Aluminium complexes containing N,N′-chelating amino-amide hybrid ligands applicable for preparation of biodegradable polymers

Article abstract of DOI:10.1016/j.jorganchem.2014.12.010

Five aluminium complexes containing N,N'-chelating ligands ([2-(Me₂NCH₂)C₆H₄N(R)]^-; R = H, SiMe₃ or benzyl (Bn)) were prepared and structurally characterized by NMR and crystallographic techniques. Aluminium atoms in all compounds are pseudotetrahedrally coordinated with extremely short intramolecular interaction of the pendant amino group (d(Al-N) = 1.96-2.00 ?). The catalytic performance of selected complexes (～0.1-0.2 mol. %), either with or without an external co-initiator, in ring opening (co)polymerization of ε-caprolactone, l-lactide and trimethylene carbonate was tested yielding satisfactory to excellent amount of polymeric material with M_n ～ 15-70 kg/mol for ε-caprolactone, and ～30 kg/mol for trimethylene carbonate with good degree of control over the molar mass distribution, initiation efficiency. An excellent conversion of l-lactide to methyl (S,S)-O-lactyllactate is observed upon catalysis by one of the complexes at room temperature.

Full text of DOI:10.1016/j.jorganchem.2014.12.010

Journal of Organometallic Chemistry 778 (2015) 35e41
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Aluminium complexes containing N,N0-chelating amino-amide hybrid
ligands applicable for preparation of biodegradable polymers
b
c
ꢀ a
ꢀ a
ꢀ a
ꢁ ꢂꢁ ꢁ
Hana Kampova , Emílie Riemlova , Jitka Klikarova , Vladimír Pejchal , Jan Merna ,
d
a
a, *
ꢀ a
ꢁ
ꢀ
ꢁ
ꢂꢁ ꢁ
Petr Vlasak , Petr Svec , Zdenka Ruzickova , Ales Ruzicka
a
ꢀ
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentska 573, CZ-532 10 Pardubice,
Czech Republic
b
ꢀ
Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studentska 573, CZ-532 10 Pardubice,
Czech Republic
c
ꢀ
Department of Polymers, Faculty of Chemical Technology, Institute of Chemical Technology, Technicka 5, CZ-166 28 Prague 6, Czech Republic
d SYNPO a.s., S.K. Neumanna 1316, CZ-532 07 Pardubice, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Five aluminium complexes containing N,N'-chelating ligands ([2-(Me2NCH2)C6H4N(R)]ꢀ; R ¼ H, SiMe3 or
benzyl (Bn)) were prepared and structurally characterized by NMR and crystallographic techniques.
Aluminium atoms in all compounds are pseudotetrahedrally coordinated with extremely short intra-
molecular interaction of the pendant amino group (d(AleN) ¼ 1.96e2.00 Å). The catalytic performance of
selected complexes (~0.1e0.2 mol. %), either with or without an external co-initiator, in ring opening (co)
Article history:
Received 26 October 2014
Received in revised form
8 December 2014
Accepted 9 December 2014
Available online 18 December 2014
polymerization of ε-caprolactone, L-lactide and trimethylene carbonate was tested yielding satisfactory
to excellent amount of polymeric material with Mn ~ 15e70 kg/mol for ε-caprolactone, and ~30 kg/mol
for trimethylene carbonate with good degree of control over the molar mass distribution, initiation ef-
Keywords:
Poly(trimethylene carbonate)
Polycaprolactone
Lactide esterification
Aluminium
ficiency. An excellent conversion of
L-lactide to methyl (S,S)-O-lactyllactate is observed upon catalysis by
one of the complexes at room temperature.
© 2014 Elsevier B.V. All rights reserved.
Amino-amide ligand
Introduction
to be monomeric with the coordination number of four and the
pseudotetrahedral arrangement with accommodation of one
solvent donor to the metal centre [3]. The largest class of
aluminium amides can be described either as homo- or heteroleptic
dimers with four-membered planar or non-planar Al2N2 or Al2X2 (N
means nitrogen ligand, X heteroatom) core [5]. Next to that, some
compounds with higher coordination numbers [6], higher aggre-
gation degrees [7], aluminium imides [8], heterometallic species [9]
and aluminium(I) amides [10] were also reported. Excluding a large
Magnesium, zinc, aluminium and tin(II) compounds are
frequently studied as initiators for ring opening polymerization
(ROP) of various cyclic precursors to biodegradable polymers [1].
One of the promising metals from this series is aluminium, where
the respective complexes could be obtained by the small molecule
(HCl, CH4, H2, etc.) or salt (LiCl) elimination reactions. Moreover,
aluminium is highly abundant and cheap metal and therefore its
applications as initiators of ROP mainly of lactides [2] and ε-cap-
rolactone [1c,d] have been accelerated in the past few years.
Aluminium amides which reveal a plethora of structural motifs,
synthetic and new materials uses, as well as numerous applications
in catalysis are the most prominent species [3]. Although the
aluminium amides containing bulky amido ligands have trigonal
planar geometry [4], there are two other structurally impressive
groups of aluminium amides. A plethora of such compounds tend
class of aluminium b-diketiminates and compounds with similar
conjugated ligands, chelated aluminium amides where the five-
membered diazametalla ring is formed [8aec,11] are much more
populated than those with a six-membered C3N2Al cycle [12] which
is probably caused by the metal size.
