Unsymmetrical bidentate ligands bearing chiral phosphetane units

Article abstract of DOI:10.1055/s-1998-2169

Bidentate ligands containing a PPh₂ group and a P-chiral phosphetane moiety have been prepared from the optically pure P-menthyl substituted phosphetane oxide 4. The PPh₂ group is introduced at a distance of three, four or five bonds from the other phosphorus atom by methodologies involving the corresponding hydroxy-substituted phosphetanes.

Full text of DOI:10.1055/s-1998-2169

SYNTHESIS
October 1998
1539
Unsymmetrical Bidentate Ligands Bearing Chiral Phosphetane Units
A. Marinetti,*✥ V. Kruger, B. Couëtoux
Laboratoire Hétéroélements et Coordination, UMR CNRS 1499, Ecole Polytechnique, F-91128 Palaiseau Cedex, France
Received 18 December 1997; revised 3 March 1998
Abstract: Bidentate ligands containing a PPh2 group and a P-
chiral phosphetane moiety have been prepared from the optically
pure P-menthyl substituted phosphetane oxide 4. The PPh2 group
is introduced at a distance of three, four or five bonds from the
other phosphorus atom by methodologies involving the corre-
sponding hydroxy-substituted phosphetanes.
ertheless, the bimetallic derivative 3 has been easily ob-
tained through standard procedures.6
Key words: electron-rich chiral phosphines, P-chiral phosphe-
tanes, p-menthylphosphetanes, phosphetane oxides, hydroxy
phosphetanes, borane complexes, catalytic hydrogenation
These few examples suggest that an increase in sterical
hindrance and/or electron density at the metal center
strongly affects the stability of the phosphetane–rhodium
or ruthenium bonds. This imposes limitations upon the
use of these phosphetanes as ligands in several common
catalytic processes. Thus, increased stability in their com-
plexes is required and should be attained by incorporating
phosphetanes into chelating species.
Exploratory studies of the potential of phosphetanes as
chiral ligands in organometallic catalysis have appeared
recently. They have been mainly concerned with the easi-
ly accessible P-menthyl substituted species 1.1
In this paper, we demonstrate a number of pathways
which allow optically pure 1-menthyl-2,2,3,3-tetrameth-
ylphosphetane oxide (4) to be transformed into unsym-
metrical bidentate ligands, while retaining the four-mem-
bered ring structure (Scheme 2). The second coordinating
group is a PPh2 unit located at a distance of three, four or
five bonds from the phosphetane phosphorus atom.
These electron-rich, rather hindered phosphines are good
ligands for palladium and their use as chiral auxiliaries in
Pd-catalyzed olefin hydrosilylation2 and allylic substitu-
tion reactions3 has been reported. However, their behavior
towards other catalytically useful transition metals, such
as rhodium or ruthenium, is more difficult to predict.
Thus, the rhodium complex cis-[(COD)RhL2]+PF6– (L =
1a) is an unstable compound,2 while the very stable trans-
complex 2 is easily obtained at room temperature accord-
ing to Scheme 1.
Scheme 2
Usually, PPh2 moieties are introduced into chiral sub-
strates by the reaction of lithium diphenylphosphide
with the mesylates of chiral alcohols. This approach has
been adopted here. Phosphetane oxides bearing an hy-
droxyl function are easily accessible from the α-formyl
and α-allyl phosphetane oxides 5 and 7 (Scheme 3),
which are in turn obtained from 4 according to published
procedures.2,3
Scheme 1
In the first two examples of Scheme 3, the OH group is
formed by sodium borohydride reduction of a formyl
functionality. For the synthesis of 8a the olefinic double
Slightly unpredictable reactivity is also observed toward bond of 7a was cleaved by ozonolysis and the intermedi-
ruthenium complexes: under the usual reaction condi- ate ozonide reduced with Me2S to the corresponding alde-
tions,4,5 phosphetane 1a failed to give the expected (p- hyde which was then conveniently reduced in situ. Com-
•(
•
cymene)RuCl2 1a) and (2-methylallyl)2Ru (1a)2 by re- pound 7a was also used as the precursor for 9, which was
placement of a chloride ligand from the dimeric complex obtained in good yield after a highly regioselective 9-
[(p-cymene)RuCl2]2 or the 1,5-cyclooctadiene (COD) BBN7 hydroboration and subsequent oxidation with
ligand from (2-methylallyl)2Ru(COD), respectively. Nev- H2O2.

