Rare-earth-metal complexes bearing phosphazene ancillary ligands: Structures and catalysis toward highly trans-1,4-selective (co)polymerizations of conjugated dienes

Article abstract of DOI:10.1021/om300967h

The bis-arylated phosphazene compounds [HN(PPh₂NAr)₂] (Ar = phenyl (HL¹), 2,6-dimethylphenyl (HL²), 2,6-diisopropylphenyl (HL³)) and the imidodiphosphinate compound HN(PPh₂O)₂ (HL⁴) have been prepared via the Staudinger reaction. Treatment of the neutral compounds HL¹, HL ², and HL³ with Ln(CH₂SiMe₃) ₃(THF)₂ (Ln = Sc, Y, Lu) generated the solvent-free bis(alkyl) complexes L¹Ln(CH₂SiMe₃)₂ (Ln = Sc (1a), Y (1b), Lu (1c)), L²Sc(CH₂SiMe ₃)₂ (2a), L³Y(CH₂SiMe ₃)₂ (3b), and L³Lu(CH₂SiMe ₃)₂ (3c), respectively. The reaction between HL ⁴ and Y(CH₂SiMe₃)₃(THF)₂ gave the rare zwitterionic complex 4b. Lithiation of the ligand HL¹ by nBuLi followed by a metathesis reaction with Nd(BH₄) ₃(THF)₃ afforded the corresponding complex L ¹Nd(BH₄)₂(THF)₂ (5). Complexes 1 upon incorporation of [Ph₃C][B(C₆F₅) ₄] and AliBu₃ led to ternary systems that initiated isoprene polymerization with high activities, among which complex 1a was the first example of a scandium catalytic precursor providing trans-1,4-selectivity (90.0%), while the lutetium analogue 1c had medium trans-1,4-selectivity (54.3%) and the yttrium complex 1b exhibited high cis-1,4-selectivity (76.3%). The ternary system based on the zwitterion 4b displayed the highest activity for the isoprene polymerization among these complexes and gave cis-1,4-regularity- enriched polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene (trans-1,4-content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved by using the borohydrido complex 5 upon the activation of dibutylmagnesium. The copolymerization of isoprene and butadiene with 1a/[Ph₃C][B(C₆F₅)₄/AliBu ₃] gave randomly arranged trans-1,4-regulated polybutadiene and polyisoprene sequences. The kinetics study displayed competitive polymerization rates of r_BD = 2.89 and r_IP = 0.41. The thermal behaviors of the (co)polymers were investigated.

Full text of DOI:10.1021/om300967h

Article
pubs.acs.org/Organometallics
Rare-Earth-Metal Complexes Bearing Phosphazene Ancillary Ligands:
Structures and Catalysis toward Highly Trans-1,4-Selective
(Co)Polymerizations of Conjugated Dienes
Weifeng Rong,†,‡ Dongtao Liu,† Huiping Zuo,§ Yupeng Pan,†,‡ Zhongbao Jian,†,‡ Shihui Li,†
and Dongmei Cui*,†
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, People’s Republic of China
‡Graduate School of the Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
§Chemistry School, Jilin University, Changchun 130012, People’s Republic of China
S
* Supporting Information
ABSTRACT: The bis-arylated phosphazene compounds
[HN(PPh2NAr)2] (Ar = phenyl (HL1), 2,6-dimethylphenyl
(HL2), 2,6-diisopropylphenyl (HL3)) and the imidodiphos-
phinate compound HN(PPh2O)2 (HL4) have been prepared
via the Staudinger reaction. Treatment of the neutral
compounds HL1, HL2, and HL3 with Ln(CH2SiMe3)3(THF)2
(Ln = Sc, Y, Lu) generated the solvent-free bis(alkyl)
complexes L1Ln(CH2SiMe3)2 (Ln = Sc (1a), Y (1b), Lu
(1c)), L2Sc(CH2SiMe3)2 (2a), L3Y(CH2SiMe3)2 (3b), and L3Lu(CH2SiMe3)2 (3c), respectively. The reaction between HL4 and
Y(CH2SiMe3)3(THF)2 gave the rare zwitterionic complex 4b. Lithiation of the ligand HL1 by nBuLi followed by a metathesis
reaction with Nd(BH4)3(THF)3 afforded the corresponding complex L1Nd(BH4)2(THF)2 (5). Complexes 1 upon incorporation
of [Ph3C][B(C6F5)4] and AliBu3 led to ternary systems that initiated isoprene polymerization with high activities, among which
complex 1a was the first example of a scandium catalytic precursor providing trans-1,4-selectivity (90.0%), while the lutetium
analogue 1c had medium trans-1,4-selectivity (54.3%) and the yttrium complex 1b exhibited high cis-1,4-selectivity (76.3%). The
ternary system based on the zwitterion 4b displayed the highest activity for the isoprene polymerization among these complexes
and gave cis-1,4-regularity-enriched polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene (trans-1,4-
content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved by using the borohydrido complex 5 upon the
activation of dibutylmagnesium. The copolymerization of isoprene and butadiene with 1a/[Ph3C][B(C6F5)4/AliBu3] gave
randomly arranged trans-1,4-regulated polybutadiene and polyisoprene sequences. The kinetics study displayed competitive
polymerization rates of rBD = 2.89 and rIP = 0.41. The thermal behaviors of the (co)polymers were investigated.
of elevated temperatures or prolonged polymerization time.14
Another is that trans-1,4-polyisoprene, although having a
INTRODUCTION
■
The stereospecific polymerization of conjugated dienes has
microstructure similar to that of natural gutta percha, has
developed extensively since the 1950s, carried along by the
been found few applications. Recently, long-life “green” tires
scientific and technical challenges of the synthetic elastomer
with low rolling resistance and slip resistance have become a
industry. In particular, great achievements have been made
concept for sustainable development of the rubber and
automobile industries because of their source and the energy
crisis. Plastic trans-1,4-polyisoprene mixed in less than 15 wt %
percent with its cis-1,4-isomer or natural rubber constructs
high-performance rubbers for preparation of the resulting green
tires, which are anticipated to have properties superior to those
of conventional butadiene−styrene copolymers. In addition,
trans-1,4-polyisoprene has been employed as a material for
medical purposes (orthopedics, reconstructive surgery).15
about cis-1,4-selective polymerization of dienes, because the
resulting polymers are the most important rubbers used for
tires and other elastic materials.1−7 Lanthanide-based catalyst
systems represent a prominent class of such high-performance
catalysts:7 for instance, the notable Ziegler−Natta catalysts
employed as the industry recipe for producing cis-1,4-
polybutadiene and the academically valuable single-sited and
cationic catalysts based on the lanthanide alkyl,8 carboxylate
(versatate),9 halide,7a,c,10 or alkoxide precursors.11,12 Compara-
tively, trans-1,4-polymerization has received rather limited
attention.13 One reason might be the lack of efficient catalysts
for this type of polymerization, and the few known systems
usually feature low activity, unpromising monomer conversion,
and less control in molecular weight, even under the conditions
Special Issue: Recent Advances in Organo-f-Element Chemistry
Received: October 17, 2012
© XXXX American Chemical Society
A
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Scheme 1. Synthesis of the NPNPN-Type Ligands HL1, HL2, and HL3
Therefore, the exploration of highly efficient catalyst systems
for trans-1,4-selective diene polymerizations has attracted
increasing research interest. The lanthanide borohydrides
chemistry has been investigated. Comparatively, the rare-earth-
metal complexes supported by such NPNPN-type ligands still
have been untapped to date, although their bis-
(phosphinimino)methanide ligand (PNCPN) supported ana-
logues have been reported.26 Recently rare-earth-metal
borohydrides have attracted research interest again, as their
easy accessibility, high temperature resistance, and wide
utilization in the polymerizations of ethylene,27 styrene,28,29
butadiene,30 isoprene,28,31,32 and some polar monomers such as
ε-caprolactone,33,34 methyl methacrylate,35 and trimethylene
carbonate.26d,36
Herein we report the synthesis and structural character-
ization of a series of bis-arylated phosphazene [HN-
(PPh2NAr)2] and imidodiphosphinate [HN(PPh2O)2] stabi-
lized rare-earth-metal dialkyl and borohydrido complexes that
show unique structures and versatile catalytic performances.
