Chiral oxazoline ligands. Synthesis and characterization of palladium, nickel and manganese complexes containing bidentate N,O and N,P moieties

Article abstract of DOI:10.1039/a703951d

Complexes of palladium, nickel and manganese, with the chiral ligand (+)-(4′R)-2-(4′-ethyl-3′,4′-dihydrooxazol-2′-yl) phenol HL^OH were synthesized and characterized by ¹H, ³¹P NMR spectroscopy, magnetic susceptibility and including the crystal structure determinations of trans-[PdL^OH₂] and [PdClL^OH(PPh₃)]. The L^OH moiety is co-ordinated in a bidentate fashion in neutral, cationic and anionic complexes, rigid on the NMR time-scale. Monodentate O-co-ordinated complexes were obtained only in the presence of phosphines. The manganese complex [MnClL^OH₂] showed little activity in the catalytic epoxidation of styrene. The first phosphinite oxazoline ligand L^OP was synthesized from HL^OH. Neutral and cationic alkyl and allyl complexes of palladium with it were obtained and characterized. The cationic complexes showed dynamic behaviour.

Full text of DOI:10.1039/a703951d

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Chiral oxazoline ligands. Synthesis and characterization of
palladium, nickel and manganese complexes containing bidentate
N,O and N,P moieties†
,
a
a
,a
a
Montserrat Gómez-Simón,* Susanna Jansat, Guillermo Muller,* David Panyella,
b
b
Mercè Font-Bardía and Xavier Solans
a
Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès, 1-11,
8028 Barcelona, Spain
Departament de Cristal lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona,
0
b
.
Martí i Franquès s/n, 08028 Barcelona, Spain
Complexes of palladium, nickel and manganese, with the chiral ligand (ϩ)-(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-
OH
1
31
2
Ј-yl)phenol HL were synthesized and characterized by H, P NMR spectroscopy, magnetic susceptibility
OH
OH
OH
and including the crystal structure determinations of trans-[PdL 2] and [PdClL (PPh )]. The L moiety is
3
co-ordinated in a bidentate fashion in neutral, cationic and anionic complexes, rigid on the NMR time-scale.
Monodentate O-co-ordinated complexes were obtained only in the presence of phosphines. The manganese
OH
complex [MnClL ] showed little activity in the catalytic epoxidation of styrene. The first phosphinite
2
OP
OH
oxazoline ligand L was synthesized from HL . Neutral and cationic alkyl and allyl complexes of palladium
with it were obtained and characterized. The cationic complexes showed dynamic behaviour.
The use of oxazoline ligands as chirality-transfer auxiliaries in a
wide range of catalytic reactions has been widely reported in
recent years. In particular, oxazolines have been used as chiral
auxiliaries, either alone or as arms in polyfunctional ligands, in
combination with several transition metals in allylic substitu-
8
X
7
6
9
1
0
5
O
11
4, 4′
N
1
2
3,4
3
tions, allylic amminations, alkene or ketone hydrosilylations,
2, 2′
5
6
alkene cyclopropanations, Diels–Alder reactions, copolymer-
1
7
8
9
ization reactions, epoxidations of olefins, Heck reactions and
X = OH (HLOH), OPPh2 (LOP
)
10
sulfide reactions. However, studies of the transition-metal
complexes containing the oxazoline groups, catalyst precursors
of the active species, are still highly limited, either from the
point of view of their preparative chemistry or reactivity pat-
terns. Several studies have been published on this aspect, above
Although the control of the stereoselectivity of the catalytic
processes with complexes containing two analogous oxazoline
18
moieties is mainly steric, some modulation with the contribu-
tion of electronic factors could be possible, as has also been
theoretically proposed, using ligands with mixed fragments
N᎐O, N᎐P . . .). It is necessary, therefore, to further our
understanding of the kind of isomers present in solid state and
in solution and of their interconversion processes, so that we
might discuss the stereoselectivity of the catalytic reactions.
This paper describes the preparation of mono(oxazoline)
11
all in the field of allyl complexes and their complexity has
13,14
12
recently been demonstrated by Sprinz et al. Yang et al.
reported a group of palladium compounds containing chiral
19
(
15
N,O-chelates. Kurosawa and co-workers have studied the dis-
tribution of diastereomers in η -allylbis(oxazoline)palladium
3
compounds which appear to be the intermediate species in the
16
allylic substitution reaction. Also, Floriani and co-workers
OH
OP
bidentate ligands HL
and L and the synthesis of pal-
prepared a number of chiral neutral and cationic alkylzirco-
nium complexes that could be used as precursors of polymer-
ization catalysts.
ladium, nickel and manganese chiral complexes, which can be
potential catalytic precursors or intermediates in catalytic pro-
cesses. The solid-state and solution structure of the anionic and
neutral complexes prepared are discussed. Also, the results of
the catalytic epoxidation of styrene with the manganese()
compound are described.
The oxazoline group alone or in combination with other
functionalities such as phosphine or pyridine type fragments
17
could be achieved in several ways. However, phosphinite–
oxazoline ligands have not previously been described in the lit-
erature. The preparation of the oxazoline fragment by reaction
between aminoalcohols and nitriles is an attractive method
since both types of compounds are commercially available
including a number of accessible enantiomerically pure amino-
alcohols. By using this synthetic procedure it is possible to
change the size of the substituents at the chiral carbon of the
oxazoline and therefore to achieve some modulation of the
asymmetric induction provided by the ligand.
Experimental
General
All compounds were prepared under a purified nitrogen atmos-
phere using standard Schlenk and vacuum-line techniques. The
solvents were purified by standard procedures and distilled
under nitrogen. -(Ϫ)-2-Aminobutanol (Janssen) was used
without previous purification. Zinc chloride (Merck) was puri-
fied following a classical procedure. Sodium hypochlorite
10%) was obtained from Panreac, Aliquat 336 and octyl-
benzene (standard for GC) from Aldrich and Fluka. Sytrene
(Fluka) was distilled immediately before use. Styrene oxide and
R-(Ϫ)-styrene oxide were from Aldrich.
20
2
0
(
†
Supplementary data available (No. SUP 57274, 2 pp.): the EPR
spectrum of complex 12a. See Instructions for Authors, J. Chem. Soc.,
Dalton Trans., 1997.
Non-SI unit employed: µ ≈ 9.27 × 10 J T
Ϫ24
Ϫ1
.
B
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764
3755

View Article Online
1
The NMR spectra were recorded on Varian XL-500 ( H,
toluene (0.35 g, 64%). M.p. = 86 ЊC (Found: C, 63.00; H, 5.27;
N, 2.30. Calc. for C H ClNO PPdؒC H : C, 62.98; H, 5.14; N,
19
standard SiMe ), Unity 300 ( F, 282 MHz, standard CFCl ),
Varian Gemini ( C, 50 MHz, standard SiMe ) and Bruker
DRX 250 ( P, 101 MHz, standard H PO ) spectrometers.
