The first application of C2-symmetric ferrocenyl phosphinite ligands for rhodium-catalyzed asymmetric transfer hydrogenation of various ketones

Article abstract of DOI:10.1016/j.ica.2015.09.003

Homogeneous catalysis has been responsible for many major recent developments in synthetic organic chemistry. The combined use of organometallic and coordination chemistry has produced a number of new and powerful synthetic methods for important classes of compounds in general and for optically active substances in particular. For this aim, a new class of chiral modular C₂-symmetric ferrocenyl phosphinite ligands has been prepared in good yields by using the inexpensive 1,1′-ferrocenedicarboxyaldehyde and various ferrocene based-amino alcohols as starting materials, and applied in the rhodium(I)-catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones to give corresponding secondary alcohols with excellent enantioselectivities and reactivities using isoPrOH as the hydrogen source (up to 99% conversion and 99% ee). The substituents on the backbone of the ligands are found to exhibit a remarkable effect on both the activity and % ee. The structures of these ligands and their complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis.

Full text of DOI:10.1016/j.ica.2015.09.003

Accepted Manuscript
The First Application of C -Symmetric Ferrocenyl Phosphinite Ligands for
2
Rhodium-Catalyzed Asymmetric Transfer Hydrogenation of Various Ketones
Bünyamin Ak, Murat Aydemir, Feyyaz Durap, Nermin Meriç, Akın Baysal
PII:
S0020-1693(15)00439-9
http://dx.doi.org/10.1016/j.ica.2015.09.003
ICA 16676
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
3 June 2015
25 August 2015
8 September 2015
Please cite this article as: B. Ak, M. Aydemir, F. Durap, N. Meriç, A. Baysal, The First Application of C -Symmetric
2
Ferrocenyl Phosphinite Ligands for Rhodium-Catalyzed Asymmetric Transfer Hydrogenation of Various Ketones,
Inorganica Chimica Acta (2015), doi: http://dx.doi.org/10.1016/j.ica.2015.09.003
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2
The First Application of C -Symmetric Ferrocenyl Phosphinite Ligands for Rhodium-
Catalyzed Asymmetric Transfer Hydrogenation of Various Ketones
a
Bünyamin Ak , Murat Aydemir , Feyyaz Durap , Nermin Meriç , Akın Baysal
a,b
a,b
a
1,a
a
Department of Chemistry, Faculty of Science, University of Dicle, 21280 Diyarbakir, Turkey
b
Science and Technology Application and Research Center (DUBTAM), Dicle University, Diyarbakir, 21280, Turkey
Abstract
Homogeneous catalysis has been responsible for many major recent developments in synthetic organic
chemistry. The combined use of organometallic and coordination chemistry has produced a number of
new and powerful synthetic methods for important classes of compounds in general and for optically
active substances in particular. For this aim, a new class of chiral modular C -symmetric ferrocenyl
2
phosphinite ligands has been prepared in good yields by using the inexpensive 1,1'-
ferrocenedicarboxyaldehyde and various ferrocene based-amino alcohols as starting materials, and
applied in the rhodium(I)-catalyzed asymmetric transfer hydrogenation (ATH) of aromatic ketones to give
corresponding secondary alcohols with excellent enantioselectivities and reactivities using isoPrOH as the
hydrogen source (up to 99% conversion and 98% ee). The substituents on the backbone of the ligands are
found to exhibit a remarkable effect on both the activity and % ee. The structures of these ligands and
their complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR
spectroscopy and elemental analysis.
ꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
To whom correspondence should be addressed: Department of Chemistry, Dicle University, TR-21280 Diyarbakır, Turkey. Tel:
1
+90 412 248 8550 (ext. 3175), Fax: +90 412 248 8300, e-mail: akinb@dicle.edu.tr
1

Keywords: Asymmetric Catalysis; C
2
-symmetric Ferrocenyl phosphinite; Asymmetric Transfer
Hydrogenation; Aromatic Ketones; Rhodium(I)
1
. Introduction
Ferrocene based ligands have gained much attention due to their peculiar chemical features,
diastereoselective metallation on the cyclopentadienyl ring [i] and retentive nucleophilic
displacement on the benzylic position [ii], which allow the preparation of a broad range of
substituted derivatives [iii]. Ferrocene derivatives have recently attracted renewed interest for
modern ligand design due to their promise for widespread applications both on a laboratory scale
and in industry [iv,v]. The interest is due to some exceptional features of ferrocene chemistry,
which include the replacement of heteroatomic ꢀ-substituents with full retention of configuration
and possibility of diastereoselective directed metallation [vi]. Especially, the ferrocene moiety
has been extensively explored as a backbone of chiral P based ligands due to its easy
modifiability and highly electron donating property. The excellent structure of ferrocenes enables
us to design a variety of chiral ferrocenyl P based ligands, which are useful tools in metal-
catalyzed asymmetric reactions [vii]. In addition, the ferrocene-derived ligands generally
crystallize readily and are relatively air stable compared to their nonferrocenyl analogues. These
features are beneficial for purification and usage of the ligands [viii].
2

In the past decades, a large number of chiral bidendate phosphorus containing ligands (P,PƗ)
having a C -symmetrical structure or holding two closely related bindings sites were widely
studied [ix,x]. C -symmetry reduces the number of possible catalyst-substrate arrangements and,
2
2
consequently, the number of competing reaction pathways by a factor of 2, which can be an
important factor in enantioselectivity [xi]. Among the recently developed efficient transition-
metal-based chiral reduction catalysts, the C -symmetric ferrocenyl phosphines were notably
2
reported [xii,xiii,xiv,xv]. Because of its great success in catalytic asymmetric reactions [xvi],
chiral ferrocenyl-phosphine ligands have attracted considerable attention in recent years
[
[
[
xvii,xviii]. These ligands are very efficient for a wide range of reactions, such as hydrogenation
xix], hydrosilylation [xx], allylic alkylation [xxi], palladium catalyzed cross-coupling reactions
xxii,xxiii,xxiv,xxv,xxvi] and cyclopropanation [xxvii]. Although ferrocenyl phosphine ligands
have found widespread applications in transition metal catalyzed asymmetric transfer
hydrogenations [xxviii,xxix,xxx], the analogous phosphinites have different chemical, electronic
and structural advantages compared to phosphines. For instance, the metal-phosphorus bond is
often stronger in phosphinites compared to the related phosphine due to the presence of electron-
withdrawing P-OR group. In addition, the empty ꢁ*-orbital of the phosphinite P(OR)R is
2
stabilized, making the phosphinite a better acceptor [xxxi]. Moreover, the most important
advantage of chiral phosphinite ligands over the corresponding P-based ligands is their facile
preparation, which leads to a substantial interest to develop highly effective chiral phosphinite
ligands for asymmetric catalysis [xxxii,xxxiii,xxxiv].
Asymmetric Transfer Hydrogenation using 2-propanol as a hydrogen source offers an attractive
route for reducing simple unfunctionalized ketones to chiral alcohols [xxxv,xxxvi,xxxvii]. The
reaction uses inexpensive reagents and is usually easy to perform. Furthermore, considering
3

advantage of both C -symmetrical ligands and phosphinites often give high levels
2
enantioselectivity in asymmetric reactions [xxxviii], in recent years our research group has
reported the synthesis [xxxix,xl,], characterization and coordination properties of this kind of
ligands [xli,xlii,xliii]. Inspired by the excellent results obtained with some of the chiral
phosphinite ligands [xliv,xlv,xlvi and references therein], we have developed a new class of C
2
-
symmetric ferrocenyl phosphinite ligands that allow good control of enantiselectivites via facile
structural manipulation. Herein, we report our preliminary results on the full synthesis and
characterization of ferrocenyl phosphinite ligands and their rhodium(I) complexes. As far as we
know, there are not many reports on asymmetric transfer hydrogenation of ketones by using
chiral rhodium C
2
-symmetric ferrocenyl phosphinites as catalyst. These C -symmetric ferrocenyl
2
phosphinites have been employed successfully as ligands in rhodium(I)-promoted asymmetric
transfer hydrogenation of various ketones.
2
2
. Experimental Section
.1. Materials and methods
Unless otherwise mentioned, all reactions were carried out under an atmosphere of argon using
conventional Schlenk glass ware, solvents were dried using established procedures and distilled
under argon just prior to use. Analytical grade and deuterated solvents were purchased from
Merck. The starting materials ferrocene, L-phenyl alaninol, L-phenyl glycinol, L-leucinol, L-
isoleucinol, (S)-(+)-1-amino-2-propanol, (R)-(-)-2-amino-1-phenylethanol, (R)-(-)-2-amino-1-
butanol, (1S,2R)-(+)-2-amino-1,2-diphenylethanol, PPh
2
Cl and Et N were purchased from Fluka
3
and used as received. 1,1'-ferrocenedicarboxyaldehyde, [xlvii] and [Rh()-Cl)(cod)]
2
[xlviii] were
1
13
31
prepared according to the literature procedures. H (at 400.1 MHz), C (at 100.6 MHz) and P-
4