Under the activation of some cocatalysts, the bis-phenylated
phosphazene scandium bis(alkyl) complex and bis-phenylated
phosphazene neodymium borohydrido complex displayed high
activity and trans-1,4-selectivity toward both isoprene and
butadiene polymerizations.
14a,b
Ln(BH4)3(THF)n and Cp*Ln(BH4)2(THF)n/Mg(nBu)2
reported by Visseaux and the lanthanide allyl complexes rac-
[{Me2C(Ind)2}Y(1,3-(SiMe3)2C3H3)] (Ln(allyl)2Cl(MgCl2)2/
AlR3)14c,d reported by Carpentier are efficient catalysts for
trans-1,4-isoprene polymerization. The yttrium mono(allyl)
complex14d is the first example of a single-component catalyst
for the preparation of trans-1,4-polyisoprene. The lanthanide
aluminate (C5Me5)Ln(AlMe4)2/organoborate14e,f discovered
by Anwander remains the most highly trans-1,4-selective
(>99%) system to date. Well-defined neodymium alkoxides/
aryloxides in combination with dialkylmagnesiums polymerize
butadiene with a high trans-1,4-stereospecificity (95%).14g
Other than these achievements, utilization of non-cyclo-
pentadienyl (non-Cp)-ligated rare-earth-metal precursors for
trans-1,4-polymerizations of conjugated dienes is still scarce.
On the other hand, rare-earth-metal bis(alkyl)s supported by
monoanionic non-Cp ancillary ligands have been demonstrated
as highly active single-component catalysts or excellent
precursors for the polymerizations of conjugated dienes and
olefins under the activation of borates or/and aluminum
alkyls.7b,8 Our group has designed a series of non-Cp-ligated
rare-earth-metal bis(alkyl)s16,17 and found that the ligands
containing N, O, and P heteroatoms play distinctive roles in
governing the catalytic performance of the attached central
metal ions. For instance, the cationic NCN-tridentate pincer
type bis(aryliminomethylene)-2,6-phenyl-1-yl and bis(N-cyclo-
carbenemethylene)-2,6-phenyl-1-yl, bis(phospheno)carbazolyl
rare-earth-metal complexes show high cis-1,4-selectivity for
diene monomers,7a,8a,10a rare-earth-metal bis(alkyl) complexes
bearing an iminophosphonamido ligand (NPN type) have been
employed as catalyst precursors to provide extremely high
activity for 3,4-selectivity polymerization of isoprene,17 and the
thiophene-NPN ligands and quinolinyl anilido ligands
supported rare-earth-metal complexes, under the activation of
organoborates and aluminum alkyls, exhibited distinguished
catalytic activity and trans-1,4-selectivity for both butadiene and
isoprene homo- and copolymerizations.17a,b Meanwhile, the
bis(silylated phosphazene) [HN(PPh2NSiMe3)2] originately
explored by Oakley and Roesky as early as the 1990s18 has been
developed into versatile NPNPN-type ligands consisting of a
five-atom scaffold, and their supported complexes based on
various metals such as Na, K, Ca,19 Al, Ga, In,20 V,21 Zn, Cd,
Hg,22 Ti,23 Zr,24 As, and U25 have been synthesized and their
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Complexes 1a−c,
2a, and 3b,c. The bis-arylated phosphazene compounds
[HN(PPh2NAr)2] (Ar = benzene (HL1), m-xylene (HL2), 1,3-
diisopropylbenzene (HL3)) were prepared via the Staudinger
reaction in two steps according to a modified literature
procedure (Scheme 1).25 The reaction of chlorodiphenylphos-
phine with hexamethyldisilazene in a 2:1 molar ratio in toluene
gave HN(PPh2)2. Treatment of HN(PPh2)2 with the
corresponding azides resulted in the formation of HL1, HL2,
1
and HL3, respectively. The H NMR spectra of these three
ligands display different chemical shifts for NH protons. The
amino proton NH of the ligand HL1 is found as a very broad
singlet around δ 3−5 ppm, which appears as a singlet at 4.06
ppm for the ligand HL2, but the NH proton in HL3 is not
observed in C6D6 or CDCl3. The 31P NMR spectra of all these
ligands reveal a singlet at δ 6.51 ppm (HL1), 1.85 ppm (HL2),
or 6.26 ppm (HL3), respectively, indicating the equivalence of
the two phosphine atoms in each molecule.
Treatment of these ligands with rare-earth metal tris(alkyl)s,
Ln(CH2SiMe3)3(THF)2, afforded the bis(alkyl) complexes
[L1−3Ln(CH2SiMe3)2] (L1, Ln = Sc (1a), Y (1b), Lu (1c);
L2, Ln = Sc (2a); L3, Ln = Y (3b), Lu (3c)) in 55−72% yields
(Scheme 2). All of these complexes are soluble in THF and
B
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Scheme 2. Synthesis of the NPNPN-Type Complexes 1a−c, 2a, and 3b,c
toluene but insoluble in n-hexane. The methylene protons of
Y−CH2SiMe3 in 1b and 3b give doublet resonances at δ 0.29
(1b) and 0.10 (3b), respectively, due to coupling with the
yttrium ion (JY−H = 2.8 Hz for both), while the methylene
protons of Sc−CH2SiMe3 and Lu−CH2SiMe3 in the scandium
and lutetium complexes 1a, 2a, 1c, and 2c exhibit singlet
resonances, respectively, suggesting that the metal alkyl species
in these complexes are fluxional in the solution state. No THF
molecule coordination is observed. The solid-state structures of
complexes 1a,c, 2a, and 3c were established by single-crystal X-
ray diffraction, as shown in Figure 1 and Figures S27−S29
170.83° for 1a, very close to 170.39° for 1c, suggesting that the
overall NPNPN skeleton has a slightly distorted planar
geometry. In contrast, the dihedral angles in complexes 2a
and 3c are much smaller (144.88° vs 139.88°), suggesting the
NPNPN skeleton is far from a plane, which might be attributed
to the Me and iPr substituents of phenyl rings increasing the
steric hindrance around the metal center. It is particularly
noteworthy that the average phosphinimine PN double-bond
lengths (1a, 1.615 Å; 1c, 1.614 Å; 2a, 1.608 Å; 3c, 1.614 Å) are
comparable to the average P−N bonds in the corresponding
complexes (1a, 1.595 Å; 1c, 1.595 Å; 2a, 1.598 Å; 3c, 1.605
Å).37 This indicates delocalization of the electrons over the
fused four-membered rings.19 The distances between the
lanthanide atoms and the central nitrogen atoms Ln−N
(2.294(2) Å (1a), 2.406(3) Å (1c), 2.472(2) Å (2a),
2.494(3) (3c) fall in the normal region reported previously.38
Synthesis and Characterization of Zwitterionic
OPNPO-Type Yttrium Bis(alkyl) Complex 4b. The
imidodiphosphinate ligand, HN(PPh2O)2 (HL4), was prepared
by treatment of chlorodiphenylphosphine with hexamethyldi-
Scheme 3. Synthesis of the OPNPO-Type Ligand HL4 and
Corresponding Complex 4b
Figure 1. X-ray structure of 1a (thermal ellipsoids at the 35%
probability level). Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Sc1−N1 = 2.237(2),
Sc1−N2 = 2.233(2), Sc1−N3 = 2.294(2), Sc1−C37 = 2.214(3), Sc1−
C41 = 2.205(3), N1−P1 = 1.616(2), N2−P2 = 1.613(2), N3−P1 =
1.593(2), N3−P2 = 1.596(2); N1−Sc1−N2 = 129.95(8), C37−Sc1−
C41 = 110.79(11), P1−N3−P2 = 158.42(15).