To the best of our knowledge, the direct use of aluminium am-
ides and in particular anilides as catalysts for preparation of
biodegradable polymers is only rarely reported up to now [13]. In
this paper we report on the synthesis and structure of N,N0-chelated
aluminium amino-amides and its use in catalytically driven ROP of
* Corresponding author. Fax: þ420 466037068.
ε-caprolactone, L-lactide and trimethylene carbonate.
ꢂꢁ ꢁ
E-mail address: ales.ruzicka@upce.cz (A. Ruzicka).
http://dx.doi.org/10.1016/j.jorganchem.2014.12.010
0022-328X/© 2014 Elsevier B.V. All rights reserved.

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H. Kampova et al. / Journal of Organometallic Chemistry 778 (2015) 35e41
36
Results and discussion
Synthetic and structural aspects
In all synthetic attempts, reported in this paper, recently re-
ported 2-(N,N-dimethylaminomethyl)aniline (ArNNH2; 1) [14], its
trimethylsilyl- (ArNN(SiMe3)H; 2), and newly prepared benzyl-
derivative (ArNN(Bn)H; 3) were used as starting compounds.
Methane elimination synthetic route has been applied for the
preparation of all desired complexes. All reactions of starting
amines with one equivalent of AlMe3 or AlMe2Cl proceeded
smoothly to desired aluminium anilides (see Scheme 1) at ꢀ20 ꢁC
except of the reaction of trimethylsilylated amine 2 with AlMe2Cl
which gave inseparable mixture of products; Me3SiCl elimination is
probably also taking place. In the cases of reactions of AlMeCl2 with
all amines 1e3 the elimination of HCl is suggested instead of
methane, because the same products as in the cases of reactions of
the same amines with AlMe2Cl in line with ArNNH2 and ArNNH2HCl
were isolated.
Fig. 1. Molecular structure of 1Al in ORTEP representation; hydrogen atoms bound to
carbon atoms are omitted for clarity; 30% probability level; selected interatomic dis-
tances (Å) and angles (ꢁ): Al(1)eN(1) 1.8514(15); Al(1)eN(2) 2.0027(15); Al(1)eC(10)
1.9655(19); Al(1)eC(11) 1.9621(18); N(1)eAl(1)eN(2) 96.34(6); N(1)eAl(1)eC(10)
114.82(8); N(1)eAl(1)eC(11) 114.35(7); C(11)eAl(1)eN(2) 106.99(8); C(10)eAl(1)e
N(2) 106.84(9); C(11)eAl(1)eC(10) 115.09(8).
Reactions of 1 with a two fold excess of AlMe3 or AlMe2Cl pro-
duced only monodeprotonated species 1Al or 1AlCl even when the
mixtures were heated at 80 ꢁC for 1 h. When pure samples of
1Ale3Al and 1AlCl were dissolved in toluene, sealed in NMR tubes
and heated to 110 ꢁC for 3 h, in order to prepare aluminium imides
or higher aggregates, no changes of spectral patterns of all 1H NMR
spectra or a precipitate were observed, documenting no elimina-
tion of methane, HCl or MeCl from all compounds. The 1H NMR
spectra of 1AlCl and 3AlCl reveal AX spectral patterns due to the
presence of non-equivalent H atoms on the methylene carbon of
the coordinated amino arm. This nonequivalence is not detected for
the rest of the compounds even at lower temperature (ꢀ40 ꢁC) as a
proof of a fast exchange process. All the methyl groups attached to
the aluminium atoms resonate at about ꢀ 10 ppm in 13C NMR
spectra.
The coordination geometry of all aluminium atoms in 1Al, 1AlCl
and 3AlCl is found to be distorted tetrahedral (Figs. 1e3) with the
large deviation in interatomic angle between amido nitrogen,
aluminium and amino nitrogen atoms which is much lower than is
ideal for tetrahedral geometry. On the other hand angles of amido
nitrogen N1-aluminium and carbon atoms (C10 or C11) are slightly
wider in all compounds. Interatomic distances between aluminium
atom and amido nitrogen atoms are in all cases much shorter than
the sum of the covalent radii of both atoms (1.97 Å [15]) similarly as
in the cases of other N,N0-chelated aluminium compounds forming
five- [11bed] or six-membered [12] aluminiumdiazacycles. Sur-
prisingly, the intramolecular coordination Al ) N of the amino
nitrogen atoms is in all compounds incomparably shortened up to
the values appropriate for covalent bonds (see Figs. 1e3 captions),
Fig. 2. Molecular structure of 1AlCl in ORTEP representation; hydrogen atoms bound
to carbon atoms are omitted for clarity; 30% probability level; selected interatomic
distances (Å) and angles (ꢁ): Al(1)eN(1) 1.8113(14); Al(1)eN(2) 1.9716(13); Al(1)e
C(10) 1.9507(17); Al(1)eCl(1) 2.1647(6); N(1)eAl(1)eN(2) 97.09(6); N(1)eAl(1)eC(10)
120.42(7); N(1)eAl(1)eCl(1) 111.61(5); C(10)eAl(1)eN(2) 111.40(7); N(2)eAl(1)eCl(1)
103.29(4); C(10)eAl(1)eCl(1) 110.91(6).
