Synthesis and characterization of bidentate rare-earth iminophosphorane o-aryl complexes and their behavior as catalysts for the polymerization of 1,3-butadiene

Article abstract of DOI:10.1021/om300389v

O-Aryllithium complexes are easily prepared from stable aminophosphonium salts, and their coordination to rare-earth metals was studied. The ligand to metal ratio in the formed complexes was shown to depend exclusively on the substituent on the nitrogen a

Full text of DOI:10.1021/om300389v

Article
pubs.acs.org/Organometallics
Synthesis and Characterization of Bidentate Rare-Earth
Iminophosphorane o-Aryl Complexes and Their Behavior As
Catalysts for the Polymerization of 1,3-Butadiene
Elsa Martinez-Arripe,† Francois Jean-Baptiste-dit-Dominique,†,‡ Audrey Auffrant,†
̧
Xavier-Frederic Le Goff,† Julien Thuilliez,‡ and Francois Nief*,†
̧
́
́
†Laboratoire Het
‡Manufacture Franca
́
er
́
oel
ise des Pneumatiques Michelin, Bat
* Supporting Information
́
em
́
ents et Coordination, Ecole Polytechnique, CNRS, 91128 Palaiseau, France
̧
̂
iment C1-Cataroux, 23, Place des Carmes, 63040 Clermont-Ferrand, France
S
ABSTRACT: O-Aryllithium complexes are easily prepared
from stable aminophosphonium salts, and their coordination
to rare-earth metals was studied. The ligand to metal ratio in
the formed complexes was shown to depend exclusively on the
substituent on the nitrogen atom of the ligand. Aryllithium
derivatives 3a and 3b, exhibiting bulky groups (SiMe3 and tBu,
respectively), gave monocoordinated yttrium complexes 4a-Y
and 4b-Y. On the other hand, with aryllithium 3a, possessing an isopropyl at nitrogen, complexes of YIII, NdIII, and GdIII with a
2:1 ligand to metal ratio could be obtained. Finally with less hindered ligands such as 6c, featuring an n-butyl substituent,
triscoordinated Y, Nd, and La complexes were accessible. X-ray crystal structures have been obtained with all three
stoichiometries. These complexes were employed as catalyst precursors for 1,3-butadiene polymerization using various activators.
Yttrium complexes were found ineffective, but some neodymium complexes achieved highly selective polymerization of 1,3-
butadiene, giving up to 95% of 1,4-cis-polybutadiene albeit with mild activity.
iminophosphoranes, and thus they have no accepting proper-
ties; moreover, because of the presence of two lone pairs at the
nitrogen atom, they behave as strong donors, and the
phosphorus−nitrogen bond is more polarized than in imines.
Iminophosphoranes, though less investigated than imines, have
shown good potential in coordination chemistry and more
recently in catalysis. In particular the Cavell and Stephan
groups used such ligands in olefin polymerization.9 For a few
years our group has developed facile and straightforward
synthetic methodologies to access different iminophosphorane-
based ligand systems,10 which rely on the Kirsanov reaction11
involving bromination of a phosphine followed by reaction with
a primary amine in the presence of a base. The advantage of
such a protocol over the more common Staudinger reaction12 is
that it avoids the handling of azides, which are often hazardous,
and allows a greater diversity of substituents on the nitrogen
atom. To the best of our knowledge, there is no example of
butadiene 1,4-cis-polymerization with lanthanide complexes
bearing iminophosphorane ligands.
INTRODUCTION
■
The search for lanthanide-based catalysts for the cis-1,4-
selective polymerization of dienes has been a very important
research area in the past decades, due to the applications of
polydienes with high stereoregularity in the rubber industry.
Research on new formulations derived from conventional
Ziegler−Natta catalysts, composed of lanthanide carboxylates,1
phosphates, or alkoxides2 with alkylaluminum and alkylalumi-
num chlorides as coactivators, has been a hot topic in both the
academic and industrial domains.3
In order to improve catalyst activity and solubility for
butadiene polymerization, new lanthanide complexes featuring
ancillary ligands have been studied. In this area, cyclo-
pentadienyl metal complexes4 have played a major role.
Other ligand systems such as pyridyl-functionalized cyclo-
pentadienyl,5 bis(phosphinophenyl)amido-ligand,6 bis(amido)-
cyclophosphazane,7 or imines8 have also been proposed.
Among them, catalysts featuring imine ligands have shown
particularly high activity and selectivity. This prompted us to
investigate the potential of iminophosphorane ligands (the
phosphorus analogue of imines) for such applications. The
apparent similarity between the imine and iminophosphorane
functional groups stems from the fact that the electro-
negativities of phosphorus and carbon are roughly the same
and thus that the polarization of the CN and PN bonds
should be similar. However, the P−N bond of an
iminophosphorane is by far more polarized than the C−N
bond of an imine. In addition, there is no π system in
The good results of Cui et al.8 with tridentate bis(imine) o-
aryl−rare-earth complexes prompted us to try to synthesize
chelating iminophosphorane o-aryl−rare-earth complexes. In
this paper we present the synthesis and isolation of
iminophosphorane o-aryllithium complexes, their use as
precursors to new iminophosphorane o-aryl−rare-earth (Y,
Received: May 9, 2012
Published: June 21, 2012
© 2012 American Chemical Society
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La, Nd, Gd) complexes, and the use of these complexes in
diene polymerization.
