New non-C2-symmetric phosphine-phosphonites as ligands in asymmetric metal catalysis

Article abstract of DOI:10.1016/S0957-4166(99)00215-3

Starting from 1,2-dibromobenzene, the synthesis of N,N,N',N'-tetraethyl-[2-(diphenylphosphino)phenyl]phosphonous acid tetraamide is possible in two simple steps. This key compound reacts with a variety of chiral diols such as (R)- and (S)-binaphthol, 1,2:5,6-diisopropylidene-D-mannitol or (1R,2R)-1,2-diphenyl-1,2-ethane diol to form the corresponding non-C₂-symmetric phosphine-phosphonite compounds. These ligands react with Rh(COD)₂BF₄ to form bidentate Rh-complexes which serve as catalysts in the asymmetric hydrogenation of dimethyl itaconate with ee values of up to 88%.

Full text of DOI:10.1016/S0957-4166(99)00215-3

Pergamon
Tetrahedron: Asymmetry 10 (1999) 2129–2137
New non-C2-symmetric phosphine-phosphonites as ligands in
asymmetric metal catalysis
Manfred T. Reetz ∗ and Andreas Gosberg
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim/Ruhr, Germany
Received 19 April 1999; accepted 28 May 1999
Abstract
Starting from 1,2-dibromobenzene, the synthesis of N,N,N0,N0-tetraethyl-[2-(diphenylphosphino)phenyl]phos-
phonous acid tetraamide is possible in two simple steps. This key compound reacts with a variety of chiral
diols such as (R)- and (S)-binaphthol, 1,2:5,6-diisopropylidene-D-mannitol or (1R,2R)-1,2-diphenyl-1,2-ethane
diol to form the corresponding non-C2-symmetric phosphine-phosphonite compounds. These ligands react with
Rh(COD)2BF4 to form bidentate Rh-complexes which serve as catalysts in the asymmetric hydrogenation of
dimethyl itaconate with ee values of up to 88%. © 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Interest in chiral non-C2-symmetric bidentate organophosphorus compounds as ligands in asymmetric
transition metal catalyzed reactions is increasing,1 phosphine-phosphite2 and phosphine-phosphinite3
compounds being prominent examples. Less is known concerning chiral phosphine-phosphonite
ligands.3 Recently, we reported the highly enantioselective Rh-catalyzed hydrogenation of olefins
using a chiral diphosphonite based on (R)- and (S)-binaphthol, the backbone being ferrocene.4 This
development arose from previous work relating to the synthesis of chiral phosphine-phosphonites
derived from chiral diols.5 A recent communication by Knight6 described the synthesis of one of these
ligands, namely compound 6, and prompts us to report our data at this time. Specifically, we describe
the synthesis of the chiral non-C2-symmetric ligands 6, 8 and 10, as well as their use in transition metal
catalyzed asymmetric hydrogenation.
∗
Corresponding author. Fax: +49 (208) 306 2985; e-mail: reetz@mpi-muelheim.mpg.de
0957-4166/99/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(99)00215-3

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2. Results and discussion
We envisioned N,N,N0,N0-tetraethyl-[2-(diphenylphosphino)phenyl]phosphonous acid diamide 3 or
[2-(diphenylphosphino)phenyl]phosphonous acid dichloride 4 as the key intermediates in the synthesis
of ligands 6, 8 and 10. Accordingly, the known (2-bromophenyl)diphenylphosphine7 2 was first prepared
by lithiation/phosphorylation of 1,2-dibromobenzene 1 (Scheme 1). Lithiation of 2 with n-butyllithium
followed by in situ reaction with ClP(NEt2)2 (accessible in excellent yield from PCl3/HNEt2)8 afforded
the desired new compound 3 in 88% yield following isolation by high-vacuum distillation. This demons-
trates that the use of two equivalents of tert-butyllithium, as recently described,6 is not necessary, one
equivalent of the cheaper n-butyllithium being perfectly suitable. Reaction of 3 with dry HCl in ether
provided the dichloride 4 in almost quantitative yield.5
Scheme 1.
Upon treating 3 with the equivalent amount of (R)-binaphthol 5 in refluxing toluene, the desired ligand
6 was formed in excellent yield (Scheme 2). Removal of the solvent and Et2NH, trituration with pentane
1
and filtration afforded a white-beige analytically pure solid (88–90%) which was characterized by H,
13C and 31P NMR spectroscopy, mass spectrometry (MS) and elemental analysis.5 The analogous result
was obtained using (S)-binaphthol.