SYNTHESIS
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1540
with mesyl chloride/Et3N and LiPPh2 under the usual ex-
perimental conditions. The PPh2 group of the final prod-
uct was complexed with BH3 in situ to prevent oxidation
during the purification process.
The borane protecting group was displaced from com-
pounds 16–18 by treatment with 1,4-diazabicyc-
lo[2.2.2]octane (DABCO)9 in toluene at 80°C. Quantita-
tive yields of the corresponding diphosphines 19–21 were
obtained after filtration of the reaction mixture on a short
alumina column (cyclohexane/Et2O, 99:1).
Selected NMR data for the trivalent phosphetanes 10–12,
their borane complexes 13–15 and the diphosphine-
bis(borane) complexes 16–18 are reported in the Table.
Additional NMR data for 18 and selected data for 19–21
are given in the experimental section.
The chiral unsymmetrical diphosphines 19–21 containing
the phosphetane moiety and a PPh2 group have the poten-
tial to undergo chelation to transition metals. To confirm
this behaviour, compounds 19–21 were allowed to react
with [(COD)2Rh]PF6 and the formation of the chelated
rhodium complexes [(COD)Rh(L)]PF6 was observed by
31P NMR spectroscopy: L = 19: δ = 105.0 (JP-Rh = 137 Hz,
JP-P = 0) and 78.5 (JP-Rh = 151 Hz); L = 20: δ = 58.2 (JP-
Rh = 134 Hz, 2JP-P = 43 Hz) and 11.9 (JP-Rh = 146 Hz); L =
21: δ = 71.2 (JP-Rh = 133 Hz, 2JP-P = 38 Hz) and 6.3 (JP-Rh
= 156 Hz). Both the chemical shifts and coupling con-
stants are consistent with chelate ring formation. For ex-
ample, the low-field shifts and small P-P coupling con-
stants expected for five-membered chelate rings10 were
observed with L = 19.
Scheme 3
The optimal procedure for the synthesis of the bidentate
species involves reduction of the phosphetane oxides 6, 8
and 9 and complexation of the corresponding phosphe-
tanes 10–12 with BH3. Successive mesylation of the hy-
droxyl function, substitution with lithium diphenylphos-
phide and addition of borane gave the bidentate ligands as
their bis(borane) complexes (Scheme 4 and 5). This reac-
tion sequence was applied to the representative SP config-
ured phosphetane oxides 6a, 8a and 9a.
These rhodium complexes were employed to catalyze the
hydrogenation of a standard substrate, trans-α-acetami-
docinnamic acid. Unlike monodentate phosphetanes, the
bidentate ligands 19–21 gave reasonably active catalysts.
The levels of enantioselectivity peak under non-optimized
reaction conditions at about 75% ee (S-enantiomer),
which was obtained with ligand (RP,RC)-19. When com-
plexed to rhodium, ligand (RP,RC)-19 forms a 5-mem-
bered metallacycle which is fused to the 4-membered cy-
clic phosphetane unit. The very restricted conformational
freedom of this bicyclic structure probably contributes to
its control of stereochemistry.