4
3
29 27
2
7
8
13
31
1
2.04%). P-{ H} NMR (CDCl ): δ 26.0.
4
3
31
3
4
Chemical shifts are reported downfield from standards. The IR
spectra were recorded on a Nicolet 520 FT-IR spectrometer.
The FAB mass chromatograms were obtained on a Fisons V6-
Quattro instrument, GC–mass spectrometric analysis on a
Hewlett-Packard 5890 Series II gas chromatograph (50 m Ultra
[2-(Benzyliminomethyl)phenyl-C,N][(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-
dihydrooxazol-2Ј-yl)phenolato-N,O]palladium(II) 3a. The cyclo-
23
metallated complex [{Pd(C H CH᎐NCH Ph)(µ-O CMe)} ]
6
4
2
2
2
OH
(0.21 g, 0.30 mmol) and HL (0.12 g, 0.60 mmol) were dis-
solved in dichloromethane (15 cm ) and stirred at room temp-
3
2
capillary column) interfaced to a Hewlett-Packard 5971 mass-
erature for 3 h. The reaction mixture was then concentrated
under reduced pressure, affording a yellow solid which was
recrystallized from dichloromethane and diethyl ether (0.21 g,
70%). M.p. (decomp.) = 135 ЊC (Found: C, 61.26; H, 4.73; N,
5.74. Calc. for C H N O Pd: C, 61.15; H, 4.93; N, 5.72%).
selective detector. Product analyses of catalytic reactions were
conducted on a Hewlett-Packard 5890 Series II gas chromato-
graph with either a 30 m Carbowax capillary column or a 25
or 50 m FS-Cyclodex β-I/P capillary column. Magnetic meas-
urements were carried out at variable temperature (300–4 K) on
polycrystalline samples with a pendulum-type magnetometer
25
23
2
2
[2-(2-Methoxyphenyliminomethyl)-4,5-dimethoxyphenyl-
C,N][(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-
N,O]palladium(II) 4a. The cyclometallated complex [{Pd[3,4-
(
Manics DSM8) equipped with a Drusch EAF 16 UE electro-
magnet. The magnetic field was approximately 1.5 T. Dia-
magnetic corrections were estimated from Pascal’s tables.
Optical rotations were measured at 25 ЊC at the sodium D
line on a Perkin-Elmer 241MC spectropolarimeter. Conduct-
ivities were obtained on a Radiometer CDM3 conductimeter.
Elemental analyses were carried out by the Serveis Científico-
Tècnics of the Universitat de Barcelona in an Eager 1108
microanalyser.
2
4
(MeO) C H CH᎐NC H OMe-2](µ-O CMe)} ] (0.09 g, 0.10
2
6
2
6
4
2
2
OH
mmol) and HL (0.04 g, 0.20 mmol) were dissolved in toluene
(15 cm ) and stirred at room temperature for 6 h. The reac-
3
tion mixture was then concentrated under reduced pressure,
affording an orange oil. The residue was dissolved in dichloro-
3
methane (10 cm ) and hexane added. After keeping the solu-
tion in a freezer overnight a yellow solid (0.10 g, 85%) was
separated. M.p. (decomp.) = 173 ЊC (Found: C, 57.20; H,
4.85; N, 4.65. Calc. for C H N O Pd: C, 57.20; H, 4.98;
Preparations
27
28
2
5
N, 4.94%).
(
؉)-(4ЈR)-2-(4Ј-Ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol,
OH
HL . This compound was synthesized following a published
procedure with certain modifications. -(Ϫ)-2-Aminobutanol
1.64 g, 18.40 mmol), 2-hydroxybenzonitrile (1.83 g, 15.40
mmol) and ZnCl (52.5 mg, 0.385 mmol) were dissolved in
toluene (25 cm ) and refluxed for 72 h under nitrogen. The
reaction mixture was filtered off and distilled in vacuo, afford-
ing a yellow oil (2.30 g, 78%), which was purified by flash chro-
matography (ethyl acetate). [α]D = ϩ52.3Њ (c 0.1, CHCl ).
21
[(4ЈR)-2-(4Ј-Ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-N,O]-
2,4,6-trimethylphenyl)(triphenylphosphine)palladium(II) 5a. n-
(
(
3
Butyllithium (0.28 cm , ca. 1.6 , 0.44 mmol) in hexane was
added to a solution of HL (0.086 g, 0.44 mmol) in tetra-
hydrofuran (10 cm ) at Ϫ78 ЊC. After 30 min the lithium
oxazolinato solution was added to a solution of [{Pd(C H -
2
OH
3
3
6
2
3
25
25
Me -2,4,6)(PPh )(µ-Br)} ] (0.24 g, 0.22 mmol) in thf (10 cm ).
3 3 2
3
After stirring for 12 h, the mixture was concentrated under
reduced pressure, affording an orange solid. The product was
recrystallized from toluene and hexane (0.20 g, 65%). M.p.
(
4ЈR)-1-(Diphenylphosphanyloxy)-2-(4Ј-ethyl-3Ј,4Ј-dihydroox-
OP OH
azol-2Ј-yl)benzene L . To a solution of compound HL (2.10
(
decomp.) = 110 ЊC (Found: C, 66.90; H, 5.93; N, 2.10. Calc. for
38 38
g, 11 mmol) and triethylamine (1.11 g, 11 mmol) in toluene (20
31 1
3
C H NOPPd: C, 67.31; H, 5.65; N, 2.07%). P-{ H} NMR
cm ) was added dropwise chlorodiphenylphosphine (2.43 g, 11
3
(CDCl ): δ 27.3.
mmol) in 10 cm of the same solvent at Ϫ78 ЊC. The mixture
3
was stirred for 6 h while the solution was warmed gradually to
room temperature. The white precipitate was filtered off and the
solution concentrated under reduced pressure to yield a dark
trans-Bis(dimethylphenylphoshine)bis[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-
dihydrooxazol-2Ј-yl)phenolato-N,O]palladium(II) 6a. To a solu-
3
3
tion of compound 1a (0.11 g, 0.22 mmol) in CH Cl (20 cm )
orange oil. This was dissolved in diethyl ether (20 cm ) and
2
2
3
was added a solution of dimethylphenylphosphine (0.09 g, 0.66
mmol) at Ϫ75 ЊC. The mixture was warmed at room temper-
ature, stirred for 2 h, then concentrated under reduced pressure,
affording a yellow solid which was recrystallized from di-
chloromethane and diethyl ether (0.13 g, 78%). M.p. = 135 ЊC
washed with degassed water (3 × 10 cm ). The organic phase
was dried over anhydrous Na SO , filtered, and the solvent was
2
4
OP
removed under reduced pressure to yield an orange oil, L
2.97 g, 72%).
