New rare earth metal bis(alkyl)s bearing an iminophosphonamido ligand. Synthesis and catalysis toward highly 3,4-selective polymerization of isoprene

Article abstract of DOI:10.1021/om700945r

New rare earth metal bis(alkyl) complexes [(NPN^Ph)Ln(CH ₂SiMe₃)₂(THF)] (NPN^Ph: N(Ph)PPh ₂=NC₆H₂Me₃-2,4,6; Ln = Sc (3a), Ln = Y (3b), Ln = Lu (3c)) and [(NPN

Full text of DOI:10.1021/om700945r

718
Organometallics 2008, 27, 718–725
New Rare Earth Metal Bis(alkyl)s Bearing an Iminophosphonamido
Ligand. Synthesis and Catalysis toward Highly 3,4-Selective
Polymerization of Isoprene
Shihui Li,†,‡ Wei Miao,†,‡ Tao Tang,† Weimin Dong,† Xuequan Zhang,† 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, and Graduate School of
the Chinese Academy of Sciences, Beijing 100039, People’s Republic of China
ReceiVed September 23, 2007
Newrareearthmetalbis(alkyl)complexes[(NPNPh)Ln(CH2SiMe3)2(THF)](NPNPh:N(Ph)PPh2dNC6H2Me3-
2,4,6; Ln ) Sc (3a), Ln ) Y (3b), Ln ) Lu (3c)) and [(NPNPy)Sc(CH2SiMe3)2(THF)] (NPNPy
)
N(Py)PPh2dNC6H2Me3-2,4,6) (3d)) have been prepared via protonolysis reaction between rare earth
metal tris(alkyl)s and the corresponding iminophosphonamines. Complexes 3a-d are analogous monomers
of THF solvate. Each metal ion coordinates to a η2-chelated NPN ligand and two cis-located alkyl groups,
adopting tetrahedron geometry. The scandium complex [(NPNPh)Sc(CH2SiMe3)2(THF)] in combination
with [PhNHMe2][B(C6F5)4] and AliBu3 forms the first non-Cp-ligated rare earth metal based catalyst
system to provide extremely high activity and 3,4-selectivity for the polymerization of isoprene. The
resultant high molecular weight polymer (Mn ) 99 × 104) with narrow molecular weight distribution
(PDI ) 1.55) has a 3,4-regularity up to 94.7% (Tp ) –40 °C, toluene, 2 h, 100% yield). The complexes
3b and 3c, with a larger ionic radius, are less regioselective, and 3d, with an electron-donating pyridyl
moiety, is inert. The probable initiation species and mechanistic scenario are also presented.
polydispersities, and regularity. In the meantime, the interest
of trans-1,4-regulated polymerization has emerged in the high-
performance rubber or tires industry.8 The Ln(allyl)2Cl(MgCl2)2/
AlR3 system has been designed to initiate the 1,4-trans
polymerization of isoprene,9 while the neodymium boron
hydrido complex Nd(BH4)3(THF)3 with the activator Mg(nBu)2
has also exhibited 1,4-trans selectivity, the catalytic performance
of which is significantly improved by introducing a Cp ligand
into the molecule to generate a half-metallocene Cp*Nd-
Introduction
The past half-century has witnessed the development of the
catalysts for the regio- and stereoselective polymerization of
conjugated dienes such as butadiene and isoprene, because the
resulting polymers find wide applications in the synthetic
elastomer industry due to their outstanding performances. The
Ziegler–Natta catalyst systems based on transition metals
including titanium, cobalt, nickel, and the distinguished lan-
thanide metal alkoxides and carboxylates under the presence
of aluminum alkyls or aluminum alkyls/borate1 provide high
cis-1,4 selectivity for the polymerization of diene to afford the
most important synthetic rubber.2 The f- and d-block element
metallocenes combined with MAO or AlR3 have also attracted
increasing attention due to their tremendously high specific cis-
1,4 selectivity.3–5 Recently, non-cyclopentadienyl (non-Cp)
ligated lanthanide alkylaluminates6 and PNP-type rare earth
metal cationic units (PNP: bis(phosphinophenyl)amido)7 have
gathered an upsurge in such research interest, which led to
controllable polymerization with respect to the molecular weight,
(3) (a) The Ban, H.; Kase, T.; Kawabe, M.; Miyazawa, A.; Ishihara, T.;
Hagihara, H.; Tsunogae, Y.; Murata, M.; Shiono, T. Macromolecules 2006,
39, 171–176. (b) Thuilliez, J.; Monteil, V.; Spitz, R.; Boisson, C. Angew.
Chem., Int. Ed. 2005, 44, 2593–2596. (c) Barbotin, F.; Montail, V.; Llauro,
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Montail, V.; Spitz, R.; Boisson, C. Polym. Int. 2004, 53, 576–581.
(4) Kaita, S.; Hou, Z.; Wakatsuki, Y. Macromolecules 1999, 32, 9078–
9079.
(5) (a) Kaita, S.; Hou, Z.; Wakatsuki, Y. Macromolecules 2001, 34,
1539–1541. (b) Kaita, S.; Doi, Y.; Kaneko, K.; Horiuchi, A. C.; Wakatsuki,
Y. Macromolecules 2004, 37, 5860–5862. (c) Kaita, S.; Yamanaka, M.;
Horiuchi, A. C.; Wakatsuki, Y. Macromolecules 2006, 39, 1359–1363. (d)
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Wakatsuki, Y. Macromol. Rapid Commun. 2003, 24, 179–184.
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2239. (b) Arndt, S.; Beckerle, K.; Zeimentz, P. M.; Spaniol, T. P.; Okuda,
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* To whom correspondence should be addressed. Fax: (+86)431-
85262773. Email: dmcui@ciac.jl.cn
† Changchun Institute of Applied Chemistry.
‡ Graduate School of the Chinese Academy of Sciences.
(1) (a) See reviews: Friebe, L.; Nuyken, O.; Obrecht, W. AdV. Polym.
Sci. 2006, 204, 1–154. (b) Fischbach, A.; Anwander, R. AdV. Polym. Sci.
2006, 204, 155–281, and references therein. (c) Fischbach, A.; Meermann,
C. Eickerling, G.; Scherer, W.; Anwander, R. Macromolecules 2006, 39,
6811–6816. (d) Taniguchi, Y.; Dong, W.; Katsumata, T.; Shiotsuki, M.;
Masuda, T. Polym. Bull. 2005, 54, 173–178. (e) Shen, Z.; Ouyang, J.; Wang,
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10.1021/om700945r CCC: $40.75
2008 American Chemical Society
Publication on Web 01/25/2008

New Rare Earth Metal Bis(alkyl)s
Organometallics, Vol. 27, No. 4, 2008 719
Scheme 1. Synthesis of Complexes 3a-d
(BH4)2(THF)2.10 In contrast, 3,4-polymerization of isoprene has
been explored less, although this polymer is used as an important
component of high-performance rubber.11 Only few catalytic
systems can initiate the 3,4-polymerization of isoprene, as
isoprene prefers to coordinate to the metal center of many
catalytic systems in a cis-1,4 mode, generating a thermally stable
η3-π-butenyl species, whereas coordinating in a 3,4-η2-mode
to leave the bulky allylic group dangling,7 the steric hin-
drance at the metal center is requisite. To date, efficient 3,4-
selective catalyst systems are a transition-metal complex domain,
such as AlEt3-Ti(OR)4,12a,b (dmpe)2CrCl2-MAO (dmpe: 1,2-
bis(dimethylphosphino)ethane),12c and some iron-based com-
plexes containing chelating nitrogen ligands.13 In a few cases,
the 3,4-selectivity is over 90%. Although rare earth metal
complexes have played significant roles in cis- and trans-
selective polymerization, they usually do not show 3,4-selectiv-
ity except for a very recent breakthrough achieved by Hou’s
group, who employed a half-metallocene yttrium precursor
activated by [Ph3C][B(C6F5)4] to provide isotactic 3,4-polyiso-
prene.14 Therefore, further exploration of new catalyst systems
of high 3,4-selectivity based on rare earth metals and other
elements is of obvious interest.
favored for initiating the polymerization of nonpolar monomers.