Scheme 4
Reduction of the phosphetane oxides with trichlorosilane/
triethylamine takes place stereospecifically, with assumed
retention of the phosphorus stereochemistry.8 The most
convenient workup procedure involves the direct addition
•
of BH3 SMe2 to the crude product from Scheme 4, but the
phosphetanes 10–12 have nonetheless been isolated and
fully characterized. The hydroxy-phosphetanes borane
complexes 13–15 were isolated and treated successively
Obviously, the catalytic hydrogenation reaction under
consideration and the enantioselectivities attained in this
paper are of only academic interest at present. However,
our intention in this work has been to show that appro-
priate elaboration of the phosphetane scaffold should al-
low the properties of these ligands to be matched to the
requirements of any given catalytic reaction. More
meaningful applications of the bidentate ligands de-
scribed here should be possible when taking advantage
of the electronic and steric dissymmetry of their two
phosphorus atoms.
Finally, it should be noted that the intermediate hydroxy-
phosphetanes 10–12 themselves are potentially versatile
functional ligands for enantioselective catalysis.11
Scheme 5

SYNTHESIS
October 1998
1541
Table. Selected NMR data for compounds 10–18;a δ, J (Hz)
Assign-
ments of
spectra
X = lone electron pair,
Y = OHb
X = BH3 Y = OHc
X = BH3
Y = Ph2P(BH3) c
10
11
12
13
14
15
16
17
18
n = 1
n = 2
n = 3
n = 1
n = 2
n = 3
n = 1
n = 2
n = 3
31P NMR
19.6
29.3
29.5
51.7
55.5
54.8
58.0, 16.0 58.6, 16.9
57.0, 15.8
13C NMR:d
C-2
42.0
(4.8)
42.4
(4.7)
42.5
(4.7)
40.5
(35.2)
40.4
(35.2)
40.3
(36.3)
39.6
(35.1)
40.2
(35.3)
40.1
(36.3)
C-3
36.3
(2.7)
36.7
(2.9)
36.4
42.8
(5.8)
43.2
(4.8)
43.4
(4.5)
43.3
(4.5)
43.4
(5.0)
43.1
(4.6)
PCH-4
42.1
36.1
39.8
42.5
36.7
40.8
34.6
42.0
40.7
(34.9)
(36.6)
(37.0)
(37.4)
(36.2, 12.3) (36.9)
PCH-3'
36.5
36.5
36.5
37.0
36.9
37.1
37.6
36.5
36.6
(menthyl)
(29.0)
(30.8)
(30.8)
(15.5)
(16.1)
(15.0)
(14.1)
(15.1)
(15.1)
CH2Y
63.4
(27.3)
62.2
(10.4)
62.8
59.6
(2.7)
61.7
(10.5)
63.0
22.8
(33.5)
25.6
26.0
(36.4, 7.9) (37.6)
(CH2)n
–
34.3
27.3
–
28.8
22.7
–
18.9
23.0
(16.9)
(18.2)
(10.2)
–
–
33.2
(8.9)
–
–
32.8
(10.2)
–
–
27.5
(14.4)
1H NMR:e
CH2OH
3.56AB
3.77AB
(11.1)
3.43
(t, 6.8)
3.35
(t, 6.3)
3.8–4.0
3.55
(t, 6.7)
3.63
(t, 6.2)
a
b Recorded in C6D6.
c Recorded in CDCl3.
d JH-P
e JH-H
.
.
13C NMR (C6D6) : δ = 142.8 (t, JP-C = 5.8 Hz, OCHO), 206.86 and
206.80 (CO).
All reactions were carried out under N2 in anhydrous solvents. NMR
spectra were recorded on a Bruker AC 200 SY spectrometer operating
1
at 200.13 MHz for H, 50.32 MHz for 13C and 81.01 MHz for 31P.
IR (CHCl3): ν = 2020 s, 1974 m, 1945 s cm–1.
Anal. Calcd. for C54H80O8P2Ru2: C, 57.84; H, 7.19. Found: C, 57.78;
H, 7.41.
Only selected NMR data are given in this section.
ClRh(CO)[1a]2 (2):
Complex 2 was obtained from 0.10 g (0.28 mmol) of [ClRh(CO)2]2
and 0.20 g (0.56 mmol) of 1a in 73% yield (0.33 g) after crystalliza-
tion of the crude reaction mixture from pentane; yellow solid.
