Ferrocenyl diphosphines containing stereogenic phosphorus atoms. Synthesis and application in the rhodium-catalyzed asymmetric hydrogenation

Article abstract of DOI:10.1021/om980754a

Enantiomerically pure (R)-2-methoxyphenyl(phenyl)-O-methylphosphinite borane (1a) and CR)-1-naphthyl(phenyl)-O-methylphosphinite borane (1b) react with 1,1′-dilithioferrocene to give (S,S)-1,1′-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene borane (2a) an

Full text of DOI:10.1021/om980754a

Organometallics 1999, 18, 1041-1049
1041
F er r ocen yl Dip h osp h in es Con ta in in g Ster eogen ic
P h osp h or u s Atom s. Syn th esis a n d Ap p lica tion in th e
Rh od iu m -Ca ta lyzed Asym m etr ic Hyd r ogen a tion
Francesca Maienza, Michael Wo¨rle,† Pascal Steffanut,‡ and Antonio Mezzetti*
Laboratorium fu¨r Anorganische Chemie, ETH-Zentrum, CH-8092 Zu¨rich, Switzerland
Felix Spindler
Scientific Services, Novartis Services Ltd, CH-4002 Basle, Switzerland
Received September 7, 1998
Enantiomerically pure (R)-2-methoxyphenyl(phenyl)-O-methylphosphinite borane (1a ) and
(R)-1-naphthyl(phenyl)-O-methylphosphinite borane (1b) react with 1,1′-dilithioferrocene to
give (S,S)-1,1′-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene borane (2a ) and (S,S)-1,1′-
bis(1-naphthyl(phenyl)phosphino)ferrocene borane (2b). Deboranation with morpholine yields
the diphosphines (S,S)-1,1′-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene (3a ) and (S,S)-
1,1′-bis(1-naphthyl(phenyl)phosphino)ferrocene (3b) in high yields and high diastereo- and
enantiomeric purity, as determined on the corresponding phosphine oxides 4a ,b. X-ray
investigations support the (S,S) configuration of 2a and disclose the coordination properties
of 3a in the platinum derivative [PtCl2(3a )] (5a ). The rhodium(I) derivatives [Rh(COD)-
(3a ,b)]BF4 (6a ,b) have been prepared and tested in the enantioselective catalytic hydrogena-
tion of various olefins and ketones. Excellent enantioselectivity is achieved in the asymmetric
hydrogenation of methyl (Z)-R-N-methyl-acetamidocinnamate to (R)-N-methyl-N-acetyl-
phenylalanine methyl ester with 6a (97% ee). Methyl (Z)-R-acetamidocinnamate is hydro-
genated to (R)-N-acetylphenylalanine methyl ester with up to 96% ee with 6b as the catalyst.
In tr od u ction
Some of the new synthetic methods exploit the dia-
stereoselective formation of a cyclic phospholidine in-
termediate3 (or related compounds)6 with a bifunctional
chiral auxiliary, in which the configuration at the P
atom is stabilized by a protecting group X. The latter
can be BH3,3a-c oxide,3d or sulfide.3e Among these, the
synthetic procedure for enantiomerically pure phosphine
boranes, developed by J uge´ (Scheme 1) starting from
the pioneering work by Imamoto,7 offers several advan-
tages in terms of chemical and configurational stability,
ease of purification and deprotection, and extension to
various substituents R.5f A further advantage is that
the intermediate phosphinite boranes P(Ph)(R)(OMe)-
(BH3) allow nucleophilic substitution at the P atom with
retention of configuration.3g
Since the early introduction of DIPAMP in the pool
of chiral ligands for enantioselective catalysis,1 the
development of diphosphines containing stereogenic P
atoms has been hampered by the lack of amenable
synthetic protocols fulfilling the requirements of large-
scale preparations.2 However, despite the apparent
oblivion, several research groups have been developing
procedures for the synthesis of enantiomerically pure
P-chiral phosphines.3,4 These investigations have been
paving the way for a number of recent applications of
P-chiral diphosphines in enantioselective catalysis.5
* To whom correspondence should be addressed. E-mail: mezzetti@
inorg.chem.ethz.ch.
† X-ray structural studies of (S,S)-2a and 5a .
‡ For the synthesis and characterization of complex 5a .
(1) Vineyard, B. D.; Knowles, W. S.; Sabacky, M. J .; Bachmann, G.
L.; Weinkauff, D. J . J . Chem. Am. Soc. 1977, 99, 5946.
(2) (a) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94, 1375.
(b) Ohff, M.; Holz, J .; Quirmbach, M.; Bo¨rner, A. Synthesis 1998, 1391.
(3) (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 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. (d) Carey, J . V.; Barker, M. D.; Brown, J . M.;
Russell, M. J . H. J . Chem. Soc., Perkin Trans. 1 1993, 831. (e) Corey,
E. J .; Zhuoliang, C.; Tanoury, G. J . J . Am. Chem. Soc. 1993, 115, 11000.
(f) Kaloun, E. B.; Merde`s, R.; Geneˆt, J . P.; Uziel, J .; J uge´, S. J .
Organomet. Chem. 1997, 529, 455 (g) Brown, J . M.; Laing, J . C. P. J .
Organomet. Chem. 1997, 529, 435. (h) Brunet, J .-J .; Chauvin, R.;
Commenges, G.; Donnadieu, B.; Leglaye, P. Organometallics 1996, 15,
1752. (i) Brodie, N.; J uge´, S. Inorg. Chem. 1998, 37, 2438.
(4) For methods based on enantioselective deprotonation, see: (a)
Muci, A. R.; Campos, K. R.; Evans, D. A. J . Am. Chem. Soc. 1995, 117,
9075. (b) Wolfe, B.; Livinghouse, T. J . Am. Chem. Soc. 1998, 120, 5116.
(5) (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]. (d) Zhu, G. X.; Terry, M.; Zhang, X. M. Tetrahedron
Lett. 1996, 37, 4475. (e) Robin, F.; Mercier, F.; Ricard, L.; Mathey, F.;
Spagnol, M. Chem. Eur. J . 1997, 3, 1365. (f) Stoop, R. M.; Mezzetti,
A.; Spindler, F. Organometallics 1998, 17, 668. (g) Imamoto, T.;
Watanabe, J .; Wada, Y.; Masuda, H.; Yamada, H.; Tsuruta, H.;
Matsukawa, S.; Yamaguchi, K. J . Am. Chem. Soc. 1998, 120, 1635.
(6) Hersh, W. H.; Xu, P.; Simpson, C. K.; Wood, T.; Rheingold, A. L.
Inorg. Chem. 1998, 37, 384.
(7) Imamoto, T.; Oshiki, T.; Onozawa, T.; Kusumoto, T.; Kazuhiko,
S. J . Am. Chem. Soc. 1990, 112, 5244.
10.1021/om980754a CCC: $18.00 © 1999 American Chemical Society
Publication on Web 02/25/1999

1042 Organometallics, Vol. 18, No. 6, 1999
Maienza et al.