Although Ti, Zr, Ni, etc., metal complexes16 with NPN-type
ligands have been reported and their chemistry has been
studied,17 the corresponding rare earth metal analogues are
unknown, as far as we are aware. Herein, we wish to report the
first example of NPN-type rare earth metal bis(alkyl)s, which
in combination with [PhNHMe2][B(C6F5)4] and AliBu3 act as
the first non-Cp group 3 metal precursors for the 3,4-selective
polymerization of isoprene. The probable active species and the
mechanistic scenario will also be discussed.
Results and Discussion
Synthesis and Characterization of NPN-Type Rare
Earth Metal Bis(alkyl) Complexes 3a-d. The iminophospho-
namines ArNHP(Ph2)dNC6H2Me3-2,4,6 (2a (NPNPhH): Ar )
Ph; 2b (NPNPyH): Ar ) 2-pyridyl) were prepared via Staudinger
reaction between aminodiphenylphosphine ArNHPPh2 (1a: Ar
) Ph; 1b: Ar ) 2-pyridyl) and 1 equiv of mesityl azide.
Protonolysis of the rare earth metal tris(alkyl)s Ln(CH2-
SiMe3)3(THF)2 with 2a or 2b gave the bis(alkyl) complexes
[(NPNPh)Ln(CH2SiMe3)2(THF)] (3a: Ln ) Sc; 3b: Ln ) Y;
3c: Ln ) Lu) or [(NPNPy)Sc(CH2SiMe3)2(THF)] (3d) in
quantitative yield, respectively (Scheme 1). The 1H NMR
spectrum of 3a displayed an AB spin at δ 0.45 and 0.77 (JH-H
) 12 Hz) assigned to the methylene protons of the metal alkyl
Sc-CH2SiMe3, indicating that the methylene protons were
diastereotopic. In contrast, the resonances of the methylene
protons of Sc-CH2SiMe3 in 3d overlapped with silylmethyl,
which might be attributed to the electron-donating pyridyl
moiety, while the methylene protons of Y-CH2SiMe3 in 3b
showed a doublet at δ 0.11 due to coupling with the yttrium
ion (JY-C-H ) 2.7 Hz) and those of Lu-CH2SiMe3 in 3c exhibited
a broad resonance around δ -0.07, suggesting that the metal
alkyl species in both 3b and 3c were fluxional in the solution
state. This difference may be attributed to the smaller ionic
Our group has been carrying out the synthesis of non-Cp-
ligated rare earth metal bis(alkyl)s that have exhibited high
catalytic activity toward polymerizations of polar monomers and
olefins.15 The complexes bearing phosphorus auxiliary ligands
have the potential for catalyzing the specific polymerization of
conjugated dienes, because the introduction of a “large” and
“soft” phosphorus donor is anticipated to increase the steric bulk
and to lower the electron density of metal center, which is
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Macromolecules 2005, 38, 3162–3169. (b) Bonnet, F.; Visseaux, M.; Pereira,
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159, 69–76.
radius of Sc3+ compared to those of Y3+ and Lu3+
.
The solid-state structures of 3a-d were confirmed by X-ray
diffraction to be isostructural monomers with a coordinated THF
molecule (Table 1, Figures 1–4).18 The coordination geometry
around the metal center is best described as a distorted
tetrahedron. The two alkyl species are located in cis-position.
(12) (a) Natta, G.; Porri, L.; Carbonaro, A. Makromol. Chem. 1964, 77,
126–138. (b) Gronski, W.; Murayama, N.; Cantow, H. J.; Miyamoto, T.
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23, 922–927. (c) Nakayama, Y.; Baba, Y.; Yasuda, H.; Kawakita, K.;
Ueyama, N. Macromolecules 2003, 36, 7953–7958. (d) Bazzini, C.;
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2875.
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Chandrasekhar, V.; Stalke, D. J. Am. Chem. Soc. 2001, 123, 1381–1388.
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2006, 25, 2514–2524. (b) Vollmerhaus, R.; Tomaszewski, R.; Shao, P.;
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tallics 2005, 24, 494–507. (c) Ahmed, S.; Hill, M.; Hitchcock, P.; Mansell,
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X.; Jing, X. Chem.-Eur. J. 2007, 13, 834–845. (c) Yang, Y.; Li, S.; Cui,
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D.; Chen, X.; Jing, X. J. Organomet. Chem. 2007, 692, 4943–4952.
(18) The 1H NMR and 13C NMR spectra of complexes 3a-d; see
Supporting Information.

720 Organometallics, Vol. 27, No. 4, 2008
Li et al.
Table 1. Summary of Crystallographic Data for Complexes 3a-d
3a
3b
3c
3d
formula
fw
cryst syst
space group
a (Å)
C39H56N2OPSi2Sc
700.97
tetragonal
I4(1)/a
20.6332(7)
20.6332(7)
38.833(3)
90
C39H56N2OPSi2Y
744.92
tetragonal
I4(1)/a
20.8477(10)
20.8477(10)
39.083(3)
90
C39H56N2OPSi2Lu
830.98
tetragonal
I4(1)/a
20.7862(19)
20.7862(19)
39.098(7)
90
90
90
16893(4)
16
1.307
C38H55N3OPSi2Sc
701.96
tetragonal
I4(1)/a
20.6088(4)
20.6088(4)
38.8061(15)
90
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
V (Å3)
Z
90
90
90
90
90
90
16532.3(14)
16
1.127
0.304
46 392
8156
16986.6(16)
16
1.165
1.496
47 759
8383
16481.8(8)
16
1.132
0.306
46 255
8130
Dc (g/cm3)
µ (mm-1
)
2.461
47 267
8321
no. of reflns collcd
no. of reflns with Io > 2σ(Io)
no. of variables
424
424
424
424
Rint
GOF
0.1280
0.833
0.1696
0.937
0.0294
1.049
0.0599
0.942
R
Rw
0.0551
0.0891
0.1442
0.1103
0.0613
0.1028
0.1703
0.1331
0.0286
0.0689
0.0393
0.0751
0.0458
0.1140
0.0697
0.1267
R(all data)
Rw(all data)
The NPN ligand chelates to the metal ion in a η2-mode, adopting
meridional configuration, leading to the two N-aryl rings
perpendicular to each other. This structure is in contrast to
related early transition-metal complexes, where the N-aryl rings
are almost parallel.16a,b The average Ln-N bond length is
2.189(3) Å for 3a, 2.342(4) Å for 3b, 2.299(2) Å for 3c, and
2.190(2) Å for 3d, while the mean Ln-C bond length is 2.220(3)
Å for 3a, 2.389(4) Å for 3b, 2.343(3) Å for 3c, and 2.227(2) Å
for 3d, respectively. Both fall within the normal values.19 The
bond length of N(1)-P (1.606(3) Å) is similar to N(2)-P
(1.616(2) Å), suggesting that the electrons delocalize within the
N-P-N fragment. The bond angles of C-Ln-C varying from
111.88(9)° (3d) to 112.90(16)° (3b) are much smaller than in
the amidinate yttrium bis(alkyl) complex (NCNPh)Y(CH2-
SiMe3)2THF,19a suggesting a more bulky environment of the
NPN ligand than the NCN ligand. It is noteworthy that in 3d
the double-bond length of N(3)-C(5) (1.342(3) Å) is similar
to the single-bond length of N(2)-C(5) (1.397(3) Å) (Figure
4), indicating an electron delocalization over N(3)-C(5)-N(2).
