[5]Ferrocenophane based ligands for stereoselective Rh-catalyzed hydrogenation and Cu-catalyzed Michael addition

Article abstract of DOI:10.1016/j.tetasy.2007.08.011

A series of homochiral [5]ferrocenophane based N/P, N/S, N/Se, Se/P and P/P ligands was prepared from (R)-N,N-dimethylamino[5]ferrocenophane. These ligands were tested in the Rh-catalyzed hydrogenation of dimethyl itaconate and in Cu-catalyzed Michael addition of Et₂Zn to cyclohex-2-enone. The best results in terms of conversion and enantioselectivity in the Rh-catalyzed hydrogenation provided bis(diphenylphosphine) ligand 2h (100% conversion and 95% ee) and aminophosphine 2a in the Cu-catalyzed conjugate addition (100% conversion 84% ee). The enantioselectivity of the Rh-catalyzed hydrogenation of methyl 2-acetamidoacrylate was lower (41% ee).

Full text of DOI:10.1016/j.tetasy.2007.08.011

Tetrahedron: Asymmetry 18 (2007) 1893–1898
[5]Ferrocenophane based ligands for stereoselective Rh-catalyzed
hydrogenation and Cu-catalyzed Michael addition
a
b
b
a,
*
ˇ
`
´
Ambroz Almassy, Katalin Barta, Giancarlo Francio, Radovan Sebesta,
Walter Leitnerb,* and Stefan Toma
ˇ
a
aDepartment of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynska dolina, 84215 Bratislava, Slovakia
bInstitute for Technical and Macromolecular Chemistry, RWTH Aachen, Worringerweg 1, 52074 Aachen, Germany
Received 8 May 2007; accepted 10 August 2007
Abstract—A series of homochiral [5]ferrocenophane based N/P, N/S, N/Se, Se/P and P/P ligands was prepared from (R)-N,N-dimethyl-
amino[5]ferrocenophane. These ligands were tested in the Rh-catalyzed hydrogenation of dimethyl itaconate and in Cu-catalyzed
Michael addition of Et2Zn to cyclohex-2-enone. The best results in terms of conversion and enantioselectivity in the Rh-catalyzed hydro-
genation provided bis(diphenylphosphine) ligand 2h (100% conversion and 95% ee) and aminophosphine 2a in the Cu-catalyzed conju-
gate addition (100% conversion 84% ee). The enantioselectivity of the Rh-catalyzed hydrogenation of methyl 2-acetamidoacrylate was
lower (41% ee).
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
PPh2
PCy2
PPh2
PPh2
Ferrocenyl derivatives represent one of the most prominent
classes among chiral ligands. The structure of these com-
pounds allows the incorporation of different elements of
chirality in the molecule.1 Since the first synthesis of a
homochiral bidentate P/N ligand by Hayashi and
Kumada2 these have found numerous applications in a
variety of transition metal-catalyzed asymmetric reactions.
Several comprehensive reviews cover their utility in asym-
metric catalysis.3–7 In particular, ferrocenyl phosphines
were successfully applied in Rh-catalyzed asymmetric
hydrogenation reactions.8–11 Ferrocenyl diphosphines and
amino phosphines were also recently found to be suitable
ligands for the Cu-catalyzed conjugate addition of
organometallic reagents to a,b-unsaturated carbonyl
compounds.12–15 Josiphos-type diphosphines (Fig. 1),
introduced by Togni16 are the most outstanding exponents
of ferrocene ligands because of their high versatility as well
as efficiency and have been included in the selection of
privileged ligand structures.17 Josiphos-type ligands have
also found application in the industrial production of
Metolachlor, dihydrojasmonate and biotin.18
PPh2
Fe
PPh2
Fe
Fe
Weissensteiner19
Šebesta23
Josiphos16
Figure 1.
