Preparation of C2-symmetric bis[2-(diphenylphosphino)ferrocen-1- yl]-methane and its use in rhodium- and ruthenium-catalyzed hydrogenation

Article abstract of DOI:10.1002/hlca.200690173

The two diphosphine ligands (R_p,R_p)- and (S _p,S_p)-bis[2-(diphenylphospino)ferrocenyl]methane, (R _p,R_p)- and (S_p,S_p)-1, resp., were prepared in six steps from (S)- and

Full text of DOI:10.1002/hlca.200690173

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Helvetica Chimica Acta – Vol. 89 (2006)
Preparation of C2-Symmetric Bis[2-(diphenylphosphino)ferrocen-1-yl]-
methane and Its Use in Rhodium- and Ruthenium-Catalyzed Hydrogenation
by Yaping Wanga), Walter Weissensteiner*a), Kurt Mereiterb), and Felix Spindler*c)
a) Institute of Organic Chemistry, University of Vienna, Währinger Straße 38, A-1090 Vienna
b) Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9,
A-1060 Vienna
c) Solvias AG, WKL 127, P. O. Box, CH-4002 Basel
Dedicated to Professor Giambattista Consiglio on the occasion of his 65th birthday
The two diphosphine ligands (Rp,Rp)- and (Sp,Sp)-bis[2-(diphenylphospino)ferrocenyl]methane,
(Rp,Rp)- and (Sp,Sp)-1, resp., were prepared in six steps from (S)- and (R)-ferrocenyl tolyl sulfoxide,
respectively (Scheme). In the solid state, both the diborane complex (Rp,Rp)-1·(BH3)2 and the palladium
dichloride complex [PdCl2((Rp,Rp)-1)] were found to adopt C2-pseudosymmetric structures according to
X-ray analyses (Figs. 2 and 3). In the Rh- and Ru-catalyzed hydrogenation of selected alkenes and
ketones in the presence of the new ligands, enantioselectivities of up to 55% ee were obtained.
1. Introduction. – Homogeneous enantioselective hydrogenation has now devel-
oped into a mature synthetic methodology, not only for scientific purposes [1], but
also for the production of enantiomerically pure bioactive ingredients and fine chem-
icals on an industrial scale [2]. Rhodium (Rh) and ruthenium (Ru) complexes of
diphosphine ligands are preferentially used for the enantioselective hydrogenation of
alkenes and ketones [3]. However, of the innumerable chiral diphosphines that have
been investigated, only a few have proven suitable for industrial processes. These
include C2-symmetric ligands like Dipamp [4], Binap [5], or Duphos [6], as well as
C1-symmetric Josiphos [7] ligands. However, despite the huge number of diphosphines
that have been tested, particularly in terms of additional industrial applications, ligand
development continues intensively.
For a long time, especially since the early development of Diop [8] and Dipamp,
ligand design has focused primarily on bidentate and C2-symmetric diphosphines,
which were considered superior to mono- or bidentate C1-symmetric ligands. This
view has changed significantly, especially since C1-symmetric Josiphos-type derivatives
were successfully used as catalyst ligands in industrial hydrogenation processes [7].
Nowadays, complexes of certain monodentate ligands are also known to catalyze
hydrogenations with excellent enantioselectivity [9]. In recent years, the successful
application of Josiphos-type ligands in enantioselective hydrogenations and other reac-
tions has boosted the further development of C1- and, to a much lesser extent, of C2-
symmetric ferrocenyl-based diphosphines [10]. In addition, our search for novel classes
of ferrocenyl diphosphines has mainly focused on C1-symmetric ligands with either a
homo- or a heteroannulene-bridged ferrocene backbone [11], e.g., Bifep-type biferro-
© 2006 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 89 (2006)
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cenes [12], or derivatives having a ferrocenyl-aryl backbone. Development of the latter
system eventually resulted in the Walphos-type ligand family [13].
Recently, in the search for new backbones, we envisaged that ligand development
could be extended to additional C2-symmetric ferrocenyl diphosphines, and we herein
report the preparation and structural analysis of (Rp,Rp)- and (Sp,Sp)-bis[2-(diphenyl-
phospino)ferrocen-1-yl)methane (1) and discuss the application of these compounds
in enantioselective hydrogenation reactions.
2. Results and Discussion. – 2.1. Synthesis. In general, chiral C2-symmetric ferrocene
derivatives can be obtained either by hetero-substitution of the ferrocene backbone or
by appropriately linking two homochiral C1-symmetric ferrocene units. Examples of
the former system include 1,1’-disubstituted P-stereogenic ferrocenes of type A (Fig.
1) [14] and Ferriphos-type ligands [15]. The latter type of compounds is represented
by Bifep [16], Trap [17], the cyclohexyldiamide-linked bisferrocenyl derivative B
[18], and the newly synthesized ligand 1 (see Scheme below).
