Pyrrolide-supported lanthanide alkyl complexes. influence of ligands on molecular structure and catalytic activity toward isoprene polymerization

Article abstract of DOI:10.1021/om7003095

The N,N-bidentate ligands 2-{(N-2,6-R)iminomethyl)}pyrrole (HL¹, R = dimethylphenyl; HL², R = diisopropylphenyl) have been prepared. HL¹ reacted readily with 1 equiv of lanthanide tris(alkyl)s, Ln(CH₂SiMe₃)₃(THF)₂, affording lanthanide bis(alkyl) complexes L¹Ln(CH₂SiMe ₃)₂(THF)_n (la, Ln = Lu, n = 2; lb, Ln = Sc, n -1) via alkane elimination. Reaction of the bulky ligand HL² with 1 equiv of Ln(CH₂SiMe₃)₃(THF)₂ gave the bis(pyrrolylaldiminato) lanthanide mono(alkyl) complexes L² ₂Ln(CH₂SiMe₃)(THF) (2a, Ln = Lu; 2b, Ln = Sc), selectively. The N,N-bidentate ligand HL³, 2- dimethylaminomethylpyrrole, reacted with Ln(CH₂SiMe₃) ₃(THF)₂, generating bimetallic bis(alkyl) complexes of central symmetry (3a, Ln = Y; 3b, Ln = Lu; 3c, Ln = Sc). Treatment of the N,N,N,N-tetmdentatc ligand H₂L⁴, 2,2′-bis(2,2- dimethylpropyldiimino)methylpyrrole, with equimolar Lu(CH₂SiMe ₃)3(THF)2 afforded a C₂-symmetric binuclear complex (4). Complexes 3a, 3b, 3c, and 4 represent rare examples of THF-free binuclear lanthanide bis(alkyl) complexes supported by non-cyclopentadienyl ligands. AU complexes have been tested as initiators for the polymerization of isoprene in the presence of AlEt3 and [Ph₃C][B(C₆F₅) ₄]. Complexes la, lb, and 3a show activity, and lb is the most active initiator, whereas 2a, 2b, 3b, 3c, and 4 are inert. The microstructure of the resultant polyisoprene has a cis-1,4 or trans-1,4 configuration depending on the initiator applied.

Full text of DOI:10.1021/om7003095

Organometallics 2007, 26, 4575-4584
4575
Pyrrolide-Supported Lanthanide Alkyl Complexes. Influence of
Ligands on Molecular Structure and Catalytic Activity toward
Isoprene Polymerization
Yi Yang,†,‡ Bo Liu,†,‡ Kui Lv,†,‡ Wei Gao,† Dongmei Cui,*,† Xuesi Chen,† and Xiabin Jing†
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 March 30, 2007
The N,N-bidentate ligands 2-{(N-2,6-R)iminomethyl)}pyrrole (HL1, R ) dimethylphenyl; HL2, R )
diisopropylphenyl) have been prepared. HL1 reacted readily with 1 equiv of lanthanide tris(alkyl)s,
Ln(CH2SiMe3)3(THF)2, affording lanthanide bis(alkyl) complexes L1Ln(CH2SiMe3)2(THF)n (1a, Ln )
Lu, n ) 2; 1b, Ln ) Sc, n ) 1) via alkane elimination. Reaction of the bulky ligand HL2 with 1 equiv
of Ln(CH2SiMe3)3(THF)2 gave the bis(pyrrolylaldiminato) lanthanide mono(alkyl) complexes L2 Ln-
2
(CH2SiMe3)(THF) (2a, Ln ) Lu; 2b, Ln ) Sc), selectively. The N,N-bidentate ligand HL3, 2-dimethyl-
aminomethylpyrrole, reacted with Ln(CH2SiMe3)3(THF)2, generating bimetallic bis(alkyl) complexes of
central symmetry (3a, Ln ) Y; 3b, Ln ) Lu; 3c, Ln ) Sc). Treatment of the N,N,N,N-tetradentate
ligand H2L4, 2,2′-bis(2,2-dimethylpropyldiimino)methylpyrrole, with equimolar Lu(CH2SiMe3)3(THF)2
afforded a C2-symmetric binuclear complex (4). Complexes 3a, 3b, 3c, and 4 represent rare examples of
THF-free binuclear lanthanide bis(alkyl) complexes supported by non-cyclopentadienyl ligands. All
complexes have been tested as initiators for the polymerization of isoprene in the presence of AlEt3 and
[Ph3C][B(C6F5)4]. Complexes 1a, 1b, and 3a show activity, and 1b is the most active initiator, whereas
2a, 2b, 3b, 3c, and 4 are inert. The microstructure of the resultant polyisoprene has a cis-1,4 or trans-1,4
configuration depending on the initiator applied.
mers,3 polar monomers,4 and olefins.5 In some cases, to reach
high activity and high cis-1,4 selectivity, the addition of the
third component AlR2Cl, AlR3, or MAO was needed,3b,e,6
Introduction
Over the past few years the synthesis of bis(alkyl) and tris-
(alkyl) complexes of group 3 metals supported by multidentate
ligands has been a research area of increasing interest.1 Recently,
rare earth metal bis(alkyl) complexes supported by monoanionic
ancillary ligands have also received much attention in organo-
lanthanide chemistry because these complexes are highly active
single-component catalysts or can be converted to the corre-
sponding cationic mono(alkyl) species after being activated by
borate, such as [Ph3C][B(C6F5)4] or [Me2NHPh][B(C6F5)4].2 The
thus resultant cationic species have demonstrated encouraging
catalytic activities for a range of polymerizations, such as highly
regio- or stereoselective polymerizations of conjugated mono-
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† State Key Laboratory of Polymer Physics and Chemistry.
‡ Graduate School of the Chinese Academy of Sciences.
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10.1021/om7003095 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 07/26/2007

4576 Organometallics, Vol. 26, No. 18, 2007
Yang et al.
Scheme 1. Synthetic Pathway for Preparation of Complexes
1a, 1b, 2a, and 2b
whereas rare earth metal bis(alkyl) species are highly reactive
and usually less sterically hindered, which makes the isolation
and application of the corresponding complexes more difficult
due to ligand redistribution and formation of salt or solvent
adducts. Tuning the ligand framework has been the efficient
manner to adjust the stability as well as the catalytic activity of
a complex.7 Heteroatom compounds have been extensively
explored to stabilize metal alkyl species by virtue of their strong
metal-ligand bonds and exceptional and tunable steric and
electronic features required for compensating coordinative
unsaturation of metal centers, such as monodentate amides,8
bidentate amidinates,9 guanidinates,10 â-diketiminates,11 salicyl-
aldiminates,12 and crown ether or THF.13 Comparatively, the
pyrrolide ligands for such usage have remained less investigated.
Up to date, Arnold reported a bis(pyrrolide) samarium mono-
(alkyl) complex initiating isospecific polymerization of MMA.14
Our group also released several pyrrolide-ligated yttrium alkyl
complexes that showed inter- or intramolecular migration of
alkyl groups to generate mono(alkyl) or bimetallic bis(alkyl)
species.15 Here we wish to report the synthesis of lanthanide
bis(alkyl) complexes bearing pyrrolide ligands and their catalytic
behaviors for polymerization of isoprene in the presence of AlEt3
and borate. We also present the significant effect of the ligand
framework on the molecular structures and the catalytic
performances of the complexes.
dimethylaniline. Treatment of Ln(CH2SiMe3)3(THF)2 with 1
equiv of HL1 in toluene afforded pyrrolylaldiminato rare earth
metal bis(alkyl) complexes L1Ln(CH2SiMe3)2(THF)n (1a, Ln
1
) Lu, n ) 2; 1b, Ln ) Sc, n ) 1) (Scheme 1). The H NMR
spectrum of 1a in C6D6 showed two sets of resonances indicating
the existence of an enantiomer besides 1a. Thus, methylene
protons of four alkyl ligands, Lu-CH2SiMe3, gave three singlet
resonances at δ -0.81, -0.70, and -0.64 with an integration
ratio of 2:2:4, suggesting that two alkyl ligands were equivalent.
Consistent with this, the imino proton CHdN also displayed
two singlets at δ 7.42 and 7.43, respectively. The pyrrolyl ring
protons appeared in the olefinic region (δ 6.56), suggesting that
the pyrrolyl anion might coordinate to the lutetium atom in η1-
N-coordination mode.15 The molecular structure of 1a (we did
not isolate the single crystal of 1a’s enantiomer) in the solid
state has been confirmed by X-ray analysis as described in
Figure 1. Selected bond distances and angles are listed in Table
1. The pyrrolide moiety chelates to the Lu ion via two nitrogen
atoms in η1/κ1-coordination mode, which combines with two
alkyl ligands and two solvated THF molecules to generate a
distorted square-bipyramidal ligand core. The imino nitrogen
N(1), the pyrrolyl nitrogen N(2), and the two alkyl carbon atoms
(C(14) C(18)) define the equatorial position with the two THF
oxygen atoms axial. The bond length of Lu-N(pyrrolyl) (Lu-
Results and Discussion
Synthesis and Characterization of Complexes 1a, 1b, 2a,
and 2b. The N,N-bidentate ligand 2-{(N-2,6-dimethylphenyl)-
iminomethyl)}pyrrole (HL1) was prepared by condensation
reaction of pyrrole-2-carboxyaldehyde with 1 equiv of 2,6-
(7) (a) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem. ReV.