Scheme 2.
The analogous exchange reactions using 1,2:5,6-diisopropylidene-D-mannitol 7 or (1R,2R)-1,2-
diphenyl-1,2-ethane diol (9) turned out to be slower (Scheme 3). Removal of Et2NH during the synthesis
led to excellent up to almost quantitative yields of 8 and 10. Ligands 6, 8 and 10 were also accessible by
reaction of the dichloride 4 with the corresponding diols in the presence of a base, although this appeared
to be less direct.5
Although compound 6 was prepared by Knight et al. from 4 and (R)-binaphthol 5, no catalytic data
were reported.6 In principle, a wide variety of transition metal complexes can be prepared on the basis
of ligands 6, 8 and 10. We began by attempting to synthesize a Rh-complex. However, upon injecting
a CH2Cl2 solution of bis[η2,η2-(Z,Z)-1,5-cyclooctadiene]rhodium(I) tetrafluoroborate [Rh(COD)2BF4]
11 into a solution of ligand 6 at room temperature, a mixture of phosphorus-containing compounds was
formed as judged by the 31P NMR spectrum of the crude product (Scheme 4).5 In contrast, a clean
reaction took place by using an inverse reaction mode at low temperatures,5 i.e. by adding a solution of
the ligand 6 to a solution of Rh(COD)2BF4 in CH2Cl2 at −78°C. Complex 12 was formed in essentially

M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
2131
Scheme 3.
quantitative yield as judged by the 31P NMR spectrum of the crude product. Following workup, the
complex was isolated in analytically pure form in 95% yield and fully characterized by 1H, 13C and 31
P
NMR spectroscopy, and elemental analysis. The 31P NMR spectrum revealed two doublets of doublets
at δ=182.4 and 58.9, in line with the structure shown (cf. 12).
Scheme 4.
As far as catalysis is concerned, either preformed complex 12 or an in situ reaction mode can be
used. In the case of ligands 8 and 10, only the in situ method was applied. Most of the initial efforts5
concentrated on the Rh-catalyzed hydrogenation of dimethyl itaconate (13–14) (Scheme 5). In the
literature, this reaction was most often carried out in methanol.1 In the present case, methanol could
not be used due to instability of the ligands in this medium.
Scheme 5.
The results summarized in Table 1 show that of the three ligands compound 6 is the most effective,
delivering an ee value of 88% in favor of the (R)-configured product 14 in the optimal case of an
in situ reaction mode. This competes favorably with some of the ligands previously reported in the
literature, but others are clearly more effective (ee >95%).1,4 It is interesting to note that BINAP,1a when
used in CH2Cl2, leads to an ee value of only 76%,8 whereas in methanol enantioselectivity is much
higher (ee >95%).1a These and other observations1,8 show that solvent effects are extremely important in
asymmetric hydrogenation.
3. Summary
The synthesis of the non-C2-symmetric ligands 6, 8 and 10 is possible in three simple steps starting
from 1,2-dibromobenzene allowing for a simple variation of the ligands chirality and steric nature. This

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M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
Table 1
Asymmetric hydrogenation of dimethyl itaconate (13 -→ 14) in CH2Cl2 (Lig/Rh=1.0, 22°C, 1.3 bar H2)
synthetic scheme makes phosphine-phosphonites with an ortho-phenylene backbone easily accessible in
an analytically pure form. Initial studies directed towards their use as chiral ligands in the asymmetric
Rh-catalyzed hydrogenation of dimethyl itaconate reveal appreciable degrees of enantioselectivity (up
to 88% ee). It remains to be seen if further ligand tuning can improve the efficiency of these types of
ligands. Studies are also under way to test them in C–C bond forming reactions.