(
trans-Bis[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol-
ato-N,O]palladium(II) 1a. To a solution of Pd(O CMe) (0.23
(Found: C, 59.50; H, 5.90; N, 3.52. Calc. for C38
C, 59.81; H, 6.08; N, 3.67%). P-{ H} NMR (CDCl
H
46
N
2
O
4
P
2
Pd:
): δ 33.8.
3
31
1
2
2
3
g, 1.05 mmol) in dichloromethane (10 cm ) was added a solu-
tion of HL (0.40 g, 2.10 mmol) in 5 cm of the same solvent.
The solution was stirred at room temperature for 2 h, then
OH
3
[(4ЈR)-2-(4Ј-Ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-N,O]-
3
(ç -2-methylallyl)palladium(II) 7a. To a solution of di(µ-chloro)-
3
3
26
concentrated to ca. 5 cm and hexane added. Orange crystals
bis(η -2-methylallyl)dipalladium
(0.25 g, 0.63 mmol) in
3
OH
(
0.38 g, 78%) were separated after keeping the solution in a
CH
2
Cl
2
(20 cm ) was added a solution of HL (0.12 g, 1.26
freezer for 2 d. M.p. (decomp.) = 145 ЊC (Found: C, 53.8; H,
mmol) and 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu) (0.19 g,
3
4
5
.92; N, 5.85. Calc. for C H N O Pd: C, 54.28; H, 4.97; N,
.75%).
1.26 mmol) in 10 cm of the same solvent. The mixture was
22
24
2
4
refluxed for 2 h. After cooling at room temperature, the solution
3
was concentrated to ca. 15 cm under reduced pressure and
Chloro[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-
N,O](triphenylphosphine)palladium(II) 2a. The complex
hexane added. A pale yellow solid (0.25 g, 57%) separated after
keeping the solution in a freezer overnight. M.p. (decomp.) =
140 ЊC (Found: C, 51.00; H, 5.30; N, 4.10. Calc. for C15H19-
22
[
PdCl(acac)(PPh )]
(acac = acetylacetonate) (0.40 g, 0.80
3
OH
mmol) and HL (0.16 g, 0.80 mmol) were dissolved in toluene
(
NO Pd: C, 51.22; H, 5.45; N, 3.98%).
2
3
20 cm ) at Ϫ78 ЊC. The mixture was warmed at room temper-
3
ature, stirred for 6 h, then concentrated under reduced pressure,
affording an orange solid. The product was recrystallized from
toluene and hexane, yielding orange crystals, which contained
(ç -Allyl)[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol-
ato-N,O]palladium(II) 8a. Complex 8a was prepared by the same
3
procedure as described above from bis(η -allyl)di(µ-bromo)-
3
756
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764

View Article Online
2
6
dipalladium (0.29 g) as a yellow solid (0.26 g, 61%). M.p.
decomp.) = 120 ЊC. (Found: C, 49.68; H, 4.88; N, 4.00. Calc.
for C H NO Pd: C, 49.79; H, 5.07; N, 4.15%).
(0.17 g, 4.01 mmol) added. The solution was again warmed at
3
(
reflux temperature for 30 min, then concentrated to ca. 5 cm
and hexane added. A green-grey solid separated, which was
recrystallized from dichloromethane and hexane (0.61 g, 50%).
M.p. (decomp.) = 98 ЊC (Found: C, 56.0; H, 5.05; N, 5.85. Calc.
14
17
2
Bis[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-
N,O]nickel(II) 9a. To a solution of Ni(O CMe) (0.60 g, 3.40
mmol) in tetrahydrofuran (15 cm ) was added a solution of
HL (2.0 g, 10.50 mmol) in 10 cm of the same solvent. The
solution was stirred at room temperature overnight. The mix-
ture was then concentrated to ca. 10 cm and hexane (15 cm )
added. A dark green solid (1.0 g, 67%) separated after keeping
the solution in a freezer overnight. M.p. (decomp.) = 110 ЊC
Found: C, 59.98; H, 5.56; N, 6.24. Calc. for C H N NiO : C,
0.17; H, 5.51; N, 6.38%).
for C H ClMnN O : C, 56.12; H, 5.14; N, 5.95%).
22 24
2
4
2
2
3
OH
3
Dichloro[(4ЈR)-1-(diphenylphosphanyloxy)-2-(4Ј-ethyl-3Ј,4Ј-
dihydrooxazol-2Ј-yl)benzene-N,P]palladium(II) 1b. To a solu-
OP
3
3
3
tion of L (0.40 g, 1.07 mmol) in toluene (10 cm ) at Ϫ78 ЊC
29
was added a solution of [PdCl (cod)] (cod = cycloocta-1,5-
diene) (0.30 g, 1.07 mmol) in chloroform (10 cm ). The mixture
2
3
was stirred at room temperature overnight. The solvent was
removed under reduced pressure, affording an orange solid
(
22 24 2 4
6
3
which was washed with diethyl ether (4 × 10 cm ). The solid was
recrystallized from dichloromethane and hexane (0.48 g, 81%).
[
(4ЈR)-2-(4Ј-Ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-
M.p. (decomp.) = 155 ЊC (Found: C, 50.02; H, 4.10; N, 2.45.
N,O](2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene)nickel(II)
perchlorate 10a. The compound [{NiL(µ-OH)} ][ClO ]
L = 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene) (0.45 g,
31
Calc. for C H Cl NO PPd: C, 49.98; H, 4.01; N, 2.53%). P-
2
7
23 22
2
2
2
4 2
1
{
H} NMR (CDCl ): δ 135.0.
3
(
0
OH
.628 mmol) and HL (0.240 g, 1.25 mmol) were dissolved in
3
Chloro[(4ЈR)-1-(diphenylphosphanyloxy)-2-(4Ј-ethyl-3Ј,4Ј-
dichloromethane (20 cm ) at room temperature and then
warmed at reflux temperature for 1 h. At room temperature a
dihydrooxazol-2Ј-yl)benzene-N,P]methylpalladium(II) 2b. To a
OP
3
solution of L (0.40 g, 1.07 mmol) in toluene (10 cm ) at
3
green solid was obtained after the addition of hexane (20 cm ).
30
Ϫ78 ЊC was added a solution of [PdCl(Me)(cod)] (0.28 g, 1.07
The product was filtered off and recrystallized from dichloro-
methane and hexane (0.60 g, 83.3%). M.p. = 180 ЊC (Found:
C, 49.80; H, 6.53; N, 9.69. Calc. for C H ClN NiO : C, 50.24;
H, 6.85; N, 9.76%). Positive-ion FAB mass spectrum: m/z 475
M ϩ 1, 73), 474 (M, 39), 473 (M Ϫ 1, 100%), 307 (28), 284
3
mmol) in 10 cm of the same solvent. After stirring for 3 h at
room temperature the mixture was filtered through Celite under
24
39
4
6
3
nitrogen. The solution was then concentrated to ca. 10 cm
under reduced pressure and hexane was added. Pale yellow
crystals (0.45 g, 79%) separated after keeping the solution in a
freezer overnight. M.p. (decomp.) = 115 ЊC (Found: C, 54.65;
H, 4.87; N, 2.75. Calc. for C H ClNO PPd: C, 54.15; H, 4.73;
(
(
2
24), 283 (40.5), 282 (51.4) and 281 (31%). Λ = 148 S cm
mol (acetonitrile, 8.8 × 10 ).
