Selective formation of homoleptic and heteroleptic 2,5-bis(N-aryliminomethyl)pyrrolyl yttrium complexes and their performance as initiators of ε-caprolactone polymerization

Article abstract of DOI:10.1021/om0101846

Tridentate 2,5-bis(N-aryliminomethyl)pyrroles (1a, aryl = 4-methoxylphenyl; 1b, aryl = 4-methylphenyl; 1c, aryl = 2-methylphenyl; 1d, aryl = 2,6-dimethylphenyl; 1e, aryl = 2,6-diisopropylphenyl) have been prepared, and their reactions with a homoleptic Y{N(SiMe₃)₂}₃ (2) have been investigated. The number of pyrrolyl ligands introduced to an yttrium atom can be controlled by varying the bulkiness of the ligand to give mono(pyrrolyl) (3), bis(pyrrolyl) (4), or tris(pyrrolyl) complexes (5) upon aminolysis. When bulky ligands such as 1d and 1e were used, a mono(pyrrolyl) complex Y(Xyl₂-pyr){N(SiMe₃)₂}₂ (3d, Xyl₂-pyr = 2,5-bis{N-(2,6-dimethylphenyl)iminomethyl}pyrrolyl) and a bis(pyrrolyl) complex Y(DIP₂-pyr)₂{N(SiMe₃)₂} (4e, DIP₂-pyr = 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl) were predominantly obtained, respectively, with the release of hexamethyldisilazane. Both complexes adopt five-coordination geometries, a distorted trigonal bipyramidal mode for 3d and a distorted square-pyramidal one for 4e, in which the N,N′-bidentate coordination of 1e to the yttrium atom was found in solution and the solid state presumably due to the bulkiness of the isopropyl substituents. In the case of p-substituted ligands, 1a and 1b, we obtained homoleptic tris-(pyrrolyl) yttrium complexes 5a and 5b, respectively. The complex 5a has three N,N′,N″-tridentate pyrrolyl ligands, and the yttrium center adopts a three-face-centered trigonal prismatic mode of nine-coordination, while we found the eight-coordinated, square-antiprismatic geometry for 5b with two N,N′,N″-tridentate and one N,N′-bidentate pyrrolyl ligand. Thus, we demonstrated that the yttrium atom was able to have a five-, eight-, and nine-coordination number, depending on the congestion by the bis(aryliminomethyl)pyrrolyl ligands. We also found that these newly prepared mono(pyrrolyl) (3d) and bis(pyrrolyl) (4e) complexes catalyzed polymerization of ε-caprolactone and that complex 4e acted as a single-site catalyst to give a polyester with a narrow molecular weight distribution (M_w/M_n = 1.2).

Full text of DOI:10.1021/om0101846

3510
Organometallics 2001, 20, 3510-3518
Selective F or m a tion of Hom olep tic a n d Heter olep tic
2,5-Bis(N-a r ylim in om eth yl)p yr r olyl Yttr iu m Com p lexes
a n d Th eir P er for m a n ce a s In itia tor s of E-Ca p r ola cton e
P olym er iza tion
Yutaka Matsuo, Kazushi Mashima,* and Kazuhide Tani
Department of Chemistry, Graduate School of Engineering Science, Osaka University
Toyonaka, Osaka 560-8531, J apan
Received March 8, 2001
Tridentate 2,5-bis(N-aryliminomethyl)pyrroles (1a , aryl ) 4-methoxylphenyl; 1b, aryl )
4-methylphenyl; 1c, aryl ) 2-methylphenyl; 1d , aryl ) 2,6-dimethylphenyl; 1e, aryl ) 2,6-
diisopropylphenyl) have been prepared, and their reactions with a homoleptic Y{N(SiMe3)2}3
(2) have been investigated. The number of pyrrolyl ligands introduced to an yttrium atom
can be controlled by varying the bulkiness of the ligand to give mono(pyrrolyl) (3), bis(pyrrolyl)
(4), or tris(pyrrolyl) complexes (5) upon aminolysis. When bulky ligands such as 1d and 1e
were used, a mono(pyrrolyl) complex Y(Xyl2-pyr){N(SiMe3)2}2 (3d , Xyl2-pyr ) 2,5-bis{N-(2,6-
dimethylphenyl)iminomethyl}pyrrolyl) and a bis(pyrrolyl) complex Y(DIP2-pyr)2{N(SiMe3)2}
(4e, DIP2-pyr ) 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl) were predominantly
obtained, respectively, with the release of hexamethyldisilazane. Both complexes adopt five-
coordination geometries, a distorted trigonal bipyramidal mode for 3d and a distorted square-
pyramidal one for 4e, in which the N,N′-bidentate coordination of 1e to the yttrium atom
was found in solution and the solid state presumably due to the bulkiness of the isopropyl
substituents. In the case of p-substituted ligands, 1a and 1b, we obtained homoleptic tris-
(pyrrolyl) yttrium complexes 5a and 5b, respectively. The complex 5a has three N,N′,N′′-
tridentate pyrrolyl ligands, and the yttrium center adopts a three-face-centered trigonal
prismatic mode of nine-coordination, while we found the eight-coordinated, square-
antiprismatic geometry for 5b with two N,N′,N′′-tridentate and one N,N′-bidentate pyrrolyl
ligand. Thus, we demonstrated that the yttrium atom was able to have a five-, eight-, and
nine-coordination number, depending on the congestion by the bis(aryliminomethyl)pyrrolyl
ligands. We also found that these newly prepared mono(pyrrolyl) (3d ) and bis(pyrrolyl) (4e)
complexes catalyzed polymerization of ꢀ-caprolactone and that complex 4e acted as a single-
site catalyst to give a polyester with a narrow molecular weight distribution (Mw/Mn ) 1.2).
In tr od u ction
â-diketiminates,18aminotroponiminates,19diamidoligands,20
and oligopyrrolyl ligands21,22 have been utilized for
preparing lanthanide and yttrium complexes. We have
been interested in the pyrrolyl derivatives as nitrogen-
based polydentate ancillary ligands for early transition
metals, and we and the other group prepared 2-(N-
aryliminomethyl)pyrrolyl complexes of group 4 metals
as catalyst precursors for ethylene polymerization.23,24
As an extension of our continuous interest in the
Recent development of organolanthanide chemistry
enables us to design the ligand environments of lan-
thanide complexes for efficient or selective catalysts.1,2
In the past two decades, extensive studies directed to
organic transformation reactions3-7 and polymeriza-
tions8-15 have been carried out using metallocene and
half-metallocene complexes of lanthanide and group 3
metals. As tunable ancillary ligands, nitrogen-based
polydentate ligands16 are anticipated to be alternatives
of cyclopentadienyl-based ligands in organolanthanide
and yttrium chemistry. For example, benzamidinates,17
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* Corresponding author. E-mail: mashima@chem.es.osaka-u.ac.jp.
Fax: 81-6-6850-6296.
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10.1021/om0101846 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/03/2001

Initiators of ꢀ-Caprolactone Polymerization
Organometallics, Vol. 20, No. 16, 2001 3511
Ch a r t 1
Tridentate ligands, 2,5-bis(N-aryliminomethyl)pyrroles
1a -e (Chart 1), were prepared by condensation reaction
of 2,5-diformylpyrrole with 2 equiv of the corresponding
aniline derivative. A series of yttrium complexes having
the tridentate ligand was conveniently obtained by
amine elimination reaction starting from a homoleptic
triamido complex Y{N(SiMe3)2}3 (2). Three kinds of
yttrium complexes, heteroleptic mono(pyrrolyl) (3) and
bis(pyrrolyl) (4) complexes and homoleptic tris(pyrrolyl)
complexes (5), are possible; however, the number of
pyrrolyl ligands bound to the yttrium atom can be
controlled in some cases by changing the congestion of
two aromatic rings of the ligand. Treatment of 2 with 1
equiv of 2,5-bis{N-(2,6-dimethylphenyl)iminomethyl}-
pyrrole (1d ) in toluene predominantly afforded a yellow,
air and moisture sensitive yttrium mono(pyrrolyl) com-
plex, Y(Xyl2-pyr){N(SiMe3)2}2 (3d , Xyl2-pyr ) 2,5-bis-
{N-(2,6-dimethylphenyl)iminomethyl}pyrrolyl) in 82%
yield along with the release of hexamethyldisilazane (eq
1). Complex 3d was found to be inert to further reaction
with 1d even at elevated temperature (50 °C).
pyrrolyl ligand system, we prepared tridentate bis-
(iminomethyl)pyrrolyl ligands (Chart 1) and their yt-
trium complexes. In this paper we report the selective
formation of homoleptic and heteroleptic pyrrolyl com-
plexes of yttrium, whose unique coordination modes
have been elucidated by crystallographic studies. Fur-
thermore, we demonstrate that the heteroleptic pyrrolyl
complexes have a capability to polymerize ꢀ-caprolactone
to give polyesters with narrow molecular weight distri-
butions.
