Diphosphines containing stereogenic P atoms: Synthesis of (S,S)-C,C′-tetramethylsilanebis-(1-naphthylphenylphosphine) and applications in enantioselective catalysis

Article abstract of DOI:10.1021/om970539e

The diphosphine (S,S)-Me₂Si(CH₂P(1-Np)(Ph))₂ (1-Np = 1-naphthyl) (1), containing stereogenic P atoms, is prepared with high diastereo- and enantiomeric purity by a multistep asymmetric synthesis via its borane adduct (S,S)-Me₂Si(CH₂P(1-Np)(Ph)(BH₃))₂ (2), obtained bv selective methyl lithiation of the enantiomerically pure phosphine borane (S)-P(1-Np)-(Ph)(Me)(BH₃) (3) and coupling onto Me₂SiCl₂. The absolute configuration of 3 is established by X-ray studies. Reacting 2 with morpholine gives free diphosphine (S,S)-1 with a (S,S): (R,R) enantiomeric ratio better than 99:1. The Rh(I) and Ru(II) derivatives [Rh(diene)-((S,S)-1)] (diene = norbornadiene, 4a; 1,5-cyclooctadiene, 4b) and [RuCl₂(PPh₃)(S,S)-1)] (5) are prepared and tested as catalyst precursors in enantioselective reactions with standard substrates. In the presence of 4b as catalyst precursor, a series of dehydroamino acid derivatives are hydrogenated with up to 97.7% ee. Complex 5 catalyzes the hydrogenation of pentane-2,4-dione to (S,S)-pentane-2,4-diol with up to 56% ee. Ligand 1 gives enantioselection also in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-3-acetoxypropene with dimethyl malonate (27% ee).

Full text of DOI:10.1021/om970539e

668
Organometallics 1998, 17, 668-675
Dip h osp h in es Con ta in in g Ster eogen ic P Atom s:
Syn th esis of (S,S)-C,C′-Tetr a m eth ylsila n ebis-
(1-n a p h th ylp h en ylp h osp h in e) a n d Ap p lica tion s in
En a n tioselective Ca ta lysis
Robert M. Stoop and Antonio Mezzetti*
Laboratorium fu¨r Anorganische Chemie, ETH-Zentrum, CH-8092 Zu¨rich, Switzerland
Felix Spindler
Novartis Services Ltd, CH-4002 Basle, Switzerland
Received J une 26, 1997
The diphosphine (S,S)-Me2Si(CH2P(1-Np)(Ph))2 (1-Np ) 1-naphthyl) (1), containing
stereogenic P atoms, is prepared with high diastereo- and enantiomeric purity by a multistep
asymmetric synthesis via its borane adduct (S,S)-Me2Si(CH2P(1-Np)(Ph)(BH3))2 (2), obtained
by selective methyl lithiation of the enantiomerically pure phosphine borane (S)-P(1-Np)-
(Ph)(Me)(BH3) (3) and coupling onto Me2SiCl2. The absolute configuration of 3 is established
by X-ray studies. Reacting 2 with morpholine gives free diphosphine (S,S)-1 with a (S,S):
(R,R) enantiomeric ratio better than 99:1. The Rh(I) and Ru(II) derivatives [Rh(diene)-
((S,S)-1)] (diene ) norbornadiene, 4a ; 1,5-cyclooctadiene, 4b) and [RuCl2(PPh3)((S,S)-1)] (5)
are prepared and tested as catalyst precursors in enantioselective reactions with standard
substrates. In the presence of 4b as catalyst precursor, a series of dehydroamino acid
derivatives are hydrogenated with up to 97.7% ee. Complex 5 catalyzes the hydrogenation
of pentane-2,4-dione to (S,S)-pentane-2,4-diol with up to 56% ee. Ligand 1 gives enanti-
oselection also in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-3-acetoxypropene with
dimethyl malonate (27% ee).
In tr od u ction
of phosphine ligands containing stereogenic P atoms.5
However, lately several groups have been developing
new methods for the asymmetric synthesis of chiral
diphosphines that fulfill the requirements of large-scale
preparation.6-8 The general strategy encompasses three
steps, namely, (a) the synthesis of an enantiomerically
pure, borane-protected phosphine, (b) coupling of two
of these moieties to form the protected diphosphine
ligand, and (c) its deprotection to give the free diphos-
phine. All the methods exploit the diastereoselective
formation of a cyclic phospholidine intermediate with a
bifunctional chiral auxiliary that bears two different
heteroatoms, such as O and N,6,7 or O and S.8 The two
heteroatoms are then stepwise substituted diastereospe-
cifically by nucleophilic aryl or alkyl groups. The
chirality at the P atom needs to be stabilized by a
protecting group X, which can be BH3,6,8 sulfide,8 or
oxide.7
During the amazing development of metal-catalyzed
enantioselective reactions, and in spite of the early
success achieved with dipamp,1 diphosphines containing
stereogenic P atoms have been outnumbered by ligands
based on alternative chiral elements.2 Among these, the
atropisomeric ligands of the BINAP family, the planar
chiral ferrocenyl phosphines, and those of the DuPHOS
group have brought about the long-awaited break-
through in enantioselective catalysis with respect to
industrial application.3 However, the very recent prepa-
ration of BIPNOR and its successful application in
enantioselective catalysis4 suggest that the potential of
diphosphines containing stereogenic P atoms has not
been exhaustively investigated.
Apparently, both synthetic problems and the wide-
spread prejudice about the low stability of the config-
uration at the P atom have hampered the development
Starting from Imamoto’s work on phosphine boranes,9
J uge´ and co-workers have developed a methodology for
* Author to whom correspondence should be addressed. E-mail:
mezzetti@inorg.chem.ethz.ch.
(1) Vineyard, B. D.; Knowles, W. S.; Sabacky, M. J .; Bachmann, G.
L.; Weinkauff, D. J . J . Chem. Am. Soc. 1977, 99, 5946.
(2) Brunner, H.; Zettlmeier, W. Handbook of Enantioselective Ca-
talysis; VCH: Weinheim, Germany, 1993.
(3) (a) Akutagawa, S. Appl. Catal. A: General 1995, 128, 171. (b)
Kumobayashi, H. Recl. Trav. Chim. Pays-Bas 1996, 115. 201. (c) Togni,
A.; Angew. Chem., Int. Ed. Engl. 1996, 35, 1475. (d) See ref 10 in Burk
et al.: Burk, M. J .; Wang, Y. M.; Lee, J . R. J . Am. Chem. Soc. 1996,
118, 5142.
(5) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94, 1375.
(6) (a) J uge´, S.; Ste´phan, M.; Laffitte, J . A.; Genet, J . P. Tetrahedron
Lett. 1990, 31, 6357. (b) J uge´, S.; Merde`s, R.; Ste´phan, M.; Geneˆt, J .
P. Phosphorus, Sulfur Silicon Relat. Elem. 1993, 77, 199. (c) J uge´, S.;
Ste´phan, M.; Merde`s, R.; Genet, J . P.; Halut-Desportes, D. J . Chem.
Soc., Chem. Commun. 1993, 531.
(7) Carey, J . V.; Barker, M. D.; Brown, J . M.; Russell, M. J . H. J .
Chem. Soc., Perkin Trans. 1 1993, 831.
(8) Corey, E. J .; Zhuoliang, C.; Tanoury, G. J . J . Am. Chem. Soc.
1993, 115, 11000.
(4) Robin, F.; Mercier, F.; Ricard, L.; Mathey, F.; Spagnol, M. Chem.
Eur. J . 1997, 3, 1365.
