Synthesis, characterization, and activity of yttrium(III) nitrate complexes bearing tripodal phosphine oxide and mixed phosphine-phosphine oxide ligands

Article abstract of DOI:10.1021/ic3010147

A series of four tripodal phosphine oxide ligands, (OPR₂) ₂CHCH₂POR₂ (1a-1d), and four mixed phosphine-phosphine oxide ligands, (OPR₂)₂CHCH ₂PR₂ (3a-3d), were synthesized and coordinated to yttrium to produce Y(NO₃)₃[(OPR₂)₂CHCH ₂POR₂] (2a-2d) and Y(NO₃)₃[(OPR ₂)₂CHCH₂PR₂](OPPh₃) (4a-4d) complexes. The previously reported ligand 1a and unknown phosphine oxide ligands 1b-1d were generated in an unprecedented trisubstitution reaction of bromoacetaldehyde diethyl acetal, while the novel partially reduced ligands 3a-3d were synthesized from 1a-1d according to a known literature protocol for the selective monoreduction of bisphosphine oxides. The neutral yttrium complexes 2a-2d are nine-coordinate and display a tricapped trigonal-prismatic geometry. Complexes 4a-4d are also neutral, nine-coordinate species and have a pendant phosphine functionality, which provides the potential to form bimetallic early-late transition-metal complexes. Additionally, yttrium complexes 2a-2d were activated with base and tested for the ring-opening polymerization of ε-caprolactone, but the results showed that base by itself was significantly more effective than the yttrium species investigated.

Full text of DOI:10.1021/ic3010147

Article
pubs.acs.org/IC
Synthesis, Characterization, and Activity of Yttrium(III) Nitrate
Complexes Bearing Tripodal Phosphine Oxide and Mixed
Phosphine−Phosphine Oxide Ligands
Peter E. Sues, Alan J. Lough, and Robert H. Morris*
Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
S
* Supporting Information
ABSTRACT: A series of four tripodal phosphine oxide ligands,
(OPR2)2CHCH2POR2 (1a−1d), and four mixed phosphine−phosphine oxide
ligands, (OPR2)2CHCH2PR2 (3a−3d), were synthesized and coordinated to
yttrium to produce Y(NO3)3[(OPR2)2CHCH2POR2] (2a−2d) and Y-
(NO3)3[(OPR2)2CHCH2PR2](OPPh3) (4a−4d) complexes. The previously
reported ligand 1a and unknown phosphine oxide ligands 1b−1d were generated
in an unprecedented trisubstitution reaction of bromoacetaldehyde diethyl acetal,
while the novel partially reduced ligands 3a−3d were synthesized from 1a−1d
according to a known literature protocol for the selective monoreduction of
bisphosphine oxides. The neutral yttrium complexes 2a−2d are nine-coordinate
and display a tricapped trigonal-prismatic geometry. Complexes 4a−4d are also
neutral, nine-coordinate species and have a pendant phosphine functionality,
which provides the potential to form bimetallic early−late transition-metal
complexes. Additionally, yttrium complexes 2a−2d were activated with base and tested for the ring-opening polymerization of ε-
caprolactone, but the results showed that base by itself was significantly more effective than the yttrium species investigated.
When spent nuclear fuels are reprocessed, the irradiated
materials are dissolved in nitric acid.47,48 Then, using liquid−
liquid extraction methods, a crucial part of the procedure is the
removal of lanthanide metals from actinides.49−51 Strong
oxygen donors bind the oxophilic lanthanides, and it has
been shown that polyfunctional extractants are more efficient
than their monofunctional analogues.47,48,52 A commonly used
ligand in the TRUEX (TRansUraniumEXtraction) process is
carbamoylphosphine oxide, which binds metal cations through
amide and phosphine oxide functionalities.53,54 Previous studies
have shown, however, that phosphine oxides are better donors
for lanthanides than amides,55−59 and it would be beneficial to
develop polyphosphine oxide ligands for liquid−liquid
extraction applications. Because of its similarity to lanthanide
rare-earth metals, yttrium is a perfect candidate for testing the
effectiveness of new extraction ligands, and because of its NMR
handles, any metal complexes thus formed would be much
easier to follow and characterize.
We have previously reported the syntheses of diary-
lphosphorylacetaldehyde diethyl acetals as convenient precur-
sors for the production of phosphonium dimers.60 The yield of
this process was somewhat low, indicating that a substantial
amount of the starting materials was either decomposing or
undergoing unwanted side reactions. Upon crystallization of the
major side product of this reaction, it was found that 1,1,2-
tris(diarylphosphoryl)ethane was being produced (see Scheme
INTRODUCTION
■
Yttrium is an industrially relevant element with applications as a
lasing medium for lanthanide-doped yttrium−aluminum garnet
(YAG) solid-state lasers1−4 and as an additive to refractory
materials for the formation of adherent metal oxide layers.5 In
addition, the radioisotope 90Y has been found to be useful in
radiotherapeutical treatments for various types of cancer.6−11
Despite its industrial significance, yttrium is one of the least
studied transition metals. Only a handful of studies have
explored the ability of this metal to catalyze chemical
transformations, which include α-olefin polymerization,12−18
asymmetric hydroamination of alkenes,19,20 hydrosilylation of
alkenes,21,22 and several other reactions.23−25 More recently,
however, interest in yttrium has increased because of its activity
in the ring-opening polymerization (ROP) of cyclic esters to
form biodegradable polyester polymers,26−38 which have
promising medical applications.39−42
A noteworthy feature of yttrium is its similarity to lanthanide
rare-earth metals.43−46 The most common oxidation state of
yttrium is 3+, and its ionic radius is comparable to those of
analogous trivalent lanthanides (intermediate between Dy3+
and Ho3+).43−46 Because of these parallels, yttrium exhibits
chemical and physical properties similar to those of lanthanide
metals, with the exception that, unlike most trivalent
lanthanides, yttrium is diamagnetic and monoisotopic (89Y =
1
100% abundant) and has a spin of I = /2. This makes yttrium
an ideal model for investigating the behavior of lanthanide
metals.
Received: May 15, 2012
Published: August 21, 2012
© 2012 American Chemical Society
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Scheme 1. Synthesis of Diarylphosphorylacetaldehyde Diethyl Acetal and 1,1,2-Tris(diarylphosphoryl)ethane
Scheme 2. Synthesis of Ligands 1a−1d Starting from Diarylphosphine Oxides
Figure 1. ORTEP3 representation (thermal ellipsoids at 50% probability; most of the hydrogen atoms are omitted for clarity) and atom numbering
for (a) 1a, (b) 1b (the solvent is also omitted for clarity), (c) 1c (the solvent is also omitted for clarity), and (d) 1d.
1). This polyfunctional phosphine oxide ligand was immedi-
ately identified as a potential extraction agent for nuclear fuel
treatment. In this paper, we describe the synthesis of 1,1,2-
tris(diarylphosphoryl)ethane ligands and their reactions with
yttrium. In addition, we endeavored to reduce the phosphine
oxide ligands and coordinate the resulting mixed phosphine−
phosphine oxide ligands to yttrium. Furthermore, several
yttrium complexes were activated with base, and their activity
toward the ROP of ε-caprolactone was investigated. With
respect to nomenclature, throughout this paper, compounds
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Scheme 3. Proposed Mechanism for the Formation of Ligands 1a−1d
will be named according to their aryl substitution pattern: a for
phenyl; b for p-tolyl; c for o-tolyl, and d for m-xylyl.
the adjacent carbon atom, opening the P2−C1−P3 bond angle
wider than the optimal tetrahedral angle of 109.45°. Similarly,
the steric bulk of the phosphoryl groups also opens the P1−
C2−C1 bond angle. The general trend for the sizes of the P2−
C1−P3 and P1−C2−C1 bond angles supports this theory, with
the most sterically encumbered phosphorus group, o-tolyl in
compound 1c, producing the largest angles, 118.8(9)° and
113(1)°, respectively (for further notable bond lengths and
angles, see the Supporting Information, Table S1). Another
interesting feature evident in the crystal structures is π−π
stacking between the aryl groups of the different phosphorus
functionalities. The aryl rings of both the equivalent and
inequivalent phosphoryl groups can be seen aligning themselves
parallel to each other, and in the case of 1c, the bulky
substituents are oriented away from each other to minimize
unfavorable steric interactions.