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of 2,5-Bis(N-
a r ylim in om eth yl)p yr r olyl Com p lexes of Yttr iu m .
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3512 Organometallics, Vol. 20, No. 16, 2001
Matsuo et al.
than that of 1d (δ 152.0). These findings indicate that
the pyrrolyl ligand coordinated to the yttrium metal in
a tridentate N,N′,N′′-meridional fashion, as confirmed
by X-ray analysis (vide infra).
In the case of the much bulkier ligand 1e, a bis-
(pyrrolyl) complex Y(DIP2-pyr)2{N(SiMe3)2} [4e, DIP2-
pyr ) 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}-
pyrrolyl] formed selectively regardless of the molar ratio
of 1e and 2, and hence a maximum yield was obtained
when 2 was treated with 2 equiv of 1e (eq 2). The two
In sharp contrast to 1d and 1e, complexation of 2,5-
bis{N-(2-methylphenyl)iminomethyl}pyrrole (1c, o-Tol2-
pyrH) to a yttrium atom could not be controlled.
Reaction of 1c with 1 equiv of 2 in toluene gave a 4:1
mixture of a mono(pyrrolyl) complex, Y(o-Tol2-pyr)-
{N(SiMe3)2}2 (3c), and a bis(pyrrolyl) complex, Y(o-Tol2-
pyr)2{N(SiMe3)2} (4c), from which we isolated 3c after
recrystallization. Unlike the complex 4e, although 4c
was characterized only by NMR spectroscopy, both of
the two pyrrolyl ligands of 4c coordinated to the yttrium
metal in an N,N′,N′′-meridional fashion.
Much less bulky tridentate pyrrolyl ligands having
p-substituted phenyl groups, 2,5-bis(4-methoxylphe-
nyliminomethyl)pyrrole (1a , An2-pyrH) and 2,5-bis(4-
methylphenyliminomethyl)pyrrole (1b, p-Tol2-pyrH), led
to the formation of homoleptic tris(pyrrolyl) complexes,
Y(An2-pyr)3 (5a ) and Y(p-Tol2-pyr)3 (5b), respectively.
In all cases when 1 or 2 equiv of 1a and 1b per 2 was
used, small amounts of the corresponding mono(pyrro-
lyl) and bis(pyrrolyl) complexes were contaminated, but
the reaction of 2 with 3 equiv of 1a and 1b gave,
bulky pyrrolyl ligands of 4e coordinated to the yttrium
metal as N,N′-bidentate ones, as revealed by the 1H
NMR spectrum; one imino proton was observed at
higher field (δ 7.37) and the other at lower field (δ 8.21)
compared with that of the free ligand (δ 7.81), indicating
that one of the two NdCH moieties coordinated to the
yttrium atom and the other is free from coordination.
The pyrrolyl ring protons were accordingly observed as
an ABq pattern (δ 6.18 for 3-pyr and δ 5.62 for 4-pyr)
with a coupling constant (3.7 Hz). This complexation
was further supported by a 2D 1H-1H NOESY mea-
surement: the proton of the imino group bound to the
metal center correlated with the neighboring pyrrolyl
ring proton, while the proton of the noncoordinating
imino group correlated with the SiMe3 group of the
amido ligand instead of the pyrrolyl proton. The number
of ligands coordinated to the metal was thus controlled
to be two, as a result of the steric congestion of 1e, whose
two bulky arylimino moieties prevented the tridentate
N,N′,N′′-coordination. It is noteworthy that one bulky
arylimino substituent was not enough to keep the
complexation found for 4e. When 2 reacted with 2 equiv
of an iminopyrrolyl ligand, 2-{N-(2,6-diisopropylphenyl)-
iminomethyl}pyrrole (6, DIP-pyrH) instead of 1e, we
obtained a mixture of a bis(pyrrolyl) complex Y(DIP-
pyr)2{N(SiMe3)2} (7) and a homoleptic complex Y(DIP-
pyr)3 (8); the latter complex was obtained quantitatively
upon treating 2 with 3 equiv of 6.
1
respectively, 5a and 5b in quantitative yields. The H
NMR spectra of 5a and 5b displayed a symmetric signal
pattern of the pyrrolyl ligand with a higher chemical
shift value of the imino proton compared with that of
the free ligand (δ 7.90 for 1a and δ 7.60 for 5a ; δ 8.02
for 1b and δ 7.57 for 5b). The 13C NMR spectra of these
complexes also displayed a single resonance due to the
imino carbon at lower field (δ 160.2 for 5a and δ 160.4
1
for 5b). The high-field shift of NdCH in the H NMR
spectrum and low-field shift of NdCH in the 13C NMR
spectrum indicate all imino groups coordinate to the
metal center, and hence the yttrium atom adopts a nine-
coordination geometry in solution, which is not often
observed for the yttrium atom.
Descr ip tion of Str u ctu r es. The structures of het-
eroleptic complexes 3d and 4e and homoleptic com-
plexes 5a and 5b were characterized by crystallographic
studies. Figure 1 shows the crystal structure of 3d , and
its selected bond distances and angles are listed in Table
1. The yttrium center of 3d has a distorted trigonal
bipyramidal geometry; two nitrogen atoms of two amido
N(SiMe3)2 groups and one nitrogen atom of the pyrrolyl
skeleton occupied equatrial positions, the planarity

Initiators of ꢀ-Caprolactone Polymerization
Organometallics, Vol. 20, No. 16, 2001 3513
ligand. The most remarkable feature of 4e is that two
bis(imino)pyrrolyl ligands 1e coordinate in an N,N′-
fashion to the yttrium atom. This dissymmetric coordi-
nation of the ligand is a consequence of the steric
bulkiness induced by the 2,6-diisopropylphenyl groups.
The noncoordinated imino moieties are situated opposite
each other to minimize the steric congestion, being in
good accordance with a NOESY measurement. The bond
distances of Y-N(pyrroly) (Y-N1 ) 2.347(4) Å and
Y-N4 ) 2.355(4) Å) are longer by 0.06 Å than that
found for 3d (2.288(3) Å). On the other hand, the bond
distances of Y-N(imino) (Y-N2 ) 2.437(5) Å and Y-N5
) 2.449(5) Å) are shorter than those of 3d (2.707(3) and
2.776(3) Å). The distances of imino linkages (N2-C5 )
1.315(6) Å and N5-C13 ) 1.290(6) Å) are substantially
longer than those of free ones (N3-C6 ) 1.270(6) Å and
N6-C14 ) 1.264(6) Å). The bond distance of Y-N(a-
mido) (Y-N7 ) 2.204(4) Å) is comparable with that of
metallocene complexes Cp*2Y{N(SiMe3)2} (2.274(5) and
2.253(5) Å)27 and (R)-(η5-C5H4)Si(Me2)[η5-(-)-menthyl-
(C5H3)]Y{N(SiMe3)2} (2.281(8) and 2.211(8) Å)28 and a
half-metallocene amido complex, [(η5-C5Me4)Si(Me2)-η′-
N-tBu]Y{N(SiMe3)2} (2.184(7) Å).29
The molecular structures of the tris(pyrrolyl) com-
plexes 5a and 5b are shown in Figures 3 and 4,
respectively, and their selected bond lengths and angles
are listed in Tables 3 and 4. Complex 5a crystallized in
cubic space group Ia3 and has a C3-axis passing through
a yttrium atom. The yttrium atom is accordingly sur-
rounded with nine nitrogen atoms of three tridentate
N,N′,N′′-ligands and adopts a three-face-centered trigo-
nal prismatic mode of nine-coordination, where the two
pairs N2, N2′, and N2′′ and N3, N3′, and N3′′ are located
at the three corners of each triangle, and N1, N1′, and
N1′′ occupy three face-centered positions. This is a quite
rare coordination number for the yttrium atom, though
many hydrated salts of the lanthanide elements, which
have much larger ionic radii, adopt the same geometry.
The bond distances of Y-N(imino) (Y-N2 ) 2.737(2) Å
and Y-N3 ) 2.758(3) Å) are similar to that found for
3d , but the bond distance of Y-N(pyrrolyl) (Y-N1 )
2.340(2) Å) is slightly longer than that of 3d .