Sch em e 1
Sch em e 2
Previous work from these laboratories showed that
highly enantioselective asymmetric hydrogenation of
dehydroamino acids is achieved with the ligand (S,S)-
Me2Si(CH2P(1-Np)(Ph))2 (1-Np ) 1-naphthyl), based on
a silane bridge.5f However, as major drawbacks, this
ligand could not be crystallized and is susceptible to
cleavage at the silane bridge. These drawbacks sug-
gested the use of the 1,1′-ferrocenediyl moiety as
diphosphine bridge, since ferrocenyl phosphines are
generally chemically stable, crystalline solids. As a
further advantage, 1,1′-(diphosphino)ferrocenes exhibit
large bite angles (typically about 100° for dppf com-
plexes).8 Thus, we have been developing a general
procedure for the introduction of two stereogenic P
atoms into a 1,1-ferrocenediyl moiety by nucleophilic
substitution of 1,1′-dilithioferrocene onto the phosphin-
ite boranes P(Ar)(Ph)(OMe)(BH3), which extends a
synthetic pathway recently devised by Brown for the
synthesis of monodentate, P-chiral ferrocenyl phos-
phines.3g The development of this approach allowed us
to prepare the ligands (S,S)-1,1′-bis(2-methoxyphenyl-
(phenyl)phosphino)ferrocene (3a ) and (S,S)-1,1′-bis(1-
naphthyl(phenyl)phosphino)ferrocene (3b) in excellent
enantiomeric purity and high to moderate yield. We
report herein the full characterization of 3a ,b and their
application in the enantioselective Rh-catalyzed hydro-
genation of various substrates. Preliminary reports of
the use of 3a ,b in asymmetric hydrogenation9a,d-f and
allylic alkylation9b,c have appeared.
recovered from the reaction mixture in 72% and 20%
chemical yield, respectively. As observed for analogous
nucleophilic substitutions,3a-c the reaction occurs with
inversion of configuration at the P atom, as supported
by an X-ray study of (S,S)-2a (see below). In the case of
the naphthyl derivative (R)-1b, only (l)-2b is formed,
albeit in lower chemical yield (48%). The free diphos-
phines 3a ,b are obtained by deboranation of 2a ,b with
morpholine at room temperature. Column chromatog-
raphy yields analytically and enantiomerically pure
(S,S)-3a ,b.10
To ascertain the diastereomeric composition and the
enantiomeric purity of the reaction products, we pre-
pared a diastereomeric mixture of (l)- and (u)-2a .
Treatment of 1,1′-dilithioferrocene with (rac)-1a (see
Experimental Section) in 2:1 mole ratio gave both
diastereomers of 2a , which were isolated from the
reaction mixture in an approximate (l):(u) ratio of 3:1.
As the introduction of the second stereocenter occurs
with significant diastereoselectivity, the epimerization
observed in the reaction of (S,S)-1a apparently occurs
in the first substitution step. The diastereomeric mix-
ture was then separated by column chromatography into
pure (l)-2a and (u)-2a . 1H and 31P NMR spectroscopies,
FAB+ MS, and elemental analysis support the chemical
identity of the latter. Deboranation as described above
converts (S,S)+(R,R)-2a into (S,S)+(R,R)-3a .
Since low solubility precluded the use of HPLC on the
chiral column, the enantiomeric purity of ligands (S,S)-
3a ,b was determined by 31P NMR spectroscopy on the
corresponding phosphine oxides. The diphosphines (S,S)-
3a ,b were oxidized with H2O2 to (R,R)-1,1′-bis(P-oxo-2-
methoxyphenyl(phenyl)phosphino)ferrocene, (R,R)-(4a )
and (R,R)-1,1′-bis(P-oxo-1-naphthyl(phenyl)phosphino)-
ferrocene, (R,R)-(4b), respectively.12 In the presence of
the chiral solvating agent (S)-(+)-2,2,2-trifluoro-1-(9-
anthryl)ethanol, (R,R)- and (S,S)-4a ,b form diastereo-
meric adducts with resolved 31P NMR signals, whose
integration shows that no more than 1% (S,S)-4a ,b is
present.13
Resu lts a n d Discu ssion
Syn t h esis of (S,S)-2a a n d (S,S)-2b . 1,1′-Dilithio-
ferrocene reacts with (R)-2-methoxyphenyl(phenyl)-O-
methylphosphinite borane3a (1a ) and (R)-1-naphthyl-
(phenyl)-O-methylphosphinite borane5f (1b) giving (S,S)-
1,1′-bis(2-methoxyphenyl(phenyl)phosphino)ferrocene
borane (2a ) and (S,S)-1,1′-bis(1-naphthyl(phenyl)phos-
phino)ferrocene borane (2b) (Scheme 2). The reaction
of anisyl analogue 1a is nearly quantitative. Partial loss
of stereochemistry occurs, with the (l)- and (u)-diaster-
eomers of 2a formed in a 3.5:1 ratio. Column chroma-
tography allows separation of (l)- and (u)-2a , which are
X-r a y An a lysis of (S,S)-2a . Crystals of 2a were
grown from THF/hexane. An ORTEP drawing is shown
(8) Gan, K. S.; Hor, T. S. A. In Ferrocenes; Togni, A., Hayashi, T.,
Eds.; VCH: Weinheim, D, 1995.
(10) The absolute configuration at the P atom is expressed in terms
of the Cahn-Ingold-Prelog sequence rules11 and, in the case of 3a ,b,
refers to the uncoordinated ligand.
(11) Cahn, R. S.; Ingold, C. K.; Prelog, V. Angew. Chem., Int. Ed.
Engl. 1966, 5, 385.
(12) (a) The oxidation at stereogenic P atoms is generally assumed
to occur with retention of configuration at the P atom.12b (b) Brown, J .
M.; Carey, J . V.; Russell, M. J . H. Tetrahedron 1990, 46, 4877.
(13) In the case of 4a , the signals were attributed by comparison
with the 31P NMR spectrum of the racemic phosphine oxide (R,R)+(S,S)-
4a recorded under the same conditions in the presence of excess (S)-
(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol, which shows two resolved
singlets (∆ν ) 8 Hz).
(9) (a) Stoop, R. M.; Maienza, F.; Wong, T. Y. H.; Spindler, F.
Mezzetti, A. OMCOS 9, Go¨ttingen, Germany, 1997, abstract 291. (b)
Nettekoven, U.; Kamer, P. C. J .; van Leeuwen, P. W. N. M. OMCOS
9, Go¨ttingen, Germany, 1997; poster 300. (c) Nettekoven, U.; Widhalm,
M.; Kamer, P. C. J .; van Leeuwen, P. W. N. M. Tetrahedron: Asym-
metry 1997, 8, 3185. (d) Maienza, F.; Stoop, R. M.; Wong, T. Y. H.;
Mezzetti, A. Assemble´e d′automne de la Nouvelle Socie´te´ Suisse de
Chimie, Lausanne, Switzerland, 1997; poster 87. (e) Maienza, F.
Laurea Thesis, Milan, Italy, May 1998. (f) Nettekoven, U.; Widhalm,
M.; Kamer, P. C. J .; van Leeuwen, P. W. N. M. ISHC 11th, St. Andrews,
Scotland, 1998; poster 28.

Ferrocenyl Diphosphines
Organometallics, Vol. 18, No. 6, 1999 1043
respectively. The ferrocenyl moieties display synclinal
(staggered) conformations: the P(1)-X(1)-X(19)-P(2)
torsional angles τ in 5a ′ and 5a ′′ are 39.7° and 34.0° (X
represent the centroids of the Cp rings).8 The angle θ
between the Cp planes is 5.4° (5a ′) and 7.4° (5a ′′), with
both P diverging from coplanarity with the Cp rings
within (0.08 Å. However, the conformations of the two
independent molecules are markedly different. Molecule
5a ′ is pseudo-C2 symmetric about the Pt-Fe vector,
since both methoxy groups are oriented toward the
metal. In the chelate ring, the phenyls are pseudoaxial,
and the anisyl groups pseudoequatorial (Figure 3). The
Fe atom lies very nearly in the Pt-Cl(1)-Cl(2)-P(1)-
P(2) plane, the distance from best plane being 0.14 Å
(Figure 2, 5a ′). The pseudo-C2 symmetry is destroyed
in 5a ′′: one OMe group is rotated away from the Pt
atom: the Pt(1′)-P(2′)-C(24′)- C(29′) torsion angle is
169.9(8)°. The torsional strain about the Pt-P(2) bond
pushes the ferrocenyl moiety away from the plane of
the complex (Figure 3): the distance between Fe and
best plane is now 1.38 Å. No Pt‚‚‚Fe interactions exist
in either 5a ′ or 5a ′′.