(9) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Kazuhiko,
S. J . Am. Chem. Soc. 1990, 112, 5244.
S0276-7333(97)00539-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/28/1998

Diphosphines Containing Stereogenic P Atoms
Organometallics, Vol. 17, No. 4, 1998 669
Ch a r t 1
Ch a r t 2
the synthesis of enantiomerically pure, borane-protected
P-chiral phosphines of the type P(Ph)(R)(Me)(BH3),6a
which can be selectively lithiated at the methyl group.
The resulting P(Ph)(R)(BH3)CH2Li gives the borane-
protected diphosphine either by oxidative coupling or
by nucleophilic substitution at R2SiCl2. The borane
adducts appear to be particularly versatile intermedi-
ates in that they are crystalline, chemically and con-
figurationally stable under vigorous reaction conditions,
and easily converted into the free diphosphine by
reaction with an amine. A different approach is the
selective deprotonation of the enantiotopic methyl groups
of the borane-protected dimethylarylphosphines P(Ar)-
(Me)2(BH3) in the presence of a chiral auxiliary, followed
by coupling onto the diphosphine framework.10
Sch em e 1
The new protocols for the synthesis of enantiopure
P-chiral ligands allow one to screen systematically
diphosphines containing stereogenic P atoms in asym-
metric catalysis. However, in spite of the effort invested
in the development of such diphosphines, reports con-
cerning their catalytic applications are still rare. Geneˆt
et al. reported that the ruthenium-catalyzed asymmetric
hydrogenation of tiglic acid using the ligand (R,R)-Me2-
Si(CH2P(o-An)(Ph))2 (o-An ) o-MeOC6H4) (dipampSi)
gives 2-methylbutyric acid with 15% ee (Chart 1).11 To
explore the potential of these ligands further, we
prepared the new diphosphine (S,S)-C,C′-tetramethyl-
silanebis(1-naphthylphenylphosphine), (S,S)-1.12 We
report herein a full experimental account of the syn-
thesis of 1 and of its derivatives [Rh(diene)((S,S)-1)]
(diene ) norbornadiene, 4a ; 1,5-cyclooctadiene, 4b) and
[RuCl2(PPh3)((S,S)-1)] (5) (Chart 2), as well as prelimi-
nary catalytic results.
literature.6a The new intermediate products 3, 7, and
8 are easily purified by conventional methods (recrys-
tallization and column chromatography). The overall
(recrystallized) yield is 35%, whereby the acid metha-
nolysis 7 f 8 (60%, recrystallized) and the deprotection
step 2 f 1 (78%) give the lower yields.
Treatment of (R)-6 with 1-naphthyllithium gives the
aminophosphine borane diastereomer (S)-7, whose con-
figuration is attributed by analogy.6a Acid-catalyzed
methanolysis yields the phosphinite borane P(OMe)(1-
Np)(Ph)(BH3), (R)-8; inversion of configuration at the
phosphorus atom is assumed.6a Recrystallization of the
crude product from hexane yields enantiomerically pure
(R)-8 in 60% yield. Methylation of the phosphinite
borane (R)-8 with MeLi and recrystallization from
hexane produces enantiomerically pure (S)-P(1-Np)(Ph)-
(BH3), (S)-3, in 81% yield. The enantiomeric purity of
3 and 8 is determined by chiral HPLC; the analytical
conditions were optimized using racemic P(OMe)(1-Np)-
(Ph)(BH3) ((rac)-8) and (rac)-P(1-Np)(Ph)(Me)(BH3) ((rac)-
3), which were prepared as described in Scheme 2.
The predicted6a S configuration of 3 is confirmed by
an X-ray crystallographic investigation. Crystals were
grown from CH2Cl2/hexane. An ORTEP drawing is
shown in Figure 1, and selected bond distances and
angles are reported in Table 1. The crystal contains
discrete P(1-Np)(Ph)(Me)(BH3) molecules with normal
nonbonded interactions. The geometry of the P atom
is approximately tetrahedral, with normal P-C and
Resu lts a n d Discu ssion
Syn th esis of (S,S)-Me2Si(CH2P (1-Np)(P h ))2 ((S,S)-
1). The synthesis of the P-chiral diphosphine (S,S)-1
follows the methodology used by J uge´ (Scheme 1)6 and
starts from oxazaphospholidine borane (R)-6, which is
prepared from (+)-(1S,2R)-ephedrine according to the
(10) Muci, A. R.; Campos, K. R.; Evans, D. A. J . Am. Chem. Soc.
1995, 117, 9075.
(11) (a) Geneˆt, J . P.; Pinel, C.; Ratovelomanana-Vidal, V.; Mallart,
S.; Pfister, X.; Can˜o De Andrade, M. C.; Laffitte, J . A. Tetrahedron:
Asymmetry 1994, 5, 665. (b) Geneˆt, J . P.; Pinel, C.; Ratovelomanana-
Vidal, V.; Mallart, S.; Pfister, X.; Bischoff, L.; Can˜o De Andrade, M.
C.; Darses, S.; Galopin, C.; Laffitte, J . A. Tetrahedron: Asymmetry
1994, 5, 675. (c) Geneˆt, J . P.; J uge´, S.; Laffitte, J . A.; Pinel, C.; Mallart,
S. (Elf Aquitaine). PCT Int. Appl. WO 01390, 1994; Chem. Abstr. 1994,
121, P156763d.
(12) Absolute configuration at the P atom is expressed in terms of
the Cahn-Ingold-Prelog sequence rules13 and, in the case of 1, refers
to the uncoordinated ligand.

670 Organometallics, Vol. 17, No. 4, 1998
Stoop et al.
HPLC. However, the l:u diastereomeric ratio16 of 99:1
found for crude 2 affords indirect evidence that the
coupling step does not affect significantly the configu-
ration at the P atom. Column chromatography does not
improve further this diastereomeric ratio, and the crude
product is used for the deprotection step.
Reaction of 2 with morpholine at room temperature
gives free diphosphine 1 as the method of choice.17 As
borane decomplexation reactions are known to occur
with retention of configuration at the phosphorus
atoms,6 the absolute configuration S,S is assigned to 1.
1
Integration of the H NMR signals of the SiMe2 groups
of crude 1 gives a diastereomeric ratio of 99:1.19 A lower
l:u diastereomeric ratio of 93:7 is achieved under condi-
tions generally used for similar ligands (refluxing in
HNEt2 overnight).6a Removal of excess amine (Et2NH
or morpholine) under vacuum yields 1 as a viscous oil.
Pure 1 is obtained by chromatography over alumina,
which efficiently removes traces of the amine borane
adduct. By contrast, free 1 partially decomposes on
silica gel, apparently due to the cleavage of one Si-
CH2-P bond. Together with unidentified products,
large amounts of the free phosphine 3 (up to 24%) are
detected in the 31P NMR spectra of samples of 1
recovered after chromatography on silica gel.
F igu r e 1. ORTEP view of (S)-P(1-Np)(Ph)(BH3) (3).