Fig. 1. Examples of C2-symmetric ferrocenyl diphosphine ligands
Attempts to build up the diferrocenylmethane backbone in one step from ortho-
lithiated ferrocenyl tolyl sulfoxide (2-Li-2) and ethyl formate failed. A similar observa-
tion was recently reported in the literature [19]. As a result, we decided to synthesize
the ligand backbone in a stepwise fashion by adopting Kagan’s sulfoxide methodology
(Scheme) [20]. First, 2-lithio-tributylstannylferrocene ((Rp)-3) was prepared by reacting
(Sc,Rp)-4, easily accessible from 4-tolylsulfinylferrocene ((Sc)-2), with t-BuLi [21]. Trap-
ping of (Rp)-3 with DMF as the electrophile gave the corresponding aldehyde (Rp)-5. In
the subsequent step, reaction of (Rp)-5 with (Rp)-3 led to the intermediate (Rp,Rp)-6 in
which the final ligand backbone is already preformed. It should be noted that, although

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Helvetica Chimica Acta – Vol. 89 (2006)
Scheme. Preparation of the New Ligand (Rp,Rp)-1 and Its Complex [PdCl2((Rp,Rp)-1)]
an alternative preparation of aldehyde 5 has been reported previously [22], in our par-
ticular case the synthesis of 5 from 4 is more suitable, given that, in this route, both pre-
cursors of 6 (i.e., 3 and 5) are accessible from a single common intermediate. Reduction
of (Rp,Rp)-6 with BH3 in THF [23] gave the bis(tributylstannyl) derivative (Rp,Rp)-7,
which was reacted with t-BuLi and chloro(diphenyl)phosphine, and subsequently trap-
ped with BH3 in THF to afford the diborane complex (Rp,Rp)-1·(BH3)2. Finally, depro-
tection with Et2CAHTRENUNG H led to the target C2-symmetric diphosphine ligand (Rp,Rp)-1. To
study the coordination behavior of ligand 1, its palladium dichloride complex
[PdCl2((Rp,Rp)-1)] was prepared by reacting (Rp,Rp)-1 with [PdCl2(MeCN)2].
2.2. Structure Elucidation. The structural integrity of all compounds was assessed by
NMR spectroscopy and, in the cases of (Rp,Rp)-1·(BH3)2 and [PdCl2((Rp,Rp)-1)], also
by single-crystal X-ray-diffraction analyses. Views of the molecular structures are
shown in Figs. 2 and 3 for (Rp,Rp)-1·(BH3)2 and [PdCl2((Rp,Rp)-1)], respectively. The
NMR results show that, in solution, both ligand 1 and its complex [PdCl2((Rp,Rp)-1)]
show twofold symmetry. However, in the solid state, they are found in asymmetric envi-
ronments, but show clear C2-pseudosymmetry.
The molecular structure of [PdCl2((Rp,Rp)-1)] is of particular interest. Both ferro-
cene units are arranged in a propeller-like fashion that places the Pd-atom and the

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Fig. 2. X-Ray crystal structure of (Rp,Rp)-1·(BH3)2. Ellipsoids are shown at the 40% level; H-atoms
have been omitted for clarity. Selected distances [Å] and angles [8]: (FeÀCCp aver, 2.046(1); P(1)À
)
C(2), 1.798(1); P(1)ÀC(22), 1.816(1); P(1)ÀC(28), 1.818(1); P(1)ÀB(1), 1.929(1); P(2)ÀC(12),
1.800(1); P(2)ÀC(34), 1.820(1); P(2)ÀB(2), 1.939(1); C(21)ÀC(1), 1.510(2); C(21)ÀC(11), 1.512(2);
C(1)ÀC(21)ÀC(11), 112.0(1); B(1)ÀP(1)ÀC(2)ÀC(1), 42.8(1); B(2)ÀP(2)ÀC(12)ÀC(11), 43.2(1);
P(1)ÀC(2)ÀC(1)ÀC(21), 1.1(2); P(2)ÀC(12)ÀC(11)ÀC(21), 2.5(2); C(2)ÀC(1)ÀC(21)ÀC(11),
80.0(1); C(12)ÀC(11)ÀC(21)ÀC(1), 72.2(1).
methylene carbon C(21) on a line that almost dissects the bond angles Cl(1)ÀPdÀ
Cl(2), P(1)ÀPdÀP(2), and C(1)ÀC(21)ÀC(11) (Fig. 3). In a perfect C2-symmetric
arrangement, this line would be the C2 symmetry axis.
