Enantioselective catalysis; 123: Octaaldehyde type chelating ligands - A divergent synthesis approach to easily tunable expanded ligands for enantioselective catalysis

Article abstract of DOI:10.1055/s-1998-2226

A broad range of optically active two-layer phosphanes was obtained by a divergent reaction sequence. Chirality was introduced into the ligands in the last step by easily performed Schiff base condensation of primary amines from the 'chiral pool' and achiral octaaldehydes containing a bisphosphane core. The two achiral precursors are 1,2-ethylene- and o-phenylene-bridged bisphosphanes with four 3,5-dicarbaldehyde-substituted phenyls, synthesized in six steps. The resulting octaimine ligands have been used in Rh, Pd and Ni complexes in several model reactions of enantioselective catalysis giving low optical inductions.

Full text of DOI:10.1055/s-1998-2226

SYNTHESIS
Papers
1742
Enantioselective Catalysis; 123:1 Octaaldehyde Type Chelating Ligands – A Divergent
Synthesis Approach to Easily Tunable Expanded Ligands for Enantioselective
Catalysis
H. Brunner,* M. Janura, S. Stefaniak
Institut für Anorganische Chemie, Universität Regensburg, D-93040 Regensburg, Germany
Fax +49(941)9434439; E-mail: henri.brunner@chemie.uni-regensburg.de
Received 17 April 1998; revised 9 May 1998
Abstract: A broad range of optically active two-layer phosphanes
was obtained by a divergent reaction sequence. Chirality was
introduced into the ligands in the last step by easily performed
Schiff base condensation of primary amines from the “chiral
pool” and achiral octaaldehydes containing a bisphosphane core.
The two achiral precursors are 1,2-ethylene- and o-phenylene-
bridged bisphosphanes with four 3,5-dicarbaldehyde-substituted
phenyls, synthesized in six steps. The resulting octaimine ligands
have been used in Rh, Pd and Ni complexes in several model reac-
tions of enantioselective catalysis giving low optical inductions.
Key words: two layer bisphosphanes, dendritic Schiff base
ligands, divergent synthesis, enantioselective catalysis
Introduction
During the last decade a vast number of optically active
phosphane ligands was synthesized and tested in different
Figure. Structure of Expanded Ligands with Strong Chelating P,P
Skeleton
model systems of enantioselective homogeneous cataly-
sis.2 Most of these conventional ligands, such as diop,3
prophos,4 bppfa,5 biphemp,6 binap7 or norphos,8 are
bis(diphenylphosphanyl) derivatives. In these ligands the
optional interactions between ligand and substrate (“bi-
chiral information is transferred to the catalytically active
functionalized catalysis”11) should be possible. The syn-
metal center via the arrangement of the phenyl rings of the
thesis of sixteen optically active bisphosphanes, in which
diphenylphosphanyl groups. Due to the limited size, long
chirality is derived from enantiomerically pure primary
range effects are not possible with these classical ligands.
amines by Schiff base condensation will be described. A
Recently, we developed the concept of the expanded
ligands.9 In this approach optically active ligands with in-
creased size are supposed to induce longe range selectivi-
ties in catalytic systems, such as the palladium catalyzed
allylic alkylation of barbiturates.10 The characteristics of
expanded ligands are a strong chelating P,P skeleton de-
prerequisite for this ultimate Schiff base condensation is
the availability of the octaaldehyde type chelating P,P
ligands octa-eth 6a and octa-phen 6b, the synthesis of
which will be reported.12
rived e.g. from Cl2PCH2CH2PCl2 or o-Cl2PC6H4PCl2, Synthesis of the Aldehydes Octa-eth 6a and Octa-phen 6b
non-chiral branching units for a space-filling construction
and a final layer consisting of chiral functional groups For a divergent reaction sequence based on Schiff base
(Figure). In this way it is possible to chirally shape the condensation, precursors with carbonyl groups are re-
surroundings of the P atoms in a wide range. After coor- quired to connect the chiral functionalities in the last step.
dination in a catalyst, an influence on the optical induction We decided to branch the phenyl rings of the well known
in enantioselective reactions is expected.
ligands Ph2PCH2CH2PPh2 and o-Ph2PC6H4PPh2 symmet-
rically with formyl groups in 3,5-position to get space fill-
ing ligand systems. By using formyl groups it should be
easy to couple enantiomerically pure primary amines un-
der mild conditions.
Up to now, such expanded ligands were synthesized in
convergent reaction sequences. The preparation included
lithiation steps of haloarene compounds and the addition
of electrophilic components, e.g. chlorophosphanes.
These steps usually were performed by metal-halogen ex- The aldehydes octa-eth 6a and octa-phen 6b were gener-
change with butyllithium. Thus, base-sensitive groups ated in a six-step synthesis starting from inexpensive com-
and functionalities unstable against nucleophilic attack mercially available compounds, such as isophthalic acid
were not tolerated in these syntheses. Here we present a or dimethyl 5-aminoisophthalate. The latter substrate was
divergent reaction sequence allowing to introduce chiral transformed by a Sandmeyer reaction into dimethyl 5-bro-
functional groups (containing e.g. hydroxy groups) in the moisophthalate (1) in 84% yield. Alternatively, 1 could be
last reaction step. Therefore, an easy ligand tuning with obtained in 94% yield by silver-catalyzed electrophilic

SYNTHESIS
December 1998
1743
Reagents and conditions: (a) 1. HBr/H2O/NaNO2, 2. CuBr/HBr, O°C; (b) Ref. 13; (c) LiAlH4/THF, –10°C; (d) PCC/CH2Cl2, reflux;
(e) HC(OMe)3/MeOH/p-TosOH, reflux
Scheme 1
substitution of isophthalic acid with bromine under drastic performed by acid-catalyzed transacetalization in aqueous
conditions,13 followed by acid-catalyzed esterification in acetone. In the case of 5a, a white precipitate formed, which
methanol. The published reduction of 1 with a suspension turned slightly yellow, when working without light protec-
of LiAlH4 in THF14 was optimized to give 3,5- tion. Octa-eth 6a is a fluffy powder, almost insoluble in
bis(hydroxymethyl)bromobenzene (2) in 98% yield. Oxi- most solvents and soluble only in traces in polar solvents
dation of 2 with pyridinium chlorochromate in dichlo- such as DMF or DMSO. It was purified by washing with
romethane gave 5-bromoisophthalaldehyde (3) in 81% acetone, diethyl ether and dichloromethane. Octa-phen 6b
yield,15 which was transferred into its acetal 4 by an acid- was isolated as a yellowish solid after recrystallization from
ified trimethyl orthoformate/methanol mixture in 93% dichloromethane/toluene (Scheme 2).
yield (Scheme 1).