Sch em e 2
The enantiomeric purity of 1 is determined by inte-
gration of the 31P NMR spectra of its (S)- and (R)-N,N-
dimethyl-1-phenylethylamine ((S)- and (R)-9) palladium-
(II) complexes [Pd((S)-9-C,N)((S,S)-1)]PF6 (10a ) and
[Pd((R)-9-C,N))((S,S)-1)]PF6 (10b) by a modification of
the procedure reported by Kyba and Rines.20 In a
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (S)-P (1-Np )(P h )(Me)(BH3)
P-C(1)
1.807(3)
1.823(3)
104.9(1)
103.2(2)
115.8(2)
P-C(17)
1.810(4)
1.920(4)
106.0(2)
116.9(2)
108.9(2)
P-C(7)
P-B
C(1)-P-C(7)
C(1)-P-C(17)
C(1)-P-B
C(7)-P-C(17)
C(7)-P-B
C(17)-P-B
preliminary experiment, the signals of diastereomers
(SC,SP,SP′)-, (SC,SP,RP′)-, and (SC,RP,RP′)-10 are assigned
by comparison of the 31P NMR spectra of 10a and 10b
prepared using a 92:8 l:u diastereomer mixture of 1
obtained from crude 3 (93% ee). Then, the enantio- and
diasteromeric purity of the free ligand (S,S)-1 is deter-
mined by reaction of (S,S)-1 (obtained from (S,S)-3 (ee
> 99%) using the procedure reported above) with (S)-9
and 31P NMR analysis of the diastereomer mixture of
10a . The 31P NMR spectrum of crude 10a exhibits,
along with the signals of the main diastereomer [Pd-
((S)-9-3C,N)((S,S)-1)]PF6, (SC,SP,SP′)-10a , two resolved
doublets for each (minor) isomer (SC,RP,SP′)-, (SC,-
P-B distances and slightly opened C-P-B angles, as
found in other phosphine borane adducts.14 The planes
of the naphthyl and phenyl rings are approximately
perpendicular to one another. Least-squares refinement
of the sign of ∆f ′′ (η ) +1.0(2)) supports the S config-
uration.15 This is consistent with retention of configu-
ration in step 6 f 7 and inversion in both steps 7 f 8
and 8 f 3 (Scheme 1).6
Deprotonation of phosphine borane 8 with sec-BuLi
yields LiCH2P(1-Np)(Ph)(BH3), which is then reacted in
situ with Me2SiCl2 (0.5 equiv) to give the borane-
protected diphosphine Me2Si(CH2P(Ph)(1-Np)(BH3))2
(2). Compound 2 is obtained as an amorphous solid by
evaporation of a CH2Cl2/hexane solution. The low
solubility of 2 in hexane/iPrOH mixtures prevents
determination of its enantiomeric purity using chiral
(16) By integration of the 1H NMR signals of the SiMe2 groups,
assigned by comparison with the spectra of a 1:1 mixture of (l)-2 and
(u)-2 prepared by coupling racemic phosphine borane (rac)-3 onto Me2-
SiCl2 (Scheme 2).
(17) Both deprotection with 1,3,5,7-tetraazaadamantane or 1,4-
18
diazabicyclo[2.2.2]octane (DABCO) and acid workup with [Et2OH]BF4
(13) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed.
Engl. 1966, 5, 385.
(14) (a) Huffmann, J . C.; Skupinski, W. A.; Caulton, K. G. Cryst.
Struct. Commun. 1982, 11, 1435. (b) Schmidbaur, H.; Wimmer, T.;
Lachmann, J .; Mu¨ller, G. Chem. Ber. 1991, 124, 275. (c) Schmidbaur,
H.; Stu¨tzer, A.; Bissinger, P.; Schier, A. Z. Anorg. Allg. Chem. 1993,
619, 1519.
resulted in extensive decomposition of 1 to P(1-Np)(Ph)(Me) and other
unidentified products.
(18) McKinstry, L.; Livinghouse, T. Tetrahedron Lett. 1994, 35, 9319.
(19) The signals of (l)- and (u)-1 were assigned by comparison with
the 1H NMR spectrum of a 1:1 mixture of (l)-1 and (u)-1, obtained by
deprotection of a mixture of (l)- and (u)-2 with morpholine (Scheme
2).
(15) J ones, P. G. Acta Crystallogr. 1984, A43, 660.
(20) Kyba, E. P.; Rines, S. P. J . Org. Chem. 1982, 47, 4800.

Diphosphines Containing Stereogenic P Atoms
Organometallics, Vol. 17, No. 4, 1998 671
CDCl3, 101.3 MHz), which splits up by lowering the
temperature and is resolved at -60 °C in a singlet and
an AX system (intensity ratio 58:42) for the symmetric
and asymmetric rotamers. In the 1H NMR spectrum
at -60 °C, the inequivalent naphthyl C2 protons of the
asymmetric rotamer give rise to well-resolved signals
at δ 9.50 and 10.18, whereas those of the symmetric one
appear as a multiplet centered at δ 9.39. The more
crowded 4b exhibits resolved 31P NMR signals for the
two rotamers at room temperature already.
Reaction of (S,S)-1 with [RuCl2(PPh3)3] (1:1 mole
ratio) in toluene at room temperature gives the ruthe-
nium derivative [RuCl2(PPh3)((S,S)-1)] (5), whose dark
red color is indicative of a five-coordinate structure. The
31P NMR spectrum recorded in CD2Cl2 is highly tem-
perature dependent; PPh3 partially dissociates from 5
in solution giving dimer 11, as previously observed for
other complexes of the type [RuCl2(PPh3)(P-P)] (P-P)
diphosphine) (eq 1).22
F igu r e 2. Lowest energy rotamers calculated for 4b and
relative energies. (COD not drawn in a, side view, and b
and c for clarity.)
SP,RP′)-, and (SC,RP,RP′)-10a . Integration of the signals
of (SC,SP,SP′)- and (SC,RP,RP′)-10a shows that the S,S:
R,R enantiomeric ratio of 1 is better than 99:1. The
value of 99:1 found for the l:u diastereomeric ratio,
independently found by H NMR, is confirmed by the
integration of the signals of (SC,RP,SP′)- and (SC,SP,RP′)-
10a .
The room temperature 31P NMR spectrum displays a
broadened ABX system, a broadened singlet at δ -6
(w1/2 ) 30 Hz), attributable to free PPh3 in chemical
exchange with 5, and broad signals in the δ 19-25 and
41-54 regions, which are assigned to dimer 11. The
PPh3 exchange process becomes slow on the NMR time
scale at low temperature: the 31P NMR spectrum at -40
°C consists of a sharp PPh3 singlet (w1/2 ) 2.5 Hz) and
a well-resolved ABX system. The integrated intensities
of these signals indicate that about 25% of starting 5 is
present as dimeric species,22 but the complicated pattern
of low-intensity signals in the δ 19-25 and 41-54
regions of the low-temperature 31P NMR spectra was
not analyzed. The 31P NMR parameters of 5 support a
trans arrangement of PPh3 and of one of the diphos-
phine P atoms, which is compatible with both a square-
pyramidal and a trigonal-bipyramidal structure.23 How-
ever, the red color of 5 is suggestive of a trigonal-
bipyramidal structure both in the solid state and in
solutions of noncoordinating solvents such as CH2Cl2.
The related species [RuCl2(L3)] (L3 ) PhP[(CH2)3P(c-
C6H11)2]2) undergoes a solvent-dependent isomerization
between a red trigonal-bipyramidal isomer and a green
square-pyramidal one,24 whereas [RuCl2(PPh3)(biphemp)]
is green in the solid state and dark brown in CD2Cl2
solution.22b
1
Solu tion NMR Stu d ies of 1. The resonances of the
1
naphthyl H atoms in the H NMR spectrum of free 1
were assigned by means of 2D NMR experiments, in
order to check whether complexation to a metal center
leads to hindered rotation of the 1-Np groups about the
P-C1 bond. The signals of naphthyl, phenyl, methyl-
ene, and methyl H atoms were attributed by means of
31P-1H and 13C-1H correlation and NOESY experi-
ments. The NOESY spectrum indicates that the 1-Np
group freely rotates in uncomplexed 1 in CDCl3 at room
temperature, as both naphthyl protons on C2 and C8
exhibit cross peaks to CH2P and (CH3)2Si.