31P NMR (C6D6) : δ = 74.5 (1JP-Rh = 116 Hz).
4-(Hydroxymethyl)phosphetane Oxides (6):
A solution of the formylphosphetane 5a (or 5b) (0.30 g, 0.96 mmol)
in EtOH was cooled to 0°C. NaBH4 (0.07 g) was then added and the
reaction mixture was warmed to r.t. for about 1 h. After hydrolysis,
extraction with Et2O and drying (MgSO4), the product was crystal-
lized from an Et2O/hexane mixture.
13C NMR (C6D6) : δ = 17.6, 22.9, 23.0, 24.1 (CH3), 24.9 (t, JC-P = 7.9 Hz,
CH3), 25.3 (t, JP-C = 5.2 Hz, CH2), 30.5 (CH), 34.1 (t, JP-C = 4.4 Hz, CH),
34.7 (CH2), 35.9 (CH2), 36.2 (CH2), 43.2 (CH), 44.7 (C), 46 (br, C), 47.1
(CH), 48.8 (br, CH), 188.3 (dt, 1JC-Rh = 71.7 Hz, 2JC-P = 16.8 Hz, CO).
IR (CH2Cl2): ν = 1954 cm–1 (C=O).
(SP,RC)-6a: yield 0.27 g (90%); colorless solid; [α]D –52 (c = 1,
CHCl3).
31P NMR (CDCl3) : δ = 73.4.
Anal. Calcd. for C49H78ClOP2Rh: C, 66.62; H, 8.90. Found: C, 66.37;
H, 8.85.
1H NMR (CDCl3) : δ = 2.44 (q, J = 6.8 Hz, 1H), 3.4 (m, 1H), 3.96 (m,
2H, CH2OH).
13C NMR (CDCl3) : δ = 40.2 (1J= 41.1 Hz, PCH), 40.9 (2J= 11.9 Hz,
CMe2), 49.0 (1J = 53.8 Hz, PCMe2), 50.8 (1J = 50.5 Hz, PCH), 58.0
(2J = 4.1 Hz, CH2OH).
Di-µ-formatotetracarbonyl-bis(phosphetane)diruthenium (3):
Ru3(CO)12 (0.15 g) was added to formic acid (6 mL) and the reaction
mixture was refluxed for 20 h. The mixture was then evaporated to
dryness to afford a yellow solid which was taken up in Et2O.
Phosphetane 1a (0.22 g, 0.62 mmol) was added to the resulting suspen-
sion at r.t. and an immediate gas evolution was observed. The solution
was concentrated and hexane was added to precipitate the final product
(0.24 g, 69%); yellow solid; mp 182°C; [α]D –64 (c = 0.2, CHCl3).
MS: m/z = 314 (M, 28%).
Anal. Calcd. for C18H35O2P: C, 68.75; H, 11.22. Found: C, 68.09; H,
11.09.
(RP,SC)-6b: yield 0.25 g (85%); [α]D –41 (c = 1, CHCl3).
31P NMR (CDCl3): δ = 69.4.
31P NMR (C6D6) : δ = 53.6.
1H NMR (CDCl3): δ = 2.53 (m, 1H), 2.8 (m, 1H), 3.9–4.0 (m, 2H,
CH2OH).
3
1H NMR (C6D6) (selected data): δ = 0.64 (CH3), 0.84 [d, JH-H
=
=
6.5 Hz, CH(CH3)2], 0.91 (d, 3JH-H = 5.8 Hz, CHCH3), 1.08 (d, 3JH-H
13C NMR (CDCl3): δ = 41.7 (2J= 12.4 Hz, CMe2), 43.3 (1J= 40.1 Hz,
PCH), 48.2 (1J = 57.1 Hz, PCMe2), 52.8 (1J = 47.6 Hz, PCH), 58.6
(CH2OH).