In the 31P{1H} NMR spectra only singlets were detected
After a halogen-metal exchange between butyllithium and at δ = –12.5 and –13.1 for 6a and 6b, respectively. In the
the aryl bromide 4 an organolithium species was 1H NMR spectra the proton H-4' (between the two formyl
formed, which reacted with Cl2PCH2CH2PCl2 and groups) was shifted to low field (6a: δ = 8.33; 6b: δ =
o-Cl2PC6H4PCl2 to give the octaacetals 5a and 5b, respec- 8.30). As expected, it gave a triplet due to coupling with
tively, as shown in Scheme 2. The octaacetal 5a was recrys- the equivalent protons H-2' and H-6'. These protons ap-
tallized from dichloromethane/methanol to give a white peared as doublets of triplets (coupling with the two phos-
6
3
solid, whilst 5b could not be crystallized. Compound 5b phorus atoms: JPH = JPH = 3.2 Hz [6a]; 3.4 Hz [6b]),
was purified by chromatography and directly used in the while in the 1H{31P} NMR spectra they were detected as
deprotection step. Deprotection of the acetal groups was doublets.
Reagents and conditions: (a) 1. BuLi/THF, –78°C, 2. TMEDA/Cl2PCH2CH2PCl2, –78°C → r.t.; (b) aq acetone/1 M HCl (6a) or p-TosOH (6b),
r.t. → reflux
Scheme 2

SYNTHESIS
Papers
1744
Inclusions Causing Analytical Problems
position. Therefore, in the Experimental section the ele-
mental analyses of these imines are left out. By adding the
necessary amounts of water and/or solvent the elemental
analysis can be fitted nicely (see Ref. 12).
Although at first glance the NMR and mass spectra of the
octaaldehydes 6a and 6b looked clean, there were prob-
lems with their elemental analyses. Whereas 6a is almost
insoluble, 6b is soluble in tetrahydrofuran and dichlo-
romethane. Despite numerous recrystallizations from tet-
rahydrofuran elemental analyses of 6b reproducibly gave
H values, which were about 0.5% too high and C values,
which were about 2.5% too low, indicating some water
content. The C,H values did not improve significantly
when drying of the samples was carried out in high vacu-
um at 80°C instead of room temperature. A closer inspec-
tion revealed the presence of small amounts of tetrahydro-
furan and dichloromethane in samples of 6b which had
been treated with these solvents, by 1H NMR spectrosco-
py and chlorine elemental analysis in quantities of about
0.5 equivalents even after drying at 80°C for two days.
The tendency to include solvents has also been found for
other expanded compounds.16 It may indicate a potential
use of these branched aldehydes and imines as stationary
phases in chromatography.
Synthesis of the Octaimine Ligands 7a–h and 8a–h
Starting with the octaaldehydes 6a and 6b and commer-
cially available optically active amino alcohols, such as
(R)-alaninol, (R)-2-aminobutan-1-ol, (S)-valinol, (S)-leu-
cinol, (S)-phenylalaninol and (1S,2S)-2-amino-1-phenyl-
propan-1,3-diol or unfunctionalized amines such as (S)-1-
phenylethylamine and (R)-1-cyclohexylethylamine as
well as (8R,9R)-9-amino(9-deoxy)epicinchonine,17 six-
teen optically active expanded ligands were accessible by
Schiff base condensation (Scheme 3).
The o-phenylene bridged octaaldehyde 6b was subjected
to a thermogravimetric and differential thermal analysis at
normal pressure under nitrogen. It showed a significant
loss of several mass percent between 120 and 140°C com-
bined with an endothermic peak, which can be associated
with the loss of solvent and/or water. Samples which had
been heated to 120–140°C were shown to be free of sol-
vents. Their H analyses turned out to be correct, the C
analyses, however, still were too low. This was not unex-
pected as tetrahydrofuran has almost the same C content
as 6b. Some decomposition may have occurred during the
harsh heating procedure.
The degassed octaaldehyde was suspended (6a) or dis-
solved (6b) in trimethyl orthoformate or trimethylortho-
formate/methanol mixtures as dehydrating solvent and the
amines were added at room temperature.18 The formation
of the imines was completed in a few hours, though typi-
cally reactions were run for 18 hours. After workup in all
cases solids remained. The imine ligands could not be pu-
rified by chromatography on silica gel or alumina, be-
cause partial hydrolysis of the imine function led to the
Obviously, solvents and/or water can be trapped in the free amine and formyl groups. All attempts to recrystal-
branched structure of the aldehydes 6a and 6b. These in- lize the ligands led to finely dispersed precipitates. When
clusion phenomena were also observed for the octaimines liquid amines were used as starting materials, the remain-
to be described below. Unfortunately, these octaimines ing solid residues were dried for several hours in high vac-
cannot be heated to higher temperatures without decom- uo. The excess of solid amines was removed by adding
Scheme 3

SYNTHESIS
December 1998
1745
diethyl ether to the solid residue and careful decanting of 1640–1643 cm–1. The spectroscopic data of the new oc-
the ethereal layer. This procedure was repeated three taimine ligands 7 and 8 are summarized in the Table.
times before the ligands were dried in high vacuo.
The FD/FAB mass spectra of the two-layer octaimine
Catalytic Results
phosphanes 7 and 8 contained the molecular ions. The 1H
NMR spectra of 7 and 8 are complex, although the
branching in 3,5-position arrange all the substituents in
meta positions. However, E/Z-equilibria are possible with
regard to the imine groups. As a consequence, a broaden-
Rhodium complexes, generated in situ from [Rh(cod)Cl]2
and the given ligands were used as catalysts in the asym-
metric hydrogenation of Z-α-N-acetamidocinnamic acid
(7a–g, 8a–g)19 and the hydrosilylation of acetophenone
with diphenylsilane (7a,b,d,e,g; 8a,b,e,h).20 Also in situ
complexes were formed with Pd(acac)2 for the palladium-
catalyzed allylation of 1,5-dimethylbarbituric acid with
allyl acetate (7c–g; 8c,e–h)10 and with anhydrous NiCl2
for the nickel-catalyzed Grignard cross-coupling of 1-
phenylethylmagnesium chloride with vinyl bromide (7a–
e,g; 8a–e,g,h).21 For the catalytic procedures, the work-up
and the determination of the chemical yield and the enan-
tiomeric excess, the methods described in the literature
were used.10,19–21
1
ing of the peaks in the H NMR spectra was observed.
