Synthesis of N-aryloxy-β-diketiminate ligands and coordination to zirconium, ytterbium, thorium, and uranium

Article abstract of DOI:10.1021/om3010355

Two examples of N-aryloxy-β-diketiminate dianions (11a,b) have been synthesized on a multigram scale, in four steps, from commercially available chemicals. The synthetic scheme relies on the sequential addition of 2,6-diisopropylaniline and 2-amino-4-tert-butylphenol (1a) (or 2-amino-4,6-di-tert-butylphenol (1b)) to acetylacetone, using Et ₃OBF₄ as an activation reagent. Both the nature of the activation reagent and the order of addition of the primary amines have a major impact on the outcome of the reaction, and acid catalysts (such as sulfuric acid or p-toluenesulfonic acid) lead to decomposition of the β-diketiminate backbone via formation of a benzoxazole derivative (3a,b). Using dianions 11a,b, mono- and bis(N-aryloxy-β-diketiminate) complexes of zirconium(IV), ytterbium(III), thorium(IV), and uranium(IV) have been synthesized (12-18), by salt metathesis reactions, and characterized by a combination of ¹H/¹³C NMR spectroscopy, elemental analysis, and X-ray crystallography. The two ligands differ in their steric bulk and exhibit different coordination behaviors, which were rationalized on the basis of geometric considerations.

Full text of DOI:10.1021/om3010355

Article
pubs.acs.org/Organometallics
Synthesis of N‑Aryloxy-β-diketiminate Ligands and Coordination to
Zirconium, Ytterbium, Thorium, and Uranium
Florian Dulong, Pierre Thuery, Michel Ephritikhine, and Thibault Cantat*
́
CEA, IRAMIS, SIS2M, CNRS UMR 3299, CEA/Saclay, 91191 Gif-sur-Yvette, France
S
* Supporting Information
ABSTRACT: Two examples of N-aryloxy-β-diketiminate
dianions (11a,b) have been synthesized on a multigram
scale, in four steps, from commercially available chemicals. The
synthetic scheme relies on the sequential addition of 2,6-
diisopropylaniline and 2-amino-4-tert-butylphenol (1a) (or 2-
amino-4,6-di-tert-butylphenol (1b)) to acetylacetone, using
Et3OBF4 as an activation reagent. Both the nature of the
activation reagent and the order of addition of the primary
amines have a major impact on the outcome of the reaction,
and acid catalysts (such as sulfuric acid or p-toluenesulfonic
acid) lead to decomposition of the β-diketiminate backbone via
formation of a benzoxazole derivative (3a,b). Using dianions
11a,b, mono- and bis(N-aryloxy-β-diketiminate) complexes of zirconium(IV), ytterbium(III), thorium(IV), and uranium(IV)
have been synthesized (12−18), by salt metathesis reactions, and characterized by a combination of 1H/13C NMR spectroscopy,
elemental analysis, and X-ray crystallography. The two ligands differ in their steric bulk and exhibit different coordination
behaviors, which were rationalized on the basis of geometric considerations.
condensation of primary amines onto 2,4-pentanedione using
simple acids as catalysts, such as hydrochloric acid, sulfuric acid,
and p-toluenesulfonic acid (PTSA).1,7,12 However, in a
preliminary contribution, we observed that introduction of
nucleophilic functional groups (e.g., a phenol group) on the
amine backbone proved problematic and prevented the
formation of the desired β-diketiminate structure.11 In order
to shed light on the origins of this chemical behavior and
expand the scope of available N-aryloxy-β-diketiminate ligands
(see targeted structures in Scheme 1), we have investigated in
detail the reaction chemistry between o-aminophenol deriva-
tives 1 and acetylacetone, under cationic activation. 2-Amino-4-
tert-butylphenol (R = H, 1a) and 2-amino-4,6-di-tert-
butylphenol (R = tBu, 1b) were considered as functionalized
aniline derivatives in order to access N-aryloxy-β-diketiminate
ligands with different steric bulks and, therefore, tune the steric
INTRODUCTION
■
β-Diketiminate ligands, the nitrogen analogues of β-diketonate
ligands, have received increased interest and found important
applications in coordination chemistry and homogeneous
catalysis because changing the substituents on the nitrogen
atoms enables a fine tuning of the ligand electronic and
geometric properties.1−4 For example, sterically encumbered β-
diketiminates are efficient ancillary ligands to support
coordinatively and electronically unsaturated complexes that
were successfully utilized as catalysts in the polymerization of
ethylene and propene.5,6 Capitalizing on the properties of this
ligands class, novel pincer ligands have been synthesized, by
introducing neutral donors (e.g., ethers and amines) on the
nitrogen substituents of the β-diketiminate backbone.7,8 Yet,
examples of di- or trianionic polydentate β-diketiminate
structures featuring an anionic alkoxide or amide functionality
remain scarce.9−11 In order to circumvent this limitation, we
have recently reported the first example of a N-aryloxy-β-
diketiminate ligand and explored its coordination chemistry
with electron-poor metal ions.11 Herein, we propose a rational
synthesis of this new class of ligands which is exemplified by the
preparation of two types of N-aryloxy-β-diketiminate ligands
with different steric bulk. Their different coordination behaviors
with zirconium(IV), ytterbium(III), thorium(IV), and uranium-
(IV) metal ions is presented.
Scheme 1. Targeted N-Aryloxy-β-diketiminate Ligands
Special Issue: Recent Advances in Organo-f-Element Chemistry
RESULTS AND DISCUSSION
■
Synthesis of N-Aryloxy-β-diketiminate Ligands. β-
Diketiminate ligands are routinely prepared by double
Received: October 31, 2012
Published: January 23, 2013
© 2013 American Chemical Society
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congestion at the metal center upon coordination. Condensa-
tion of 1 with acetylacetone is thermally available and affords
the acnac pro-ligands 2 in high yields without catalytic
assistance (Scheme 2, eq 1). 2 has a lower electrophilicity
(1H/13C NMR). This transformation is unusual in the
chemistry of keto-enamines and β-diketimines; yet, it is
somewhat reminiscent of the rearrangement observed by
Inamoto and co-workers for functionalized α-diketimines, in
the presence of oxidants.13 A simple mechanistic model is
proposed in Scheme 2. Protonation of the carbonyl group, by
PTSA, is known to enhance the electrophilicity of the keto-
enamine fragment in 2.1 While this activation is classically
utilized to promote the condensation of an incoming primary
amine, the intramolecular addition of the nucleophilic phenol
group is favored in 2. A series of equilibria, involving keto−enol
tautomerism and prototropy, is then possible and leads to the
formation of 3 after elimination of acetone. The driving force of
the reaction is likely the formation of a stable aromatic
benzoxazole heterocycle. In order to avoid formation of 3, it is
therefore necessary to avoid keto−enol tautomerism and/or
prototropy equilibria preceding the irreversible elimination of
acetone. Using a stoichiometric amount of triethyloxonium
tetrafluoroborate,14 alkylation of the carbonyl group in 2 cleanly
resulted in the quantitative formation of the iminium salt 4.
Because the latter is highly sensitive toward moisture, the cation
Scheme 2. Synthesis of 2 and 3
1
was not isolated but characterized, in solution, using H/13C
NMR and reacted in situ with 1 molar equiv of 1 (or 2,6-
diisopropylaniline). Although 4 is thermally stable and does not
eliminate 3 and acetone, proton exchanges are made possible in
the presence of a primary amine, and rearrangement to 3 was
found to be competitive, with elimination of the iminium salt of
the primary amine 5 as a byproduct (Scheme 3, eq 3), following
a mechanism similar to the aforementioned rearrangement of
2a to 3a (see Scheme 3). As a result, utilization of 2 is
unproductive in the formation of N-aryloxy-β-diketiminate
ligands and ligands II are clearly unavailable using this synthetic
scheme. Nonetheless, as presented in Scheme 3, unsymmetrical
N-aryloxy-β-diketiminate ligands I can be prepared by
introducing the o-aminophenol 1 in the second step of the
condensation strategy, to avoid nucleophilic attack of the
phenol group at the iminium functionality (see Scheme 4). In
fact, reaction of the acnac pro-ligand 67,11 with Et3OBF4 in
CH2Cl2 at 25 °C yielded 7 within 1 h (Scheme 3, eq 4), which
was isolated as a white solid and was fully characterized by
1H/13C NMR and X-ray diffraction analysis. Addition of 1a or
1b to a THF solution of 7 cleanly affords the protonated form
of new functionalized β-diketiminate ligands 8 (Scheme 3, eq
4) in 85% yield for both 8a and 8b.
than acetylacetone, and its activation is required to promote the
condensation of another 1 equiv of a primary amine.
Nonetheless, in the presence of a catalytic amount of sulfuric
acid or PTSA, reaction of 2 and 1 (or 2,6-diisopropylaniline)
led to a mixture of numerous products with loss of the
conjugated keto-enamine backbone. In fact, 2a is unstable in
the presence of PTSA (1.0 mol %) and is transformed
quantitatively to the benzoxazole derivative 3a (Scheme 2, eq
2), within 24 h at 100 °C in toluene. 3a has been successfully
1
characterized by a combination of H/13C NMR spectroscopy
and mass spectrometry (see the Experimental Section), and
acetone is the only observed byproduct of this reaction
a
Scheme 3. Successful and Unsuccessful Synthetic Approaches to 8a,b
a
Reaction conditions: (i) 1 equiv of Et3OBF4, CH2Cl2, room temperature, 1 h; (ii) (2,6-iPr2-C6H4)NH2, CH2Cl2, room temperature, 1 h; (iii) 1a,b,
THF, room temperature, 1 h.
