Asymmetric Catalysis. Part 149 [1]. Synthesis of New Chiral Tridentate Ligands for Enantioselective Catalysis

Article abstract of DOI:10.1007/s00706-003-0039-8

The synthesis of new chiral tridentate ligands is reported which coordinate transition metals in a meridional way. The ligands contain a pyridine ring, an oxazoline ring, and a strongly coordinating diphenylphosphanyl group. The methionine-derived ligand

Full text of DOI:10.1007/s00706-003-0039-8

Monatshefte f€ur Chemie 134, 1253–1269 (2003)
DOI 10.1007/s00706-003-0039-8
Asymmetric Catalysis. Part 149 [1].
Synthesis of New Chiral Tridentate
Ligands for Enantioselective Catalysis
ꢀ
Henri Brunner , Christian Zettler, and Manfred Zabely
€
Institut f€ur Anorganische Chemie, Universitat Regensburg, D-93040 Regensburg, Germany
Received March 4, 2003; accepted March 4, 2003
Published online August 18, 2003 # Springer-Verlag 2003
Summary. The synthesis of new chiral tridentate ligands is reported which coordinate transition metals
in a meridional way. The ligands contain a pyridine ring, an oxazoline ring, and a strongly coordinating
diphenylphosphanyl group. The methionine-derived ligand forms a copper complex, which has been
studied by X-ray crystallography. The new ligands were tested in models of enantioselective catalyses,
such as hydrogenation of ketopantolactone, hydrosilylation of acetophenone, and transfer hydrogena-
tion of acetophenone.
Keywords. Tridentate ligands; Chirality; Enantioselective catalysis; X-ray structure analysis.
Introduction
In the beginning of enantioselective catalysis with transition metal compounds
chiral monodentate ligands played a crucial role. Soon, however, chiral bidentate
ligands took over [2]. Chiral tridentate ligands, which may coordinate the metal
atom of a catalyst in a meridional or a facial way, have not been used exten-
sively in enantioselective catalysis. In the present paper we describe series of
chiral tridentate ligands which contain a pyridine ring, an oxazoline ring, ren-
dered chiral by way of its aminoalcohol constituent, and a strongly coordinating
diphenylphosphanyl group or a methylsulfanyl group [3]. The new ligands were
tested in different models of enantioselective catalysis including hydrogenations,
for which the diphenylphosphanyl group proved essential to activate molecular
hydrogen [3].
ꢀ
Corresponding author. E-mail: henri.brunner@chemie.uni-regensburg.de
y
X-ray structure analyses

1254
H. Brunner et al.
Results and Discussion
Synthesis of Pyridine-Oxazoline Ligands with a CH2P(O)Ph2
Group as a Pyridine Substituent
To synthesize pyridine derivatives with different substituents in 2,6-position, one of
the two hydroxy groups of commercially available 2,6-(dihydroxymethyl)pyridine
(1) had to be protected as a silyl ether. This was achieved by reaction with NaH
t
followed by addition of Ph2 BuSiCl to give the monosilyl ether 2 in 77% yield [4].
The free hydroxy group in 2 was transformed into the tosylate leaving group in 3 with
TosCl [5]. In the reaction with LiPPh2 tosylate was replaced by diphenylphosphide.
Subsequent oxidation with air gave the phosphanoyl derivative 4. Deprotection of the
silyl ether group in 5 was accomplished with Bu4NF [6]. The free hydroxy group in 5
was oxidised to the aldehyde group in 6 by a Swern oxidation [7, 8]. Aldehyde 6 was
converted into oxime 7 with hydroxylamine [9]. Addition of 1,10-carbonyldiimidazol
to 7 afforded the nitrile 8 [10], which was transformed into the carbomethoxyimidate
9 with NaOMe [11]. The precursors 1–9 are shown in Scheme 1.
The oxazoline rings in compounds 10–13 were built up in the reaction of 9 with
the 2-aminoalcohols (R)-2-aminobutanol, (S)-valinol, (S)-phenylalaninol, and (S)-
phenylglycinol (Scheme 2) [12]. Unfortunately, the phosphanoyl groups in these
compounds could not be reduced to the phosphanyl functionality with HSiCl3, which
normally is used for such reductions [13, 14]. In these reactions diphenylphosphinic
acid was cleaved off, characterised by 31P NMR and X-ray crystallography [3].
Scheme 1

New Chiral Tridentate Ligands
1255
Scheme 2
Synthesis of Pyridine-Oxazoline Ligands with a CH2PPh2
Group as a Pyridine Substituent
As the reduction of the phosphanoyl group in compounds 10–13 failed, oxidation
of the phosphorus atom in the diphenylphosphanyl moiety must be prevented. A
suitable protecting group for phosphorus in phosphanes is BH3. By addition of
BH3ꢁTHF after the reaction of tosylate 3 with LiPPh2, the phosphorus-protected
product 14 was formed (Scheme 1) [15, 16]. A crystal structure proved the coordina-
tion of the BH3 group to the phosphorus atom (Fig. 1). The following steps implying
the intermediates 14–19 (Scheme 1) and the oxazoline derivatives 20–23 (Scheme 2)
are analogous to those described above for the synthesis of 4–9 and 10–13. The
protecting BH3 groups in 20–23 were removed by stirring with Et2NH [17] yielding
the target ligands 24–27 (Scheme 3), air-sensitive compounds even as solids.
The results of the catalytic reactions with ligands 24–27 did not meet the
expectations (see below). An explanation could be the dissociation of the oxazoline
nitrogen from the metal atom. Thus, the chiral centre would be too far away from
the reaction centre to appreciably influence the formation of the product config-
uration. To avoid this dissociation, we tried to synthesize a pyridine-oxazoline
ligand having the strongly coordinating diphenylphosphanyl group as a substituent
directly on the oxazoline ring.
Synthesis of a Pyridine-Oxazoline Ligand with a CH2PPh2 Group
as an Oxazoline Substituent
The synthesis of target ligands of type 32 started from the methyl ester of (S)-
serine. Its derivatisation by introducing a Boc group at the nitrogen atom and by
forming an oxazolidine ring on reaction with 2,2-dimethoxypropane as well as by

1256
H. Brunner et al.
ꢂ
˚
Fig. 1. View of 14 (H atoms omitted for clarity); selected bond lengths (A) and angles ( ): P1–C7
1.8303(18), P1–B1 1.914(2), Si1–O1 1.6482(12); C7–P1–C24 104.40(7), C7–P1–B1 112.25(9)
Scheme 3
reduction of the ester group to a primary alcoholic group and by transformation
into the tosylate 28 has been reported [18]. Reaction of tosylate 28 with LiPPh2
followed by addition of BH3ꢁTHF and HCl cleavage of the oxazolidine ring in 29
has been mentioned in literature [19]. However, 29 and 30 (Scheme 4) have not
been characterised. Therefore, they are included in the Experimental Part. The ring
cleavage in 29 was achieved by stirring with MeOH saturated with HCl for 5 min
[20]. Longer reaction times led to loss of the borane protecting group. The 2-
aminoalcohol 30 was converted to the oxazoline 31 with pyridine-2-carbomethoxy-
imidate. The target ligand 32 (Scheme 4) was obtained by deprotection of the
phosphorus with Et2NH as described above.

