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Typical Procedure for Preparation of Phosphinous Acid-Boranes by Reaction of Secondary
Phosphine Oxide Anions and BH
3
·THF complex:
In a reaction flask equipped with magnetic stirrer and dry argon inlet was placed
secondary phosphine oxide (0.5 mmol) in 15 mL of dry THF. Next, an equimolar amount
of a base (NaH or butyllithium) (0.5 mmol) was added under argon atmosphere. After
15 min at r.t. 1 M BH3·THF complex (0.75 mmol) in THF was added. The reaction mixture was then stirred at
r.t. for two h. Aq HCl (1 mL) was added and the reaction mixture was extracted several
times with CH2Cl2, organic layers were collected, dried over anhyd MgSO4, and evaporated. The crude product was purified by flash chromatography using hexane:EtOAc
(2:1) as eluent.
t-Butylphenylphosphinous Acid-Borane (2a). Yield 98% (74%). 1H NMR (CDCl3): δ = 0.00-1.70 (br m, 3 H), 1.14 (d, J
P-C = 14.66 Hz, 9 H), 4.52 (br s, 1 H), 7.41-7.89 (m, 3 H), 7.69-7.85 (m, 2 H) ppm. 13C NMR (CDCl3): δ = 23.85, 23.92, 31.31, 32.13, 127.82, 128.03, 131.20, 131.26, 131.46 ppm. 31P NMR (CDCl3): δ = 114.39 ppm (m). Anal. Calcd for C10H18BOP: C, 61.27; H, 9.26. Found: C, 61.26; H, 9.08.
Benzylphenylphosphinous Acid-Borane (2b). Yield 63%. 1H NMR (CDCl3): δ = 0.07-1.65 (br m, 3 H), 3.38 (d,
J
P-H = 10.22 Hz, 2 H), 4.90 (br s, 1 H), 7.01-7.13 (m, 2 H), 7.21-7.34 (m, 3 H), 7.40-7.75
(m, 5 H) ppm. 13C NMR (CDCl3): δ = 39.41, 40.14, 126.68, 126.74, 127.98, 128.03, 128.08, 128.28, 129.95, 130.04,
130.19, 130.41, 131.06, 131.13, 131.18, 131.51, 131.56, 132.32 ppm. 31P NMR (CDCl3): δ = 101.64 ppm (m). Anal. Calcd for C13H16BOP: C, 67.87; H, 7.01. Found: C, 67.96; H, 7.18.
(2-Naphthylmethyl)phenylphosphinous Acid-Borane (2c). Yield 63% (67%). 1H NMR (CDCl3): δ = 0.05-1.72 (br m, 3 H), 3.52 (d, J
P-H = 9.98 Hz, 2 H), 3.60 (br s, 1 H), 7.11-7.21 (m, 1 H), 7.36-7.56 (m, 5 H), 7.56-7.89
(m, 6 H) ppm. 13C NMR (CDCl3): δ = 39.64, 40.36, 125.71, 126.02, 127.39, 127.51, 127.68, 128.12, 128.25, 128.46,
128.64, 128.77, 128.89, 130.26, 130.48, 131.73, 131.77, 132.22 ppm. 31P NMR (CDCl3): δ = 103.16 ppm (m). Anal. Calcd for C17H18BOP: C, 72.99; H, 6.48. Found: C, 73.04, H, 6.53.
o-Anisylphenylphosphinous Acid-Borane (2d). Yield 43%. 1H NMR (CDCl3): δ = 0.20-1.96 (br m, 3 H), 3.81 (s, 3 H), 5.11 (br s, 1 H), 6.91-7.04 (m, 1 H),
7.10-7.22 (m, 1 H), 7.38-7.76 (m, 6 H), 7.83-8.00 (m, 1 H) ppm. 13C NMR (CDCl3): δ = 55.98, 111.37, 121.49, 121.75, 128.13, 128.34, 130.04, 130.27, 131.10, 131.15,
134.11, 134.33 ppm. 31P NMR (CDCl3): δ = 98.00 ppm (m). Anal. Calcd for C13H16BO2P: C, 63.46; H, 6.55. Found: C, 63.44; H, 6.57.
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Reetz T.
J. Am. Chem. Soc.
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5039
<A NAME="RG29603ST-10">10</A>
General Procedure for the Synthesis of Phosphinous Acid-Boranes by the Reaction of
Secondary Phosphine Oxides with NaBH
4
/BF
3
:
To the solution of secondary phosphine oxide (0.5 mmol) in 15 mL of dry THF ethereal
solution of BF3 (2 mmol) was added under argon atmosphere. Promptly after, NaBH4 (1.5 mmol) was added to the reaction mixture. Then, the reaction flask was fitted
with a reflux condenser and the reaction mixture was heated to reflux for 3 h. The
reaction mixture was then allowed to cool to r.t. and aq HCl (1 mL) was added to quench
the reaction. The reaction mixture was extracted several times with CH2Cl2, organic layers were collected, dried over anhyd MgSO4, and evaporated. The crude product was purified by flash chromatography using hexane/EtOAc
(2:1) as eluent.