Furthermore, all the signals deriving from aromatic pro-
tons appeared doubled. There were two groups of signals
for the equivalent H-2's and H-6's in ortho position and
two separate signals for the H-4's in para position. The
integration showed in all cases a 1:1 ratio. The splitting of
the ortho protons (H-2' and H-6') as well as the azome-
thine protons, in principle, could arise from a diastereoto-
py within a phenyl substituent (hindered rotation) or from
a diastereotopy of the two phenyl substituents bound to
the same phosphorus atom (induced by the chiral imine
substituents). The splitting of the para protons H-4', lying
on the symmetry axis of the phenyl rings, is only in accord
with the second explanation.
The 31P NMR spectra showed singlets for all ligands,
strongly dependent on the solvent used. Thus, 7f and 8f ex-
hibited broad multiplets in CDCl3, but sharp singlets in
CD3OD. In the IR spectra the strong carbonyl peak at 1700
cm–1 of the precursors 6a and 6b disappeared and the char-
acteristic C=N peak of the imine ligands was found at
Enantioselective Hydrogenation of Z-α-N-Acetamidocin-
namic Acid: The Rh-catalyzed hydrogenation of Z-α-N-
acetamidocinnamic acid was carried out in methanol at 30
bar H2 pressure. The average reaction time was 20 hours
and the Rh:substrate ratio was 1:100. In all cases except
7h, 100% hydrogenation was achieved. However, the op-
tical inductions were low (0–6% ee).12 No difference be-
tween the labile ethylene-bridged ligands 7 and the more
rigid o-phenylene-bridged ligands 8 was recognized. Ob-
viously, the chirality located at the surface of the ligands,
Table. Properties and Spectroscopic Data for Octaimine Type Expanded Ligands 7 and 8
Product
mp (°C)
110–115
[α]λ
(c, solv.)
MS
(FAB)
31P NMRa, b 1H NMRa, b
δ (s)
δ, J (Hz)
7a
(0.43, CH2Cl2)
–50 (589 nm)
–53 (578 nm)
–62 (546 nm)
1448.2
13.1
8.41–8.07 (m, 12 H, Ar'), 7.79 (br s, 8 H, CHN), 7.47–7.22 (m, 40
H, Ph), 4.60–4.46 (m, 8 H, CHCH3), 2.49–2.24 (m, 4 H,
PCH2CH2P), 1.64–1.53 (m, 24 H, CHCH3)
7b
7c
76–80
(0.17, CH2Cl2)
–115 (589 nm)
–125 (578 nm)
–146 (546 nm)
–232 (436 nm)
1496.2
13.1
12.7
8.17 (s, 4 H, CHN), 8.15 (s, 4 H, CHN), 8.08 (s, 2 H, p-H), 8.06
(s, 2 H, p-H), 7.75 (m, 4 H, o-H), 7.44 (m, 4 H, o-H), 3.00–2.95
(m, 8 H, CHCH3), 2.26 (s, 4 H, PCH2CH2P), 1.80–0.82 (m, 112
H, CHCH3, cyclohexyl)
146–148
(0.10, CH2Cl2)
+83 (589 nm)
+85 (578 nm)
+100 (546 nm)
+190 (436 nm)
1079.5
8.31 (s, 4 H, CHN), 8.27 (s, 4 H, CHN), 8.12 (s, 2 H, p-H), 8.08
(s, 2 H, p-H), 7.87–7.84 (m, 4 H, o-H), 7.84–7.82 (m, 4 H, o-H),
3.65–3.37 (m, 24 H, CHCHaHbOH), 2.29 (m, 4 H, PCH2CH2P),
1.19 (d, 3J = 6.5 Hz, 24 H, CHCH3)
7d
7e
94–98
76–82
(0.44, MeOH)
–3.9 (589 nm)
–5.7 (578 nm)
–4.1 (546 nm)
1191.7
1304.8
12.7
13.6
8.29 (s, 4 H, CHN), 8.24 (s, 4 H, CHN), 8.17 (s, 2 H, p-H), 8.11 (s,
2 H, p-H), 7.90–7.88 (m, 4 H, o-H), 7.86–7.84 (m, 4 H, o-H), 3.71–
3.56 (m, 16 H, CHCHaHbOH), 3.25–3.16 (m, 8 H, CHCHaHbOH),
1.68–1.43 (2 m, 16 H, CHaHbCH3), 0.82 (m, 24 H, CHaHbCH3)
(0.17, MeOH)
–39 (589 nm)
–46 (578 nm)
–52 (546 nm)
8.16–7.40 (m, 20 H, CHN, Ar'), 4.00–3.90 (m, 8 H, CHaHbOH),
3.90–3.78 (m, 8 H, CHaHbOH), 3.14–2.94 (m, 8 H, CHCHaHbOH),
2.53–2.48 (m, 4 H, PCH2CH2P), 1.95–1.70 (m, 8 H, CHMe2),
1.08–0.81 (m, 48 H, CH3)

SYNTHESIS
Papers
Table (continued)
1746
Product
mp (°C)
[α]λ
MS
31P NMRa, b 1H NMRa, b
(c, solv.)
