Organoaluminium complexes derived from anilines or schiff bases for the ring-opening polymerization of ε-caprolactone, δ-valerolactone and rac-lactide

Article abstract of DOI:10.1002/ejic.201601415

Reaction of R¹R²CHN=CH(3,5-tBu₂C₆H₂-OH-2) (R¹ = R² = Me L¹H R¹ = Me, R² = Ph L²H R¹ = R² = Ph L³with slightly greater than one equivalent of R³ 3Al (R³ = Me, Eafforded the complexes [(L^1-3)AlR³ 2] (L¹, R³ = Me 1, R³ = Et 2 L², R³ = Me 3, R³ = Et 4 L³ R³ = Me 5, R³ = Et 6) complex 1 has been previously reported. Use of the N,O-ligand derived from 2,2′-diphenylglycine afforded either 5 or the byproduct [Ph₂NCH₂(3,5-tBu₂C₆H₂-O-2)AlMe₂] (7). The known Schiff base complex [2-Ph₂PC₆H₄CH₂(3,5-tBu₂C₆H₂-O-2)AlMe₂] (8) and the product of the reaction of 2-diphenylphosphinoaniline 1-NH₂,2-PPh₂C₆H₄ with Me₃Al, namely {Ph₂PC₆H₄N[(Me₂Al)₂μ-Me]-(μ-Me₂Al)} (9), were also isolated. For structural and catalytic comparisons, complexes resulting from the interaction of Me3Al with diphenylamine (or benzhydrylamine), namely {Ph₂ N[(Me₂Al)₂μ-Me]} (10) and[Ph₂CHNH(μ-Me₂Al)]₂·MeCN (11), were prepared. The molecular structures of the Schiff proligands derived from Ph₂CHNH₂ and 2,2′-Ph₂C(CO₂H)(NH₂), together with those of complexes 5, 7 and 9-11·MeCN were determined 5 contains a chelating imino/phenoxide ligand, whereas 7 contains the imino function outside of the metallocyclic ring. Complex 9 contains three nitrogen-bound Al centres, two of which are linked by a methyl bridge, whilst the third bridges the N and P centres. In 10, the structure resembles 9 with a bridging methyl group, whereas the introduction of the extra carbon in 11 results in the formation of a dimer. All complexes have been screened for their ability to promote the ring-opening polymerization (ROε-caprolactone, δ-valerolactone or rac-lactide, in the presence of benzyl alcohol, with or without solvent present. Reasonable conversions were achievable at room temperature for ε-caprolactone when using complexes 7, 9 and 12, whilst at higher temperatures (80-110 °C), all complexes produced good (> 65 %) to quantitative conversions over periods as short as 3 min, albeit with poor control. In the absence of solvent, conversions were nearly quantitative at 80 °C in 5 min with better agreement between observed and calculated molecular weight (M_n). For rac-lactide, conversions were typically in the range 71-86 % at 110 °C in 12 h, with poor control affording atactic polylactide (PLA), whilst for δ-valerolactone more forcing conditions (12-24 h at 110 °were required for high conversion. Co-polymerization of ε-caprolactone with rac-lactide afforded co-polymers with appreciable lactide content (35-62.5 %) the reverse addition was ineffective, affording only (polycaprolactonPCL.

Full text of DOI:10.1002/ejic.201601415

A Journal of
Accepted Article
Title: Organoaluminium complexes derived from Anilines or Schiff
bases for ring opening polymerization of epsilon-caprolactone,
delta-valerolactone and rac-lactide
Authors: Carl Redshaw, Xue Wang, Ke-Qing Zhao, Yahya Al-Khafaji,
Shanyan Mo, Timothy J Prior, and Mark R.J. Elsegood
This manuscript has been accepted after peer review and appears as an
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content of this Accepted Article.
To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201601415
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
catalytic comparisons, complexes resulting from
interaction of Me3Al with diphenylamine or
benzhydrylamine, namely {Ph2N[(Me2Al)2-Me]}
(10) and [Ph2CHNH(-Me2Al)]2·MeCN (11), were
prepared. The molecular structures of the Schiff pro-
ligands derived from Ph2CHNH2 and 2,2/-
Ph2C(CO2H)(NH2), together with complexes 5, 7 and
9 - 11·MeCN were determined; 5 contains a
chelating imino/phenoxide ligand, whereas 7 contains
the imino function outside of the metallocyclic ring.
Complex 9 contains three nitrogen-bound Al centres,
two of which are linked via a methyl bridge, whilst
the third bridges the N and P centres. In 10, the
structure resembles 9 with a bridging methyl group,
whereas the introduction of the extra carbon in 11
results in the formation of a dimer. All complexes
have been screened for their ability to ring opening
Organoaluminium
complexes
derived from Anilines or Schiff
bases for ring opening
polymerization of -caprolactone,
-valerolactone and rac-lactide
Xue Wang,a Ke-Qing Zhao,a Yahya Al-Khafaji,b
Shangyan Mo,b Timothy J. Prior,b Mark R. J. Elsegoodc
and Carl Redshawa,b*
a
College of Chemistry and Materials Science, Sichuan Normal
University, Chengdu, 610066, China.
b
Department of Chemistry, University of Hull, Hull, HU6 7RX,
U.K.
c
Chemistry
Department,
Loughborough
University,
Loughborough, Leicestershire, LE11 3TU, U.K.
polymerization
(ROP)
-caprolactone,
-
Abstract: Reaction of R1R2CHN=CH(3,5-tBu2C6H2-
OH-2) (R1 = R2 = Me L1H; R1 = Me, R2 = Ph L2H; R1
= R2 = Ph L3H) with slightly greater than one
valerolactone or rac-lactide, in the presence of benzyl
alcohol, with or without solvent present. Reasonable
conversions were achievable at room temperature for
-caprolactone using complexes 7, 9 and 12, whilst at
higher temperatures (80 – 110 °C), all complexes
produced good (> 65%) to quantitative conversions
over periods as short as 3 min. albeit with poor
control. In the absence of solvent, conversions were
near quantitative at 80 °C over 5 min. with better
agreement between observed and calculated
molecular weight (Mn). For rac-lactide, conversions
were typically in the range 71 – 86% at 110 °C over
12 h, with poor control affording atactic polylactide
(PLA), whilst for -valerolactone more forcing
conditions (12 - 24 h at 110 °C) were required for
equivalent of R3 Al (R3 = Me, Et) afforded the
3
complexes [(L1-3)AlR3 ] (L1, R3 = Me 1, R3 = Et 2;
2
L2, R3 = Me 3, R3 = Et 4; L3 R3 = Me 5, R3 = Et 6);
complex 1 has been previously reported. Use of the
N,O-ligand derived from 2,2/-diphenylglycine
afforded either 5 or the by-product [Ph2NCH2(3,5-
tBu2C6H2-O-2)AlMe2] (7). The known Schiff base
complex [2-Ph2PC6H4CH2(3,5-tBu2C6H2-O-2)AlMe2]
(8) and the product of the reaction of 2-
diphenylphosphinoaniline 1-NH2,2-PPh2C6H4 with
Me3Al, namely {Ph2PC6H4N[(Me2Al)2-Me](-
Me2Al)} (9) were also isolated. For structural and
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
6, 7]
Having employed this type of ligand set
high conversion. Co-polymerization of
-
recently
in
vanadium-based
-olefin
caprolactone with rac-lactide afforded co-polymers
with appreciable lactide content (35 – 62.5%); the
reverse addition was ineffective affording only
(polycaprolactone) PCL.
polymerization,[8] we now, as part of our
continued interest in designing new aluminium-
based initiators/catalysts for the ROP of cyclic
esters,[6t] report our results on the series of
Introduction
complexes
2)AlMe2] (R1 = R2 = R3 = Me
Et
; R1 = R3 = Me, R2 = Ph ; R1 = Me, R2 = Ph,
R3 = Et ; R1 = R2 = Ph, R3 = Me ; R1 = R2 =
Ph, R3 = Et
) and compare their behaviour
[R1R2CHN=CH(3,5-tBu2C6H2-O-
; R1 = R2 = R3 =
The use of ring opening polymerization (ROP)
of cyclic esters remains a topical area given the
ease of access to a range of biodegradable
polymers.[1] The polymer products have wide
potential, finding use in, for example, the
packaging industry as well in the biomedical
field (e.g. as implants).[2] Of the complexes
employed as catalysts in such ROP reactions,
aluminium species, given both their low toxicity
and high Lewis acidity, continue to attract the
interest of a number of research groups.[3] For
alkylaluminium complexes, the addition of an
alcohol, typically benzyl alcohol or isopropanol,
generates the required catalytic alkoxide species.
1
2
3
4
5
6
against organoaluminium complexes derived
from the amine component only (i.e. minus the
phenoxy-containing
3,5-di-tert-butylsalicyl
motif, see Schemes 1 and 2). We note that
Nomura has previously investigated the effect of
the imino substituent on the ROP of -CL, and
observed greatly enhanced activity for aryl
substituents (C6F5, 2,6-iPr2C6H3) versus aliphatic
substituents (adamantyl, tert-butyl).[7] Herein,
we initially targeted diphenylglycine and
derivatives thereof given the tendency of related
motifs to form highly crystalline products.[9]
However, the loss of CO2 during the formation
L3H (dpg), see discussion below, led us to
explore the family of pro-ligands with both
aliphatic and aromatic substituents bound to the
N-bound CH group.
Easily prepared pro-ligands are also
a
prerequisite if such systems are to be employed
on a bulk scale. With this in mind, the use of
phenoxyimine type ligation has attracted
interest, and a number of structure/activity
relationships have been identified.[4] Indeed, a
search of the CSD revealed 343 hits for
dialkylaluminium where N and O complete the
coordination environment, and of these hits, 76
contained chelating phenoxyimine ligand sets.[5]
For an overview of the phenoxyimine aluminium
systems that have previously been employed in
the ROP of cyclic esters, see Table S1 (SI).[4b,e,h,k
Results and Discussion
Pro-ligands L1-5
H
The Schiff-base pro-ligands used herein were
prepared by standard condensation procedures in
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
good yields > 90% except in the case of L3dpg
(63%).[10]
were grown from a saturated acetonitrile solution
at ambient temperature. The molecular structure
is shown in Figure 1, with selected bond lengths
and angles given in the caption. There are two
unique molecules in the asymmetric unit with
slightly different arrangement of the phenyl
groups and methyl groups. In each of the two
molecules the core is essentially planar; there is
an intramolecular hydrogen bond between the
phenol and the imine groups.