The mechanism of formation for compounds 1a−1d is, at
the same time, intriguing and poorly understood. Several
attempts were made to generate structures similar to the
polyfunctional phosphine oxides by first installing a unique
functional group (phosphino or amino) in place of the bromide
on the bromoacetaldehyde diethyl acetal precursor. Then, the
isolated, monosubstituted product was subjected to an excess of
deprotonated diarylphosphine oxide in an endeavor to replace
the ethoxides with phosphoryl moieties. Unfortunately, every
effort resulted in no incorporation of the phosphine oxide
functionalities and in the recovery of the monosubstituted
starting material. If, on the other hand, diarylphosphorylace-
taldehyde diethyl acetal was exposed to 2 equiv of deprotonated
diarylphosphine oxide, full conversion to the trisubstituted
product was achieved.
It is therefore believed that the initial substitution of bromine
by phosphine oxide is crucial in initiating the trisubstitution
process (Scheme 3). Once incorporated into the carbon
backbone, a phosphoryl group would greatly increase the
acidity of the α-carbon through inductive effects, as well as
through resonance stabilization of the conjugate base. This, in
conjunction with the fact that the medium is extremely basic,
makes it feasible for a deprotonated diarylphosphine oxide to
abstract a proton from the α-carbon, with the resulting
carbanion being stabilized by the adjoining phosphoryl group.
Subsequently, in an E1cb fashion, an ethoxide could be
eliminated with concomitant C−C double-bond formation.
The unsaturated intermediate generated, however, would be
susceptible to nucleophilic attack by a phosphoryl anion at the
more electrophilic carbon, which would regenerate a resonance-
stabilized carbanion at the previously deprotonated carbon.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Tridentate Phos-
phine Oxide Ligands 1a−1d. Compounds 1a−1d were
prepared using an unprecedented trisubstitution reaction where
3 equiv of diarylphosphine oxide were deprotonated with KH
and combined directly with bromoacetaldehyde diethyl acetal
to yield white, air-stable powders in moderate yields (55−70%).
In this reaction, the bromide and ethoxide groups of
bromoacetaldehyde diethyl acetal have been replaced by
diarylphosphoryl functionalities (see Scheme 2). Compound
1a has been reported previously and was prepared via several
alternative synthetic routes employing vinyl chlorides61,62 but
was never fully characterized. Moreover, various trisubstitution
reactions of bromoacetaldehyde diethyl acetal have previously
been reported, but these were two-step processes that required
the use of an acid to in situ deprotect the protected aldehyde to
facilitate the loss of ethanol and the incorporation of the
desired functional groups.63−67
The 31P{1H} NMR spectra of compounds 1a, 1b, and 1d all
show characteristic peaks in the phosphine oxide region. The
two equivalent phosphorus nuclei display a doublet around 32
ppm and are coupled to the remaining inequivalent phosphorus
nucleus, which displays a triplet around 29 ppm. The 31P{1H}
NMR spectrum of 1c, on the other hand, displays a triplet
around 32 ppm, much like the other compounds, but the
doublet for the two equivalent phosphorus nuclei is missing. In
its place is a broad singlet at 40 ppm, which arises from the
coalescence of resonances for interconverting rotamers in
solution; the rate of exchange is a rapid process on the NMR
time scale. This type of behavior has been seen previously with
bulky o-tolyl substituents,60 which are known to have restricted
rotation about the C−P bond (barriers of rotation of up to 19.5
kJ/mol).68 The H NMR spectra of compounds 1a−1d also
1
exhibit several diagnostic peaks. The proton α to the two
equivalent phosphorus centers displays a unique multiplet in
the range between 5.2 and 4.4 ppm, as do the protons α to the
lone phosphorus center, between 3.5 and 2.9 ppm.
In addition to NMR experiments, compounds 1a−1d were
characterized in the solid state utilizing single-crystal X-ray
diffraction studies (see Figure 1). All of the 1,1,2-tris-
(diarylphosphoryl)ethane ligands display typical bond lengths
and angles, with the exception of the P2−C1−P3 and P1−C2−
C1 bond angles. Presumably, the steric bulk of the two
equivalent diarylphosphoryl moieties distorts the geometry of
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Scheme 4. Synthesis of Yttrium Complexes 2a−2d Using Ligands 1a−1d
Figure 2. ORTEP3 representation (thermal ellipsoids at 50% probability; the solvent and most of the hydrogen atoms are omitted for clarity) and
atom numbering for 2a−2d.
Following this, another E1cb-type reaction could eliminate the
last ethoxide group and produce a 1,2-bis(diarylphosphoryl)-
ethylene species. In the last step, protonated diarylphosphine
oxides in solution could react with the disubstituted
intermediate and hydrophosphinate the double bond, thus
generating the observed polyfunctional phosphine oxide
products.
Efforts have been made to isolate some of the possible
intermediates in the proposed mechanism, with emphasis put
on trapping of the 1,2-bis(diarylphosphoryl)ethylene species,
but these attempts have met with little success to date. Despite
control of the stoichiometry of the reactants and the addition of
only 1 equiv of deprotonated phosphine oxide at a time at −78
°C and then warming to room temperature, the only products
isolated were the trisubstituted ligand and the starting materials.
If trimethylsilane was added in order to trap either of the
proposed unsaturated intermediates, the only products
observed were the 1,1,2-tris(diarylphosphoryl)ethane species,
the reactants, and some unrecognizable decomposition
products. Indirect evidence, however, for a 1,2-bis-
(diarylphosphoryl)ethylene intermediate was obtained by
combining di-o-tolylphosphorylacetaldehyde diethyl acetal
with 2 equiv of deprotonated diphenylphosphine oxide. Two
products were evident in the NMR spectrum of the crude
product: one with a triplet and a doublet corresponding to a
product with geminal diphenylphosphoryl moieties and one
with two sets of doublet of doublets and one doublet
corresponding to a product with germinal diphenylphosphoryl
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Scheme 5. Synthesis of Ligands 3a−3d Using Ligands 1a−1d
and di-o-tolylphosphoryl functionalities. Sequential displace-
ment of ethoxy groups would only generate the former product,
while hydrophosphination of an unsaturated intermediate could
produce both of the products that were seen. Further studies
probing the exact mechanism of the formation for compounds
1a−1d are needed.
the aryl groups of the different phosphorus functionalities is
evident in the solid-state structures. The aryl rings are aligned
parallel to each other, and for 2c, the methyl substituents are
oriented away from each other to minimize unfavorable steric
interactions.
An exciting feature of these systems is that the solubility of
the complexes in organic solvents can be switched on and off
depending on the concentration of the ligand present. When an
excess of the ligand is present in solution, the yttrium nitrate
species are freely soluble in acetonitrile and other polar organic
solvents. If, on the other hand, there is a 1:1 ratio of yttrium to
ligand, then the metal complexes rapidly precipitate out of
solution. By control of the stoichiometry of the ligand versus
the metal center in solution, a desired metal cation could be
taken up into an organic solvent and then crashed out later with
the addition of more of the metal precursor to isolate very pure
complexes. These features of this polyfunctional phosphine
oxide system would greatly expedite the removal and
subsequent purification of lanthanides in nuclear fuel
reprocessing.
Synthesis and Characterization of Yttrium Complexes
2a−2d. Popovici et al. have recently reported the synthesis of
bis(phosphinic amide)phosphine oxide ligands, which they
coordinated to yttrium, a well-established model for the rare-
earth metals, in order to explore whether or not their ligands
were suitable for nuclear fuel extraction applications.69 These
ligands had three P−O double-bond moieties, much like our
tripodal phosphine oxide compounds 1a−1d, and as such, we
thought that our ligands would exhibit similar coordination
modes. To generate yttrium complexes, 1 equiv of compound
1a, 1b, 1c, or 1d was dissolved in acetonitrile and a solution of
Y(H2O)6(NO3)3 in acetonitrile was added (see Scheme 4). The
mixtures were stirred for 15 min to yield the corresponding
complexes 2a−2d, which precipitated out of solution as white,
air-stable powders in very good yield (85−95%). These white
powders were insoluble in most solvents, except for methanol
and dimethyl sulfoxide (DMSO), despite being neutral species.