As a result, the electron-donating nitrogen (N(3)) of the pyridyl
ring affects the electron negativity of the scandium ion although
no direct bond between Sc and N(3) is observed, which has a
significant influence on the catalytic performance of 3d (Vide
infra).
with the previously reported systems.4–6,21 Upon addition of a
slight excess of AliBu3 ([Al]0/[Sc]0 ) 10) to [(NPNPh)Sc-
(CH2SiMe3)(THF)]+[B(C6F5)4]-, the polymerization took place
immediately ([IP]0/[Sc]0 ) 1000) to reach a complete conversion
in 5 min at 20 °C. For the lutetium and yttrium counterparts,
3b and 3c, rapid polymerization was also observed albeit with
slightly low activity. This suggested that the Lewis-acidic Sc
ion is more favored for the coordination and insertion of
nonpolar isoprene. The resultant polyisoprene (PIP) has high
molecular weight (Mn ) (26.6–48.7) × 104) with narrow
polydispersity (Mw/Mn ) 1.32–1.71), indicating the single-site
nature of this catalyst system. Strikingly, a high 3,4-selectivity
of 88.5% was achieved in the case of scandium precursor 3a,
which dropped slightly to 80.1% for the lutetium analogue 3c.
However, for the yttrium counterpart 3c, the selectivity de-
creased greatly to 43.8% (Table 2, entries 4–6). Obviously, the
specific selectivity is strongly dependent on the ionic radius of
the central metal ion in a trend of Sc > Lu >Y, reverse of the
trend of ionic radius Sc (0.89 Å) < Lu (1.00 Å) < Y (1.04
Å).22 The smaller the ion radius, the more steric hindrance can
be found around the metal center, which leads to the 4,3-
insertion of isoprene. This result was in disagreement with the
(20) Complex 3a was treated with 1 equiv of [PhNHMe2][B(C6F5)4] in
C6D6. The resulting solution was transferred to an NMR tube and analyzed
by NMR spectroscopy, which showed the absence of resonances for complex
3a and quantitative formation of SiMe4 and PhNMe2 and signals assigned
to the newly formed cationic species [(NPNPh)Sc(CH2SiMe3)-
(THF)][B(C6F5)4]. 1H NMR (400 MHz, C6D6, 25 °C): δ 0.11 (s, 12H,
SiMe4), 0.29 (s, 9H, CH2SiMe3), 0.73 (s, 2H, CH2SiMe3), 1.38 (s, 6H,
o-NC6H2Me2), 1.40 (br, THF), 2.23 (d, 4JH-H ) 2.4 Hz, 3H, p-NC6H2Me),
2.63 (s, 6H, PhNMe2), 3.79 (br, THF), 6.74, 6.76 (sd, 4H, NC6H2, PhNMe2),
6.81–6.87 (m, 3H, PhNMe2), 6.91 (t, 3JH-H ) 7.2 Hz, 1H, p-NC6H5), 7.05–
7.11 (m, 6H, m,p-P(C6H5)2), 7.19 (t, 3JH-H ) 7.6 Hz, 2H, m-NC6H5), 7.33–
7.37 (dd, 2H, o-NC6H5), 7.51–7.56 (m, 4H, o-P(C6H5)2). 19F NMR (282.4
Polymerization of Isoprene. The catalytic performance of
NPN-type bis(alkyl) precursors 3 for the polymerization of
isoprene (IP) has been investigated. We noted that they showed
no activity alone. The binary system of 3a/AlR3 also did not
induce visible polymerization. Activation of 3a with the
Brønsted acid [PhNHMe2][B(C6F5)4] was attempted to generate
the ion pair [(NPNPh)Sc(CH2SiMe3)(THF)]+[B(C6F5)4]- via
alkyl abstraction;20 however, the resulting cations could not
provide polymerization. This suggested that the resulting ion
pair might exist as a contact adduct of less activity, consistent
3
MHz, C6D6, 25 °C): δ -56.13 (d, JF-F ) 11.3 Hz, ortho-F), -86.75 (t,
3
3JF-F ) 19.8 Hz, para-F), -90.71 (t, JF-F ) 16.9 Hz, meta-F). 11B NMR
(96.3 MHz, C6D6, 25 °C): δ -16.78.
(21) (a) Eividge, B.; Arndt, S.; Zeimentz, P.; Spaniol, T.; Okuda, J. Inorg.
Chem. 2005, 44, 6777–6788. (b) Kramer, M.; Robert, D.; Nakajima, Y.;
Englert, U.; Spaniol, T.; Okuda, J. Eur. J. Inorg. Chem. 2007, 5, 665–674.
(c) Evans, W. J.; Champagne, T.; Giarikos, D.; Ziller, J. Organometallics
2005, 24, 570–579. (d) Evans, W. J.; Champagne, T.; Giarikos, D.; Ziller,
J. Chem. Commun. 2005, 5925–5927.
(19) (a) Bambirra, S.; Leusen, D. V.; Meetsma, A.; Hessen, B.; Teuben,
J. H. Chem. Commun. 2003, 522–523. (b) Bambirra, S.; Bouwkamp, M. W.;
Meetsma, A.; Hessen, B. J. Am. Chem. Soc. 2004, 126, 9182–9183.
(22) Effective ionic radius of Ln3+ for coordination number 6: Shannon,
R. D. Acta Crystallogr., Sect. A 1976, 32, 751–767.

New Rare Earth Metal Bis(alkyl)s
Organometallics, Vol. 27, No. 4, 2008 721
Figure 3. X-ray structure of 3c with 35% probability thermal
ellipsoids. Selected bond lengths (Å) and angles (deg): Lu-N(1)
) 2.290(2), Lu-N(2) ) 2.308(2), Lu-O ) 2.297(2), Lu-C(32)
) 2.332(3), Lu-C(36) ) 2.354(3), N(1)-Lu-N(2) ) 64.74(9),
C(32)-Lu-C(36) ) 112.51(12), O-Lu-C(32) ) 95.61(11),
O-Lu-C(36) ) 94.54(11), Lu-C(32)-Si(1) ) 129.80(19),
Lu-C(36)-Si(2) ) 123.09(17).