Fig. 3. Molecular structure of one of independent molecules of 3AlCl in ORTEP rep-
resentation; hydrogen atoms bound to carbon atoms are omitted for clarity; 30%
probability level; selected interatomic distances (Å) and angles (ꢁ), appropriate pa-
rameters for the second molecule are given in parenthesis: Al(1)eN(1) 1.827(3)
(1.818(4)); Al(1)eN(2) 1.961(4) (1.951(4)); Al(1)eC(17) 1.988(5) (1.955(4)); Al(1)eCl(1)
2.1545(18) (2.1380(18)); N(1)eAl(1)eN(2) 98.66(15) (99.43(17)); N(1)eAl(1)eC(17)
117.9(2) (118.39(18)); N(1)eAl(1)eCl(1) 110.46(13) (110.37(13)); N(2)eAl(1)eC(17)
109.5(2) (110.0(2)); N(2)eAl(1)eCl(1) 105.21(12) (104.38(13)); C(17)eAl(1)eCl(1)
113.35(19) (112.59(16)).
Scheme 1.

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H. Kampova et al. / Journal of Organometallic Chemistry 778 (2015) 35e41
37
which could be a reason for the extraordinary stabilization of these
aluminium amides towards further deprotonation.
solution. In the case of the precursor 1AlCl, which has a higher
Lewis acidity on the central metal atom, similar catalytic perfor-
mances of the system with slightly better conversions and Ð values
but lower number average molar masses (Table 1, entries 5e9)
were observed. This is in strong contrast to similar aluminium
complexes [16] used for co-initiation of a ROP together with an
alcohol, where lower activity is observed for methylchlor-
oaluminium than for dimethylaluminium species, which could be
explained by higher stability of 1Al towards protonolysis than other
complexes in use. Complex 1AlCl revealed catalytic activity even at
room temperature (entry 5), addition of BnOH (entry 7) decreased
molar masses and the Ð value significantly, and from the polymer
parameters comparison of diluted (entry 8) and concentrated
(entry 9) reaction mixtures it is seen that no deactivation of active
species during the ROP of CL is taking place. Decreased monomer/Al
ratio (entry 9) leads to proportional decrease of polymer molar
mass as expected in case of controlled polymerization. It is sug-
gested, on the basis of all results, that the ROP of CL proceeds in a
“controlled-living” manner with initiator acting via a coordination
insertion mechanism [17]. On the other hand, broader distribution
of molar masses, discrepancies in experimental and theoretical Mn,
and NPM (number of polymer molecules per catalyst molecule)
values are in some cases far from ideal value of 1 (one molecule of
aluminium complex per polymer chain). Presumably polymer
transesterification during the catalytic run can be suggested as a
reason. In spite of this, the Ð values are found in the range of
1.30e1.69, and it is still believed that both 1Al and 1AlCl act as
single-site catalysts. In comparison to the literature data, it seems
that the results obtained are very close to those of other aluminium
complexes bearing N,O-chelating or similar ligands [18]. In at-
tempts to clarify the nature of the catalytically active species,
complexes 1Al and 1AlCl were reacted with benzyl alcohol and
water in an equimolar ratio leading in all cases inseparable to
mixtures of starting compounds and products of non identified
composition.
Polymerization results
Polymerization tests were performed on three different sub-
strates using complexes of aluminium 1Al and 1AlCl as catalyst
precursors. The selection of two complexes from the number of
prepared compounds is based on very easy synthetic access to both
of them, by just one step, from substituted aniline and commercial
solutions of AlMe3 and AlMe2Cl, respectively, and the stability in
the presence of the monomer at room temperature. In all cases the
amount of precursor is about 0.2 mol.% and the presence or absence
of an external co-precursor (i.e., benzylalcohol (BnOH) or iso-
propylalcohol (iPrOH)) is denoted in Table 1. The polymerization
tests where the concentration of precursors is varied to > 0.6 mol%
were not representative because high activity of precursors caused
immediate increase of viscosity of even diluted samples and thus
the yield of polymers with large dispersities as products of non-
controlled reactions with non-reproducible results. On the other
hand, the concentration of precursors < 0.1 mol.% is too low for
sufficient initiation of polymerizations and only low yields of
polymeric materials were obtained. When about 0.2 mol. % of
dimethylaluminium amide complex 1Al is used for polymerization
of ε-caprolactone (CL), moderate yields of about 70% with Mn being
~50 000 g/mol and slightly higher dispersity indexes (Ð, Entries
1e4) were detected. Addition of 1 M eq. of BnOH is as a co-initiator
caused slight increase of the polymer yield (entry 3), similarly as in
the case of lowering the monomer concentration by a dilution of
the reaction mixture to a half of an initial volume by 3 mL of toluene
(entry 2). In the same order, the number average molar masses
decreased as a consequence of increased amount of initiating eOR
groups, but having negligible influence to Ð values. One of the in-
dustrial demands is the stability of stock solutions of precursors for
several days. Appropriate ageing test has been performed, the ac-
tivity of 1Al solution stored in a fridge for two weeks decreased
only slightly (comparison of entries 1 and 4) which could be
attributed to a partial decomposition of the precursor in stock
To the best of our knowledge, there is only a limited number of
examples of aluminium complexes used as well defined initiators
for trimethylene carbonate (TMC) ROP [19].
