Chiral bidentate aminophosphine ligands: Synthesis, coordination chemistry and asymmetric catalysis

Article abstract of DOI:10.1039/b414668a

Chiral aminophosphines Ph₂PN(R)(CH₂) _nN(R)PPh₂1-4 [n = 2, R = CH(CH₃)(Ph) 1; n = 3, R = CH(CH₂CH₃)(Ph) 2, n = 2, R = CH(CH₃)(1- naphthyl) 3; n = 2, R = CH(CH₃)(C₆H₁₁) 4] were synthesized by the reaction of ClPPh₂ with the appropriate easily accessible enantiopure amine building blocks. For compounds 1 and 2, the corresponding selenides 5 and 6 were prepared to determine the electronic character of the phosphine moieties. By reaction of 1 with either PdCl ₂(cod) or PdCl(CH₃)(cod) the cis-complexes 7 and 8 were obtained. The molecular structure for complex 7, cis-[PdCl₂(1)], was determined by X-ray crystallography. Reaction of PtCl₂(cod) with 1 or 2 yielded the corresponding monomeric cis-isomers 9 and 10. The rhodium derivative [RhCl(CO)(1)] (11) was obtained as a mixture of cis and trans-isomers. Preliminary results in the rhodium catalyzed hydroformylation of styrene and vinyl acetate, with ee's up to 51% and high regioselectivities, showed the potential of these chiral aminophosphines for homogeneous catalysis.

Full text of DOI:10.1039/b414668a

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F U L L P A P E R
Chiral bidentate aminophosphine ligands: synthesis, coordination
chemistry and asymmetric catalysis
Eric J. Zijp,a Jarl Ivar van der Vlugt,a Duncan M. Tooke,b Anthony L. Spekb and Dieter Vogt*a
a Schuit Institute of Catalysis, Laboratory of Homogeneous Catalysis, Eindhoven University of
Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands
b Laboratory for Crystal and Structural Chemistry, Department of Chemistry, Utrecht
University, Padualaan 8, 3584 CH, Utrecht, The Netherlands. E-mail: d.vogt@tue.nl;
Fax: ++31 (0)40 2455054; Tel: ++31 (0)40 2472483
Received 23rd September 2004, Accepted 26th November 2004
First published as an Advance Article on the web 4th January 2005
Chiral aminophosphines Ph2PN(R)(CH2)nN(R)PPh2 1–4 [n = 2, R = CH(CH3)(Ph) 1; n = 3, R = CH(CH2CH3)(Ph)
2, n = 2, R = CH(CH3)(1-naphthyl) 3; n = 2, R = CH(CH3)(C6H11) 4] were synthesized by the reaction of ClPPh2
with the appropriate easily accessible enantiopure amine building blocks. For compounds 1 and 2, the corresponding
selenides 5 and 6 were prepared to determine the electronic character of the phosphine moieties. By reaction of 1 with
either PdCl2(cod) or PdCl(CH3)(cod) the cis-complexes 7 and 8 were obtained. The molecular structure for complex
7, cis-[PdCl2(1)], was determined by X-ray crystallography. Reaction of PtCl2(cod) with 1 or 2 yielded the
corresponding monomeric cis-isomers 9 and 10. The rhodium derivative [RhCl(CO)(1)] (11) was obtained as a
mixture of cis and trans-isomers. Preliminary results in the rhodium catalyzed hydroformylation of styrene and vinyl
acetate, with ee’s up to 51% and high regioselectivities, showed the potential of these chiral aminophosphines for
homogeneous catalysis.
Introduction
The coordination chemistry of diphosphine ligands with a
variety of transition metals is widely studied and several types of
coordination modes have been established over the years.1 Nu-
merous families of novel (chiral) ligands have been synthesized,2
with emphasis on cis-chelating properties to form monomeric
metal complexes. Besides ligand design based on desired be-
haviour towards transition metal complexes and the catalytic
activity of such systems, the approach of modular design and
availability of cheap resources has gained significant importance.
We have previously shown the transformation of the bulk
chemical Bisphenol A into diphosphine ligands, suited for
complexation with transition metals.3 Especially in asymmetric
catalysis such a modular approach is highly desirable, since full
understanding of the factors governing the enantioselectivity
during the catalytic cycle is often lacking and the availability
of tunable ligand families would greatly enhance the generation
Fig. 1 Representation of ligand systems based on substituted het-
of data leading to new insight. We have therefore set out to
explore new and hitherto neglected chiral auxiliaries such as
chiral amines as functional groups.
eroatoms: piperazine (A) and 1,2-diaminobenzene (B), developed by
the group of Woollins4 and the SEMI-ESPHOS (C) and ESPHOS
compounds (D) reported by Wills et al.11
The synthesis and limited use of heteroatom substituted
phosphines (Fig. 1) and their transition metal complexes has
received quite some attention again lately,4–6 due to the search
for new structural diversity and catalytic activities. However,
little has appeared on the use of chiral amines as backbone
structures for phosphorus ligands, although some reports de-
scribed their application in the asymmetric hydrogenation of
various substrates.7–10 Wills et al. have described the synthesis
and application of the so-called ESPHOS ligand system (Fig. 1)
in the rhodium catalyzed asymmetric hydroformylation of
vinyl acetate, with high enantioselectivities.11 Chiral amines are
widely available nowadays due to heavy industrial investments
in commercially viable synthetic intermediates and specialty
chemicals. We were therefore interested to investigate their
applicability for the synthesis of novel aminophosphine ligands.
