Notable effect of fluoro substituents in the imino group in ring-opening polymerization of ε-caprolactone by Al complexes containing phenoxyimine ligands

Article abstract of DOI:10.1021/om8011882

A series of Al complexes containing phenoxyimine ligands of the types R¹(R¹)Al[O-2-^tBu-6-{(C₆F ₅)N=CH}C₆H₃] [R¹ R² = Me, Me (la); Et, Et (lb); Me, C1 (1c)]

Full text of DOI:10.1021/om8011882

Organometallics 2009, 28, 2179–2187
2179
Notable Effect of Fluoro Substituents in the Imino Group in
Ring-Opening Polymerization of ε-Caprolactone by Al Complexes
Containing Phenoxyimine Ligands
Naruhito Iwasa,†,‡ Shohei Katao,† Jingyu Liu,† Michiya Fujiki,† Yoshiro Furukawa,‡ and
Kotohiro Nomura*,†
Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama,
Ikoma, Nara 630-0101, and Research Laboratories, Daiso Company, Ltd., 9 Otakasu, Amagasaki, Hyogo
660-0842, Japan
ReceiVed December 15, 2008
A series of Al complexes containing phenoxyimine ligands of the types R1(R2)Al[O-2-tBu-6-
{(C6F5)NdCH}C6H3] [R1, R2 ) Me, Me (1a); Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-
(ArNdCH)C6H3] [Ar ) 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)] have been prepared and
identified on the basis of NMR spectra and elemental analyses. Their structures were determined by
X-ray crystallography, and these complexes fold a distorted tetrahedral geometry around Al. The ring-
opening polymerizations (ROPs) of ε-caprolactone (CL) using 1a-c in the presence of PhCH2OH
proceeded efficiently in a living manner, and the propagation rates were somewhat influenced by the
anionic donor ligand employed (Me, Et, or Cl). The catalytic activity by 1a-6a [Ar ) C6H5 (5a), 2,6-
Me2C6H3 (6a)]-PhCH2OH catalyst systems was strongly affected by the aromatic substituent (Ar) in the
imino group, and placement of fluorine substituents especially in the ortho-position strongly affected the
catalytic activity. The ROPs by 2a-6a were accompanied by a certain degree of side reactions
(transesterification), whereas the living polymerization systems can be accomplished using the C6F5
analogues (1a-c). Therefore, the C6F5 substituent in the imino group plays an essential key role in the
ROP of CL in terms of both the catalytic activity and maintaining a living manner.
that the imino substituent (R) in Me2Al[O-2-tBu-6-(RNd
CH)C6H3] plays a crucial role in efficient ROP; the catalytic
activity (turnover number, TON) in the ROP increased in the
order R ) C6F5 . R ) 2,6-Me2C6H3 > R ) 2,6-iPr2C6H3 > R
Introduction
Certain aliphatic polyesters are known to possess promising
characteristics as biodegradable and bioassimilable materials not
only due to their practical biodegradability, but also due to their
biocompatibility for medical and pharmaceutical applications.1
Aluminum alkoxides are known to be one of the important
reagents employed as initiators for ring-opening polymerization
(ROP) of cyclic esters2 such as lactides3,4c and lactones,3j,n,4,5
and considerable attention has thus been paid to the synthesis
and structural determinations of monomeric/dimeric Al com-
plexes.6
t
) C6H5 > R ) cyclohexyl > R ) Bu > R ) adamantyl
(negligible activity).4a,b Moreover, the PDI value (Mw/Mn)
increased without a notable increase in the Mn values at high
CL conversion (ca. 80%) in the ROP by Me2Al[O-2-tBu-6-
{(cyclohexyl)NdCH}C6H3]-nBuOH catalyst, whereas the
Mw/Mn values remained constant (Mw/Mn ) 1.17-1.19) in the
ROP by the C6F5 analogue-nBuOH catalyst under the same
conditions (at 60 °C).4b
We recently demonstrated that Me2Al[O-2-tBu-6-{(C6F5)
NdCH}C6H3] (1a) exhibits unique characteristics for a rapid
living ROP of ε-caprolactone (CL) and δ-valerolactone (VL)
(3) For examples of polymerization of lactide by Al, see: (a) Trofimoff,
L.; Aida, T.; Inoue, S. Chem. Lett. 1987, 991. (b) Spassky, N.; Wisniewski,
M.; Pluta, C.; LeBorgne, A. Macromol. Chem. Phys. 1996, 197, 2627. (c)
Montaudo, G.; Montaudo, M. S.; Puglisi, C.; Samperi, F.; Spassky, N.;
LeBorgne, A.; Wisniewski, M. Macromolecules 1996, 29, 6461. (d)
Wisniewski, M.; LeBorgne, A.; Spassky, N. Macromol. Chem. Phys. 1997,
198, 1227. (e) Kowalski, A.; Duda, A.; Penczek, S. Macromolecules 1998,
31, 2114. (f) Cameron, P. A.; Jhurry, D.; Gibson, V. C.; White, A. J. P.;
Williams, D. J.; Williams, S. Macromol. Rapid Commun. 1999, 20, 616.
(g) Ovitt, T. M.; Coates, G. W. J. Am. Chem. Soc. 1999, 121, 4072. (h)
Bhaw-Luximon, A.; Jhurry, D.; Spassky, N. Polym. Bull. 2000, 44, 31. (i)
Radano, C. P.; Baker, G. L.; Smith, M. R. J. Am. Chem. Soc. 2000, 122,
1552. (j) Ovitt, T. M.; Coates, G. W. J. Polym. Sci., Part A: Polym. Chem.
2000, 38, 4686. (k) Huang, C.-H.; Wang, F.-C.; Ko, B.-T.; Yu, T.-L.; Lin,
C.-C. Macromolecules 2001, 34, 356. (l) Chisholm, M. H.; Navarro-Llobet,
D.; Simonsick, W. J., Jr. Macromolecules 2001, 34, 885. (m) Nomura, N.;
Ishii, R.; Akakura, M.; Aoi, K. J. Am. Chem. Soc. 2002, 124, 5938. (n)
Ovitt, T. M.; Coates, G. W. J. Am. Chem. Soc. 2002, 124, 1316. (o)
Chakraborty, D.; Chen, E. Y.-X. Organometallics 2003, 22, 769.
4
n
in the presence of BuOH (1.0 equiv). We also demonstrated
* To whom correspondenc should be addressed. Phone: +81-743-72-
6041. Fax: +81-743-72-6049. E-mail: nomurak@ms.naist.jp.
† Nara Institute of Science and Technology.
‡ Daiso Co., Ltd.
(1) For example, see: (a) Cox, M. K. In Biodegradable Polymers and
Plastics; Vert, M., Feijen, J., Albertsson, A., Scott, G., Chiellini, E., Eds.;
The Royal Society of Chemistry: Cambridge, U.K., 1992; p 95. (b) Doi,
Y.; Kumagai, Y.; Tanahashi, N.; Mukai, K. In Biodegradable Polymers
and Plastics; Vert, M., Feijen, J., Albertsson, A., Scott, G., Chiellini, E.,
Eds.; The Royal Society of Chemistry: Cambridge, U.K., 1992; p 139. (c)
Okada, M. Prog. Polym. Sci. 2002, 27, 87.
(2) For a recent review article, see: (a) Mecerreyes, D.; Jerome, R.;
Dubois, P. AdV. Polym. Sci. 1999, 147, 1. (b) O’Keefe, B. J.; Hillmyer,
M. A.; Tolman, W. B. J. Chem. Soc., Dalton Trans. 2001, 2215. (c)
Stridsberg, K. M.; Ryner, M.; Albertsson, A. C. AdV. Polym. Sci. 2002,
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(e) Dechy-Cabaret, O.; Martin-Vaca, B.; Bourissou, D. Chem. ReV. 2004,
104, 6147.
(4) (a) Iwasa, N.; Liu, J.; Nomura, K. Catal. Commun. 2008, 9, 1148.
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10.1021/om8011882 CCC: $40.75
2009 American Chemical Society
Publication on Web 03/06/2009

2180 Organometallics, Vol. 28, No. 7, 2009
Iwasa et al.