Figure 1. X-ray structure of 3a with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Sc-N(1) ) 2.175(2), Sc-N(2) )
2.203(3), Sc-O ) 2.197(2), Sc-C(32) ) 2.220(3), Sc-C(36) )
2.220(3), Sc-P ) 2.874(3), N(1)-P ) 1.606(3), N(2)-P )
1.616(2),N(1)-Sc-N(2))64.56(9),C(32)-Sc-C(36))111.90(12),
O-Sc-C(32))93.28(11),O-Sc-C(36))94.75(11),Sc-C(32)-Si(1)
) 132.88(17), Sc-C(36)-Si(2) ) 125.30(16).
Figure 4. X-ray structure of 3d with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond
lengths (Å) and angles (deg): Sc-N(1) ) 2.1780(17), Sc-N(2) )
2.2021(18), Sc-O ) 2.1974(16), Sc-C(32) ) 2.222(2), Sc-C(36)
) 2.232(2), Sc-P ) 2.8942(7), N(1)-P ) 1.6164(18), N(2)-P )
1.6246(18), N(3)-C(5) ) 1.342(3), N(2)-C(5) ) 1.397(3),
N(1)-Sc-N(2) ) 67.37(6), C(31)-Sc-C(35) ) 111.88(9),
O-Sc-C(31))95.05(8),O-Sc-C(35))94.11(8),Sc-C(31)-Si(1)
) 124.79(12), Sc-C(35)-Si(2) ) 131.76(13).
Figure 2. X-ray structure of 3b with 35% probability thermal
ellipsoids. Selected bond lengths (Å) and angles (deg): Y-N(1) )
2.335(3), Y-N(2) ) 2.349(4), Y-O ) 2.332(3), Y-C(32) )
2.373(4), Y-C(36) ) 2.404(4), N(1)-Y-N(2) ) 63.37(12),
C(32)-Y-C(36) ) 112.90(16), O-Y-C(32) ) 95.82(15),
O-Y-C(36))94.47(15),Y-C(32)-Si(1))123.1(2),Y-C(36)-Si(2)
) 129.0(2).
half-metallocene dimeric systems, where Y shows the highest
3,4-selectivity among the rare earth metals.14 It is also in contrast
to the Ziegler–Natta-type catalysts that the Nd catalysts are the
most active and specifically selective (cis-1,4) for the diene
polymerization.2c,5c Surprisingly, 3d did not exhibit activity with
the addition of both activators, which could be attributed to the
electrodonating pyridyl fragment in 3d compared to the phenyl
ring in 3a resulting in an increase of the electron negativity of
the Sc metal center (Table 2, entry 7).
Besides the central metal type, the steric bulkiness of the
aluminum alkyls is crucial to adjust the activity and selectivity.
When AlMe3 was used as coactivator, the combination of 3a/
[PhNHMe2][B(C6F5)4]/[AlMe3] exhibited not only low selectiv-
ity (76.5%) but also low activity. This might be attributed to
the adduct formation between the sterically less demanding
aluminum methyl and the cationic rare earth metal catalyst,
resulting in a less active aluminate species.9,23,24 For the more
steric AlEt3, both the catalytic activity and the selectivity of
the corresponding system increased obviously. With the more
bulky AliBu3 as the coactivator, a 3,4-regularity as high as
88.5% could be reached (Table 2, entries 4, 8, 9). It is worth
noting that an equimolar amount of AliBu3 is insufficient to
activate the precursors. Rapid polymerization could only be
achieved with at least 5 equiv of AliBu3.2c,d,4–6,21 The roles of
AlR3 were to coordinate to the inert contact ion pair (Vide supra)
to generate the highly active bimetallic species (Vide infra).21d
More importantly, AlR3 can abstract the THF molecules
coordinated to the catalytic precursor and the ammonium borate
salt under the formation of [AlR3(THF)x],21b as the presence
of the solvated THF molecule in the living metal center is well-
known to compete with the coordination of the nonpolar
isoprene monomer, resulting in cleavage of the alkyl-bridged
bimetallic active species by generating the inert monomeric THF
solvates.23 High loading of AliBu3 resulted in high activity;
(23) (a) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed.
2003, 42, 5075–5079. (b) Zimmermann, M.; Törnroos, K.; Anwander, R.
Angew. Chem., Int. Ed. 2007, 46, 3126–3130.
(24) Bochmann, M.; Lancaster, S. Angew. Chem. Int. Ed. 1994, 33,
1634–1637.

722 Organometallics, Vol. 27, No. 4, 2008
Li et al.
Table 2. Polymerization of Isoprene by Using Various Catalyst Systemsa
b
microstructure
c
entry
cat.
AlR3
AliBu3
0
[Al]/[Ln]
temp, °C
time, min
yield, %
3,4 (%)
1,4 (%)
Mn × 10-4
Mw/Mn
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
B
3+B
0
0
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
50
0
720
720
720
5
10
10
10
20
20
20
20
5
5
5
5
20
20
120
120
720
trace
trace
trace
100
95
3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AlMe3
AlEt3
50
10
10
10
10
10
10
2
3a+B
3b+B
3c+B
3d+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
3a+B
88.5
43.8
80.1
11.5
56.2
19.9
13.9
6.8
12.2
1.54
1.32
1.71
95
67
100
38
76.5
81.5
86.0
86.1
87.8
87.2
88.0
87.5
71.1
90.6
92.7
94.7
95.0 d
23.5
18.5
14.0
15.5
12.2
12.8
12.0
12.5
28.9
9.4
12.0
9.6
15.4
15.2
9.6
7.6
6.0
6.3
9.8
1.80
1.62
1.65
1.61
1.52
1.73
2.06
2.52
1.61
1.58
1.57
1.55
1.59
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
AliBu3
5
91
20
40
50
70
10
10
10
20
50
100
100
100
100
100
100
94
54.3
70.2
99.0
150.7
-20
-40
-60
7.3
5.3
5.0
97
52
a Toluene, 5 mL; B: [PhNHMe2][B(C6F5)4]; [IP]0:[Ln]0 ) 1000; [B]:[Ln] ) 1 (mol/mol). b On the basis of 1H NMR and 13C NMR integration in
CDCl3. c Determined by means of GPC against polystyrene standards. d 3,4-:cis-1,4:trans-1,4 ) 95:4.13:0.87.
however chain transfer leads to a decrease in the experimental
Mn of the resultant PIP and a broadening of the molecular weight
distribution as well (Table 2, entries 10–16).