6.5 Hz, CH(CH3)2], 1.16 (t, JH-P = 5.5 Hz, CH3), 1.36 (t, JH-P = 9.0 Hz,
CH3), 1.58 (CH3), 8.22 (OCHO).

SYNTHESIS
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1542
(SP,SC)-4-(2-Hydroxyethyl)phosphetane Oxide (8a):
A stream of O3 was passed through a cooled solution (–78°C) of the
4-allylphosphetane oxide 7a (1.0 g, 3 mmol) in CH2Cl2 (100 mL).
The reaction was complete in about 0.5 h. Reduction of the interme-
diate ozonide with excess Me2S (10 mL) and NaBH4 (0.26 g) took
place between –78 and 25°C. After hydrolysis, extraction with CHCl3
and evaporation of the solvent, the residue was crystallized from hex-
ane to afford (SP,SC)-8a; yield: 0.68 g (67%); colorless solid; mp
192°C.
2 mmol) and Et3N (0.33 mL) in CH2Cl2. The mixture was stirred for
18 h at r.t. and then hydrolyzed with aq NH4Cl solution. The organic
layer was evaporated, the residue taken up in hexane/EtOAc (80:20)
and filtered over a short alumina column to afford the desired mesy-
late as a colorless solid. The mesylate was dissolved in THF and
cooled to –78°C before addition of a THF solution of Ph2PLi
(2 mmol, 0.5M). [A 0.5 M solution of lithium diphenylphosphide was
prepared either by reacting Ph2PCl (0.78 mL, 4 mmol) with an excess
lithium in THF (8 mL) at r.t. or by metallation of Ph2PH (0.37 g,
2 mmol) with BuLi in THF (40 mL) between –78 and 25°C]. The
reaction mixture was warmed to r.t., a few drops of H2O and
BH3•Me2S (0.2 mL, 2 mmol) were added successively at 0°C. After
hydrolysis and extraction with Et2O, the final product was purified by
chromatography on alumina with hexane/Et2O (95:5) as eluent and
crystallized from hexane. The borane complex (RP,SC)-18 was ob-
tained in 47% yield (0.48 g) as a colorless solid.
31P NMR (CDCl3): δ = 73.6.
1H NMR (CDCl3): δ = 2.34 (q, J = 7.1 Hz, 1H), 3.5–3.7 (m, CH2OH).
13C NMR (CDCl3): δ = 27.4 (2J = 5.6 Hz, PCHCH2), 40.2 (1J =
40.8 Hz, PCH), 41.4 (2J = 11.7 Hz, CMe2), 46.1 (1J = 52.0 Hz, PCH),
48.5 (1J = 54.1 Hz, PCMe2), 61.3 (3J = 9.9 Hz, CH2OH).
MS: m/z = 328 (M, 20%).
Anal. Calcd. for C19H37O2P: C, 69.48; H, 11.35. Found: C, 68.17; H,
11.02.
1H NMR (CDCl3): δ = 0.76 (d, 3JH-H = 6.7 Hz, CH3), 0.79 (d, 3JH-H
=
3
6.9 Hz, CH3), 0.90 (s, CH3), 0.94 (d, JH-H = 6.7 Hz, CH3), 1.05 (d,
3JH-P = 17.4 Hz, CH3), 1.16 (s, CH3), 1.22 (d, 3JH-P = 12.9 Hz, CH3),
7.4-7.7 (C6H5).
4-(3-Hydroxypropyl)phosphetane Oxides (9):
A solution of 7a (or 7b) (2.3 g, 7.2 mmol) in THF was cooled to 0°C
and 9-BBN (0.5 M solution in THF, 30 mL) was added slowly. The
reaction mixture was then warmed to r.t. After stirring for 3 h, the
organoborane was oxidized at 0°C by adding, successively MeOH
(2 mL), 20% NaOH (1.4 mL) and 35% H2O2 (2.1 mL). The mixture
was stirred at r.t. for 1 h, hydrolyzed with a Na2S2O5 solution and
extracted with Et2O. The organic layer was separated and the aqueous
layer was reextracted with Et2O. After evaporation, the final product
was purified by column chromatography on alumina with an Et2O/
MeOH gradient (up to 96:4) as eluent (Rf 0.5).