Ligand tuning was pursued by systematic variation of the
substituents at the phosphorus atoms. A different approach
for modifying such compounds was suggested by Weisen-
steiner, who introduced additional three membered homo-
and heteroannular bridges19 leading to an increased
conformational rigidity of the ligand backbone. These
ligands show good enantioselectivities in Rh and Ir-catalyzed
hydrogenations of olefins, ketones and imines althouth
heteroannularly-bridged derivatives were inferior to Josi-
phos in the above mentioned reactions. Erker introduced
similar [3]ferrocenophane diphosphines with an additional
methyl group on the bridge and used them in the
Rh-catalyzed hydrogenation.20 Besides the well-known
P/P and P/N ligands, bidentate sulfur and selenium ferro-
cene derivatives can also be useful in some catalytic reac-
tions.21,22 Recently, we published the synthesis of new
[5]ferrocenophane-based diphosphine, 2h, which proved to
be a valuable ligand for Pd-catalyzed allylic substitution.23
*
Corresponding authors. Tel.: +421 2 60296376; fax: +421 2 60296337
ˇ
(R.S.); tel.: +49 241 8026480; fax: +49 241 8022177 (W.L.); e-mail
addresses: sebesta@fns.uniba.sk; leitner@itmc.rwth.aachen.de
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.08.011

1894
A. Alma´ssy et al. / Tetrahedron: Asymmetry 18 (2007) 1893–1898
Table 1. Diastereoselectivity of the reaction of ortho-lithiated (R)-1 with
electrophiles
NMe2
NMe2
NMe2
NMe2
NMe2
PPh2
PPh2
PPh2
2a X= PPh2
Y=
Y
2b
2c
2d
2e
2f
PCy2
P(t-Bu)2
SPh
Product
Reagent
ds (%)
Yield (%)
58a
48a
40a
62b
68b
X
Fe
SePh
SePh
PCy2
PPh2
2a
2b
2c
2d
2e
PPh2Cl
PCy2Cl
P(t-Bu)2Cl
PhSSPh
PhSeSePh
93
93
100
90
2g
2h
(R,pS)-2a-h
93
a Determined by 31P NMR.
b Determined by 1H NMR.
Figure 2.
Herein we report a series of new heteroannularly-bridged
[5]ferrocenophane ligands 2a–h bearing a variety of combi-
nations of donor groups (Fig. 2). These novel ligands have
been used in Rh-catalyzed asymmetric hydrogenation as
well as in Cu-catalyzed conjugate addition.
2. Results and discussion
Using a previously described procedure,23 key intermediate
(R)-dimethylamino[5]ferrocenophane 1 was synthesized.
Amine 1 was then lithiated diastereoselectively using
n-BuLi in Et2O and quenched with various electrophiles
to introduce different donor groups (Scheme 1).
NMe2
NMe2
1) BuLi, Et2O
2) EX
Figure 3.
X
Fe
Fe
Fe
(Scheme 1).16 In this way, ligands 2f, 2g and 2h were
prepared starting from 2e, 2b and 2a, respectively. Ligands
2g and 2h could be obtained in pure form by crystallization
from hot ethanol, whereas ligand 2f was purified by column
chromatography in the form of its BH3-adduct. The free
ligand 2f was obtained by treatment with Et2NH. It should
be noted that all these ligands are, to a certain extent, air-
and acid-sensitive.
1
2a-e
NMe2
PPh2
HPPh2
AcOH
X
Fe
X
2f-h
2a,b,e
The Rh-catalyzed hydrogenation of dimethyl itaconate 3
was chosen as a benchmark reaction for the first evaluation
of ligands 2a–h in catalysis (Scheme 2). The catalysts were
preformed in situ by mixing equimolar amounts of the
ligand and [Rh(cod)2]BF4 in CH2Cl2 or methanol. The
hydrogenation reactions were carried out within a standard
reaction time of 14 h at a catalyst loading of 1 mol %.
Conversions and enantiomeric excesses were determined
by GC analysis. The results are summarized in Table 2.
Scheme 1.
In this way, three homochiral [5]ferrocenophane amino
phosphines 2a–c, sulfur/N 2d and selenium/N 2e deriva-
tives were prepared (Fig. 2). The overall reaction proceeded
with high diastereoselectivities (P90%) and was only
slightly affected by the nature of the electrophile. Ligands
2a–e were purified by column chromatography. Selectivi-
ties and yields are summarized in Table 1.
H2
(30atm)
*
CO2Me
CO2Me
MeO2C
MeO2C
The structure of ligand 2e was determined by X-ray crystal-
lographic analysis (Fig. 3) confirming the expected absolute
stereochemistry.
[Rh] / L*
3
4
Scheme 2.
Further structural diversification was achieved by nucleo-
philic substitution of the dimethylamino with a diphenyl-
phosphino group. This reaction is known to proceed
with retention of configuration at the stereogenic centre
Full conversion of the starting material was achieved in all
the reactions. Good enantioselectivity (72% ee) was
obtained in the presence of diphenylphosphino/N-ligand

A. Alma´ssy et al. / Tetrahedron: Asymmetry 18 (2007) 1893–1898
Table 3. Rh/2h-catalyzed hydrogenation of 3 and 5
1895
2a, whereas using ligands 2b and 2c containing the more
basic and sterically demanding dicyclohexyl and di-t-butyl
phosphine groups resulted in the formation of diester 4 as a
racemic mixture. (Table 2, entries 3 and 4). A sharp
decrease in enantioselectivity was observed when 2 equiv
of 2a per [Rh] were used, suggesting that the catalytic
species, which imparts enantioinduction is bearing only
one (chelating) ligand (Table 2, entry 2 vs 1). The reactions
with 2b and 2c were also carried out in methanol but the
change in solvent did not improve the enantioselectivity
(Table 2, entries 5 and 6). Almost no enantioinduction
was observed for S/N 2d, Se/N 2e and Se/P 2f ligands
(Table 2, entries 7–9).
