Chiral N,O-chelate Schiff base
915
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452 (100) [M þ H]þ, and 242 (10) [H2L1 þ H]þ. H-NMR (200 MHz, CDCl3): ꢆ ¼ 1.82
(dd, JHH ¼ 8.0 Hz, 4H, CH2codexo), 2.37 (s, 1H, OH), 2.48 (m, 4H, CH2codendo), 3.80
(m, 2H, CHcod), 3.94 (d, JHH ¼ 7.7 Hz, 2H, H1), 4.45 (m, 1H, H2), 4.62 (m, 2H,
CHcod), 6.45 (dd, JHH ¼ 6.8 Hz, JHH ¼ 1 Hz, 1H, H12), 6.85 (dd, JHH ¼ 7.0 Hz,
JHH ¼ 1.2 Hz, 1H, H14), 6.97 (dd, JHH ¼ 6.2 Hz, JHH ¼ 1.8 Hz, 1H, H6), 7.23–7.33
(m, 2H, H5,7), 7.34–7.38 (m, 4H, H4,8,13,15), and 7.98 (s, 1H, H9).
2.3.3. [Rh(g4-cod){(rac)-2 -(salicylaldiminato)-1-phenylethanol-j2N,O}], [Rh(g4-cod)(rac-
HL2)] (3). Yield: 110 mg (76%). Calcd for [C23H26NO2Rh] (451.37) (%): C 61.20;
H 5.81; N 3.01. Found (%): C 60.65; H 6.00; N 2.63. IR (KBr, cmꢁ1): 3224sh (ꢄO–Halc.),
3055sh, 3026w (ꢄH–Ar), 1629vs (ꢄC¼N), and 1583sh (ꢄC¼C). UV-Vis (8.575 ꢂ
10ꢁ5 mol dmꢁ3, CHCl3): ꢅmax (nm) ("max (molꢁ1 dm3 cmꢁ1)) ¼ 242.0 (61,248) and 398.0
(6808). FAB-MS (pos.): m/z 452 (50) [M þ H]þ, 451 (40) [M]þ, 343 (100)
[M–cod ¼ Rh(HL2)]þ, 241 (10) [H2L2]þ, and 211 (15) [Rh(cod)]þ. 1H-NMR
(400 MHz, CDCl3): ꢆ ¼ 1.83, 1.93 (m, 4H, CH2codexo), 2.36 (s, 1H, OH), 2.49 (m, 4H,
CH2codendo), 3.30 (dd, JHH ¼ 8.0 Hz, JHH ¼ 1.5 Hz, 1H, H8), 3.37 (dd, JHH ¼ 8.5 Hz,
JHH ¼ 1.5 Hz, 1H, H8), 3.70, 3.75 (m, 2H, CHcod), 4.54, 4.60 (m, 2H, CHcod), 4.94 (dd,
JHH ¼ 7.7 Hz, JHH ¼ 1.0 Hz, 1H, H1), 6.55 (dt, JHH ¼ 6.8 Hz, JHH ¼ 1.0 Hz, 1H, H12),
6.83 (d, JHH ¼ 8.6 Hz, 1H, H14), 7.14 (d, JHH ¼ 7.9 Hz, 1H, H6), 7.26–7.34 (m, 3H,
H
4–5,7), 7.35–7.37 (m, 3H, H8,13,15), and 7.96 (s, 1H, H9). 1H-NMR (400 MHz, DMSO-
d6): ꢆ ¼ 1.80, 1.92 (m, 4H, CH2codexo), 2,30 2.42 (m, 4 H, CH2codendo), 3.20 (dd,
JHH ¼ 8.6 Hz, JHH ¼ 1.0 Hz, 1H, H8), 3.25 (d, JHH ¼ 8.7 Hz, 1H, H8), 3.72 (m, 2H,
CHcod), 4.33, 4.44 (m, 2H, CHcod), 4.74 (m, 1H, H1), 5.64 (d, JHH ¼ 4.8 Hz, 1H, OH),
6.53 (dt, JHH ¼ 6.9 Hz, JHH ¼ 1.0 Hz, 1H, H12), 6.65 (d, JHH ¼ 8.3 Hz, 1H, H14), 7.24–
7.36 (m, 3H, H4–6), 7.35–7.37 (m, 4H, H7–8,13,15), and 8.11 (s, 1H, H9). 13C-NMR
(100 MHz, CDCl3) 28.5, 29.3, 31.2, 32.2 (CH2cod), 66.6 (C8), 69.7 (d, JCRh ¼ 16.6 Hz,
CHcod), 72.7 (d, JCRh ¼ 15.0 Hz, CHcod), 74.9 (C1), 84.9 (d, JCRh ¼ 16.4 Hz, CHcod),
85.6 (d, JCRh ¼ 15.9 Hz, CHcod), 114.6 (C12), 119.1 (C14), 121.4 (C10), 125.9 (C3,7),
127.5 (C5), 128.6 (C4,6), 134.8 (C15), 135.4 (C13), 141.1 (C2), 166.2 (C9), and
167.4 (C11).
2.4. Catalytic reduction of acetophenone into (rac)-1-phenylethanol
Acetophenone (482 mg, 4.02 mmol), [Rh(ꢀ4-cod)Cl]2 (10 mg, 0.02 mmol, [Rh]/[acet-
ophenone] ¼ 1 : 201), and (S)-2 -(salicylaldimine)-2-phenylethanol (S-H2L1) (23.1 mg,
0.096 mmol, [Rh]/[S-H2L1] ¼ 1 : 4.8) were combined into a 50 mL Schlenk tube
containing 5 mL CH2Cl2. The mixture was then degassed thrice times by evacuation
and refilling with N2, and the Schlenk tube was left standing in an ice bath (0–5ꢀC).
After 10–15 min, diphenylsilane (DPS) (780 mg, 4.24 mmol, [Rh]/[DPS] ¼ 1 : 212) was
very slowly added into the reaction mixture with a syringe and continued stirring until
the reaction was completed. The progress of the catalytic reaction was monitored by
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taking H-NMR spectra of the reaction mixture after 1 h, 6 h, and 28 h in CDCl3.
In course of reaction, the singlet for CH3 of acetophenone disappeared, and
simultaneously, a doublet for (rac)-1-phenylethanol appeared. Comparison of integra-
tion values for these two peaks gave the conversion (%) of acetophenone into (rac)-1-
phenylethanol. The same procedure was followed using (S)-2-amino-2-phenylethanol
with [Rh(cod)Cl]2.