F igu r e 1. ORTEP view of (S,S)-1,1′-bis(2-methoxyphenyl-
(phenyl)phosphino)ferrocene borane, 2a .
Ta ble 1. Selected In ter a tom ic Dista n ces (Å) a n d
An gles (d eg) in 2a
P(1)-C(1)
P(1)-C(6)
P(1)-C(13)
P(1)-B(1)
1.794(5)
1.808(4)
1.819(4)
1.940(6)
P(2)-C(19)
P(2)-C(24)
P(2)-C(31)
P(2)-B(2)
1.788(4)
1.819(4)
1.814(4)
1.924(6)
In agreement with the X-ray data, molecular model-
ing (UFF calculations based on the Cerius2 program)15
indicates that 5a ′ and 5a ′′ have nearly the same total
energy (1403.93 and 1405.48 kcal mol-1, respectively).
Thus, we have investigated the solution behavior of 5a
with respect to the interconversion of the conformers.
C(1)-P(1)-C(6)
C(1)-P(1)-C(13)
C(1)-P(1)-B(1)
C(6)-P(1)-C(13)
C(6)-P(1)-B(1)
C(13)-P(1)-B(1)
C(11)-O(1)-C(12)
104.8(2)
105.4(2)
116.4(3)
108.6(2)
112.2(3)
108.9(2)
118.1(4)
C(19)-P(2)-C(24)
C(19)-P(2)-C(31)
C(19)-P(2)-B(2)
C(24)-P(2)-B(2)
C(24)-P(2)-C(31)
C(31)-P(2)-B(2)
C(29)-O(2)-C(30)
103.5(2)
106.3(2)
111.4(2)
115.5(2)
104.9(2)
114.3(2)
117.5(4)
1
The H and 31P NMR of 5a indicate that the 2-meth-
oxyphenyl substituents freely rotate at room tempera-
ture: a single H NMR signal is observed for the two
in Figure 1, and selected bond distances and angles are
reported in Table 1. The crystal contains discrete
molecules of 2a with normal nonbonded interactions.
The distorted tetrahedral geometry of the P atom is
typical of phosphine borane adducts.14 The conformation
is anticlinal staggered:8 the P(1)-X(1)-X(19)-P(2) tor-
sional angle τ is -116.2° (X are the centroids of the Cp
rings). The Cp rings are parallel within 1°, and P(1) and
P(2) are slightly pushed away from the Fe atom: the
distances from the corresponding planes of the Cp rings
are 0.019 and 0.026 Å, respectively. The (S,S)-configu-
ration of the P atoms is supported by refinement of the
Flack x parameter and is in agreement with inversion
of configuration occurring at the P atom in the nucleo-
philic substitution step (Scheme 2).
[P tCl2((S,S)-3a)] (5a). The platinum derivative [PtCl2-
((S,S)-3a )] (5a ) was prepared by reaction of [PtCl2-
(PhCHdCH2)2] with (S,S)-3a in toluene. An X-ray study,
whose results are summarized in Table 2 and Figure 2,
discloses the details of the coordination mode of 3a . The
unit cell contains two crystallographically independent
[PtCl2((S,S)-3a )] units (molecules 5a ′ and 5a ′′), together
with one CH2Cl2 molecule as solvent of crystallization.
Least-squares refinement of the sign of ∆f ′′ (η )
+1.0(2)) supports the (S,S)-configuration, in agreement
with the above assumption that deboranation occurs
with retention of configuration.
1
equivalent methoxy groups, and the 31P NMR spectrum
exhibits a sharp singlet with 195Pt satellites. The low-
temperature 1H and 31P NMR spectra show that the
anisyl rotation slows down upon cooling, since the 31P
NMR signals broaden below -20 °C (w1/2 of the central
signal is 81 Hz at -80 °C). However, the barrier to
rotation must be low, as the signals of the two conform-
1
ers do not decoalesce down to -90 °C. In the H NMR
spectra, the Cp and OMe signals broaden below -40
°C, but decoalescence is not achieved at -90 °C, the
lowest available temperature.
[Rh (COD)(3a ,b)]BF 4 (6a ,b). The rhodium deriva-
tives [Rh(COD)(P-P*)]BF4 (P-P* ) (S,S)-3a , 6a ; P-P*
) (S,S)-3b, 6b) were prepared by reaction of the free
ligands 3a ,b with [Rh(COD)2]BF4. The solution NMR
spectra of 6a ,b indicate a dynamic behavior apparently
related to the restricted rotational freedom of the
o-anisyl or 1-naphthyl substituents. The room-temper-
ature 31P NMR spectrum of 6a consists of a broad
doublet centered at δ 18.9 (CD2Cl2, 162 MHz, w1/2 ) 291
Hz, J RhP ) 144 Hz). This signal coalesces at 0 °C into a
broad hump centered at δ 17.3 (w1/2 ≈ 340 Hz), which
resolves into a doublet upon further cooling. At -80 °C,
a sharp doublet at δ 17.08 (J RhP ) 153 Hz) is the only
signal. The solution behavior of 6a ,b can be explained
assuming the presence of two conformers with different
populations, whereby the symmetric one 6′ predomi-
nates over the asymmetric conformer 6′′. At room
temperature, the two conformers are interconverted on
the NMR time scale, giving an unresolved, broad
The overall geometry of the ligand 3a is similar in
both independent molecules and is analogous to that of
dppf in square planar complexes of platinum(II),8 with
bite angles of 102.0(1)° and 99.6(1)° in 5a ′ and 5a ′′,
(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.
(15) (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.

1044 Organometallics, Vol. 18, No. 6, 1999
Maienza et al.
Ta ble 2. Selected In ter a tom ic Dista n ces (Å) a n d An gles (d eg) in 5a
5a ′ 5a ′′
Pt(1)-P(1)
Pt(1)-P(2)
Pt(1)-Cl(2)
Pt(1)-Cl(1)
Pt(1)‚‚‚Fe(1)
P(1)‚‚‚P(2)
2.254(3)
2.254(3)
2.342(3)
2.353(3)
4.288(2)
3.504(4)
Pt(1′)-P(1′)
Pt(1′)-P(2′)
Pt(1′)-Cl(2′)
Pt(1′)-Cl(1′)
Pt(1′)‚‚‚Fe(1′)
P(1′)‚‚‚P(2′)
2.266(3)
2.268(3)
2.334(3)
2.344(3)
4.240(2)
3.463(4)
P(1)-Pt(1)-P(2)
P(1)-Pt(1)-Cl(2)
P(2)-Pt(1)-Cl(2)
P(1)-Pt(1)-Cl(1)
P(2)-Pt(1)-Cl(1)
Cl(2)-Pt(1)-Cl(1)
102.0(1)
P(1′)-Pt(1′)-P(2′)
P(1′)-Pt(1′)-Cl(2′)
P(2′)-Pt(1′)-Cl(2′)
P(1′)-Pt(1′)-Cl(1′)
P(2′)-Pt(1′)-Cl(1′)
Cl(2′)-Pt(1′)-Cl(1′)
99.6(1)
170.1(1)
89.1(1)
85.6(1)
174.8(1)
85.9(1)
169.6(1)
87.0(1)
84.4(1)
170.0(1)
87.4(1)
Pt(1)-P(1)-C(6)-C(11)
-66.7(9)
8.7(9)
Pt(1′)-P(1′)-C(6′)-C(11′)
Pt(1′)-P(1′)-C(13′)-C(14′)
Pt(1′)-P(2′)-C(24′)-C(29′)
Pt(1′)-P(2′)-C(31′)-C(32′)
-57(1)
Pt(1)-P(1)-C(13)-C(14)
Pt(1)-P(2)-C(24)-C(29)
Pt(1)-P(2)-C(31)-C(32)
-33(1)
-68.6(9)
169.9(8)
-77.5(9)
0(1)
F igu r e 3. Ball and stick view of 5a ′ and 5a ′′ along the
P-Cl vectors (X-ray data).