Entry
Subst.
[Rh]/subst.
Conversion (%)
ee (%)
1
2
3
4
3
3
5
5
1:100
1:1000
1:100
1:500
100
84
100
100
95 (S)a
95 (S)a
41 (R)b
17 (R)b
Reaction was carried out at p(H2) = 30 atm, during 14 h.
a Determined by GC on Lipodex E column, isotherm. 85 ꢁC.
b Determined by GC on Lipodex
E
column, gradient 80–150 ꢁC,
3 ꢁC/min.
H2
*
(30atm)
MeOOC
NHAc
MeOOC
NHAc
[Rh] / 2a
Table 2. Rh-catalyzed hydrogenation of dimethyl itaconate
5
6
Entry
Ligand
L:Rha
Solvent
Time (h)
eeb (%)
Scheme 3.
1
2
3
4
5
6
7
8
9
2a
2a
2b
2c
2b
2c
2d
2e
2f
1:1
2:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
1:1
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
MeOH
MeOH
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
14
14
14
14
1
72 (S)
7 (S)
0
0
0
material and an enantioselectivity of 41% (Table 3, entry
3). By increasing the S/C ratio to 500:1, the enantioselectiv-
ity dropped to 17% while conversion remained quantitative
(Table 3, entry 4).
1
0
14
14
14
14
14
4 (S)
0
4 (R)
95 (S)
58 (S)
Next we decided to examine ligands 2a, 2b, 2d, 2e and 2g in
the Cu-catalyzed conjugate addition of Et2Zn to cyclohex-
2-enone. Copper(I) triflate was chosen as the Cu-source
and the reaction was carried out under typical conditions.25
The results are summarized in Table 4. A promising
enantioselectivity of 78% ee at ꢀ15 ꢁC was obtained with
P/N ligand 2a (Table 4, entry 1), which could be further
increased to 84% ee at ꢀ35 ꢁC (Table 4, entry 2). Again,
a dramatic drop in enantioselectivity was observed using
the dicyclohexylphosphino derivative 2b instead of 2a.
The product was obtained almost quantitatively, albeit as
a racemic mixture (Table 4, entry 3). A very low enantio-
selectivity (up to 2% ee) was achieved with the other ligands
(Table 4, entries 4–6) (Scheme 4).
10
11
2h
2g
a Ratio [Rh]/3 1:100 and p(H2) = 30 atm in all cases. Full conversion was
achieved in all reactions.
b Determined by GC on Lipodex E column, isotherm. 85 ꢁC.
High enantioselectivity (95% ee) was obtained in the pres-
ence of bis-diphenylphosphino ligand 2h (Table 2, entry
10). This result compares very well with the enantioselectiv-
ity obtained with the corresponding Josiphos ligand (PPh2)
(96% ee).24 In contrast, moderate enantioselectivity (58%
ee) was achieved with dicyclohexylphosphino-diphenyl-
phosphino derivative 2g (Table 2, entry 11). This result is
surprising taking into account the very high enantioselec-
tivity obtained with similar not-bridged Josiphos ligand
(PCy2) (99% ee).16 On the other hand, a similar consider-
able decrease in enantioselectivity was observed when 2b
was used instead of 2a (Table 2, cf. entries 1 and 3 vs entries
10 and 11), indicating that the [5]ferrocenophane backbone
is more sensitive to steric/electronic variation than the
more adaptive Josiphos-type ligands. In the same reaction,
[3]ferrocenophane derivatives led to an enantioselectivity of
up to 43%.19 It should be pointed out, however, that no
direct comparison can be made between [3]- and [5]ferro-
cenophane-based ligands because of the different relative
position of the phosphine substituents.
Table 4. Cu-catalyzed conjugate addition of Et2Zn to enone 7
Entry
Ligand
Temperature
Conversion (%)
eea (%)
1
2
3
4
5
6
2a
2b
2d
2e
2a
2g
ꢀ15
ꢀ15
ꢀ15
ꢀ15
ꢀ35
ꢀ35
100
95
42
73
100
80
78 (R)
0
2 (R)
0
84 (R)
0
Lig/Cu 1:1, [Cu]/subst. 1:80.
a Determined by GC on Lipodex E column, isotherm. 100 ꢁC.
