Scandium and yttrium complexes of an hybrid phenoxy-amidopyridinate ligand. Use in ROP of racemic lactide

Article abstract of DOI:10.1016/j.jorganchem.2016.09.014

The new multidentate hybrid phenol-aminopyridine proligand {N^Me2NN^Me2C^iPr2O}H₂(1-H₂) was prepared and used in σ-bond metathesis reactions with the trialkyl precursors M(CH₂SiMe₃)

Full text of DOI:10.1016/j.jorganchem.2016.09.014

Journal of Organometallic Chemistry 823 (2016) 34e39
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Scandium and yttrium complexes of an hybrid
phenoxy-amidopyridinate ligand. Use in ROP of racemic lactide
,
**
Jad El Haj Hassan a, Vasily Radkov a, Vincent Dorcet b, Jean-François Carpentier a
,
,
*
Evgueni Kirillov a
a
1
ꢀ
Organometallics: Materials and Catalysis, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Universite de Rennes 1, Rennes, France
b
ꢀ
ꢀ
Centre de Diffractometrie X, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Universite de Rennes 1, Rennes, France
a r t i c l e i n f o
a b s t r a c t
The new multidentate hybrid phenol-aminopyridine proligand {NMe2NNMe2CiPr2O}H2 (1-H2) was pre-
pared and used in -bond metathesis reactions with the trialkyl precursors M(CH2SiMe3)3(THF)2
Article history:
Received 7 June 2016
Received in revised form
16 August 2016
Accepted 16 September 2016
Available online 19 September 2016
s
(M ¼ Sc, Y). These reactions afforded cleanly the corresponding alkyl complexes {NMe2NNMe2CiPr2O}
M(CH2SiMe3)(THF) (M ¼ Sc (1-Sc), Y (1-Y)), which were characterized by NMR spectroscopy and
microanalysis. Upon crystallization, 1-Sc disproportionates to form the bis(ligand) complex 2-Sc which
was isolated and characterized by X-ray crystallography. Complexes 1-Sc and 1-Y were used as initiators
in the ring-opening polymerization (ROP) of racemic lactide, alone or in combination with iPrOH, to give
atactic PLAs with controlled molecular weights.
Keywords:
Group 3 metals
Nitrogen-based ligands
Alkyl complexes
Structure elucidation
ROP
© 2016 Elsevier B.V. All rights reserved.
Cyclic esters
1. Introduction
[6], which were found competent for initiating ROP of cyclic esters
and catalyzing polymerization of ethylene, respectively.
Simultaneous implementation of both phenoxide [1] and ami-
dinate [2] anionic ligands into coordination chemistry of early
transition metals has engendered evolution of several new classes
of polymerization precursors. Group 3 metal complexes with
mixed-ligands (Scheme 1, A) have been used as initiators in cyclic
esters ring-opening polymerization (ROP) processes [3], while their
group 4 metal counterparts [4] have been assessed as olefin
(ethylene) polymerization precursors. In more recent studies,
incorporation of the two anionic motifs in a single molecular as-
sembly has been successfully achieved, yielding new hybrid
chelating dianionic platforms (B and C). For example, Kempe, Kol
and coworkers [5] have reported on amidopyridinate/phenoxy-
imino ligand systems (B), which upon coordination onto group 4
metal centers afforded isoselective catalysts for living polymeri-
zation of 1-hexene. Also, we have described complexes of group 3
and group 4 metals incorporating phenoxy-amidinate ligands (C)
In our efforts for developing new discrete catalytic systems for
the controlled ROP of cyclic esters via modification/functionaliza-
tion of dianilinopyridinate-type systems [7], we here report a new
chelating ligand assembly incorporating phenoxide and amidinate
anionic moieties. The coordination chemistry of this ligand system
with group 3 metals (Sc and Y) has been investigated, and the ac-
tivity of the resulting new alkyl complexes was preliminarily
assessed in ROP of racemic lactide (rac-LA).
2. Results and discussion
2.1. Synthesis of the hybrid phenol-aminopyridine proligand
{NMe2NNMe2CiPr2O}H2 (1-H2) [8].
In our previous studies [7], we have achieved an efficient and
straightforward synthesis of a series of amidine-aminopyridine
proligands by the one-step condensation of 2,6-bis(2,6-
dimethylphenylamino)pyridine with imidoyl chlorides. For the
synthesis of proligand 1-H2, a multi-step protocol was used starting
from the condensation of 2,6-bis(2-dimethylphenylamino)pyridine
with 2-(chlorocarbonyl)-4,6-diisopropylphenyl acetate, followed
* Corresponding author.
** Corresponding author.
E-mail address: evgueni.kirillov@univ-rennes1.fr (E. Kirillov).
http://www.univ-rennes1.fr.
1
http://dx.doi.org/10.1016/j.jorganchem.2016.09.014
0022-328X/© 2016 Elsevier B.V. All rights reserved.

