Rare-Earth Metal Complexes Supported by Polydentate Phenoxy-Type Ligand Platforms: C-H Activation Reactivity and CO2/Epoxide Copolymerization Catalysis

Article abstract of DOI:10.1021/acs.inorgchem.0c02112

Mono- and dinuclear group 3 metal complexes incorporating polydentate bis(imino)phenoxy {N2O}- and bis(amido)phenoxy {N2O}3- ligands were synthesized by alkane elimination reactions from the tris(alkyl) M(CH2SiMe3)3(THF)2 and M(CH2C6H4-o-NMe2)3 (M = Sc, Y

Full text of DOI:10.1021/acs.inorgchem.0c02112

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Article
Rare-Earth Metal Complexes Supported by Polydentate Phenoxy-
Type Ligand Platforms: C−H Activation Reactivity and CO2/Epoxide
Copolymerization Catalysis
Liye Qu, Thierry Roisnel, Marie Cordier, Dan Yuan,* Yingming Yao,* Bei Zhao, and Evgueni Kirillov*
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ABSTRACT: Mono- and dinuclear group 3 metal complexes
incorporating polydentate bis(imino)phenoxy {N2O}− and bis-
(amido)phenoxy {N2O}3− ligands were synthesized by alkane
elimination reactions from the tris(alkyl) M(CH2SiMe3)3(THF)2
and M(CH2C6H4-o-NMe2)3 (M = Sc, Y) precursors. Complex 1a-
Y was used for the selective C−H activation of 2-phenylpyridine at
the 2′-phenyl position affording the corresponding bis(aryl)
product 3a-Y, which was found to be reacted reluctantly with
weak electrophiles (styrene, imines, hydrosilanes). The mechanism of formation of 3a-Y was established by DFT calculations, which
also corroborated high stability of the complex toward insertion of styrene, apparently stemming from the inability to form the
corresponding adduct. Copolymerization of cyclohexene oxide and CO2 promoted by 1a-Y (0.1−0.5 mol %) was demonstrated to
proceed under mild conditions (toluene, 70 °C, PCO2 = 12 bar) giving polycarbonates with high efficiency (maximal TON of 460)
and selectivity (97−99% of carbonate units).
Scheme 1. Proligands 1a-H and 1b-H3 Used in This Study
INTRODUCTION
■
Phenolate-based ligand platforms constitute a strong and
convenient alternative to cyclopentadienyl-type ligands for the
modern coordination chemistry of the early transition metals,
largely thanks to their remarkable tunability allowing diverse
sterico-electronic variations.1 In particular, these hard, electro-
negative π-donor ligands are attractive because they offer
strong metal−oxygen bonds that are expected to stabilize
complexes of highly oxophilic and electropositive metals (e.g.,
Group 3 metals).2 Rare-earth metal alkyl complexes have
shown great utility in many 100% atom-economy catalytic
reactions involving heteroatom-containing substrates, such as
C−H activation/functionalization of anilines, anisoles, amines,
and heterocycles,3,4 (co)polymerization of polar monomers
(lactones, carbonates, epoxides),5 and activation of CO2.6,7 As
such, there is continued interest in designing better performing
and more stable catalysts that also exhibit improved functional
group tolerance.
alkyl complexes; (ii) evaluation of potential of the titled alkyl
complexes as precatalysts of C−H activation of 2-phenyl-
pyridine and hydroarylation of styrene; (iii) stoichiometric
reactions between alkyl complexes and 2-phenylpyridine
mimicking the C−H activation step; (iv) evaluation of the
efficacy of some complexes obtained during this study in
copolymerization reactions of CO2 with cyclohexene oxide
(CHO).
Herein we report the synthesis and characterization of group
3 metal complexes supported by bulky multidentate bis-
(imino)phenolate and bis(anilino)phenolate ligand systems
(Scheme 1). The multidentate nature and high coordination
abilities of these ligand platforms have initially been anticipated
as beneficial for the preparation of dinuclear complexes or
formation of dinuclear intermediates in catalytic processes.
Special emphasis has been placed on (i) studies of the
coordination chemistry of this ligand systems with scandium
and yttrium, starting from tris(carbyl) precursors LnR3(THF)x,
in order to achieve selective synthesis of the corresponding
RESULTS AND DISCUSSION
■
Synthesis of Rare-Earth Metal Complexes Derived
from Proligands {N2O}H (1a-H) and {N2O}H3 (1b-H3). The
Received: July 16, 2020
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Scheme 2. Formation of Complexes 1a-M (M = Sc, Y) and 1a-Sc′
proligands, bis(imino)phenol 1a-H and bis(anilino)phenol 1b-
H3, were prepared in good yields (29−60%) using the
protocols reported in the literature.8 To study the coordination
ability of these ligand platforms with group 3 metals (Sc, Y), σ-
bond metathesis reactions between the corresponding
proligands and metal tris(alkyls) MR3(THF)2 were inves-
tigated.
Sc, substantial broadening was observed for the signals in the
aromatic region; thus, suggesting the existence of some
fluxional dynamic process probably related to the exchange
between the coordinated and pending imino functions.10
A
small amount (15% yield) of pure complex 1a-Sc was isolated
by recrystallization and characterized by X-ray crystallography
(vide infra).
Similar NMR scale reaction between 1a-H and 1 equiv of
Y(CH2SiMe3)3(THF)2 in C6D6 afforded 1a-Y quantitatively as
judged by 1H NMR spectroscopy. Thus, the scaled-up
synthesis was repeated allowing isolation of pure 1a-Y in
67% yield after recrystallization (Scheme 2). Complex 1a-Y
was characterized by 1H and 13C NMR spectroscopy and X-ray
crystallography. For this compound, a complex fluxional
behavior in solution was observed over a broad temperature
range. For example, the room-temperature 1H NMR spectrum
of 1a-Y (Figure S8) exhibited a series of broadened signals,
only a few of them could be unequivocally assigned: very broad
signals at δH 9.00−7.50 ppm from the CHN and C6H2
groups, broad multiplet at δH 3.18 ppm from the CH(CH3)2
protons and singlets at δH 0.12 and −0.71 ppm from the
Si(CH3)3 and CH2 protons, respectively, of the Y-CH2Si-
(CH3)3 groups. Upon lowering temperature to −40 °C (Figure
S9), the broad signals in the aromatic regions split into two
pairs of broad singlets, while the resonance from the CH2
protons in the high-field split into a series of three broad
signals. Although more detailed information about the solution
structure of 1a-Y could not be obtained, these observations are
consistent with the existence of the same exchange processes as
those depicted for 1a-Sc and I-Sc.9
The molecular structures of 1a-Sc (Figure S1) and 1a-Y
(Figure 1) are comparable to those of the penta-coordinate
{η2-1-[CHN−Ar]-2-O-3-tBu-C6H3}Y(CH2SiMe3)2(THF)
and six-coordinate {η2-1-[CHN−Ar]-2-O-3-tBu-C6H3}Y-
(CH2SiMe3)2(THF)2 complexes, respectively, reported pre-
viously.9 Thus, the respective distorted trigonal-bipyramidal
and octahedral coordination environments around the metal
centers are perfectly reproduced in the structures of 1a-Sc and
1a-Y. In 1a-Y, the Y−C(carbyl) and Y−N(1) bond lengths
(2.423(2), 2.438(2), and 2.5159(18) Å, respectively) are in the
range of those observed in the two yttrium complexes (2.398−
2.440 and 2.466−2.661 Å, respectively),9 while the Y−O(1)
distance (2.1994(15) Å) is only slightly longer (2.121−2.166
Å). In 1a-Sc, the same bond lengths (2.2100(16), 2.2333(16),
2.0198(11), and 2.3502(13) Å, respectively) are shorter than
those in the yttrium congener, which is in line with the
decrease of the effective ionic radii of the Sc(3+) metal ion.11
In the attempts to synthesize dinuclear complexes,
potentially incorporating two M-(CH2SiMe3)x groups united
by one multifunctional {N2O}− ligand scaffold, upon reacting
The reaction between 1a-H and 1 equiv of Sc-
1
(CH2SiMe3)3(THF)2 in C6D6 (Scheme 2), monitored by H
NMR spectroscopy, proceeded readily in the −25 to 25 °C
range, completely consuming both reagents. However, the final
1H NMR spectrum (Figure S4) showed two series of
resonances corresponding to two different products, mono-
ligand bis(alkyl) 1a-Sc and bis(ligand) monoalkyl 1a-Sc′ in a
respective ∼1:0.3 ratio. This observation is in line with that by
Piers et al. describing the preferential formation of a related
bis(phenoxy-imino) scandium monoalkyl complex {η2-1-
[CHN−Ar]-2-O-3-tBu-C6H3}2ScCH2SiMe3 (I-Sc) along
with small amounts of the monoligand bis(alkyl) congener in
the reaction between the equimolar amounts of the
corresponding proligand and Sc(CH2SiMe3)3(THF)2.9 In our
case, the increased steric bulk of {1a}− contributes to a better
stabilization of the monoligand bis(alkyl) species.