Our further investigation concentrated on the most effec-
tive ligand 2h (Table 3). The hydrogenation of dimethyl
itaconate 3 proceeded with the same high enantioselectivity
(95% ee) even at a substrate to catalyst (S/C) ratio of
1000:1 with an average turnover frequency (TOFav) of
60 hꢀ1 (Table 3, entry 2). Hydrogenation of methyl 2-acet-
amido-acrylate 5 (Scheme 3) under standard reaction con-
ditions resulted in the full conversion of the starting
O
O
Et2Zn, [Cu]/L*
toluene
*
8
7
Scheme 4.

1896
A. Alma´ssy et al. / Tetrahedron: Asymmetry 18 (2007) 1893–1898
3. Conclusion
form solution. [a]D = ꢀ207 (c 0.70, acetone). 1H NMR
(acetone-d6, 300 MHz): d 4.34 (dd, 1H, J = 2.5, 2.5 Hz, H
CFc), 4.30 (ddd, 1H, J = 2.5, 1.5, 1.3 Hz, HCFc), 4.14
(dd, 1H, J = 2.4, 1.3 Hz, HCFc), 4.12 (ddd, 1H, J = 2.4,
2.4, 1.3 Hz, HCFc), 4.02 (ddd, 1H, J = 2.4, 1.4, 1.4 Hz,
HCFc), 3.97 (ddd, 1H, J = 2.4, 1.3, 1.3 Hz, HCFc), 3.81–
3.84 (m, 1H, HCFc), 3.63 (dddd, 2H, J = 12.3, 6.6, 2.5,
2.4 Hz), 2.24–2.46 (m, 2H), 2.10 (s, 6H, (CH3)2N), 2.05–
2.17 (m, 2H), 1.16–1.96 (m, 24H). 13C NMR (acetone-d6,
75 MHz): 96.8 (d, J = 22.3 Hz), 91.1, 79.7 (d,
J = 20.0 Hz), 69.7 (d, J = 2.2 Hz), 69.3 (d, J = 3.3 Hz),
68.8 (d, J = 5.0 Hz), 68.0 (d, J = 4.8 Hz), 67.9, 67.1, 66.6,
60.0 (d, J = 11.2 Hz), 43.9, 39.7, 35.8 (d, J = 14.5 Hz),
35.1 (d, J = 12.7 Hz), 33.3 (d, J = 24.8 Hz), 31.6 (d, J =
14.5 Hz), 30.1 (d, J = 5.8 Hz), 29.8, 27.8 (d, J = 4.9 Hz),
27.6 (d, J = 8.8 Hz), 27.4, 27.3 (d, J = 15.0 Hz), 27.2 (d,
J = 6.4 Hz), 26.3 (d, J = 2.6 Hz), 25.2, 24.0 (d, J =
6.4 Hz), 22.0. 31P NMR (acetone-d6, 121 MHz): ꢀ12.6.
IR (neat) m: 2922.0, 2852.5, 2775.3, 1447.5, 1262.2,
1084.7, 1019.0, 802.9, 752.7 cmꢀ1. HR-MS: calcd for
C29H45FeNP, 494.2634; found 494.2639.
Novel heteroannular bridged, homochiral bidentate [5]fer-
rocenophane based ligands 2a–h have been synthesized.
Depending on the substituents at the phosphorus moiety,
different results in the catalysis were obtained when
compared to the corresponding non-bridged Josiphos type
ligands. In the hydrogenation of dimethyl itaconate 3,
bidentate bis-diphenylphosphino derivative 2h led to high
enantioselectivities (95% ee vs 96% ee with corresponding
Josiphos), while only modest ee was obtained with 2g
(58% ee vs 98% ee for the corresponding Josiphos). In
the same reaction, good enantioselectivities were observed
also for P/N derivative 2a (72% ee). Lower enantioselectiv-
ity was achieved in the hydrogenation of methyl 2-acet-
amidoacrylate 5 using 2h as the ligand. Moreover, amino
phosphine 2a turned out to be useful for the Cu-catalyzed
Michael addition of Et2Zn to cyclohex-2-enone 7 (84% ee
at ꢀ35 ꢁC). Further investigations on the ligand structure
and possibilities of their utilization in other asymmetric
reactions are currently underway in our laboratory.