An additional striking feature of the molecular structure of [PdCl2((Rp,Rp)-1)] is
that each of the substituted ferrocenyl cyclopentadienyl (Cp) rings is oriented nearly
parallel to one of the phenyl (Ph) rings (e.g., the Cp ring made of C(1) to C(5) is parallel
to the Ph ring consisting of C(34) to C(39), etc.) and shows pronounced p-stacking inter-
actions
with
very
short
C···C
contacts
(e.g.,
C(1)···C(34)=3.134,
C(5)···C(35)=3.160, C(11)···C(22)=3.115, and C(13)···C(27)=3.193 Å). This stack-
ing interaction certainly contributes a great deal to the stability of the observed C2-sym-
metric conformer. This phenomenon is also present in (Rp,Rp)-1·(BH3)2, albeit to a
lesser extent (only one C···C contact <3.20 Å).
However, although one might expect a C2-symmetric or higher-symmetric diphos-
phine ligand to form a palladium dichloride complex adopting the same symmetry as
the free ligand, this is not necessarily the case. For example, in the solid state, the molec-
ular structure of [PdCl2(Binap)] [24] and also of the related Rh norbornadiene (NBD)
complex [Rh(Binap)(NBD)]ClO4 [25] have C2 pseudosymmetry. In contrast, the palla-
dium dichloride complex of bis[2-(diphenylphosphino)phenyl]methane, [PdCl2(8)]
[26], with a maximum ligand and complex symmetry of C2v, adopts an asymmetric con-
formation (Fig. 4,a). In solution, average C2 and Cs symmetry is observed for
[PdCl2(Binap)] and [PdCl2(8)], respectively. Since the ligand backbones of 1 and 8

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Helvetica Chimica Acta – Vol. 89 (2006)
Fig. 3. X-Ray crystal structure of [PdCl2((Rp,Rp)-1)]·CHCl3. Ellipsoids are shown at the 40% level;
H-atoms have been omitted for clarity. Selected distances ([Å] and angles [8]: PdÀP(1), 2.277(1);
PdÀP(2), 2.278(1); PdÀCl(1), 2.352(1); PdÀCl(2), 2.362(1); (FeÀCCp
)
,
2.048(4); P(1)ÀC(2),
aver
1.798(4); P(1)ÀC(22), 1.813(4); P(1)ÀC(28), 1.838(4); P(2)ÀC(12), 1.812(4); P(2)ÀC(34), 1.810(4);
P(2)ÀC(40), 1.814(4); C(21)ÀC(1), 1.503(5); C(21)ÀC(11), 1.499(6); C(1)ÀC(21)ÀC(11), 117.9(3);
PdÀP(1)ÀC(2)ÀC(1), À90.3(4); PdÀP(2)ÀC(12)ÀC(11), À87.8(4); P(1)ÀC(2)ÀC(1)ÀC(21),
À15.2(6); P(2)ÀC(12)ÀC(11)ÀC(21), À7.5(7); C(2)ÀC(1)ÀC(21)ÀC(11), 40.8(6); C(12)ÀC(11)À
C(21)ÀC(1), 31.6(7).
are structurally related to each other (8 can be obtained from 1 by replacing the ferro-
cenyl units by aryl rings), we envisaged that, like [PdCl2(8)], complex [PdCl2(1)] could
adopt C1-symmetric conformers. We, therefore, carried out simple force-field calcula-
tions (for details see Exper. Part) and found that [PdCl2(1)] can, indeed, adopt not
only a C2-symmetric conformer (very similar to that found in the solid state), but
two homomeric C1-symmetric conformers also seem to be accessible [27]. In principle,
both C1-symmetric conformers are interchangeable by rotation of the ferrocenyl units
about the ferrocenyl–CH2 bonds. Therefore, the observed twofold symmetry of
[PdCl2(1)] in solution could arise either from a C2- and/or from two interchanging
1
C1-symmetric conformers (Fig. 4,b). Since low-temperature H- and 31P{1H}-NMR
studies did not show evidence for any exchange phenomena, neither possibility can
be excluded (see Exper. Part).
Although unexpected, superposition of the molecular structures of complex
[PdCl2((Rp,Rp)-1)], ACHTRENGUwhich forms an ACHRTEeUGN ight-membered chelate ring system, and com-
plexes [PdCl2((S)-Binap)] or [Rh((S)-(Binap))(NBD)]ClO4 (with seven-membered
chelate rings) shows surprising similarities. The arrangement of the substituted Cp
rings is almost identical to that of the naphthyl groups of Binap, placing the P-atoms
and, in particular, the attached Ph rings and the transition metal in comparable posi-
tions.