Rh od iu m a n d Ru th en iu m Der iva tives. The rhod-
ium derivatives [Rh(diene)((S,S)-1)]BF4 (diene ) nor-
bornadiene, 4a ; diene ) 1,5-cyclooctadiene, 4b) are
prepared from [Rh(diene)2]BF4 and 1 in THF solution
and characterized by 1H and 31P NMR spectroscopy,
FAB+ mass spectrometry, and microanalysis. Molecular
modeling (UFF calculations based on the Cerius2 pro-
gram)21 shows that the chelate ring of 4b adopts a twist
conformation with equatorial 1-naphthyl groups (Figure
2). Hindered rotation of the 1-naphthyl groups about
the P-C1 bonds gives rise to three rotamers, a, b, and
c, with increasing calculated energies as reported in
Figure 2. The less crowded NBD derivative 4a exhibits
an analogous situation, but the energy differences
among rotamers a-c are smaller.
Rh od iu m -Ca ta lyzed Hyd r ogen a tion . Rhodium(I)
derivative 4b (0.5 mol %) catalyzes the asymmetric
hydrogenation of (acylamino)cinnamate derivatives with
high enantioselectivity (Table 2). Z-1-Methylacetami-
docinnamate (12a ) is converted to (R)-N-acetylphen-
ylalanine methylester (13a ) with 97.7% enantiomeric
excess under 1 atm of H2 at 30 °C. Z-1-Methylaceta-
midocinnamic acid (12b) is hydrogenated under similar
The solution behavior of 4a ,b is consistent with
naphthyl group rotation being slow on the NMR time
scale. The room temperature 31P NMR spectrum of 4a
(22) (a) J ung, C. W.; Garrou, P. E.; Huffman, P. R.; Caulton, K. G.
Inorg. Chem. 1984, 23, 726. (b) Mezzetti, A.; Costella, L.; Del Zotto,
A.; Rigo, P. Gazz. Chim. Ital. 1993, 123, 155 and references therein.
(23) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365.
(24) J ia, G.; Lee, I.; Meek, D. W.; Gallucci, J . C. Inorg. Chim. Acta
1990, 177, 81.
2
shows a broad doublet (w1/2 ≈ 430 Hz, J PP′ ≈ 160 Hz,
(21) (a) Rappe´, A. K.; Casewit, C. J .; Colwell, K. S.; Goddard, W. A.,
III; Skiff, W. M. J . Am. Chem. Soc. 1992, 114, 10024. (b) Rappe´, A. K.;
Colwell, K. S.; Casewit, C. J . Inorg. Chem. 1993, 32, 3438.

672 Organometallics, Vol. 17, No. 4, 1998
Stoop et al.
Ta ble 2. Asym m etr ic Hyd r ogen a tion of 12 to 13
Sch em e 3
entry
R1
R2
R3
ee (%)
config
a
Ph
Ph
H
Ph
Ph
Ph
H
H
H
Me
Me
Me
Me
Me
Me
Me
Ph
97.7
97.1
64.1
96.2
96.5
0
R
R
R
R
R
Sch em e 4
ba
c
d
e
fb
Ph
a
b
Free acid as substrate. (E) isomer as substrate.
conditions to (R)-N-acetylphenylalanine (13b) with about
the same enantioselectivity. These values are even
better than found with the dipamp/rhodium system on
the same substrates.1 High enantioselection is retained
when the free acid 12b is used provided that a small
amount of triethylamine is added (4 equiv vs 4b), a
procedure largely used in the catalytic hydrogenation
of 1-(acylamino)acrylic acids as an alternative to the use
of the corresponding esters.25 The use of the free acid
leads to a decline of the ee values in the rhodium-
catalyzed hydrogenation with the recently reported
planar chiral diphosphine 4,12-bis(diphenylphosphino)-
[2.2]-paracyclophane ([2.2]PHANEPHOS), but the au-
thors do not specify whether the addition of NEt3
improves the enantioselectivity.26
enantioselectivity (8% ee). Quantitative conversion to
(S,S)-15 (56% ee) is achieved at 80 °C under 150 bar of
H2 (Scheme 3).
Ligand 1 was also tested in the palladium-catalyzed
substitution reaction of racemic allylic acetates by soft
carbon nucleophiles. Racemic 1,3-diphenyl-3-acetoxy-
propene (16) was treated with dimethyl malonate under
standard conditions30 in the presence of 1 mol % of the
catalyst (generated in situ from [Pd2Cl2(η3-C3H5)2] and
(S,S)-1) (Scheme 4). The alkylation product (R)-17 was
obtained in nearly quantitative yield after 4 h of reaction
time at room temperature, but with low enantioselec-
tivity (27% ee). Decreasing the reaction temperature
to 0 °C lowers the enantioselectivity (10% ee).31
The system is sensitive to the substitution pattern at
the â-C atom, as often observed in related systems.
When Ph is replaced by H the enantioselectivity drops
from 97.7 (12a ) to 64.1% ee (12c). The closely related
[Rh(COD)((l)-bnpe)] (bnpe)1,2-bis(1-naphthylphenylphos-
phino)ethane) hydrogenates acetamido acrylic acid with
76% ee.27 Interestingly, increasing the steric hindrance
at the amido group by N-methylation and introducing
a benzamido group (12d ,e) is not detrimental to activity
and enantioselectivity, whereas the dipamp system
hydrogenates the free acid analogue of 12e sluggishly
and with moderate enantioselectivity.1 Reports of cata-
lytic hydrogenation of N-substituted enamides are still
rare, and the best enantioselectivity achieved does not
exceed 75%.28 The well-known loss of enantioselectivity
observed on changing from the Z to the E configuration
is particularly dramatic here: the E isomer 12f yields
racemic 13f.
Oth er Ca ta lytic Ap p lica tion s. The ruthenium(II)
derivative 5 catalyzes the hydrogenation of pentane-2,4-
dione (14) to (S,S)-pentane-2,4-diol (15) with moderate
enantioselectivity (Scheme 3). The reaction catalyzed
by 5 is generally slower than with the binap and
biphemp analogues.29 At 50 °C, the monohydrogenated
product 2-hydroxypentan-4-one is formed as the major
product (95% yield at 38% conversion) with very low
Con clu sion
Homochiral diphosphine ligands can be prepared in
good overall yields with high diastereomeric and enan-
tiomeric purity from the corresponding enantiomerically
pure phosphine boranes. Bulky substituents are found
to be effective in stabilizing the configuration of the
stereogenic P atoms. The excellent results obtained in
the rhodium-catalyzed enantioselective hydrogenation
indicate that placing a stereogenic P atom in the
immediate proximity of the metal is a successful strategy
even with a motif other than P(o-An)(Ph)(CH2R). Im-
provements in the ligand design would involve the
chemical stability and conformational rigidity of the
diphosphine bridge. Our efforts are presently directed
to developing more stable and rigid linkages between
the stereogenic P atoms and to studying the effect of
the bite angle of the diphosphine on its stereodifferen-
tiating properties, in order to enlarge the scope of these
ligands.
Exp er im en ta l Section
Gen er a l Com m en ts. Reactions with air- or moisture-
sensitive materials were carried out under an argon atmo-
(25) Zhu, G.; Cao, P.; J iang, Q.; Zhang, X. J . Am. Chem. Soc. 1997,
119, 1799 and references cited therein.
(30) (a) von Matt, P.; Pfaltz, A. Angew. Chem., Int. Ed. Engl. 1993,
32, 566. (b) Togni, A.; Breutel, C.; Schnyder, A.; Spindler, F.; Landert,
H.; Tijani, A. J . Am. Chem. Soc. 1994, 116, 4062, and references
therein.
(31) During the preparation of this paper, a communication has
appeared on the synthesis of the related ligand (R,R)-1,1′-bis(1-
naphthylphenylphosphino)ferrocene. Its application in the palladium-
catalyzed allylic alkylation gave ee values up to 73%.32
(32) Nettekoven, U.; Widhalm, M.; Kamer, P. C. J .; van Leeuwen,
P. W. N. M. Tetrahedron: Asymmetry 1997, 8, 3185.
(26) Pye, P. J .; Rossen, K.; Reamer, R. A.; Tsou, N. N.; Volante, R.