If an excess of the tridentate ligand was used, however, the
complexes remained soluble in acetonitrile and could be
precipitated out of solution with less polar solvents such as
ether.
Variable-temperature NMR studies probing the nature of the
2:1 mixtures were carried out, but the results provided little
insight as to what is occurring in solution. The 31P NMR
spectra showed at least 12 separate broad peaks at −40 °C in
deuterated acetonitrile, indicating that the system is dynamic
and involves at least four interconverting species.
Synthesis and Characterization of Tridentate Mixed
Phosphine−Phosphine Oxide Ligands 3a−3d. After the
synthetic route for generating the 1,1,2-tris(diarylphosphoryl)-
ethane ligands was shown to be a general method for producing
polyphosphine oxide compounds and it had been established
that the sterically bulky ligands could be accommodated on
transition metals, it was thought that the fully reduced forms of
the ligands, which would resemble a fusion of bis-
(diarylphosphino)methane and 1,2-bis(diarylphosphino)-
ethane, would be interesting synthetic targets. All conventional
methods of reducing phosphine oxides were employed, but all
attempts to reduce compounds 1a−1d resulted in fragmenta-
tion of the ligands. Regardless of the reducing agents or the
conditions utilized, the production of diarylphosphines, diary-
lphosphine oxides, and other decomposition products was
always seen. It is known in the literature that the bridging
carbon of bis(diphenylphosphino)methane is prone to
deprotonation,70−74 and analogously it was believed that the
increased acidity of the carbon with two phosphoryl moieties
was a major contributor to the instability of compounds 1a−1d
under reduction conditions. It was anticipated that once one or
more of the phosphine oxides were reduced, the pKa of the
acidic C−H bond would increase greatly, which would impart
more stability to the ligands and allow for the subsequent
reduction of the remaining phosphine oxide functionalities
utilizing conventional methods. Extremely mild, weakly basic
conditions for the partial reduction of phosphine oxides were
therefore investigated.
Because of the insolubility of complexes 2a−2d in solvents
other than methanol or DMSO, which showed only free
displaced ligands in the NMR spectra, the yttrium species could
not be characterized by conventional spectroscopic methods.
Fortunately, crystals of the yttrium complexes were easily
grown from the slow diffusion of ether into an acetonitrile
solution containing 2 equiv of ligand 1a, 1b, 1c, or 1d and 1
equiv of yttrium nitrate hexahydrate. Accordingly, 2a−2d were
all characterized by single-crystal X-ray diffraction studies.
The yttrium compounds were found to be nine-coordinate
neutral species that displayed a distorted tricapped trigonal-
prismatic geometry. The polyfunctional phosphoryl ligands
form three vertices of the trigonal prism, while the three
bidentate nitrate ligands occupy the other three vertices of the
prism, as well as the three capping positions outside of the
rectangular faces of the trigonal prism (see Figure 2).
Moreover, in the crystal structures for 2a−2d, the P2−C1−
P3 bond angle is constrained to be around 110° because of
coordination of the oxygen moieties to the yttrium metal
center; for all of the ligands, this represents a compression of
this angle from the free ligand form. In addition, the P1−C2−
C1 angle has been drastically increased upon coordination to
the metal. It increased from 107−113° in 1a−1d up to 116−
119° in 2a−2d in order to accommodate the tricapped trigonal-
prismatic geometry enforced by the yttrium center (for further
notable bond lengths and angles, see the Supporting
Information, Table S2). Furthermore, π−π stacking between
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Scheme 6. Synthesis of Yttrium Complexes 4a−4d Using Ligands 3a−3d
In 2008, Jenkins et al. reported a procedure for the selective
monoreduction of bisphosphine oxides employing N,N-
diisopropylethylamine, an extremely bulky base, and 1-
pentanethiol as the reductant.75 The reaction conditions are
extremely mild, and various test reactions showed that the
crowded amine base was unable to deprotonate the sterically
encumbered acidic carbon atom of compounds 1a−1d, even at
elevated temperatures. Using the same synthetic procedure
outlined in the paper, previously unknown partially reduced
compounds 3a−3d were generated in modest yields (32−48%)
and isolated as white powders (see Scheme 5).
of the completely oxidized forms 1a−1d, all conventional
methods for reducing phosphine oxides were employed, but all
reducing conditions led to the decomposition of compounds
3a−3d, as seen previously. Although a disappointing result, the
partially reduced ligands are interesting in and of themselves.
The mixed phosphine−phosphine oxide compounds contain
two very different types of donor groups; the phosphine oxides
are very hard donors, while the phosphine functionalities are
much softer. These ligands therefore have the potential to
support early−late bimetallic transition-metal systems, where
the oxygen moieties coordinate early transition metals and the
phosphines preferentially bind late transition metals. Further-
more, because the phosphine oxide functionalities are such
poor donors for late transition metals, compounds 3a−3d
could find applications in catalytic systems where multidentate
hemilabile ligands are desirable. Several rhodium- and
palladium-based catalysts employing mixed phosphine−phos-
phine oxide ligands have been reported that were successful in
the catalytic hydrogenation alkenes and in Suzuki coupling,
respectively.76 In both cases, the phosphine moiety provided a
firm anchor to the metal center and the phosphine oxide
displayed a dynamic behavior, which helped the catalysts switch
between different states.76
The 31P{1H} NMR spectra of compounds 3a−3d were
remarkably similar to those of compounds 1a−1d with one
significant difference: the phosphoryl triplet around 29−32
ppm representing the single, nonequivalent phosphine oxide
group was shifted to the negative region (between −12 and
−37 ppm), indicating that the phosphine oxide functionality
was reduced to a phosphine moiety. The doublets around 32−
40 ppm, however, remained, for the most part, unchanged, 30−
38 ppm, and, additionally, 3c displayed a doublet in this region
instead of a broad singlet, as was seen for 1c, signifying that
rotation about the P−C bonds had a lower barrier for the
partially reduced ligand. It is interesting to note that the
phosphine oxide reduction was completely chemoselective, as
seen by 31P NMR; only the nonequivalent phosphoryl group
was reduced. Although the yields of these reactions are quite
low, which can be attributed to an incomplete reaction as large
amounts of starting material are recovered, there is no evidence
of any significant reduction of the other phosphoryl moieties in
the reaction mixture or the crude products. This behavior may
be due to the steric encumbrance of the other phosphoryl
functionalities, which precludes their reduction.
Jenkins et al. invoked a mechanism in which a thiolate attacks
a phosphorus atom, generating a phosphonium intermediate.75
Another equivalent of thiolate then either directly attacks the
phosphorus again and the two thiolates reductively eliminate or
the second thiolate attacks the coordinated thiolate directly,
thus reducing the phosphorus center.75 In both cases, the least
crowded phosphorus moiety would be most available for attack
by the thiolate reductants, which explains the selectivity of the
reaction for the reduction of the most accessible phosphoryl
group.
Synthesis and Characterization of Yttrium Complexes
4a−4d. In order to demonstrate the selectivity of the different
phosphorus functionalities of ligands 3a−3d for the binding of
transition metals, yttrium complexes of the mixed phosphine−
phosphine oxide ligands were synthesized. A total of 1 equiv of
3a, 3b, 3c, or 3d was dissolved in acetonitrile, and a solution of
Y(H2O)6(NO3)3 in acetonitrile was added. 31P NMR spectra of
the reaction mixtures revealed that two products were
generated in solution, which had very similar doublets of
doublets representing coordinated phosphoryl groups, between
40 and 30 ppm (2JYP approximately 6 Hz) and nearly identical
triplets corresponding to uncoordinated diarylphosphine in the
negative region. It was thought that the two species in solution
arose from acetonitrile or water from the starting material
coordinating to a vacant site on the metal center. The addition
of molecular sieves to the reaction mixtures did cause one of
the species in solution to become more prevalent, while the
other diminished in intensity, but the conversion process was
slow, taking several days without reaching completion. A total
of 1 equiv of triphenylphosphine oxide in acetonitrile was
therefore added to the reaction mixtures to readily substitute
for acetonitrile or water on yttrium (see Scheme 6). Complexes
4a−4d, with three phosphine oxide ligands and a dangling
diarylphosphine moiety, were isolated as white powders in
moderate yields (63−77%).