4. Experimental
4.1. General
All manipulations were carried out under strict exclusion of air and humidity using standard Schlenk-
type techniques. NMR spectra were recorded at room temperature on Bruker AC 200, AM 200 and
AMX 300 spectrometers. Chemical shifts are given in ppm relative to TMS or 85% H3PO4 as external
standards, and coupling constants are given in hertz. Electron ionization (70 eV) mass spectra were
recorded on a Finnigan MAT 8200 instrument using fractional evaporation. High resolution electron
ionization (70 eV) mass spectra were recorded on a Finnigan MAT 95 instrument. Fourier transform IR
spectra were recorded on a Nicolet Magna-IR 750 spectrometer. Elemental analyses were carried out
by Mikroanalytisches Labor H. Kolbe, Mülheim an der Ruhr. GC analyses were carried out on Carlo
Erba 5300 and Hewlett–Packard 5890 instruments (conditions given below). The assignment of absolute
configuration of product 14 was done by comparison with a commercial sample of (R)-(+)-2-methyl
dimethyl succinate (Aldrich).
4.2. Materials
Ether, THF, pentane, benzene and toluene were all distilled from sodium tetraethylalanate.
Dichloromethane and trichloromethane were distilled from calcium hydride. Ethanol was dried

M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
2133
with magnesium or sodium ethanolate and diethyl phthalate and distilled. Solvents were stored
under argon until use. n-Butyllithium was obtained from Chemetall GmbH as a 1.6 M solution in
hexane. Chlorodiphenylphosphine was obtained from Aldrich and distilled prior to use. 1,2:5,6-
Diisopropylidene-D-mannitol was obtained from Fluka; (R)- and (S)-binaphthol (R: 98% ee, S: 99%
ee) and 1,2-dibromobenzene were purchased from Aldrich and used without further purification.
Bis(diethylamino)chlorophosphine,9a (1R,2R)-1,2-diphenyl-1,2-ethane diol 99b and bis[η2,η2-(Z,Z)-1,5-
cyclooctadiene]rhodium(I) tetrafluoroborate9c 11 were all prepared according to literature procedures.
The density of bis(diethylamino)-chlorophosphine was determined to be 0.978 kg l−1. Dimethyl itaconate
was obtained from Fluka and distilled under reduced pressure prior to use.
4.3. Improved synthesis of (2-bromophenyl)diphenylphosphine 2
The synthesis follows a protocol published by Ravindar et al.7b A 1 l three-necked round-bottom flask
equipped with a 500 ml dropping funnel and an overhead stirring device was charged with 125 ml of a
1.6 M solution of n-butyllithium in hexane (200 mmol) and 500 ml THF. This mixture was cooled down
to −130°C (pentane/liq. N2) and a solution of 24.0 ml (199 mmol) of 1,2-dibromobenzene in 200 ml THF
was slowly added within 2 h under vigorous stirring. After completely adding the 1,2-dibromobenzene,
the reaction mixture was stirred for a further 20 min at −130°C before a solution of 36.8 ml (200 mmol)
of chlorodiphenylphosphine in 200 ml THF was added. The resulting mixture was then allowed to slowly
warm to room temperature affording a slightly yellow solution from which any insoluble residues were
filtered off. It was necessary to carefully avoid too intensive cooling, i.e. by adding too much liquid
nitrogen to the cooling bath.
The solvent was then removed in vacuo yielding a yellow-green, oily residue. Methanol (100 ml) was
immediately added to this and the suspension was stirred overnight. The yellow solution was filtered
off and the solid residue was washed twice with 100 ml of methanol. The crude product was then
recrystallized from ethanol to afford a crystalline, slightly greenish solid which was dried in vacuo (46.84
1
g, 69%). H NMR (300 MHz, C6D6): δ 7.15–7.05 (m, 5H), 6.83–6.76 (m, 6H), 6.63 (m, 1H), 6.51 (m,
1H), 6.43 (m, 1H). 31P{1H} NMR (121 MHz, C6D6): δ −4.1 (s). 13C{1H} NMR (50 MHz, CDCl3): δ
133.8 (d, 1JCP=11.4 Hz, CPAr2), 131.7 (d, 1JCP=10.7 Hz, CPC6H4-o-Br), 129.3 (s), 128.9 (d, 2JCP=20.2
2
2
Hz, C6H5-o-PAr), 127.8 (d, JCP=2.4 Hz, C6H4-o-Br), 125.0 (s), 124.8 (d, JCP=31.1 Hz, CBr), 123.9
3
(s, C6H5-p-PAr), 123.5 (d, JCP=7.2 Hz, C6H5-m-PAr), 122.3 (s). MS (EI, 70 eV, pos. ions): m/z=340
(85%, M+), 339 (87%, [M−H]+), 260 (17%, [M−Br]+), 183 (82%, [9-phosphafluorenyl]+ ).
