Synthesis and resolution of a new P-chiral hydroxy phosphine

Article abstract of DOI:10.1016/S0022-328X(00)00190-X

The synthesis of the functionalized P-chiral phosphine BzPhP{CH(OH)Ph}and its resolution by palladium metallacycles is reported. The cyclopalladated compound containing the primary amine 1-(1-naphthyl)ethylamine has been shown to be a better resolving agent for this phosphine than the corresponding metallacycle containing the tertiary amine N,N-dimethyl-1-(1-naphthyl)ethylamine

Full text of DOI:10.1016/S0022-328X(00)00190-X

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 603 (2000) 235–239
Synthesis and resolution of a new P-chiral hydroxy phosphine
Joan Albert, J. Magali Cadena, Sergio Delgado, Jaume Granell *
Departament de Qu´ımica Inorga`nica, Uni6ersitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain
Received 19 February 2000; received in revised form 13 March 2000
Abstract
The synthesis of the functionalized P-chiral phosphine BzPhP{CH(OH)Ph}and its resolution by palladium metallacycles is
reported. The cyclopalladated compound containing the primary amine 1-(1-naphthyl)ethylamine has been shown to be a better
resolving agent for this phosphine than the corresponding metallacycle containing the tertiary amine N,N-dimethyl-1-(1-naph-
thyl)ethylamine © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Hydroxyphosphines; P-chiral; Metallacycles; Resolution; Palladium
2. Discussion and results
1. Introduction
(9)-Benzylphenylphoshine [4] was synthesized by
reaction of dibenzylphenylphosphine and lithium metal
in tetrahydrofuran under a dry nitrogen atmosphere.
After 16 h of stirring at room temperature (r.t.) com-
plete cleavage of one of the CH2ꢀP bonds of the
starting phosphine was accomplished, with formation
of the phenylbenzylphosphide anion. The 31P-NMR
spectrum, under nitrogen, illustrated clearly the forma-
tion of this anion (l= −37.1 ppm) [5]. Subsequent
addition of H2O gave the secondary phosphine (9)-1
in THF solution (Scheme 1). The reaction between the
secondary phosphine PHBzPh and benzaldehyde af-
forded the functionalized phosphine BzPhP{CH-
(OH)Ph} (2), containing two stereogenic centers, the
phosphorus and one carbon atom, as a 1:1 mixture of
diastereomers.
The versatility of ortho-palladated derivatives of op-
tically active N-donor ligands as resolving agents for
Lewis bases has been demonstrated convincingly. Cy-
clopalladated derivatives of the tertiary amines N,N-
dimethyl-1-(1-naphthyl)ethylamine and N,N-dimethyl-
a-methylbenzylamine have been used widely for the
resolution of bidentate and monodentate ligands [6],
and recently the application of some new cyclometal-
lated compounds in this field have been explored [7].
The optically pure cyclopalladated dinuclear com-
pounds 3 were obtained from the optically active
Spectacular progress has been made in the field of
asymmetric catalysis by using homogeneous catalysts
based on transition metal complexes modified by chiral
ligands. Thus, chiral phosphines have become very
important in asymmetric catalysis [1]. Among the great
number of chiral phosphines developed for application
in asymmetric catalysis, examples of monodentate lig-
ands possessing a stereogenic phosphorus atom are
rare, even though metal complexes featuring marked
asymmetry near the catalytic center are considered to
be excellent optical inducers [2]. In addition, it has been
shown that active functional groups (such as hydroxy
or amino group) situated properly can enhance the
stereo-discriminating ability of a metal catalyst as a
consequence of attractive interactions (e.g. by hydrogen
bonding) of the functional group with suitable reagents
[3]. We describe here the synthesis of the functionalized
phosphine BzPhP{CH(OH)Ph} containing two stereo-
genic centers, the phosphorus and the hydroxy-substi-
tuted carbon atom, and its resolution by palladium
metallacycles, derived from 1-(1-naphthyl)ethylamines.
* Corresponding author. Fax: +34-934-907725.