(Supporting Information) along with selected bond lengths and
bond angles. These complexes are structural analogues. There
are two alkyl species σ-bound to each central metal ion.
Meanwhile, the pincer-type ligands adopt a κ3 coordination
mode via the three nitrogen atoms, which bisects the C−Ln−C
bond angle formed by the alkyl groups and the central metal
ion, generating a heavily distorted trigonal bipyramidal
geometry around the central metal. It is worth noting that
the NPNPN skeleton consists of two planar fused four-
membered rings with the covalent bond Ln−N as the sharing
edge. The dihedral angle of the fused four-membered rings is
silazane followed by oxidation with H2O2 (Scheme 3).39 The
1H NMR spectrum of HL4 in CDCl3 shows three resonances
within the regions of δ 7.78−7.83, 7.39−7.42, and 7.27−7.32 in
a 2:1:2 ratio, which are assignable to the phenyl protons. The
NH proton resonance is broad and weak. The 31P NMR
spectrum in CDCl3 shows a single resonance at δ 20.27 ppm,
corresponding to two equivalent phosphorus atoms as observed
in the literature.39 Treatment of HL4 with 1 equiv of
Y(CH2SiMe3)3(THF)2 at room temperature afforded the
C
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Organometallics
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bis(alkyl) complex L4Y(CH2SiMe3)2(THF)2 (4b) in 65% yield.
The 1H NMR spectrum of 4b exhibits two doublets at δ −0.30
and −0.69 ppm assigned to the methylene protons Y−
CH2SiMe3, which is in good correlation with the two doublets
at δ 33.91, 33.56 ppm (JYC = 35.3 Hz) and 29.93, 29.54 ppm
(JYC = 39.5 Hz) in its 13C NMR spectrum, suggesting that the
methylene protons are diastereotopic and the two alkyl
moieties might be located in different chemical environments.40
In addition, there are two coordinated THF molecules in 4b,
neodymium analogue is impossible by following the same
procedure as for the preparation of complexes 1a, as the
neodymium tris(alkyl) precursor Nd(CH2SiMe3)3(THF)2 has
not been isolated as a stable product to date. Therefore, we
modified the above synthetic method by lithiating the ligand
HL1 (HN(PPh2NPh)2) with nBuLi and then adding
NdCl3(THF)3 and LiCH2SiMe3 in situ to the system
sequentially. Unfortunately, this attempt also failed, which
might be due to the larger Nd3+ radius and its higher
coordination number. Thus, the bulky precursor Nd-
(BH4)3(THF)3 was employed instead of NdCl3(THF)3.
Delightfully, the neodymium bis(borohydrido) complex L1Nd-
(BH4)2(THF)2 (5) was successfully isolated under the
optimized conditions (Scheme 4). As Nd3+ is paramagnetic,
1
evidenced by signals at 1.31 and 3.80 ppm in the H NMR
spectrum. Interestingly, complex 4b is a zwitterion, as revealed
by X-ray diffraction analysis (Figure 2). The anionic OPNPO
Scheme 4. Synthesis of the NPNPN-Type Borohydride
Complex 5
the NMR spectrum analysis of 5 is uninformative, and its
structure was resolved by X-ray diffraction analysis to be a
monomer with two THF solvate molecules. The metal center is
seven-coordinate, adopting a pentagonal-bipyamidal geometry
with the two η3-tetrahydridoborate moieties in the axial
positions (B−Nd−B = 169.83(13)°), and the two THF
molecules and tridentate [N(PPh2NPh)2]− ligand occupying
the equatorial sites (Figure 3). The Nd···B contacts (Nd···B1 =
2.729(5) Å, Nd···B2 = 2.703(4) Å) are comparable to the
reported data.31,42 The dihedral angle formed by the planes
Nd1−N1−P1−N2 and Nd1−N1−P2−N3 (151.29°) is
between those found in complexes 1c, 2a, and 3c. This
means the combination of the steric bulkiness of ligand L1 with
the higher coordination number of borohydride in complex 5
contributes to the stability of this Nd-based complex.
Polymerization of Isoprene. We explored the isoprene
polymerization catalyzed by these precursors in toluene under
different conditions. The representative polymerization data are
summarized in Table 1. It was noted that complexes 1−4 alone
showed no activity, and the binary catalytic systems generated
by combining aluminum alkyls (AlR3) also did not induce
visible polymerization. Delightfully, as soon as an organoborate
was added, the formed ternary systems initiated polymerization
immediately. Overall, both the ligands and the types of the
central metals exerted significant influences on the catalytic
performances. Complexes 1a−c with the sterically less bulky
ligand L1 (N(PPh2NAr)2, Ar = phenyl) showed similar high
activity upon activation with 1 equiv of [Ph3C][B(C6F5)4] and
10 equiv of AliBu3, achieving complete conversion within 5 h at
room temperature (Table 1, entries 1, 6, and 7), which were
comparable to those of the lanthanide allyl complexes rac-
[{Me2C(Ind)2}Y(1,3-(SiMe3)2C3H3)]/CTA14d and the lantha-
nide aluminate [(C5Me5)Ln(AlMe4)2]/organoborate,14e while
complexes 2a and 3b,c bearingthe larger ligands N(PPh2NAr)2
(Ar = 2,6-dimethylphenyl, 2,6-diisopropylphenyl) were totally
inert under the same conditions, suggesting that more crowded
Figure 2. X-ray structure of 4b (thermal ellipsoids at the 35%
probability level). Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Y1−O1 = 2.229(2), Y1−
O2 = 2.303(2), Y1−O3 = 2.365(2), Y1−O4 = 2.465(2), Y1−C25 =
2.421(4), Y1−C29 = 2.438(4), N1−P1 = 1.578(3), N1−P2 =
1.587(3), P1−O1 = 1.521(2), P2−O2 = 1.510(2); O1−Y1−O2 =
84.20(8), C25−Y1−C29 = 102.56(13), Y1−O1−P1 = 135.18(14),
Y1−O2−P2 = 131.93(13), P1−N1−P2 = 129.41(19).
chelates to the yttrium ion in a bidentate κ2 coordination mode
via the two neutral oxygen atoms,41a while the nitrogen anion
has no bond to the yttrium ion with a long Y···N distance of
3.856 Å. The bond distances between the coordinated oxygen
atoms and the yttrium ion are approximately equal (Y1−O1 =
2.229(2) Å, Y1−O2 = 2.303(2) Å) and are slightly shorter than
that of oxygen atom from THF and the yttrium ion (Y1−O3 =
2.365(2) Å, Y1−O4 = 2.465(2) Å), suggesting that the
coordination of THF molecules is fluxional. Meanwhile, the
bond lengths between the yttrium ion and the alkyl carbons
(Y1−C25 = 2.421(4) Å, Y1−C29 = 2.438(4) Å) fall within the
normal range for yttrium trimethylsilylmethyl complexes. The
average P−N bond length (1.583 Å) is much shorter than the
corresponding values found in structurally characterized
organometallic complexes containing P−N single bonds such
as [NiCl2(PN-iPr)] (1.6839 Å)41b but are very close to the P
N double-bond lengths of the neutral bis(phosphinimine)-
pyrrole-based ligand (1.562 Å, 1.572 Å).37a This can be ascribed
to the strong electron-donating ability of oxygen and the highly
electropositive nature of the metal center. Although the
zwitterionic metal complexes have been reported to possess
special properties and unique catalysis,41c,d those based on rare-
earth metals are scarce and their reactivity has remained less
explored.41a
Synthesis and Characterization of NPNPN-Type Neo-
dymium Bis(borohydrido) Complex 5. The synthesis of the
D
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Figure 3. X-ray structure of 5 (thermal ellipsoids at the 35% probability level): (A) hydrogen atoms omitted for clarity, except for the freely refined
B−H atoms; (B) all the hydrogen and carbon atoms omitted for clarity. Selected bond lengths (Å) and angles (deg): Nd1−N1 = 2.464(3), Nd1−N2
= 2.617(3), Nd1−N3 = 2.483(3), Nd1−B1 = 2.729(5), Nd1−B2 = 2.703(4), Nd1−H1A = 2.4869, Nd1−H1B = 2.7784, Nd1−H1C = 2.4673,
Nd1−H2A = 2.4719, Nd1−H2B = 2.5766, Nd1−H2C = 2.6237, N1−P1 = 1.600(3), N2−P1 = 1.597(3), N2−P2 = 1.598(3), N3−P2 = 1.603(3);
B2−Nd1−B1 = 169.83(13), N1−Nd1−N3 = 112.13(10), N1−Nd1−O1 = 91.73(9), O2−Nd1−O1 = 76.63(9), N1−Nd1−N2 = 58.74(10), N3−
Nd1−N2 = 58.77(9), P1−N2−P2 = 146.0(2).