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Scheme 4. Proposed Mechanisms for the Selective Formation of 3a,b and 8a,b from 4a,b and 1a,b, Respectively
Scheme 5. Synthesis of 9a
Deprotonation of 8a,b was then attempted to prepare the
dianionic β-diketiminate ligands. Unexpectedly, addition of 3
equiv of butyllithium to a THF solution of 8 at −78 °C results
in the formation of the new borate species 9, with elimination
of LiF salt (Scheme 5, eq 5). Though the tetrafluoroborate
anion is a stable counteranion, fluoride displacement at boron
has been observed in rare instances and utilized for the
synthesis of a handful of acac difluoroboron compounds.15
While formation of 9b was observed by 1H/13C NMR
spectroscopy in a mixture of products (see the Experimental
Section), 9a was isolated by recrystallization from an
acetonitrile solution and was fully characterized by X-ray
diffraction (Figure 1), 1H/13C NMR spectroscopy, mass
spectrometry, and elemental analysis. 9a features a tetrahedral
boron center substituted by one fluorine atom and one κ3-
coordinated N-aryloxy-β-diketiminate group. The B−F and B−
N bond distances of 1.405(4) and 1.539(4) Å, respectively, fall
in the range of isoelectronic boron−dipyrromethene (BODI-
PY) derivatives (average B−F and B−N distances of 1.39 and
1.55 Å, respectively).16 Importantly, formation of 9a, by
deprotonation of 8a, was also observed in the presence of
chloride complexes, such as ZrCl4 and ThCl4(DME)2. This
suggests a greater stability of the boron derivative 9a compared
to the putative zirconium(IV) and thorium(IV) complexes. As
Figure 1. Molecular structure of 9a with displacement ellipsoids drawn
at the 50% probability level. Hydrogen atoms and CH3 groups of the
iPr and tBu substituents have been omitted. Selected bond distances
(Å) and angles (deg): O1−B1 = 1.462(4), N1−B1 = 1.539(4), N2−
B1 = 1.538(4), B1−F1 = 1.405(4), N1−C11 = 1.347(4), C11−C12 =
1.387(4), C12−C13 = 1.403(4), C13−N2 = 1.343(4); N1−C11−C12
= 118.3(3), C11−C12−C13 = 122.8(3), C12−C13−N2 = 120.7(3).
−
the presence of a BF4 anion in 8 proved detrimental to the
synthesis of the N-aryloxy-β-diketiminate dianions, successive
deprotonation reactions were conducted so as to eliminate the
counteranion prior to the formation of the anionic phenoxide
and β-diketiminate donors (Scheme 6). Deprotonation of 8a
with 1 equiv of NEt3, in Et2O, led to the immediate formation
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a
Scheme 6. Synthesis of 10a,b and 11a,b
a
Reaction conditions: (i) NEt3, Et2O, room temperature, 1 h; (ii) n-BuLi, THF, −78 °C.
of pro-ligand 10a (Scheme 6, eq 6), with the concomitant
precipitation of the HNEt3BF4 salt. After filtration and solvent
evaporation, 10a was isolated as a yellow oil and characterized
by 1H/13C NMR spectroscopy and elemental analyses. 10b was
also isolated following the same transformation. However, 10b
was found to exist as a mixture of the two isomers 10b′ and
10b″ in a 3:1 ratio. While the β-diketimine form is
predominant (10b′), a minor cyclic isomer (10b″) featuring
a dihydrobenzoxazole group was found present both in solution
and in the solid state and its structure was unambiguously
established by X-ray diffraction analysis on monocrystals
obtained by recrystallization of 10b in cold (−40 °C) pentane
(see the Experimental Section). Fortunately, cyclization of 10b′
to 10b″ was found to be reversible and addition of 2 molar
equiv of n-butyllithium to 10b yielded the unique dianion 11b
(Scheme 6, eq 7). Similarly, 11a was quantitatively obtained
from 10a. Following this synthetic scheme, the desired N-
aryloxy-β-diketiminate dianions 11a,b were successfully pre-
pared on multigram scales (>5.0 g), with an overall yield higher
than 75% from commercially available compounds. The
centrosymetric dimeric structure of 11a is shown in Figure 2.
It differs from that of 11b by the number of coordinated
lithium cations to the oxygen atom of the phenoxy group.11
While the phenoxy donor O(1) in 11a bridges three lithium
ions, it is bound to two cations in the more congested tBu
derivative 11b. Overall, the two monomeric units in 11a are
linked not only by the bridging phenolic oxygen atom O(1)
between Li(1), Li(1′), and Li(2′) but also by the THF oxygen
atom O(2) between Li(2) and Li(1′). The β-diketiminate
fragment is planar in the usual U-shaped conformation, and this
plane also contains the Li(2) atom, linked to N(1) and N(2)
(rms deviation of 0.08 Å). Delocalization of the charge within
the β-diketiminate backbone is indicated by the average C−C
and C−N distances of 1.41(2) and 1.33(2) Å, respectively.
Coordination Chemistry. Preliminary results gathered
using dianion 11b showed that the N-aryloxy-β-diketiminate
ligand belongs to the LX2 covalent bond classification and is
able to support zirconium(IV), ytterbium(III), and thorium-
(IV) chloride complexes. Having in hand two versions of 11
with different steric bulks in the plane of the ligand (11a, R =
H; 11b, R = tBu), we have investigated the differences in
coordination chemistry between the two series and prepared
the first uranium complexes of the N-aryloxy-β-diketiminate
ligands. Salt metathesis reactions between 11a and ZrCl4,
YbCl3, and ThCl4(DME)2 (in a 1:1 ratio) afforded 12a−14a,
respectively (eqs 8−10 in Scheme 7). Under similar reaction
conditions, complexes 12b−14b were obtained using 11b as a
starting material and described in a preliminary communica-
tion.11 The X-ray crystal structure of zirconium complex 12a,
depicted in Figure 3, is reminiscent of the structure obtained for
12b, with a dimeric structure featuring two hexacoordinated
zirconium(IV) centers supported by a κ3-coordinated N-
aryloxy-β-diketiminate ligand. However, while the metal
coordination sphere is completed by one terminal and two
bridging chloride ligands in 12b, the phenoxy donor acts as the
bridging ligand in 12a. This different coordination behavior
most likely results from a greater steric hindrance in the dianion
of 11b, which possesses a bulky tBu group in the plane of the
N-aryloxy-β-diketiminate backbone. This observation is also
noticeable in the X-ray structures of the ytterbium(III) (13a,
Figure 4) and thorium(IV) (14a, Figure 5) complexes.
Interestingly, although the reaction of 11b with YbCl3 in
pyridine affords a monomeric YbIII complex (13b), whose
coordination sphere is saturated by three pyridine molecules, a
dimeric complex (13a) is obtained when 11a is used in place of
11b, also in pyridine. The bond distances and angles in 12a−
14a are unexceptional and similar to the parameters found in
the analogous complexes 12b−14b. Noticeably, while the N-
Figure 2. Molecular structure of 11a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms and CH3 groups
of the iPr and tBu substituents have been omitted. Symmetry code: (′)
1 − x, 1 − y, 2 − z. Selected bond distances (Å) and angles (deg):
N1−C11 = 1.344(2), N2−C13 = 1.320(2), C11−C12 = 1.397(2),
C12−C13 = 1.422(2), Li1−N1 = 2.111(3), Li1−O1 = 1.929(3), Li1−
O1′ = 1.896(3), Li2−N1 = 2.018(3), Li2−N2 = 1.983(3), Li2−O2 =
2.275(3), Li2−O1′ = 1.905(3); N1−C11−C12 = 124.0(2), C11−
C12−C13 = 129.2(2), C12−C13−N2 = 125.0(2).
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Scheme 7. Synthesis of 12a−14a and Structures of 12b−14b11
Figure 4. Molecular structure of 13a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms and CH3 groups
of the iPr and tBu substituents have been omitted. Selected bond
distances (Å): Yb1−O1 = 2.325(3), Yb2−O2 = 2.260(3), Yb1−N1 =
2.275(4), Yb2−N3 = 2.240(4), Yb1−N2 = 2.398(4), Yb2−N4 =
2.418(4), Yb1−Cl1 = 2.6726(12), Yb2−Cl1 = 2.6329(12), N1−C11 =
1.346(6), C11−C12 = 1.405(7), C12−C13 = 1.439(7), C13−N2 =
1.318(6).
Figure 3. Molecular structure of 12a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms and CH3 groups
of the iPr and tBu substituents have been omitted. Selected bond
distances (Å) and angles (deg): N1−C11 = 1.381(7), N2−C13 =
1.337(7), C11−C12 = 1.366(8), C12−C13 = 1.394(9), Zr1−N1 =
2.129(4), Zr2−N3 = 2.112(4), Zr1−N2 = 2.243(5), Zr2−N4 =
2.326(5), Zr1−O1 = 2.119(4), Zr2−O2 = 2.214(4); N1−C11−C12 =
121.6(2), C11−C12−C13 = 129.3(6), C12−C13−N2 = 121.7(5).
intractable products, a 1:1 mixture of the uranium(IV) iodide
complex and 11b afforded 15b as the sole N-aryloxy-β-
diketiminate complex. As revealed by the X-ray structure
depicted in Figure 6, 15b is a six-coordinate complex with a
uranium(IV) cation stabilized by two κ3-N-aryloxy-β-diketimi-
nate ligands. It was therefore conveniently prepared, in 89%
isolated yield, from a 2:1 mixture of 11b and UI4(1,4-dioxane)2
(eq 11, Scheme 8). This reaction shows that, despite the steric
congestion induced by the tBu substituent on the phenoxide
donor, bis complexes of the N-aryloxy-β-diketiminate ligand
11b are available. Examples of complexes featuring two N-
aryloxy-β-diketiminate ligands are not limited to 15b, and using
the same stoichiometry, the analogous zirconium(IV),
ytterbium(III), and thorium(IV) complexes 16b−18b, respec-
tively, were synthesized (eqs 12−14 in Scheme 8). 16b and 18b
are isostructural with 15b (see structures in the Supporting
aryloxy-β-diketiminate behaves as a LX2-type ligand in 12 and
13, the β-diketiminate fragment is η5 coordinated in 14a and
the ligand is L2X2, with an average Th−C distance of 3.0(1)
Å.11,17 These features are similar to those observed and
discussed previously for the analogous 14b compound.11
Despite the widespread use of β-diketiminate ligands in
transition metal and lanthanide coordination chemistry,1 β-
diketiminate complexes of uranium are limited to a handful of
examples, namely uranium(III,VI) and uranyl(V) com-
plexes.18−21 The N-aryloxy-β-diketiminate pincer anions 11
being successful precursors for the synthesis of thorium β-
diketiminate complexes 14, their coordination behavior toward
UI4(1,4-dioxane)2 was investigated. While addition of 11a to
UI4(1,4-dioxane)2 led to the formation of a mixture of
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Scheme 8. Synthesis of 15b−18b
Figure 5. Molecular structure of 14a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms, CH3 groups of
the iPr and tBu substituents, and countercation Li(THF)4 have been
omitted. Selected bond distances (Å): Th1−O1 = 2.436(6), Th2−O2
= 2.475(6), Th1−N1 = 2.360(8), Th2−N3 = 2.407(8), Th1−N2 =
2.512(7), Th2−N4 = 2.508(7), Th1−Cl3 = 2.833(2), Th2−Cl3 =
2.914(2), Th1−C12 = 2.983(10), Th2−C39 = 2.977(9), N1−C11 =
1.35(2), C11−C12 = 1.39(2), C12−C13 = 1.44(8), C13−N2 =
1.34(2).