Table 1
Polymerization of ε-caprolactone (CL), trimethylene carbonate (TMC) and
L-lactide (LLA) catalysed by Al complexes in presence/absence of benzylalcohol (BnOH) or iso-
propylalcohol (iPrOH) at 100 ꢁC (for CL and LLA) or 80 ꢁC (for TMC).
Ðb
NPMd
c
Entry
Catalyst
Monomer
Catalyst (
mmol)
Age of solution
(days)
ROH (
m
mol)
Monomer/Catalyst
Monomer
Mnb (kg/mol)
Mn
conversiona (%)
1
1Al
1Al
1Al
1Al
1AlCl
1AlCl
1AlCl
1AlCl
1AlCl
1Al
1Al
1AlCl
1Al
CL
CL
CL
CL
CL
CL
CL
CL
16
17
15
18
16
19
13
17
43
20
17
18
42
42
40
42
Fresh
Fresh
5
e
e
620
500
650
510
540
500
760
600
140
440
500
520
500
500
500
500
66
87
77
69
17
92
74
81
70
62
70
86
>99
>99
>99
>99
50.9
39.4
41.2
50.7
14.8
34.0
24.8
69.9
19.4
32.4
26.8
33.4
0.18
0.18
0.18
0.18
46.7
49.6
57.1
40.2
10.5
52.5
64.2
55.5
11.2
27.8
35.7
45.7
71.3
71.3
71.3
71.3
1.69
1.72
1.60
1.76
1.36
1.62
1.30
1.48
1.42
1.54
1.30
1.58
1.04
1.04
1.04
1.04
0.9
1.3
1.4
0.8
0.7
1.5
2.6
0.8
0.6
0.95
1.47
1.51
e
2e
3
15 (BnOH)
e
4
14
5f
6
Fresh
Fresh
1
1
1
Fresh
Fresh
Fresh
Fresh
Fresh
Fresh
Fresh
e
e
7
15 (BnOH)
e
8e
9
CL
e
10
11
12
13
14
15
16
TMC
TMC
TMC
LLA
LLA
LLA
LLA
e
e
e
e
1AlCl
1Al
1AlCl
e
e
400 (iPrOH)
e
420 (iPrOH)
e
Polymerization time 90 min.
a
Estimated from 1H NMR spectra.
Number average molar mass and dispersity (Mw/Mn) determined by SEC-MALS.
b
c
d
e
f
Mn,theo ¼ [monomer]/[complex] ꢂ conversion ꢂ Mw(monomer) þ Mw(co-initiator)
.
Number of polymer molecules per catalyst molecule, determined as Mn/(mass of polymer/mol of catalyst) ꢀ initiation efficiency.
Diluted by 3 mL of toluene.
Room temperature.

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H. Kampova et al. / Journal of Organometallic Chemistry 778 (2015) 35e41
38
All three catalytic runs performed with similar TMC/precursor
coordinate very strongly to the metal centre in a bidentate
fashion. Two of these complexes revealed promising activity as
precursors of ROP or selective ring-opening esterification to
methyllactyllactate.
ratios without a co-initiator gave moderate to high monomer
conversion values (entries 10e12), rather high number average
molar masses and acceptable molar mass distributions. It seems
that the precursor 1AlCl is slightly more active and the activity and
parameters of polymers are comparable with the results described
in the literature [19]. In order to analyse the end-groups of the
polymers, a low molar mass polycaprolactone and trimethylene
carbonate (Mn ~ 5 kg molꢀ1) were prepared by using 1Al as a
precatalyst in 50:1 ratio of monomer:1Al (1 eq. of BnOH is added in
the case of CL polymerization). In the case of CL polymerization, the
1H NMR analysis showed the dominant presence of eCH2eOH
Experimental section
General methods
NMR spectroscopy
NMR spectra were recorded at 295 K from solutions in benzene-
d6 and CDCl3 on a Bruker Avance III 500 spectrometer, equipped
with a z-gradient 5 mm Prodigy™ cryoprobe probehead, operating
at 500.2 MHz for 1H and 125.76 MHz for 13C{1H} nuclei. All
deuterated solvents were degassed and then stored over K or Na
mirror under an argon atmosphere. Solutions were obtained by
dissolving of approximately 20 mg of each compound in 0.5 mL of
deuterated solvent. Values of 1H chemical shifts were calibrated to
(3.67 ppm) as the a
-end groups from the termination by Hþ. The
NMR based molar mass Mn ¼ 4.2 kg molꢀ1 is consistent with SEC-
MALS results. Benzyl
u-end-groups (PheCH2eO at 5.12 ppm and
PheCH2eO at 7.35 ppm e Fig. S1), coming from the co-initiator
were observed in approximately 10% of chains - the rest is termi-
nated by OH groups coming from residual water present in the
monomer. No anilide end-groups from 1Al catalyst structure were
detected showing the products of ligand or methyl substitution by
benzylalcohol or by water from monomer being the truly initiating
species. In the TMC case, the 1H NMR spectrum (Fig. S2) is perfectly
consistent with the spectrum of telechelic PTMC-(OH)2 presented
elsewhere [20], which is similarly as in the case of CL a proof of
water co-initiation.