1
More comprehensive NMR data (13C{1H}, H−1H COSY)
were collected for this sample that allowed understanding of
the solution structures of both products and making assign-
ments of characteristic resonances. For example, for 1a-Sc, the
key resonances in the room-temperature 1H and 13C{1H}
NMR spectra (Figures S4 and S7, respectively) include (a) two
broad signals from the two CHN groups (δH 9.20, 8.16 ppm
and δC 172.5, 158.6 ppm, respectively), (b) two broad signals
from the C6H2 moiety (δH 9.02, 7.35 ppm and δC 131.6, 135.2
ppm, respectively), (c) one resonance for the ScCH2 groups
(δH −0.01 ppm and δC 40.4 ppm, respectively), (d) singlet
resonance for the SiMe3 groups (δH 0.08 ppm and δC 3.3 ppm,
respectively). For 1a-Sc′, similar key resonances include (a)
two sharp signals from the two pairs of the equivalent
coordinated and noncoordinated CHN groups (δH 7.93,
7.45 ppm and δC 172.5, 156.8 ppm, respectively), (b) two
sharp signals from the nonequivalent protons of the two C6H2
moieties (δH 8.90, 7.19 ppm and δC 132.3, 134.8 ppm,
respectively), (c) in the 1H NMR spectrum, two doublets from
the diastereotopic ScCHH protons (δH 0.67 and −0.25 ppm)
and a tiny singlet (δC 42.9 ppm) in the 13C{1H} NMR
spectrum, (d) singlet resonance for the SiMe3 groups (δH 0.00
ppm and δC −0.4 ppm, respectively). Upon increasing the
temperature to 72 °C (Figure S5), both products appeared to
be stable in solution, and no significant change in the pattern
of signals was observed for 1a-Sc′. On the other hand, for 1a-
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M(CH2SiMe3)3(THF)2 confirmed the quantitative formation
of these products, while 1 equiv of the tris(alkyl) precursor
remained intact in each case. The larger scale syntheses of
complexes [1b-M]2 were optimized by using equimolar
amounts of the two reagents. Both compounds were found
stable in benzene-d6 or toluene-d8 solutions at 60 °C for days.
Both complexes featured fluxional behavior in a broad range
of temperatures, apparently associated with a restricted
rotation of bulky bis(isopropyl)phenyl groups. The room-
temperature 1H NMR spectra of [1b-Sc]2 and [1b-Y]2
(Figures S12 and S16, respectively) contained in each case a
series of resonances consistent with the average C2-symmetry
of molecules. For [1b-Sc]2, the four broadened characteristic
signals from the two pairs of diastereotopic protons of the
CH2N groups were observed at δH 5.29, 4.06, 3.85, and 2.97
1
ppm in the H NMR spectrum and the corresponding two
resonances at δC 62.8 and 55.8 ppm in the 13C NMR spectrum.
The same groups in [1b-Y]2 afforded two well-resolved
doublets δH 5.25 and 3.95 ppm (2JHH = 14.6 Hz) and two
resonances at δC 62.6 and 59.5 ppm at in the corresponding 1H
and 13C{1H} NMR spectra.
The molecular structures of [1b-Sc]2 and [1b-Y]2 are
depicted in Figure S3 and Figure 2, respectively. The unit cell
Figure 1. Molecular structure of {N2O}Y(CH2SiMe3)2(THF)2 (1a-
Y) (all hydrogen atoms and 2,6-iPr2 groups are omitted for clarity;
thermal ellipsoids drawn at the 50% probability). Selected bond
distances (Å) and angles (deg): Y(1)−O(1), 2.1994(15); Y(1)−
O(51), 2.3779(18); Y(1)−N(1), 2.5159(18); Y(1)−C(41),
2.423(2); Y(1)−C(45), 2.438(2); Y(1)−O(61), 2.4637(17);
O(51)−Y(1)−N(1), 160.20(6); C(45)−Y(1)−O(61), 86.17(7);
C(41)−Y(1)−O(61), 168.96(8).
1a-H with 2 equiv of M(CH2SiMe3)3(THF)2, only the
formation of 1a-M together with the unreacted tris(alkyl)
1
precursor took place, as judged by H NMR spectroscopic
studies of the corresponding crude reaction mixtures.
In attempts to synthesize dinuclear complexes, in which two
metal centers are linked by a single ligand platform, regular
alkane elimination reactions of 1b-H3 with the corresponding
rare-earth metal precursors M(CH2SiMe3)3(THF)2 (M = Sc,
Y) in the corresponding 1:2 ratio were studied. However, only
alkyl group-free dinuclear bis(ligand) complexes [1b-M]2 were
1
isolated (Scheme 3). For instance, monitoring by H NMR
spectroscopy of the reaction of 1b-H3 with 2 equiv of
Scheme 3. Formation of Complexes [1b-M]2
Figure 2. Molecular structure of [1b-Y]2 (all hydrogen atoms and iPr
groups are omitted for clarity; thermal ellipsoids drawn at the 50%
probability). Selected bond distances (Å) and angles (deg): Y(1)−
O(1), 2.278(4); Y(1)−O(2), 2.337(4); Y(1)−N(1), 2.212(5);
Y(1)−N(2), 2.190(4); O(1)−Y(1)−N(1), 83.12(15); O(2)−Y(1)−
N(2), 116.62(18); N(1)−Y(1)−N(2), 106.17(17).
of [1b-Y]2 contains three independent molecules featuring
very similar geometrical parameters (bond lengths and angles)
and overall organizations, and therefore the structural details of
only one of them is discussed hereafter. Isostructural [1b-Sc]2
and [1b-Y]2 exhibit each the two five-coordinated metal atoms
whose geometries are best described as distorted trigonal
bipyramidal composed by two nitrogen and three oxygen
atoms of the two {N2O}3− ligands and one THF molecule.
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Scheme 4. Formation of Complex 3a-Y from 1a-Y and 2-Phenylpyridine
Thus, the M−O and M−N bonds (2.090(3)−2.143(3) and
2.006(3)−2.087(3) Å, respectively) with ligand in [1b-Sc]2 are
shorter than those in the yttrium analogue (2.278(4)−
2.337(4) and 2.190(4)−2.212(5) Å, respectively) by 0.14−
0.24 Å, in line with the larger ionic radius of yttrium.11 In
addition, the intermetallic M···M distances in these dinuclear
molecules (3.4832(12) and 3.9228(16) Å, respectively) are
not exceptional12 and are larger than the sum of the
corresponding ionic radii (1.490 and 1.800 Å, respectively).11
Stoichiometric and Catalytic Studies on the Reac-
tivity of Bis(Alkyl) Complex 1a-Y with 2-Phenylpyridine.
The C−H bond addition of heterocycles (hydroarylation) to
alkenes or imines, catalyzed by alkyl complexes of group 3
metals, is known to follow a multistep mechanism3,4 involving
the ortho-C(sp2)-H activation reaction of an aromatic molecule
affording aryl intermediate, followed by insertion of the CC
or CN bond into the M-aryl bond. Stoichiometric reactivity
of group 3 metals alkyls with 2-phenylpyridine has also been
the subject of several studies. For example, the formation of
different C−H bond activation products incorporating η2-N,C-
6-phenylpyridyl,13 η2-N,C-2′-phenylpyridyl,13a,14,15 or the 2-
phenypyridine-derived biheterocyclic13a,b,c,14b ligands have
been reported. In particular, Diaconescu et al.13a observed in
the corresponding yttrium and lutetium complexes the slow
rearrangement process for the 2-phenylpyridine ligand from
the η2-N,C-6-phenylpyridyl (three-membered-ring metallo-
cycle) to the more stable η2-N,C-2′-phenylpyridyl (five-
membered-ring metallocycle) coordination mode.
arising from ligand rearrangement. The 1H and 13C{1H} NMR
spectra (Figures S19 and S22) exhibited a single set of
resonances, consistent with an average Cs-symmetric species on
the NMR time scale, in which the two η2-N,C-2′-phenylpyridyl
fragments are equivalent. In particular, the 13C{1H} NMR
spectrum of 3a-Y (Figure S22) contained only one character-
istic doublet (δC 190.8 ppm,1JY−C = 41.6 Hz)14 for the two Y-C
carbon nuclei of the two 2-phenyl-pyridyl groups. Upon
lowering the temperature to −33 °C (Figure S20), the very
broad signal from the CHN groups split into two single
resonances at δH of 9.57 to 8.76 ppm, while for many other
signals, the pattern did not change significantly. At higher
temperature (80 °C), a new series of resonances appeared after
1 h suggesting gradual decomposition of the compound
affording unidentified products.
The five-membered-ring metallocyclic ring of complex 3a-Y
exhibiting η2-N,C-2′-phenylpyridyl coordination of the ligand
parallels previous results obtained by different groups.13a,14,15 It
should be also mentioned that the existence of a possible
isomerization process in solution similar to that described by
Diaconsescu et al.13a and consisting in our case of the change
of the mode of coordination of the 2-phenyl-pyridyl ligand in
3a-Y from η2-N,C-2′-phenylpyridyl to η2-N,C-6-phenylpyridyl
type could not be unequivocally established by our
experimental techniques.
The molecular structure of 3a-Y (Figure 3) revealed the
yttrium atom in a seven-coordinated environment provided
with the oxygen atom and the nitrogen atom of the {N2O}−
ligand, the two carbon and two nitrogen atoms of the two
monoanionic phenyl-pyridine ligands, and the oxygen atom of
the coordinated THF molecule. In 3a-Y, the Y−O and Y−N
distances (2.2225(16) and 2.519(2) Å) for the coordinated
phenoxy-imino ligand are very close to those in the parent 1a-
Y. The Y−C(aryl) and Y−N(aryl) bond lengths (2.502(2),
2.505(2), and 2.504(2), 2.583(2) Å, respectively) in the seven-
coordinated 3a-Y are longer than those (2.449−2.480 and
2.453−2.506 Å, respectively) observed for the previously
reported five- and six-coordinated yttrium complexes bearing
the same η2-N,C-2′-phenylpyridyl ligands.13−15
In order to assess the potential of bis(alkyl) complex 1a-Y in
C(sp2)-H activation/hydroarylation reactions, its reactivity
with 2-phenylpyridine was preliminarily studied. Monitoring
1
by H NMR spectroscopy of the reaction between equimolar
amounts 1a-Y and 2-phenylpyridine in C6D6 at room
temperature (Figure S18) showed slow disappearance of the
signal at δH −0.71 ppm from the CH2 protons of the Y-
(CH2Si(CH3)3)2 groups, and the appearance of a new signal at
δH −0.28 ppm. The latter apparently belongs to the Y-
CH2Si(CH3)3 group from a new mixed monoalkyl/aryl species
resulted from the C−H activation reaction of 2-phenylpyridine
(Scheme 4). Unfortunately, all attempts to isolate and
authenticate this putative product failed.