Figure 6. Molecular structure of 15b with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms and CH3 groups
of the iPr and tBu substituents have been omitted. Symmetry code: (i)
3
1 − x, y, /2 − z. Selected bond distances (Å): U−O1 = 2.1900(13),
U−N1 = 2.3679(17), U−N2 = 2.4566(16), U−C16 = 3.097, N1−C15
= 1.325(2), C15−C16 = 1.408(3), C16−C17 = 1.425(3), C17−N2 =
1.321(2).
Figure 7. Molecular structure of 17b crystallized from a Et2O solution
(THF molecules from 17b have been displaced by Et2O solvent upon
crystallization). The displacement ellipsoids are drawn at the 50%
probability level. Hydrogen atoms and CH3 groups of the iPr and tBu
substituents have been omitted. Selected bond distances (Å): Yb−O1
= 2.2242(12), Yb−O2 = 2.2345(12), Yb−N1 = 2.3507(13), Yb−N3 =
2.3425(14), Yb−N2 = 2.3792(14), Yb−N4 = 2.3725(14), N1−C15 =
1.329(2), C15−C16 = 1.412(2), C16−C17 = 1.403(2), C17−N2 =
1.346(2).
Information), and the X-ray structure of 17b, obtained by
diffusion of pentane into a Et2O solution, is represented in
Figure 7. In 15b−18b, the N-aryloxy-β-diketiminate ligand is κ3
coordinated and the metal−oxygen and metal−nitrogen bond
distances are unexceptional and follow the trend expected from
the change in metal ionic radius. In complexes 15b, 16b, and
18b, the metal ion adopts a pseudo-trigonal-prismatic
coordination geometry, as exemplified by trigonal twist angles
θ (defined as the mean angle between the medians of the two
trigonal faces defined by atoms O(1), N(1), and N(2i) and
their image by the inversion center for the other face) close to
0° (θ < 13°; see Scheme 10). As a result, the metal ion is
significantly displaced from the plane defined by the three
donor atoms of the N-aryloxy-β-diketiminate ligand (1.42(1) Å
in 15b, 1.36(1) Å in 16b, 1.44(1) Å in 18b). In contrast, the
anionic ytterbium(III) complex 17b is best described as a
pseudo-octahedron with a trigonal twist angle θ of 50.9° and
the Yb3+ ion is located in the plane of the pincer ligand
(deviation of 0.18(1) Å). Given that formation of coordination
polyhedra is primarily governed by electrostatic interactions in
the f-element series,22 these structural differences likely result
from the presence of a chelated lithium cation in the X-ray
structure of 17b and not from specific covalent interactions.
Synthesis of the bis(N-aryloxy-β-diketiminate) complexes
with the less hindered 11a dianion was subsequently attempted.
Reaction of 2 equiv of 11a with ThCl4(DME)2 in THF solution
gave a mixture of numerous N-aryloxy-β-diketiminate com-
plexes, among which the tris(N-aryloxy-β-diketiminate)-
thorium(IV) complex 19a crystallized, in small amounts, at
25 °C following slow diffusion of n-pentane over a Et2O
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solution of the crude mixture. The X-ray structure of 19a,
depicted in Figure 8, reveals the coordination of three N-
these samples, as the analogous 11b−17b complexes, prepared
following a similar synthetic route, yielded satisfactory EAs. In
addition, good EAs were obtained for zirconium complex 12a.
Though X-ray-quality crystals could not be obtained for 17a,
the structure of 16a was established by X-ray diffraction and is
presented in Figure 9. Unlike 16b, the coordination polyhedron
Figure 8. Molecular structure of 19a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms, CH3 groups of
the tBu substituents, 2,6-diisopropylphenyl groups, and carbon atoms
of diethyl ether (O5) and tetrahydrofuran (O4) have been omitted.
The three β-diketiminate ligands are depicted in different shades of
gray, and the bonds between lithium cations and N or O donors are
dashed for easier description. Selected bond distances (Å) (κ3-β-
diketiminate ligand−Th, black): Th−O1 = 2.356(2), Th−N1 =
2.418(3), Th−N2 = 2.581(3), Th−C12 = 3.221, N1−C11 = 1.334(4),
C11−C12 = 1.407(5), C12−C13 = 1.427(5), C13−N2 = 1.311(4).
Figure 9. Molecular structure of 16a with displacement ellipsoids
drawn at the 50% probability level. Hydrogen atoms and CH3 groups
of the iPr and tBu substituents have been omitted. Selected bond
distances (Å): Zr1−O1 = 2.011(2), Zr1−O2 = 2.029(2), Zr1−N1 =
2.289(3), Zr1−N3 = 2.225(3), Zr1−N2 = 2.259(3), Zr1−N4 =
2.258(3), N1−C11 = 1.337(5), C11−C12 = 1.400(6), C12−C13 =
1.395(5), C13−N2 = 1.337(5).
aryloxy-β-diketiminate ligands and the presence of three lithium
cations and one chloride anion. The ThIV ion is supported by
three N-aryloxy-β-diketiminate ligands and one chloride ligand.
While one N-aryloxy-β-diketiminate ligand is κ3 coordinated, a
second β-diketiminate ligand is κ2(O,N) coordinated with the
extra nitrogen donor coordinated to a lithium cation. Finally,
the last N-aryloxy-β-diketiminate ligand interacts with the
actinide atom via a bridging μ-phenoxide donor. This
aggregation state most probably results from the lower steric
hindrance of the phenoxy group in 11a compared to 11b, and
each of the three phenoxide donors in 19a bridges one lithium
and one thorium ion. Nonetheless, for the smaller zirconium-
(IV) (ionic radius (ir) = 0.72 Å vs 0.94 Å for Th4+) and
ytterbium(III) (ir = 0.87 Å), synthesis of bis(N-aryloxy-β-
diketiminate) complexes is possible and 16a and 17a were
isolated in 87 and 82% yields from ZrCl4 and YbCl3,
respectively (eqs 15 and 16 in Scheme 9). Low carbon
elemental analyses were observed for compounds 11a, 13a,
14a, 16a, and 17a (with good H and N EAs) even on isolated
monocrystals. We believe that LiCl is not a contaminant in
in 16a is best described as a pseudo-octahedron with a trigonal
twist of θ = 40.5° compared to 9.2° in 16b (Scheme 10). Again,
this difference in coordination behavior between the two N-
aryloxy-β-diketiminate classes of ligands (R = H vs tBu)
presumably has geometric origins. It is indeed well established
that deviation from the stable octahedron to the trigonal prism
is classically favored in the presence of chelate ligands with
increased steric congestion and that the distortion minimizes
the repulsion between ligands.23−25
Scheme 10
Scheme 9. Synthesis of 16a and 17a
CONCLUSION
■
Two examples of N-aryloxy-β-diketiminate ligands have been
synthesized on a multigram scale, in four steps, from
commercially available chemicals. The synthetic scheme relies
on the sequential addition of 2,6-diisopropylaniline and 2-
amino-4-tert-butylphenol (or 2-amino-4,6-di-tert-butylphenol)
to acetylacetone, using Et3OBF4 as an activation reagent. Both
the nature of the activation reagent and the order of addition of
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ppm (s, 1H, Ar-H). 13C NMR (C6D6, 298 K): δ 14.0 (s, CH3); 31.8 (s,
C(CH3)3); 34.8(s, C(CH3)3); 109.5 (s, Ar); 116.8 (s, Ar); 122.2 (s,
Ar); 147.5 (s, Ar); 149.7 (s, Ar); 163.9 ppm (s, CN). GC/MS (EI;
m/z): 189 (M+, 21), 174 (100), 146 (24), 133 (26).
Synthesis of 3b. A 125 mL round-bottom flask was charged with a
stir bar, 2b (185 mg, 0.606 mmol), p-toluenesulfonic acid hydrate (1.1
mg, 1% mol), and toluene (10 mL). The solution was stirred at 90 °C
for 2 days. The volatiles were then removed under reduced pressure to
yield the benzoxazole 3b (150 mg, 100%). 1H NMR (C6D6, 298 K): δ
1.29 (s, 9H, C(CH3)3); 1.48 (s, 9H, C(CH3)3); 1.58 (acetone); 2.14
(s, 3H, CH3); 7.37 (s, 1H, Ar-H); 7.78 ppm (s, 1H, Ar-H).
the primary amines have a major impact on the outcome of the
reaction, and acid catalysts (such as sulfuric acid or p-
toluenesulfonic acid) lead to decomposition of the β-
diketiminate backbone. Using dianions 11a,b, mono- and
bis(N-aryloxy-β-diketiminate) complexes of zirconium(IV),
ytterbium(III), thorium(IV), and uranium(IV) have been
synthesized, by salt metathesis reactions. The two ligands differ
in their steric bulk and exhibit different coordination behaviors,
which were rationalized on the basis of geometric consid-
erations. We are presently exploring the potential of these new
ligands in supporting catalysts and complexes featuring metal−
main-group-element multiple bonds within the f-element series.
