Hemilabile Site of Bis(phosphine) Monoxide Ligands
2952, 1449, 1403, 1256, 1171, 1139, 1130, 1010, 968, 852, 794,
776, 710, 679 cm-1; LRMS (APCI) calcd for C14H23O4P2 (M +
H)+ 317.1, found 317.1. Anal. Calcd for C14H22O4P2: C, 53.17; H,
7.01. Found: C, 53.11; H, 6.96.
mg, 3.0 mmol) was added to a solution of diphenyl(2-phosphi-
nophenyl)phosphine (853 mg, 2.9 mmol) in distilled THF (30 mL)
at -30 °C (internal temperature). The orange solution was allowed
to warm slowly to 0 °C (1 h) and was cannulated to a solution of
cyclic sulfate 2447 (523 mg, 2.9 mmol) in distilled THF (3 mL) at
rt and stirred for 2 h. The reaction was diluted with distilled THF
(30 mL), and t-BuOK (342 mg, 3.0 mmol) was added to the solution
at rt and stirred for 48 h. The resulting white solution was treated
with BH3 ·DMS (10 M, 580 µL, 5.8 mmol) at rt and stirred for
2 h. Concentration under vacuum gave the crude material which
was taken up in THF and stirred with silica gel for 7 h.
Concentration under vacuum gave a dry pack which was purified
by flash chromatography on silica gel (10% EtOAc/hexane) to
afford borane adduct 40 as a white solid (400 mg, 34%).
The borane adduct 40 (100 mg, 0.26 mmol) was then dissolved
in THF (3 mL), and H2O2 (34% in H2O) (72 µL, 0.65 mmol) was
added at rt. The reaction was stirred at rt until completion. Then a
saturated solution of Na2SO3 was slowly added at 0 °C, and the
mixture was stirred for 30 min at rt. The suspension was then filtered
and washed with EtOAc. Concentration under vacuum gave borane
adduct 16a•BH3 as a white solid (105 mg, quantitative): 1H NMR
(300 MHz, CDCl3) δ 8.50 (ddd, J ) 12.2, 7.4, 3.7 Hz, 1H),
7.68-7.34 (m, 12H, Ar-H), 7.25-7.12 (m, 1H), 3.71-3.50 (m,
1H), 2.62-2.46 (m, 1H), 2.25-1.89 (m, 3H), 1.74-1.53 (m, 1H),
1.05 (dd, J ) 15.1, 7.2 Hz, 3H), 0.58 (dd, J ) 16.1, 6.9 Hz, 3H),
1.21-0.19 (br m, 3H); 13C NMR (100 MHz, CDCl3) δ 139.5 (dd,
J ) 17.1, 10.5 Hz), 135.2 (dd, J ) 15.8, 7.8 Hz), 135.6 (d, J )
97.6 Hz), 133.9 (d, J ) 13.4 Hz), 132.9 (d, J ) 35.7 Hz), 132.7
(d, J ) 8.6 Hz), 132.2 (d, J ) 9.7 Hz, 2 C), 132.1-131.9 (m),
131.6 (d, J ) 9.6 Hz, 2 C), 131.6-131.4 (dd, J ) 11.5, 2.6 Hz, 2
C), 129.7 (dd, J ) 12.5, 1.9 Hz), 128.7 (d, J ) 12.1 Hz, 2 C),
128.5 (d, J ) 12.3 Hz, 2 C), 35.1 (d, J ) 37.8 Hz), 34.1 (d, J )
10.0 Hz), 32.8, 31.0 (d, J ) 33.7 Hz), 16.4 (d, J ) 4.1 Hz), 12.2
(d, J ) 3.9 Hz); 31P NMR (162 MHz, CDCl3) δ 52.0-50.0 (br m,
PBH3), 33.7 (d, J ) 4.9 Hz, P(V)).
{(2R,5R)-2,5-Dimethyl-1-[2-(1-oxidophospholan-1-yl)phenyl]phos-
pholanium-1-yl}(trihydrido) borate(1-) (29). A solution of phos-
phonate 33 (450 mg, 1.4 mmol) in dry THF (2 mL) was cannulated
to a suspension of LAH (135 mg, 3.5 mmol) in dry Et2O (12 mL)
at -78 °C. The resulting suspension was allowed to warm to -45
°C (internal temperature) and stirred for 30 min at -45 °C. (It was
crucial to maintain the internal temperature below -40 °C to avoid
excessive reduction and decomposition.) The mixture was cannu-
lated over Na2SO4 ·10H2O (3 g) at -78 °C and stirred for 1 h at rt.
The mixture was filtered under argon and washed with dry Et2O.