F igu r e 1. Molecular structure of 3d . Hydrogen atoms are
omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces a n d An gles for
3d
Bond Distances (Å)
Y-N1
Y-N2
Y-N3
Y-N4
Y-N5
N1-C1
N1-C4
2.288(3)
2.707(3)
2.776(3)
2.254(3)
2.246(3)
1.358(5)
1.359(5)
C1-C2
C2-C3
C3-C4
C1-C5
C4-C6
N2-C5
N3-C6
1.403(5)
1.386(6)
1.409(5)
1.425(5)
1.431(5)
1.295(5)
1.295(5)
Bond Angles (deg)
N1-Y-N2
N1-Y-N3
N1-Y-N4
N1-Y-N5
N2-Y-N3
N2-Y-N4
N2-Y-N5
N3-Y-N4
N3-Y-N5
N4-Y-N5
65.2(1)
63.9(1)
Y-N1-C1
Y-N1-C4
C1-N1-C4
Y-N2-C5
Y-N2-C7
C5-N2-C7
Y-N3-C6
Y-N3-C8
C6-N3-C8
125.8(2)
127.6(3)
106.6(3)
110.8(2)
134.1(2)
113.8(3)
110.7(3)
133.8(2)
114.4(3)
118.2(1)
119.9(1)
129.1(1)
113.8(1)
89.0(1)
90.5(1)
116.1(1)
121.9(1)
around the yttrium atom being revealed by the sum of
three angles (360°), while two nitrogen atoms of two
imino groups were placed at two apical positions with
the angle N2-Y-N3 (129.1(1)°) much deviated from
180° owing to the chelating ligation of 1d . Two phenyl
rings in 3d are oriented perpendicular to the plane of
the pyrrolyl moiety. The bond distance of Y-N(pyrrolyl)
(Y-N1 ) 2.288(3) Å) is comparable with that of the
lutetium-pyrrolyl complex, LuCp2(C4H4N)(THF) (2.289-
(4) Å),25 on taking into account the difference of ionic
radii of metals. The metal-imino nitrogen bond dis-
tances (Y-N2 ) 2.707(3) Å and Y-N3 ) 2.776(3) Å)
are longer than the Y-N1 distance. The bond distances
of Y-N(amido) (Y-N4 ) 2.254(3) Å and Y-N5 ) 2.246-
(3) Å) are comparable with those found for bis(amido)
yttrium complexes, Y{N(SiMe3)2}2{OSitBu(2-C6H4(CH2-
NMe2))2} (2.237(9) Å)26 and Y{N(SiMe3)2}2{N-isopropyl-
2-(isopropylamino)troponiminato} (2.236(3) Å).19b
Complex 4e adopts a square-pyramidal geometry
where four corners of the square plane are occupied by
the four nitrogen atoms (N1, N2, N4, and N5) of two
bidentate pyrrolyl ligands and an amido ligand is
capped, as illustrated in Figure 2, and selected bond
distances and bond angles of 4e are listed in Table 2.
The yttrium atom deviates from an equatrial N4-plane
by 1.036(2) Å to approach toward the capped amido
On the other hand, the solid-state structure of 5b,
despite its solution behavior is quite similar to 5a , and
proved to have an eight-coordination number and a
square-antiprismatic arrangement around the yttrium
atom, where one pyrrolyl ligand attaches in a bidentate
N,N′-fashion to the yttrium atom and the others coor-
dinate to the yttrium atom as meridional tridentate
ligands. The bond distances of Y-N (tridentate pyrrolyl)
(Y-N1 ) 2.309(5) Å and Y-N4 ) 2.306(5) Å) are shorter
than that of Y-N(bidentate pyrrolyl) (Y-N7 ) 2.401-
(6) Å). The bond distances of Y-N(imino) in the triden-
tate parts (Y-N2 ) 2.667(5) Å, Y-N3 ) 2.652(5) Å,
Y-N5 ) 2.652(5) Å, and Y-N6 ) 2.716(5) Å) are longer
than that of the bidentate one (Y-N8 ) 2.484(5) Å).
P olym er iza tion of E-Ca p r ola cton e Ca ta lyzed by
P yr r olyl Com p lexes of Yttr iu m . Mono(pyrrolyl) 3d
(27) Den Haan, K. H.; De Boer, J . L.; Teuben, J . H.; Spek, A. L.;
Kojic-Prodic, B.; Hays, G. R.; Huis, R. Organometallics 1986, 5, 1726.
(28) Giardello, M. A.; Conticello, V. P.; Brard, L.; Sabat, M.;
Rheingold, A. L.; Stern, C. L.; Marks, T. J . J . Am. Chem. Soc. 1994,
116, 10212.
(25) Schumann, H.; Lee, P. R.; Dietrich, A. Chem. Ber. 1990, 123,
1331.
(26) Shao, P.; Berg, D. J .; Bushnell, G. W. Inorg. Chem. 1994, 33,
6334.
(29) Mu, Y.; Piers, W. E.; MacDonald, M.-A.; Zaworotko, M. Can. J .
Chem. 1995, 73, 2233.

3514 Organometallics, Vol. 20, No. 16, 2001
Matsuo et al.
F igu r e 2. Molecular structure of 4e. Hydrogen atoms are omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
4e
Bond Distances (Å)
Y-N1
2.347(4)
2.437(5)
2.355(4)
2.449(5)
2.204(4)
1.368(6)
1.352(6)
1.375(6)
1.358(7)
1.371(7)
1.421(7)
1.453(7)
N2-C5
1.315(6)
1.270(6)
1.365(6)
1.374(6)
1.394(7)
1.384(7)
1.392(7)
1.429(7)
1.456(8)
1.290(6)
1.264(6)
Y-N2
N3-C6
Y-N4
N4-C9
Y-N5
N4-C12
C9-C10
C10-C11
C11-C12
C9-C13
C12-C14
N5-C13
N6-C14
Y-N7
N1-C1
N1-C4
C1-C2
C2-C3
C3-C4
C1-C5
C4-C6
Bond Angles (deg)
N1-Y-N2
N4-Y-N5
N1-Y-N5
N2-Y-N4
N1-Y-N7
N4-Y-N7
N1-Y-N4
N2-Y-N5
N2-Y-N7
N5-Y-N7
Y-N1-C1
73.2(2)
71.6(1)
87.0(1)
Y-N1-C4
142.8(4)
104.5(5)
110.2(4)
132.9(4)
116.1(5)
113.7(4)
141.3(4)
104.2(5)
112.0(4)
131.0(3)
116.7(5)
C1-N1-C4
Y-N2-C5
87.4(1)
Y-N2-C7
C5-N2-C7
Y-N4-C9
Y-N4-C12
C9-N4-C12
Y-N5-C13
Y-N5-C15
C13-N5-C15
110.1(1)
108.9(1)
141.0(1)
116.5(1)
121.4(2)
122.2(2)
112.1(3)
and bis(pyrrolyl) 4e complexes were found to catalyze
polymerization of ꢀ-caprolactone, which was consumed
within 10 min (Table 5), while homoleptic pyrrolyl
complexes 5a and 5b had no activity (entries 5 and 6),
suggesting that a Y-N(pyrrolyl) bond did not have any
ability to initiate the polymerization. The bis(pyrrolyl)
complex 4e, which has one Y-N(amido) bond, gave the
poly(ꢀ-caprolactone) with narrow polydispersity (Mw/Mn
) 1.3) (entry 1), and the polymer using the mono-
(pyrrolyl) complex 3d , which has two Y-N(amido)
bonds, was inferior in its polydispersity (Mw/Mn ) 2.0)
(entry 3), indicating that the number of Y-N(SiMe3)2
bonds significantly affected molecular weight distribu-
tions. The spectral characterization of the polymers
showed the presence of a terminal bis(trimethylsilyl)-
amide group, which was derived from a nucleophilic
attack at the lactone-carbon atom followed by acyl-
oxygen bond cleavage. These observations are consistent
with the reported polymerization of ꢀ-caprolactone using
the homoleptic complex 2, which gave poly(ꢀ-caprolac-
tone) with a very broad polydispersity (Mw/Mn ) 2.9).30
F igu r e 3. (a) Molecular structure of 5a . Hydrogen atoms
are omitted for clarity. (b) Schematic drawing of the three-
face-centered trigonal prismatic geometry of the yttrium
atom.
Polymerization at 0 °C resulted in the polymer having
a rather narrower molecular weight distributions (en-
tries 2 and 4; Mw/Mn ) 1.2 for 4e and Mw/Mn ) 1.6 for
3d ).