(FAB)
δ (s)
δ, J (Hz)
7f
120–125
(0.49, CH2Cl2)
–50 (589 nm)
–53 (578 nm)
–62 (546 nm)
1416.1
12.9
8.31 (s, 4 H, CHN), 8.28 (s, 4 H, CHN), 8.15 (br s, 2 H, p-H), 8.11
(br s, 2 H, p-H), 7.93–7.89 (m, 4 H, o-H), 7.89–7.85 (m, 4 H, o-
H), 3.67–3.36 (m, 24 H, CHCHaHbOH), 2.49–2.39 (m, 4 H,
PCH2CH2P), 1.61–1.20 (m, 24 H, CHaHbCHMe2), 0.91–0.76 (m,
48 H, CH3)
7g
7h
69–73
(0.43, MeOH)
–167 (589 nm)
–177 (578 nm)
–206 (546 nm)
1687.8
2826.8
13.9
13.4
8.21–7.57 (m, 20 H, CHN, Ar'), 7.31–7.00 (m, 40 H, CHaHbPh),
3.91–3.47 (m, 24 H, CHCHaHbOH), 2.98–2.76 (m, 16 H,
CHaHbPh), 2.44–2.37 (m, 4 H, PCH2CH2P)
190–195
(1.2, MeOH)
+97 (589 nm)
+102 (578 nm)
+118 (546 nm)
8.82 (d, 3J = 5.0 Hz, 8 H, H-2qui), 8.34–8.06 (m, 36 H, CHN, Ar',
H-5qui, H-8qui), 7.72–7.48 (m, 24 H, H-6qui, H-7qui, H-3qui), 5.86–
5.73 (m, 8 H, H-10nu), 5.10–5.02 (m, 16 H, H-11nu), 4.76 (br s, 8
H, H-9nu), 3.07–2.65 (m, 40 H, Hnu), 2.31–2.25 (m, 8 H, Hnu),
2.12–2.09 (br s, 4 H, PCH2CH2P), 1.60–0.81 (m, 40 H, Hnu)c
8a
8b
92–95
(0.58, CH2Cl2)
–47 (589 nm)
–49 (578 nm)
–58 (546 nm)
1495.7
1544.2
15.4
14.6
8.15–8.00 (m, 12 H, Ar´), 7.52 (br s, 8 H, CHN), 7.40–7.22 (m, 44
H, H-3–H-6, Ph), 4.42–4.31 (m, 8 H, CHCH3), 1.52–1.48 (m, 24
H, CHCH3)
110–115
(0.16, CH2Cl2)
–112 (589 nm)
–120 (578 nm)
–138 (546 nm)
8.10 (t, 4J = 1.5 Hz, 2 H, p-H), 8.06 (t, 4J = 1.5 Hz, 2 H, p-H), 8.03
(s, 4 H, CHN), 8.01 (s, 4 H, CHN), 7.49 (dt, 3JPH = 6JPH = 3.8 Hz,
4J = 1.5 Hz, 4 H, o-H), 7.44 (dt, 3JPH = 6JPH = 3.8 Hz, 4J = 1.5 Hz,
4 H, o-H), 7.34–7.30 (m, 2 H, H-4, H-5), 7.23–7.19 (m, 2 H, H-3,
H-6), 2.94–2.91 (m, 8 H, CHCH3), 1.78–0.80 (m, 112 H, CHCH3,
cyclohexyl)
8c
8d
8e
8f
170–175
82–83
(0.44, MeOH)
+73 (589 nm)
+74 (578 nm)
+85 (546 nm)
1127.4
1239.9
1351.8
1463.9
13.1
14.9
14.6
12.8
8.23 (s, 4 H, CHN), 8.21 (s, 4 H, CHN), 8.17 (s, 2 H, p-H), 8.14
(s, 2 H, p-H), 7.62–7.59 (m, 8 H, o-H), 7.41–7.38 (m, 2 H, H-4,
H-5), 7.26–7.21 (m, 2 H, H-3, H-6), 3.64–3.38 (m, 24 H,
CHCHaHbOH), 1.17 (d, 3J = 6.2 Hz, 24 H, CHCH3)
(0.57, CH2Cl2)
–2.8 (589 nm)
–3.0 (578 nm)
–3.5 (546 nm)
8.22–7.32 (m, 24 H, CHN, H-3–H-6, Ar'), 3.70–3.55 (m, 16 H,
CHCHaHbOH), 3.25–3.16 (m, 8 H, CHCHaHbOH), 1.65–1.36 (m,
16 H, CHaHbCH3), 0.78 (m, 24 H, CHaHbCH3)
68–72
(0.18, MeOH)
–40 (589 nm)
–46 (578 nm)
–51 (546 nm)
8.22–7.34 (m, 24 H, CHN, H-3–H-6, Ar'), 4.11–3.68 (m, 16 H,
CHCHaHbOH), 3.17–2.90 (m, 8 H, CHCHaHbOH), 1.99–1.74 (m,
8 H, CHMe2), 1.06–0.80 (m, 48 H, CH3)
105–110
(0.2, MeOH)
–46 (589 nm)
–51 (578 nm)
–58 (546 nm)
–111 (436 nm)
8.23–8.19 (m, 12 H, CHN, p-H), 7.64–7.59 (m, 8 H, o-H), 7.43–
7.40 (m, 2 H, H-4, H-5), 7.33–7.30 (m, 2 H, H-3, H-6), 3.64–3.47
(m, 16 H, CHCHaHbOH), 3.40–3.34 (m, 8 H, CHCHaHbOH),
1.58–1.44 (m, 16 H, CHaHbCHMe2), 1.36Ð1.28 (m, 8H,
CHaHb(-HMe2,), 0.90Ð0.84 (m, 48 H, CH3)
8g
83 (dec.)
82 (dec.)
(2.5, CH2Cl2)
–34 (589 nm)
–36 (578 nm)
–42 (546 nm)
1736.8
1864.2
14.9
13.3
8.21–7.60 (m, 24 H, CHN, H-3–H-6, Ar'), 7.20–7.07 (m, 40 H,
CHaHbPh), 3.88–3.40 (m, 24 H, CHCHaHbOH), 2.95–2.74 (m, 16
H, CHaHbPh)
8h
(0.17, CH2Cl2)
+70 (589 nm)
+72 (578 nm)
+82 (546 nm)
8.25–7.55 (m, 24 H, CHN, H-3–H-6, Ar'), 7.39–7.25 (m, 40 H,
CHOHPh), 4.84–4.65 (m, 8 H, CHOHPh), 3.74–3.63 (m, 16 H,
CHCHaHbOH), 3.28–3.23 (m, 8 H, CHCHaHbOH)
a
Solvents for 31P and 1H NMR spectra: CDCl3 for 7a, b, d, e, g, h, 8a–e, g; CD3OD for 7c, f, 8f, h.
The protons on the substituted four aromatic rings are indicated as Ar' for all 12 protons. Wherever assignments are possible they are referred
specifically as o- and p-protons with reference to the phosphorus atom. Phenyl substituents on R containing 5 protons are abbreviated as Ph.
qui = quinoline, nu = quinuclidine.
b
c

SYNTHESIS
December 1998
1747
in a beaker. After cooling in an ice-bath a microcrystalline suspension
was obtained, to which a 2.5 M NaNO2 solution (84 mL, 210 mmol)
was added under vigorous stirring. The resulting yellow diazonium
compound was transferred to a cooled dropping funnel (–5°C) and
added to a cooled solution (ice bath) of CuBr (36.4 g, 0.25 mmol) in
concd HBr (100 mL) under vigorous stirring. Excessive foaming was
prevented by adding some drops of n-butanol as defoaming agent
when necessary. When the addition was completed, the solution was
heated on a steam bath, until no further nitrogen emission was ob-
served (about 1 h). After cooling, the acidic phase was extracted three
times with Et2O (250 mL). The ethereal layers were washed with H2O
(600 mL) and the H2O layers extracted with Et2O. The solvent was
removed in vacuo and the yellowish crude product was dissolved in
CH2Cl2 and passed through a pad of silica gel (10 × 6 cm). After re-
moval of the solvent in vacuo 1 was obtained as a colorless solid
(43.9 g, 161 mmol, 84%), mp 88–89°C (Lit.14 mp 88–89°C).