1
{
H} NMR (at 162.0 MHz) spectra were recorded on a Bruker AV 400 spectrometer, with TMS
1
13
(
tetramethylsilane) as an internal reference for H NMR and C NMR or 85% H
3
PO as an
4
3
1
1
external reference for P-{ H} NMR. The IR spectra were recorded on a Mattson 1000 ATI
UNICAM FT-IR spectrometer as KBr pellets. Specific rotations were taken on a Perkin-Elmer
3
41 model polarimeter. Elemental analysis was carried out on a Fisons EA 1108 CHNS-O
instrument. Melting points were recorded by a Gallenkamp Model apparatus with open
capillaries. GC analyses were performed on a Shimadzu GC 2010 Plus Gas Chromatograph
equipped with a cyclodex-B (Agilent) capillary column (30 m x 0.32 mm I.D. x 0.25 )m film
thickness). Racemic samples of alcohols were obtained by reduction of the corresponding
ketones with NaBH and used as the authentic samples for % ee determination. The GC
4
parameters for asymmetric transfer hydrogenation of ketones were as follows; initial
temperature, 50 ºC; initial time 1.1 min; solvent delay, 4.48 min; temperature ramp 1.3 ºC/min;
final temperature, 150 ºC; initial time 2.2 min; temperature ramp 2.15 ºC/min; final temperature,
2
50 ºC; initial time 3.3 min; final time, 44.33 min; injector port temperature, 200 ºC; detector
temperature, 200 ºC, injection volume, 2.0 )L.
2
.2. General procedure for the transfer hydrogenation of ketones
Typical procedure for the catalytic hydrogen-transfer reaction: a solution of the Rh(I)-complexes
7-24, (0.01mmol), NaOH (0.05 mmol) and the corresponding ketone (1mmol) in degassed
1
isoPrOH (10 mL) was refluxed until the reaction completed. Then, a sample of the reaction
mixture is taken off, diluted with acetone and analyzed immediately by GC, conversions
obtained are related to the residual unreacted ketone.
2
2
.3. General procedures for the synthesis of C -symmetric ferrocenyl amino alcohols
5

Method A, for compound, 1-4 and 8: A mixture of ferrocenedicarboxaldehyde (1.00 g, 4.13
mmol) and amino alcohol (12.4 mmol) in previously dried CH Cl (250 ml) containing
2
2
molecular sieves (4Å, 5.00 g) was refluxed under argon for 10 h. The mixture was filtered
through Celite 545. The solvent was removed under reduced pressure and the residue was re-
dissolved in dry methanol (150 ml). Solid NaBH
portions at 0 ºC. After stirring for 1h, the reaction was quenched by addition of a saturated
solution of NH Cl (250 ml) and extracted with CH Cl (3 x 30ml). The combined organic
extracts were dried over Na SO and evaporated. The subsequent purification by column
4
(0.79 g, 20.8 mmol) was added in small
4
2
2
2
4
chromatography yielded the desired ferrocenyl amino alcohols.
Method B, for compound, 5-7: The procedure for the preparation of ferrocenyl-substituted !-
amino alcohols was used for 5-7. A mixture of ferrocenedicarboxaldehyde (484 mg, 2 mmol) and
amino alcohol (4.2 mmol) were dissolved in dry chloroform (25 ml) and the solution was
refluxed under argon for 1.5 h. Then, the solution was allowed to cooling to room temperature
and the solvent was evaporated under reduced pressure. The residue was re-dissolved in dry
methanol (40 ml). The methanolic solution was cooled to 0 ºC and solid NaBH (0.79 g, 20.8
4
mmol) was added in small portions. After stirring for further 1 h at 0 ºC and 1.5 h at room
temperature, the reaction was terminated by addition of 10 % aqueous NaOH (40 ml) and
extracted with CH
2
Cl
2
(2 x 25 ml). The combined organic layers were dried over MgSO ,
4
evaporated and the residue was chromatographed over a silica column.
2
.3.1.(S)-bis[N-(2-hydroxy-1-benzyl)ethyl]-1,1'-ferrocenylmethyldiamine, (1)
(
S)-bis[N-(2-hydroxy-1-benzyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (S)-
phenyl alaninol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through
6

column chromatography (SiO
2
, eluent: CH
3
OH/Et
+42.8 (c 1.2, MeOH)]; H NMR (CDCl , ppm): ꢂ 7.21-7.35 (m, 10H, CH
m, 8H, C ), 3.68 (m, 2H, -CH OH (a)), 3.38-3.42 (m, 2H, CH OH (b) and 4H, CH
m, 2H, CHNH), 2.80 (m, 4H, CH Ph), 2.34 (br, 4H, NH and OH). C NMR (CDCl
38.55 (i-C ), 129.19, 128.65, 126.55 (C ), 87.36 (i-C ), 68.22, 68.15, 68.13, 68.00
), 62.63 (CH OH), 60.05 (CHNH), 45.88 (CH NH), 38.14 (CH Ph). IR (KBr pellet in cm
͵(O-H): 3418, (N-H): 3291, (C=C-Cp): 1450, (C-H): 2861, 2906, 3025, 3078. Anal. calcd. for
Fe, C, 70.30; H, 7.09; N, 5.47, found: C, 70.17; H, 6.94; N, 5.32 %.
3
N: 20/0.5). Yield: 1.65 g, yellow oil (77%).
Ph), 3.71-4.03
NH), 3.02
, ppm): ꢂ
2
0
1
[
(
(
ꢀ]
D
3
2
5
H
4
2
2
2
1
3
2
3
1
6
H
5
6
H
5
5
H
4
-
(
C
5
H
4
2
2
2
1
)
C
30
H
36
N
2
O
2
2
.3.2. (S)-bis[N-(2-hydroxy-1-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine, (2)
(
S)-bis[N-(2-hydroxy-1-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (S)-
phenylglycinol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through
column chromatography (SiO
2
, eluent: CHCl
3
/CH
3
CN: 7/3). Yield: 1.40 g, yellow crystals
2
0
1
(
70%). Mp: 130-132 ºC. [ꢀ]
D
+31.6 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm) ꢂ:7.28-7.40 (m,
OH (a)), 3.66-
NH (a)), 3.16 (d, J=12.7 Hz, 2H, CH NH
, ppm): ꢂ 139.73 (i-C ), 128.71, 127.75,
), 68.86, 68.16, 67.90 (C ), 67.01 (CH OH), 65.13 (CHN), 46.08
NH). IR (KBr pellet in cm ) ͵(O-H): 3420, (N-H): 3283, (C=C-Cp): 1451, (C-H): 3081,
1
0H, C
6
H
5
), 3.98-4.33 (m, 8H, C
5
H
4
), 3.96 (m, 2H, CHN), 3.78-3.82 (m, 2H, CH
2
3
.71 (m, 2H, CH
2
OH (b)), 3.42 (d, J=12.7 Hz, 2H, CH
2
2
13
(
b)), 2.98 (br, 4H, NH and OH). C NMR (CDCl
27.48 (C ), 87.96 (i-C
CH
3
6
H
5
1
6
H
5
5
H
4
5
H
4
2
-1
(
2
3
6
027, 2915, 2839. Anal. calcd. for C28
.48; N, 5.63 %.
H
32
N
2
2
O Fe, C, 69.41; H, 6.67; N, 5.78, found: C, 69.12; H,
2
.3.3. (S)-bis[N-(2-hydroxy-1-iso-butyl)ethyl]-1,1'-ferrocenylmethyldiamine, (3)
7