Here we report on the synthesis of the chiral bidentate
aminophosphine ligands 1–4 (Fig. 2) together with a study
of their coordination chemistry towards the transition metals
palladium, platinum and rhodium and preliminary results in
rhodium catalyzed asymmetric hydroformylation.
Fig.
2
Bis(aminophosphine) ligands; Np
cyclohexyl.
=
1-naphthyl; Cy
=
Results and discussion
Preparation of diphosphines 1–4
Compounds 1–3 were made in a two-step procedure starting
from the primary amine and a dihaloalkane (Scheme 1). The first
step involved nucleophilic SN2 substitution on the dihaloalkane
to form two secondary amines. By reaction with ClPPh2 in
the presence of NEt3, the corresponding diphosphines were
obtained in good overall yields. Compounds 1–3 were fully
5 1 2
D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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Scheme 2 Preparation of Pd and Pt complexes 7–10.
Scheme 1 Generic synthetic route, illustrative for compounds 1–3.
is analogous to the well studied ligand dppb, for which only the
cis-isomer is reported.16
To further elucidate the structure of complex 7, ligand 1 was
reacted with [PdCl(CH3)(cod)] (Scheme 2) to give complex 8 as a
micro-crystalline yellow solid. Characterization of this species in
solution by 31P NMR spectroscopy showed an AB system with
characterized by 1H, 13C and 31P NMR spectroscopy, as well as
by elemental analysis, see the Experimental section for details.
For compound 4 an alternative synthetic methodology was
devised, to avoid tedious destillation of unreacted amine starting
material during purification of the desired product. Condensa-
tion of glyoxal with two equivalents of the appropriate chiral
amine gave the corresponding diimine in high yield. Reduction
of the imine with LiAlH4 and subsequent reaction of the amino-
functionalities with ClPPh2 in the presence of NEt3 gave the
aminophosphine 4 in good yield. Washing with acetonitrile
afforded the pure compound without the need for further purifi-
cation. Also this new compound was fully characterized by 1H,
13C and 31P NMR spectroscopy, as well as by elemental analysis.
The 31P NMR spectra of all compounds 1–4 showed one
singlet with a chemical shift of around d 50 ppm, significantly
downfield from a triarylphosphine such as PPh3. In the 1H
NMR spectra a distinctive pattern, including P–H coupling,
was present for the chiral carbon moiety adjacent to the
nitrogen atoms. In the 13C NMR spectra through-space P–
C coupling was observed. In short, the geometry around the
nitrogen atoms was trigonal planar, implying that the nitrogen
atoms are sp2 hybridized, which indicates a significant degree
of P–N p-bonding.5 This is currently being further investigated
by theoretical calculations, combined with experimental data,
including the molecular structure of 4.12
two doublets at d 91.3 and 81.0 ppm with coupling constants
1
JP of 28 Hz, while in the H NMR spectrum a doublet of
–P
doublets was present at d 0.47 ppm for the methyl ligand at
palladium. Both observations clearly indicate the sole formation
of cis-[PdCl(CH3)(1)],17 with the downfield doublet at d 91.3 ppm
corresponding to the phosphine trans to chloride and the upfield
doublet at d 81.0 ppm to the phosphine trans to the methyl
ligand. Furthermore, in the 1H NMR spectrum two triplets at d
4.26 and 4.41 ppm were found for the inequivalent CH2-groups
in the backbone. Both complexes 7 and 8 were surprisingly very
soluble in acetonitrile, but we could obtain single crystals by
slow diffusion of hexane into a CH2Cl2 solution of complex 7.
The molecular structure of this compound was unequivocally
determined by X-ray crystallography. Fig. 3 shows the structure
of 7 together with data on selected bond lengths and angles.
The asymmetric unit cell contained two independent molecules
that differed mainly in the orientation of the phenyl rings on
A simple and efficient method to evaluate the r-donor
character and hence the basicity of a phosphine moiety is to
measure the magnitude of the coupling constant 1JSe P in the 31
P
–
NMR spectrum of the 77Se isotopomer of the corresponding
diphenylphosphine selenide.13,14 An increase in the coupling
constant is indicative of increasing s-character of the phosphorus
lone-pair and hence of lower basicity. Compounds 1 and 2 were
reacted with elemental selenium for 30 min in toluene at 70 ◦C. In
the 31P NMR spectrum of the corresponding selenides 5 and 6
in CH2Cl2, a singlet was found at d 70.3 ppm and 69.1 ppm,
respectively. Both signals were flanked by two 77Se-satellites,
and the coupling constants JSe were 752 Hz and 750 Hz,
–P
respectively, showing that both ligands are essentially identical
in their electronic character of the phosphorus moieties. These
values are in agreement with the few available literature data
4a,5
on aminophosphines.
The JSe values are higher than for
–P
corresponding diarylphosphines, which implies lower basicity
of the phosphine moiety, due to higher electronegativity of the
adjacent nitrogen atom.15
The coordination behaviour of these chiral amine-based
diphosphine ligands was studied with the representative ligand
1 towards palladium, platinum and rhodium precursors.