M
Ϫ1
Ϫ4
2
4
25
2
31
1
N, 2.63%). P-{ H} NMR (CDCl ): δ 149.4.
3
Tetraethylammonium [(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-
2
Ј-yl)phenolato-N,O]bis(pentafluorophenyl)nickel(II) 11a. The
Acetonitrile-[(4ЈR)-1-(diphenylphosphanyloxy)-2-(4Ј-ethyl-
3Ј,4Ј-dihydrooxazol-2Ј-yl)benzene-N,P]methylpalladium(II)
tetrafluoroborate 3b. To a solution of compound 2b (0.30 g, 0.56
28
salt [NEt ] [{Ni(C F ) (µ-OH)} ] (0.16 g, 0.148 mmol) and
HL (0.057 g, 0.296 mmol) were dissolved in dichloromethane
4
2
6
5
2
2
OH
3
3
(
5 cm ) and stirred at room temperature for 2 h. The reaction
mmol) in dichloromethane (10 cm ) was added a solution of
3
mixture was concentrated under reduced pressure, affording a
yellow oil. The residue was washed with diethyl ether and dis-
solved in dichloromethane (5 cm ) and hexane (20 cm ). A yel-
low solid was obtained after cooling the solution in a refriger-
ator overnight. The product was filtered off, washed with hex-
ane, and dried under reduced pressure (0.17 g, 80.5%). M.p.
silver tetrafluoroborate (0.11 g, 0.56 mmol) in 5 cm of the same
solvent in the dark. The solution was stirred for 20 min then
acetonitrile (0.03 g, 0.73 mmol) was added. After stirring for 1 h
the mixture was filtered through Celite under nitrogen and the
3
3
3
filtrate concentrated to ca. 5 cm and toluene added. An orange
solid (0.20 g, 57%) separated after keeping the solution in a
freezer for 3 d. M.p. (decomp.) = 112 ЊC (Found: C, 49.75; H,
4.35; N, 4.70. Calc. for C H BF N O PPd: C, 50.00; H, 4.52;
(
decomp.) = 138 ЊC (Found: C, 52.00; H, 4.85; N, 4.02. Calc. for
C H F N NiO : C, 52.19; H, 4.52; N, 3.93%). Negative-ion
31
32 10
2
2
26 28
2
4
2
2
Ϫ1
Ϫ4
FAB mass spectrum: m/z 584 (M ϩ 1, 42), 582 (M Ϫ 1, 100),
3
8
N, 4.48%). Λ = 135 S cm mol (acetonitrile, 8.8 × 10 ).
M
2
Ϫ1
31
1
91 (24) and 315 (11%). Λ = 130 S cm mol (acetone,
P-{ H} NMR (CDCl ): δ 135.0.
M
3
Ϫ4
19
.8 × 10 ). F NMR (CDCl ): δ Ϫ122.1 (1 F , m), Ϫ123.9 (2
3
o
3
F , m), Ϫ125.3 (1 F , m), Ϫ170.1 [1 F , t, J(FF) 19.8], Ϫ171.5
[(4ЈR)-1-(Diphenylphosphanyloxy)-2-(4Ј-ethyl-3Ј,4Ј-dihydro-
o
o
p
3
3
[
1 F , t, J(FF) 19.8 Hz], Ϫ172.4 (3 F , m) and Ϫ173.4 (1 F ,
oxazol-2Ј-yl)benzene-N,P](ç -2-methylallyl)palladium(II) tetra-
p
m
m
3
m).
fluoroborate 4b. To a solution of (cycloocta-1,5-diene)(η -2-
31
methylallyl)palladium tetrafluoroborate (0.30 g, 0.84 mmol)
3
OP
in dichloromethane (10 cm ) was added a solution of L (0.32
Bis[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenolato-
N,O]manganese(II) 12a. To a solution of Mn(O CMe) ؒ4H O
3
g, 0.84 mmol) in 10 cm of the same solvent. After stirring for 1
2
2
2
3
h at room temperature, the mixture was concentrated under
(
0.64 g, 2.61 mmol) in absolute ethanol (20 cm ) was added a
OH 3
3
reduced pressure and dichloromethane (10 cm
) and diethyl
solution of HL (1.00 g, 5.23 mmol) in 10 cm of the same
solvent. The solution was concentrated under reduced pressure,
affording a dark oil. The residue was treated with diethyl ether
and hexane. A green solid was obtained after cooling the
solution in a refrigerator overnight, filtered off, washed with
hexane and dried under reduced pressure (0.82 g, 72%). M.p.
3
ether (10 cm ) were added. An orange solid (0.40 g, 77%) separ-
ated after keeping the solution in a freezer overnight. M.p.
(
decomp.) = 130 ЊC (Found: C, 51.90; H, 4.35; N, 2.15. Calc. for
C H BF NO PPd: C, 52.04; H, 4.69; N, 2.25%). Λ = 136 S
27 29
2
4
2
M
Ϫ1
Ϫ4
31
1
cm mol (acetonitrile, 8.8 × 10 ). P-{ H} NMR (CDCl ):
3
δ 125.0.
(
decomp.) = 90 ЊC (Found: C, 60.00; H, 5.40; N, 6.60. Calc. for
C H MnN O : C, 60.69; H, 5.56; N, 6.43%).
22
24
2
4
Catalytic epoxidation reactions
Chlorobis[(4ЈR)-2-(4Ј-ethyl-3Ј,4Ј-dihydrooxazol-2Ј-yl)phenol-
ato-N,O]manganese(III) 13a. To a solution of Mn(O CMe) ؒ
All reactions were carried out under nitrogen at room temper-
ature in a Schlenk tube (25 cm ) equipped with a stirring bar
3
2
2
3
4
H O (0.64 g, 2.61 mmol) in absolute ethanol (20 cm ) was
and an air-tight rubber septum. Styrene (5.7 mmol) and octyl-
2
OH
3
3
added a solution of HL
(1.00 g, 5.23 mmol) in 10 cm
benzene (2.2 mmol) in dichloromethane (5 cm ) were added to
of the same solvent. The solution was stirred at reflux tem-
perature for 1 h, then cooled at room temperature and LiCl
metal catalyst (0.044 mmol) and aliquat 336 (0.1 mmol). The
GC analyses were performed by withdrawing several aliquots
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764
3757

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with the aid of a hypodermic syringe. After the initial analysis,
NaOCl (7 cm ) was immediately added. The products (styrene
oxide and phenylacetaldehyde) were quantified by the internal
standard method. Oxidation products were isolated by column
chromatography. Unchanged styrene was eluted with pentane
3
13
a
Table 1 Proton (250) and C (50 MHz) NMR data for the oxazoline
b
ligands. Multiplicity and coupling constants (in Hz) in parentheses
1
13
Ligand δ( H)
δ( C)
OH
HL
1: 0.99 (3 H, t, 7.5)
2, 2Ј: 1.61 (1 H, ph, 7.0), 1.66 (1 H, ph, 7.0)
1: 10.0
2: 28.7
3: 66.7
and oxidation products were eluted with pentane–ether
1
(
75:25). The H NMR spectrum indicated that the styrene
3
: 4.25 (1 H, m)
oxide to phenylacetaldehyde ratio was 15:1. The enantiomeric
excess of the epoxide was determined by capillary GC using a
4
5
: 71.4
: 164.9
3
0 m Carbowax column coupled to a 50 m Cyclodex-β column
6: 125.2
7: 159.8
(
oven temperature 85 ЊC isothermal). The optical purity of
4
8
8
8
9
7
, 4Ј: 3.99 (1 H, pt, 7.8), 4.42 (1 H, dd, 9.5, Aromatic CH:
the epoxide was also analyzed by reduction to 1- and 2-
phenylethanol by lithium aluminium hydride in thf and GC
analysis on a 25 m Cyclodex-β column (oven temperature 85 ЊC
isothermal).
