Tantalum complexes supported by asymmetric [ONO] ligands. the role of weakly coordinating anions on their reactivity

Article abstract of DOI:10.1021/om201199p

The tantalum complex [TaCp*Me₂(OOCPhN=CHPhO- κ³O,N,O)] (2) has been synthesized by reaction of [TaCp*Me₄] (Cp* = η⁵-C₅Me ₅) with 2-(salicylideneamino)benzoic acid. Complex 2 reacts with HOTf to yield the new tantalum derivative [TaCp*Me(OTf)(OOCPhN=CHPhO- κ³O,N,O)] (3). Moreover, compound 3 reacts with ^tBuNC or xylylNC to yield the iminoacyl-containing complexes [TaCp*(C(Me)=NR-κ²C,N)(OTf)(OOCPhN=CH] PhO-κ³O,N,O)] (R = ^tBu (4), 2,6-Me₂C ₆H₃ (5)). Compound 4 reacts with water to render the corresponding aqua adduct [TaCp*(C(Me)=N^tBu- κ²C,N)(H₂O)(OOCPhN=CHPhO-κ³O,N,O)] OTf (6). The reaction of 2 with B(C₆F₅)₃ in a 1:1 molar ratio yields the corresponding carboxylate adduct [TaCp*Me ₂(OOCPhN=CHPhO?B(C₆F₅)₃- κ³O,N,O)] (7). The reaction of compound 2 with H[BF ₄] gives the BF₃ adduct [TaCp*FMe(OOCPhN=CHPhO. BF₃-κ³O,N,O)] (8). Compound 8 decomposes in CH ₂Cl₂ at room temperature to render [BF(OOCPhN=CHPhO- κ³O,N,O)] (9). The molecular structures of complexes 2, 3, 6, and 9 have been established by X-ray diffraction methods.

Full text of DOI:10.1021/om201199p

Article
pubs.acs.org/Organometallics
Tantalum Complexes Supported by Asymmetric [ONO] Ligands.
The Role of Weakly Coordinating Anions on Their Reactivity
Rosa Fandos,*,† Antonio Otero,*,‡ Ana M. Rodríguez,§ and Sara Suizo†
†Departamento de Química Inorgan
́ ́
ica, Organica y Bioquímica, Instituto de Nanociencia, Nanotecnología y Materiales Moleculares
(INAMOL), Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Avenida Carlos III, s/n, 45071 Toledo,
Spain
‡Facultad de Químicas, Universidad de Castilla-La Mancha, Avenida Camilo Jose
́
Cela, 10, 13071 Ciudad Real, Spain
§ETS Ingenieros Industriales, Universidad de Castilla-La Mancha, Campus de Ciudad Real, Avenida Camilo Jose
13071 Ciudad Real, Spain
́
Cela, 3,
S
* Supporting Information
ABSTRACT: The tantalum complex [TaCp*-
Me2(OOCPhNCHPhO-κ3O,N,O)] (2) has been synthe-
sized by reaction of [TaCp*Me4] (Cp* = η5-C5Me5) with 2-
(salicylideneamino)benzoic acid. Complex 2 reacts with HOTf
to yield the new tantalum derivative [TaCp*Me(OTf)-
(OOCPhNCHPhO-κ3O,N,O)] (3). Moreover, compound
t
3 reacts with BuNC or xylylNC to yield the iminoacyl-
containing complexes [TaCp*(C(Me)NR-κ2C,N)(OTf)-
t
(OOCPhNCH]PhO-κ3O,N,O)] (R = Bu (4), 2,6-Me2C6H3 (5)). Compound 4 reacts with water to render the
corresponding aqua adduct [TaCp*(C(Me)NtBu-κ2C,N)(H2O)(OOCPhNCHPhO-κ3O,N,O)]OTf (6). The reaction of 2
with B(C6F5)3 in a 1:1 molar ratio yields the corresponding carboxylate adduct [TaCp*Me2(OOCPhNCHPhO·B(C6F5)3-
κ3O,N,O)] (7). The reaction of compound 2 with H[BF4] gives the BF3 adduct [TaCp*FMe(OOCPhNCHPhO.BF3-
κ3O,N,O)] (8). Compound 8 decomposes in CH2Cl2 at room temperature to render [BF(OOCPhNCHPhO-κ3O,N,O)] (9).
The molecular structures of complexes 2, 3, 6, and 9 have been established by X-ray diffraction methods.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
Alkoxides and carboxylates are ubiquitous ligands in early
transition metal chemistry. Their strong σ- and π-donor ability
along with their versatility makes them appropriate precursors
in sol−gel processes,1 as well as in the construction of metal−
organic frameworks2 or in bioinorganic chemistry.3 In organo-
metallic chemistry they are normally used as ancillary ligands
on account of the above-mentioned properties and because
they are able to tune the reactivity of M−C bonds by
appropriately designing the coordination environment of the
metallic center.4 Moreover, the use of multidentate ligands
normally enhances the complex stability, preventing reorgan-
ization processes and enforcing constrained coordination
geometries when compared to that of their monodentate
analogues.5
A well-established procedure for the synthesis of early
transition metal alkoxides or carboxylates is the protonolysis
reaction of a metal alkyl bond with the corresponding alcohol
or carboxylic acid. Accordingly, the reaction of [TaCp*Me4]
(1) with 2-(salicylideneamino)benzoic acid in a 1:1 molar ratio
yields the corresponding complex [TaCp*Me2(OOCPhN
CHPhO-κ3O,N,O)] (2), which was isolated in good yield
(85%) as a yellow solid after appropriate workup (Scheme 1).