CH2SiMe3 differentiated from the AB spin in 3a. Addition of
excess isoprene to A exhibited no new signals beyond isoprene
and A, suggesting that A, a contact ion pair bearing a solvated
THF molecule, could not initiate the polymerization. However,
upon addition of excess AliBu3, A transferred into B, the
scandium-alkyl-aluminate ion pair [(NPNPh)Sc(µ-CH2SiMe3)-
AliBu2(µ-CH2CH(CH3)2]+[B(C6F5)4]-.24–26 A doublet at δ
-0.73wasassignedtoScandAlunitsofSc(µ-CH2SiMe3)Al.2c,21c,27
Meanwhile the methylene protons of the isopropyl group
bridging the Sc and Al units, Sc(µ-CH2CH(CH3)2)Al, gave a
doublet at δ 0.28, while those from the terminal Al-
CH2CH(CH3)2 showed a doublet at δ 0.31. Both were different
from the methylene protons of free AliBu3 (δ0.23), suggesting
that the alkyl-exchange reaction among the bridged, terminal,
and free alkyl fragments were slow on the NMR time scale for
this system. THF resonances shifted from δ 3.79 in A to δ 3.48,
Since the activity of the Sc system is very high, we examined
its low-temperature behavior. As expected, the high activity
remained even at -40 °C such that a complete conversion could
be achieved in 2 h, whereas at a much lower temperature of
-60 °C, the reaction became sluggish (52%) even with a high
loading of AliBu3 ([Al]/[Ln] ) 50) and prolonged reaction time
(12 h). Strikingly, with a decrease of temperature, an obvious
increase of 3,4-regularity from 88.5% at 20 °C to 92.5% at -20
°C was observed. A much higher value of 94.7% was achieved
when the temperature was lowered to -40 °C and reached 95%
at -60 °C. In the meantime, the molecular weight of the
resulting PIP increased greatly varying from 9.8 × 104 to 150
× 104 with the decrease of the temperature, while the molecular
weight distribution kept a narrow range, possibly as a result of
a decrease in chain transfer, etc., side reactions (Table 2, entries
4, 17–20). On the contrary, when the polymerization was
performed at a high temperature of 50 °C, the selectivity dropped
drastically to 71.1% accompanied by lower molecular weight
and broadened polydispersity albeit at the same level of activity
(Table 2, entry 16).
(25) Treatment of complex 3a by [PhNHMe2][B(C6F5)4] in C6D6 at room
temperature for several minutes afforded cationic units [(NPNPh)Sc-
(CH2SiMe3)(THF)][B(C6F5)4], which upon addition of 10 equiv of AliBu3
generated cationic scandium-aluminute [(NPNPh)Sc(µ-CH2SiMe3)AliBu2(µ-
CH2CH(CH3)][B(C6F5)4]. 1H NMR (400 MHz, C6D6, 25 °C): δ -0.72,
-0.74 (AB, 2JH-H ) 8 Hz, 2H, CH2SiMe3), 0.12 (s, 12H, SiMe4), 0.23 (d,
3
3JH-H ) 6.4 Hz, 12H, Al(CH2CH(CH3)2)3), 0.28 (d, JH-H ) 6 Hz,
3
2H, µ-CH2CH(CH3)2AliBu2), 0.31 (d, JH-H
)
7.2 Hz, 4H,
µ-iBuAl(CH2CH(CH3)2)2), 0.39 (s, 9H, CH2SiMe3), 1.10 (br, THF), 1.30
The Active Species. To investigate the active species,
isolation of single crystals deduced from the ternary system 3a/
[PhNHMe2][B(C6F5)4]/AliBu3, was attempted but failed. For-
3
(d, JH-H ) 6 Hz, 36H, Al(CH2CH(CH3)2)3), 1.33 (s, 6H, o-NC6H2Me2),
3
1.36 (d, JH-H ) 6.8 Hz, 18 H, Al(CH2CH(CH3)2)3), 2.08 (s, 6H,
Al(CH2CH(CH3)2)3), 2.21–2.27 (m, 6H, (µ-CH2CH(CH3)2)Al(CH2-
CH(CH3)2)2, p-NC6H2Me), 2.39 (s, 6H, PhNMe2), 3.48 (br, THF), 6.74 (s,
2H, NC6H2), 6.78–6.87 (m, 3H, PhNMe2), 6.94–7.02 (m, 3H, o,p-NC6H5),
7.08–7.18 (m, 8H, m,p-P(C6H5)2, PhNMe2, m-NC6H5), 7.45–7.60 (m, 4H,
o-P(C6H5)2). 19F NMR (282.4 MHz, C6D6, 25 °C): δ -56.12 (s, o-F),
-86.65 (t, 3JF-F ) 19.8 Hz, p-F), -90.59 (br, m-F). 11B NMR (96.3 MHz,
C6D6, 25 °C): δ -16.78. The 1H NMR spectrum and 1H-1H COSY of
adduct 3a/[PhNHMe2][B(C6F5)4]/AliBu3, see Supporting Information.
(26) (a) Petros, R. A.; Norton, J. R. Organometallics 2004, 23, 5105–
5107. (b) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem.
Commun. 2005, 3313–3315.
1
tunately, monitoring the reaction mixture by H NMR spec-
troscopy provided information about the reaction species, which
shed some lights on the probable mechanistic aspect of the
polymerization. As shown in Scheme 2, first, complex 3a was
dealkylated by the Brønsted acid [PhNHMe2][B(C6F5)4] to
generate the ion pair [(NPNPh)Sc(CH2SiMe3)(THF)]+[B-
(C6F5)4]- (A),20 accompanied by the release of SiMe4 (δ ) 0
ppm in the 13C NMR spectrum) and PhMe2N (δ ) 2.39 ppm).
No signals of 3a were observed. The newly formed A showed
a singlet at δ 0.73 assigned to the methylene protons of Sc-
(27) (a) Dietrich, H. M.; Raudaschl-Sieber, G.; Anwander, R. Angew.
Chem., Int. Ed. 2005, 44, 5303–5306. (b) Fischbach, A.; Perdih, F.;
Herdtweck, E.; Anwander, R. Organometallics 2006, 25, 1626–1642.

New Rare Earth Metal Bis(alkyl)s
Organometallics, Vol. 27, No. 4, 2008 723
Scheme 2. Proposed Active Species and Mechanistic Scenario
prepared according to published procedures.28 Isoprene (99%,
Acros) was dried over CaH2 under stirring for 48 h and distilled
indicating that THF is abstracted from A by AliBu3 to generate
AliBu3(THF)x. Thus, B should be the true active species that
prefers to coordinate to isoprene in an η2-mode owing to the
geometry (or sterics) of the NPN ancillary ligand as well as the
steric demand of the aluminum alkyl. The bimetallic structure
is thought to remain intact during the polymerization and seems
crucial for the regiospecificity of these catalyst systems.
1
before use. H and 13C NMR spectra were recorded on a Bruker
1
AV400 (FT, 400 MHz for H; 100 MHz for 13C) or AV300 (FT,
300 MHz for 1H; 75 MHz for 13C). NMR assignments were
confirmed by 1H-1H (COSY) and 1H-13C (HMQC) experiments
when necessary. 11B NMR spectra were referenced to an external
standard of BF3 · Et2O (0.0 ppm) in C6D6. 19F NMR spectra are
referenced to CF3COOH using an external standard in C6D6. IR
spectra were recorded on a VERTEX 70 FT-IR. Elemental analyses
were performed at National Analytical Research Centre of Chang-
chun Institute of Applied Chemistry (CIAC). The molecular weights
(Mn) were measured by TOSOH HLC-8220 GPC at 40 °C using
THF as eluent (the flow rate is 0.35 mL/min) against polystyrene
standards.