Scheme 1. Compounds (pro-ligands) employed herein.
Figure 1. Representation of the asymmetric unit of
L3H (dpa). Hydrogen atoms attached to carbon have
been omitted for clarity. Dashed lines indicate
intramolecular hydrogen bonds. Selected bond lengths
(Å) and angles (°): O1–H1A 0.96(4), O1···N1
2.602(3), O2–H2A 1.02(4), O2···N2 2.597(3) Å; O1–
H1A···N1 149(4), O2–H2A···N2 154(3).
Scheme 2. Complexes studied herein
The IR spectra contained a relatively strong
The packing of the molecules is largely
unremarkable. There is some evidence of short
C–H···π distances (e.g. H15 lies approximately
1
v(C=N) band at ca. 1628 cm–1, whilst in the H
NMR spectrum,
 OH typically appeared at 13.68
ppm. The pro-ligands L1H and L4H have been
previously reported.[10,11] Crystals suitable for
single crystal X-ray diffraction of L3H (dpa),
obtained via the use of benzhydrylamine (dpa)
2.80
Å above the plane of ring C31–C36; H35 lies
approximately 2.95
C8 I [i = 1=x, y, z]).
Å
from the plane of ring C3i–
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Similar use of diphenylglycine (dpg), 2,2/-
Ph2C(CO2H)(NH2), resulted in loss of CO2 during
the conditions employed herein and formation of
a pale yellow product. A crystal structure
crystals of
5
suitable for an X-ray diffraction
study were grown from acetonitrile on prolonged
standing at ambient temperature. The molecular
structure is shown in Figure 2 with selected bond
lengths and angles given in the caption;
crystallographic data are presented in Table 2.
determination revealed that the structure of L3
H
(dpg) was identical to that obtained using dpa
(see Fig. S1 in the SI for overlap of the structures
and Fig. S2 for the molecular structure and bond
lengths and angles for L3H (dpg)). A phase
change accounts for the differing unit cells in
Table 7 which were collected at 150 and 293 K.
The asymmetric unit of
5 contains one molecule
of the complex; there is no solvent of
crystallization. The C–N bond at 1.32(3) Å is
consistent with an imine linkage, whilst the Al–N
bond length (1.98(2) Å) is typical of reported Al–
N imine bonds.[12] In the packing of the complex,
Organoaluminium complexes
the structure adopted is layered, with C–H···

interactions between layers.
Reaction with 1.1 equivalents of Me3Al with the
parent Schiff bases in refluxing toluene afforded,
after work-up, moderate to good yields (55 –
97%) of the complexes [R1R2CHN=CH(3,5-
Figure 2. Molecular structure of [Ph2CHN=CH(3,5-
tBu2C6H2-O-2)AlMe2] ), showing the atom
tBu2C6H2-O-2)AlMe2] (R1 = R2 = R3 = Me
= R2 = R3 = Et ; R1 = R3 = Me, R2 = Ph
Me, R2 = Ph, R3 = Et ; R1 = R2 = Ph, R3 = Me
R1 = R2 = Ph, R3 = Et
), see scheme 3. Complex
was previously reported by Milione et al, and
used for halide anion binding via H-bonding,[11]
whilst the debutylated version of complex has
recently been employed by Chiang, Chen and
Chen and coworkers for the ROP of
caprolactone and L-lactide; the structure of
debutylated
was not reported.[6z] Herein,
1
; R1
(
5
numbering scheme. Hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and
angles (o): Al(1)–O(1) 1.769(11), Al(1)–N(1)
1.991(14), Al(1)–C(1) 1.965(16), Al(1)–C(2) 2.04(2),
N(1)–C(17) 1.317(19), N(1)–C(18) 1.522(19), C(8)–
C(17) 1.50(2); O(1)–Al(1)–N(1) 92.5(6), C(1)–Al(1)–
C(2) 118.0(10), Al(1)–O(1)–C(3) 125.7(11), Al(1)–
N(1)–C(18) 126.0(9).
2
3
; R1 =
4
5;
6
1
5

-
5
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
using synchrotron radiation were isolated in 56%
yield.[13] As shown in Figure 4, the complex (9)
contains three tetrahedral dimethylaluminium centres,
two of which are bound to what was the amino
nitrogen N(1), and also to each other via a methyl
bridge. A search of the CSD revealed 30 hits for
methyl bridging of aluminium centres (see Chart S1,
SI).[14, 15] In 9, two out of three H atoms on the CH3
group at C(7) are disordered. In the difference
electron density map, one clear peak is seen with a
peak height of ca. 0.9 eÅ–3 which is refined fully
occupied as H(7A). There are also ca. four smaller
peaks of between 0.4-0.5 eÅ–3 which are refined in
pairs as the other bridging methyl H atoms. The third
aluminium centre Al(1) bridges N(1) and P(1). The
structure is reminiscent of [(Me2Al)2(-Me)(-NPh2)]
(I, see top chart S1, SI), obtained via the reaction
between diphenylamine and Me3Al.[14b] In I, the three
H atoms were modelled as all pointing away from the
Al–C bonds, i.e. no equivalent of the H(7A) atom in
9. The Al–C bond lengths {2.145(5) and 2.139(5) in I
and 2.176(3) and 2.146(3) Å in 9} and Al–C–Al
angle {78.92(17) in I and 77.40(11) ° in 9} are,
however, remarkably similar. Mild geometrical
restraints were applied to make all the C(7)–H
distances similar, and also to keep the H···H
distances similar for the pairs of disordered H atoms.
While a model could be refined with restraints for all
three H atoms pointing away, there remained the
large peak nearer the Al atoms, and the R factor was
worse. The two approximately trigonal planar
disorder components are approximately 90° apart,
with the minor disorder {48(4)% occupancy)
Figure 3. Molecular structure of [Ph2CHNCH2(3,5-
tBu2C6H2-O-2)AlMe2]
(7), showing the atom
numbering scheme. Hydrogen atoms and non-
coordinated solvent molecules have been omitted for
clarity. Selected bond lengths (Å) and angles (°):
Al(1)–O(1) 1.7675(11), Al(1)–N(1) 2.0088(13),
Al(1)–C(1) 1.9636(17), Al(1)–C(2) 1.9537(16), N(1)–
C(17) 1.4900(17), N(1)–C(18) 1.2894(19), C(8)–
C(17) 1.512(2); O(1)–Al(1)–N(1) 94.06(5), C(1)–
Al(1)–C(2) 119.65(8), Al(1)–O(1)–C(3) 129.65(9),
Al(1)–N(1)–C(18) 129.57(10).
On one occasion, we also isolated the complex
[Ph2NCH2(3,5-tBu2C6H2-O-2)AlMe2]
(7),
the
molecular structure of which is shown in Figure 3.
The difference here (cf 5) is the position of the C=N
bond which no longer is contained within the
metallocyclic ring. The geometrical parameters for 5
versus 7 are illustrated in figure S3 in the SI. The
nitrogen N(1) is not protonated here as the sum of the
angles is 360o and planar (i.e. not pyramidal).
For comparative ROP studies (see later), we also
prepared the known Schiff base complex [2-
Ph2PC6H4CH2(3,5-tBu2C6H2-O-2)AlMe2] (8),[10] and
studied
the
interaction
of
2-
diphenylphosphinoaniline, 1-NH2,2-PPh2C6H4, with
an excess of Me3Al. In the case of
diphenylphosphinoaniline, following work-up, small
colourless crystals suitable for X-ray diffraction
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
component being less planar than the major. There is
There is one molecule of 10 in the asymmetric
unit (no solvent of crystallization), which is
shown in Figure 5 with selected bond lengths and
angles given in the caption.
no solvent of crystallization in 9.
Figure
{Ph2PC6H4N[(Me2Al)2
4
.
Top:
Molecular
structure
of
),

-CH3]( -Me2Al)}

(
9
showing the atom numbering scheme. Bottom:
Structure around Al(2) and Al(3) core. Selected bond
lengths (Å) and angles (°): Al(1)–N(1) 1.9432(19),
Al(1)–P(1) 2.4481(9), Al(2)–N(1) 1.9465(18), Al(2)–
C(7) 2.176(3), Al(3)–N(1) 1.9551(18), Al(3)–C(7)
2.146(3), Al(1)–Al(2) 3.4374(10), Al(2)–Al(3)
2.7022(10); N(1)–Al(1)–P(1) 83.76(6), Al(2) –C(7)–
Al(3) 77.40(11), Al(2)–N(1)–Al(3) 87.67(7).
Figure
{Ph2N[(Me2Al)2
5
.
Top:
-Me]}
Molecular
structure
of

(
10), showing the atom
numbering scheme. Bottom: Structure around Al(1)
and Al(2) core. Selected bond lengths (Å) and angles
(°): Al(1)–N(1) 2.0014(18), Al(2)–N(1) 1.9944(18),
Al(1)–C(5) 1.957(2), Al(2)–C(5) 2.145(2); Al(1)–
N(1)–Al(2) 85.90(7), Al(1)–C(5)–Al(2) 78.77(8),
C(6)–N(1)–C(12) 113.15(15).
Given the nature of the bridging methyl group in
The group at C(5) tallies with the conclusion for
9
versus that reported for I [14b]
, we decided to re-
I
. The Al2NC butterfly in 10 has a shallow hinge
angle of 28.24(10)°, which is somewhat
shallower than that observed in at 15.19(18)°.