Synthesis of 4a. A 25 mL flask was charged with a stir bar, 2a (500
mg, 2.02 mmol), triethyloxonium tetrafluoroborate (384 mg, 2.02
mmol), and methylene chloride (1 mL). The reaction mixture was
stirred at room temperature for 1 h, generating in situ the O-alkylated
cationic intermediate in a yellow solution. The volatiles were then
removed under reduced pressure to yield the intermediate 4a, directly
EXPERIMENTAL SECTION
■
Unless otherwise noted, all reactions and manipulations were
performed at 20 °C in a recirculating mBraun LabMaster DP inert-
atmosphere (Ar) drybox and vacuum Schlenk lines. Glassware was
dried overnight at 120 °C before use. All NMR spectra were obtained
1
used for further synthesis of 3a and 5. H NMR (CD2Cl2, 298 K): δ
1.28 (s, 9H, C(CH3)3); 1.51 (t, J = 8.0 Hz, 3H, OCH2CH3); 2.38 (s,
6H, α-CH3); 4.51 (q, J = 6.0 Hz, 2H, OCH2CH3); 5.63 (s, 1H, β-CH);
7.08−7.38 (m, 3H, Ar-H); 7.80 (br s, 1H, OH); 11.2 ppm (s, 1H,
NH). 13C NMR (CD2Cl2, 298 K): δ 14.8 (s, OCH2CH3); 20.7 (s, α-
CH3); 21.8 (s, α-CH3); 31.3 (s, C(CH3)3); 34.4 (s, C(CH3)3); 69.5 (s,
OCH2CH3); 101.0 (s, β-CH); 117.0 (s, Ar); 122.1 (s, Ar); 122.3 (s,
Ar); 128.3 (s, Ar); 144.1 (s, Ar); 148.2 (s, Ar); 175.4 (s, CN); 181.0
ppm (s, CO).
1
using a Bruker DPX 200 MHz spectrometer. Chemical shifts for H
and 13C{1H} NMR spectra were referenced to solvent impurities.
Elemental analyses were performed at Analytische Laboratorien at
Lindlar (Germany) and Medac Ltd. at Chobham (United Kingdom).
Mass spectrometer data were collected on a Shimadzu GCMS-
QP2010 Ultra gas chromatograph mass spectrometer equipped with a
Supelco SLB-ms fused silica capillary column (30 m × 0.25 mm × 0.25
μm). Unless otherwise noted, reagents were purchased from
commercial suppliers and dried over 4 Å molecular sieves prior to
use. Celite (Aldrich) and 4 Å molecular sieves (Aldrich) were dried
under dynamic vacuum at 250 °C for 48 h prior to use.
Tetrahydrofuran (THF), tetrahydrofuran-d8 (THF-d8), n-pentane,
diethyl ether, and benzene-d6 were dried over a sodium(0)/
benzophenone mixture and distilled before use. Pyridine and
pyridine-d5 were dried over potassium(0) prior to use. Triethylamine,
dichloromethane, and dichloromethane-d2 were dried over CaH2 and
distilled before use. ThCl4(1,4-dimethoxyethane)2,26 UI4(1,4-diox-
ane)2,27 1b,11 2b,11 5,11 6,7,11 8b,11 12b,11 14b,11 and 15b11 were
prepared according to literature procedures.
Synthesis of 4b. A 100 mL flask was charged with a stir bar, 2b
(5.62 g, 21.7 mmol), triethyloxonium tetrafluoroborate (4.12 g, 21.7
mmol), and methylene chloride (13 mL). The reaction mixture was
stirred at room temperature for 1 h, generating in situ the O-alkylated
cationic intermediate in a brown-orange solution. The volatiles were
then removed under reduced pressure to yield the intermediate 4b,
directly used for further synthesis of 3b and 5. 1H NMR (CD2Cl2, 298
K): δ 1.29 (s, 9H, C(CH3)3); 1.38 (s, 9H, C(CH3)3); 1.46 (t, J = 8.0
Hz, 3H, OCH2CH3); 2.24 (s, 3H, α-CH3); 2.38 (s, 3H, α-CH3); 4.53
(q, J = 8.0 Hz, 2H, OCH2CH3); 5.68 (s, 1H, β-CH); 6.76 (br s, 1H,
OH); 6.97 (d, J = 2.0 Hz, 1H, Ar-H); 7.42 (d, J = 2.0 Hz, 1H, Ar-H);
10.9 ppm (br s, 1H, NH). 13C NMR (CD2Cl2, 298 K): δ 14.8 (s,
OCH2CH3); 21.0 (s, α-CH3); 21.7 (s, α-CH3); 29.7 (s, C(CH3)3);
30.1 (s, C(CH3)3); 34.8 (s, C(CH3)3); 35.7 (s, C(CH3)3); 69.6 (s,
OCH2CH3); 101.1 (s, β-CH); 120.7 (s, Ar); 124.4 (s, Ar); 126.0 (s,
Ar); 140.1 (s, Ar); 144.2 (s, Ar); 147.4 (s, Ar); 177.9 (s, CN); 182.6
ppm (s, CO).
Caution! Natural thorium (primary isotope 232Th) is a weak α
emitter (4.012 MeV) with a half-life of 1.41 × 1010 years, and depleted
uranium (primary isotope 238U) is a weak α emitter (4.197 MeV) with
a half-life of 4.47 × 109 years; manipulations and reactions should be
carried out in monitored fume hoods or in an inert-atmosphere drybox
in a radiation laboratory equipped with α- and β-counting equipment.
Synthesis of 2a. A 100 mL round-bottom flask was charged with a
stir bar, acetylacetone (1.7 mL, 17 mmol), 2-amino-4-tert-butylphenol
1a (1.0 g, 6.1 mmol), and THF (10 mL). The resulting solution was
sheltered from light and stirred for 24 h at room temperature. Solvent
and excess acetylacetone were removed at 50 °C under reduced
pressure to give a light yellow solid. Pentane (50 mL) was added, and
the suspension was immersed in an ultrasound bath (80 W, 40 kHz)
for 10 min, yielding a white solid and a brown solution. The solid was
filtered off at −40 °C and washed with cold (−40 °C) pentane (10
mL) to afford 2a as a white powder (0.96 g, 63%). Colorless
translucent crystals were obtained by slow diffusion of pentane into a
Synthesis of 3a and 5. 2,6-Diisopropylaniline (19.7 μL, 0,104
mmol) was added to a dichloromethane solution of intermediate 4a
(0.104 mmol), and the reaction mixture was stirred for 2 days at 60
°C. The volatiles were then removed under reduced pressure. Toluene
(2 mL) was added to the mixture, leading to the formation of two
phases. Iminium salt 5 was found as the major compound in the lower
phase (dark brown oil), while 3a is the major constituent of the upper
light brown solution. Differences between 13C NMR spectra led to
complete recognition of all products. 13C NMR (CD2Cl2, 298 K)
(crude mixture): δ 14.6 (s, CH3, 3a); 15.4 (s, Et2O); 18.4 (s, EtOH);
23.1 (s, CH(CH3)2, 5); 24.1 (s, CH3, 5); 26.1 (s, CH3, 5); 29.1 (s,
CH(CH3)2, 5); 31.4 (s, CH(CH3)2, 5); 31.9 (s, C(CH3)3, 3a); 35.1(s,
C(CH3)3, 3a); 58.4 (s, EtOH); 66.0 (s, Et2O); 109.7 (s, Ar, 3a); 115.9
(s, Ar, 3a); 122.6 (s, Ar, 3a); 125.3 (s, Ar, 5); 130.4 (s, Ar, 5); 131.8 (s,
Ar, 5); 141.4 (s, Ar, 3a); 143.6 (s, Ar, 5); 148.1 (s, Ar, 3a); 149.3 (s,
Ar, 3a); 164.7 (s, CN, 3a); 197.6 ppm (s, CN+, 5).
1
THF solution. H NMR (CD2Cl2, 298 K): δ 1.26 (s, 9H, C(CH3)3);
1.82 (s, 3H, α-CH3); 2.04 (s, 3H, α-CH3); 5.19 (s, 1H, β-CH); 6.88
(d, J = 8.0 Hz, 1H, Ar-H); 7.04 (d, J = 2.0 Hz, 1H, Ar-H); 7.21 (dd, J =
2.0 Hz, 8.0 Hz, 1H, Ar-H); 8.16 (s, 1H, OH); 11.7 ppm (s, 1H, NH).
13C NMR (THF-d8, 298 K): δ 19.3 (s, α-CH3); 28.7 (s, α-CH3); 31.6
(s, C(CH3)3); 34.4 (s, C(CH3)3); 97.0 (s, β-CH); 116.4 (s, Ar); 124.4
(s, Ar); 124.7 (s, Ar); 126.6 (s, Ar); 142.8 (s, Ar); 150.6 (s, Ar); 161.7
(s, C−NH); 194.8 ppm (s, C−O).
Synthesis of 3a. A 125 mL round-bottom flask was charged with a
stir bar, 2a (150 mg, 0.606 mmol), p-toluenesulfonic acid hydrate (1.1
mg, 1% mol), and toluene (10 mL). The solution was stirred overnight
at 90 °C. The volatiles were then removed under reduced pressure to
yield the benzoxazole 3a (115 mg, 100%). 1H NMR (C6D6, 298 K): δ
1.21 (s, 9H, C(CH3)3); 2.10 (s, 3H, CH3); 7.16 (m, 2H, Ar-H); 7.85
Synthesis of 7. A 100 mL flask was charged with a stir bar, 6 (5.62
g, 21.7 mmol), triethyloxonium tetrafluoroborate (4.12 g, 21.7 mmol),
and methylene chloride (13 mL). The reaction mixture was stirred at
room temperature for 1 h, generating in situ the O-alkylated cationic
intermediate 2. The volatiles were then removed under reduced
pressure to yield intermediate 7, directly used for further synthesis.
Colorless translucent monocrystals suitable for X-ray diffraction
1
analysis were collected from a THF/pentane solution of 7. H NMR
(C6D6, 298 K): δ 1.13−120 (m, 9H, CH(CH3)2, OCH2CH3); 1.30 (d,
J = 6.0 Hz, 6H, CH(CH3)2); 1.94 (s, 3H, α-CH3); 2.03 (s, 3H, α-
CH3); 2.97 (m, 2H, CH(CH3)2); 4.07 (q, J= 6.0 Hz, 2H, OCH2CH3);
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6.30 (s, 1H, β-CH); 7.12−7.36 (m, 3H, Ar-H); 11.2 ppm (s, 1H, NH).
13C NMR (C6D6, 298 K): δ 14.8 (s, OCH2CH3); 20.6 (s, α-CH3);
20.9 (s, α-CH3); 22.7 (s, CH(CH3)2); 24.0 (s, CH(CH3)2); 29.0
(CH(CH3)2); 68.9 (s, OCH2CH3); 100.2 (s, β-CH); 124.7 (s, Ar);
130.5 (s, Ar); 130.9 (s, Ar); 144.7 (s, Ar); 178.8 (s, CN); 182.7
ppm (s, CO).