New Chiral Tridentate Ligands
1257
Scheme 4
Scheme 5
Synthesis of the CuCl2 Complex of a Pyridine-Oxazoline
Ligand with a CH2CH2SMe Substituent
The tridentate ligands 24–27 and 32 should coordinate to a metal centre in a
meridional way. With the carbon chain of the oxazoline substituent being longer,
the ligand would have the possibility to lift its ‘‘arm’’ and coordinate facially to a
metal centre. We tested this idea with ligand 33 synthesised starting from L-
methionine via the aminoalcohol (S)-methioninol [12]. In methanol CuCl2 and
33 gave crystals of the complex 34 (Scheme 5) suitable for X-ray analysis
(Fig. 2). The coordination geometry at the copper atom is square pyramidal. The
two chlorine atoms remain bonded. Ligand 33 coordinates meridionally to the
copper atom.
Catalytic Hydrogenation of Ketopantolactone
In the enantioselective hydrogenation of ketopantolactone the procatalyst
[Rh(cod)Cl]2 was dissolved in 7 cm3 of toluene or THF. The chiral ligand was
dissolved in 1 cm3 of the solvent (1.1-fold excess of ligand) and added. The colour
changed from yellow to dark violet indicating complexation. After stirring the
solution at room temperature for 30 min the reaction was started by addition
of 200 equivalents of ketopantolactone. The hydrogenation was carried out at a
hydrogen pressure of 50 bar and 50ꢂC under careful exclusion of air [21, 22].

1258
H. Brunner et al.
ꢂ
˚
Fig. 2. View of 34 (H atoms omitted for clarity); selected bond lengths (A) and angles ( ): Cu1–S1
2.4085(7), Cu1–Cl1 2.4353(6), Cu1–N2 1.9700(17); N2–Cu1–S1 90.76(5), N1–Cu1–Cl2 94.01(5),
Cl1–Cu1–Cl2 102.67(2)
Table 1. Enantioselective hydrogenation of ketopantolactone with in situ catalysts [Rh(cod)Cl]2=24–
27 and 32a
Procatalyst
Ligand
Solvent
Yield %b
ee %
Config.
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
24
25
26
27
32
32
THF
THF
THF
THF
THF
toluene
18.2
3.1
4.1
<1.0
1.2
(S)
(R)
(R)
(R)
(S)
(S)
14.1
24.8
40.4
36.5
1.2
1.8
17.1
a
Conditions: Rh:ligand:substrate ¼ 1:1.1:200, p ¼ 50 bar, T ¼ 50ꢂC, t ¼ 40 h; work-up and enantio-
b
mer analysis see Ref. [22]; yield of pantolactone
After a reaction time of 40 h the colour of the solution was still dark violet. The
colour changed to yellow on contact with air. Table 1 shows that the hydrogenation
yields are in the lower and middle area. The in situ catalyst [Rh(cod)Cl]2=32
afforded 36.3% yield and 17% ee.
Catalytic Hydrosilylation of Acetophenone
To the procatalyst [Rh(cod)Cl]2 a 1.1-fold excess of a solution of the ligand in
CH2Cl2 was added. The colour changed to dark violet. The solution was stirred at

New Chiral Tridentate Ligands
1259
Table 2. Enantioselective hydrosilylation of acetophenone with in situ catalysts [Rh(cod)Cl]2=24–27,
32, and 33a
Procatalyst
Ligand
HS %b
EE %c
Yield %d
ee %
Config.
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
[Rh(cod)Cl]2
24
25
26
27
32
33
86.0
86.9
85.2
84.6
83.5
76
9.0
6.4
78.3
81.4
76.5
72.2
49.3
39.6
<1.0
<1.0
<1.0
6.9
(R)
(S)
(S)
(R)
(S)
(R)
10.2
14.7
41.2
47.9
8.8
<1.0
a
Conditions: Rh:ligand:substrate:diphenylsilane ¼ 1:1.1:400:400, T ¼ 0ꢂC ! rt, t ¼ 24h; work-up and
enantiomer analysis see Ref. [24]; b HS¼ hydrosilylation; c EE¼ enolether; d yield of 1-phenylethanol
room temperature for 30 min. Then the solvent was removed. The reaction was
started by addition of acetophenone and diphenylsilane [23, 24]. Yields were good
(Table 2), however, the enantiomeric excess was very low in all runs, except for
ligand 27 (6.9% ee) and ligand 32 (8.8% ee).
Catalytic Hydrogenation of Acetophenone
After adding a 1.1-fold excess of ligand to the procatalyst [RuCl2(PPh3)3] the
2-propanol solution was stirred at room temperature for 1 h. Then the substrate
Table 3. Enantioselective transfer hydrogenation of acetophenone with in situ catalysts
[RhCl2(PPh3)3]=24–27, 32, and 33a
Procatalyst
Ligand
Time h
Yield %b
ee %
Config.
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
[RuCl2(PPh3)3]
24
25
26
27
32
32
33
15
15
15
15
15
72
15
15.9
4.3
10.8
9.0
(R)
(S)
(S)
(S)
(S)
(S)
(R)
20.6
15.2
1.8
6.7
1.3
34.2
38.1
15.1
2.8
1.9
a
Conditions: Ru:ligand:substrate:KOtBu ¼ 1:1.1:200:1, solvent 2-propanol, T ¼ 28ꢂC; work-up and
b
enantiomer analysis see Ref. [26]; yield of 1-phenylethanol

1260
H. Brunner et al.
acetophenone (200-fold excess) and the base potassium-tert-butanolate were added
[25, 26]. The results are shown in Table 3. The highest enantiomeric excess was
38% ee obtained with ligand 32.
Experimental
Chromatography: Silica gel 60 (Merck). NMR spectra: Bruker AC 250, Bruker ARX 400 spectrometer.
Mass spectra: Finnigan Mat 95 (FD and FAB), Finnigan 311A (EI), Thermoquest TSQ 7000 (ESI). The
most intense peak is specified. Optical rotations: Perkin Elmer polarimeter 241.
(R)-(ꢃ)-2-Aminobutanol was commercially available. (S)-(þ)-Valinol, (S)-(ꢃ)-phenylalaninol,
(S)-(ꢃ)-phenylglycinol, and (S)-(þ)-methioninol were obtained by reduction of the corresponding
aminoacids [27]. (S)-N-Boc-2,2-dimethyl-4-tosyloxymethyloxazolidine 28 was synthesised as de-
scribed starting from (S)-(þ)-serine [18].
6-[(tert-Butyldiphenylsilyl)oxymethyl]-2-(hydroxymethyl)pyridine (2, C23H27NO2Si)
To a suspension of 1.11 g of NaH (46.0mmol) in 40cm3 of THF 5.85 g of 2,6-dihydroxymethylpyr-
idine (1, 42.0mmol), dissolved in 250 cm3 of THF, were added at room temperature within 2 h under
an atmosphere of dry N2. A solution of 10.8 cm3 of tert-butyldiphenylchlorosilane (42 mmol) in 5 cm3
of THF was added dropwise with stirring at room temperature. The brown suspension was poured into
a mixture of 165 cm3 of diethyl ether and 22cm3 of a 10% Na2CO3 solution. The organic layer was
dried (Na2SO4) and evaporated. The resulting pale yellow oil was chromatographed on a SiO2 column
(35 ꢄ 4 cm) with petroleum ether:ethyl acetate ¼ 2:1. After the first fraction, consisting of the doubly
silylated compound, the main fraction was 2 (colourless solid). The unprotected dialcohol 1 remained
on the column. Yield 12.27 g (77%); mp 133ꢂC; PI DCI MS: m=z ¼ 378 (M, 100); 1H NMR (250 MHz,
CDCl3, TMS): ꢀ ¼ 7.72 (m, 5H, Ph, Py), 7.59 (d, J ¼ 7.4 Hz, H3-Py), 7.41 (m, 6H, Ph), 7.09
(d, J ¼ 7.6 Hz, H5-Py), 4.88 (s, CH2OSi), 4.70 (d, J ¼ 4.8 Hz, CH2OH), 3,71 (t, J ¼ 4.8 Hz, CH2OH),
1.14 (s, C(CH3)3).
6-[(tert-Butyldiphenylsilyl)oxymethyl]-2-(tosyloxymethyl)pyridine (3, C30H33NO4Si)
Powdered KOH (1.72 g, 30.7 mmol) was added to a solution of 7.18g of 2 (19.0 mmol) in 30cm3 of
THF. To this suspension a solution of 4.20g of TosCl (22.0 mmol) in 15cm3 of THF was added
dropwise at 0ꢂC. The suspension was stirred for 5 h at 0ꢂC and 12h at room temperature. After
filtration the residue was washed with a small amount of THF and the combined solutions were
evaporated. The resulting solid was chromatographed (SiO2, 40ꢄ 6 cm) with petroleum ether:ethyl
acetate ¼ 7:1 to give 3 as a colourless solid. Yield 10.10 g (89%); mp 63–64ꢂC; PI FD MS (CH2Cl2):
1
m=z ¼ 474 (M–C(CH3)3, 100); H NMR (250MHz, CDCl3, TMS): ꢀ ¼ 7.71 (m, 8H, Ph, Py), 7.34
(m, 9H, Ph, Py), 5.05 (s, CH2OTos), 4.77 (s, CH2OSi), 2.41 (s, CH3), 1.12 (s, C(CH3)3).
2-[(tert-Butyldiphenylsilyl)oxymethyl]-6-[(diphenylphosphanoyl)methyl]pyridine
(4, C35H36NO2PSi)
Under N2 a solution of 3.50 g of 3 (6.58 mmol) in 50cm3 of THF was cooled to ꢃ50ꢂC. An equimolar
solution of LiPPh2 (1 molar) in THF was added dropwise. Each drop was immediately decolourized.
The resulting pale yellow solution was stirred for 1 h at ꢃ50ꢂC and for 2 h at room temperature. Then
the solution was stirred for 3 h on air. After removal of the solvent the residue was chromatographed
(SiO2, 35ꢄ 4 cm) with CH2Cl2:methanol¼ 50:1 to afford 4 as a colourless solid. Yield 2.25g (61%);
1
PI FD MS (CH2Cl2): m=z ¼ 562 (M, 4), 504 (M–C(CH3)3, 100); H NMR (250MHz, CDCl3, TMS):