Scheme 1
It has been generally proposed that the ROP proceeds via
coordination and insertion of CL,7 and the presence of two types
of side reactions, intra- and intermolecular transesterifications,
is also known (Scheme 1).8 Therefore, this fact (broadening of
the molecular weight distributions in the ROP by the cyclohexyl
analogue) would suggest a possibility of (probably intramo-
lecular) transesterification accompanying the catalytic ROP as
a side reaction.4b However, there is no detailed information
concerning a ligand effect toward the polymerization behavior
especially for the precise control in the ROP without a side
reaction such as transesterification.
(5) For examples of ROP of lactones etc., see: (a) Ko, B.-T.; Lin, C.-C.
Macromolecules 1999, 32, 8296. (b) Taden, I.; Kang, H.-C.; Massa, W.;
Spaniol, T. P.; Okuda, J. Eur. J. Inorg. Chem. 2000, 441. (c) Chakraborty,
D.; Chen, E. Y.-X. Organometallics 2002, 21, 1438. (d) Hsueh, M.-L.;
Huang, B.-H.; Lin, C.-C. Macromolecules 2002, 35, 5763. (e) Yu, R.-C.;
Hung, C.-H.; Huang, J.-H.; Lee, H.-Y.; Chen, J.-T. Inorg. Chem. 2002, 41,
645. (f) Zheng, G.; Sto¨ver, H. D. H. Macromolecules 2003, 36, 7439. (g)
Alcazar-Roman, L. M.; O’Keefe, B. J.; Hillmyer, M. A.; Tolman, W. B.
Dalton Trans. 2003, 3082. (h) Chen, C.-T.; Huang, C.-A.; Huang, B.-H.
Macromolecules 2004, 37, 7968. (i) Lewinsky, J.; Horeglad, P.; Tratkiewicz,
E.; Grzenda, W.; Lipkowski, J.; Kolodziejczyk, E. Macromol. Rapid
Commun. 2004, 25, 1939. (j) Nomura, N.; Aoyama, T.; Ishii, R.; Kondo,
T. Macromolecules 2005, 38, 5363. (k) Amgoune, A.; Lavanant, L.; Thomas,
C. M.; Chi, Y.; Welter, R.; Dagorne, S.; Carpentier, J.-F. Organometallics
2005, 24, 6279. (l) Majoumo-Mbe, F.; Smolensky, E.; Lo¨nnecke, P.;
Shpasser, S.; Eisen, M. S.; Hey-Hawkins, E. J. Mol. Catal. A 2005, 240,
91. (m) Yao, W.; Mu, Y.; Gao, A.; Su, Q.; Liu, Y.; Zhang, Y. Polymer
2008, 49, 2486.
(6) For selected examples of synthesis and structural determinations of
monomeric/dimeric Al complexes, see: (a) Atwood, D. A.; Jegier, J. A.;
Rutherford, D. Inorg. Chem. 1996, 35, 63. (b) Qian, B.; Ward, D. L.; Smith,
M. R, III. Organometallics 1998, 17, 3070. (c) Radzewich, C. E.; Coles,
M. P.; Jordan, R. F. J. Am. Chem. Soc. 1998, 120, 9384. (d) Cameron,
P. A.; Gibson, V. C.; Redshaw, C.; Segal, J. A.; Bruce, M. D.; White,
A. J. P.; Williams, D. J. Chem. Commun. 1999, 1883. (e) Mun˜oz-Herna´ndez,
M.-A.; Keiser, T. S.; Patrick, B.; Atwood, D. A. Organometallics 2000,
19, 4416. (f) Liu, S.; Munoz-Hernandez, M.-A.; Atwood, D. A. J.
Organomet. Chem. 2000, 596, 109. (g) Cameron, P. A.; Gibson, V. C.;
Redshaw, C.; Segal, J. A.; Solan, G. A. J. Chem. Soc., Dalton Trans. 2001,
1472. (h) Hill, M. S.; Hutchison, A. R.; Keiser, T. S.; Parkin, S.; VanAelstyn,
M. A.; Atwood, D. A. J. Organomet. Chem. 2001, 628, 71. (i) Redshaw,
C.; Elsegood, M. R. J. Chem. Commun. 2001, 2016. (j) Cameron, P. A.;
Gibson, V. C.; Redshaw, C.; Segal, J. A.; White, A. J. P.; Williams, D. J.
J. Chem. Soc., Dalton Trans. 2002, 415. (k) Chakraborty, D.; Chen, E. Y.-
X. Macromolecules 2002, 35, 13. (l) Lewin´ski, J.; Zachara, J.; Starowieyski,
K. B.; Ochal, Z.; Justyniak, I.; Kopec, T; Stolarzewicz, P.; Dranka, M.
Organometallics 2003, 22, 3773. (m) Lewinski, J.; Horeglad, P.; Dranka,
M.; Justyniak, I. Inorg. Chem. 2004, 43, 5789. (n) Dagorne, S.; Lavanant,
L.; Welter, R.; Chassenieux, C.; Haquette, P.; Jaouen, G. Organometallics
2003, 22, 3732. (o) Braune, W.; Okuda, J. Angew. Chem., Int. Ed. 2003,
42, 64. (p) Zhu, H.; Chen, E. Y.-X. Inorg. Chem. 2007, 46, 1481.
(7) Dittrich, W.; Shultz, R. C. Angew. Macromol. Chem. 1971, 15, 109.
In this study, we thus investigated synthesis and structural
analysis of a series of four-coordinate R1(R2)Al[O-2-tBu-
6-{(C6F5)NdCH}C6H3] [R1, R2 ) Et, Et (1b); Me, Cl (1c)] and
conducted the ROPs of CL by 1a-c in the presence of 1 equiv
of PhCH2OH. Through this research, we explored the effect of
an anionic (alkyl or chloro) ligand (R1, R2) on both the catalytic
activity (propagation rate) and the polymerization behavior. We
also investigated synthesis and structural analysis of the series
Me2Al[O-2-tBu-6-(ArNdCH)C6H3] [Ar ) 2,6-F2C6H3 (2a), 2,4-
F2C6H3 (3a), 3,4-F2C6H3 (4a)] and explored the effect of the
imino substituent on both the activity and the polymerization
behavior in the ROPs of CL using a series of 1a-6a-PhCH2OH
catalyst systems [Ar ) C6H5 (5a), 2,6-Me2C6H3 (6a)]. Through
this project, we present important factors to establish the fast,
controlled ring-opening polymerization of the cyclic esters
exemplified as CL.
(8) Selected reports concerning transesterification in the ROP of CL and
DL-lactide: (a) Duda, A.; Penczek, S. Macromolecules 1995, 28, 5981. (b)
Montaudo, G.; Montaudo, M. S.; Puglisi, C.; Samperi, F.; Spassky, N.;
LeBorgne, A.; Wisniewski, M. Macromolecules 1996, 29, 6461. (c) Spassky,
N.; Simic, V.; Montaudo, M. S.; Hubert-Pfalzgraf, L. G. Macromol. Chem.
Phys. 2000, 201, 2432. (d) Jhurry, D.; Bhaw-Luximon, A.; Spassky, N.
Macromol. Symp. 2001, 175, 67. (e) Cayuela, J.; Bounor-Legare´, V.;
Cassagnau, P.; Michel, A. Macromolecules 2006, 39, 1338.