(
S)-bis[N-(2-hydroxy-1-iso-butyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (S)-
leucinol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through column
chromatography (SiO
2
, eluent: CH
3
OH/Et N: 20/0.5).Yield: 1.32 g, yellow crystals (72%). Mp:
3
2
0
1
9
2-94 ºC. [ꢀ]
.71-3.74 (m, 2H, CH
NH (b)), 3.37-3.42 (m, 2H, CH
), 1.36-1.43 (m, 2H, CHCH (a)), 1.27-1.34 (m, 2H, CHCH
, ppm): ꢂ 86.54 (i-C ), 69.00, 68.61, 68.52, 68.33 (C
NH), 40.33 (CHCH ), 24.99 (CHCH ), 23.24, 22.51
). IR (KBr pellet in cm ) ͵(O-H): 3425, (N-H): 3290, (C=C-Cp): 1455, (C-H): 2956,
919, 2870, 2824. Anal. calcd. for C24 Fe: C, 64.85; H, 9.09; N, 6.30, found: C, 64.70;
H, 8.96; N, 6.21 %.
D
+56.6 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 4.14-4.27 (m, 8H, C
NH (a) and 4H, NH and OH), 3.48 (d, 2H,
OH (b)), 2.83 (br, 2H, CHN), 1.61-1.67 (m, 2H,
(b)), 0.90-0.93 (m, 12H,
), 63.05
5 4
H ),
3
2
OH (a)), 3.61-3.64 (m, 2H, CH
2
J= 12.8 Hz, CH
2
2
CHCH
3
3
2
2
13
CHCH
). C NMR (CDCl
3
5
H
4
5
H
4
(
(
CH
2
OH), 56.96 (CHN), 45.57 (CH
2
2
3
-1
CHCH
3
2
H
40
N
2
O
2
2
.3.4. (S)-bis[N-(2-hydroxy-1-sec-butyl)ethyl]-1,1'-ferrocenylmethyldiamine, (4)
(
S)-bis[N-(2-hydroxy-1-sec-butyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (S)-
isoleucinol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through
column chromatography (SiO
2
, eluent: CH
3
OH/Et
3
N: 20/0.5). Yield: 1.25 g, yellow crystals
2
0
1
(
68%). Mp: 64-66 ºC. [ꢀ]
), 3.63 (dd, 2H, J= 4.0 and 10.7 Hz, CH
.36-3.41 (m, 2H, CH OH (b) and 2H, CH NH (b)), 2.62 (m, 2H, CHN), 2.48 (br, 4H, NH and
OH), 1.61-1.67 (m, 2H, CHCH ), 1.44-1.50 (m, 2H, CH CH (a)), 1.18-1.27 (m, 2H, CH CH
b)), 0.95 (t, 6H, J=7.4 Hz, CH CH ), 0.89 (d, 6H, J = 6.9 Hz, CHCH
ppm): ꢂ 87.84 (i-C ), 68.49, 68.42, 68.29, 68.06 (C ), 62.56 (CHN), 60.34 (CH
CH NH), 35.33 (CHCH ), 26.45 (CH CH ), 14.39 (CHCH ), 11.87 (CH CH ). IR (KBr pellet
D
+53.9 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 4.11-4.21 (m, 8H,
C
5
H
4
2
OH (a)), 3.55 (d, 2H, J=12.8 Hz, CH
2
NH (a)),
3
2
2
3
2
3
2
3
1
3
(
2
3
3
). C NMR (CDCl
3
,
5
H
4
5
H
4
2
OH), 46.20
(
2
3
2
3
3
2
3
8

-1
in cm ) ͵ (O-H): 3416, (N-H): 3279, (C=C-Cp): 1456, (C-H): 2958, 2929, 2871, 2830. Anal.
calcd. for C24 Fe: C, 64.85; H, 9.09; N, 6.30, found: C, 64.79; H, 8.96; N, 6.24 %.
H
40
N
2
O
2
2
.3.5. (S)-bis[N-(2-hydroxypropyl)ethyl]-1,1'-ferrocenylmethyldiamine (5)
(
S)-bis[N-(2-hydroxypropyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (S)-1-
amino-2-propanol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through
column chromatography (SiO , eluent: CH Cl /CH OH: 10/1).Yield: 640 mg, yellow oil (88%).
+46.0 (c 1.2, MeOH)]; H NMR (CDCl , ppm): ꢂ 4.19 (s, 2H, C ), 4.16 (s, 2H, C ),
.12 (br, 4H, C ), 3.87 (br, 2H, CHOH), 3.56 (d, 2H, J=13.1 Hz, CH NH (a)), 3.46 (d, 2H, J=
3.1 Hz, CH NH (b)), 3.20 (br, 4H, NH and OH), 2.75 (dd, 2H, J = 2.1 and 11.9 Hz, CH CH
). C NMR (CDCl
), 65.43 (CHOH), 56.65 (CH CH),
). IR (KBr pellet in cm ) ͵ (O-H): 3405, (N-H): 3270, (C=C-
Cp): 1475, (C-H): 2946, 2919, 2850, 2814. Anal. calcd. for C18 Fe: C, 60.01; H, 7.85; N,
2
2
2
3
2
0
1
[
ꢀ]
D
3
5
H
4
5 4
H
4
1
5
H
4
2
2
2
1
3
(
a)), 2.50 (m, 2H, CH
ppm): ꢂ 86.83 (i-C
8.26 (CH NH), 20.74 (CHCH
2
CH (b)), 1.53 (dd, 6H, J= 6.1 and 25.6 Hz, CHCH
3
3
,
5
H
4
), 68.89, 68.66, 68.36, 68.25 (C
5
H
4
2
-1
4
2
3
H
28
N
2
O
2
7
.78, found: C, 59.90; H, 7.72; N, 7.63 %.
2
.3.6. (R)-bis[N-(2-hydroxy-2-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine (6)
(
R)-bis[N-(2-hydroxy-2-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (R)-2-
amino-1-phenylethanol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified
through column chromatography (SiO
2
, eluent: CHCl
3
/CH
3
CN: 7/3).Yield: 140 mg, yellow
2
0
1
crystals (83%). Mp: 163-165 ºC. [ꢀ]
D
-23.5 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 7.19-
7
8
2
.39 (m, 10H, CHPh), 4.91 (d, 2H, J=7.6 Hz, CHOH), 4.45 (br, 4H, NH and OH), 4.10-4.35 (m,
H, C ), 3.67 (q, 4H, J =13.8 Hz, CH ), 2.94 (d, 2H, J=10.2 Hz, CH NH (a)), 2.84 (t,
H, J=10.6 Hz, CH
5
H
4
2
C
5
H
4
2
1
3
2
NH (b)). C NMR (CDCl
3
, ppm): ꢂ 142.24 (i-C
6
H
5
), 128.45, 127.63, 125.90
9

(
CH
2
C
6
H
5
), 84.80 (i-C
5
H
4
), 71.08 (CHOH), 69.38, 69.26, 68.77, 68.69 (C
5
H
4
), 56.02 (CH NH),
2
-
1
4
3
6
7.46 (CH ). IR (KBr pellet in cm ) ͵ (O-H): 3390, (N-H): 3253, (C=C-Cp): 1460, (C-H):
2
C
5
H
4
091, 3035, 2920, 2840. Anal. calcd. for C28
9.21; H, 6.54; N, 5.65 %.
H
32
N
2
O Fe: C, 69.41; H, 6.67; N, 5.78, found: C,
2
2
.3.7. (R)-bis[N-(2-hydroxy-1-ethyl)ethyl]-1,1'-ferrocenylmethyldiamine (7)
(
R)-bis[N-(2-hydroxy-1-ethyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from (R)-2-
amino-1-butanol and 1,1'-ferrocenedicarboxyaldehyde. The crude product was purified through
column chromatography (SiO , eluent: CH Cl /CH OH: 10/1).Yield: 700 mg, yellow oil (90%).
-36.8 (c 1.2, MeOH)]; H NMR (CDCl , ppm): ꢂ 4.24 (s, 2H, C ), 4.17 (s, 2H, C ),
.12 (s, 4H, C ), 3.70 (dd, 2H, J= 3.4 and 10.8 Hz, CH OH (a)), 3.54 (d, 2H, J = 12.7 Hz,
NH (a)), 3.36-3.41 (m, 4H, CH OH and CH NH (b)), 2.63 (br, 2H, CHNH; 2H, NH and 2H,
OH), 1.53-1.60 (m, 2H, CH CH (a)), 1.39-1.46 (m, 2H, CH CH (b)), 0.94 (t, 6H, J = 7.5 Hz,
, ppm): ꢂ 84.74 (i-C ), 68.68, 68.30, 68.24, 68.01 (C ), 62.84
OH), 60.61 (CHN), 45.72 (CH NH), 24.04 (CH CH ), 10.42 (CH CH ). IR (KBr pellet in
cm ) ͵(O-H): 3435, (N-H): 3280, (C=C-Cp): 1475, (C-H): 2966, 2939, 2860, 2834. Anal. calcd.
Fe: C, 61.85; H, 8.32; N, 7.21, found: C, 61.70; H, 8.20; N, 7.09 %.
2
2
2
3
2
0
1
[
ꢀ]
D
3
5
H
4
5 4
H
4
5
H
4
2
CH
2
2
2
2
3
2
3
1
3
CH
2
CH
3
). C NMR (CDCl
3
H
5 4
5
H
4
(
CH
2
2
2
3
2
3
-1
for C20
H
32
N
2
O
2
2
.3.8. (1S,2R)-bis[N-(2-hydroxy-1,2-diphenyl)ethyl]-1,1'-ferrocenylmethyldiamine, (8)
(
(
1S, 2R)-bis[N-(2-hydroxy-1,2-diphenyl)ethyl]-1,1'-ferrocenylmethyldiamine was obtained from
1S, 2R)-2-amino-1,2-diphenyl ethanol and 1,1'-ferrocenedicarboxyaldehyde. The crude product
was purified through column chromatography (SiO
2
, eluent: CH
3
OH/Et
3
N: 20/0.5). Yield: 1.62
2
0
1
g, yellow crystals (65%). Mp: 121-123 ºC. [ꢀ]
ꢂ 7.21-7.31 (m, 20H, C
D
+24.7 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm):
6
H
5
), 4.77 (d, 2H, J = 5.8 Hz, CHOH), 4.19 (d, 2H, J= 5.9 Hz, CHNH),
1
0