4.4. Synthesis of N,N,N0,N0-tetraethyl-[2-(diphenylphosphino)phenyl]phosphonous acid diamide 3
A 250 ml three-necked round-bottom flask equipped with a 50 ml dropping funnel was charged with
10.55 g (30.92 mmol) of (2-bromophenyl)diphenylphosphine 2 and 150 ml THF. The solution was cooled
down to −78°C and 21.5 ml of a 1.6 M solution of n-butyllithium in hexane (34.4 mmol) was added
within 10 min via a syringe. The resulting orange solution was then stirred for another 30 min at this
temperature.
To this mixture was added, over a period of 30 min, a solution of 7.3 ml (34 mmol) of
bis(diethylamino)chlorophosphine in 45 ml THF. The reaction mixture was then allowed to slowly warm
up to room temperature. Removal of the solvent in vacuo afforded a viscous brown residue to which 150
ml of pentane was added. The resulting suspension was filtered over Celite and the solvent evaporated in
vacuo. Fractional distillation of the brown and very viscous raw product under high vacuum afforded two
fractions (43°C and 130°C/<10−6 mbar) containing side products and a bright yellow, very viscous oil

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M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
1
(bp 170–180°C/<10−6 mbar) as the pure product (11.66 g, 89%). H NMR (300 MHz, CDCl3): δ 7.65
(m, 1H), 7.31 (m, 1H), 7.27–7.22 (m, 10H), 7.15 (m, 1H), 7.05 (m, 1H), 3.07–2.82 (m, 8H, NCH2), 0.97
3
1
2
(t, JHH=18.3 Hz, 12H, CH3). 13C{1H} NMR (50 MHz, CDCl3): δ 149.0 (dd, JCP=42 Hz, JCP=13
Hz, C6H4PN2), 139.9 (dd, 2JCP=29.6 Hz, 1JCP=14.8 Hz, C6H4PAr2), 138.1 (dd, 1JCP=14 Hz, 4JCP=4.4
Hz, C6H5PAr2), 135.1 (dd, JCP=4.4 Hz, JCP=1.5 Hz, C6H4-m-PN2-o-PAr2), 133.4 (d, 2JCP=19.6 Hz,
2
3
C6H5-o-PAr2), 129.9 (dd, 2JCP=8 Hz, 3JCP=4 Hz, C6H4-o-PN2-m-PAr2), 128–127.7 (m), 127.4 (s), 43.1
2
2
3
(d, JCP=18.3 Hz, CH2), 43.06 (d, JCP=18.3 Hz, CH2), 14.4 (d, JCP=3.4 Hz, CH3). 31P{1H} NMR
(121 MHz, CDCl3): δ 93.5 (d, 3JPP=135 Hz, PN2), −14.5 (d, PPh2). MS (EI, 70 eV, pos. ions): m/z=436
(18%, M+), 364 (100%, [M−C4H10N]+), 293 (40%, [M−C8H19N2]+), 183 (11%, [9-phosphafluorenyl]+).
˜
HRMS (EI, 70 eV, pos. ions): m/z=436.2192 (5) (436.2197 calcd). IR (capillary): ν=ν(_C−H) 3069,
3050 (s), ν(C_C) 1434 (s, br.), ν(C–N) 1185 (s, br.), ν(P–N) 919 (s-m, br.) cm−1.
4.5. Synthesis of [2-(diphenylphosphino)phenyl]phosphonous acid dichloride 4
A round-bottom flask was charged with 817 mg (2.25 mmol) of N,N,N0,N0-tetraethyl-[2-
(diphenylphosphino)phenyl]phosphonous acid diamide 3 and 50 ml of diethyl ether. To this solution was
added 10 ml of a 5.8 M solution of hydrogen chloride in diethyl ether at room temperature, affording
a colorless suspension. The colorless precipitate was filtered off and the solvent evaporated from the
clear filtrate under reduced pressure, yielding a greenish solid which was dried in vacuo (910 mg, 98%).