Conclusions
A new type of non-Cp-ligated rare earth metal bis(alkyl)
complexes bearing the NPN (iminophosphonamido) ancillary
ligand, (NPN)Ln(CH2SiMe3)2(THF), have been synthesized and
well-defined. These complexes in combination with an am-
monium borate salt and AlR3 provide high activity and 3,4-
selectivity for the polymerization of isoprene. The catalyst
performances are influenced significantly by the kind of center
metal ion, the electron negativity of the ligand, the steric bulk
of the aluminum alkyl, and the polymerization conditions. High
activity and up to 95% 3,4-selectivity could be achieved with
the optimum ternary system composed of the more Lewis acidic
scandium complex [(NPNPh)Sc(CH2SiMe3)2(THF)] and [Ph-
NHMe2][B(C6F5)4] and the bulky AliBu3 at low temperature.
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
-86.5 °C on a Bruker SMART APEX diffractometer with a CCD
area detector, using graphite-monochromated Mo KR 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 anisotro-
pically for all non-hydrogen atoms by the full-matrix least-squares
method. The hydrogen atoms were placed at the calculated positions
and were included in the structure calculation without further
refinement of the parameters.
Synthesis of PhNHPPh2dNC6H2-2,4,6-Me3 (2a, NPNPhH). In
a 100 mL Schlenk flask, a THF solution (15 mL) of mesityl azide
(6.1 mmol, 0.97 g) was added dropwise to a THF solution (30 mL)
of phenylaminodiphenylphosphine (1a) (6.0 mmol, 1.66 g) at 0 °C
Experimental Section
General Considerations. All manipulations were performed
under a dry and oxygen-free argon atmosphere using standard high-
vacuum Schlenk techniques or in a glovebox. All solvents were
purified from an MBraun SPS system. ClPPh2, AlMe3, AlEt3,
AliBu3, LnCl3, and LiCH2SiMe3 were purchased from Aldrich.
Mesityl azide, 2-pyridyl-NHPPh2, PhNHPPh2, [PhNHMe2]-
[B(C6F5)4], and Ln(CH2SiMe3)3(THF)2 (Ln ) Sc, Y, Lu) were
(28) (a) Murata, S.; Abe, S.; Tomioka, H. J. Org. Chem. 1997, 62, 3055–
3061. (b) Contreras, R.; Grevy, J. M.; G-Hernandez, Z.; G-Rodriguez, M.;
Wrackmeyer, B. Heteroat. Chem. 2001, 12, 542–550. (c) Tjaden, E. B.;
Swenson, D. C.; Jordan, R. F. Organometallics 1995, 14, 371–386. (d)
Lappert, M. F.; Pearce, R. J. Chem. Soc., Chem. Commun. 1997, 126–126.

724 Organometallics, Vol. 27, No. 4, 2008
Li et al.
under nitrogen atmosphere. The reaction mixture was stirred for
12 h at room temperature. Removal of volatiles gave white solids
that were further purified by washing with diethyl ether/hexane to
afford pure white solids of NPNPhH (2a) (1.80 g, 73%). 1H NMR
(300 MHz, CDCl3, 25 °C): δ 2.06 (s, 6H, o-NC6H2Me3), 2.19 (s,
3H, p-NC6H2 Me3), 5.28 (br, 1H, NH), 6.71 (s, 2H, NC6H2), 6.84
2C, m-NC6H2), 131.18 (s, 1C, ipso-NC6H2), 131.92,132.34 (s, 2C,
2
ipso-NC6H2), 132.15 (s, 2C, p-PC6H5) 133.20 (d, Jp-c ) 10 Hz,
1
4C, o-PC6H5), 135.30 (d, Jp-c ) 5 Hz, 2C, ipso-PC6H5), 141.75
(s, 1C, ipso-NC6H2), 148.80 (s, 1C, ipso-NC6H5). IR (KBr pellets):
V 3644 (w), 3056 (w), 2947 (s), 2858 (w), 1595 (s), 1570 (w), 1495
(m), 1478 (s), 1437 (s), 1374 (w), 1300 (s), 1248 (s), 1182 (w),
1163 (m), 1117 (s), 1079 (w), 1035 (m), 1003 (s), 981 (m), 948
(w), 863 (s), 804 (s), 752 (s), 719 (s), 692 (s), 679 (m). Anal. Calcd
(%) for C39H56N2OPSi2Sc: C, 66.82; H, 8.05; N, 4.00. Found: C,
66.79; H, 7.96; N, 3.87.
3
3
(t, JH-H ) 7.5 Hz, 1H, p-NC6H5), 6.95 (d, JH-H ) 7.8 Hz, 2H,
3
o-NC6H5), 7.12 (t, JH-H ) 7.8 Hz, 2H, m-NC6H5), 7.37–7.43 (m,
4H, m-PC6H5), 7.47–7.53 (m, 2H, p-PC6H5), 7.73–7.80 (m, 4H,
o-PC6H5). 13C NMR (75.5 MHz, CDCl3, 25 °C): δ 20.35 (s, 2C,
3
Synthesis of (NPNPh)Y(CH2SiMe3)2(THF) (3b). Following a
similar procedure described for the preparation of 3a, complex 3b
was isolated from the reaction of Y(CH2SiMe3)3(THF)2 (0.198 g,
0.4 mmol in 3.0 mL hexane) with 1 equiv of 2a (0.164 g, 0.4 mmol
in 4 mL THF) in a 57% yield (0.17 g). Single crystals grew from
o-NC6H2Me3), 20.65 (s, 1C, p-NC6H2Me3), 118.35 (d, Jp-c ) 6.0
Hz, 2C, o-NC6H5), 120.72 (s, 1C, p-NC6H5), 128.58 (s, 2C,
3
m-NC6H2), 128.74 (d, Jp-c ) 13.0 Hz, 4C, m-PC6H5), 129.04 (s,
1
2C, m-NC6H5), 129.120 (d, Jp-c ) 27.9 Hz, 2C, ipso-PC6H5),
131.10(s, 1C, ipso-NC6H2), 131.70 (s, 2C, p-PC6H5), 132.07 (d,
2Jp-c ) 9.4 Hz, 4C, o-PC6H5), 132.83 (s, 2C, ipso-NC6H2), 142.07
(s, 1C, ipso-NC6H5), 142.65 (s, 1C, ipso-NC6H2). IR (KBr pellets):
V 3326 (s), 3057 (m), 2909 (m), 2851 (w), 1605 (s), 1501 (s), 1478
(s), 1435 (s), 1390 (w), 1340 (s), 1283 (s), 1230 (s), 1185 (w),
1173 (w), 1160 (w), 1120 (s),1075 (w), 1060 (s), 1029 (m), 1000
(m), 929 (w), 888 (s), 862 (s), 790 (m), 755 (s), 723 (m), 713 (m),
695 (s). Anal. Calcd (%) for C27H27N2P (410.49): C, 79.00; H, 6.63;
N, 6.82. Found: C, 78.86; H, 6.53; N, 6.76.