4.2. (R,pS)-1-(Di-tert-butylphosphanyl)-2,10-[1-(dimethyl-
amino)pentan-1,5-diyl]ferrocene 2c
4. Experimental
Homochiral amine (R)-1, ligands (R,pS)-2a and (R,pS)-2h
were prepared following a procedure developed by our
research group.23 All reactions were carried out under an
argon atmosphere using standard Schlenk technique. The
solvents were degassed. Column chromatography was per-
formed on 40/100 mesh silica gel columns. GC analysis was
performed on Sichromat 1-4 Gas Chromatograph
equipped with FID detector. The NMR spectra were
recorded on a Varian Gemini 2000 spectrometer and
Same procedure as in previous except that ClP(t-Bu)2
(290 mg, 1.60 mmol) was used. Yield: 166 mg (40%) of a
red crystalline compound. Compound decomposes in chlo-
roform solution. Mp: 66–69 ꢁC. [a]D = ꢀ395 (c 0.45, meth-
1
anol). H NMR (acetone-d6, 300 MHz): d 4.56 (ddd, 1H,
J = 2.5, 2.5, 1.2 Hz, HCFc), 4.50–4.53 (m, 1H, HCFc),
4.31 (dd, 1H, J = 2.4, 1.2 Hz, HCFc), 4.20 (ddd, 1H,
J = 2.4, 2.4, 1.4 Hz, HCFc), 4.08 (ddd, 1H, J = 2.5, 1.3,
1.2 Hz, HCFc), 4.04 (ddd, 1H, J = 2.4, 2.4, 1.3 Hz, HCFc),
3.86 (ddd, 1H, J = 2.5, 1.3, 1.3 Hz, HCFc), 3.57 (ddd, 1H,
J = 6.0, 4.1, 4.1 Hz, HC(1)), 2.13–2.42 (m, 3H), 2.09 (s, 6H,
(CH3)2N), 1.69–1.92 (m, 5H), 1.52 (d, 9H, J = 12.0 Hz,
t-Bu–P), 0.94 (d, 9H, J = 11.0 Hz, t-Bu–P). 13C NMR (ace-
tone-d6, 75 MHz): d 88.7, 77.4, 75.2, 71.4 (d, J = 4.6 Hz),
70.7 (d, J = 5.4 Hz), 68.6, 67.5, 66.6, 66.4, 62.5 (d,
J = 14.2 Hz), 44.4, 33.6 (d, J = 19.7 Hz), 31.8 (d,
J = 17.3 Hz), 30.9 (d, J = 13.0 Hz), 30.7 (d, J = 12.2 Hz),
28.5, 26.9, 23.4, 22.4, 19.3. 31P NMR (acetone-d6,
121 MHz): d 15.6. IR (neat) m: 2925.9, 2860.3, 2817.8,
2771.5, 1455.2, 1362.6, 1262.2, 1173.4, 1030.6, 814.5,
756.6 cmꢀ1. Elem. Anal. Calcd for C25H40FeNP (441.4):
C, 68.02; H, 9.13; N, 3.17. Found: C, 69.35; H, 9.74; N,
3.10. HR-MS: calcd for C25H41FeNP, 442.2321; found
442.2328.
1
Bruker NMR at 300 MHz for H, 75 MHz for 13C and
121 MHz for 31P NMR. TMS was used as an internal stan-
dard. The chemical shift values are given in ppm and listed
coupling constants are in Hz. The IR spectra were recorded
on a Mettler-Toledo ReactIR instrument with the scale in
cmꢀ1. Elemental analyses were performed on a Carlo Erba
Instrumentazione analyzer. HR-MS was measured on
Finnigan Mat 95. Melting points were measured on a Barn-
stead Electrothermal IA9200 apparatus and are
uncorrected.