J. El Haj Hassan et al. / Journal of Organometallic Chemistry 823 (2016) 34e39
35
Scheme 1. Mixed (A) and hybrid (B, C) phenoxy-amidinate ligand systems used in the development of polymerization catalysts.
by reduction and deprotection steps (Scheme 2). 1-H2 was isolated
in satisfactory yield as an air-stable solid and characterized by 1H
and 13C NMR spectroscopy (see the Supporting Information,
Figures S5 and S6, respectively) and combustion analysis.
Crystals of 1-H2 suitable for X-ray diffraction were grown by
slow evaporation of a CHCl3 solution in air. Fig. 1 shows the mo-
lecular structure of 1-H2, along with selected metrical data.
2.2. Group 3 metal alkyl complexes {NMe2NNMe2CiPr2O}
M(CH2SiMe3)(THF)
Regular
s-bond metathesis reactions between 1-H2 and tri-
salkyls M(CH2SiMe3)3(THF)2 (M ¼ Sc and Y) were conducted in
benzene or in toluene (Scheme 3). In situ monitoring by 1H NMR
spectroscopy showed that M(CH2SiMe3)3(THF)2 readily reacts with
1 equiv of proligand at ꢀ30 ꢁC in toluene-d8. Scaling up this pro-
tocol followed by workup allowed the isolation of analytically pure
alkyl THF-adducts 1-Sc and 1-Y in high yields.
Fig. 1. Molecular structure of 1-H2 (all hydrogen atoms except those of the amidine
and phenol moieties are omitted for clarity; thermal ellipsoids drawn at the 50%
probability). Selected bond distances (Å) and angles (ꢁ): C(1)eN(1), 1.3742(17); C(1)
eN(2), 1.3509(15); C(2)eN(2), 1.3471(16); C(2)eN(3), 1.3768(15); N(1)eH(1), 0.857;
O(1)eH(2), 0.957; N(2)eH(2), 1.746.
The 1H and 13C{1H} NMR spectra of both 1-Sc and 1-Y display
single sets of resonances, consistent with their apparent C1-sym-
metries. For example, the 1H NMR spectrum of 1-Sc (Figure S7; see
4.32 ppm; 2JH-H ¼ 15.1 Hz and
d
5.98 and 3.98 ppm; 2JH-H ¼ 13.7 Hz,
respectively). Other aliphatic parts of the 1H NMR spectra for both
compounds are quite similar and include three multiplets for each
of the iPr groups and a series of singlets for the methyl groups of
two 2,6-dimethylanilinic units. The aromatic region of the spectra
features a characteristic pattern of two doublets and one triplet
(3JH-H ¼ 8.0 Hz) for the pyridine linker and multiplets for the aniline
hydrogens.
the SI) exhibits two characteristic doublets (d 0.53 and 0.28 ppm;
2JH-H ¼ 11.8 Hz) for the diastereotopic hydrogens of the CHHSiMe3
group. In the 1H NMR spectrum of 1-Y (Figure S10), the same set of
2
signals is found shifted upfield (
d
ꢀ0.44 and ꢀ0.62 ppm; JH-
¼ 11.0 Hz). In the 13C{1H} NMR spectra of 1-Sc and 1-Y (Figures S9
H
and S11, respectively), the CH2SiMe3 group appears as one singlet (
d
1
All attempts to grow crystals of 1-Sc and 1-Y suitable for X-ray
crystallography failed. Both compounds were found stable in aro-
matic hydrocarbon solutions over several days at room tempera-
ture. Nevertheless, ageing a benzene solution of 1-Sc at room
35.9 ppm) and one characteristic doublet (
d 25.9 ppm, JY-
¼ 41.4 Hz), respectively. Also, the diastereotopic hydrogens of the
C
CHH linker in the molecules of both compounds appear as two
doublets in the corresponding 1H NMR spectra (
6.38 and
d
Scheme 2. Synthesis of the hybrid amidine-phenolate proligand [NMe2NNMe2CiPr2O]H2 (1-H2). Conditions: (i) acetic anhydride (6 equiv), H2SO4 (cat), 160 ꢁC, 15 min, 63% yield; (ii)
SOCl2 (20 equiv), THF, 0 ꢁCeRT, overnight, >99% yield; (iii) Et3N (3 equiv), xylenes, 190 ꢁC, overnight, 54% yield; (iv) NaOH (1 M), THF-H2O, RT, 5 h, 61% yield; (v) BH3$THF (5 equiv),
THF, 0e50 ꢁC, 1 h, 30% yield.