Fig. 3 ORTEP representation of the first of two independent molecules
of complex 7, cis-[PdCl2(1)]. Displacement ellipsoids are drawn at 50%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
◦
˚
lengths (A) and angles ( ): Pd1–P1 2.2681(6), Pd1–P2 2.2549(5), Pd1–Cl1
2.3507(5), Pd1–Cl2 2.3489(6), N1–P1 1.6811(18), N2–P2 1.6591(19),
N1–C1 1.460(3), N2–C2 1.470(3), N1–C3 1.499(3), N2–C4 1.504(3),
C1–C2 1.506(3), N1–N2 3.089(2), P1–P2 3.3808(8); P1–Pd1–P2 96.74(2),
Cl1–Pd1–Cl2 90.19(2), P1–Pd1–Cl1 83.36(2), P1–Pd1–Cl2 173.41(2),
P2–Pd1–Cl1 173.66(2), Pd1–P1–N1 120.84(7), Pd1–P2–N2 115.31(6),
P1–N1–C1 116.56(14), P2–N2–C2 119.39(14), P1–N1–C3 125.83(14),
P2–N2–C4 123.21(14), C1–N1–C3 113.91(17), C2–N2–C4 116.04(17),
C1–C2–N2 113.90(18), C2–C1–N1 115.35(18).
Preparation of palladium(II) complexes 7 and 8
Reaction of [PdCl2(cod)] with 1 for 2 h at room temperature
resulted in a yellow solid compound, complex (7) (Scheme 2),
for which the 31P NMR spectrum showed a singlet at d 87.3 ppm.
Little structural information can be deduced from this chemical
shift however. The ligand backbone skeleton (viz. size, flexibility)
D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7
5 1 3

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the phosphorus atoms. For clarity only one residue molecule is
shown.
mCO 1968 cm−1, which is in the range found for complexes with
r-donor ligands at the Rh center.24–27
The geometry around the palladium atom in complex 7,
cis-[PdCl2(1)], is slightly distorted square planar, with the
aminophosphine moieties coordinated in a mutual cis-fashion,
in agreement with the spectroscopic data. The distortion is
evident from the bite angle P1–Pd1–P2 of 96.74(2)◦, which led to
P1–Pd1–Cl1 and P1–Pd1–Cl2 angles of 83.36(2)◦ and 173.41(2)◦,
respectively. The Flack parameter refined to 0.01(9) for the
absolute structure shown in Fig. 3, consistent with the (S) con-
figuration of the amine starting material. The seven-membered
chelate ring has a boat or open-envelope conformation. Values
found for the Pd–P, Pd–Cl and P–N bond lengths were within
the ranges reported for similar aminophosphine complexes.4,18–20
Asymmetric hydroformylation of styrene and vinyl acetate
In order to evaluate the catalytic properties of chiral aminophos-
phines and encouraged by reports on their usefulness in rhodium
catalyzed asymmetric hydrogenation of alkenes,7–10 we chose
to apply these ligands in the rhodium-catalyzed asymmetric
hydroformylation of styrene and vinyl acetate (Scheme 3).
Rh(acac)(CO)2 was used as a standard rhodium precursor and
before introduction of the substrate, the catalytic system was
activated for 1 h with 20 bar syngas at 60 ◦C to generate
the catalytic resting state Rh(H)(CO)2(PˆP). Standard reaction
conditions for the catalytic runs were a temperature of 60 ◦C and
20 bar of syngas (CO : H2 = 1 : 1), with a reaction time of 15 h
in case of styrene. The substrate to rhodium ratio and ligand to
rhodium ratio were 1500 and 2 : 1, respectively. For vinyl acetate
20 h reaction time and a substrate to rhodium ratio of 1250 : 1
were used.
˚
The two P–N bond lengths were 1.6591(19) A for P2–N2 and
˚
1.6811(18) A for P1–N1. The ethane backbone is severely twisted
with a torsion angle N1–C1–C2–N2 of −66.1(2)◦. Notably, the
geometry around the nitrogen atoms N1 and N2 is trigonal
planar, with bond angles of between 116.04(17) and 125.83(14)◦,
˚
and N1 and N2 displaced by 0.1722(17) and 0.1041(18) A
respectively from the C–C–P mean planes. This is again a
clear indication of considerable double-bond character (via a
p-interaction) between the P and N atoms. The intramolecular
˚
P1–P2 distance was 3.3808(8) A while the N1–N2 distance was
˚
3.089(2) A.
Preparation of dichloroplatinum(II) complexes 9 and 10
Reaction of [PtCl2(cod)] with ligand 1 yielded the straight-
forward formation of a white solid compound, complex 9
(Scheme 2). Characterization of the species present in solu-
tion by 31P NMR spectroscopy showed a single peak at d
62.1 ppm, flanked by 195Pt satellites and a coupling constant
JPt of 4151 Hz. This latter value is a clear indication of
–P
Scheme 3 General reaction-scheme for the Rh-catalyzed hydroformy-
cis-coordination of the diphosphine to the platinum center,
yielding cis-[PtCl2(1)].21 The chemical shift is remarkably high
for a diphosphine-based cis-platinum complex and reflects the
electronic influence of the amino-groups. It is virtually similar to
a silsesquioxane-based diphosphinite Pt-complex developed pre-
viously in our group.22 When the same reaction was performed
with ligand 2 an off-white solid was obtained, complex 10, for
which the 31P NMR spectrum a singlet at 60.5 ppm, together
with 195Pt satellites and a coupling constant JPt of 4285 Hz,
lation of styrene (top) and vinyl acetate (bottom).