.5)
116.6, 118.5,
127.9, 133.1
, 11: 7.00 (1 H, dd, 8.0, 1.0), 7.63 (1 H, dd,
.0, 2.0)
, 10: 6.84 (1 H, td, 7.5, 1.5), 7.34 (1 H, td,
.5, 2.0)
OH: 12.3 (1 H, br)
1: 0.95 (3 H, t, 7.5)
Crystallography
OP c
L
1: 9.6
The crystal data and data-collection parameters are given in
Table 4. Crystals of complex 1a were obtained by slow diffusion
of hexane over a dichloromethane solution of the complex.
Similarly, crystals of 2a were obtained by slow diffusion of
hexane over a toluene solution of the complex.
The crystal data for complex 1a were measured on an Enraf-
Nonius CAD4 four-circle diffractometer. Unit-cell parameters
were determined from automatic centring of 25 reflections
2
3
, 2Ј: 1.56 (1 H, ph, 7.0), 1.68 (1 H, ph, 7.0)
2: 28.3
3: 66.3
: 4.16 (1 H, m)
4
5
: 71.0
: 164.6
6: 110.3
7: 159.6
Aromatic CH:
133–117
4
1
, 4Ј: 3.86 (1 H, pt, 8.0), 4.30 (1 H, dd,
0.0, 8.0)
Aromatic H: 8.2–7.0 (14 H, m)
(
12 < θ < 21Њ) and refined by the least-squares method. Inten-
a
13
Spectra recorded in CDCl ; C NMR spectra were proton decoupled;
sities were collected with graphite-monochromatized Mo-Kα
radiation (λ 0.710 69 Å), using the ω–2θ scan technique. 6604
Reflections were measured in the range 2.21 < θ < 29.96Њ, 6257
of which were non-equivalent by symmetry [Rint (on I) =
3
b
δ in ppm. Abbreviations: br = broad; d = doublet; h = hextuplet;
c 31
m = multiplet; p = pseudo; t = triplet.
P31 (101 MHz) NMR spectrum
recorded in CDCl ; proton decoupled; δ( P) 111.3.
3
0
.012]. 5568 Reflections were assumed as observed applying the
factor was 0.036, wR = 0.074 and goodness of fit = 0.987 for all
observed reflections. Number of refined parameters 465. Max-
imum shift/e.s.d. = 4.0, mean = 0.15. Maximum and minimum
condition I > 2σ(I). Three reflections were measured every 2 h
as orientation and intensity controls; significant intensity decay
was not observed. Lorentz-polarization but not absorption
corrections were made.
Ϫ3
peaks in final difference synthesis 0.448 and Ϫ0.340 e Å ,
respectively.
CCDC reference number 186/662.
The structure was solved by Patterson synthesis, using the
32
SHELXS computer program and refined by full-matrix least
squares with SHELXL 93, using 6257 reflections (very neg-
ative intensities were ignored). The function minimized was
33
Results and Discussion
Ligands
2
2 2
2
2 Ϫ1
Σw F | Ϫ |F | | , where w = [σ (I) ϩ (0.0634P) ]
and P =
o
c
2
2
(
|F | ϩ 2|F | )/3; f, f Ј and f Љ were taken from ref. 34. The extinc-
o
c
OH
The oxazoline HL was prepared in a one-pot synthesis from
tion coefficient was 0.0060(6). The chirality was defined from
35
the Flack coefficient, 0.02(3). Twenty-three H atoms were
located by a difference synthesis and refined with an overall
isotropic thermal parameter and 25 were computed and refined
with an overall isotropic thermal parameter using a riding
commercially available starting materials, following general
published procedures with minor modifications. It was purified
in two steps: first by a distillation under reduced pressure, fol-
lowed by a silica gel column chromatography of the residue.
2
OP
OH
model. The final R (on F) factor was 0.032, wR (on |F| ) = 0.085
The phosphinite L
was prepared from HL by treatment
with PPh2Cl in presence of triethylamine. The ease with which
the compound was oxidized is noteworthy and as a result it was
not possible to measure the optical rotation of the pure com-
pound accurately. Full details of the syntheses are given in the
Experimental section; NMR data are given in Table 1. All
methylene protons are diastereotopic appearing in different
positions.
and goodness of fit = 1.151 for all observed reflections. Number
of refined parameters 617. Maximum shift/e.s.d. = 0.01, mean
shift/e.s.d. = 0.00. Maximum and minimum peaks in the final
Ϫ3
difference synthesis were 1.056 and Ϫ0.482 e Å , respectively.
The crystal data for complex 2a were measured on a Philips
PW-1100 four-circle diffractometer. Unit-cell parameters were
determined from automatic centring of 25 reflections (8 <
θ < 12Њ) and refined by the least-squares method. Intensities
were collected as above. 5254 Reflections were measured in
the range 2.25 < θ < 29.95Њ, 4310 reflections being assumed as
observed applying the condition I > 2σ(I). Significant intensity
decay was not observed. Corrections as above.
OH
Complexes of L
OH
The proton of the hydroxo group in the oxazoline HL was
acid enough to react easily with metallic salts containing basic
anions such as acetate or acetylacetonate (Scheme 1), affording
compounds with the anionic bidentate chiral ligand. In this way
we obtained homochiral bis(oxazolinato)-palladium, -nickel
The structure was solved and refined as for complex 1a, using
5
204 reflections (very negative intensities were not considered).