ROP by Al Complexes with Phenoxyimine Ligands
Organometallics, Vol. 28, No. 7, 2009 2181
Scheme 2
F2C6H3). Various Al complexes containing different anionic
(alkyl, halogen) ligands, R1(R2)Al[O-2-tBu-6-{(C6F5)NdCH}
C6H3] [R1, R2 ) Et, Et (1b); Me, Cl (1c)], have been prepared
by treatment of AlEt3 or Me2AlCl with 1 equiv of 2-tBu-6-
(ArNdCH)C6H3OH in n-hexane (Scheme 2).9 The synthetic
procedures are analogous to that for Me2Al[O-2-tBu-
6-{(C6F5)NdCH}C6H3] (1a), and the complexes were identified
1
on the basis of their H and 13C NMR spectra and elemental
analyses. The structures of 1b and 1c were determined by X-ray
crystallography (Figure 1), and the selected bond distances and
angles are summarized in Table 1.10
Complexes 1b and 1c have a distorted tetrahedral geometry
around the Al, as seen in 1a.4b The Al-O bond distances in
1b,c [1.753(2) and 1.7479(11) Å, respectively] are shorter than
that in 1a [1.7737(16) Å], and the Al-N bond distance in 1c
[1.9429(12) Å] is shorter than those in 1a,b [1.9780(19) and
1.986(2) Å, respectively]. One Al-carbon bond distance in 1b
[2.127(10) Å] is apparently longer than the Al-C bond distances
in 1a,c [1.9304(17)-1.951(2) Å]; this can probably be explained
as due to the steric bulk of two ethyl groups in 1b. The Al-Cl
bond distance [2.1547(6) Å] in 1c seems similar to the reported
values [ca. 2.1238-2.1239 Å in (TTP)AlCl2, TTPH ) 2-(p-
tolylamino)-4-(p-tolylimino)-2-pentene].6b The bond angle C(in
Me or Et)-Al-C(Me, Et) or C-Al-Cl is influenced by the
anionic ligand (Me, Et, or Cl) employed, and the angle increases
in the order C(12)-Al-C(14) [127.0(2)°] (1b) > C(1)-Al-C(2)
[118.12(12)°] (1a) > Cl(1)-Al-C(8) [113.88(6)°] (1c). The
O-Al-N angle in 1c [95.45(5)°] is somewhat larger than those
Results and Discussion
Synthesis and Structural Analysis of R1(R2)Al[O-2-tBu-6-
{(C6F5)NdCH}C6H3] (R1, R2 ) Et, Et; Me, Cl) and Me2Al[O-
2-tBu-6-(ArNdCH)C6H3] (Ar ) 2,6-F2C6H3, 2,4-F2C6H3, 3,4-
Figure 1. ORTEP drawings of Et2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1b; left) and Me(Cl)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1c;
right). Thermal ellipsoids are drawn at the 50% probability level, and H atoms are omitted for clarity.10
Table 1. Selected Bond Distances (Å) and Angles (deg) for Me2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1a), Et2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3]
(1b), and Me(Cl)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1c)a
1a
1b
1c
Bond Distances (Å)
Al(1)-O(1)
Al(1)-N(1)
Al(1)-C(1)
Al(1)-C(2)
N(1)-C(3)
N(1)-C(10)
1.7737(16)
1.9780(19)
1.951(2)
1.941(2)
1.300(2)
1.436(2)
Al(1)-O(1)
1.753(2)
1.986(2)
1.920(4)
2.127(10)
1.308(4)
1.423(3)
Al(1)-O(1)
Al(1)-N(1)
Al(1)-C(8)
Al(1)-Cl(1)
N(1)-C(7)
N(1)-C(13)
1.7479(11)
1.9429(12)
1.9304(17)
2.1547(6)
1.3104(19)
1.4344(19)
Al(1)-N(1)
Al(1)-C(12)
Al(1)-C(14)
N(1)-C(7)
N(1)-C(16)
Bond Angles (deg)
O(1)-Al(1)-N(1)
C(1)-Al(1)-C(2)
Al(1)-O(1)-C(9)
Al(1)-N(1)-C(3)
Al(1)-N(1)-C(10)
O(1)-Al(1)-C(1)
O(1)-Al(1)-C(2)
N(1)-Al(1)-C(1)
N(1)-Al(1)-C(2)
93.17(7)
O(1)-Al(1)-N(1)
C(12)-Al(1)-C(14)
Al(1)-O(1)-C(1)
Al(1)-N(1)-C(7)
Al(1)-N(1)-C(16)
O(1)-Al(1)-C(12)
O(1)-Al(1)-C(14)
N(1)-Al(1)-C(12)
N(1)-Al(1)-C(14)
93.26(10)
127.0(2)
132.06(15)
121.32(18)
120.8(2)
109.72(18)
106.67(16)
110.75(16)
104.2(2)
O(1)-Al(1)-N(1)
Cl(1)-Al(1)-C(8)
Al(1)-O(1)-C(1)
Al(1)-N(1)-C(7)
Al(1)-N(1)-C(13)
O(1)-Al(1)-C(8)
Cl(1)-Al(1)-O(1)
N(1)-Al(1)-C(8)
Cl(1)-Al(1)-N(1)
95.45(5)
118.12(12)
133.89(14)
122.97(14)
120.55(14)
113.73(10)
113.71(10)
105.34(9)
109.26(10)
113.88(6)
131.10(9)
120.78(10)
121.82(9)
116.16(7)
110.01(3)
117.86(7)
101.22(4)
a For detailed analysis conditions, see the Supporting Information.10

2182 Organometallics, Vol. 28, No. 7, 2009
Iwasa et al.
(Me, Et, or Cl). These results may be important in considering
the influences of the anionic donor ligands.
Al complexes containing phenoxyimine ligands with a series
of fluorinated aromatic substituents in the imino group, Me2Al[O-
2-tBu-6-(ArNdCH)C6H3] [Ar ) 2,6-F2C6H3 (2a), 2,4-F2C6H3
(3a), 3,4-F2C6H3 (4a)], were prepared by treating AlMe3 with
the corresponding iminophenols9 in n-hexane, and their synthetic
procedures are also analogous to that for 1a.4b The resultant
complexes were identified on the basis of the 1H and 13C NMR
spectra and elemental analyses. The structures of 2a, 3a, and
4a were also determined by X-ray crystallography (Figure 2),
and the selected bond distances and angles are summarized in
Table 2.10
The structures of 2a-4a indicate that these complexes fold
a distorted tetrahedral geometry around Al. The Al-N bond
distances are not strongly influenced by the imino substituent
[1.968(3)-1.9692(14) Å], and the Al-O bond distance in 4a
[1.759(2) Å] is somewhat shorter than those in 1a-3a
[1.7680(15)-1.7737(16) Å]. The Al-C(in Me) bond distances
in 4a [1.921(4) and 1.930(4) Å] are shorter than those in 1a
and 3a [1.941(2)-1.956(2) Å] and are apparently shorter than
those in 2a [1.963(2) and 1.973(2) Å]. The C-Al-C bond
angles increase in the order 3a [119.29(11)°] > 1a, 2a
[118.12(12)° and 118.00(10)°, respectively] > 4a [117.51(19)°],
and some bond angles are also influenced by the imino
substituent.
Attempted reaction of Me2Al[O-2-tBu-6-{(C6F5)NdCH}
C6H3] (1a) with 1.0 equiv of PhCH2OH in C6D6 at 25 °C
afforded a mixture of products that seemed difficult for their
identifications.11 The reaction of Me2Al(OCH2Ph) with 2-tBu-
6-{(C6F5)NdCH}C6H3OH in C6D6 also afforded a mixture of
products, and a trimetallic Al complex, [Me2Al(µ2-OCH2Ph)]2
[Al{O-2-tBu-6-{(C6F5)NdCH}C6H3}(µ2-OCH2Ph)2] (7), deter-
mined by X-ray crystallography, was isolated from the chilled
n-hexane solution (53% yield).11 The results suggest that both
the PhCH2OH and CL should be required for generating the
actual catalytically active species (assumed by the chain-end
analysis4) from 1a in this catalysis.
