27, 28.04, 27.90, 27.78, 27.53, 25.78, 25.47, 25.26, 25.14,
24.58, 24.36, 23.45, 23.13, 23.08, 22.76, 21.89; IR: 2923 (s), 2856
(s), 1608 (w), 1552 (w), 1459 (s), 1410 (w), 1376 (m), 1250 (m),
1167 (w), 1111 (w), 1058 (w), 798 (w), 723 (w). Anal. calcd for
C52H61ClN3O4Ta: C 61.93, H 6.10, N 4.17. Found: C 62.02, H
5.96, N 4.15. Melting point: 185 ◦C (decomposition).
Crystallography
Summaries of crystal data and collection parameters for crystal
structures of 16, 17, 18, 20, 23 and 24 are provided in Table 2.
Detailed descriptions of data collection, as well as data solu-
tion, are provided below. ORTEP diagrams were generated with
the ORTEP-3 software package.67 For each sample, a suitable
crystal was mounted on a pulled glass fiber using Paratone-
N hydrocarbon oil. The crystal was transferred to a Siemens
SMART68 diffractometer with a CCD area detector, centered in
the X-ray beam, and cooled to the indicated temperature using a
nitrogen-flow low-temperature apparatus that had been previously
calibrated by a thermocouple placed at the same position as the
crystal. An arbitrary hemisphere of data was collected using 0.3◦
w scans, and the data were integrated by the program SAINT.69
The final unit cell parameters were determined by a least-squares
refinement of the reflections with I > 10s(I). Data analysis using
Siemens XPREP70 and the successful solution and refinement
of the structure determined the space group. An empirical
absorption correction was applied using SADABS.71 Equivalent
reflections were averaged, and the structures were solved by
direct methods using the SHELXTL software package.72 Unless
otherwise noted, all non-hydrogen atoms were refined anisotrop-
ically, and hydrogen atoms were included as fixed atoms but not
refined.
1
(d, 3 H, J = 6.6 Hz), 0.710 (d, 3 H, J = 6.6 Hz). 13C{ H} NMR
(C6D6, 150 MHz): major isomer (25): d 183.68, 180.74, 178.99,
178.90, 158.04, 150.94, 150.74, 150.43, 149.32, 149.10, 148.55,
142.95, 141.24, 133.38, 132.34, 131.34, 130.72, 129.97, 128.89,
128.75, 128.54, 126.44, 125.85, 125.79, 124.47, 123.22, 121.97,
121.53, 108.18, 106.25, 100.37, 100.13, 28.26, 27.58, 25.43, 24.58,
24.22, 24.19, 20.48, 18.64, 18.19, 18.01, 17.13; minor isomer (25a):
184.30, 182.57, 178.01, 172.39, 150.36, 150.22, 149.68, 149.54,
147.80, 147.21, 133.02, 132.91, 131.71, 130.10, 129.46, 127.97,
127.49, 125.65, 125.42, 125.03, 124.59, 123.70, 123.30, 121.82,
108.06, 107.33, 106.01, 101.71, 100.92, 100.31, 29.96, 28.85, 28.51,
26.24, 24.82, 22.36, 21.16, 20.14, 19.75, 19.63, 19.23, 18.53, 18.05;
IR: 3175 (w), 2926 (s), 2864 (s), 1550 (m), 1492 (w), 1456 (s), 1373
(s), 1347 (w), 1243 (m), 1119 (w), 1088 (w), 1046 (m), 937 (w), 823
(w), 761 (w). Anal. calcd for C46H49ClN3O4Ta: C 59.77, H 5.34,
◦
N 4.55. Found: C 59.63, H 5.32, N 4.33. Melting point: 150 C
16. X-ray quality crystals were grown from a saturated solu-
tion of diethyl ether at -20 ◦C. The asymmetric unit contains one
half molecule of disordered solvent located at an inversion center.
Additionally, one ligand methyl group is disordered over two po-
sitions. The disordered solvent molecule was refined isotropically.
The final cycle of full-matrix least-squares refinement was based
on 11 698 observed reflections and 558 variable parameters and
converged yielding final residuals: R = 0.0814, Rall = 0.1200 and
GOF = 1.002.
(decomposition).