In order to evaluate the feasibility of the alkylation of styrene
with 2-phenylpyridine in the presence of 1a-Y, stoichiometric
reactions between complex 3a-Y and styrene were monitored
Similar reaction between 1a-Y and 2 equiv of 2-phenyl-
pyridine after 16 h resulted in a complete consumption of 1a-Y
and in formation of complex 3a-Y (Scheme 4). Complex 3a-Y
was reprepared on a larger scale and isolated in 54% as dark
green crystals. The nature of the compound was authenticated
1
by H NMR spectroscopy. Unfortunately, no reaction was
observed in the temperature range 25−60 °C with 1−10 equiv
of styrene. Further increasing of the temperature to 100 °C
resulted only in decomposition of 3a-Y, with no detectable
insertion of styrene into the Y-(pyridine-2′-ylbenzene) bond.
To gain a better insight into the mechanism of C−H
activation of 2-phenylpyridine with the bis(alkyl) complex 1a-
1
by H and 13C NMR spectroscopy and X-ray crystallography.
1
In particular, the room-temperature H NMR spectrum of 3a-
Y was slightly broadened due to fluxional behavior possibly
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affording the corresponding isomeric E′(THF)x product. In
addition, the reactivity of the two products of the ortho-
metalation reactions, bis(aryl) complexes E(THF)x and
E′(THF)x (x = 0, 1), toward styrene was probed computa-
tionally, and the role of the presence of coordinated THF
molecules on the stability and reactivity of key intermediates
was assessed. The computational results were found to be in
agreement with the experimental reactivity trends (see SI for
details and discussion).
The catalytic performance of 1a-Y, in combination with
B(C6F5)3,4a [Ph3C]+[B(C6F5)4]−,4b or nBu2NH4g as cocata-
lysts, was briefly explored in hydroarylation of styrene with 2-
phenylpyridine. Each reaction was carried out in a Teflon-
valved sealed NMR tube, and the progress of reaction was
1
monitored by H NMR spectroscopy.
For benchmarking purposes, the catalytic performance of
4b
several bis(alkyl) complexes of scandium and yttrium CpMR
and {N4}MR16 (Scheme 5) as reference catalyst precursors was
explored under our experimental conditions (70−100 °C,
C6D6; Table S2). Among the most successful results, the
combination (10 mol %) of CpScR with B(C6F5)3 afforded
selectively 2-phenyl-6-(2-phenylethyl)pyridine (5) with 53%
conversion after 96 h at 70 °C. In addition, the high selectivity
in alkylation of 2-phenylpyridine with styrene was achieved
with the binary system {N4}MR/[Ph3C]+[B(C6F5)4]− at 100
°C (Table S2, entries 8−10). The catalytic system of CpYR/
[Ph3C]+[B(C6F5)4]− (2.5 mol %) appeared to be active in
ortho-alkylation of anisole with styrene affording quantitatively
1-MeO-2-(2-phenylethyl)benzene after 24 h, which fits well
with the result of Hou et al. reported to provide 94% yield
under the same conditions.4b
Under the same or modified conditions, poor catalytic
results were achieved using complex 1a-Y as precatalyst (Table
S4). For example, only the combination 1a-Y/[Ph3C]+[B-
(C6F5)4]− afforded small amounts (6%) of 5 at 100 °C (Table
S4, entries 4 and 5). Given that the molecules of 1a-Y and 3a-Y
both contain coordinated THF molecules, the absence of
activity in catalysis, and particularly, reactivity toward styrene,
could be attributed to a strong coordination of THF ligand,
thus, impeding its displacement by such a poor donor as
Figure 3. Molecular structure of 3a-Y (all hydrogen atoms and iPr
groups are omitted for clarity; thermal ellipsoids drawn at the 50%
probability). Selected bond distances (Å) and angles (deg): Y(1)−
O(1), 2.2225(16); Y(1)−O(2), 2.4167(17); Y(1)−C(47), 2.502(2);
Y(1)−C(58), 2.505(2); Y(1)−N(1), 2.519(2); Y(1)−N(3),
2.504(2); Y(1)−N(4), 2.583(2); O(1)−Y(1)−O(2), 85.46(6);
O(1)−Y(1)−C(47), 132.75(7); O(1)−Y(1)−N(3), 82.26(7);
N(4)−Y(1)−C(58), 66.40(8); N(3)−Y(1)−C(47), 66.73(7).
Y, DFT computations were conducted (Scheme S2). The
objectives of these non-exhaustive computations were to assess
and compare the energy profiles for several possible concurrent
processes: (a) C−H activation reaction of 2-phenyl-pyridine at
the 2′-phenyl position resulting in formation of 3a-Y
(E(THF)x, where x = 1), (b) an alternative C−H activation
reaction of 2-phenyl-pyridine at the 6-pyridyl position
Scheme 5. Hydroarylation of Styrene with 2-Phenylpyridine
E
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styrene. In order to address this issue, several catalytic
experiments were conducted in the presence of substoichio-
metric or stoichiometric amounts of LiCl or AlMe3 as possible
scavengers of THF. However, only in one experiment using
AlMe3 (20 mol %) was formation of only a small amount of 2-
(2-(1-phenylethyl)-phenyl)-pyridine (6, 5%) observed (Table
S4, entry 8). No visible formation of products was detected
when other electrophilic substrates (e.g., N-R-1-phenyl-
methanimine (R = Ph, iPr), PhSiH3, Et3SiH) were used in
the place of styrene.
Studies on Copolymerization of CO2 with Cyclo-
hexene Oxide. The mononuclear bis(alkyl) 1a-Y and
dinuclear alkyl-free complexes [1b-M]2 were then tested as
initiators of copolymerization of CO2 with cyclohexene oxide
(Scheme 6). For benchmarking purposes, first the copoly-
concentration.18 To our delight, using complex 1a-Y as catalyst
under the same conditions gave 95% conversion and 97%
selectivity for polymers (entry 2). The yields remained almost
unchanged when the loading of 1a-Y decreased from 0.5 to 0.2
mol % (entries 3 and 5). Decreasing the concentration of 1a-Y
to 0.1 mol % led to a significantly lower conversion of 57%
(entry 12), suggesting high sensitivity of the initiating system
to the presence of impurities. Similar observation on the
decrease of the polymer conversion upon reducing the catalyst
loading to 0.1 mol % was reported for the series of β-diimine
bis(alkyl) yttrium complexes.7b
The reaction temperature appeared to have a significant
influence on the copolymerization activity. While the experi-
ment conducted at room temperature resulted in no polymer
formation (entry 4), at 50 °C, a conversion of 86% was
observed after 18 h (entry 6). The highest conversion of 92%,
using 500 equiv of CHO (TON of 460), was achieved after 5 h
at 70 °C (entry 11). Compared to the reported bis(alkyl)
yttrium complex supported by β-diiminate ligand giving TON
of 300 at 130 °C and 15 bar CO2 pressure,7b 1a-Y proved to be
one of the most efficient mononuclear rare-earth metal-based
catalyst for polycarbonate synthesis. However, the activity of
1a-Y is still lower than those reported for most highly active
catalysts systems,19 such as Lu’s bifunctional Co(III)-salen
catalysts,19a Rieger’s very active dizinc macrocyclic systems,19b
La/Zn heteropolymetallic catalysts of Okuda and Mashima,19c
Nozaki’s porphyrin-based catalysts,19d and Williams’s hetero-
bimetallic Mg/Co complexes.19e
Scheme 6. Copolymerization of Cyclohexene Oxide (CHO)
and CO2 Catalyzed by Complex 1a-Y
In order to determine orders on CHO and catalyst, a series
of kinetic studies was undertaken. Kinetic monitoring of
copolymerization under regular conditions (Figure S25) did
not exhibit a significant induction period, regardless of the
catalyst concentration, suggesting rapid initiation with Y-
CH2SiMe3 groups. The latter fact was corroborated by
MALDI-ToF spectroscopy (Figure S31) demonstrating the
presence of CH2SiMe3 end-groups in the low-molecular-weight
polycarbonate sample (Table 1, entry 9). The first-order
merization reactions initiated by {BDI}Zn(N(SiMe3)2)17 was
studied at 70 °C and 12 bar CO2 pressure (Table 1, entry 1)
affording 10% conversion of monomer after 64 h. The low
activity compared with the result reported by Coates et al.,17
which gave 44% conversion at 50 °C after 2 h, is apparently
due to the addition of solvent (toluene), as the copolymeriza-
tion rate law features a first order dependence on monomer
a
Table 1. Copolymerization of CO2 with CHO Catalyzed by Complex 1a-Y
b
c
c
c
e
e
entry
initiator (%)
T (°C)
time (h)
conversion (%)
polymer
carbonate units
M
n,GPC(Mn,calc) 103 g·mol−1
Đ
1
2
3
4
5
6
7
8
BDIZnNTMS2 (0.5)
1a-Y (0.5)
1a-Y (0.5)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.2)
1a-Y (0.1)
1a-Y (0.2)
1a-Y/ZnEt2 (0.2)
1a-Y/MgBu2 (0.2)
1a-Y/AlMe3 (0.2)
[1b-Sc]2 (0.2)
[1b-Y]2 (0.2)
70
70
70
25
70
50
70
70
70
70
70
70
70
70
70
70
70
70
64
64
18
18
18
18
1
2
3
4
5
18
18
18
18
18
18
18
10
95
95
<1
95
86
22
41
75
84
92
57
60
9
89
97
97
-
>99
>99
>99
>99
>99
>99
>99
>99
99
99
99
99
-
-
-
8.1 (27.0)
2.4 (27.0)
-
1.49
1.92
-
99
99
99
99
99
99
99
98
99
99
99
99
<1
<1
7.9 (67.5)
10.6 (61.1)
5.0 (15.6)
5.4 (29.1)
6.1 (56.9)
5.8 (59.7)
6.6 (65.4)
12.4 (80.9)
10.9 (42.6)
-
1.99
3.30
2.65
2.10
1.78
1.90
1.89
7.75
8.30
-
9
10
11
12
f
13
14
15
16
17
18
99
99
95
>99
>99
8
-
-
14
14
31
4.1 (10.0)
2.2 (6.86)
3.0 (15.2)
3.38
2.92
1.72
a
Reaction conditions: solvent = toluene (1.0 mL); [CHO]0 = 4.95 mol·L−1; 70 °C; PCO2 = 12 bar; [CO2]/[CHO] = 5.3; n.o. = not observed.
b
c
d
Reaction times were not necessarily optimized. Conversion of product and selectivity were determined by 1H NMR spectroscopy. Determined
e
f
by DSC. Determined by GPC; Đ = Mw/ Mn. Experiment conducted in the presence of cyclohexane-1,2-diol (2 equiv vs 1a-Y).