1995, 95, 865. (b) Arndt, S.; Okuda, J. Chem. ReV. 2002, 102, 1953. (c)
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Chem.-Eur. J. 2003, 9, 4916. (e) Arnold, P. L.; Liddle, S. T. Chem.
Commun. 2005, 5638. (f) Liddle, S. T.; Arnold, P. L. Organometallics 2005,
24, 2597. (g) Arnold, P. L.; Liddle, S. T. Organometallics 2006, 25, 1485.
(h) Patel, D.; Liddle, S. T.; Mungur, S. A.; Rodden, M.; Blake, A. J.; Arnold,
P. L. Chem. Commun. 2006, 1124. (i) Cantat, T.; Jaroschik, F.; Ricard, L.;
Le Floch, P.; Nief, F.; Mezailles, N. Organometallics 2006, 25, 1329. (j)
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Figure 1. X-ray structure of 1a with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.

Pyrrolide-Supported Lanthanide Alkyl Complexes
Organometallics, Vol. 26, No. 18, 2007 4577
Table 1. Selected Bond Distances (Å) and Angles (deg) for
1a and 1b
1a
1b
Lu-N(1)
Lu-N(2)
Lu-O(1)
Lu-O(2)
Lu-C(14)
Lu-C(18)
O(1)-Lu-O(2)
N(1)-Lu-N(2)
C(14)-Lu-C(18)
2.540(3)
2.349(3)
2.313(2)
2.326(2)
2.351(3)
2.401(3)
169.04(7)
68.87(8)
106.09(11)
Sc-N(1)
Sc-N(2)
Sc-O
2.2977(16)
2.1872(16)
2.1990(14)
Sc-C(14)
Sc-C(18)
2.226(2)
2.212(2)
N(1)-Sc-N(2)
C(14)-Sc-C(18)
74.46(6)
110.64(8)
N(2) ) 2.349(3) Å) is comparable to that found in a lutetium-
pyrrolyl complex, Cp2Lu(C4H4N)(THF) (2.289(4) Å).16 The
metal-imino nitrogen bond length (Lu-N(1) ) 2.540(3) Å) is
longer than the distance of the metal-pyrrolyl nitrogen (Lu-
N(2) ) 2.349(3) Å). The bond angle of C-Lu-C (106.09(11)°)
is comparable to those in the rare earth metal bis(alkyl)
complexes supported by triazacyclononane (99.41(8)°),17 tri-
amino-amide (101.96(6)°),18 and â-diketiminate (108.90(13)°),19
indicating the similar steric environment of these ligands, but
it is smaller than those in a THF-solvated amidinato yttrium
bis(alkyl) complex (119.5(2)°)20 and in amido-phoshine-ligated
lanthanide bis(alkyl) complexes (av 115.55°).21
Figure 2. X-ray structure of 1b with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Interestingly, under the same conditions, the reaction of
Sc(CH2SiMe3)3(THF)2 with ligand HL1 gave the mono-THF-
coordinated complex 1b, L1Sc(CH2SiMe3)2(THF), in contrast
to the bis-THF-solvated 1a, which could be attributed to the
1
smaller ionic radii of the Sc atom. H NMR of complex 1b
demonstrated that the methylene protons of the alkyl ligands,
Sc-CH2SiMe3, gave a singlet resonance at a downfield region
(δ 0.45), which was different from the three singlet resonances
at upfield regions (δ -0.81, -0.70, and -0.64) in complex 1a
and its enantiomer. Accordingly, the geometry of the metal
center in 1b becomes a distorted square pyramid (Figure 2).
The average Sc-C bond length (2.219(2) Å) (Table 1) is very
close to those found in other scandium bis(alkyl) complexes,
such as [1,3-(SiMe3)2C5H3]Sc(CH2SiMe3)2(THF) (2.215(1) Å),3k
[2,6-iPr2C6H3N(SiMe3)]Sc(CH2SiMe3)2(THF) (2.211(2) Å),8 and
[PhC(N-2,6-iPr2C6H3)2Sc(CH2SiMe3)2(THF) (2.212(3) Å).9d The
bond distances Sc-N and Sc-O are comparable to the
corresponding ones in 1a, if the difference of the ionic radii is
considered,22 whereas the bond angles (N(1)-Sc-N(2) 74.46(6)°
and C(14)-Sc-C(18) 110.64(8)°) are much larger than those
in complex 1a (N(1)-Lu-N(2) 68.87(8)° and C(14)-Lu-
C(18) 106.09(11)°) due to the less steric metal center and one
THF coordination.
Surprisingly, switching from the sterically less demanding
HL1 to the more bulky HL2 ligand, the analogous reaction with
1 equiv of Ln(CH2SiMe3)3(THF)2 generated the mono(alkyl)
complexes 2a (Ln ) Lu) and 2b (Ln ) Sc) (Scheme 1), owing
to ligand redistribution. The resonance for the pyrrolyl ring
protons in the 1H NMR spectrum of 2a showed up in the olefinic
region (δ 6.47). The singlet resonance at δ -0.49 was assignable
to the equivalent methylene protons of Lu-CH2SiMe3. The
Figure 3. X-ray structure of 2a with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg)
for 2a
Lu(1)-N(1)
2.286(4)
2.329(4)
2.314(3)
83.29(13)
108.69(17)
Lu(1)-N(2)
2.437(4)
2.433(4)
2.344(6)
84.02(13)
108.13(14)
Lu(1)-N(3)
Lu(1)-N(4)
Lu(1)-O(1)
N(1)-Lu(1)-O(1)
N(1)-Lu(1)-C(35)
Lu(1)-C(35)
O(1)-Lu(1)-N(3)
N(4)-Lu(1)-N(2)
methylene protons of Sc-CH2SiMe3 in complex 2b gave a
singlet resonance at a downfield region (δ 0.44), which was
different from the singlet resonance at the upfield region (δ
-0.49) in complex 2a, but the same as the singlet resonance (δ
0.44) in complex 1b. Complex 2a adopts a distorted square-
bipyramidal geometry (Figure 3) with the imino nitrogen atom
N(4), two pyrrolyl nitrogen atoms N(1) and N(3), and the alkyl
carbon C(35) occupying the equatorial positions, while the THF
oxygen and another imino nitrogen atom, N(2), are axial.
Selected bond distances and angles (Table 2) in complex 2a
are similar to the corresponding values in 1a and need not be
discussed further.
Synthesis and Characterization of Complexes 3a, 3b, and
3c. Treatment of 2-(Me2NCH2)-C4H3NH (HL3) with 1 equiv
of Ln(CH2SiMe3)3(THF)2 afforded the colorless complexes [(2-
(Me2NCH2)-C4H3N)Ln(CH2SiMe3)2]2 (3a, Ln ) Y; 3b, Ln )
Lu; 3c, Ln ) Sc) in moderate yields. Complexes 3a, 3b, and
(16) Schumann, H.; Lee, P. R.; Dietrich, A. Chem. Ber. 1990, 123, 1331.
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Hessen, B.; Teuben, J. H. Organometallics 2004, 23, 936.
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Organometallics 2004, 23, 1891.
(19) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.; Noack, C. L.; Piers,
W. E.; Parvez, M. Organometallics 2003, 22, 1577.
(20) Bambirra, S.; van Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J.
H. Chem. Commun. 2003, 522.
(21) Liu, B.; Cui, D.; Ma, J.; Chen, X.; Jing, X. Chem.-Eur. J. 2007,
13, 834.
(22) Shannon. R. D. Acta Crystallogr. 1976, A 32, 751.

4578 Organometallics, Vol. 26, No. 18, 2007
Scheme 2. Synthetic Pathway for Preparation of Complexes 3a, 3b, and 3c
Yang et al.
Table 3. Selected Bond Distances (Å) and Angles (deg)
for 3a
3c were extremely air- and moisture-sensitive and showed good
solubility in THF and toluene but were insoluble in hexane.
The probable reaction pathway is described as Scheme 2. The
neutral ligand HL3 protonated one metal alkyl species of
Ln(CH2SiMe3)3(THF)2 to give the bis(alkyl) intermediate A.
Dimerization of two molecules of A via the pyrrolyl ring in
one A attaching to the lanthanide ion in another A in a η5-
coordination mode afforded a binuclear tetra(alkyl) complex.