(5)2Ta(N-2,6-iPr2C6H3)Cl (26). To a flask containing both
14 (0.60 g, 1.1 mmol) and 5Li (0.813 g, 2.58 mmol), pentane
(100 mL) was added, forming a yellow slurry. The mixture was
stirred at room temperature for 24 h, forming an orange slurry.
The mixture was filtered, washed with pentane (3 ¥ 30 mL), and
dried under vacuum, leaving a fine orange solid. The fine powder
was redissolved in toluene and the insoluble LiCl was filtered
off. Volatiles were removed under vacuum. The resulting oil was
recrystallized from ether at -25 ◦C, yielding an orange crystalline
solid (0.74 g, 75%). 1H NMR (C6D6, 600 MHz): d 8.050 (s, 1 H),
7.957 (s, 1 H), 7.281 (d, 1 H, J = 7.8 Hz), 7.261 (d, 1 H, J =
7.8 Hz), 7.188–6.906 (m, 8 H), 6.639 (d, 1 H, J = 7.8 Hz), 6.573
(d, 1 H, J = 7.8 Hz), 6.440 (d, 1 H, J = 7.8 Hz), 5.161 (s, 1 H),
5.078 (s, 1 H), 5.058 (s, 1 H), 4.953 (s, 1 H), 4.754 (sept, 1 H,
J = 6.6 Hz), 4.116 (sept, 1 H, J = 6.6 Hz), 3.739 (sept, 1 H, J =
6.6 Hz), 3.339 (sept, 1 H, J = 6.6 Hz), 2.780 (sept, 1 H, J = 6.6 Hz),
2.685 (sept, 1 H, J = 6.6 Hz), 1.303 (d, 3 H, J = 6.6 Hz), 1.260
(d, 3 H, J = 6.6 Hz), 1.170 (d, 3 H, J = 6.6 Hz), 0.991–0.862 (m,
18 H), 0.826 (d, 3 H, J = 6.6 Hz), 0.721 (d, 3 H, J = 6.6 Hz),
17. X-ray quality crystals were grown from a saturated so-
lution of diethyl ether at -20 ◦C. The final cycle of full-matrix
least-squares refinement was based on 10 183 observed reflections
and 496 variable parameters and converged yielding final residuals:
R = 0.0361, Rall = 0.0903 and GOF = 0.928.
18. X-ray quality crystals were grown from a saturated so-
lution of diethyl ether at -20 ◦C. The final cycle of full-matrix
least-squares refinement was based on 9101 observed reflections
and 424 variable parameters and converged yielding final residuals:
R = 0.0389, Rall = 0.0863 and GOF = 0.936.
20. X-ray quality crystals were grown from a saturated solu-
tion of diethyl ether at -20 ◦C. The asymmetric unit contained two
independent molecules of compound 20, as well as two ordered
1
0.671 (d, 3 H, J = 6.6 Hz). 13C{ H} NMR (C6D6, 150 MHz):
d 177.01, 176.35, 153.28, 151.03, 150.53, 150.52, 149.32, 143.78,
4998 | Dalton Trans., 2009, 4987–5000
This journal is
The Royal Society of Chemistry 2009
©

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Table 2 Crystal data and collection parameters
Compound
Formula
16
17
18
20
23
24
C50H57ClN3NbO4· C46H49ClN3NbO4
C38H49ClN3NbO4
C100H114Cl2N6Nb2O8· C54H65ClN3O4Ta·
C50H57ClN3O4Ta·
1 C4H10O
2C4H10O
1932.93
2C7H8
1 C4H10O
2
2
FW
929.41
836.24
P21/c (#14)
140(2)
13.4669(6)
12.2295(5)
25.270(1)
90.000
99.774(1)
90.000
740.16
Pbca (#61)
140(2)
17.678(1)
11.2151(7)
36.896(2)
90.000
90.000
90.000
7314.9(8)
8
1.344
1220.76
C2/c (#15)
140(2)
20.5332(8)
14.7874(6)
39.729(2)
90.000
99.180(1)
90.000
11908.6(8)
8
1017.45
¯
¯
Space group
T/K
P1 (#2)
P21/n (#14)
170(2)
24.0051(8)
18.6894(6)
24.3056(8)
90.000
113.790(1)
90.000
9977.9(6)
4
P1 (#2)
175(2)
200(2)
˚
a/A
9.557(1)
12.424(2)
21.471(3)
106.767(3)
91.047(3)
101.570(3)
2383.4(5)
2
9.5748(5)
12.4236(6)
21.464(1)
106.673(1)