3
.84-3.93 (m, 8H, C
CH NH, (b)), 1.71 (br, 4H, NH and OH). C NMR (CDCl
28.36, 128.30, 128.20, 127.91, 127.71, 127.61 (C ), 87.08 (i-C
8.18, 68.03, 67.97 (C ), 61.88 (CHNH), 45.96 (CH NH). IR (KBr pellet in cm ) ͵ (O-H):
332, (N-H): 3281, (C=C-Cp): 1453, (C-H): 3078, 3027, 2890, 2826. Anal. calcd. for
Fe, C, 75.46; H, 6.35; N, 5.40; found: C, 75.32; H, 6.21; N, 4.28 %.
5
H
4
), 3.28 (d, 2H, J = 13.1 Hz, CH
2
NH, (a)), 3.15 (d, 2H, J = 13.1 Hz,
, ppm): ꢂ 140.62, 139.54 (i-C
), 78.31 (CHOH), 68.52,
1
3
2
3
6
5
H ),
1
6
3
6
H
5
5
H
4
-
1
5
H
4
2
C
40
H
40
N
2
O
2
2
2
.4. General procedure for synthesis of ferrocene based C -symmetric phosphinites (9-16)
To a solution of ferrocenylaminoalcohol (1 equiv.) in dry toluene (20 ml) was added
triethylamine (2 equiv.) and the mixture was stirred for 10 min under argon atmosphere. To this
solution was added dropwise monochlorodiphenylphosphine, PPh Cl (2 equiv.). The mixture
2
was then stirred at room temperature until all the reactions were completed. A white precipitate
of triethylamine hydrochloride was removed by filtration under argon and the remaining organic
phase was evaporated under reduced pressure to produce a yellow viscous oily product.
2
.4.1. (S)-bis[N-2-diphenylphosphinite-1-benzyl)ethyl]-1,1'-ferrocenylmethyldiamine, (9)
2
0
1
Yield: 100 mg, (83%). [ꢀ]
D
+37.2 (c 1.2, MeOH)]; H NMR (CDCl
and 4H, CH OP), 3.50 (d, 2H, J =12.9 Hz,
NH (b)), 3.13 (m, 2H, CHN), 2.89 (m, 2H, CH
Ph (b)). C NMR (CDCl , ppm): ꢂ 141.87 (d, J=18.1 Hz, i-C P), 138.68
), 130.62 (d, J= 11.1, o-C PO), 129.45, 129.38, 129.32, 129.06, 128.51 (p-C PO, m-
PO, o-, m-, p-C ), 87.15 (i-C ), 71.19 (d, J= 18.0, CH OP), 68.58, 68.50, 68.37, 68.31
), 59.52 (d, J=8.1 Hz, CHN), 46.41 (CH NH), 38.09 (CH
3
, ppm): ꢂ 7.15-7.56 (m, 30
H, C
6
H
5
and C
6
H
5
P), 3.81-3.99 (m, 8H, C
5
H
4
2
CH NH (a)), 3.43 (d, 2H, J=12.9 Hz, CH
2
2
2
Ph
1
3
(
a)), 2.80 (m, 2h, CH
i-C
2
3
6
H
5
(
6
H
5
6
H
5
6
H
5
C
6
H
5
6
H
5
5
H
4
2
3
1
1
(
C
5
H
4
2
2
Ph). P-{ H} NMR (CDCl
3
,
-1
ppm): ꢂ 114.66 (s, OPPh
2
). IR (KBr pellet in cm ) ͵ (N-H): 3330, (C=C-Cp): 1454, (O-P): 1027,
1
1

(
C-H): 3036, 3025, 2923, 2864. Anal. calcd. for C54
H
54
N
2
O
2
P Fe: C, 73.62; H, 6.19; N, 3.18,
2
found: C, 73.46; H, 6.05; N, 3.08 %.
2
.4.2. (S)-bis[N-2-diphenylphosphinite-1-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine, (10)
2
0
1
Yield: 95 mg, (77%). [ꢀ]
D
+56.1 (c 1.2, MeOH)]; H NMR (CDCl
and 2H, CHN), 3.93 (m, 4H, CH
NH (a)), 3.22 (d, 2H, J=13.1 Hz, CH NH (b)), 2.42 (br, 2H, NH). C NMR
, ppm): ꢂ 141.76 (d, J=18.6 Hz, i-C PO), 140.11 (i-C ), 130.61, 130.47, 130.39,
29.44, 128.51, 128.45, 128.38, 127.92, (o-C PO, p-C PO, m-C PO, o-, p-, m-C ),
3
, ppm): ꢂ 7.28-7.65 (m, 30
H, C
H, J=13.1 Hz, CH
CDCl
6
H
5
PO and C
6
H
5
), 4.02-4.07 (m, 8H, C
5
H
4
2
OP), 3.41 (d,
13
2
2
2
(
3
6
H
5
6
H
5
1
6
H
5
6
H
5
6
H
5
6
H
5
8
7.06 (i-C
5
H
4
), 74.74 (d, J=18.1 Hz, (CH
2
OP), 68.68, 68.49, 68.42, 68.18 (C
5
H
4
), 63.39 (d,
, ppm): ꢂ 116.76 (s, OPPh ). IR (KBr
pellet in cm ) ͵(N-H): 3331, (C=C-Cp): 1436, (O-P): 1020, (C-H): 3068, 3028, 2922, 2862.
Anal. calcd. for C52 Fe: C, 73.23; H, 5.92; N, 3.29, found: C, 73.11; H, 5.82; N, 3.18
3
1
1
J=8.0 Hz, CHN), 46.18 ((CH
2
NH). P-{ H} NMR (CDCl
3
2
-1
H
50
N
2
O P
2 2
%
.
2
.4.3. (S)-bis[N-2-diphenylphosphinite-1-iso-butyl)ethyl]-1,1'-ferrocenylmethyldiamine,
(
11)
2
0
1
Yield: 110 mg, (85%). [ꢀ]
P), 7.38-7.42 (m, 12H, m- and p-C
.58 (br, 4H, CH NH), 2.96 (br, 2H, CHN), 1.64-1.71 (m, 2H, CHCH
CHCH ), 0.91 (d, 6H, J=6.6 Hz, CHCH , (a)), 0.86 (d, 6H, J=6.5 Hz, CHCH
CDCl , ppm): ꢂ 141.84 (d, J= 19.2 Hz, i-C P), 130.47 (d, J= 20.1 Hz, o-C
P), 128.42 (d, J=6.0 Hz, m-C P), 87.15 (i-C ), 71.48 (d, J=16.1 Hz, CH
9.14, 68.73, 68.66 (C ), 55.81 (d, J=7.0 Hz, CHN), 45.90 (CH NH), 40.46 (CHCH
D
+35.3 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 7.55 (m, 8H, o-
), 3.89 (m, 4H, CH OP),
), 1.38-1.45 (m, 4H,
C
6
H
5
6
H
5
P), 4.02-4.16 (m, 8H, C
5
H
4
2
3
2
3
13
2
3
3
, (b)). C NMR
P), 129.47 (s, p-
OP), 69.24,
), 24.90
(
3
6
H
5
6
H
5
C
6
H
5
6
H
5
5
H
4
2
6
5
H
4
2
2
1
2

3
1
1
(
CHCH
OPPh ). IR (KBr pellet in cm ) ͵(N-H): 3332, (C=C-Cp): 1435, (O-P): 1023, (C-H): 3069, 2953,
867. Anal. calcd. for C48 Fe: C, 70.92; H, 7.21; N, 3.45, found: C, 70.76; H, 7.06; N,
.32 %.
3
), 22.80 (CHCH
3
, (a)), 22.98 (CHCH
3
, (b)). P-{ H} NMR (CDCl
3
, ppm): ꢂ 114.26 (s,
-1
2
2
3
H
58
N
2
O P
2 2
2
.4.4. (S)-bis[N-2-diphenylphosphinite-1-sec-butyl)ethyl]-1,1'-ferrocenylmethyldiamine,
(
12)
2
0
1
Yield: 105 mg, (82%). [ꢀ]
P), 7.38-7.46 (m, 12H, m- and p- C
.52 (br, 4H, CH NH), 2.81 (br, 2H, CHN), 1.68 (br, 2H, CHCH
.24 (m, 2H, CH CH (b)), 0.88-0.95 (m, 12H, CHCH , (a) and CH
, ppm): ꢂ 142.00 (d, J=17.1 Hz, i-C PO), 130.41 (d, J=21.5Hz, o-C
PO), 128.39 (s, J=5.1 Hz, m-C PO), 87.06 (i-C ), 69.67, 69.49, 68.97, 68.88, 68.40
), 61.83 (CHN), 46.70 (CH NH), 35.79 (CHCH ), 26.07 (CH CH ), 14.82
, ppm): ꢂ 115.66 (s, OPPh ). IR
KBr pellet in cm ) ͵ (N-H): 3332, (C=C-Cp): 1437, (O-P): 1026, (C-H): 3069, 2960, 2926,
D
+66.2 (c 1.2, MeOH)]; H NMR (CDCl
P), 4.02-4.18 (m, 8H, C
), 1.53 (m, 2H, CH
3
, ppm): ꢂ 7.53 (m, 8H, o-
), 3.92 (m, 4H, CH OP),
CH (a)),
, (b)). C NMR
PO), 129.36 (s,
C
6
H
5
6
H
5
5
H
4
2
3
1
2
3
2
3
1
3
2
3
3
2
CH
3
(
CDCl
3
6
H
5
6
H
5
p-C
6
H
5
6
H
5
5
H
4
(
(
(
CH
2
OP, C
5
H
4
2
3
2
3
3
1
1
CHCH
3
, (a)), 12.14 (CH
2
CH
3
, (a)). P-{ H} NMR (CDCl
3
2
-
1
2
3
873. Anal. calcd. for C48
.30 %.
H
58
N
2
O
2
2
P Fe: C, 70.92; H, 7.21; N, 3.45, found: C, 70.75; H, 7.06; N,
2
.4.5. (S)-bis[N-2-diphenylphosphinite propyl]-1,1'-ferrocenylmethyldiamine, (13)
2
0
1
Yield: 100 mg, (92%). [ꢀ]
D
+53.4 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 7.25-7.83 (m, 20
NH), 2.84
H, C
6
H
5
PO), 4.23 (m, 2H, CHOP), 4.00-4.06 (m, 8H, C
m, 2H, CH CH (a)), 2.75 (m, 2H, CHCH (b)), 1.31 (d, 6H, J= 4.1 Hz, CHCH
CDCl , ppm): ꢂ 142.87 (d, J=16.9 Hz, i-C P), 130.11 (d, J=21.3 Hz, o-C
5
H
4
), 3.39-3.49 (m, 4H, CH
2
1
3
(
(
2
2
3
). C NMR
3
6
H
5
6
H
5
P), 129.05 (s, p-
1
3