Synthesis of 10a. A 100 mL flask was charged with a stir bar, 8a
(2.76 g, 5.58 mmol), and diethyl ether (40 mL). Triethylamine (0.93
mL, 6.70 mmol) was slowly added to the white suspension using a
syringe, leading to the immediate formation of a yellow suspension.
The mixture was stirred for 1 h. The white solid of triethylamonium
tetrafluoroborate was then filtered off through a Celite padded coarse
frit, and the yellow solution was introduced into a 100 mL two-neck
round-bottom flask. The volatiles were removed under reduced
pressure overnight, leading to 10a as a yellow oil (2.20 g, 97%). Anal.
Calcd for C27H38N2O: C, 79.76; H, 9.42; N, 6.89. Found: C, 79.38; H,
Synthesis of 8a. After removal of the volatiles, 7 was directly
reacted with 2-amino-4-tert-butylphenol (1a; 3.76 g, 22.8 mmol) in
THF (13 mL) at room temperature. The resulting yellow suspension
was vigorously stirred for 30 min at room temperature, leading to a
complete dissolution of 1a. After drying under reduced pressure for 12
h, pentane (150 mL) was added to the yellow-brown foam and the
mixture was immersed in an ultrasound bath (80 W, 40 kHz) for 90
min, yielding a well-defined white suspension. The white solid was
recovered by filtration and washed with cold (−40 °C) diethyl ether (3
× 30 mL) to afford 8a as a white powder (9.16 g, 85%). Colorless
translucent crystals were obtained by slow diffusion of pentane into a
THF solution of 8a. Anal. Calcd for C27H39BF4N2O: C, 65.59; H,
1
9.47; N, 7.08. H NMR (C6D6, 298 K): δ 1.13 (d, J = 6.0 Hz, 6H,
CH(CH3)2); 1.19 (d, J = 6.0 Hz, 6H, CH(CH3)2); 1.28 (s, 9H,
C(CH3)3); 1.66 (s, 3H, α-CH3); 1.91 (s, 3H, α-CH3); 3.23 (m, 2H,
CH(CH3)2); 4.97 (s, 1H, β-CH); 7.04−7.22 (m, 6H, Ar-H); 9.16 ppm
(br s, 1H, NH); no OH signal had been identified. 13C NMR (C6D6,
298 K): δ 20.6 (s, α-CH3); 21.0 (s, α-CH3); 22.9 (s, CH(CH3)2); 24.5
(s, CH(CH3)2); 28.8 (s, CH(CH3)2); 31.8 (s, C(CH3)3); 34.2 (s,
C(CH3)3); 96.7 (β-CH); 114.9 (s, Ar); 121.3 (s, Ar); 122.6 (s, Ar);
123.6 (s, Ar); 126.5 (s, Ar); 133.2 (s, Ar); 139.7 (s, Ar); 139.7 (s, Ar);
143.0 (s, Ar); 143.1 (s, Ar); 148.0 (s, Ar); 161.4 (s, C−N); 164.7 ppm
(s, C−N).
1
7.95; N, 5.67; Found: C, 65.05: H, 7.98; N, 5.60. H NMR (THF-d8,
298 K): δ 1.02 (d, J = 6.0 Hz, 6H, CH(CH3)2); 1.09 (d, J = 6.0 Hz,
6H, CH(CH3)2); 1.13 (s, 9H, C(CH3)3); 2.63 (s, 3H, α-CH3); 2.72 (s,
3H, α-CH3); 2.80 (m, 2H, CH(CH3)2); 4.67 (s, 1H, β-CH); 6.58 (d, J
= 8.0 Hz, 1H, Ar-H); 6.81 (s, 1H, Ar-H); 7.03−7.28 (m, 4H, Ar-H);
8.13 (s, 1H, OH); 9.44 ppm (s, 2H, NH). 13C NMR (THF-d8, 298 K):
δ 21.9 (s, α-CH3); 23.4 (s, α-CH3); 24.4 (s, CH(CH3)2); 28.9 (s,
CH(CH3)2); 31.5 (s, C(CH3)3); 34.4 (s, C(CH3)3); 92.2 (s, β-CH);
117.0 (s, Ar); 117.1 (s, Ar); 123.2 (s, Ar); 124.4 (s, Ar); 127.2 (s, Ar);
129.8 (s, Ar); 132.3 (s, Ar); 143.2 (s, Ar); 146.1 (s, Ar); 150.5 (s, C−
OH); 172.0 (s, CNH); 172.4 ppm (s, CNH).
Synthesis of 10b. A 100 mL flask was charged with a stir bar, 8b
(2.31 g, 4.19 mmol), and diethyl ether (40 mL). Triethylamine (0.64
mL, 4.61 mmol) was slowly added to the white suspension using a
syringe, leading to the immediate formation of a yellow suspension.
The mixture was stirred for 1 h. The white solid of triethylamonium
tetrafluoroborate was then filtered off through a Celite padded coarse
frit, and the yellow solution was introduced into a 100 mL two-neck
round-bottom flask. The volatiles were removed under reduced
pressure overnight, leading to two isomeric forms (10b′:10b″ 75:25)
of 10b as a yellow oil (1.94 g, 100%). Yellow monocrystals of the
minor isomer 10b″ suitable for X-ray diffraction analysis were
recovered by recrystallization of 10b in pentane. Anal. Calcd for
C31H46N2O: C, 80.47; H, 10.02; N, 6.05. Found: C, 80.18; N, 10.22;
H, 5.96. 1H NMR of 10b′ (THF-d8, 298 K): δ 1.13 (d, J = 6.0 Hz, 6H,
CH(CH3)2); 1.22 (d, J = 6.0 Hz, 6H, CH(CH3)2); 1.27 (s, 9H,
C(CH3)3); 1.40 (s, 9H, C(CH3)3); 1.71 (s, 3H, α-CH3); 1.87 (s, 3H,
α-CH3); 3.11 (m, 2H, CH(CH3)2); 5.04 (s, 1H, β-CH); 6.78 (s, 1H,
Synthesis of 9a. A 50 mL flask was charged with a stir bar, 8a
(2.15 g, 4.35 mmol), and solid methyllithium (335 mg, 15.22 mmol).
Diethyl ether (10 mL) was condensed in, yielding a yellow solution
with a white precipitate. The suspension was stirred for 7 days. The
volatiles were then removed under reduced pressure, and THF (30
mL) was condensed in. The solid was removed from the resulting
suspension by centrifugation. The volatiles were then removed under
reduced pressure to afford 9a as an air- and water-stable yellow powder
(1.20 g, 64%). Yellow needles of 9a were obtained by slow evaporation
of a CH3CN solution of 9a. Anal. Calcd for C27H36BFN2O: C, 74.65;
1
OH); 6.90−7.25 (m, 5H, Ar-H); 12.1 ppm (s, 1H, NH). Partial H
1
NMR of 10b″ (THF-d8, 298 K): δ 1.36 (s, 9H, C(CH3)3); 1.64 (s, 3H,
CH3); 1.76 (s, 3H, CH3); 5.54 ppm (s, 1H, NH). 13C NMR of 10b′
(THF-d8, 298 K): δ 20.4 (s, α-CH3); 21.0 (s, α-CH3); 23.1 (s,
CH(CH3)2); 24.5 (s, CH(CH3)2); 28.9 (s, CH(CH3)2); 29.7 (s,
C(CH3)3); 31.8 (s, C(CH3)3); 34.7 (s, C(CH3)3); 35.5 (s, C(CH3)3);
97.0 (s, β-CH); 120.8 (s, Ar); 123.2 (s, Ar); 123.5 (s, Ar); 125.5 (s,
Ar); 131.9 (s, Ar); 135.7 (s, Ar); 141.5 (s, Ar); 141.6 (s, Ar); 142.5 (s,
Ar); 148.3 (s, C−OH); 162.2 (s, C-NH); 163.5 ppm (s, C−NH). 13C
NMR of 10b″ (THF-d8, 298 K): δ 22.8 (s, CH(CH3)2); 23.0 (s,
CH3); 23.4 (s, CH(CH3)2); 23.5 (s, CH(CH3)2); 23.8 (s, CH(CH3)2);
28.4 (s, CH(CH3)2); 28.6 (s, CH(CH3)2); 28.9 (s, CH3); 29.8 (s,
C(CH3)3); 32.1 (s, C(CH3)3); 34.5 (s, C(CH3)3); 35.0 (s, C(CH3)3);
48.9 (s, CH2CN); 101.1 (s, Ar); 108.4 (s, Ar); 115.1 (s, Ar); 123.6
(s, Ar); 124.1 (s, Ar); 131.0 (s, Ar); 136.6 (s, Ar); 136.7 (s, Ar); 139.1
(s, Ar); 142.5 (s, Ar); 146.5 (s, Ar); 146.7 (s, Ar); 170.1 ppm (s, C
N).
H, 8.35; N, 6.45. Found: C, 74.49; H, 8.35; N, 6.37. H NMR (THF-
d8, 298 K): δ 1.07 (d, J = 4.0 Hz, 3H, CH(CH3)2); 1.10 (d, J = 4.0 Hz,
3H, CH(CH3)2); 1.42 (pseudo-t, J = 6.0 Hz, 6H, CH(CH3)2); 1.50 (s,
9H, C(CH3)3); 2.06 (s, 3H, α-CH3); 2.32 (m, 1H, CH(CH3)2); 2.81
(s, 3H, α-CH3); 3.50 (m, 1H, CH(CH3)2); 5.78 (s, 1H, β-CH); 6.84
(d, J = 8.0 Hz, 1H, Ar-H); 7.22 (dd, J = 8.0 Hz, 2.0 Hz, 1H, Ar-H);
7.31 (pseudo-t, J = 4.0 Hz, 1H, Ar-H); 7.45 (s, 1H, Ar-H); 7.48 (d, J =
2.0 Hz, 1H, Ar-H); 7.64 ppm (d, J = 2.0 Hz, 1H, Ar-H). 13C NMR
(C6D6, 298 K): δ 20.6 (s, α-CH3); 21.2 (s, α-CH3); 23.8 (s,
CH(CH3)2); 24.0 (s, CH(CH3)2); 24.6 (s, CH(CH3)2); 25.9 (s,
CH(CH3)2); 26.0 (s, CH(CH3)2); 28.8 (s, CH(CH3)2); 31.9 (s,
C(CH3)3); 34.5 (s, C(CH3)3); 99.9 (s, β-CH); 112.8 (s, Ar); 113.7 (s,
Ar); 123.2 (s, Ar); 124.1 (s, Ar); 124.7 (s, Ar); 133.5 (s, Ar); 136.6 (s,
Ar); 141.2 (s, Ar); 145.6 (s, Ar); 146.6 (s, Ar); 153.0 (s, C−O); 156.7
(s, CN); 161.3 ppm (s, CN). MS: (EI; m/z): 434 (M+, 24), 419
(22); 230 (60), 202 (100).