Scheme 1
In the last years, we have carried out studies based on the
synthesis of several families of early transition metal complexes
with dicarboxylate or dialkoxide pincer ligands, finding out that
the bonding of the [ONO] ligands to the metal center is
remarkably stable.6,7 This outstanding stability has allowed the
synthesis of water-soluble compounds7 or the functionalization
of the ligand on the coordination sphere of the metal center
through sequential C−H activation/C−C coupling processes.8
Now, we want to extend our study to [ONO] asymmetric
ligands9 with a less constrained coordination geometry as well
as to the role of weakly coordinating anions on their reactivity.
Compound 2 is moisture sensitive, and it is soluble in CH2Cl2,
toluene, or THF and less soluble in Et2O or pentane.
Received: December 1, 2011
Published: February 13, 2012
© 2012 American Chemical Society
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Complex 2 has been characterized by the usual analytical and
spectroscopic techniques. The 1H NMR spectrum exhibits
resonances at −0.79 and −0.64 ppm assigned to the methyl
groups bonded to the tantalum center. The Cp* ligand gives
rise to a singlet at 2.10 ppm, while the aromatic protons of the
tridentate ligand appear as a multiplet signal in the region
between 6.98 and 7.95 ppm. The singlet at 8.52 ppm can be
assigned to the eneamine moiety proton. The ratio of the
integrals is consistent with the proposed stoichiometry. The
different chemical environment of the methyl groups suggests a
cis disposition and the coordination of the κ3-[ONO] ligand in
a fac fashion, with the eneamine nitrogen atom in trans position
The crystal of 2 consists of discrete molecules separated by
van der Waals distances. The tantalum atom is bonded to the
cyclopentadienyl ring in a η5-mode. In addition, the tridentate
ligand is bonded to the metal center in a bent mode through
two oxygen atoms, which are located in the equatorial plane
and are cis to each other, and the central nitrogen atom
occupies the position trans to the Cp* group. The coordination
geometry around the metal is best described as pseudo-
octahedral. The Ta(1)−O(1) [1.996(4) Å] and Ta(1)−O(2)
bond distances [2.030(4) Å] are within the normal range for
tantalum alkoxide complexes10,11 or carboxylate derivatives.12
The Ta(1)−N(1) bond length [2.307(5) Å] is significantly
longer than that found in complexes bearing carboxylate-
containing pincer ligands.8 As a result of its fac coordination
mode, the [ONO] ligand is bent and the angles O(1)−Ta(1)−
O(2) and C(7)−N(1)−C(8) are 100.6(2)° and 114.6(5)°,
respectively. It is worth noticing the tridentate fac coordination
of the [ONO] ligand, in contrast with the tridentate mer
coordination in a “pincer” fashion, which exhibits less flexible
dialkoxide- or dicarboxylate-related ligands.8 In order to study
the reactivity of the Ta−Me bonds in complex 2 with
unsaturated organic molecules, we carried out some NMR-
scale experiments. Surprisingly, complex 2 does not react with
xylyl or tert-butyl isocyanides in C6D6, at room temperature,
over a period of 48 h, even when a 2-fold excess of isocyanide is
used. This behavior is clearly different from what was previously
observed for related complexes of tantalum bearing dialkoxide-
containing “pincer” ligands. For example, it was observed that
complex cis-[TaCp*Me2{(OCH2)2py-κ3ONO}]8 reacts readily
with xylyl and tert-butyl isocyanide to give the corresponding
azatantalacyclopropane complexes.
1
to the cyclopentadienyl ligand (see Scheme 1). A H VTNMR
experiment, in CDCl3, shows no significant changes in the
spectrum upon heating to 330 K. The 13C NMR spectrum is
also in agreement with the proposed disposition (see
Experimental Section).
In order to confirm the coordination mode of the κ3-[ONO]
ligand, the molecular structure of compound 2 was established by X-
ray diffraction. Some selected bond distances and angles for complex
2 are listed in Table 1, and the ORTEP view is shown in Figure 1.
Table 1. Selected Bond Lengths [Å] and Bond Angles [deg]
for 2 and 3
2
3
Bond Lengths
1.996(4)
Ta(1)−O(1)
Ta(1)−O(2)
Ta(1)−N(1)
Ta(1)−C(25)
Ta(1)−C(26)
N(1)−C(7)
N(1)−C(8)
Ta(1)−O(3)
Ta(1)−O(1)
Ta(1)−N(1)
Ta(1)−C(24)
Ta(1)−O(4)
N(1)−C(7)
N(1)−C(6)
1.923(6)
1.971(7)
2.283(8)
2.202(9)
2.261(7)
1.28(1)
2.030(4)
2.307(5)
2.214(7)
2.219(7)
1.291(8)
1.429(8)
Given the lack of reactivity of compound 2 toward insertion
processes with unsaturated molecules, we decided to explore
the synthesis of potential cationic complexes using different
precursors of weakly coordinating anions and to compare their
role in the reactivity of the tantalum center in different isolated
complexes.
Because of their well-known ability to improve the reactivity
of metal complexes, the use of weakly coordinating anions is of
broad interest in synthesis as well as in catalysis.13 Among
possible candidates, the triflate anion stands out because of its
remarkable stability.14
1.43(1)
Bond Angles
O(1)−Ta(1)−O(2)
O(1)−Ta(1)−C(25)
O(2)−Ta(1)−C(26)
C(25)−Ta(1)−C(26)
O(1)−Ta(1)−N(1)
C(7)−N(1)−C(8)
100.6(2)
O(3)−Ta(1)−O(1)
O(3)−Ta(1)−C(24)
O(1)−Ta(1)−C(24)
O(3)−Ta(1)−O(4)
O(1)−Ta(1)−O(4)
C(7)−N(1)−C(6)
153.3(3)
96.9(3)
91.9(3)
80.5(3)
80.5(3)
114.7(9)
82.7(3)
86.9(2)
77.8(3)
75.7(2)
114.6(5)
Thus, the tantalum complex 2 reacts with triflic acid in a 1:1
molar ratio to yield the corresponding triflate compound
[TaCp*Me(OTf)(OOCPhNCHPhO-κ3O,N,O)] (3), which
was isolated in excellent yield (96%) as a yellow solid after
appropriate workup (Scheme 2).