Y-N(1)
2.735(2)
Y-C(1)
Y-C(3)
Y-N(1A)
Y-C(8)
2.725(3)
2.743(3)
2.446(2)
2.408(4)
Y-C(2)
2.738(3)
2.735(3)
2.588(3)
2.402(3)
91.99(13)
66.55(8)
90.35(11)
Y-C(4)
Y-N(2A)
Y-C(9)
C(9)-Y-C(8)
N(1A)-Y-N(2A)
C(8)-Y-N(1)#1
N(1A)-Y-N(1)
C(9)-Y-N(2A)
71.47(9)
85.15(10)
1
Complexes 3a, 3b, and 3c showed similar H NMR spectra.
The methylene protons of the alkyl ligand, Ln-CH2SiMe3, in
both 3a and 3b exhibited four discrete AB spins, and the
trimethylsilyl protons SiMe3 also gave four singlet resonances,
indicating molecular symmetry to some degree. The structure
of 3a is confirmed by X-ray analysis as a solvent-free dimer of
central symmetry (Ci) (Figure 4). The yttrium ion bonds to two
alkyl moieties arranged in trans-positions to form a unit. Such
two units are bridged by two tridentate pyrrolyl anions in η5/
η1:κ1-modes, generating a dimer containing two distorted
trigonal-bipyramidal cores. Interestingly, the two pyrrole rings
are almost parallel, and the two nitrogen atoms combined with
two yttrium atoms to form a plane. Two alkyl species locate
the endo coordination of the plane, while the other two alkyl
ligands are exo. Although the pyrrolyl ring coordinates to the
lanthanide metal center in a η5-mode like that found in the large
cyclic or polymeric complexes23 and in our previously reported
imino pyrrolide complexes,15 complex 3a represents the first
example of an amino pyrrolide-stabilized lanthanide bis(alkyl)
complex with respect to the pyrrole ring as a η5-heterocyclo-
pentadinyl ligand. The bond distances between yttrium and the
pyrrolyl carbon in 3a, Y-η5-C(pyr ring), ranging from 2.725(3)
to 2.743(3) Å (Table 3), are comparable to that in [2-(2-
Ph2PC6H3NC(H)(CH2SiMe3))-C4H3N]2Y2(CH2SiMe3)2(THF)
(2.690(5) to 2.738(6) Å).15 It is also noteworthy that all Y-η5-C
(pyr ring) bond lengths are close, varying in a narrow range
that is compared with lanthanocene complexes (2.646(3)-
2.674(4) Å).24 The bond distance Y-N(1) (2.735(2) Å) is longer
than Y-N(2A) (2.588(3) Å) and Y-N(1A) (2.446(2) Å), well
consistent with the η5/η1:κ1-coordination mode of the pyrrolide
ligand, which is comparable to the bond length of Y-N in a
η1:κ1-pyrrolyl yttrium amido complex.25 The bond distances
Y-C(8) (2.408(4) Å) and Y-C(9) (2.402(3) Å) have been found
to be comparable to those in the previously reported yttrium
bis(alkyl) complexes (Y-C, av 2.40 Å).5h,7h,26 However, the
corresponding bond angle (C(9)-Y-C(8) (91.99(13)°) is much
smaller than the reported value (C-Y-C, av 101.5°),5h,7h,26 and
it is also much smaller than C-Lu-C (106.09(11)°) and
C-Sc-C (110.64(8)°) found in complexes 1a and 1b discussed
previously, suggesting the bulky environment around the central
metal.
Synthesis and Characterization of Complex 4. Compound
H2L4, containing two amino protons, was prepared by conden-
sation reaction of pyrrole-2-carboxyaldehyde with 2,2-dimethyl-
1,3-propanediamine without addition of formic acid. Treatment
of H2L4 by equimolar Lu(CH2SiMe3)3(THF)2 afforded yellow
crystals of complex 4 in a quantitative yield (65%). The probable
reaction pathway could be described as follows (Scheme 3):
Two alkyl ligands of Lu(CH2SiMe3)3(THF)2 were abstracted
by the neutral ligand H2L4 to give a mono(alkyl) intermediate
B. B readily reacted with another molecule of H2L4 to yield C
via metal alkyl abstraction, which bore no alkyl ligand. The
protonolysis reaction between the amino proton in C and another
molecule of lutetium tris(alkyl)s accompanied by the coordina-
tion of the neutral pyrrole ring to Lu ions in η5-mode afforded
the final product 4. The two discrete AB spins in the upfield
region at δ -1.05 and -0.87 were attributed to the methylene
protons of the metal alkyl species, indicating the symmetric
character of the molecule. This is confirmed by an X-ray
crystallographic diffraction study, suggesting that complex 4 is
a C2-symmetric dimer. The two dianionic N,N,N,N-tetradentate
pyrrolide ligands bond to lutetium Lu(1) in η5/η5-modes to form
reverse sandwich geometry, whereas they bond to Lu(2) in η1:
κ1:η1/η1:κ1:η1-coordination modes to generate a twisted square-
pyramidal geometry (Figure 5). The base of the pyramid is
(23) (a) Dube, T.; Conoci, T.; Gambarotta, S.; Yap, G. P. A.; Vasapollo,
G. Angew. Chem., Int. Ed. 1999, 38, 3657. (b) Dube, T.; Ganesan, M.;
Conoci, S.; Gambarotta, S.; Yap, G. P. A. Organometallics 2000, 19, 3716.
(c) Dube, T.; Gambarotta, S.; Yap, G. P. A.; Conoci, S. Organometallics
2000, 19, 115. (d) Dube, T.; Conoci, S.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2000, 19, 1182. (e) Ganesan, M.; Lalonde, M. P.;
Gambarotta, S.; Yap, G. P. A. Organometallics 2001, 20, 2443. (f) Ganesan,
M.; Gambarotta, S.; Yap, G. P. A. Angew. Chem., Int. Ed. 2001, 40, 766.
(g) Berube C. D.; Yazdanbakhsh, M.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2003, 22, 3742.
(24) Evans, W. J.; Fujimoto, C. H.; Johnston, M. A.; Ziller, J. W.
Organometallics 2002, 21, 1825.
(25) Matsuo, Y.; Mashima, K.; Tani, K. Organometallics 2001, 20, 3510.
(26) (a) Hayes, P. G.; Welch, G. C.; Emslie, D. J. H.;. Noack, C. L.;
Piers, W. E. Parvez, M. Organometallics 2003, 22, 1577. (b) Bambirra, S.;
Meetsma, A.; Hessen, B. Organometallics 2006, 25, 3486.
Figure 4. X-ray structure of 3a with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.

Pyrrolide-Supported Lanthanide Alkyl Complexes
Organometallics, Vol. 26, No. 18, 2007 4579
Scheme 3. Synthetic Pathway for Preparation of Complex 4
defined by the eight nitrogen atoms, which contributes to
stabilize the complex.27 The two alkyl moieties coordinate to
Lu(1) in cis-positions against the two pyrrolyl rings. It is
noteworthy that the pyrrolyl rings coordinate to Lu(1) as a
neutral ligand and negatively charged species, respectively. The
bond lengths of Lu(1) to η5-C and η5-N of each pyrrolyl ring
are unequal, varying in a wide range (Lu(1)-N(1), 2.593(2)
Å; Lu(1)-C(1), 2.650(3) Å; Lu(1)-C(2), 2.759(3) Å; Lu(1)-
C(3), 2.749(3) Å; Lu(1)-C(4), 2.627(3) Å) (Table 4), which is
consistent with Y-η5-C (pyr ring) (2.631(6) to 2.851(6) Å) in
{[2-(2,6-iPr2C6H3NC(H)(CH2SiMe3))-C4H3N]Y(CH2SiMe3)-
(THF)}2.15 The bond distances between Lu(2) and nitrogen
atoms N(1), N(2), N(3), and N(4), averaging 2.434 Å, are within
the range typically observed for Lu-N bonds.28 The Lu-
CH2SiMe3 bond length in 4 (2.312(4) Å) is comparable with
those found in (C5Me5)Lu(CH2SiMe3)2(THF) (2.332(4) Å),29
(C5Me4SiMe3)Lu(CH2SiMe3)2(THF) (2.335(3) Å),30 and 1a
(2.351(3) and 2.401(3) Å). The bond angle C(16)-Lu(1)-
C(16A) (104.47(19)°) is close to that in 1a (C-Lu-C )
Table 4. Selected Bond Distances (Å) and Angles (deg) for 4
Lu(1)-N(1)
Lu(1)-C(1)
Lu(1)-C(2)
Lu(1)-C(3)
Lu(1)-C(4)
2.593(2)
2.650(3)
2.759(3)
2.749(3)
2.627(3)
Lu(2)-N(1)
Lu(2)-N(2)
Lu(2)-N(3)
Lu(2)-N(4)
Lu(1)-C(16)
2.448(3)
2.416(3)
2.483(3)
2.389(3)
2.312(4)
65.81(11)
C(16)-Lu(1)-C(16A) 104.47(19) N(1)-Lu(1)-N(1A)
N(1)-Lu(2)-N(3A)
N(4)-Lu(2)-N(2A)
68.79(8)
69.77(10)
N(2A)-Lu(2)-N(3A) 70.21(9)
106.09(11)°) and 1b (C-Sc-C ) 110.64(8)°), showing the
similar steric environment of the ligands; however, it is much
larger than that in 3a (C-Y-C ) 91.99(13)°) and the values
(C-Y-C ) 96.4(2)°) we reported previously.15
Isoprene Polymerization. All complexes had been tested as
initiators for the polymerization of isoprene activated by AlEt3
and borate ([Ph3C][B(C6F5)4]). Representative data are sum-
marized in Table 5.