4.1. (R,pS)-1-(Dicyclohexylphosphanyl)-2,10-[1-(dimethyl-
amino)pentan-1,5-diyl]ferrocene 2b
To a stirred solution of amine (R)-1 (288 mg, 0.94 mmol) in
anhydrous Et2O (10 mL) n-BuLi (0.90 mL, 1.44 mmol,
1.6 M hexane soln) was added dropwise. The mixture was
stirred at ambient temperature for 2.5 h and then cooled
to 0 ꢁC. A solution of ClPCy2 (380 mg, 1.60 mmol) in
Et2O (5 mL) was added dropwise. The reaction mixture
was stirred overnight. Then H2O (10 mL) was added, the
layers separated and the aqueous layer was extracted with
Et2O (3 · 10 mL). The combined organic extracts were
washed with H2O (4 · 10 mL), dried over Na2SO4 and
the solvent vacuum evaporated. The crude product was
purified by column chromatography (SiO2, hexane/Et2O
1:1 + 1% Et3N). Pure phosphine 2b (222 mg, 48%) was iso-
lated as an orange oil. Compound decomposes in chloro-
4.3. (R,pS)-1-(Phenylsulfanyl)-2,10-[1-(dimethylamino)pen-
tan-1,5-diyl]ferrocene 2d
To a stirred solution of (R)-1 (250 mg, 0.84 mmol) n-BuLi
(790 lL, 1.26 mmol, 1.6 M hexane soln) was added drop-
wise and the mixture stirred for 2.5 h. The reaction mixture
was cooled in ice-salt bath, solid PhSSPh (312 mg,
1.43 mmol) was added during 45 min and the mixture
was stirred overnight. The reaction was quenched with
H2O (10 mL). The layers were separated and aqueous layer
extracted with Et2O (2 · 10 mL). The combined organic
extracts were washed with H2O (3 · 10 mL), dried over

A. Alma´ssy et al. / Tetrahedron: Asymmetry 18 (2007) 1893–1898
1897
Na2SO4 and the solvent was vacuum evaporated. The
crude product was purified by column chromatography
(SiO2, PhH/Et3N 99:1). Thioether 2d (210 mg, 62%) was
isolated as a yellow crystalline solid. Analytical sample
was recrystallized from Et2O. Mp: 85–88 ꢁC. [a]D = ꢀ155
(c 0.79, CHCl3). 1H NMR (CDCl3, 300 MHz): d 7.10–
7.21 (m, 4H, HCPh), 7.00–7.06 (m, 1H, HCPh), 4.52 (dd,
1H, J = 2.4, 1.4 Hz, HCFc), 4.39 (dd, 1H, J = 2.6,
2.6 Hz, HCFc), 4.34 (dd, 1H, J = 2.6, 1.3 Hz, HCFc),
4.27 (dd, 1H, J = 2.5, 2.4, 1.3 Hz, HCFc), 4.11 (ddd, 1H,
J = 2.4, 2.4, 1.3 Hz, HCFc), 3.99 (ddd, 1H, J = 2.4, 1.3,
1.2 Hz, HCFc), 3.89 (ddd, 1H, J = 2.5, 1.3, 1.2 Hz, HCFc),
3.30 (dd, 1H, J = 6.5, 2.1 Hz, HC(1)), 2.44 (ddd, 1H,
J = 15.8, 8.2, 3.9 Hz), 1.81-2.16 (m, 7H), 1.90 (s, 6H,
(CH3)2N). 13C NMR (CDCl3, 75 MHz): d 140.3, 128.5,
126.3, 124.9, 94.1, 93.4, 75.7, 74.5, 71.7, 69.7, 68.9, 68.6,
68.3, 67.4, 61.5, 42.6, 29.9, 26.8, 24.6, 24.3. IR (neat):
3080.3, 2929.7, 2856.4, 2821.7, 2771.5, 1582.6, 1474.5,
1443.6, 1262.2, 1080.8, 1022.9, 853.1, 814.5, 737.3,
690.9 cmꢀ1. Elem. Anal. Calcd for C23H27FeNS (405.4):
C, 68.15; H, 6.71; N, 3.46. Found: C, 68.40; H, 6.49; N,
3.56.
crystalline compound. Analytical sample was recrystallized
from hexane. Mp: 55–59 ꢁC. [a]D = ꢀ259 (c 0.27, CHCl3).
1H NMR (CDCl3, 300 MHz): d 7.82–7.90 (m, 2H, HCAr),
7.43–7.52 (m, 4H, HCAr), 7.04–7.17 (m, 7H, HCAr), 6.83–
6.92 (m, 2H, HCAr), 4.90–4.92 (m, 1H, HC(1)), 4.41 (dd,
1H, J = 2.5, 1.4 Hz, HCFc), 4.32 (dd, 1H, J = 2.6,
2.6 Hz, HCFc), 4.14 (dd, 1H, J = 4.2, 2.1 Hz, HCFc),
4.03–4.05 (m, 2H, HCFc), 3.66–3.69 (m, 1H, HCFc),
3.54–3.61 (m, 1H, HCFc), 2.07–2.34 (m, 4H), 1.62–2.03
(m, 4H), 0.40–1.00 (br s, 3H, BH3). 13C NMR (acetone-
d6, 75 MHz):
d
133.0 (d, J = 8.1 Hz), 132.7 (d,
J = 8.6 Hz), 131.2, 130.3, 128.9, 128.7 (d, J = 9.5 Hz),
127.9 (d, J = 9.9 Hz), 126.3, 92.7, 73.8, 71.3, 68.8 (d,
J = 4.1 Hz), 68.4, 66.9, 55.6, 55.0, 34.1, 27.6, 24.1, 23.7,
21.0. 31P NMR (CDCl3, 121 MHz): d 24.6 (br s). HR-
MS: calcd C33H31FePSe, 594.0678; found 594.0705.