-40 °C, a sharp doublet (δ 19.0, J RhP ) 151 Hz) for 6b′
and two slightly broadened doublets of doublets (δA 19.3,
F igu r e 2. ORTEP view of 5a ′ and 5a ′′.
spectrum. Lowering the temperature below 0 °C not
only slows down the exchange process but also shifts
the conformer population toward the more stable sym-
metric species. Thus, at -80 °C only the latter is
observed in the case of the anisyl derivative 6a . Molec-
ular modeling confirms this interpretation (Figure 4; see
the Supporting Information for details): the C2-sym-
metric conformer 6a ′ is more stable than the C1-
symmetric 6a ′′ by ca. 6 kcal mol-1 (6a ′ 1719.95 kcal
mol-1, 6a ′′ 1726.17 kcal mol-1).
J RhP ) 153, J PP′ ) 17.8 Hz; δB 16.1, J RhP ) 147, J PP′ )
17.8 Hz). Integration of these signals gives a 6b′:6b′′
1
ratio of 54:46. In the H NMR spectrum at -60 °C, the
inequivalent naphthyl C2 protons of the asymmetric
conformer give rise to well-resolved signals at δ 10.1
and 10.7, whereas those of the symmetric one appear
as a multiplet centered at δ 8.4.
Molecular modeling predicts, at least qualitatively,
the different behavior of 6b compared to 6a , the energy
gap being lower (ca. 5 kcal mol-1; 6b′, 1736.75 kcal
mol-1, 6b′′ 1741.73 kcal mol-1) than in 6a . However, a
quantitative correlation between the calculated total
energy and the observed conformer distribution in the
31P NMR experiment cannot be expected, since the
In the case of 6b, both conformers are observed at low
temperature. The broad 31P NMR spectrum observed
at room temperature (δ 19.3, w1/2 ) 360 Hz, CD2Cl2,
162 MHz) decoalesces between 20 and 0 °C to give, at

Ferrocenyl Diphosphines
Organometallics, Vol. 18, No. 6, 1999 1045
Ta ble 3. Asym m etr ic Hyd r ogen a tion of 7 to 8a
run
catalyst
R
p(H2) (bar)
T (°C)
ee (%)
1
2
3
4
5
6
7
6a
6a
Me
Me
Me
Me
Me
H
1
5
1
1
20
1
20
20
20
35
35
35
20
96
94
91
88
85
88
92
3a b
3a b
3a b
3a b,c
6b
Me
1
a
Reaction conditions: MeOH (10 mL) as solvent, S/C ) 200
(unless otherwise stated), reaction time 15-20 h, conversion
b
95-99.5%. Catalyst formed in situ from 3a (18 µmol) and [Rh-
(NBD)2]BF4 (6.4 mg, 17 µmol), 3/Rh ) 1.05. c S/C ) 100, NEt3 (9.5
µL) added to the reaction solution.
Ta ble 4. Asym m etr ic Hyd r ogen a tion of 9 to 10a
run
catalyst
R
p(H2) (bar)
ee (%)
1
2
3
4
5
6a
6a
6a
6b
6b
Me
Me
Ph
Me
Me
1
5
5
1
5
97
97
93
90
83
a
Reaction conditions: MeOH (10 mL) as solvent, S/C ) 200, T
) 25 °C, reaction time 17 h, conversion 99%.
F igu r e 4. Conformers 6a ′ (symmetric) and 6a ′′ (asym-
metric) with minimized energies (Cerius2 molecular model-
ing calculations).
7), but significantly lower than that obtained with the
closely related precatalyst [Rh(COD)((S,S)-Me2Si(CH2P-
(1-Np)(Ph))2)]+ (98% ee).5f
barriers to rotation probably play a role in preventing
the system reaching the thermal equilibrium as the
sample temperature is lowered. Also, the absolute total
energy values calculated for 6a and 6b indicate that the
1-naphthyl derivative 3b is more bulky than its anisyl
analogue 3a .
Ligands 3a ,b exhibit superior efficiency and enantio-
discrimination in the asymmetric hydrogenation of
N-substituted acetamidocinnamates, a class of sub-
strates that is hydrogenated slowly and with much
lower ee’s than the unsubstituted analogues by most
rhodium-based systems.1,16,17 Thus, 6a quantitatively
hydrogenates methyl (Z)-R-N-methyl-acetamidocinnam-
ate (9) to (R)-N-methyl-N-acetylphenylalanine methyl
ester (10) with 97% ee (Table 4, run 1). This value,
which is slightly higher than that obtained with
[Rh(COD)((S,S)-Me2Si(CH2P(1-Np)(Ph))2)]BF4,5f is the
best ever observed for N-substituted enamides. It should
be also noted that recent reports of the hydrogenation
of dehydroamino acids,18 even with P-chiral diphos-
phines,5g do not encompass applications to N-substituted
enamides. Introducing a benzamido group is detrimen-
tal to the enantioselectivity (run 3). With catalyst 6b,
10 is obtained with lower enantioselectivity (90%, run
4) than with 6a , confirming the trend observed with
acetamidocinnamic acid 7.
Rh odiu m -Catalyzed Hydr ogen ation . Ligands 3a,b
were tested in the rhodium(I)-catalyzed hydrogenation
of functionalized olefins and ketones. The results of the
asymmetric hydrogenation of R-acetamidocinnamic acid
derivatives are summarized in Tables 3 and 4. The
isolated complex 6a hydrogenates methyl (Z)-R-acet-
amidocinnamate (7) to (R)-N-acetylphenylalanine meth-
yl ester (8) with 96% ee at 20 °C and 1 bar H2 (Table 3,
run 1). By contrast, the catalytic system formed in situ
from 3a and [Rh(COD)2]BF4 gives only 91% ee under
identical reaction conditions (run 3). Since the enantio-
meric purity of the ligands has been systematically
checked, this significantly different enantioselectivity
is possibly due to partial epimerization of the uncoor-
dinated ligand under reaction conditions before the
complex is formed. Increasing the temperature or the
initial H2 pressure decreases the enantioselectivity (runs
2, 4, 5). (Z)-R-Acetamidocinnamic acid is hydrogenated
to (R)-N-acetylphenylalanine with the same enantio-
selectivity (run 6) as the methyl ester under the same
conditions (run 4). The hydrogenation of 7 is catalyzed
by complex 6b with good enantioselectivity (92%, run
(16) Glaser, R.; Geresh, S.; Twaik, M.; Benoiton, N. L. Tetrahedron
1978, 34, 3617.
(17) Buser, H. P.; Pugin, B.; Spindler, F.; Sutter, M. Tetrahedron
1991, 47, 5709.
(18) (a) Pye, P. J .; Rossen, K.; Reamer, R. A.; Tsou, N. N.; Volante,
R. P.; Reider, P. J . J . Am. Chem. Soc. 1997, 119, 6207. (b) Zhu, G.;
Cao, P.; J iang, Q.; Zhang, X. J . Am. Chem. Soc. 1997, 119, 1799.

1046 Organometallics, Vol. 18, No. 6, 1999
Maienza et al.