Again, VSEPR theory suggests this centre should
be trigonal planar. We note that in , the three H
examine the structure of the diphenylamine
derived aluminium structure. Single crystals of
10 suitable for X-ray diffraction were grown
from hexane in ca 63% yield, which proved to be
a two component twin with domains related by a
180 ° rotation about real and reciprocal axes 010.
9
I
atoms are modelled as all pointing away from the
Al–C bonds, i.e. no equivalent of the H(7A) atom
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
in
9
or the H(5A) atom in 10. The Al–C bond
C6H4(-Me2Al)](-Me2Al)}2, [1,3-(Me3AlOMe),NH-
C6H4(-Me2Al)]2 and [1,4-(Me3AlOMe),NH-C6H4(-
Me2Al)]2 and the pyrrolyl-methylamide complexes
lengths {2.145(5) and 2.139(5) in
2.146(3) in , and 2.145(2) and 2.146(2) Å in 10
and Al–C–Al angle {78.92(17) in , 77.40(11) in
, and 78.77(8)° in 10} are, however, remarkably
I, 2.176(3) and
9
}
I
{[C4H3N(2-CH2HtBu)]AlH}2
and
{[C6H3N(2-
9
CH2HtBu)]Al(OCHMe2)}2 in that the Al–N bond
lengths are ca. 1.96 Å (found in the 1,4-anisidine
derived complex and the pyrrolyl-methylamide),
whilst the angles are ca. 88 ° (found in the1,2/1,3-
anisidine derived complexes).[16] In 11·MeCN, both
N–H groups point ‘up’, and there is one, well-
behaved MeCN solvent molecule of crystallization
which is H-bonded to one of the two N–H moieties;
the dimensions associated with the H-bonding are
given in the SI (Table S2).
similar. Mild geometrical restraints were applied
to make all the C(5)–H distances similar, and also
to keep the H···H distances similar for the pairs
of disordered H atoms. While a model could be
refined with restraints for all three H atoms
pointing away, there remained the large peak
nearer the Al atoms, and again the R factor was
worse. The two approximately trigonal planar
disorder components are approximately 90°
apart, with the minor disorder {47(4)%
occupancy) component being less planar than the
major. One electron density peak remained
approximately 180° away from H(5A).
Introduction of an extra carbon in the form of
benzhydrylamine and subsequent treatment with two
equivalents of Me3Al led to the formation of
[Ph2CHNH(µ-Me2Al)]2·MeCN
(11·MeCN)
in
moderate yield (47%). Single crystals were grown
from a saturated acetonitrile solution on prolonged
standing (12 h) at 0 °C. The molecular structure is
shown in Figure 6; selected bond lengths and angles
given in the caption. One Al dimer and one MeCN of
crystallization comprise the asymmetric unit. The
Al2N2 core adopts a shallow butterfly shape with a
dihedral angle of 9.66(6)°. Interestingly, the
geometrical parameters associated with the Al2N2
square are somewhat of a hybrid of those observed
for the anisidine derived complexes {[1,2-(OMe),N-
Figure 6. Molecular structure of [Ph2CHNH(
-
Me2Al)]2·MeCN 11·MeCN), showing the atom
(
numbering scheme. Most hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and
angles (°): Al(1)–N(1) 1.9597(10), Al(1)–N(2)
1.9484(10), Al(2)–N(1) 1.9620(10), Al(2)–N(2)
1.9528(10), N(1)–C(5) 1.4771(14), N(2)–C(18)
1.4836(13); Al(1)–N(1)–Al(2) 91.72(4); Al(1)–N(2)–
Al(2) 92.35(4), N(1)–Al(1)–N(2) 86.67(4), N(1)–
Al(2)–N(2) 87.48(4).
Ring Opening Polymerization (ROP) of
Caprolactone ( -CL)
ε-
ε
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
2.08), but producing polymers with lower
molecular weight than the calculated Mn values.
Prolonging the reaction time to 12 h (runs 8 and
9) led to decreased conversions rates, presumably
due to catalyst decomposition; at 110 oC in
toluened8 in a sealed NMR tube, the spectrum
reveals distinct changes even after 1 h.
Given that aluminium compounds are known to
be efficient catalysts for ring opening
polymerization (ROP) of cyclic esters,[3] the
catalytic behavior of 1 - 11 was explored toward
In addition, we investigated the behaviour of the
other complexes herein towards the ROP of ε-CL,
using the ratio 250:1:1 (see Table 1). Generally, these
aluminium complexes displayed good catalytic
conversions, particularly at temperatures of 80 °C or
higher (> 92%). Catalytic systems employing
complexes 7, 9, 10 and 11 outperformed the others at
110 °C, affording quantitative conversions over 13
mins or less. For complexes 1 - 6, the trend is for the
methyl derivatives to outperform the ethyl derivatives
at both 80 and 100 °C, a trend that has been seen
previously,[17]; the opposite trend has also been
reported.[6z] Within the series 1 - 6, on changing the
sterics of the precursor aniline, there is little change
in the conversion rates for either the
methylaluminium or ethylaluminium derivatives.
the ROP of
-CL in the presence of benzyl
alcohol (BnOH), scheme 4. One equivalent (per
aluminium) of BnOH were employed in the runs
herein. Despite the apparent mismatch of
stoichiometry, the use of one equivalent of BnOH
(per aluminium) for R2Al containing pre-catalysts
is well established; the use of two equivalents
(per aluminium) has been found to afford inferior
results.[6a,c,e] In our systems, extending the
reaction time (see Table S3) or varying the
amount of BnOH was not found to be beneficial.
Pre-catalyst
optimum conditions (see Table S4), and was
found to be effective for the ROP of -CL at
temperatures of 80 to 110 oC affording
conversions > 67%. A linear relationship
2 was employed to ascertain the

Typically, on increasing the temperature, the
conversion rates increase, e.g. Figure S6 (SI) for
between [CL]/[Al] ratio and average molecular
weight (Mn), suggests the systems still retain the
classical features of a living polymerization
process (Figs. S4, SI). Elevation of the
temperature generally resulted in higher
molecular weight polymer and high conversion
(Fig. S5, SI) with an increase in the monomer/Al
ratio from 62.5:1 to 1000:1 at 110 °C, the
molecular weight increased from 3.1 × 103 to
38.5 × 103, with little change of PDI (1.23 -
complex
from 1-NH2,2-PPh2C6H4
complex appears to be more efficient and more
5
. In the case of the systems derived
(
8
and ), use of
9
9
controlled (narrower PDI). Similar trends are
observed for those systems derived from
diphenylaniline with complex 10 outperforming
the systems bearing the phenoxyimine motif.
However, it should be noted that isolated polymer
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
yields were moderate to good, for example for
revealed the presence of a benzyloxy initiating group
and a series of peaks separated by 114.14 mass units
(the molecular weight of the monomer). A ‘blank
run’ conducted under the same conditions but using
only trimethylaluminium and BnOH (i.e. no dpg or
benz-derived ligands were present) failed to afford
any polymer (see Table S6, SI).
run 21 (table 1) using
8, the yield was 36 %.
Again, these systems produced polymers with
lower molecular weight than the calculated Mn
values, particularly at lower temperatures. The
much lower observed molecular weight obtained
in some cases is suggestive of either the presence
water acting as a chain transfer agent and/or side
reactions. If the loadings of 9, 10 and 11 are such
Table 1. ROP of ε-caprolactone using complexes 1 –
11 (not 2). Insert here (see end of paper).
that only one equivalent of Al is present (and
using one equiv. of BnOH, see runs 28, 32 and 36
Table 1), the conversions and molecular weights
observed are similar, although longer reaction
times (3h) are required.
A kinetic study of the -CL polymerization using 1,
5, 9 and 10 (see Figs. 7 and 8) was undertaken by
removing 0.3 ml from the reaction mixture and
analyzing by 1H NMR spectroscopy at the
When conducting the polymerizations in the
absence of solvent (Table S5, SI), the observed
molecular weights were in general much closer to
the calculated Mn values, and at 80 °C for 13
mins or less, all complexes achieved excellent
conversions (> 97%) with varying degrees of
control (PDIs 1.28 – 3.55).
1H and 13C NMR spectra of selected polymers (Table
1, entries 4 and 11) were obtained in order to verify
the molecular weights and to identify the end groups
present (see Figs. S7 and S8, SI). For entries using
pre-catalyst 3 (and 5), peaks at  7.33 ppm
(C6H5CH2-), 5.27 ppm (C6H5CH2-), and 3.62 ppm
(CH2CH2OH) with an integral ratio of 5:2:2 indicated
that the polymers were capped by a benzyl alkoxy
appropriate
time
under
the
conditions[CL]:[Cat]:[BnOH] = [250]:[1]:[1] at 80
°C in toluene. The polymerization rate of the ROP of
-CL exhibited a first order dependence on the -CL
concentration (Fig. 8, top) and that the -CL
conversion reached >95 % over 80 min (Fig. 8,
bottom). From Fig. 8, the rate order 1 > 5 > 9 > 10
was observed suggesting that the presence of the
phenoxy (salicylaldimine) motif may well be
beneficial, although this is only a tentative suggestion
given the differing structures of the complexes.
Indeed, it could be argued that the presence of the
multiple metal centres in 9 and 10 is detrimental to
the rate. The data here (and that for the ROP of rac-
LA) also suggested that these catalysts require an
induction period, suggestive of slow activation.
13
group and a hydroxyl end group. C NMR data also
revealed peaks at  127.52 ppm (C6H5CH2-), 69.21
ppm (C6H5CH2-) and 64.24 ppm (CH2CH2OH). The
MALDI-ToF spectrum of the PCL (see Fig. S9, SI)
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10.1002/ejic.201601415
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The ROP of rac-Lactide (rac-LA) was conducted
using 1 - 11 in the presence of BnOH (scheme 5). All
complexes were active, and the polymerizations were
mostly well controlled (PDIs 1.04 – 2.36; only 3 runs
gave PDIs > 1.5), although conversions were
somewhat lower than those observed for ε-CL.