Effect of a Ligand on the Ring-Opening Polymerization
of ε-Caprolactone Using R1(R2)Al[O-2-tBu-6-(ArNdCH)
C6H3]-PhCH2OH Catalyst Systems. We recently demon-
strated that rapid living ROPs of both CL and VL were
achieved with high catalyst (initiation) efficiencies by using
Me2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1a) in the presence
of nBuOH (1.0 equiv).4 We also reported that the imino
Figure 2. ORTEP drawings of Me2Al[O-2-tBu-6-{(2,6-F2C6H3)
NdCH}C6H3] (2a; top), Me2Al[O-2-tBu-6-{(2,4-F2C6H3)NdCH}
C6H3] (3a; middle), and Me2Al[O-2-tBu-6-{(3,4-F2C6H3)Nd
CH}C6H3] (4a; bottom). Thermal ellipsoids are drawn at the 50%
probability level, and H atoms are omitted for clarity.10
in 1a,b [93.17(7) and 93.26(10), respectively], and the other
angles are also influenced by the anionic donor ligands employed
Table 2. Selected Bond Distances (Å) and Angles (deg) for Me2Al[O-2-tBu-6-{(2,6-F2C6F3)NdCH}C6H3] (2a),
Me2Al[O-2-tBu-6-{(2,4-F2C6H3)NdCH}C6H3] (3a), and Me2Al[O-2-tBu-6-{(3,4-F2C6H3)NdCH}C6H3] (4a)a
2a
3a
4a
Bond Distances (Å)
Al(1)-O(1)
Al(1)-N(1)
Al(1)-C(8)
Al(1)-C(9)
N(1)-C(7)
N(1)-C(14)
1.7680(15)
1.9692(14)
1.963(2)
1.973(2)
1.300(2)
1.435(2)
Al(1)-O(1)
1.7713(19)
1.9692(16)
1.956(2)
1.954(3)
1.302(2)
1.436(2)
Al(1)-O(1)
Al(1)-N(1)
Al(1)-C(8)
Al(1)-C(9)
N(1)-C(7)
N(1)-C(14)
1.759(2)
1.968(3)
1.930(4)
1.921(4)
1.312(5)
1.427(4)
Al(1)-N(1)
Al(1)-C(8)
Al(1)-C(9)
N(1)-C(7)
N(1)-C(14)
Bond Angles (deg)
O(1)-Al(1)-N(1)
C(8)-Al(1)-C(9)
Al(1)-O(1)-C(1)
Al(1)-N(1)-C(7)
Al(1)-N(1)-C(14)
O(1)-Al(1)-C(8)
O(1)-Al(1)-C(9)
N(1)-Al(1)-C(8)
N(1)-Al(1)-C(9)
93.15(6)
118.00(10)
133.60(11)
122.84(12)
119.56(11)
112.97(8)
112.13(9)
109.06(8)
108.54(8)
O(1)-Al(1)-N(1)
C(8)-Al(1)-C(9)
Al(1)-O(1)-C(1)
Al(1)-N(1)-C(7)
Al(1)-N(1)-C(14)
O(1)-Al(1)-C(8)
O(1)-Al(1)-C(9)
N(1)-Al(1)-C(8)
N(1)-Al(1)-C(9)
93.01(7)
119.29(11)
134.54(14)
123.09(14)
119.52(12)
113.02(10)
110.79(10)
107.91(9)
109.52(9)
O(1)-Al(1)-N(1)
C(8)-Al(1)-C(9)
Al(1)-O(1)-C(1)
Al(1)-N(1)-C(7)
Al(1)-N(1)-C(14)
O(1)-Al(1)-C(8)
O(1)-Al(1)-C(9)
N(1)-Al(1)-C(8)
N(1)-Al(1)-C(9)
93.28(13)
117.51(19)
133.4(2)
122.0(2)
120.0(2)
111.57(17)
110.47(16)
112.64(16)
108.74(15)
a For detailed analysis conditions, see the Supporting Information.10

ROP by Al Complexes with Phenoxyimine Ligands
Organometallics, Vol. 28, No. 7, 2009 2183
Table 5. Ring-Opening Polymerization of CL Initiated by
Me2Al[O-2-tBu-6-(ArNdCH)C6H4] [Ar ) C6F5 (1a), 2,6-F2C6H3 (2a),
2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a), C6H5 (5a), 2,6-Me2C6H3
(6a)]-PhCH2OH Catalyst Systemsa
Scheme 3
c
Mn(GPC)
×
Mw/
c
complex Ar
C6F5 (1a)
C6F5 (1a)
time/min conversionb/%
10-4
Mn Nd/µmol
15
30
48
81
94
21
49
73
89
25
59
87
97
19
46
73
89
14
31
50
69
82
91
14
35
55
72
83
90
3.15
4.87
5.53
1.06
2.16
2.99
3.35
1.20
2.45
3.47
3.94
0.95
1.92
2.82
3.24
0.67
1.37
1.93
2.55
2.79
2.99
0.79
1.74
2.61
3.19
3.53
3.74
1.19
1.21
1.22
1.12
1.24
1.42
1.50
1.11
1.18
1.32
1.48
1.13
1.17
1.41
1.58
1.11
1.16
1.28
1.43
1.78
1.98
1.11
1.14
1.14
1.21
1.31
1.42
31
33
34.
39
46
49
51
41
48
50
49
40
47
51
55
40
45
52
54
59
61
36
41
42
45
47
48
C6F5 (1a)
45
30
60
90
2,6-F2C6H3 (2a)
2,6-F2C6H3 (2a)
2,6-F2C6H3 (2a)
2,6-F2C6H3 (2a)
2,4-F2C6H3 (3a)
2,4-F2C6H3 (3a)
2,4-F2C6H3 (3a)
2,4-F2C6H3 (3a)
3,4-F2C6H3 (4a)
3,4-F2C6H3 (4a)
3,4-F2C6H3 (4a)
3,4-F2C6H3 (4a)
C6H5 (5a)
120
60
120
180
240
60
Table 3. Living Ring-Opening Polymerization of CL Initiated by
R1(R2)Al[O-2-tBu-6-{(C6F5)NdCH}C6H4] [R1, R2 ) Me, Me (1a); Et,
Et (1b); Me, Cl (1c)]-PhCH2OH Catalyst Systemsa
c
120
180
240
60
Mn(GPC)
×
c
complex R1, R2 time/min conversionb/%
10-4
Mw/Mn Nd/µmol
Me, Me (1a)
Me, Me (1a)
Me, Me (1a)
Et, Et (1b)
Et, Et (1b)
Et, Et (1b)
Me, Cl (1c)
Me, Cl (1c)
Me, Cl (1c)
15
30
45
15
30
45
15
30
45
48
81
94
48
78
91
53
83
93
3.15
4.87
5.53
2.32
3.50
4.12
2.46
3.57
3.96
1.19
1.21
1.22
1.24
1.23
1.21
1.12
1.14
1.12
31
33
34
41
45
44
43
47
47
C6H5 (5a)
C6H5 (5a)
C6H5 (5a)
C6H5 (5a)
120
180
240
300
360
60
C6H5 (5a)
2,6-Me2C6H3 (6a)
2,6-Me2C6H3 (6a)
2,6-Me2C6H3 (6a)
2,6-Me2C6H3 (6a)
2,6-Me2C6H3 (6a)
2,6-Me2C6H3 (6a)
120
180
240
300
360
a Conditions: Al (40 µmol), PhCH2OH (40 µmol), CL (10.0 mmol)
(CL/Al ) 250), toluene, [CL]0 ) 1.0 mmol/mL, 50 °C. b Estimated by
1H NMR spectra. c By gel permeation chromatography (GPC) in THF vs
polystyrene standards. d Estimated number of polymer chains (µmol) )
mass of CL reacted (mg) based on conversion/{Mn(GPC) × 0.56}.12
a Conditions: Al (40 µmol), PhCH2OH (40 µmol), CL (10.0 mmol)
(CL/Al ) 250), toluene, [CL]0 ) 1.0 mmol/mL, 50 °C. b Estimated
by 1H NMR spectra. c By GPC in THF vs polystyrene standards.
d Estimated number of polymer chains (µmol) ) mass of CL reacted
(mg) based on conversion/{Mn(GPC) × 0.56}.12
Table 4. Summary of the Rate Constants in Living Ring-Opening
Polymerization of CL Initiated by
R1(R2)Al[O-2-tBu-6-{(C6F5)NdCH}C6H4] [R1, R2 ) Me, Me (1a); Et,
Et (1b); Me, Cl (1c)]-PhCH2OH Catalyst Systemsa
b
e
kobsd
×
relative
krcor
×
complex R1, R2
10-2 min-1
Nc/µmol
efficiencyd
10-2 min-1
Me, Me (1a)
Et, Et (1b)
Me, Cl (1c)
2.8
2.4
2.6
34
44
47
0.72
0.94
1.0
3.9
2.6
2.6
a Polymerization conditions are shown in Table3. b Estimated on the
basis of Figure4 (slope). c Estimated number of polymer chains (µmol)
) mass of CL reacted (mg) based on conversion/{Mn(GPC) × 0.56}, cited
from Table3 (after 45 min).12 d Relative efficiency on the basis of N
(µmol) by 1c [)N(by 1a or 1b)/N(by 1c)]. e Corrected relative k value based on
kobsd and the relative efficiency.