Table 1. Polymerization of Isoprene under Various Conditions
d
amt of AlR3 (equiv) [R or Mg
compd]
Tp
(°C)
time
(h)
yield
b
cis-1,4/trans-1,4/3,4 microstructure
Mn
×
M /
wd
a
c
e
entry
cat.
(%)
(%)
10−4
Mn
Tg/Tm (°C)
1
2
3
4
5
6
7
8
9
10
1a + A
1a + A
1a + A
1a + B
1a + C
1b + A
1c + A
4b + A
5 + A
5
10 [iBu]
25
25
25
25
25
25
25
25
25
25
50
5
5
100
82
1.3/90.0/8.7
11.3/78.6/10.1
67.3/23.2/9.5
1.8/88.8/9.4
1.27
1.24
2.48
1.70
1.47
2.05
2.13
1.49
−63.2/23.5
−64.1/25.9
−60.0/−
10 [Et]
10 [Me]
5
75
10 [iBu]
5
100
0
−63.7/25.0
10 [iBu]
5
10 [iBu]
5
100
100
100
93
76.3/11.5/12.2
34.1/54.3/11.6
70.6/9.2/20.2
6.0/92.7/1.3
1.2/97.0/1.8
2.37
1.94
5.64
4.38
2.37
2.15
1.54
1.66
1.59
1.38
1.18
1.34
−58.6/−
−61.3/−
−53.9/−
10 [iBu]
5
10 [iBu]
0.5
5
1 [Mg(nBu)2]
1 [Mg(nBu)2]
1 [Mg(nBu)2]
−69.1/32.5
−61.5/37.3
12
62
f
g
h
11
5
12
60
2.6/94.0/3.4
48.3/90.6
a
General conditions: 10−5 mol of Ln complex; toluene 5 mL; [IP]0:[Ln]0 = 1000:1; [activator]0:[Ln]0 = 1:1 (activator = [Ph3C][B(C6F5)4] (A),
b
c
d
[PhNHMe2][B(C6F5)4] (B), B(C6F5)3 (C)). Isolated yield of polymer. Determined by 13C NMR and 1H NMR. Determined by GPC in THF at
e
f
40 °C against a polystyrene standard. Determined from the second heating cycle of DSC measurements run at 10 °C min−1. Monomer: butadiene,
g
h
[BD]0:[Ln]0 = 1000. 1,2-vinyl polybutadiene. Tt/Tm.
metal center hinders the orientation and insertion of the
incoming monomer after incorporation of one isoprene
molecule.17a Among these complexes the zwitterion complex
4b exhibited the highest catalytic activity, finishing the
polymerization in 30 min, which might be attributed to the
smaller steric hindrance of the ligand L4 (N(PPh2O)2) as well
as the larger Y metal ion (Table 1, entry 8). Although
zwitterionic complexes have been known to catalyze organic
synthesis, there is only one case reported previously by us that a
heteroscopionate yttrium zwitterion complex could initiate
heteroselective polymerization of rac-lactide. Therefore, com-
plex 4b is the first zwitterionic complex to show catalysis
toward isoprene polymerization. The borohydrido complex 5,
although it could not be activated by aluminum alkyls and zinc
alkyls, in combination with 1 equiv of Mg(nBu)2 exhibited
activity similar to those of complexes 1 toward the polymer-
ization of isoprene at room temperature (for butadiene, a
higher polymerization temperature was needed). Addition of
organoborate to the 5/Mg(nBu)2 system dramatically accel-
erated the polymerization rate; both the conversion and the
molecular weight almost doubled (Table 1, entries 9 and 10).
The selectivity of the polymerization showed strong
dependence on the central metal ions. Bearing the same L1
ligand, scandium complex 1a provided high trans-1,4-selectivity
(90.0%), while the lutetium complex 1c had medium trans-1,4-
selectivity (54.3%). In contrast, both yttrium complexes 1b and
4b displayed enriched cis-1,4-selectivity (76.3 and 70.6%)
(Table 1, entries 1 and 6−8). These results were consistent
with those found in the catalytic system composed of the
scandium dialkyl complex bearing a thiophene-NPN ligand,
which initiated the highly trans-1,4-selective polymerization of
butadiene activated by [NHMe2Ph][B(C6F5)4] and AliBu3.17a
The stereoselectivity can be explained on the basis of the well-
established mechanism for polymerization of conjugated
dienes.43a The polymerization was initiated by the coordination
of the monomer to the metal center followed by its insertion
into a metal−σ-alkyl (allyl) active species for propagation. The
monomer η2-trans coordinates to the metal center to form
mainly the syn Ln−allyl transition state species, which is
inserted by the monomer at the C1−Ln bond to give trans-1,4-
regulated polyisoprene. When the attached ligand was electron-
withdrawing, the addition of isoprene monomer to the Ln−C3
carbon was favored to arouse the advantage of 3,4-regularity. In
E
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Table 2. Copolymerization of Butadiene (BD) and Isoprene (IP) using Complex 1a/[Ph3C][B(C6F5)4]/AliBu3
c
BD/IP
(mmol/mmol)
PBD content
(%)
cis-1,4/trans-1,4/1,2 BD
cis-1,4/trans-1,4/3,4 IP
Mn
×
M /
wc
a
b
b
d
entry
microstructure(%)
microstructure(%)
10−4
Mn
Tg/Tm (°C)
1
2
3
4
5
6
0/20
4/16
8/12
12/8
16/4
20/0
0
20
−/−/−
3.1/87.3/9.6
3.1/87.1/9.8
5.2/84.2/10.6
5.6/83.1/11.3
5.9/82.6/11.5
−/−/−
3.96
3.55
4.04
3.79
3.99
3.60
1.80
1.50
1.42
1.57
1.54
1.64
−64.7/23.3
−66.3/−
−72.4/−
20.4/69.5/10.1
21.7/69.8/8.5
21.2/70.7/8.1
20.3/71.8/7.9
18.3/74.1/7.6
40
60
−75.5/−
80
−76.0/15.4
e
100
41.9/62.5
a
General conditions: 10−5 mol of complex 1a (Sc); toluene 5 mL; Tp 25 °C; [Ph3C][B(C6F5)4]:[Sc] = 1:1; [Al]:AliBu3; [Al]/[Sc] = 10. Yield of
b
c
d
copolymers: 100%. Determined by 13C NMR and 1H NMR. Determined by GPC in THF at 40 °C against a polystyrene standard. Determined
e
from the second heating cycle of DSC measurements run at 10 °C min−1. Tt/Tm.
contrast, if the monomer η2-cis or η4-cis coordinates to the
metal center to form mainly the anti Ln−allyl transition state
species which is attached by monomer at the C1−Ln bond to
give cis-1,4-regulated polyisoprene.1,14d,43 Therefore, the
geometry of the ligand and the specific environment around
the central metal play a significant role in governing the
selectivity. For complex 1a, the the Sc3+ ion is so small that the
ligand provides efficient steric shielding to the metal center,
which only allows isoprene η2-trans coordination and favors the
formation of trans-1,4-polyisoprene. With an increase of the
ionic radius size,44 the Y and Lu complexes 1b,c endowed a
more open space for isoprene η4 coordination. Thus, cis-1,4-
selectivity increased with the ionic radius. In the presence of
AlEt3, the catalytic system provided good activity and moderate
trans-1,4-stereoselectivity (78.6%); however, on switching to
AlMe3, the trans-1,4-selectivity decreased significantly to 23.2%.