the internal standard e tetramethylsilane (
d
(1H) ¼ 0.00) or to re-
sidual signals of benzene or chloroform (
d
(1H) ¼ 7.16 or 7.27), values
of 13C chemical shifts were calibrated to signals of benzene or
chloroform (
d(
13C) ¼ 128.4 or 77.23) and measured using the in-
verse gated proton broad band decoupling mode.
Crystallography
At desired reaction conditions, both precursors are totally inactive
in sense of polymer production by ROP of L-lactide (LLA-entries
The X-ray diffraction data (Table 2) obtained from crystals of
compounds 1Al, 1AlCl and 3AlCl were obtained at 150 K using an
Oxford Cryostream low-temperature device on a Nonius KappaCCD
13e16) and essentially quantitative conversion of LLA to oligomers
was observed in all cases. The increase of the complex 1Al concen-
tration up to 2 mol.% (without a co-initiator) had no significant in-
fluence on LLA to polymer conversion, and only starting LLA and
diffractometer with MoKa radiation (
l
¼ 0.71073 Å), a graphite
monochromator, and the and scan mode. Data reductions were
f
c
performed with DENZO-SMN [22]. The absorption was corrected by
integration methods [23]. Structures were solved by direct methods
oligomerized L
-lactic acid was isolated after 1 h of reaction at 100 ꢁC.
On the other hand, the selective LLA conversion to the lactic acid or
its oligomers (lactyllactates) or esters has attracted great interest as
environmentally benign route to valuable chemical products [21].
We conducted the reaction of one equivalent of the appropriate
catalyst 1Al or 1AlCl with 50 eq. of LLA and 200 eq. of methanol in
dichloromethane at room temperature. The aliquots were taken after
1, 15 and 30 min and 24 h of reactions. Monitoring of the reaction by
1H as well as 13C NMR spectroscopy showed that ~15% of the cyclic
dimer LLA is consumed within the first minute of the reaction cat-
alysed by 1Al (~4% in the case of 1AlCl catalyst) yielding lactic acid,
its methylester and methyl (S,S)-O-lactyllactate. After one day, the
reaction catalysed by 1Al produced ~94% (89% after washing of the
resulting oil with cold pentane) of methyl (S,S)-O-lactyllactate
(identified by NMR spectroscopy; 1H, 500.2 MHz, C6D6, ppm: 5.04
(1H, q, 3JHeH ¼ 6.75, CH), 4.23 (1H, q, 3JHeH ¼ 6.93, CH), 3.22 (3H, s,
OCH3), 1.45 (3H, d, 3JHeH ¼ 6.93, Me), 1.15 (3H, d, 3JHeH ¼ 6.75, Me).
13C, 125.77 MHz, C6D6, ppm: 175.3, 170.8, 69.3, 67.0, 51.9, 20.6, 16.6).
When the reaction of the stoichiometric amount of 50 eq. of LLA and
50 eq. of methanol in the presence of 1 eq. of catalyst 1Al in
dichloromethane is conducted at the same conditions, the mixture
composed of LLA (~20%), HOCH(Me)CO2Me (~60%) HOCH(Me)
CO2OCH(Me)CO2Me (~15%) and minority of oligomeric lactides was
established according to 1H NMR spectra integration [21g]. On the
other hand, the same reaction carried out in the presence of 1AlCl
reveals ~55% yield of methyl (S,S)-O-lactyllactate along with a
number of presumably oligomeric byproducts of similar
composition.
Table 2
Crystallographic data for compounds 1Al, 1AlCl and 3AlCl.
Compound
1Al
1AlCl
3AlCl
Formula
Cell setting
Space group
a (Å)
b (Å)
c (Å)
C11H19AlN2
Monoclinic
P21
6.3730(2)
10.3021(5)
9.6140(4)
90
104.486(4)
90
2
C10H16AlClN2
Monoclinic
P21/c
9.8640(7)
13.2990(3)
10.6331(8)
90
119.773(6)
90
4
C17H22AlClN2
Monoclinic
Pc
9.8580(5)
18.8941(19)
11.5070(10)
90
124.628(7)
90
4
a
b
g
Z
(ꢁ)
(ꢁ)
(ꢁ)
Volume (Å3)
611.14(4)
1.121
1210.74(15)
1.244
1763.6(3)
1.193
Density (g cmꢀ3
)
Crystal size (mm) 0.59 ꢂ 0.47 ꢂ 0.36 0.42 ꢂ 0.40 ꢂ 0.13 0.59 ꢂ 0.59 ꢂ 0.25
Crystal description Block
Crystal colour Colourless
(mmꢀ1
F(000)
Block
Colourless
0.354
Block
Colourless
0.262
m
)
0.133
224
480
672
Tmin; Tmax
h; k; l min, max
0.931; 0.964
ꢀ8, 6; ꢀ11,
13; ꢀ12, 12
3.85; 27.50
5272
0.895; 0.969
ꢀ12, 11; ꢀ16,
17; ꢀ13, 13
2.38; 27.50
10,555
2747 (0.0345)
2335
127
0.880; 0.942
ꢀ12, 12; ꢀ24,
22; ꢀ13, 14
2.16; 27.50
11,442
6292 (0.0891)
5976
379
q
min; max (ꢁ)
Reflections nr.