P.; Reider, P. J . J . Am. Chem. Soc. 1997, 119, 6207.
(27) Yoshikuni, T.; Bailar, J . C., J r. Inorg. Chem. 1982, 21, 2129.
(28) (a) Glaser, R.; Geresh, S.; Twaik, M. Tetrahedron 1978, 34,
3617. (b) Buser, H. P.; Pugin, B.; Spindler, F.; Sutter, M. Tetrahedron
1991, 47, 5709.
(29) Mezzetti, A.; Tschumper, A.; Consiglio, G. J . Chem. Soc, Dalton
Trans. 1995, 49 and references therein.

Diphosphines Containing Stereogenic P Atoms
Organometallics, Vol. 17, No. 4, 1998 673
sphere using Schlenk techniques. Solvents were purified
according to standard procedures; 6 was prepared according
to the literature.6a 1H and 31P positive chemical shifts in ppm
are downfield from tetramethylsilane and external 85% H3PO4,
respectively. The 1H and 31P NMR spectra of the PfBH3
borane adducts 2, 3, 7, and 8 are partially relaxed, nonbino-
mial 1:1:1:1 quartets due to coupling to 11B (80.1% natural
paste. Yield: 12.54 g (96%, crude), 93% ee (HPLC, OD-H;
hexane/iPrOH ) 99.5:0.5, tR [(S)-3] ) 39.4 min, tR [(R)-3] )
33.2 min). Enantiomerically pure (R)-3 (only the R enantiomer
detected) was obtained by recrystallization from hot hexane:
yield 10.58 g (81%); mp 110 °C; 1H NMR (CDCl3) δ 8.10-7.34
(m, 12 H, Ph, 1-Np), 2.02 (d, 3 H, PCH3, 2J PH ) 9.9 Hz), 2.05-
1
0.5 (br q, 3 H, BH3, J BH ) 93 Hz); 31P NMR (CDCl3) δ 9.5 (br
1
1
abundance); 1J BH and J PB were measured between the central
q, 1 P, J PB ) 68 Hz); [R]20 ) +43.6 ( 0.17 (CHCl3, C ) 1);
D
peaks. 2D NMR experiments (31P-1H and 13C-1H correlation,
NOESY) were carried out on a Bruker DRX 400 spectrometer
using standard pulse sequences; the phase-sensitive NOESY
experiments used mixing times of 600 ms. Mass spectra were
measured by the MS service of the Laboratorium fu¨r Orga-
nische Chemie (ETH Zu¨rich). A 3-NOBA (3-nitrobenzyl
alcohol) matrix and a Xe atom beam with a translational
energy of 8 keV were used for FAB+ MS. HPLC was performed
on a Hewlett-Packard 1050 chromatograph equipped with a
variable-wavelength detector and Daicel Chiralcel OD-H or
OB-H columns (0.46 × 25 cm). Optical rotations were
measured using a Perkin-Elmer 341 polarimeter with a 1-dm
cell. Elemental analyses were carried out by the Laboratory
of Microelemental Analysis (ETH Zu¨rich). Melting points were
measured in open capillaries with a Bu¨chi-510 apparatus and
are uncorrected.
MS (EI), m/z 264.1 (M+, 0.3), 261.1 (M+ - 3H, 13), 249.1 (M+
- CH3, 100). Anal. Calcd for C17H18BP: C, 77.31; H, 6.87.
Found: C, 77.55; H, 6.93.
X-r a y Str u ctu r e of (S)-P (1-Np )(P h )(Me)(BH3) (3). Col-
orless prismatic crystals (0.5 × 0.6 × 0.8 mm) were grown from
CH2Cl2/hexane, orthorhombic, P212121, a ) 7.406(6) Å, b )
8.630(8) Å, c ) 24.38(2) Å, V ) 1558(2) Å3, Z ) 4, Mw ) 264.1,
dc ) 1.126 Mg m-3, µ ) 0.160 mm-1, F(000) ) 560, Syntex
P21 diffractometer, Mo KR (λ ) 0.710 73 Å, graphite mono-
chromated), 3 e 2θ e 40°, ω-scan, scan speed 1.0-4.0 deg
min-1 in ω, scan range 1.0°, 1 standard reflection measured
every 120 reflections. Index ranges: -7 e h e 7, -8 e k e 8,
-23 e l e 23, 3488 reflections collected, of which 1445 were
independent (Rint ) 3.3%) and 1374 observed (F g 4.0 σ). No
correction for absorption was performed. The structure was
solved and refined using direct methods with Siemens SHELX-
TL PLUS (VMS). In the full-matrix least squares, the quantity
minimized was ∑w(Fo - Fc)2. The absolute structure was
(S P ,1R ,2S )-P (N(Me )CH (Me )CH (P h )OH )(1-Np )(P h )-
(BH3) (7). A cooled THF solution (-78 °C) of 1-naphthyl-
lithium (82.9 mmol) (freshly prepared from 17.2 g of 1-bro-
monaphthalene (82.9 mmol) dissolved in THF (17 mL) and 51.8
mL of a 1.6 M hexane solution of BuLi (82.9 mmol) at -78 °C)
was added by cannula to a THF solution (53 mL) of 6 (18.1912
g, 63.8 mmol) precooled at -78 °C. After stirring for 30 min
at -78 °C, the resulting yellow creamy mixture was allowed
to warm to room temperature. The cloudy orange solution was
quenched with H2O (40 mL), and the THF was then evapo-
rated. The product was extracted with CH2Cl2 and dried over
MgSO4. Evaporation of the solvent and flash chromatography
(silica gel, toluene/AcOEt (95:5)) yielded crude 7 as a pale
yellow oil. Yield: 26.01 g (99%). Recrystallization from
toluene/hexane yielded pure 7: yield 22.70 g (82%); mp 115
determined by the η method using atomic scattering factors
anomal
of the type fo
) fo + ∆f ′ + iη∆f ′′; refinements gave η )
1.0(2) for the S configuration irrespective of the starting value
of η (+1 or -1). An extinction correction was performed
according to F* ) F[1 + 0.002øF2/sin(2θ)]-1/4, where ø )
0.0064(9). The H atom contribution was held constant (riding
model, fixed anisotropic U). The weighting scheme was w-1
) σ2(F) + 0.0051F2, and 246 parameters were refined. The
final refinement cycle gave R ) 2.7%, Rw ) 3.6% (observed
data), goodness of fit 0.50, largest and mean ∆/σ 0.331 and
0.048, data-to-parameter ratio 5.6:1, largest positive and
negative difference peaks 0.20 and -0.27 e Å-3
.
(S,S)-Me2Si(CH2P (1-Np )(P h )(BH 3))2 (2). A hexane solu-
tion (15.2 mL, 1.38 M) of sec-BuLi (21.0 mmol; 1.1 equiv vs 3)
was added dropwise over a period of 20 min to a THF solution
(54 mL) of 3 (5.05 g, 19.1 mmol) at -78 °C. After the solution
was stirred for 2 h, Me2SiCl2 (1.153 mL, 9.56 mmol; 0.5 equiv
vs 3) was added rapidly via syringe, and the resulting solution
was allowed to reach room temperature (17 h). The reaction
was quenched with 2 M HCl (30 mL), and the THF was
removed under vacuum. The product was extracted with CH2-
Cl2 from the aqueous phase, washed with K2CO3, and dried
over MgSO4. Evaporation of the solvent gave 2 as an oil.