The solvent was pumped off to yield a colorless oil, and distilled
THF (2 mL) was added. An aliquot was taken: a mixture of starting
material 33 (∼35%), desired primary phosphine 34 (∼35%), 41
(∼18%), and 42 (∼12%) was obtained: 31P NMR (162 MHz, C6D6)
δ 60.6 (d, J ) 5.2 Hz, P(V)dO (34)), -115.1 (P(III) (34)); 58.7
(d, J ) 9.1 Hz, PdO (33)), 16.2 (d, J ) 9.1 Hz, P(O)(OEt)2 (33));
54.2 (42); -20.9 (d, J ) 99.3 Hz, P(III) (41)), -126.2 (d, J )
99.2 Hz, PH2 (41))).
t-BuOK (159 mg, 1.4 mmol) was added to a solution of
phosphines (1.4 mmol) in distilled THF (15 mL) at -30 °C (internal
temperature). The orange solution was allowed to warm slowly to
0 °C (1 h) and was cannulated to a solution of cyclic sulfate 2447
(255 mg, 1.4 mmol) in distilled THF (2 mL) at rt and stirred for
2 h. t-BuOK (159 mg, 1.4 mmol) was added to the solution at rt
and stirred for 48 h. The resulting white solution was treated with
BH3 ·DMS (10 M, 200 µL, 2.0 mmol) at rt and stirred for 2 h. The
reaction was then concentrated under vacuum to give a solid residue
which was triturated with CH2Cl2 and filtered on Celite. Concentra-
tion under vacuum gave the crude material which was purified by
flash chromatography on silica gel (60 to 90 to 100% EtOAc/hexane
then 5% MeOH/EtOAc) to afford borane adduct 29 as a white solid
(20.8 mg, 5%): Rf 0.15 (100% EtOAc); mp 100-102 °C; [R]20
(2R,5R)-1-[2-(Diphenylphosphoryl)phenyl]-2,5-dimethylphos-
pholane (16a). DABCO (40 mg, 0.35 mmol) and borane adduct
16a·BH3 (95 mg, 0.23 mmol) were placed in a 10 mL flask which
was purged with argon. Dry PhH (2.3 mL) was then added, and
the reaction was stirred at 50 °C for 17 h (monitored by TLC).
The reaction was then cooled to rt and concentrated under vacuum.
The crude material was purified quickly by flash chromatography
on silica gel (70% degassed EtOAc/hexane) to afford ligand 16a
as a white solid (74.3 mg, 82%): Rf 0.36 (70% EtOAc/hexane);
mp 124-126 °C; [R]20D -12.8 (c 1.8, PhH); 1H NMR (400 MHz,
C6D6) δ 7.88-7.75 (m, 4H), 7.52-7.38 (m, 2H), 7.13-6.96 (m,
7H), 6.93-6.86 (m, 1H), 2.58-2.29 (m, 2H), 1.98-1.72 (m, 2H),
1.41-1.25 (m, 1H), 1.16-1.05 (m, 1H), 1.02 (d, J ) 7.9 Hz, 3H),
0.99 (dd, J ) 10.2, 7.4 Hz, 3H); 13C NMR (100 MHz, C6D6) δ
144.5 (dd, JC-P ) 40.2, 11.0 Hz), 141.7 (dd, JC-P ) 102.9, 30.9
Hz), 136.5 (dd, JC-P ) 104.0, 2.1 Hz), 135.5 (d, JC-P ) 102.4
Hz), 134.7 (dd, JC-P ) 11.3, 2.7 Hz), 134.1 (dd, JC-P ) 13.3, 8.7
Hz), 132.9 (dd, JC-P ) 9.1, 0.6 Hz, 2 C), 132.1 (dd, JC-P ) 9.6,
3.3 Hz, 2 C), 131.2 (d, JC-P ) 2.6 Hz), 130.7 (dd, JC-P ) 12.6,
D
1
-101.8 (c 1.7, PhH); H NMR (400 MHz, CDCl3) δ 7.88 (tapp, J
) 8.8 Hz, 1H), 7.61-7.41 (m, 3H), 3.15-2.86 (m, 2H), 2.54-1.78
(m, 10H), 1.73-1.52 (m, 2H), 1.34 (dd, J ) 14.2, 6.9 Hz, 3H),
0.98 (dd, J ) 14.9, 7.3 Hz, 3H), 1.08-0.27 (br m, 3H); 13C NMR
(100 MHz, CDCl3) δ 139.0 (dd, JC-P ) 85.5, 7.8 Hz), 134.8 (tapp
JC-P ) 9.0 Hz), 133.3 (dd, JC-P ) 34.8, 7.4 Hz), 131.0 (dd, JC-P
) 8.2, 2.8 Hz), 130.9 (dd, JC-P ) 12.2, 6.3 Hz), 130.2 (dd, JC-P
,
)
11.9, 2.1 Hz), 33.7 (d, JC-P ) 37.0 Hz), 32.2 (d, JC-P ) 14.2 Hz),
31.8 (dd, JC-P ) 36.7, 6.0 Hz, 2 C), 31.0, 29.9 (d, JC-P ) 35.0
Hz), 25.2 (dd, JC-P ) 20.3, 8.4 Hz, 2 C), 18.9 (d, JC-P ) 5.9 Hz),
13.8 (d, JC-P ) 2.4 Hz); 31P NMR (121 MHz, CDCl3) δ 64.1 (d,
JP-P ) 5.8 Hz, P(V)dO), 49.6 (br dapp, JP-P ) 59.3 Hz, P(III));
IR (neat) 2922, 2852, 2355, 1455, 1262, 1162, 1125, 1058, 753,
680, 630 cm-1; HRMS (ESI) calcd for C16H27BONaP2 (M + Na)+
331.1534, found 331.1522.