New Chiral Tridentate Ligands
1261
ꢀ ¼ 7.66 (m, 9H, Ph, Py), 7.40 (m, 14H, Ph, Py), 4.66 (s, CH2OSi), 3.84 (d, J ¼ 14.2Hz, CH2P), 1.10
(s, C(CH3)3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.58 (s, POPh2) ppm.
6-(Diphenylphosphanoyl-ꢁP-methyl)-2-(hydroxymethyl)pyridine (5, C19H18NO2P)
Bu4NFꢁ3H2O (1.61 g, 5.11 mmol) was added to a solution of 2.61 g of 4 (4.65 mmol) in 50cm3 of THF.
The colour of the solution turned yellow. After stirring for 2 h at room temperature the solvent was
evaporated and the residue was chromatographed (SiO2, 25ꢄ 3 cm) with CH2Cl2:methanol ¼ 20:1 to
give the colourless solid 5. Yield 1.29 g (86%); mp 126ꢂC; PI EI MS: m=z ¼ 323 (M, 9), 201 (Ph2PO,
73), 199 (M–Ph–CH2OH, 100); 1H NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.55 (ddd, J ¼ 7.7, 7.7, 0.4Hz,
H4-Py), 7.52 (m, 3H, Ph), 7.45 (m, 7H, Ph), 7.66 (ddd, J ¼ 7.7, 1.8, 0.9Hz, 1H, H3=5-Py), 7.73 (ddd,
J ¼ 7.7, 1.8, 0.9 Hz, 1H, H3=5-Py), 4.54 (s, CH2OH), 3.93 (d, J ¼ 14.0Hz, CH2P), 3.60 (s, CH2OH)
ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.60 (s, POPh2) ppm.
6-[(Diphenylphosphanoyl)methyl]pyridine-2-carbaldehyde (6, C19H16NO2P)
Under N2 a solution of 310 mm3 of oxalyl chloride (3.61 mmol) in 8 cm3 of CH2Cl2 was cooled to
ꢃ80ꢂC. A solution of 530 mm3 of DMSO (7.46 mmol) in 2 cm3 of CH2Cl2 was added dropwise such
thatgasevolutionwasnottoovigorous.After5 minasolutionof1.0gof5(3.11 mmol)in8 cm3 ofCH2Cl2
was added dropwise and stirred for 15min at ꢃ80ꢂC. After adding 2.20cm3 of NEt3 (15.87 mmol) a
brown precipitate formed immediately. The suspension was stirred while warming to room temperature.
H2O (16 cm3) was added which dissolved the precipitate. The yellow-orange organic layer was washed
twice with H2O, dried (Na2SO4), and the solvent was evaporated. The residue was chromatographed
(SiO2, 25ꢄ 3 cm) withdichloromethane:methanol ¼ 30:1. The resulting6 was obtainedasa yellow solid.
Yield 0.96 g (96%); mp 105ꢂC; PI EI MS: m=z ¼ 321 (M, 5), 201 (POPh2, 100); 1H NMR (400 MHz,
CDCl3, TMS): ꢀ ¼ 9.83 (d, J ¼ 0.6 Hz, CHO), 7.77 (m, 6H, Ph, Py), 7.58 (m, 7H, Ph, Py), 4.02 (d,
J ¼ 13.9Hz, CH2P) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.32 (s, POPh2) ppm.
6-[(Diphenylphosphanoyl)methyl]pyridine-2-carbaldoxime (7, C19H17N2O2P)
H2NOHꢁHCl (2.02 g, 29.1mmol) was dissolved in 18cm3 of a 10% Na2CO3 solution and stirred until
gas evolution stopped. This solution was added to a solution of 6.00g of 6 (18.7 mmol) in 40cm3 of
MeOH and stirred for 24h at room temperature. After a few min a colourless precipitate formed. The
suspension was concentrated and the precipitate was filtered off and washed with petroleum ether.
The filtrate was evaporated and the residue was chromatographed (SiO2, 25ꢄ3 cm) with
CH2Cl2:methanol¼ 20:1. Compound 7 was obtained as a colourless solid. Yield 5.10g (81%); mp
1
217–218ꢂC; PI EI MS: m=z ¼ 336 (M, 4), 318 (M–H2O, 6), 201 (POPh2, 100); H NMR (400 MHz,
DMSO-d6, TMS): ꢀ ¼ 11.63 (s, HCNOH), 7.82 (m, 5H, Ph, HCNOH), 7.67 (dd, J ¼ 7.7, 7.7 Hz, H4-
Py), 7.53 (m, 7H, Ph, H5-Py), 7.25 (ddd, J ¼ 7.7, 1.9, 1.1 Hz, H3-Py), 4.10 (d, J ¼ 11.9Hz, CH2P) ppm;
31P{1H} NMR (DMSO-d6, H3PO4 ext.): ꢀ ¼ 28.92 (s, 1P, POPh2) ppm.
6-[(Diphenylphosphanoyl)methyl]pyridine-2-carbonitrile (8, C19H15N2O2P)
To a solution of 2.0g of 7 (6.2mmol) in 70cm3 of dried DMSO 1.17g of 1,10-carbonyldiimidazol
(7.2mmol) were added. After stirring for 2 h at room temperature the solvent was evaporated. The
residue was chromatographed (SiO2, 25ꢄ3 cm) with CH2Cl2:methanol¼ 30:1. Compound 8 was
obtained as a colourless solid. Yield 1.82 (92%); mp 147ꢂC; PI EI MS: m=z ¼ 318 (M, 15), 201
1
(POPh2, 100); H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.78 (dd, J ¼ 8.0, 1.1 Hz, H3-Py), 7.75
(m, 4H, Ph), 7.71 (dd, J ¼ 8.0, 8.0 Hz, H4-Py), 7.49 (m, 7H, Ph, H5-Py), 3.96 (s, CH2P) ppm; 31P{1H}
NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.39 (s, POPh2) ppm.

