Organometallics
Article
reference to the residual solvent resonances. Assignment of signals was
made from 2D 1H−1H COSY and 1H−13C HMQC and HMBC NMR
experiments. 19F chemical shifts were determined by external reference
to an aqueous solution of NaBF4. NMR coupling constants are
reported in hertz. Elemental analyses (C, H, N) were performed using
a Flash EA1112 CHNS Thermo Electron apparatus and are the
average of two independent determinations.
Size exclusion chromatography (SEC) analyses of PLAs and PCLs
were performed in THF (1.0 mL min−1) at 20 °C using a Polymer
Laboratories PL-GPC 50 plus apparatus equipped with a PLgel 5 μm
MIXED-C 300 × 7.5 mm column and RI and dual angle LS (PL-LS
45/90) detectors. The number-average molecular masses (Mn) and
polydispersity indexes (Mw/Mn) of the polymers were calculated with
reference to a universal calibration vs polystyrene standards. The Mn
values of PCLs and PLAs were corrected with factors of 0.56 and 0.58,
respectively, to account for the difference in hydrodynamic volumes
with polystyrene.28
MALDI-ToF mass spectra of PCL were obtained with a Bruker
Daltonic MicroFlex LT, using a nitrogen laser source (337 nm, 3 ns)
in linear mode with a positive acceleration voltage of 20 kV. Samples
were prepared as follows: 1 μL of a 2:1 mixture of a saturated solution
of α-cyano-4-hydroxycinnamic acid (Bruker Care) in HPLC-quality
acetonitrile and a 0.1% solution of trifluoroacetic acid in ultrapure
water was deposited on the sample plate. After total evaporation, 1 μL
of a 5−10 mg mL−1 solution of the polymer in HPLC-quality THF
was deposited. Bruker Care Peptide Calibration Standard and Protein
Calibration Standard I were used for external calibration.
N), 6.62−6.37 (m, 10Haro). 19F{1H} NMR (188 MHz, C6D6, 298 K):
δ −78.19 (s, 6F). 13C{1H} NMR (75 MHz, C6D6, 298 K): δ 1.18
(Al(CH3)2), 37.93 (CH2C(CF3)2), 123.24, 127.13, 127.61, 127.66,
127.88, 127.93, 127.98, 128.25, 128.41, 129.23, 130.67, 135.69 (all
Caro), 175.26 (CN); quartet resonances for CF3 groups were not
observed due to their low intensity. Anal. Calcd for C19H18AlF6NO: C,
54.68; H, 4.35; N, 3.36. Found: C, 54.8; H, 4.4; N, 3.4.
{ONPh,Cy}AlMe2 (2d). This compound was prepared as described
above for 2a, starting from a solution of proligand {ONPh,Cy}H (1d;
100 mg, 0.27 mmol) in hexanes (4 mL) and a solution of AlMe3 (0.14
mL of a 2.0 M solution in heptane, 0.28 mmol) in hexane (1 mL).
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Workup gave 2d as a white powder (102 mg, 90%). H NMR (500
MHz, CD2Cl2, 298 K): δ −0.67 (s, 6H, Al(CH3)2), 0.97−1.15 (m, 3H,
cyclohexyl), 1.55−1.91 (m, 7H, cyclohexyl), 3.25 (s, 2H, CH2CN),
3.55−3.61 (m, 1H, cyclohexyl), 7.20 (m, 2Haro), 7.53 (m, 2Haro).
19F{1H} NMR (188 MHz, CD2Cl2, 298 K): δ −78.96 (s, 6F). 13C{1H}
NMR (125 MHz, CD2Cl2, 298 K): δ −7.50 (Al(CH3)2), 25.40, 32.54
(cyclohexyl), 38.88 (CH2C(CF3)2), 65.22 (CH cyclohexyl), 77.96
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(C(CF3)2), 123.33, 125.36, 125.82 (q, JCF = 293.3, CF3), 130.25,
131.19, 137.81 (all Caro), 179.88 (CN). Anal. Calcd for
C19H24AlF6NO: C, 53.90; H, 5.71; N, 3.31. Found: C, 53.9; H, 5.8;
N, 3.2.