The 1H NMR spectra of compounds 3a−3d were also nearly
identical with those of 1a−1d. The mixed phosphine−
phosphine oxide ligands had very similar distinctive peaks for
the protons α to the phosphorus atoms, which were shifted
only moderately from their fully oxidized forms. The proton α
to the two equivalent phosphoryl functionalities displayed a
unique multiplet between 4.1 and 3.1 ppm, while the protons α
to the reduced phosphorus center appeared as triplets of
doublets, around 3.0 to 2.4 ppm.
The 31P NMR spectra of yttrium complexes 4a−4d displayed
a major product in solution as well as several minor products all
with similar chemical shifts. The phosphorus peaks were
somewhat broad, indicating that an equilibrium between the
different species in solution was occurring on a time scale
With the partially reduced ligands in hand, further attempts
to fully reduce the ligands met with little success. As in the case
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Figure 3. ORTEP3 representation (thermal ellipsoids at 50% probability) and atom numbering for 4a. Most of the hydrogen atoms are omitted for
clarity.
comparable to that of the NMR experiment. For 4c especially,
the phosphorus peaks were quite broad because not only was
an equilibrium near the time scale of the NMR experiment
occurring between the different structural isomers but also an
interconversion of various rotamers. Variable-temperature
NMR studies on 4a−4d illustrated that these processes could
be frozen out, with all of the minor species, as well as the peaks
representing the phosphoryl rotamers for 4c, becoming more
distinct. Three separate sets of peaks could be identified for
4a−4d: the pendant diarylphosphine functionality (−44 to −10
ppm), the equivalent phosphoryl groups (around 40 ppm), and
the triphenylphosphine oxide ligand (around 36 ppm). The
phosphoryl functionalities for 4a−4c coupled to the yttrium
center (2JYP approximately 6 Hz) as well as the pendant
diarylphosphine throughspace and thus exhibited a doublet of
doublets, whereas 4c did not show any coupling even at −60
°C. In addition, the triphenylphosphine oxide ligand coupled to
the yttrium center and displayed a doublet for all of the yttrium
complexes (2JYP approximately 10 Hz).
For 4a−4d, only one broad peak was seen in the negative
region, which we believe represents overlapping signals for the
reduced phosphorus centers of the major and minor species in
solution. It is also believed that the different species in solution
are very fluxional and the different phosphorus peaks represent
interconverting structural isomers that differ in the arrangement
of the nitrate and triphenylphosphine oxide ligands, as well as
yttrium species that differ in the number of triphenylphosphine
oxide ligands on the metal.
solution could not be differentiated from one another because
their chemical shifts were nearly identical and overlapped. The
distinctive peak for the protons α to the diarylphosphine was
found to be between 4.5 and 3.8 ppm, while the distinctive peak
for the proton α to the phosphoryl groups was found to be
between 3.2 and 2.4 ppm, much like compounds 1a−d and
3a−3d. Moreover, for 4a−4c, the proton α to the diary-
lphosphine moiety coupled to the phosphorus and adjacent
proton and therefore exhibited a doublet of triplets, while 4c
displayed only a broad signal at −40 °C.
Crystals of 4a suitable for single-crystal X-ray diffraction
studies were grown from a concentrated solution of the
complex in acetonitrile. It is evident from the crystal structure
that the reduced phosphorus functionality is indeed pendant
and the phosphine oxide functionalities preferentially bind the
early transition metal (see Figure 3). Much like 2a−2d, the
yttrium complex is nine-coordinate and has a distorted
tricapped trigonal-prismatic geometry. Three of the vertices
of the trigonal prism are occupied by nitrate oxygen atoms,
while the other three vertices are comprised of the
triphenylphosphine oxide ligand, a nitrate oxygen atom, and
one phosphoryl moiety of the mixed phosphine−phosphine
oxide ligand (O3P4). The three capping positions outside of
the rectangular faces of the trigonal prism are occupied by two
nitrate oxygen atoms and the remaining phosphoryl group of
ligand 3a. Furthermore, the P2−C1−P3 bond angle is more
compressed for 4a than for 2a, 108.4(1)° versus 110.6(5)°, and
the P1−C2−C1 angle, which is no longer constrained by three
sites binding to the metal center, has relaxed from 119.6(9)° to
111.8(5)° (for further notable bond lengths and angles, see the
Supporting Information, Table S3). When crystals of 4a were
dissolved in an NMR solvent and a 31P NMR spectrum was
taken, the same fluxional behavior that was discussed previously
was seen. This supports the hypothesis that the minor species
present in solution are the result of rapid equilibria between
various closely related structural isomers and that this fluxional
behavior is a product of dissolving the complexes in a solvent.
With respect to the possibility of using ligands 3a−3d for the
synthesis of early−late bimetallic complexes, it has been shown
in this work that the hard phosphoryl functionalities of the
Additional variable-temperature NMR studies were con-
ducted to further elucidate what was occurring in solution. We
found that the addition of 1 or 2 equiv of OPPh3 increased the
intensity of several signals assigned to minor species in solution,
but not all of them. This indicated that some of the species in
solution do arise from different numbers of OPPh3 binding to
the same metal center, a redistribution process well-known in
the literature,77,78 but some of the minor species arise from
different arrangements of the nitrate and phosphine oxide
ligands.
1
The H NMR spectra of 4a−4d supported these findings in
that the peaks were fairly broad and the different species in
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Inorganic Chemistry
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partially reduced ligands preferentially bind early transition
metals and that the softer phosphine moieties do not. It is
known in the literature that heterobimetallic systems can have
unique reactivity that involves the cooperation of both metals,
where electron-poor early transition metals and electron-rich
late transition metals create an ideal environment for the
heterolytic cleavage of polar bonds.79−84 With these ligands in
hand, we are currently investigating their properties for the
synthesis of heterobimetallic systems and the application of
these systems for the cooperative, heterolytic cleavage of polar
substrates.
mild reduction conditions reported by Jenkins et al. employing
1-pentanethiol and triflic anhydride for the partial reduction of
diphosphine oxides were successful in partially reducing the
ligand without causing ligand fragmentation.75 The conditions
utilized were chemoselective for the reduction of the unique,
less-crowded phosphoryl functionality, and the resulting mixed
phosphine−phosphine oxide ligands, 3a−3d, were recognized
as ligands capable of supporting early−late bimetallic
complexes. To test the selectivity of the different phosphorus
moieties of the partially reduced ligands for the binding of
transition metals, compounds 3a−3d were also bound to
yttrium. The yttrium complexes generated, 4a−4d, were found
to be neutral, nine-coordinate species, much like 2a−2d, but
with a pendant phosphine functionality. This finding supports
the hypothesis that the hard phosphoryl functionalities of 3a−
3d preferentially bind early transition metals, while the softer
phosphine moieties do not, and gives promise for utilizing these
ligands to synthesize heterobimetallic systems. Yttrium
complexes 2a−2d were activated with base, and their activity
for the ROP of ε-caprolactone was investigated. It was found
that the catalytic systems were extremely slow and that the base
by itself was actually a superior catalyst to the activated yttrium
complexes, which could, in fact, be acting as base inhibitors.