In the hydroformylation of styrene the chemoselectivity to
aldehyde products was typically >99%, with regioselectivities
(b/l ratio) of up to 12 for ligand 3. Turnover frequencies of up
to 78 h−1 were obtained, which is comparable to activities found
for benchmark systems. The enantioselectivity was low with a
maximum of only 12% with ligand 4. Since it is known that the
outcome of the hydroformylation with a given catalytic system
can be highly dependent on the substrate,11,28 we were interested
to see if the asymmetric hydroformylation of vinyl acetate would
render different results. The substrate vinyl acetate differs from
styrene in two important aspects, viz. (a) vinyl acetate cannot
–P
suggesting formation of cis-[PtCl2(2)].
Preparation of chlorocarbonylrhodium(I) complex 11
3
Grimblot et al. have previously reported X-ray photoelectron
and IR spectroscopy studies on RhCl(CO)-complexes with
various phosphine ligands, including aminophosphines, and
their correlation with the results obtained in rhodium catalyzed
hydroformylation of 1-hexene.23 Their initial studies on the
influence of the (amino)phosphine ligand on the CO stretching
frequency in the corresponding Rh-complex led to the conclu-
sion that all tested ligands led to trans-complexes except for
dppe.
form g -complexes and (b) the carbonyl oxygen can participate
in bonding to the metal.
With ligand 3 we were able to reach an enantiomeric excess
of 34% at 60 ◦C, which is significantly higher than the best
result obtained for styrene. The regioselectivity was extremely
high with a b/l ratio exceeding 17. Even more encouragingly,
the enantiomeric excess increased to 51% upon decreasing
the reaction temperature to 40 ◦C. Although these results
do not outperform other chiral diphosphine ligands, further
improvements should be feasible by adjustment of the various
tunable fragments in our aminophosphine scaffold. Research is
ongoing to determine optimal ligand design.
Upon addition of ligand
1 to a CH2Cl2-solution of
[RhCl(CO)2]2, the solution immediately turned yellow. After 2 h
of reaction at room temperature, removal of volatiles left a clear
yellow microcrystalline solid, complex 11.
The 31P NMR spectrum for this complex showed a mixture
of the cis- and trans-isomers in a ratio of 34:66 in favour of the
trans-isomer. This latter species was characterized by a doublet
Conclusions
We have shown the successful synthesis of aminophosphine
compounds 1–4, based on chiral primary amines as well as
the selenide derivatives 5 and 6. The coordination behaviour of
ligand 1 and ligand 2 towards Pd, Pt and Rh is described. The lig-
ands show clear tendencies to coordinate in a cis-fashion to these
transition metals, as indicated by 31P NMR spectroscopy. For the
complex cis-[PdCl2(1)] the molecular structure is determined,
showing a relatively small bite angle of 96.74◦ for ligand 1.
at d 81.0 ppm, and a coupling constant of JRh P 133 Hz, which is
–
a typical value for diphenylphosphine ligands. The cis-complex
appeared as a set of two doublets of doublets at d 99.6 ppm and d
75.3 ppm. The respective coupling constants JRh were 180 Hz
–P
for the P trans to the Cl ligand and 133 Hz for the P trans to
the CO ligand, while the JP was 33 Hz. The related FT-IR-
–
P
spectrum showed an absorption band in the carbonyl region at
5 1 4
D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7

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3
We have demonstrated the successful application of these chiral
aminophosphine ligands in the asymmetric hydroformylation
of both styrene and vinyl acetate, with enantioselectivities of
up to 51%. We are currently expanding on the theme of chiral
amine-based phosphorus ligands, together with a theoretical
study aimed at underpinning the electronic character of these
ligands.
4H, CHCH2CH3), 0.81 (t, 6H, CHCH2CH3, JH = 7.7 Hz),
–H
0.72 (m, 2H, CH2CH2CH2).
13C NMR (CDCl3) d 143.4 (s, Ph), 140.1, 139.9 (2d, Ph, 1JP
=
–
C
67 Hz), 132.6, 131.5 (2d, Ph, 2JP C = 21 Hz), 128.3, 128.0, 128.0,
–
127.7, 127.6, 127.5, 126.8 (7s, Ph), 66.3 (d, CHCH2CH3, 2JP
=
–C
26 Hz), 47.2 (d, CH2N, 2JP C = 11 Hz), 28.5 (CHCH2CH3), 28.2
–
(CH2CH2CH2), 11.8 (CHCH2CH3).
31P NMR (CDCl3) d 45.8.
Anal. Calc. for C45H48N2P2: C, 79.62; H, 7.13; N, 4.13. Found:
C, 79.30; H, 7.09; N, 4.03%.
Experimental
General
N,Nꢀ-Bis[S(−)-(1-(1-naphthyl)ethyl)]-N,Nꢀ-bis(diphenylphos-
phino)-ethane-1,2-diamine (3). N,Nꢀ-Bis[S(−)-(1-(1-naphthyl)-
ethyl)]ethane-1,2-diamine was prepared following the procedure
for 1, starting from S(−)-(1-(1-naphthyl))ethylamine (15.1 g,
88 mmol) and 1,2-dibromoethane (8.3 g, 44 mmol). After
removal of the access of amine the diamine was obtained in 95%
yield as a brownish syrup (15.47 g, 42 mmol) which solidified
upon standing.