Con clu sion
Several heteroleptic and homoleptic 2,5-bis(N-arylim-
inomethyl)pyrrolyl complexes of yttrium have been
prepared by aminolysis of Y{N(SiMe3)2}3 with the
corresponding pyrrolyl ligand. We found that the num-
ber of pyrrolyl ligands coordinated to a yttrium metal
can be controlled by changing the substituent(s) on aryl

Initiators of ꢀ-Caprolactone Polymerization
Organometallics, Vol. 20, No. 16, 2001 3515
Ta ble 4. Selected Bon d Dista n ces a n d An gles
for 5b
Bond Distances (Å)
Y-N1
Y-N2
Y-N3
Y-N4
Y-N5
Y-N6
Y-N7
Y-N8
N1-C1
N1-C4
C1-C2
C2-C3
C3-C4
2.309(5)
2.667(5)
2.652(5)
2.306(5)
2.652(5)
2.716(5)
2.401(6)
2.484(5)
1.375(7)
1.370(7)
1.387(8)
1.395(9)
1.383(9)
C1-C5
1.427(9)
1.439(9)
1.308(8)
1.300(7)
1.389(8)
1.354(8)
1.395(9)
1.40(1)
1.405(10)
1.383(9)
1.444(10)
1.309(8)
1.275(8)
C4-C6
N2-C5
N3-C6
N7-C9
N7-C12
C9-C10
C10-C11
C11-C12
C9-C13
C12-C14
N8-C13
N9-C14
Bond Angles (deg)
N1-Y-N2
N1-Y-N3
N1-Y-N4
N1-Y-N5
N1-Y-N6
N1-Y-N7
N1-Y-N8
N2-Y-N3
N2-Y-N4
N2-Y-N5
N2-Y-N6
N2-Y-N7
N2-Y-N8
N3-Y-N4
N3-Y-N5
N3-Y-N6
N3-Y-N7
N3-Y-N8
N4-Y-N5
N4-Y-N6
N4-Y-N7
N4-Y-N8
64.3(2)
64.2(2)
132.9(2)
132.0(2)
83.4(2)
86.5(2)
140.0(2)
128.4(2)
83.4(2)
77.8(2)
91.5(2)
106.7(2)
152.7(2)
131.9(2)
145.4(2)
79.0(2)
73.9(2)
77.8(2)
64.7(2)
63.3(2)
137.4(2)
82.0(2)
N5-Y-N6
N5-Y-N7
N5-Y-N8
N6-Y-N7
N6-Y-N8
N7-Y-N8
Y-N1-C1
Y-N1-C4
C1-N1-C4
Y-N2-C5
Y-N2-C7
C5-N2-C7
Y-N3-C6
Y-N3-C8
C6-N3-C8
Y-N7-C9
Y-N7-C12
C9-N7-C12
Y-N8-C13
Y-N8-C15
C13-N8-C15
127.7(2)
77.0(2)
75.2(2)
152.8(2)
102.2(2)
70.5(2)
127.3(4)
126.8(4)
105.7(5)
113.2(4)
130.9(4)
115.9(5)
114.4(4)
127.2(4)
116.1(6)
113.6(4)
140.7(5)
105.7(6)
111.6(5)
127.2(4)
120.4(6)
Ta ble 5. P olym er iza tion of E-Ca p r ola cton e
Ca ta lyzed by Yttr iu m -P yr r olyl Com p lexesa
F igu r e 4. (a) Molecular structure of 5b. Hydrogen atoms
are omitted for clarity. (b) Schematic drawing of the square-
antiprismatic geometry of the yttrium atom.
d
d
entry catalyst temp (°C) time (min) yieldc Mn (%) Mw/Mn
1
2
3
4
5
6
4e
4e
3d
3d
5a
5b
20
0
20
0
20
20
20
5
5
5
99
99
99
71
trace
trace
65
58 700
61 300
42 000
66 000
1.3
1.2
2.0
1.6
Ta ble 3. Selected Bon d Dista n ces a n d An gles
for 5a a
5
Bond Distances (Å)
300
300
90
Y-N1
Y-N2
Y-N3
N1-C1
N1-C4
C1-C2
2.340(2)
2.737(2)
2.758(3)
1.346(3)
1.357(4)
1.417(4)
C2-C3
C3-C4
C1-C5
C4-C6
N2-C5
N3-C6
1.341(4)
1.410(4)
1.418(4)
1.424(4)
1.299(3)
1.283(3)
b
Y{N(SiMe3)2}3
524 000
2.9
a
b
General conditions: in toluene, [Y] ) 20 mM, S/C ) 100. Ref
30. c Yield ) weight of polymer obtained/weight of monomer used.
Measured by GPC calibrated with standard polystyrene samples.
d
Bond Angles (deg)
N1-Y-N1′
N1-Y-N2
N1-Y-N2′
N1-Y-N2′′
N1-Y-N3
N1-Y-N3′
N1-Y-N3′′
Y-N1-C1
119.965(4)
63.15(8)
75.51(8)
137.72(9)
63.71(8)
136.91(8)
71.05(8)
127.6(2)
Y-N1-C4
C1-N1-C4
Y-N2-C5
Y-N2-C7
C5-N2-C7
Y-N3-C6
Y-N3-C8
C6-N3-C8
126.3(2)
106.1(3)
111.8(2)
131.0(2)
117.2(3)
111.2(2)
130.9(2)
116.5(3)
centered trigonal prismatic structure for 5a and a
square-antiprismatic one for 5b. Moreover, the mono-
(pyrrolyl) and bis(pyrrolyl) complexes 3d and 4e were
found to be catalysts for polymerization of ꢀ-caprolactone
to give polyesters with narrow polydispersities (Mw/Mn
) 1.6 for 3d , Mw/Mn ) 1.2 for 4e). Thus, the complex
4e acted as a single site initiator of ꢀ-caprolactone
polymerization. The unique complexation of tridentate
pyrrolyl ligands to other metals and their catalytic
performance will be described in a subsequent paper.
a
Atoms with primes and double-primes are crystallographically
equivalent to those having the same number without primes.
rings of the pyrrolyl ligand, resulting in the selective
formation of a mono(pyrrolyl) complex 3d , a bis(pyrrolyl)
complex 4e, and homoleptic tris(pyrrolyl) complexes 5a
and 5b. Of particular interest is the diversity of the
coordination mode; a distorted trigonal bipyramidal
geometry and a distorted square-pyramidal one were
observed for 3d and 4e, respectively, and the homoleptic
complexes 5a and 5b were found to have rare structures
with eight- and nine-coordination numbers, a three-face-
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations involving air- and
moisture-sensitive yttrium complexes were carried out using
standard Schlenk techniques under argon. Hexane, THF, and
toluene were dried and deoxygenated by distillation over
sodium benzophenone ketyl under argon. Benzene-d6 was
distilled from Na/K alloy and thoroughly degassed by trap-to-

3516 Organometallics, Vol. 20, No. 16, 2001
Matsuo et al.
trap distillation before use. ꢀ-Caprolactone was purchased and
purified before use. 2-{N-(2,6-Diisopropylphenyl)iminomethyl}-
pyrrole (6),23 Y{N(SiMe2)2}3 (2),29 and 2,5-diformylpyrrole31
were prepared according to the literature.
mg, 4.87 mmol) and 2.1 equiv of 2,6-dimethylaniline (1.26 mL,
10.2 mmol) were dissolved in toluene (30 mL) at room
temperature. After two drops of formic acid was added to the
solution, the mixture was refluxed for 12 h using a water
separator. After cooling, the solvent was evaporated to dryness.
The resulting yellow oil was purified by column chromatog-
raphy on silica gel (hexane/AcOEt ) 10:1) to give 1d as yellow
1
The H (500, 400, 300, and 270 MHz) and 13C (125, 100, 75,
and 68 MHz) NMR spectra were measured on a Varian Unity
Inova-500, a J EOL J NM-AL400, a Varian Mercury-300, or a
J EOL GSX-270 spectrometer. When benzene-d6 was used as
the solvent. The spectra were referenced to the residual solvent
protons at δ 7.20 in the 1H NMR spectra and to the residual
solvent carbons at δ 128.0 in the 13C NMR spectra. Assign-
ments for 1H and 13C NMR peaks for some complexes were
aided by 2D 1H-1H COSY, 2D 1H-1H NOESY, 2D 1H-13C
HMQC, and 2D 1H-13C HMBC spectra. Elemental analyses
were recorded by a Perkin-Elmer 2400 at the Faculty of
Engineering Science, Osaka University. The gel permeation
chromatographic analyses were carried out at 40 °C using a
Shimadzu LC-10A liquid chromatograph system and a RID-
10A refractive index detector, equipped with a Shodex KF-
806L column, which was calibrated versus commercially
available polystyrene standards (SHOWA DENKO). All melt-
ing points were measured in sealed tubes under argon
atmosphere and were not corrected.