F
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dependence both on the CHO concentration (Figure 4) and
on the concentration of catalyst (Figure S26) was determined
from the corresponding linear plots, indicating a mononuclear
pathway.18,20
which is diagnostic of poorly controlled transfer processes
operating under these conditions and/or of multisite behavior
of the catalytic system.
Alkyl compounds of main-group metals are known not only
to promote the copolymerization of CO2 with epoxides,24 but
also to contribute to the formation of highly active polynuclear
systems derived from transition metals.6d,19 The effect of the
addition of such alkyl metal (Zn, Mg, Al) reagents to 1a-Y was
also investigated in copolymerization (entries 14−16) and,
despite our expectations, appeared to be detrimental. The
efficiency of the resulting binary systems was found to be much
lower than that of the monocomponent 1a-Y.
Dinuclear alkyl group-free complexes [1b-Sc]2 and [1b-Y]2
were also probed as promoters of copolymerization (entries 17
and 18, respectively). Under identical conditions (70 °C, 18
h), only small amounts of polymers were isolated (14% and
31% conversion, respectively), which were identified by NMR
spectroscopy as polyethers (Figure S32),7a homopolymers of
CHO. The different nature of initiating groups (alkyl vs
phenolate group) may account for the reactivity and selectivity
differences in these systems.25 This observation also parallels
the results reported by Chakraborty et al. for dinuclear
titanium and zirconium complexes, which produced poly-
(cyclohexene oxide) polymers in the absence of a nucleophilic
cocatalyst.26
Figure 4. Plot of ln([CHO]0/[CHO]t) as a function of time for the
copolymerization of CO2 with CHO catalyzed by complex 1a-Y
(0.05−0.2 mol %); conditions: toluene, PCO2 = 12 bar, 70 °C,
[CHO]0 = 4.95 mol·L−1.
CONCLUSIONS
■
In summary, we investigated complexation of two types of
ligand platforms, namely, bis(imino)phenoxy and bis(amido)-
phenoxy, with group 3 metals. During this study, a series of
new complexes of scandium and yttrium were obtained by σ-
bond metathesis (alkane elimination) and completely charac-
terized. Among them, bis(alkyl) complex {N2O}Y-
(CH2SiMe3)2(THF)2 (1a-Y) was used for studies on
stoichiometric C−H activation of 2-phenylpyridine selectively
affording under mild conditions an original bis(aryl) product,
complex {N2O}Y(η2-N,C-2′-PhPy)2(THF) (3a-Y). The latter
was found stable in solution under ambient conditions and
completely reluctant in reactions with weak electrophiles, such
as styrene, imines, and hydrosilanes. This reaction of formation
of 3a-Y from 1a-Y and 2-phenylpyridine through a series of
C−H activation steps was studied by DFT calculations, and
the inactivity of 3a-Y toward styrene was also rationalized.
Attempts to use 1a-Y in combination with borane and borate
activators for the hydroarylation of styrene and imines were
also unsuccessful.
Gratifyingly, 1a-Y found application as initiator of
copolymerization of CO2 with cyclohexene epoxide under
mild conditions (70 °C, 12 bar of CO2 pressure, toluene). The
corresponding polycarbonate polymers were obtained with
nearly quantitative conversion over 5 h of polymerization and
high selectivity (97−99% of carbonate units). Yet, this system
constitutes a rare example of most efficient rare-earth metal
alkyl complexes for copolymerization of CO2 with epoxides
(TON of 460) operating under mild conditions. These results
again highlight the high potential of group 3 metal alkyl
complexes in catalysis. Further studies of the development of
new ligand platforms for C−H activation chemistry and CO2
transformations are ongoing in our laboratories.
Predominantly alternating polycarbonates rather than cyclic
carbonates were isolated in all experiments involving 1a-Y
(e.g., entries 6 and 7), regardless of the reaction temperature.
The polycarbonate polymers produced were essentially atactic
as judged from the corresponding 13C{1H} NMR data (Figure
S29) obtained for the sample of low Mn of 8100 g·mol−1 (entry
2). Thus, in the carbonyl region, the intensity pattern of the
corresponding key resonances at δC 153.8 ppm from the
isotactic tetrads ([mmm], [mmr]) and at δC 153.1−153.4 ppm
([mrm], [rrm], [rrr], [rmr]) compares well with those reported
in the literature for the atactic analogues.21 The thermal
properties of several copolymer samples (entries 2 and 10)
were also examined by DSC analysis revealing the Tg values of
88.7 (Figgure S30) and 87.3 °C, respectively. These values are
typical for such low-molecular-weight polymers falling in the
regular range of those (45.0−118.9 °C) reported for
polycarbonates.22 No melting transitions were detected in
these cases.
The fact that the experimentally determined by GPC
average-number molecular weights are systematically lower
than the theoretical values, calculated from the initial
monomer-to-initiator ratio and conversion values, is diagnostic
of several possible phenomena operating under our conditions:
initiation and growing of two polymer chains per one metal
center, and occurrence of side transfer reactions, e.g., chain
transfer to cyclohexane-1,2-diol generated from CHO in the
presence of adventitious protic impurities (H2O).23 The latter
phenomenon can also be responsible for the broadening of the
molecular weight distributions of polymers obtained in the
experiments carried out with low amounts of 1a-Y (entry 12).
In order to probe this hypothesis, a copolymerization
experiment with 2 equiv of cyclohexane-1,2-diol was carried
out (entry 13). Thus, the lower CHO conversion (60%) was
achieved as compared to that in the experiment without
cyclohexane-1,2-diol (95% conversion, entry 5). The PDI value
was found to be much broader (8.30 vs 1.99, respectively),
EXPERIMENTAL SECTION
General Considerations. All manipulations were performed
under a purified argon atmosphere using standard Schlenk techniques
■
G
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or in a glovebox. Solvents were distilled from Na/benzophenone
(THF, Et2O) and Na/K alloy (toluene, pentane) under argon,
degassed thoroughly, and stored under nitrogen prior to use.
Deuterated solvents (benzene-d6, toluene-d8, THF-d8, >99.5% D,
Deutero GmbH and Euroisotop) were vacuum transferred from Na/
K alloy into storage tubes. The ligand precursors 1a-H,8a 1b-H3,8b
Me3SiCH2Li,27 M(CH2SiMe3)3(THF)2, M(CH2C6H4-o-NMe2)3,28
150.9 (Ar), 150.7 (Ar), 148.1 (Ar), 140.1 (Ar), 140.0 (Ar), 139.9
(Ar), 139.8 (Ar), 136.6 (Ar), 134.8 (Ar), 132.3 (Ar), 126.9 (Ar),
126.0 (Ar), 123.9 (Ar), 123.4 (Ar), 123.0 (Ar), 122.6 (Ar), 42.9
(ScCH2), 33.8 (CH), 30.8 (CH), 29.8 (CH), 28.1 (CH), 25.1 (CH3),
23.3 (CH3), 22.4 (CH3), 22.0 (CH3), 21.9 (CH3), −0.4 (Si(CH3)3).
All volatiles were removed in vacuum and hexane (1 mL) was
added. Colorless crystals of 1a-Sc (0.0070 g, 15%), suitable for X-ray
diffraction study, were isolated after the solution was kept for 7 days at
−25 °C.
Synthesis of Complex 1a-Y. A solution of 1a-H (0.525 g, 1.0
mmol) in hexane (5.0 mL) was added quickly to a solution of
Y(CH2Si(CH3)3)3(THF)2 (0.495 g, 1.0 mmol) in hexane (5.0 mL) at
−25 °C. The resulted reaction mixture was stirred at room
temperature for 2 h. Green crystals of 1a-Y were obtained (0.623 g,
67%) after the solution was kept for 2 days at −25 °C. 1H NMR (500
MHz, C7D8, 25 °C): δ 8.70−8.02 (br m, 4H, CHN + Ar), 7.20−
7.14 (m, 6H, Ar), 3.79 (s, 8H, α-CH2, THF), 3.20 (br m, 4H,
16
CpScR,4a CpYR,4b and {N4}MR (M = Sc, Y) were prepared
according to the published procedures. Styrene and cyclohexene oxide
were distilled from CaH2 and stored in the fridge at −25 °C. 2-
Phenylpyridine, PhOMe, PhNMe2, PhSiH3, and Et3SiH were dried
with 4 Å molecular sieves and stored under argon. Other starting
materials were purchased from Acros, Strem, and Aldrich, and used as
received.
Instruments and Measurements. NMR spectra of complexes
were recorded on Bruker AM-400, and AM-500 spectrometers in
1
Teflon-valved NMR tubes at 25 °C, unless otherwise indicated. H
and 13C chemical shifts are reported in ppm vs SiMe4 (0.00), as
determined by reference to the residual solvent peaks. The resonances
CH(CH3)2), 1.36−1.25 (m, 52H, β-CH2 (THF) + CH(CH3)2 +
C(CH3)3), 0.12 (s, 18H, Si(CH3)3), −0.71 (s, 4H, YCH2). 13C{1H}
NMR (125 MHz, C7D8, 25 °C) (many aromatic signals were not
observed due to fluxional dynamics and overlapping): δ 165.4 (C
N), 151.0 (CN), 139.1 (Ar), 133.9 (Ar), 123.6 (Ar), 70.4 (α-CH2,
THF), 34.1 (CHCH3), 32.3 (br s, YCH2), 31.4 (CHCH3), 28.6
(CH3), 25.4 (CH3), 23.9 (β-CH2, THF), 4.4 (Si(CH3)3). Anal. Calcd
for C52H85N2O3Si2Y: C, 67.06; H, 9.20; N, 3.01. Found: C, 67.30; H,
9.46; N, 2.92.