1262
H. Brunner et al.
6-[(Diphenylphosphanoyl)methyl]pyridine-2-carbomethoxyimidate (9, C20H19N2O2P)
A solution of 8 (1.35 g, 3.9 mmol) in 80 cm3 of MeOH was reacted with a solution of 0.096g of sodium
(4.2mmol) in 10cm3 of MeOH under N2. After stirring for 48h at room temperature 280 mm3 of
glacial acetic acid (4.9mmol) were added. The solvent was removed and the residue was dissolved in
CH2Cl2. The solution was extracted twice with H2O, the organic layer was dried over Na2SO4, and the
solvent was evaporated to give 9 as a colourless solid. Yield 1.28 (94%); mp 176–177ꢂC; PI EI MS:
m=z ¼ 350 (M, 2), 319 (M–OCH3, 12), 201 (POPh2, 100); 1H NMR (250MHz, CDCl3, TMS): ꢀ ¼ 8.62
(bs, NH), 7.79 (m, 4H, Ph), 7.68 (ddd, J ¼ 7.7, 7.7, 0.5 Hz, H4-Py), 7.61 (ddd, J ¼ 7.7, 1.4, 1.3 Hz, H5-
Py), 7.50 (m, 7H, Ph, H3-Py), 3.96 (d, J ¼ 14.0 Hz, CH2P), 3.93 (s, OCH3) ppm; 31P{1H} NMR
(CDCl3, H3PO4 ext.): ꢀ ¼ 30.57 (s, POPh2) ppm.
General Procedure for the Synthesis of Compounds 10–13 from 9 with 2-Aminoalcohols
9 was dissolved in ca. 30cm3 of chlorobenzene at 80ꢂC. The corresponding 2-aminoalcohol
(2.93 mmol) and one drop of conc. HCl as catalyst were added. N2 was bubbled through the solution
for 20 h to remove the compounds with low boiling points like MeOH or NH3 displacing the equilib-
rium to the product side. After evaporating the solvent the residue was chromatographed (SiO2,
20ꢄ3 cm) with CH2Cl2:methanol ¼ 30:1.
(R)-2-[(Diphenylphosphanoyl)methyl]-6-(4-ethyl-4,5-dihydrooxazol-2-yl)pyridine
(10, C23H23N2O2P)
From (R)-(ꢃ)-2-aminobutanol as aminoalcohol. Colourless resin. Yield 1.05 g (94%); PI EI MS:
1
m=z ¼ 390 (M, 14), 361 (M–C2H5, 8), 201 (Ph2PO, 100); H{31P} NMR (400MHz, CDCl3, TMS):
ꢀ ¼ 7.85 (ddd, J ¼ 7.6, 1.3, 1.4 Hz, H3-Py), 7.77 (m, 4H, Ph), 7.71 (ddd, J ¼ 7.8, 1.3, 1.7 Hz, H5-Py),
7.65 (dd, J ¼ 7.6, 7.8 Hz, H4-Py), 7.44 (m, 6H, Ph), 4.53 (dd, J ¼ 8.1, 9.6 Hz, OCHAHBCHN), 4.28 (m,
OCHAHBCHN), 4.11 (dd, J ¼ 8.1, 8.1 Hz, OCHAHBCHN), 4.06 (d, J ¼ 14.2Hz, CHAHBPO), 4.05 (d,
J ¼ 14.2Hz, CHAHBPO), 1.79 (m, CHAHBCH3), 1.63 (m, CHAHBCH3), 1.00 (t, J ¼ 7.2 Hz,
CHAHBCH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.50 (s, POPh2); IR (KBr): ꢂꢀ¼ 1200
(s) cmꢃ 1; [ꢃ]D ¼ þ 37.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.0, CH2Cl2).
(S)-2-[(Diphenylphosphanoyl)methyl]-6-(4-isopropyl-4,5-dihydrooxazol-2-yl)pyridine
(11, C24H25N2O2P)
From (S)-(þ)-valinol as aminoalcohol. Colourless resin. Yield 0.80 g (69%); PI EI MS: m=z ¼ 404 (M,
1
29), 361 (M–C3H7, 63), 201 (Ph2PO, 100); H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.86 (ddd,
J ¼ 7.5, 1.5, 1.5 Hz, H3-Py), 7.77 (m, 4H, Ph), 7.69 (ddd, J ¼ 7.8, 1.5, 1.7 Hz, H5-Py), 7.64 (dd, J ¼ 7.5,
7.8 Hz, H4-Py), 7.44 (m, 6H, Ph), 4.45 (dd, J ¼ 8.7, 7.5 Hz, OCHAHBCHN), 4.17 (m, OCHAHBCHN),
4.07 (d, J ¼ 14.7Hz, CHAHBP), 4.04 (d, J ¼ 14.7Hz, CHAHBP), 1.90 (m, CHCH3CH3), 1.02
(d, J ¼ 6.8 Hz, CHCH3CH3), 0.93 (d, J ¼ 6.7 Hz, CHCH3CH3) ppm; 31P{1H} NMR (CDCl3, H3PO4
ext.): ꢀ ¼ 30.51 (s, POPh2) ppm; IR (KBr): ꢂꢀ¼ 1200 (s) cmꢃ 1; [ꢃ]D ¼ ꢃ 40.0ꢂ cm3 gꢃ 1 dmꢃ 1
(c ¼ 1.0, CH2Cl2).
(S)-2-[(Diphenylphosphanoyl)methyl]-6-(4-benzyl-4,5-dihydrooxazol-2-yl)pyridine
(12, C28H25N2O2P)
From (S)-(ꢃ)-phenylalaninol as aminoalcohol. Colourless solid. Yield 0.78g (61%); mp 148–149ꢂC;
1
PI DCI MS: m=z ¼ 470 (Mþ NH4, 27), 453 (M, 100); H{31P} NMR (400 MHz, CDCl3, TMS):
ꢀ ¼ 7.85 (dd, J ¼ 7.4, 1.3Hz, H3-Py), 7.77 (m, 4H, Ph), 7.72 (dd, J ¼ 7.8, 1.3 Hz, H5-Py), 7.66 (dd,
J ¼ 7.5, 7.8 Hz, H4-Py), 7.42 (m, 6H, Ph), 7.28 (m, 5H, Ph), 4.62 (m, OCHAHBCHN), 4.40 (dd, J ¼ 8.6,