P r ep a r a tion of 2,5-Bis(a r ylim in om eth yl)p yr r oles: 2,5-
Bis{N-(4-m eth oxyp h en yl)im in om eth yl}p yr r ole (1a ). A
solution of p-anisidine (1.00 g, 8.12 mmol) in ethanol (20 mL)
was added to a solution of 2,5-diformylpyrrole (0.50 g, 4.06
mmol) in ethanol (20 mL) at room temperature. After the
mixture was stirred for 2 h at room temperature, a yellow
slurry was formed. The resulting yellow powder was collected
by filtration, washed with cold ethanol and hexane, and then
dried under vacuum. Yield: 1.18 g (3.55 mmol, 87%), mp 223-
232 °C (dec). 1H NMR (C6D6, 35 °C): δ 3.38 (s, 6H, OCH3),
6.50 (s, 2H, 3,4-pyr), 6.84 (d, 4H, m-C6H4), 7.18 (d, 4H, o-C6H4),
8.04 (s, 2H, NdCH), 10.32 (br s, 1H, NH). 13C NMR (CDCl3,
1
powders. Yield: 1.11 g (3.37 mmol, 69%), mp 139-140 °C. H
NMR (CDCl3, 35 °C): δ 2.19 (s, 12H, CH3), 6.68 (s, 2H, 3,4-
pyr), 6.96 (t, 3J H-H ) 7.5 Hz, 2H, p-C6H3), 7.07 (d, 3J H-H ) 7.5
Hz, 4H, m-C6H3), 8.05 (s, 2H, NdCH), 10.24 (br s, 1H, NH).
1
13C NMR (CDCl3, 35 °C): δ 18.4 (q, J C-H ) 128 Hz, CH3),
1
1
116.1 (d, J C-H ) 173 Hz, 3,4-pyr), 123.8 (d, J C-H ) 159 Hz,
1
p-C6H3), 127.4 (s, o-C6H3), 128.1 (d, J C-H ) 153 Hz, m-C6H3),
1
133.4 (s, 2.5-pyr), 150.6 (s, ipso-C6H3), 152.0 (d, J C-H ) 163
Hz, NdCH). EI-MS: m/z 329 (M+, base peak), 314 (M - CH3)+.
Anal. Calcd for C22H23N3: C, 80.21; H, 7.04; N, 12.75. Found:
C, 80.19; H, 6.70; N, 12.80.
2,5-B is {N -(2,6-d iis o p r o p y lp h e n y l)im in o m e t h y l}-
p yr r ole (1e).24b A solution of 2,6-diisopropylaniline (9.19 mL,
48.7 mmol) in methanol (10 mL) was added to a solution of
2,5-diformylpyrrole (3.00 g, 24.4 mmol) in methanol (20 mL)
at room temperature. After a few drops of acetic acid was
added, the reaction mixture was stirred for 4 h at 10 °C. The
resulting yellow precipitate was collected by filtration and then
was dried under vacuum. Recrystallization from hexane gave
1
1e (4.77 g, 10.8 mmol, 44%), mp 206-208 °C (dec). H NMR
(C6D6, 35 °C): δ 1.14 (d, 24H, CHMe2), 3.08 (sept, 4H, CHMe2),
6.44 (s, 2H, 3,4-pyr), 7.17 (m, 6H, C6H3), 7.81 (s, 2H, NdCH),
1
10.48 (br s, 1H, NH). 13C NMR (C6D6, 35 °C): δ 23.9 (q, J C-H
1
) 125 Hz, CHMe2), 28.5 (d, J C-H ) 129 Hz, CHMe2), 116.2
(d, 1J C-H ) 172 Hz, 3,4-pyr), 123.4 (d, 1J C-H ) 155 Hz, m-C6H3),
1
124.8 (d, J C-H ) 159 Hz, p-C6H3), 134.0 (s, 2,5-pyr), 138.2 (s,
1
o-C6H3), 149.4 (s, ipso-C6H3), 151.8 (d, J C-H ) 163 Hz, Nd
CH). EI-MS: m/z 441 (M+), 426 [(M - CH3)+], 398 [(M -
CHMe2)+, base peak]. Anal. Calcd for C30H39N3: C, 81.59; H,
8.90; N, 9.51. Found: C, 81.23; H, 9.20; N, 9.46.
1
1
35 °C): δ 55.6 (q, J C-H ) 144 Hz, OCH3), 114.5 (d, J C-H
)
1
158 Hz, m-C6H4), 116.0 (d, J C-H ) 166 Hz, 3,4-pyr), 122.0 (d,
1J C-H ) 158 Hz, o-C6H4), 134.0 (s, 2,5-pyr), 144.3 (s, ipso-C6H4),
Syn th esis of Y(o-Tol2-p yr ){N(SiMe3)2}2 (3c). A solution
of 2,5-di{N-(2-methylphenyl)iminomethyl}pyrrole (1c) (130
mg, 0.433 mmol) in toluene (3 mL) was added to a toluene
solution (3 mL) of 2 (247 mg, 0.433 mmol) cooled at -50 °C.
The reaction mixture was allowed to warm to room temper-
ature and stirred further for 4 h. After removal of insoluble
products by centrifugation, all volatiles were removed in vacuo.
The 1H NMR spectrum of the resulting yellow crystalline solid
showed signals due to a complex bis(pyrrolyl) complex 3c and
a bis(pyrrolyl) complex Y(o-Tol2-pyr)2{N(SiMe3)2} (4c) in 4:1
ratio. Recrystallization from a toluene/hexane mixture gave
analytically pure yellow crystals of 3c (160 mg, 0.225 mmol,
52% yield), mp 199-205 °C (dec). 3c: 1H NMR (C6D6, 35 °C):
δ 0.22 (s, 36H, SiMe3), 2.30 (s, 6H, C6H4-CH3), 6.56 (s, 2H,
3,4-pyr), 7.03 (t, 2H, 4-C6H4), 7.07 (d, 2H, 3-C6H4), 7.15 (t, 2H,
5-C6H4), 7.39 (d, 2H, 6-C6H4), 7.45 (s, 2H, NdCH). 13C NMR
1
146.7 (d, J C-H ) 161 Hz, NdCH), 158.2 (s, p-C6H4). EI-MS:
m/z 333 (M+, base peak), 318 [(M - CH3)+]. Anal. Calcd for
C
20H19N3O2: C, 72.05; H, 5.74; N, 12.60. Found: C, 71.78; H,
5.87; N, 12.58.
2,5-B is {N -(4-m e t h y lp h e n y l)im in o m e t h y l}p y r r o le
(1b): 54% yield, mp 197-198 °C. 1H NMR (C6D6, 35 °C): δ
2.19 (s, 6H, CH3), 6.47 (s, 2H, 3,4-pyr), 7.05 (d, 4H, m-C6H4),
7.14 (d, 4H, o-C6H4), 8.02 (s, 2H, NdCH), 10.33 (br s, 1H, NH).
13C NMR (C6D6, 35 °C): δ 21.2 (q, 1J C-H ) 126 Hz, CH3), 116.1
(d, 1J C-H ) 171 Hz, 3,4-pyr), 121.4 (d, 1J C-H ) 158 Hz, o-C6H4),
130.0 (d, 1J C-H ) 158 Hz, m-C6H4), 134.5 (s, 2.5-pyr), 135.7 (s,
p-C6H4), 147.6 (d, 1J C-H ) 161 Hz, NdCH), 149.3 (s, ipso-C6H4).
EI-MS: m/z 301 (M+, base peak). Anal. Calcd for C20H19N3:
C, 79.70; H, 6.35; N, 13.94. Found: C, 79.57; H, 6.30; N, 13.87.
2,5-Bis{N-(2-m eth ylp h en yl)im in om eth yl}p yr r ole (1c):
60% yield, mp 107-108 °C. 1H NMR (CDCl3, 35 °C): δ 2.38
(s, 6H, CH3), 6.70 (s, 2H, 3,4-pyr), 6.94 (d, 2H, C6H4), 7.12 (t,
2H, C6H4), 7.21 (t, 2H, C6H4), 7.23 (d, 2H, C6H4), 8.22 (s, 2H,
NdCH), 10.15 (br s, 1H, NH). 13C NMR (CDCl3, 35 °C): δ 18.2
1
1
(C6D6, 35 °C): δ 5.4 (q, J C-H ) 117 Hz, SiMe3), 19.8 (q, J C-H
) 127 Hz, C6H4-CH3), 118.8 (d, 1J C-H ) 170 Hz, 3,4-pyr), 124.4
(d, 1J C-H ) 156 Hz, 6-C6H4), 125.7 (d, 1J C-H ) 159 Hz, 5-C6H4),
1
1
126.8 (d, J C-H ) 159 Hz, 4-C6H4), 131.1 (d, J C-H ) 158 Hz,
3-C6H4), 131.9 (s, 2-C6H4), 142.1 (s, 2,5-pyr), 151.1 (s, 1-C6H4),
163.8 (d, J C-H ) 167 Hz, NdCH). Anal. Calcd for C32H54N5-
1
1
(q, J C-H ) 127 Hz, CH3), 116.5 (d, J C-H ) 173 Hz, 3,4-pyr),
1
1
1
117.7 (d, J C-H ) 157 Hz, C6H4), 125.9 (d, J C-H ) 160 Hz,
Si4Y: C, 54.13; H, 7.67; N, 9.86. Found: C, 54.30; H, 7.35; N,
9.59.