E-mail address: jgranell@kripto.qui.ub.es (J. Granell)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00190-X

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J. Albert et al. / Journal of Organometallic Chemistry 603 (2000) 235–239
Scheme 1. (i) Li, THF, r.t., 16h. (ii) H2O, THF, r.t., 10 min: PhCHO, 30 min. (iii) CHCl3, r.t., 45 min, under nitrogen.
amines as reported [8]. Reaction of dimers 3 with the
phosphine afforded the mononuclear diastereomers [Pd-
Cl(CꢀN)(BzPhP{CH(OH)Ph})], compounds 4, as a mix-
ture 1:1:1:1 of diastereomers. All the new
organometallic compounds obtained were characterized
by elemental analysis, IR spectra, and 1H- and 31P-
NMR spectra. In some cases, 2D-NMR experiments
and positive FAB-mass spectra, were carried out to
complete the characterization. The high-field shift of the
aromatic protons of the palladated ring in 4, due to the
aromatic rings of the phosphine, indicates the cis dispo-
sition of the phosphorus relative to the metallated
carbon atom and the chemical shift of the phosphorus
confirms this arrangement [9]. This arrangement is usual
in cyclopalladated compounds containing phosphines
[10].
The efficiency of cyclopalladated compounds derived
from 1-(1-naphthyl)ethylamine as resolving agents has
been related to the locked asymmetric envelop confor-
mation of the metallacycle, due to the fact that the
methyl substituent of the chiral carbon atom adopts an
axial disposition to avoid the unfavorable interaction
with H6 (see Scheme 1). [11] The NOESY spectra of
compounds 4 showed that the methinic proton of the
chiral carbon atom H7 had strong negative off-diagonal
peaks with H6 and Hb and, in contrast, the methyl
protons of the chiral carbon atom presented only strong
NOE interaction with Ha and H7. These data confirmed
the axial disposition of this methyl group and the
equatorial disposition of H7 in this complexes [12].
The aromatic proton in ortho position in relation to
the metal atom is very high field shifted in 4a%%%% (l=5.79
ppm) and appears at higher fields compared to their
PPh3 analog (l=6.60 ppm). This fact shows that the
rotation around PdꢀP is rather restricted and that
rotamers with the nearly orthogonal orientation of two
aromatic rings of the phosphine with respect to the
metallated ring are predominant in this diastereomer.
Analogous results have been found for cyclopalladated
compounds containing monodentate phosphines such as
P(But)(C6H5)(4-BrC6H4) [7c].
The NOESY spectra of diastereomers 4b% and 4b%%%%
showed that only one of the signals of the CH2 protons
presented strong NOE interaction with the metallated
ring proton H1, suggesting a restricted rotation around
the CH2ꢀP bond.
The action of 1,2-bisdiphenylphosphinoethane (dppe)
on the optically pure cyclopalladated derivatives 4 led to
the free phosphine BzPhP{CH(OH)Ph}. No racemiza-
tion of the phosphine was observed and the displace-
ment proceeded with retention of the configuration at
phosphorus as verified by the quantitative regeneration
of the same starting material 4 (optically pure) from the
free ligand and the corresponding dinuclear cyclopalla-
dated derivative 3.
2.1. Resolution of the phosphine
The 1:1:1:1 mixture of 4a diastereomers (400 mg) was
eluted carefully in a SiO2 column with chloroform–ace-
tone (100:4) as eluent. The first and second
diastereomers 4a% and 4a%% were eluted as a mixture in
70% yield (140 mg). The third diastereomer separated
4a%%% was obtained in 30% yield (30 mg), with a d.e.
higher than 95%, and the last diastereomer eluted 4a%%%%
was not obtained in a pure form {the superscripts (%),
(%%), (%%%) and (%%%%) indicate the first, the second, the third
and the forth diastereomer eluted in the column, respec-
tively}. Nevertheless, better results were obtained with
4b. The 1:1:1:1 mixture of 4b diastereomers (400 mg)
was eluted carefully, in a SiO2 column with chloro-
form–acetone (100:3) as eluent. The first diastereomer
eluted 4b% was separated in 30% yield (30 mg), with a
d.e. higher than 95%. And the last, 4b%%%% was obtained in
60% yield (60 mg), with a d.e. higher than 95%. The
second and third diastereomers eluted 4b%% and 4b%%% were
obtained as a mixture in 40% yield (80 mg). Recrystal-
lization of this mixture of diastereomers from a satu-
rated solution of diethylether at 20°C afforded 4b%%% with
a d.e. higher than 95%.