Evaporation under vacuum of a hexane/CH2Cl2 solution gave
1
°C; H NMR (CDCl3) δ 8.27-7.17 (m, 17 H, Ph, 1-Np), 5.03-
5.01 (m, 1 H, CH(Ph)OH), 4.58-4.44 (m, 1 H, NCHMe), 2.64
(d, 3 H, NCH3, 3J PH ) 7.5 Hz), 1.31 (d, 3 H, CH3NCHCH3, 3J HH′
1
) 6.9 Hz); 31P NMR (CDCl3) δ 70.2 (br q, 1 P, J PB ) 54 Hz);
[R]20 ) 78.9 ( 0.26 (CHCl3, C ) 1). Anal. Calcd for C26H29
-
D
NOBP: C, 75.56; H, 7.07; N, 3.39. Found: C, 75.69; H, 7.16;
N, 3.29.
(R)-P (OMe)(1-Np )(P h )(BH3) ((R)-8). Concentrated H2SO4
(6.13 g, 3.35 mL, 62.5 mmol) was added to a MeOH solution
(500 mL) of 7 (25.81 g, 62.5 mmol), and the solution was stirred
overnight. Evaporation of the solvent and flash chromatog-
raphy (silica gel, hexane/AcOEt (95:5)) gave the analytically
pure product as a thick oil. Yield: 13.10 g (75%, crude).
Enantiomeric purity: 92.1% ee (HPLC, OD-H; hexane/iPrOH
(99.5:0.5), tR [(R)-8] ) 17.8 min, tR [(S)-8] ) 19.1 min).
Enantiomerically pure (R)-8 (only the R enantiomer detected)
was obtained by recrystallization from hot hexane: yield 10.50
g (60%); mp 82 °C; 1H NMR (CDCl3) δ 8.33-7.36 (m, 12 H,
a hard white foam: yield 5.48 g (98%); 1H NMR (CDCl3) δ 8.2-
2
7.2 (m, 24 H, Ph, 1-Np), 1.89 (d × d, 2 H, SiCHH′P, J HH′
)
)
)
2
2
14.0 Hz, J PH ) 16.1 Hz), 1.68 (d × d, 2 H, SiCHH ′P, J HH′
14.0 Hz, J PH′ ) 13.6 Hz), -0.37 (s, 6 H, Si(CH3)2); [R]20
2
D
-34.7 ( 0.15 (C ) 1); 31P NMR (CDCl3) δ 12.9 (br s, 2 P); MS
(EI), m/z 584.5 (M+, 0.2), 569.3 (M+ - BH3, 2), 556.3 (M+
-
2BH3, 2), 479.2 (M+ - Ph, 3), 429.2 (M+ - 1-Np, 11), 353.2
M+ - 1-Np - Ph, 4), 321.2 (M+ - P(1-Np)(Ph), 5), 307.2 (M+
- P(1-Np)(Ph)(CH2), 7), 249.2 (M+ - P(1-Np)(Ph)(CH2SiMe2),
9), 171.1 (P(1-Np)(CH2), 28), 135.1 (SiMe2(Ph), 100), 185.2
(SiMe2(1-Np), 61). Anal. Calcd for C36H40B2P2Si: C, 73.99;
H, 6.90. Found: C, 73.99; H, 7.13.
3
Ph, 1-Np), 3.79 (d, 3 H, POCH3, J PH ) 12.2 Hz), 1.95-0.5 (q,
1
3 H, BH3, J BH ) 82 Hz); 31P NMR (CDCl3) δ 110.4 (br q, 1 P,
1J PB ) 79 Hz); [R]20 ) -22.9 ( 0.25 (CHCl3, C ) 1); MS (EI),
D
m/z 277.1 (M+ - 3H, 9), 266.1 (M+ - BH3, 100), 251.1 (M+
-
BH3 - CH3, 54). Anal. Calcd for C17H18OBP: C, 72.89; H,
6.48. Found: C, 72.66; H, 6.19.
(S,S)-Me2Si(CH2P (1-Np )(P h ))2 ((S,S)-1). Compound 2
(1.32 g, 2.26 mmol) was dissolved in morpholine (70 mL), and
the colorless solution was stirred overnight at room temper-
ature. The resulting white precipitate was filtered off, and
the yellowish solution was evaporated to dryness. Flash
chromatography (alumina, toluene as eluent) yielded 1 as a
colorless oil: yield 0.98 g (78%); 1H NMR (CDCl3) δ 8.60-8.54
(m, 2 H, naphthyl C2-H), 7.85-7.17 (m, 22 H, Ph, other 1-Np),
1.6-1.2 (m, 4 H, SiCH2P), -0.19 (s, 6 H, Si(CH3)2); 31P NMR
(S)-P (1-Np )(P h )(Me)(BH3) (3). A hexane solution (49.4
mL, 1.6 M) of MeLi (79.0 mmol; 1.6 equiv vs 8) was added
dropwise to a THF solution (42 mL) of 8 (13.83 g, 49.4 mmol)
at -40 °C. After 1 h of stirring at -40 °C, the solution was
allowed to slowly reach room temperature (10 h). The reaction
was quenched with H2O (60 mL), and the THF was removed
under vacuum. The crude product was extracted with CH2-
Cl2 and dried over MgSO4: removal of the solvent gave a white

674 Organometallics, Vol. 17, No. 4, 1998
Stoop et al.
2
2
(CDCl3) δ -35.74 (s, 2 P); MS (EI), m/z 556.3 (M+, 19), 479.2
(M+ - Ph, 20), 429.2 (M+ - 1-Np, 60), 352.4 M+ - 1-Np - Ph,
trace), 321.4 (M+ - (1-Np)P(Ph), 12), 307.4 (M+ - CH2P(1-
Np)(Ph), 16), 249.3 (M+ - Me2Si(CH2P(1-Np)(Ph)), 19), 171.1
(CH2P(1-Np), 36), 135.1 (Me2Si(Ph), 100), 185.2 (Me2Si(1-Np),
95).
33.21 (d, 1 P, J PP′ ) 45.0 Hz), 11.82 (d, 1 P, J PP′ ) 45.0 Hz);
2
SC,RP,RP′ isomer δ 26.05 (d, 1 P, J PP′ ) 41.0 Hz), 4.24 (d, 1 P,
2J PP′ ) 41.0 Hz); SC,SP,RP′ + SC,RP,SP′ isomers δ 30.6 (d, 1 P,
2J PP′ ) 41.1 Hz), 29.8 (d, 1 P, 2J PP′ ) 41.7 Hz), 7.8 (d, 1 P, 2J PP′
) 41.1), 7.1 (d, 1 P, J PP′ ) 41.7). MS (FAB+): m/z 810.2 (M+,
2
64), 661.1 (M+ - C10H15N, 35), 391.2 (C23H25P2Si+, 100). [Pd-
((R)-9-C,N)((S,S)-1)]PF6 (10b) was prepared and characterized
analogously.