All manipulations were carried out under argon using standard
Schlenk techniques. Chemicals were purchased from VWR,
Acros, Lancaster or Aldrich and solvents were either taken
HPLC-grade from an argon-flushed column, packed with
aluminium oxide, or distilled under argon prior to use over
an appropriate drying agent. NMR spectra were recorded at
room temperature on a Varian Mercury 400 MHz spectrometer.
Chemical shifts are given in ppm and spectra are referenced to
1H NMR (CDCl3) d 8.15 (m, 2H, Ph), 7.84 (m, 2H, Ph), 7.78
(d, 2H, 3JH H = 8.1 Hz), 7.67 (d, 2H, Ph, 3JH H = 7.5 Hz), 7.45–
CDCl3 (1H, 13C{ H}) or 85% H3PO4 (31P{ H}). FT-IR spectra
were taken on an AVATAR E.S.P. 360 FTIR spectrometer.
PdCl2(cod),29 PdCl(CH3)(cod)30 and PtCl2(cod)31 were prepared
according to literature procedures.
1
1
–
–
–
3
7.55 (m, 8H, Ph), 4.53 (q, 2H, CHCH3, JH = 6.6 Hz), 2.68
H
(s, 4H, CH2CH2), 2.02 (br s, 2H, NH), 1.53 (d, 6H, CHCH3,
3JH = 6.6 Hz).
–H
13C NMR (CDCl3) d 141.5, 134.0, 131.6, 129.2, 127.4,
126.0, 125.9, 125.6, 124.0, 123.2 (10s, Ph), 53.9 (CHCH3), 47.7
(CH2NH), 24.0 (CHCH3).
Syntheses
N,Nꢀ-Bis[S(−)-a-methylbenzyl]-N,Nꢀ-bis(diphenylphosphino)-
Following the (modified) procedure for 1, starting
from N,Nꢀ-bis[S(−)-(1-(1-naphthyl)ethyl)]ethane-1,2-diamine
(1.95 g, 5.3 mmol) in 20 mL toluene, chlorodiphenylphosphine
(2.38 g, 10.8 mmol) and 2 mL triethylamine (1.45 g, 14.3 mmol)
in 30 mL toluene and a reaction overnight at 80 ◦C, 3 was
obtained as a white powder (2.33 g, 3.2 mmol) in 60% yield.
1H NMR (CDCl3) d 7.85 (m, 4H, Ph), 7.65 (m, 2H, Ph), 7.47
(m, 2H, Ph), 7.36 (m, 2H, Ph), 7.08–7.30 (m, 20 H, Ph), 6.96 (m,
ethane-1,2-diamine (1). N,Nꢀ-Bis[S(−)-a-methylbenzyl]ethane-
1,2-diamine was prepared by following
a procedure by
Mimoun et al.32 To a flask containing 4 equivalents of S(−)-a-
methylbenzylamine (46.7 g, 385 mmol) at 130 ◦C was added
dropwise 1,2-dibromoethane (17.0 g, 91 mmol). After 1 h at
elevated temperature the mixture was cooled to 80 ◦C and a 4 M
aqueous solution of KOH (28.4 g, 506 mmol) was added. After
extraction of the mixture with ethyl acetate and concentration,
the mixture was fractionally distilled at◦2.5 mbar, the diamine
(18.3 g, 68 mmol) was obtained at 155 C as a colorless oil in
75% yield. Spectral properties were similar as described before.
Compound 1 was prepared by adding the diamine (2.51 g,
9.45 mmol) dropwise to a mixture of triethylamine (2.5 g,
25 mmol) and chlorodiphenylphosphine (4.22 g, 19.1 mmol)
in diethyl ether. The produced ammonium salts are removed
from the suspension by filtration and the mixture concentrated,
forming a white solid. After stripping with hexanes and recrys-
tallization from hot acetonitrile the analytically pure compound
1 (4.21 g, 6.61 mmol) was obtained as a white semi-crystalline
solid in 70% yield. Spectral properties were similar as described
before.
3
3
4H, Ph), 4.72 (dq, 2H, CHCH3, JP = 13 Hz; J = 6.6 Hz),
–
H
2.69 (s, 4H, CH2CH2), 1.42 (d, 6H, CHCH3, 3J = 6.6 Hz).
13C NMR (CDCl3) d 140.4 (s, Ph), 140.4, 139.6 (2d, Ph, 1JP
=
–C
85 Hz), 134.1, 132.4 (2s, Ph), 132.4 (d, Ph, 2JP C = 40 Hz), 131.6,
–
128.9, 128.4 (3s, Ph), 128.1, 128.0 (2d, Ph, 3JP C = 6 Hz), 127.8,
–
–
125.8, 125.5, 125.3, 124.6, 56.6 (d, CHCH3, 2JP = 31 Hz), 49.9
(d, CH2N,2JP = 9 Hz), 21.0 (d, CHCH3, 3JP C = 10 Hz).
–
C
–C
31P NMR (CDCl3) d 55.9.
N, Nꢀ -Bis[S(−)-(1-cyclohexylethyl)]-N,Nꢀ -bis(diphenylphos-
phino)ethane-1,2-diamine (4). Following a procedure of Weber
33
et al.
a solution of S(−)-(1-cyclohexyl)ethylamine (12.1 g,
95 mmol) in 50 mL hexanes was added to a 40 wt% aqueous
solution of glyoxal (47 mmol). After 30 min of reaction the
phases were separated and the water layer was extracted with
hexanes. After drying over MgSO4, concentration in vacuo
afforded the corresponding diimine as a white powder (12.3 g,
44 mmol, 95%) with similar spectral properties as described in
literature and which was used without any purification.