1H NMR (300 MHz, CDCl3): δ 8.13 (m, 1H), 7.59 (m, 1H), 7.45 (m, 1H), 7.33 (m, 1H), 7.27–7.16 (m,
10H). 13C{1H} NMR (50 MHz, CDCl3): δ 146.0 (dd, 1JCP=55 Hz, 2JCP=29 Hz, C6H4PCl2), 140.8 (dd,
2
1
3
1JCP=9.51 Hz, JCP=33.2 Hz, C6H4PAr2), 134.9 (dd, JCP=9 Hz, JCP=9 Hz, C6H5PAr2), 133.4 (d,
2JCP=2.4 Hz), 133.3 (d, JCP=18.5 Hz, C6H5-o-PAr2), 132.1 (s), 130.2 (dd, JCP=8 Hz, JCP=4 Hz),
2
2
3
130.1 (s), 128.8 (s), 128.4 (d, JCP=6.1 Hz). 31P{1H} NMR (81 MHz, CDCl3): δ 157.1 (d, JPP=336
3
3
Hz, PCl2), −19.6 (d, PPh2). MS (EI, 70 eV, pos. ions): m/z=362 (48%, M+), 327 (100%, [M−Cl]+), 183
+
˜
(73%, [9-phosphafluorenyl] ). IR (KBr): ν=ν(_C–H) 3067, 3051 (s), ν(C_C) 1583, 1478, 1434 (s),
ν(P–Cl) 481 cm−1. Anal. calcd for C18H14Cl2P2: C, 59.53; H, 3.88; Cl, 19.52; P, 17.06. Found: C, 58.20;
H, 4.36; Cl, 19.42; P, 17.18.
4.6. Synthesis of phosphine-phosphonites
4.6.1. General procedure for the synthesis of phosphine-phosphonites
A 100 ml round-bottom flask equipped with a reflux condenser was charged with a weighed
amount of the appropriate diol. Added to this was an equimolar amount of N,N,N0,N0-tetraethyl-[2-
(diphenylphosphino)phenyl]phosphonous acid diamide 3 as a solution in toluene (usually about 45–145
mmol l−1) and the mixture was heated to reflux. The reaction can be followed by 31P NMR and was
usually complete within 24 to 48 h (mmolar scale). After cooling to room temperature, the solvent was
removed under reduced pressure and the oily residue was stirred in 20–50 ml of pentane overnight. The
liquid phase was then filtered off and the solid residue washed again with pentane. Finally, the powdery
solid was dried in vacuo. 31P NMR did not indicate the formation of side products and isolated yields
typically ranged from 80 to 95%.
4.6.2. Synthesis of (R)-2-[2-(diphenylphosphino)phenyl]-1,3,2-dinaphtho[d1,2 ,f1,2]dioxaphosphepine 6
(R)-Binaphthol (378 mg, 1.32 mmol) and 9.10 ml of a 0.145 M solution of N,N,N0,N0-tetraethyl-2-
(diphenylphosphino)phenylphosphonous acid diamide (3) (1.32 mmol) were reacted as outlined above,
affording a white-beige powder (606 mg, 80%). 1H NMR (300 MHz, CDCl3): δ 7.91 (m, 1H), 7.83 (m,

M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
2135
1H), 7.72 (m, 1H), 7.5–7.4 (m, 4H), 7.4–7.32 (m, 4H), 7.32–7.0 (m, 13H), 6.96 (m, 1H), 6.07 (d, JHP=8.8
Hz, 1H). 13C{1H} NMR (75 MHz, CDCl3) δ 135.1 (s), 134.8 (s), 133.8 (d, JCP=4 Hz), 133.5 (s), 133.2
(s), 131.4 (s), 130.5 (s), 129.3 (s), 129.1 (s), 128.8 (s), 128.7 (s), 128.6 (s), 128.5 (s), 128.4 (s), 128.2 (s),
126.9 (s), 126.1 (s), 125.9 (s), 124.8 (s), 124.6 (s), 121.9 (s), 121.7 (s); (75 MHz, D5C6CD3): δ 152.3 (s),
149.5 (d, JCP=1.9 Hz), 148.2 (d, JCP=7.1 Hz), ca. 143 (m). 31P{1H} NMR (81 MHz, CDCl3): δ 174.6
(d, 3JPP=212 Hz, PO2), −19.2 (d, 3JPP=212 Hz, PPh2). MS (EI, 70 eV, pos. ions): m/z=576 (100%, M+),
575 (92%, [M−H]+), 499 (98%, [M−C6H5]+), 449 (64%, [M−C10H7]+), 435 (30%, [M−C10H5O]+), 252
+
+
˜
(8%, [C20H12] ), 183 (41%, [9-phosphafluorenyl] ). IR (KBr): ν=ν(aryl–O) 1230 (s), ν(P–O) 951 (s)
cm−1. Anal. calcd for C38H26O2P2: C, 79.16; H, 4.54; P, 10.74. Found: C, 78.98; H, 4.64; P, 10.65.