1
of organometallic complexes were assigned from 2D H−1H COSY,
1H−13C HSQC, and HMBC NMR experiments. Coupling constants
are given in hertz. Elemental analyses (C, H, N) were performed using
a Flash EA1112 CHNS Thermo Electron apparatus and are the
average of two independent determinations. DSC measurements were
performed on a SETARAM Instrumentation DSC 131 differential
scanning calorimeter at a heating rate of 10°/min; first and second
runs were recorded after cooling to 30 °C. Size exclusion
chromatography (SEC) of polycarbonate samples was performed in
THF (1 mL·min−1) at 20 °C using a Polymer Laboratories PL50
apparatus equipped with PLgel 5 μm MIXED-C 300 × 7.5 mm
columns, and combined RI and Dual angle LS (PL-LS 45/90°)
detectors. The number-average molecular weights (Mn) and
polydispersities (Đ) of the polymers were calculated with reference
to a universal calibration vs. polystyrene standards. The micro-
structure of polycarbonate was determined by 1H and 13C NMR
spectroscopy according to the published procedures.21 MALDI-TOF
spectra were acquired on a Bruker Ultraflex-III TOF/TOF mass
spectrometer (Bruker Daltonics, Inc., Billerica, MA) equipped with a
Nd:YAG laser (355 nm). CH3COONa was added for facilitating ion
formation, and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-
propenylidene]malononitrile was used as matrix.
Reaction between 1b-H3 and Sc(CH2SiMe3)3(THF)2. Forma-
tion of Complex [1b-Sc]2. Using a similar procedure, described for
1a-Y, complex [1b-Sc]2 was prepared from 1b-H3 (0.053 g, 0.1
mmol) and Sc(CH2SiMe3)3(THF)2 (0.045 g, 0.1 mmol). Colorless
crystals of [1b-Sc]2 (0.029 g, 45%) were obtained after the solution
was kept for 3 days at −25 °C. 1H NMR (500 MHz, C6D6, 25 °C): δ
7.39 (br m, 6H, Ar), 7.32−6.74 (br m, 8H, Ar), 6.74 (br m, 2H, Ar),
5.60 (br m, 2H, CH2N), 5.29 (br m, 2H, CH2N), 4.41 (br m, 2H,
CH(CH3)2), 4.06 (br m, 2H, CH2N), 4.00 (br m, 4H, α-CH2, THF),
3.85 (br m, 2H, CH2N), 3.53 (br m, 6H, α-CH2, THF + CH(CH3)2),
2.97 (br m, 4H, CH(CH3)2), 1.77 (br m, 6H, C(CH3)3), 1.60−0.70
(br m, 62H, CH(CH3)2 + β-CH2 (THF) + C(CH3)3), 0.43 (br m,
6H, C(CH3)3). 13C{1H} NMR (125 MHz, C6D6, 25 °C) (due to a
strong fluxional dynamics some of the aromatic signals could not be
observed): δ 153.7 (Ar), 152.2 (Ar), 145.3 (Ar), 123.6 (Ar), 71.6 (α-
CH2, THF), 62.8 (CH2N), 55.8 (CH2N), 31.1 (CHCH3), 29.3
(CHCH3), 28.1 (CH3), 26.8 (CH3), 23.8 (β-CH2, THF), 22.6 (CH3).
Anal. Calcd for C72H98N4O2Sc2: C, 75.76; H, 8.65; N, 4.91. Found C,
75.84; H, 8.69; N, 4.73.
Reaction between 1a-H and Sc(CH2SiMe3)3(THF)2. Formation
of Complex 1a-Sc. In the glovebox, in a Teflon-valved NMR tube
was placed 1a-H (0.026 g, 0.05 mmol), Sc(CH2SiMe3)3(THF)2
(0.023 g, 0.05 mmol). To this mixture, C6D6 (ca. 0.5 mL) was
vacuum-transferred in at −25 °C and the tube was shaken for 1 h at
room temperature. 1H NMR spectroscopy indicated quantitative
consumption of both reagents and formation of 1a-Sc and 1a-Sc′ in
∼1:0.3 ratio, respectively. Compound 1a-Sc (some resonances could
not be assigned unequivocally): 1H NMR (500 MHz, C6D6, 25 °C): δ
9.20 (br s, 1H, CHN), 9.00 (br s, 1H, Ar), 8.16 (br s, 1H, CH
N), 7.35 (br s, 1H, Ar), 3.89 (br m, 4H, α-CH2, THF), 3.29 (br m,
4H, CH(CH3)2), 1.34 (m, 4H, β-CH2, THF), 1.39−1.26 (m, 24H,
CH(CH3)2), 1.21 (s, 9H, C(CH3)3), 0.08 (s, 18H, Si(CH3)3), −0.01
(s, 4H, ScCH2). 13C{1H} NMR (125 MHz, C6D6, 25 °C): δ 172.4
(CHN), 158.6 (CHN), 150.9 (Ar), 148.9 (Ar), 140.9 (Ar),
137.4 (Ar), 135.2 (Ar), 131.6 (Ar), 127.1 (Ar), 124.1 (Ar), 122.9
(Ar), 122.3 (Ar), 68.6 (α-CH2, THF), 40.4 (ScCH2), 28.6 (CH), 28.2
(CH), 28.1 (CH3), 25.8 (CH3), 25.0 (β-CH2, THF), 23.1 (CH3), 22.2
(CH3), 3.3 (Si(CH3)3).
Reaction between 1b-H3 and Y(CH2SiMe3)3(THF)2. Formation
of Complex [1b-Y]2. Using a similar procedure, described for 1a-Y,
complex [1b-Y]2 was prepared from 1b-H3 (0.053 g, 0.1 mmol) and
Y(CH2Si(CH3)3)3(THF)2 (0.050 g, 0.1 mmol). Yellow crystals of
[1b-Y]2 (0.024 g, 39%) were obtained after the solution was kept for
1
7 days at −25 °C. H NMR (500 MHz, toluene-d8, 25 °C): δ 7.20−
6.96 (m, 16H, Ar), 5.25 (d, 2JHH = 14.6, 4H, CH2N), 3.95 (d, 2JHH
=
14.6, 4H, CH2N), 3.80−3.00 (br m, 16H, α-CH2, THF +
CH(CH3)2), 1.34−1.11 (m, 74H, β-CH2 (THF) + CH(CH3)2
+
C(CH3)3). 13C{1H} NMR (125 MHz, toluene-d8, 25 °C): δ 152.5
(Ar), 145.2 (Ar), 131.8 (Ar), 128.1 (Ar), 127.8 (Ar), 127.2 (Ar),
125.3 (Ar), 124.3 (Ar), 123.4 (Ar), 122.6 (Ar), 70.7 (α-CH2, THF),
62.6 (CH2N), 59.5 (CH2N), 33.5 (CHCH3), 31.6 (CHCH3), 31.3
(CHCH3), 28.2 (CH3), 25.2 (β-CH2, THF), 24.9 (CH3), 22.8 (CH3).
Anal. Calcd for C72H98N4O2Y2: C, 70.34; H, 8.04; N, 4.56. Found C,
70.05; H, 8.40; N, 4.03.
1a-Sc′ (Some Resonances Could Not Be Assigned Unequiv-
1
4
Synthesis of Complex 3a-Y. To a solution of 1a-Y (0.093 g, 0.10
mmol) in hexane (2.0 mL) was added 2-phenylpyridine (28.4 μL,
0.20 mmol) in hexane (1.0 mL) at −25 °C. The solution was stirred
at room temperature for 3 h. Dark green crystals of 3a-Y (0.053 g,
54%) were obtained after the solution was kept for 7 days at −25 °C.
1H NMR (500 MHz, toluene-d8, 25 °C): δ 8.74 (br m, 2H, CHN),
8.57 (d, J = 4.8, 1H, Ar), 8.46 (d, J = 4.8, 2H, PhPy), 8.11 (d, 2H, J =
7.6, PhPy), 7.81 (br m, 2H, PhPy), 7.61 (d, 2H, J = 4.8, PhPy), 7.45
(d, 2H, J = 7.8, PhPy), 7.27 (m, 3H, Ar), 7.20 (d, 1H, J = 8.0, Ar),
ocally). H NMR (500 MHz, C6D6, 25 °C): δ 8.90 (d, J = 2.6, 2H,
Ar), 7.93 (s, 2H, CHN), 7.45 (s, 2H, CHN), 7.30−7.19 (m,
10H, Ar), 7.19 (d, 4J = 2.6, 2H, Ar), 6.93 (d, J = 7.5, 2H, Ar), 6.82 (d,
J = 7.5, 2H, Ar), 6.57 (t, J = 7.5, 2H, Ar), 3.22 (q, J = 6.8, 2H,
CH(CH3)2), 3.10 (q, J = 6.8, 4H, CH(CH3)2), 2.63 (q, J = 6.8, 2H,
CH(CH3)2), 1.18 (s, 18H, C(CH3)3), 1.00−0.82 (m, 48H, CH-
(CH3)2), 0.67 (d, 2JHH = 12.7, 1H, ScCH2), 0.08 (s, 18H, Si(CH3)3),
−0.25 (d, 2JHH = 12.7, 1H, ScCH2). 13C{1H} NMR (125 MHz, C6D6,
25 °C): δ 172.5 (CHN), 164.2 (Ar), 164.1 (Ar), 156.8 (CHN),
H
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7.18−7.12 (m, 4H, Ar), 6.95 (t, 3H, J = 7.6, PhPy), 6.70 (dd, J = 4.8,
7.6, 1H, Ar), 6.23 (t, J = 6.2, 2H, PhPy), 3.42 (br m, 4H, α-CH2,
THF), 3.14 (br m, 4H, CH(CH3)2), 1.43−1.10 (m, 16H, β-CH2
(THF) + CH(CH3)2), 0.94−0.87 (m, 9H, C(CH3)3). 13C{1H} NMR
(125 MHz, toluene-d8, 25 °C) (some of the quaternary aromatic
signals could not be observed): δ 190.8 (d,1JY−C = 41.6, Y-C(PhPy)),
166.6 (CNH), 165.7 (PhPy), 157.1 (CNH), 149.5 (PhPy),
149.2 (PhPy), 145.7 (PhPy), 139.6 (Ar), 139.6 (PhPy), 138.2 (Ar),
137.8 (Ar), 137.4 (Ar), 135.8 (Ar), 129.9 (PhPy), 128.8 (Ar), 128.2
(Ar), 126.8 (Ar), 124.5 (Ar), 123.1 (PhPy), 121.5 (Ar), 119.5 (Ar),
118.6 (PhPy), 68.5 (α-CH2, THF), 33.7 (CH(CH3)2), 31.6 (CH3),
31.1 (C(CH3)), 28.4 (CH3), 24.8 (CH(CH3)2), 23.5−22.7 (br m, β-
CH2 (THF) + CH(CH3)2 + C(CH3)). Anal. Calcd for C62H70N4O2Y:
C, 75.06; H, 7.11; N, 5.65. Found C, 75.18; H, 7.39; N, 5.77.