[(2-Methyl)-1-naphthyl]phenylphosphinous Acid-Borane (2f). Yield 86%. 1H NMR (CDCl3): δ = 0.30-1.96 (br m, 3 H), 2,77 (s, 3 H), 5.65 (br s, 1 H), 7.32-7.54 (m, 6 H),
7.54-7.72 (m, 2 H), 7.78-7.98 (m, 2 H), 8.40-8.58 (m, 1 H) ppm. 13C NMR (CDCl3): δ = 24.14, 24.27, 112.20, 125.27, 126.54, 126.89, 127.03, 128.44, 128.57, 128.66,
129.94, 130.03, 130.17, 130.24, 131.16, 131.20, 132.88, 132.93 ppm. 31P NMR (CDCl3): δ = 99.14 ppm (m). Anal. Calcd for C17H18BOP: C, 72.99; H, 6.48. Found: C, 73.11; H, 6.59.
Phenyl-o-tolylphosphinous Acid-Borane (2g). Yield 82%. 1H NMR (CDCl3): δ = 0.30-2.00 (br m, 3 H), 2.28 (s, 3 H), 4.45 (br s, 1 H), 7.18-7.60 (m, 6 H),
7.60-7.78 (m, 2 H), 7.92-8.10 (m, 1 H) ppm. 13C NMR (CDCl3): δ = 21.28, 21.38, 125.58, 125.81, 128.43, 128.64, 130.68, 130.92, 131.35, 131.52,
131.61, 132.04, 132.64, 132.93 ppm. 31P NMR (CDCl3): δ = 98.57 ppm (m). Anal. Calcd for C13H16BOP: C, 67.87; H, 7.01. Found: C, 67.94; H, 7.16.
Di-c-hexylphosphinous Acid-Borane (2h). Yield 91%. 1H NMR (CDCl3): δ = -0.45-1.35 (br m, 3 H), 1.15-1.62 (m, 10 H), 1.66-1.97 (m, 12 H), 4.13 (br
s, 1 H) ppm. 13C NMR (CDCl3): δ = 24.79, 24.84, 25.70, 25.94, 26.35, 26.54, 26.61, 34.20, 34.95 ppm. 31P NMR (CDCl3): δ = 119.36 ppm (m). Anal. Calcd for C12H26BOP: C, 63.18; H, 11.49. Found: C, 63.04; H, 11.40.
i-Propylphenylphosphinous Acid-Borane (2i). Yield 82%. 1H NMR (CDCl3): δ = -0.09-1.5 (br m, 3 H), 1.02-1.23 (m, 6 H), 2.02-2.24 (m, 1 H), 4.65 (br s,
1 H), 7.43-7.61 (m, 3 H), 7.71-7.87 (m, 2 H) ppm. 13C NMR (CDCl3): δ = 15.31, 15.49, 28.91, 29.77, 128.13, 128.33, 128.66, 128.86, 130.56, 130.77,
131.31, 131.36 ppm. 31P NMR (CDCl3): δ = 110.09 ppm (m). Anal. Calcd for C9H16BOP: C, 59.39; H, 8.86. Found: C, 59.28; H, 8.85.
c-Hexylphenylphosphinous Acid-Borane (2j). Yield 90%. 1H NMR (CDCl3): δ = -0.09-1.5 (br m, 3 H), 1.11-1.64 (m, 6 H), 1.64-2.02 (m, 5 H), 4.25 (br s,
1 H), 7.42-7.61 (m, 3 H), 7.70-7.85 (m, 2 H) ppm. 13C NMR (CDCl3): δ = 25.05, 25.16, 25.79, 26.10, 26.36, 38.80, 39.65, 128.11, 128.31, 130.55, 130.76,
131.20, 131.24 ppm. 31P NMR (CDCl3): δ = 107.13 ppm (m). Anal. Calcd for C12H20BOP: C, 64.90; H, 9.08. Found: C, 64.83; H, 9.18.
Di-n-hexylphosphinous Acid-Borane (2k). Yield 90%. 1H NMR (CDCl3): δ = -0.30-1.40 (br m, 3 H), 0.84-1.04 (m, 6 H), 1.24-1.52 (m, 12 H), 1.52-1.92
(m, 8 H), 4.08 (br s, 1 H) ppm. 13C NMR (CDCl3): δ = 14.06, 21.79, 22.48, 28.68, 29.47, 30.54, 30.797, 31.35, 31P NMR (CDCl3): δ = 116.06 ppm (m). Anal. Calcd for C12H30BOP: C, 62.08; H, 13.03. Found: C, 61.99; H, 12.97.
Phenyl-p-tolylphosphinous Acid-Borane (2l). Yield 65%. 1H NMR (CDCl3): δ = 0.20-1.95 (br m, 3 H), 2.41 (s, 3H), 5.08 (br s, 1 H), 7.21-7.32 (m, 2 H),
7.36-7.56(m, 3 H), 7.56-7.81 (m, 4 H) ppm. 13C NMR (CDCl3): δ = 21.54, 128.30, 128.52, 129.12, 129.34, 130.67, 130.83, 130.90, 131.07, 131.34
ppm. 31P NMR (CDCl3): δ = 93.65 ppm (m). Anal. Calcd for C13H16BOP: C, 67.87; H, 7.01. Found: C, 67.66; H, 7.17.
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