4c: 1H NMR (C6D6, 35 °C): δ 0.13 (s, 18H, SiMe3), 1.78 (s,
12H, Ar-CH3), 6.55 (s, 4H, 3.4-pyr), 6.75-7.17 (m, 12H, 3,4,5-
C6H4), 7.40 (s, 4H, 6-C6H4), 7.49 (s, 4H, NdCH).
1
1
C6H4), 126.9 (d, J C-H ) 160 Hz, C6H4), 130.5 (d, J C-H ) 158
1
Hz, C6H4), 132.3 (s, 2.5-pyr), 134.2 (s, 2-C6H4), 148.6 (d, J C-H
) 163 Hz, NdCH), 150.7 (s, 1-C6H4). EI-MS: m/z 301 (M+,
base peak), 286 [(M - CH3)+]. Anal. Calcd for C20H19N3: C,
79.70; H, 6.35; N, 13.94. Found: C, 79.51; H, 5.98; N, 14.09.
P r ep a r a tion of Y(Xyl2-p yr ){N(SiMe3)2}2 (3d ). A solution
of 2,5-bis{N-(2,6-dimethylphenyl)iminomethyl}pyrrole (1d )
(127 mg, 0.384 mmol) in toluene (2 mL) was added to a solution
of 2 (219 mg, 0.384 mmol) in toluene (2 mL) at room
temperature. The reaction mixture was stirred for 2 h at 60
°C to liberate hexamethyldisilazane, detected by GC-MS and
1H NMR spectroscopy. After insoluble products were separated
2,5-Bis{N-(2,6-d im et h ylp h en yl)im in om et h yl}p yr r ole
(1d ). In a 100 mL round-bottom flask, 2,5-diformylpyrrole (600
(30) Hultzsch, K. C.; Spaniol, T. P.; Okuda, J . Organometallics 1997,
16, 4845.
(31) (a) Miller, R.; Olsson, K. Acta Chem. Scand. 1981, B35, 303.
(b) Tayim, H. A.; Salameh, A. S. Polyhedron 1986, 5, 687.

Initiators of ꢀ-Caprolactone Polymerization
Organometallics, Vol. 20, No. 16, 2001 3517
1
by centrifugation, the supernatant toluene solution was con-
centrated to ca. 1.5 mL to give a yellow suspension, which was
recrystallized from toluene to give yellow crystals of 3d (232
123.6 (d, J C-H ) 160 Hz, o-C6H4), 143.7 (s, 2,5-pyr), 145.0 (s,
1
ipso-C6H4), 158.3 (s, p-C6H4), 158.4 (br, J C-H ) 161 Hz, Nd
CH).
1
Syn th esis of Y(p-Tol2-p yr )3 (5b). A mixture of 2,5-di{N-
(4-methylphenyl)iminomethyl}pyrrole (1b, 414 mg, 1.374 mmol)
and 2 (261 mg, 0.458 mmol) in toluene (6 mL) at room
temperature was stirred for 2 h at 60 °C. Yellow precipitates
(423 mg, 93%) were recrystallized from a mixture of toluene
and hexane to give analytically pure yellow crystals of 5b (340
mg, 82% yield), mp 210-215 °C (dec). H NMR (C6D6, 35 °C):
δ 0.23 (s, 36H, SiMe3), 2.33 (s, 12H, Ar-CH3), 6.54 (s, 2H, 3,4-
pyr), 7.00 (s, 6H, C6H3), 7.34 (s, 2H, NdCH). 13C NMR (C6D6,
1
1
35 °C): δ 5.5 (q, J C-H ) 117 Hz, SiMe3), 21.7 (q, J C-H ) 127
Hz, Ar-CH3), 119.1 (d, 1J C-H ) 170 Hz, 3,4-pyr), 125.9 (d, 1J C-H
1
) 160 Hz, p-C6H3), 129.1 (d, J C-H ) 159 Hz, m-C6H3), 130.3
1
mg, 0.344 mmol, 75% yield), mp 156-162 °C (dec). H NMR
(s, o-C6H3), 142.0 (s, 2,5-pyr), 151.2 (s, ipso-C6H3), 164.9 (d,
1J C-H ) 164 Hz, NdCH). Anal. Calcd for C34H58N5Si4Y: C,
55.23; H, 7.92; N, 9.49. Found: C, 55.27; H, 7.33; N, 9.52.
(C6D6, 35 °C): δ 2.17 (s, 18H, CH3), 6.24 (d, 12H, o-C6H4), 6.56
(s, 6H, 3,4-pyr), 6.93 (d, 12H, m-C6H4), 7.57 (s, 6H, NdCH).
13C NMR (C6D6, 35 °C): δ 21.1 (q, 1J C-H ) 126 Hz, CH3), 116.9
(d, 1J C-H ) 168 Hz, 3,4-pyr), 122.5 (d, 1J C-H ) 159 Hz, o-C6H4),
128.7 (d, 1J C-H ) 158 Hz, m-C6H4), 133.9 (s, p-C6H4), 143.0 (s,
P r ep a r a tion of Y(DIP 2-p yr )2{N(SiMe3)2} (4e). To a solu-
tion of 2 (384 mg, 0.674 mmol) in toluene (2.5 mL) at room
temperature was added a solution of 2,5-bis{N-(2,6-diiso-
propylphenyl)iminomethyl}pyrrole (1e) (672 mg, 1.35 mmol)
in toluene (2.5 mL). The reaction mixture was stirred for 12 h
at 60 °C. The resulting yellow microcrystals were washed with
a small amount of cold hexane. These microcrystals (737 mg,
0.652 mmol, 97%) were recrystallized from a mixture of toluene
and hexane to give analytically pure yellow crystals of 4e (598
1
2,5-pyr), 151.1 (s, ipso-C6H4), 160.4 (d, J C-H ) 161 Hz, Nd
CH). Anal. Calcd for C60H54N9Y: C, 72.79; H, 5.50; N, 12.73.
Found: C, 72.64; H, 5.89; N, 13.03.
In the case of 1:1 reaction, the signals due to bis(pyrrolyl)
complex Y(p-Tol2-pyr)2{N(SiMe3)2} (4b) were observed and its
content was estimated to be 13%. 4b: 1H NMR (C6D6, 35 °C):
δ 0.09 (s, 18H, SiMe3), 2.08 (s, 12H, CH3), 6.79 (s, 4H, 3,4-
pyr), 6.86 (br, 16H, C6H4), 7.91 (s, 4H, NdCH). 13C NMR (C6D6,
1
mg, 78% yield), mp 205-210 °C (dec). H NMR (C6D6, 35 °C):
δ 0.30 (s, 18H, SiMe3), 0.45 (d, 6H, CHMe2 (noncoordinated)),
1.01 (d, 6H, CHMe2 (noncoordinated)), 1.15 (d, 6H, CHMe2
(coordinated)), 1.18 (d, 6H, CHMe2 (coordinated)), 1.19 (d, 6H,
CHMe2 (noncoordinated)), 1.28 (d, 6H, CHMe2 (coordinated)),
1.30 (d, 6H, CHMe2 (noncoordinated)), 1.77 (d, 6H, CHMe2
(coordinated)), 2.31 (sept, 2H, CHMe2 (noncoordinated)), 2.68
(sept, 2H, CHMe2 (noncoordinated)), 3.13 (sept, 2H, CHMe2
(coordinated)), 3.62 (sept, 2H, CHMe2 (coordinated)), 5.62 (d,
3J H-H ) 3.7 Hz, 2H, 4-pyr), 6.18 (d, 3J H-H ) 3.7 Hz, 2H, 3-pyr),
7.20 (m, 12H, C6H3), 7.37 (s, 2H, NdCH (coordinated)), 8.21
(s, 2H, NdCH (noncoordinated)). 13C NMR (C6D6, 35 °C): δ
5.0 (q, 1J C-H ) 118 Hz, SiMe3), 21.9, 22.4, 23.3, 23.5, 23.8, 24.6,
1
1
35 °C): δ 4.8 (q, J C-H ) 117 Hz, SiMe3), 21.0 (q, J C-H ) 126
Hz, CH3), 118.5 (d, 1J C-H ) 167 Hz, 3,4-pyr), 122.5 (d, 1J C-H
)
1
159 Hz, o-C6H4), 129.2 (d, J C-H ) 158 Hz, m-C6H4), 135.2 (s,
p-C6H4), 143.8 (s, 2,5-pyr), 149.3 (s, ipso-C6H4), 162.1 (d, 1J C-H
) 166 Hz, NdCH).