1
the mixture of THF/hexane (1:5 v/v) at -30 °C within 12 h. H
NMR (400 MHz, C6D6, 25 °C): δ 0.12 (s, 4H, CH2SiMe3), 0.59 (s,
18H, SiMe3), 1.05 (br, 4H, THF), 1.77 (s, 6H, o-NC6H2Me3), 2.20
(s, 3H, p-NC6H2Me3), 3.66 (br, 4H, THF), 6.70 (s, 2H, NC6H2),
3
6.84 (t, JH-H ) 7.2 Hz, 1H, p-NC6H5), 7.01–7.13 (m, 6H, p,m-
3
3
PC6H5), 7.22 (t, JH-H ) 7.6 Hz, 2H, m-NC6H5), 7.34 (d, JH-H
)
8 Hz, 2H, o-NC6H5), 7.80–7.83 (m, 4 H, o-PC6H5). 13C NMR (100
MHz, C6D6, 25 °C): δ 5.05 (s, 6C, SiMe3), 20.90 (s, 2C,
o-NC6H2Me3), 21.17 (s, 1C, p-NC6H2Me3), 25.54 (s, 2C, THF),
Synthesis of 2-Pyridyl-NHPPh2dNC6H2-2,4,6-Me3 (2b,
NPNPyH). Following the similar procedure, treatment of mesityl
azide (6.1 mmol, 0.97 g, in 30 mL THF) with 2-pyridylamino-
diphenylphosphane (1b) (6.0 mmol, 1.64 g in 30 mL THF) yielded
NPNPyH (2b) (1.70 g, 69%). 1H NMR (300 MHz, CDCl3, 25 °C):
δ 2.07 (s, 6H, o-NC6H2Me3), 2.15 (s, 3H, p-NC6H2Me3), 6.47 (br,
1H, 4-Py), 6.64 (s, 2H, NC6H2), 6.86 (d, 3JP-H ) 8.1 Hz,1H, 6-Py),
1
37.71 (d, JY-C ) 39.9 Hz, 2C, CH2SiMe3), 70.09 (br, 2C, THF),
120.33 (s, 1C, p-NC6H5), 122.41 (d, 3Jp-c ) 15 Hz, 2C, o-NC6H5),
129.06 (d, 3Jp-c ) 11 Hz, 4C, m-PC6H5), 129.69 (s, 2C, m-NC6H5),
129.81 (s, 2C, m-NC6H2), 131.54 (s, 1C, ipso-NC6H2), 131.67,132.59
(s, 2C, ipso-NC6H2), 132.00 (s, 2C, p-PC6H5), 132.94 (d, 2Jp-c ) 9
Hz, 4C, o-PC6H5), 135.14 (d, 1Jp-c ) 6 Hz, 2C, ipso-PC6H5), 142.03
(s, 1C, ipso-NC6H2), 148.85 (s, 1C, ipso-NC6H5). IR (KBr pellets):
V 3654 (w), 3055 (w), 2947 (s), 2856 (w), 1595 (s), 1568 (w), 1494
(m), 1477 (s), 1437 (s), 1372 (w), 1300 (s), 1284 (s), 1182 (w),
1162 (m), 1117 (s), 1079 (w), 1036 (m), 1003 (s), 978 (m), 947
(w), 860 (s), 798 (s), 752 (s), 719 (m), 693 (s). Anal. Calcd (%)
for C39H56N2OPSi2Y: C, 62.88; H, 7.58; N, 3.76. Found: C, 62.81;
H, 7.60; N, 3.69.
1
7.30–7.39 (m, 1H, 5-Py, 4H, m-PC6H5), 7.45 (t, JH-H ) 7.8 Hz,
2H, p-PC6H5), 7.73–7.79 (m, 4H, o-PC6H5), 7.84 (br, 1H, 3-Py).
13C NMR (75.5 MHz, CDCl3, 25 °C): δ 20.06 (s, 2C, o-NC6H2Me3),
21.06 (s, 1C, p-NC6H2Me3), 112.86 (br, 1C, 6-Py), 117.34 (br, 1C,
2
4-Py), 128.50 (d, Jp-c ) 12.8 Hz, 4C, o-PC6H5), 129.26 (s, 2C,
m-NC6H2), 129.82 (br, 2C, ipso-NC6H2), 131.52 (s, 1C, ipso-
4
3
NC6H2), 132.00 (d, JP-C ) 1.6 Hz, p-PC6H5), 133.13 (d, JP-C
)
Synthesis of (NPNPh)Lu(CH2SiMe3)2(THF) (3c). Follow-
ing a similar procedure described previously, treatment of
Lu(CH2SiMe3)3(THF)2 (0.232 g, 0.4 mmol in 3.0 mL toluene) with
1 equiv of 2a (0.164 g, 0.4 mmol in 4 mL of THF) afforded
complex 3c (0.22 g, 68%). Single crystals grew from the mixture
9.3 Hz, m-PC6H5), 136.54 (s, 1C, ipso-NC6H5), 137.50 (s, 1C, 5-Py),
147.34 (s, 1C, 3-Py). IR (KBr pellets): V 3305(s), 2962(w), 2914(w),
1590(s), 1546(s), 1481(s), 1460(s), 1428(s), 1364(m), 1334(s),
1281(s), 1221(s), 1179(m), 1158(m), 1140(w), 1120(s), 1107(s),
1071(m), 1048(s), 1025(s), 1000(m), 982(s), 911(s), 861(s), 801(s),
774(s), 749(m), 742(m), 719(s), 706(s), 694(s). Anal. Calcd (%)
for C26H26N3P: C, 75.89; H, 6.37; N, 10.21. Found: C, 75.84; H,
6.36; N, 10.13.
1
of THF/hexane (1:5 v/v) at -30 °C within 12 h. H NMR (400
MHz, C6D6, 25 °C): δ 0.07 (br, 4H, CH2SiMe3), 0.58 (s, 18H,
SiMe3), 1.05 (br, 4H, THF), 1.78 (s, 6H, o-NC6H2Me3), 2.22 (s,
3H, p-NC6H2Me3), 3.68 (br, 4H, THF), 6.71 (s, 2H, NC6H2), 6.84
(t, 3JH-H ) 7.2 Hz, 1H, p-NC6H5), 7.05–7.11 (m, 6H, m,p-PC6H5),
7.22 (t, 3JH-H ) 7.6 Hz, 2H, m-NC6H5), 7.34 (d, 3JH-H ) 8 Hz, 2H,
o-NC6H5), 7.78–7.82 (m, 4H, o-PC6H5). 13C NMR (100 MHz, C6D6,
25 °C): δ 5.22 (s, 6C, SiMe3), 20.81 (s, 2C, o-NC6H2Me3), 21.13
Synthesis of (NPNPh)Sc(CH2SiMe3)2(THF) (3a). To a hexane
solution (3.0 mL) of Sc(CH2SiMe3)3(THF)2 (0.180 g, 0.4 mmol)
was dropwise added 1 equiv of 2a (0.164 g, 0.4 mmol in 4 mL
THF) at room temperature. The mixture remained stirring for 3 h
at room temperature and then was concentrated to about 1 mL.