1H NMR (80 MHz, CDCl3): δ = 8.6 (m, 1 H, H-2), 8.4 (m, 2 H, H-4,
H-6), 4.0 (s, 6 H, OCH3).
including the optional interactions between the hydroxy
groups in the ligands and the substrate, did not lead to sig-
nificant optical inductions.
Enantioselective Hydrosilylation of Acetophenone with
Diphenylsilane: In the hydrosilylation of acetophenone
with diphenylsilane, the catalysts were generated in situ in
acetophenone [when 7d was used, THF (2 mL) was added
to form the in situ catalyst] and the Rh:substrate ratio was
1:200. All experiments were carried out under argon. The
average reaction time was 66 hours (conversion checked
by 1H NMR). In all cases, the ethylene-bridged ligands 7
gave slightly higher optical inductions [7a: 2.8% ee (R);
7b: 10.3% ee (S); 7e: 18.1% ee (S)] than the analogous
more rigid o-phenylene-bridged ligands 8 [8a: 2.4% ee
(R); 8b: 2.6% ee (R); 8e: 0% ee].
IR (KBr): ν = 3090 (ar. C–H), 2970 (aliph. C–H), 1730 (C=O), 1600,
Enantioselective Allylation of 1,5-Dimethylbarbituric
Acid with Allylacetate: A detailed description of the re-
sults of octaimine ligands of type 7 and 8 is given in Ref.
10b. The newly synthesized ligands 7c–g and 8c,e–h in-
duced enantioselectivities in the range of 5–11% ee. The
average reaction time was 66 hours and the average chem-
ical conversion about 70%.
1580 cm–1 (C=C).
3,5-Bis(hydroxymethyl)bromobenzene (2):
A solution of diester 1 (20.6 g, 75.4 mmol) in anhyd THF (80 ml) was
added dropwise at –10°C to a stirred suspension of LiAlH4 (3.5 g,
92 mmol) in anhyd THF (200 mL). After the addition was complete,
the mixture was boiled under reflux for 30 min. After cooling to r.t.,
excess LiAlH4 was decomposed by dropwise addition of a satd aq
Na2SO4 solution (30 mL). The ethereal layer was decanted and the
precipitate was washed several times with Et2O. The combined ethe-
real solutions were washed with brine (2 × 50 mL), dried (Na2SO4)
and concentrated to give the colorless solid 2 (16.04 g, 73.9 mmol,
98%); mp 90–91°C (Lit.15 mp 90–91°C).
Enantioselective Grignard Cross-Coupling of 1-Phenyl-
ethylmagnesium Chloride with Vinyl Bromide: Only race-
mates and low chemical conversions were obtained with
in situ generated Ni-catalysts of octaimine type ligands.12
1H NMR (250 MHz, acetone-d6): δ = 7.41 (m, 2 H, H-4, H-6), 7.31
(m, 1 H, H-2), 4.37 (d, 3J = 5.6 Hz, 4 H, CH2OH), 4.36 (t, 3J = 5.6 Hz,
2 H, OH).
All manipulations involving phosphanes were performed under exclu-
sion of air using standard Schlenk techniques under purified N2. If orga-
nometallic reagents were involved, H2O was also excluded. Solvents
were dried and degassed according to standard procedures22 and stored
under N2. H2O and solvents for chromatography were degassed by bub-
bling N2 through the fluids for at least 8 h. Chromatographic materials
[silica gel 60 (65–200 µm), Merck], and alumina 90 (neutral, activity II–
III, Merck) were saturated with N2. TLC was performed on Merck silica
gel 60 F254 plates (visualisation with UV light and KMnO4 solution).
IR (KBr): ν = 3500–3000 (OH and ar. C–H); 2950, 2920, 2880, 2840
(aliph. C–H); 1600, 1580 cm–1 (ar. C=C).
5-Bromoisophthalaldehyde (3):
To a solution of pyridinium chlorochromate (48.0 g, 223 mmol) in
CH2Cl2 (250 mL) was added 2 (15.0 g, 69 mmol) and refluxed for 4 h.
After cooling to r.t., the organic phase was decanted and the black oily
residue was treated twice with hot Et2O (100 mL). The combined
ethereal layers were reduced in vacuo to give a greenish black solu-
tion, which was passed through a silica gel column (6 × 10 cm) with
Et2O as eluent. After removal of the solvent 11.92 g (56 mmol, 81%)
of the colorless, fluffy solid 3 remained; mp 125°C (Lit.15 mp
124 °C).
Melting points were determined using SMP-20 (Büchi) and are not
corrected. Vibrational spectra were recorded on a Beckman spectro-
meter IR 4240 or a Bio-Rad FT-IR FTS 155 as films or as KBr pellets.
For MS, the MAT 311 A (EI) and the MAT 95 (FD) apparatus (both
Finnigan) were used. The intensities are relative to the basic peak (I =
100%), possible interpretations are given within brackets. Optical ro-
tations were measured with a Perkin-Elmer model 241 polarimeter on
the specified solutions in 1 dm cells at r.t. Elemental analyses were
performed by the Mikroanalytisches Labor of the Universität Regens-
burg. 1H NMR spectra were recorded using the following spectrome-
ters: AW-80 (80 MHz, Bruker), AC 250 (250 MHz, Bruker) and ARX
400 (400 MHz, Bruker). The chemical shifts are given in units of the
δ scale relative to internal TMS. Data are reported as follows: chem-
ical shift, multiplicity, coupling constants in Hertz, integration and
assignment. For the 31P NMR spectra (1H-decoupled), the ARX 400
(162 MHz), external standard 85% H3PO4, was used.
1H NMR (80 MHz, CDCl3): δ = 10.0 (s, 2 H, CHO), 8.2 (m, 3 H,
ArH).
IR (KBr): ν = 3080 (ar. C–H), 2980, 2965, 2860 (aliph. C–H), 1700
(C=O), 1600, 1580 cm–1 (C=C).