2
2 2
The function minimized was Σw F | Ϫ |F | | , where w =
and -manganese complexes 1a, 9a and 12a respectively, and
o
c
2
2
2
Ϫ1
2
OH
[
σ (I) ϩ (0.0368P) ϩ 1.5024P] and P = (|F | ϩ 2|F | )/3. The
[PdClL (PPh )] 2a. The chlorobis(oxazolinato)mangan-
o
c
3
extinction coefficient was 0.006 55. The Flack coefficient was
.05(3). A toluene group was located in a disordered position
and the occupancy factor was refined for each position, giving
.70(1) for the non-primed atoms. Nineteen H atoms were
located from a difference synthesis and eight were computed
and refined with an overall isotropic thermal parameter using
a riding model for computed hydrogen atoms. The final R
ese() complex 13a was obtained by refluxing ethanolic solu-
tionsof 12awithLiClunderaerobicconditions.Thereactionwas
monitored by EPR spectroscopy at room temperature. Initially,
the ethanolic reaction mixture showed bands expected for man-
ganese() compounds; the reflux was maintained until no
absorption bands were observed in the EPR spectra, since the
manganese() species are EPR silent.
0
0
3
758
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764

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Pd(O2CMe)2
MeCO2H
Ni(O2CMe)2
1
a
–
OH
9
a
–
MeCO2H
O
2
Mn(O2CMe)2•4H2O
LiCl/O2
N *
12a
13a
–
MeCO2H
Et
HLOH
[
PdCl(acac)PPh3]
Hacac
2a
–
Et
*
PPh3
Cl
O
O
O
N
N
O
Pd
M
N
O
*
O
Et
O
*
Et
Fig. 1 View of the molecular structure of complex 1a (molecule A),
showing the atom labelling scheme. Hydrogen atoms have been omitted
for clarity
2a
1
9
1
a, M = Pd
a, M = Ni
2a, M = Mn
Et
*
O
N
N
O
compound 1a. Similar nickel complexes described in the liter-
ature showed only one isomer in solution.
The molecular structure of complex 1a is shown in Fig. 1.
Selected bond lengths and angles are presented in Table 5. The
palladium atom is bonded to two nitrogen and two oxygen
atoms; both pairs are in trans position (O᎐Pd᎐N angles 88.5–
Mn
Cl
14
O
*
Et
1
3a
9
1.5 ЊC). This arrangement forces the molecule to orient the
Scheme 1
two ethyl groups of the oxazoline ligands to the same side of
the molecular plane. The unit cell of 1a contains two non-
symmetric equivalent molecules which are pseudo-related by a
two-fold axis parallel to the crystallographic a axis (Fig. 2).
Each molecule is formed by six rings: this means two phenyl
groups, two oxazoline groups and two six-membered rings; the
latter are connected by the metal atom. Except for the phenyl
groups, the other rings are not strictly planar. For the oxazoline
N
Et
Et
O
N
O
O
N
PMe Ph
2
CH2Cl2
O
Pd
Et
+ 2 PMe Ph
2
Pd
O
O
PhMe2P
O
*
O
N
3
moieties, the two sp -carbon atoms are twisted with regard to
2
the heteroatoms and the sp -carbon atom of the ring. More-
1a
over, the two six-membered rings containing the palladium are
not coplanar. The angle between them is 7.82Њ for molecule A
and 9.84Њ for B. On the other hand, the angle between the
phenyl ring and the six-membered palladacycle is very small
Et
6
a
Scheme 2
(
0.2–3.7Њ). So, the loss of the planarity of the whole molecule is
The new complexes prepared in this work have been fully
characterized by a range of techniques. Proton NMR data for
the diamagnetic compounds of nickel and palladium are given
in Tables 2 and 3. For the paramagnetic ones, magnetic sus-
ceptibility and EPR measurements have been done. In order to
due to the tetrahedral distortion in the palladium co-ordination
sphere. If we compare the two inequivalent molecules in the
unit cell the shortest intermolecular distance, i.e. that between
the palladium atom of one molecule and that of the other, is the
Pd᎐N distance [e.g. Pd(A) ؒ ؒ ؒ N(1B) 3.795, Pd(B) ؒ ؒ ؒ N(2A)
3.687 Å].
1
elucidate the isomeric composition in solution of 1a and 9a, H
NMR spectra were recorded in CDCl over the range Ϫ50 to
ϩ50 ЊC. For 1a the H NMR study showed that, in solution,
only one isomer was present. Moreover, the reactivity of 1a
The crystal structure of complex 2a (Fig. 3) showed the pres-
ence of discrete mononuclear molecules, separated by van der
Waals distances. Selected bond lengths and angles are listed in
Table 6; all the bond distances are in the expected range. The
complex exhibits an almost square-planar geometry with the
nitrogen and phosphorus atoms in trans position. The following
small displacements (Å) are observed from the least-squares
plane defined by the atoms of the co-ordination sphere PdP-
ClNO(1) (plane A): Pd, 0.022; P, 0.006; Cl, Ϫ0.016; N, 0.006;
O(1), Ϫ0.018 Å. Slight alternative displacements from the least-
squares plane NO(2)C(7)C(8)C(9) (plane B) are observed for
the atoms of the oxazoline group: N, Ϫ0.071; O(2), 0.075; C(7),
Ϫ0.001; C(8), Ϫ0.111; C(9), 0.108 Å. The cycle PdO(1)C(1)-
C(6)C(7)N (plane C) shows a boat conformation with devi-
ations of Pd Ϫ0.258 and C(6) Ϫ0.021 Å from the plane defined
by the other four atoms. The angles between normal to the
planes AB, AC and BC are 11.54, 14.71 and 4.43Њ, showing the
planarity of the whole molecule. The greater trans influence of
3
1
towards dimethylphenylphosphine (Scheme 2) afforded a yel-
31
low solid 6a; its P NMR spectrum (over the range Ϫ50 to
ϩ50 ЊC) showed a single resonance (δ 33.8, at 298 K). Owing
to the lack of a symmetry plane in the square-planar co-
1
ordination sphere, the H NMR spectrum showed two singlets
for the different phosphine methyl groups. Besides, 1a was
characterized by X-ray diffraction, demonstrating that this iso-
mer was the trans one. A similar trans structure has been deter-
14
mined by Nicholas and co-workers. For 9a the spectra of the
green solution showed the presence of two isomers (cis and
trans), with a major:minor isomer ratio of 2:1. The isomeric
composition was unchanged in the whole range of temperature
tested, and no line broadening was detected. So, the exchange
between both isomers was not appreciable. Probably, the major
isomer is the trans one, according to the analogous chemical
shifts observed for the protons 2, 2Ј and 3 for the palladium
the PPh ligand in the complex is clearly observed: the bond
3
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764
3759

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+
Et
*
2+
O
N
H
O
N
N
O
CH2Cl2
– H2O
1/2
N
Ni
N
N
Ni
N
ClO4–
2
ClO4–
10a
HLOH
+
–
Et
*
2
-
O
H
O
N
O
CH2Cl2
F5C6
F5C6
F5C6
F5C6
NEt4+
1/2
Ni
Ni
–
H2O
2
NEt4+
11a
macrocycle N
N
N :
N
NH
N
Scheme 3
Fig. 2 Unit cell for complex 1a showing the two non-symmetric
equivalent molecules
Fig. 4 Plot of χ T vs. T for complex 10a. The solid line shows the best
m
fitting (see Results and Discussion section)
ordinated in a bidentate form. For the five-co-ordinated com-
plex 10a, the magnetic susceptibility value at room temperature
corresponds to two unpaired electrons (µeff = 3.22 µ ), but with
B
a large orbital contribution. The molar magnetic susceptibility
was measured over the temperature range 291–4.8 K. At room
3
Ϫ1
temperature χ T is 1.30 cm K mol ; this value decreases slow-
m
3
Ϫ1
ly until 25 K (1.17 cm K mol ) and at temperatures below 16 K
the decrease is rapid, reaching 0.11 cm K mol at 4.8 K. The
3
Ϫ1
experimental data were fitted using equation (1) where x is D/
Fig. 3 View of the molecular structure of complex 2a, showing the
atom labelling scheme
2
2
Ϫ1
Ϫ1
2
Ng µ 2x Ϫ 2 exp(Ϫx)x ϩ exp(Ϫx)
χ =
(1)
m
3
kT
1 ϩ 2 exp(Ϫx)
distance Pd᎐N is 2.051(4) Å, whereas those in 1a are in the
range 1.999(4)–2.010(4) Å.