In conclusion
a new functionalized phosphine
BzPhP{CH(OH)Ph}, containing two stereogenic cen-

J. Albert et al. / Journal of Organometallic Chemistry 603 (2000) 235–239
237
ters, has been prepared and resolved. It has also been
3.2. Synthesis of 4a
shown that the cyclopalladated compound of the pri-
mary amine 1-(1-naphthyl)ethylamine is a better resolv-
ing agent for this ligand than the corresponding
metallacycle containing the tertiary amine N,N-
dimethyl-1-(1-naphthyl)ethylamine.
A mixture of compound 3a (0.25 mmol, 170 mg) and
the hydroxyphosphine 2 (0.25 mmol, 76.6 mg) in THF
(30 ml) was stirred for 30 min at r.t. and then filtered.
The filtrate was concentred in vacuo and the solid was
recrystallized from acetone to obtain the 1:1:1:1 mix-
ture of 4a diastereomers, as a yellow solid in 75% yield.
3. Experimental
3.2.1. Characterization data for 4a
Anal. (%) Calc. for C34H35NOClPPd: C: 63.17, H:
5.46, N: 2.17. Found: C, 63.2; H, 5.3; N, 2.2. 31P{1H}-
NMR (101.26 MHz, CDCl3): l=52.6 s, 51.5 s, 41.5 s
and 41.4 s.
1H-NMR at 200 and 500 MHz, and 31P{1H} at
101.26 MHz spectra were recorded, respectively, on
Varian Gemini 200, Varian VXR 500 and Bruker DRX
250 spectrometers. Chemical shifts (in ppm) were mea-
1
sured relative to SiMe4 for H and to 85% H3PO4 for
3.2.2. Separation of 4a diastereomers
1
31P. The solvents used were CDCl3 in H and THF or
The 1:1:1:1 mixture of 4a diastereomers (400 mg) was
eluted carefully at r.t., in a SiO2 column (30×400 mm,
30 g SiO2) with chloroform–acetone (100:4) as eluent.
The eluted solution was collected in fractions of 15 ml,
concentrated in vacuo and checked by 31P{1H}-NMR
spectroscopy (101.26 MHz). The first and second
diastereomers eluted 4a% and 4a%% were obtained as a
mixture in 70% yield (140 mg). The third diastereomer
eluted 4a%%% was obtained in 30% yield (30 mg), with a
d.e. higher than 95%. The last diastereomer eluted 4a%%%%
was not obtained in a pure form.
CHCl3 in 31P. Microanalyses were performed at the
Institut de Qu´ımica Bio-Orga`nica de Barcelona and the
Serveis Cient´ıfico-Te`cnics de la Universitat de
Barcelona. The optical rotations of the complexes were
determined at 20°C using a Perkin–Elmer 241-MC
polarimeter. Infrared spectra were recorded as KBr
disks on a Nicolet 520 FT-IR spectrometer.
Materials and Synthesis. All the reactions involving
free phosphines were carried out using Schlenk tech-
niques under nitrogen atmosphere. All solvents were
dried and degassed by standard methods. Tetrahydro-
furan was distilled over sodium–benzophenone, under
nitrogen, before use. All chemicals were of commercial
grade and used as received. Cyclopalladated com-
pounds 3a and 3b, and PPhBz2 were prepared accord-
ing to procedures described elsewhere [8,13].
BzPhP{CH(OH)Ph} was prepared following the proce-
dure described for related monohydroxyphosphines
[14].