RESULTS AND DISCUSSION
■
Ligands Synthesis. Steiner and Stalke have shown that the
iminophosphorane Ph3PNSiMe3 (2a) could undergo o-
lithiation of one phenyl group using an alkyllithium, thus
yielding the corresponding lithium salt 3a, which was
structurally characterized as a solvated dimer: [(o-C6H4-
PPh2NSiMe3)Li]2(Et2O) (3a·0.5 Et2O)2.13
Scheme 1. Synthesis of Iminophosphorane Anion 3a
The Kirsanov procedure allows the synthesis of diversely
substituted aminophosphonium salts, which can be transformed
in situ into the corresponding iminophosphoranes by action of
a strong base. Thus, reaction of aminophosphonium salts 1b−d
(respectively bearing tBu, iPr, and nBu groups at nitrogen) with
Figure 1. ORTEP plots (50% ellipsoids) of lithium complexes [(o-
C6H4-PPh2NtBu)Li]2(THF), (3b·0.5THF)2 (top), and [(o-C6H4-
PPh2NtBu)Li]2(THF)2, (3c·THF)2 (bottom). There are four
independent but similar molecules of (3b·0.5THF)2 and two
independent but similar molecules of (3c·THF)2 in the unit cells,
and only one of each is represented. Hydrogen atoms are omitted for
clarity. Selected bond lengths (Å) and angles (deg) for (3b·0.5THF)2:
C(2)−Li(1) = 2.318(6), C(24)−Li(1) = 2.333(6), N(1)−Li(1) =
2.037(5), N(2)−Li(1) = 2.041(5, C(24)−Li(2) = 2.118(7), C(2)−
Li(2) = 2.128(7), O(1)−Li(2) = 1.931(6), N(1)−Li(1)−N(2) =
135.1(3), N(1)−Li(1)−C(2) = 90.3(2), C(2)−Li(1)−C(24) =
107.5(2), N(2)−Li(1)−C(24) = 87.6(2), Li(1)−C(2)−Li(2) =
63.2(2), C(2)−Li(2)−C(24) = 124.1(3), Li(2)−C(24)−Li(1) =
63.1(2), C(24)−Li(1)−C(2) = 107.5(2), O(1)−Li(2)−C(2) =
113.3(3), O(1)−Li(2)−C(24) = 115.5(3); for (3c·THF)2: C(2)−
Li(1) = 2.199(2), C(2)−Li(1_1) = 2.321(2), N(1)−Li(1) = 2.046(2),
O(1)−Li(1) = 1.964(3), Li(1)−C(2)−Li(1_1) = 67.3(1), N(1)−
Li(1)−C(2) = 92.2(1), O(1)−Li(1)−C(2_1) = 101.3(1), O(1)−
Li(1)−N(1) = 114.8(1), C(2)−Li(1)−C(2_1) = 112.7(1).
n
2 equiv of BuLi in toluene/hexane directly generated the
iminophosphorane anions as unsolvated lithium salts 3b−d in a
one-pot procedure, without isolation of the intermediate
iminophosphoranes (Scheme 2).
Colorless monocrystals of compounds 3b−d as solvates
could be obtained by slow diffusion of pentane in THF or ether
after several days at room temperature. The dimeric X-ray solid-
state structure of [(o-C6H4-PPh2NtBu)Li]2(THF),
(3b·0.5THF)2, is depicted in Figure 1 (there are four
independent but similar molecules in the unit cell, and only
one is represented), and that of [(o-C6H4-PPh2NnBu)-
Li]2(Et2O), (3d·0.5Et2O)2, is given in the Supporting
Information. The crystallographic data of the reported
structures are gathered in Table 1. Both structures are similar
to that of (3a·0.5Et2O)2,13 where one lithium atom (Li1) is
bonded to the two PN moieties and the other lithium (Li2)
is coordinated to the solvent. For these compounds, Li1 resides
in a distorted tetrahedral environment, while Li2 is almost
planar trigonal. The Li1−C distances (Li1−C mean = 2.35(4)Å
for (3b·0.5THF)2, 2.39(3) Å for (3d·0.5Et2O)2) are on average
0.2 Å longer than the Li2−C distances (Li2−C2 mean =
2.13(4) Å for (3b·0.5THF)2, 2.15(1) Å for (3d·0.5Et2O)2). In
contrast, [(o-C6H4-PPh2NtBu)Li]2(THF)2, (3c·THF)2, dis-
plays an original centrosymmetric dimeric structure, which is
depicted in Figure 1. The two PN functions are bonded to
different lithium atoms, which are both coordinated to THF
(Figure 1). Here, the two lithium atoms have an identical
tetrahedral geometry and show different Li−C distances for
each lithium atom (Li1−C2 mean = 2.17(1) Å and Li1_1−C2
mean = 2.37(2) Å).
Rare-Earth Complexes Synthesis. Reactions of Aryl-
lithiums 3a−d with [LnCl3(THF)3] (Ln = Y, La, Nd, Gd).
Preliminary experiments between aryllithium precursors in
varying stoichiometric amounts and [LnCl3(THF)3] were
performed in NMR tubes and monitored by 31P NMR
spectroscopy (except with Ln = Gd, for which complexes are
NMR silent because of severe line broadening and isotropic
magnetic susceptibility of GdIII). It soon appeared that the
ligand:metal ratio in the complexes formed in solution was
Scheme 2. Synthesis of Aminophosphonium Salts 1b−d and Iminophosphorane Anions 3b−d
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Scheme 3. Reactions of Iminophosphorane Anions 3a−d with [LnCl3(THF)3] in Molar Ratios 1:1 (a), 2:1 (b), and 3:1 (c)
much more dependent on the steric properties of the nitrogen
substituent of the iminophosphorane than on the size of the
rare-earth ion.
For example, it was found that with ligand 3c the optimum
ligand:metal (Y, Gd, or Nd) ratio was 2:1. When
[LnCl3(THF)3] (Ln = Y or Nd) and 3c were mixed in
proportions 1:1 and slightly above, 31P NMR showed the
disappearance of 3c and the appearance of two new resonances,
which were attributed to complexes with 1:1 and 2:1
ligand:metal ratios; when these proportions were raised to
3:1 or above, the reaction did not go to completion since 31P
NMR revealed the presence of both 2:1 and 3:1 complexes
together with that of starting 3c. When the 3c:LnCl3
proportion was exactly 2:1, there was a major peak, and indeed
it has been possible to isolate the corresponding 2:1 complex
(see below).
Figure 2. ORTEP plot (50% ellipsoids) of [o-C6H4-(Ph2)PN-
SiMe3]YCl4Li2(THF)4 (4a-Y·2LiCl·4THF) showing the atom-labeling
Likewise, with ligand 3d, it has been determined by similar
experiments that the optimum ligand:metal ratio was 3:1.