A powder sample of the paramagnetic bright green manga-
Ϫ1
kT (Fig. 4). The best fit is given by D = 14.9 cm and g = 2.20.
The parameter D is related to the geometry around the nickel()
ion. In this case, the high value obtained is in accordance with
nese() complex 12a showed a µeff = 6.43 µ at 290 K, which was
B
38
higher than expected for five unpaired electrons (µeff = 5.92 µB
spin only) and the EPR spectrum (SUP 57274) showed an intense
broad absorption in the g ≈ 2 region at room temperature and
at 77 K. However, for an ethanolic sample at 77 K, the six-line
the high anisotropy for the five-co-ordinated species.
The F NMR spectrum of complex 11a showed the signals
of two different C F groups according to the cis configuration.
Moreover, in the proton NMR spectrum a large unexpected
high-field shift for proton 3 with respect to that of complex 9a
was observed, probably due to the increase in electron density
in the co-ordination sphere of the anionic complex.
with bridged hydroxopalladium
species, [{PdPh(PPh )(µ-OH)} ] was tested, but it was not
19
6
5
55
5
2
36
splitting by the Mn nuclei (I = –) was observed. The grey-
green manganese() complex 13a gave a µef 4f = 4.91 µ at 294 K
B
37
close to the spin-only value expected for a d ion (4.90 µ ).
B
2
8
OH
Since OH bridges react easily towards protic acids, we also
The reactivity of HL
OH
25
studied the reactivity of HL
with bridging hydroxonickel
3 2
species (Scheme 3), like [{NiL(µ-OH)} ][ClO ] (L = 2,4,4,9-
possible to separate the expected organometallic compound,
because the reaction mixture decomposed affording Pd . How-
2
4 2
0
tetramethyl-1,5,9-triazacyclododec-1-ene) and [NEt ] [{Ni-
4
2
OH
(
C F ) (µ-OH)} ] affording the paramagnetic [NiL (L)]ClO4
ever, when the reaction was performed with bridging acetato
6
5
2
2
OH
OH
complex 10a and the diamagnetic [NEt ][Ni(C F ) L ] com-
plex 11a, respectively. In both cases, the L ligand remained co-
species we obtained the [Pd(C,N)L ] complexes, where C,N is
4
6
5 2
OH
a strongly anchored imine fragment [C,N is C H CH᎐NCH Ph
6
4
2
3
760
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764

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a
Table 2 Proton NMR (500 MHz) data for the oxazolinato and phosphinite complexes. Multiplicity and coupling constants (in Hz) in parentheses
Proton
Complex
1
2, 2Ј
1.00 (t, 7.5) 1.70 (m), 4.48 (m) 4.43 (dd, 7.8,
.08 (m) 3.25), 4.53 (t, 7.5)
3
4, 4Ј
11
10
9
8
Other
—
1
a
7.57 (dd, 6.54
1.8, 8.5) (ddd,
7.20
6.80 (dd,
1.0, 8.5)
2
(ddd,
8.5, 7.0,
1.5)
8
1
.5, 7.0,
.5)
2
a
0.94 (t, 7.5) 1.66 (m), 4.80 (m) 4.37 (dd, 8.8,
.08 (m) 3.75), 4.46 (t, 8.5)
7.56 (dd, 6.49
7.02
6.08 (dd,
8.5, 10)
—
2
8.25,
.8)
(ddd,
8.0, 7.0,
1
(ddd,
8.5, 7.0,
1.5)
1
.5)
0.91 (t, 7.5) 1.70 (m), 4.77 (m) 4.34 (dd, 8.0, 4.5), 7.55 (dd, 6.44
.92 (m) 4.57 (t, 8.7) 8.0, 2.0)
0.58 (t, 7.5) 2.02 (m), 4.41 (m) 4.65 (dd, 8.0, 4.5), 7.54 (dd,
.55 (m) 3.99 (t, 8.5) 8.0, 1.7)
0.93 (t, 7.7) 1.65 (m), 4.79 (m) 4.35 (dd, 8.7, 3.7), 7.57 (dd, 6.50
.05 (m) 4.44 (t, 8.5) 8.0, 2) (ddd,
3
4
5
a
a
a
7.19
6.44
CH᎐N: 7.87 (s)
CH N: 4.92 (d, 14), 5.19 (d, 14)
CH᎐N: 7.85 (s), 7.0–7.5 (m)
OMe: 3.85 (s), 4.09 (s), 4.20 (s)
᎐
2
1
6.51 (t,
7.9)
᎐
2
7.02
6.00 (dd, PPh : 7.4–7.5 (m), 7.7–7.8 (m)
8.5, 1.0) Mesityl: 2.14 (s), 2.27 (s), 2.80
(s), 6.38 (s), 6.52 (s)
3
2
(ddd,
8.5, 7.0,
1.5)
8
1
.0, 7.0,
.5)
6
9
a
a
0.87 (t, 7.4) 1.13 (m), 4.16 (m) 3.90 (t, 7.7), 4.34 7.50 (dd, 6.87 (d,
.05 (m) (t, 8.7) 7.0, 1.5) 8.3)
6.73 (t,
6.5)
6.39 (t,
8.0)
PMe Ph: 1.58 (s), 1.64 (s), 7.6
(m)
—
2
2
b
0.97 (t, 7.5) 1.60 (m), 4.03 (m) 4.28 (m), 4.40 (m) 7.43 (m) 6.44 (m) 7.05 (m) 6.52 (m)
.00 (m)
.02 (t, 7.5) 1.67 (m),
.07 (m)
2
1
3.95 (m) 4.26 (m), 4.35 (m)
2
1
1a
0.54 (t, 7.2) 1.60 (m)
2.85 (m) 4.04 (dd, 8.5, 3.5), 7.46 (dd, 6.32 (pt, 7.01
6.43 (pd, NEt : CH , 1.20 (t, 7.2); CH ,
4
3
2
c
4.07 (t, 8.5)
7.8, 1.8) 7.4)
(ddd,
8.4)
3.11 (q, 7.2)
8
1
e
.6, 6.8,
.8)
d
1
2
b
b
1.03 (t, 7.5) 1.60 (m)
4.30 (m) 4.00 (dd, 8.5, 6.0),
e
e
e
e
6.10 (m)
—
4
.40 (dd, 9.0, 9.8)
0.69 (t, 7.5) 1.55 (m), 5.23 (m) 4.19 (dd, 8.7,
.73 (m) 6.25), 4.54 (dd,
e
6.03 (dt, Pd᎐Me:
7.5, 1.5) 0.58 (d, 3.5)
f
1
8
.8, 9.8)
a
b
Spectra recorded in CDCl ; δ in ppm, qnt = quintuplet. In italic, data for the minor isomer. No assignment was possible for the aromatic protons
3
c
d
of the two isomers. Overlapped with the resonance of the methyl proton of the tetraethylammonium cation. Spectrum recorded on a 300 MHz
spectrometer. Aromatic protons in the range δ 8.2–6.5. H-{ P} NMR spectrum has been recorded.