Ta ble 5. Asym m etr ic Hyd r ogen a tion of Keton esa
Sch em e 3
run
ligand
substrate
S/C
ee (%)
1
2
3
4
3a
3a
3a
3b
21
22
23
22
100
100
100
200
26
11
29
34
a
Reaction conditions: catalyst formed in situ from 3a ,b and
[RhCl(NBD)]2 (2:1 mol ratio); toluene (10 mL) as solvent, p(H2) )
40 bar, T ) 25 °C, reaction time 16-72 h, conversion 82-99%.
phenylalanine methyl ester (8). This fact, together with
the low activity observed for 6b in the hydrogenation
of 15, indicates that the catalytic system is highly
sensitive to steric factors. As for â-unsusbsituted sub-
strates, methyl 2-(N-2,6-dimethylphenyl-acetylamino)-
acrylate (17) gives the corresponding alanine derivative
(18) in 47% ee with 6a as the catalyst, whereas 6b is
nearly inactive. Finally, 1-phenylvinyl acetate (19) gives
1-phenylethyl acetate (20) with low enantioselectivity
(27-28%). Taken together, these results suggest that
the scope of ligands 3a ,b in the rhodium-catalyzed
asymmetric hydrogenation of functionalized olefins is
narrower than in the case of Imamoto’s ligands (R)(Me)-
PCH2CH2P(R)(Me)5g or DUPHOS.19
Sch em e 4
The in situ catalytic system 3a ,b/[RhCl(COD)] hy-
drogenates ketones with low to moderate enantioselec-
tivity (Table 5). Phenylglioxylic acid methyl ester (21),
ethyl piruvate (22), and keto pantolactone (23) give
methyl mandelate, ethyl lactate, and pantolactone with
ee’s between 34 and 11%. These values further indicate
that the scope of ligands 3a ,b is essentially restricted
to functionalized acetamido cinnamates, at least in the
rhodium-catalyzed asymmetric hydrogenation.
Con clu d in g Rem a r k s. The rhodium(I) derivatives
of 3a ,b are excellent catalysts for the asymmetric
hydrogenation of acetamidocinnamates with high enan-
tioselectivities, in particular N-alkylated derivatives.
This gives access to N-alkylated amino acids, a class of
compounds that are potentially interesting intermedi-
ates for pharmaceuticals. Also, ligands 3a ,b are among
the first examples of a class of diphosphines bearing
stereogenic P atoms in connection with large bite angles
(≈100°). The comparison with the previously reported
ligand (S,S)-Me2Si(CH2P(1-Np)(Ph))2 (bite angle ≈ 93°
according to molecular modeling) shows that the size
of the bite angle does not improve ipso facto the catalytic
performance in the rhodium-catalyzed hydrogenation of
dehydroamino acids. In fact, our X-ray and NMR
investigations on the Pt(II) and Rh(I) derivatives 5 and
6 show that different conformations are simultaneously
present both in solution and in the solid state. This is
apparently due to the torsional flexibility of the 1,1′-
ferrocenediyl bridge and to the rotational freedom about
the P-C bond of the aryl substituents at the P atoms.
We are currently trying to enhance the rigidity of the
ligand backbone with the aim of improving the enantio-
The directing effect of the acylamino and the ester
groups has been investigated. Both directing groups are
necessary for high enantioselection. Thus, when the
amido group is substituted with methyl, as in (E)-1-
methylcinnamic acid (11), the ee values of the hydro-
genation product (E)-1-methylhydrocinnamic acid (12)
drop to 37-27% (Scheme 3). Also, (E)-2-acetamido-1-
phenylpropene (13) is hydrogenated to 2-acetamido-
phenylpropane (14) with low enantioselectivity (25-
47%). Also the substitution pattern at enamide â-C atom
plays a major role for enantioselection (Scheme 4). Thus,
6a hydrogenates a â-disubstitued substrate such as
acetylamino(cyclohexylidene)acetic acid methyl ester
(15) to (S)-2-cyclohexylglycine methyl ester (16) with
only 28% ee, whereas 6b gives nearly racemic product.
Interestingly, in both cases the sign of the enantio-
selection is reversed as compared to (R)-N-acetyl-
(19) See, for instance: Burk, M. J .; Gross, M. F.; Martinez, J . P J .
Am. Chem. Soc. 1995, 117, 9375.

Ferrocenyl Diphosphines
Organometallics, Vol. 18, No. 6, 1999 1047
monochromated), λ ) 0.71073 Å, F(000) ) 336. The data were
collected at room temperature on a STOE IPDS (image plate
detector system) in the θ range 4.13-24.22°. Unit cell dimen-
sions determination, data reduction, and absorption correction
were performed with the STOE program package. The struc-
ture was solved with SHELXS-96 using direct methods.21 Of
the 9431 measured reflections with index ranges -9 e h e 9,
-10 e k e 10, -15 e l e 15, 4872 independent reflections
(Rint ) 0.0630) were used in the refinement, 414 parameters,
selectivity of the catalytic hydrogenation of a larger
scope of substrates.
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-
sphere using Schlenk techniques. Solvents were purified
according to standard procedures; (R)-1a ,3a (R)-1b,5f and [PtCl2-
(η2-styrene)2]20 were prepared by published procedures. NMR
spectra were recorded on Bruker DPX 250 or, when specified,
400 spectrometers. 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 2a ,b are partially relaxed, nonbinomial 1:1:
1:1 quartets due to coupling to 11B (80.1% natural abundance);
2
full-matrix least-squares on F2, quantity minimized ∑w(|Fo|
- |Fc| )2 (w-1 ) σ2(Fo2) + (0.0155P)2 + 0.51P, where 3P )
2
max(Fo2,0) + 2Fc2) with anisotropic displacement parameters
for all non-H atoms. Hydrogen atoms were introduced at
calculated positions and refined with the riding model and
individual isotropic thermal parameters for each group. The
H atoms on B(1) and B(2) were fully refined. The absolute
configuration at the P atoms was determined to be (S,S) by
refinement of the Flack x parameter ) -0.014(17). Final
residuals (I > 2σ(I)) were R1 ) 0.0372 and wR2 ) 0.0863 (all
data R1 ) 0.0428 and wR2 ) 0.0920), GOF 1.065. Max. and
min. difference peaks were +0.26 and -0.25 eÅ-3; largest and
mean ∆/σ ) 0.008 and 0.001. Molecular graphics were per-
formed with the program XP with 50% ellipsoids. Atomic
coordinates, anisotropic displacement coefficients, and an
extended list of interatomic distances and angles are available
as Supporting Information. Selected interatomic distances and
angles are reported in Table 1.
1
1J BH and J PB were measured between the central peaks. Mass
spectra were measured by the MS service of the Laboratorium
fu¨r Organische Chemie (ETH Zu¨rich). A 3-NOBA (3-nitroben-
zyl 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 cm × 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.
(S ,S )-1,1′-Bis(1-n a p h t h yl(p h e n yl)p h osp h in o)fe r r o-
cen e Bor a n e, (S,S)-2b. An Et2O solution (21 mL) of 1b (1.50
g, 5.36 mmol) is added dropwise to a THF solution (8 mL) of
1,1′-dilithioferrocene (2.7 mmol), prepared as described above.
After stirring the dark red solution for 2 h, the reaction is
quenched with H2O (10 mL). Workup is as for 2a . Flash
chromatography (silica gel, hexane/AcOEt (9:1)) gives analyti-
cally pure (S,S)-2b (Rf 0.15) as an orange crystalline solid.
(S,S)-1,1′-Bis(2-m et h oxyp h en yl(p h en yl)p h osp h in o)-
fer r ocen e Bor a n e, (S,S)-2a . 1,1′-Dilithioferrocene is pre-
pared by addition of BuLi (25.7 mL, 0.0404 mol, 1.57 M in
hexane) and TMEDA (4.69 g, 0.0404 mol, d 0.775 g/mL, 6.0
mL) to a hexane solution (150 mL) of ferrocene (3.76 g, 0.0202
mol) at room temperature. The orange precipitate formed upon
stirring for 4 h is filtered off and dissolved in THF (150 mL).