Helvetica Chimica Acta – Vol. 89 (2006)
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Fig. 4. a) Schematic representation of the molecular structure of [PdCl2(8)] in the solid state. b) Calcu-
lated Structures of C1-and C2-symmetric conformers of [PdCl2(1)]
2.3. Catalysis. The catalytic behavior of ligand (Sp,Sp)-1 was assessed by screening it
in catalytic hydrogenations of the olefins and ketones 9–14. All catalyst precursors
were formed in situ using an appropriate Rh or Ru source (Table). Each hydrogenation
reaction gave quantitative or nearly quantitative conversion (Table, Entry 6), except
when methyl 2-oxo-2-phenylacetate (13) was used as the substrate. However, the prod-
ucts were formed with only low-to-moderate enantioselectivities. For example, regard-
less of the Rh source used, hydrogenation of methyl a-(acetamido)cinnamate (9)
afforded N-acetylphenylalanine methyl ester in 55% enantiomeric purity (Entries 1
and 2), and ethyl (Z)-3-(acetamido)but-2-enoate (10) gave the corresponding buta-
noate in an enantiomeric excess (ee) of 53% (Entry 3). Unfortunately, hydrogenation
of the other olefins tested gave products in only very poor enantiomeric purities (17
and 8% ee for 11 (Entry 4) and 12 (Entry 5), resp.). Similar low ee values were obtained
for the Rh- and Ru-mediated hydrogenation of the a- and b-oxo esters 13 and 14 (6 and
15% ee, resp.; Entries 6 and 7).
3. Conclusions. – The C2-symmetric bis[2-(diphenylphosphino)ferrocenyl]methane
ligands (Rp,Rp)- and (Sp,Sp)-1 were synthesized in six steps from (S)- and (R)-ferrocenyl
tolyl sulfoxide, respectively. In the solid state, the complex [PdCl2((Rp,Rp)-1)] adopts a
C2-pseudosymmetric conformation, with the chiral pocket being surprisingly similar to
those of the Binap complexes [PdCl2((S)-Binap)] and [Rh((S)-(Binap))(NBD)]ClO4.
However, when diphosphine 1 was used as the ligand in Rh- and Ru-catalyzed hydro-
genations of olefins and ketones, only low-to-moderate enantioselectivities were
obtained. Based on the X-ray crystal structure of [PdCl2(8)] (8=bis[2-(diphenylphos-

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Table. Rhodium-and Ruthenium-Catalyzed Hydrogenations of Alkenes and Ketones in the Presence of the
New Ligand (Sp,Sp)-1
Entry Substrate Catalyst precursor Additive
Conditiona) p (H2)
T
Conv. ee
Config.
[bar]
[h] [%] [%]
1
2
3
4
5
6
7
9
9
[Rh(NBD)2]BF4
[Rh(COD)(acac)] HBF4 ·Et
[Rh(NBD)2]BF4
[Rh(NBD)2]BF4
[Rh(NBD)2]BF4
[Rh(NBD)Cl]2
–
A
A
B
A
A
C
D
1
1
1
5
1
1
1
1
100
100
99
55b) (R)
55b) (R)
53c) (R)
17d) (R)
8e) (R)
6f) (R)
15g) (R)
O
OH
10
11
12
13
14
CF
–
–
–
U
N
20 100
1
20
19 100
100
18
80
80
[RuI2(p-cymene)]2 HCl
a) A: MeOH (10 ml); substrate/catalyst (S/C): 200 :1, 258. B: EtOH (10 ml), S/C 100 :1, 258. C: Toluene
b
(10 ml), S/C 200 :1, 258. D: EtOH (10 ml), S/C 200 :1, 258. ) Determined by GC (Chirasil-L-Val, 1708,
isothermal). c) By GC (Lipodex E, 1308, isothermal). d) By HPLC (Chiralcel OB, hexane/i-PrOH
f
98 :2, 0.1 ml/min) of Me ester. e) By GC (Lipodex E, 808, isothermal). ) By HPLC (Chiralcel OJ, hex-
ane/i-PrOH 90 :10, 1.0 ml/min). g) By GC (Lipodex E, 808, isothermal) of TFA derivative.
phino)phenyl]methane) and corroborated by simple force-field calculations on
[PdCl2(1)], we assume that, unlike in the case of Binap in solution, transition-metal
complexes of ligand 1 are much more flexible and are not only able to adopt C2- but
also C1-symmetric conformations, an observation that could well be responsible for
the low enantioselectivities observed.
This work was supported by Solvias AG (Basel) and by the Österreichischer Akademischer Aus-
tauschdienst.