With ligands 3a and 3b, the results were only conclusive in
the case of yttrium, for which the corresponding 1:1 complexes
were isolated. (Scheme 3).
scheme. Hydrogen atoms are omitted for clarity. Selected bonds
lengths [Å] and angles [deg]: Y1−N1 = 2.426(3), Y1−C2 = 2.442(4),
Y1−Cl4 = 2.639(1), Y1−Cl1 = 2.657(1), Y1−Cl3 = 2.675(1), Y1−Cl2
= 2.709(1), N1−Y1−C2 = 77.0(1), Cl4−Y1−Cl3 = 83.50(3), Cl1−
Y1−Cl2 = 83.75(3), Cl3−Y1−Cl2 = 88.19(3).
Monocoordinated Complexes 4a-Y and 4b-Y. Solutions of
1 equiv of compounds 3a and 3b in THF were added to a
suspension of [YCl3(THF)3] (1 equiv) in THF and stirred 30
min. After solubilization of the mixture and appearance of a
yellow coloration, the 31P NMR indicated the formation of a
new product. Coordination of the ligands to yttrium was
evidenced by a downfield shift, from a singlet at 16 ppm
(respectively 12 ppm) to a doublet at 28 ppm (respectively 25
ppm), with a JPY coupling constant of 10 Hz (respectively 18
Hz), corresponding to complexes 4a-Y (respectively 4b-Y). In
the solid state, 4a-Y is present as an ate-complex, [o-C6H4-
(Ph2)PN-SiMe3]Y[(μ-Cl)2Li(THF)2]2 (4a-Y·2LiCl·4THF),
as established by single-crystal X-ray diffraction (Figure 2).
Although the conversion appeared complete by NMR, no more
than a few crystals of pure compound could be obtained by
concentration of the reaction mixture. X-ray analyses showed
that complex 4a-Y·2LiCl·4THF crystallizes in the monoclinic
space group P21/c with four molecules per unit cell. The
bridging chlorides are bonded with two lithium atoms, which
are each solvated by two molecules of THF. The molecule thus
adopts a pseudo-octahedral geometry, with the atoms C2, Cl1,
Cl2, and Cl4 equatorial and N1 and Cl3 in apical positions.
1
4b-Y was characterized only by 31P, H, and 13C NMR
spectroscopy. The 31P NMR spectrum confirms that the
yttrium is metalated, as the iminophosphorane gives a doublet
2
with a JPY = 18 Hz, a value that is typical for Y−P coupling.
The signal of the proton in ortho-position of the metallic center
in the 1H NMR is deshielded from 8.31 ppm in 3b to 8.62 ppm
in 4b-Y.
Formation of rare-earth ate-complexes is less likely to occur
when starting from organopotassium precursors because
potassium salts are easier to eliminate by precipitation due to
their lower solubility. In order to try to synthesize a potassium
precursor analogous to 3, a Li/K exchange was attempted by
reacting 3d with KOtBu in hexane. However, to our surprise, no
potassium analogue 3d′ of 3d was observed, but a potassium
phosphamide 8 was isolated instead; a mechanism for this
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transformation is proposed in Scheme 4. Presumably, the
higher nucleophilicity of the transient potassium anion 3d′
Y−C and Y−N bond lengths are close to those obtained for the
monocoordinated complex 4a-Y·2LiCl·4THF.
Triscoordinated Complexes 6d-Ln (Ln = Y, La, Nd). In the
same manner, addition of 3 equiv of the lithiated compound 3d
to 1 equiv of [LnCl3(THF)3] in THF followed by 30 min of
stirring allowed the formation of unsolvated, homoleptic
complexes 6d-Y, 6d-Nd, and 6d-La. After evaporation of the
solvent, the reaction mixture was extracted with toluene and
LiCl separated by centrifugation. Monocrystals of [o-C6H4-
(Ph2)PN-nBu]3Nd (6d-Nd) and [o-C6H4-(Ph2)P
N-nBu]3La (6d-La) were obtained by a slow diffusion of
pentane in THF (5:1) at −30 °C. The solid-state structure of
complex 6d-Nd is presented in Figure 4, and that of complex
6d-La in the Supporting Information.
Scheme 4. Proposed Mechanism for the Formation of
Compound 8
induces a nucleophilic attack on an adjacent phenyl ring. This
mechanism is reminiscent of that involved in the formation of
dibenzophospholes from the reaction of amides with
tetraphenylphosphonium salts.14
Biscoordinated Complexes 5c-Ln (Ln = Y, Nd, Gd).
Complexes 5c-Y and 5c-Gd have been synthesized with a
synthetic protocol similar to 4a. 31P NMR monitoring confirms
the formation of the compounds 5c-Y and 5c-Nd, with 31P
NMR shifts at 35 and 58 ppm in THF, respectively, and a
3
coupling constant JY−P = 17 Hz for the complex 5c-Y. For
Figure 4. ORTEP plot (30% ellipsoids) of [o-C6H4-(Ph2)P
N-nBu]3Nd (6d-Nd) showing the atom-labeling scheme. Hydrogen
atoms are omitted for clarity. Selected bonds lengths [Å] and angles
[deg]: Nd1−N1 = 2.490(3), Nd1−N2 = 2.500(3), Nd1−N3 =
2.579(3), Nd1−C43 = 2.601(4), Nd1−C19 = 2.611(4), Nd1−C2 =
2.647(3), N3−Nd1−C43 = 68.3(1), N1−Nd1−C2 = 71.2(1), N2−
Nd1−C19 = 71.6(1).
small metal centers (Y, Gd) workup by coevaporation of THF
with toluene and centrifugation of LiCl salts yielded analytically
pure products, while during the workup, 5c-Nd was always
accompanied by an impurity presumably because of ligand
redistribution reaction. The NMR data in the Experimental
Section thus refer to 5c-Nd obtained in situ. Monocrystals
could be obtained by slow diffusion of pentane in a THF
solution of 5c-Y, which crystallized as a solvate, [o-C6H4-
(Ph2)PN-iPr]2YCl(THF) (5c-Y·THF), the solid-state struc-
ture of which was established by single-crystal X-ray diffraction
(Figure 3). This complex adopts a pseudo-octahedral geometry,
with the atoms C2, C23, Cl1, and O in equatorial positions and
the nitrogen atom in apical position. The Y−C bonds are nearly
equivalent (Y−C = 2.455(2) Å, Y−C = 2.491(3) Å), as are Y−
N distances (Y1−N1 2.421(2) Å, Y1−N2 2.386(2) Å). These
Complex 6d-Nd crystallizes in the triclinic space group P1
with two molecules per unit cell. The molecule adopts a
distorted-octahedral geometry, with the atoms C2, N1, N2, and
N3 in equatorial positions and C19 and C43 in apical positions.