Total (Rint)a
2282 (0.0430)
2241
gt [I > 2s(I)]
Nr. of parameters 127
Max/min
t
/e Åꢀ3 0.170; 0.156
1.061
0.266/- 0.225
1.125
0.0327/0.0774
0.483/ꢀ0.445
The attempt to catalyse the copolymerization of CL (250 eq.) and
TMC (250 eq.) by 1 M eq. of 1Al or 1AlCl at 80 ꢁC for 1 h led sur-
prisingly to the mixture of unreacted CL and partially polymerized
(~70e85% by 1H NMR) TMC.
To conclude, we synthesized a couple of methylaluminium
complexes bearing the amino-amide ligand which is able to
GOFb
1.121
Rc/wRc
0.0306/0.0824
0.0617/0.1604
P
P
a
b
c
Rint
¼
jF2o ꢀ F2o,meanj/ F2o.
P
S ¼ [ (w(F2o ꢀ F2c)2)/(Ndiffr. ꢀ Nparam.)] .
½
Weighting scheme: w ¼ [
s
2(F2o) þ (w1P)2 þ w2P]ꢀ1, where P ¼ [max(Fo2) þ 2F2c],
P
P
P
P
R(F) ¼ jjFoj ꢀ jFcjj/ jFoj, wR(F2) ¼ [ (w(F2o ꢀ F2c)2)/( w(Fo2)2)] .
½

ꢀ
H. Kampova et al. / Journal of Organometallic Chemistry 778 (2015) 35e41
39
(Sir92) [24] and refined by full matrix least-square based on F2
(SHELXL97) [25]. Hydrogen atoms were mostly located on a dif-
ference Fourier map, however to ensure uniformity of the treat-
ment of the crystal, all hydrogen atoms were recalculated into
idealized positions (riding model) and assigned temperature fac-
tors Hiso(H) ¼ 1.2 Ueq(pivot atom) or of 1.5Ueq for the methyl
moiety, using CeH bond distances of 0.96, 0.97, and 0.93 Å for
methyl, methylene and aromatic hydrogen atoms, respectively, and
0.86 Å for NeH bonds.
6.53 (dd, 3JHeH ¼ 7.3, 3JHeH ¼ 7.5, 1H, ArH); 6.37 (d, 3JHeH ¼ 8.0 Hz,
1H, ArH); 3.11 (s, 2H, NCH2); 3.04 (s, 1H, NH); 1.65 (s, 6H,
N(CH3)2); ꢀ0.58 (s, 6H, Al(CH3)2). 13C{1H} NMR (125.76 MHz, C6D6,
ppm) d: 153.09 (ArC); 130.51 (ArC); 130.46 (ArC); 117.84 (ArC);
116.56 (ArC); 113.87 (ArC); 63.61 (NCH2); 44.47 (N(CH3)2); ꢀ9.36
(Al(CH3)2). Anal. found: C 64.05, N 13.58, H 9.28%; Calcd for
C11H19AlN2: C 64.1, N 13.6, H 9.3%.
Preparation of ArNN(H)AlMeCl (1AlCl)
Solution of 3.33 mL of AlMe2Cl (1 M in hexanes, 3.33 mmol) was
added to the solution of 1 (500 mg, 3.33 mmol) in diethyl ether
at ꢀ 20 ꢁC. The reaction mixture was stirred overnight and then
reduced to the half of its initial volume in vacuo. 294 mg of 1AlCl
was obtained as single crystals by crystallization from the diethyl
ether at ꢀ 20 ꢁC (yield 39%). M. p. 79 ꢁC. 1H NMR (500.2 MHz, 295 K,
Synthetic procedures
Preparations of all complexes were performed using standard
Schlenk techniques under inert atmosphere of argon (99.999%).
Inert gas was passed through the oxygen/moisture trap before
entering to the vacuum/inert line. Solvents and reactants were
purchased from commercial sources. n-Butyllithium (1.6 M in
hexanes), trimethylaluminium (2.0 M in hexanes), dimethylalu-
minium chloride solution (1.0 M in hexanes), methylaluminium
dichloride solution (1.0 M in hexanes), sodium borohydride (p.a.),
sodium sulphate (99.0%, anhydrous) were used without further
purification. Solvents (diethyl ether, hexane or petrolether) were
purified by solvent purification system, degassed and stored under
an argon atmosphere over K mirror. Compounds ArNNH2 (1),
ArNNHLi (1Li), ArNN(SiMe3)H (2) were obtained by published
methods [14]. Compositional analyses were determined under an
inert atmosphere of argon on an EA 1108 automatic analyzer by
Fisons Instruments.