P r ep a r a tion of Y(DIP -p yr )3 (7) a n d Y(DIP -p yr )2{N(Si-
Me3)2} (8). A solution of 2 (400 mg, 0.702 mmol) in toluene (2
mL) was cooled at -50 °C, and then a solution of 2-{N-(2,6-
diisopropylphenyl)iminomethyl}pyrrole (6, 357 mg, 1.40 mmol)
in toluene (2 mL) was added. The resulting mixture was allow-
ed to warm to room temperature and then stirred further for
4 h at 50 °C. After insoluble products were separated by centri-
fugation, all volatiles were removed in vacuo. The 1H NMR
spectrum of the resulting white microcrystals showed signals
due to a homoleptic complex, Y(DIP-pyr)3 (7), and a bis-
(pyrrolyl) complex, Y(DIP-pyr)2{N(SiMe3)2} (8), in 57:43 ratio.
7: 1H NMR (400 MHz, C6D6, 35 °C): δ 0.61 (d, 9H, CHMe2),
0.89 (d, 9H, CHMe2), 0.93 (d, 9H, CHMe2), 0.94 (d, 9H, CHMe2),
2.44 (sept, 3H, CHMe2), 2.85 (sept, 3H, CHMe2), 6.40 (dd, 3J H-H
) 1.6 and 3.6 Hz, 3H, 4-pyr), 6.84 (d, 3H, 3-pyr), 6.89 (br s,
3H, 5-pyr), 7.06 (m, 9H, C6H3), 7.63 (s, 3H, NdCH). 13C NMR
1
25.9, and 26.1 (q, J C-H ) 121-126 Hz, CHMe2), 27.4, 27.9,
29.6, and 30.2 (q, 1J C-H ) 127-129 Hz, CHMe2), 117.2 (d, 1J C-H
1
) 174 Hz, 4-pyr), 122-128 (d, J C-H ) 157-159 Hz, six sets
1
of p- and m-C6H3), 125.8 (d, J C-H ) 172 Hz, 3-pyr), 134.9 (s,
5-pyr), 135.4, 137.1, 141.0, and 141.4 (s, o-C6H3), 144.7 (s, ipso-
1
C6H3), 146.7 (s, 2-pyr), 148.5 (s, ipso-C6H3), 153.7 (d, J C-H
)
1
170 Hz, NdCH (noncoordinated)), 165.9 (d, J C-H ) 164 Hz,
NdCH (coordinated)). Anal. Calcd for C66H94N7Si2Y: C, 70.12;
H, 8.38; N, 8.67. Found: C, 69.94; H, 8.41; N, 8.54. FAB-MS:
1
i
m/z 969 [{M - N(SiMe3)2}+], 883 [{M - N(SiMe3)2 - Pr2}+].
(100 MHz, C6D6, 35 °C): δ 22.9, 23.4, 26.0, and 26.4 (q, J C-H
1
) 123-126 Hz, CHMe2), 28.5 and 29.0 (d, J C-H ) 128 Hz,
P r ep a r a tion of Y(An 2-p yr )3 (5a ). A mixture of 2,5-di{N-
(4-methoxyphenyl)iminomethyl}pyrrole (1a , 526 mg, 1.58
mmol) and 2 (300 mg, 0.526 mmol) in toluene (4 mL) was
stirred for 2 h at 60 °C. Supernatant liquid was concentrated
in vacuo, and then the resulting yellow microcrystals were
washed with a small amount of cold hexane. The microcrystals
(544 mg, 0.501 mmol, 95%) were recrystallized from a mixture
of toluene and hexane to give analytically pure yellow crystals
of 5a (463 mg, 81% yield), mp 150-153 °C (dec). 1H NMR
(C6D6, 35 °C): δ 3.37 (s, 18H, OCH3), 6.31 (d, 12H, o-C6H4),
6.58 (s, 6H, 3,4-pyr), 6.76 (d, 12H, m-C6H4), 7.61 (s, 6H, Nd
CH). 13C NMR (C6D6, 35 °C): δ 55.2 (q, 1J C-H ) 143 Hz, OCH3),
1
1
CHMe2), 113.8 (d, J C-H ) 168 Hz, 4-pyr), 123.5 (d, J C-H
)
1
168 Hz, 3-pyr), 124-127 (d, J C-H ) 157-159 Hz, p- and
1
m-C6H3), 136.6 (s, o-C6H3), 140.3 (d, J C-H ) 172 Hz, 5-pyr),
143.1 (s, 2-pyr), 147.2 (s, ipso-C6H3), 164.3 (d, 1J C-H ) 161 Hz,
NdCH).
8: 1H NMR (400 MHz, C6D6, 35 °C): δ 0.21 (s, 18H, SiMe3),
0.59 (d, 3H, CHMe2), 0.99 (d, 3H, CHMe2), 1.05 (d, 6H, CHMe2),
1.11 (d, 6H, CHMe2), 1.25 (d, 3H, CHMe2), 1.58 (d, 3H, CHMe2),
2.90 (sept, 2H, CHMe2), 3.71 (sept, 2H, CHMe2), 6.40 (dd, 1J H-H
) 2.0 and 3.6 Hz, 2H, 4-pyr), 6.19 (br s, 2H, 5-pyr), 6.63 (d,
2H, 3-pyr), 7.07 (m, 6H, C6H3), 7.74 (s, 2H, NdCH). 13C NMR
(100 MHz, C6D6, 35 °C): δ 4.9 (q, 1J C-H ) 117 Hz, SiMe3), 22.4,
1
1
113.6 (d, J C-H ) 158 Hz, m-C6H4), 116.9 (d, J C-H ) 168 Hz,
1
22.8, 24.1, 25.7, 26.4, and 26.5 (q, J C-H ) 123-126 Hz,
1
3,4-pyr), 123.5 (d, J C-H ) 159 Hz, o-C6H4), 143.0 (s, 2,5-pyr),
146.9 (s, ipso-C6H4), 157.6 (s, p-C6H4), 160.2 (d, J C-H ) 161
1
CHMe2), 29.3 and 29.6 (d, J C-H ) 128 Hz, CHMe2), 113.4 (d,
1
1J C-H ) 168 Hz, 4-pyr), 123.7 (d, 1J C-H ) 168 Hz, 3-pyr), 124-
127 (d, 1J C-H ) 157-159 Hz, p- and m-C6H3), 136.6 (s, o-C6H3),
138.4 (d, 1J C-H ) 173 Hz, 5-pyr), 141.7 (s, 2-pyr), 146.2 (s, ipso-
Hz, NdCH). Anal. Calcd for C60H54N9O6Y: C, 66.36; H, 5.01;
N, 11.61. Found: C, 66.75; H, 5.36; N, 11.21.
1
In the case of 1:1 reaction, the signals due to bis(pyrrolyl)
complex Y(p-An2-pyr)2{N(SiMe3)2} (4a ) were observed together
with 5a and its content was estimated to be 16%. 4a : 1H NMR
(C6D6, 35 °C): δ 0.11 (s, 18H, SiMe3), 3.30 (s, 18H, OCH3), 6.68
(d, 8H, m-C6H4), 6.79 (s, 4H, 3,4-pyr), 6.84 (br, 8H, o-C6H4),
7.91 (br s, 4H, NdCH). 13C NMR (C6D6, 35 °C): δ 4.9 (q, 1J C-H
C6H3), 163.2 (d, J C-H ) 162 Hz, NdCH).
Recrystallization from a mixture of toluene and hexane gave
analytically pure colorless crystals of 7 in 34% yield, mp 190-
198 °C (dec). Anal. Calcd for C51H63N6Y: C, 72.15; H, 7.48; N,
9.90. Found: C, 71.92; H, 7.72; N, 10.00.
P olym er iza tion of ꢀ-Ca p r ola cton e. In a typical reaction,
to a solution of 4e (13.3 mg, 0.0118 mmol) in toluene (0.59
mL, to generate 20 mM solution) was added ꢀ-caprolactone
1
) 116 Hz, SiMe3), 55.1 (q, J C-H ) 143 Hz, OCH3), 114.0 (d,
1
1J C-H ) 160 Hz, m-C6H4), 118.3 (d, J C-H ) 167 Hz, 3,4-pyr),

3518 Organometallics, Vol. 20, No. 16, 2001
Matsuo et al.
