Organometallics
Article
137.9, 132.7, 133.0, 130.7, 129.8, 127.3, 127.1, 126.3, 125.0, 118.4,
115.5.
CONCLUSIONS
■
Salen-type frameworks containing dinaphthaleneimine bridge
were selected to prepare dinuclear aluminum complexes to
feature two metal sites allocated in rigid coordinative pockets
at an opportune distance from one another. All complexes,
activated by isopropyl alcohol, promoted controlled homo-
polymerizations of lactide, caprolactone, and cyclohexene
oxide, showing different activities depending on the nature of
the substituents in the phenoxy moieties. The high activities
achieved support the hypothesis of metallic cooperativity that
is more efficient for a monomer with less emcumbrance and/or
a more flexible growing chain. Additionally, such complexes
were revealed to be active in the copolymerization of phthalic
anhydride with cyclohexene oxide and limonene oxide and in
the terpolymerization of these monomers with lactide to
produce diblock polyesters.
Synthesis of Proligand R-L1. The synthetic procedure was the
same as that described for the related chiral proligand rac-L1, but the
chiral diamine was used. To (R)-1,1′-binaphthyl-2.2′-diamine (505
mg, 1.76 mmol) in ethanol (50 mL) was added 3,5-di-tert-butyl-2-
hydroxybenzaldehyde (833 mg, 3.52 mmol). The solution was stirred
at reflux for 12 h. The solid product was isolated by filtration and
washed with fresh ethanol. Yield: 89%. [α]D = −432.28.
25
Complex rac-1. To a stirred solution containing AlMe3 (0.083 g,
1.1 mmol) in benzene (2 mL) was added dropwise a solution of the
proligand precursor rac-L1 (0.400 g, 0.56 mmol) in benzene (4 mL).
The solution was stirred for 3 h at room temperature. The solvent was
removed under vacuum, forming a pale yellow solid in almost
1
quantitative yield (96%). H NMR (300 MHz, C6D6, 298 K): δ 7.82
(s, 2H, CHN), 7.63 (d, J = 2.4 Hz, 2H, ArH), 7.51 (d, J = 8.4 Hz,
2H, ArH), 7.43 (d, J = 8.7 Hz, 2H, ArH), 7.28 (d, J = 8.4 Hz, 2H,
ArH), 7.24 (d, J = 8.7 Hz, 2H, ArH), 7.14 (t, J = 7.4 Hz, 2H, ArH),
7.01 (t, J = 7.1 Hz, 2H, ArH), 6.36 (d, J = 2.4 Hz, 2H, ArH), 1.54 (s,
18H, t-Bu), 1.23 (s, 18H, t-Bu), −0.45 (s, 6H, Al−CH3), −0.75 (s,
6H, Al-CH3). 13C NMR (100 MHz, C6D6, 298 K): δ 173.7, 163.0,
144.7, 140.8, 139.2, 134.9, 133.2, 132.7, 131.0, 130.1, 126.6, 125.4,
124.2, 119.6 (Ar or ArCNH), 35.5 (C(CH3)3), 34.0 (C(CH3)3), 31.4
(CH3), 29.7 (CH3), −9.1 (Al−CH3). Anal. Calcd for C54H66Al2N2O2
(%): C, 78.23; H, 8.02; N, 3.38. Found: C, 78.44; H, 7.97; N, 3.30.
Complex R-1. To a stirred solution containing AlMe3 (0.044 g,
0.54 mmol) in benzene (2 mL) was added dropwise a solution of the
proligand precursor R-L1 (0.193 g, 0.27 mmol) in benzene (4 mL).
The solution was stirred for 3 h at room temperature. The solvent was
removed under vacuum, forming a pale yellow solid in almost
quantitative yield (94%). The NMR characterization was reported for
the complex rac-1. Anal. Calcd for C54H66Al2N2O2: C, 78.23; H, 8.02;
N, 3.38. Found: C, 78.13; H, 7.94; N, 3.41.
EXPERIMENTAL SECTION
■
General Considerations. All manipulations of air- and/or water-
sensitive compounds were carried out under a dry nitrogen
atmosphere using a Braun Labmaster glovebox or standard Schlenk
line techniques. Glassware and vials used in the polymerization were
dried in an oven at 120 °C overnight and exposed three times to
vacuum−nitrogen cycles.
Reagents and Solvents. Benzene, hexane, and toluene (Sigma-
Aldrich) were distilled under nitrogen over sodium benzophenone.
The aluminum precursor AlMe3 was purchased from Aldrich and was
used as received. Deuterated solvents were dried over molecular
sieves. ε-Caprolactone, cyclohexene oxide were purchased from
Aldrich, freshly distilled from CaH2 under nitrogen, and degassed
thoroughly by freeze−vacuum−thaw cycles prior to use. rac-lactide
and L-lactide were purchased from Aldrich, dried in vacuo over P2O5
for 72 h, and stored afterward at −20 °C in a glovebox. PPNCl was
dissolved in dichloromethane and precipitated with diethyl ether
twice. DMAP was cristallizated by toluene. All other chemicals were
commercially available and were used as received unless stated
otherwise.