Scheme 2
Complex 3 is soluble in toluene or THF and less soluble in
pentane. It has been characterized by the usual spectroscopic
and analytical techniques. As a consequence of the substitution
Figure 1. ORTEP view showing the molecular structure of
[TaCp*Me2(κ3-ONO-OOCPhNCHPhO)] (2). Displacement el-
lipsoids are drawn at the 30% probability level.
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of the methyl ligand by the triflate group, the signals of the
methyl and Cp* ligands in the 1H NMR spectrum are shifted to
lower field, while the signals corresponding to the [ONO]
ligand show no significant change (see the Experimental
Section). For this complex the spectroscopic data do not allow
us to unequivocally establish the coordination mode of the κ3-
[ONO] ligand. In order to determine the coordination
environment of the tantalum center, we carried out an X-ray
diffraction study of the molecular structure. Figure 2 shows the
Scheme 3
example, the 1H NMR spectrum of 4 shows two singlet signals
at 1.06 and 2.12 ppm, which are assigned to the tBu group and
the Cp* ligand. The iminoacyl methyl group gives rise to a
singlet at 3.12 ppm. In addition, the spectrum shows several
multiplet signals due to the aromatic protons and a singlet at
9.09 ppm corresponding to the eneamine moiety proton.
Furthermore, the 13C NMR spectrum shows, among others, a
singlet signal at 216.7 ppm, which we assigned to the carbon
atom of the iminoacyl ligand. All attempts to crystallize com-
plex 4 or 5 in order to accurately establish the coordination
environment of the tantalum atom have been so far
unsuccessful. Interestingly, colorless crystals of [TaCp*(C-
(Me)NtBu-κ2C,N)(H2O)(OOCPhNCHPhO-κ3O,N,O)]-
OTf (6) were obtained when the crystallization of 4 is carried
out in CH2Cl2 in the presence of water (Scheme 4). However,
Figure 2. ORTEP view of the molecular structure of [TaCp*Me-
(OTf)(κ3-ONO−OOCPhNCHPhO)] (3). Displacement ellipsoids
are drawn at the 30% probability level.
Scheme 4
molecular diagram of 3. Some selected bond distances and
angles for this complex are listed in Table 1. As in complex 2,
the crystal structure of 3 consists of discrete molecules
separated by van der Waals distances in which the coordination
geometry around the tantalum atom can be described as
pseudo-octahedral.
The κ3-[ONO] group is bonded to the metal in a mer fashion
through two oxygen atoms that are placed in the equatorial
plane and to the nitrogen of the eneamine moiety, which is in
trans position to the Cp* group. In addition, the methyl group
and the triflate ligand are in the equatorial plane, in trans
position to each other.
1
the H NMR spectrum of compound 4 does not change upon
addition of water. It probably means that, in solution, the
triflate group remains in the coordination sphere of the
tantalum center.
The molecular structure of 6 has been established by an
X-ray diffraction study. Figure 3 shows an ORTEP of the
molecular structure of this complex. The molecular structure of
3 can be described as a pseudopentagonal bipyramid with the
Cp* ligand and the nitrogen atom of the κ3-[ONO] ligand
placed in apical positions. The iminoacyl group is η2-C,N
coordinated to the metal with the nitrogen and the carbon
atoms placed in the equatorial plane. Bond distances within the
tantalum-iminoacyl unit are similar to previously reported
ones.15 The tridentate ligand is bonded to the tantalum, as in
complex 4, in a mer fashion.
The aqua ligand is trans to the CN bond of the iminoacyl
moiety. The Ta(1)−O(4) bond distance, 2.210(3) Å, compares
well with that found in previously reported aqua-tantalum
complexes.6c,7b
In the crystal, each water molecule hydrogen bonds one
carboxylate oxygen atom of a second molecule and to the
triflate anion, yielding a dinuclear arrangement (Figure 3b).
Furthermore, a broadly used strategy to enhance the
reactivity of a metal center is the reaction of a metal complex
The Ta(1)−O(1) and Ta(1)−O(3) bond distances
(1.971(7) and 1.923(6) Å) as well as the Ta(1)−N(1) and
Ta(1)−C(24) bond lengths (2.283(8) and 2.202(9) Å) are
shorter than that found in complex 2.
It is noteworthy that the κ3-[ONO] ligand is flexible enough
to change from a fac coordination mode in complex 2 to a mer
one in complex 3.10 In order to compare the reactivity of
compounds 2 and 3, we have studied the reaction of 3 with the
above mentioned isocyanides. We have found different results.
t
In fact, complex 3 reacts with one molar equivalent of Bu- or
xylyl-isocyanide, at room temperature, to yield the correspond-
ing iminoacyl complexes [TaCp*(C(Me)NR-κ2C,N)(OTf)-
t
(OOCPhNCH]PhO-κ3O,N,O)] (R = Bu (4), 2,6-Me2C6H3
(5)), which were isolated as yellow solids in 76% and 79%
yield, respectively (Scheme 3). Both complexes have been
characterized by the usual analytical and spectroscopic
techniques.