A THF solution (50 mL) of (R)-1a (10.51 g, 0.0404 mol) is added
thereto dropwise. After stirring the resulting dark red solution
for 2 h, the reaction is quenched with H2O (50 mL). The
product is extracted with t-BuOMe, and the combined organic
layers are washed twice with a CuSO4 solution and then with
a NH4Cl solution and dried with MgSO4. Evaporation of the
solvent and flash chromatography (silica gel, hexane/AcOEt
(4:1)) gives analytically pure (S,S)-2a (Rf 0.12) and (R,S)-2a
(Rf 0.19) as orange crystalline solids. (S,S)-2a : Yield: 9.27 g
Yield: 0.88 g (48%); mp 163 °C. [R]20 ) +45.8° (CHCl3, c )
D
1). 31P NMR (CDCl3): δ 16.2 (br, 2P). 1H NMR (CDCl3): δ
7.95-7.77, 7.59-7.21 (2 m, 24H, ArH), 4.67 (s, 4H, 2 CpH),
4.57, 3.83 (2 s, 4H, 2 CpH), 1.56-0.86 (m, 6H, 2 BH3). MS
(FAB+): m/z 681.1 (M+, 30), 668.1 (M+ - BH3, 25), 654.0 (M+
- 2 BH3, 100), 577.0 (M+ - 2 BH3 - Ph, 4). Anal. Calcd for
C
42H38B2FeP2: C, 73.95; H, 5.61. Found: C, 73.93; H, 5.69.
(S,S)-1,1′-Bis(2-m et h oxyp h en yl(p h en yl)p h osp h in o)-
fer r ocen e, (S,S)-3a . Compound (S,S)-2a (9.270 g, 14.4 mol)
is dissolved in morpholine (30 mL), and the solution is stirred
overnight at room temperature, evaporated to dryness (at room
temperature), and purified by flash chromatography (silica gel,
hexane/AcOEt (4:1), Rf 0.4). Yield: 7.62 g (86%); mp 152 °C.
(72%); mp 168 °C. [R]20 ) -60.5° (CHCl3, c ) 1). 31P NMR
D
1
(CDCl3): δ 12.9 (br q, 2P). H NMR (CDCl3): δ 7.70-7.61 (m,
2H, H6 o-An), 7.49-7.26 (m, 12H, 2 C6H5, H4 o-An), 7.03-6.99
(m, 2H, H5 o-An), 6.86-6.81 (m, 2H, H3 o-An), 4.43-4.33 (m,
8H, 2 CpH), 3.42 (s, 6H, 2 OCH3), 1.56-0.66 (m, 6H, 2 BH3).
MS (FAB+): m/z 642 (M+, 1), 628 (M+ - BH3, 5), 614 (M+ - 2
BH3, 100). Anal. Calcd for C36H38B2FeO2P2: C, 67.34; H, 5.96.
Found: C, 67.14; H, 6.21. (R,S)-2a : Yield: 2.67 g (21%). 31P
NMR (CDCl3): δ 13.0 (br q, 2P). 1H NMR (CDCl3): δ 7.92-
7.83 (m, 2H, H6 o-An), 7.54-7.18 (m, 12H, 2 C6H5, H4 o-An),
7.11-6.99 (m, 2H, H5 o-An), 6.89-6.85 (m, 2H, H3 o-An), 4.57-
4.15 (m, 8H, 2 CpH), 3.44 (s, 6H, 2 OCH3), 1.56-0.66 (m, 6H,
2 BH3). MS (FAB+): m/z 641 (M+, 49), 628 (M+ - BH3, 39),
614 (M+ - 2 BH3, 100), 507 (M+ - 2 BH3 - o-An, 6). Anal.
Calcd for C36H38B2FeO2P2: C, 67.34; H, 5.96. Found: C, 67.53;
H, 6.16.
[R]20 ) +176.1° (CHCl3, c ) 1). 31P NMR (CDCl3): δ -30.1
D
(s, 2P). 1H NMR (CDCl3): δ 7.37-6.77 (2 m, 18H, 2 C6H5,
2
o-An), 4.41, 4.40, 4.39, 3.58 (4 s, 8H, 2 CpH), 3.67 (s, 6H, 2
OCH3). MS (FAB+): m/z 614.1 (M+, 100), 537.1 (M+ - Ph, 4),
507.0 (M+ - Ph - o-An, 4). Anal. Calcd for C36H32FeO2P2: C,
70.37; H, 5.25. Found: C, 70.12; H, 5.21.
(S ,S )-1,1′-Bis(1-n a p h t h yl(p h e n yl)p h osp h in o)fe r r o-
cen e, (S,S)-3b. Compound (S,S)-2b (0.548 g, 0.803 mmol) is
dissolved in morpholine (30 mL), and the solution is stirred
24 h at room temperature and then evaporated to dryness (at
room temperature). Flash chromatography (silica gel, hexane/
AcOEt (4:1), Rf 0.4) yields (S,S)-3b, which is recrystallized from
hexane. Yield: 400 mg (76%); mp 153 °C. [R]20 ) +157.7°
D
(CHCl3, c ) 1). 31P NMR (CDCl3): δ -26.7 (s, 2P). 1H NMR
(CDCl3): δ 8.37-8.32 (m, 2H, ArH), 7.82-7.68 (m, 4H, ArH),
7.46-7.11 (m, 18H, ArH), 4.38, 4.34, 4.26, 3.69 (4 s, 8H, 2
CpH). MS (FAB+): m/z 654.1 (M+, 100), 577.1 (M+ - Ph, 4).
Anal. Calcd for C42H32FeP2: C, 77.07; H, 4.93. Found: C, 77.20;
H, 5.00.
X-r a y An a lysis of (S,S)-2a . Orange crystals of (S,S)-2a
suitable for X-ray analysis were grown from THF/hexane (1:
3). A prism (0.48 × 0.30 × 0.27 mm) was mounted on a glass
capillary. Crystal data for C36H38B2FeO2P2 (fw 614.43): tri-
clinic, space group P1, cell dimensions (298 K) a ) 7.8770(10)
Å, b ) 8.7930(10) Å, c ) 13.087(2) Å, R ) 93.309(13)°, â )
105.005(12)°, γ ) 108.641(12)°, and V ) 819.77(19) Å3 with Z
) 1 and Dc ) 1.301 Mg/m3, µ ) 0.589 mm-1 (Mo KR, graphite
(R,R)-1,1′-Bis(P -oxo-2-m et h oxyp h en yl(p h en yl)p h os-
p h in o)fer r ocen e, (R,R)-4a . H2O2 (30%, 2 mL) is added to a
(21) SHELXTL Program Package V. 5.1; Bruker AXS, Madison, WI,
1997.
(20) Caseri, W. R.; Pregosin, P. S. Organometallics 1988, 7, 1373.

1048 Organometallics, Vol. 18, No. 6, 1999
Maienza et al.
THF solution (5 mL) of 3a (50 mg, 0.078 mmol). After stirring
for 15 min, H2O (10 mL) is added, the THF is evaporated, and
the product is extracted with CH2Cl2. Evaporation of the
solvent gives an orange oil. Yield: 52 mg (99%). 31P NMR
(CDCl3): δ 26.7 (s, 2P). After addition of (S)-(+)-2,2,2-trifluoro-
1-(9-anthryl)ethanol (3 equiv vs 4a ): 31P NMR (CDCl3): (R,R)-
4a , δ 30.04 (s, 2P, >99%); (S,S)-4a , δ 30.12 (s, 2P, <1%); >98%
ee.