Instead, the cis-1,4-selectivity increased to 67.3% (Table 1,
entries 2 and 3). Similar results arising from a change of AlR3
cocatalysts was found previously by Hou et al., who proved
preliminarily that the generated cationic Ln−Al heteronuclear
species might be attributed to the cis-1,4-polymerization of
isoprene.45a The trityl and anilinium borate activators A and B
showed similar influences on the polymerization activity and
selectivity (Table 1, entries 2 and 5), indicating that the
resulting cationic active species had a weak connection with the
counterion groups. The neutral borane compound C showed
poor activity (Table 1, entry 5), which was observed in many
systems reported previously.7c,10b To date only a few
organometallic complexes have been activated by neutral
borane.45b The catalytic system composed of complex 5 and
Mg(nBu)2 exhibited the highest trans-1,4-selectivity (97.0%) in
this work at room temperature (Table 1, entry 10), in
accordance with the formation of a Nd/Mg bimetallic
compound bearing a bridging Mg−BH4 group.4,45e
crystalline-type (monoclinic-hexagonal) transition temperature
(Tt, 48.3 °C) and a much higher Tm value (90.6 °C).5c,17a,b
Copolymerization of Isoprene and Butadiene. The
copolymerization of butadiene with isoprene is usually adopted
as an efficient way to reduce the crystallinity of the trans-1,4-
regulated polydiene homopolymers in order to improve their
processing and mechanical properties.46 We found that the
system 1a/[Ph3C][B(C6F5)4]/AliBu3 was able to initiate
butadiene polymerization in a trans-1,4-selective manner with
an activity similar to that for isoprene. Thus, the copolymeriza-
tion of butadiene and isoprene was explored under various
monomer feed ratios. The representative polymerization data
are given in Table 2. It can be seen that all the
copolymerizations could occur fluently to achieve complete
conversions. The compositions of the copolymers were
precisely consistent with the BD-to-IP feed ratios. In the
copolymers, the trans-1,4-regularities of both the PIP and PBD
sequences dropped slightly in comparison with the homopol-
1
ymers, as evidenced by the H NMR spectroscopy analysis.
This was understandable, as the tacticity is usually lost at the
joints of the polyisoprene and polybutadiene units in the
copolymer, in particular when the two-type units are arranged
randomly. The Fineman−Ross45f plot for the copolymerization
performed at 25 °C is depicted in Figure 4. A plot of F(f − 1)/f
as the ordinate and F2/f as the abscissa is a straight line whose
slope is rBD and whose intercept is −rIP (F = [BD]/[IP] in feed,
f = [BD]/[IP] in copolymer). The monomer competitive
The thermal behaviors of the obtained polymers were
examined by DSC. Generally the trans-1,4-regulated poly-
isoprenes isolated from this work had a Tg value in the range of
−50 to −70 °C, in agreement with the earlier literature.45c
Meanwhile, the melting transition temperature Tm could also
be observed, which appears as a low value within the range 22−
26 °C (with low intensity) for those polymers obtained by
using complexes 1 as the precursors, while a much higher Tm
value is found around 30−40 °C for the samples produced by
the borohydrido catalytic system, which, as reported previously,
depends on the molecular weights of polyisoprenes and their
trans-1,4-contents as well as the length of the trans-1,4-
sequences.14d,45c,d,g Obviously, trans-1,4-polybutadiene having
more regular polymeric chains in comparison to trans-1,4-
polyisoprene (without side methyl groups) possesses a
Figure 4. Fineman−Ross plot for copolymerization of butadiene (BD)
and isoprene (IP) with 1a/[Ph3C][B(C6F5)4]/AliBu3 at 25 °C (F =
[BD]/[IP] in feed, f = [BD]/[IP] in copolymer, rBD = 2.89, rIP = 0.41).
F
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polymerization rates were calculated to be rBD = 2.89 and rIP =
0.41, respectively, which is very close to the values for the
copolymerization with the V(acac)3/MAO system,46c indicating
an activity of butadiene slightly higher than that of isoprene and
the random copolymerization tendency because of time value
rBD × rIP = 1.18.43c,46a−c The thermal behavior of the obtained
butadiene−isoprene copolymers was also examined by DSC. As
shown in Figure 5, the crystalinity of the trans-1,4-polyisoprene
analogues 2a and 3b,c with the sterically more bulky NPNPN-
type ligands are totally inert, as the steric shielding around the
metal center inhibits isoprene coordination. The micro-
structures of the polymers obtained are highly dependent on
the central metals. Polyisoprene with very high trans-1,4-
content (90.0%) can be obtained from the smaller scandium
precursor 1a, which is the first example of a scandium catalytic
precursor initiating trans-1,4-selective polymerization of iso-
prene. With an increase of the metal ionic radius, which
facilitates isoprene η4 coordination, the cis-1,4-stereoselectivity
obviously increases. The neutral system composed of complex
5 and Mg(nBu)2 provides a much higher trans-1,4-selectivity
toward homopolymerizations of both butadiene and isoprene
(trans-1,4-contents 94.0% for butadiene and 97.0% for
isoprene). The copolymerization of butadiene and isoprene
by using the 1a/[Ph3C][B(C6F5)4]/AliBu3 system yields
random but noncrystalline copolymers with trans-1,4-regularity
for both PBD and PIP sequences, which might find potential
application for the preparation of low-rolling-resistance and
high-slip-resistance tires.
EXPERIMENTAL SECTION
■
General Methods and Materials. All reactions were carried out
under a dry and oxygen-free argon atmosphere by using Schlenk
techniques or under a nitrogen atmosphere in a MBraun glovebox. All
solvents were purified with a MBraun SPS system. Organometallic
samples for NMR spectroscopic measurements were prepared in the
glovebox by use of NMR tubes sealed by paraffin film. H and 13C
1
Figure 5. DSC curves of the resulting polymers given in Table 2: (1)
100% PIP (polyisoprene); (2) 20% PBD (polybutadiene); (3) 40%
PBD; (4) 60% PBD; (5) 80% PBD; (6) 100% PBD.
NMR spectra were recorded on a Bruker AV400 (FT, 400 MHz for
1
1H; 100 MHz for 13C) or Bruker AV600 (FT, 600 MHz for H; 150
MHz for 13C) spectrometer. 31P NMR spectra were recorded on a
Bruker AV400 (FT, 162 MHz) spectrometer. Elemental analyses were
performed at the National Analytical Research Centre of the
Changchun Institute of Applied Chemistry (CIAC). Isoprene was
dried over CaH2 with stirring for 48 h and distilled under vacuum
before use. Hexamethyldisilazane, MgnBu2 (1.0 M in heptane), nBuLi
(1.6 M in hexane), LnCl3, and NaBH4 were purchased from Aldrich or
Fluka. Phenyl azide,47a 2,6-dimethylphenyl azide,47b 2,6-diisopropyl-
phenyl azide,47c,d Ph2P−NH−PPh2,25 HN(PPh2O)2 (HL4),39 Ln-
(CH2SiMe3)3(THF)2,48 Nd(BH4)3(THF)3,49 [Ph3C][B(C6F5)4], and
[PhNMe2H][B(C6F5)4]50 were synthesized as reported. The micro-
was suppressed dramatically via incorporation of polybutadiene
units over 20 mol %, as the endothermic peak (melting
temperature Tm) disappeared completely (traces 2−4), which
was attributed to damage of the ordered arrangement of
isoprene repeating units. When the content of the poly-
butadiene units increased up to 80 mol %, a broad endothermic
peak appeared at 15.4 °C (trace 5), assigned to the overlapped
monoclinic-hexagonal transition and melting temperatures (Tt
and Tm) of the highly trans-1,4-regulated PBD sequences,17b
which is much lower than Tt, = 41.5 °C and Tm = 62.5 °C of
the homo-polybutadiene sample (trace 6). This indicates that
the crystallinity of the trans-1,4-regulated polybutadiene and
polyisoprene can be easily adjusted by the random copoly-
merization if a properly chosen catalytic precursor is employed.