C
6
H
5
P), 128.51 (d, J= 10.5 Hz, m-C
8.30 (C ), 55.97 (d, J=5.0 Hz, CH
H} NMR (CDCl , ppm): ꢂ 107.12 (s, OPPh
6
H
5
P), 86.46 (i-C
5
H
4
), 76.65 (s, CHOP), 68.88, 68.86, 68.33,
3
1
6
5
H
4
2
CH), 48.61 (CH
2
NH), 20.48 (d, J = 6.4 Hz, CHCH ). P-
3
1
-1
{
3
2
). IR (KBr pellet in cm ) ͵(N-H): 3343, (C=C-
Cp): 1438, (O-P): 1024, (C-H): 3057, 2968, 2928, 2884. Anal. calcd. for C42
H
46
N
2
O
2
2
P Fe: C,
6
9.23; H, 6.38; N, 3.85, found: C, 69.10; H, 6.25; N, 3.68 %.
2
.4.6. (R)-bis[N-2-diphenylphosphinite-2-phenyl]-1,1'-ferrocenylmethyldiamine, (14).
2
0
1
Yield: 125 mg. (91%). [ꢀ]
D
-56.3 (c 1.2, MeOH)]; H NMR (CDCl
3
, ppm): ꢂ 7.84-7.28 (m,
), 3.46-3.38 (m, 4H,
3
0H, C
CH Cp), 3.18-3.12 (m, 2H, CH
ppm): ꢂ 142.15 (J = 14.8 Hz, i-C
6
H
5
and C
6
H
5
PO), 5.05 (m, 2H, CHOP), 4.08-3.94 (m, 8H, C
NH (a)), 2.97-2.89 (m, 2H, CH NH (b)). C NMR (CDCl
PO), 141.93 (i-C ), 129.49, 129.05, 128.58, 128.49,
PO), 86.03 (i-C ), 81.92 (d, J= 20.6 Hz, CHOP), 68.67, 68.62,
), 56.66 (CH NH), 48.48 (CH
5
H
4
1
3
2
2
2
3
,
6
H
5
6
H
5
1
6
28.42, 128.39 (C
8.51, 68,24 (C
). IR (KBr pellet in cm ) ͵ (N-H): 3360, (C=C-Cp): 1448, (O-P): 1014, (C-H): 3087,
030, 2937, 2874. Anal. calcd. for C52 Fe: C, 73.23; H, 5.92; N, 3.29, found: C, 73.10;
6
H
5
and C
6
H
5
5
H
4
31
1
5
H
4
2
2
Cp). P-{ H} NMR (CDCl , ppm): ꢂ 112.79
3
-1
(
s, OPPh
2
3
H
50
N
2
O P
2 2
H, 5.75; N, 3.18 %.
2
.4.7. (R)-bis[N-2-diphenylphosphinite-1-ethyl]-1,1'-ferrocenylmethyldiamine, (15).
2
0
1
Yield: 95 mg, (90%). [ꢀ]
D
-42.8 (c 1.2, MeOH)]; H NMR (CDCl
), 3.81-3.88 (m, 4H, CH OP), 3.53 (m, 4H, CH
CH ), 0.92 (t, 6H, J=7.4 Hz, CH
P), 130.54, 130.35, 130.32 (o-, m-, p- C
OP), 68.91, 68.86, 68.45, 68.44 (C ), 59.32 (d, J= 8.0 Hz,
). P-{ H} NMR (CDCl , ppm): ꢂ
3
, ppm): ꢂ 7.80-7.27 (m, 20
NH),
). C NMR (CDCl
), 86.59 (i-
H, C
.81(m, 2H, CHN), 1.59 (m, 4H, CH
ppm): ꢂ 141.75 (d, J= 9.0 Hz, i-C
), 71.21 (d, J= 18.1 Hz, CH
CHN), 46.09 (CH NH), 24.03 (CH
6
H
5
PO), 3.89-4.09 (m, 8H, C
5
H
4
2
2
1
3
2
2
3
2
CH
3
3
,
6
H
5
6
H
5
C
5
H
4
2
5
H
4
3
1
1
2
2
CH
3
), 10.28 (CH
2
CH
3
3
1
4

-
1
1
3
6
14.38 (s, OPPh ). IR (KBr pellet in cm ) ͵ (N-H): 3378, (C=C-Cp): 1438, (O-P): 1030, (C-H):
2
072, 2959, 2928, 2873. Anal. calcd. for C44
9.70; H, 6.50; N, 3.58 %.
H
50
N O
2 2
2
P Fe: C, 69.83; H, 6.67; N, 3.70, found: C,
2
.4.8. (1S,2R)-bis[N-2-diphenylphosphinite-1,2-diphenyl)ethyl]-1,1'-ferrocenylmethyldi-
amine, (16).
2
0
1
Yield: 95 mg, (86 %). [ꢀ]
D
+17.6 (c 1.2, MeOH)]; H NMR (CDCl , ppm): ꢂ 7.03-7.44 (m,
3
4
0H, C
), 3.18 (m, 2H, CH
CDCl , ppm): ꢂ 141.65 (d, J= 19.4 Hz, i-C
30.63, 130.41, 129.67, 128.86, 128.73, 128.60, 128.46, 128.38, 128.28 (C
), 87.35 (i-C ), 86.31 (d, J=19.1 Hz, (CHOP), 68.11, 67.99, 67.78, 67.72 (C
7.65 (s, CHN), 45.86 (CH
6
H
5
P and C
6 5
H ), 4.94-4.86 (m, 2H, CHN), 4.09 (m, 2H, CHOP), 3.60-3.90 (m, 8H,
1
3
C
5
H
4
2
NH (a)), 2.98 (m, 2H, CH
2
NH (b)), 1.35 (br, 2H, NH). C NMR
,(a) and i-C
PO and i-C
(
3
6
H
5
PO), 139.87, 140.82 (i-C
6
H
5
6
H
5
, (b)),
,(a)
),
). IR (KBr
pellet in cm ) ͵(N-H): 3319, (C=C-Cp): 1451, (O-P): 1015, (C-H): 3068, 3057, 3027, 2925.
Anal. calcd. for C64 Fe: C, 76.48; H, 5.83; N, 2.79, found: C, 76.38; H, 5.71; N, 2.72
1
6
H
5
6
H
5
and i-C
6
H
5
5
H
4
5
H
4
3
1
1
6
2
NH). P-{ H} NMR (CDCl
3
, ppm): ꢂ 112.54 (s, OPPh
2
-1
H
58
N
2
O P
2 2
%
.
2
2
.5. Synthesis of Rhodium complexes of the ferrocene based C -symmetric phosphinites
(
17-24)
2
.5.1. (S)-bis[[N-2-diphenylphosphinite-1-benzyl)ethyl]-1,1'-ferrocenylmethyldiamine
4
chloro ͝ -1,5-cyclooctadiene rhodium(I))], (17)
(
A solution of (S)-bis[N-2-diphenylphosphinite-1-benzyl)ethyl]-1,1'-ferrocenylmethyl diamine, 9
176 mg, 0.20 mmol) in CH Cl (15 ml) was added dropwise to the solution of [Rh(COD)Cl]
(
2
2
2
1
5