New Chiral Tridentate Ligands
1263
9.4 Hz, OCHAHBCHN), 4.19 (dd, J ¼ 8.6, 7.6 Hz, OCHAHBCHN), 4.08 (d, J ¼ 14.9 Hz, CHAHBP),
4.03 (d, J ¼ 14.9Hz, CHAHBP), 3.27 (dd, J ¼ 13.7, 5.0 Hz, CHAHBPh), 2.75 (dd, J ¼ 13.7, 8.9Hz,
CHAHBPh) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.48 (s, POPh2) ppm; IR (KBr): ꢂꢀ ¼ 1190
(s) cmꢃ 1; [ꢃ]D ¼ ꢃ20.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.0, CH2Cl2).
(S)-2-[(Diphenylphosphanoyl)methyl]-6-(4-phenyl-4,5-dihydrooxazol-2-yl)pyridine
(13, C27H23N2O2P)
From (S)-(ꢃ)-phenylglycinol as 2-aminoalcohol. Colourless resin. Yield 0.50 (40%); LT PI LSI MS:
1
m=z ¼ 439 (M, 100); H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.94 (dd, J ¼ 7.3, 1.5 Hz, H3-Py),
7.78 (m, 4H, Ph), 7.72 (dd, J ¼ 7.8, 1.5Hz, H5-Py), 7.68 (dd, J ¼ 7.3, 7.8 Hz, H4-Py), 7.39 (m, 11H,
Ph), 5.41 (dd, J ¼ 10.1, 8.3Hz, OCHAHBCHN), 4.84 (dd, J ¼ 10.1, 8.5Hz, OCHAHBCHN), 4.34 (dd,
J ¼ 8.3, 8.5 Hz, OCHAHBCHN), 4.10 (d, J ¼ 14.7Hz, CHAHBP), 4.04 (d, J ¼ 14.7Hz, CHAHBP) ppm;
31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 30.56 (s, POPh2) ppm; IR (KBr): ꢂꢀ ¼ 1190 (s) cmꢃ 1
;
[ꢃ]D ¼ þ54.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.0, CH2Cl2).
Trihydroborane[2-[(tert-butyldiphenylsilyl)oxymethyl]-6-(diphenylphosphanyl-
ꢁP-methyl)pyridine] (14, C35H39BNOPSi)
After LiPPh2 had been added, as described in the synthesis of 4, the solution was stirred for 3 h under
exclusion of air. The protecting group was introduced by adding BH3ꢁTHF (1 molar) in 6.58cm3 of
THF to the solution and stirring for 3 h at room temperature. After removal of the solvent the residue
was chromatographed (SiO2, 35ꢄ4 cm) with petroleum ether:ethyl acetate¼ 6:1. The main fraction
was 14 forming a colourless solid. Yield 2.80g (76%); mp 87–89ꢂC; PI FD MS (CH2Cl2): m=z ¼ 559
1
(M, 8), 546 (M–BH3, 6), 502 (M–C(CH3)3, 100); H NMR (400 MHz, CD3OD, TMS): ꢀ ¼ 7.63
(m, 9H, Ph, Py), 7.41 (m, 13H, Ph, Py), 7.06 (m, 1H, Py), 4.55 (s, CH2OSi), 3.81 (d, J ¼ 12.0Hz,
CH2P), 1.09 (s, C(CH3)3) ppm; 31P{1H} NMR (CD3OD, H3PO4 ext.): ꢀ ¼ 19.75 (d, J ¼ 50.4Hz,
PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2400 (s) cmꢃ 1
.
Trihydroborane[6-(diphenylphosphanyl-ꢁP-methyl)-2-(hydroxymethyl)pyridine]
(15, C19H21BNOP)
Procedure as described for 14, including molar amounts of reactants and quantities of solvent as in the
synthesis of 5. The eluent in the chromatography was petroleum ether:ethyl acetate ¼ 1:2 to give 15 as
a colourless solid. Yield 1.33 g (89%); mp 125–126ꢂC; PI FD MS (CH2Cl2): m=z ¼ 321 (M, 100), 307
(M–BH3, 10); 1H NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.70 (m, 4H, Ph), 7.54 (ddd, J ¼ 7.7, 7.7, 0.6Hz,
H4-Py), 7.46 (m, 6H, Ph), 7.15 (ddd, J ¼ 7.7, 1.8, 1.0 Hz, 1H, H3=5-Py), 6.97 (ddd, J ¼ 7.7, 1.8, 0.9Hz,
1H, H3=5-Py), 4.51 (d, J ¼ 4.8 Hz, CH2OH), 3.84 (d, J ¼ 11.9Hz, CH2P), 3.21 (t, J ¼ 4.8 Hz, CH2OH)
ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.78 (d, J ¼ 65.6Hz, PPh2BH3) ppm; IR (KBr):
ꢂ ¼ 2400 (s) cmꢃ 1
.
Trihydroborane[6-(diphenylphosphanyl-ꢁP-methyl)pyridine-2-carbaldehyde]
(16, C19H19BNOP)
Procedure as described for 14, including molar amounts of reactants and quantities of solvent as in the
synthesis of 6. The residue was chromatographed (SiO2, 25ꢄ3 cm) with petroleum ether:ethyl ace-
tate¼ 4:1. Compound 16 was obtained as a yellow solid. Yield 0.78g (79%); mp 65–66ꢂC; PI FD MS
(CH2Cl2): m=z ¼ 319 (M, 100), 305 (M–BH3, 13); 1H NMR (400MHz, CDCl3, TMS): ꢀ ¼ 9.75
(s, CHO), 7.73 (m, 6H, Ph, Py), 7.45 (m, 7H, Ph, Py), 3.93 (d, J ¼ 12.0Hz, CH2P) ppm; 31P{1H}
NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.97 (d, J ¼ 68.7Hz, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2380 (s), 1710
(s) cmꢃ 1
.

1264
H. Brunner et al.
Trihydroborane[6-(diphenylphosphanyl-ꢁP-methyl)pyridine-2-carbaldoxime]
(17, C19H20BN2OP)
Procedure as described for 14, including molar amounts of reactants and quantities of solvent as in the
synthesis of 7. The residue was chromatographed (SiO2, 25ꢄ3 cm) with petroleum ether:ethyl ace-
tate¼ 1:1. Compound 17 was obtained as a colourless solid. Yield 6.22g (99%); mp 139–140ꢂC; PI
1
FD MS (CH2Cl2): m=z ¼ 334 (M, 45), 320 (M–BH3, 100); H NMR (400MHz, DMSO-d6, TMS):
ꢀ ¼ 11.72 (s, HCNOH), 7.77 (d, J ¼ 1.3 Hz, HCNOH), 7.74 (m, 4H, Ph), 7.67 (dd, J ¼ 7.7, 7.7 Hz, H4-
Py), 7.54 (m, 7H, Ph, H5-Py), 7.15 (ddd, J ¼ 7.7, 1.6, 1.3 Hz, H3-Py), 4.05 (d, J ¼ 12.5Hz, CH2P) ppm;
31P{1H} NMR (DMSO-d6, H3PO4 ext.): ꢀ ¼ 18.65 (bs, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2380 (s) cmꢃ 1
.
Trihydroborane[6-(diphenylphosphanyl-ꢁP-methyl)pyridine-2-carbonitrile]
(18, C19H18BN2P)
Procedure as described for 14, including molar amounts of reactants and quantities of solvent as in the
synthesis of 8. Compound 18 formed a colourless solid. Yield 1.58 g (83%); mp 91ꢂC; PI FD MS
(CH2Cl2): m=z ¼ 316 (M, 100), 302 (M–BH3, 28); 1H NMR (400MHz, CDCl3, TMS): ꢀ ¼ 7.70
(m, 5H, Ph, Py), 7.57 (ddd, J ¼ 8.0, 1.7, 1.1Hz, H5-Py), 7.48 (m, 7H, Ph, Py), 3.88 (d, J ¼ 12.1Hz,
CH2P) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.82 (d, J ¼ 65.2Hz, PPh2BH3) ppm; IR (KBr):
ꢂꢀ ¼ 2400 (s) cmꢃ 1
.
Trihydroborane[6-(diphenylphosphanyl-ꢁP-methyl)pyridine-2-carbomethoxyimidate]
(19, C20H22BN2OP)
Procedure as described for 14, including molar amounts of reactants and quantities of solvent as in the
synthesis of 9. Compound 19 was obtained as a colourless solid. Purification by chromatography (Al2O3,
25ꢄ3 cm) with petroleum ether:ethyl acetate ¼ 4:1 decreased the yield. Yield 1.15g (82%); mp
88–89ꢂC; PI FD MS (CH2Cl2): m=z ¼ 348 (M, 76), 335 (M–BH3, 100); 1H NMR (250MHz, CDCl3,
TMS): ꢀ ¼ 7.91 (ddd, J ¼ 7.8, 1.5, 1.1 Hz, H3-Py), 7.74 (m, 4H, Ph), 7.68 (ddd, J ¼ 7.8, 7.8, 0.5 Hz, H4-
Py), 7.44 (m, 7H, Ph, H5-Py), 3.97 (d, J ¼ 12.1 Hz, CH2P), 3.93 (s, OCH3) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ 18.79 (d, J ¼ 66.7Hz, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2390 (s), 1720 (s) cmꢃ 1
.
General Procedure for the Synthesis of Compounds 20–23 from 19 with 2-Aminoalcohols
To a solution of 800 mg of 19 (2.30 mmol) in 40cm3 of CH2Cl2 a solution of 2.30mmol of the
corresponding 2-aminoalcohol (2.30 mmol) was added under N2. Stirring was continued for 4 d at
room temperature. After removal of the solvent the residue was chromatographed on Al2O3 (20ꢄ3 cm)
with petroleum ether:ethyl acetate ¼ 3:1.
(R)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-ethyl-4,5-
dihydrooxazol-2-yl)pyridine] (20, C23H26BN2OP)
From (R)-(ꢃ)-2-aminobutanol as aminoalcohol. Colourless resin. Yield 343 mg (38%); PI FD MS
(CH2Cl2): m=z ¼ 388 (M, 31), 374 (M–BH3, 100); 1H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.83
(dd, J ¼ 7.7, 1.0Hz, H3-Py), 7.73 (m, 4H, Ph), 7.60 (dd, J ¼ 7.7, 7.8 Hz, H4-Py), 7.44 (m, 7H, Ph, H5-Py),
4.50 (dd, J ¼ 8.2, 9.4 Hz, OCHAHBCHN), 4.27 (m, OCHAHBCHN), 4.09 (dd, J ¼ 8.2, 8.2Hz,
OCHAHBCHN), 4.00 (d, J ¼ 14.0Hz, CHAHBPBH3), 3.93 (d, J ¼ 14.0Hz, CHAHBPBH3), 1.77
(m, CHAHBCH3), 1.63 (m, CHAHBCH3), 0.99 (t, J ¼ 7.3 Hz, CHAHBCH3) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ 18.56 (d, J ¼ 48.8Hz, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1; [ꢃ]D ¼ þ30.0,
[ꢃ]578 ¼ þ32.2,[ꢃ]546 ¼ þ37.5,[ꢃ]436 ¼ þ72.7,[ꢃ]365 ¼ þ143.8ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 2.67, CH2Cl2).

