New Chiral Tridentate Ligands
1265
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-isopropyl-4,5-
dihydrooxazol-2-yl)pyridine] (21, C24H28BN2OP)
From (S)-(þ)-valinol as aminoalcohol. Colourless resin. Yield 266 mg (30%); PI FD MS (CH2Cl2):
1
m=z ¼ 402 (M, 39), 388 (M–BH3); H{31P} NMR (400MHz, CDCl3, TMS): ꢀ ¼ 7.85 (dd, J ¼ 7.8,
1.0 Hz, H3-Py), 7.73 (m, 4H, Ph), 7.60 (dd, J ¼ 7.8, 7.8 Hz, H4-Py), 7.42 (m, 7H, Ph, H5-Py), 4.44 (dd,
J ¼ 9.0, 7.6 Hz, OCHAHBCHN), 4.15 (m, OCHAHBCHN), 4.02 (d, J ¼ 13.9Hz, CHAHBPBH3), 3.91
(d, J ¼ 13.9Hz, CHAHBPBH3), 1.89 (m, CHCH3CH3), 1.03 (d, J ¼ 6.8 Hz, CHCH3CH3), 0.93
(d, J ¼ 6.8 Hz, CHCH3CH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.62 (d, J ¼ 48.8Hz,
PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1; [ꢃ]D ¼ ꢃ40.5, [ꢃ]578 ¼ ꢃ43.9, [ꢃ]546 ¼ ꢃ50.0,
[ꢃ]436 ¼ ꢃ99.3, [ꢃ]365 ¼ ꢃ200.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.48, CH2Cl2).
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-benzyl-4,5-
dihydrooxazol-2-yl)pyridine] (22, C28H28BN2OP)
From (S)-(ꢃ)-phenylalaninol as aminoalcohol. Colourless resin. Yield 307 mg (30%); PI FD MS
(CH2Cl2): m=z ¼ 450 (M, 42), 436 (M–BH3, 100); 1H{31P} NMR (400MHz, CDCl3, TMS):
ꢀ ¼ 7.84 (dd, J ¼ 7.8, 1.1 Hz, H3-Py), 7.74 (m, 4H, Ph), 7.61 (dd, J ¼ 7.8, 7.8 Hz, H4-Py), 7.42
(m, 7H, Ph, H5-Py), 7.27 (m, 5H, Ph), 4.61 (m, OCHACHBCHN), 4.38 (dd, J ¼ 8.6, 9.4 Hz,
OCHAHBCHN), 4.17 (dd, J ¼ 8.6, 7.5 Hz, OCHAHBCHN), 4.01 (d, J ¼ 13.8Hz, CHAHBPBH3),
3.93 (d, J ¼ 13.8 Hz, CHAHBPBH3), 3.26 (dd, J ¼ 13.7, 5.1Hz, CHAHBPBH3), 2.74 (dd, J ¼ 13.7,
8.9 Hz, CHAHBPBH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.54 (d, J ¼ 56.5Hz, PPh2BH3)
ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1; [ꢃ]D ¼ ꢃ29.9, [ꢃ]578 ¼ ꢃ29.9, [ꢃ]546 ¼ ꢃ34.0, [ꢃ]436 ¼ ꢃ68.7,
[ꢃ]365 ¼ ꢃ134.7ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.47, CH2Cl2).
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-phenyl-4,5-
dihydrooxazol-2-yl)pyridine] (23, C27H26BN2OP)
From (S)-(ꢃ)-phenylglycinol as aminoalcohol. Colourless resin. Yield 378mg (38%); PI FD MS
(CH2Cl2): m=z ¼ 437 (M, 34), 422 (M–BH3, 100); 1H{31P} NMR (400MHz, CDCl3, TMS):
ꢀ ¼ 7.96 (dd, J ¼ 7.7, 1.5 Hz, H3-Py), 7.69 (m, 5H, Ph, H4-Py), 7.38 (m, 12H, Ph, H5-Py), 5.41 (dd,
J ¼ 10.1, 8.5 Hz, OCHAHBCHN), 5.15 (m, OCHAHBCHN), 4.83 (dd, J ¼ 10.1, 8.6 Hz, OCHAHBCHN),
4.03 (d, J ¼ 13.8Hz, CHAHBPBH3), 3.94 (d, J ¼ 13.8Hz, CHAHBPBH3) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ 18.73 (d, J ¼ 47.3 Hz, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2400 (s) cmꢃ 1; [ꢃ]D ¼
þ 60.5, [ꢃ]578 ¼ þ63.8, [ꢃ]546 ¼ þ76.2, [ꢃ]436 ¼ þ155.2, [ꢃ]365 ¼ þ330.5ꢂ cm3 gꢃ 1 dmꢃ 1
(c ¼ 1.05, CH2Cl2).
General Procedure for the Synthesis of the Borane-free Compounds 24–27 (and 32)
In an atmosphere of dry N2 0.75mmol of the borane complex were dissolved in 15cm3 of Et2NH and
stirred for 5 h at 50ꢂC. After removing the solvent and the volatiles, the residue was dried for 2 h in
high vacuum with gentle heating to give the borane-free products 24–27 and 32.
(R)-2-[(Diphenylphosphanyl)methyl]-6-(4-ethyl-4,5-dihydrooxazol-2-yl)pyridine
(24, C23H23N2OP)
From 20. Colourless resin. Yield 261 mg (93%); PI DCI MS: m=z ¼ 391 (M þ NH4, 100), 375 (MH, 8);
1H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.84 (dd, J ¼ 7.8, 1.0 Hz, H3-Py), 7.45 (m, 5H, Ph, H4-
Py), 7.31 (m, 6H, Ph), 6.96 (dd, J ¼ 7.8, 1.0 Hz, H5-Py), 4.55 (dd, J ¼ 8.2, 9.5 Hz, OCHAHBCHN), 4.28
(m, OCHAHBCHN), 4.13 (dd, J ¼ 8.2, 8.2 Hz, OCHAHBCHN), 3.76 (d, J ¼ 13.5Hz, CHAHBPPh2),
3.72 (d, J ¼ 13.5Hz, CHAHBPPh2), 1.81 (m, CHAHBCH3), 1.63 (m, CHAHBCH3), 1.01 (t, J ¼ 7.4 Hz,