ROP of ε-Caprolactone Utilizing 2a−2d. Several yttrium
complexes have been reported in the literature that are effective
catalysts for the ROP of ε-caprolactone.85−94 All of the yttrium
catalysts described employ various bases coordinated to the
metal center that are used to initiate the polymerization
reaction. It is also known that anionic initiators themselves can
catalyze the ROP of ε-caprolactone and that the nature of the
products depends on the concentration of the monomer in
solution: at low concentrations, cyclic oligomers form, but at
higher concentrations, linear polymers are preferred.95−97
In order to generate catalysts capable of ROP, complexes
2a−2d were preactivated with base before being exposed to a
solution of ε-caprolactone. These systems were extremely slow,
often taking over 1 day to reach complete conversion, and we
saw a general trend that, as the electron-donating ability of the
ligands increased, there was a concomitant increase in the
activity of the catalysts (see the Supporting Information, Table
S6). In addition, the polydispersity indexes (PDIs) generated
by the yttrium systems were quite large, which indicates that
the catalysts most likely do not perform living polymerization.
Our findings also suggest, however, that base alone is sufficient
to effectively catalyze the ROP of ε-caprolactone under the
reaction conditions; KOtBu was actually more effective than all
of our activated complexes by a significant amount. This
indicates that 2a−2d may not be catalysts at all but may act as
base inhibitors, and the elevated activity of the more electron-
rich systems could reflect a lower affinity for binding alkoxide
base.
EXPERIMENTAL SECTION
■
General Considerations. All procedures and manipulations were
performed under an argon or nitrogen atmosphere using standard
Schlenk-line and glovebox techniques unless stated otherwise. All
solvents were degassed and dried using standard procedures prior to
all manipulations and reactions unless stated otherwise. Deuterated
solvents were purchased from Cambridge Isotope Laboratories or
Sigma Aldrich, degassed, and dried over activated molecular sieves
prior to use. ε-Caprolactone used for polymerization experiments was
degassed and dried over activated molecular sieves prior to use. All
other reagents were purchased from commercial sources and utilized
without further purification. KOtBu used for the polymerization
experiments was purchased from Sigma Aldrich and was 99.99% pure
(sublimed). The electrospray ionization mass spectrometry (ESI-MS)
data were collected on an AB/Sciex QStar mass spectrometer with an
ESI source, the electron impact mass spectrometry (EI-MS) data were
collected on a Waters GC ToF mass spectrometer with an EI/CI
source, and the DART-MS data were collected on a JEOL AccuTOF-
DART mass spectrometer with a DART-ion source (no solvent is
required). NMR spectra were recorded at ambient temperature and
pressure using a Varian Gemini 400 MHz spectrometer (400 MHz for
1H, 100 MHz for 13C, and 161 MHz for 31P) unless stated otherwise.
CONCLUSION
■
We have synthesized a series of four phosphine oxide ligands,
1a−1d, and four mixed phosphine−phosphine oxide ligands,
3a−3d, which were coordinated to yttrium to generate early-
transition-metal complexes 2a−2d and 4a−4d. The tripodal
phosphine oxide ligands 1a−1d were produced in an
unexpected trisubstitution reaction of bromoacetaldehyde
diethyl acetal and were identified as promising extraction
agents for nuclear fuel treatment. Although the mechanism of
this process is currently unknown, it is suspected that the
products are generated through a series of E1cb reactions and
unsaturated intermediates, all of which depend on the crucial
first substitution of a bromide with a phosphoryl functionality.
In order to investigate the ability of the trisphosphine oxide
ligands to act as lanthanide extraction agents, their coordination
behavior toward yttrium, a well-established model for the rare-
earth metals, was examined. The yttrium complexes thus
synthesized, 2a−2d, were neutral nine-coordinate species that
displayed a tricapped trigonal-prismatic geometry, and their
solubility in organic solvents could be tuned depending on the
amount of ligand in solution. Attempts were made to reduce
compounds 1a−1d, but all conventional methods for reducing
phosphine oxides met with little success. Only the extremely
1
The H and 13C NMR spectra were measured relative to partially
deuterated solvent peaks but are reported relative to tetramethylsilane.
All 31P chemical shifts were measured relative to 85% phosphoric acid
as an external reference. Elemental analyses were performed at the
Department of Chemistry, University of Toronto, on a Perkin-Elmer
2400 CHN elemental analyzer. Single-crystal X-ray diffraction data
were collected using a Nonius Kappa CCD or Bruker Kappa APEX
DUO diffractometer with Mo Kα radiation (λ = 0.71073 Å). The
CCD data were integrated and scaled using the Denzo-SMN package.
The structures were solved and refined using SHELXTL V6.1.
Refinement was by full-matrix least squares on F2 using all data.
Number-average molecular weights (Mn) and PDIs were measured by
size-exclusion chromatography (SEC) using a Waters 1515 system
equipped with a Waters 2707 autosampler, a Waters 2414 refractive
index detector, and a Styragel HR 5E THF 7.8 × 300 mm column
using tetrahydrofuran (THF) as the eluent at a flow rate of 1.0 mL/
min at 40 °C, calibrated with commercial polystyrene standards.
Because of the structural differences between polycaprolactone (PCL)
and polystyrene (PSt) units, we used a reported relationship to
calculate the PCL molecular weights from PS-based SEC values
(Mn,PCL = 0.56Mn,PSt).86
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Article
Synthesis of 1a (C38H33O3P3). Diphenylphosphine oxide (1.186 g,
5.9 mmol) was dissolved in THF (5 mL) and added to a suspension of
KH (0.235 g, 5.9 mmol) in THF (3 mL). Gas evolved, and the
solution turned orange in color. After 30 min, gas evolution ceased and
the solution was clear and orange. Bromoacetaldehyde diethyl acetal
(0.677 g, 2.0 mmol) was added, and the solution turned less orange
and cloudier over 15 min. The reaction was stirred overnight and
turned milky orange in color. Water (20 mL) was added, and the
solution was extracted with dichloromethane (DCM; 2 × 20 mL) and
ether (2 × 20 mL). The combined organic layers were dried over
MgSO4 and filtered. The solvent was removed under reduced pressure,
and the white solid was washed with ether. Yield: 61.1% (0.753 g).
Crystals of 1a suitable for X-ray diffraction studies were grown from
(d, C−P, 1JCP = 17.9 Hz), 131.79 (s, Ar−CH), 131.70 (t, Ar−CH, 2JCP
1
= 9.0 Hz), 131.56−131.46 (m, Ar−CH), 130.37 (d, C−P, JPP = 9.6
Hz), 128.82 (s, Ar−CH), 128.60 (s, Ar−CH), 128.53 (s, Ar−C),
128.44 (t, Ar−CH, 2JCP = 12.8 Hz), 40.31 (td, CH, 1JCP = 55.8 Hz, 2JCP
1
= 14.0 Hz), 24.92 (d, CH2, JCP = 21.4 Hz). Anal. Calcd for
C38H33O2P3·0.5C4H10O: C, 73.72; H, 5.41. Found: C, 73.98; H, 5.64.
MS (DART; m/z+): 615.2 ([C38H34O2P3]+).
Synthesis of 3b (C44H45O2P3). Similar to the synthesis of 3a; see
the Supporting Information, pages S6 and S7.
Synthesis of 3c (C44H45O2P3). Similar to the synthesis of 3a; see
the Supporting Information, pages S7 and S8.
Synthesis of 3d (C44H45O2P3). Similar to the synthesis of 3a; see
the Supporting Information, pages S8 and S9.
1
Synthesis of 4a [Y(NO3)3(OPPh3)(3a)]. 3a (0.100 g, 0.163 mmol)
was dissolved in 3 mL of CH3CN. A solution of [Y(H2O)6][NO3]3
(0.062 g, 0.163 mmol) in 1 mL of CH3CN was added. The mixture
was allowed to stir for 5 min. A solution of triphenylphosphine oxide
(0.045 g, 0.163 mmol) in 1 mL of CH3CN was added. The solution
was removed under reduced pressure, and the white solid was washed
with a 5:1 mixture of ether/DCM (5 mL). Yield: 66.8% (0.127 g).