Crystal Structure Determination of Complexes 1a-M, 2a-M,
[1b-M]2, and 3a-Y (M = Sc and Y). Diffraction data were collected
at 150(2) K using a Bruker APEX CCD diffractometer with graphite-
monochromatized Mo Kα radiation (λ = 0.71073 Å). The crystal
structures were solved by direct methods, remaining atoms were
located from difference Fourier synthesis followed by full-matrix least-
squares refinement based on F2 (programs SIR97 and SHELXL-
97).29 Many hydrogen atoms could be located from the Fourier
difference analysis. Other hydrogen atoms were placed at calculated
positions and forced to ride on the attached atom. The hydrogen
atom positions were calculated but not refined. All non-hydrogen
atoms were refined with anisotropic displacement parameters. Crystal
data and details of data collection and structure refinement for the
different compounds are given in Table S1. Crystal data, details of
data collection, and structure refinement for all compounds (CCDC
2016816−2016822, respectively) can be obtained from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
Computational Studies. The calculations were performed using
the Gaussian 0930 program employing B3PW9131 functional, and
using a standard double-ζ polarized basis set, namely, the LANL2DZ
set, augmented with a single polarization f function on yttrium
(0.835) and a single polarization d function on silicon (0.296). The
solvent effects, in our case for toluene, were taken into account during
all the calculations by means of the SMD model.32 All stationary
points were fully characterized via analytical frequency calculations as
either true minima (all positive eigenvalues) or transition states (one
imaginary eigenvalue). The IRC procedure was used to confirm the
nature of each transition state connecting two minima.33 Zero-point
vibrational energy corrections (ZPVE) were estimated by a frequency
calculation at the same level of theory, to be considered for the
calculation of the total energy values at T = 298 K in the same way as
in the approach used by Castro et al.34
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c02112.
■
sı
Crystallographic data; representative NMR and MALDI-
TOF spectra of complexes and polymers; DSC curves;
DFT computations (PDF)
Accession Codes
CCDC 2016816−2016822 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
Dan Yuan − Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry, Chemical Engineering and
Materials Science, Dushu Lake Campus, Soochow University,
Suzhou 215123, People’s Republic of China; orcid.org/
0000-0002-4816-0842; Email: yuandan@suda.edu.cn
Yingming Yao − Key Laboratory of Organic Synthesis of
Jiangsu Province, College of Chemistry, Chemical Engineering
and Materials Science, Dushu Lake Campus, Soochow
University, Suzhou 215123, People’s Republic of China;
orcid.org/0000-0001-9841-3169; Email: yaoym@
suda.edu.cn
Evgueni Kirillov − Universite Rennes, CNRS, ISCR (Institut
des Sciences Chimiques de Rennes), UMR 6226, F-35700
Rennes, France; orcid.org/0000-0002-5067-480X;
Email: evgueni.kirillov@univ-rennes1.fr
Authors
Liye Qu − Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry, Chemical Engineering and
Materials Science, Dushu Lake Campus, Soochow University,
Suzhou 215123, People’s Republic of China; Universite
Rennes, CNRS, ISCR (Institut des Sciences Chimiques de
Rennes), UMR 6226, F-35700 Rennes, France
Thierry Roisnel − Centre de Crystallographie, Universite
Rennes, CNRS, ISCR (Institut des Sciences Chimiques de
Rennes), UMR 6226, F-35700 Rennes, France
Marie Cordier − Centre de Crystallographie, Universite
Rennes, CNRS, ISCR (Institut des Sciences Chimiques de
Rennes), UMR 6226, F-35700 Rennes, France
Bei Zhao − Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry, Chemical Engineering and
Materials Science, Dushu Lake Campus, Soochow University,
Suzhou 215123, People’s Republic of China; orcid.org/
0000-0001-8687-2632
Typical Procedure for Hydroarylation of Styrene with 2-
Phenyl-Pyridine in the Presence of Group 3 Metal Complexes.
In a typical experiment (Table S1, entry 4), in the glovebox, into a
Teflon-valved NMR tube was placed 1a-Y (0.0093 g, 0.01 mmol), 2-
phenylpyridine (14.20 μL, 0.10 mmol), and styrene (11.50 μL, 0.10
mmol), and C6D6 (0.5 mL) was added at −25 °C. The tube was
sealed at room temperature and the mixture was heated at the
required temperature for the desired time. Progress of the reaction
1
was monitored by H NMR spectroscopy.
Typical Procedure for Copolymerization of CO2 with CHO.
In a typical experiment (Table 1, entry 5), in the glovebox, a Schlenk
tube was charged with CHO (1.0 mL, 9.9 mmol), 1a-Y (0.02 g, 0.05
mmol), and toluene (1.0 mL). The mixture was transferred to an
autoclave equipped with a magnetic stirring bar under argon and then
pressurized at CO2 (12 bar). The reaction mixture was stirred
vigorously at the required temperature for the desired time. After
cooling to room temperature, CO2 was released, and a small amount
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c02112
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
1
■
of the resulting mixture was analyzed by H NMR spectroscopy to
The authors are grateful to the PHC Cai Yuanpei program
between Campus France and Chinese Scholarship Council.
E.K. thanks ENSCR and the CTI group of ISCR for
computational facilities, and acknowledges support from
determine the conversion and selectivity. The reaction mixture was
quenched by the addition of MeOH/HCl, and then poured into a
large amount of MeOH to precipitate the polymer, which was dried
under vacuum at 40 °C and weighed.
I
https://dx.doi.org/10.1021/acs.inorgchem.0c02112
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Polymeric Carbonates: Principles and Applications. Green Chem.
2019, 21, 406−448.
ANR-17-CE06-0006-01 “CO22CHEM”. We are grateful to Dr.
Vincent Dorcet (Univ Rennes) for resolving the structure of
1a-Y and to Lihua Hu (Soochow University) for MALDI-ToF
analyses.
(7) For recent articles, see: (a) Cui, D.; Nishiura, M.; Hou, Z.
Alternating Copolymerization of Cyclohexene Oxide and Carbon
Dioxide Catalyzed by Organo Rare Earth Metal Complexes.
Macromolecules 2005, 38, 4089−4095. (b) Zhang, Z.; Cui, D.; Liu,
X. Alternating Copolymerization of Cyclohexene Oxide and Carbon
Dioxide Catalyzed by Noncyclopentadienyl Rare-Earth Metal Bis-
(Alkyl) Complexes. J. Polym. Sci., Part A: Polym. Chem. 2008, 46,
6810−6818. (c) Decortes, A.; Haak, R. M.; Martín, C.; Belmonte, M.
M.; Martin, E.; Benet-Buchholz, J.; Kleij, A. W. Copolymerization of
CO2 and Cyclohexene Oxide Mediated by Yb(Salen)-Based
Complexes. Macromolecules 2015, 48, 8197−8207. (d) Qin, J.; Xu,
B.; Zhang, Y.; Yuan, D.; Yao, Y. Cooperative Rare Earth Metal-Zinc
Based Heterometallic Catalysts for Copolymerization of CO2 and
Cyclohexene Oxide. Green Chem. 2016, 18, 4270−4275. (e) Hua, L.;
Li, B.; Han, C.; Gao, P.; Wang, Y.; Yuan, D.; Yao, Y. Synthesis of
Homo- and Heteronuclear Rare-Earth Metal Complexes Stabilized by
Ethanolamine-Bridged Bis(Phenolato) Ligands and Their Application
in Catalyzing Reactions of CO2 and Epoxides. Inorg. Chem. 2019, 58,
8775−8786. (f) Ho, C. H.; Chuang, H. J.; Lin, P. H.; Ko, B. T.
Copolymerization of Carbon Dioxide with Cyclohexene Oxide
Catalyzed by Bimetallic Dysprosium Complexes Containing Hydra-
zine-Functionalized Schiff-Base Derivatives. J. Polym. Sci., Part A:
Polym. Chem. 2017, 55, 321−328. (g) Xu, R.; Hua, L.; Li, X.; Yao, Y.;
Leng, X.; Chen, Y. Rare-Earth/Zinc Heterometallic Complexes
Containing Both Alkoxy-Amino-Bis(Phenolato) and Chiral Salen
Ligands: Synthesis and Catalytic Application for Copolymerization of
CO2 with Cyclohexene Oxide. Dalton Trans. 2019, 48, 10565−10573.
(h) Nagae, H.; Aoki, R.; Akutagawa, S.; Kleemann, J.; Tagawa, R.;
Schindler, T.; Choi, G.; Spaniol, T. P.; Tsurugi, H.; Okuda, J.;
Mashima, K. Lanthanide Complexes Supported by a Trizinc Crown
Ether as Catalysts for Alternating Copolymerization of Epoxide and
CO2: Telomerization Controlled by Carboxylate Anions. Angew.
Chem., Int. Ed. 2018, 57, 2492−2496.