3
3
C6D6, ppm)
d
: 7.01 (dd, JHeH ¼ 6.5, JHeH ¼ 6.8, 1H, ArH); 6.64 (d,
3JHeH ¼ 6.5 Hz, 1H, ArH); 6.50 (bs, 1H, ArH); 6.32 (d, 3JHeH ¼ 7.5 Hz,
1H, ArH); 3.64 and 2.94 (AX spin system, Dd
¼
350 Hz,
3JHeH ¼ 12.7 Hz, 2H, NCH2); 3.22 (s, 1H, NH); 1.99, 1.71 (aniso-
chronous signals, s, 6H, N(CH3)2); ꢀ0.51 (s, 3H, Al(CH3)). 13C{1H}
NMR (125.76 MHz, C6D6, ppm) d: 151.20 (ArC); 130.52 (ArC); 130.51
(ArC); 117.88 (ArC); 116.59 (ArC); 115.42 (ArC); 63.06 (N(CH3)2);
45.38 (N(CH3)2); 43.55 (NCH2); ꢀ10.95 (Al(CH3)). Anal. found: C
53.0, N 12.3, H 7.2%; Calcd for C10H16AlClN2: C 52.98, N 12.36, H
7.11%.
Preparation of ArNN(SiMe3)AlMe2 (2Al)
Solution of 1.49 mL of Me3Al (2 M in hexanes, 2.98 mmol) was
added to the solution of 663 mg of 2 (2.98 mmol) in 15 mL of diethyl
ether at ꢀ 20 ꢁC. The reaction mixture was stirred overnight and
then evaporated in vacuo. 672 mg of the dense liquid 2Al was ob-
Preparation of ArNN(Bn)H (3)
Following reaction was performed without using of an inert
atmosphere. Compound 1 (4.5 g, 30 mmol) was added to the so-
lution of PhC(O)H (3.2 g, 30 mmol) in 120 mL of methanol. The
reaction mixture was stirred for 2 days at room temperature and
then evaporated in vacuo. 6 g of light yellow oil product ArNN]
CHPh was obtained (yield 85%). Methanolic solution of NaBH4
(1.9 g, 50 mmol) was added dropwise to the solution of ArNN]Bn
(6 g, 25 mmol) in 120 mL of methanol. The reaction mixture was
stirred for 12 h at room temperature. 30 mL of water was added to
the reaction mixture and stirred for 30 min. The product was
extracted two times with 50 mL of dichloromethane and the
resulting organic layer was dried by sodium sulphate (anhydrous).
Finally, dichloromethane was distilled off and an oily product was
dried in vacuo. 5.4 g of light yellow oil product 3 was obtained (yield
tained (yield 81%). 1H NMR (500.2 MHz, 295 K, C6D6, ppm)
d:
7.21e7.14 (m, 2H, ArH); 6.76e6.71 (m, 2H, ArH); 3.12 (s, 2H, NCH2);
1.70 (s, 6H, N(CH3)2); 0.46 (s, 9H, Si(CH3)3); ꢀ0.55 (s, 6H, Al(CH3)2).
13C{1H} NMR (125.76 MHz, C6D6, ppm)
d: 153.81 (ArC); 131.06
(ArC); 130.18 (ArC); 125.13 (ArC); 123.55 (ArC); 117.31 (ArC); 63.77
(NCH2); 45.56 (N(CH3)2); 3.26 (Si(CH3)3); ꢀ7.56 (Al(CH3)2). Anal.
found: C 60.4, N 10.1; H 9.8%; Calcd for C14H27AlN2Si: C 60.39, N
10.06, H 9.77%.
Preparation of ArNN(Bn)HAlMe2 (3Al)
Solution of 1.02 mL of AlMe3 (2 M in hexanes, 2.04 mmol) was
added to the solution of 3 (490 mg, 2.04 mmol) in 30 mL of diethyl
ether at /20 ꢁC. The reaction mixture was stirred overnight and
then evaporated in vacuo. 472 mg of white powder of 3Al was
isolated (yield 78%). M.p. 203 ꢁC. 1H NMR (500.2 MHz, 295 K, C6D6,
90%). 1H NMR (500.2 MHz, 295 K, C6D6, ppm)
d: 7.30 (d,
3JHeH ¼ 7.5 Hz, 2H, ArH); 7.19e7.14 (m, 3H, ArH); 7.08 (dd,
3JHeH ¼ 7.2, 3JHeH ¼ 7.6, 1H, ArH); 6.99 (d, 3JHeH ¼ 7.2 Hz, 1H, ArH);
6.79 (bs,1H, NH); 6.73 (dd, 3JHeH ¼ 8.1, 3JHeH ¼ 7.6, 1H, ArH); 6.61 (d,
3JHeH ¼ 8.1 Hz, 1H, ArC); 4.20 (AB spin system, Dd ¼ 5.6 Hz, 2H,
CH2); 3.33 (s, 2H, NCH2); 1.93 (s, 6H, N(CH3)2). 13C{1H} NMR
ppm)
d
: 7.33 (d, 3JHeH ¼ 7.5 Hz, 2H, ArH); 7.18 (m, 3JHeH ¼ 7.4 Hz, 2H,
ArH); 7.06e7.02 (m, 2H, ArH); 6.71 (d, 3JHeH ¼ 7.2 Hz, 1H, ArH); 6.58
3
3
3
(d, JHeH ¼ 8.3 Hz, 1H, ArH); 6.53 (dd, JHeH ¼ 7.2, JHeH ¼ 7.5, 1H,
ArH); 4.54 (s, 2H, CH2); 3.22 (s, 2H, NCH2); 1.68 (s, 6H,
N(CH3)2); ꢀ0.58 (s, 6H, Al(CH3)2). 13C{1H} NMR (125.76 MHz, C6D6,
(125.76 MHz, C6D6, ppm) d: 148.70 (ArC); 140.64 (ArC); 130.24
(ArC); 129.08 (ArC); 128.76 (ArC); 127.35 (ArC); 127.06 (ArC); 123.10
(ArC); 116.68 (ArC); 110.89 (ArC); 64.24 (CH2); 47.61 (NCH2); 44.65
(N(CH3)2). Anal. found: C 79.8, N 11.7, H 8.4%; Calcd for C16H20N2: C
79.96, N 11.66, H 8.39%.