To a solution of the diimine (1.79 g, 6.5 mmol) in 25 mL
diethyl ether was added in portions LiAlH4 (1.05 g, 27.7 mmol).
After one hour the excess of LiAlH4 was neutralized by
carefully adding water. After drying over MgSO4, extraction
with diethyl ether and concentration the corresponding diamine
was obtained in quantitative yield as a colorless mobile oil
(1.82 g, 6.5 mmol).
N,Nꢀ -Bis[R(−)-a-ethylbenzyl]-N,Nꢀ -bis(diphenylphosphino)-
propane-1,3-diamine (2). The procedure described for 1 was
followed, starting from R(−)-a-ethylbenzylamine (49.07 g,
363 mmol) and 1,3-dibromopropane (17.35 g, 86 mmol).
◦
Distillation at 1.5 mbar at 165 C afforded N,Nꢀ-bis[R(−)-a-
ethylbenzyl]propane-1,3-diamine (16.33 g, 53 mmol) in 61%
yield.
1H NMR (CDCl3) d 7.2–7.4 (10H, Ph), 3.43 (t, 2H,
3
CHCH2CH3, JH = 6.2 Hz), 2.49 (m, 4H, CH2NH), 1.55–
–
H
1.80 (m, 8H, CH2CH2CH2; CHCH2CH3; NH), 0.79 (t, 6H,
CHCH2CH3, 3JH = 7.3 Hz).
–
H
13C NMR (CDCl3) d 144.4, 128.5, 127.5, 127.1 (4s, Ph),
65.5 (CHCH2CH3), 46.8 (CH2NH), 31.2 (CHCH2CH3), 30.4
(CH2CH2NH), 11.1 (CHCH2CH3).
1H NMR (CDCl3) d 2.83 (dq, 2H, CHCH3, 3J = 5.4 Hz), 2.64
(m, 2H, CH2NH), 2.46 (m, 2H, CH2NH), 2.04 (br s, 2H, NH),
1.73 (m, 10H, Cy), 1.20 (m, 12H, Cy), 1.06 (d, 6H, CHCH3, 3J =
5.4 Hz).
Starting from N,Nꢀ-bis[R(−)-a-ethylbenzyl]propane-1,3-
diamine (2.64 g, 8.5 mmol), chlorodiphenylphosphine (3.83 g,
17.4 mmol) and triethylamine (2.4 g, 24 mmol), compound 2
(5.14 g, 7.57 mmol) was obtained as a white solid in 89% yield.
1H NMR (CDCl3) d 7.40–7.34 (m, 10H, Ph), 7.28–7.14 (m,
16H, Ph), 6.91–6.85 (m, 4H, Ph), 3.43 (dt, 2H, CHCH2CH3,
3JP H = 16.1 Hz,3JH H = 6.2 Hz), 2.40 (m, 4H, CH2N), 2.20 (m,
13C NMR (CDCl3) d 58.0 (CHCH3), 47.1 (CH2NH), 42.8,
29.9, 28.2, 26.8, 26.6, 26.5 (6s, Cy), 16.9 (CHCH3).
Following the procedure described for 1 starting from
N,Nꢀ-bis[S(−)-(1-cyclohexylethyl)]ethane-1,2-diamine (1.03 g,
3.67 mmol), chlorodiphenylphosphine (1.65 g, 7.48 mmol)
and triethylamine (1.5 mL, 10.7 mmol) the analytically pure
–
–
D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7
5 1 5

View Article Online
compound (4) (1.98 g, 3.05 mmol) was obtained as a white semi-
crystalline solid in 83% yield.
cis-[PtCl2(1)] (complex 9). PtCl2(cod) (36.3 mg, 97.0 lmol)
and 1 (66.3 mg, 104.1 lmol) were dissolved in 5 mL CH2Cl2 and
stirred for 2 h at r.t. Then the solvent was removed in vacuo. After
that the remaining traces of solvent were removed by stripping
2 times with 5 mL hexanes to leave complex 9 as a white powder.
Yield: 92% (80.6 mg, 89.3 lmol).
1H NMR (CDCl3) d 7.12–7.22 (10H, PPh2), 2.64 (dm, 4H,
3
CH2N, JP = 36.2 Hz), 2.23 (m, 2H, CHCH3), 1.89 (m, 2H,
–H
Cy), 1.68 (m, 8H, Cy), 1.50 (m, 2H, Cy), 1.17 (m, 6H, Cy), 1.06
(d, 6H, CHCH3, 3J = 6.3 Hz), 0.75 (m, 4H, Cy).
13C NMR (CDCl3) d 140.7, 140.5 (2d, Ph, JP = 48 Hz),
1H NMR (CDCl3) d 7.99 (dd, 4H, J1 = 8.0 Hz), 7.73 (dd,
4H, J1 = 8.0 Hz), 7.49 (m, 4H), 7.40 (s, 6H), 7.42 (t, 8H, J1 =
6.8 Hz), 7.32 (t, 6H, J1 = 6.8 Hz), 6.90 (dd, 4H, J1 = 7.6 Hz,
J2 = 1.2 Hz), 4.29 (t, 2H, CH, J1 = 7.2 Hz), 3.60 (dt, 4H, CH2,
J1 = 14.4 Hz, J2 = 2.8 Hz), 3.01 (t, 4H, CH2, J1 = 13.6 Hz), 0.80
(d, 6H, CH3, J1 = 6.8 Hz).