1
The H and 13C NMR spectra of both complexes confirm
that the insertion of the isocyanide into the Ta−Me bond has
taken place with the formation of an iminoacyl ligand. As an
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Scheme 5
Me−B moiety is observed in the 1H NMR spectrum. In the 19
F
NMR all the signals are shifted to lower field when compared
to those of free B(C6F5)3 and are comparable to those reported
for adducts of B(C6F5)3 with carboxylic acids.20 The 13C NMR
spectrum displays two resonances at 166.9 and 170.8 ppm
corresponding to the carbon atoms of eneamine and carboxylic
carbon atoms.
Taking into account all spectroscopic data, we propose that
the B(C6F5)3 unit is bonded to the carboxylate moiety (Scheme 5)
in an analogous way to that found in other carboxylate tantalum
derivatives.6c
In order to study the effect of the B(C6F5)3 coordination on
the Ta−Me bond reactivity when compared to that of complex
2, we have carried out the reaction of compound 7 with one
molar equivalent of tBuNC. We have found out that the process
does not give the corresponding insertion derivative; instead,
the reaction yields the dimethyl derivative 2 along with boron
adduct (C6F5)3B·CNtBu (Scheme 6).21
Scheme 6
Figure 3. (a) ORTEP view showing the molecular structure of
compound 6. Displacement ellipsoids are drawn at the 30% probability
level. (b) Hydrogen bonding in [TaCp*(η2-MeCNtBu)(H2O)(κ3-
ONO−OOCPhNCHPhO)]OTf (6). Hydrogen atoms and the Cp*
́
ligand are omitted for clarity. Selected distances (Å): Ta(1)−O(3)
2.043(3); Ta(1)−O(1) 2.081(3); Ta(1)−C(15) 2.134(5); Ta(1)−
N(2) 2.151(4); Ta(1)−O(4) 2.210(3); Ta(1)−N(1) 2.278(4);
N(1)−C(8) 1.302(5); N(2)−C(15) 1.244(5). Bond Angles (deg):
O(3)−Ta(1)−O(1) 145.5(1); O(3)−Ta(1)−N(2) 83.1(1); O(3)−
Ta(1)−C(15) 116.4(1); O(3)−Ta(1)−O(4) 77.3(1); O(1)−Ta(1)−
O(4) 72.3(1); C(7)−N(1)−Ta(1) 120.0(3); C(8)−N(1)−Ta(1)
125.1(3); C(8)−N(1)−C(7) 114.9(4).
Taking into mind our initial aim of exploring the synthesis of
cationic complexes with several precursors of weakly
coordinating anions, and following a synthetic procedure
analogous to that used in the synthesis of compound 3,
complex 2 reacts with H[BF4] in a 1:1 molar ratio, to yield the
carboxylate adduct [TaCp*FMe(OOCPhNCHPhO.BF3-
κ3O,N,O)] (8) (Scheme 7). Complex 8 was isolated as a
with different Lewis acids. Among Lewis acids, B(C6F5)3 is
widely used because it is able to abstract an alkyl group from
early transition metal complexes to form cationic as well as
zwitterionic derivatives.16−18 In addition, in some instances,
activation can occur by attachment of the B(C6F5)3 moiety at a
site not directly bonded to the metal center. In this way, the
partial positive charge at the metal center is less pronounced
than in related cationic counterparts.19
Scheme 7
Thus, complex 2 reacts with B(C6F5)3 in a 1:1 molar ratio, in
CH2Cl2, to yield the corresponding carboxylate adduct
[TaCp*Me2(OOCPhNCHPhO·B(C6F5)3-κ3O,N,O)] (7)
(Scheme 5). Complex 7 was isolated as an orange solid,
soluble in CH2Cl2, less soluble in toluene, and insoluble in
pentane. In the process, the foreseeable abstraction of the
methyl unit by the B(C6F5)3 does not take place, but
alternatively the Lewis acid interacts with the oxygen atom of
a carboxylic moiety, giving rise to the corresponding adduct 7.
Complex 7 has been characterized by the usual analytical and
spectroscopic techniques. Formation of the [MeB(C6F5)3]−
anion can be ruled out because no broad signal attributable to a
yellow solid, soluble in CH2Cl2, less soluble in toluene, and
insoluble in pentane. Surprisingly, the neutral complex 8,
containing a fluorine ligand, was isolated instead of the
−
expected cationic complex with a BF4 counterion. Fluoride
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Scheme 8
−
transfer processes from the BF4 fragment to early transition
metals is not unusual and has also been reported for tantalum
derivatives.15,22 In the 1H NMR of 8 we found that the methyl
group bonded to the tantalum atom gives rise to a doublet
signal, indicating that the tantalum atom is also coordinated to
a fluorine ligand.22
geometry around the boron atom can be described as
pseudotetrahedral. The B−O bond distances are in the normal
range found for boron aryloxide or carboxylate compounds.27
The B−N bond length is also within the expected range in
boron derivatives with [O,N] ligands.28
Additionally, the 19F NMR NMR spectrum of 8 shows two
singlet signals at 39.0 and −148.0 ppm. The lack of coupling
between the two chemically different fluorine atoms and the
wide difference in chemical shifts of the two signals point to the
coordination mode proposed in Scheme 7.23 Moreover, the
response in the 1H NOESY-2D experiment from the proton in
ortho position of the aryloxi fragment and the imine proton
upon irradiating the tantalum-bonded methyl group is also in
CONCLUSIONS
■
A new class of κ3-[ONO] ligand more flexible that previous
dicarboxylate or dialkoxide pincer ones has been used in the
stabilization of tantalum complexes. We have seen that the
terdentate ligand is rather versatile and can bind the tantalum
atom displaying fac as well as mer coordination modes
depending on the nature of the coordination environment of
the tantalum atom; for example it changes when a methyl group
is replaced by a triflate ligand. We have studied the reactivity of
[TaCp*Me2(OOCPhNCHPhO-κ3O,N,O)] with different
precursors of weakly coordinating anions, determining that
the triflate moiety is able to stabilize neutral as well as cationic
complexes. In contrast, B(C6F5)3 forms an adduct with the
carboxylate group, but it does not improve the reactivity of the
Ta−Me bond toward isocyanides compared to that shown by
[TaCp*Me2(OOCPhNCHPhO-κ3O,N,O)]. Furthermore,
the reaction of [TaCp*Me2(OOCPhNCHPhO-κ3O,N,O)]
with tetrafluoroboric acid occurs with protonolysis of the
1
agreement with this proposal. In contrast, an analogous H
NOESY-2D experiment carried out for complex 3, with a mer
coordination mode for the tridentate ligand, shows the
interaction of the tantalum-coordinated methyl group not
only with the imine proton and that in ortho position of the
aryloxi fragment but also with the proton in ortho position to
the nitrogen of the imine fragment in the carboxylate aromatic
moiety.