91.012(1)
101.091(1)
2393.0(2)
2
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
3
˚
V/A
4101.4(3)
4
1.354
Z
D
calcd/g cm-3
1.295
1.287
1.362
1.412
Diffractometer
Radiation
Siemens SMART
Mo Ka
Siemens SMART
Mo Ka
Siemens SMART
Mo Ka
Siemens SMART
Mo Ka
Siemens SMART
Mo Ka
Siemens SMART
Mo Ka
˚
˚
˚
˚
˚
˚
(l = 0.71069 A)
(l = 0.71069 A)
(l = 0.71069 A)
(l = 0.71069 A)
(l = 0.71069 A)
(l = 0.71069 A)
Monochromator
Detector
Graphite
Graphite
Graphite
Graphite
Graphite
Graphite
CCD area detector CCD area detector CCD area detector CCD area detector
CCD area detector CCD area detector
Scan type, width
Scan speed
No. of reflections
measured
w, 0.3◦
w, 0.3◦
40 s/frame
Hemisphere
w, 0.3◦
45 s/frame
Hemisphere
w, 0.3◦
30 s/frame
Hemisphere
w, 0.3◦
w, 0.3◦
40 s/frame
Hemisphere
30 s/frame
Hemisphere
30 s/frame
Hemisphere
2q range/◦
Crystal
2.0–56.9
0.60 ¥ 0.16 ¥ 0.06
3.1–56.6
0.20 ¥ 0.10 ¥ 0.10
2.2–56.6
0.08 ¥ 0.06 ¥ 0.02
2.0–56.6
0.34 ¥ 0.18 ¥ 0.06
2.1–56.6
0.14 ¥ 0.10 ¥ 0.08
2.0–56.6
0.20 ¥ 0.05 ¥ 0.05
dimensions/mm
No. of reflections
measured
No. of unique
reflections
No. of
observations
Rint
25 946
11 698
11 698
0.0724
45 419
10 183
10 183
78 495
9101
112 567
24 814
24 814
66 517
14 845
14 845
27 256
11 859
11 859
9101
0.0727
496
0.1337
424
0.0940
1153
0.0614
669
0.0443
549
No. of parameters 558
R, Rw, Rall
0.0814, 0.2050,
0.1200
1.002
0.0361, 0.0903,
0.0546
0.928
0.0389, 0.0865,
0.0863
0.936
0.0586, 0.1287,
0.1117
1.011
0.0406,0.0929,
0.0545
1.044
0.0451, 0.0976,
0.0623
1.028
GOF
diethyl ether solvent molecules. The final cycle of full-matrix least-
squares refinement was based on 24 814 observed reflections and
1153 variable parameters and converged yielding final residuals:
R = 0.0586, Rall = 0.1117 and GOF = 1.011.
Acknowledgements
We gratefully acknowledge The University of Toledo for generous
start-up funding, as well as Dr Kristin Kirschbaum (University
of Toledo) and Dr Allen Oliver (University of Notre Dame) for
assistance with X-ray crystallography.
23. X-ray quality crystals were grown from a layered solution
of toluene and pentane at -20 ◦C. In addition to compound 23, the
asymmetric unit contained two molecules of disordered toluene,
located in three separate regions. Additionally, one isopropyl
methyl group is disordered over two positions. The toluene
molecules were refined isotropically. The final cycle of full-matrix
least-squares refinement was based on 14 845 observed reflections
and 669 variable parameters and converged yielding final residuals:
R = 0.0406, Rall = 0.0545 and GOF 1.044.
References
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Wiley & Sons, 1988.
2 D. S. Williams, D. W. Thompson and A. V. Korolev, J. Am. Chem. Soc.,
1996, 118, 6526–6527.
3 K. S. Heinselman, V. M. Miskowski, S. J. Geib, L. C. Wang and M. D.
Hopkins, Inorg. Chem., 1997, 36, 5530–5538.
4 D. S. Williams and A. V. Korolev, Inorg. Chem., 1998, 37, 3809–
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5000 | Dalton Trans., 2009, 4987–5000
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