REFERENCES
■
(1) (a) Bradley, D. C.; Mehrotra, R. M.; Rothwell, I. P.; Singh, A.
Alkoxo and Aryloxo Derivatives of Metals; Academic Press: London,
2001. (b) The Chemistry of Metal Phenolates in PATAI’S Chemistry
of Functional Groups, Zabicky, J., Ed.; John Wiley & Sons, Ltd, 2014.
(2) Edelmann, F. T.; Freckmann, D. M. M.; Schumann, H. Synthesis
and Structural Chemistry of Non-Cyclopentadienyl Organolanthanide
Complexes. Chem. Rev. 2002, 102, 1851−1896.
(3) Arnold, P. L.; McMullon, M. W.; Rieb, J.; Kuhn, F. E. C-H Bond
Activation by f-Block Complexes. Angew. Chem., Int. Ed. 2015, 54,
82−100.
(4) For recent articles, see: (a) Guan, B.-T.; Hou, Z. Rare-Earth-
Catalyzed C-H Bond Addition of Pyridines to Olefins. J. Am. Chem.
Soc. 2011, 133, 18086−18089. (b) Oyamada, J.; Hou, Z.
Regioselective C-H Alkylation of Anisoles with Olefins Catalyzed by
Cationic Half-Sandwich Rare Earth Alkyl Complexes. Angew. Chem.,
Int. Ed. 2012, 51, 12828−12832. (c) Guan, B.-T.; Wang, B.; Nishiura,
M.; Hou, Z. Yttrium-Catalyzed Addition of Benzylic C-H Bonds of
Alkyl Pyridines to Olefins. Angew. Chem., Int. Ed. 2013, 52, 4418−
4421. (d) Song, G.; Luo, G.; Oyamada, J.; Luo, Y.; Hou, Z. Ortho-
Selective C-H Addition of N,N-Dimethyl Anilines to Alkenes by a
Yttrium Catalyst. Chem. Sci. 2016, 7, 5265−5270. (e) Nako, A. E.;
Oyamada, J.; Nishiura, M.; Hou, Z. Scandium-Catalysed Intermo-
lecular Hydroaminoalkylation of Olefins with Aliphatic Tertiary
Amines. Chem. Sci. 2016, 7, 6429−6434. (f) Nagae, H.; Shibata, Y.;
Tsurugi, H.; Mashima, K. Aminomethylation Reaction of ortho-
Pyridyl C−H Bonds Catalyzed by Group 3 Metal Triamido
Complexes. J. Am. Chem. Soc. 2015, 137, 640−643. (g) Kundu, A.;
Inoue, M.; Nagae, H.; Tsurugi, H.; Mashima, K. Direct Ortho-C-H
Aminoalkylation of 2-Substituted Pyridine Derivatives Catalyzed by
Yttrium Complexes with N,N′-Diarylethylenediamido Ligands. J. Am.
Chem. Soc. 2018, 140, 7332−7342.
(5) See some recent reviews: (a) Guillaume, S. M. Recent Advances
in Ring-Opening Polymerization Strategies toward α,ω-Hydroxy
Telechelic Polyesters and Resulting Copolymers. Eur. Polym. J.
2013, 49, 768−779. (b) Trifonov, A. A.; Lyubov, D. M. A Quarter-
Century Long Story of Bis (Alkyl) Rare-Earth (III) Complexes.
Coord. Chem. Rev. 2017, 340, 10−61. (c) Lyubov, D. M.; Tolpygin, A.
O.; Trifonov, A. A. Rare-Earth Metal Complexes as Catalysts for Ring-
Opening Polymerization of Cyclic Esters. Coord. Chem. Rev. 2019,
392, 83−145.
(6) See some recent reviews: (a) Coates, G. W.; Moore, D. R.
Discrete Metal-Based Catalysts for the Copolymerization of CO2 and
Epoxides: Discovery, Reactivity, Optimization, and Mechanism.
Angew. Chem., Int. Ed. 2004, 43, 6618−6639. (b) Klaus, S.;
Lehenmeier, M. W.; Anderson, C. E.; Rieger, B. Recent Advances
in CO2/Epoxide Copolymerization-New Strategies and Cooperative
Mechanisms. Coord. Chem. Rev. 2011, 255, 1460−1479. (c) Kember,
M. R.; Buchard, A.; Williams, C. K. Catalysts for CO2/Epoxide
Copolymerisation. Chem. Commun. 2011, 47, 141−163. (d) Taher-
imehr, M.; Pescarmona, P. P. Green Polycarbonates Prepared by the
Copolymerization of CO2 with Epoxides. J. Appl. Polym. Sci. 2014,
131, 1−17. (e) Poland, S. J.; Darensbourg, D. J. A Quest for
Polycarbonates Provided: Via Sustainable Epoxide/CO2 Copolymer-
ization Processes. Green Chem. 2017, 19, 4990−5011. (f) Kozak, C.
M.; Ambrose, K.; Anderson, T. S. Copolymerization of Carbon
Dioxide and Epoxides by Metal Coordination Complexes. Coord.
Chem. Rev. 2018, 376, 565−587. (g) Scharfenberg, M.; Hilf, J.; Frey,
H. Functional Polycarbonates from Carbon Dioxide and Tailored
Epoxide Monomers: Degradable Materials and Their Application
Potential. Adv. Funct. Mater. 2018, 28, 1704302. (h) Kamphuis, A. J.;
Picchioni, F.; Pescarmona, P. P. CO2-Fixation into Cyclic and
(8) (a) Wang, L.; Sun, W.; Han, L.; Li, Z.; Hu, Y.; He, C.; Yan, C.
Cobalt and Nickel Complexes Bearing 2,6-Bis(imino)phenoxy
Ligands: Syntheses, Structures and Oligomerization Studies. J.
Organomet. Chem. 2002, 650, 59−64. (b) Hu, Q.; Jie, S.;
Braunstein, P.; Li, B.-G. Highly Active Tridentate Amino-phenol
Zinc Complexes for the Catalytic Ring-opening Polymerization of ε-
Caprolactone. J. Organomet. Chem. 2019, 882, 1−9.
(9) Emslie, D. J. H.; Piers, W. E.; Parvez, M.; McDonald, R.
Organometallic Complexes of Scandium and Yttrium Supported by a
Bulky Salicylaldimine Ligand. Organometallics 2002, 21, 4226−4240.
(10) For the structurally close complexes {η2-1-[CHN-Ar]-2-O-3-
tBu-C6H3}Y(CH2SiMe3)2(THF)n (n = 1 and 2 (I-Y)), a fluxional
dynamic process was explained by a reversible decoordination of THF
molecule and interconversion between isomers arising from the
relative positioning of the two alkyl groups around the metal center;
see ref 9.
(11) Effective ionic radii for 6-coordinate centers: Sc3+, 0.745 Å; Y3+,
0.900 Å. Shannon, R. D. Revised effective ionic radii and systematic
studies of interatomic distances in halides and chalcogenides. Acta
Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976,
A32, 751−767.
(12) Duan, Y.-L.; He, J.-X.; Wang, W.; Zhou, J.-J.; Huang, Y.; Yang,
Y. Synthesis and Characterization of Dinuclear Rare-Earth Complexes
Supported by Amine-Bridged Bis(Phenolate) Ligands and Their
Catalytic Activity for the Ring-Opening Polymerization of -Lactide.
L
Dalton Trans. 2016, 45, 10807−10820.
(13) (a) Carver, C. T.; Diaconescu, P. L. Ring-Opening Reactions of
Aromatic N-Heterocycles by Scandium and Yttrium Alkyl Complexes.
J. Am. Chem. Soc. 2008, 130, 7558−7559. (b) Carver, C. T.; Benitez,
D.; Miller, K. L.; Williams, B. N.; Tkatchouk, E.; Gooddard, W. A., III;
Diaconescu, P. L. Reactions of Group III Biheterocyclic Complexes. J.
Am. Chem. Soc. 2009, 131, 10269−10278. (c) Williams, B. N.; Huang,
W.; Miller, K. L.; Diaconescu, P. L. Group 3 Metal Complexes of
Radical-Anionic 2,2′-Bipyridyl Ligands. Inorg. Chem. 2010, 49,
J
https://dx.doi.org/10.1021/acs.inorgchem.0c02112
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
11493−11498. (d) Williams, B. N.; Benitez, D.; Miller, K. L.;
Tkatchouk, E.; Goddard, W. A., III; Diaconescu, P. L. An Unusual
Hydrogen Migration/C-H Activation Reaction with Group 3 Metals.
J. Am. Chem. Soc. 2011, 133, 4680−4683.
(14) (a) Kaneko, H.; Nagae, H.; Tsurugi, H.; Mashima, K. End-
Functionalized Polymerization of 2-Vinylpyridine through Initial C-H
Bond Activation of N-Heteroaromatics and Internal Alkynes by
Yttrium Ene-Diamido Complexes. J. Am. Chem. Soc. 2011, 133,
19626−19629. (b) Shibata, Y.; Nagae, H.; Sumiya, S.; Rochat, R.;
Tsurugi, H.; Mashima, K. 2,2’-Bipyridyl Formation from 2-
Arylpyridines through Bimetallic Diyttrium Intermediate. Chem. Sci.
2015, 6, 5394−5399.
(15) (a) Zhu, X.; Li, Y.; Guo, D.; Wang, S.; Wei, Y.; Zhou, S.
Versatile Reactivities of Rare-Earth Metal Dialkyl Complexes
Supported by a Neutral Pyrrolyl-Functionalized β-Diketiminato
Ligand. Dalton Trans. 2018, 47, 3947−3957. (b) Zhang, Y.; Zhang,
J.; Hong, J.; Zhang, F.; Weng, L.; Zhou, X. Versatile Reactivity of β-
Diketiminato-Supported Yttrium Dialkyl Complex toward Aromatic
N-Heterocycles. Organometallics 2014, 33, 7052−7058.