In an attempt to grow crystals of 8 from CH2Cl2 at room
temperature we found that it is unstable under these conditions,
yielding the known boron derivative [BF(OOCPhN
CHPhO-κ3O,N,O)] (9)24 along with a mixture of fluorine
pentamethylcyclopentadienyl tantalum derivatives in which we
were able to identify only [TaCp*F4]25 (ca. 50%) (Scheme 8).
The boron derivative 9 is interesting because some fluorine−
boron complexes, as the analogues of BODIPY, have been
reported to achieve high solid-state emission intensity and have
been adopted as fluorescent positional tags in biological
systems.26 The molecular structure of compound 9 has been
determined by X-ray diffraction (Figure 4).
−
Ta−Me bond and abstraction of a fluorine atom from the BF4
fragment, yielding a tantalum fluoride organometallic complex.
Moreover, it has been found that the bonding of the [ONO]
ligand to the tantalum center is not as robust as could be
expected for a tridentate ligand, as it can be transferred from
the tantalum to a boron center.
EXPERIMENTAL SECTION
■
General Procedures. The preparation and handling of described
compounds were performed, unless stated otherwise, with rigorous
exclusion of air and moisture under a nitrogen atmosphere using
standard vacuum line and Schlenk techniques. All solvents were dried
and distilled under a nitrogen atmosphere.
The tantalum complex [TaCp*Me4]29 was prepared by literature
procedures: The commercially available compounds LiMe in diethyl
ether, HOTf, B(C6F5)3, and HBF4 were used as received from Aldrich.
1H, 19F, and 13C NMR spectra were recorded on a 400 Bruker
Avance FT spectrometer. Trace amounts of protonated solvents were
used as references, and chemical shifts are reported in units of parts
per million relative to SiMe4.
IR spectra were recorded in the region 4000−400 cm−1 with a
JASCO/IR-4100 FT infrared spectrometer.
Synthesis of [TaCp*Me2(OOCPhNCHPhO-κ3O,N,O)] (2). To
a solution of [TaCp*Me4] (0.58 g, 1.55 mmol) in THF at −40 °C
(10 mL) was added 2-(salicylideneamino)benzoic acid (0.38 g,
1.55 mmol). The mixture was allowed to reach room temperature
and was stirred for 1 h. The solvent was removed under vacuum, and
the residue washed with pentane to yield 0.77 g of a yellow compound
characterized as 2 (85%). IR (cm−1): 1662 (s), 1612 (s), 1599 (m),
1549 (m), 1475 (w), 1448 (m), 1381 (w), 1305 (s), 1298 (s), 1276
Figure 4. ORTEP view of the molecular structure of compound 9.
Displacement ellipsoids are drawn at the 30% probability level.
́
Selected distances (Å): N(1)−B(1) 1.580(7); O(1)−B(1) 1.450(7);
O(3)−B(1) 1.444(8); F(1)−B(1) 1.381(7).
The crystal structure of 9 consists of discrete molecules
separated by van der Waals distances in which the coordination
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(m), 1242 (m), 1196 (m), 1150 (m), 1133 (m), 1129 (m), 1091 (w),
1066 (w), 1038 (w), 1024 (w), 978 (w), 957 (w), 928 (w), 869 (m),
852 (m), 806 (m), 764 (s), 738 (w), 714 (m), 617 (m), 600 (m), 578
Anal. Calcd for C35H36O6N2SF3Ta: C, 49.41; H, 4.26; N, 3.29; S, 3.77.
Found: C, 48.95; H, 4.20; N, 3.11; S, 3.59.
Crystallization of [TaCp*(C(Me)NtBu-κ2C,N)(H2O)-
(OOCPhNCHPhO-κ3O,N,O)]OTf (6). Crystallization of 6 was
achieved by slow diffusion of Et2O into a solution of compound 4
(0.073 g, 0.091 mmol) in CH2Cl2 (0.5 mL) and water (2 μL). Yield:
1
(m), 566 (s), 539 (s). H NMR (400 MHz, CDCl3): δ −0.79 (s, 3H,
Me), −0.64 (s, 3H, Me), 2.10 (s, 15H, Cp*), 6.98 (m, 1H, Ar), 7.04
(m, 1H, Ar), 7.37 (m, 2H, Ar), 7.56 (m, 3H, Ar), 7.95 (m, 1H, Ar),
8.52 (s, 1H, CH). 13C{1H} NMR (CDCl3): δ 11.4 (Cp*), 41.3 (Me),
47.1 (Me), 120.5 (Ar), 121.3 (Ar), 121.4 (Ar), 121.5 (Cipso), 122.8
(Cipso), 126.9 (Ar), 128.5 (Cp*), 130.1 (Ar), 132.0 (Ar), 133.9 (Ar),
135.9 (Ar), 152.1 (Cipso), 160.5 (Cipso), 165.4 (CN), 166.6 (CO).