1
structure of polyisoprene was determined by H NMR and 13C NMR
spectra. The molecular weights (Mn) and molecular weight
distributions (Mw/Mn) of polyisoprene were measured by a TOSOH
HLC-8220 GPC instrument. Elemental analyses were performed at
the National Analytical Research Centre of the Changchun Institute of
Applied Chemistry. DSC was performed on a Mettler TOPEM TM
DSC instrument under a nitrogen atmosphere. The thermal history
difference in the polymers was eliminated by first heating the specimen
to 120 °C, cooling at 10 °C min−1 to −110 °C, and then a second
heating from −110 to 120 °C at 10 °C min−1 was performed. The
reactivity ratios r1 and r2 were determined using the Fineman−Ross
method and the linear relationship F(f − 1)/f = r1(F2/f) − r2, where F
and f are the butadiene/isoprene molar ratios in the feed and the
CONCLUSION
■
We have demonstrated that the synthesis of a new family of bis-
arylated phosphazene (NPNPN-type) and imidodiphosphinate
(OPNPO-type) rare-earth-metal bis(alkyl) and borohydrido
complexes can be accessed by amino proton abstraction or
sequential metathesis reactions. All these complexes are well-
defined; in particular, the OPNPO-type yttrium bis(alkyl)
complex 4b adopts a rare zwitterionic structure. Furthermore,
the catalytic performances of these complexes under the
activation of proper metal alkyls or/and organoborate for
isoprene or/and butadiene polymerization have been inves-
tigated. The zwitterionic yttrium alkyl complex 4b bearing the
imidodiphosphinate OPNPO-type ligand shows the highest
activity, providing cis-1,4-enriched polyisoprene, while the
complexes 1a−c bearing a bis-phenylated phosphazene
NPNPN-type ligand exhibit higher activities; nevertheless, the
1
polymer (by H NMR analysis), respectively.
X-ray Crystallographic Studies. Crystals for X-ray analysis were
obtained as described in the preparations. The crystals were
manipulated in a glovebox. Data collections were performed at
−88.5 °C on a Bruker SMART APEX diffractometer with a CCD area
detector, using graphite-monochromated Mo Kα radiation (λ =
0.71073 Å). The determination of crystal class and unit cell parameters
was carried out by the SMART program package. The raw frame data
were processed using SAINT and SADABS to yield the reflection data
file. The structures were solved by using the SHELXTL program.
Refinement was performed on F2 anisotropically for all non-hydrogen
atoms by the full-matrix least-squares method. The hydrogen atoms
G
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were placed at calculated positions and were included in the structure
calculations without further refinement of the parameters.
ppm, 25 °C): δ 0.30 (d, JYH = 2.8 Hz, 4H, CH2SiMe3), 0.40 (s, 18H,
3
CH2SiMe3), 6.72−6.83 (m, 10H, NC6H5), 6.90 (t, JHH = 7.2 Hz, 4H,
Synthesis of [C6H5NPPh2HNPh2PNC6H5] (HL1). Phenyl
azide (2.86 g, 24 mmol) in 10 mL of toluene was added dropwise to a
toluene solution (50 mL) of bis(diphenylphosphine)amine
(Ph2PNHPPh2) (3.85 g, 10 mmol) at 60 °C by releasing nitrogen
gas. The reaction mixture was refluxed until the evolution of nitrogen
gas ceased. Finally, the solution was concentrated to approximately 20
mL and was kept at −30 °C for 2 h. Filtering, washing with hexane,
and evaporating the residual solvents afforded HL1 as a pale yellow
solid (5.36 g, 90%). 1H NMR (300 MHz, CDCl3, 7.26 ppm, 25 °C): δ
3.00−5.00 (very broad s, 1H, NH), 6.62−6.70 (m, 6H, o-NC6H5 and
p-NC6H5), 6.94 (t, 3JHH = 7.5 Hz, 4H, o-NC6H5), 7.30−7.42 (m, 12H,
m-PC6H5), 7.06 (t, JHH = 7.6 Hz, 4H, m-PC6H5), 7.20 (d, 3JHH = 8.0
3
Hz, 4H, p-PC6H5), 7.50 (m, 8H, o-PC6H5). 13C NMR (150 MHz,
C6D6, 128.06 ppm, 25 °C): δ 4.84 (s, 6C, CH2SiMe3), 39.22 (d, JYC
=
41 Hz, 2C, CH2SiMe3), 121.74 (s, aromatic CH), 122.70 (m, aromatic
CH), 128.69 (m, aromatic CH), 128.96 (m, aromatic CH), 129.68 (s,
aromatic CH), 129.97 (s, aromatic CH), 130.43 (d, JPC = 7.2 Hz, 2C,
aromatic ipso-C), 131.16 (d, JPC = 7.2 Hz, 2C, aromatic ipso-C), 132.32
(m, aromatic CH), 132.51 (s, aromatic CH), 147.36 (s, aromatic ipso-
C). Anal. Calcd for C32H52N3P2Si2Y: C, 46.27; H, 6.27; N, 5.06.
Found: C, 46.49; H, 6.12; N, 4.90.
Synthesis of L1Lu(CH2SiMe3)2 (1c). By a procedure similar to
that described for the preparation of 1a, treatment of Lu-
(CH2SiMe3)3(THF)2 (0.290 g, 0.50 mmol) with HL1 (0.297 g, 0.50
mmol) gave yellow crystals of 1b (0.330 g, 72%). Single crystals
suitable for X-ray analysis were obtained from a THF/toluene mixture
3
m-PC6H5 and p-PC6H5), 7.82 (quart, JHH = 7.2 Hz, 8H, o-PC6H5).
31P NMR (162 MHz, CDCl3, 25 °C): δ 6.51 ppm (s). Anal. Calcd for
C24H31N3P2: C, 68.09; H, 7.33; N, 9.93. Found: C, 68.35; H, 7.20; N,
9.79.