Synthesis of 11a. A 100 mL two-neck round-bottom flask was
charged with a stir bar, 10a (2.20 g, 5.41 mmol), and THF (20 mL). n-
Butyllithium (6.80 mL, 10.8 mmol) was slowly added at −78 °C under
an argon flow, using a syringe. The resulting deep yellow solution was
warmed to room temperature, yielding an orange solution with a
yellow precipitate. After concentration of the solution to 10 mL, the
solid was filtered off and washed with cold pentane (2 × 10 mL, −40
°C), to provide 11a as a yellow powder (2.82 g, 93%). Yellow crystals
of 11a were recovered by slow diffusion of pentane over a THF
solution and used for further NMR analysis after moderate drying
under reduced pressure to avoid desolvation. Anal. Calcd for
C27H36Li2N2O·THF: C, 75.90; H, 9.04; N, 5.71. Found: C, 73.76;
H, 9.54, N, 5.75. Several attempts of elemental analysis led to poor C
correlation each time. 1H NMR (C6D6, 298 K): δ 1.22 (m, 12H,
THF); 1.30 (pseudo-t, J = 6.0 Hz, 12H, CH(CH3)2); 1.40 (s, 9H,
Synthesis of 9b. A 50 mL flask was charged with a stir bar, 8b
(821 g, 1.49 mmol), and diethyl ether (15 mL). n-Butyllithium (2.80
mL, 4.47 mmol) was slowly added at −78 °C under an argon flow,
using a syringe. The reaction mixture was warmed to room
temperature and stirred for 7 days. After decantation, an aliquot of
the solution was analyzed by 1H NMR spectroscopy and 9b was
identified as the major compound among other degradation
products.1H NMR (C6D6, 298 K): δ 0.86 (dd, J = 6.0 Hz, 2.0 Hz,
3H, CH(CH3)2); 1.24 (d, J = 8.0 Hz, 3H, CH(CH3)2); 1.28 (d, J = 8.0
Hz, 3H, CH(CH3)2); 1.34 (s, 9H, C(CH3)3); 1.44 (s, 9H, C(CH3)3);
1.60 (d, J = 8.0 Hz, 3H, CH(CH3)2); 1.65 (s, 3H, α-CH3); 2.01 (s, 3H,
α-CH3); 2.88 (m, 1H, CH(CH3)2); 3.88 (m, 1H, CH(CH3)2); 5.20 (s,
1H, β-CH); 7.01 (dd, J = 6.0 Hz, 2.0 Hz, 1H, Ar-H); 7.16 (m, 1H, Ar-
H); 7.21 (d, J = 2.0 Hz, 1H, Ar-H); 7.24 (d, J = 2.0 Hz, 1H, Ar-H);
7.32 ppm (d, J = 2.0 Hz, 1H, Ar-H).
1336
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Organometallics
Article
C(CH3)3); 1.91 (s, 3H, α-CH3); 2.18 (s, 3H, α-CH3); 3.34 (m, 12H,
THF); (m, 2H, CH(CH3)2); 5.01 (s, 1H, β-CH); 6.70−7.20 ppm (m,
6H, Ar-H). 13C NMR (C6D6, 298 K): δ 24.1 (s, α-CH3); 24.4 (s, α-
CH3); 25.5 (s, CH(CH3)2, THF); 28.2 (s, CH(CH3)2); 32.2 (s,
C(CH3)3); 34.0 (s, C(CH3)3); 68.2 (s, THF); 96.8 (s, β-CH); 118.8
(s, Ar); 119.1 (s, Ar); 122.0 (s, Ar); 123.2 (s, Ar); 123.4 (s, Ar); 138.1
(s, Ar); 140.9 (s, Ar); 144.8 (s, Ar); 149.7 (s, Ar); 157.9 (s, Ar); 165.2
(s, C−N); 165.3 ppm (s, C−N).
was added to the flask, the white precipitate of LiCl was filtered off
over a fine-porosity fritted filter, and the yellow-orange solution was
dried under reduced pressure to provide 14a as a yellow powder (204
mg, 87%). Yellow monocrystals of 14a·2THF were recovered by slow
diffusion of pentane over a THF solution. 14a is probably unstable
over time in the solid state, which causes poor elemental analysis
correlation. Anal. Calcd for C62H92Cl5LiN4O6Th2: C, 45.47; H, 5.66;
N, 3.42. Found: C, 39.36; H, 5.43; N, 2.99. 1H NMR (pyridine-d5, 298
K): δ 1.00−1.40 (m, 12H, CH(CH3)2); 1.36 (s, 9H, C(CH3)3); 2.20
(s, 3H, α-CH3); 2.58 (s, 3H, α-CH3); 5.70 (s, 1H, β-CH); 6.96 (s, 2H,
Ar-H); 7.08 (m, 1H, Ar-H); 7.23 ppm (m, 3H, Ar-H); THF signals are
missing due to the drying process. 13C NMR (THF-d8, 298 K): δ 21.8
(s, α-CH3); 24.8 (s, α-CH3); (s, CH(CH3)2); 28.5 (br s, CH(CH3)2);
32.3 (s, C(CH3)3); 34.5 (s, C(CH3)3); 92.1 (s, β-CH); 114.8 (s, Ar);
117.5 (s, Ar); 119.9 (s, Ar); 123.3 (br s, Ar); 125.4 (s, Ar); 139.7 (s,
Ar); 140.3 (s, Ar); 142.7 (br s, Ar); 148.4 (s, Ar); 154.3 (s, Ar); 160.4
(s, CN); 165.6 ppm (s, CN).
Synthesis of 11b. A 100 mL two-neck round-bottom flask was
charged with a stir bar, 10b (2.50 g, 5.41 mmol), and THF (20 mL). n-
Butyllithium (6.80 mL, 10.8 mmol) was slowly added at −78 °C under
an argon flow, using a syringe. The resulting deep yellow solution was
warmed to room temperature, yielding an orange solution with a
yellow precipitate. After concentration of the solution to 10 mL, the
solid was filtered off and washed with cold pentane (2 × 10 mL, −40
°C). 11b was finally isolated as a pale yellow powder (3.18 g, 95%).
Yellow crystals of [11b]2·0.5(n-pentane) were obtained by slow
diffusion of pentane into a THF solution. Elemental analyses were
made with samples used in NMR spectroscopy with C6D6. Anal. Calcd
for C39H60Li2N2O3.0.5C6H6: C, 76.68; H, 9.65; N, 4.26. Found: C,
76.68; H, 9.62; N, 4.70. 1H NMR (C6D6, 298 K): δ 1.18 (d, J = 8.0 Hz,
6H, CH(CH3)2); 1.26 (d, J = 8.0 Hz, 6H, CH(CH3)2); 1.34 (s, 9H,
C(CH3)3); 1.73 (s, 9H, C(CH3)3); 1.96 (s, 3H, α-CH3); 2.19 (s, 3H,
α-CH3); 3.50 (m, 2H, CH(CH3)2); 5.14 (s, 1H, β-CH); 6.85 (d, J =
2.0 Hz, 1H, Ar-H); 7.10−7.30 ppm (m, 4H, Ar-H). 13C NMR (C6D6,
298 K): δ 23.7 (s, α-CH3); 23.9 (s, CH(CH3)2); 24.2 (s, CH(CH3)2);
24.6 (s, α-CH3); 25.5 (s, THF); 28.2 (s, CH(CH3)2); 31.1 (s,
C(CH3)3); 32.3 (s, C(CH3)3); 34.2 (s, C(CH3)3); 35.3 (s, C(CH3)3);
68.1 (s, THF); 98.0 (s, β-CH); 118.1 (s, Ar); 120.2 (s, Ar); 123.5 (s,
Ar); 128.4 (s, Ar); 135.8 (s, Ar); 136.2 (s, Ar); 140.6 (s, Ar); 145.6 (s,
Ar); 149.2 (s, Ar); 154.2 (s, C−O); 161.3(s, CN); 170.2 ppm (s,
CN).
Synthesis of 15b. A 25 mL flask was charged with UI4(1,4-
dioxane)2 (179 mg, 0.194 mmol), 11b (240 mg, 0.388 mmol), and
toluene (50 mL). The red suspension was heated to 100 °C for 12 h.
The complex is poorly soluble in toluene and was extracted in a
Soxhlet apparatus under an inert atmosphere using toluene and dried
under reduced pressure to provide 15b as a red powder (201 mg,
89%), which was recrystallized from toluene to afford dark red
monocrystals. Anal. Calcd for C62H88N4O2U: C, 64.23; H, 7.65; N,
1
4.83. Found: C, 63.83; H, 7.70; N, 4.99. H NMR (C6D6, 298 K): δ
−24.4 (s, 1H); −20.0 (s, 3H); −15.7 (s, 3H); −8.1 (s, 9H); −6.9 (s,
1H); −4.6 (s, 1H); −1.9 (s, 3H); −1.1 (s, 3H); 3.6 (s, 1H); 3.7 (s,
1H); 10.3 (s, 9H); 17.8 (s, 1H); 18.6 (s, 3H); 23.6 (s, 3H); 29.2 (s,
1H); 45.1 ppm (s, 1H).