The steric hindrance around the Nd metal center influences the
Nd−N and Nd−C bond lengths. Indeed, one ligand moiety is
more distant from Nd with longer Nd−C (2.647(3) Å) and
Nd−N (2.579(3) Å) bonds vs 2.606(4) and 2.495(3) Å on
average for the two other ligands.
̅
Protonation of 6d-Y (respectively 6d-Nd) with stoichio-
metric HNEt3BPh4 in THF was monitored by 31P NMR
spectroscopy. After 5 min, two new signals, at 40 and 3 ppm
(respectively 43 and 3 ppm) in a 2:1 ratio were present in the
spectrum; in the yttrium case, a doublet structure with a 2JPY
=
16.5 Hz was present on the peak at 40 ppm. The peak at 3 ppm
corresponds to the chemical shift of free iminophosphorane.
These data are consistent with selective protonation of one aryl
group by HNEt3BPh4, thus yielding a neutral iminophosphor-
ane and a biscoordinated cationic lanthanide complex (Scheme
5)
Preliminary Results on Butadiene Polymerization. As
noted in the Introduction, cis-1,4-selective polymerization of
dienes is a very important process in the rubber industry, and
among the variety of organometallic complexes used for
butadiene polymerization, rare earth metal based ones are
efficient and attractive candidates. Among these catalysts, only
Figure 3. ORTEP plot (50% ellipsoids) of [o-C6H4-(Ph2)P
N-iPr]2YCl(THF) (5c-Y·THF) showing the atom-labeling scheme.
Hydrogen atoms are omitted for clarity. Selected bonds lengths [Å]
and angles [deg]: Y(1)−N(2) 2.386(2), Y(1)−N(1) 2.421(2), Y(1)−
C(23) 2.455(2), Y(1)−C(2) 2.491(3), N(2)−Y(1)−N(1) 166.81(7),
N(2)−Y(1)−C(23) 76.26(7), N(1)−Y(1)−C(2) 74.98(7), C(23)−
Y(1)−C(2) 86.63(8).
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Scheme 5. Reaction of 6d-Y and 6d-Nd with a Stoichiometric Amount of HNEt3BPh4 in THF
a
Table 2. Summary of the Butadiene Polymerization Results
b
b
c
entry
complexes ([Ln])
activator ([Act]/[Ln])
HDIBA (10)
conv (%)
1,4-cis (%)
1,4-trans(%)
1,2 (%)
1
2
3
4
5
6
5c-Y
2
21
40
70
3
n.d.
95
n.d.
5
n.d.
<1
5c-Nd
5c-Nd
5c-Nd
6d-Y
HDIBA (10)
HNMe2Ph[B(C6F5)](1)/TIBA (10)
HNMe2Ph[B(C6F5)](2)/TIBA (10)
HNEt3BPh4/TIBA (10)
91
9
<1
87
8
5
n.d.
n.d.
n.d.
6d-Nd
HNEt3BPh4/TIBA (10)
2
n.d.
n.d.
n.d.
a
b
Conditions: 0.1 mmol of [Ln] in 60 mL of methylcyclohexane, Bd/[Ln] = 5000, T = 70°C, 2 h. Determined by 13C NMR spectroscopy.
c
1
Determined by H NMR spectroscopy.
one system involving an amido-iminophosphorane bifunctional
ligand had been tested, which has shown medium activity and
high trans-selectivity.15 To the best of our knowledge, there are
no examples of catalyst systems including iminophosphorane-
based complexes yielding cis-polybutadiene. The catalytic
performance of yttrium and neodymium complexes 5c-Y, 5c-
Nd, 6d-Y, and 6d-Nd for the polymerization of butadiene (Bd)
has thus been investigated, in the presence of activators:
di(isobutyl)aluminum (HDIBA), tris(isobutyl)aluminum
(TIBA), and a proton source, (HNMe2Ph)[B(C6F5)4]. The
polymerization data are summarized in Table 2.
These results show that the polymerization activity was
drastically affected by the nature of the metal center, since none
of the yttrium complexes were found to be active. Although the
complexes alone do not induce the polymerization of
butadiene, addition of HDIBA (HDIBA/Nd = 10) to complex
5c-Nd can initiate polymerization, giving high selectivity with
95% 1,4-cis-polybutadiene but low activity with only 20% yield
of polymer after 2 h. The activity could be increased to 40%
after addition of 1 equiv of the proton source (HNMe2Ph)-
[B(C6F5)4] and TIBA, with a slight decrease of the selectivity. If
another equivalent of proton source is added, activity is again
increased, together with a larger decrease in selectivity. No
activity was obtained by protonation of complexes 6d-Y and
6d-Nd, which may be due to an interaction of the vacant site
either with the counterion or with the liberated free
iminophosphorane acting as a Lewis base.
tal ratio in the isolated complexes can be 1:1, 2:1, or 3:1
depending on the nitrogen substituent of the iminophosphor-
ane. X-ray crystal structures have been obtained with all three
stoichiometries. Preliminary attempts at the polymerization of
1,3-butadiene with the title complexes were achieved. We
report the first example of highly selective (up to 95%) 1,4-cis-
polybutadiene synthesized with some of these complexes as
catalysts, with medium activity, however. Using the complexes
in the present study as starting materials, we plan to develop
new complexes, such as bis-alkyl o-aryl iminophosphorane rare-
earth compounds, that may have higher activity in the 1,3-
butadiene polymerization reaction.15
EXPERIMENTAL SECTION
■
General Procedures. All reactions involving air-sensitive com-
pounds were performed under a protective atmosphere of dry nitrogen
or argon with oxygen-free solvents. Triethylamine was dried on KOH
before use, and all other commercially available reagents were obtained
from the suppliers and used without further purification. Lithium salt
3a was prepared from iminophosphorane 2a as described in the
literature.12 NMR spectra of all synthesized compounds were
measured at ambient temperature (20 °C) with a Bruker Avance
300 spectrometer. Chemical shifts are expressed in parts per million
(ppm) relative to tetramethylsilane. The microstructure of polymers
was determined by NMR using a Bruker DRX 400 spectrometer.