(16) Radkov, V.; Roisnel, T.; Trifonov, A.; Carpentier, J.-F.; Kirillov,
E. Neutral and Cationic Alkyl and Amido Group 3 Metal Complexes
of Amidine-Amidopyridinate Ligands: Synthesis, Structure and
Polymerization Catalytic Activity. Eur. J. Inorg. Chem. 2014, 2014
(25), 4168−4178.
Polym. Sci., Part A: Polym. Chem. 2016, 54, 2785−2793. (c) Mandal,
M.; Chakraborty, D. Group 4 Complexes Bearing Bis(Salphen)
Ligands: Synthesis, Characterization, and Polymerization Studies. J.
Polym. Sci., Part A: Polym. Chem. 2016, 54, 809−824. (d) Nakano, K.;
Nakamura, M.; Nozaki, K. Alternating Copolymerization of Cyclo-
hexene Oxide with Carbon Dioxide Catalyzed by (Salalen)CrCl
Complexes. Macromolecules 2009, 42, 6972−6980.
(23) (a) Kember, M. R.; Williams, C. K. Efficient Magnesium
Catalysts for the Copolymerization of Epoxides and CO 2; Using
Water to Synthesize Polycarbonate Polyols. J. Am. Chem. Soc. 2012,
134, 15676−15679. (b) Nakano, K.; Nakamura, M.; Nozaki, K.
Alternating Copolymerization of Cyclohexene Oxide with Carbon
Dioxide Catalyzed by (Salalen)CrCl Complexes. Macromolecules
2009, 42, 6972−6980. (c) Wu, G. P.; Darensbourg, D. J. Mechanistic
Insights into Water-Mediated Tandem Catalysis of Metal-Coordina-
tion CO2/Epoxide Copolymerization and Organocatalytic Ring-
Opening Polymerization: One-Pot, Two Steps, and Three Catalysis
Cycles for Triblock Copolymers Synthesis. Macromolecules 2016, 49,
807−814. (d) Darensbourg, D. J. Chain Transfer Agents Utilized in
Epoxide and CO2 Copolymerization Processes. Green Chem. 2019, 21,
2214−2223.
(24) (a) Inoue, S.; Koinuma, H.; Tsuruta, T. Copolymerization of
Carbon Dioxide and Epoxide with Organometallic Compounds.
Makromol. Chem. 1969, 130, 210−220. (b) Zhang, D.; Zhang, H.;
Hadjichristidis, N.; Gnanou, Y.; Feng, X. Lithium-Assisted Copoly-
merization of CO2/Cyclohexene Oxide: A Novel and Straightforward
Route to Polycarbonates and Related Block Copolymers. Macro-
molecules 2016, 49, 2484−2492. (c) Ghosh, S.; Pahovnik, D.; Kragl,
U.; Mejía, E. Isospecific Copolymerization of Cyclohexene Oxide and
Carbon Dioxide Catalyzed by Dialkylmagnesium Compounds.
Macromolecules 2018, 51, 846−852.
(25) (a) Spegazzini, N.; Ruisanchez, I.; Larrechi, M. S.; Serra, A.;
Mantecon, A. Spectroscopic Evidence of the Mechanism Involved in
the Cationic Diglycidyl Ether of Bisphenol a Curing with Rare Earth
Metal Triflates. Appl. Spectrosc. 2010, 64, 104−111. (b) Liu, Y.; Yu, H.
Y.; Lu, X. B. Fast Ring-Opening Polymerization of 1,2-Disubstituted
Epoxides Initiated by a CoIII-Salen Complex. Macromol. Chem. Phys.
2019, 220, 1900377.
(26) Mandal, M.; Monkowius, U.; Chakraborty, D. Synthesis and
Structural Characterization of Titanium and Zirconium Complexes
Containing Half-Salen Ligands as Catalysts for Polymerization
Reactions. New J. Chem. 2016, 40, 9824−9839.
(27) Lewis, H. L.; Brown, T. L. Association of Alkyllithium
Compounds in Hydrocarbon Media. Alkyllithium-Base Interactions. J.
Am. Chem. Soc. 1970, 92, 4664−4670.
(28) Hultzsch, K. C.; Voth, P.; Beckerle, L.; Spaniol, T. P.; Okuda, J.
Single-Component Polymerization Catalysts for Ethylene and
Styrene: Synthesis, Characterization, and Reactivity of Alkyl and
Hydrido Yttrium Complexes Containing a Linked Amido−Cyclo-
pentadienyl Ligand. Organometallics 2000, 19, 228−243.
(29) (a) Sheldrick, G. M. SHELXS-97, Program for the Determination
of Crystal Structures; University of Goettingen (Germany), 1997.
(b) Sheldrick, G. M. SHELXL-97, Program for the Refinement of
Crystal Structures; University of Goettingen (Germany), 1997.
(c) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr.
2008, A64, 112.
(17) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. Single-Site β-Diiminate Zinc
Catalysts for the Alternating Copolymerization of CO2 and Epoxides:
Catalyst Synthesis and Unprecedented Polymerization Activity. J. Am.
Chem. Soc. 2001, 123, 8738−8749.
(18) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates, G. W.
Mechanism of the Alternating Copolymerization of Epoxides and
CO2 Using β-Diiminate Zinc Catalysts: Evidence for a Bimetallic
Epoxide Enchainment. J. Am. Chem. Soc. 2003, 125, 11911−11924.
(19) (a) Ren, W. M.; Zhang, X.; Liu, Y.; Li, J. F.; Wang, H.; Lu, X. B.
Highly Active, Bifunctional Co(III)-Salen Catalyst for Alternating
Copolymerization of CO2 with Cyclohexene Oxide and Terpolyme-
rization with Aliphatic Epoxides. Macromolecules 2010, 43, 1396−
1402. (b) Kissling, S.; Lehenmeier, M. W.; Altenbuchner, P. T.;
Kronast, A.; Reiter, M.; Deglmann, P.; Seemann, U. B.; Rieger, B.
Dinuclear Zinc Catalysts with Unprecedented Activities for the
Copolymerization of Cyclohexene Oxide and CO2. Chem. Commun.
2015, 51, 4579−4582. (c) Nagae, H.; Aoki, R.; Akutagawa, S. N.;
Kleemann, J.; Tagawa, R.; Schindler, T.; Choi, G.; Spaniol, T. P.;
Tsurugi, H.; Okuda, J.; Mashima, K. Lanthanide Complexes
Supported by a Trizinc Crown Ether as Catalysts for Alternating
Copolymerization of Epoxide and CO2: Telomerization Controlled by
Carboxylate Anions. Angew. Chem., Int. Ed. 2018, 57, 2492−2496.
(d) Deng, J.; Ratanasak, M.; Sako, Y.; Tokuda, H.; Maeda, C.;
Hasegawa, J. Y.; Nozaki, K.; Ema, T. Aluminum Porphyrins with
Quaternary Ammonium Halides as Catalysts for Copolymerization of
Cyclohexene Oxide and CO2: Metal-Ligand Cooperative Catalysis.
Chem. Sci. 2020, 11, 5669−5675. (e) Deacy, A. C.; Kilpatrick, A. F.
R.; Regoutz, A.; Williams, C. K. Understanding Metal Synergy in
Heterodinuclear Catalysts for the Copolymerization of CO2 and
Epoxides. Nat. Chem. 2020, 12, 372−380.
(20) Thevenon, A.; Cyriac, A.; Myers, D.; White, A. J. P.; Durr, C.
B.; Williams, C. K. Indium Catalysts for Low-Pressure CO2/Epoxide
Ring-Opening Copolymerization: Evidence for a Mononuclear
Mechanism? J. Am. Chem. Soc. 2018, 140, 6893−6903.
(21) Nakano, K.; Nozaki, K.; Hiyama, T. Spectral Assignment of
Poly[Cyclohexene Oxide-Alt-Carbon Dioxide]. Macromolecules 2001,
34, 6325−6332.
(22) (a) Lee, I. K.; Ha, J. Y.; Cao, C.; Park, D.-W.; Ha, C.-S.; Kim, I.
Effect of Complexing Agents of Double Metal Cyanide Catalyst on
the Copolymerizations of Cyclohexene Oxide and Carbon Dioxide.
Catal. Today 2009, 148, 389−397. (b) Meng, Q. Y.; Pepper, K.;
Cheng, R. H.; Howdle, S. M.; Liu, B. P. Effect of Supercritical CO2 on
the Copolymerization Behavior of Cyclohexene Oxide/CO2 and
Copolymer Properties with DMC/Salen-Co(III) Catalyst System. J.
(30) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi,
R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar,
S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox,
J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.;
Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.;
K
https://dx.doi.org/10.1021/acs.inorgchem.0c02112
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
pubs.acs.org/IC
Article
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A.
̈
D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J.
Gaussian 09, Revision D.01; Gaussian Inc.: Pittsburgh, PA, 2009.
(31) (a) Becke, A. D. Density-Functional Exchange-Energy
Approximation with Correct Asymptotic Behavior. Phys. Rev. A: At.,
Mol., Opt. Phys. 1988, 38, 3098−3100. (b) Becke, A. D. Density-
functional thermochemistry. III. The role of exact exchange. J. Chem.
Phys. 1993, 98, 5648−5652.
(32) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. Universal
Solvation Model Based on Solute Electron Density and on a
Continuum Model of the Solvent Defined by the Bulk Dielectric
Constant and Atomic Surface Tensions. J. Phys. Chem. B 2009, 113,
6378−6396.
(33) Gonzalez, C.; Schlegel, H. B. An Improved Algorithm for
Reaction Path Following. J. Chem. Phys. 1989, 90, 2154−2161.
(34) Castro, L.; Kirillov, E.; Miserque, O.; Welle, A.; Haspeslagh, L.;
Carpentier, J.-F.; Maron, L. Are Solvent and Dispersion Effects
Crucial in Olefin Polymerization DFT Calculations? Some Insights
from Propylene Coordination and Insertion Reactions with Group 3
and 4 Metallocenes. ACS Catal. 2015, 5, 416−425.
L
https://dx.doi.org/10.1021/acs.inorgchem.0c02112
Inorg. Chem. XXXX, XXX, XXX−XXX