36
J. El Haj Hassan et al. / Journal of Organometallic Chemistry 823 (2016) 34e39
Scheme 3. Synthesis of complexes 1-Sc, 1-Y and isolation of 2-Sc.
temperature over one week afforded crystals of the bis(ligand)
product 2-Sc, which apparently resulted from a ligand redistribu-
tion reaction [9]. The molecular solid state structure of complex 2-
Sc is shown in Fig. 2. The six-coordinate metal center adopts a
geometry that is best described as distorted octahedral with three
nitrogen atoms of the two amidinate ligands and one oxygen atom
of one phenoxy group in the equatorial plane, and one nitrogen
atom (amidinate) and one oxygen of the second phenoxy group in
the axial positions, respectively. The metrical parameters (bond
lengths and angles) of the two equivalent dianionic ligands are
identical suggesting the presence of a proton (Hþ) in this presum-
ably zwitterionic structure [10]; however, the latter could not be
localized from the X-ray diffraction data. The Sc(1)eN(12) and Sc(1)
eN(22) (2.258(2) Å) bond distances in 2-Sc are in the regular range
(2.183e2.281 Å) observed in related amidopyridinate-scandium
complexes [7b,c]. The Sc(1)eN(11) and Sc(1)eN(21) (2.331(3) Å)
are somewhat longer and can be compared with those
(2.233e2.370 Å) reported for dipyridylamide scandium congeners
[11]. The ScꢀO (1.921(2) Å) bonds are also in the normal range of
those found in scandium complexes of phenoxy-based ligands
(1.853e1.969 Å) [12].
a co-initiator. Representative results are summarized in Table 1(see
Scheme 4).
ROP of rac-LA with 1-Sc and 1-Y proceeded sluggishly in toluene
at room temperature (entries 1 and 7, respectively); better perfor-
mance and control over the molecular weights were achieved upon
adding 1 equiv of iPrOH as a co-initiator. The initiating system 1-Sc/
iPrOH (1:1) appeared to be significantly more active at higher
temperature (60 ꢁC), enabling high conversion of 100 equiv of rac-
LA within 15 min (entry 5). When the same experiment was carried
out with 500 equiv, the 1-Sc/iPrOH system showed much lower
productivity (entry 6); this probably reflects the high sensitivity of
the active scandium species towards minute (protic) impurities
contained in the polar monomer. On the other hand, the 1-Y/iPrOH
system proved to be operational at room temperature, and able to
withstand monomer loadings up to 500 equiv; introduction of
larger amounts of iPrOH (5 equiv vs. Y) proved, however, detri-
mental in terms of activity (entries 11 and 12). Size-exclusion
chromatography (SEC) of the polymers produced with both alkyl
complexes alone or in the presence of iPrOH showed monomodal
traces with polydispersities (ÐM) in the range 1.18e1.58
(Figure S12). The measured Mn,SEC and Mn,NMR values were in
general in good agreement with respect to the calculated ones,
indicative of essential quantitative initiation. An analysis by 1H
NMR spectroscopy of the PLAs produced from 1-Sc and 1-Y
revealed the presence of trimethylsilyl resonances (around
2.3. Preliminary studies on ring-opening polymerization of
racemic-lactide
d
0.00 ppm, CDCl3), [13] consistent with COCH2SiMe3 end-groups at
Alkyl complexes 1-Sc and 1-Y were evaluated as initiators for
ROP of rac-lactide (rac-LA). In some experiments, iPrOH was used as
one terminus of the polymer chain. However, the molecular
weights calculated from these resonances were found much larger
than the theoretical ones, which may be indicative of partial scis-
sion of CeSi bonds during the hydrolytic workup. All the PLAs
produced in the presence of iPrOH were shown by NMR spectros-
copy to be selectively end-capped with hydroxy- and iso-
propylcarbonyl groups (Figure S13). The microstructural analysis of
the PLA samples obtained with both 1-Sc and 1-Y revealed that they
are essentially atactic, with Pr values in the range 0.50e0.56.
Amidine-amidopyridinate scandium and yttrium bis(-
trimethylsilylmethyl) analogues of 1-Sc and 1-Y also provided
atactic atactic PLAs, but appeared to be somewhat more active ROP
initiators [7b].
3. Conclusions
The synthesis of a new hybrid phenol-aminopyridine proligand
has been developed. Reactions between the proligand [NMe2NN-
Me2CiPr2O]H2 (1-H2) and M(CH2SiMe3)3(THF)2 (M ¼ Sc and Y)
afforded selectively the corresponding monoalkyl complexes 1-Sc
and 1-Y. Both compounds allowed ROP of rac-lactide under rather
mild conditions, providing good control over the polymerization
parameters, especially when iPrOH was used as a co-initiator, but
with essentially no stereoselectivity as observed with their bis(-
trimethylsilylmethyl) analogues incorporating monoanionic
Fig. 2. Molecular structure of 2-Sc (all hydrogen atoms and the four 2,6-dimethyl-
phenyl groups (Ar) are omitted for clarity; thermal ellipsoids drawn at the 50%
probability). Selected bond distances (Å) and angles (ꢁ): Sc(1)eN(11), 2.331(3); Sc(1)
eN(12), 2.258(2); Sc(1)eO(11), 1.921(2); Sc(1)eN(12), 2.331(3); Sc(1)eN(22), 2.258(2);
Sc(1)eO(22), 1.921(2); C(11)eN(11), 1.427(5); C(11)eN(12), 1.383(6); C(12)eN(12),
1.360(6); C(12)eN(13), 1.360(4); N(11)eSc(1)ꢀO(11), 158.50(10); N(12)eSc(1)ꢀN(21),
87.15(10); O(11)eSc(1)ꢀO(22), 99.24(15).