Figure 3. Mn and Mw/Mn vs monomer conversion in the ring-
opening polymerization of ε-caprolactone initiated by R1(R2)Al[O-
2-tBu-6-{(C6F5)NdCH}C6H4] [R1, R2 ) Me, Me (1a; [, ]); Et,
Et (1b; b, O); Me, Cl (1c; 9, 0)]-PhCH2OH catalyst systems.
The detailed conditions are summarized in Table 3.
substituent strongly affects both the catalytic activity and the
catalyst efficiency. As described above, to explore the details
concerning major roles of the anionic donor ligand (Me, Et,
Cl) and the imino substituents (Ar) in both the catalytic
activity and the polymerization behavior (including a pos-
sibility of accompanying side reactions such as transesteri-
fication), we thus conducted the ROPs of CL using the series
R1(R2)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] [R1, R2 ) Me, Me
(1a); Et, Et (1b); Me, Cl (1c)] in the presence of PhCH2OH.
We also conducted the ROPs of CL using the series Me2Al[O-
2-tBu-6-(ArNdCH)C6H3] [Ar ) C6F5 (1a), 2,6-F2C6H3 (2a),
2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a), C6H5 (5a), 2,6-Me2C6H3
(6a)] in the presence of PhCH2OH, especially to explore the
role of the fluorinated substituent in the imino group (Scheme
the ROP of CL in terms of the activity as seen in the ROP by
1a reported previously.4 The PDI values (Mw/Mn) of 1c were
somewhat lower than those of 1a,b. As shown in Figure 3, linear
relationships between the monomer conversions and Mn values
were observed in these ROPs consistently with narrow molecular
weight distributions, and no significant differences were ob-
served in the N values [number of polymer chains estimated
by the Mn(GPC) values and the conversions] during the time
course.13 These results thus clearly indicate that these ROPs
by 1b,c proceeded in a living manner as demonstrated by 1a.4
n
3). PhCH2OH was chosen in place of BuOH, because the
ROP (conversion of monomers) can be easily monitored by
1H NMR spectra as references to the benzyl protons.12 The
results are summarized in Tables 3-5.12
It turned out that the ROPs of CL using the C6F5 derivatives
(1a-c) were almost completed after 45 min (conversion
91-94%, Table 3), indicating that 1b,c are also effective in
(9) (a) Syntheses of various salicylaldimine ligands: Fujita, T.; Tohi,
Y.; Mitani, M. European Patent EP 0874005A1, 1998. (b) Use of this ligand
for synthesis of group 4 transition-metal complexes for highly active olefin
polymerization catalysts was also reported by the same authors (Fujita, T.;
Mitani, M.; et al.), as introduced previously.3
(10) The detailed structural results including the CIF file are shown in
the Supporting Information.

2184 Organometallics, Vol. 28, No. 7, 2009
Iwasa et al.
monomer conversions [e.g., Mw/Mn ) 1.16 (conversion 31%), 1.78
(conversion 82%), 1.98 (conversion 91%), Table 5], and an increase
in the N value (number of polymer chains) was also seen at high
CL conversion. The results strongly suggest that a certain degree
of transesterification (shown in Scheme 1)8 accompanied the
propagation in the ROP of CL. Similarly, increases in both the
Mw/Mn and the N values at high monomer conversion
were observed in the ROPs of CL using the above Al complexes
(2a-6a, Figure 5), whereas no significant changes in both the Mw/
Mn and the N values were seen in the ROP using the C6F5 analogue
(1a). The results also suggest that a certain degree of transesteri-
fication would be present in the ROPs under these conditions,
although the degree of the transesterification seemed to decrease
in the presence of an ortho-substituent [5a (C6H5) vs 6a (2,6-
Me2C6H3), 5a (C6H5) vs 2a (2,6-F2C6H3), 3a (2,4-F2C6H3) vs 4a
(3,4-F2C6H3), Table 5]. We thus assume that the presence of a rather
strong electron-withdrawing group (C6F5) would be required to
prohibit the transesterification from accompanying the propagation
in the ROP, probably by a weak H-F interaction as well as better
stabilization of the propagating species.14,15 Taking into account
these results, use of the C6F5 substituent in the imino group is thus
essential in terms of both the catalytic activity and the ROP
proceeding in the living manner.
Figure 4. log[[CL]/[CL]0] vs time in the ring-opening polymeri-
zation of ε-caprolactone initiated by R1(R2)Al[O-2-tBu-6-
{(C6F5)NdCH}C6H4] [R1, R2 ) Me, Me (1a; ]); Et, Et (1b; O);
Me, Cl (1c; 0)]-PhCH2OH catalyst systems.
As shown in Figure 4, the propagation rates in the ROPs by
1a-c were first-order-dependent upon the monomer concentration,
suggesting that the ROPs proceeded without catalyst deactivation.
The observed rates (kobsd) by 1a-c seemed to be close (kobsd
)
(2.4-2.8) × 10-2 min-1, Table 4); however, the estimated N value
of 1a was lower than those of 1b,c, due to their different catalyst
efficiencies.13 Therefore, the actual k value (propagation rate
constant) of 1a should be higher than those of 1b,c (Table 4). We
assume that the observed difference between 1a and 1c would
probably be due to a different electronic nature of the propagating
Al species between Me and Cl, and the methyl group in 1c would
be reacted with PhCH2OH to generate the initiating species. We
also speculate that the observed difference between the methyl (1a)
and ethyl (1b) analogues would be due to the steric bulk around
the propagating Al center, as seen in the unique Al-C bond angle
in both Figure 1 and Table 1, although we do not have any clear
evidence to explain this speculation.
Concluding Remarks
A series of Al complexes containing phenoxyimine ligands
of the types R1(R2)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] [R1, R2
) Et, Et (1b); Me, Cl (1c)] and Me2Al[O-2-tBu-6-(ArNd
CH)C6H3] [Ar ) 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3
(4a)] have been prepared and identified on the basis of NMR
spectra and elemental analyses, and their structures were
determined by X-ray crystallography. The ROPs of CL using
1a-c in the presence of PhCH2OH proceeded efficiently in a
living manner, and the propagation rates were affected by the
anionic donor ligand employed (Me, Et, or Cl). The catalytic
activity using 1a-6a [Ar ) C6H5 (5a), 2,6-Me2C6H3 (6a)]-
PhCH2OH catalyst systems was highly affected by the aromatic
substituent in the imino group, and fluorinated substituents
especially in the ortho-position affected the catalytic activity.
The ROPs using 2a-6a-PhCH2OH catalyst systems were
accompanied by a certain degree of side reactions such as
transesterification, whereas the living polymerization systems
can be accomplished using the C6F5 analogues (1a-c). Although
we could not find a more efficient catalyst than 1a reported
previously,4 these results clearly indicate that the C6F5 substitu-
ent in the imino group plays an essential key role in the ROP
of CL in terms of both the catalytic activity and the ROP
proceeding in a living manner.
It also turned out that the catalytic activity in the ROPs of
CL using a series of Al complexes containing phenoxyimine
ligands (with different fluorinated aromatic substituents in the
imino group), Me2Al[O-2-tBu-6-(ArNdCH)C6H3], increased in
the order Ar ) C6F5 (1a) . Ar ) 2,6-F2C6H3 (2a) > Ar )
2,4-F2C6H3 (3a) > Ar ) 3,4-F2C6H3 (4a) > Ar ) 2,6-Me2C6H3
(6a) > Ar ) C6H5 (5a) (Table 5). The results clearly indicate
that substitution of the ortho-position, especially the fluorine
substituent, strongly affects the catalytic activity. As described
above, the ROP by the C6F5 analogue (1a) proceeded in a living
manner; a linear relationship between the monomer conversions
and the Mn values consistently with low Mw/Mn values was
observed (Figure 5, plotted as [,]).