Experimental Part
General. All manipulations were carried out under Ar atmosphere using standard Schlenk techni-
ques. Solvents were distilled from the appropriate drying agents, and degassed before use. Chromato-
graphic separations were performed under gravity, either on silica gel (40–62 mm; Merck) or on alumina
(activity II–III, 63–200 mm; Merck). Petroleum ether (PE) with a boiling range of 55–658 was used for
column chromatography (CC). (Sc)-(4-Methylphenyl)sulfinylferrocene ((Sc)-2) and 2-[(4-methylphenyl)-
sulfinyl]-1-(tributylstannyl)ferrocene ((Sc,Rp)-4) were prepared according to [21]. Melting points (m.p.)
were determined on a Kofler melting-point apparatus; uncorrected. Optical rotations were measured
on a Perkin Elmer 241 polarimeter. NMR Spectra were recorded on a Bruker DPX-400 spectrometer

Helvetica Chimica Acta – Vol. 89 (2006)
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in CDCl3; chemical shifts d in ppm rel. to CHCl3 (1H: 7.26 ppm), CDCl3 (13C{1H}: 77.0 ppm), or 85%
H3PO4 (31P{1H}: 0 ppm); coupling constants J in Hz; in the 13C-NMR spectra, the J values refer to
13C,31P couplings. Abbreviations: br., s, d, t, and q refer to broad, singlet, doublet, triplet, and quartet,
resp., and Cq (13C-NMR) stands for quaternary C-atom; for arbitrary atom numbering, see Fig. 2.
Low-temp. NMR spectra of [PdCl2(1)] were recorded on a Bruker Avance-300 spectrometer in CD2Cl2
in a temp. range of À80 to +258. Mass spectra were recorded on a Finnigan MAT-8230 apparatus
(EI) or on Finnigan MAT-900S (FD); in m/z. Elemental analyses were performed by the Mikroanaly-
tisches Laboratorium der Fakultät für Chemie der Universität Wien.
2-(Tributylstannyl)ferrocene-1-carbaldehyde ((Rp)-5). To a degassed soln. of (Sc,Rp)-4 (9 g, 14.6
mmol) in THF (80 ml) at À788 under Ar gas was added dropwise 1.7M t-BuLi in pentane (9.46 ml,
16.09 mmol) via syringe. The soln. was stirred at À788 for 5 min. Then, DMF (3.41 ml, 43.89 mmol)
was added, and the soln. was stirred for an additional 2 h at À788. Then, the reaction was quenched
with H2O (20 ml). The product was extracted with Et2ACHTREUONG , the org. phase was washed with H2O and
brine, dried (MgSO4), and concentrated under reduced pressure. The residue was purified by CC
2A
(Alox 90; PE/Et CHTREUNOG 9 :1) to afford (Rp)-5 (6.42 g) in 87% yield. The spectroscopic and physical data
were identical with those reported in [22]. Red oil. 1H-NMR (400 MHz): 0.91 (t, J=7.3, 3 Me);
1.01–1.15 (m, 3 CH2); 1.30–1.42 (m, 3 CH2); 1.47–1.62 (m, 3 CH2); 4.22 (s, 5 H of Cp’); 4.45–4.51 (m,
1 H of Cp); 4.74 (t, J=2.4, 1 H of Cp); 4.90–4.94 (m, 1 H of Cp); 9.94 (s, HCO).
(Rp,Rp)-Bis[(2-(tributylstannyl)ferrocen-1-yl]methanol (Rp,Rp)-6. To a degassed soln. of (Sc,Rp)-4
(7.85 g, 12.76 mmol) in THF (80 ml) at À788 under Ar gas was added dropwise 1.7M t-BuLi in pentane
(8.26 ml, 14.04 mmol) via syringe, and the soln. was stirred at À788 for 5 min. A degassed soln. of (Rp)-5
(6.42 g, 12.76 mmol) in THF (5 ml) was added, and the mixture was stirred for another 2 h at À788. Then,
the mixture was allowed to reach r.t., and the reaction was quenched with H2O (20 ml). The product was
extracted with Et
O, the org. phase was washed with H2O and brine, dried (MgSO4), and concentrated
2AO 100 :1) to afford (Rp,Rp)-6
under reduced pressure. The residue was purified by CC (Alox 90; PE/Et CTHREUNG
(9.94 g) in 80% yield. Due to its rather low stability, the compound was immediately used in the next
step. Orange oil. 1H-NMR (400 MHz): 0.85–0.98 (m, 6 Me); 1.00–1.14 (m, 6 CH2); 1.32–1.45 (m, 6
CH2); 1.49–1.66 (m, 6 CH2); 2.28 (d, J=2.4, OH); 3.93–3.96 (m, 1 H of Cp); 3.97–4.00 (m, 1 H of
Cp); 4.12 (s, 5 H of Cp’); 4.15–4.17 (m, 1 H of Cp); 4.18 (s, 5 H of Cp’); 4.22 (t, J=2.3, 1 H of Cp);
4.28 (t, J=2.4, 1 H of Cp); 4.32–4.36 (m, 1 H of Cp); 5.08 (d, J=2.4, 1 CH). 13C{1H}-NMR (100.6
MHz): 10.92 (CH2); 11.59 (CH2); 13.72 (Me); 13.77 (Me); 27.53 (CH2); 27.62 (CH2); 29.34 (CH2);
29.47 (CH2); 66.92 (Cq of Cp); 67.82 (CH); 68.26 (Cp’); 68.59 (Cp’); 69.40 (CH); 69.51 (Cq of Cp);
69.66 (CH); 70.13 (CH); 70.75 (CH); 74.19 (CH); 74.24 (CH); 97.44 (Cq of Cp); 102.21 (Cq of Cp).