New Chiral Tridentate Ligands
1265
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-isopropyl-4,5-
dihydrooxazol-2-yl)pyridine] (21, C24H28BN2OP)
From (S)-(þ)-valinol as aminoalcohol. Colourless resin. Yield 266 mg (30%); PI FD MS (CH2Cl2):
1
m=z ¼ 402 (M, 39), 388 (M–BH3); H{31P} NMR (400MHz, CDCl3, TMS): ꢀ ¼ 7.85 (dd, J ¼ 7.8,
1.0 Hz, H3-Py), 7.73 (m, 4H, Ph), 7.60 (dd, J ¼ 7.8, 7.8 Hz, H4-Py), 7.42 (m, 7H, Ph, H5-Py), 4.44 (dd,
J ¼ 9.0, 7.6 Hz, OCHAHBCHN), 4.15 (m, OCHAHBCHN), 4.02 (d, J ¼ 13.9Hz, CHAHBPBH3), 3.91
(d, J ¼ 13.9Hz, CHAHBPBH3), 1.89 (m, CHCH3CH3), 1.03 (d, J ¼ 6.8 Hz, CHCH3CH3), 0.93
(d, J ¼ 6.8 Hz, CHCH3CH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.62 (d, J ¼ 48.8Hz,
PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1; [ꢃ]D ¼ ꢃ40.5, [ꢃ]578 ¼ ꢃ43.9, [ꢃ]546 ¼ ꢃ50.0,
[ꢃ]436 ¼ ꢃ99.3, [ꢃ]365 ¼ ꢃ200.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.48, CH2Cl2).
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-benzyl-4,5-
dihydrooxazol-2-yl)pyridine] (22, C28H28BN2OP)
From (S)-(ꢃ)-phenylalaninol as aminoalcohol. Colourless resin. Yield 307 mg (30%); PI FD MS
(CH2Cl2): m=z ¼ 450 (M, 42), 436 (M–BH3, 100); 1H{31P} NMR (400MHz, CDCl3, TMS):
ꢀ ¼ 7.84 (dd, J ¼ 7.8, 1.1 Hz, H3-Py), 7.74 (m, 4H, Ph), 7.61 (dd, J ¼ 7.8, 7.8 Hz, H4-Py), 7.42
(m, 7H, Ph, H5-Py), 7.27 (m, 5H, Ph), 4.61 (m, OCHACHBCHN), 4.38 (dd, J ¼ 8.6, 9.4 Hz,
OCHAHBCHN), 4.17 (dd, J ¼ 8.6, 7.5 Hz, OCHAHBCHN), 4.01 (d, J ¼ 13.8Hz, CHAHBPBH3),
3.93 (d, J ¼ 13.8 Hz, CHAHBPBH3), 3.26 (dd, J ¼ 13.7, 5.1Hz, CHAHBPBH3), 2.74 (dd, J ¼ 13.7,
8.9 Hz, CHAHBPBH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 18.54 (d, J ¼ 56.5Hz, PPh2BH3)
ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1; [ꢃ]D ¼ ꢃ29.9, [ꢃ]578 ¼ ꢃ29.9, [ꢃ]546 ¼ ꢃ34.0, [ꢃ]436 ¼ ꢃ68.7,
[ꢃ]365 ¼ ꢃ134.7ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 1.47, CH2Cl2).
(S)-Trihydroborane[2-(diphenylphosphanyl-ꢁP-methyl)-6-(4-phenyl-4,5-
dihydrooxazol-2-yl)pyridine] (23, C27H26BN2OP)
From (S)-(ꢃ)-phenylglycinol as aminoalcohol. Colourless resin. Yield 378mg (38%); PI FD MS
(CH2Cl2): m=z ¼ 437 (M, 34), 422 (M–BH3, 100); 1H{31P} NMR (400MHz, CDCl3, TMS):
ꢀ ¼ 7.96 (dd, J ¼ 7.7, 1.5 Hz, H3-Py), 7.69 (m, 5H, Ph, H4-Py), 7.38 (m, 12H, Ph, H5-Py), 5.41 (dd,
J ¼ 10.1, 8.5 Hz, OCHAHBCHN), 5.15 (m, OCHAHBCHN), 4.83 (dd, J ¼ 10.1, 8.6 Hz, OCHAHBCHN),
4.03 (d, J ¼ 13.8Hz, CHAHBPBH3), 3.94 (d, J ¼ 13.8Hz, CHAHBPBH3) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ 18.73 (d, J ¼ 47.3 Hz, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2400 (s) cmꢃ 1; [ꢃ]D ¼
þ 60.5, [ꢃ]578 ¼ þ63.8, [ꢃ]546 ¼ þ76.2, [ꢃ]436 ¼ þ155.2, [ꢃ]365 ¼ þ330.5ꢂ cm3 gꢃ 1 dmꢃ 1
(c ¼ 1.05, CH2Cl2).
General Procedure for the Synthesis of the Borane-free Compounds 24–27 (and 32)
In an atmosphere of dry N2 0.75mmol of the borane complex were dissolved in 15cm3 of Et2NH and
stirred for 5 h at 50ꢂC. After removing the solvent and the volatiles, the residue was dried for 2 h in
high vacuum with gentle heating to give the borane-free products 24–27 and 32.
(R)-2-[(Diphenylphosphanyl)methyl]-6-(4-ethyl-4,5-dihydrooxazol-2-yl)pyridine
(24, C23H23N2OP)
From 20. Colourless resin. Yield 261 mg (93%); PI DCI MS: m=z ¼ 391 (M þ NH4, 100), 375 (MH, 8);
1H{31P} NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.84 (dd, J ¼ 7.8, 1.0 Hz, H3-Py), 7.45 (m, 5H, Ph, H4-
Py), 7.31 (m, 6H, Ph), 6.96 (dd, J ¼ 7.8, 1.0 Hz, H5-Py), 4.55 (dd, J ¼ 8.2, 9.5 Hz, OCHAHBCHN), 4.28
(m, OCHAHBCHN), 4.13 (dd, J ¼ 8.2, 8.2 Hz, OCHAHBCHN), 3.76 (d, J ¼ 13.5Hz, CHAHBPPh2),
3.72 (d, J ¼ 13.5Hz, CHAHBPPh2), 1.81 (m, CHAHBCH3), 1.63 (m, CHAHBCH3), 1.01 (t, J ¼ 7.4 Hz,