Microanalytical data were obtained through the London Metropolitan
University Science Centre.
Synthesis of Ph3P+-NH-R·Br−, 1b−d (R = tBu, iPr, nBu).
Bromine (38.1 mmol) was slowly added to a solution of
triphenylphosphine (38.1 mmol) in dichloromethane (200 mL)
cooled to −78 °C. After 30 min, R-NH2 (38.1 mmol) and
triethylamine (38.1 mmol) were added to the cloudy solution of the
bromophosphonium salt. The clear solution obtained after cold bath
removal was washed twice with water and extracted with dichloro-
methane (2 × 100 mL). The organic layer was dried over MgSO4 and
concentrated to 50 mL under vacuum. Et2O (150 mL) were then
added, whereupon a precipitate appeared. After filtration, this
CONCLUSION
■
We have found a simple and efficient method for the synthesis
of iminophosphorane o-aryllithium complexes directly from
stable aminophosphonium salts, without the need to isolate the
intermediate iminophosphoranes. These aryllithium salts have
been successively used as precursors to the respective rare-earth
iminophosphorane o-aryl complexes. The optimum ligand:me-
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precipitate was washed with Et2O (50 mL) and dried, and compounds
1b−d were obtained as white solids.
3JCP = 3.7 Hz, CH3), 128.4 (d, 3JCP = 3.5 Hz, p-CH (PhYP)), 128.9 (d,
3
3JCP = 11.3 Hz, m-CH (Ph2P)), 131.5 (d, JCP = 2.7 Hz, m-CH
1b (R = tBu): yield 80%. 31P{1H} NMR (CDCl3): δ 30.8 (s, P). 1H
NMR (CDCl3): δ 7.96 (m, 6H, HAr), 7.74 (m, 3H, HAr), 7.62 (m, 6H,
4
2
(PhYP)), 132.1 (d, JCP = 2.2 Hz, p-CH (Ph2P)), 132.7 (d, JCP = 10
Hz, m-CH (PhYP)), 134.0 (d, 2JCP = 9.8 Hz, o-CH (Ph2P)), 134.9 (d,
1JCP = 85.5 Hz, Cquat (Ph2P)), 140.4 (d, 1JCP = 26.3 Hz, o-CH (PhYP)),
t
HAr), 7.43 (s, 1H, NH), 1.34 (s, 9H, Bu).
1c (R = iPr): yield 84%. 31P{1H} NMR (CDCl3): δ 37.9 (s, P). 1H
NMR (CDCl3): δ 7.98 (m, 7H, NH and HAr), 7.71 (m, 3H, HAr), 7.62
1
1
143.3 (d, JCP = 124.7 Hz, o-CH (PhYP)), 195.4 (d, JCP = 45.5 Hz,
Cquat (PhYP)).
i
i
Synthesis of [o-C6H4-(Ph2)PN-tBu]YCl2, 4b-Y. To a suspen-
sion of YCl3(THF)3.5] (0.19 mmol) in THF was added a solution of
3b (0.19 mmol) in THF (5 mL) at room temperature. The solution
was stirred for 30 min and evaporated under vacuum. LiCl salts were
precipitated with toluene and removed by centrifugation. After
evaporation to dryness under vacuum, a yellow powder was obtained.
4b-Y: yield 60%. 31P{1H} NMR (THF-d8): δ 25.3 (d, 1P, JP−Y = 18
(m, 6H, HAr), 3.21 (m, 1H, Pr), 1.42 (d, 6H, Pr).
1d (R = nBu): yield 85%. 31P{1H} NMR (CDCl3): δ 36.0 (s, P). 1H
NMR (CDCl3): δ 7.99 (m, 1H, NH), 7.84 (m, 9H, HAr), 7.63 (m, 6H,
HAr), 3.02 (m, 2H,NCH2), 2.62 (m, 2H,NCH2CH2), 1.18 (m,
2H,CH2CH3), 0.71 (d, 3H, CH3).
t
i
n
Synthesis of [o-C6H4-Ph2PN-R]Li, 3b−d (R = Bu, Pr, Bu).
n-Butyllithium (3.75 mL, 1.6 M in hexane, 6 mmol) was added
dropwise to a suspension of aminophosphonium salts 1b−d (6 mmol)
in toluene (30 mL) cooled to −78 °C. After cold bath removal, the
reaction was stirred for 30 min. Salts were centrifuged, and compounds
3b−d were obtained as yellow to orange solids after evaporation to
dryness, washing of the residue with 20 mL of pentane, and drying
under vacuum. The crude, unsolvated 3b−d were of sufficient purity
to be used as starting materials for the synthesis of compounds 4, 5,
and 6, as shown by NMR, while analytically pure products were
obtained as solvates by slow diffusion of pentane into THF or diethyl
ether solutions of the compounds at 25 °C.