Indeed, in most cases, it proved necessary to conduct
the polymerizations over 12 h to achieve reasonable
conversion. For reduced loadings of 9, 10 and 11
representing only one equivalent of Al (runs 31, 33
and 36 Table 2), conversions and molecular weights
observed were only slightly lower. Increasing the
molar ratio of rac-LA to [Al] did not drastically
influence the conversion rates but appeared, in
general, to increase the polymer molecular weight
(Mn); increasing the polymerization time tended to
have the same effect. The relationship between Mn
and PDI of the polymer and the mole ratio [rac-
LA]/[BnOH] for 3 (Table 2 entries 4-8) is displayed
in Fig. S10 (SI), and reveals a saturation curve for the
former. In the case of the PDI, the relationship with
[rac-LA]/[BnOH] suggests that transesterification
might be an issue at high monomer loadings leading
to molecular weight suppression.
Figure 7. Complexes used in the kinetic study.
For 3 (Table 2 entries 4-8) the relationship between
monomer conversions and Mn values (Fig. S11, SI) is
exponential.
Figure 8. Top: Plot of ln[CL]o/[CL]t vs time using
complex 1, 5, 9 and 10; Bottom : Relationship between
conversion and time for the polymerization of CL using
complex 1, 5, 9 and 10.
1H and 13C NMR spectra of selected polymers (Table
2, entries 3 and 14) were obtained in order to verify
the molecular weights and to identify the end groups
present (see Figs. S12 and S13, SI). For entries using
pre-catalyst 5 and 6), peaks at  7.12, 5.11, and 3.60
Ring Opening Polymerization (ROP) of rac
Lactide (rac-LA)
-
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10.1002/ejic.201601415
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ppm (5:2:2) indicated that the polymers were capped
by a benzyl alkoxy group and a hydroxyl end group.
13C NMR data also revealed peaks at  127.63
(C6H5CH2-), 69.06 (C6H5CH2-) and 63.99 ppm
(CH2CH2OH). The MALDI TOF spectrum of the
PLA (Figs. S14 and S15, SI; runs 17 and 23, Table 2)
revealed the presence of a benzyloxy initiating group
and a series of peaks separated by the mass of one
lactide unit (72.0).
A kinetic study of the rac-LA polymerization using
1, 5, 9 and 10 was undertaken by removing 0.3 ml
1
from the reaction mixture and analyzing by H NMR
spectroscopy at the appropriate time under the
conditions [rac-LA]:[Cat]:[BnOH] = [100]:[1]:[1] at
110 °C in toluene. The polymerization rate of the
ROP of rac-LA exhibited approximate first order
dependence on the rac-LA concentration (Fig. 9, top)
and that the rac-LA conversion reached >70% over
12 h. (Fig 9, bottom). The same order of reactivity
was observed here as for the -CL case, although for
1 and 5 there was a clear rate enhancement after 6
and 8 h respectively.
Figure 9. Top: Plot of ln[rac-LA]o/[rac-LA]t vs time using
1, 5, 9 and 10; Bottom: Relationship between conversion
and time of polymerization rac-LA using 1, 5, 9 and 10.
To assign the stereochemistry of the PLA polymers,
we employed 2D J-resolved and homonuclear
decoupled 1H NMR spectroscopy, and assigned peaks
by reference to the literature.[18] Representative
spectra for runs 21 and 26 are given in the SI (Figs.
S16 – S19), with the assignments given on the
respective figures; these systems gave atactic PLA as
reported elsewhere for this observed spectral
pattern.[19]
Table
2
.
ROP of rac-Lactide (rac-LA) using
-11. Insert here (see end of paper).
complexes
1
Of the complexes displayed in Chart S1 (SI), pre-
catalysts III, V, X and XXVII closely resemble
structures 1 - 8 herein. System 3 bearing an imine-
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
bound pentafluorophenyl group and only one (ortho)
tert-butyl substituent on the phenoxy moiety is more
active at lower temperatures over shorter reaction
times affording higher molecular weight products,
particularly in the case of -CL and -VL.[6c] Pre-
catalyst V, bearing a 2,4-difluorophenyl group at N,
is a little slower than III for the ROP of -CL and is
comparable with 1 – 8 herein, although the polymer
molecular weight is somewhat reduced cf III, it is
still higher than observed for the PCL herein.[6e]
System X, possessing a para isopropyl substituent on
the N bound aryl but bearing 3, 5-di-tert-butyl groups
on the phenoxy as for 1 – 8 herein, has comparable
activity for the ROP of rac-LA requiring 48 h to
achieve complete conversion but affords higher
molecular weight PLA.[6i] Pre-catalysts XXVII
possess an N bound CHPh2, but with no tert-butyl
substituents on the phenoxy (or thiophenoxy)
motif,[6z] and these Me2Al systems can most closely
be compared with 5. For -CL, results using 5 (run 9,
Table 1) at ambient temperature are similar to those
of the phenoxy version of XXVII (MnGPC = 3100,
PDI, 89 %) albeit under slightly different conditions
(ROP of XXVII employed a ratio of 100:1:2 [-
CL]:[Al]:[OH] over 6 h). For the ROP of L-LA,
XXVII required a higher temperature than for -CL
(as observed herein) and afforded PLA with MnGPC in
the 5000 – 6000 region.
of -CL with rac-LA under the optimum conditions
found for the homo-polymerizations in toluene, i.e. at
80°C for 1 h with -CL followed by stirring for 12 h
at 110 °C with rac-LA. In all cases (Table 3), good
yields (54 - 88%) of co-polymer were formed, and
with appreciable lactide content (35 to 62.6%) as
1
observed by 1H NMR spectra (Fig. S20, SI); both H
and 13C NMR spectra (Fig. S21, SI) were assigned as
per the literature.[20] The highest % incorporation of
LA was found for 1 (62.6%). Observed molecular
weights (3680 - 6670) are best described as low to
moderate, however we note there is interest in low
molecular
weight
poly(lactide/caprolactone)
polymers as bio-adhesives.[21] Thermal analysis of the
co-polymers by DSC revealed two melting points at
55.7 °C (PCL) and 125.9 °C (PLA), see Fig. S22, SI.
Table 3. Synthesis of diblock co-polymers from cyclic
ester monomers (-CL+ rac-LA).
c
Runa Cat CL:LAb
Yield
Mn
PDId
1
2
37.5:62.5
38.5:61.5
70
77
4850
5000
1.31
1.23
1
2
3
45:55
54
80
62
56
88
55
70
60
65
6670
6500
4620
4650
5840
3680
6000
5500
5770
1.43
1.26
1.29
1.22
1.34
1.66
1.23
1.48
1.41
3
4
44.5:55.5
59:41
4
5
5
6
57.5:42.5
57:43
6
7
7
8
65:35
8
9
55.5:44.5
43.5:56.5
42.5:57.5
9
10
10
11
11
a Optimum conditions: 1h -CL 80 °C/12h rac-LA 110 °C,
(100 -CL: 100 rac-LA: 1 BnOH). b Ratio of LA to CL
observed in the co-polymer by H NMR. c Mn values were
1
Co-polymerization of -Caprolactone and rac-
Lactide (rac-LA)
determined by GPC in THF vs PS standards and were
corrected with a Mark–Houwink factor (Mn,
% PCL + Mn,GPC × 0.58 × % P rac-LA). PDI were
× 0.56 ×
GPC
d
Complexes 1 - 11 have also been screened for their
determined by GPC.
potential to act as catalysts for the co-polymerization
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
reveals that they are inferior to the phenoxyimine
system III bearing a C6F5 group at the imino N which
operates under milder conditions and affords far
higher molecular weight products, but are
comparable with the performance of system VI.[6c, 6f]
Ring Opening Polymerization (ROP) of -
valerolactone
Table 4. ROP of -valerolactone using Al complex 1-11
Insert here (reviewers, please see end of paper).
For the -VL ROP reactions (Table 4, scheme 6), 110
°C over 12 h was generally required to achieve
reasonable conversion, and the resulting ROP
reactions were all well-behaved with PDIs in the
range 1.10 - 1.73. The relationship between Mn and
PDI of the PVL and the mole ratio [VL]/[BnOH] for
5 (Table 4 entries 7-10) are near linear (Fig. S23, SI).
In general, the ROP of -VL was slower than that of
-CL, which is consistent with the thermodynamic
parameters for these lactones.[22] Within the series 1 -
6, %conversions increased on increasing bulk of the
aniline derived moiety. In the case of 7 and 8, the
presence of either the amine linkage or phosphine
function respectively, appeared to be detrimental to
the activity. The non-Schiff-base systems 9 - 11
required longer (24 h) to achieve reasonable
%conversion. Molecular weights (Mn) for all systems
were somewhat lower than calculated values.
Conclusion
In conclusion, we have prepared and structurally
characterized
a
number of organoaluminium
phenoximine complexes and have also investigated
the structures of the complexes resulting from
reaction
of
the
precursor
anilines
with
organoaluminium reagents, i.e. minus the
salicylaldimine motif. In the presence of benzyl
alcohol the complexes were active for the ROP of -
caprolactone, -valerolactone and rac-lactide and
were also capable of the co-polymerization of -
caprolactone/rac-lactide with reasonable (up to
62.6%) lactide incorporation. In the case of the ROP
of -CL and rac-LA, there was indication of catalytic
misbehaviour with non-linear plots and slightly broad
(c.a. 2.0) PDIs. The systems bearing the
salicylaldimine motif exhibited increased rates for
these ROP studies. However, given that those
complexes which did not possess this motif had more
than one metal centre present, we can only tentatively
propose that the presence of the salicylaldimine
(phenoxy) motif is beneficial in the systems studied
herein. In the case of -valerolactone, shorter
polymerization times were possible for the Schiff-
base systems.
For reduced loadings of 9, 10 and 11 representing
only one equivalent of Al (runs 17, 20 and 23 Table
4), %conversions were far lower, but the molecular
weights observed were similar.
1H NMR spectra of the resultant polymers (e.g. Fig.