J. El Haj Hassan et al. / Journal of Organometallic Chemistry 823 (2016) 34e39
37
Table 1
ROP of rac-LA using complexes 1-Sc and 1-Y.a
Entry Complex [rac-LA]0/[M]0/[iPrOH]0 T [oC] Timeb [min] Convc [%] Mn,theod [g/mol] (ꢂ103) Mn,SECe [g/mol] (ꢂ103) DM
Mn,NMRf [g/mol] (ꢂ103) Pr
e
g
1
2
3
4
5
6
7
8
1-Sc
1-Sc
1-Sc
1-Sc
1-Sc
1-Sc
1-Y
1-Y
1-Y
1-Y
1-Y
100:1:0
100:1:0
100:1:0
100:1:1
100:1:1
500:1:1
100:1:0
500:1:0
100:1:1
100:1:1
500:1:1
500:1:5
25
60
60
25
60
60
25
25
25
25
25
25
420
30
90
960
15
90
1200
60
100
165
60
4
nd
nd
nd
nd
nd
nd
nd
nd
nd
0.56
0.56
nd
nd
0.50
nd
0.54
0.54
0.55
nd
29
51
98
87
4
65
10
94
92
96
25
4.18
7.35
14.12
12.54
nd
9.37
7.21
13.55
13.26
13.84
3.60
11.39
16.53
15.33
nd
4.54
nd
15.79
17.63
16.58
nd
1.41 9.45
1.18 12.38
1.21 11.87
nd
1.32 13.1
nd nd
1.58 12.9
1.46 9.26
1.49 8.79
nd
9
10
11
12
1-Y
165
nd
nd
a
General conditions: [rac-LA] ¼ 1.0 mol Lꢀ1, toluene.
b
c
d
e
f
Reaction times were not optimized.
Conversion of rac-LA was determined by 1H NMR spectroscopy on the crude reaction mixture.
Theoretical Mn values were calculated considering one polymer chain per metal center from the relation: Mn,calc ¼ Conv.[LA] ꢂ [rac-LA]0/[M or iPrOH]0 ꢂ MLA
Experimental Mn,SEC and ÐM values were determined by GPC in THF vs. PS standards and corrected by a factor of 0.58.
Determined by 1H NMR spectroscopy.
.
g
Pr is the probability of racemic linkage between monomer units, as determined from the methane region of the homonuclear decoupled 1H NMR spectra.
25 ꢁC, unless otherwise indicated. 1H and 13C chemical shifts are
reported in ppm vs SiMe4 ( 0.00), as determined by reference to
d
the residual solvent peaks. Assignment of resonances was made
from 2D 1He1H COSY,1He13C HMQC, and HMBC NMR experiments.
Coupling constants are given in hertz. The number average mo-
lecular masses (Mn) and polydispersity indexes (Ðm) of polymers
were calculated with reference to a universal calibration vs. poly-
styrene standards. The raw Mn,SEC values of PLAs were corrected
with a factor of 0.58 to account for the difference in hydrodynamic
volumes between polystyrene and polylactide [16]. The Mn,NMR
values of PLAs were determined by 1H NMR spectroscopy in CDCl3
on Bruker AM-400 or AC-500 spectrometers. The microstructure of
PLAs was determined by homodecoupling 1H NMR spectroscopy at
25 ꢁC in CDCl3 with a Bruker AC-400 spectrometer operating at
400 MHz.
Scheme 4. Ring-opening polymerization of rac-LA.
amidine-amidopyridinate ligand systems [7b]. We assume that the
lower ROP activity of 1-Sc and 1-Y can be attributed to a larger
steric hindrance around the Lewis acidic metal centers coordinated
by those bulky dianionic phenoxy-amidopyridinate ligands.
Ongoing studies in this field will be focused on further elaboration
of new polymerization catalysts incorporating hybrid
amidopyridinate-based ligand systems.
4.3. 2-Acetoxy-3,5-diisopropylbenzoic acid
2-Hydroxy-3,5-diisopropylbenzoic acid (25.0 g, 112.4 mmol)
and acetic anhydride (70 mL, 674.4 mmol) were charged in a
250 mL two-necked flask equipped with a condenser and a stirring
bar. The mixture was heated under reflux at 160 ꢁC and 10 drops of
concentrated H2SO4 were added; the reaction mixture was refluxed
for additional 15 min. The mixture was cooled down to room
temperature, mixed with water (200 mL) and extracted with
CH2Cl2 (2 ꢂ 50 mL). The organic phases were combined and dried
over Na2SO4, filtered, and the solvent was evaporated under
reduced pressure. The resulting oily phase was recrystallized from
petroleum ether to afford white-off crystals (20.7 g, 63%). 1H NMR
4. Experimental section
4.1. General considerations
All reactions, except those for the ligand synthesis were per-
formed under a purified argon atmosphere using standard Schlenk
techniques or in a glovebox. Solvents were distilled from Na/
benzophenone (THF, Et2O, DME) and Na/K alloy (toluene, hexane,
and pentane) under nitrogen, degassed thoroughly, and stored
under nitrogen prior to use. Deuterated solvents (benzene-d6,
toluene-d8; >99.5% D, Euroisotop) were vacuum-transferred from
Na/K alloy into storage tubes. CDCl3 and CD2Cl2 were kept over
calcium hydride and vacuum-transferred before use. The pre-
cursors bis(dimethylphenylamino)pyridine [14] and Ln(CH2Si-
Me3)3(THF)2 (Ln ¼ Sc, Y) [15] were prepared according to literature
protocols. Rac-lactide (Aldrich) was recrystallized once from iPrOH
and twice from dry toluene and then dried under vacuum and
stored in the glovebox at ꢀ30 ꢁC. Other starting materials were
purchased from Acros, Strem, Aldrich, Alfa Aser and used as
received.