13C NMR (CDCl3): δ = 17.3 (CH3), 19.6 (CH3), 21.4 (CH3), 21.5
(CH3), 22.4 (CH3), 22.6 (J = 4.4 Hz, CH3), 24.5 (J = 10.2 Hz, CH2),
27.3 (J = 15.6 Hz, CH3), 30.5 (J = 4.4 Hz, CH), 33.3 (J = 10.4 Hz,
CH), 34.0 (CH2), 34.9 (CH2), 41.6 (CH).
Displacement of Diphosphines 19–21 from their Borane Com-
plexes; General Procedure (Scheme 5):
The phosphine-borane complex (RP,RC)-16 (50 mg, 0.10 mmol) was
heated with DABCO (23 mg, 0.20 mmol) in benzene at 80°C for 2 h.
Quantitative formation of the diphosphine (RP,RC)-19 was observed
by 31P NMR analysis of the reaction mixture. The final product was
obtained in quantitative yield after chromatography on a short alumi-
na column with cyclohexane/Et2O (99:1) as eluent.
(SP,SC)-9a: yield 2.2 g (89%); colorless solid; mp 148°C; [α]D –45 (c
= 1, CHCl3).
31P NMR (CDCl3): δ = 70.8.
1H NMR (CDCl3): δ = 2.20 (q, J = 6.7 Hz, 1H), 3.63 (t, J = 6.2 Hz,
CH2OH).
13C NMR (CDCl3): δ = 20.0 (J = 5.7 Hz, CH2), 32.6 (J = 9.6 Hz,
CH2), 40.1 (1J = 40.0 Hz, PCH), 41.2 (2J = 13.4 Hz, CMe2), 48.6 (1J
= 54.0 Hz, PCMe2), 49.2 (1J = 52.3 Hz, PCH), 62.4 (CH2OH).
(RP,RC)-9b: yield 2.1 g (85%).
(RP,RC)-19: [α]D –25 (c = 1, CH2Cl2).
31P NMR (C6D6): δ = 33.3 and –18.5 (3JP-P = 23 Hz).
1H NMR (C6D6) (selected data): δ = 0.71 (d, 3JH-H = 6.8 Hz, CH3),
0.87 (d, 3JH-H = 6.4 Hz, CH3), 0.97 (d, 3JH-H = 6.9 Hz, CH3), 0.99 (s,
CH3), 0.98 (d, 3JH-P = 3.8 Hz, CH3), 1.09 (d, 3JH-P = 15.4 Hz, CH3),
1.14 (s, CH3), 7.0–7.7 (C6H5).
31P NMR (CDCl3):δ = 68.1.
1H NMR (CDCl3):δ = 3.59 (t, J = 6.1 Hz, CH2OH).
13C NMR (CDCl3):δ = 19.9 (J = 4.7 Hz, CH2), 32.3 (J = 11.3 Hz,
CH2), 42.0 (2J = 12.3 Hz, CMe2), 44.0 (1J = 39.0 Hz, PCH), 47.8 (1J
= 56.3 Hz, PCMe2), 51.2 (1J = 49.2 Hz, PCH), 62.2 (CH2OH).
MS: m/z = 342 (M, 45%).
13C NMR (C6D6): δ = 16.6 (CH3), 22.1 (2J = 10.7 Hz, CH3), 22.5
(CH3), 22.8 (2 CH3), 23.9 (2J = 23.3 Hz, CH3), 25.3 (J = 9.5 Hz, CH2),
26.6 (t, J = 6.9 Hz, CH3), 30.0 (J = 13.4 Hz, CH), 31.0 (dd, J = 36.6,
18.3 Hz, PCH2), 33.9 (J = 5.0 Hz, CH), 35.1 (CH2), 35.9 (J= 9.2 Hz,
CH-4), 36.2 (C-3), 36.7 (J = 31.7 Hz, CH-3’), 37.4 (CH2), 43.2 (J =
3.8 Hz, C-2), 48.8 (J = 22.1 Hz, CH), 126–140 (C6H5).
MS: m/z = 466 (M, 9%), 243 (PCHCH2PPh2, 100%).