4.6.3. Synthesis of (4R,5R)-4,5-bis[(4R)-2,2-dimethyl-1,3-dioxolan-4-yl]-2-[2-(diphenylphosphino)-
phenyl]-1,3,2-dioxaphospholane 8
1,2:5,6-Diisopropylidene-D-mannitol (236 mg, 900 µmol) and 20.0 ml of a 45.0 M solution of
N,N,N0,N0-tetraethyl-[2-(diphenylphosphino)phenyl]phosphonous acid diamide 3 (900 µmol) were re-
acted as outlined above affording a white-beige powder (434 mg, 87%). In some cases it was necessary
to remove the solvent completely after 48 h reflux and redissolve the residue in fresh toluene to afford
complete conversion upon further heating. In one case this procedure had to be carried out twice (96 h
reaction time in this case). 1H NMR (300 MHz, CDCl3): δ 7.53 (m, 1H), 7.37–7.23 (m, 7H), 7.23–7.06
(m, 6H), 4.31 (dd, JHH=5.8 Hz, JHH=6 Hz, 1H, anti-HCOPO), 4.14 (ddd, 3JHH=6 Hz, 3JHH=5 Hz, 3JHH=5
3
2
3
Hz, 1H, OCH2CHO), 3.95 (dd, JHH=5 Hz, JHH=6.3 Hz, 2H, OCH2CHO), 3.68 (ddd, JHH=9 Hz,
3JHP=8.9 Hz, JHH=5.8 Hz, 1H, anti-HCOPO), 3.31 (dd, JHH=4 Hz, JHH=8.9 Hz, 1H, OCH2CHO),
3
3
2
3
3
3
2
3
3.21 (ddd, JHH=9 Hz, JHH=4 Hz, JHH=6 Hz, 1H, OCH2CHO), 2.94 (dd, JHH=8.9 Hz, JHH=6
Hz, 1H, OCH2CHO), 1.37 (s, 3H), 1.28 (s, 3H), 1.21 (s, 3H), 1.03 (s, 3H). 13C{1H} NMR (75 MHz,
1
2
1
2
CDCl3): δ 150.5 (dd, JCP=55.9 Hz, JCP=30.4 Hz, C6H4PO2), 138.6 (dd, JCP=11.2 Hz, JCP=22.2
Hz, C6H4PAr2-o-PO2), 136.5 (dd, 1JCP=9.1 Hz, 4JCP=5 Hz, C6H5PAr2), 134.4 (dd, 1JCP=8 Hz, 4JCP=2
Hz, C6H5PAr2), 134.3 (s), 133.1 (d, 2JCP=19.6 Hz, C6H5-o-PAr2), 132.0 (d, 2JCP=18 Hz, C6H5-o-PAr2),
129.1 (s), 128.3 (s), 128.1 (s), 127.6 (d, 3JCP=7.6 Hz, C6H5-m-PAr2), 127.3 (d, JCP=6.2 Hz, C6H5-m-
3
2
3
PAr2), 127.3 (s), 126.5 (dd, JCP=13.3 Hz, JCP=7.5 Hz, C6H4-o-PO2-m-PAr2), 108.7 (s, O2C(CH3)2),
108.5 (s, O2C(CH3)2), 80.1 (d, 3JCP=9.4 Hz, POCH), 79.5 (d, 3JCP=9.8 Hz, POCHR2), 75.3 (d, 4JCP=3.2
Hz, OCHCH2O), 74.9 (s, OCHCH2O), 65.8 (s, OCHCH2O), 64.4 (s, OCHCH2O), 25.7 (s, CH3), 25.4 (s,
CH3), 24.3 (s, CH3), 24.1 (s, CH3). 31P{1H} NMR (81 MHz, CDCl3): δ 171.1 (d, 3JPP=132 Hz, PO2),
−20.8 (d, PPh2). MS (EI, 70 eV, pos. ions): m/z=552 (100%, M+), 537 (24%, [M−CH3]+), 325 (83%,
[M−C12H19O4]+), 228 (1%, [C12H20O4]+), 183 (12%, [9-phosphafluorenyl]+), 43 (21%, [CH3CO]+). IR
(KBr): ν=ν(_C–H) 3056 (s), δs(CH3) 1368 (s), ν(O–C–O) 1146, 1086, 1056 (s, br.) cm . Anal. calcd
for C30H34O6P2: C, 65.21; H, 6.20; P, 11.21. Found: C, 65.36; H, 6.19; P, 11.31.