(400 MHz, C6D6, 298 K):
d
11.52 (s, 1H, COOH), 7.96 (d, 4J ¼ 2.2, 1H,
Ar), 7.31 (d, 4J ¼ 2.2, 1H, Ar), 3.17 (hept, 3J ¼ 6.9, 1H, CH(CH3)2), 2.62
(hept, 3J ¼ 6.9, 1H, CH(CH3)2), 2.09 (s, 3H), 1.16 (d, 3J ¼ 6.9, 6H,
(CH3)2CH), 1.05 (d, 3J ¼ 6.9, 6H, (CH3)2CH).
4.4. 2-(Chlorocarbonyl)-4,6-diisopropylphenyl acetate
2-Acetoxy-3,5-diisopropylbenzoic acid (5.0 g, 18.9 mmol) was
dissolved in dry THF (20 mL). Thionyl chloride (27.4 mL, 378 mmol)
was added slowly at 0 ꢁC under nitrogen, and the mixture was
stirred overnight. Volatiles were removed under vacuum and the
resulting dark orange oil was used directly in the next step without
4.2. Instruments and measurements
NMR spectra of complexes and ligands were recorded on Bruker
AM-400 and AM-500 spectrometers in Teflon-valved NMR tubes at
further purification. 1H NMR (400 MHz, C6D6, 298 K):
d 7.87 (d,
4J ¼ 2.0, 1H, Ar), 7.27 (d, 4J ¼ 2.0, 1H, Ar), 3.03 (m, 1H, CH(CH3)2),

38
J. El Haj Hassan et al. / Journal of Organometallic Chemistry 823 (2016) 34e39
2.54 (m, 1H, CH(CH3)2), 1.98 (s, 3H), 1.07 (d, 3J ¼ 6.9, 6H, (CH3)2CH),
0.99 (d, 3J ¼ 6.9, 6H, (CH3)2CH).
140.3 (p-Py), 138.8, 137.7, 136.7, 136.5, 136.2, 129.0, 128.3, 128.3,
127.6,126.8,126.6,124.2,123.4, 96.9 (m-Py), 93.3 (m-Py), 50.6 (CH2),
33.6 (CH(CH3)2), 28.0 (CH(CH3)2), 24.2 (CH(CH3)2), 22.8 (CH(CH3)2),
18.0 (NC(CH3)N), 17.7 ((CH3)2C6H3N). Anal. Calcd for C34H41N3O: C,
80.43; H, 8.14; N, 8.28. Found: C, 80.55; H, 8.27; N, 8.85.
4.5. 2-(N-(6-(2,6-dimethylphenylamino)pyridin-2-yl)-N-(2,6-
dimethylphenyl)carbamoyl)-4,6-di-isopropylphenyl acetate
To a solution of bis(dimethylphenylamino)pyridine (4.61 g,
14.5 mmol) in o-xylene (20 mL) was added Et3N (6.1 mL,
43.6 mmol) under argon. A solution of 2-(chlorocarbonyl)-4,6-
diisopropylphenyl acetate (18.9 mmol) in o-xylene (10 mL) was
transferred under argon to the reaction mixture under rigorous
stirring. The reaction mixture was refluxed at 190 ꢁC overnight. The
solvent was removed under reduced pressure. The resulting black
oil was dissolved in CH2Cl2 (50 mL) and eluted through an Al2O3
pad using a 1:1 mixture of CH2Cl2eheptane as eluent. The eluate
was concentrated under vacuum and the product was recrystal-
lized from heptane to afford the desired product as a brownish
crystalline material (4.3 g, 52%). 1H NMR (400 MHz, C6D6, 298 K):
4.8. {NMe2NNMe2CiPr2O}Sc(CH2SiMe3)(THF) (1-Sc)
To a solution of 1-H2 (300 mg, 0.591 mmol) in toluene (5 mL)
was added
a solution of Sc(CH2SiMe3)3(THF)2 (266.4 mg,
0.591 mmol) in toluene (5 mL) at ꢀ30 ꢁC. The reaction mixture was
stirred overnight at room temperature. Volatiles were evaporated
under vacuum and the crude solid residue was dried overnight,
washed with hexane (10 mL), to afford the desired product as