(r a c)-P (NEt2)(1-Np )(P h ). A cooled (-78 °C) THF solution
of 1-naphthyllithium (44 mmol) (prepared by dropwise addition
of a 1.6 M hexane solution of BuLi (27.9 mL, 44.6 mmol) to a
cooled (-78 °C) THF solution (17 mL) of 1-bromonaphthyl (9.2
g, 44.4 mmol)) was added by cannula to a solution of P(Cl)-
(NEt2)(Ph) (9.0 g, 41.5 mmol) in THF (53 mL) at -78 °C. The
mixture was stirred for 30 min at -78 °C; the resulting yellow
creamy mixture was then allowed to warm to room tempera-
ture. The reaction was quenched with H2O (5 mL), and THF
was removed under vacuum. The crude product was extracted
with CH2Cl2, dried over MgSO4, and distilled: yield 10.6 g
[Rh (NBD)((S,S)-1)]BF 4 (4a ). [Rh(NBD)2]BF4 (95 mg, 0.26
mmol) and (S,S)-1 (142 mg, 0.26 mmol) were dissolved in
CH2Cl2 (8 mL), and the resulting solution was stirred overnight
at room temperature. tBuOMe (10 mL) was added, and the
solution was then concentrated under vacuum. A yellow
precipitate was formed, filtered off, and dried in vacuo. The
1H NMR spectrum shows the presence of 0.5 mol of BuOMe/
t
mol of 1: yield 181 mg (81%); mp 154 °C; 1H NMR (CDCl3,
293 K) δ 9.1 (br, 2 H, naphthyl C2-H), 8.23-7.15 (m, 22 H,
Ph, other 1-Np), 4.76 (br, 2 H, bridgehead CH), 4.07 (br, 2 H,
dCH), 3.98 (br, 2 H, dCH), 1.97-1.60 (m, 4 H, PCH2), 1.53
(br s, 2 H, bridging CH2), -1.17 (br s, 6 H, Si(CH3)2); 31P NMR
(82%); 1H (CDCl3) δ 8.25-7.26 (m, 12 H, Ph, 1-Np), 3.24-3.11
3
(m, 4 H, P(NCH2CH3)2), 0.91 (t, 6 H, P(NCH2CH3)2, J HH′
)
7.1 Hz); 31P NMR (CDCl3) δ 53.5 (s, P); MS (EI), m/z 307.2
(M+, 85), 235.1 (M+ - NEt2, 91), 233.1 (M+ - NEt2 - 2H, 100),
180.1 (M+ - 1-Np, 39), 166.1 (M+ - 1-Np - CH2, 89). Anal.
Calcd for C20H22NP: C, 78.15; H, 7.21; N, 4.56. Found: C,
77.61; H, 7.45; N, 4.56.
(CDCl3, 293 K) δ 18.0 (br d, 2 P, J RhP ) 160 Hz). 1H NMR
1
(CD2Cl2, 213 K): rotamer a δ 9.43-9.35 (m, 2 H, naphthyl
C2-H), 4.87 (br, 2 H, bridgehead CH), 3.91 (br, 2 H, dCH), 3.78
(br, 2 H, dCH), -1.38 (s, 6 H, Si(CH3)2); rotamer b δ 10.18 (br
d, 1 H, naphthyl C2-H), 9.50 (br dd, 1 H, naphthyl C2-H ′), 4.56
(br, 1 H, bridgehead CH), 3.95-3.57 (m, 4 H, dCH), -1.08 (s,
3 H, Si(CH3)), -1.39 (s, 3 H, Si(CH′3)). 31P NMR (CD2Cl2, 213
K): rotamer a (58%) δ 21.26 (d, 2 P, 1J RhP ) 157.6 Hz); rotamer
b (42%) δ 21.21 (dd, 1 P, J RhP ) 151.3 Hz, J PP′ ) 36.8 Hz),
11.00 (dd, 1 P, 1J RhP ) 159.6 Hz, 2J PP′ ) 36.8 Hz). MS (FAB+)
m/z 751.2 (M+, 100), 657.1 (M+ - NBD - H, 30). Anal. Calcd
for C44H46BF4P2SiRh‚0.5C5H12O: C, 61.92; H, 5.48. Found: C,
61.20; H, 5.61.
(r a c)-P (OMe)(1-Np )(P h )(BH3) ((r a c)-8). HCl gas was
bubbled through a MeOH solution (50 mL) of P(NEt2)(1-Np)-
(Ph) (10.0 g, 32.5 mmol) until complete esterification was
achieved as evidenced by 31P NMR spectroscopy. The solvent
was evaporated, the residue was dissolved in toluene (20 mL),
and dimethyl sulfide borane (3.2 mL, 32.5 mmol) was then
added at room temperature. The resulting solution was stirred
for 2 h and then concentrated. The crude product was
recrystallized from toluene at 4 °C. Yield: 7.0 g (77%).
Analytic and spectroscopic properties are as given for (R)-8.
(r a c)-P (1-Np )(P h )(Me)(BH3) ((r a c)-3). A 1.6 M hexane
solution of MeLi (14.5 mL, 23.2 mmol) was added dropwise to
a solution of (rac)-8 (6.00 g, 21.4 mmol) in 20 mL of THF at
-78 °C. The mixture was allowed to reach room temperature
within 2 h. The reaction was quenched with 50 mL of H2O,
and the THF was removed under vacuum. The crude product
was extracted with CH2Cl2, dried over MgSO4, and recrystal-
lized from Et2O/hexane. Yield: 5.3 g (94%). Analytic and
spectroscopic properties are as given for (S)-3.
(l)- + (u )-Me2Si(CH2P (1-Np )(P h )(BH3))2 ((l)- + (u )-2). A
1.6 M hexane solution of BuLi (8.0 mL, 12.8 mmol) was added
dropwise to a THF solution (15 mL) of (rac)-3 (3.0 g, 11.4
mmol). After stirring for 2 h at -78 °C, Me2SiCl2 (0.65 mL,
5.4 mmol) was added thereto, and the resulting solution was
allowed to reach room temperature. Workup was the same
as for (S,S)-2. Yield: 2.5 g (79%). 1H NMR (CDCl3): u isomer
(50%) δ -0.29 (s, 3 H, SiCH3), -0.46 (s, 3 H, SiCH ′3); l isomer
(50%) δ -0.37 (s, 6 H, Si(CH3)2). 31P NMR (CDCl3): δ 13.4
(br, l and u isomers not resolved). Analytic and MS properties
are as given for (S,S)-2.
(l)- + (u )-Me2Si(CH2P (1-Np )(P h ))2 ((l)- + (u )-1). Depro-
tection was carried out as described above for (S,S)-1. 1H NMR
(CDCl3): u isomer (50%) δ -0.18 (s, 3 H, SiCH3), -0.22 (s, 3
H, SiCH ′3); l isomer (50%) δ -0.19 (s, 6 H, Si(CH3)2). 31P NMR
(CDCl3): l isomer (50%) δ -35.74 (s, 2 P); u isomer (50%) δ
-35.67 (s, 2 P). Analytic and MS properties are as given for
(S,S)-1.
[P d ((S)-d im eth yl(1-m eth ylben zyl)a m in a to-C,N)((S,S)-
1)]P F 6 (10a ). A solution of 1 (114 mg, 0.205 mmol) in 5 mL
of CH2Cl2 was added to a solution of bis(µ-chloro)bis[(S)-
dimethyl(1-methylbenzyl)aminato-C,N]dipalladium(II) (60 mg,
0.102 mmol) in 5 mL of MeOH. After the resulting clear yellow
mixture was stirred for 12 h, TlPF6 (43 mg, 0.122 mmol) was
added. Additional stirring overnight, filtration over Celite, and
evaporation to dryness gave a pale yellow solid. The residue
was extracted with CD2Cl2, and the 31P NMR spectrum of the
solution was recorded. 31P NMR (CDCl3): SC,SP,SP′ isomer δ
1
2
[Rh (COD)((S,S)-1)]BF 4 (4b). [Rh(COD)2]BF4 (190 mg,
0.467 mmol) and (S,S)-1 (260 mg, 0.467 mmol) were dissolved
in THF (8 mL), and the resulting solution was stirred for 7 h
at room temperature. Evaporation of the solvent gave a yellow
solid, which was washed with hot hexane and dried in vacuo:
yield 0.37 g (92%); mp 181 °C. 1H NMR (CDCl3): rotamer a δ
9.68-9.59 (m, 2 H, naphthyl C2-H), 4.86 (br, 2 H, dCH), 4.01
(br, 2 H, dCH), -1.35 (s, 6 H, Si(CH3)2); rotamer b δ 10.65
(br, 1 H, naphthyl C2-H), 9.74 (br, 1 H, naphthyl C2-H ′), 4.90
(br, 1 H, dCH), 4.61 (br, 1 H, dCH), 4.23 (br, 1 H, dCH), 3.84
(br, 1 H, dCH), -0.92 (s, 3 H, SiCH3). 31P NMR (CDCl3):
1
rotamer a (61%) δ 17.60 (d, 2 P, J RhP ) 144.7 Hz); rotamer b
(39%) δ 15.36 (dd, 1 P, 1J RhP ) 144.7 Hz, 2J PP′ ) 33.2 Hz), 7.09
(dd, 1 P, J RhP ) 144.7 Hz, J PP′ ) 33.2 Hz). MS (FAB+): m/z
1
2
767.2 (M+, 100), 659.1 (M+ - COD, 86). Anal. Calcd for
C
44H46BF4P2SiRh‚H2O: C, 60.56; H, 5.54. Found: C, 60.46;
H, 5.58. The presence of water was evidenced by IR spectros-
copy (3420 cm-1, br, KBr pellet).