FD-MS: 978.0 (M+).
(Rp,Rp)-Bis[2-(tributylstannyl)ferrocen-1-yl]methane ((Rp,Rp)-7). To a degassed soln. of (Rp,Rp)-6
(5 g, 5.11 mmol) in THF (40 ml) was added dropwise 1M BH3 in THF (40.88 ml, 40.88 mmol). The mix-
ture was heated at reflux for 7 h, until the starting material was consumed according to TLC analysis (alu-
mina; PE). The mixture was cooled to 08, quenched by addition of H2O, extracted with Et
H2O and brine, dried (MgSO4), and concentrated under reduced pressure. The residue was purified by
CC (Alox 90; PE/Et2A
O 100 :1) to afford (Rp,Rp)-7 (3.82 g) in 78% yield. Orange oil. [a]2l0 (l in nm):
2ACHTREOUGN , washed with
CTHREUNG
À17.4 (589), À20.0 (578), À36.9 (546) (c=0.88, CHCl3). 1H-NMR (400.1 MHz): 0.97 (t, J=7.33, 6
Me); 1.05–1.24 (m, 6 CH2); 1.37–1.48 (m, 6 CH2), 1.55–1.70 (m, 6 CH2); 3.38 (s, 1 CH2); 3.83 (dd,
J=2.3, 1.3, 2 H of Cp, exchangeable); 4.06 (s, 2×5 H of Cp’); 4.13–4.16 (m, 2 H of Cp, exchangeable);
4.17 (t, J=2.3, 2 H of Cp). 13C{1H}-NMR (100.6 MHz): 10.85 (CH2); 13.72 (Me); 27.57 (CH2); 29.40
(CH2); 33.38 (CH2); 68.60 (Cp’); 69.57 (Cq of Cp); 70.34 (C(4) of Cp); 70.38 (C(5) of Cp); 73.82 (C(3)
of Cp); 94.75 (Cq of Cp). FD-MS: 962 (M+).
(m-{(Rp,Rp)-Bis[2-(diphenylphosphino)ferrocen-1-yl]methane-P,P})hexahydrodiboron ((Rp,Rp)-1·
(BH3)2). To a degassed soln. of (Rp,Rp)-7 (2.5 g, 2.6 mmol) in THF (20 ml) at 08 under Ar gas was
added dropwise 1.6M BuLi (in hexane; 3.41 ml, 5.46 mmol) via syringe. The soln. was stirred at this.
temp. for 10 min, and Ph
min at 08, and then allowed to reach r.t. Stirring was continued, until all starting material was consumed
(TLC control (alumina; PE/Et2AO 10 :1)). Then, 1M BH3 in THF (20.8 ml, 20.8 mmol) was added, and the
mixture was stirred for a further 16 h at r.t. The mixture was quenched with sat. aq. NaHCO3 soln.,
2ACHTREPUNG Cl (1.4 ml, 7.8 mmol) was added. The mixture was stirred for a further 30
CTHREUNG

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Helvetica Chimica Acta – Vol. 89 (2006)
extracted with Et2ACHTROENGU , washed with H2O and brine, dried (MgSO4), and concentrated under reduced pres-
sure. The residue was purified by CC (Alox 90; PE/Et
2AO/Et3AN 10 :4 :0.1) to afford (Rp,Rp)-1 (0.64 g) in
CHTREUNG
32% yield. Yellow solid. M.p.>2438 (dec.). [a]2l0 (l in nm): +129.0 (589), +128.4 (578), +103.2 (546)
(c=0.98, CHCl3). 1H-NMR (400.1 MHz): 1.24–2.18 (very br. s, 2 BH3); 3.42–3.46 (m, 2 H of Cp); 3.71
(t, J=2.5, 2 H of Cp); 3.90–3.93 (m, 2 H of Cp); 4.13 (s, 2×5 H of Cp’); 4.14 (s, 1 CH2); 7.31–7.38 (m,
4 H of Ph); 7.39–7.52 (m, 12 H of Ph); 7.60–7.72 (m, 4 H of Ph). 13C{1H}-NMR (100.6 MHz): 26.93
(CH2); 67.42 (d, J=65.0, Cq of Cp); 69.54 (d, J=6.1, C(4) of Cp); 70.49 (Cp’); 72.37 (d, J=3.8, C(3)
of Cp); 74.27 (d, J=7.6, C(5) of Cp); 92.86 (d, J=15.7, Cq of Cp); 128.08, 128.15, 128.18, 128.25 (2d, 4
m-C of Ph); 130.68 (d, J=2.3, 2 p-C of Ph); 130.85 (d, J=2.3, 2 p-C of Ph); 131.29, 131.48, 132.04 (4
ipso-C of Ph); 132.99 (d, J=9.2, 2 o-C of Ph); 133.32 (d, J=9.2, 2 o-C of Ph). 31P{1H}-NMR (162.0
MHz): 15.68 (br. s). EI-MS (2708): 780 (1, M+), 766 (9, [MÀBH3]+), 752 (100, [MÀ2 BH3]+), 566 (96),
500 (18), 445 (16).