1
at −30 °C within 2 days. H NMR (600 MHz, C6D6, 7.16 ppm, 25
Synthesis of [2,6-Me2C6H3NPPh2HNPh2PNC6H3Me2-2,6]
(HL2). 2,6-Dimethylphenyl azide (3.53 g, 24 mmol) in 10 mL of
toluene was added dropwise to a toluene solution (50 mL) of
bis(diphenylphosphine)amine (Ph2PNHPPh2) (3.85 g, 10 mmol) at
room temperature under a nitrogen atmosphere. The reaction mixture
was stirred for 2 h and then heated to 70 °C for 12 h for the complete
evolution of nitrogen gas. Removal of the volatiles gave a reddish solid,
which was further purified by washing with hexane to afford reddish
solids (5.05 g, 81%). 1H NMR (400 MHz, CDCl3, 7.26 ppm, 25 °C):
δ 1.99 (s, 12H, CH3), 4.06 (br s, 1H, NH), 6.69 (t, 3JHH = 7.6 Hz, 2H,
p-NC6H3), 6.82 (d, 3JHH = 3.6 Hz, 4H, m-NC6H3), 7.19−7.23 (m, 8H,
°C): δ 0.16 (s, 4H, CH2SiMe3), 0.41 (s, 18H, CH2SiMe3), 6.72−6.79
(m, 10H, NC6H5), 6.90 (t, 3JHH = 7.2 Hz, 4H, m-PC6H5), 7.06 (t, 3JHH
= 7.8 Hz, 4H, m-PC6H5), 7.23 (d, 3JHH = 8.4 Hz, 4H, p-PC6H5), 7.50
(m, 8H, o-PC6H5). 13C NMR (150 MHz, C6D6, 128.06 ppm, 25 °C):
δ 4.68 (s, 6C, CH2SiMe3), 46.03 (s, 2C, CH2SiMe3), 121.43 (s,
aromatic CH), 122.55 (m, aromatic CH), 128.35 (s, aromatic CH),
128.63 (m, aromatic CH), 129.34 (s, aromatic CH), 129.48 (s,
aromatic CH), 130.08 (d, JPC = 7.0 Hz, 2C, aromatic ipso-C), 130.86
(d, JPC = 7.0 Hz, 2C, aromatic ipso-C), 131.96 (m, aromatic CH),
132.22 (s, aromatic CH), 146.83 (s, aromatic ipso-C). Anal. Calcd for
C32H52N3P2Si2Lu: C, 41.92; H, 5.68; N, 4.59. Found: C, 41.67; H,
5.82; N, 4.73.
3
3
m-PC6H5), 7.32 (t, JHH = 7.2 Hz, 4H, p-PC6H5), 7.66 (quart, JHH
=
7.2 Hz, 8H, o-PC6H5). 31P NMR (162 MHz, CDCl3, 25 °C): δ 1.85
ppm (s). Anal. Calcd for C28H39N3P2: C, 70.15; H, 8.14; N, 8.77.
Found: C, 69.80; H, 8.31; N, 8.87.
Synthesis of L2Sc(CH2SiMe3)2 (2a). By a procedure similar to that
described for the preparation of 1a, treatment of Sc-
(CH2SiMe3)3(THF)2 (0.225 g, 0.50 mmol) with HL2 (0.312 g, 0.50
mmol) gave yellow solids of 2a (0.232 g, 55%). Single crystals suitable
for X-ray analysis were obtained from a THF/toluene mixture at −30
°C overnight. 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ 0.24 (s,
18H, CH2SiMe3), 0.60 (s, 4H, CH2SiMe3), 2.37 (s, 12H, C6H3CH3),
i
Synthesis of [2,6-iPr2C6H3NPPh2HNPh2PNC6H3 Pr2-2,6]
(HL3). Following a similar procedure described for the preparation
of ligand HL2, the ligand HL3 was isolated from the Staudinger
reaction of Ph2PNHPPh2 (3.85 g, 10 mmol) with 2.4 equiv of 2,6-
diisopropylphenyl azide (4.87 g, 24 mmol) as a pale white powder
(6.47 g, 88%). 1H NMR (300 MHz, CDCl3, 7.26 ppm, 25 °C): δ 0.76
3
3
6.78 (t, JHH = 8.0 Hz, 8H, m-PC6H5), 6.88 (t, JHH = 6.8 Hz, 4H, m-
NC6H3), 6.95 (t, 3JHH = 6.8 Hz, 2H, p-NC6H3), 7.04 (d, 3JHH = 7.2 Hz,
4H, p-PC6H5), 7.52 (m, 8H, o-PC6H5). 13C NMR (150 MHz, C6D6,
128.06 ppm, 25 °C): δ 4.09 (s, 6C, CH2SiMe3), 21.79 (s, 4C,
C6H3CH3), 46.95 (s, 2C, CH2SiMe3), 124.43 (s, aromatic CH), 122.55
(m, aromatic CH), 128.35 (s, aromatic CH), 128.63 (m, aromatic
CH), 129.34 (s, aromatic CH), 129.59 (s, aromatic CH), 131.61 (s,
aromatic CH), 131.79 (s, aromatic CH), 132.91 (d, JPC = 6.0 Hz, 2C,
aromatic ipso-C), 134.01 (d, JPC = 6.0 Hz, 2C, aromatic ipso-C), 135.54
(s, aromatic CH), 142.81 (s, aromatic ipso-C). Anal. Calcd for
C36H60N3P2Si2Sc: C, 51.31; H, 7.13; N, 4.99. Found: C, 51.66; H,
7.02; N, 4.84.
3
3
(d, JHH = 6.9 Hz, 24H, CH(CH3)2), 3.55 (sept, JHH = 6.9 Hz, 4H,
CH(CH3)2), 6.91 (s, 6H, p-C6H3 and m-NC6H3), 7.20−7.30 (m, 8H,
3
3
m-PC6H5), 7.38 (t, JHH = 7.2 Hz, 4H, p-PC6H5), 7.49 (quart, JHH
=
7.2 Hz, 8H, o-PC6H5) (the NH signal did not appear). 31P NMR (162
MHz, CDCl3, 25 °C): δ 6.26 ppm (s). Anal. Calcd for C36H55N3P2: C,
73.10; H, 9.31; N, 7.11. Found: C, 73.48; H, 9.38; N, 6.95.
Synthesis of L1Sc(CH2SiMe3)2 (1a). To a hexane solution (2.0
mL) of Sc(CH2SiMe3)3(THF)2 (0.225 g, 0.5 mmol) was added
dropwise 1 equiv of HL1 (0.297 g, 0.5 mmol in 2 mL of THF) at room
temperature. The mixture was stirred for 3 h at room temperature and
then concentrated to about 0.5 mL. Addition of 1 mL of hexane and
cooling to −30 °C for 2 days afforded crystalline solids, which were
washed with a small amount of hexane to remove impurities and dried
in vacuo to give pale yellow solids of 1a (0.236 g, 60%). Single crystals
suitable for X-ray analysis were obtained from a THF/toluene mixture
Synthesis of L3Y(CH2SiMe3)2 (3b). By a procedure similar to that
described for the preparation of 1a, treatment of Y-
(CH2SiMe3)3(THF)2 (0.247 g, 0.50 mmol) with HL3 (0.368 g, 0.50
mmol) gave yellow solids of 3b (0.335 g, 67%). Single crystals suitable
for X-ray analysis were not obtained. 1H NMR (400 MHz, C6D6, 7.16
ppm, 25 °C): δ 0.10 (d, JYH = 2.8 Hz, 4H, CH2SiMe3), 0.34 (s, 18H,
1
at −30 °C within 2 days. H NMR (400 MHz, C6D6, 7.16 ppm, 25
°C): δ 0.39 (s, 18H, CH2SiMe3), 0.91 (s, 4H, CH2SiMe3), 6.71−6.82
3
(m, 10 H, NC6H5), 6.88 (t, 3JHH = 7.2 Hz, 4H, m-PC6H5), 7.09 (t, 3JHH
CH2SiMe3), 0.63 (d, JHH = 5.6 Hz, 12H, C6H3CH(CH3)2), 1.55 (d,
3
3JHH = 5.6 Hz, 12H, C6H3CH(CH3)2), 3.81 (sept, JHH = 6.8 Hz, 4H,
3
= 7.6 Hz, 4H, m-PC6H5), 7.38 (d, JHH = 7.8 Hz, 4H, p-PC6H5), 7.52
(m, 8H, o-PC6H5). 13C NMR (100 MHz, C6D6, 128.06 ppm, 25 °C):
δ 4.19 (s, 6C, CH2SiMe3), 44.62 (br s, 2C, CH2SiMe3), 121.63 (s,
aromatic CH), 123.10 (m, aromatic CH), 128.60 (m, aromatic CH),
129.33 (s, aromatic CH), 129.60 (d, JPC = 4.3 Hz, 2C, aromatic ipso-
C), 130.75 (d, JPC = 4.3 Hz, 2C, aromatic ipso-C), 132.11−132.28 (m,
aromatic CH), 147.07 (s, aromatic ipso-C). Anal. Calcd for
C32H52N3P2Si2Sc: C, 48.85; H, 6.62; N, 5.34. Found: C, 48.53; H,
6.52; N, 5.57.