white-yellow powder of 1-Sc (382 mg, 91%). 1H NMR (400 MHz,
C6D6, 298 K):
d
7.20e6.80 (m, 7H, Ar), 6.70 (t, 3J ¼ 8.1, 1H, p-Py), 6.52
(d, 4J ¼ 2.3, 1H, Ar), 6.38 (d, 2J ¼ 15.1, 1H, CHH), 5.07 (d, 3J ¼ 8.0, 1H,
m-Py), 5.02 (d, 3J ¼ 8.0, 1H, m-Py), 4.32 (d, 2J ¼ 15.1, 1H, CHH), 3.85
(br m, 4H, THF), 3.62 (hept, 3J ¼ 7.0, 1H, CH(CH3)2), 2.73 (hept,
3J ¼ 7.0, 1H, CH(CH3)2), 2.48 (s, 3H, (CH3)2C6H3N), 2.26 (s, 3H,
(CH3)2C6H3N), 2.04 (s, 3H, (CH3)2C6H3N), 1.64 (s, 3H, (CH3)2C6H3N),
1.49 (m, 6H, (CH3)2CH), 1.18 (d, 3J ¼ 6.9, 3H, (CH3)2CH), 1.15 (d,
3J ¼ 7.0, 3H, (CH3)2CH), 1.08 (br m, 4H, THF), 0.53 (d, 2J ¼ 11.8, 1H,
d
7.20 (s,1H, Ar), 6.93 (m, 7H, Ar þ p-Py), 6.68 (br m, 2H, Ar þ m-Py),
5.71 (br s, 1H, NH), 5.45 (m, 1H, m-Py), 3.17 (hept, 3J ¼ 7.0, 1H,
CH(CH3)2), 2.58 (hept, 3J ¼ 7.0, 1H, CH(CH3)2), 2.44 (s, 3H, CH3C(O)),
2.04 (s, 6H, (CH3)2C6H3N), 1.89 (s, 6H, (CH3)2C6H3N), 1.19 (d, 3J ¼ 7.0,
6H, (CH3)2CH), 1.00 (d, 3J ¼ 6.9, 6H, (CH3)2CH).
CHHSiMe3), 0.31 (s, 9H, SiMe3), 0.28 (d, 2J ¼ 11.8, 1H, CHHSiMe3). 13
C
4.6. N-(6-(2,6-dimethylphenylamino)pyridin-2-yl)-2-hydroxy-3,5-
diisopropyl-N-(2,6-dimethylphenyl)benzamide
{1H} NMR (125 MHz, C6D6, 298 K):
d 165.6 (NC(CH3)N), 158.5, 155.1,
146.2, 141.9 (p-Py), 141.5, 139.0, 136.5, 135.1, 134.2, 133.1, 129.5,
128.7, 126.7, 126.5, 123.5, 123.2, 93.1 (m-Py), 91.2 (m-Py), 68.8 (
CH2 THF), 51.6 (CH2), 35.9 (CH2SiMe3), 33.6 (CH(CH3)2), 27.5
(CH(CH3)2), 25.1 ( -CH2 THF), 24.4 (CH(CH3)2), 23.9 (CH(CH3)2), 23.1
(CH(CH3)2), 22.8 (CH(CH3)2), 18.9 ((CH3)2C6H3N), 18.3
a
-
2-(N-(6-(2,6-dimethylphenylamino)pyridin-2-yl)-N-(2,6-
dimethylphenyl)carbamoyl)-4,6-diisopropylphenyl acetate (4.20 g,
7.95 mmol) was dissolved in a mixture of MeOH (50 mL) and THF
(70 mL). A 1 M NaOH solution (90 mL) was added dropwise at room
temperature and progress of the reaction was monitored by TLC.
After 5 h, CH2Cl2 (100 mL) was added and the organic phase was
extracted with water (2 ꢂ 200 mL). The organic phases were
combined, dried over Na2SO4 and then filtrated. The resulting so-
lution was passed through a short pad of silica. Volatiles were
evaporated and the white residue was dried to give the desired
b
((CH3)2C6H3N), 18.2 ((CH3)2C6H3N), 17.8 ((CH3)2C6H3N), 3.6 (SiMe3).
Anal. Calcd for C42H58N3O2ScSi: C, 71.05; H, 8.23; N, 5.92. Found: C,
71.70; H, 8.64; N, 6.05.
4.9. {NMe2NNMe2CiPr2O}Y(CH2SiMe3)(THF) (1-Y)
pure product (2.40 g, 61%). 1H NMR (400 MHz, C6D6, 298 K):
d
11.84
NMR-scale Protocol A. In the glove box, a J-Young Teflon-valved
NMR tube was charged with 1-H2 (15.0 mg, 0.030 mmol) and
Y(CH2SiMe3)3(THF)2 (15.0 mg, 0.031 mmol). To this mixture, C6D6
(ca. 0.6 mL) was vacuum-transferred in and the tube was shaken for
15 min at room temperature. 1H NMR spectroscopy indicated that
1-Y formed quantitatively.