The same procedure applied to the borane complexes (RP,SC)-17 and
(RP,SC)-18 afforded the diphosphines (RP,SC)-20 and (RP,SC)-21 re-
spectively.
Anal. Calcd. for C20H39O2P: C, 70.14; H, 11.48. Found: C, 70.01; H,
11.52.
Reduction of Phosphetane Oxides 6a, 8a and 9a: (RP,SC)-12a;
Typical Procedure (Scheme 4):
Compound 9a (2.2 g, 6.4 mmol) was dissolved in anhyd benzene
(30 mL). Et3N (1.8 mL, 2 equiv) and Cl3SiH (1.3 mL, 2 equiv) were
then added at 5°C. The mixture was stirred at r.t. for about 4 h, cooled
to 5°C and hydrolyzed with 20% NaOH (10 mL). The organic layer
was chromatographed directly, under argon, on a short alumina col-
umn with Et2O as eluent. Phosphetane (RP,SC)-12a was obtained in
95% yield (2.0 g) as a colorless solid. All reduction reactions are
quantitative according to 31P NMR analysis of the reaction mixtures.
For the direct synthesis of the borane complexes 13–15, the organic
layers obtained from the reductions above were dried (MgSO4), fil-
tered, and treated with excess BH3•Me2S (1.3 equiv). After evapora-
tion, the residue was purified by chromatography on alumina using
hexane/EtOAc (80:20) as eluent.
(RP,SC)-20:
31P NMR (CDCl3): δ = 29.2 and –17.2.
1H NMR (CDCl3) (selected data): δ = 0.78 (d, 3JH-H = 6.9 Hz, CH3),
0.94 (s, CH3), 0.94 (d, 3JH-H = 6.9 Hz, CH3), 1.00 (d, 3JH-H = 6.2 Hz,
CH3), 1.14 (d, 3JH-P = 14.9 Hz, CH3), 1.24 (d, 3JH-P = 5.1 Hz, CH3),
1.29 (s, CH3), 7.2 (C6H5).
13C NMR (CDCl3) (selected data): δ = 33.9 (J = 18.4, CH2), 36.4 (J
= 2.9 Hz, CH-4), 36.7 (J = 4.5 Hz, C-3), 36.0 (J = 29.0, CH-3'), 42.2
(J = 4.6 Hz, C-2), 44.5 (J = 10.7, CH2), 48.6 (J = 21.6 Hz, CH-4).
(RP,SC)-21:
31P NMR (CDCl3): δ = 30.2 and –16.0.
Diphosphine-bis(borane) Complexes 16–18: (RP,SC)-18; Typical
Procedure (Scheme 5):
Mesyl chloride (0.18 mL, 2.4 mmol) was added to a cooled solution
(0°C) of the phosphetane borane complex (RP,SC)-15 (0.68 g,
1H NMR (C6D6) (selected data): δ = 0.77 (d, 3JH-H = 6.7 Hz, CH3),
0.78 (s, CH3), 0.94 (d, 3JH-H = 6.4 Hz, CH3), 0.99 (d, 3JH-H = 6.8 Hz,
CH3), 1.09 (d, 3JH-P = 15.0 Hz, CH3), 1.12 (d, 3JH-P = 4.9 Hz, CH3),
1.18 (s, CH3), 7.1–7.5 (C6H5).

SYNTHESIS
October 1998
1543
13C NMR (C6D6): δ = 26.6 (dd, J = 16.0, 9.4 Hz, CH2), 29.0 (J = 12.9,
CH2), 32.9 (dd, J = 12.5, 18.0 Hz, CH2), 36.3 (C-3), 36.5 (J = 31.5,
CH-3'), 39.8 (CH-4), 42.5 (J = 5.3 Hz, C-2), 48.9 (J = 22.1 Hz, CH-
4').