(Rp,Rp)-Bis[2-(diphenylphosphino)ferrocen-1-yl]methane ((Rp,Rp)-1). A soln. of (Rp,Rp)-1·(BH3)2
(1.14 g, 1.46 mmol) in freshly distilled Et
was consumed (TLC). The solvent was removed under reduced pressure, and the residue was purified by
CC (Alox 90; PE/Et2AO/Et3AN 70 :30 :3) to afford (Rp,Rp)-1 (1.07 g) in 98% yield. Yellow solid. M.p.
2ACHTRENUNG H (20 ml) was stirred for 4 h at r.t., until the starting material
C
CHTREUNG
154–1588. [a]2l0 (l in nm): +267.7 (589), +278.4 (578), +318.8 (546) (c=0.96, CHCl3). 1H-NMR
(400.1 MHz): 3.46–3.52 (m, 2 H of Cp, exchangeable); 3.70 (t, J=2.4, 2 H of Cp); 3.88 (s, 2×5 H of
Cp’); 3.90 (s, 1 CH2); 3.92–3.95 (m, 2 H of Cp, exchangeable); 7.03–7.12 (m, 4 H of Ph); 7.16–7.23
(m, 6 H of Ph); 7.32–7.40 (m, 6 H of Ph); 7.49–7.59 (m, 4 H of Ph). 13C{1H}-NMR (100.6 MHz): 28.83
(t, J=9.1, CH2); 68.59 (C(4) of Cp); 69.53 (Cp’); 70.48 (d, J=3.8, C(3) of Cp); 73.03 (t, J=4.6, C(5) of
Cp); 74.38 (d, J=6.1, Cq of Cp); 93.55 (d, J=27.1, Cq of Cp); 127.60 (2 p-C of Ph); 127.69 (d, J=6.1, 4
m-C of Ph); 127.99 (d, J=8.4, 4 m-C of Ph); 128.98 (2 p-C of Ph); 132.64 (d, J=17.59, o-C of Ph);
135.19 (d, J=20.6, o-C of Ph); 137.68 (d, J=6.9, 2 ipso-C of Ph); 140.10 (d, J=8.4, 2 ipso-C of Ph).
31P{1H}-NMR (162.0 MHz): À22.55 (s). EI-MS (2308): 752 (67, M+), 566 (100), 500 (12), 424 (13).
Anal. calc. for C45H38Fe2P2: C 71.83, H 5.09, P 8.23, found: C 71.95, H 5.44, P 8.06.
Dichloro(m-{(Rp,Rp)-bis[2-(diphenylphosphino)ferrocen-1-yl]methane-P,P})palladium(II) ([PdCl2ACHTREUGN-
((Rp,Rp)-1)]. A degassed soln. of (Rp,Rp)-1 (75 mg, 0.1 mmol) in benzene (2 ml) was added to a suspen-
sion of [PdCl2(MeCN)2] (24 mg, 0.094 mmol) in benzene (2 ml) through a Teflon tube. The mixture was
stirred for 18 h at r.t., and the resulting precipitate was filtered off and washed with both benzene (2×2
ml) and Et2CAHTREOUNG (3×3 ml) to afford the title compound (81 mg) in 87% yield. Red solid. M.p.>2158 (dec.).
[a]2D0 =À838 (c=0.06, CHCl3). H-NMR (400.1 MHz): 3.64–3.67 (m, 2 H of Cp); 3.68–3.71 (m, 2 H of
Cp); 3.77 (s, 2×5 H of Cp’); 3.91 (s, 1 CH2); 3.96–4.01 (m, 2 H of Cp); 7.27–7.33 (m, 4 m-H of Ph1);
7.33–7.40 (m, 2 p-H of Ph1); 7.41–7.49 (m, 4 m-H of Ph2); 7.50–7.56 (m, 2 p-H of Ph2); 7.56–7.66 (m,
4 o-H of Ph1); 8.51–8.62 (m, 4 o-H of Ph2); the Ph2 H-atoms are stacking to the Cp ring. 13C{1H}-
NMR (100.6 MHz): 31.96 (CH2); 69.83 (br. s, C(4) of Cp); 70.66 (Cp’); 73.08 (d, J=16.1, C(3) of Cp);
75.03 (br. s, C(5) of Cp); 126.61 (d, J=12.2, 4 m-C of Ph1); 128.42 (d, J=11.5, 4 m-C of Ph2); 130.34
(2 p-C of Ph); 131.81 (2 p-C of Ph); 134.36 (d, J=11.8, o-C of Ph1); 135.90 (d, J=13.0, o-C of Ph2);
the Cq- and ipso-C-atoms of the Ph rings were not observed. 31P{1H}-NMR (162.0 MHz): 31.60 (s).