Crystals suitable for X-ray diffraction studies were obtained from a
the slow evaporation of ether. H NMR (400 MHz, CD3Cl): δ 7.82−
7.75 (m, 4H, Ar−H), 7.71−7.63 (m, 4H, Ar−H), 7.35−7.13 (m, 22H,
Ar−H), 4.75−4.59 (m, 1H, CH), 3.16−3.02 (m, 2H, CH2). 31P NMR
3
(161 MHz, CD3Cl): δ 30.78 (d, J = 14.1 Hz), 28.45 (t, JPP = 14.1
1
Hz). 13C NMR (100 MHz, CD3Cl): δ 133.34 (d, Ar−C, JCP = 100.9
1
Hz), 131.96−131.68 (m, Ar−CH), 131.73 (dd, Ar−C, JCP = 100.8
Hz, 4JCP = 3.7 Hz), 131.55−131.39 (m, Ar−CH), 130.57 (d, Ar−CH, J
= 9.6 Hz), 128.62−128.19 (m, Ar−CH), 35.05 (td, CH, J = 56.3 and
4.7 Hz), 24.24 (d, CH2, 1JCP = 66.2 Hz). Anal. Calcd for C38H33O3P3:
C, 72.38; H, 5.27. Found: C, 72.25; H, 5.65. MS (DART; m/z+): 631.1
([C38H34O3P3]+).
1
concentrated sample of 3a in CH3CN. H NMR (400 MHz, CD2Cl2,
−20 °C): δ 7.68−7.09 (m, 38H, Ar−H), 6.83 (t, 6H, Ar−H, 2JCP = 7.4
Hz), 4.03−3.89 (m, 1H, CH), 2.51 (td, 2H, CH2, 1JCP = 15.7 Hz, 2JCP
= 6.2 Hz). Major product. 31P NMR (161 MHz, CD2Cl2, −20 °C): δ
Synthesis of 1b (C44H45O3P3). Similar to the synthesis of 1a; see
the Supporting Information, pages S2 and S3.
Synthesis of 1c (C44H45O3P3). Similar to the synthesis of 1a; see
the Supporting Information, pages S3 and S4.
Synthesis of 1d (C50H57O3P3). Similar to the synthesis of 1a; see
3
2
39.79 (dd, Ar2PO−CH, JPP = 11.2 Hz, JYP = 5.9 Hz, 36.5%), 35.72
(d, OPPh3, 2JYP = 10.1 Hz, 21.5%), −14.05 (app t, Ar2P−CH2, 19.0%).
Minor species in solution. 31P NMR (161 MHz, CD2Cl2, −20 °C): δ
41.40 (d, 2JYP = 7.9 Hz, 2.1%), 40.16 (dd, 3JPP = 11.6 Hz, 2JYP = 5.8 Hz,
2.1%), 39.40 (d, 2JYP = 5.7 Hz, 4.4%), 39.02 (dd, 3JPP = 13.9 Hz, 2JYP
=
the Supporting Information, pages S4 and S5.
2
5.2 Hz, 1.4%), 38.13−37.78 (m, 0.7%), 37.55 (d, JYP = 10.9 Hz,
Synthesis of 2a [Y(NO3)3(1a)]. 1a (0.100 g, 0.16 mmol) was
dissolved in CH3CN (4 mL). A solution of [Y(H2O)6][NO]3 (0.061 g,
0.14 mmol) in CH3CN (1 mL) was added, and the mixture was stirred
for 15 min. A white precipitate formed. The precipitate was filtered
and washed with DCM (2 × 5 mL). Yield: 95.4% (0.137 g). Crystals
suitable for X-ray diffraction studies were obtained from a 2:1 mixture
of 1a and [Y(H2O)6][NO]3 in CH3CN diffused with ether. NMR
spectra could not be obtained because 2a was sparingly soluble in
common NMR solvents other than DMSO-d6, in which the DMSO
displaced the phosphine oxide ligand. Anal. Calcd for
C38H33N3O12P3Y: C, 50.40; H, 3.67; N, 4.64. Found: C, 50.68; H,
3.71; N, 4.86. MS (DART; m/z+): 631.2 ([C38H34O3P3]+).
Synthesis of 2b [Y(NO3)3(1b)]. Similar to the synthesis of 2a; see
the Supporting Information, page S5.
2
3.2%), 37.36 (d, JYP = 5.5 Hz, 1.4%), 36.69−36.56 (m, 3.5%), 35.18
2
(d, JYP = 9.4 Hz, 4.6%). 13C NMR (100 MHz, CD2Cl2, −20 °C): δ
136.15 (d, C−P, 1JCP = 14.3 Hz), 133.57 (s, Ar−CH), 133.48 (s, Ar−
CH), 132.85 (s, Ar−CH), 132.64 (s, Ar−CH), 132.53−132.09 (m,
Ar−CH), 131.40−131.1 (m, Ar−CH), 131.03−130.65 (m, Ar−CH),
129.47−128.26 (m, Ar−CH), 127.56 (d, C−P, 1JCP = 22.5 Hz), 124.17
(d, C−P, 1JCP = 104.5 Hz), 35.94 (td, CH, 1JCP = 53.6 Hz, 3JCP = 18.2
1
Hz), 23.62 (d, CH2, JCP = 21.6 Hz). Anal. Calcd for
C56H48N3O12P4Y·0.5CH2Cl2: C, 56.07; H, 4.08; N, 3.47. Found: C,
56.08; H, 4.22; N, 3.78. MS (ESI; DCM; m/z+): 615.2
([C38H34O2P3]+).
Synthesis of 4b [Y(NO3)3(OPPh3)(3b)]. Similar to the synthesis
of 4a; see the Supporting Information, pages S9 and S10.
Synthesis of 4c [Y(NO3)3(OPPh3)(3c)]. Similar to the synthesis of
4a; see the Supporting Information, pages S10 and S11.
Synthesis of 2c [Y(NO3)3(1c)]. Similar to the synthesis of 2a; see
the Supporting Information, page S6.
Synthesis of 4d [Y(NO3)3(OPPh3)(3d)]. Similar to the synthesis
of 4a; see the Supporting Information, pages S11 and S12.
Polymerization Procedure. Under a nitrogen atmosphere in a
glovebox, a stock solution of 0.012 g of KOtBu in 10 mL of THF was
prepared. A vial was charged with 0.0111 mmol of catalyst (0.010 g for
2a, 0.011 g for 2b or 2c, and 0.012 g for 2d) and 1 mL of the stock
base solution and stirred for 5 min. A solution of 0.630 g of
caprolactone (5.56 mmol) in 2.12 mL of THF was then added. The
polymerization reaction was quenched with an excess of 1.0 M HCl
and dried under vacuum to a constant weight.
Synthesis of 2d [Y(NO3)3(1d)]. Similar to the synthesis of 2a; see
the Supporting Information, page S6.
Synthesis of 3a (C38H33O2P3). The preparation of 3a was
conducted using a synthesis previously reported by Jenkins et al.75 1a
(0.744 g, 1.18 mmol) was dissolved in 15 mL of DCM. The solution
was cooled to 0 °C, and triflic anhydride (0.111 g, 0.393 mmol) was
added. The solution turned pale yellow in color. After aging for 30
min, 1-pentanethiol (0.492 g, 4.72 mmol) and N,N-diisopropylethyl-
amine (0.305 g, 2.36 mmol) were added. The solution quickly turned
darker yellow in color. The solution was left for 16 h. The solution
turned darker yellow in color. The reaction mixture was washed with a
5% NaHCO3 solution (2 × 30 mL) and dried over anhydrous Na2SO4.
The mixture was filtered, and the solvent was removed under reduced
pressure. The crude yellow oil was dissolved in DCM and immobilized
on a silica plug. The silica was washed with DCM and acetonitrile. The
product was eluted with methanol, the solvent was removed under
reduced pressure, and the yellow paste was recrystallized with cold
ether and THF to yield a fine white powder. Yield: 48.3% (0.350 g).