Anal. Calcd for C26H30NO3Ta: C, 53.34; H, 5.16; N, 2.39. Found: C,
53.49; H, 5.38; N, 2.39.
1
t
0.020 g, 27%. H NMR (CDCl3): δ 1.03 (s, 9H, Bu), 2.09 (s, 15H,
Cp*), 2.15 (brs, 2H, OH2), 3.12 (s, 3H, Me), 6.70 (m, 1H, Ar), 7.14
(m, 1H, Ar), 7.56 (m, 1H, Ar), 7.65 (m, 2H, Ar), 7.82 (m, 1H, Ar),
7.95 (m, 1H, Ar), 8.04 (m, 1H, Ar), 9.00 (s, 1H, CHN). 13C{1H}
NMR (CDCl3): δ 11.0 (Cp*), 19.3 (Me), 28.6 (tBu), 65.4 (tBu),
117.8 (Ar), 121.4 (Cipso), 123.0 (Ar), 124.8 (Ar), 126.1 (Cp*), 126.4
(Ar), 129.4 (Cipso), 130.8 (Ar), 134.7 (Ar), 136.7 (Ar), 139.4 (Ar),
148.0 (Cipso), 160.4 (Cipso), 164.8 (CeneamineN), 174.2 (CO),
216.7 (CiminoacylN). Anal. Calcd for C31H38O7N2SF3Ta·1/2CH2Cl2:
C, 43.83; H, 4.55; N, 3.24; S, 3.71. Found: C, 43.41; H, 4.46; N, 3.22;
S, 3.46.
Synthesis of [TaCp*Me(OTf)(OOCPhNCHPhO-κ3O,N,O)]
(3). To a solution of compound 2 (0.26 g, 0.45 mmol) in 7 mL of
CH2Cl2 at −40 °C was added triflic acid (40 μL, 0.45 mmol). The
mixture was allowed to reach room temperature and then was stirred
for 1 h; afterward, the solvent was removed under vacuum and the
residue washed with pentane to yield a yellow compound that was
identified as 3 (0.31 g, 96%). IR (cm−1): 1685 (m), 1611 (m), 1558
(m), 1488 (w), 1474 (w), 1447 (m), 1390 (w), 1323 (s), 1293 (m),
1262 (m), 1236 (m), 1200 (s), 1183 (m), 1156 (m), 1133 (m), 1094
(w), 1046 (w), 1028 (m), 1001 (s), 963 (w), 931 (m), 864 (m), 807
Synthesis of [TaCp*Me2(OOCPhNCHPhO·B(C6F5)3-
κ3O,N,O)] (7). To a solution of compound 2 (0.17 g, 0.29 mmol)
in CH2Cl2 (7 mL) was added [B(C6F5)3] (0.15 g, 0.29 mmol). The
reaction mixture was stirred for 15 min, and then the solvent was
removed under vacuum. The residue was washed with pentane to yield
an orange complex that was identified as 7 (0.27 g, 81%). IR (cm−1):
1644 (m), 1614 (s), 1583 (m), 1541 (m), 1514 (s), 1462 (vs), 1395
(s), 1376 (s), 1285 (s), 1214 (m), 1150 (m), 1087 (vs), 1030 (m), 968
(vs), 907 (m), 806 (m), 759 (s), 707 (s), 665 (s), 618 (m). 1H NMR
(400 MHz, CDCl3): δ −0.75 (s, 3H, Me), −0.47 (s, 3H, Me), 1.96 (s,
15H, Cp*), 6.92 (m, 1H, Ar), 7.20 (m,1H, Ar), 7.45 (m, 1H, Ar), 7.51
(m, 1H, Ar), 7.64 (m, 1H, Ar), 7.72 (m, 2H, Ar), 8.01 (m, 1H, Ar),
8.64 (s, 1H, CH). 13C{1H} NMR (CDCl3): δ 10.9 (Cp*), 45.2 (Me),
55.8 (Me), 121.1 (Ar), 121.8 (Cipso), 122.3 (Ar), 123.5 (Cp*), 127.5
(Ar), 127.9 (Ar), 128.0 (Cipso), 129.6 (Ar), 134.1 (Ar), 134.7 (Ar),
137.7 (Ar), 151.4 (Cipso), 159.6 (Cipso), 166.7 (CN), 172.9 (CO).
19F{1H} NMR (C6D6) δ −134.8 (m, 6F, o-F), −158.3 (m, 3F, p-F),
1
(w), 767 (s), 740 (m), 710 (m), 690 (m), 626 (s), 566 (s). H NMR
(400 MHz, CDCl3): δ 0.39 (s, 3H, Me), 2.30 (s, 15H, Cp*), 6.88 (m,
1H, Ar), 7.13 (m, 2H, Ar), 7.44 (m, 1H, Ar), 7.64 (m, 3H, Ar), 8.03
(m, 1H, Ar), 8.62 (s, 1H, CH). 13C{1H} NMR (CDCl3): δ 11.3
(Cp*), 51.1 (Me), 119.8 (Ar), 122.7 (Ar), 124.2 (Ar), 124.3 (Cipso),
126.5 (Cp*), 126.6 (Cipso), 128.5 (Ar), 131.5 (Ar), 133.5 (Ar), 135.8
(Ar), 137.5 (Ar), 149.7 (Cipso), 158.5 (Cipso), 163.9 (CN), 167.9
(CO). Anal. Calcd for C26H27O6NSF3Ta·1/2CH2Cl2: C, 41.77; H,
3.69; N, 1.83; S, 4.20. Found: C, 41.38; H, 3.56; N, 1.96; S, 4.16.