3,5-Bis(dimethoxymethyl)bromobenzene (4):
To a solution of 3 (46.0 g, 216 mmol) in MeOH (500 mL) were added
trimethyl orthoformate (100 mL) and p-TosOH (~20 mg). After re-
fluxing this mixture for 2 h and cooling down to r.t., K2CO3 (0.3 g)
was added and the solvent was removed. The viscous residue was
distilled in vacuo yielding 61.7 g (202 mmol, 93%) of the colorless oil
4; bp 111°C/10–2 Torr.
The following compounds were synthesized according to the litera-
ture: 1,2-bis(dichlorophosphanyl)ethylene,23 o-bis(dichlorophosphan-
yl)-benzene,24 (8R,9R)-(+)-9-amino-9-deoxyepicinchonine.17 BuLi
was purchased from Aldrich.
1H NMR (80 MHz, CDCl3): δ = 7.6 (br s, 2 H, H-4, H-6), 7.5 (br s, 1
H, H-2), 5.4 (s, 2 H, OCHO), 3.30 (s, 12 H, OCH3).
IR (film): ν = 3070 (ar. C–H), 2980, 2920, 2880 (aliph. C–H), 2820
(OCH3), 1570 cm–1 (C=C).
Dimethyl 5-Bromoisophthalate (1):
C12H17BrO4 calc.
(305.2) found
C
47.23
47.17
H
5.61
5.61
Br
26.18
26.07
Commercial dimethyl 5-aminoisophthalate (40.0 g, 191 mmol) was
dissolved at about 60°C in half concentrated HBr (180 mL) contained

SYNTHESIS
Papers
1748
cooling to r.t., the solvents were removed in vacuo. The remaining
residue was dissolved in CH2Cl2 and extracted with H2O (2 × 3 mL).
The organic layer was passed through a short pad of silica gel (1
× 3 cm) and Na2SO4 (2 × 3 cm). The pad was washed with an addi-
tional amount of CH2Cl2 (50 mL) and the solvents were removed. The
remaining yellowish solid was recrystallized from THF/toluene (1:1)
to give 4.00 g (6.0 mmol, 70%) of the product 6b; mp 250°C.
1H NMR (400 MHz, CDCl3): δ = 10.00 (s, 8 H, CHO), 8.30 (t, 4J =
1.5 Hz, 4 H, p-H), 7.91 (dt, 3JPH = 6JPH = 3.4 Hz, 4J = 1.5 Hz, 8 H, o-
H), 7.49 (dd, 3J = 5.7 Hz, 4J = 3.3 Hz, 2 H, H-4, H-5), 7.12 (ddt, 3JPH
= 4JPH = 4.0 Hz, 3J = 5.7 Hz, 4J = 3.3 Hz, 2 H, H-3, H-6).
13C NMR (100.6 MHz, CDCl3): δ = 190.2 (s, C=O), 140.5 (t, J =
11.5 Hz), 138.8 (t, J = 10.4 Hz), 138.5 (t, J = 5.2 Hz), 137.3 (t, J = 2.9
Hz), 134,6 (t, J = 3.4 Hz), 131.9 (s), 131.6 (s).
1,2-Bis{di[3',5'-bis(dimethoxymethyl)phenyl]phosphanyl}ethane
(5a):
To a cooled solution (–78°C) of 4 (18.32 g, 60 mmol) in anhyd THF
(300 mL) were added dropwise BuLi (37.5 mL ,60 mmol, 1.6 M in
hexane). After stirring the solution for 30 min at this temperature,
TMEDA (9.0 mL, 60 mmol) and Cl2PCH2CH2PCl2 (3.48 g, 2.26 mL,
15 mmol) were added. The solution was allowed to warm up to r.t.
within 12 h. The solvent was completely removed in vacuo and the
residue was dissolved in Et2O (200 mL). H2O was added (20 mL) and
the layers were separated. The ethereal layer was dried (Na2SO4),
then passed through a silica gel pad (1 × 3 cm). After removal of the
solvent, a yellowish oily residue remained, which was recrystallized
from CH2Cl2/MeOH to give 10.5 g (10.6 mmol, 71%) of the colorless
solid 5a; mp 76°C.
31P NMR (162 MHz, CDCl3): δ = –13.1 (s).
1H NMR (400 MHz, CDCl3): δ = 7.47–7.38 (m, 12 H, ArH), 5.32 (s,
IR (KBr): ν = 3030 (ar. C–H), 2930, 2905, 2820 (aliph. C–H), 2710
(CHO), 1700 (C=O), 1580 (C=C), 1450, 1425 (P–ar.), 1410, 1360,
1235, 1130, 950, 870 cm–1.
8 H, OCHO), 3.226 and 3.233 (2 s, 48 H, OCH3), 2.10 (t, JPH
4.3 Hz, 4 H, PCH2CH2P).
=
31P NMR (162 MHz, CDCl3): δ = –11.3 (s).
MS (FD, acetone): m/z = 670.2 (M+).
IR (KBr): ν = 3070 (ar. C–H), 2980, 2900 (aliph. C–H), 2850 (OCH3),
1600, 1580 cm–1 (C=C).
C38H24O8P2
(670.6)
calc.
found
C
68.07
65.24
H
3.61
3.87
MS (FD, acetone): m/z = 991.7 (MH+).
C50H72O16P2
(991.1)
calc.
found
C
60.59
60.30
H
7.32
7.22
Octaimine Type Expanded Ligands 7 and 8; General Procedure:
Degassed trimethyl orthoformate (50 mL) or a MeOH/trimethyl
orthoformate mixture (1:1, 50 mL) was added to the octaaldehydes 6a
and 6b, respectively, under an inert gas atmosphere to give a slightly
yellow solution using 6b or a yellowish suspension using the almost
insoluble octaaldehyde 6a. Liquid amines were added in a molar ratio
of up to 12:1 (50% excess for each formyl unit) at r.t. via a syringe,
solid amines were dissolved in 10% excess of MeOH and added drop-
wise. After stirring at r.t. for 20 h, the solvents were removed in vac-
uo, at the end on a water bath. When liquid amines were used as start-
ing materials, the remaining solid residue was dried for several hours
in high vacuo. The excess of solid amines was removed by adding
Et2O to the solid residue and careful decanting of the ethereal layer.
This procedure was repeated three times before the ligands were dried
in high vacuo.
1,2-Bis{di[3',5'-bis(dimethoxymethyl)phenyl]phosphanyl}ben-
zene (5b):
According to the procedure described above, a solution of 4 (12.21 g,
40 mmol) in THF (200 mL) was treated with BuLi (25 mL, 40 mmol,
1.6 M in hexane) at –78°C and reacted with 1,2-Cl2PC6H4PCl2
(2.80 g, 10.0 mmol) to give 8.83 g (8.5 mmol, 85%) of the yellow
viscous oil 5b, which could not be crystallized. It was purified by
chromatography on silica gel using Et2O as a solvent.