1H NMR (400 MHz, CD3Cl): δ 7.71−7.59 (m, 8H, Ar), 7.44−7.35
(m, 4H, Ar−H), 7.34−7.17 (m, 14H, Ar−H), 7.03−6.96 (m, 4H, Ar−
H), 3.48−3.31 (m, 1H, CH), 2.58 (td, 2H, CH2, 1JHH = 14.6 Hz, 2JHP
= 6.9 Hz). 31P NMR (161 MHz, CD3Cl): δ 30.44 (d, 3JPP = 13.3 Hz),
ASSOCIATED CONTENT
■
S
* Supporting Information
Extended experimental section, crystal structure bond lengths
and angles for 1a−1d, 2a−2d, and 4a, crystallographic data
tables for 1a−1d, 2a−2d, and 4a (including CIF files), and
ROP of ε-caprolactone using 2a−2d and base. This material is
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
3
−13.17 (t, JPP = 13.3 Hz). 13C NMR (100 MHz, CD3Cl): δ 137.60
Corresponding Author
*E-mail: rmorris@chem.utoronto.ca.
(d, C−P, 1JCP = 16.6 Hz), 132.06 (d, Ar−CH, 2JCP = 19.5 Hz), 132.25
9330
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Inorganic Chemistry
Article
(32) Lofgren, A.; Albertsson, A.-C.; Dubois, P.; Jer
́
o
̂
me, R. J.
̈
Notes
Macromol. Sci., Part C: Polym. Rev. 1995, 35, 379−418.
(33) Li, X.; Zhu, Y.; Ling, J.; Shen, Z. Macromol. Rapid Commun.
2012, 33, 1008−1013.
(34) Li, G.; Lamberti, M.; Mazzeo, M.; Pappalardo, D.; Roviello, G.;
Pellecchia, C. Organometallics 2012, 31, 1180−1188.
(35) Platel, R. H.; White, A. J. P.; Williams, C. K. Inorg. Chem. 2011,
50, 7718−7728.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank NSERC Canada for a Discovery grant to R.H.M. and
Fatme Dahcheh for assistance in running polymerization
samples.
(36) Broderick, E. M.; Guo, N.; Vogel, C. S.; Xu, C.; Sutter, J.; Miller,
J. T.; Meyer, K.; Mehrkhodavandi, P.; Diaconescu, P. L. J. Am. Chem.
Soc. 2011, 133, 9278−9281.
REFERENCES
(1) Byer, R. L. Science 1988, 239, 742−747.
(2) Lu, J.; Ueda, K.-I.; Yagi, H.; Yanagitani, T.; Akiyama, Y.;
Kaminskii, A. A. J. Alloys Compd. 2002, 341, 220−225.
(3) Kinsman, K. M.; McKittrick, J.; Sluzky, E.; Hesse, K. J. Am.
Ceram. Soc. 1994, 77, 2866−2872.
(4) Linares, R. C. Solid State Commun. 1964, 2, 229−231.
(5) Evans, W. J.; Sollberger, M. S. Inorg. Chem. 1988, 27, 4417−4423.
(6) Parker, D. Chem. Soc. Rev. 1990, 19, 271−291.
(7) Jang, Y. H.; Blanco, M.; Dasgupta, S.; Keire, D. A.; Shively, J. E.;
Goddard, W. A. J. Am. Chem. Soc. 1999, 121, 6142−6151.
(8) Werner, M. E.; Karve, S.; Sukumar, R.; Cummings, N. D.; Copp,
J. A.; Chen, R. C.; Zhang, T.; Wang, A. Z. Biomaterials 2011, 32,
8548−8554.
(9) Jankovic, D.; Vranjes-djuric, S.; Djokic, D.; Markovic, M.;
Ajdinovic, B.; Jaukovic, L.; Nikolic, N. J. Pharm. Sci. 2012, 101, 2194−
2203.
(10) Liu, Z.; Shi, J.; Jia, B.; Yu, Z.; Liu, Y.; Zhao, H.; Li, F.; Tian, J.;
Chen, X.; Liu, S.; Wang, F. Mol. Pharm. 2011, 8, 591−599.
(11) Poorbaygi, H.; Aghamiri, S. M. R.; Sheibani, S.; Kamali-asl, A.;
Mohagheghpoor, E. Appl. Radiat. Isot. 2011, 69, 1407−1414.
(12) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2001, 637−638.
(13) Coughlin, E. B.; Bercaw, J. E. J. Am. Chem. Soc. 1992, 114,
7606−7607.
(14) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2002, 103, 283−
316.
■
(37) Tschan, M. J. L.; Brule, E.; Haquette, P.; Thomas, C. M. Polym.
Chem. 2012, 3, 836−851.
(38) Carpentier, J.-F. Angew. Chem., Int. Ed. 2010, 49, 2662−2663.
(39) Williams, C. K.; Hillmyer, M. A. Polym. Rev. 2008, 48, 1−10.
(40) Platel, R. H.; Hodgson, L. M.; Williams, C. K. Polym. Rev. 2008,
48, 11−63.
(41) Inkinen, S.; Hakkarainen, M.; Albertsson, A.-C.; Sodergard, A.
̈
̊
Biomacromolecules 2011, 12, 523−532.
(42) Dove, A. P. Chem. Commun. 2008, 6446−6470.
(43) Vicente, G.; Zinner, L. G.; Rothschild, L. Inorg. Chim. Acta 1974,
9, 213−216.
(44) Vicentini, G.; Machado, L. C. J. Inorg. Nucl. Chem. 1981, 43,
1676−1680.
(45) Zinner, L. B.; Vicentini, G.; Rothschild, L. J. Inorg. Nucl. Chem.
1974, 36, 2499−2505.
(46) Vicentini, G.; Prado, J. C. J. Inorg. Nucl. Chem. 1972, 34, 1309−
1317.
(47) Turanov, A. N.; Karandashev, V. K.; Baulin, V. E. Solvent Extr.
Ion Exch. 2007, 25, 165−186.
(48) Turanov, A. N.; Karandashev, V. K.; Baulin, V. E.; Yarkevich, A.
N.; Safronova, Z. V. Solvent Extr. Ion Exch. 2009, 27, 551−578.
(49) Nash, K. L.; Barrans, R. E.; Chiarizia, R.; Dietz, M. L.; Jensen, M.
P.; Rickert, P. G.; Moyer, B. A.; Bonnesen, P. V.; Bryan, J. C.;
Sachleben, R. A. Solvent Extr. Ion Exch. 2000, 18, 605−631.
(50) Eccles, H. Solvent Extr. Ion Exch. 2000, 18, 633−654.
(51) Nilsson, M.; Nash, K. L. Solvent Extr. Ion Exch. 2007, 25, 665−
701.
(15) Gromada, J. R. M.; Carpentier, J.-F.; Mortreux, A. Coord. Chem.
Rev. 2004, 248, 397−410.
(16) Yasuda, H.; Ihara, E. Tetrahedron 1995, 51, 4563−4570.
(17) Kaneko, H.; Nagae, H.; Tsurugi, H.; Mashima, K. J. Am. Chem.
Soc. 2011, 133, 19626−19629.
(52) Dam, H. H.; Reinhoudt, D. N.; Verboom, W. Chem. Soc. Rev.
2007, 36, 367−377.
(53) Lumetta, G. J.; Gelis, A. V.; Vandegrift, G. F. Solvent Extr. Ion
Exch. 2010, 28, 287−312.
(18) Jian, Z.; Petrov, A. R.; Hangaly, N. K.; Li, S.; Rong, W.; Mou, Z.;
Rufanov, K. A.; Harms, K.; Sundermeyer, J. R.; Cui, D. Organometallics
2012, 31, 4267−4282.
(54) Mathur, J. N.; Murali, M. S.; Nash, K. L. Solvent Extr. Ion Exch.
2001, 19, 357−390.
(19) Hannedouche, J.; Aillaud, I.; Collin, J.; Schulz, E.; Trifonov, A.
Chem. Commun. 2008, 3552−3554.
(55) Berny, F.; Muzet, N.; Troxler, L.; Dedieu, A.; Wipff, G. Inorg.
Chem. 1999, 38, 1244−1252.
(20) Kim, J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 1737−1739.
(21) Molander, G. A.; Knight, E. E. J. Org. Chem. 1998, 63, 7009−
7012.
(56) Boehme, C.; Wipff, G. Inorg. Chem. 2002, 41, 727−737.
(57) Coupez, B.; Boehme, C.; Wipff, G. Phys. Chem. Chem. Phys.