(1) Marinetti, A.; Ricard, L. Tetrahedron 1993, 49, 10291.
(2) Marinetti, A. Tetrahedron Lett. 1994, 35, 5861.
Marinetti, A.; Ricard, L. Organometallics 1994, 13, 3956.
(3) Marinetti, A.; Kruger, V.; Ricard, L. J. Organomet. Chem.
1997, 529, 465.
Catalytic Hydrogenation Reactions:
(4) Bennett, M.A.; Smith, A.K. J. Chem. Soc. Dalton Trans. 1974,
233.
The hydrogenation reaction with the rhodium complex of (RP,RC)-19
is given as a representative example. The phosphine-borane complex
(RP,RC)-16 (10 mg, 0.02 mmol) was reacted with DABCO (4.5 mg,
0.02 mmol) in toluene at 70°C for about 3 h, after which time the
rhodium complex [(COD)2Rh]PF6 (1 equiv, 10 mg) was added.
Quantitative formation of the diphosphine (RP,RC)-19 and the corre-
sponding rhodium complex were confirmed by 31P NMR spectrosco-
py of the crude reaction mixtures.
Pertici, P.; Pitzalis, E.; Marchetti, F.; Rosini, C.; Salvadori, P.;
Bennett, M. A. J. Organomet. Chem. 1994, 466, 221.
(5) Powell, G.; Shaw, B.L. J. Chem. Soc. (A) 1968, 159.
(6) Crooks, G.R.; Johnson, B.F.G.; Lewis, J.; Williams, I.G. J.
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(7) Brown, H.C.; Knights, E.F.; Scouten, C.G. J. Am. Chem. Soc.
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(8) Cremer, S.E.; Chorvat, R.J. J. Org. Chem. 1967, 32, 4066.
Mislow, K. Acc. Chem. Res. 1970, 3, 321.
Analogous procedures starting from (RP,SC)-17 and (RP,SC)-18 af-
forded the rhodium complexes of phosphetanes 20 and 21, respective-
ly, which were used in situ for catalytic hydrogenation reactions.
Small amounts of byproducts were observed in the reaction mixture
obtained from 15.
See also ref. 2 and 3.
Hydrogenation of the α-acetamidocinnamic acid (2 mmol) was per-
formed in MeOH (20 mL), under 3 bars of H2 at r.t. Published proce-
dures were used to remove the catalyst and to isolate the final product;
optical yields were calculated from the [α]D values {[α]D +47.4 (c =
2, EtOH) for (S)-N-acetylphenylalanine}.12
(9) Brisset, H.; Gourdel, Y.; Pellon, P.; Le Corre, M. Tetrahedron
Lett. 1993, 34, 4523.
(10) Crumbliss, A.L.; Topping, R.J. In Methods in Stereochemical
Analysis, Vol. 8; Verkade, J.G.; Quin, L. D., Eds.; VCH: Wein-
heim, 1987, p 531.
(11) For a recent review on chiral hydroxyphosphines, see:
Holz, J.; Quirmbach, M.; Börner, A. Synthesis 1997, 983.
(12) Dang, T.P.; Poulin, J-C.; Kagan, H.B. J. Organomet. Chem.
1975, 91, 105.
✥ Present address: Laboratoire de Synthèse Sélective Organique et
Produits Naturels, UMR CNRS 7573, Ecole Nationale Supérieure
de Chimie de Paris, 11, rue Pierre et Marie Curie, F-75231 Paris Ce-
dex 05, France.
Samuel, O.; Couffignal, R.; Lauer, M.; Zhang, S.Y.; Kagan,
H.B. Nouv. J. Chim. 1981, 5, 15.
Nagel, U.; Rieger, B. Organometallics 1989, 8, 1534.