C6H3CH(CH3)2), 6.78−6.88 (m, 12H, m-PC6H5 and p-PC6H5), 7.15
(s, 6H, m-NC6H3 and p-NC6H3), 7.38 (m, 8H, o-PC6H5). 13C NMR
(100 MHz, C6D6, 128.06 ppm, 25 °C): δ 4.48 (s, 6C, CH2SiMe3),
23.30 (s, 4C, C6H3CH(CH3)2), 27.75 (s, 4C, C6H3CH(CH3)2), 29.20
(s, 4C, C6H3CH(CH3)2), 46.95 (d, JYC = 27.7 Hz, 2C, CH2SiMe3),
124.66 (s, aromatic CH), 124.90 (s, aromatic CH), 125.70 (s, aromatic
CH), 129.33 (s, aromatic CH), 131.48 (s, aromatic CH), 132.12 (m,
aromatic CH), 132.78 (d, JPC = 5.4 Hz, 2C, aromatic ipso-C), 133.51
(d, JPC = 5.4 Hz, 2C, aromatic ipso-C), 139.16 (s, aromatic ipso-C),
145.67 (s, aromatic ipso-C). Anal. Calcd for C44H76N3P2Si2Y: C, 52.80;
H, 7.60; N, 4.20. Found: C, 53.05; H, 7.49; N, 4.08.
Synthesis of L1Y(CH2SiMe3)2 (1b). By a procedure similar to that
described for the preparation of 1a, treatment of Y-
(CH2SiMe3)3(THF)2 (0.247 g, 0.50 mmol) with HL1 (0.297 g, 0.50
mmol) gave yellow solids of 1b (0.241 g, 58%). Single crystals suitable
for X-ray analysis were not obtained. 1H NMR (600 MHz, C6D6, 7.16
Synthesis of L3Lu(CH2SiMe3)2 (3c). Following a procedure
similar to that described for the preparation of 1a, treatment of
H
dx.doi.org/10.1021/om300967h | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Lu(CH2SiMe3)3(THF)2 (0.290 g, 0.50 mmol) with HL3 (0.368 g, 0.50
mmol) gave yellow solids of 3c (0.348 g, 64%). Single crystals suitable
for X-ray analysis were obtained from a THF/toluene mixture at −30
°C overnight. 1H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ −0.10
(s, 4H, CH2SiMe3), 0.35 (s, 18H, CH2SiMe3), 0.66 (d, 3JHH = 6.8 Hz,
supplementary crystallographic data for this paper. These data
can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
3
12H, C6H3CH(CH3)2), 1.56 (d, JHH = 6.8 Hz, 12H, C6H3CH-
AUTHOR INFORMATION
Corresponding Author
*E-mail: dmcui@ciac.jl.cn. Fax: (+86) 431 85262774. Tel: +86
431 85262773.
3
■
(CH3)2), 3.87 (sept, JHH = 6.8 Hz, 4H, C6H3CH(CH3)2), 6.75−6.84
(m, 12H, m-PC6H5 and p-PC6H5), 7.16 (s, 6H, m-NC6H3 and p-
NC6H3), 7.40 (m, 8H, o-PC6H5). 13C NMR (150 MHz, C6D6, 128.06
ppm, 25 °C): δ 4.62 (s, 6C, CH2SiMe3), 23.50 (s, 4C, C6H3CH-
(CH3)2), 27.80 (s, 4C, C6H3CH(CH3)2), 29.11 (s, 4C, C6H3CH-
(CH3)2), 47.31 (s, 2C, CH2SiMe3), 124.69 (s, aromatic CH), 125.07
(s, aromatic CH), 130.73 (s, aromatic CH), 131.51 (s, aromatic CH),
132.22 (m, aromatic CH), 132.77 (d, JPC = 5.4 Hz, 2C, aromatic ipso-
C), 133.50 (d, JPC = 5.4 Hz, 2C, aromatic ipso-C), 139.04 (s, aromatic
ipso-C), 145.89 (s, aromatic ipso-C). Anal. Calcd for C44H76N3P2Si2Lu:
C, 48.57; H, 6.99; N, 3.86. Found: C, 48.95; H, 6.74; N, 3.75.
Synthesis of L4Y(CH2SiMe3)2(THF)2 (4b). Following a procedure
similar to that described for the preparation of 1a, treatment of
Y(CH2SiMe3)3(THF)2 (0.247 g, 0.50 mmol) with HL4 (0.208 g, 0.50
mmol) gave yellow solids of 4b (0.268 g, 65%). Single crystals suitable
for X-ray analysis were obtained from a toluene/hexane mixture at
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by the National Natural
Science Foundation of China for project nos. 20934006,
51073148, and 51021003 and by the Ministry of Science and
Technology of China for project nos. 2009AA03Z501 and
2011DF50650.
REFERENCES
1
■
−30 °C overnight. H NMR (400 MHz, C6D6, 7.16 ppm, 25 °C): δ
2
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−0.69 (d, JYH = 2 Hz, 2H, CH2SiMe3), −0.30 (s, 2H, CH2SiMe3),
0.29 (s, 18H, CH2SiMe3), 1.31 (m, 8H, THF), 3.80 (m, 8H, THF),
7.00−7.11 (m, 12H, m-PC6H5 and p-PC6H5), 7.95−8.01 (m, 8H, o-
PC6H5). 13C NMR (100 MHz, C6D6, 128.06 ppm, 25 °C): δ 4.64 (s,
6C, CH2SiMe3), 25.25 (s, 4C, THF), 29.73 (d, JYC = 39.5 Hz, 1C,
CH2SiMe3), 33.73 (d, JYC = 35.3 Hz, 1C, CH2SiMe3), 69.78 (s, 4C,
THF), 125.70 (s, aromatic CH), 128.57 (s, aromatic CH), 129.33 (s,
aromatic CH), 130.50 (s, aromatic CH), 131.04 (s, aromatic CH),
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(d, JPC = 3.0 Hz, 2C, aromatic ipso-C), 138.97 (d, JPC = 3.0 Hz, 2C,
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7.04; N, 1.70. Found: C, 58.57; H, 6.91; N, 1.60.
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phere, nBuLi (1.6 M in hexane, 0.66 mL, 1.05 mmol) was added
dropwise to a THF solution (25 mL) of HL1 at 0 °C (0.595 g, 1
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Found: C, 57.52; H, 6.03; N, 4.77.
Polymerization of Isoprene. A typical procedure for the
polymerization was as follows (Table 1, entry 1): in a glovebox, a
toluene solution of 1a (2.0 mL, 10 μmol, 6.4 mg), a toluene solution of
[Ph3C][B(C6F5)4] (1.0 mL, 10 μmol, 9.2 mg), 0.1 mmol of AliBu3,
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hydrochloric acid to precipitate the white solids. The precipitated
polymer was collected by filtration, washed with methanol, and dried
under vacuum at 40 °C to a constant weight to afford 0.68 g (100%
yield) of polyisoprene. The copolymerization of butadiene and
isoprene was carried out by a similar procedure.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, a table, and CIF files giving H and 13C NMR spectra
1
of all complexes and the crystallographic data and structure
refinement details for complexes 1a,c, 2a, 3c, 4b, and 5. This
material is available free of charge via the Internet at http://
pubs.acs.org. CCDC 904968 (1a), 899206 (1c), 899207 (2a),
899208 (3c), 899209 (4b), and 899210 (5) also contain
194, 1389. (b) Colamarco, E.; Milione, S.; Cuomo, C.; Grassi, A.
I
dx.doi.org/10.1021/om300967h | Organometallics XXXX, XXX, XXX−XXX

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dx.doi.org/10.1021/om300967h | Organometallics XXXX, XXX, XXX−XXX