1H NMR (400 MHz, CDCl3): δ = 7.48 (t, 4J = 1.5 Hz, 4 H, H-4'), 7.24–
3
4
7.19 (m, JPH = 3.8 Hz, J = 1.5 Hz, 10 H, H-2', H-6', H-4, H-5),
7.00 (m, 3JPH = 4.8 Hz, 3J = 5.3 Hz, 4J = 1.9 Hz, 5J = 0.4 Hz, 2 H, H-
3, H-6), 5.26 (s, 8 H, OCHO), 3.23 (s, 24 H, OCH3), 3.21 (s, 24 H,
OCH3).
31P NMR (162 MHz, CDCl3): δ = –12.4 (s).
MS (FD, acetone): m/z = 1038.4 (M+).
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-1''-phenylethylamine)-
phenyl]phosphanyl}ethane (7a): According to the General Procedure,
6a (0.40 g, 0.64 mmol) and (S)-(-)-1-phenylethylamine (1.00 mL,
8.0 mmol) afforded 0.87 g (0.60 mmol, 93%) of 7a; mp 110–115°C.
C54H72O16P2
(1039.1)
calc.
found
C
62.42
61.04
H
6.98
6.59
1,2-Bis[di(3',5'-diformylphenyl)phosphanyl]ethane (6a):
The acetal phosphane 5a (10.5 g, 10.6 mmol) was dissolved in aq
degassed acetone (100 mL) to make a 0.1 M solution, which was acid-
ified with a few drops of 1 N HCl. The clear yellowish solution was
heated under reflux. Though a white solid precipitated after 2 to 3 h,
it was necessary to reflux the suspension for an additional 15 h to
deprotect all acetal functions. After cooling to r.t., the remaining off-
white residue was filtered and washed successively with acetone,
Et2O and CH2Cl2. After drying in vacuo 6.26 g (10.1 mmol, 95%) of
the fluffy solid 6a remained; mp 170°C (dec.).
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(R)-1''-cyclohexylethy-
lamine)phenyl]phosphanyl}ethane (7b): According to the General
Procedure, 6a (0.54 g, 0.87 mmol) and (R)-(–)-1-cyclohexyl-
ethylamine (1.5 mL, 10.2 mmol) yielded 1.17 g (0.78 mmol, 90%) of
7b; mp 76–80°C.
(+)-1,2-Bis{bis[3',5'-bis(N-methyliden-(R)-alaninol)phenyl]phosph-
anyl}ethane (7c): According to the General Procedure, 6a (0.51 g,
0.82 mmol) and (R)-(-)-alaninol (0.55 ml, 7.05 mmol) gave 0.89 g
(0.76 mmol, 93%) of 7c; mp 146–148°C.
1H NMR (400 MHz, CDCl3): δ = 10.02 (s, 8 H, CHO), 8.33 (t, 4J =
1.5 Hz, 4 H, p-H), 8.17 (dt, 3JPH = 6JPH = 3.2 Hz, 4J = 1.5 Hz, 8 H, o-
H), 2.50 (t, 4 H, PCH2CH2P).
(–)-1,2-Bis{bis[3',5'-bis(N-methyliden-(R)-2''-aminobutan-1''-
ol)phenyl]phosphanyl}ethane (7d): According to the General Proce-
dure, 6a (0.39 g, 0.63 mmol) and (R)-(-)-2-aminobutan-1-ol
(0.47 mL, 5.01 mmol) yielded 0.69 g (0.58 mmol, 92%) of 7d; mp
94–98°C.
31P NMR (162 MHz, CDCl3): δ = –12.5 (s).
IR (KBr): ν = 3060 (ar. C–H); 2960, 2920, 2850 (al. C–H); 2765
(CHO); 1700 (C=O); 1590 (C=C); 1460; 1425 (P-ar.); 1380; 1140;
1125; 885 cm–1.
MS (FD, DMSO): m/z = 622.1 (M+).
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-valinol)phenyl]phospha-
nyl}ethane (7e): According to the General Procedure, 6a (0.44 g,
0.70 mmol) and (S)-(+)-valinol (0.58 g, 5.65 mmol) gave 0.88 g
(0.68 mmol, 97%) of 7e; mp 76–82°C.
C34H24O8P2
(622.5)
calc.
found
C
65.60
62.94
H
3.89
4.36
1,2-Bis[di(3',5'-diformylphenyl)phosphanyl]benzene (6b):
Analogous to the description above compound 5b was deprotected.
The acetone solution was acidified with p-TosOH (~20 mg). After
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-leucinol)phenyl]phos-
phanyl}ethane (7f): According to the General Procedure, 6a (0.54 g,

SYNTHESIS
December 1998
1749
0.87 mmol) and (S)-(+)-leucinol (0.97 g, 8.20 mmol) afforded 1.20 g
(0.85 mmol, 98%) of 7f; mp 120–125°C.
We thank the Bayerische Forschungsverband Katalyse (FORKAT)
and the Fonds der Chemischen Industrie for support of this work.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-phenylalaninol)phenyl]-
phosphanyl}ethane (7g): According to the General Procedure, 6a
(0.54 g, 0.87 mmol) and (S)-(–)-phenylalaninol (1.07 g, 7.07 mmol)
yielded 1.21 g (0.72, mmol, 82%) of 7g; mp 69–73°C.
(1) Part 122. Brunner, H.; Haßler, B. Z. Naturforsch. 1998, 53b,
126.
(2) (a) Ojima, I. Catalytic Asymmetric Synthesis; VCH: New York,
1993.
(b) Brunner, H.; Zettlmeier, W. Handbook of Enantioselective
Catalysis; VCH: Weinheim, 1993.
(3) Kagan, H.B.; Dang, T.P. J. Am. Chem. Soc. 1972, 94, 6429.
(4) Fryzuk, M.D.; Bosnich, B. J. Am. Chem. Soc. 1978, 100, 5491.
(5) Hayashi, T.; Yamamoto, K.; Kumada, M. Tetrahedron Lett.
1974, 4405.
(+)-1,2-Bis{bis[3',5'-bis(N-methyliden-(8R,9R)-9-amino-9-deoxy-
epicinchonine)phenyl]phosphanyl}ethane (7h): According to the
General Procedure, 6a (0.50 g, 0.80 mmol) and (8R,9R)-(+)-9-ami-
no(9-deoxy)epicinchonine (2.10 g, 7.16 mmol) yielded 2.15 g
(0.76 mmol, 95%) of 7h; mp 190–195°C.