(
99 mg, 0.20 mmol) in CH
2
Cl (15 ml) at -78 °C. The reaction mixture was warmed slowly to
2
room temperature within 30 min, and stirred at this temperature for an additional 10 min. The
resulting yellow solution was concentrated to 2 ml under reduced pressure, and addition of
hexane (30 ml) caused the precipitation of a dark yellow solid. The supernatant solution was
decanted, the solid was washed with hexane: diethylether (1:1) and dried by vacuum, yielding
o
31
1
rhodium complex, 17. Yield: 230 mg, 84%, m.p: 105-107 C. P-{ H} NMR (CDCl
3
, 162.0
MHz, ppm): 119.65 (d, JRhP = 179.8 Hz). IR (KBr pellet in cm ): ͵ (NH): 3330, (CH): 3070,
038, 2925, 2850, (C-C-Cp): 1457, (O-P): 1031; Anal. Calc. for [C70 FeRh Cl
1373.88 g/mol): C 61.87, N 2.04, H 5.73; found: C 61.74, N 1.90, H 5.60 %.
−
1
3
H
78
N
2
O
2
P
2
2
2
]
(
2
.5.2. (S)-bis[[N-2-diphenylphosphinite-1-phenyl)ethyl]-1,1'-ferrocenylmethyldiamine
4
chloro ͝ -1,5-cyclooctadiene rhodium(I))], (18)
(
A solution of (S)-bis[N-2-diphenylphosphinite-1-phenyl)ethyl]-1,1'-ferrocenylmethyl diamine,
0 (171 mg, 0.20 mmol) in CH Cl (15 ml) was added dropwise to the solution of
Rh(COD)Cl] (99 mg, 0.20 mmol) in CH Cl (15 ml) at -78 °C. The reaction mixture was
1
2
2
[
2
2
2
warmed slowly to room temperature within 30 min, and stirred at this temperature for an
additional 15 min. The resulting yellow solution was concentrated to 2 ml under reduced
pressure, and addition of hexane (30 ml) caused the precipitation of a dark yellow solid. The
supernatant solution was decanted, the solid was washed with hexane : diethylether (1:1) and
o
31
dried by vacuum, yielding rhodium complex, 18. Yield: 245 mg, 90%, m.p: 120-122 C. P-
1
−1
{
H} NMR (CDCl
3
, 162.0 MHz, ppm): 120.02 (d, JRhP = 179.8 Hz). IR (KBr pellet in cm ): ͵
(
N H): 3313, (CH): 3054, 3015, 2907, 2855, (C-C-Cp): 1426, (O-P): 1008; Anal. Calc. for
1
6

[
C
68
H
74
N
2
O
2
P
2
FeRh
2
Cl ] (1345.82 g/mol): C 60.68, N 2.08, H 5.55; found: C 60.53, N 1.96, H
2
5
.40 %.
2
.5.3. (S)-bis[[N-2-diphenylphosphinite-1-iso-butyl)ethyl]-1,1'-ferrocenylmethyldiamine
4
chloro ͝ -1,5-cyclooctadiene rhodium(I))], (19)
(
A solution of (S)-bis[N-2-diphenylphosphinite-1-iso-butyl)ethyl]-1,1'-ferrocenyl methyldiamine,
1 (163 mg, 0.20 mmol) in CH Cl (15 ml) was added dropwise to the solution of
Rh(COD)Cl] (99 mg, 0.20 mmol) in CH Cl (15 ml) at -78 °C. The reaction mixture was
1
2
2
[
2
2
2
warmed slowly to room temperature within 30 min, and stirred at this temperature for an
additional 20 min. The resulting yellow solution was concentrated to 2 ml under reduced
pressure, and addition of hexane (30 ml) caused the precipitation of a dark yellow solid. The
supernatant solution was decanted, the solid was washed with hexane:diethylether (1:1) and
o
31
dried by vacuum, yielding rhodium complex, 19. Yield: 215 mg, 82%, m.p: 115-117 C. P-
1
−1
{
H} NMR (CDCl
H): 3335, (CH): 3075, 2966, 2960, 2872, (C-C-Cp): 1441, (O-P): 1026; Anal. Calc. for
FeRh Cl ] (1305.84 g/mol): C 58.86, N 2.15, H 6.34; found: C 58.72, N 2.08, H
3
, 162.0 MHz, ppm): 119.03 (d, JRhP=179.8 Hz). IR (KBr pellet in cm ): ͵ (N-
[
C
64
H
82
N
2
O
2
P
2
2
2
6
.20 %.
2
.5.4. (S)-bis[[N-2-diphenylphosphinite-1-sec-butyl)ethyl]-1,1'-ferrocenylmethyldiamine
4
chloro ͝ -1,5-cyclooctadiene rhodium(I))], (20)
(
A solution of (S)-bis[N-2-diphenylphosphinite-1-sec-butyl)ethyl]-1,1'-ferrocenylmethyldiamine,
2 (163 mg, 0.20 mmol) in CH Cl (15 ml) was added dropwise to the solution of
Rh(COD)Cl] (99 mg, 0.20 mmol) in CH Cl (15 ml) at -78 °C. The reaction mixture was
warmed slowly to room temperature within 30 min, and stirred at this temperature for an
1
2
2
[
2
2
2
1
7

additional 20 min. The resulting yellow solution was concentrated to 2 ml under reduced
pressure, and addition of hexane (30 ml) caused the precipitation of a dark yellow solid. The
supernatant solution was decanted, the solid was washed with hexane : diethylether (1:1) and
o
31
dried by vacuum, yielding rhodium complex, 20. Yield: 230 mg, 87%, m.p: 112-114 C. P
1
−1
{
H}-NMR (CDCl
3
, 162.0 MHz, ppm): 119.64 (d, JRhP=178.2 Hz). IR (KBr pellet in cm ): ͵
(
[
N-H): 3327, (CH): 3070, 2964, 2915, 2876, (C-C-Cp): 1455, (O-P): 1020; Anal. Calc. for
C
64
H
82
N
2
O
2
P
2
FeRh
2
Cl
2
] (1305.84 g/mol): C 58.86, N 2.15, H 6.34; found: C 58.68, N 2.02, H
6
.15 %.
4
.5.5. (S)-bis[[N-2-diphenylphosphinite propyl]-1,1'-ferrocenylmethyldiamine(chloro ͝ -
2
1
,5-cyclooctadiene rhodium(I))], (21)
A solution of (S)-bis[N-2-diphenylphosphinite propyl]-1,1'-ferrocenylmethyldiamine, 13 (146
mg, 0.20 mmol) in CH
2
2
Cl
2
(15 ml) was added dropwise to the solution of [Rh(COD)Cl]
2
(99
mg, 0.20 mmol) in CH
Cl
2
(15 ml) at -78 °C. The reaction mixture was warmed slowly to room
temperature within 30 min, and stirred at this temperature for an additional 10 min. The resulting
yellow solution was concentrated to 2 ml under reduced pressure, and addition of hexane (30 ml)
caused the precipitation of a dark yellow solid. The supernatant solution was decanted, the solid
was washed with hexane : diethylether (1:1) and dried by vacuum, yielding rhodium complex,
o
31
1
2
1. Yield: 208 mg, 85%, m.p: 121-123 C. P-{ H} NMR (CDCl
3
, 162.0 MHz, ppm): 118.2 (d,
RhP = 174.96 Hz). IR (KBr pellet in cm ): ͵ (N H): 3328, (CH): 3080, 2974, 2945, 2876, (C-C-
Cp): 1455, (O-P): 1030; Anal. Calc. for [C58 FeRh Cl ] (1221.68 g/mol): C 57.01, N
.29, H 5.79; found: C 56.78, N 2.10, H 5.55 %.
−
1
J
H
70
N
O
2 2
P
2
2
2
2
1
8

4
.5.6. (R)-bis[[N-2-diphenylphosphinite-2-phenyl]-1,1'-ferrocenylmethyldiamine(chloro ͝ -
2
1
,5-cyclooctadiene rhodium(I))], (22)
A solution of (R)-bis[N-2-diphenylphosphinite-2-phenyl]-1,1'-ferrocenylmethyl diamine, 14 (171
mg, 0.20 mmol) in CH
2
2
Cl
2
(15 ml) was added dropwise to the solution of [Rh(COD)Cl]
2
(99
mg, 0.20 mmol) in CH
Cl
2
(15 ml) at -78 °C. The reaction mixture was warmed slowly to room
temperature within 30 min, and stirred at this temperature for an additional 20 min. The resulting
yellow solution was concentrated to 2 ml under reduced pressure, and addition of hexane (30 ml)
caused the precipitation of a dark yellow solid. The supernatant solution was decanted, the solid
was washed with hexane : diethylether (1:1) and dried by vacuum, yielding rhodium complex,
o
31
1
2
2. Yield: 240 mg, 89%, m.p: 130-132 C. P-{ H} NMR (CDCl
3
, 162.0 MHz, ppm): 119.94 (d,
−
1
J
RhP = 178.2 Hz). IR (KBr pellet in cm ): ͵ (NH): 3325, (CH): 3074, 2974, 2918, 2876, (C-C-
Cp): 1445, (O-P): 1030; Anal. Calc. for [C68
H
74
N O
2 2
P
2
FeRh
2
Cl
2
] (1345.82 g/mol): C 60.68, N
2
.08, H 5.55; found: C 60.48, N 1.86, H 5.36 %.
4
.5.7. (R)-bis[[N-2-diphenylphosphinite-1-ethyl]-1,1'-ferrocenylmethyldiamine(chloro ͝ -
2
1
,5-cyclooctadiene rhodium(I))], (23)
A solution of (R)-bis[N-2-diphenylphosphinite-1-ethyl]-1,1'-ferrocenylmethyldiamine, 15 (151
mg, 0.20 mmol) in CH Cl (15 ml) was added dropwise to the solution of [Rh(COD)Cl] (99 mg,
.20 mmol) in CH Cl (15 ml) at −78 °C. The reaction mixture was warmed slowly to room
2
2
2
0
2
2
temperature within 30 min, and stirred at this temperature for an additional 10 min. The resulting
yellow solution was concentrated to 2 ml under reduced pressure, and addition of hexane (30 ml)
caused the precipitation of a dark yellow solid. The supernatant solution was decanted, the solid
was washed with hexane : diethylether (1:1) and dried by vacuum, yielding rhodium complex, 23
1
9