−1
˜
4.6.4. Synthesis of (4R,5R)-4,5-diphenyl-2-[2-(diphenylphosphino)phenyl]-1,3,2-dioxaphospholane 10
(1R,2R)-1,2-Diphenyl-1,2-ethane diol (482 mg, 2.2 mmol) and 50.0 ml of a 45 M solution of
N,N,N0,N0-tetraethyl-[2-(diphenylphosphino)phenyl]phosphonous acid diamide 3 (2.25 mmol) were re-
acted as outlined above affording a white-beige powder (993 mg, 88%). In some cases it was necessary
to remove the solvent completely after 48 h reflux and redissolve the residue in fresh toluene to afford
complete conversion upon further heating. This procedure had to be carried out up to two times (96 h
reaction time in this case). 1H NMR (400 MHz, CDCl3): δ 7.63 (m, 1H), 7.36 (m, 21H), 6.69 (dd, JHP=1
Hz, JHH=7.4 Hz, 2H), 4.76 (dd, 3JHH=9.3 Hz, 3JHP=1.1 Hz, 1H, anti-POCH), 4.65 (d, 3JHH=9.3 Hz, 1H,
1
2
syn-POCH). 13C{1H} NMR (100 MHz, CDCl3): δ 150.2 (dd, JCP=55 Hz, JCP=31.1 Hz, C6H4PO2),
1
2
1
4
139.2 (dd, JCP=21 Hz, JCP=11.6 Hz, C6H4PAr2), 136.0 (dd, JCP=8.4 Hz, JCP=3.6 Hz, C6H5PAr2),

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135.0 (s, C6H5CHO), 135.1 (dd, 1JCP=13.3 Hz, 4JCP=3.5 Hz, C6H5PAr2), 134.2 (s), 132.9 (d, 2JCP=18.9
Hz, C6H5-o–PAr2), 132.3 (d, 2JCP=18.1 Hz, C6H5-o-PAr2), 129.0 (s), 128.1 (s), 127.6 (s), 127.4 (s), 127.3
(s), 127.23 (s), 127.17 (s), 127.0 (s), 126.8 (dd, 2JCP=13.5 Hz, 3JCP=8 Hz, C6H4-o-PO2-m-PAr2), 126.4
(s), 126.0 (s), 86.1 (d, 2JCP=8.6 Hz, OCHCHO), 83.2 (d, 2JCP=7.2 Hz, OCHCHO). 31P{1H} NMR (121
3
MHz, CDCl3): δ 173.1 (d, JPP=120 Hz, PO2), −19.4 (d, PPh2). MS (EI, 70 eV, pos. ions): m/z=504
(3%, M+), 324 (32%, [M−C14H12]+), 323 (42%, [M−C14H13]+), 183 (22%, [9-phosphafluorenyl]+),
+
−1
˜
180 (100%, [C14H12] ). IR (KBr): ν=ν(C_C) 1433 (m-s), ν(P–O) 985, 963 (s) cm . Anal. calcd for
C32H26O2P2: C, 76.18; H, 5.19; P, 12.28. Found: C, 76.07; H, 5.15; P, 12.12.