Free ligand 2f was liberated from BH3 just prior to use by
treating 2fÆBH3 with Et2NH in anhydrous Et2O followed
1
by high vacuum. 2f. H NMR (CDCl3, 300 MHz): 7.42–
7.61 (m, 2H, HCAr), 7.31–7.36 (m, 2H, HCAr), 7.10–7.16
(m, 5H, HCAr), 7.08–6.95 (m, 4H, HCAr), 6.86–6.94 (m,
2H, HCAr), 4.38–4.44 (m, 2H, HCFc), 4.28 (dd, 1H,
J = 2.4, 2.4 Hz, HCFc), 4.15–4.19 (m, 1H, HCFc), 4.07–
4.10 (m, 1H, HCFc), 4.00–4.03 (m, 1H, HCFc), 3.79–3.82
(m, 1H, HCFc), 3.32 (ddd, 1H, J = 7.1, 7.1, 2.5 Hz,
HC(1)), 2.32–2.44 (m, 1H), 2.06–2.29 (m, 3H), 1.74–1.96
(m, 4H). 31P NMR (PhH-d6, 121 MHz): d ꢀ0.5.
4.4. (R,pS)-1-(Phenylselenyl)-2,10-[1-(dimethylamino)pen-
tan-1,5-diyl]ferrocene 2e
Same procedure as in previous except that PhSeSePh
(446 mg, 1.43 mmol) was used. Yield: 258 mg (68%) of
brown crystalline compound. Mp: 76.3–78.9 ꢁC [Et2O].
[a]D = ꢀ148 (c 0.85, CHCl3). 1H NMR (CDCl3,
300 MHz): 7.28–7.34 (m, 2H, HCPh), 7.05–7.18 (m, 3H,
HCPh), 4.49 (dd, 1H, J = 2.4, 1.3 Hz, HCFc), 4.40 (dd,
1H, J = 2.6, 2.5 Hz, HCFc), 4.29 (dd, 1H, J = 2.6,
1.3 Hz, HCFc), 4.23 (ddd, 1H, J = 2.5, 2.4, 1.3 Hz, HCFc),
4.13 (ddd, 1H, J = 2.4, 2.4, 1.3 Hz, HCFc), 4.00 (ddd, 1H,
J = 2.5, 1.3, 1.3 Hz, HCFc), 3.84 (dd, 1H, J = 2.4, 1.3,
1.3 Hz, HCFc), 3.33 (dd, 1H, J = 6.5, 2.0 Hz, HC(1)),
2.43 (ddd, 1H, J = 15.9, 8.3, 3.7 Hz), 2.02–2.14 (m, 2H),
1.79–2.02 (m, 5H), 1.88 (s, 6H, (CH3)2N). 13C NMR
(CDCl3, 75 MHz): d 134.9, 129.5, 128.5, 125.9, 94.1, 93.3,
75.4, 70.9, 69.4, 69.1, 68.2, 67.4, 62.4, 42.4, 29.8, 27.3,
24.7, 24.4. IR (neat): 3072.6, 2929.7, 2856.4, 2821.7,
2775.3, 1578.7, 1474.5, 1443.6, 1219.8, 1065.4, 1022.9,
814.5, 752.7, 733.4, 690.9, 663.9 cmꢀ1. Elem. Anal. Calcd.
for C23H27FeNSe (452.3): C, 61.08; H, 6.02; N, 3.10.
Found: C, 61.95 H, 5.71; N, 3.20. HR-MS: calcd for
C23H28FeNSe, 454.0731; found, 454.0710.
4.6. (R,pS)-1-(Dicyclohexylphosphanyl)-2,10-[1-(diphenyl-
phosphanyl)pentan-1,5-diyl]ferrocene, bis(borane) complex
2gÆ(BH3)2
To a solution of (R,pS)-2b (75 mg, 0.152 mmol) in anhy-
drous AcOH (3 mL), HPPh2 (37 mg, 0.20 mmol) was
added. The reaction mixture was heated to 85 ꢁC and stir-
red in darkness for 12 h. The solvent was evaporated under
vacuum and the crude product was recrystallized from
anhydrous degassed EtOH to yield ligand (R,pS)-2g
(45 mg, 47%) as orange crystals. 1H NMR (acetone-d6,
300 MHz): d 7.54–7.66 (m, 3H, HCPh), 7.42–7.50 (m,
3H, HCPh), 7.17–7.24 (m, 4H, HCPh), 4.29–4.35 (m, 2H,
HCFc), 4.21–4.25 (m, 1H, HCFc), 4.11–4.16 (m, 1H,
HCFc), 4.07–4.11 (m, 1H, HCFc), 3.99–4.06 (m, 2H,
HCFc), 3.59–3.68 (m, 1H, HC(1)), 0.80–2.50 (m, 30H).