o
31
1
Yield: 220 mg, 88%; m.p:124-126 C. P-{ H} NMR (CDCl
3
, 162.0 MHz, ppm): 119.21 (d,
RhP=175.0 Hz). IR (KBr pellet in cm ): ͵ (N H): 3320, (CH): 3090, 2954, 2935, 2879, (C C-
Cp): 1454, (O-P): 1022; Anal. Calc. for [C60 FeRh Cl ] (1249.74 g/mol): C 57.65, N
−
1
J
H
74
N O
2 2
P
2
2
2
2
.24, H 5.98; found: C 57.40, N 1.96, H 5.58 %.
2
.5.8. (1S,2R)-bis[[N-2-diphenylphosphinite-1,2-diphenyl)ethyl]-1,1'-ferrocenylmethyldi-
4
amine(chloro͝ -1,5-cyclooctadiene rhodium(I))], (24)
A solution of (1S,2R)-bis[N-2-diphenylphosphinite-1,2-diphenyl)ethyl]-1,1'-ferrocenyl
methyldiamine, 16 (201 mg, 0.20 mmol) in CH
2
Cl
2
(15 ml) was added dropwise to the solution
of [Rh(COD)Cl] (99 mg, 0.20 mmol) in CH Cl
2
2
2
(15 ml) at -78 °C. The reaction mixture was
warmed slowly to room temperature within 60 min, and stirred at this temperature for an
additional 30 min. The resulting yellow solution was concentrated to 2 ml under reduced
pressure, and addition of hexane (30 ml) caused the precipitation of a dark yellow solid. The
supernatant solution was decanted, the solid was washed with hexane : diethylether (1:1) and
o
31
1
dried by vacuum, yielding rhodium complex, 24. Yield: 270 mg, 90%, m.p:136-138 C. P-{ H}
−
1
NMR (CDCl
367, (CH):3078, 3008, 2917, 2870, (C-C-Cp): 1458, (O-P): 1023; Anal. Calc. for
FeRh Cl ] (1498.02 g/mol): C 64.13, N 1.87, H 5.53; found: C 63.74, N 1.60, H
3
, 162.0 MHz, ppm): 117.72 (d, JRhP= 176.6 Hz). IR (KBr pellet in cm ): ͵ (NH):
3
[
C
80
H
82
N
2
O
2
P
2
2
2
5
.35 %.
3
3
. Results and discussion
2
.1. Synthesis and characterization of the amino alcohols, C -symmetric ferrocenyl-
phosphinites and their rhodium(I) complexes
2
0

The synthetic strategy and reaction conditions adopted in this work are described in Scheme 1.
We first established an easy methodology for the synthesis of ferrocene-1,1'-dicarboxyaldehyde
based, in part, on conditions reported by Pelinski and Mueller-Westerhoff [xlix]. Following the
references, tetramethylethylenediamine (TMEDA) (5.32 ml, 35.4 mmol) was added to a solution
of ferrocene (3.00 g., 16.2 mmol) in dry n-hexane and the suspension was stirred for 5 min under
argon. n-BuLi (22 ml, 35.4 mmol, 1.7 M in hexane) was added dropwise with a syringe. The
mixture was left to stirring at room temperature overnight. After stirring at -78 ºC for 15 min,
THF followed by anhydrous DMF were added to the reaction mixture. The solution was
quenched with brine and CH
2
Cl . The phases were separated and the aqueous phase was
2
extracted with CH Cl (3 x 30ml). The combined organic layers were dried over MgSO and
2
2
4
evaporated under reduced pressure. The residue was purified through column chromatography
giving the ferrocene-1,1'-dicarboxaldehyde as bright red crystalline solid in third fraction
(
Scheme 1). Subsequently, in separate experiments, ferrocene-1,1'-dicarboxyaldehyde was
reacted with commercially available L-phenyl alaninol, L-phenyl glycinol, L-leucinol, L-
isoleucinol, (S)-(+)-1-amino-2-propanol, (R)-(-)-2-amino-1-phenylethanol, (R)-(-)-2-amino-1-
butanol or (1S,2R)-(+)-2-amino-1,2-diphenylethanol in the presence of molecular sieves, and
reduction of the crude reactions mixtures with NaBH
4
in methanol provided the corresponding
1
enantimerically pure ferrocene based amino alcohols, 1-8 in good yields (60-88 %). The H
NMR spectra of compounds 1-8 show characteristic features: the ꢀ- and !-cyclopentadienyl (Cp)
protons in the amino alcohols with relatively small non-resolved multiplets appear approximately
at ꢂ 4.00 ppm The magnetic non-equivalence of the monosubstituted Cp ring was observed,
1
3
1
which is caused by their planar structure. The C-{ H} NMR spectra also exhibit the typical
1
13
signals for substituted ferrocenes. All H NMR and C NMR spectra were given in SI (for
2
1

details see experimental section and supporting information). The structures for these ferrocene
based chiral amino alcohols are consistent with the data obtained from IR spectroscopy and
elemental analysis.
Insert Scheme 1 Here
ꢀ
ꢀ
The synthetic procedure for the preparation of the ligands is shown in Scheme 1. Chiral C
symmetric phosphinite ligands based on ferrocenyl group, 9-16 were synthesized by hydrogen
abstraction from the described ferrocene based chiral amino alcohols 1-8, by a base (Et N) and
the subsequent reaction with two equivalents of Ph PCl, in anhydrous toluene under inert argon
atmosphere. The progress of these reactions was conveniently followed by P-{ H} NMR
spectroscopy. The signal of the starting material PPh Cl at ꢂ 81.0 ppm disappeared and new
singlets appeared downfield due to the C -symmetric ferrocenyl phosphinite ligands. Both of the
phosphorus atoms are equivalent in each ligand and exhibit singlets approximately at 107-114
2
-
3
2
3
1
1
2
2
3
1
1
ppm, and the P-{ H} NMR spectra of the free ligands are [l] in line with the values previously
observed for similar compounds [li,lii,liii]. Solution of the ligands in CDCl and in air, prepared
under anaerobic condition, is stable (up to 36 h) and decomposes very slowly gradually to give
oxide and the hydrolysis product diphenylphosphinous acid, Ph P(O)H [liv]. Furthermore, the
3
2
3
1
1
P-{ H} NMR spectrum also displays formation of PPh
2
PPh
2
and P(O)Ph
2
PPh
2
, as indicated by
1
signals at about ꢂ -15.6 ppm as singlet and ꢂ 35.4 ppm and ꢂ -21.8 ppm as doublets with J(PP)
1
2
20 Hz, respectively, after the 72 h [lv]. The assignment of the H chemical shifts was derived
2
2