1
t
Hz). H NMR (THF-d8): δ 1.27 (s, 9H, HBu), 6.74 (m, 1H, o-PhY),
6.90 (m, 2H, o-PhY, m-PhY), 7.43 (m, 6H, o-(Ph2P), p-(Ph2P)), 7.86
3
(d, JHY = 6 Hz, 1H, o-PhY), 8.09 (m, 4H, o-Ph2P). 13C{1H} NMR
3
(THF-d8): δ 26.1 (s, THFsolv), 33.3 (d, JCP = 8.4 Hz, CH3), 55.5 (d,
2
JCP = 5.7 Hz, CBu), 68.01 (s, THFsolv), 124.8 (d, 2JCP = 15.5 Hz, o-CH
t
(PhY)), 127.7 (s, p-CH (PhY)), 128.6 (d, 3JCP = 11 Hz, m-CH (Ph2P)),
129.1 (s, m-CH (PhY)), 131.6 (s, p-CH (Ph2P)), 133.1 (d, JCP = 9.5
3
1
Hz, o-CH (PhY)), 134.5 (d, JCP = 77.4 Hz, Cquat-(Ph2P)), 134.6 (d,
2JCP = 9.5 Hz, o-CH (Ph2P)), 141.5 (d, 1JCP = 133.3 Hz, o-Cquat (PhY)),
184.4 (d, 2JCP = 39 Hz, i-Cquat (PhY)). No meaningful analysis could be
obtained.
3b (R = tBu): yield 61%. 31P{1H} NMR (toluene-d8): δ 12.8 (s, P).
1H (C6D6): δ 8.31 (m, 1H, HAr), 7.94 (m, 4H, HAr), 7.28 (m, 2H,
HAr), 7.03 (m, 7H, HAr), 1.13 (s, 9H, HtBu). 13C{1H} NMR (C6D6): δ
35.69 (s, CH3), 52.8 (s, Cquat), 125.1 (d, 2JCP = 16 Hz, o-CH (PhLiP)),
127.8 (s, p-CH (PhLiP)), 128.5 (d, m-CH (Ph2P)), 130.5 (d, 3JCP = 27
Hz, m-CH (PhLiP)), 130.8 (s, p-CH (Ph2P)), 134.2 (d, 2JCP = 9 Hz, o-
CH (Ph2P)), 136.8 (d, 1JCP = 73 Hz, Cquat-(Ph2P)), 139.8 (d, 3JCP = 27
Hz, m-CH (PhLiP)), 146.6 (d, 1JCP = 143 Hz, Cquat-(PhLiP)), 189.6 (d,
2JCP = 47 Hz, CLi (PhLiP)). Anal. Calcd for 3b·Et2O, C26H33LiNPO
(406.52): C, 75.53; H, 8.04; N, 3.39. Found: C, 75.41; H, 7.82; N,
3.28.
Synthesis of [o-C6H4-(Ph2)PN-iPr]2LnCl, 5c-Ln (Ln = Y, Nd,
Gd). Compounds 5c-Ln were prepared following the same
experimental procedure as that described for 4b-Y, in which
[LnCl3(THF)3] (Ln = Y, Nd, Gd) (1 mmol) was reacted with 3c
(2 mmol) in THF (20 mL).
5c-Y: yield 72%. 31P{1H} NMR (THF-d8): δ 35.7 (d, 1P, JP−Y = 17
Hz). 1H (THF-d8): δ 7.87 (m, 8H, HAr), 7.78 (m, 2H, HAr), 7.49 (m,
12H, HAr), 7.09 (m, 2H, HAr), 6.99 (m, 2H, HAr), 6.88 (m, 2H, HAr),
3.65 (2H, CHi‑Pr), 1.23 (d, 12H, HMe). 13C{1H} NMR (THF-d8): δ
24.9 (d, 3JCP = 8 Hz, CH3), 46.2 (d, 2JCP = 5 Hz, CH), 122.1 (d, 2JCP
=
3c (R = iPr): yield 64%. 31P{1H} NMR (toluene-d8): δ 22.6 (s, P).
1H NMR (C6D6): δ 8.19 (m, 1H, HAr), 7.71 (m, 4H, HAr), 7.28 (m,
2H, HAr), 7.13 (m, 7H, HAr), 3.28 (m, 1H, HCH), 0.98 (d, 6H, HiPr).
13C{1H} NMR (C6D6) δ 28.9 (d, 3JCP = 16 Hz, Me), 46.3 (d, 2JCP = 11
15 Hz, o-CH (PhYP)), 125.9 (s, p-CH (PhyP)), 126.4 (d, 3JCP = 11 Hz,
3
m-CH (Ph2P)), 127.4 (d, JCP = 28 Hz, m-CH (PhYP)), 129.5 (s, p-
CH (Ph2P)), 131.3 (d, 1JCP = 61 Hz, Cquat-(Ph2P)), 131.9 (d, 2JCP = 9
1
Hz, o-CH (Ph2P)), 135.9 (d, JCP = 128 Hz, Cquat-(PhYP)), 137.9 (d,
2
3JCP = 28 Hz, m-CH (PhYP)), 195.9 (d, JCP = 42 Hz, CY (PhYP)).
2
Hz, CH), 124.9 (d, JCP = 15 Hz, o-CH (PhLiP)), 128.7 (s, p-CH
3
(PhLiP)), 129.6 (s, p-CH (Ph2P)), 131.1 (d, JCP = 15 Hz, m-CH
Anal. Calcd for 5c-Y, C42H42ClN2P2Y (761.10): C, 66.28; H, 5.56; N,
3
2
(Ph2P)), 131.3 (d, JCP = 15 Hz, m-CH (PhLiP)), 133.8 (d, JCP = 9
3.68. Found: C, 66.12; H, 5.42; N 3.63.
1
1
5c-Nd: 31P{1H} NMR (THF-d8): δ 58 (s, P). H NMR (THF-d8):
Hz, o-CH (Ph2P)), 135.1 (d, JCP = 75 Hz, Cquat-(Ph2P)), 140.8 (d,
3JCP = 26 Hz, m-CH (PhLiP)), 142.5 (d, 1JCP = 136 Hz, Cquat-(PhLiP)),
δ −17.7 (bs, 12H, Me), 7.48 (m, 14H, m-H (PhNd), m-H (Ph2P), p-H
(Ph2P)), 10.5 (bs, 8H, o-H (Ph2P)), 17.52 (bs, 2H), 19.11 (bs, 2H),
25.29 (bs, 2H). No signal for CH-iPr could be found, presumably
because of the paramagnetism of NdIII. 13C{1H} NMR (THF-d8): δ
28.6 (d, 3JCP = 13.6 Hz, Me), 127.9 (d, 2JCP = 11.4 Hz, m-CH (PhNd)),
128.97 (s, m-CH (Ph2P)), 130.48 (s, p-CH (PhNd)), 131.45 (s, p-CH
(Ph2P)), 132.3 (d, 3JCP = 8.8 Hz, m-CH (PhNd)), 134.1 (d, 1JCP = 95.4
Hz, Cquat (Ph2P)), 135.6 (bs, o-CH (PhNd)), 136.8 (s, o-CH (Ph2P)),
2
190.8 (d, JCP = 47 Hz, CLi (PhLiP)). Anal. Calcd for 3c·Et2O,
C25H31LiNPO (399.43): C, 75.17; H 7.82; N, 3.51. Found: C 74.89,
H, 7.69; N, 3.68.