S24, SI) indicated the presence of benzyloxy and OH
end groups. As mentioned previously, comparison
with the systems in Table S1 for the ROP of -VL
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10.1002/ejic.201601415
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was then refluxed for an additional 6 h. Upon cooling
to ambient temperature, the volatiles were removed
under vacuo, and the residue was recrystallized from
ethanol at −20 °C to give L2H as a yellow powder.
Yield 3.2 g, 95%. Elemental analysis calculated for
C23H31NO: C, 81.85; H, 9.26; N, 4.15. Found: C,
81.67; H, 9.33; N, 4.27%. IR (nujol null, KBr): 3441
(m), 2967 (s), 2868 (m), 2358 (w), 1626 (s), 1585
(w), 1464 (w), 1452 (w), 1438 (w), 1383 (m), 1360
(m), 1343 (w), 1322 (w), 1270 (m), 1248 (s), 1207
(m), 1174 (s), 1135 (w), 1115 (w), 1075 (m), 1029
(w), 976 (m), 906 (w), 880 (w), 824 (m), 773 (m),
759 (s), 730 (w), 700 (s), 644 (w), 631 (w), 594 (w),
541 (m), 499 (w). MS (ESI, positive mode): 338.4
Experimental
General:
All manipulations were carried out under an
atmosphere of dry nitrogen using conventional
Schlenk and cannula techniques or in a conventional
nitrogen-filled glove box. Hexane and Toluene was
refluxed over sodium. Acetonitrile was refluxed over
calcium hydride. All solvents were distilled and
degassed prior to use. IR spectra (nujol mulls, KBr
windows) were recorded on a Nicolet Avatar 360 FT
1
IR spectrometer; H NMR spectra were recorded at
room temperature on a Varian VXR 400 S
spectrometer at 400 MHz or a Gemini 300 NMR
spectrometer or a Bruker Advance DPX-300
spectrometer at 300 MHz. The 1H NMR spectra were
calibrated against the residual protio impurity of the
deuterated solvent. Elemental analyses were
performed by the elemental analysis service at the
London Metropolitan University and in the
Department of Chemistry, the University of Hull. The
precursor 1-NH2,2-PPh2C6H4 was prepared by the
literature method.[23] The pro-ligands L1H and L4H,
and the complexes 1 and 7 were prepared as
described previously.[10, 11]
1
MH+. H NMR (400 MHz, CDCl3): δ 13.68 (s, 1 H,
OH), 8.43 (s, 1 H, CH=N), 7.40 - 7.33 (m, 5 H, Ar-
H), 7.28 - 7.26 (m, 1 H, Ar-H), 7.86 (d, J = 2.4 Hz, 1
H, Ar-H), 4.56 - 4.52 (m, 1 H, CH(CH3)), 1.65 (d, J =
6.4 Hz, 3 H, CH(CH3)), 1.46 (s, 9 H, C(CH3)3), 1.30
(s, 9 H, C(CH3)3).
Synthesis of Ph2CHN=CH(3,5-tBu2C6H2-OH-2) L3H
By using the procedure described above for synthesis
of L2H, the ligand L3H was obtained by the reaction
of 3,5-di-tert-butylsalicylaldehyde (2.34 g, 10.0
mmol) with benzhydrylamine (1.83 g, 10.0 mmol) as
a yellow power in 92% yield. Elemental analysis
calculated for C28H33NO: C, 84.17; H, 8.32; N, 3.51.
Found: C, 84.35; H, 8.43; N, 3.47%. IR (nujol mull,
KBr, cm–1): 3435 (m), 3060 (w), 3029 (w), 2956 (w),
2868 (w), 2361 (w), 1631 (s), 1586 (w), 1493 (w),
1455 (m), 1386 (m), 1357 (m), 1342 (w), 1322 (w),
1269 (m), 1246 (s), 1204 (m), 1171 (s), 1133 (w),
Synthesis of Ph,MeCHN=CH(3,5-tBu2C6H2-OH-2)
L2H
To a solution of 3,5-di-tert-butylsalicylaldehyde
(2.34 g, 10.0 mmol) with a few drops of glacial acetic
acid in anhydrous ethanol (15 ml) under argon at 50
°C was added a solution of α-methylbenzylamine
(1.21 g, 10.0 mmol) in anhydrous ethanol (15 ml)
over a period of 30 min with stirring. The mixture
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10.1002/ejic.201601415
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1089 (m), 1050 (s), 1028 (s), 980 (w), 916 (w), 880
(w), 846 (w), 827 (m), 800 (w), 766 (m), 746 (m),
733 (w), 703 (s), 644 (w), 620 (w), 612 (w), 561 (w),
538 (w), 509 (w), 468 (w). MS (ESI, positive mode):
Synthesis of [iPrCHN=CH(3,5-tBu2C6H2-O-2)AlEt2]
(2)
A solution of AlEt3 (1.9 ml, 3.0 mmol, 2 M in
toluene) was added at room temperature to a solution
of iPrCHN=CH(3,5-tBu2C6H2-OH-2) L1H (0.74 g,
2.7 mmol) in toluene (25 mL) over a period of 30
min with stirring. Then the mixture was refluxed for
an additional 12 h. Upon cooling to room
temperature, the volatiles were removed under vacuo,
and the residue was recrystallized from acetonitrile to
give 2 as a yellow solid. Yield 0.53 g, 55%.
Elemental analysis calculated for C22H38AlNO: C,
73.50; H, 10.65; N, 3.90. Found: C, 73.33; H, 10.35;
N, 3.73%. IR (nujol mull, KBr, cm–1): 3730 (w),
2959 (s), 2871 (m), 1629 (s), 1553 (m), 1470 (m),
1445 (m), 1422 (m), 1385 (m), 1361 (m), 1318 (w),
1276 (m), 1258 (m), 1238 (w), 1203 (w), 1179 (m),
1163 (w), 1118 (s), 1058 (w), 1025 (w), 977 (w), 955
(w), 855 (m), 785 (m), 754 (w), 716 (w), 647 (w),
526 (w), 411 (w). MS (ES, positive mode): 359.2 M.
1H NMR (400 MHz, CDCl3): δ: 8.12 (s, 1 H, CH=N),
7.42 (d, J = 2.0 Hz, 1 H, Ar-H), 6.90 (d, J = 2.0 Hz, 1
H, Ar-H), 3.72 - 3.65 (m, 1 H, CH(CH3)2), 1.37 (d, J
= 3.2 Hz, 6 H, -CH(CH3)2), 1.34 (s, 9 H, -C(CH3)3),
1.21 (s, 9 H, C(CH3)3), 0.94 - 0.90 (m, 6 H,
1
400.2 MH+. H NMR (400 MHz, CDCl3) δ: 13.74 (s,
1 H, OH), 8.41 (s, 1 H, CH=N), 7.32 (d, J = 2.4 Hz, 1
H, Ar-H), 7.28 - 7.23 (m, 8 H, Ar-H), 7.19 - 7.15 (m,
2 H, Ar-H), 7.01 (d, J = 2.4 Hz, 1 H, Ar-H), 5.52 (s,
1 H, CH(Ph)2), 1.38 (s, 9 H, C(CH3)3), 1.21 (s, 9 H,
C(CH3)3).
Synthesis of Ph2CHN=CH2(3,5-tBu2C6H2-OH-2) L3H
via dpg
2,2/-Diphenylglycine (1.13 g, 5.00 mmol) and 2-
hydroxy-3,5-di-tert-butylsalicylaldehyde (1.17 g,
5.00 mmol) were refluxed in ethanol for 3 days using
a Dean-Stark condenser. Following removal of the
ethanol, the residue was triturated with methanol (50
ml), filtered and dried. Yield: 1.26 g, 63%.
C28H33NO·⅔MeOH requires C 81.82, H 8.54, N 3.33
%. Found: C 81.96, H 8.65, N 3.34%. IR (nujol mull,
KBr, cm–1): 3432 (bs), 1629 (s), 1603 (m), 1577 (w),
1477 (s), 1446 (s), 1393 (m), 1361 (m), 1297 (w),
1260 (s), 1236 (m), 1203 (m), 1163 (m), 1078 (w),
1025 (m), 947 (w), 875 (m), 780 (w), 758 (m), 726
(w), 686 (s), 672 (w), 646 (w), 592 (w), 539 (w), 454
Al(CH2CH3)2), –0.07
-
(–0.22) (m,
4
H,
1
(w). MS (ES, positive mode): 400.4 MH+. H NMR
Al(CH2CH3)2). 13C NMR (400 MHz, CDCl3): δ
165.46, 160.07, 129.26, 128.84, 119.92, 50.12,
35.13, 30.99, 23.94, -5.91, -11.60.
(400 MHz, CDCl3) δ: 13.84 (s, 1 H, OH), 8.52 (s, 1
H, CH=N), 7.42 (d, J = 2.4 Hz, 1 H, Ar-H), 7.37 -
7.34 (m, 8 H, Ar-H), 7.29 - 7.26 (m, 2 H, Ar-H),
7.26 (d, J = 2.4 Hz, 1 H, Ar-H), 5.63 (s, 1 H,
CH(Ph)2), 1.49 (s, 9 H, C(CH3)3), 1.32 (s, 9 H,
C(CH3)3).
Synthesis of [Me,PhCHN=CH(3,5-t-Bu2C6H2-O-
2)AlMe2] (3)
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
A solution of AlMe3 (1.6 mL, 2.50 mmol, in toluene
1.6 M) was added at room temperature to a solution
of Ph,MeCHN=CH(3,5-tBu2C6H2-OH-2) L2H (0.77 g
2.30 mmol) in hexane (25 mL). The resulting yellow
solution was stirred for 12 h. The solution was
filtered and concentrated, affording 3 a yellow solid.