Preparative-scale Protocol B. Using a procedure similar to that
described above for 1-Sc, pure 1-Y (420 mg, 86%) was obtained
from 1-H2 (300 mg, 0.591 mmol) and Y(CH2SiMe3)3(THF)2
(292.3 mg, 0.591 mmol) in toluene (5 mL). 1H NMR (400 MHz,
(s, 1H, OH), 7.1 (s, 1H, Ar), 6.94 (m, 7H, Ar), 6.77 (br t, 3J ¼ 7.0, 1H, p-
Py), 6.26 (br m, 1H, m-Py), 5.51 (d, 4J ¼ 7.0, 1H, m-Py), 5.18 (s, 1H,
NH), 3.67 (hept, 3J ¼ 6.9, 1H, CH(CH3)2), 2.57 (hept, 3J ¼ 6.9, 1H,
CH(CH3)2), 2.26 (s, 6H, (CH3)2C6H3N), 1.86 (s, 6H, (CH3)2C6H3N), 1.32
(d, 3J ¼ 6.9, 6H, (CH3)2CH), 1.01 (d, 3J ¼ 6.9, 6H, (CH3)2CH).
4.7. Proligand {NMe2NNMe2CiPr2O}H2 (1-H2)
In a Schlenk flask, N-(6-(2,6-dimethylphenylamino)pyridin-2-
yl)-2-hydroxy-3,5-diisopropyl-N-(2,6-dimethylphenyl)benzamide
(2.2 g, 4.217 mmol) was dissolved in dry THF (15 mL) under argon
atmosphere. BH3$THF (21.0 mL of a 1 M solution in THF, 21.0 mmol)
was added dropwise at 0 ꢁC. The reaction mixture was stirred at
50 ꢁC for 1 h, then cooled down to room temperature and quenched
by addition of a 10% NH4Cl solution (10 mL). Volatiles were evap-
orated and the solid residue was dissolved in CH2Cl2 (50 mL). The
resulting solution was passed through a short pad of silica, the
solution was concentrated under vacuum and the white residue
was recrystallized from methanol to afford the desired proligand as
an analytically pure white powder (0.63 g, 30%). 1H NMR (400 MHz,
C6D6, 298 K):
d
7.25e6.80 (m, 7H, Ar), 6.75 (t, 3J ¼ 8.0, 1H, p-Py),
6.30 (d, 4J ¼ 2.1, 1H, Ar), 5.98 (d, 2J ¼ 13.7, 1H, CHH), 5.29 (d, 3J ¼ 8.0,
1H, m-Py), 5.03 (d, 3J
¼
8.0, 1H, m-Py), 3.98 (3, 2H,
CHH þ CH(CH3)2), 3.80 (br m, 4H, THF), 2.69 (hept, 3J ¼ 6.8, 1H,
CH(CH3)2), 2.46 (s, 3H, (CH3)2C6H3N), 2.37 (s, 3H, (CH3)2C6H3N),
2.14 (s, 3H, (CH3)2C6H3N), 1.55 (s, 3H, (CH3)2C6H3N), 1.49 (d,
3J ¼ 6.8, 3H, (CH3)2CH), 1.40 (d, 3J ¼ 6.8, 3H, (CH3)2CH), 1.28 (br m,
4H, THF), 1.13 (m, 6H, (CH3)2CH), 0.32 (s, 9H, SiMe3), e0.44 (br d,
2J ¼ 11.0, 1H, CHHSiMe3), e0.62 (br d, 2J ¼ 11.0, 1H, CHHSiMe3). 13
C
{1H} NMR (125 MHz, C6D6, 298 K):
d 167.1 (NC(CH3)N), 158.2, 157.1,
147.9, 141.1 (p-Py), 140.7, 139.3, 136.4, 135.8, 135.2, 132.7, 132.2,
128.0, 127.2, 125.9, 123.3, 122.5, 95.1 (m-Py), 91.1 (m-Py), 69.6 (
CH2 THF), 49.4 (CH2), 33.7 (CH(CH3)2), 26.9 (CH(CH3)2), 25.9 (d, 1JY-
-CH2 THF), 24.9 (CH(CH3)2), 24.6
C6D6, 298 K):
d
12.27 (s, 1H, OH), 7.21 (d, 4J ¼ 2.1, 1H, Ar), 6.97 (m,
a-
6H, Ar) 6.72 (t, 3J ¼ 7.0, 1H, p-Py), 6.47 (d, 4J ¼ 2.1, 1H, Ar), 5.96 (s,1H,
NH), 5.28 (d, 3J ¼ 7.0, 2H, m-Py), 4.89 (br s, 2H, CH2), 3.86 (hept,
3J ¼ 6.9, 1H, CH(CH3)2), 2.69 (hept, 3J ¼ 6.9, 1H, CH(CH3)2), 2.17 (s,
6H, (CH3)2C6H3N), 1.78 (s, 6H, (CH3)2C6H3N), 1.49 (d, 3J ¼ 6.9, 6H,
(CH3)2CH), 1.15 (d, 3J ¼ 6.9, 6H, (CH3)2CH). 13C{1H} NMR (100 MHz,
¼ 41.4, CH2SiMe3), 25.7 (
b
C
(CH(CH3)2), 24.0 (CH(CH3)2), 22.7 (CH(CH3)2), 19.6 ((CH3)2C6H3N),
19.5 ((CH3)2C6H3N), 17.9 ((CH3)2C6H3N), 17.8 ((CH3)2C6H3N), 4.2
(SiMe3). Anal. Calcd for C42H58N3O2YSi: C, 66.91; H, 7.75; N, 5.57.