1266
H. Brunner et al.
CHAHBCH3) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ ꢃ 10.17 (s, PPh2) ppm; [ꢃ]D ¼ þ15.0,
[ꢃ]578 ¼ þ19.4, [ꢃ]546 ¼ þ21.9, [ꢃ]436 ¼ þ 26.9ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 2.12, CH2Cl2).
(S)-2-[(Diphenylphosphanyl)methyl]-6-(4-isopropyl-4,5-dihydrooxazol-2-yl)pyridine
(25, C24H25N2OP)
1
From 21. Colourless resin. Yield 270 mg (93%); PI FD MS (CH2Cl2): m=z ¼ 388 (M, 100); H{31P}
NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.86 (ddd, J ¼ 7.8, 1.1, 1.1 Hz, H3-Py), 7.50 (ddd, J ¼ 7.8, 7.8,
0.3 Hz, H4-Py), 7.44 (m, 4H, Ph), 7.31 (m, 6H, Ph), 6.97 (ddd, J ¼ 7.8, 1.1, 1.2 Hz, H5-Py),
4.49 (dd, J ¼ 8.2, 9.5 Hz, OCHAHBCHN), 4.22 (dd, J ¼ 8.2, 8.3 Hz, OCHAHBCHN), 4.14
(m, OCHAHBCHN), 3.76 (d, J ¼ 13.3Hz, CHAHBPPh2), 3.71 (d, J ¼ 13.3Hz, CHAHBPPh2), 1.90
(m, CHCH3CH3), 1.05 (d, J ¼ 6.8 Hz, CHCH3CH3), 0.94 (d, J ¼ 6.8 Hz, CHCH3CH3) ppm; 31P{1H}
NMR (CDCl3, H3PO4 ext.): ꢀ ¼ ꢃ10.10 (s, PPh2) ppm; [ꢃ]D ¼ ꢃ16.6, [ꢃ]578 ¼ ꢃ17.9,
[ꢃ]546 ¼ ꢃ21.2, [ꢃ]436 ¼ ꢃ41.3ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 3.92, CH2Cl2).
(S)-2-[(Diphenylphosphanyl)methyl]-6-(4-benzyl-4,5-dihydrooxazol-2-yl)pyridine
(26, C28H25N2OP)
1
From 22. Colourless resin. Yield 288 mg (88%); PI FD MS (CH2Cl2): m=z ¼ 436 (M, 100); H{31P}
NMR (400 MHz, CDCl3, TMS): ꢀ ¼ 7.84 (ddd, J ¼ 7.8, 1.2, 1.1 Hz, H3-Py), 7.52 (ddd, J ¼ 7.8, 7.8,
0.3 Hz, H4-Py), 7.44 (m, 4H, Ph), 7.31 (m, 8H, Ph), 7.25 (m, 3H, Ph), 6.98 (ddd, J ¼ 7.8, 1.2, 1.2Hz,
H5-Py), 4.63 (m, OCHAHBCHN), 4.43 (dd, J ¼ 8.6, 9.4 Hz, OCHAHBCHN), 4.23 (dd, J ¼ 8.6, 7.6Hz,
OCHAHBCHN), 3.76 (d, J ¼ 13.4Hz, CHAHBPPh2), 3.72 (d, J ¼ 13.4Hz, CHAHBPPh2), 3.30 (dd,
J ¼ 13.7, 4.8 Hz, CHAHBPh), 2.75 (dd, J ¼ 13.7, 9.3Hz, CHAHBPh) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ ꢃ10.06 (s, PPh2) ppm; [ꢃ]D ¼ ꢃ15.3, [ꢃ]578 ¼ ꢃ17.4, [ꢃ]546 ¼ ꢃ20.4,
[ꢃ]436 ¼ ꢃ47.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c ¼ 0.98, CH2Cl2).
(S)-2-[(Diphenylphosphanyl)methyl]-6-(4-phenyl-4,5-dihydrooxazol-2-yl)pyridine
(27, C27H23N2OP)
From 23. Colourless resin. Yield 285 mg (90%); PI DCI MS: m=z ¼ 423 (MH, 100), 239 (MH–PPh2,
1
50); H{31P} NMR (400MHz, CDCl3, TMS): ꢀ ¼ 7.94 (ddd, J ¼ 7.8, 2.1, 1.1 Hz, H3-Py), 7.53 (dd,
J ¼ 7.8, 7.8 Hz, H4-Py), 7.36 (m, 15H, Ph), 7.01 (ddd, J ¼ 7.8, 1.1, 1.2 Hz, H5-Py), 5.42 (dd, J ¼ 8.5,
10.3Hz, OCHAHBCHN), 4.88 (dd, J ¼ 8.5, 10.3Hz, OCHAHBCHN), 4.37 (dd, J ¼ 8.5, 8.5Hz,
OCHAHBCHN), 3.78 (d, J ¼ 13.2Hz, CHAHBPPh2), 3.74 (d, J ¼ 13.2Hz, CHAHBPPh2) ppm;
31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ ꢃ9.83 (s, PPh2) ppm; [ꢃ]D ¼ þ15.5, [ꢃ]578 ¼ þ16.9,
[ꢃ]546 ¼ þ21.0, [ꢃ]436 ¼ þ43.9ꢂ cm3 gꢃ 1 dmꢃ 1 (c¼ 1.48, CH2Cl2).
Trihydroborane[(S)-N-Boc-4-(diphenylphosphanyl-ꢁP-methyl)-2,2-dimethyloxazolidine]
(29, C23H33BNO3P)
(S)-N-Boc-2,2-dimethyl-4-(tosyloxymethyl)oxazolidine (28, 1.50g, 3.89 mmol) was dissolved in 50cm3
of THF under N2. An equimolar amount of LiPPh2 in THF was added dropwise at 0ꢂC. After stirring for
3 h at 0ꢂC 3.89 cm3 of a solution of BH3ꢁTHF (3.89 mmol) were added and the solution was stirred for 3 h
at room temperature. The solvent was removed and the residue was chromatographed (SiO2, 25ꢄ 3 cm)
with petroleum ether:ethyl acetate ¼ 6:1. 29 was obtained as a colourless solid. Yield 1.10g (68%); mp
1
82–83ꢂC; PI FD MS (CH2Cl2): m=z ¼ 413 (M, 7), 399 (M–BH3, 100); H NMR (250 MHz, CDCl3,
TMS): Two isomers, ratio 1:1.4; signals of the minor isomer in brackets: ꢀ ¼ 7.70 (m, 10H, Ph), 4.29
[3.85] (m, CHAHBO), 4.09 [3.66] (m, CHNBoc), 4.15 [3.78] (m, CHAHBO), 3.09 [2.59] (m, CHAHBP),
2.59 [2.29] (m, CHAHBP), 1.51 (m, C(CH3)2) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 11.74
(m, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2380 (s) cmꢃ 1
.