Yield 0.60 g, 67%. Elemental analysis calculated for
C25H36AlNO: C, 76.30; H, 9.22; N, 3.56. Found: C,
76.25; H, 9.31; N, 3.40%. IR (nujol mull, KBr, cm–1):
3429 (s), 3064 (w), 3037 (w), 2960 (s), 2866 (m),
2358 (w), 2335 (w), 1616 (s), 1553 (m), 1543 (m),
1469 (m), 1454 (m), 1439 (m), 1414 (m), 1391 (m),
1355 (m), 1322 (s), 1299 (w), 1275 (w), 1254 (s),
1237 (w), 1200 (m), 1178 (s), 1138 (w), 1085 (m),
1058 (w), 1029 (w), 990 (w), 932 (w), 910 (w), 880
(w), 855 (s), 816 (w), 782 (m), 763 (s), 702 (s), 674
(s), 613 (w), 596 (w), 537 (m), 490 (w), 410 (w). MS
solid. Yield 0.6 g, 62%. Elemental analysis calculated
for C27H40AlNO: C, 76.92; H, 9.56; N, 3.32. Found:
C, 76.65; H, 9.33; N, 3.28%. IR (nujol mull, KBr,
cm–1): 3423 (w), 2954 (s), 2866 (w), 1627 (s), 1559
(m), 1473 (m), 1444 (w), 1422 (m), 1388 (w), 1361
(w), 1277 (m), 1258 (m), 1236 (w), 1202 (m), 1176
(s), 1134 (w), 1120 (w), 1081 (w), 1056 (w), 1034
(w), 982 (w), 910 (w), 874 (w), 852 (m), 787 (w),
758 (m), 715 (w), 699 (w), 605 (w), 524 (w). MS
m
1
(ESI): /z 392 [M – Et] + 363 [M – 2Et] +. H NMR
,
(400 MHz, CDCl3) δ: 8.12 (s, 1 H, CH=N), 7.49 (d, J
= 2.0 Hz, 1 H, Ar-H), 7.42-7.34 (s, 5 H, Ar-H), 6.88
(d, J = 2.0 Hz, 1 H, Ar-H), 4.56 - 4.51 (m, 1 H,
CH(CH3)), 1.78 (d, J = 7.0 Hz, 3 H, CH(CH3)), 1.40
(s, 9 H, CH(CH3)), 1.26 (s, 9 H, CH(CH3)), 0.97 -
0.85 (m, 6 H, Al(CH2CH3)2), –0.72 - (–0.31) (m, 4 H,
Al(CH2CH3)2). 13C NMR (400 MHz, CDCl3): δ
165.12, 155.17, 147.82, 139.97, 137.50, 126.41,
119.11, 113.82, 65.73, 36.15, 33.33, 26.88, 25.34, -
0.42, -6.92.
m
1
(ESI): /z 378.6 [M – Me] +, 363.6 [M – 2Me]+. H
NMR (400 MHz, CDCl3) δ: 8.11 (s, 1 H, CH=N),
7.49 - 7.36 (m, 5 H, Ar-H), 7.18 (s, 1 H, Ar-H), 6.90
(s, 1 H, Ar-H), 4.93 - 4.92 (m, 1 H, CH(CH3)), 1.78 -
1.76 (d, J = 4.0 Hz, 3 H, CH(CH3)), 1.39 (s, 9 H,
C(CH3)3), 1.27 (s, 9 H, C(CH3)3), –0.79 (s, 3 H,
AlCH3), –0.93 (s, 3 H, AlCH3). 13C NMR (400 MHz,
CDCl3): δ 164.62, 157.77, 143.82, 140.65, 137.50,
128.38, 122.84, 117.84, 68.13, 35.75, 34.38, 31.72,
31.31, 29.87, 29.41, 24.18, -3.68.
Synthesis of [Ph2CHN=CH(3,5-tBu2C6H2-O-
2)AlMe2] (5)
As for 2, but using Ph2CHN=CH(3,5-tBu2C6H2-OH-
2) L3H (1.00 g, 2.50 mmol) and AlMe3 (1.70 mL,
2.70 mmol, in toluene 1.6 M) afforded 3 as yellow
crystals. Single crystals suitable for X-ray analysis
were grown from a saturated hexane solution. The
solution was filtered and concentrated, affording 5 as
a yellow crystalline solid. Yield 0.90 g, 79%.
Elemental analysis calculated for C30H38AlNO: C,
79.09; H, 8.41; N, 3.07. Found: C, 79.19; H, 8.28; N,
Synthesis of [Me,PhCHN=CH(3,5-tBu2C6H2-O-
2)AlEt2] (4)
As for 2, but using Me,PhCHN=CH(3,5-tBu2C6H2-
OH-2) L2H (0.77 g, 2.30 mmol) and AlEt3 (1.6 ml,
2.50 mmol, 1.6 M in toluene) affording 4 as a yellow
This article is protected by copyright. All rights reserved.

10.1002/ejic.201601415
European Journal of Inorganic Chemistry
3.20%. IR (nujol mull, KBr, cm–1): 3428 (w), 2965
(s), 2866 (w), 1616 (s), 1561 (w), 1543 (s), 1469 (s),
1441 (m), 1424 (s), 1389 (m), 1362 (m), 1344 (w),
1318 (s), 1275 (w), 1258 (s),1241 (w), 1199 (w),
1183 (s), 1164 (m), 1148 (m), 1134 (m), 1026 (w),
995 (m), 965 (w), 924 (w), 887 (m), 855 (s), 807 (w),
784 (m), 760 (s), 708 (w), 677 (s), 641 (w), 602 (m),
mull, KBr, cm–1): 3694 (w), 3428 (w), 2954 (s), 2855
(w), 1616 (s), 1556 (w), 1543 (m), 1493 (w), 1463
(w), 1417 (w), 1392 (m), 1359 (w), 1329 (w), 1280
(w), 1254 (w), 1232 (w), 1198 (w), 1174 (m), 1004
(m), 988 (w), 916 (w), 879 (w), 852 (w), 784 (w),
757 (w), 730 (w), 699 (s), 640 (m), 538 (w). MS
calculated for 6 (m/z): 483.31 (100.0%), 484.31
m
m
552 (m), 491 (m), 410 (w). MS (ESI): /z 423.6 [M -
(35.5%), 485.31 (6.1%). Found MS (ESI): /z 423.7
1
1
2Me] +. H NMR (400 MHz, CDCl3) δ: 8.00 (s, 1 H,
[M – Et]+. H NMR (400 MHz, CDCl3) δ: 7.99 (s, 1
CH=N), 7.52 (d, J = 2.6 Hz, 1 H, Ar-H), 7.42 - 7.32
(m, 6 H, Ar-H ), 7.23 - 7.18 (m, 4 H, Ar-H), 6.81 (d,
J = 2.5 Hz, 1 H, Ar-H), 6.23 (s, 1 H, CHPh2), 1.40 (s,
9 H, C(CH3)3), 1.26 (s, 9 H, C(CH3)3), –0.96 (s, 3 H,
AlCH3), –0.97 (s, 3 H, AlCH3). 13C NMR (400 MHz,
CDCl3): δ 164.75, 158.01, 144.05, 139.79, 137.03,
129.30, 124.90, 118.08, 68.74, 34.62, 34.01, 31.85,
31.42, 29.81, 29.41, 25.01, -10.05. For the by-product
[Ph2CHNCH2(3,5-tBu2C6H2-OH-2)AlMe2] (7): Yield
ca. 10 %. Elemental analysis calculated for
C30H38AlNO: C, 79.08; H, 8.41; N, 3.08. Found: C,
78.92; H, 8.34; N, 2.88%. 1H NMR (C6D6, 400 MHz)
δ: 7.31 - 6.40 (6× m, 12H, Ar-H), 4.09 (s, 2H, CH2),
1.42 (s, 9 H, C(CH3)3), 1.13 (s, 9 H, C(CH3)3), –0.97
(s, 6 H, AlCH3). 13C NMR (C6D6): –10.01 (AlCH3).
H, CH=N), 7.51 (d, J = 2.8 Hz, 1 H, Ar-H), 7.39 -
7.35 (m, 6 H, Ar-H), 7.22 - 7.20 (m, 4 H, Ar-H), 6.78
(d, J = 2.8 Hz, 1 H, Ar-H), 6.20 (s, 1 H, CHPh2), 1.41
(s, 9 H, C(CH3)3), 1.25 (s, 9 H, C(CH3)3), 0.87 - 0.83
(m, 6H, Al(CH2CH3)2), –0.23 - –0.36 (m, 4 H,
Al(CH2CH3)2). 13C NMR (400 MHz, CDCl3): δ
172.11, 166.40, 162.11, 158.49, 140.44, 139.09,
137.91, 132.03, 129.19, 128.34, 118.13, 69.55, 35.82,
34.15, 31.43, 29.58, -0.22, -7.98.
Synthesis of {Ph2PC6H4N[(Me2Al)2µ-CH3](µ-
Me2Al)} (9)
To 1-NH2,2-PPh2C6H4 (1.50 g, 5.41 mmol) in toluene
(20 ml) was added Me3Al (5.41 ml, 2.0 M, 10.8
mmol) and the system was refluxed for 12 h. On
cooling, the volatiles were removed in vacuo, and the
residue was extracted into warm MeCN (20 ml).
Prolonged standing (2 - 3 days) at ambient
temperature afforded small white prisms of 9. Yield
1.12 g, 56%. Elemental analysis calculated for
C25H35Al3NP·0.87MeCN·0.39toluene: C, 66.43; H,
7.64; N, 4.2 %. Found: C, 66.39; H, 7.64; N, 4.92%.
IR (nujol mull, KBr, cm–1): 2940 (m), 2923 (s), 2853
(s), 2725 (w), 2671 (w), 1610 (m), 1586 (w), 1457
Synthesis of [Ph2CHN=CH(3,5-tBu2C6H2-O-2)AlEt2]
(6)
As for 5, but using Ph2CHN=CH(3,5-tBu2C6H2-OH-
2) L3H (1.00 g, 2.50 mmol) and AlEt3 (1.35 ml, 2.75
mmol, 2.0 M in toluene) affording 6 as a yellow
solid. Yield 0.76 g, 63%. Elemental analysis
calculated for C32H42AlNO: C, 79.46; H, 8.75; N,
2.90. Found: C, 79.25; H, 8.33; N, 2.67%. IR (nujol
This article is protected by copyright. All rights reserved.