Synthesis of [TaCp*(C(Me)NtBu-κ2C,N)(OTf)(OOCPhN
CH]PhO-κ3O,N,O)] (4). To a solution of 3 (0.16 g, 0.22 mmol) in
t
CH2Cl2 at room temperature (5 mL) was added BuNC (0.025 mL,
−164.7 (m, 6F, m-F). Anal. Calcd for C44H30BF15NO3Ta: C, 48.11; H,
2.75; N, 1.27. Found: C, 47.69; H, 2.64; N, 1.20.
0.22 mmol). The mixture was stirred for 2 h, and then the solvent was
removed under vacuum. The residue was washed with pentane to yield
a yellow compound that was identified as 4 (0.14 g, 76%). IR (cm−1):
1676 (m), 1659 (m), 1606 (m), 1589 (w), 1541 (m), 1470 (w), 1443
(w), 1381 (w), 1262 (s), 1226 (m), 1195 (m), 1142 (s), 1024 (s), 935
(w), 876 (m), 864 (w), 808 (m), 759 (m), 710 (m), 684 (w), 639 (s),
601 (w), 567 (m). 1H NMR (400 MHz, CDCl3): δ 1.06 (s, 9H, tBu),
2.12 (s, 15H, Cp*), 3.12 (s, 3H, Me), 6.71 (m, 1H, Ar), 7.18 (m, 1H,
Ar), 7.57 (m, 1H, Ar), 7.64 (m, 1H, Ar), 7.81 (m, 1H, Ar), 7.86 (m,
1H, Ar), 8.03 (m, 2H, Ar), 9.09 (s, 1H, CH). 13C{1H} NMR (CDCl3):
δ 11.1 (Cp*), 19.3 (Me), 28.7 (tBu), 65.4 (tBu), 117.7 (Ar), 121.5
(Cipso), 123.1 (Cipso), 124.9 (Ar), 126.1 (Ar), 126.4 (Ar), 129.4 (Cp*),
130.8 (Ar), 134.8 (Ar), 136.9 (Ar), 139.4 (Ar), 148.1 (Cipso), 160.4
(Cipso), 164.8 (CeneamineN), 174.4 (CO), 216.7 (CiminoacylN).
Anal. Calcd for C31H36O6N2SF3Ta: C, 46.38; H, 4.52; N, 3.49; S, 3.99.
Found: C, 46.01; H, 4.45; N, 3.39; S, 3.85.
Synthesis of [TaCp*FMe(OOCPhNCHPhO.BF3-κ3O,N,O)]
(8). To a solution of complex 2 (0.22 g, 0.38 mmol) in CH2Cl2
(9 mL) was added HBF4·Et2O (0.05 mL, 0.38 mmol). The reaction
mixture was stirred for 1 h and then was filtered; the solvent was
removed under vacuum. The residue was washed with pentane to yield
a yellow complex that was identified as 8 Yield: 0.19 g, 77%. IR
(cm−1): 1692 (m), 1617 (m), 1597 (s), 1547 (vs), 1449 (m), 1382
(m), 1289 (s), 1199 (m), 1121 (s), 1058 (s), 1031 (m), 988 (m), 859
(vs), 812 (s), 765 (vs), 734 (s), 714 (s), 684 (s), 608 (s), 584 (m), 552
1
(vs). H NMR (400 MHz, CDCl3): δ −0.07 (d, JH−F = 8.4 Hz, 3H,
Me), 2.25 (s, 15H, Cp*), 6.97 (m, 1H, Ar), 7.15 (m, 1H, Ar), 7.39 (m,
1H, Ar), 7.45 (m, 1H, Ar), 7.61 (m, 1H, Ar), 7.67 (m, 1H, Ar), 7.73
(m, 1H, Ar), 8.06 (m, 1H, Ar), 8.52 (s, 1H, CH). 13C{1H} NMR
(CDCl3): δ 10.9 (Cp*), 44.6 (d, J = 8.7 Hz), 120.7 (Ar), 120.8 (Ar),
121.9 (Cipso), 122.8 (Ar), 125.9 (Cipso), 126.0 (Cp*), 128.0 (Ar), 130.8
(Ar), 134.4 (Ar), 135.3 (Ar), 137.6 (Ar), 150.3 (Cipso), 159.8 (Cipso),
166.9 (CN), 170.8 (CO). 19F{1H} NMR (CDCl3): δ −148.0 (s,
3F, BF3), 39.0 (s, 1F, Ta−F). Anal. Calcd for C25H27F4NBO3Ta: C,
45.68; H, 4.14; N, 2.13. Found: C, 46.05; H, 4.45; N, 1.94.