1
3
from 2D HH-COSY spectra and the appropriate assignment of the C chemical shifts from
DEPT and 2D HMQC spectra. Furthermore, IR spectra and C, H, N elemental analyses are in
agreement with the proposed structures for C -symmetric ferrocenyl phosphinite ligands. Typical
2
spectra of these ligands are illustrated in SI.
Rhodium complexes of these new ligands were prepared as indicated in experimental section and
illustrated in Scheme 1. Complexation reactions were straightforward, with coordination to
rhodium being carried out at room temperature. All the rhodium complexes were readily
synthesized in good yields and the whole reactions resulting 17-24 are depicted in Scheme 1.
Treatment of [Rh()-Cl)(cod)]
molar ratio in toluene resulted in the formation of dinuclear complexes 17-24 as crystalline air
stable solids. The C -symmetric ferrocenyl phosphinites were expected to cleave the [Rh()-
Cl)(cod)] dimer to give the corresponding complexes, 17-24 via monohapto coordination of the
phosphinite group. Furthermore, the reactions between rhodium(I) precursor and ferrocenyl-
phosphinites are not affected by the molar ratio of [Rh()-Cl)(cod)] as well as the steric and
electronic properties of the donor phosphorus atoms. The initial color change was attributed to
the dimer cleavage most probably by the C -symmetric ferrocenyl phosphinite ligand. All the
2
with C
2
-symmetric ferrocenyl phosphinite ligands 9-16 in 1:1
2
2
2
2
3
1
1
complexes were isolated as indicated by doublets in the P-{ H} NMR spectra at approximately
1
ꢂ 120 ppm (d, JRhP: 178-180 Hz), in line with the values previously observed for similar
lvii
compounds [lvi, ] with a coordination shift of approximately ꢂ 8.0 ppm (see SI) attributed to
1
formation of the corresponding C
2
-symmetric ferrocenyl phosphinites. Interestingly, H NMR
spectra of these complexes are featured by very broad signals at room temperature. Upon
lowering the temperature to -80 ºC, the signals remain unresolved; hence their clear assignment
cannot be accomplished. Elemental analyses of the complexes are also consistent with the
2
3

suggested molecular formulas. The absorption bands corresponding to Rh(I)-C -symmetric
2
ferrocenyl phosphinite complexes in the IR spectra do not exhibit significant differences with
respect to those of free ligands (see SI and experimental section).ꢀ
3
.2. Rh(I)-catalyzed asymmetric transfer hydrogenation of ketones using isoPrOH and
base
In the studies of Asymmetric Transfer Hydrogenation, the isoPrOH/base [lviii,lix,lx,lxi] and
formic acid/triethylamine [lxii,lxiii] system has long been used as a source of hydrogen. We
preferred to examine the asymmetric transfer hydrogenation of simple ketones by using a
isoPrOH/base system in the presence of a catalytic amount of Rh(I)-C -symmetric ferrocenyl
2
ligands (17-24). In a preliminary study, complexes 17-24 were tested as precursors for the
catalytic asymmetric transfer hydrogenation of acetophenone and the results are summarized in
Table 1. A typical procedure using acetophenone as substrate was as follows. 0.01 mmol of the
complex and 1 mmol of acetophenone were added to a solution of NaOH in isoPrOH (0.05 mmol
of NaOH in 10 mL isoPrOH) and refluxed at 82 ºC, while the reaction was monitored by GC. In
all reactions, these complexes catalyzed the reduction of ketones to the corresponding alcohols
via hydrogen transfer from isoPrOH. A comparison of complexes 17-24 as precatalysts for the
asymmetric hydrogenation of acetophenone by isoPrOH is given in Table 1. Catalytic
experiments were carried out under inert (Ar) atmosphere using standard Schlenk-line
techniques. These systems catalyzed the reduction of acetophenone to corresponding alcohol
(
(S)-, (R)-1-phenylethanol) in the presence of NaOH.
At room temperature, transfer hydrogenation of acetophenone occurred very slowly [lxiv], with
low conversions (up to 52 %, 48 h) and moderate to high enantioselectivities (up to 96 % ee) in
2
4

the reactions (Table 1, entries 1-8). Because of the reversibility at room temperature the
prolonging the reaction time (96 h) led to a slight decreasing of enantioselectivity, as indicated
[b]
by the catalytic results collected with catalyst, 22 (Entry 6, ) [lxv,lxvi]. Furthermore, as can be
inferred from the Table 1 (Entries 9-16), the presence of base is necessary to observe appreciable
conversions. It is well-known that the base facilitates the formation of rhodium alkoxide by
abstracting proton of the alcohol and subsequently alkoxide undergoes !-elimination to give
metal hydride, which is an active species in this reaction [lxvii,lxviii,lxix,lxx]. Namely, role of
the base is to generate a more nucleophilic alkoxide ion which would rapidly attack the rhodium
complex responsible for dehydrogenation of isoPrOH. In addition, the choice of base, such as
KOH and NaOH, had little influence on the conversion and enantioselectivity (Table 1, entry
[
e]
2
2, ) and with a catalyst/NaOH ratio of 1/5, the complexes are very active leading to a
[f]
quantitative transformation of the acetophenone (Table 1, entries 25-28, ).
Insert Table 1 Here
Insert Table 2 Here
Reduction of acetophenone into (S)- or (R)-1-phenylethanol could be achieved in high yield by
o
increasing the temperature up to 82 C (Table 1, entries 17-24). Furthermore, the conversions
2
5

gradually decreased with increasing the mole ratios of [acetophenone]/[Rh] from 250/1 to 500/1
or 1000/1, except the time lengthened, the enantioselectivities were still high (up to 92% ee, table
2
, entries 1-9). Namely, the ee’s remained unchanged when the molar ratios of substrate to
catalyst were increased and these C -phosphinite ligands with ferrocenyl moiety show much
higher activity and high enantioselectivity. Similar tendency was reported in earlier studies
lxxi,lxxii], indicating that these kind of ligands play an important role in metal-ligand catalytic
system [lxxiii,lxxiv]. Furthermore, it is noteworthy that the catalytic systems, 17-24 display the
differences in reactivity. These results indicate that the structural difference of the C -ferrocenyl
2
[
2
phosphinite ligands is a crucial factor for catalytic activity. It was seen that when the chiral
center is near the rhodium center, the % ee is high. So, from the results, one can say that
complexes 21, 22 and 24 were effective catalysts for the hydrogenation of acetophenone,
yielding products up to 96% ee. It has also been shown that the catalytic activities in the studied
hydrogen transfer reactions were generally much higher for Rh(I)-(R)-bis[N-2-
diphenylphosphinite-2-phenyl]-1,1'-ferrocenylmethyldiamine, 22 than for the other complexes.
Furthermore, aryl moiety (complex 22 and 24) is more responsible for high activity than alkyl
moiety (complexes 17-20 and 23). This different behavior in enantioselectivity can be explained
on the basis of aromatic moiety (phenyl) attaches to chiral carbon center in the ligand backbone
enabling the optimization molecular rigidity. These results have also shown that enantiomeric
purity of the product can be affected by electronic factors, and steric factors of the substituents
on the ligands. As seen from Tables, the catalytic activities in the studied hydrogen transfer
reactions were generally much higher for the 21, 22 and 24 than those for the other complexes
Insert Table 3 Here
2
6

In order to check the application range of the rhodium-catalyzed transfer hydrogenation,
acetophenone derivatives were subjected to asymmetric reduction using the conditions optimized
for acetophenone. Table 3 illustrates conversions of the reduction performed in a 0.1 M of
isoPrOH solution containing 21, 22 and 24 and NaOH (Ketone:Cat.:NaOH = 100:1:5). The
results demonstrate that a range of acetophenone derivatives can be hydrogenated with high
enantioselectivities. Substitution of the phenyl ring of the acetophenone substrate led to a marked
decrease in the catalytic activity and % ee. That’s to say, electronic properties (the nature and
position) of the substituents on the phenyl ring of the ketone caused the changes in the reduction
rate. The introduction of electron withdrawing substituents to the para position of the aryl ring of
the ketone decreased the electron density of the C=O bond so that the activity was improved
resulting in easier hydrogenation [lxxv,lxxvi] As expected, the lowest enantioselectivity was
observed in transfer hydrogenation of p-methoxyacetophenone. From the results, it is obvious
that the introduction of an electron-donating group such as methoxy group to the p-position
decelerates the reaction, but that to the o-position increases the rate and improves the
enantioselectivity. On the contrary, the introduction of electron-withdrawing substituents, such
as F or NO , to the para positions of the aryl ring of the ketone, resulted in improved activity
2
with good enantioselectivity (Table 3, entries 1-3 and 10-12). The examination of the results
indicates clearly that with each of the tested complexes, the highest enantioselectivity was found
for o-methoxyacetophenone (99% ee) when Rh(I)-(R)-bis[N-2-diphenylphosphinite-2-phenyl]-
1
,1'-ferrocenylmethyldiamine, 22 was used as the catalyst precursor.
2
7

4
. Conclusions
In summary, we have developed a new class of C
2
-symmetric ferrocenyl phosphinite ligands,
which exhibited excellent enantiselectivities in the rhodium(I)-catalyzed asymmetric transfer
hydrogenation of aromatic ketones (up to 97% ee). This type of ligands has salient features such
as cheap starting materials and facile preparation, structural tunability, as well as remote
stereocontrol capability of backbone substituents. The chirality of carbon center in the ligand
backbone is of particular importance for asymmetric induction offering an obvious target for
further optimization. The simplicity and efficiency clearly make it an excellent choice of catalyst
for practical preparation of invaluable alcohols via catalytic asymmetric transfer hydrogenation
of aromatic ketones. Furthermore, the development of a practical synthesis of C -symmetric
2
ferrocenyl phosphinites and demonstration that they are competent auxiliaries for catalysis open
up a neglected vein in the rich chemistry of phosphorus ligands. Further work on modifying the
ligand structure for improvement of the enantioselectivity as well as broadening the substrate
scope of the asymmetric transfer hydrogenation (ATH) is undergoing in this lab.
Acknowledgements
Partial support from Tubitak (Project number: 111T419) is gratefully acknowledged.
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2
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