Synthesis of 16a. A 25 mL flask was charged with a stir bar, ZrCl4
(64.9 mg, 0.278 mmol), 11a (273 mg, 0.557 mmol), and toluene (10
mL). The deep red suspension was stirred for 12 h at room
temperature. The white precipitate was then filtered off over a fine-
porosity fritted filter, and the volatiles were removed under reduced
pressure to provide 16a as a red powder (220 mg, 87%). Red
monocrystals of [16a]2·1.5(n-pentane) were recovered by recrystalli-
zation in pentane. Anal. Calcd for C54H72N4O2Zr: C, 72.03; H, 8.06;
N, 6.22. Found: C, 70.12; H, 8.23; N, 6.16. As for ligand 11a, poor C
correlations were obtained while several attempts had been made,
including with isolated monocrystals. 1H NMR (C6D6, 298 K): δ
1.03−1.25 (m, 12H, CH(CH3)2); 1.25(s, 9H, C(CH3)3); 1.60 (s, 3H,
α-CH3); 1.89 (s, 3H, α-CH3); 3.25 (m, 2H, CH(CH3)2); 4.95 (s, 1H,
β-CH); 6.31 (d, J = 8.0 Hz, 1H, Ar-H); 6.68 (d, J = 8.0 Hz, 1H, Ar-H);
6.75 (s, 1H, Ar-H); 7.01 ppm (m, 3H, Ar-H). 13C NMR (C6D6, 298
K): δ 23.7 (s, α-CH3); 24.4 (s, α-CH3); 25.5 (s, CH(CH3)2); 25.5 (s,
CH(CH3)2); 25.7 (s, CH(CH3)2); 25.9 (s, CH(CH3)2); 28.0 (s,
CH(CH3)2); 30.2 (s, CH(CH3)2); 31.9 (s, C(CH3)3); 34.1 (s,
C(CH3)3); 105.6 (s, β-CH); 113.9 (s, Ar); 118.3 (s, Ar); 121.7 (s, Ar);
123.1 (s, Ar); 125.4 (s, Ar); 126.7 (s, Ar); 139.8 (s, Ar); 140.3 (s, Ar);
143.4 (s, Ar); 145.0 (s, Ar); 145.1 (s, Ar); 158.5 (s, Ar); 162.5 (s, C
N); 166.1 ppm (s, CN).
Synthesis of 12a. A 25 mL flask was charged with a stir bar, ZrCl4
(159 mg, 0.682 mmol), 11a (328 mg, 0.669 mmol), and toluene (15
mL). The orange suspension was heated to 100 °C for 1 day and then
cooled to room temperature. The white precipitate of LiCl was filtered
off over a fine-porosity fritted filter. The resulting red solution was
dried under reduced pressure to provide a red-orange powder (315
mg, 83%). Red monocrystals were obtained by recrystallization from
deuterated benzene, leading to [12a]2·6.5C6D6 as a dimer. Anal. Calcd
for C27H36Cl2N2OZr·C6D6: C, 61.47; H, 6.57; N, 4.34. Found: C,
1
60.98; H, 6.78; N, 4.55. H NMR (C6D6, 298 K): δ 0.89 (m, 12H,
CH(CH3)2); 1.24 (s, 9H, C(CH3)3); 1.65 (s, 3H, α-CH3); 2.01 (s, 3H,
α-CH3); 2.25 (m, 1H, CH(CH3)2); 3.82 (m, 1H, CH(CH3)2); 5.72 (s,
1H, β-CH); 6.69 (s, 1H, Ar-H); 7.04 (m, 4H, Ar-H), 8.08 ppm (d, J =
6.0 Hz, 1H, Ar-H). 13C NMR (C6D6, 298 K): δ 21.5 (s, α-CH3); 22.1
(s, α-CH3); 24.1−24.3 (multiple broad signals, CH(CH3)2); 25.1 (s,
CH(CH3)2); 31.7 (s, C(CH3)3); 34.4 (s, C(CH3)3); 111.9 (s, β-CH);
115.6 (s, Ar); 119.4 (s, Ar); 120.2 (s, Ar); 124.3 (s, Ar); 127.1 (s, Ar);
138.8 (s, Ar); 141.5 (s, Ar); 144.4 (s, Ar); 149.2 (s, Ar); 153.5 (s, Ar);
155.4 (s, CN); 171.2 ppm (s, CN).
Synthesis of 13a. A 25 mL flask was charged with a stir bar, YbCl3
(229 mg, 0.819 mmol), 11a (402 mg, 0.820 mmol), and pyridine (20
mL). The deep red solution was stirred for 1 h at room temperature
and then concentrated to less than 1 mL. Toluene (20 mL) was
condensed in and the white precipitate filtered off over a fine-porosity
fritted filter. The resulting red solution was dried under reduced
pressure to provide 13a as a red-orange powder (580 mg, 97%). Red
monocrystals of 13a were recovered by slow diffusion of pentane over
a pyridine solution of 13a. Anal. Calcd for C69H87Cl2N7O2Yb2·0.5Py:
C, 54.59; H, 5.95; N, 5.37. Found: C, 51.05; H, 5.98; N, 5.28. Several
attempts at elemental analysis led to poor C correlation, including
Synthesis of 16b. A 25 mL flask was charged with a stir bar, ZrCl4
(35.0 mg, 0.154 mmol), 11b (191 mg, 0.308 mmol), and toluene (15
mL). The orange suspension was heated to 100 °C for 1 day and then
cooled to room temperature. The white precipitate was filtered off
over a fine-porosity fritted filter. The volatiles were then removed
under reduced pressure to provide 16b as an orange powder (145 mg,
93%). Orange monocrystals were obtained by recrystallization from
toluene. Anal. Calcd for C62H88N4O2Zr: C, 73.54; H, 8.76; N, 5.53.
Found: C, 73.42; H, 8.70; N, 5.53. 1H NMR (THF-d8, 298 K): δ 0.81
(m, 21H, CH(CH3)2, C(CH3)3); 1.24 (s, 9H, C(CH3)3); 1.66 (s, 3H,
α-CH3); 2.17 (br s, 3H, α-CH3); 3.01 (m, 2H, CH(CH3)2); 5.16 (s,
1H, β-CH); 6.71 (s, 2H, Ar-H); 7.00 ppm (m, 4H, Ar-H). 13C NMR
(C6D6, 298 K): δ 23.0−26.5 (multiple broad signals, α-CH3,
CH(CH3)2); 28.1 (s, CH(CH3)2); 30.2 (s, C(CH3)3); 32.1 (s,
C(CH3)3); 34.5 (s, C(CH3)3); 34.9 (s, C(CH3)3); 118.6 (s, Ar); 123.7
(s, Ar); 125.2 (s, Ar); 126.5 (s, Ar); 131.2 (br s, Ar); 134.6 (s, Ar);
139.5 (s, Ar); 140−144 (multiple broad signals, Ar); 157.9 (s, CN);
167.0 ppm (s, CN).
1
from isolated crystals. H NMR (pyridine-d5, 298 K): δ −49.6 (br s,
1H); −33.1 (br s, 1H); −24.0 (br s, 3H); −21.5 (br s, 3H); −17.6 (br
s, 6H); −15.2 (br s, 2H); −11.4 (br s, 6H); −2.3 (s, 9H); 18.7 (br s,
1H); 22.0 (br s, 1H); 23.0 (br s, 1H); 25.3 ppm (br s, 1H).
Synthesis of 14a. A 25 mL flask was charged with a stir bar,
ThCl4(DME)2 (159 mg, 0.287 mmol), 11a (141 mg, 0.287 mmol),
and THF (15 mL). The yellow suspension was stirred for 12 h at
room temperature and then concentrated to 1 mL. Toluene (25 mL)
1337
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Organometallics
Article
Table 1. Crystal Data and Structure Refinement Details
7
8a
9a
10b″
11a
chem formula
mol wt
C19H30BF4NO
375.25
orthorhombic
P212121
10.5912(5)
14.0519(7)
14.0695(5)
90
C27H39BF4N2O
494.41
monoclinic
P21/n
C27H36BFN2O
434.39
monoclinic
P21/n
C37H52N2O
540.81
C62H88Li4N4O4
981.12
cryst syst
space group
a (Å)
triclinic
triclinic
P1
̅
P1
̅
16.1246(13)
10.6141(11)
34.007(3)
90
18.9985(15)
6.8889(3)
21.2758(16)
90
9.9061(6)
13.0594(10)
14.8115(12)
103.480(3)
108.736(4)
103.910(4)
1658.0(2)
2
9.5402(14)
10.9327(11)
14.383(2)
73.960(8)
87.426(7)
86.955(9)
1439.0(3)
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
90
100.304(6)
90
115.889(3)
90
90
2093.91(16)
4
5726.4(9)
8
2505.1(3)
4
Z
Dcalcd (g cm−3
)
1.190
1.147
1.152
1.083
1.132
μ(Mo Kα) (mm−1
F(000)
)
0.096
0.086
0.074
0.064
0.068
800
2112
936
592
532
no. of rflns collcd
no. of indep rflns
35900
2253
129840
10853
78144
4747
89409
40602
5395
8571
no. of obsd rflns (I > 2σ(I))
2014
4873
3918
4688
3931
Rint
0.026
0.070
0.027
0.049
0.051
no. of params refined
243
649
298
373
343
R1
wR2
S
0.053
0.061
0.071
0.055
0.051
0.154
0.147
0.174
0.145
0.137
1.135
0.988
1.151
0.976
1.030
Δρmin (e Å−3
)
−0.21
0.29
−0.19
0.17
−0.24
0.23
−0.21
0.18
−0.19
0.27
Δρmax (e Å−3
)
12a
13a
14a
15b
16a
19a
chem formula
C90H108Cl4N4O2Zr2
1602.04
C74H92Cl2N8O2Yb2
1542.54
monoclinic
P21/c
C74H112Cl5LiN4O7Th2
1817.95
C62H88N4O2U
1159.39
monoclinic
C2/c
C59H84N4O2Zr
972.52
C89H126ClLi3N6O5Th
1648.27
mol wt
cryst syst
space group
a (Å)
triclinic
triclinic
triclinic
triclinic
P1
̅
P1
̅
P1
P1
̅
̅
17.4358(9)
17.4360(12)
32.131(2)
89.401(3)
80.627(3)
65.259(4)
8734.9(10)
4
14.8213(7)
21.6499(5)
24.1822(11)
90
15.8182(5)
19.2508(5)
19.7418(6)
111.6569(12)
107.7145(14)
101.935(2)
4964.6(3)
2
21.2552(10)
10.7158(5)
25.9523(7)
90
15.5297(7)
18.9498(9)
21.2327(9)
75.631(2)
78.574(3)
70.549(2)
5661.8(5)
4
13.1462(6)
16.4882(6)
23.2295(11)
97.148(2)
104.141(2)
113.277(2)
4345.0(3)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
Dcalcd (g cm−3
μ(Mo Kα) (mm−1
98.984(2)
90
102.364(3)
90
7664.4(5)
4
5774.0(4)
4
)
1.218
1.337
1.216
1.334
1.141
1.260
)
0.407
2.541
3.167
2.855
0.236
1.798
F(000)
3360
3128
1816
2384
2088
1716
no. of rflns collcd
no. of indep rflns
292190
33105
270809
19782
179951
156817