3d (R = nBu): yield 60%. 31P{1H} NMR (toluene-d8): δ 25.1 (s, P).
1H NMR (THF-d8): δ 8.08 (d, 1H, HAr), 7.65 (m, 4H, HAr), 7.38(m,
6H, HAr), 7.01 (m, 1H, HAr), 6.83 (m, 1H, HAr), 6.64 (m, 1H, HAr),
2.93 (m, 2H, HBu), 1.56 (m, 2H, HBu), 1.33 (m, 2H, HBu),0.88 (d, 3H,
HBu). 13C{1H} NMR (C6D6): δ 14.4 (s, CH3), 21.2 (s, CH2), 37.8 (d,
1
147.1 (d, JCP = 76.6 Hz, o-Cquat (PhNd)), 184.4 (bs, i-Cquat (PhNd)).
2
2
3JCP = 17 Hz, CH2), 45.9 (d, JCP = 6 Hz, CH2), 124.5 (d, JCP = 15
No meaningful analysis could be obtained.
Hz, o-CH (PhLiP)), 130.9 (s, m-CH (PhLiP)), 131.1 (s, m-CH
5c-Gd: yield 64%. Anal. Calcd for 5c-Gd, C42H42ClGdN2P2
(829.45): C, 60.82; H, 5.10; N, 3.38. Found: C, 60.90; H, 5.18; N 3.25.
Synthesis of [o-C6H4-(Ph2)PN-nBu]3Ln, 6d-Ln (Ln = Y, Nd,
La). Compounds 6d-Ln were prepared following the same
experimental procedure as that described for 4b-Y, in which
[LnCl3(THF)3] (Ln = Y, Nd, La) (1.2 mmol) was reacted with 3d
(3.6 mmol) in THF (20 mL).
2
(Ph2P)), 133.8 (d, JCP = 8 Hz, o-CH (Ph2P)), 133.9. Anal. Calcd for
3d·THF, C26H31LiNPO (411.45): C, 75.90; H, 7.59; N, 3.40. Found:
C, 75.73; H, 7.92; N, 3.48.
Synthesis of [o-C6H4-(Ph2)PN-SiMe3]YCl2, 4a-Y. To a
suspension of [YCl3(THF)3.5] (0.2 mmol) in THF was added a
solution of 3a (0.2 mmol) in THF (5 mL) at room temperature. The
solution was stirred for 30 min and concentrated to 1 mL under
vacuum. Few crystals of [o-C6H4-(Ph2)PN-SiMe3]Y[(μ-Cl)2Li-
(THF)2]2 (4a-Y·2LiCl·4THF) were obtained at −30 °C. Because of
this, the NMR data refer to 4a-Y obtained in situ.
6d-Y: yield 70%. 31P{1H} NMR (THF-d8): δ 36.4 (d, 1P, JP−Y = 15
1
Hz). H NMR (THF-d8): δ 7.95 (m, 3H, HAr), 7.77 (m, 12H, HAr),
7.45 (m, 18H, HAr), 7.13 (m, 3H, HAr), 6.94 (m, 3H, HAr), 6.85 (m,
3H, HAr), 3.19 (m, 6H, HBu), 1.26 (m, 6H, HBu), 0.68 (m, 6H, HBu),
0.37 (t, 9H, HBu). 13C{1H} NMR (C6D6): δ 14.3 (s, CH3), 21.4 (s,
4a-Y: yield 5%. 31P{1H} NMR (THF-d8): δ 28.9 (s, 2JYP = 10.8 Hz).
1H{31P} NMR (THF-d8): 0.04 (s, 9H, CH3), 6.82 (m, 2H, p-CH
(PhY), 6.96 (m, 1H, m-CH (PhY)), 7.43 (m, 6H, p-H (Ph2P), m-H
2
2
CH2), 37.2 (s, CH2), 47.3 (d, JCP = 6 Hz, CH2), 123.5 (d, JCP = 14
Hz, o-CH (PhyP)), 128.7 (s, m-CH (Ph2P)), 129.3 (s, p-CH (PhYP)),
129.6 (s, 3JCP = 26 Hz, m-CH (PhYP)), 130.3 (s, p-CH (Ph2P)), 132.8
(d, 1JCP = 76 Hz, Cquat-(PhYP)), 134.6 (d, 2JCP = 9 Hz, o-CH (Ph2P)),
2
1
(Ph2P)), 7.7 (dd, 4H, JHH = 1.6 Hz, JHH, 8.2 Hz, o-H (Ph2P)), 8.05
(d, 1H, J = 7.2 Hz, o-CH (PhY)). 13C{1H} NMR (THF-d8): δ 4.7 (d,
4860
dx.doi.org/10.1021/om300389v | Organometallics 2012, 31, 4854−4861

Organometallics
Article
139.1 (d, 1JCP = 134 Hz, Cquat-(Ph2P)), 141.0 (d, 3JCP = 27 Hz, m-CH
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1
1
(PhYP)), 200.9 (dd, JCY = 37 Hz, JCP = 45 Hz, CY (PhYP)).