ppm) d: 158.55 (ArC); 152.85(ArC); 141.94 (ArC); 130.46 (ArC);
130.27 (ArC); 128.83 (ArC); 127.15 (ArC); 126.48 (ArC); 113.79 (ArC);
113.33 (ArC); 63.58 (NCH2); 49.49 (CH2); 44.28 (N(CH3)2); ꢀ10.66
(Al(CH3)2). Anal. found: C 73.0, N 9.4, H 8.5%; Calcd for C18H25AlN2:
C 72.94, N 9.45, H 8.50%.
Preparation of ArNN(H)AlMe2 (1Al)
Solution of 1.44 mL of AlMe3 (2 M in hexanes, 2.88 mmol) was
added to the solution of 1 (433 mg, 2.88 mmol) in diethyl ether
at ꢀ 20 ꢁC. The reaction mixture was stirred overnight and then
reduced to the half of its initial volume in vacuo. 428 mg of single
crystals of 1Al were obtained by crystallization from the diethyl
ether at ꢀ 20 ꢁC and subsequent drying in vacuo (yield 72%). M.p.
Preparation of ArNN(Bn)AlMeCl (3AlCl)
Solution of 1.44 mL of AlMe2Cl (1 M in hexanes, 1.44 mmol) was
added to the solution of 3 (345 mg, 1.44 mmol) in 15 mL of diethyl
ether at ꢀ 20 ꢁC. The reaction mixture was stirred for 1 day. 214 mg
of 3AlCl was obtained as single crystals (suitable for XRD analysis)
from saturated diethyl ether solution at room temperature (yield
39 ꢁC. 1H NMR (500.2 MHz, 295 K, C6D6, ppm)
d
: 7.08 (dd,
47%). M.p. 74 ꢁC. 1H NMR (500.2 MHz, 295 K, C6D6, ppm)
d: 7.37 (d,
3JHeH ¼ 8.0, 3JHeH ¼ 7.5, 1H, ArH); 6.64 (d, 3JHeH ¼ 7.3 Hz, 1H, ArH);
3JHeH ¼ 7.7 Hz, 2H, ArH); 7.18 (d, 3JHeH ¼ 7.6 Hz, 2H, ArH); 7.06e6.99

ꢀ
40
H. Kampova et al. / Journal of Organometallic Chemistry 778 (2015) 35e41
3
(m, 2H, ArH); 6.63e6.62 (m, 2H, ArH); 6.55 (dd, JHeH ¼ 7.3,
3JHeH ¼ 7.7, 1H, ArH); 4.57 (AB spin system, Dd ¼ 15.3 Hz,
2JHeH ¼ 16.9 Hz, 2H, CH2); 3.62 and 2.90 (AX spin system,
Dd ¼ 355 Hz, 3JHeH ¼ 13.4 Hz, 2H, NCH2); 1.87, 1.57 (anisochronous
signals, s, 6H, N(CH3)2); ꢀ0.46 (s, 3H, Al(CH3)). 13C{1H} NMR
Appendix A. Supplementary material
CCDC 1012893e1012895 contain the supplementary crystallo-
graphic 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.
(125.76 MHz, C6D6, ppm) d: 151.56 (ArC); 141.10 (ArC); 130.59 (ArC);
130.24 (ArC); 128.61 (ArC); 127.25 (ArC); 126.72 (ArC); 118.09 (ArC);
115.18 (ArC); 113.99 (ArC); 63.07 (NCH2); 49.35 (N(CH3)2); 45.07
(N(CH3)2); 43.34 (CH2); ꢀ11.94 (Al(CH3)). Anal. found: C 64.5, N 8.8,
H 7.1%; Calcd for C17H22AlClN2: C 64.45, N 8.84, H 7.00%.
Appendix B. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2014.12.010.
Typical (co)polymerization and esterification procedures
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Schlenk tube was charged by ε-caprolactone (1e3 g,
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