X-Ray Crystal-Structure Determination1) of (Rp,Rp)-1·(BH3)2 and [PdCl2((Rp,Rp)-1)]·CHCl3. Crys-
1
tals of (Rp,Rp)-1·(BH3)2 were obtained by layering a CH2Cl2 soln. with Et2CAHTREOUNG , and crystals of [PdCl2((Rp,
Rp)-1)]·CHCl3 were obtained by evaporation of a CHCl3 soln. of the target compound. X-ray data were
collected on a Bruker Smart CCD area-detector diffractometer using graphite-monochromated MoKa
radiation (l=0.71073 Å), with 0.38 w-scan frames covering the complete spheres of the reciprocal
space. After frame data integration with the SAINT program [28], corrections were applied for absorp-
tion, l/2 effects, and crystal decay using the SADABS program [28]. The structures were solved by direct
1
)
CCDC 299604-299606 contain the supplementary crystallographic data for this paper. These data can
be obtained, free of charge, from the Cambridge Crystallographic Data Centre at www.ccdc.cam.
ac.uk/data_request/cif. Note that the data includes the room-temperature structure of
[PdCl2((Rp,Rp)-1)]·ACTHERCUNG H3NO2, a nitromethane solvate that is isostructural with [PdCl2((Rp,Rp)-1)]·
CHCl3.

Helvetica Chimica Acta – Vol. 89 (2006)
1781
methods using the program SHELXS97 [29]. Structure refinement on F2 was carried out with the pro-
gram SHELXL97 [29]. All non-H-atoms were refined anisotropically. H-Atoms were inserted in ideal-
ized positions, and were refined riding with the atoms to which they are bonded. Views of the molecular
structures are shown in Figs. 2 and 3, and selected geometric data are given in the figure legends.
Crystal data for (Rp,Rp)-1·(BH3)2. Formula, C45H44B2Fe2P2; Mr 780.06; T=100(2) K; orthorhombic,
space group P212121 (No. 19); a=12.2672(14), b=13.9364(16), c=22.063(3) Å; V=3771.8(8) Å3; Z=4;
m=0.89 mmÀ1. Of 55,054 reflections collected (qmax =308), 10,961 were independent; final R indices:
R1 =0.0209 (all data), wR2 =0.0529 (all data); Flack absolute structure parameter=À0.008(5).
Crystal data for [PdCl2((Rp,Rp)-1)]·CHCl3. Formula, C46H39Cl5Fe2P2Pd, Mr 1049.06; T=100(2) K;
tetragonal, space group P43212 (No. 96); a=14.2830(12), c=40.512(4) Å; V=8264.7(12) Å3; Z=8;
m=1.56 mmÀ1. Of 109,989 reflections collected (qmax =28.38), 10,160 were independent; final R indices:
R1 =0.0449 (all data), wR2 =0.0903 (all data); Flack absolute structure parameter=À0.011(18).
Standard Procedure for Hydrogenation Reactions. The substrate (2.53 mmol) and the catalyst
(formed in situ, for details see Table) were dissolved separately in 5 ml of the solvent under Ar gas
(total volume: 10 ml). The catalyst soln. was stirred for 15 min. Both the catalyst and the substrate
soln. were then transferred through a steel capillary either into a 180-ml thermostated glass reactor or
into a 50-ml stainless-steel autoclave. The inert gas was then replaced by H2 (three cycles), and the pres-
sure was set. After completion of the reaction (1–20 h according to GC analysis), the product was iso-
lated quantitatively after filtration through a plug of SiO2 to remove the catalyst. The enantiomeric purity
of the product was determined either by GC or HPLC (see Table).
Force-Field Calculations. Computer modeling was carried out with the program PCMODEL (vers.
8.50.0) [27] and Allinger’s MMX force field. The minimization ‘Steepest Descent’ followed by New-
ton–Raphson were applied in each case. A square-planar Pd coordination sphere was predefined. All
conformers of [PdCl2(1)] were minimized in two different ways: by including PI calculations as well as
by using a predefined atom type (atom type 40) for all aromatic C-atoms. With both methods, the C1-sym-
metric conformer was calculated to be more stable than the C2-symmetric one (3.2 (PI) vs. 4.9 kcal/mol,
resp.).
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Received March 29, 2006