1
–C
2
4
132.4, 132.0 (2d, Ph, JP = 21 Hz), 128.0 (d, Ph, JP
=
=
–
C
C
–
–
C
3
2
4 Hz), 127.9 (d, Ph, JP = 6 Hz), 61.8 (d, CHCH3, JP
–
C
26 Hz), 49.3 (d, CH2N,2JP = 26 Hz), 42.8 (d, CHCHCH3,
–
C
3JP = 10 Hz), 31.2, 30.0, 26.4, 26.2, 26.0 (5s, Cy), 19.2 (d,
–C
CHCH3, 3JP = 11 Hz).
–C
31P NMR (CDCl3) d 46.0.
31P NMR (CDCl3) d 62.1 (s, JPt = 4151 Hz).
–
P
Anal. Calc. for C42H54N2P2: C, 77.75; H, 8.39; N, 4.32. Found:
C, 77.53; H, 8.53; N, 4.24%.
cis-PtCl2(2) (complex 10). Following the same procedure as
for complex 9, but using ligand 2 (75.0 mg, 110.5 lmol) and
PtCl2(cod) (35.3 mg, 94.3 lmol) complex 10 was obtained in a
yield of 95% (84.7 mg, 89.6 lmol).
N,Nꢀ-Bis[S(−)-a-methylbenzyl]-N,Nꢀ-bis(diphenylphosphino)-
ethane-1,2-diamine selenide (5). 1 (85.9 mg, 134.9 lmol) was
dissolved in 5 mL toluene and excess black selenium was added.
The reaction mixture was stirred for 30 min at 70 ◦C. Filtration
to remove unreacted selenium by cannula was followed by
evaporation of the filtrate to dryness, leaving 5 as a white solid.
Yield: 95% (101.8 mg, 128.2 lmol).
1H NMR (CDCl3) d 8.24 (dd, 4H, J1 = 4.4 Hz, J2 = 6.8 Hz),
7.96 (dd, 4H, J1 = 4.4 Hz, J2 = 6.8 Hz), 7.51 (t, 14H, J1
=
7.2 Hz), 7.26 (t, 4H, J1 = 2.4 Hz), 6.99 (t, 4H, J1 = 3.6 Hz),
3.83 (t, 2H, NCH, J1 = 8.4 Hz), 3.00 (m, NCH2), 2.67 (m, 2H,
NCH2), 1.76 (m, 2H, CH2CH2CH2), 1.35 (m, 4H, CH2CH3),
0.30 (t, 6H, CH3, J1 = 7.6 Hz).
31P NMR (CDCl3) d 70.3 (s, JSe = 752 Hz).
–P
31P NMR (CDCl3) d 60.5 (s, JPt = 4285 Hz).
Anal. Calc. for C42H42N2P2Se2: C, 63.48; H, 5.33; P, 3.53.
Found: C, 63.55; H, 5.41; P, 3.58%.
–
P
[Rh(Cl)(CO)(1)] (complex 11). [Rh(l-Cl)(CO)2]2 (56.9 mg,
146.3 lmol) and 1 (186.4 mg, 292.7 lmol) were stirred in 10 mL
of CH2Cl2 for 16 h, giving a light yellow solution. After removal
of the solvent in vacuo, 11 was obtained as a bright-yellow
microcrystalline solid.
N,Nꢀ-Bis[R(−)-a-ethylbenzyl]-N,Nꢀ-bis(diphenylphosphino)-
propane-1,3-diamine selenide (6). Following the same pro-
cedure as for compound 4, ligand 2 (92.1 mg, 135.7 lmol) was
converted to selenide 6 in a yield of 98% (111.3 mg, 133.0 lmol).
31P NMR (CDCl3) d 69.1 (s, JSe = 750 Hz).
31P NMR (CDCl3) d 99.6 (dd, cis, P trans to Cl, JRh
=
–
P
–
P
Anal. Calc. for C45H48N2P2Se2: C, 64.59; H, 5.78; P, 3.35.
Found: C, 64.74; H, 5.82; P, 3.38%.
180 Hz, JP P = 33 Hz), 81.0 (d, trans, JRh P = 133 Hz), 75.3 (dd,
–
–
cis, P trans to CO, JRh = 133 Hz, JP = 33 Hz).
–P
–P
FTIR (ATR mode, solid, cm−1): m 1967.5 (Rh(CO)).
Anal. Calc. for C43H42ClN2OP2Rh: C, 64.31; H, 5.27; P, 3.49.
Found: C, 64.13; H, 5.37; P, 3.55%.
cis-[PdCl2(1)] (complex 7). PdCl2(cod) (32.9 mg, 115.2 lmol)
and 1 (73.4 mg, 115.3 lmol) were dissolved in 5 mL CH2Cl2
and stirred for 12 h at r.t. Solvents were then evaporated in
vacuo. After that the remaining traces of solvent were removed
by stripping twice with 5 mL CH2Cl2 to leave complex 7 as a pure
yellow solid. Yield: 96% (90.1 mg, 110.6 lmol). Layering with
CH2Cl2/CH3CN under slight argon flow gave yellow rectangular
single crystals, suitable for X-ray analysis.