{ONPh,Bn}2AlMe (3a). In a Schlenk flask, a solution of proligand
{ONPh,Bn}H (1a; 200 mg, 0.53 mmol) in toluene (5 mL) was added
dropwise onto a solution of AlMe3 (0.13 mL of a 2.0 M solution in
heptane, 0.26 mmol) in toluene (5 mL) at room temperature. The
reaction mixture was stirred at 60 °C for 24 h. Volatiles were removed
under vacuum, and the solid residue was washed with cold hexanes (3
× 3 mL) and finally dried under vacuum for 12 h, to give 3a as a white
powder (92 mg, 45%). Single crystals of 3a suitable for X-ray
diffraction analysis were obtained from a concentrated hexanes/THF
solution (2/1 mL) at −30 °C. 1H NMR (500 MHz, CD2Cl2, 298 K): δ
−0.98 (s, 3H, AlCH3), 3.20 (s, 4H, CH2CN), 4.78 and 4.98 (2d, J =
14.4, 4H, ArCHH), 7.00−7.38 (m, 10HAr). 1H NMR (300 MHz,
C6D6, 298 K): δ −0.40 (s, 3H, AlCH3), 3.16 and 3.28 (2d, J = 17.3, 2
× 2H, CHHCN), 4.98 and 5.18 (2d, J = 13.8, 2 × 2H, ArCHH),
6.77−7.28 (m, 10HAr). 19F{1H} NMR (188 MHz, CD2Cl2, 298 K): δ
−78.24 (q, J = 10.3, 6F), −79.02 (q, J = 10.3, 6F). 13C{1H} NMR (75
MHz, CD2Cl2, 298 K): δ 13.86 (AlCH3), 37.77 (CH2C(CF3)2), 54.91
The microstructures of PLAs were determined by homodecoupling
1H NMR spectroscopy at 20 °C in CDCl3 on a Bruker AC-500
spectrometer.
{ONPh,Bn}AlMe2 (2a). In a Schlenk flask, a solution of proligand
{ONPh,Bn}H (1a; 200 mg, 0.53 mmol) in hexanes (2 mL) was added
dropwise onto a solution of AlMe3 (0.27 mL of a 2.0 M solution in
heptane, 0.54 mmol) in hexanes (3 mL), precooled at −80 °C. The
solution was slowly warmed to room temperature and stirred
overnight. Volatiles were removed under vacuum, and the residue
was washed with cold hexanes (3 mL) and dried under vacuum.
Compound 2a was isolated as a yellowish solid (0.184 g, 80%). Single
crystals of 2a suitable for X-ray diffraction analysis were obtained from
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a concentrated hexanes solution at −30 °C. H NMR (300 MHz,
(ArCH2), 124.26 (q, JCF = 284.5, CF3), 124.97, 125.23, 125.92,
CD2Cl2, 298 K): δ −0.92 (s, 6H, Al(CH3)2), 3.41 (s, 2H, CH2CN),
4.85 (s, 2H, ArCH2), 7.09−7.15 (m, 3HAr), 7.34−7.37 (m, 5HAr),
7.56−7.59 (m, 2HAr). 19F{1H} NMR (188 MHz, CD2Cl2, 298 K): δ
126.51, 127.04, 127.74, 128.19, 128.81, 128.96, 129.34, 138.01 (all
Caro), 176.90 (CN). Anal. Calcd for C37H31AlF12N2O2: C, 56.21; H,
3.95; N, 3.54. Found: C, 56.1; H, 4.0; N, 3.5.
−79.05 (s, 6F). 13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ −10.53
{ONMe,Bn}2AlMe (3b). This compound was prepared as described
for 3a, starting from proligand {ONMe,Bn}H (1b; 200 mg, 0.63 mmol)
and AlMe3 (0.16 mL of a 2.0 M solution in heptane, 0.32 mmol) in
toluene (15 mL). Crystallization from a hexanes/toluene solution (5
mL; 3/2 v/v) at −30 °C yielded colorless crystals of 3b (90 mg, 44%).
1H NMR (300 MHz, CD2Cl2, 298 K): δ −0.89 (s, 3H, AlCH3), 1.94
(s, 6H, NCCH3), 2.86 (s, 4H, CH2CN), 4.72 and 4.99 (2d, J =
15.0, 2 × 2H, ArCHH), 7.16−7.28 (m, 10Haro). 1H NMR (300 MHz,
C6D6, 298 K): δ −0.52 (s, 3H, AlCH3), 1.22 (s, 6H, NCCH3), 2.57
(s, 4H, CH2CN), 4.72 and 5.00 (2d, J = 15.0, 2 × 2H, ArCHH),
7.14−7.27 (m, 10Haro). 19F{1H} NMR (188 MHz, C6D6, 298 K): δ
−77.82 (q, J = 10.3, 6F), −78.85 (q, J = 10.3, 6F). 13C{1H} NMR (75
MHz, C6D6, 298 K): δ 14.28 (AlCH3), 23.45 (NCCH3), 36.81
(CH2C(CF3)2), 54.17 (ArCH2), 78.18 (C(O)(CF3)2), 122.76, 127.07,
127.51, 128.22 (q, 1JCF = 289.8, CF3), 128.61, 137.85 (all Caro), 177.18
(CN). Anal. Calcd for C27H27AlF12N2O2: C, 48.66; H, 4.08; N, 4.20.