In contrast, as shown in Figure 5 (right), the molecular weight
distributions (Mw/Mn values) in the resultant polymers prepared
by the C6H5 analogue (5a, plotted as 0) became broad after certain
Figure 5. Mn and Mw/Mn vs monomer conversion in the ring-opening polymerization of ε-caprolactone initiated by Me2Al[O-2-tBu-6-
(ArNdCH)C6H4]-PhCH2OH catalyst systems: (left) Ar ) C6F5 (1a), 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a); (right) Ar ) C6F5
(1a), C6H5 (5a), 2,6-Me2C6H3 (6a). The detailed conditions are summarized in Table 5.

ROP by Al Complexes with Phenoxyimine Ligands
Organometallics, Vol. 28, No. 7, 2009 2185
Table 6. Crystal Data and Structure Refinement Parameters for Et2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1b),
Me(Cl)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1c), and Me2Al[O-2-tBu-6-(ArNdCH)C6H3] [Ar ) 2,6-F2C6H3 (2a), 2,4-F2C6H3 (3a), 3,4-F2C6H3 (4a)]a
1b
1c
2a
3a
4a
empirical formula
fw
C21H23AlF5NO
427.39
C18H16AlClF5NO
419.76
C19H22AlF2NO
345.37
C19H22AlF2NO
345.37
C19H22AlF2NO
345.37
cryst color, habit
cryst size (mm)
cryst syst
space group
a (Å)
yellow, block
0.62 × 0.44 × 0.24
monoclinic
C2/c (No. 15)
32.263(3)
7.9795(5)
20.2578(16)
124.982(2)
4272.9(6)
8
1.329
1776.00
19796
2862
285
0.0554
0.0921
1.004
colorless, block
0.32 × 0.20 × 0.15
monoclinic
P21/a (No. 14)
12.4278(6)
12.3734(6)
12.7793(7)
91.7271(17)
1964.24(17)
4
1.419
856.00
19089
3467
260
0.0319
0.0948
1.007
colorless, block
0.22 × 0.20 × 0.18
triclinic
colorless, block
0.54 × 0.42 × 0.35
triclinic
yellow, block
0.30 × 0.18 × 0.15
monoclinic
P21/c (No. 14)
7.0439(3)
20.8564(11)
26.5114(13)
93.2474(13)
3888.5(3)
8
1.180
1456.00
31362
3306
485
0.0456
0.1167
1.006
j
j
P1 (No. 2)
P1 (No. 2)
7.5473(4)
9.8452(7)
12.7096(7)
74.8131(14)
906.84(9)
2
1.265
364.00
9121
3214
239
0.0433
0.1619
1.000
7.7061(4)
9.7853(6)
12.7343(8)
105.4480(18)
915.65(10)
2
1.253
364.00
9074
3460
239
0.0681
0.2190
1.000
b (Å)
c (Å)
ꢀ (deg)
V (Å3)
Z
Dcalcd (g/cm3)
F000
no. of reflns measd
no. of observations
no. of variables
R1
wR2
goodness of fit
a Detailed conditions are shown in the Supporting Information.10
On the basis of simple PM3 calculations for energy evalu-
ations for stabilization in the model propagating species
(R2)Al[O-2-tBu-6-(ArNdCH)C6H3][O(CH2)5C(O)OMe] [R2 )
Me and Ar ) Ph, 2,6-Me2C6H3, 2,6-F2C6H3, 2,4-F2C6H3, 3,4-
F2C6H3; R2 ) Me, Et, Cl and Ar ) C6F5], after geometry
optimization, an introduction of fluorine into the aryl group (Ar)
drastically increases the stability of the catalytically active
species; the C6F5 analogue was the most suited among these
aryl substituents.14Moreover, weak H-F interactions were
observed when C6F5 and 2,6-F2C6H3 were used as the aryl
substituent, which would form a favored geometry for subse-
quent CL coordination and insertion (without coordination of
CL from the other site forming a dormant species).14,15 Although
more precise calculations are necessary, we would assume that
this fact should provide appropriate explanations of why the
C6F5 analogue is the most suited in terms of both the activity
and efficiency. We believe that the results obtained here should
be highly promising for designing more efficient catalysts of
living ROP of cyclic esters.
Experimental Section
General Procedures. All experiments were carried out under a
nitrogen atmosphere in a Vacuum Atmospheres drybox or using
standard Schlenk techniques. Anhydrous-grade n-hexane and
toluene (Kanto Kagaku Co., Ltd.) were transferred into a bottle
containing molecular sieves (a mixture of 3A 1/16, 4A 1/8, and
13X 1/16) in the drybox under a N2 stream and were passed through
a short alumina column under a N2 stream before use. All chemicals
used were of reagent grade and were purified by the standard
purification procedures. Reagent-grade AlMe3, AlEt3, and Me2AlCl
in n-hexane (Kanto Kagaku Co. Ltd.) were stored in the drybox
and were used as received. Various salicylaldimines (iminophenols)
containing different substituents on the imino groups, 2-tBu-6-
(RNdCH)C6H3OH [R ) Ph, 2,6-Me2C6H3, C6F5, 2,6-F2C6H3, 2,4-
F2C6H3, 3,4-F2C6H3] were prepared according to the reported
procedures.9 Syntheses of Al complexes (1, 5, 6a) were as described
in our previous papers.4a,b Elemental analyses were performed by
using a PE2400II series (Perkin-Elmer Co.) instrument. All 1H and
13C NMR spectra were recorded on a JEOL JNM-LA400 spec-
(11) Attempted reaction of Me2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] with
1.0 equiv of PhCH2OH in C6D6 and Me2Al(OCH2Ph) with 2-tBu-
6-{(C6F5)NdCH}C6H3OH in C6D6 afforded a mixture of products including
[Me2Al(µ2-OCH2Ph)]2[Al{O-2-tBu-6-{(C6F5)NdCH}C6H3}(µ2-
OCH2Ph)2] (7) determined by X-ray crystallography. On the basis of the
above reaction results and the fact that the living polymerization was initiated
by the AlOCH2Ph species (by the chain end analysis), it is thus clear that
both PhCH2OH and CL should be required to generate the assumed initiating
species from Me2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3]. Details on attempted
experiments including isolation and analysis results for 7 are shown in the
Supporting Information.
(12) We estimated conversions of CL by 1H NMR spectra, and most of
the spectra are shown in the Supporting Information. Moreover, the exact
Mn values for ring-opened poly(CL)s were corrected from the Mn values
1
trometer (399.65 MHz for H, 100.40 MHz for 13C). All spectra
by GPC vs polystyrene standards according to the equation Mn(PCL)
)
were obtained in the solvent indicated at 25 °C unless otherwise
0.56Mn(GPC vs polystyrene standards) according to the following reference: (a) Save,
M.; Schappacher, M.; Soum, A. Macromol. Chem. Phys. 2002, 203, 889.
(b) Duda, A.; Kowalski, A.; Penczek, S. Macromolecules 1998, 31, 2114.
We did not estimate the Mn values from the 1H NMR spectra, because the
spectra were a mixture of the reaction products [CL, poly(CL), toluene,
etc.] and seemed to be lacking accuracy. As demonstrated previously,4
PhCH2OH (1.0 equiv relative to Al) was prerequisite for generating the
aluminum alkoxide (as proposed initiating species for the ROP), and the
polymerization did not take place in the absence of PhCH2OH. Addition of
more than 1 equiv of PhCH2OH will afford a mixture of mono- and
bisalkoxide, and this is not suited for the precise control in this catalysis.
(13) On the basis of the results for estimation of the number of polymer
chains (N value), N values by 1b,c were slightly larger than the Al complex
charged. We assume that this would be due to the accuracy of the Mn values
corrected, because the corrected Mn values used for the estimation were
based on the Mn value measured by GPC in THF vs polystyrene standards.
Since the number of polymer chains (N values) did not change during the
time course, we assume that the ROPs by 1b,c proceeded with quantitative
initiation efficiencies. The catalyst efficiency by 1a estimated on the basis
of the N value by 1c is 72%, and the value is relatively close to that estimated
previously by 1H NMR spectra (68%).4b,c
noted, and their chemical shifts are given in parts per million and
1
are referenced to SiMe4 (δ 0.00, H, 13C). The molecular weights
and molecular weight distributions of the resultant polymers were
measured by GPC. GPC was performed at 40 °C on a Shimadzu
SCL-10A using an RID-10A detector (Shimadzu Co. Ltd.) in THF
(containing 0.03 wt % 2,6-di-tert-butyl-p-cresol, flow rate 1.0 mL/
min). GPC columns (ShimPAC GPC-806,- 804, and -802, 30 cm
× 8.0 mm L, spherical porous gel made of styrene/divinylbenzene
copolymer, ranging from MW < 102 to MW ) 2 × 107) were
calibrated versus polystyrene standard samples.