Complex 1a was inactive in the polymerization of isoprene
and when treated with 1 equiv of [Ph3C][B(C6F5)4] was also
inert (Table 5, entry 1). Upon addition of the third component,
AlEt3, the system showed versatile activity depending on the
molar ratio of [Al]/[Ln].3b,e,6 When the ratio was 1:1, no
polymerization took place (Table 5, entry 2). Increasing the ratio
to 2:1, complete conversion could be reached in 5 h at room
temperature, and the resulting polyisoprene had high molecular
weight but broad molecular weight distribution (Table 5, entry
3). In order to investigate the nature of the initiator, the reaction
of 1a and 1 equiv of [Ph3C][B(C6F5)4] in C6D6 was monitored
1
by H NMR technique. The spectrum showed that the reso-
nances for one metal alkyl species disappeared accompanied
by the quantitative formation of Ph3CCH2SiMe3;3h the methylene
protons from the other alkyl species shifted downfield to δ 0.01
and 0.03, indicating the generation of cation [L1Lu(CH2SiMe3)-
(27) Cameron, T. M.; Gordon, J. C.; Michalczyk, R.; Scott, B. L. Chem.
Commun. 2003, 2282.
(28) Jantunen, K. C.; Scott, B. L.; Hay, P. J.; Gordon, J. C.; Kiplinger,
J. L. J. Am. Chem. Soc. 2006, 128, 6322.
(29) Cameron, T. M.; Gordon, J. C.; Scott, B. L. Organometallics 2004,
23, 2995.
(30) Tardif, O.; Nishiura, M.; Hou, Z. Organometallics 2003, 22, 1171.
Figure 5. X-ray structure of 4 with 35% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.

4580 Organometallics, Vol. 26, No. 18, 2007
Table 5. Isoprene Polymerization with Alkyl Complexes/[Ph3C][B(C6F5)4] with Various Amounts of AlEt3
Yang et al.
a
1,4d(%)
entry
cat.
[Ip]/[Ln]
[Al]/[Ln]
time (min)
conv (%)
M
calcd (104)b
Mn (104)c
PDIc
cis
trans
3,4d (%)
effe (%)
1
2
3
4
5
6
7
8
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
2a
2b
3a
3b
3c
4
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
500:1
1500:1
2000:1
3000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
1000:1
0
1:1
2:1
3:1
5:1
10:1
3:1
3:1
3:1
3:1
300
300
300
300
300
300
300
300
300
1200
1
1
1
1
1
1
1
500
500
300
500
500
500
0
0
99
100
100
100
100
100
100
96
6.81
6.81
6.81
6.81
3.41
10.2
13.6
19.6
10.7
6.89
4.59
3.70
3.56
11.5
15.9
22.6
4.39
3.16
3.03
3.47
3.71
3.42
3.59
3.39
75.0
62.0
65.3
69.1
74.3
70.2
63.0
65.9
16.5
27.1
25.3
23.2
16.2
21.2
27.9
24.2
8.5
10.9
9.4
7.7
9.5
8.6
9.1
9.9
64
99
148
184
96
89
86
87
9
10 f
11
12
13
14
15
16
17
18
19
20g
21g
22g
23
0
0
0.25:1
0.5:1
1:1
1.5:1
2:1
5:1
5:1
5:1
5:1
100
100
100
100
100
100
0
0
99
0
trace
0
6.81
6.81
6.81
6.81
6.81
6.81
36.5
29.5
29.8
10.1
12.8
10.8
2.15
1.94
2.03
1.55
1.70
1.85
75.9
75.6
76.0
76.7
73.7
76.4
15.0
15.6
14.5
14.3
17.7
14.4
9.1
8.8
9.5
9.0
8.6
9.2
19
23
23
67
53
63
3.37
1.34
1.37
15.2
70.4
14.4
251
5:1
5:1
5:1
b
a General condition: 20 °C, toluene; [Ip]0 ) 2.0 mol/L, [Ln] ) 2.0 mmol/L, [B]/[Ln] ) 1.0 (B ) [Ph3C][B(C6F5)4]). Mcalcd ) ([Ip]/[Ln]) × 68.12 ×
1
X (X ) conversion). c Measured by GPC calibrated with standard polystyrene samples. d Determined by H NMR. e Catalyst efficiency ) Mn(calculated)/
Mn(measured). f [Ln] ) 0.5 mmol/L. g [B]/[Ln] ) 2.0.
(THF)2]+.31 Then, excess AlEt3 was added to the above cationic
system. The resonances arising from the ligand remained
unchanged, while that from metal alkyl protons shifted slightly
(δ 0.02). Obvious changes were found for the signals from
solvated THF molecules, which gave a triplet resonance at δ
3.45 upfield-shifted compared to the singlet resonance at δ 3.78
in complex 1a. Analysis of the NMR spectrum of a mixture of
1a and AlEt3 in C6D6 excluded the possibility of cleavage of
the ligand from the metal center and the alkylation of the imino
function CHdN of the ligand by AlEt3 (CHdN proton still
peaked at δ 7.31 compared with δ 7.42 in complex 1a). Thus,
we assumed that the cation [L1Lu(CH2SiMe3)(THF)2]+ was the
initiator of the polymerization of isoprene. The role of AlEt3
was that it could trap and coordinate to a THF molecule,32 which
reduced the electron density of the metal center and decreased
the competitive coordination ability of THF with the monomer
isoprene.33 Hessen has reported that a bis-THF-solvated yttrium
bis(alkyl) complex showed no activity if activated only by
borate; addition of AlR3 is crucial.20 In our system, AlEt3 also
removed impurities and behaved as a chain transfer agent if
excess AlEt3 was added, as shown in Table 5 (entries 4-6).
When the [Al]/[Ln] ratio was 10:1, the molecular weight of
polyisoprene, Mn ) 37 000, was much smaller than that (Mn )
107000) when the ratio was 2:1, consistent with a previous
result.34
The effect of monomer-to-initiator ratio on the polymerization
was also investigated. At an [Al]/[Ln] of 3:1, the polymerization
of isoprene was performed under various [Ip]/[Ln] ratios ranging
from 500 to 2000. With an increase in the ratio, the molecular
weight of polyisoprene increased close to the theoretical value
Mcalcd and the catalytic efficiency was high (86-96%) (Table
5, entries 7-9). When the ratio was 3000:1, the polymerization
became sluggish due to the too low concentration of the initiator
(0.5 mmol/L) compared to that when the ratio was 500:1 (2.0
mmol/L), whereas a complete conversion could also be reached
if the polymerization time was prolonged to 20 h, to afford
polyisoprene with a molecular weight as high as 22.6 × 104
(96%, Table 5, entry 10). On the whole, the molecular weight
distribution of polyisoprene was broad, which might be at-
tributed to the faster chain transfer reaction than propagation.
It is surprising that the combination of 1b/[Ph3C][B(C6F5)4]
with a small amount of AlEt3 was highly active (Tp ) 1 min)
compared to its analogous 1a (Tp ) 300 min), although no
polymerization was observed without AlEt3 (the major role of
which might be removal of impurities). This high catalytic
activity of 1b could be attributed to the smaller Sc ionic radius,
allowing mono-THF coordination. Thus, the metal center was
(31) 1H NMR monitoring of the reaction of complex 1a with 1 equiv of
[Ph3C][B(C6F5)4] in C6D6 at 25 °C showed almost quantitative formation
of Ph3CCH2SiMe3 (δ 7.42-7.43 (m, 6H, o-Ph), 7.19-7.21 (m, 9H, m,p-
Ph), 2.17 (s, 2H, CH2), -0.10 (s, 9H, SiMe3)). Additional signals were
observed at δ 6.95-7.03 (m, 3H, m,p-C6H3), 6.44, 6.80, 6.82 (s, 3H, pyr),
3.26 (s, 8H, THF), 1.68 (s, 6H, C6H3Me2), 1.25 (s, 8H, THF), 0.11 (s, 9H,
Lu-CH2SiMe3), 0.01, 0.03 (s, 2H, Lu-CH2SiMe3), which may be assigned
to [L1Lu(CH2SiMe3)(THF)2][B(C6F5)4], although the proton in the ligand
CHdN could not be unequivocally assigned due to possible overlap with
the other signals (o-Ph).
(32) (a) Arndt, S.; Spaniol, T. P.; Okuda, J. Angew. Chem., Int. Ed. 2003,
42, 5075. (b) Arndt, S.; Beckerle, K.; Zeimentz, P. M.; Spaniol, T. P.; Okuda,
J. Angew. Chem., Int. Ed. 2005, 44, 7473.
(33) (a) Evans, W. J.; DeCoster, D. M.; Greaves, J. Macromolecules
1995, 28, 7929. (b) Evans, W. J.; Giarikos, D. G.; Allen, N. T.;
Macromolecules 2003, 36, 4256.