Found: C, 48.6; H, 4.2; N, 4.1.
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(Al(CH3)2), 38.37 (CH2C(CF3)2), 56.42 (ArCH2), 126.78 (q, JCF
=
281.1, CF3), 128.22, 128.42, 128.68, 129.42, 131.11, 134.41, 135.72 (all
Caro), 181.47 (CN). Anal. Calcd for C20H20AlF6NO: C, 55.69; H,
4.67; N, 3.25. Found: C, 55.6; H, 4.7; N, 3.1.
{ONMe,Bn}AlMe2 (2b). This compound was prepared as described
for 2a, starting from proligand {ONMe,Bn}H (1b; 300 mg, 0.95 mmol)
and AlMe3 (0.48 mL of a 2.0 M solution in heptane, 0.96 mmol).
Crystals of 2b suitable for X-ray diffraction were prepared by
prolonged crystallization from a hexane solution (3 mL) at −30 °C
1
to yield colorless crystals of 2b (110 mg, 31%). H NMR (300 MHz,
CD2Cl2, 298 K): δ −0.90 (s, 6H, Al(CH3)2), 2.30 (s, 3H, NCCH3),
3.06 (s, 2H, CH2CN), 4.83 (s, 2H, ArCH2), 7.16−7.49 (m, 5HAr).
1H NMR (300 MHz, C6D6, 298 K): δ −0.49 (s, 6H, Al(CH3)2), 1.11
(s, 3H, NCCH3), 2.42 (s, 2H, CH2CN), 4.04 (s, 2H, ArCH2),
6.78−7.03 (m, 5HAr). 19F{1H} NMR (188 MHz, CD2Cl2, 298 K): δ
−79.31 (s, 6F). 13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ −11.20
(Al(CH3)2), 37.96 (CH2C(CF3)2), 53.96 (ArCH2), 121.86, 123.70 (q,
1JCF = 295.0, CF3), 125.45, 127.39, 128.09, 128.97, 134.50 (all Caro),
183.78 (CN). Anal. Calcd for C15H18AlF6NO: C, 48.79; H, 4.91; N,
3.79. Found: C, 48.9; H, 4.9; N, 3.9.
{ONPh,Ph}AlMe (3c). This compound was prepared as described
above for 3a, starting from a solution of proligand {ONPh,Ph}H (1c;
200 mg, 0.55 mmol) in toluene (5 mL) and AlMe3 (0.14 mL of a 2.0
M solution in heptane, 0.27 mmol) in toluene (15 mL). Reaction for
24 h at 60 °C and workup afforded 3c as colorless crystals (78 mg,
{ONPh,Ph}AlMe2 (2c). This compound was prepared as described
above for 2a, starting from a solution of proligand {ONPh,Ph}H (1c;
200 mg, 0.55 mmol) in hexanes (4 mL) and a solution of AlMe3 (0.27
mL of a 2.0 M solution in heptane, 0.55 mmol) in hexanes (1 mL).
Workup afforded 2c as a white powder (187 mg, 81%). 1H NMR (300
MHz, C6D6, 298 K): δ −0.42 (s, 6H, Al(CH3)2), 3.12 (s, 2H, CH2C
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38%). H NMR (300 MHz, C6D6, 298 K): δ −0.89 (s, 3H, AlCH3),
3.26 and 3.42 (2d, J = 15.0, 2 × 2H, CHHC(O)(CF3)2), 6.66−6.98
(m, 20 Haro). 19F{1H} NMR (188 MHz, C6D6, 298 K): δ −76.46 (q, J
= 10.3, 6F), −79.48 (q, J = 10.3, 6F). 13C{1H} NMR (75 MHz, C6D6,
298 K): δ 14.23 (AlCH3), 37.32 (CH2C(O)(CF3)2), 124.13, 125.98,
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dx.doi.org/10.1021/om200907x | Organometallics 2012, 31, 1458−1466