100), 335.1 (M+ - Ph, 9), 323.1 (M+ - BH3 - Ph, 12), 307.1
(M+ - o-An, 49).
(l)-3a . Deboranation and purification as described for (S,S)-
2a . Yield: 86%; mp 152 °C. 31P NMR (CDCl3): δ -30.1 (s, 2P).
1H NMR (CDCl3): δ 7.37-6.77 (2 m, 18H, 2 C6H5, 2 o-An), 4.41,
4.40, 4.39, 3.58 (4 s, 8H, 2 CpH), 3.67 (s, 6H, 2 OCH3).
(u )-3a . Compound (u)-2a (100 mg, 0.156 mmol) is dissolved
in morpholine (5 mL), and the solution is stirred overnight at
room temperature, evaporated to dryness (at room tempera-
ture), and purified by flash chromatography (silica gel, hexane/
AcOEt (4:1), Rf 0.4). Yield: 78 mg (82%); mp 155 °C. 31P NMR
(R,R)+(S,S)-1,1′-Bis(P -oxo-2-m eth oxyp h en yl(p h en yl)-
p h osp h in o)fer r ocen e, (l)-4a . Racemic (l)-4a is similarly
prepared from (l)-3a . 31P NMR (CDCl3): δ 26.7 (s, 2P). After
addition of (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol (3 equiv
vs 4a ): 31P NMR (CDCl3): (S,S)-4a , δ 29.61 (s, 2P, 50%); (R,R)-
4a , δ 29.69 (s, 2P, 50%).
(R,R)-1,1′-Bis(P -oxo-1-n a p h th yl(p h en yl)p h osp h in o)fer -
r ocen e, (R,R)-4b. The compound is prepared as described for
4a from 3b. 31P NMR (CDCl3): δ 31.4 (s, 2P). After addition
of (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol (3 equiv vs 4b):
31P NMR (CDCl3): (R,R)-4b, δ 32.60 (s, 2P, >99%); (S,S)-4b,
δ 32.68 (s, 2P, <1%); >98% ee.
1
(CDCl3): δ -30.4 (s, 2P). H NMR (CDCl3): δ 7.40-7.24 (m,
12H, ArH), 6.88-6.77 (m, 6H, ArH), 4.41, 4.30, 4.25, 3.59 (4
s, 8H, 2 CpH), 3.69 (s, 6H, 2 OCH3). MS (FAB+): m/z 614.1
(M+, 100), 537.1 (M+ - Ph, 4), 507.1 (M+ - Ph - o-An, 5).
Anal. Calcd for C36H32FeO2P2: C, 70.37; H, 5.25. Found: C,
70.37; H, 5.37.
[P tCl2((S,S)-3a )] (5a ). A toluene solution (5 mL) of (S,S)-
3a (77 mg, 0.126 mmol) is slowly added to a suspension of
[PtCl2(PhCHdCH2)2] (60 mg, 0.126 mmol) in toluene (20 mL).
The resulting solution is then stirred at room temperature for
8 h. After removing the solvent under vacuum, the resulting
powder is washed twice with pentane (3 mL). Column chro-
matography (silica gel, CH2Cl2/MeOH (5:1)) gives the pure
product. Yield: 92%. 1H NMR (300 MHz, CDCl3): δ 3.68 (s,
6H, OCH3), 4.27 (m, 2H, CpH), 4.36 (m, 2H, CpH), 4.43 (m,
4H, CpH), 6.75 (t × d, 2H, AnH), 6.93 (d × d, 2H, AnH), 7.76
(m, 8H, ArH), 7.81 (m, 2H, ArH), 7.92 (m, 4H, ArH). 31P NMR
(CD2Cl2, 162 MHz): δ 10.17 (s+Pt-satellites, 1J PtP ) 3901 Hz).
Anal. Calcd for C36H32O2P2Cl2FePt‚0.25CH2Cl2: C, 48.29; H,
3.63. Found: C, 47.81; H, 3.60.
(r a c)-N,N-Dieth ylam in o(2-m eth oxyph en yl)ph en ylph os-
p h in e. A solution of 2-methoxyphenyllithium (prepared add-
ing BuLi (15.1 mL, 30 mmol, 1.98 M in hexane) to a THF
solution (5 mL) of 2-bromoanisole (5.611 g, 30 mmol, d 1.502
g/mL, 3.8 mL) at -78 °C and stirring for 30 min) is slowly
added by cannula to a THF solution (45 mL) of (rac)-P(NEt2)-
(Ph)Cl (6.041 g, 30 mmol) precooled at -78 °C. The reaction
solution is slowly warmed to room temperature and then
quenched with H2O (5 mL). After evaporation of THF under
vacuum, the reaction crude is extracted with CH2Cl2, dried
over MgSO4, and distilled. Yield: 7.667 g (89%). 31P NMR
X-r a y An a lysis of 5a . Orange crystals suitable for X-ray
analysis were grown by slow diffusion of pentane into a CH2Cl2
solution of 5a . A platelet (0.50 × 0.46 × 0.15 mm) was mounted
on a glass capillary. Crystal data for C73H66Cl6Fe2O4P4Pt2 (fw
1845.76): orthorhombic, space group P212121, cell dimensions
(293 K) a ) 14.0951(5) Å, b ) 16.8149(6) Å, c ) 29.3881(11)
Å, and V ) 6965.2(4) Å3 with Z ) 4 and Dc ) 1.760 Mg/m3, µ
) 4.784 mm-1 (Mo KR, graphite monochromated), λ ) 0.71073
Å, F(000) ) 3624. The data were collected at room temperature
1
(CDCl3): δ 51.5 (s, P). H NMR (CDCl3): δ 8.15-7.23 (m, 9H,
ArH), 3.27-3.13 (m, 4H, P-N(CH2CH3)2), 0.94 (t, 6H,P-
3
N(CH2CH3)2, J HH′ ) 7.1 Hz).
(r a c)-2-Met h oxyp h en yl(p h en yl)-O-m et h ylp h osp h in -
ite Bor a n e, (r a c)-1a . (rac)-P(NEt2)(o-An)(Ph) (7.667 g, 26.7
mmol) is dissolved in a MeOH solution (50 mL) of H2SO4 (1
mL, 97%). After stirring 15 h at room temperature, the solvent
is evaporated and the residue is dissolved in toluene (20 mL).
BH3‚SMe2 (2.037 g, 26.7 mmol, d 0.801 g/mL, 2.5 mL) is added,
and the solution is stirred 2 h at room temperature. Evapora-
tion of the solvent under vacuum yields a yellow oil, which is
purified by column chromatography (silica gel, hexane/AcOEt
(4:1), Rf 0.5). Yield: 4.25 g (61%). Same NMR data as for (R)-
2-methoxyphenyl(phenyl)-O-methylphosphinite borane.3a
on
a Siemens SMART platform (CCD detector, detector
distance 40 mm) in the θ range 1.39-24.71 (ω-scans, exposure
time ) 5 s). Unit cell dimensions determination and data
reduction were performed by standard procedures, and an
empirical absorption correction (SADABS) was applied. The
structure was solved with SHELXS-96 using direct methods
as described for 2a . Of the 38772 measured reflections with
index ranges -16 e h e 16, 0 e k e 19, 0 e l e 34, 11875
independent reflections (Rint ) 0.0892) were used in the
refinement (820 parameters, full-matrix least-squares on F2
with anisotropic displacement parameters for all non-H atoms.
