PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
1,4-dibromobutane, affording the corresponding phosphine a syringe filter the reaction mixture was quenched with n-
borane 3c and 3d in 94% and 95% yield, respectively OctBr (0.2 mmol, 35 mL) and stirred at room temperature
(entries 5 and 6). However, except for isopropyl iodide for 0.5 h. The final mixture was added to 2.0 mL EtOAc and
(entry 8), the reactions with isopropyl chloride (entry 7) and washed with H2O (3 ꢃ 1 mL). Then the organic layer was
dried over anhydrous MgSO4 and the solvent was removed
under reduced pressure. The crude product was purified by
GPC to afford 3a (56.2 mg, colorless oil, 0.18 mmol, 90%
tert-butyl bromide (entry 9) did not take place, perhaps due
to inert C-Cl bond of i-PrCl and large steric hindrance of t-
BuBr. In addition, by prolonging the reaction time, treat-
ment of diarylphosphine borane Ph2Pn-Bu(BH3) and dialky-
l(aryl)phosphine borane PhPEt2(BH3) with SD could also
lead to the corresponding R2PNa(BH3) intermediate. Finally,
the new generated phosphine boranes were produced in
moderated yields (Table 1, entries 10 and 11).
Unfortunately, the coupling reactions of Ph2PNa(BH3) with
aromatic chloride such as p-chlorotoluene gave complicated
results and no expected product could be detected even in
the presence of a palladium catalyst.[11]
1
yield); H NMR (400 MHz, CDCl3): d ¼ 7.70–7.65 (m, 4H),
7.47–7.40 (m, 6H), 2.23–2.16 (m, 2H), 1.57–1.47 (m, 2H),
1.41–1.33 (m, 2H), 1.29–1.23 (m, 8H), 0.86 (t, J ¼ 6.8 Hz,
3H); 13C NMR (100 MHz, CDCl3): d ¼ 132.2 (d, JPC
¼
9.1 Hz), 131.2 (d, JPC ¼ 1.8 Hz), 129.8 (d, JPC ¼ 54.4 Hz),
128.9 (d, JPC ¼ 9.6 Hz), 31.9, 31.2 (d, JPC ¼ 13.7 Hz), 29.1
(d, JPC ¼ 7.6 Hz), 25.9, 25.6, 23.1, 22.7, 14.2; 31P NMR
(162 MHz, CDCl3): d ¼ 16.5 (JBP ¼ 57.2 Hz).
General experimental procedures for the reaction of phos-
phine boranes with sodium
Conclusions
A Schlenk tube was charged with phosphine borane
R3PꢀBH3 1 (0.2 mmol) and 1.0 mL of THF; then under stir-
ring SD (0.42 mmol, 42 mL) was added to the solution and
stirring of the mixture was continued at room temperature
for the indicated time (2 h, 12 h, 16 h, 30 h). Then the excess
of sodium was removed by a syringe filter followed by
quenching of the reaction mixture with RX (0.2 mmol) and
stirring at room temperature for 0.5 h. The crude mixture
was analyzed by 31P NMR and the estimated yield of 3 was
calculated by integration based on the phosphine borane
1 used.
In conclusion, we have developed an efficient transformation
of arylphosphine boranes via the selective P-Ph bond cleav-
age by using SD, which not only completes our previously
established systematical studies on the P-C bond cleavage by
sodium, but also provides a new approach to alkylated phos-
phine boranes.
Experimental
Materials
The solvent THF and reagents alkyl halides were purchased
and used without further purification. Triphenylphosphine bor-
ane 1a and SD (ꢂ10 mol/L) was provided by Tokyo Chemical
Industry Co., Ltd. Ph2n-BuP(BH3) and Et2PhP(BH3) was pre-
pared from Ph2n-BuP and Et2PhP by treating with BH3·THF
solution, respectively. The Supplemental Materials contains
Acknowledgements
This work was primarily supported by joint research between AIST
and Maruzen Petrochemical Co., Ltd.
1
sample H, 13C and 31P NMR spectra for the product, 3 (mul-
ORCID
tiple runs, Figures S1–S18).
Jian-Qiu Zhang
Li-Biao Han
Instrumentation
1H, 31P and 13C NMR spectra were recorded with a JEOL
JNM-ECS400 instrument operating at 400 MHz (1H),
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