Synthesis of 2-tBu-6-{(2,4-F2C6H3)NdCH}C6H3OH. A mixture
of 2,4-difluoroaniline (1.42 g, 11.0 mmol), 3-tert-butyl-2-hydroxy-
benzaldehyde (1.78 g, 10.0 mmol), and p-toluenesulfonic acid (3
mg, 17 µmol) in toluene (25 mL) was refluxed for 17 h. Removal
of the solvent from the reaction mixture by a rotary evaporator in
vacuo gave a dark yellow oil, and purification by silica gel column
chromatography using n-hexane afforded a yellow oil (2.87 g, 99%

2186 Organometallics, Vol. 28, No. 7, 2009
Iwasa et al.
1
t
yield). H NMR (C6D6): δ 1.58 (s, 9H, Bu), 6.30-6.48 (m, 3H,
aromatic), 6.77 (t, 1H, J ) 8 Hz, aromatic), 6.88 (d, 1H, J ) 7 Hz,
aromatic), 7.36 (d, 1H, J ) 7 Hz, aromatic), 7.95 (s, 1H, CHdN),
14.01 (s, 1H, OH). 13C NMR (C6D6): δ 29.6, 35.2, 104.8 (dd, J1 )
3 Hz, J2 ) 2 Hz), 111.5 (dd, J1 ) 22 Hz, J2 ) 4 Hz), 118.7, 119.3,
121.9 (dd, J1 ) 10 Hz, J2 ) 2 Hz), 131.2, 132.9 (dd, J1 ) 11 Hz,
J2 ) 4 Hz), 138.1, 156.0 (dd, J1 ) 252 Hz, J2 ) 12 Hz), 161.2
(dd, J1 ) 247 Hz, J2 ) 11 Hz), 161.3, 165.0. Anal. Calcd for
C17H17F2NO: C, 70.58; H, 5.92; N, 4.84. Found: C, 70.20; H, 6.10;
N, 4.80.
(878 mg, 85% yield). 1H NMR (C6D6): δ -0.21 (t, J ) 1 Hz, 6H,
AlMe2), 1.49 (s, 9H, tBu), 6.38-6.49 (m, 3H, aromatic), 6.53 (t, J
) 8 Hz, 1H, aromatic), 6.59 (dd, J1 ) 8 Hz, J2 ) 2 Hz, 1H,
aromatic), 7.37 (m, 2H, aromatic, CHdN). 13C NMR (C6D6): δ
-10.0, 29.4, 35.3, 112.1-112.3 (m), 117.5, 119.6, 124.1 (t, J ) 2
Hz), 134.5, 136.0, 142.0, 156.5 (dd, J1 ) 250 Hz, J2 ) 4 Hz),
165.8, 176.1-176.2 (m). Anal. Calcd for C19H22AlNO: C, 66.08;
H, 6.42; N, 4.06. Found: C, 66.06; H, 6.12; N, 4.04.
Synthesis of Me2Al[O-2-tBu-6-{(2,4-F2C6H3)NdCH}C6H3]
(3a). To a stirred solution containing 2-tBu-6-{(2,4-F2C6H3)
NdCH}C6H3OH (1.16 g, 4.00 mmol) in n-hexane (10.0 mL) was
added AlMe3 (0.43 M n-hexane solution, 9.67 mL, 4.20 mmol of
Al) dropwise over a 10 min period at -20 °C. The solution was
allowed to warm to room temperature and was stirred for 3 h
(Scheme 2). The mixture was then concentrated in vacuo, and the
chilled solution (-20 °C) afforded colorless microcrystals of 3a
Synthesis of 2-tBu-6-{(3,4-F2C6H3)NdCH}C6H3OH. A mixture
of 3,4-difluoroaniline (1.42 g, 11.0 mmol), 3-tert-butyl-2-hydroxy-
benzaldehyde (1.78 g, 10.0 mmol), and p-toluenesulfonic acid (3
mg, 17 µmol) in toluene (25 mL) was refluxed for 18 h. The solution
was then concentrated in vacuo, and purification by silica gel
column chromatography using n-hexane afforded a yellow oil (2.81
1
t
g, 97% yield). H NMR (C6D6): δ 1.61 (s, 9H, Bu), 6.23-6.60
(m, 3H, aromatic), 6.79 (t, 1H, J ) 8 Hz, aromatic), 6.89 (d, 1H,
J ) 7 Hz, aromatic), 7.37 (d, 1H, J ) 7 Hz, aromatic), 7.75 (s,
1H, CHdN), 13.79 (s, 1H, OH). 13C NMR (C6D6): δ 29.6, 35.2,
110.1 (d, J ) 190 Hz), 117.5 (d, J ) 18 Hz), 117.8 (dd, J1 ) 5 Hz,
J2 ) 3 Hz), 118.8, 119.1, 131.1, 131.2, 145.0 (dd, J1 ) 6 Hz, J2 )
3 Hz), 149.4 (dd, J1 ) 246 Hz, J2 ) 13 Hz), 150.8 (dd, J1 ) 248
Hz, J2 ) 14 Hz), 161.0, 164.0. Anal. Calcd for C17H17F2NO: C,
70.58; H, 5.92; N, 4.84. Found: C, 70.81.; H, 6.27; N, 4.73.
Synthesis of Et2Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1b). To
a stirred solution containing 2-tBu-6-{(C6F5)NdCH}C6H3OH (1.37
g, 4.00 mmol) in n-hexane (5.0 mL) was added AlEt3 (0.90 M
n-hexane solution, 4.67 mL, 4.20 mmol of Al) dropwise over a 10
min period at -20 °C. The solution was allowed to warm to room
temperature slowly and was stirred for 3 h. The mixture was then
concentrated in vacuo, and the chilled solution (-20 °C) afforded
1
(1.28 g, 93% yield). H NMR (C6D6): δ -0.26 (s, 6H, AlMe2),
t
1.52 (s, 9H, Bu), 6.26-6.36 (m, 2H, aromatic), 6.50-6.64 (m,
3H, aromatic), 7.34 (s, 1H, CHdN), 7.40 (d, J ) 7 Hz, 1H,
aromatic). 13C NMR (C6D6): δ -9.6, 29.4, 35.3, 105.3 (t, J ) 25
Hz), 111.9 (dd, J1 ) 22 Hz, J2 ) 3 Hz), 117.6, 119.7, 126.0 (d, J
) 10 Hz), 130.9 (dd, J1 ) 11 Hz, J2 ) 3 Hz), 134.3, 135.7, 141.9,
155.5 (dd, J1 ) 251 Hz, J2 ) 12 Hz), 161.6 (dd, J1 ) 248 Hz, J2
) 11 Hz), 165.3, 173.5. Anal. Calcd for C19H22F2AlNO: C, 66.08;
H, 6.42; N, 4.06. Found: C, 66.16; H, 6.54; N, 4.08.
Synthesis of Me2Al[O-2-tBu-6-{(3,4-F2C6H3)NdCH}C6H3]
(4a). To a stirred solution containing 2-tBu-6-{(3,4-F2C6H3)
NdCH}C6H3OH (1.16 g, 4.00 mmol) in n-hexane (10.0 mL) was
added AlMe3 (1.09 M n-hexane solution, 4.67 mL, 4.20 mmol of
Al) dropwise over a 10 min period at -20 °C. The solution was
allowed to warm to room temperature and was stirred for 3 h
(Scheme 2). The mixture was then concentrated in vacuo, and the
chilled solution (-20 °C) afforded colorless microcrystals of 4a
1
yellow microcrystals of 1b (1.26 g, 74% yield). H NMR (C6D6):
δ 0.33 (s, 4H, AlCH2CH3), 1.36 (s, 6H, AlCH2CH3), 1.49 (s,
9H,tBu), 6.52 (br, 1H, aromatic), 6.64 (br, 1H, aromatic), 7.33 (s,
1H, CHdN), 7.40 (br, 1H, aromatic). 13C NMR (C6D6): δ 0.3, 9.1,
29.3, 35.3, 118.0, 119.3, 121.6-121.9 (m), 134.7, 136.7-137.0 (m),
137.3, 138.8-139.5 (m), 140.4-140.6 (m), 141.4-141.7 (m),
142.3, 143.0-143.1 (m), 167.0, 177.3. Anal. Calcd for
C21H23F5AlNO: C, 59.02; H, 5.42; N, 3.28. Found: C, 58.71; H,
5.18; N, 3.12.