10.1002/ejic.201601415
European Journal of Inorganic Chemistry
(s), 1377 (s), 1301 (m), 1260 (m), 1182 (w), 1157
(w), 1089 (m), 1068 (m), 1026 (m), 891 (w), 801 (m),
743 (m), 722 (m), 695 (s), 548 (w), 505 (w), 492 (w),
474 (w). MS (ES, positive mode): m/z 389 [M –
AlCH3). 13C NMR (400 MHz, CDCl3): δ 149.76,
133.58, 128.81, 118.34, 115.55, 18.47, -18.50.
Synthesis of [Ph2CHNH(µ-Me2Al)]2·MeCN
(11·MeCN)
1
Al(CH3)3]. H NMR (CDCl3) δ: 7.36 - 7.34 (m, 2H,
C6H2), 7.32-7.28 (m, 10H, PhP), 6.78–6.66 (m, 2H,
As for 9, but using Ph2CHNH2 (0.91 g, 5.0 mmol)
and Me3Al (2.5 ml, 2.0 M, 5.0 mmol) affording 10 as
colourless needles. Yield 1.12 g, 47.2%. C30H36Al2N2
requires C 75.29, H 7.58, N 5.89%. Found: C 74.68,
H 8.20, N 5.72 %. IR (nujol mull, KBr, cm–1): 3286
(m), 2925 (s), 2857 (s), 2726 (w), 2672 (w), 1967
(w), 1946 (w), 1799 (w), 1622 (m), 1539 (w), 1494
(s), 1453 (s), 1377 (s), 1316 (m), 1259 (m), 1187 (s),
1080 (s), 1039 (s), 1017 (s), 916 (m), 874 (s), 819 (s),
758 (m), 742 (m), 697 (s), 594 (m), 570 (m), 509 (m),
499 (m), 479 (m), 451 (w). MS (ES, positive mode):
C6H2), 2.33(s, H, toluene), 2.26 (bs, 3H, Al-CH3-Al),
13
2.00(s,3H, MeCN –0.81(bs, 18H, CH3-Al). C NMR
(400 MHz, CDCl3): δ 158.15, 154.40, 153.33,
152.66, 137.34, 134.52, 133.32, 127.66, 122.90,
121.04, 22.13, 16.16, -4.57, -14.71. 31P NMR
(CDCl3) δ: –19.80.
Synthesis of {Ph2N[(Me2Al)2 µ-Me]} (10)
To Ph2NH (0.84 g, 5.0 mmol) in toluene (30 ml) was
added Me3Al (5.0 ml, 2.0 M, 10.0 mmol), and the
system was refluxed for 12 h. On cooling, the
volatiles were removed in-vacuo, and the residue was
extracted into warm acetonitrile (30 ml). Cooling to 0
°C afforded colourless prisms of 10: 0.92 g, 62.5%.
X-ray quality crystals were obtained from MeCN.
C17H25Al2N·⅓MeCN requires C 68.22, H 8.35, N
5.98 %. Found: C 68.76, H 8.35, N 6.00%. IR (nujol
mull, cm–1): 3414 (w), 3192 (w), 2953 (s), 2922 (s),
2852 (s), 2727 (w), 2670 (w), 1936 (w), 1876 (w),
1788 (w), 1594 (s), 1520 (s), 1493 (s), 1415 (s), 1376
(s), 1339 (w), 1310 (m), 1261 (m), 1201 (s), 1079 (s),
1029 (s), 1005 (w), 917 (m), 846 (s), 801 (s), 746
(m), 694 (s), 608 (m), 570 (m), 524 (m), 503 (m),
482 (w), 479 (m). MS (ES, positive mode): 225.6 M+
1
MH+ 479, [MH+ + MeCN] 519. H NMR (400 MHz,
CDCl3) δ: 7.40 - 7.15 (m, 20H, Ar-H), 5.10 (s, 1H,
CH(Ph)2), 5.07(s, 1H, CH(Ph)2), 2.17 (s, 1H, N-H),
2.14 (s, 1H, N-H), 1.98 (s,3H, MeCN), –0.97(s, 6H,
13
AlCH3), –1.02(s, 6H, AlCH3). C NMR (400 MHz,
CDCl3): δ 150.15, 130.42, 128.37, 123.61, 143.34, -
8.91.
Ring opening polymerization.
Typical polymerization procedures in the presence of
one equivalent of benzyl alcohol (Table 4, run 1) are
as follows. A toluene solution of 3 (0.010 mmol, 1.0
mL toluene) and BnOH (0.010 mmol) were added
into a Schlenk tube in the glove-box at room
temperature. The solution was stirred for 2 min, and
then -caprolactone (2.5 mmol) along with 1.5 mL
1
–Al(CH3)3. H NMR (400 MHz, CD3CN) δ: 7.17 -
6.77 (m, 10H, Ar-H), 2.17 (s, 1H, N-H), 1.94 (s, 3H,
Al-CH3-Al), –0.87 (s, 6H, AlCH3), –0.96 (s, 6H,
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
toluene was added to the solution. The reaction
mixture was then placed into an oil bath pre-heated to
the required temperature, and the solution was stirred
for the prescribed time. The polymerization mixture
was then quenched by addition of an excess of glacial
acetic acid (0.2 mL) into the solution, and the
resultant solution was then poured into methanol (200
mL). The resultant polymer was then collected on
filter paper and was dried in vacuo.
methods.[27] The details are presented in Table 7. For
5 the crystal examined was twinned. The structure
was refined using all observed reflections within
SHELXL using the HKLF5 formalism. Samples
L3H(dpa) and L3H(dpg) were collected at different
temperatures from samples made in the same way. In
each case the structure determination was repeated
using a second crystal to confirm the correctness of
the crystal structure at that temperature. Diffraction
data for 9 were collected using synchrotron radiation
at Daresbury Laboratory Station 9.8. For 10: The
structure was refined as a two-component twin using
the HKLF5 protocol as above for 5. The two domains
were related by a 178.8° rotation about the real and
direct [010] direction. Two out of three H atoms on
DSC Procedure
About 2 mg of polymer sample was taken and first
heated to the desired temperature 180 oC then cooled
o
down to a low temperature 25 C and heated again to
+
CH3 group at C(5) are disordered. In the difference
the same temprature. Both heating and cooling rates
were (10 oC/min).
electron density map, one clear peak is seen with a
peak height of ca. 0.9 eÅ–3 which is refined fully
occupied as H(5A). There are also ca. four smaller
peaks of between 0.4-0.6 eÅ–3 which are refined in
Crystallography
Structures were solved using automated direct
methods within SHELXS-86 or intrinsic phasing
within SHELXT.[24] Structures were refined by full-
+
pairs as the other CH3 H atoms. A similar pattern of
electron density peaks and partial H-atom disorder
was observed in 9.
matrix least squares refinement within SHELXL-
26]
2014 using all unique data.[25,
Hydrogen atoms
CCDC 1480938
-
1480944 contain the
were placed using a riding model. Where data were
sufficiently good, methyl group orientations were
refined. Many of the structures displayed disorder in
the position of methyl groups or in solvent of
crystallisation. This disorder was modelled using
standard techniques.
supplementary crystallographic data for this paper.
These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgements
Sichuan Normal University and the National Natural
Science Foundation of China (grants 51443004 and
51273133) are thanked for financial support. Shanyan
Diffraction data were collected on a range of
different CCD diffractometers and were corrected for
absorption and Lp effects using multi-scan
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Mo thanks Beijing University of Technology for an
International Joint Graduate-Training Program
Scholarship. CR thanks the EPSRC for an overseas
travel grant (EP/L012804/1). YAK thanks the Higher
Committee for Education Development in Iraq for
financial support. We thank the STFC for the award
of beam time at Daresbury Laboratory and Dr. Simon
J. Teat for scientific support.
3978-3988; e) N. Iwasa, S. Katao, J. Liu, M.
Fujiki,
Y.
Furukawa,
K.
Nomura,
Organometallics, 2009, 28, 2179-2187; f) N.
Nomura, T. Aoyama, R. Ishii, T. Kondo,
Macromolecules, 2005, 38, 5363-5366; g) D.
Pappalardo, L. Annunziata, C. Pellecchia,
Macromolecules, 2009, 42, 6056-6062. h) X. -
F. Yu, Z. -X. Wang, Dalton Trans. 2013, 42,
3860-3868. (i) T. -L. Huang and C. -T. Chen.
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Supporting
Information
Available:
Crystallographic files CIF format for the structures of
compound L3Hdpa, L3Hdpg, 5, 7 and 9-11·MeCN.
[5] Of 343 hits for dialkylaluminium where N
and O complete the coordination environment,
76 contained chelating phenoxyimine as of
November 2016. F. H. Allen, Acta Crystallogr.,
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European Journal of Inorganic Chemistry
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Table 1. ROP of ε-caprolactone using complexes 1 – 11 (not 2).
b
c
Cat
Run
1
2
3
4
5
6
7
8
T (°C)
80
110
110
80
110
110
80
110
25
CL : M :BnOH Time (h) Conva (%) Mn
Mn,Cal
PDId
1.23
1.73
1.65
1.54
1.73
1.52
1.23
1.46
1.12
1.17
1.19
1.76
1.36
1.47
1.63
1.21
1.01
1.69
1.81
---
1.52
1.60
1.11
1.28
1.32
1.28
1.28
1.19
1.08
1.63
1.19
1.49
1.12
1.66
1.95
1.51
,GPC
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
250 : 1:1
250 : 1:1
250 : 1:2
250 : 1:1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
1
3
3
3
4
4
5
5
5
5
5
5
6
6
7
7
7
8
8
8
9
9
9
97
96
89
95
93
94
65
92
67
75
90
95
96
85
84
95
35
99.5
100
80
99
99.7
65
98
98
100
96
85
45
100
93
91
94
100
95
90
24690
13340
4670
17340
13480
4150
3660
6300
3840
4690
5650
15830
16050
5120
2500
2770
1180
7120
10770
---
4670
10190
2070
7770
7690
17240
9000
14330
4950
29040
3730
26470
10520
27380
5470
18920
27790
27500
12750
27220
26650
13470
18660
26360
19230
21510
25790
27220
27500
12180
24080
27220
10000
28360
28650
---
28360
28560
18660
28070
28070
28640
13750
24360
12950
28640
13270
26080
26930
28640
13610
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28е
29
30
31
32е
33
34
35
36е
45
60
80
110
110
80
110
25
80
110
80
1
1
13min
3
1
3
1
110
110
25
80
1
110
110
110
110
25
110
110
110
25
5min
1
1
3
9
9
9
1
10
10
10
10
11
11
11
11
10min
1
3
1
3 min
1
110
110
110
3
25790
Runs conducted in toluene using 0.05 mmol of catalyst; CL = -caprolactone. a Determined by H NMR spectroscopy; b Mn
GPC values corrected considering Mark-Houwink factors (0.56 poly(ε-caprolactone)) from polystyrene standards in THF.