1H-NMR data (500 MHz, CDCl3) for 4a%%%: l=8.08
(t, 2H, JHH=7.2 Hz, Ar), 7.91–6.92 (m, 16H, Ar), 6.55
(d, 1H, JHH=8.4 Hz, Ar), 6.25 (d, 1H, JHH=8.4 Hz,
H2), 5.72 (dd., 1H, JHH=7.0 Hz, JHP=1.5 Hz,
HCOH), 5.66–5.52 (m., 2H, H1 and HOCH), 4.33–
4.17 (m., 1H, HCMe), 4.08–3.96 (m, 1H, H2CP), 3.72
(m, 1H, H2CP), 3.10–2.93 (d, JHH=3.4 Hz, 3H,
MebN), 2.78–2.63 (d, JHH=1.6 Hz, 3H, MeaN), 1.92
(d, JHH=6.1 Hz, 3H, H3CH). 31P{1H}-NMR (101.26
MHz, CDCl3): l=51.5 s. [a]2D0= −38.92 deg cm2 g−1
c=6.0 mg ml−1
,
3.1. Synthesis of (9)-PHBzPh and
BzPhP{CH(OH)Ph}
.
1H-NMR data (500 MHz, CDCl3) for the mixture of
4a% and 4a%%: l=7.62–6.95 (m, 38 H, Ar), 6.92–6.81
(m, 4H, Ar), 6.72–6.64 (m, 1H), 6.18–6.10 (m., 1H),
5.97–5.86 (m., 2H), 4.35–4.02 (m., 2H, HCMe), 3.52–
3.31 (m., 4H, H2CP), 2.87 (d, JHH=3.4Hz, 3H, MebN),
2.78 (d, JHH=3.2 Hz, 3H, MebN), 2.67 (d, JHH= 1.6
Hz, 3H, MeaN), 2.60 (d, JHH=1.4 Hz, 3H, MeaN),
1.52 (d., 3H, JHH=6.2 Hz, H3CH)), 1.21 (d., 3H,
Small pieces of lithium (0.086 g, 12.4 mmol) were
added to a solution of dibenzylphenylphosphine (1.5 g,
5.17 mmol) in THF (40 ml) and the reaction mixture
was stirred for 16 h at 20°C. The excess of lithium was
removed by decantation, and then 0.5 ml of water was
added and the mixture was stirred for 10 min. The
resulting solution was dried over anhydrous Na2SO4
and filtered off and the filtrate was concentred in vacuo
to obtain (9)-PHBzPh in 90% yield. 31P-NMR (101.26
J
HH=6.6 Hz, H3CH). 31P{1H}-NMR (101.26 MHz,
CDCl3): l=41.5 s and 41.4 s.
MHz, THF): l= −41.0 (d, JH P=205 Hz).
3.3. Synthesis of 4b
ꢀ
A mixture of 2.5 mmol (500 mg) of secondary phos-
phine PHBzPh and 3.0 mmol (265.3 mg) of benzalde-
hyde was stirred for 30 min at 0°C to obtain
BzPhP{CH(OH)Ph} (1:1 mixture of diastereomers) in
90% yield as an oily material, easy oxidable. 31P{1H}-
NMR (101.26 MHz, THF): l=1.4 s and 1.1 s.
A mixture of compound 3b (0.25 mmol, 156 mg) and
the hydroxyphosphine 2 ( 0.25 mmol, 76.6 mg) in THF
(30 ml) was stirred for 30 min at r.t. and then filtered.
The filtrate was concentred in vacuo and the solid
formed was purified by column chromatography over

238
J. Albert et al. / Journal of Organometallic Chemistry 603 (2000) 235–239
SiO2, with chloroform–acetone (100:7) as eluent to
obtain the 1:1:1:1 mixture of 4b diastereomers, as
yellow solid in 70% yield.
Ar), 6.86 (d, JHH=7.5 Hz, 2H, Ar), 6.55 (d, JHH=8.5
Hz, 1H, H2), 5,85 (dd, JPH=10.5 Hz, JHH=3.0 Hz,
1H, HCOH), 5.79 (dd, JHH=9.0 Hz, JPH=5.5 Hz, 1H,
H1), 5.28 (d, JHH=2.5 Hz, 1H, HOCH), 5,11 (q,
3.3.1. Characterization data for 4b
JHH=5.5 Hz, 1H, HCMe), 3.9 (m, 2H, H2CP and Hb),
Anal. (%) Calc. for C32H31NOClPPd: C: 62.15, H:
5.05, N: 2.26. Found: C, 62.5; H, 5.0; N, 2.1. 31P{1H}-
NMR (101.26 MHz, CDCl3): l=46.6 s, 45.6 s, 41.9 s,
39.5 s. MS-Positive FAB: 582 [(MꢀCl)+]
3.5 (t, JHH=JHP=13.5 Hz, 1H, H2CP), 3.39 (br, 1H,
Ha), 1.92 (d, JHꢀH=6.5 Hz, 3H, H3CH) 31P{1H}-NMR
(101.26 MHz, CDCl3): l=46.6 s. [a]2D0= +66.62 deg
cm2 g−1, c=10.1 mg ml−1
.