Ta ble 6. Cr ysta l Da ta a n d Da ta Collection
P a r a m eter s of 3d , 4e, 5a , a n d 5b
(100 equiv, 0.131 mL, 1.18 mmol) at 0 °C. The yellow solution
was stirred for 5 min at 0 °C. The polymerization was
terminated by the addition of methanol and aqueous hydrogen
chloride. The resulting white polymer was collected by filtra-
tion and dried in vacuo at 60 °C. The yield of poly(ꢀ-
caprolactone) was found to be quantitative. The resulting
poly(ꢀ-caprolactone) was analyzed by means of gel permeation
chromatography.
3d
4e‚0.5(hexane)
formula
C
34H58N5Si4Y
C69H101N7Si2Y
1173.68
monoclinic
P21/n (No. 14)
13.8792(4)
26.8160(7)
19.2282(5)
fw
738.12
cryst syst
space group
orthorhombic
Pna21 (No. 33)
17.6103(5)
13.4670(4)
16.7900(5)
a, Å
b, Å
c, Å
Ch a r a cter iza tion of p oly(E-ca p r ola cton e). Complex 4e
(5.0 mg, 4.4 µmol) and 30 equiv of ꢀ-caprolactone (15 mg, 0.133
mmol) were dissolved in 0.58 mL of toluene-d8 at 0 °C in a 5φ
mm NMR tube. After polymerization was complete the 1H
NMR spectrum showed signals due to a terminal N,O-bis-
R, deg
â, deg
102.3942(8)
γ, deg
V, Å3
3981.9(2)
4
30 314 (3.8-55.0°)
6989.6(3)
4
70 142 (3.3-55.0°)
Z
no. of reflns for cell
determ (2θ range)
1
(trimethylsilyl)amide group of poly(ꢀ-caprolactone). H NMR
D
calcd, g/cm-3
1.231
1.115
(toluene-d8, 35 °C): δ -0.26 (s, SiMe3), 0.27 (s, SiMe3), 1.18
(m, COCH2CH2CH2CH2CH2O), 1.44 (m, COCH2CH2CH2CH2-
CH2O), 1.52 (m, COCH2CH2CH2CH2CH2O), 2.10 (t, COCH2-
CH2CH2CH2CH2O), 3.97 (t, COCH2CH2CH2CH2CH2O). Poly(ꢀ-
caprolactone) with Mn ) 16 400 exhibited an end-group signal
of NH2 by hydrolysis of the terminal N,O-bis(trimethylsilyl)-
amide group, -C(OSiMe3)dNSiMe3. 1H NMR (500 MHz,
CDCl3, 50 °C): δ 1.31 (m, Hh), 1.31 (m, Hm), 1.38 (m, Hc), 1.45
(m, Hn), 1.55 (m, Hd), 1.55 (m, Hg), 1.55 (m, Hi), 1.55 (m, Hl),
1.70 (m, Hb), 2.23 (t, Hf), 2.23 (t, Hk), 2.28 (t, Ha), 3.65 (br s,
Ho), 4.00 (t, Hj), 4.24 (t, He).
F(000)
1568.00
2524.00
µ[Mo KR], cm-1
T, K
16.10
9.12
100(1)
213(1)
cryst size, mm
no. of images
total oscillation
angles (deg)
exposure time
(min per deg)
2θmin, 2θmax, deg
no. of reflns measd
(total)
0.70 × 0.64 × 0.61
0.24 × 0.20 × 0.16
78
185
232.0
370.0
0.30
0.7
5.0, 55.0
36 755
5.0, 55.0
89 811
no. of refl. measd
(unique)
8982 (Rint ) 0.111)
15978 (Rint ) 0.202)
no. of variables
R1, wR2 (all data)
R (I > 2.0σ(I))
GOF on F2
396
0.060, 0.124
0.051
1.03
0.48, -0.51
697
0.233, 0.099
0.057
0.52
1.54, -2.16
∆, e Å-3
5a
5b‚1.5(toluene)
formula
C
60H54N9O6Y
C70.50H66N9Y
1128.26
Cr ysta llogr a p h ic Da ta Collection s a n d Str u ctu r e De-
ter m in a tion of 3d , 4e, 5a , a n d 5b. Crystals of 3d , 4e, 5a ,
and 5b suitable for X-ray diffraction studies were sealed in
glass capillaries under an argon atmosphere and were mounted
on a Rigaku RAXIS-RAPID imaging plate diffractometer for
data collection using Mo KR (graphite monochromated, λ )
0.71069) radiation. Crystal data and data statistics are sum-
marized in Table 6. Each indexing was performed from two
oscillations. The camera radius was 127.40 mm. Readout was
performed in the 0.100 mm pixel mode. A symmetry-related
absorption correction using the program ABSCOR32 was
applied. Each data was corrected for Lorentz and polarization
effects.
The structures of complex 3d , 4e, and 5a were solved by
the direct method (SHELXS-97)33 and expanded using Fourier
techniques (DIRDIF-94).34 The structure of complex 5b was
solved by the heavy-atom Patterson method (PATTY-94)34 and
expanded using Fourier techniques (DIRDIF-94).34 The non-
hydrogen atoms were refined anisotropically by the full-matrix
least-squares method. Hydrogen atoms were placed at calcu-
lated positions (C-H ) 0.95 Å) and kept fixed. Measured
nonequivalent reflections were used for the structure deter-
fw
1086.05
cryst syst
cubic
triclinic
space group
Ia3 (No. 206)
27.6372
P1h (No. 2)
15.4867(2)
16.2113(5)
13.7190(3)
98.023(3)
91.686(2)
62.368(2)
3019.1(1)
2
a, Å
b, Å
27.6372
27.6372
c, Å
R, deg
â, deg
γ, deg
V, Å3
21109.7
16
77 367 (3.6-55.0°)
Z
no. of reflns for cell
determ (2θ range)
13 289(3.8-55.0°)
D
calcd, g/cm-3
1.367
1.241
F(000)
9024.00
11.68
1182.00
µ[Mo KR], cm-1
T, K
10.17
213(1)
213(1)
cryst size, mm
no. of images
total oscillation
angles (deg)
exposure time
(min per deg)
2θmin, 2θmax, deg
no. of reflns measd
(total)
0.32 × 0.30 × 0.26
0.28 × 0.22 × 0.14
111
74
222.0
222.0
0.70
1.20
5.0, 55.0
90 311
5.0, 55.0
25 537
no. of reflns measd
(unique)
10 672 (Rint ) 0.101) 13 247 (Rint ) 0.095)
no. of variables
R1, wR2 (all data)
R (I > 2.0σ(I))
GOF on F2
251
0.136, 0.053
0.047
0.52
3.30, -1.77
694
0.219, 0.185
0.110
0.98
1.43, -1.69
2
mination. In the subsequent refinement, the function ∑w(Fo
- Fc2)2 was minimized, where |Fo| and |Fc| are the observed
and calculated structure factor amplitudes, respectively. The
agreement indices are defined as R1 ) ∑(||Fo| - |Fc||)/∑|Fo|
∆, e Å-3
Ack n ow led gm en t. We thank Dr. T. Yamagata
(Osaka University) for his help for the X-ray analysis
of 3d . The present research was supported in part by
the grant-in-aid for Scientific Research on Priority Areas
“Molecular Physical Chemistry” from the Ministry of
Education, Science, Culture, and Sports. Y.M. is a
research fellow of the J apan Society for the Promotion
of Science, 1998-2000.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
parameters, thermal displacement parameters, bond lengths,
and bond angles for 3d , 4e, 5a , and 5b. This material is
available free of charge via the Internet at http://pubs.acs.org.
and wR2 ) [∑w(Fo - Fc2)2/∑(wFo4)]1/2. All calculations were
2
performed using the teXsan crystallographic software package,
and illustrations were drawn by ORTEP. The quality of the
crystals of 4e was not good presumably due to the presence of
solvent molecules. The absolute structure parameter (Flack
parameter, ø) of 3d was found to be -0.005(5).
(32) Higashi, T. Program for Absorption Correction; Rigaku Corpo-
ration: Tokyo, J apan, 1995.
(33) Sheldrick, G. M. Program for the Solution of Crystal Structures;
University of Goettingen: Germany, 1997.
(34) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
de Gelder, R.; Israel, R.; Smits, J . M. M. The DIRDIF-94 program
system, Technical Report of the Crystallography Laboratory; University
of Nijmegan: The Netherlands, 1994.
OM0101846