4.6.5. Synthesis of {(R)-2-[2-(diphenylphosphino)phenyl]-1,3,2-dinaphtho[d1,2,f1,2]dioxaphosphepine}-
[η2,η2-(Z,Z)-1,5-cyclooctadiene]rhodium(I) tetrafluoroborate 12
A 100 ml Schlenk tube was charged with 16.0 ml of a 29.1 M solution of bis[η2,η2-(Z,Z)-1,5-
cyclooctadiene]rhodium(I) tetrafluoroborate 11 (466 µmol) in dichloromethane. At −78°C a solution of
271 mg (470 µmol) of (R)-2-[2-(diphenylphosphino)phenyl]-1,3,2-dinaphtho[d1,2 ,f1,2]dioxaphosphepine
6 in 20 ml of dichloromethane was added over a period of 70 min via a syringe pump. The orange solution
was allowed to warm up to room temperature and the solvent was removed under reduced pressure. The
orange, slightly oily residue was then suspended in 25 ml of pentane and stirred overnight at room
temperature. Finally the liquid phase was filtered off and the residue was dried in vacuo, affording a
bright orange powder (385 mg, 95%). 1H NMR (300 MHz, CD2Cl2): δ 8.26 (d, JHH=8.8 Hz, 1H), 8.10
(d, JHH=8.2 Hz, 1H), 8.03 (d, 1H, JHH=9.4 Hz, 1H), 8.00 (d, JHH=9.1 Hz, 1H), 7.95–7.48 (m, 15H),
7.4–7.2 (m, 5H), 7.12–6.90 (m, 2H), 5.77 (m, 1H, CH2CH_C), 5.46 (m, 1H, CH2CH_C), 5.21 (m,
1H, CH2CH_C), 4.98 (m, 1H, CH2CH_C), 2.65–2.00 (m, 8H, CH2CH_C). 13C{1H} NMR (75 MHz,
CD2Cl2): δ 148.5 (d, JCP=13.7 Hz), 147.8 (d, JCP=7.3 Hz), 144.8 (ddd, J=56.0 Hz, J=39.9 Hz, J=8.4
Hz), ca. 140 (m), 135.7 (d, J=5.8 Hz), 133.7–133.5 (m), 132.9 (m), 132.6–132.5 (m), 132.2–132.0 (m),
132.1 (s), 131.5 (s), 130.7 (s), 130.5 (s), 130.3–130.0 (m), 129.1 (s), 129.0 (s), 127.5 (s), 127.3 (s), 127.3
(s), 127.2 (s), 126.3 (s), 126.0 (s), 122.7 (dd, J=82.7 Hz, J=3.0 Hz), 121.1–120.7 (m), 111.8 (dd, J=27.8
Hz, J=33.4 Hz, CH2CH_), 111.3 (dd, J=4.9 Hz, J=11.0 Hz, CH2CH_), 105.2 (m, CH2CH_), 100.4
(m, CH2CH_), 31.6–28.4 (m, CH2). 31P{1H} NMR (121 MHz, CD2Cl2): δ 182.4 (dd, 1JPRh=227.2 Hz,
2JPP=32.8 Hz, PO2), 58.9 (dd, 1JPRh=153.0 Hz, PPh2). Anal. calcd for C46H38BF4O2P2Rh: C, 63.18; H,
4.38; P, 7.08; Rh, 11.78. Found: C, 63.08; H, 4.38; P, 7.04; Rh, 11.66.
4.7. General procedure for the hydrogenation of dimethyl itaconate 13
Hydrogenations were carried out in 25 or 50 ml round-bottom flasks which were charged with 1
ml dimethyl itaconate 13 1 M in dichloromethane and measured volumina of solutions of bis[η2,η2-
(Z,Z)-1,5-cyclooctadiene]rhodium(I) tetrafluoroborate 11 [Rh(cod)2BF4] 1 M in dichloromethane as well
as one of the ligands 6, 8 and 10 1 M in dichloromethane according to the ligand-to-rhodium ratio
(L:Rh) and the substrate-to-catalyst ratio (S:C), i.e. 1 ml [Rh(cod)2BF4] (11) 1 M in dichloromethane
and 1 ml ligand 1 M in dichloromethane for L:Rh=1 and S:C=1000. To the mixture thus obtained,
dichloromethane was added to a total volume of 10 ml, the argon atmosphere was replaced by hydrogen
(1.3 bar) and the mixture was stirred for a given period of time (1–20 h). An aliquot of the mixture was
then filtered over silica and analyzed via capillary GC: 30 m RTX-1 100% dimethylpolysiloxane (0.25
mm), 0.6 bar H2, 60°C/5°C min−1−300°C/4 min; tR=7.2 min, 2-methyl dimethyl succinate (14); 7.9 min,
dimethyl itaconate (13). 30 m GT-A, trifluoroactyl γ-cyclodextrin (0.25 mm), 0.9 bar H2, 60°C/0.8°C
min−1−87°C/5°C min−1−127°C; tR=24.0 min, (S)-14; 25.0 min, (R)-14.

M. T. Reetz, A. Gosberg / Tetrahedron: Asymmetry 10 (1999) 2129–2137
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