Complex rac-2. To a stirred solution containing AlMe3 (0.050 g,
0.62 mmol) in benzene (2 mL) was added dropwise a solution of the
proligand precursor rac-L1 (0.250 g, 0.31 mmol) in benzene (4 mL).
The solution was stirred for 3 h at room temperature. The solvent was
removed under vacuum, forming a pale yellow solid in almost
1
quantitative yield (97%). H NMR (400 MHz, C6D6, 298 K): δ 7.56
(d, J = 2.3 Hz, 2H), 7.51 (d, J = 8.8 Hz, 2H), 7.43 (d, J = 8.8 Hz, 2H),
7.23 (s, 2H), 7.10 (t, J = 7.0 Hz, 2H), 7.09 (d, J = 8.6 Hz, 2H) 6.90 (t,
J = 7.1 Hz, 2H), 6.89 (d, J = 8.6 Hz, 2H), 6.58 (d, J = 2.3 Hz, 2H),
−0.67 (s, 6H), −1.25 (s, 6H). 13C NMR (75 MHz, C6D6, 298 K): δ
143.0, 142.7, 136.2, 134.3, 132.7, 131.4, 128.4, 128.3, 128.2, 128.,
127.2, 127.1, 124.8, 123.3, 120.6, 120.6, 117.6, 108.9. Anal. Calcd for
C38H30Al2Br4N2O2: C, 49.60; H, 3.29; N, 3.04. Found: C, 49.65; H,
3.32; N, 3.10.
NMR Analysis. The NMR spectra were recorded on Bruker
Advance 300, 400, and 600 MHz spectrometers at 25 °C, unless
stated otherwise. Chemical shifts (δ) are expressed as parts per
1
million and coupling constants (J) in hertz. H NMR spectra are
referenced using the residual solvent peak at δ 7.16 for C6D6 and δ
7.27 for CDCl3. 13C NMR spectra are referenced using the residual
solvent peak at δ 128.06 for C6D6 and δ 77.23 for CDCl3.
Synthesis of Proligands rac-L1 and rac-L2. Both proligands
were synthesized by modifying a procedure previously reported in the
literature.61 In a 100 mL two-neck round-bottom flask equipped with
a reflux condenser, to a stirred solution containing rac-1.1′-
binaphthyl-2,2′-diamine (0.510 g, 1.76 mmol) in ethanol (50 mL)
was added 2 equiv (3.54 mmol) of the opportune aldehyde (3,5-di-
tert-butyl-2-hydroxybenzaldehyde, 0.825 g; 3,5-dibromo-2-hydroxy-
benzaldehyde, 0.991 g). The solution was stirred at reflux for 12 h.
The solid products were isolated by filtration and washed with fresh
ethanol. Yields: 86% for rac-L1 and 84% for rac-L2.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
Cartesian coordinates of the calculated structure (XYZ)
NMR spectra of complexes, experimental details of the
polymerization reactions; NMR spectra and GPC traces
1
rac-L1. H NMR (300 MHz, C6D6, 298 K): δ 13.23 (s, 2H), 8.31
(s, 2H), 7.88 (d, J = 8.5 Hz, 2H), 7.81 (d, J = 8.1 Hz, 2H), 7.52 (d, J =
8.3 Hz, 2H), 7.39 (d, J = 2.1 Hz, 2H),7.24 (d, J = 8.6 Hz, 2H), 7.20
(t, J = 7.8 Hz, 2 H), 7.02 (t, J = 6.9 Hz, 2H), 6.88 (d, J = 2.2 Hz, 2H),
1.40 (s, 18H), 1.23 (s, 18H). 13C NMR (100 MHz, C6D6, 298 K): δ
163.2, 158.9, 144.3, 139.9, 136.9, 133.9, 133.0, 130.1, 129.8, 127.3,
127.1, 126.9, 126.0, 118.9, 117.7, 35.2, 34.1, 31.6, 29.5.
AUTHOR INFORMATION
■
Corresponding Author
1
rac-L2. H NMR (300 MHz, C6D6, 298 K): δ 13.12 (s, 2H), 7.75
Mina Mazzeo − University of Salerno, Department of Chemistry
and Biology “A. Zambelli”, 84084 Fisciano, Salerno, Italy;
(s, 2H), 7.84 (d, J = 8.5 Hz, 2H), 7.73 (d, J = 8.1 Hz, 2H), 7.29 (d, J =
8.3 Hz, 2H), 7.24(d, J = 2.1 Hz, 2H),7.23 (d, J = 8.6 Hz, 2H), 7.14 (t,
J = 7.8 Hz, 2 H), 6.98 (t, J = 6.9 Hz, 2H), 6.55 (d, J = 2.1 Hz, 2H).
13C NMR (100 MHz, C6D6, 298 K): δ 164.2, 157.3, 144.2, 139.5,
F
Organometallics XXXX, XXX, XXX−XXX