Crystal structure determination of 7
Intensity data for the complex 7 were collected using graphite-
monochromated Mo-Ka radiation, on a Nonius KappaCCD
diffractometer. A semi-empirical absorption correction based
1H NMR (CDCl3) d 7.99 (dd, 2H, ArH, J1 = 4.0 Hz, J2 =
11.2 Hz), 7.70 (dd, 2H, ArH, J1 = 4.0 Hz, J2 = 11.2 Hz), 7.55
(t, 1H, ArH, J1 = 6.8 Hz), 7.49 (d, 1H, ArH, J1 = 5.6 Hz), 7.41
(t, 6H, ArH, J1 = 7.2 Hz), 7.30 (d, 6H, ArH, J1 = 7.6 Hz), 6.99
(t, 4H, ArH, J1 = 7.2 Hz), 6.90 (dd, 4H, ArH, J1 = 7.6 Hz, J1 =
1.2 Hz), 4.27 (m, 2H, CH), 3.59 (dd, 2H, CH2, J1 = 6.8 Hz, J2 =
11.2 Hz), 3.05 (dd, 2H, CH2, J1 = 4.0 Hz, J2 = 11.2 Hz), 0.82
(d, 6H, CH3, J1 = 6.8 Hz).
34a
on multiple measurements was applied using SADABS. The
structure was solved by automated Patterson methods using
2
34b
34c
DIRDIF, and refined on F using SHELXL97. One of the
six phenyl rings in the structure is disordered over two confor-
mations and was refined with a disorder model. All hydrogen
atoms were constrained to idealized geometries and allowed
to ride on their carrier atoms with an isotropic displacement
parameter related to the equivalent displacement parameter of
their carrier atoms. The Flack parameter refined to −0.01(9) for
the absolute structure shown in Fig. 3. Structure validation and
molecular graphics preparation were performed with the PLA-
TON package.35 Formula C42H42Cl2N2P2Pd; molecular weight
814.02 g mol−1; monoclinic; space group P21 (no. 4); unit cell
dimensions: a = 11.3330(10), b = 26.0777(10), c = 12.6339(10)
31P NMR (CDCl3) d 87.3 (s).
Anal. Calc. for C42H42Cl2N2P2Pd: C, 61.97; H, 5.20; N, 3.44.
Found: C, 62.03; H, 5.24; N, 3.48%.
cis-[PdCl(CH3)(1)] (complex 8). Following the same pro-
cedure as for complex 7, but starting from PdCl(CH3)(cod)
(10.5 mg, 39.6 lmol) and 1 (27.2 mg, 42.7 lmol), complex
8 was obtained as a pure yellow solid. Yield: 94% (29.6 mg,
37.2 lmol).
◦
3
˚
˚
A, b = 92.7710(10) ; V = 3279.4(5) A ; T = 150 K; Z = 4; l(Mo-
Ka) = 0.760 mm−1; total reflections = 52367; unique reflections
(Rint) = 14632 (0.026); wR2 (F2) (all data) = 0.0444; R1 (F) =
0.0219.
1H NMR (CDCl3) d 7.87 (dt, 2H, ArH, J1 = 8.8 Hz, J2 =
1.6 Hz), 7.83 (m, 2H, ArH), 7.63 (ddd, 2H, ArH, J1 = 11.2 Hz,
J1 = 1.2 Hz), 7.54 (ddd, 2H, ArH, J1 = 11.2 Hz, J1 = 1.2 Hz),
7.45 (d, 5H, ArH, J1 = 2.0 Hz), 7.35 (d, 5H, ArH, J1 = 7.6 Hz),
7.7.32 (m, 2H, ArH), 7.28 (m, 2H, ArH), 7.22 (dd, 4H, ArH,
J1 = 9.2 Hz, J1 = 2.0 Hz), 7.16 (dd, 2H, ArH, J1 = 7.2 Hz, J1 =
2.8 Hz), 6.73 (dd, 2H, ArH, J1 = 8.0 Hz, J1 = 1.6 Hz), 4.41 (t,
2H, CH2), 4.26 (t, 2H, CH2), 3.35 (m, 2H, CH), 1.01 (d, 3H,
CH3, J1 = 7.6 Hz), 0.73 (d, 3H, CH3, J1 = 6.8 Hz), 0.47 (dd, 3H,
Pd(CH3), J1 = 7.6 Hz, J1 = 4.4 Hz).
CCDC reference number 250561.
See http://www.rsc.org/suppdata/dt/b4/b414668a/ for cry-
stallographic data in CIF or other electronic format.
Acknowledgements
This work was financially supported by Avantium Technologies
(E. Z.), the National Research School Combination for Catalysis
(NRSCC) (J. I. v. d. V.), and in part (D. M. T. and A. L. S.) by the
Netherlands Organisation for Scientific Research (NWO). We
31P NMR (CDCl3) d 91.3 (d, JP P = 28 Hz, P trans to Cl), 81.0
–
(d, JP = 28 Hz, P trans to CH3).
–
P
5 1 6
D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7

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thank Dr Marco Fioroni (Indiana University, Bloomington) for
scientific discussions. O. M. G. is acknowledged for a generous
loan of various transition metal complexes. BASF A.G. is
thanked for a kind gift of chiral amines.
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Soc., Dalton Trans., 2002, 2308.
18 A. D. Burrows, M. F. Mahon and M. T. Palmer, J. Chem. Soc., Dalton
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D a l t o n T r a n s . , 2 0 0 5 , 5 1 2 – 5 1 7
5 1 7