(2R,5R)-2,5-Dimethyl-1-[2-(1-oxidophospholan-1-yl)phenyl]phos-
pholane (10). DABCO (12 mg, 0.11 mmol) and borane adduct 29
(21 mg, 0.07 mmol) were placed in a 5 mL flask which was purged
with argon. Dry PhH (1 mL) was then added, and the reaction was
stirred at 50 °C for 8 h (monitored by TLC). The reaction was
then cooled to rt. Concentration under vacuum (care should be taken
at that stage to avoid oxidation of the ligand by air) gave the crude
material which was purified quickly by flash chromatography on
silica gel (5 to 10% degassed MeOH/EtOAc) to afford ligand 10
2.5 Hz, 2 C), 128.4 (d, JC-P ) 11.7 Hz, 2 C), 128.2 (d, JC-P
12.2 Hz, 2 C), 127.7 (d, JC-P ) 12.4 Hz), 36.9 (d, JC-P ) 2.2 Hz),
)
36.5 (d, JC-P ) 4.4 Hz), 35.4 (d, JC-P ) 13.0 Hz), 35.1 (d, JC-P
)
15.2 Hz), 20.0 (d, JC-P ) 37.1 Hz), 17.5 (d, JC-P ) 2.9 Hz); 31P
NMR (162 MHz, C6D6) δ 28.3 (d, JP-P ) 15.6 Hz, P(V)dO), 3.1
(d, JP-P ) 15.6 Hz, P(III)); IR (neat) 3053, 2920, 2860, 1479, 1436,
1193, 1113, 729, 717, 693, 678 cm-1; LRMS (APCI) calcd for
C24H27O2P2 (M(O) + H)+ 409.1, found 409.1. Anal. Calcd for
C24H26OP2: C, 73.46; H, 6.68. Found: C, 73.19; H, 6.70.
1
as a sticky oil (14.9 mg, 75%): Rf 0.24 (100% EtOAc); H NMR
(400 MHz, C6D6) δ 7.88-7.77 (m, 1H), 7.39 (d, J ) 6.9 Hz, 1H),
7.14-7.03 (m, 2H), 2.54-2.34 (m, 2H), 2.34-2.15 (m, 1H),
2.16-1.43 (m, 9H), 1.43-1.28 (m, 1H), 1.21 (dd, J ) 18.4, 7.1
Hz, 3H), 1.22-1.13 (m, 1H), 0.88 (dd, J ) 9.5, 7.1 Hz, 3H); 31P
NMR (162 MHz, C6D6) δ 58.2 (d, J ) 10.3 Hz, P(V)dO), 2.0 (d,
J ) 10.3 Hz, P(III)).
[(2R,5R)-1-(2-Bromophenyl)-2,5-dimethylphospholanium-1-yl-
](trihydrido)borate(1-) (36). t-BuOK (623 mg, 5.6 mmol) was added
to a solution of primary phosphine 31 (1.0 g, 5.3 mmol) in distilled
THF (53 mL) at -30 °C (internal temperature). The orange solution
was allowed to warm slowly to 0 °C (1 h) and was cannulated to
a solution of cyclic sulfate 2447 (953 mg, 5.3 mmol) in distilled
{(2R,5R)-1-[2-(Diphenylphosphoryl)phenyl]-2,5-dimethylphos-
pholanium-1-yl}(trihydrido) borate(1-) (16a ·BH3). t-BuOK (342
J. Org. Chem. Vol. 73, No. 16, 2008 6339