(34) (a) Taniguchi, Y.; Dong, W.; Katsumata, T.; Shiotsuki, M.; Masuda,
T. Polym. Bull. 2005, 54, 173. (b) Kaita, S.; Yamanaka, M.; Horiuchi, A.
C.; Wakatsuki, Y. Macromolecules 2006, 39, 1359. (c) Fischbach, A.;
Perdih, F.; Herdtweck, E.; Anwander, R. Organometallics 2006, 25, 1626.

Pyrrolide-Supported Lanthanide Alkyl Complexes
Organometallics, Vol. 26, No. 18, 2007 4581
Table 6. Summary of Crystallographic Data for 1-4
1a
1b
2a
3a
4-C7H8
formula
cryst size, mm
fw
cryst syst
space group
a (Å)
C29H51N2O2Si2Lu
0.18 × 0.15 × 0.13
690.87
monoclinic
P2(1)/c
9.4569(6)
16.4263(10)
21.2020(13)
90
92.3310(10)
90
C25H43N2OSi2Sc
0.25 × 0.18 × 0.16
488.75
monoclinic
P2(1)/n
11.5805(8)
14.0152(10)
17.7458(13)
90
90.5080(10)
90
2880.1(4)
4
C42H59N4OSiLu
0.18 × 0.13 × 0.11
838.99
triclinic
P1h
10.3754(6)
19.2503(11)
20.9445(12)
88.3420(10)
89.6590(10)
88.0490(10)
4179.0(4)
4
C30H66N4Si4Y2
0.18 × 0.15 × 0.13
773.05
triclinic
P1h
9.4442(8)
10.4910(9)
11.4717(10)
77.9230(10)
84.3380(10)
65.7770(10)
1013.49(15)
1
C45H66N8Si2Lu2
0.13 × 0.09 × 0.07
1125.18
tetragonal
P4(3)2(1)2
14.9571(7)
14.9571(7)
21.8098(14)
90
90
90
4879.2(4)
4
1.532
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
3290.8(4)
4
1.394
D
calcd (g/cm3)
1.127
1.334
1.267
radiation (λ), Å
Mo KR (0.71073)
Mo KR (0.71073)
Mo KR (0.71073)
Mo KR (0.71073)
Mo KR (0.71073)
2θmax (deg)
52.06
52.08
52.00
52.08
52.08
µ (cm-1
F(000)
)
30.98
1416
3.56
1056
24.26
1728
29.90
408
41.10
2248
no. of obsd reflns
6444
5680
16 002
3900
4826
no. of params refnd
352
288
905
189
266
GOF
R1
0.928
0.0252
1.021
0.0416
0.870
0.0405
0.996
0.0389
0.965
0.0184
wR2
0.0515
0.1114
0.0860
0.0987
0.0411
electronically much more positive than that of 1a, which was
favored by the coordination and insertion of the nonpolar
monomer isoprene, in agreement with the previous results that
mono-THF-coordinated bis(alkyl) complexes displayed high
activity under the presence of equimolar borate without AlEt3.3h,20
The molecular weight of the resulting polyisoprene was much
higher compared to the theoretic value, which was attributed
to the extremely rapid propagation rather than initiation, leading
to the reduction of the catalyst efficiency (Table 5, entries 11-
14).35 If the ratio was raised in the range 1.5:1-5:1, the
molecular weight of polyisoprene decreased due to the transfer-
agent role of AlEt3 (Table 5, entries 15-17).
The microstructures of polymers obtained were cis-1,4
ranging from 62% to 75% by using system 1a, which varied
within a narrow range of 74%-77% with system 1b.
The catalytic activities of THF-free bimetallic tetra(alkyl)
complexes 3a-c with cocatalysts AlEt3 and [Ph3C][B(C6F5)4]
were relatively low compared with monosolvated complexes
1a,b (Table 5, entries 20-22). However, the effect of the ionic
radius of the central metal ion on the catalytic activity was
consistent with 1a,b in the trend Y >> Sc g Lu. In contrast,
the polyisoprene isolated was dominated by 1,4-trans-regularity
(70%), which might be attributed to the spatial environment of
the metal center.
of isoprene than the bis-THF-solvated counterpart and the THF-
free bimetallic bis(alkyl)s. The resulting polyisoprene has a
predominant cis- or trans-configuration depending on the
initiator employed.
Experimental Section
General Methods. All reactions were carried out under a dry
and oxygen-free argon atmosphere by using Schlenk techniques or
under a nitrogen atmosphere in an MBraun glovebox. All solvents
were purified from an MBraun SPS system. Organometallic samples
for NMR spectroscopic measurements were prepared in the
1
glovebox by use of NMR tubes sealed by paraffin film. H and
13C NMR spectra were recorded on a Bruker AV400 (FT, 400 MHz
1
for H; 100 MHz for 13C) spectrometer. NMR assignments were
confirmed by 1H-1H COSY and 1H-13C HMQC experiments when
necessary. IR spectra were recorded on a VERTEX 70 FT-IR. The
molecular weight and molecular weight distribution of the polymers
were measured by a TOSOH HLC-8220 GPC. Elemental analyses
were performed at National Analytical Research Centre of Chang-
chun Institute of Applied Chemistry (CIAC). Pyrrole-2-carboxy-
aldehyde was prepared according to the literature.36
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. The crystallographic data and the
refinement of complexes 1a, 1b, 2a, 3a, and 4 are summarized in
Table 6.
The monoalkyl complexes 2a,b and the bimetallic bis(alkyl)
complex 4 were inert to the polymerization of isoprene even
when activated by borate and AlEt3 due to the absence of a
metal alkyl initiator in the former two cases and the very electron
negative metal center in the latter case (Table 5, entries 18, 19,
and 23).
Conclusion
We have demonstrated a series of rare earth metal bis(alkyl)
complexes bearing η1- or η5-coordinated pyrrolide moieties,
which have been well-defined with novel structures dependent
strongly on the ligand framework and the ionic radius of the
central metal. In the presence of AlEt3 and borate ([Ph3C]-
[B(C6F5)4]), the monomeric mono-THF-solvated bis(alkyl)
complex has exhibited a higher activity toward polymerization
2-(2,6-Me2C6H3NdCH)-C4H3NH (HL1). To a dried MeOH
solution (20 mL) of pyrrole-2-carboxyaldehyde (1.90 g, 20 mmol)
were added 2,6-dimethylaniline (2.42 g, 20 mmol) and a catalytic
(35) Zhang, L.; Suzuki, T.; Luo, Y.; Nishiura, M.; Hou, Z. Angew. Chem.,
Int. Ed. 2007, 46, 1909.
(36) Wallace, D. M.; Leung, S. H.; Senge, M. O.; Smith, K. M. J. Org.
Chem. 1993, 58, 7245.

4582 Organometallics, Vol. 26, No. 18, 2007
Yang et al.
amount of formic acid (0.25 mL) under stirring. The reaction
mixture was stirred for 4 h at room temperature. Subsequently, the
yellow solution was concentrated and cooled to -30 °C. Then some
colorless crystals precipitated, separated by filtration, and then
washed with cold methanol. Removal of the solvents afforded
2H, 5-pyr), 7.96 (s, 2H, NdCH), 9.06 ppm (br, 2H, N-H). 13C
NMR (300 MHz, CDCl3, 25 °C): δ 24.87 (2C, CMe2), 37.71 (1C,
CMe2), 70.24 (2C, NCH2), 109.86 (2C, 5-pyr), 114.92 (2C, 4-pyr),
122.66 (2C, 3-pyr), 130.69 (2C, ipso-pyr), 153.26 ppm (2C, Nd
CH). IR (KBr pellets): ν 3131, 3085, 2971, 2892, 2844, 1739, 1639,
1553, 1464, 1452, 1436, 1420, 1384, 1358, 1332, 1317, 1299, 1257,
1244, 1196, 1164, 1139, 1129, 1058, 1036, 992, 974, 941, 929,
881, 850, 788, 736, 608, 534, 445 cm-1. Anal. Calcd for C15H20N4
(%): C, 70.28; H, 7.86; N, 21.86. Found: C, 70.10; H, 7.69; N,
21.94.