3.3.2. Separation of 4b diastereomers
The 1:1:1:1 mixture of 4b diastereomers (400 mg) was
eluted carefully at r.t., in a SiO2 column (30×400 mm,
30 g SiO2) with chloroform–acetone (100:3) as eluent.
The eluted solution was collected in fractions of 15 ml,
concentrated in vacuo and checked by 31P{1H}-NMR
spectroscopy (101.26 MHz). The first diastereomer
eluted 4b% was obtained in 30% yield (30 mg), with a
d.e. higher than 95%. And the last diastereomer eluted
4b%%%% was obtained in 60% yield (60 mg), with a d.e.
higher than 95%. The second and third diastereomers
eluted 4b%% and 4b%%% were obtained as a mixture in 40%
yield. The recrystallization of this mixture of
diastereomers from a saturated solution of diethylether
at 20°C afforded 4b%%% with a d.e. higher than 95%.
1H-NMR data (500 MHz, CDCl3) for 4b%: l=7.55
(m, 2H, Ar), 7.50 (m, 2H, Ar), 7.48 (d, JHH=8.2 Hz,
1H, H6), 7.40–7.05 (m, 11H, Ar), 6.94–6.82 (m, 4H
Ar), 6.50 (dd, JPH=5.8 Hz, JHH=8.4 Hz, 1H, H1),
5.75 (d, JPH=8.5 Hz, 1H, HCOH), 5.57 (m, 1H,
HOCH), 4.97 (q, JHH=5.0 Hz, 1H, HCMe), 3.87 (br,
1H, Hb), 3.50 (t, JHH=JPH=14.8 Hz, 1H, H2CP), 3.23
(br, 1H, Ha), 3.02 (dd, JHH=14.6 Hz, JPH=10.6 Hz,
1H, H2CP), 1.39 (d, JHH=6.2 Hz, 3H, H3CH).
31P{1H}-NMR (101.26 MHz, CDCl3): l=41.9 s.
1H-NMR data (500 MHz, CDCl3) for 4b%%: l=7.5–
7.4 (m, 4H, Ar), 7.32–7.01 (m, 14H, Ar), 6.8 (d,
Acknowledgements
This work was supported by the DGICYT and by
the Comissionat per a Universitats i Recerca. J.M.C.
thanks the Agencia Espan˜ola de Cooperacio´n Interna-
cional for a fellowship.
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HH=8.0 Hz, 2H, Ar), 6.47 (dd, JHH=8.0 Hz, JPH=
5.4 Hz, 1H, H1), 5.84 (br, 1H, HCOH), 5.7 (br, 1H,
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(br, 1H, Hb), 3.46 (br, 1H, Ha), 3.29 (br, 2H, H2CP),
1.6 (d, JHH=6.2 Hz, 3H, H3CH). 31P{1H}-NMR
(101.26 MHz, CDCl3): l=39.5 s
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7.8 (m, 2H, Ar), 7.61 (d, JHH=8.2 Hz, 1H, H6), 7.5 (d,
JHH=7.6 Hz, 1H, Ar), 7.34–7.0 (m, 13H, Ar), 6.92–
6.89 (m, 2H, Ar), 6.67 (d, JHH=8.8 Hz, 1H, H2), 5.88
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HCOH), 5.48 (br, 1H, HOCH), 5.22 (q, JHH=5.4 Hz,
1H, HCMe), 4.02 (br, 1H, Hb), 3.75 (m, 2H, H2CP),
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Hz, 1H, H5), 7.18–7.11 (m, 7H, Ar), 7.09–6,97 (m, 5H,

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