(6) Schmid, R.; Cereghetti, M.; Heiser, B.; Schönholzer, P.; Han-
sen, H.-J. Helv. Chim. Acta 1988, 71, 897.
(7) Tani, K.; Yamagata, T.; Akutagawa, S.; Kumobayahi, H.; Take-
tomi, T.; Takaya, H.; Miyashita. A.; Noyori, R.; Otsuka, S. J.
Am. Chem. Soc. 1984, 106, 5208.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-1''-phenylethylamine)-
phenyl]phosphanyl}benzene (8a): According to the General Proce-
dure, 6b (1.00 g, 1.49 mmol) and (S)-(-)-1-phenylethylamine (1.83 mL,
14.3 mmol) gave 1.75 g (1.17 mmol, 79%) of 8a; mp 92–95°C.
(8) Brunner, H.; Pieronczyk, W. Angew. Chem. 1979, 91, 655; An-
gew. Chem., Int. Ed. Engl. 1979, 18, 620.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(R)-1''-cyclohexylethy-
lamine)phenyl]phosphanyl}benzene (8b): According to the General
Procedure, 6b (0.58 g, 0.86 mmol) and (R)-(–)-1-cyclohexyl-
ethylamine (1.03 mL, 7.0 mmol) afforded 1.10 g (0.71 mmol, 83%)
of 8b; mp 110–115°C.
(9) Brunner, H. J. Organomet. Chem. 1995, 500, 39.
(10) (a) Brunner, H.; Fürst, J. Inorg. Chim. Acta 1994, 220, 63.
(b) Brunner, H.; Reißer, W. Eur. J. Org. Chem. 1998, in press.
(11) (a) Ward, J.; Börner, A.; Kagan, H.B. Tetrahedron: Asymmetry
1992, 3, 849.
(+)-1,2-Bis{bis[3',5'-bis(N-methyliden-(R)-alaninol)phenyl]phosph-
anyl}benzene (8c): According to the General Procedure, 6b (0.75 g,
1.12 mmol) and (R)-(-)-alaninol (0.72 mL, 9.23 mmol) yielded 1.15 g
(1.02 mmol, 91%) of 8c; mp 170–175°C.
(b) Börner, A.; Kless, A.; Holz, J.; Baumannn, W.; Tillack, A.;
Kadyrov, R. J. Organomet. Chem. 1995, 490, 213.
(c) Börner, A.; Kless, A.; Kempe, R.; Heller, D.; Holz, J.; Bau-
mann, W. Chem.Ber. 1995, 128, 767.
(12) Janura, M. Dissertation, University of Regensburg, Germany,
1997.
(13) Crandall, E.W.; Harris, L. Org. Prep. Proced. Intl. 1969, 1,
147.
(14) Sherrod, S.A.; da Costa, R.L.; Barnes, R.A.; Boeckelheide, V.
J. Am. Chem. Soc. 1974, 96, 1575.
(–)-1,2-Bis{bis[3',5'-bis(N-methyliden-(R)-2''-aminobutan-1''-
ol)phenyl]phosphanyl}benzene (8d): According to the General Proce-
dure, 6b (0.71 g, 1.06 mmol) and (R)-(–)-2-aminobutan-1-ol
(1.88 mL, 20.0 mmol) yielded 1.29 g (1.04 mmol, 98%) of 8d; mp
82–83°C.
(15) Netzke, K.; Snatzke, G. Chem. Ber. 1989, 122, 1365.
(16) Brunner, H.; Altmann, S. Chem. Ber. 1994, 127, 2285.
(17) Brunner, H.; Bügler, J.; Nuber, B. Tetrahedron: Asymmetry
1995, 6, 1699.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-valinol)phenyl]phospha-
nyl}benzene (8e): According to the General Procedure, 6b (0.50 g,
0.75 mmol) and (S)-(+)-valinol (0.63 g, 6.1 mmol) yielded 0.98 g
(0.72 mmol, 97%) of 8e; mp 68–72°C.
(18) Look, G.C.; Murphy, M.M.; Campbell, D.A.; Gallop, M.A.
Tetrahedron Lett. 1995, 36, 2937.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-leucinol)phenyl]phos-
phanyl}benzene (8f): According to the General Procedure, 6b (0.50 g,
0.74 mmol) and (S)-(+)-leucinol (0.71 g, 6.06 mmol) gave 1.07 g
(0.73 mmol, 98%) of 8f; mp 105–110°C.
(19) Brunner, H.; Pieronczyk, W.; Schönhammer, B.; Streng, K.;
Bernal, I.; Korp, J. Chem. Ber. 1981, 114, 1137.
(20) (a) Brunner, H.; Obermann, U. Chem. Ber. 1989, 122, 499.
(b) Brunner, H.; Kürzinger, A. J. Organomet. Chem. 1988, 346,
413.
(21) Brunner, H.; Lautenschlager, H.-J.; König, W.A.; Krepper, R.
Chem. Ber. 1990, 123, 847.
(22) Synthetic Methods of Organometallic and Inorganic Chemistry
(Herrmann/Brauer), Herrmann, W.A.; Salzer, A., Eds.; Thie-
me: Stuttgart, Vol. I, 1996.
(–)-1,2-Bis{bis[3',5'-bis(N-methylidene-(S)-phenylalaninol)phenyl]-
phosphanyl}benzene (8g): According to the General Procedure, 6b
(1.00 g, 1.49 mmol) and (S)-(–)-phenylalaninol (2.00 g, 13.2 mmol)
yielded 2.44 g (1.41 mmol, 94%) of 8g; mp 83°C (dec.).
(+)-1,2-Bis{bis[3',5'-bis(N-methyliden-(1S,2S)-2-amino-1-phenyl-
propane-1,3-diol)phenyl]phosphanyl}benzene (8h): According to the
General Procedure, 6b (0.53 g 0.80 mmol) and (1S,2S)-(+)-2-amino-
1-phenylpropane-1,3-diol (1.09 g, 6.5 mmol) yielded 1.44 g
(0.77 mmol, 98%) of 8h; mp 82°C (dec.).
(23) Burt, R.J.; Chatt, J.; Hussain, W. J. Organomet. Chem. 1979,
182, 203.
(24) (a) Kyba, E.P.; Liu, S.-T.; Harris, R.L. Organometallics 1983,
2, 1877.
(b) Kyba, E.P.; Kerby, M.C.; Rines, S.P. Organometallics 1986,
5, 1189.