1
product in 63% yield (2.50 g). H NMR (300 MHz, CDCl3, 25
°C): δ 2.18 (s, 6H, C6H3Me2), 6.26 (m, 1H, 4-pyr), 6.63 (m, 1H,
3-pyr), 6.67 (s, 1H, 5-pyr), 6.98-7.11 (m, 3H, m,p-C6H3), 7.99 (s,
1H, NdC-H), 10.35 ppm (br, 1H, N-H). 13C NMR (300 MHz,
CDCl3, 25 °C): δ 18.89 (2C, C6H3Me2), 110.41 (1C, 5-pyr), 117.38
(1C, 4-pyr), 124.47 (1C, 3-pyr), 128.68 (3C, m,p-C6H3), 128.88
(1C, ipso-pyr), 130.42 (2C, o-C6H3), 151.19 (1C, ipso-C6H3), 153.81
ppm (1C, NdCH). IR (KBr pellets): ν 3202, 2977, 2905, 2863,
1633, 1590, 1554, 1475, 1446, 1415, 1378, 1338, 1313, 1253, 1246,
1188, 1162, 1137, 1088, 1035, 973, 916, 883, 860, 833, 793, 767,
743, 731, 607, 527, 502, 422 cm-1. Anal. Calcd for C13H14N2 (%):
C, 78.75; H, 7.12; N, 14.13. Found: C, 78.54; H, 7.07; N, 14.33.
[2-(2,6-Me2C6H3NdCH)-C4H3N]Lu(CH2SiMe3)2(THF)2 (1a).
To a toluene solution (5.0 mL) of Lu(CH2SiMe3)3(THF)2 (0.210 g,
0.362 mmol), equivalent HL1 (0.071 g, 0.360 mmol in 2 mL
toluene) was dropwise added at room temperature. The mixture
was then stirred for 1 h. Removal of the volatiles gave a deep red
oily residue. The residue was dissolved with 3 mL of hexane and
then cooled to -30 °C for 12 h to give colorless solids, which
were washed carefully by a small amount of hexane (0.5 mL) and
then dried under vacuum to afford complex 1a in 64% yield (0.160
g). Colorless single crystals for X-ray analysis grew from hexane
at -30 °C within a day. 1H NMR (400 MHz, C6D6, 25 °C, 1a and
its enantiomer): -0.81, -0.70 (s, 4H, CH2SiMe3), -0.64 (s, 4H,
CH2SiMe3), 0.18 (s, 6H, CH2SiMe3), 0.37 (s, 30H, CH2SiMe3), 1.34
(s, 16H, THF), 1.98, 2.14 (s, 12H, C6H3Me2), 3.78 (s, 16H, THF),
6.56, 6.63 (s, 2H, 4-pyr), 6.92 (m, 2H, 3-pyr), 6.99 (s, 4H, m-C6H3),
7.05 (m, 2H, p-C6H3), 7.13, 7.68 (s, 2H, 5-pyr), 7.42, 7.43 ppm (s,
2H, NdC-H). 13C NMR (100 MHz, C6D6, 25 °C): δ 5.13 (m,
12C, CH2SiMe3), 18.87, 19.31 (s, 4C, C6H3Me2), 25.71 (s, 8C,
THF), 39.58, 42.23 (s, 4C, CH2SiMe3), 71.07 (s, 8C, THF), 113.76,
113.82 (s, 2C, 4-pyr), 121.99 (s, 2C, 3-pyr), 122.90 (s, 2C, 5-pyr),
125.45, 125.77 (s, 2C, p-C6H3), 129.08 (s, 4C, m-C6H3), 130.76,
131.72 (s, 4C, o-C6H3), 139.38, 139.51 (s, 2C, ipso-pyr), 150.56
(s, 2C, ipso-C6H3), 163.58, 164.46 ppm (s, 2C, CHdN). IR (KBr
pellets): ν 2949, 1598, 1575, 1463, 1440, 1390, 1340, 1305, 1234,
1198, 1174, 1094, 1036, 1018, 981, 857, 779, 746, 705, 667, 610,
575, 533, 494 cm-1. Anal. Calcd for C29H51N2O2Si2Lu (%): C,
50.42; H, 7.44; N, 4.05. Found: C, 50.19; H, 7.23; N, 4.29.
2-(2,6-iPr2C6H3NdCH)-C4H3NH (HL2). To a dried MeOH
solution (20 mL) of pyrrole-2-carboxyaldehyde (1.90 g, 20 mmol)
were added 2,6-diisopropylaniline (3.6 g, 20 mmol) and a catalytic
amount of formic acid (0.25 mL) under stirring. The reaction
mixture was stirred for 4 h at room temperature. Subsequently, the
white precipitate was separated by filtration and then washed with
cold methanol. Removal of the solvents afforded HL2 in 74% yield
1
(3.75 g). H NMR (300 MHz, CDCl3, 25 °C): δ 1.12 (d, JH-H
)
6.9 Hz, 12H, CHMe2), 3.06 (hepta, JH-H ) 6.9 Hz, 2H, CHMe2),
6.20 (m, 1H, 4-pyr), 6.49 (s, 1H, 3-pyr), 6.60 (t, 1H, 5-pyr), 7.15
(m, 3H, m,p-C6H3), 7.95 (s, 1H, NdC-H), 10.39 ppm (br, 1H,
N-H). 13C NMR (300 MHz, CDCl3, 25 °C): δ 24.03 (4C, CHMe2),
28.35 (2C, CHMe2), 110.31 (1C, 5-pyr), 117.14 (1C, 4-pyr), 123.65
(1C, 3-pyr), 124.61 (2C, m-C6H3), 124.97 (1C, p-C6H3), 130.33
(1C, ipso-pyr), 139.43 (2C, o-C6H3), 148.92 (1C, ipso-C6H3), 153.16
ppm (1C, NdCH). IR (KBr pellets): ν 3235, 3060, 2964, 2926,
2869, 1628, 1586, 1554, 1458, 1418, 1384, 1363, 1338, 1311, 1253,
1181, 1133, 1108, 1089, 1056, 1033, 932, 883, 860, 832, 803, 781,
760, 746, 607 cm-1. Anal. Calcd for C17H22N2 (%): C, 80.27; H,
8.72; N, 11.01. Found: C, 80.54; H, 8.07; N, 10.93.
2-(Me2NCH2)-C4H3NH (HL3). A solution of 17 g (0.21 mol)
of dimethylamine hydrochloride in 15.8 g (0.21 mol) of 40%
formalin was added slowly to 13.4 g (0.20 mol) of pyrrole over 60
min. Stirring was continued for 1 h after the addition was completed.
It was then poured into 100 mL of 25% sodium hydroxide solution
and extracted with ether (3 × 50 mL). The combined ether extracts
were washed with water (2 × 20 mL) and dried over anhydrous
sodium sulfate. The ether was removed, and the residue was distilled
at reduced pressure. The product was collected at 60-80 °C (0.5
mm) and crystallized in the receiver in the form of white crystals.
[2-(2,6-Me2C6H3NdCH)-C4H3N]Sc(CH2SiMe3)2(THF) (1b).
Following a procedure similar to that described for the preparation
of 1a, treatment of a toluene solution (5.0 mL) of Sc(CH2SiMe3)3-
(THF)2 (0.205 g, 0.455 mmol) with 1 equiv of HL1 (0.090 g, 0.455
mmol in 2 mL of toluene) afforded complex 1b (0.185 g, 83%).
1H NMR (400 MHz, C6D6, 25 °C): δ 0.33 (s, 18H, CH2SiMe3),
0.45 (s, 4H, CH2SiMe3), 1.12 (s, 4H, THF), 2.10 (s, 6H, C6H3Me2),
3.68 (s, 4H, THF), 6.61 (m, 1H, 4-pyr), 6.90 (m, 1H, 3-pyr), 6.92
(m, 3H, m, p-C6H3), 7.13 (s, 1H, 5-pyr), 7.95 ppm (s, 1H, NdC-
H). 13C NMR (100 MHz, C6D6, 25 °C): δ 4.11 (s, 6C, CH2SiMe3),
19.69 (s, 2C, C6H3Me2), 25.09 (s, 2C, THF), 47.21 (br, 2C,
CH2SiMe3), 71.66 (s, 2C, THF), 114.03 (s, 1C, 4-pyr), 122.67 (s,
1C, 3-pyr), 125.87 (s, 1C, 5-pyr), 126.55 (s, 1C, p-C6H3), 128.95
(s, 2C, m-C6H3), 131.54 (s, 2C, o-C6H3), 140.45 (s, 1C, 2-pyr),
149.66 (s, 1C, ipso-C6H3), 163.86 ppm (s, 1C, CHdN). IR (KBr
pellets): ν 3649, 3218, 2950, 2895, 2855, 1628, 1598, 1577, 1496,
1467, 1444, 1390, 1342, 1297, 1263, 1248, 1178, 1134, 1091, 1037,
984, 896, 883, 860, 795, 769, 745, 683, 605, 577, 536, 473, 433
cm-1. Anal. Calcd for C25H43N2OSi2Sc (%): C, 61.42; H, 8.87; N,
5.73. Found: C, 61.53; H, 8.61; N, 5.70.
[2-(2,6-iPr2C6H3NdCH)-C4H3N]2Lu(CH2SiMe3)(THF) (2a).