Synthesis of [TaCp*(C(Me)Nxylyl-κ2C,N)(OTf)(OOCPhN
CH]PhO-κ3O,N,O)] (5). To a solution of 3 (0.22 g, 0.30 mmol) in
CH2Cl2 at room temperature (5 mL) was added xylylNC (0.039 g,
0.30 mmol). The mixture was stirred for 1 h, and then the solvent was
removed under vacuum. The residue was washed with pentane to yield
a yellow compound that was identified as 5 (0.20 g, 79%). IR (cm−1):
1677 (m), 1631 (m), 1600 (m), 1588 (w), 1539 (m), 1469 (w), 1443
(w), 1380 (w), 1277 (s), 1262 (s), 1240 (s), 1189 (m), 1147 (s), 1089
(w), 1027 (s), 929 (w), 880 (m), 865 (w), 811 (m), 758 (s), 710 (m),
690 (m), 630 (s), 601 (m), 568 (m). 1H NMR (400 MHz, CDCl3): δ
1.49 (s, 3H, Me), 1.89 (s, 3H, Me), 2.20 (s, 15H, Cp*), 2.83 (s, 3H,
Me), 6.74 (m, 2H, Ar), 6.82 (m, 1H, Ar), 6.88 (m, 1H, Ar), 7.44 (m,
1H, Ar), 7.50 (m, 2H, Ar), 7.56 (m, 2H, Ar), 7.82 (m, 1H, Ar), 8,15
(m, 1H, Ar), 8.85 (s, 1H, CH). 13C{1H} NMR (CDCl3): δ 11.3
(Cp*), 19.9 (Me), 20.2 (Me), 20.5 (Me), 119.0 (Ar), 121.4 (Cipso),
123.1 (Ar), 124.8 (Cipso), 125.6 (Ar), 126.5 (Cipso), 127.1 (Cp*), 127.3
(Cipso), 127.9 (Cipso), 128.3 (Ar), 129.1 (Ar), 129.3 (Ar), 129.6 (Ar),
130.2 (Ar), 131.5 (Ar), 135.3 (Ar), 136.6 (Ar), 138.8 (Cipso), 147.5
(Cipso), 159.8 (CeneamineN), 172.9 (CO), 223.6 (CiminoacylN).
X-ray Crystallography. A summary of crystal data collection and
refinement parameters for all compounds is given in Table 2.
Single crystals of 2, 3, 6, and 9 were mounted on a glass fiber and
transferred to a Bruker X8 APEX II CCD-based diffractometer
equipped with a graphite-monochromated Mo Kα radiation source
(λ = 0.71073 Å). The highly redundant data sets were integrated using
SAINT30 and corrected for Lorentz and polarization effects. An
absorption correction was performed with the program SADABS.31
The software package SHELXTL version 6.1232 was used for space
group determination, structure solution, and refinement by full-matrix
least-squares methods based on F2. A successful solution by the direct
methods provided most non-hydrogen atoms from the E-map. The
remaining non-hydrogen atoms were located in an alternating series of
least-squares cycles and difference Fourier maps. All non-hydrogen
atoms were refined with anisotropic displacement coefficients unless
1854
dx.doi.org/10.1021/om201199p | Organometallics 2012, 31, 1849−1856

Organometallics
Article
Table 2. Crystal Data and Structure Refinement for 2, 3, 6, and 9
2
3
6
9
empirical formula
fw
C26H30NO3Ta
585.46
C26H27F3NO6STa
719.50
C31H38F3N2O7STa
820.64
C14H9BFNO3
269.03
temperature (K)
wavelength (Å)
cryst syst
space group
a (Å)
180(2)
230(2)
230(2)
230(2)
0.71073
0.71073
0.71073
0.71073
monoclinic
P21/c
orthorhombic
Pccn
triclinic
monoclinic
C2/c
P1
̅
9.752(5)
12.043(8)
10.885(9)
21.82(2)
20.483(4)
14.542(2)
18.930(5)
15.959(8)
13.032(6)
13.59(1)
b (Å)
12.598(6)
16.062(8)
71.26(1)
c (Å)
α (deg)
β (deg)
101.51(2)
82.31(1)
122.39(1)
γ (deg)
volume (Å3)
69.52(1)
2803(4)
5638(2)
1750(1)
2387(2)
8
Z
4
8
2
density (calcd) (g/cm3)
1.387
1.695
1.557
1.497
0.115
1104
absorp coeff (mm−1
)
3.944
4.032
3.261
F(000)
1160
2832
820
cryst size (mm3)
index ranges
0.25 × 0.20 × 0.19
−14 ≤ h ≤ 15
−13 ≤ k ≤ 13
−27 ≤ l ≤ 27
19 086
0.36 × 0.22 × 0.08
−24 ≤ h ≤ 23
−17 ≤ k ≤ 12
−21 ≤ l ≤ 22
23 912
0.09 × 0.08 × 0.08
−10 ≤ h ≤ 11
−13 ≤ k ≤ 14
−19 ≤ l ≤ 19
14 986
0.22 × 0.08 × 0.08
−17 ≤ h ≤ 18
−15 ≤ k ≤ 12
−16 ≤ l ≤ 14
4520
reflns collected
indep reflns
5902
4821
5989
2062
[R(int) = 0.0543]
5902/0/219
0.930
[R(int) = 0.1163]
4821/0/333
0.869
[R(int) = 0.0345]
5989/0/416
1.052
[R(int) = 0.0891]
2062/0/181
0.908
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R1 = 0.0439
wR2 = 0.1155
1.294 and −0.831
R1 = 0.0567
wR2 = 0.1268
2.182 and −1.192
R1 = 0.0327
wR2 = 0.0766
0.727 and −0.913
R1 = 0.0641
wR2 = 0.1006
0.261 and −0.240
largest diff peak and hole (e Å−3
)
specified otherwise. Hydrogen atoms were placed using a “riding
model” and included in the refinement at calculated positions.
Complexes 2 and 3 show a rotational disorder for the Cp* ligand,
which were modeled with a 50:50 occupation, and their atoms were
refined isotropically. In addition, for complex 2 a rigid group refine-
ment has been necessary. For complexes 2, 3, and 6, the crystals show
some molecules of solvent highly disordered, and the squeeze option
has been used.33 The derived quantities (Mr, F(000), μ, and Dx) in the
crystal data do not contain the contribution from this disordered
solvent.
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* Supporting Information
■
S
A CIF file giving details of data collection, refinement, atom
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The authors declare no competing financial interest.
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