31P NMR (acetone-d6, 121 MHz): d 2.1, ꢀ17.6. For analyt-
ical purposes, the BH3 complex was prepared. Mp: 234 ꢁC
(dec.). [a]D = ꢀ204 (c 0.32, CHCl3) 1H NMR (CDCl3,
300 MHz): d 8.15 (m, 2H), 7.54 (m, 3H), 7.33 (m, 2H),
7.18 (m, 1H), 7.08 (m, 2H), 5.61 (s, 1H), 4.48 (t,
J = 2.6 Hz, 1H), 4.40 (m, 1H), 4.18 (m, 1H), 4.14 (m,
2H), 4.09 (m, 2H), 2.83 (m, 1H), 2.39 (m, 4H), 2.19 (td,
J = 16.5, 3.9 Hz, 1H), 2.04–1.29 (m, 22H), 1.12–0.70 (m,
6H), 0.20 (m, 2H); 13C NMR (CDCl3, 75 MHz): d 131.2
(d, J = 2.2 Hz), 133.7 (d, J = 8.8 Hz), 133.6 (d,
J = 8.3 Hz), 130.1 (d, J = 2.5 Hz), 129.3 (d, J = 51.9 Hz),
128.2 (d, J = 55.5 Hz), 128.8 (d, J = 9.6 Hz), 127.7 (d,
J = 9.9 Hz), 96.3 (dd, J = 14.2, 6.5 Hz), 91.2, 74.4 (dd,
J = 49.4, 4.4 Hz), 71.2 (d, J = 2.7 Hz), 71.0 (dd, J = 7.5,
4.6 Hz), 70.7, 69.1 (d, J = 5.8 Hz), 68.4, 67.7, 66.7, 39.6
(d, J = 33.9 Hz), 34.5, (d, J = 35.0 Hz), 30.8 (d,
J = 32.7 Hz), 29.3, 29.0 (d, J = 6.4 Hz), 27.8 (d,
4.5. (R,pS)-1-(Phenylselenyl)-2,10-[1-(diphenylphosphan-
yl)pentan-1,5-diyl]ferrocene, borane complex 2fÆBH3
To a solution of (R,pS)-2e (600 mg, 1.33 mmol) in AcOH
(10 mL), HPPh2 (360 mg, 1.73 mmol) was added dropwise.
The reaction mixture protected from light was stirred and
heated to 85 ꢁC for 15 h. The solvent was vacuum evapo-
rated and the residue was dissolved in anhydrous Et2O
(15 mL) and cooled to 0 ꢁC. BH3ÆSMe2 (700 lL,
1.40 mmol, 2 M THF soln) was added dropwise and the
mixture was stirred for 20 min at 0 ꢁC. Solvents were evap-
orated under vacuum and the crude mixture was purified
by column chromatography (SiO2, hexane/Et2O 3:1). Prod-
uct (R,pS)-2fÆBH3 (474 mg, 59%) was isolated as an orange

1898
A. Alma´ssy et al. / Tetrahedron: Asymmetry 18 (2007) 1893–1898
J = 12.9 Hz), 27.7, 27.2 (d, J = 2.1 Hz), 27.1 (d,
J = 16.5 Hz), 26.7 (dd, J = 22.9, 11.5 Hz), 26.1, 25.71,
25.67 (d, J = 3.3 Hz), 24.0 (d, J = 12.9 Hz), 23.4, 22.3.
31P NMR (CDCl3, 121.5 MHz): d 25.8 (br s), 21.0 (br s).
HR-MS: calcd for C39H48FeP2, 634.2581; found, 634.2577.
VEGA, Grant No. 1/3569/06 and Fonds der Chemischen
Industrie. NMR measurements provided by Slovak State
Programme Project No. 2003SP200280203. We thank Dr.
´
ˇ
´
Ivana Cısarova (Charles University Prague) for X-ray
measurement.
4.7. Crystal structure data for 2e
References
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0.30 · 0.27 · 0.20 mm, C23H27FeNS, Mr 405.37. Mono-
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3
˚
˚
c = 16.130(4) A, V = 970.7(4) A from 11,785 reflectioꢀns3,
˚
T = 150(2) K, k = 0.71069 A, Z = 2, Dx = 1.387 g cm
,
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´
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´
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Acknowledgements
We gratefully acknowledge support from European project
LIGBANK NMP3-2003-505267 and Slovak Grant Agency
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