Found: C, 70.12; H, 7.98; N, 5.75.
C6D6, 298 K):
d 156.5 (NC(CH3)N), 156.4 (o-Py), 152.6 (o-Py), 141.1,

J. El Haj Hassan et al. / Journal of Organometallic Chemistry 823 (2016) 34e39
39
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4.10. General procedure for polymerization of rac-lactide
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923e927;
In a typical experiment (Table 1, entry 4), in the glovebox, a
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Schlenk flask was charged with complex 1-Sc (12.0 mg, 16.0
Outside the glovebox and under argon, complex 1-Sc was dissolved
in toluene (1.69 mL) and iPrOH (8.5 L of a 2.0 M solution in toluene,
16.9 mol, 1 equiv vs. [M]0) was added. The reaction mixture was
mmol).
m
m
immediately stirred with a magnetic stirring bar at 25 ꢁC for 16 h.
The reaction was quenched with water (1 mL of a 10 mol% solution
in THF). Volatiles were evaporated and the conversion was deter-
mined by 1H NMR spectroscopy from the crude material. Monomer
(LA) conversions were calculated from 1H NMR spectra of the crude
reaction mixtures in CDCl3, from the integration (Int.) ratio Int.pol-
ymer/[Int.polymer þ Int.monomer], using the methyl hydrogen reso-
(b) V. Radkov, T. Roisnel, A. Trifonov, J.-F. Carpentier, E. Kirillov, Eur. J. Inorg.
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Soc. 138 (2016) 4350e4353.
nances for PLA at d 1.49 ppm and for LA at d 1.16 ppm. The polymer
was dissolved in THF (5 mL) and reprecipitated with pentane (ca.
100 mL). The polymer was filtered and dried under vacuum till
constant weight. The microstructure of the PLA was determined by
homodecoupling 1H NMR spectroscopy experiment at 25 ꢁC in
CDCl3 on a Bruker AC-500 spectrometer.
[8] The following numbering scheme is used:
4.11. Crystal structure determination of 1-H2 and 2-Sc
Diffraction data were collected at 150(2) K using a Bruker APEX
CCD diffractometer with graphite-monochromatized Mo-K
a radi-
ation (
l
¼ 0.71073 Å). The crystal structures were solved by direct
[9] Ligand redistribution reactions resulting in formation of bis(ligand) products
have been described for alkyl and iodo complexes of group 3 metals incor-
porating amidinate, amido and related ligands; see: (a) C. HultzschK, P. Voth,
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J.H. Teuben, Organometallics 19 (2000) 3197e3204;
methods, remaining atoms were located from difference Fourier
synthesis followed by full-matrix least-squares refinement based
on F2 (programs SIR97 and SHELXL-97) [17]. Many hydrogen atoms
could be located from the Fourier difference analysis. Other
hydrogen atoms were placed at calculated positions and forced to
ride on the attached atom. The hydrogen atom positions were
calculated but not refined. All non-hydrogen atoms were refined
with anisotropic displacement parameters. For 2-Sc, the contribu-
tion of the disordered solvents to the calculated structure factors
was estimated following the BYPASS algorithm [18], implemented
as the SQUEEZE option in PLATON [19]. Crystal data and details of
data collection and structure refinement for the different com-
pounds are given in Table S1. Detailed crystallographic data
(excluding structure factors) are available as Supporting Informa-
tion, as cif files.
(c) S. Bambirra, D. Van Leusen, C.G.J. Tazelaar, A. Meetsma, B. Hessen,
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[10] Zwitterionic group 3 metal complexes incorporating two dianionic bis(phe-
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H.E. Dyer, A.D. Schwarz, R. Duchateau, P. Mountford, Chem. Commun. 46
(2010) 271e275;
(b) H.E. Dyer, S. Huijser, A.D. Schwarz, C. Wang, R. Duchateau, P. Mountford,
Dalton Trans. (2008) 32e35.
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Appendix A. Supplementary data
(b) M. Normand, E. Kirillov, T. Roisnel, J.-F. Carpentier, Organometallics 31
(2012) 1448e1455.
[14] F.A. Cotton, L.M. Daniels, P. Lei, C.A. Murillo, X. Wang, Inorg. Chem. 40 (2001)
2778e2784.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2016.09.014.
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