6d-Nd: yield 85%. 31P{1H} NMR (THF-d8): δ 43.9 (s, P). 1H NMR
(THF-d8): δ −19.2 (bs, 6H, PNCH2), −8.51 (bs, 6H, PNCH2CH2),
−5.82 (bs, 6H, CH2CH3), −3.5 (bs, 9H, CH3), 7.75 (m, 6H, p-CH
(Ph2P)), 8.00 (m, 12H, m-CH (Ph2P)), 9.7 (bs, 3H, m-CH (PhNd)),
10.4 (m, 12H, o-CH (Ph2P)), 10.6 (bs, 3H, p-CH (PhNd)), 10.9 (bs,
3H, m-CH (PhNd)), 15.5 (bs, 3H, o-CH (PhNd)). 13C{1H} NMR
(THF-d8): δ −14.78 (bs, PNCH2), 9.1 (s, CH2CH3), 10.5 (bs,
PNCH2CH2), 12.8 (s, CH3), 123.6 (d, 2JCP = 15.4 Hz, m-CH (PhNd)),
3
3
128.7 (d, JCP = 11.4 Hz, p-CH (PhNd)), 129.6 (d, JCP = 9.1 Hz, m-
1
CH (Ph2P)), 132.04 (s, P-CH (Ph2P)), 133.96 (d, JCP = 93.8 Hz,
2
1
Cquat (Ph2P)), 135.4 (d, JCP = 7.3 Hz, o-CH (Ph2P)), 144.07 (d, JCP
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9078−9079. (b) Kaita, S.; Hou, Z.; Wakatsuki, Y. Macromolecules
2001, 34, 1539−1541. (c) Kaita, S.; Takeguchi, Y.; Hou, Z.; Nishiura,
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= 75.6 Hz, o-Cquat (PhNd)), 169.03 (s, m-CH (PhNd)), 176.7 (d, 3JCP
=
25.7 Hz, o-CH (PhNd)).
1
6d-La: yield 79%. 31P{1H} NMR (THF-d8): δ 36.7 ppm. H NMR
(THF-d8): δ 0.36 (t, 3JHH = 7.3 Hz, 9H, HBu), 0.75 (m, 6H, HBu), 1.05
(m, 6H, HBu), 3.15 (m, 6H, HBu), 6.78 (m, 3H, HAr), 6.92 (m, 3H,
HAr), 7.11 (m, 3H, HAr),7.2 (m, 12H, HAr), 7.34 (m, 6H, HAr), 7.65
(m, 12H, HAr), 8.11 (d, JHH = 6.6 Hz, 3H, HAr). 13C{1H} NMR
3
(THF-d8): δ 14.2 (s, CH3), 21.3 (s, CH2), 36.4 (s, CH2), 46.3 (d, 2JCP
= 6 Hz, CH2), 123.85 (d, 2JCP = 14 Hz, m-CH (PhLa)), 127.6 (d, 4JCP
(5) Paolucci, G.; Zanella, A.; Bortoluzzi, M.; Sostero, S.; Longo, P.;
Napoli, M. J. Mol. Catal. A: Chem. 2007, 272, 258−264.
3
= 3.9 Hz, m-CH (PhLa)), 128.7 (d, JCP = 10.8 Hz, m-CH (Ph2P)),
3
129.51 (d, JCP = 28.2 Hz, p-CH (PhLa)), 131.5 (s, p-CH (Ph2P)),
(6) Zhang, L.; Suzuki, T.; Luo, Y.; Nishiura, M.; Hou, Z. Angew.
Chem., Int. Ed. 2007, 46, 1909−1913.
133.8 (d, 1JCP = 74.1 Hz, i-Cquat (Ph2P)), 133.9 (d, 2JCP = 8.5 Hz, o-CH
1
2
(Ph2P)), 139.7 (d, JCP = 136.8 Hz, o-CH (PhLa)), 139.8 (d, JCP
=
(7) Rastaetter, M.; Muterle, R. B.; Roesky, P. W.; Thiele, S. K. H.
Chem.−Eur. J. 2009, 15, 474−481.
2
27.7 Hz, o-Cquat(PhLa)), 214.7 (d, JCP =47.6 Hz, i-CH (PhLa)).
Synthesis of C12H8P-N(K)-nBu, 8. To a solution of 3d (250 mg)
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6343−6352.
in a mixture of diethyl ether (3 mL) and petroleum ether (5 mL) was
t
added BuOK in small portions. After 5 min of stirring, the mixture
was evaporated to dryness and 8 was obtained as a solid, which was
washed with 5 mL of pentane and dried under vacuum.
8: yield 72%. 31P{1H} NMR (THF-d8): δ 45.5 ppm. 1H NMR
(THF-d8): δ 7.79 (d, 2H, HAr, J = 7.2 Hz), 7.65 (dd, 2H, J = 7.2 Hz, J
= 2.0 Hz), 7.1 (m, 4H, HAr), 2.51 (q, 2H, J = 7.9 Hz), 1.22 (m, 4H),
0.77 (d, 3H, J = 7.1 Hz). Anal. Calcd for C16H17KNP (293.38): C,
65.50; H, 5.84; N, 4.77. Found: C, 65.42; H, 5.77; N, 4.69.
Polymerization Procedure. Polymerizations were performed
under nitrogen in a 250 mL glass reactor equipped with a stainless
steel blade stirrer. The protonating agent or aluminum cocatalysts and
the yttrium or neodymium precursor, prepackaged in ampules, were
introduced in a flask closed by Teflon and steel caps. After adding 60
mL of methylcyclohexane and butadiene via syringe, the ampules were
broken by stirring. The mixture was then stirred for 2 h at 60 °C. At
the end of the polymerization reaction, the mixture was quenched with
1 mL of methanol. The polymer was then precipitated with methanol,
washed, and dried under vacuum.
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ASSOCIATED CONTENT
■
S
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: francois.nief@polytechnique.edu.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financed by the CNRS, Ecole Polytechnique,
and the Manufacture Franca
̧
ise des Pneumatiques Michelin.
REFERENCES
■
(1) (a) Mazzei, A. Macromol. Chem. Phys., Suppl. 1981, 4, 61−72.
(b) Wilson, D. J.; Jenkins, D. K. Polym. Bull. 1992, 27, 407−411.
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dx.doi.org/10.1021/om300389v | Organometallics 2012, 31, 4854−4861