Addition of 3 mL of hexane and cooling to -30 °C for 12 h
afforded crystalline solids, which were washed with a small amount
of hexane to remove impurities and dried in Vacuo to give white
powders of 3a (0.17 g, 61%). Single crystals grew from the mixture
(s, 1C, p-NC6H2Me3), 25.19 (s, 2C, THF), 44.44 (s, 2C, CH2SiMe3),
3
70.67 (br, 2C, THF), 120.25 (s, 1C, p-NC6H5), 122.40 (d, Jp-c
)
3
15 Hz, 2C, o-NC6H5), 129.06 (d, Jp-c ) 12 Hz, 4C, m-PC6H5),
129.55 (s, 2C, m-NC6H5), 129.75 (s, 2C, m-NC6H2), 131.71,132.63
(s, 2C, ipso-NC6H2), 132.06 (s, 2C, p-PC6H5), 132.98 (d, 2Jp-c ) 9
Hz, 4C, o-PC6H5), 135.36 (d, 1Jp-c ) 6 Hz, 2C, ipso-PC6H5), 141.90
(s, 1C, ipso-NC6H2), 148.72 (s, 1C, ipso-NC6H5). IR (KBr pellets):
V 3655 (w), 3056 (w), 2946 (s), 2855 (w), 1595 (s), 1569 (w), 1494
(m), 1478 (s), 1437 (s), 1372 (w), 1300 (s), 1248 (s), 1182 (w),
1163 (m), 1118 (s), 1109 (m), 1079 (w), 1036 (m), 1003 (s), 994
(w), 979 (m), 947 (w), 861 (s), 801 (s), 752 (s), 714 (s), 691 (s).
Anal. Calcd (%) for C39H56N2OPSi2Lu: C, 56.37; H, 6.79; N, 3.37.
Found: C, 56.30; H, 6.73; N, 3.31.
1
of THF/hexane (1:5 v/v) at -30 °C within 12 h. H NMR (400
2
MHz, C6D6, 25 °C): δ 0.44, 0.47 (AB, JH-H ) 11.6 Hz, 2H,
2
CH2SiMe3), 0.57 (s, 18H, SiMe3), 0.76, 0.79 (AB, JH-H ) 11.2
Hz, 2H, CH2SiMe3), 1.02 (br, 4H, THF), 1.73 (s, 6H, o-NC6H2Me3),
2.21 (s, 3H, p-NC6H2Me3), 3.85 (br, 4H, THF), 6.71 (s, 2H, NC6H2),
6.88 (t, 3JH-H ) 7.2 Hz, 1H, p-NC6H5), 7.01–7.05 (m, 4H, m-PC6H5),
7.08–7.09 (m, 2H, p-PC6H5), 7.27 (t, 3JH-H ) 7.6 Hz, 2H, m-NC6H5),
7.48 (d, 3JH-H ) 8 Hz, 2H, o-NC6H5), 7.78–7.83 (m, 4H, o-PC6H5).
13C NMR (100 MHz, C6D6, 25 °C): δ 4.70 (s, 6C, SiMe3), 20.91
(s, 2C, o-NC6H2Me3), 21.19 (s, 1C, p-NC6H2Me3), 25.02 (s, 2C,
THF), 42.56 (br, 2C, CH2SiMe3), 71.72 (s, 2C, THF), 120.33 (s,
1C, p-NC6H5), 122.46 (d, 3Jp-c ) 15 Hz, 2C, o-NC6H5), 129.06 (d,
3Jp-c ) 11 Hz, 4C, m-PC6H5), 129.50 (s, 2C, m-NC6H5), 129.81 (s,
Synthesis of (NPNPy)Sc(CH2SiMe3)2(THF) (3d). According to
the same workup procedure as that of 3a, 2b (0.164 g, 0.4 mmol
in 4 mL of toluene) was used instead of 2a to react with
Sc(CH2SiMe3)3(THF)2 (0.180 g, 0.4 mmol) to generate complex

New Rare Earth Metal Bis(alkyl)s
Organometallics, Vol. 27, No. 4, 2008 725
3d in a high yield (0.18 g, 69%). Single crystals were isolated from
a mixture of toluene/hexane (1:5 v/v) at -30 °C within 12 h. H
g, 10.0 mmol). The reaction apparatus was placed in a bath at the
designated temperature. The polymerization took place immediately
upon addition of 1.0 mL of a toluene solution (0.5 M) of AliBu3.
After stirring for 5 min, the viscous mixture was poured into ethanol
(ca. 30 mL) containing a small amount of hydrochloric acid to
terminate the polymerization. The precipitated polymer was isolated
by filtration, washed with ethanol, and then dried under vacuum at
40 °C to a constant weight (0.68 g, 100%).
1
NMR (400 MHz, C6D6, 25 °C): δ 0.55–0.61 (m, 22H, CH2SiMe3),
1.07 (br, 4H, THF), 1.78 (s, 6H, o-NC6H2Me2), 2.20 (s, 3H,
p-NC6H2Me3), 3.85 (br, 4H, THF), 6.39 (t, 1H, 4-Py), 7.06 (s, 2H,
NC6H2), 7.06–7.12(m, 6H, m,p-PC6H5), 7.40 (t, 1H, 5-Py),
7.86–7.93(m, 2H, 3,6-Py; 4H, m-PC6H5). 13C NMR (100 MHz,
C6D6, 25 °C): δ 4.66 (s, 6C, SiMe3), 21.09 (s, 2C, o-NC6H2Me3),
21.16 (s, 1C, p-NC6H2Me3), 25.31 (s, 2C, THF), 42.51 (br, 2C,
CH2SiMe3), 70.88 (s, 2C, THF), 115.33(s, 1C, 4-Py), 116.67(d,
3Jp-c ) 17 Hz, 1C, 6-Py), 129.79(s, 1C, m-NC6H2), 131.59(s, 2C,
p-PC6H5), 131.90(s,1C, ipso-NC6H2), 132.21,132.86(s, 2C, ipso-
Acknowledgment. The authors are grateful for financial
support from The National Natural Science Foundation of
China for Projects Nos. 20571072 and 20674081; The
Ministry of Science and Technology of China for Project
No. 2005CB623802; and the “Hundred Talent Scientist
Program” of Chinese Academy of Sciences.
NC6H2), 133.27(d, 2Jp-c ) 10 Hz, 4C, o-PC6H5), 135.36(d, 1Jp-c
)
5 Hz, 2C, ipso-PC6H5), 137.65(s, 1C, 5-Py), 142.26(s, 1C, ipso-
NC6H2), 147.94(s, 1C, 3-Py), 161.23(s, 1C, ipso-Py). IR (KBr
pellets): V 3653(w), 3057(w), 2947(s), 2858(w), 1589(s), 1555(m),
1465(s), 1427(s), 1335(s), 1304(s), 1288(w), 1251(s), 1186(w),
1163(m), 1147(m), 1118(s), 1046(m), 1017(w), 999(s), 980(w),
947(w), 862(s), 779(s), 744(s), 719(s), 693(s), 682(m). Anal. Calcd
(%) for C38H55N3OPSi2Sc (701.96): C, 65.02; H, 7.90; N, 5.99.
Found: C, 64.95; H, 7.84; N, 5.94.
Supporting Information Available: The 1H NMR spectrum of
polyisoprene, the details of the preparation and 1H NMR and
1H-1H COSY spectra of complexes 3a-d, and the crystallographic
information file (CIF) for complexes 3a-d. This material is
available free of charge via the Internet at http://pubs.acs.org.
Isoprene Polymerization. To a 50 mL flask were added 3a (7.0
mg, 0.010 mmol), toluene (2 mL), and a toluene solution (3 mL)
of [PhMe2NH][B(C6F5)4] (8.0 mg, 0.010 mmol) and isoprene (0.68
OM700945R