To a toluene solution (5.0 mL) of Lu(CH2SiMe3)3(THF)2 (0.235 g,
0.405 mmol) was added dropwise 1 equiv of HL2 (0.103 g, 0.405
mmol in 2 mL of toluene) at room temperature. The mixture was
then stirred for 1 h. Removal of the volatiles gave a deep yellow,
oily residue. The residue was dissolved with 3 mL of hexane and
then cooled to -30 °C for 12 h to give colorless solids, which
were washed carefully by a small amount of hexane (0.5 mL) and
then dried under vacuum to afford complex 2a in 36% yield (0.121
g). Colorless single crystals for X-ray analysis grew from hexane
1
The yield was 9.6 g (39%). H NMR (300 MHz, CDCl3, 25 °C):
δ 2.24 (s, 6H, NMe2), 3.43 (s, 2H, CH2N), 6.03 (s, 1H, 3-pyr),
6.10 (m, 1H, 4-pyr), 6.70 (s, 1H, 5-pyr), 9.40 ppm (br, 1H, N-H).
13C NMR (300 MHz, CDCl3, 25 °C): δ 45.41 (2C, NMe2), 57.17
(1C, CH2N), 107.83 (1C, 3-pyr), 108.27 (1C, 4-pyr), 118.63 (1C,
5-pyr), 129.32 ppm (1C, ipso-pyr). IR (KBr pellets): ν 3184, 3090,
2981, 2949, 2909, 2861, 2826, 2782, 2707, 2609, 1714, 1586, 1507,
1469, 1456, 1407, 1355, 1306, 1264, 1252, 1237, 1176, 1155, 1131,
1095, 1038, 1022, 1011, 968, 885, 842, 717, 639, 614, 461, 408
cm-1. Anal. Calcd for C7H12N2 (%): C, 67.70; H, 9.74; N, 22.56.
Found: C, 67.45; H, 9.88; N, 22.83.
2-C4H3NH-CHdNCH2CMe2CH2NdCH-2-C4H3NH (H2L4).
To a dried MeOH solution (10 mL) of pyrrole-2-carboxyaldehyde
(3.10 g, 32.6 mmol) was added 2,2-dimethyl-1,3-propanediamine
(1.66 g, 16.3 mmol) under stirring. The reaction mixture was stirred
for 4 h at room temperature. Subsequently, the white precipitate
was separated by filtration and then washed with cold methanol.
1
Removal of the solvents afforded H2L4 in 76% yield (3.2 g). H
NMR (300 MHz, CDCl3, 25 °C): δ 0.93 (s, 6H, CMe2), 3.41 (s,
4H, NCH2), 6.22 (m, 2H, 4-pyr), 6.44 (m, 2H, 3-pyr), 6.85 (m,

Pyrrolide-Supported Lanthanide Alkyl Complexes
Organometallics, Vol. 26, No. 18, 2007 4583
1
at -30 °C within a day. H NMR (400 MHz, C6D6, 25 °C): δ
treatment of a toluene solution (5.0 mL) of Lu(CH2SiMe3)3(THF)2
(0.210 g, 0.361 mmol) with 1 equiv of HL3 (0.046 g, 0.367 mmol
in 2 mL of toluene) afforded complex 3b (0.247 g, 72%). 1H NMR
(400 MHz, C6D6, 25 °C): δ -1.10, -1.08 (s, 2H, CH2SiMe3),
-0.93, -0.91 (s, 2H, CH2SiMe3), -0.86, -0.83 (s, 2H, CH2SiMe3),
-0.71, -0.68 (s, 2H, CH2SiMe3), 0.31, 0.41, 0.43, 0.49 (s, 36H,
CH2SiMe3), 1.91, 1.98, 2.08, 2.32 (s, 12H, NMe2), 2.91, 2.95, 3.78,
4.10 (d, J ) 12.0 Hz, 4H, CH2N), 6.42 (s, 1H, 3-pyr), 6.54 (s, 2H,
3-pyr, 5-pyr), 6.69 (s, 2H, 4-pyr, 5-pyr), 6.84 ppm (s, 1H, 4-pyr).
13C NMR (100 MHz, C6D6, 25 °C): δ 4.94, 5.31 (s, 12C,
CH2SiMe3), 35.93 (s, 1C, CH2SiMe3), 39.45, 39.64 (s, 2C,
CH2SiMe3), 42.34 (s, 1C, CH2SiMe3), 43.53, 46.08, 48.43, 50.41
(s, 4C, NMe2), 60.19, 61.58 (s, 2C, CH2N), 111.62, 113.41 (s, 2C,
3-pyr), 115.82, 116.84 (s, 2C, 5-pyr), 126.65, 127.72 (s, 2C, 4-pyr),
135.03, 139.68 ppm (s, 2C, ipso-pyr). IR (KBr, pellets): ν 3095,
2947, 2880, 2865, 2816, 2799, 1583, 1465, 1434, 1424, 1408, 1350,
1297, 1267, 1245, 1233, 1171, 1157, 1146, 1102, 1035, 1004, 977,
963, 858, 782, 746, 714, 673, 629, 450 cm-1. Anal. Calcd for
C30H66N4Si4Lu2 (%): C, 38.12; H, 7.04; N, 5.93. Found: C, 38.03;
H, 7.33; N, 5.66.
-0.49 (s, 2H, CH2SiMe3), 0.18 (s, 9H, CH2SiMe3), 0.98-1.33 (m,
24H, CHMe2), 1.36 (s, 4H, THF), 3.25 (m, 4H, CHMe2), 3.79 (s,
4H, THF), 6.47 (br, 2H, 3-pyr), 6.88 (br, 2H, 4-pyr), 7.17 (s, 2H,
5-pyr), 7.19 (s, 6H, m,p-C6H3), 7.83 ppm (s, 2H, NdC-H). 13C
NMR (100 MHz, C6D6, 25 °C): δ 4.87 (s, 3C, SiMe3), 23.50, 29.00
(s, 4C, CHMe2), 26.02, 26.58 (s, 8C, CHMe2), 26.34 (s, 2C, THF),
32.63 (s, 1C, CH2SiMe3), 71.14 (br, 2C, THF), 114.17 (s, 4C, 3,4-
pyr), 123.48 (br, 2C, 5-pyr), 124.37 (s, 4C, m-C6H3), 127.00 (s,
2C, p-C6H3), 137.38 (2C, ipso-pyr), 140.18 (s, 2C, o-C6H3), 142.61
(s, 2C, o-C6H3), 148.27 (s, 2C, ipso-C6H3), 164.45 ppm (s, 2C,
NdCH). IR (KBr pellets): ν 2963, 1594, 1575, 1485, 1461, 1441,
1391, 1362, 1343, 1321, 1299, 1260, 1235, 1168, 1109, 1033, 1012,
983, 934, 881, 857, 804, 786, 748, 708, 668, 607, 564, 469, 434
cm-1. Anal. Calcd for C42H59N4OSiLu (%): C, 60.13; H, 7.09; N,
6.68. Found: C, 60.16; H, 7.23; N, 6.50.
[2-(2,6-iPr2C6H3NdCH)-C4H3N]2Sc(CH2SiMe3)(THF) (2b).
Following a procedure similar to that described for the preparation
of 2a, treatment of a toluene solution (5.0 mL) of Sc(CH2SiMe3)3-
(THF)2 (0.176 g, 0.390 mmol) with 1 equiv of HL2 (0.099 g, 0.390
mmol in 2 mL of toluene) afforded complex 2b (0.105 g, 38%).
1H NMR (400 MHz, C6D6, 25 °C): δ 0.28 (s, 9H, CH2SiMe3),
0.44 (s, 2H, CH2SiMe3), 0.72, 0.96, 0.98, 1.08, 1.10, 1.14, 1.24,
1.55 (d, J ) 6.8 Hz, 24H, CHMe2), 1.32 (s, 4H, THF), 3.26, 3.77
(sept, J ) 6.8 Hz, 4H, CHMe2), 3.96 (s, 4H, THF), 6.15, 6.40 (m,
2H, 3-pyr), 6.48, 6.68 (s, 2H, 4-pyr), 6.82, 7.07 (s, 2H, 5-pyr),
7.20-7.26 (m, 6H, m,p-C6H3), 7.67 ppm (s, 2H, NdC-H). 13C
NMR (100 MHz, C6D6, 25 °C): δ 3.38 (s, 3C, SiMe3), 23.06, 23.50,
23.81, 26.65 (s, 4C, CHMe2), 14.79, 21.90, 24.32, 25.98, 26.27,
28.41, 29.22, 30.40 (s, 8C, CHMe2), 25.65 (s, 2C, THF), 32.41 (s,
1C, CH2SiMe3), 72.45 (br, 2C, THF), 114.11 (s, 2C, 3-pyr), 123.19
(s, 2C, 4-pyr), 124.23 (s, 2C, 5-pyr), 124.48 (s, 4C, m-C6H3), 127.49
(s, 2C, p-C6H3), 139.81 (2C, ipso-pyr), 142.51 (s, 2C, o-C6H3),
143.10 (s, 2C, o-C6H3), 145.86 (s, 2C, ipso-C6H3), 163.81 ppm (s,
2C, NdCH). IR (KBr pellets): ν 3225, 3064, 2962, 2927, 2868,
1627, 1595, 1576, 1461, 1445, 1419, 1392, 1363, 1340, 1325, 1296,
1247, 1172, 1135, 1108, 1092, 1058, 1036, 985, 960, 934, 898,
883, 861, 803, 781, 746, 680, 605, 473 cm-1. Anal. Calcd for
C42H59N4OSiSc (%): C, 71.15; H, 8.39; N, 7.90. Found: C, 71.53;
H, 8.11; N, 8.01.