Calculated from ([Monomer]0/[cat]0) × conv.(%) × Monomer molecular weight + Molecular weight of BnOH. From GPC.
1
c
d
e
Using 1/3 amount of cat. 9 and ½ of cat. 10 and 11.
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Table 2. ROP of rac-Lactide (rac-LA) using complexes 1-11.
Conv (%)a
Mn,calc
b
[rac-LA] :[cat]:[BnOH]
Run
Cat
T (°C)
Time (h)
Mn, GPC
PDI
1
2
3
4
5
6
7
8
9
110
110
110
110
110
110
110
110
110
110
110
110
70
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
100 : 1:1
200 : 1:1
100:1:1
50:1:1
12
12
12
12
12
12
12
12
12
1
75
78
64
30
65
79
80
82
73
71
75
75
78
79
78
84
86
72
---
65
49
74
80
85
---
---
74
---
55
78
63
56
49
72
66
50
10920
22590
9330
2270
9480
22880
46230
70910
84280
41040
10920
43350
45080
45650
11350
24320
49690
10380
---
9480
3640
10780
17400
24610
---
---
10770
---
1
1
2
3
3
3
3
3
3
3
3
3
3
4
5
5
5
6
7
7
7
7
7
7
8
8
8
9
9
9
9
8770
10180
9800
1560
7480
15050
21240
22950
28660
6600
4260
6010
6750
11060
6750
8280
7640
6530
---
4370
2260
4370
4520
6870
---
---
4270
---
1.76
1.32
1.21
1.13
1.26
1.37
1.46
1.68
2.36
1.15
1.41
1.28
1.25
1.60
1.16
1.23
1.15
1.19
---
1.09
1.04
1.09
1.21
1.23
---
---
1.27
---
100 : 1:1
200 : 1:1
400 : 1:1
600 : 1:1
800 : 1:1
400 : 1:1
100 : 1:1
400 : 1:1
400 : 1:1
400 : 1:1
100 : 1:1
200 : 1:1
400 : 1:1
100:1:1
100:1:1
100:1:1
50:1:1
100:1:1
150:1:1
200:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:2
100:1:1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31e
32
33e
34
35
36e
5
6
12
12
12
12
12
12
1
6
12
12
12
12
1
6
12
1
6
8040
11350
9190
8180
7170
10380
4810
7310
2810
4680
4320
3870
2470
5330
3270
2360
1.11
1.21
1.77
1.23
1.22
1.18
1.50
1.37
12
12
12
12
12
12
12
10
10
11
11
11
Runs conducted in toluene using 0.02 mmol of catalyst; a Determined by H NMR spectroscopy; b Mn GPC values corrected
1
c
considering Mark-Houwink factors (0.58 poly (rac-lactide)) from polystyrene standards in THF; Calculated from
([Monomer]0/[OH]0) × conv.(%) × Monomer molecular weight. e Using 1/3 amount of cat. 9 and ½ of cat. 10 and 11.
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Table 4. ROP of -valerolactone using Al complex 1-11
c
d
Runa
Cat
Time/h
Conv.%b
Mn
Mn,Cal
PDIe
VL : BnOH :M
1
2
100:1:1
100:1:1
12
12
34
20
1920
1500
3510
2110
1.35
1.23
1
2
3
100:1:1
100:1:1
100:1:1
100:1:1
50:1:1
12
12
6
89
60
---
97
77
98
97
98
---
90
72
50
---
80
59
---
99
62
---
88
77
3220
1900
---
9010
6110
---
1.29
1.35
---
3
4
4
5
5
6
12
24
24
24
24
12
24
12
12
12
24
24
12
24
24
12
24
24
2790
2370
3850
5350
8310
500
9820
3960
9920
1.75
1.43
1.36
1.73
1.38
1.03
1.38
1.44
1.13
1.01
1.32
1.74
---
5
7
5
8
100:1:1
150:1:1
200:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
100:1:1
5
9
14680
19710
---
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
5
6
3670
2280
1700
510
9120
7310
5110
---
6
7
8
9
4520
3290
---
8120
6010
---
9
9
10
10
10
11
11
11
7340
4870
---
10020
6210
---
1.10
1.82
---
8920
7810
3960
3870
1.52
1.64
b
a Runs conducted in toluene using 0.05 mmol of catalyst at 110 °C. Determined by 1H NMR spectroscopy; c, e Determined by
e
GPC. d Calculated from ([Monomer]0/[OH]0) × conv.(%) × Monomer molecular weight + Molecular weight of BnOH. Using
1/3 amount of cat. 9 and ½ of cat. 10 and 11.
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Table 7. Crystallographic data for pro-ligands L3Hdpa and L3Hdpg and complexes 5 and 7
Compound
L3Hdpa
L3Hdpg
5
7
Formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C28H33NO
399.55
Triclinic
P1
C28H33NO
399.55
C30H38AlNO
455.59
C30H38AlNO
455.59
Monoclinic
P21/c
Monoclinic
P21
Triclinic
P1
10.0491(4)
11.8421(5)
22.5152(9)
86.153(3)
88.412(3)
67.738(4)
2474.05(19)
4
19.264(5)
5.9804(7)
22.048(3)
90
12.019(7)
9.329(2)
12.761(6)
90
10.4155(6)
12.2889(7)
22.1595(13)
78.099(2)
80.513(2)
80.731(2)
2713.5(3)
4
b (Å)
c (Å)
α (º)
β (º)
111.594(15)
90
111.22(5)
90
γ (º)
V (Å3)
2361.8(8)
4
1333.8(11)
2
Z
Temperature (K)
Wavelength (Å)
Calculated density
(g.cm–3)
293(2)
150(2)
0.71073
1.124
150(2)
0.71073
1.134
160(2)
0.71073
1.073
0.71073
1.115
0.10
Absorption coefficient
(mm–1)
0.064
0.067
0.097
Transmission factors
(min./max.)
0.716/1.000
0.955/0.979
0.977/0.986
0.936/0.978
Crystal size (mm3)
0.70 × 0.52 × 0.23
0.7 × 0.4 × 0.2
0.45 × 0.25 × 0.05
0.28 × 0.20 × 0.19
θ(max) (°)
Reflections measured
Unique reflections
Rint
29.226
32360
11750
0.0319
6867
25.235
8827
25.331
7484
28.865
20453
12306
0.0183
4231
7484
0.0620
2051
0.1661
3692
Reflections with F2 > 2σ(F2)
10043
611
Number of parameters
548
280
287
R1 [F2 > 2σ(F2)]
wR2 (all data)
0.0762
0.2324
1.042
0.0494
0.1135
0.804
0.1195
0.3432
1.007
0.0464
0.1186
1.019
GOOF, S
Largest difference
peak and hole (e Å–3)
0.673 and –0.468
0.237 and –0.316
0.719 and –0.427
0.363 and –0.275
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10.1002/ejic.201601415
European Journal of Inorganic Chemistry
Table 7 con’t. Crystallographic data for complexes 9, 10 and 11·MeCN
Compound
9
10
11·MeCN
Formula
C25H35Al3NP
461.45
C17H25Al2N
297.34
C32H39Al2N3
519.62
Formula weight
Crystal system
Triclinic
Monoclinic
P21/n
Triclinic
Space group
P1
P1
Unit cell dimensions
a (Å)
b (Å)
8.7689(14)
12.714(2)
12.722(2)
79.822(2)
77.110(2)
75.776(2)
1329.0(4)
2
12.9996(3)
9.1655(2)
14.6167(2)
90
11.13092(14)
11.31747(15)
14.07252(15)
104.6534(10)
108.3655(11)
105.3906(11)
1508.40(3)
2
c (Å)
α (º)
β (º)
91.416(2)
90
γ (º)
V (Å3)
1741.02(6)
4
Z
Temperature (K)
Wavelength (Å)
Calculated density
(g.cm–3)
150(2)
100(2)
100(2)
0.6861
0.71073
0.71075
1.153
0.193
1.134
0.158
1.144
0.12
Absorption coefficient
(mm–1)
Transmission factors
(min./max.)
0.977/0.996
0.475/1.000
0.872/1.000
0.24 × 0.19 × 0.10
0.19 × 0.15 × 0.10
Crystal size (mm3)
0.12 × 0.08 × 0.02
θ(max) (°)
Reflections measured
Unique reflections
Rint
29.349
8760
27.483
25639
6880
27.482
39175
6903
6934
0.0274
4786
0.0136
6178
0.0224
6628
Reflections with F2 > 2σ(F2)
Number of parameters
R1 [F2 > 2σ(F2)]
wR2 (all data)
293
202
347
0.0478
0.1339
1.014
0.0700
0.2052
1.059
0.0366
0.0958
1.024
GOOF, S
Largest difference
peak and hole (e Å–3)
0.525 and –0.320
0.769 and –0.302
0.388 and –0.317
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