8792
200992
21468
159943
18483
16265
no. of obsd rflns (I > 2σ
(I))
20664
12225
13984
7705
15185
13674
Rint
0.079
1853
0.073
0.225
1.033
−0.50
1.33
0.061
865
0.050
926
0.030
324
0.042
1299
0.054
0.165
1.064
−0.83
1.88
0.057
975
no. of params refined
R1
wR2
S
0.044
0.119
1.010
−0.95
1.27
0.079
0.230
1.044
−2.08
6.02
0.025
0.059
0.989
−0.94
0.90
0.036
0.081
1.022
−0.85
1.03
Δρmin (e Å−3
)
Δρmax (e Å−3
)
16b
17b
18b
19a
chem formula
mol wt
C62H88N4O2Zr
C70H108LiN4O4Yb
1249.58
C62H88N4O2Th
C89H126ClLi3N6O5Th
1648.27
1012.58
monoclinic
C2/c
1153.40
cryst syst
space group
a (Å)
monoclinic
P21/c
monoclinic
C2/c
triclinic
P1
̅
21.0006(3)
10.7340(2)
25.6378(5)
90
16.0461(2)
21.2603(5)
20.5180(5)
90
21.2874(9)
10.7327(3)
26.0590(11)
90
13.1462(6)
16.4882(6)
23.2295(11)
97.148(2)
b (Å)
c (Å)
α (deg)
1338
dx.doi.org/10.1021/om3010355 | Organometallics 2013, 32, 1328−1340

Organometallics
Article
Table 1. continued
16b
17b
18b
19a
104.141(2)
β (deg)
γ (deg)
V (Å3)
Z
102.3059(6)
90
107.9728(13)
90
102.213(2)
90
113.277(2)
4345.0(3)
2
5646.50(17)
4
6658.1(2)
4
5819.0(4)
4
Dcalcd (g cm−3
)
1.191
0.240
2176
1.247
1.453
2644
1.317
2.606
2376
1.260
1.798
1716
μ(Mo Kα) (mm−1
)
F(000)
no. of rflns collcd
no. of indep rflns
97610
5305
229111
20303
16366
0.032
749
92726
7405
159943
16265
13674
0.057
975
no. of obsd rflns (I > 2σ(I))
4787
6173
Rint
0.021
324
0.044
324
no. of params refined
R1
wR2
S
0.031
0.081
1.022
−0.44
0.38
0.028
0.069
1.008
−1.19
0.48
0.031
0.063
0.970
−1.40
0.55
0.036
0.081
1.022
−0.85
1.03
Δρmin (e Å−3
)
Δρmax (e Å−3
)
Synthesis of 17a. A 25 mL flask was charged with a stir bar, YbCl3
(41.6 mg, 0.149 mmol), 11a (146 mg, 0.298 mmol), and toluene (15
mL). The orange suspension was stirred at 70 °C for 2 days. The white
precipitate of LiCl was then filtered off through a Celite padded coarse
frit, and the volatiles were removed under reduced pressure to provide
17a as a deep orange powder (108 mg, 82%). Anal. Calcd for
C62H88LiN4O4Yb: C, 65.70; H, 7.83; N, 4.94. Found: C, 64.14; H,
7.98; N, 5.21. As for ligand 11a, poor C correlations were obtained
(s, Ar); 139.0 (s, Ar); 140.5 (s, Ar); 142.6 (s, Ar); 143.3 (s, Ar); 157.0
(s, C−O); 160.2 (s, CN); 165.1 ppm (s, CN).
Structure Determination by X-ray Diffraction. The data were
collected at 150(2) K on a Nonius Kappa-CCD area detector
diffractometer28 using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). The crystals were introduced into glass capillaries with a
protecting “Paratone-N” oil (Hampton Research) coating. The unit
cell parameters were determined from 10 frames and then refined on
all data. The data (combinations of φ and ω scans with a minimum
redundancy of 4 for 90% of the reflections) were processed with
HKL2000.29 Absorption effects were corrected empirically with the
program SCALEPACK,29 except for the compounds containing only
light atoms. The structures were solved by direct methods or Patterson
map interpretation with SHELXS-97 (except when an isostructural
model could be used as a starting point), expanded by subsequent
Fourier-difference synthesis, and refined by full-matrix least squares on
F2 with SHELXL-97.30 All non-hydrogen atoms were refined with
anisotropic displacement parameters. When present, the hydrogen
atoms bound to oxygen or nitrogen atoms were found on Fourier
difference maps. The carbon-bound hydrogen atoms were introduced
at calculated positions; all hydrogen atoms were treated as riding
atoms with an isotropic displacement parameter equal to 1.2 times that
of the parent atom (1.5 for CH3). In the absence of a suitable
anomalous scatterer in 7, the Friedel pairs have been merged. In both
12a and 14a, one tert-butyl substituent was found to be rotationally
disordered over two positions, which were refined with occupancy
parameters constrained to sum to unity. In 12a−14a, some solvent
molecules were given an occupancy parameter of 0.5 in order to retain
acceptable displacement parameters. Voids in the lattice of 14a likely
indicate the presence of other, unresolved solvent molecules. Crystal
data and structure refinement parameters are given in Table 1. The
molecular plots were drawn with ORTEP-3.31
1
while several attempts had been made. H NMR (THF-d8, 298 K): δ
−40.9 (s, 1H); −36.1 (s, 3H); −17.1 (s, 1H); −6.8 (s, 9H); −5.0 (s,
3H); 4.6 (s, 1H); 8.8 (s, 3H); 13.6 (s, 1H); 13.7 (s, 1H); 15.1 (s, 3H);
15.4 (s, 3H); 18.4 (s, 3H); 21.1 (s, 1H); 21.6 (s, 1H); 45.0 (br s, 1H);
78.1 ppm (br s, 1H).
Synthesis of 17b. A 25 mL flask was charged with a stir bar, YbCl3
(26.4 mg, 0.0945 mmol), 11b (117 mg, 0.189 mmol), and toluene (15
mL). The yellow-orange suspension was stirred for 12 h at room
temperature. The white precipitate was then filtered off through a
Celite padded coarse frit, and the volatiles were removed under
reduced pressure to provide 17b as a deep orange powder (108 mg,
82%). Orange monocrystals of 17b·Et2O, with Li(Et2O) countercation
instead of Li(THF)2, were recovered by slow diffusion of pentane over
a diethyl ether solution of 17b and were analyzed using NMR
spectroscopy. Anal. Calcd for C70H104LiN4O4Yb: C, 67.50; H, 8.42; N,
1
4.50. Found: C, 67.83; H, 8.32; N, 4.65. H NMR (C6D6, 298 K): δ
−45.1 (s, 1H); −27.1 (s, 3H); −22.9 (s, 1H); −14.5 (s, 3H); −8.0 (s,
3H); −5.6 (m, 1H+2H(Et2O)); −2.56 (s, 3H); 2.1 (s, 2H); 3.7 (s, 9H,
C(CH3)3); 7.1 (m, 3H, Et2O); 7.7 (s, 1H); 14.2 (s, 3H); 15.0 (s, 9H,
C(CH3)3); 17.5 (s, 1H); 20.5 (s, 1H); 37.2 ppm (s, 3H).
Synthesis of 18b. A 25 mL flask was charged with a stir bar,
ThCl4(DME)2 (239 mg, 0.431 mmol), 11b (534 mg, 0.862 mmol),
and toluene (25 mL). The orange suspension was heated to 100 °C for
1 day and then cooled to room temperature. The white precipitate was
filtered off over a fine-porosity fritted filter. The volatiles were
removed under reduced pressure to provide 18b as a yellow powder
(495 mg, 99%). Yellow monocrystals were recovered by recrystalliza-
tion from toluene. Anal. Calcd for C62H88N4O2Th: C, 64.56; H, 7.69;
N, 4.86. Found: C, 64.34; H, 7.65; N, 4.92. 1H NMR (C6D6, 298 K): δ
1.03 (dd, J = 4.0 Hz, 6.0 Hz, 6H, CH(CH3)2); 1.24 (s, 9H, C(CH3)3);
1.25 (dd, J = 4.0 Hz, 6.0 Hz, 6H, CH(CH3)2); 1.34 (s, 9H, C(CH3)3);
1.66 (s, 3H, α-CH3); 2.02 (s, 3H, α-CH3); 3.02 (m, 2H, CH(CH3)2);
4.69 (s, 1H, β-CH); 6.77 (d, J = 2.0 Hz, 1H, Ar-H); 7.03 (m, 3H, Ar-
H); 7.12 ppm (s, 1H, Ar-H). 13C NMR (C6D6, 298 K): δ 23.4 (s, α-
CH3); 24.6 (s, CH(CH3)2); 24.9 (s, CH(CH3)2); 25.1 (s, CH(CH3)2);
25.7 (s, α-CH3); 25.8 (s, CH(CH3)2); 28.8 (s, CH(CH3)2); 30.2 (s,
C(CH3)3); 31.5 (s, CH(CH3)2); 32.1 (s, C(CH3)3); 34.4 (s,
C(CH3)3); 35.0 (s, C(CH3)3); 97.5 (s, β-CH); 117.4 (s, Ar); 119.1
(s, Ar); 124.3 (s, Ar); 124.9 (s, Ar); 126.3 (s, Ar); 128.4 (s, Ar); 135.8
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving atomic positions and displacement parameters,
anisotropic displacement parameters, and bond lengths and
bond angles. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: thibault.cantat@cea.fr. Fax: +33 1 6908 6640. Tel: +33
1 6908 4338.
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dx.doi.org/10.1021/om3010355 | Organometallics 2013, 32, 1328−1340

Organometallics
Article
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
For financial support of this work, we acknowledge the CEA,
CNRS, ANR (Starting Grant to T.C.) and GNR PARIS
(Research Grant to T.C.).
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