[Ru Cl2(P P h 3)((S,S)-1)] (5). [RuCl2(PPh3)3] (1.018 g, 1.061
mmol) and (S,S)-1 (0.650 g, 1.17 mmol) were dissolved in
toluene, and the resulting solution was stirred at room
temperature for 24 h. Addition of hexane and partial evapora-
tion of the solvent yielded dark red microcrystals, which were
recrystallized from CH2Cl2/hexane: yield 1.05 g (89%); mp 140
1
°C; H NMR (CDCl3) δ 8.1-6.0 (m, 39 H, Ph, 1-Np), 2.0-1.4
(m, 4 H, (PCH2)2Si), -0.2 (s, 6 H, (CH3)2Si); 31P NMR (CD2Cl2,
-40 °C) ABX system, δA 39.7 (2J AB ) 303.5 Hz, J AX ) 28.7
2
Hz), δB 35.2 (2J BX ) 39.6 Hz), δX 103.8; MS (FAB+), m/z 919.18
(M+ - 2Cl - H, 43), 692.06 (M+ - Cl - H - PPh3, 34), 657.09
(M+ - 2Cl - H - PPh3, 100). Anal. Calcd for C54H49Cl2P3-
SiRu: C, 65.45; H, 4.98; Cl, 7.16. Found: C, 65.85; H, 5.02;
Cl, 6.99.
En a n tioselective Hyd r ogen a tion w ith 4b. The stan-
dard procedure was as follows: the substrate (1.64 mmol) and
4b (6.9 mg, 8.2 µmol, 0.5 mol %) were dissolved in 10 mL of
MeOH under argon. The solution was stirred for 15 min and
then transferred via a steel capillary into a 180-mL glass
reactor thermostated at 30 °C. The inert gas was then

Diphosphines Containing Stereogenic P Atoms
Organometallics, Vol. 17, No. 4, 1998 675
replaced by hydrogen (three cycles), and the pressure was set
at 1.0 bar. After completion of the reaction (total reaction
times 16-65 h), the conversion was found to be quantitative
by gas chromatography, and the product was isolated in ca.
100% yield after filtration of the reaction solution on a plug of
silica to remove the catalyst. An analogous procedure was
followed for the hydrogenation of 12b using 1 mol % of catalyst
and adding NEt3 (5 µL, 4 equiv vs Rh) to the reaction solution.
The enantiomeric purities of 13a -c were determined by GC
(L-Chirasil-Val column, on column injection), those of 13d -f
by HPLC (Chiracel OD-H column, eluent: hexane/iPrOH). The
enantiomeric purity of 13b was determined by GC after
conversion to the methyl ester 13a . Further details are given
in the Supporting Information.
En a n tioselective Hyd r ogen a tion w ith 5. All manipula-
tions involving solutions of 5 were performed in a glovebox
under an atmosphere of purified nitrogen. A typical procedure
consisted of transferring 5 (49.5 mg, 50 µmol), weighed in a
glass insert, into the glovebox, adding pentane-2,4-dione (10.0
g, 99.9 mmol) and ethanol (10.0 g), and inserting the glass
vessel into a 250-mL steel autoclave, which was then closed
off and taken out of the box. The lines were flushed several
times with hydrogen before the autoclave was connected to
the hydrogen source (99.9999%). The nitrogen in the autoclave
was then replaced by three cycles of pressurization with 50
bar of hydrogen followed by careful ventilation. The required
pressure was introduced, the autoclave was transferred into
a thermostatic oil bath equipped for mechanical stirring, and
the hydrogen pressure vs time data collection was started.
After initial equilibration of the system (about 15-30 min),
the progress of the reaction was monitored by the decrease of
the H2 pressure.
determined by comparison of the sign of optical rotation
(Perkin-Elmer 241 polarimeter) with that reported.33
P a lla d iu m -Ca ta lyzed Allylic Alk yla tion . The ligand
(S,S)-1 (8.2 mg, 0.015 mmol) and [Pd2Cl2(η3-C3H5)2] (1.8 mg,
4.9 µmol) were dissolved in 5 mL of freshly distilled CH2Cl2
under an Ar atmosphere. Racemic 1,3-diphenyl-1-acetoxypro-
pene (81.2 mg, 0.322 mmol), dimethyl malonate (85.0 mg, 0.644
mmol), N,O-bis(trimethylsilyl)acetamide (131 mg, 0.644 mmol),
and potassium acetate (4.7 mg, 0.048 mmol) were then added
in that order, and the reaction was monitored by thin-layer
chromatography (eluent: ethyl acetate/hexane, 1:5 by volume;
product 17, Rf 0.29). No starting material 16 was detected
after 4 h. After 24 h the orange slurry was filtered and the
filtrate was concentrated under reduced pressure. Column
chromatography on silica gel (same eluent as for TLC) yielded
99.2 mg (0.306 mmol, 95%) of 17 as a colorless oil, which
solidified upon standing at -20 °C. The enantiomeric purity
was determined by HPLC (Daicel Chiralcel OD-H column,
hexane/iPrOH (98:2), flow 0.5 mL/min, tR[(R)-17] ) 18.3 min,
tR[(S)-17] ) 19.6 min). The absolute configuration was deter-
mined by the sign of optical rotation. Enantiomeric excesses
were 27% (20 °C) and 10% (0 °C).
Ack n ow led gm en t. A.M. thanks the Swiss National
Science Foundation for financial support. The authors
are grateful to Dr. V. Gramlich (Institut fu¨r Kristallog-
raphie und Petrographie, ETH Zu¨rich) for the X-ray
crystallographic analysis, to Mr. S. Chaloupka (LAC,
ETHZ) for the synthesis of the racemic phosphine
borane, to Mrs. A. Holderer and Mrs. A. Markovic for
performing the catalytic hydrogenation reactions, and
to Mr. U. Burckhardt (LAC, ETHZ) for experimental
assistance with the alkylation reactions.
The clear, red reaction solutions were then analyzed by GC
using a Carlo Erba GC 6000 gas chromatograph equipped with
a 50-m cross-linked methyl silicon gum capillary column. The
enantiomeric excesses were determined by GC analysis of the
distilled products using an HP 5890 gas chromatograph
equipped with a 50-m Lipodex C chiral column (T ) 90 °C,
isothermic, 120 kPa H2 carrier, split 1:50, tR[(R,S)-15] ) 28.20
min, tR[(R,R)-15] ) 30.40 min, tR[(S,S)-15 ) 32.61 min). The
absolute configuration of the hydrogenation products was
Su p p or tin g In for m a tion Ava ila ble: A listing of atomic
coordinates, anisotropic displacement coefficients, bond dis-
tances and angles, and H atom coordinates (5 pages). Ordering
information is given on any current masthead page.
OM970539E
(33) Ito, K.; Harada, T.; Tai, A. Bull. Chem. Soc. J pn. 1980, 53, 3367.