New Chiral Tridentate Ligands
1267
Trihydroborane[(S)-2-amino-3-diphenylphosphanyl-ꢁP-propanol]hydrochloride
(30, C15H21BNOPꢁHCl)
Under N2 200 mg of 29 (0.4mmol) were dissolved in 5 cm3 of MeOH. To this solution 5 cm3 of a
methanol solution saturated with HCl were added at 0ꢂC. With a reaction time of 5 min it is possible to
cleave the oxazolidine ring without destroying the phosphorus-borane complex. 30 was formed as
the hydrochloride. Yield 124 mg (100%); PI DCI MS: m=z ¼ 274 (MH, 4), 260 (M–BH3, 100), 187
(Ph2PH, 35); 1H NMR (250MHz, CDCl3, TMS): ꢀ ¼ 8.15 (bs, CHNH3Cl), 7.70 (m, 4H, H2-Ph), 7.40
(m, 6H, H3-Ph, H4-Ph), 3.63 (m, HOCH2CHNH2), 2.86 (m, CH2P) ppm; 31P{1H} NMR (CDCl3,
H3PO4 ext.): ꢀ ¼ 12.43 (s, PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2390 (s) cmꢃ 1
.
Trihydroborane[(S)-2-[4-(diphenylphosphanyl-ꢁP-methyl)-
4,5-dihydrooxazol-2-yl]pyridine] (31, C21H22BN2OP)
Pyridine-2-carbomethoxyimidate (375 mg, 1.21mmol) was dissolved in 20cm3 of CH2Cl2 and 151 mm3
of 30 (1.21 mmol) were added. After addition of 171 mm3 of NEt3 (2.3mmol) to deprotect the amino
function of 30, the solution was stirred for 4 d at room temperature. The solvent was removed and the
residue was chromatographed (Al2O3, 20 ꢄ 1.5 cm) with petroleum ether:ethyl acetate ¼ 3:1. 31 was
isolated as a colourless resin. Yield 388 mg (40%); PI FD MS (CH2Cl2): m=z ¼ 360 (M, 89), 346 (M–
BH3,100);1H{31P}NMR(400 MHz,CDCl3,TMS):ꢀ ¼ 8.70(ddd,J ¼ 4.8, 1.8,0.9 Hz,H6-Py),7.90(ddd,
J ¼ 7.9, 1.1, 0.9Hz, H3-Py), 7.80 (m, 2H, Ph), 7.76 (ddd, J ¼ 7.6, 7.9, 1.8 Hz, H4-Py), 7.68 (m, 2H, Ph),
7.47 (m, 6H, Ph), 7.39 (ddd, J ¼ 4.8, 7.6, 1.1 Hz, H5-Py), 4.59 (dd, J ¼ 8.7, 17.7Hz, OCHAHBCHN), 4.52
(m,OCHAHBCHN),4.28(dd,J ¼ 8.7,7.1 Hz,OCHAHBCHN), 3.16(dd, J ¼ 14.4,2.5 Hz,CHAHBP),2.35
(dd, J ¼ 14.4, 10.6Hz, CHAHBP) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ 12.28 (d, J ¼ 62.6Hz,
PPh2BH3) ppm; IR (KBr): ꢂꢀ ¼ 2380 (s) cmꢃ 1; [ꢃ]D ¼ þ32.0, [ꢃ]578 ¼ þ32.8, [ꢃ]546 ¼ þ40.0,
[ꢃ]436 ¼ þ84.4, [ꢃ]365 ¼ þ180.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c¼ 1.25, CH2Cl2).
(S)-2-[4-[(Diphenylphosphanyl)methyl]-4,5-dihydrooxazol-2-yl]pyridine
(32, C21H19N2OP)
From 31 according to the general procedure for removal of the BH3 protecting group. Colourless resin.
Yield 235 mg (90%); PI FD MS (CH2Cl2): m=z ¼ 346 (M, 100); 1H{31P} NMR (400 MHz, CDCl3, TMS):
ꢀ ¼ 8.69 (ddd, J ¼ 4.8, 1.8, 0.9 Hz, H6-Py), 7.96 (ddd, J ¼ 7.9, 1.1, 0.9 Hz, H3-Py), 7.74 (ddd, J ¼ 7.9, 7.6,
1.8 Hz, H4-Py), 7.51 (m, 2H, Ph), 7.43 (m, 2H, Ph), 7.37 (ddd, J ¼ 4.8, 7.6, 1.8 Hz, H5-Py), 7.33 (m, 6H,
Ph), 4.53 (dd, J ¼ 8.4, 9.1 Hz, OCHAHBCHN), 4.37 (m, OCHAHBCHN), 4.26 (dd, J ¼ 8.4, 7.9 Hz,
OCHAHBCHN), 2.86 (ddd, J ¼ 13.5, 4.1, 1.9 Hz, CHAHBPPh2), 2.22 (ddd, J ¼ 13.5, 10.2, 2.7 Hz,
CHAHBPPh2) ppm; 31P{1H} NMR (CDCl3, H3PO4 ext.): ꢀ ¼ ꢃ22.03 (s, PPh2) ppm; [ꢃ]D ¼ þ16.9,
[ꢃ]578 ¼ þ18.8, [ꢃ]546 ¼ þ21.1, [ꢃ]436 ¼ þ37.0ꢂ cm3 gꢃ 1 dmꢃ 1 (c¼ 3.84, CH2Cl2).
(S)-2-[4-[2-(Methylthio)ethyl]-4,5-dihydrooxazol-2-yl]pyridine
(33, C11H14H2OS)
[ꢃ]D ¼ ꢃ88.2, [ꢃ]578 ¼ ꢃ94.1, [ꢃ]546 ¼ ꢃ107.8, [ꢃ]436 ¼ ꢃ201.0, [ꢃ]365 ¼ ꢃ371.6ꢂ cm3 gꢃ 1 dmꢃ 1
(c¼ 1.02, CH2Cl2).
(S)-2-[4-[2-(Methylthio)ethyl]-4,5-dihydrooxazol-2-yl]pyridineꢁCuCl2
(34, C11H14Cl2CuN2OS)
To a solution of 87.4mg of 33 (0.39 mmol) in 15cm3 of MeOH, a solution of 67.0mg of CuCl2ꢁ2H2O
(0.40 mmol) in 5 cm3 of MeOH was added. The colour changed immediately to blue=turquoise. After
stirring for 2 h at room temperature the solvent was removed. The residue was dissolved in a small

1268
H. Brunner et al.
amount of MeOH and ether was added. After a few days at ꢃ30ꢂC green crystals were obtained, which
were suitable for X-ray structure analysis. Yield 110 mg (77%); LT PI LSI MS: m=z ¼ 385
(Mþ MeOH, 16), 320 (M–Cl, 73), 285 (M–2Cl, 100).
X-Ray Structure Analysis of 14 and 34
Data were collected with an imaging plate diffraction system (Stoe-IPDS, Stoe & CIE GmbH, Darm-
˚
stadt, Germany), using Mo-Kꢃ radiation, ꢄ ¼ 0.71073 A, with a graphite monochromator. Numerical
absorption correction was applied for compound 34. For data reduction the Stoe-IPDS software (Stoe
1998) was used [28]. The structure was solved with direct methods (SIR-97) [29] and refined by full-
matrix least-squares techniques (SHELXL 97) [30]. All H atoms were included at calculated positions
and refined using a riding model.
These data can be obtained free of charge at www.ccdc.cam.ac.uk=conts=retrieving.html or from
the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (inter-
nat.) þ 44-1223=336-033, E-mail: deposit@ccdc.cam.ac.uk].
Crystal data of 14. C35H39BNOPSi, M ¼ 559.54, T ¼ 173(1) K, translucent colourless prism,
monoclinic, P21=a, a ¼ 14.8737(9), b ¼ 12.4055(6), c ¼ 18.1180(12) A, ꢅ ¼ 112.640(7)ꢂ,
˚
3
V ¼ 3085.4(4)A , Z ¼ 4, ꢆ ¼ 0.156 mmꢃ 1, reflections collected ¼ 27171, independent ¼ 5009, final
˚
R indices [I > 2ꢇI]: R1 ¼ 0.0412, wR2 ¼ 0.1101. CCDC 199583.
Crystal data of 34. C11H14Cl2CuN2OS, M ¼ 356.76, T ¼ 173(1) K, translucent blue-green rod,
3
˚
˚
orthorhombic, P212121, a ¼ 8.3529(6), b ¼ 10.7267(7), c ¼ 16.0409(13)A, V ¼ 1437.25(18) A ,
Z ¼ 4, ꢆ ¼ 2.025 mmꢃ 1, reflections collected ¼ 18994, independent ¼ 2741, final R indices [I > 2ꢇI]:
R1 ¼ 0.0207, wR2 ¼ 0.0488. CCDC 199582.
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New Chiral Tridentate Ligands
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