Hydrogen atoms were treated as for 2a . The absolute config-
uration at the P atoms was determined to be (S,S) by
refinement of the Flack x parameter ) -0.0153(65). Final
residuals (I > 2σ(I)) were R1 ) 0.0462 and wR2 ) 0.0947 (all
data R1 ) 0.0676 and wR2 ) 0.1029), GOF 0.985. Max. and
min. difference peaks were +1.089 and -1.536 e Å-3; largest
and mean ∆/σ ) -0.26 and 0.017. Molecular graphics were
performed with the program XP (50% ellipsoids). Atomic
coordinates, anisotropic displacement coefficients, and an
extended list of interatomic distances and angles are available
as Supporting Information. Selected interatomic distances and
angles are reported in Table 2.
(l)+(u )-1,1′-Bis(2-m eth oxyp h en yl(p h en yl)p h osp h in o)-
fer r ocen e Bor a n e, (l)+(u )-2a . A THF solution (10 mL) of
(rac)-1a (3.430 g, 13.2 mmol) is added dropwise to a hexane
solution of 1,1′-dilithioferrocene (prepared adding BuLi (8.9
mL, 13.2 mmol, 1.48 M in hexane) and TMEDA (1.227 g, 13.2
mmol, d 0.775 g/mL, 2.0 mL) to ferrocene (1.521 g, 6.6 mmol)
dissolved in hexane (40 mL) and stirring for 4 h). Flash
chromatography as for (S,S)-2a . (R,S)-2a : Yield: 381 mg (9%).
31P NMR (CDCl3): δ 13.0 (br q, 2P). 1H NMR (CDCl3): δ 7.92-
7.83 (m, 2H, H6 o-An), 7.54-7.18 (m, 12H, 2 C6H5, H4 o-An),
7.11-6.99 (m, 2H, H5 o-An), 6.89-6.85 (m, 2H, H3 o-An), 4.57-
4.15 (m, 8H, 2 CpH), 3.44 (s, 6H, 2 OCH3), 1.56-0.66 (m, 6H,
2 BH3). (R,R+S,S)-2a : Yield: 1.338 g (32%). 31P NMR
1
(CDCl3): δ 12.9 (br q, 2P). H NMR (CDCl3): δ 7.70-7.61 (m,
2H, H6 o-An), 7.49-7.26 (m, 12H, 2 C6H5, H4 o-An), 7.03-6.99
(m, 2H, H5 o-An), 6.86-6.81 (m, 2H, H3 o-An), 4.43-4.33 (m,
8H, 2 CpH), 3.42 (s, 6H, 2 OCH3), 1.56-0.66 (m, 6H, 2 BH3).
A third reaction product (Rf 0.37) is identified as ferrocenyl-
[Rh (COD)((S,S)-3a )]BF 4 (6a ). [Rh(COD)2]BF4 (66 mg,
0.163 mmol) and (S,S)-3a (100 mg, 0.163 mmol) are dissolved
in THF (8 mL). After stirring for 2 h at room temperature,
the orange solid is filtered off, washed with THF and hexane,
2-methoxyphenylphenylphosphine borane.3g Yield: 332 mg
1
(12%); mp 172 °C. 31P NMR (CDCl3): δ 13.6 (br d, P, J BP
)
68 Hz). 1H NMR (CDCl3): δ 7.83-7.74 (m, 1H, ArH), 7.57-
7.27 (m, 6H, ArH), 7.10-7.03 (m, 1H, ArH), 6.90-6.86 (m, 1H,
ArH), 4.68 (s, 1H, P-C5H4), 4.53 (s, 1H, P-C5H4), 4.49 (s, 2H,
P-C5H4), 4.03 (s, 5H, CpH), 3.47 (s, 3H, OCH3), 1.54-0.89 (m,
3H, BH3). MS (FAB+): m/z 414.2 (M+, 55), 400.1 (M+ - BH3,
and dried in vacuum. Yield: 120 mg (81%). 31P NMR (CD2Cl2,
1
162 MHz, 293 K): δ 18.9 (br, 2P); 193 K: δ 17.1 (d, J RhP
)
153 Hz). 1H NMR (CDCl3, 293 K): δ 8.40-6.88 (m, 18H, ArH),
4.40-4.12 (m, 10H, 4 dCH, 6 CpH), 3.97 (s, 6H, 2 OCH3), 3.75

Ferrocenyl Diphosphines
Organometallics, Vol. 18, No. 6, 1999 1049
(s, 2H, 2 CpH), 2.36-1.86 (m, 8H, 4 CH2). MS (FAB+): m/z
825.1 (M+ - BF4, 40), 717.0 (M+ - BF4 - COD, 100). The
presence of water was evidenced by IR spectroscopy (3426
hydrogen (three cycles), and the pressure was set. After
completion of the reaction (total reaction times 15-20 h), the
conversion was determined by gas chromatography, and the
product was recovered quantitatively after filtration of the
reaction solution on a plug of silica to remove the catalyst.
The enantiomeric purity of 8 was determined by GC (L-
Chirasil-Val column, on column injection). N-Acetylphenyl-
alanine was converted to the methyl ester before analysis. The
ee of (R)-N-methyl-N-acetylphenylalanine 10 was determined
by HPLC (Chiracel OD-H column, eluent: hexane/i-PrOH, 90:
10). Experimental and analytical details for all substrates are
given in the Supporting Information.
1
cm-1, br, KBr pellet) and by H NMR (CDCl3) (δ 1.58, s, 6H, 3
H2O). Anal. Calcd for C44H44BFeF4O2P2Rh‚3H2O: C, 54.68; H,
5.00. Found: C, 54.48; H, 4.90.
[Rh (COD)((S,S)-3b)]BF 4 (6b). [Rh(COD)2]BF4 (44 mg,
0.107 mmol) and (S,S)-3b (70 mg, 0.107 mmol) were dissolved
in THF (5 mL). After stirring for 15 h at room temperature,
the solution is concentrated under vacuum (1 mL), and Et2O
is added. The resulting yellow precipitate is filtered off, washed
with Et2O, and dried in vacuum. Yield: 80 mg (78%). 31P NMR
1
(CD2Cl2, 162 MHz): δ 19.3 (br, 2P); 233 K: δ 19.1 (d, J RhP
)
1
151 Hz). H NMR (CDCl3, 293 K): δ 8.33 (m, 2H, NpH), 8.10
(m, 2H, NpH), 7.94-7.45 (m, 20H, ArH), 4.58 (m, 4H, 4 dCH),
4.28, 4.11, 3.95, 3.75 (4 s, 8H, 2 CpH), 2.36-1.93, 1.60-1.58
(2 m, 8H, 4 CH2). MS (FAB+): m/z 865.1 (M+ - BF4, 82), 757.0
(M+ - BF4 - COD, 100). The presence of water was evidenced
by IR spectroscopy (3444 cm-1, br, KBr pellet) and by 1H NMR
(CDCl3) (δ 1.85, s, 6H, 3 H2O). Anal. Calcd for C50H44BFeF4P2-
Rh‚3H2O: C, 59.67; H, 5.01. Found: C, 59.69; H, 4.76.
Ca ta lytic Hyd r ogen a tion s. The standard procedure was
as follows: the substrate (1.64 mmol) and the catalyst (ac-
cording to method, see the Supporting Information) were
dissolved in 10 mL of the solvent under argon. The solution
was stirred for 15 min and then transferred via a steel
capillary into a 180 mL thermostated glass reactor or a 50 mL
stainless steel autoclave. The inert gas was then replaced by
Ack n ow led gm en t. A.M. thanks the Swiss National
Science Foundation (CHiral 2 project) for financial
support to F.M. The authors are grateful to Mrs. A.
Holderer, Mrs. A. Balzer, and Mr. P. Imhof for perform-
ing the catalytic hydrogenation reactions.
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 for (S,S)-2a and
5a , drawings of conformers for 6a ,b, and details of the
hydrogenation reactions. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM980754A