2002, 457165729.
(22) Molander, G. A.; Nichols, P. J. J. Am. Chem. Soc. 1995, 117,
(58) Ward, T. M.; Allcox, I. L.; Wahl, G. H., Jr. Tetrahedron Lett.
1971, 12, 4421−4424.
4415−4416.
(23) Evans, W. J.; Shreeve, J. L.; Doedens, R. J. Inorg. Chem. 1993, 32,
245−246.
(59) Baaden, M.; Berny, F.; Boehme, C.; Muzet, N.; Schurhammer,
R.; Wipff, G. J. Alloys Compd. 2000, 303−304, 104−111.
(60) Sues, P. E.; Lough, A. J.; Morris, R. H. Organometallics 2011, 30,
4418−4431.
(24) Cao, Y.; Du, Z.; Li, W.; Li, J.; Zhang, Y.; Xu, F.; Shen, Q. Inorg.
Chem. 2011, 50, 3729−3737.
(25) Qian, C.; Zhu, D. J. Chem. Soc., Dalton Trans. 1994, 1599−1603.
(26) Cao, T.-P.-A.; Buchard, A.; Le Goff, X. F.; Auffrant, A.; Williams,
C. K. Inorg. Chem. 2012, 51, 2157−2169.
(61) Khachatryan, R. A. G.; Yu, N.; Indzhikyan, M. G. Russ. J. Gen.
Chem. 1994, 64, 1134−1138.
(62) Kabachnik, M. I.; Medved, T. Y.; Polikarpov, Y. M.; Yudina, K.
S. Russ. Chem. Bull. 1967, 16, 568−572.
(27) Amgoune, A.; Thomas, C. M.; Carpentier, J.-F. Macromol. Rapid
Commun. 2007, 28, 693−697.
(63) Zhang, J.; Li, A.; Hor, T. S. A. Dalton Trans. 2009, 9327−9333.
(64) Zhang, J.; Braunstein, P.; Hor, T. S. A. Organometallics 2008, 27,
4277−4279.
(28) Alaaeddine, A.; Thomas, C. M.; Roisnel, T.; Carpentier, J.-F.
Organometallics 2009, 28, 1469−1475.
(29) Ovitt, T. M.; Coates, G. W. J. Am. Chem. Soc. 1999, 121, 4072−
4073.
(65) Reger, D. L.; Semeniuc, R. F.; Gardinier, J. R.; O’Neal, J.;
Reinecke, B.; Smith, M. D. Inorg. Chem. 2006, 45, 4337−4339.
(66) Reger, D. L.; Elgin, J. D.; Semeniuc, R. F.; Pellechia, P. J.; Smith,
M. D. Chem. Commun. 2005, 4068−4070.
(30) Chamberlain, B. M.; Sun, Y.; Hagadorn, J. R.; Hemmesch, E.
W.; Young, V. G.; Pink, M.; Hillmyer, M. A.; Tolman, W. B.
Macromolecules 1999, 32, 2400−2402.
(31) Zhong, Z.; Dijkstra, P. J.; Feijen, J. Macromol. Chem. Phys. 2000,
201, 1329−1333.
(67) Lopez Aparicio, F. J.; Zorrilla Benitez, F. J.; Alvarez-Manzaneda
Roldan, E. J. An. Quim., Ser. C 1988, 84, 277−284.
9331
dx.doi.org/10.1021/ic3010147 | Inorg. Chem. 2012, 51, 9322−9332

Inorganic Chemistry
Article
(68) Yavari, I.; Hadigheh-Rezvan, V. Phosphorus, Sulfur, Silicon Relat.
Elem. 2001, 174, 151−162.
(69) Popovici, C.; Fernandez, I.; Ona-Burgos, P.; Roces, L.; Garcia-
Granda, S.; Ortiz, F. L. Dalton Trans. 2011, 40, 6691−6703.
(70) Ge, Y. W.; Sharp, P. R. Inorg. Chem. 1992, 31, 379−384.
(71) Ye, C.; Sharp, P. R. Inorg. Chem. 1995, 34, 55−59.
(72) Wells, K. D.; McDonald, R.; Ferguson, M. J.; Cowie, M. Inorg.
Chem. 2011, 50, 3523−3538.
(73) Sharp, P. R.; Ge, Y. W. J. Am. Chem. Soc. 1987, 109, 3796−3797.
(74) Ge, Y. W.; Sharp, P. R. Organometallics 1988, 7, 2234−2236.
(75) Petersson, M. J.; Loughlin, W. A.; Jenkins, I. D. Chem. Commun.
2008, 4493−4494.
(76) Zhang, W.-H.; Chien, S. W.; Hor, T. S. A. Coord. Chem. Rev.
2011, 255, 1991−2024.
(77) Deakin, L.; Levason, W.; Popham, M. C.; Reid, G.; Webster, M.
J. Chem. Soc., Dalton Trans. 2000, 2439−2447.
(78) Hill, N. J.; Levason, W.; Popham, M. C.; Reid, G.; Webster, M.
Polyhedron 2002, 21, 445−455.
(79) Kalck, P.; Serra, C.; Machet, C.; Broussier, R.; Gautheron, B.;
Delmas, G.; Trouve, G.; Kubicki, M. Organometallics 1993, 12, 1021−
1022.
(80) Oishi, M.; Kato, T.; Nakagawa, M.; Suzuki, H. Organometallics
2008, 27, 6046−6049.
(81) Baranger, A. M.; Hollander, F. J.; Bergman, R. G. J. Am. Chem.
Soc. 1993, 115, 7890−7891.
(82) Cornelissen, C.; Erker, G.; Kehr, G.; Frohlich, R. Organometallics
̈
2004, 24, 214−225.
(83) Ozawa, F.; Park, J. W.; Mackenzie, P. B.; Schaefer, W. P.;
Henling, L. M.; Grubbs, R. H. J. Am. Chem. Soc. 1989, 111, 1319−
1327.
(84) Ferguson, G. S.; Wolczanski, P. T.; Parkanyi, L.; Zonnevylle, M.
C. Organometallics 1988, 7, 1967−1979.
(85) Save, M.; Schappacher, M.; Soum, A. Macromol. Chem. Phys.
2002, 203, 889−899.
(86) Ling, J.; Liu, J.; Shen, Z.; Hogen-Esch, T. E. J. Polym. Sci. A,
Polym. Chem. 2011, 49, 2081−2089.
(87) Stevels, W. M.; Ankone,
Macromolecules 1996, 29, 8296−8303.
(88) Martin, E.; Dubois, P.; Jer me, R. Macromolecules 2000, 33,
1530−1535.
́
M. J. K.; Dijkstra, P. J.; Feijen, J.
́ ̂
o
(89) Gou, P.; Zhu, W.; Shen, Z. Front. Chem. Eng. China 2008, 3,
330−337.
(90) Wang, Y.; Onozawa, S.-Y.; Kunioka, M. Green Chem. 2003, 5,
571−574.
(91) Susperregui, N.; Kramer, M. U.; Okuda, J.; Maron, L.
Organometallics 2011, 30, 1326−1333.
(92) Wang, L.; Cui, D.; Hou, Z.; Li, W.; Li, Y. Organometallics 2011,
30, 760−767.
(93) Jenter, J.; Roesky, P. W.; Ajellal, N.; Guillaume, S. M.;
Susperregui, N.; Maron, L. Chem.Eur. J. 2010, 16, 4629−4638.
(94) Ni, X.; Liang, Z.; Ling, J.; Li, X.; Shen, Z. Polym. Int. 2011, 60,
1745−1752.
(95) Ito, K.; Hashizuka, Y.; Yamashita, Y. Macromolecules 1977, 10,
821−824.
(96) Gitsov, I.; Ivanova, P. T.; Frec
Commun. 1994, 15, 387−393.
(97) Stridsberg, K.; Ryner, M.; Albertsson, A.-C. Adv. Polym. Sci.
2002, 157, 41−65.
́
het, J. M. J. Macromol. Rapid
9332
dx.doi.org/10.1021/ic3010147 | Inorg. Chem. 2012, 51, 9322−9332