Synthesis of Me(Cl)Al[O-2-tBu-6-{(C6F5)NdCH}C6H3] (1c).
To a stirred solution containing 2-tBu-6-{(C6F5)NdCH}C6H3OH
(0.87 g, 3.00 mmol) in a mixture of n-hexane (10.0 mL) and toluene
(4 mL) was added Me2AlCl (0.46 M n-hexane solution, 6.90 mL,
3.15 mmol of Al) dropwise over a 10 min period at -20 °C. The
solution was allowed to warm to room temperature and was stirred
for 3 h (Scheme 2). The mixture was then concentrated in vacuo,
and the chilled solution (-20 °C) afforded colorless microcrystals
1
(1.12 g, 87% yield). H NMR (C6D6): δ -0.28 (s, 6H, AlMe2),
1.53 (s, 9H, tBu), 6.40-6.46 (m, 3H, aromatic), 6.61 (t, J ) 8 Hz,
1H, aromatic), 6.66 (dd, J1 ) 8 Hz, J2 ) 2 Hz, 1H, aromatic), 7.19
(s, 1H, CHdN), 7.42 (dd, J1 ) 7 Hz, J2 ) 2 Hz, 1H, aromatic).
13C NMR (C6D6): δ -8.9, 29.4, 35.3, 117.59, 118.12 (dd, J1 ) 18
Hz, J2 ) 2 Hz), 118.74 (dd, J1 ) 6 Hz, J2 ) 3 Hz), 119.74, 134.24,
135.56, 141.84, 143.19 (dd, J1 ) 7 Hz, J2 ) 4 Hz), 149.90 (dd, J1
) 249 Hz, J2 ) 13 Hz), 150.78 (dd, J1 ) 250 Hz, J2 ) 14 Hz),
164.89, 170.72. Anal. Calcd for C19H22F2AlNO: C, 66.08; H, 6.42;
N, 4.06. Found: C, 66.28; H, 6.59; N, 4.03.
ROP of CL. Typical polymerization procedures (Table 3) are
as follows. To a sealed Schlenk tube containing a toluene solution
of 1a (40 µmol/0.100 mL of toluene) was added PhCH2OH (0.040
mmol/0.096 mL of toluene) in the drybox at room temperature.
The solution was stirred for 10 min, and then toluene (8.76 mL)
and ε-caprolactone (5.0 mmol) were added. The reaction mixture
was then placed into an oil bath preheated at 50 °C, and the solution
was stirred for the prescribed time (15 min). A small amount of
the reaction mixture was partly taken out from the mixture for a
certain period to monitor the reaction, especially to analyze the
1
of 1c (939 mg, 78% yield). H NMR (C6D6): δ -0.06 (t, J ) 2
Hz, 3H, Me), 1.44 (s, 9H, Bu), 6.52 (t, J ) 8 Hz, 3H, aromatic),
t
6.60 (dd, J1 ) 8 Hz, J2 ) 2 Hz, aromatic), 7.26 (s, 1H, NdCH),
7.39 (dd, J1 ) 7 Hz, J2 ) 2 Hz, 1H, aromatic). 13C NMR (C6D6):
δ -11.1, 29.3, 35.3, 119.2, 119.2, 120.1-120.5 (m), 134.9,
136.6-137.0 (m), 138.1, 139.1-139.5 (m), 140.5-140.7 (m),
141.9-142.1 (m), 142.5, 142.9-143.2 (m), 165.4, 177.91. Anal.
Calcd for C18H16F5AlClNO: C, 51.50; H, 3.84; N, 3.34. Found: C,
51.38; H, 3.79; N, 3.23.
Synthesis of Me2Al[O-2-tBu-6-{(2,6-F2C6H3)NdCH}C6H3]
(2a). To a stirred solution containing 2-tBu-6-{(2,6-F2C6H3)
NdCH}C6H3OH (0.87 g, 3.00 mmol) in n-hexane (7.5 mL) was
added AlMe3 (0.47 M n-hexane solution, 6.67 mL, 3.15 mmol of
Al) dropwise over a 10 min period at -20 °C. The solution was
allowed to warm to room temperature and was stirred for 3 h
(Scheme 2). The mixture was then concentrated in vacuo, and the
resultant solid was dissolved in a minimum amount of toluene. The
chilled solution (-20 °C) afforded colorless microcrystals of 2a
(14) The results for geometry optimizations for proposed catalytically
active species (R2)Al[O-2-tBu-6-(ArNdCH)C6H3][O(CH2)5C(O)OMe] [R2
) Me and Ar ) Ph, 2,6-Me2C6H3, 2,6-F2C6H3, 2,4-F2C6H3, C6F5; R2
)
Me, Et, Cl and Ar ) C6F5] and energy evaluations [equilibrium geometry
at the ground state with semiempirical PM3, geometry optimization, RHF/
PM3D Spartan ’06 for Windows (Wavefunction Inc.)] are shown in the
Supporting Information. Geometry optimizations (for confirmation of the
results in PM3 calculations) were also explored with the DFT B3LYP/6-
31G* method (initial PM3 data). These results are shown in the Supporting
Information.
(15) Previous report which introduces that weak H-F interaction in the
C6F5 group plays a role in the living polymerization of ethylene: Mitani,
M.; Mohri, J.; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.;
Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.; Matsugi, T.; Kashiwa,
N; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327.

ROP by Al Complexes with Phenoxyimine Ligands
Organometallics, Vol. 28, No. 7, 2009 2187
1
monomer conversion [by H NMR (400 MHz)] and Mn and Mw/
Mn (by GPC).
Acknowledgment. N.I. and K.N. express their thanks to
Daiso Co., Ltd. for support, and J.L. thanks the JSPS (Japan
Society for the Promotion of Science) for a postdoctoral
fellowship (Grant P05397).
Crystallographic Analysis. All measurements were made on a
Rigaku RAXIS-RAPID imaging plate diffractometer with graphite-
monochromated Mo KR radiation. The selected crystal collection
parameters are summarized in Table 6, and the detailed results are
described in the Supporting Information.10 All structures were
solved by direct methods and expanded using Fourier techniques,16
and the non-hydrogen atoms were refined anisotropically. Hydrogen
atoms were included but not refined. All calculations for complexes
1b,c and and 2a-4a were performed using the Crystal Structure17,18
crystallographic software package.
Supporting Information Available: Text giving (i) detailed
polymerization results including 1H NMR spectra in the ring-
opening polymerization of CL by 1a-c and 2a-6a in the presence
of PhCH2OH, (ii) attempted reaction of Me2Al[O-2-tBu-6-
{(C6F5)NdCH}C6H3] with 1.0 equiv of PhCH2OH in C6D6 and
Me2Al(OCH2Ph) with HO-2-tBu-6-{(C6F5)NdCH}C6H3 in C6D6
including the structure of [Me2Al(µ2-OCH2Ph)]2[Al{O-2-tBu-
6-{(C6F5)NdCH}C6H3}(µ2-OCH2Ph)2] (7), (iii) results for geometry
optimizations for proposed catalytically active species and energy
evaluations (by PM3 and DFT), and (iv) CIF files and structure
reports for 1b,c, 2a-4a, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
(16) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Delder, R.; Israel, R.; Smits, J. M. M. The DIRDIF94 Program System;
Technical Report of Crystallography Laboratory; University of Nijmegen:
Nijmegen, The Netherlands, 1994.
(17) Crystal Structure 3.6.0: Crystal Structure Analysis Package; Rigaku
and Rigaku/MSC: The Woodlands, TX, 2000-2004.
(18) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.
CRYSTALS Issue 10; Chemical Crystallography Laboratory: Oxford, U.K.,
1996.
OM8011882