[(2-(Me2NCH2)-C4H3N)Sc(CH2SiMe3)2]2 (3c). Following a
procedure similar to that described for the preparation of 3a,
treatment of a toluene solution (5.0 mL) of Sc(CH2SiMe3)3(THF)2
(0.178 g, 0.395 mmol) with 1 equiv of HL3 (0.049 g, 0.395 mmol
in 2 mL of toluene) afforded complex 3c (0.179 g, 66%). 1H NMR
(400 MHz, C6D6, 25 °C): δ -0.65, -0.46, -0.22, -0.12 (s, 8H,
CH2SiMe3), 0.46 (s, 36H, CH2SiMe3), 2.13, 2.25, 2.31, 2.38 (s,
12H, NMe2), 3.00, 3.10, 3.89, 4.12 (s, 4H, CH2N), 6.49 (s, 1H,
3-pyr), 6.72 (br, 4H, 3, 4, 5-pyr), 7.05 ppm (s, 1H, 4-pyr). 13C
NMR (100 MHz, C6D6, 25 °C): δ 4.53, 4.81 (s, 12C, CH2SiMe3),
60.70 (s, 2C, CH2N), 106.75 (s, 2C, 3-pyr), 109.08 (s, 2C, 5-pyr),
126.06 (s, 2C, 4-pyr), 134.79 (s, 2C, ipso-pyr). IR (KBr, pellets):
ν 3092, 2949, 2868, 2833, 1560, 1466, 1444, 1405, 1347, 1305,
1248, 1237, 1178, 1157, 1135, 1098, 1038, 1026, 1002, 969, 881,
854, 792, 743, 721, 672, 619, 456, 426, 410 cm-1. Anal. Calcd for
C30H66N4Si4Sc2 (%): C, 52.59; H, 9.71; N, 8.18. Found: C, 52.16;
H, 9.33; N, 8.47.
[2-C4H3N-CHdNCH2CMe2CH2NdCH-2-C4H3N]2Lu2-
(CH2SiMe3)2 (4). To a toluene solution (5.0 mL) of Lu(CH2SiMe3)3-
(THF)2 (0.230 g, 0.396 mmol) was dropwise added 1 equiv of H2L4
(0.101 g, 0.394 mmol in 2 mL of toluene) at room temperature.
The mixture was then stirred for 5 h. Removal of the volatiles gave
a yellow oil, which was dissolved in a small amount of hexane
(0.5 mL) and then cooled to -30 °C to afford complex 4 (yellow
solids) in 65% yield (0.265 g). Colorless single crystals for X-ray
analysis grew from hexane at -30 °C within a few days. 1H NMR
(400 MHz, C6D6, 25 °C): δ -1.06, -1.03, -0.88, -0.85 (s, 4H,
CH2SiMe3), 0.29 (s, 6H, C(CH3)2), 0.42 (s, 18H, CH2SiMe3), 0.67
(s, 6H, C(CH3)2), 2.38, 2.58, 2.66, 1.54 (d, J ) 12.0 Hz, 8H, NCH2),
6.60 (m, 4H, 3-pyr), 6.72, 6.84 (m, 4H, 4-pyr), 7.09, 7.20 (s, 4H,
5-pyr), 7.46, 7.77 (s, 4H, NdC-H). 13C NMR (100 MHz, C6D6,
25 °C): δ 5.12 (s, 6C, CH2SiMe3), 22.35, 26.76 (s, 4C, C(CH3)2),
25.67 (s, 2C, C(CH3)2), 36.70, 38.12 (s, 2C, CH2SiMe3), 68.56,
72.27 (s, 4C, NCH2), 111.51, 116.40 (s, 4C, 3-pyr), 117.46, 119.94
(s, 4C, 4-pyr), 131.87, 137.16 (s, 4C, 5-pyr), 135.49, 138.71 (s,
4C, ipso-pyr), 160.30, 160.64 ppm (s, 4C, CHdN). IR (KBr,
pellets): ν 3602, 3246, 3100, 2954, 2894, 2842, 1626, 1606, 1508,
1470, 1440, 1397, 1389, 1366, 1355, 1324, 1293, 1249, 1078, 1034,
977, 894, 862, 811, 794, 742, 694, 613 cm-1. Anal. Calcd for
C45H66N8Si2Lu2 (%): C, 48.04; H, 5.91; N, 9.96. Found: C, 48.40;
H, 5.53; N, 10.05.
[(2-(Me2NCH2)-C4H3N)Y(CH2SiMe3)2]2 (3a). To a toluene
solution (5.0 mL) of Y(CH2SiMe3)3(THF)2 (0.185 g, 0.374 mmol)
was dropwise added 1 equiv of HL3 (0.046 g, 0.374 mmol in 2
mL of toluene) at room temperature. The mixture was then stirred
for 5 h. Removal of the volatiles gave white solids, which were
washed carefully by a small amount of hexane (0.5 mL) and then
dried under vacuum to afford complex 3a in 59% yield (0.086 g).
Colorless single crystals for X-ray analysis grew from toluene at
-30 °C within a day. 1H NMR (400 MHz, C6D6, 25 °C): δ -0.86,
-0.70, -0.64, -0.44 (d, JY-C-H ) 8.0 Hz, 8H, CH2SiMe3), 0.33,
0.41, 0.43, 0.49 (s, 36H, CH2SiMe3), 1.94, 1.97, 2.08, 2.29 (s, 12H,
NMe2), 2.89, 2.95, 3.76, 4.14 (d, J ) 15.2 Hz, 4H, CH2N), 6.48,
6.55 (s, 2H, 3-pyr), 6.60, 6.70 (s, 2H, 5-pyr), 6.73, 6.88 ppm (s,
2H, 4-pyr). 13C NMR (100 MHz, C6D6, 25 °C): δ 4.83, 5.10, 5.20
(s, 12C, CH2SiMe3), 31.41 (d, JY-C ) 41.4 Hz, 1C, CH2SiMe3),
35.00 (d, JY-C ) 36.8 Hz, 1C, CH2SiMe3), 35.77 (d, JY-C ) 40.8
Hz, 1C, CH2SiMe3), 38.16 (d, JY-C ) 38.4 Hz, 1C, CH2SiMe3),
43.37, 45.16, 48.35, 50.16 (s, 4C, NMe2), 59.90, 61.27 (s, 2C,
CH2N), 112.19, 113.35 (s, 2C, 3-pyr), 115.91, 116.50 (s, 2C, 5-pyr),
126.80, 127.99 (s, 2C, 4-pyr), 135.71, 139.84 ppm (s, 2C, ipso-
pyr). IR (KBr, pellets): ν 3098, 2945, 2885, 2867, 2817, 2798,
1583, 1468, 1438, 1424, 1409, 1350, 1299, 1267, 1248, 1236, 1176,
1157, 1146, 1100, 1037, 1005, 977, 964, 854, 789, 740, 714, 671,
625, 453 cm-1. Anal. Calcd for C30H66N4Si4Y2 (%): C, 46.61; H,
8.61; N, 7.25. Found: C, 46.50; H, 8.33; N, 7.36.
Isoprene Polymerization. A detailed polymerization procedure
(Table 5, entry 4) is described as a typical example. In a glovebox,
the monomer (1.0 mL, 10 mmol) was added into a 25 mL flask.
Then, 3 equiv of AlEt3 (4.1 µL, 0.05 mmol), a toluene solution
(5.0 mL) of 1a (6.9 mg, 0.01 mmol), and 1 equiv of [Ph3C]-
[B(C6F5)4] (9.6 mg, 0.01 mmol) were added to the flask. After the
[(2-(Me2NCH2)-C4H3N)Lu(CH2SiMe3)2]2 (3b). Following a
procedure similar to that described for the preparation of 3a,

4584 Organometallics, Vol. 26, No. 18, 2007
Yang et al.
reaction was stirred for 5 h, the flask was moved outside. Methanol
was injected to terminate the polymerization. The reaction mixture
was poured into a large quantity of methanol and then dried under
vacuum at ambient temperature to constant weight.
Science and Technology of China for Project No. 2005CB623802;
and the “Hundred Talent Scientist Program” of CAS.
Supporting Information Available: CIF files and crystal-
lographic data for 1a, 1b, 2, 3a, and 4 including atomic coordinates,
full bond distances, and bond angles as well as anisotropic thermal
parameters are available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. We acknowledge financial support from
Jilin Provincial Science and Technology Bureau for Project No.
20050555; The National Natural Science Foundation of China
for Project Nos. 20571072 and 20674081; The Ministry of
OM7003095