e
f 1
31
1
a
Table 3 Selected H NMR (500 MHz) data for complexes 7a and 8a. Coupling constants (in Hz) in parentheses
R
Hsyn
Hanti
b
c
d
1
2, 2Ј
3
4, 4Ј
Hsyn
3.12
Hanti
R
Complex
7
a
0.91
7.5)
0.89
(7.5)
1.54
(m)
1.72
(m)
1.79
(m)
1.55
(m)
1.90
(m)
4.10
(m)
4.16
(m)
4.24
4.25
(8.5, 1.5)
4.39
(17.5, 6.5)
4.41
(8.5, 1.5)
4.51
3.22
(2.5)
3.78
(2.5)
3.22
(br)
2.53
2.95
2.52
2.90
2.11
2.16
(
(8.5, 1.5)
4.39
(15, 8.5)
3.16
(8.5, 1.5)
3.43
(15, 8.5)
(3.0)
3.77
(3.0)
3.16
(pt)
1
.63
(
m)
8
a
1.18
7.5)
0.98
(7.5)
1.80
(m)
3.80
(m)
4.45
(m)
2.40
2.80
2.33
2.90
5.30
(m)
5.20
(m)
(
1
.70
3.52
(br)
3.48
(br)
(
m)
(15, 8.5)
a
b
c
d
Spectra recorded in CDCl ; δ in ppm. Left column, major isomer; right column, minor isomer. Triplet. Doublet of doublets. Doublet.
3
for 3a and 3,4-(MeO) C H CH᎐NC H (OMe-2) for 4a]
the position of the ethyl group of the oxazoline ligand relative
2
6
2
᎐
6
OH
4
(
Scheme 4). Also, the reactivity of HL with bridging bromo
to the substitution on the central allyl carbon (exo and endo
n
13
1
precursors in the presence of a base, such as dbu or LiBu , was
studied. In the latter case the oxazoline HL was previously
deprotonated by LiBu in thf and the resulting lithium salt
isomers). A variable-temperature H NMR study of complex
7a showed that the isomer ratio did not suffer significant
changes over the temperature range Ϫ50 to ϩ50 ЊC. Further-
more, a change was not observed in the isomer composition
OH
n
added directly over the bridging bromo precursor, [{Pd-
(
C H Me -2,4,6)(PPh )(µ-Br)} ], giving the aryl complex 5a.
after standing the complex at room temperature in CDCl for a
6
2
3
3
2
3
The geometry of the complex must be analogous to that
observed in 2a since the proton NMR spectra of the ligands are
identical. The lack of a symmetry plane in the co-ordination
sphere was evident because the two o-methyl and the two
phenyl protons of the mesitylene ligand appeared with different
chemical shifts. Using dbu as a base, it was possible to separate
the allyl complexes 7a and 8a in good yields (Scheme 4). These
were obtained as a mixture of two isomers (ratio 55:45), due to
week. Therefore the isomer interconversion is not appreciable
(Scheme 5). Besides, the averaging of the syn and anti protons
of the allyl fragment was not observed.
13
Nicholas and co-workers have reported a crystal structure
OH
determination of an allyl complex, containing this type of L
ligand. Low-temperature NMR spectra showed only one iso-
mer in solution, but at room temperature two diastereoisomers,
exo and endo, were observed in a 1:1 ratio.
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764
3761

View Article Online
Table 4 Crystal data for complexes 1a and 2a
Table 5 Selected bond lengths (Å) and angles (Њ) for complex 1a
1
a
2a
Pd(A)᎐O(1A)
Pd(A)᎐O(2A)
Pd(A)᎐N(1A)
Pd(A)᎐N(2A)
N(1A)᎐C(7A)
N(2A)᎐C(18A)
O(1A)᎐C(1A)
O(2A)᎐C(12A)
C(6A)᎐C(7A)
C(1A)᎐C(6A)
C(12A)᎐C(17A)
C(17A)᎐C(18A)
1.968(3)
1.979(3)
2.001(4)
2.010(4)
1.306(7)
1.286(7)
1.320(7)
1.300(6)
1.443(8)
1.408(9)
1.429(7)
1.423(8)
Pd(B)᎐O(1B)
Pd(B)᎐O(2B)
Pd(B)᎐N(1B)
Pd(B)᎐N(2B)
N(1B)᎐C(7B)
N(2B)᎐C(18B)
O(1B)᎐C(1B)
O(2B)᎐C(12B)
C(6B)᎐C(7B)
C(1B)᎐C(6B)
C(12B)᎐C(17B)
C(17B)᎐C(18B)
1.967(4)
1.977(4)
1.999(4)
2.004(4)
1.282(7)
1.288(7)
1.310(6)
1.308(6)
1.443(8)
1.427(7)
1.416(8)
1.414(9)
Formula
M
Crystal dimensions/mm
T/K
Crystal system
Space group
C H N O Pd C H ClNO PPdؒC H
22 24 2 4 29 27 2 7 8
486.84
0.1 × 0.1 × 0.2 0.1 × 0.2 × 0.1
293
Monoclinic
P21
11.094(3)
17.301(11)
11.3899(12)
106.87(2)
2092(2)
4
1.564
992
0.917
6604
686.50
293
Orthorhombic
P2 2 2
20.420(3)
18.078(3)
8.803(2)
1
1 1
a/Å
b/Å
c/Å
β/Њ
3
U/Å
3250(2)
4
1.401
1404
0.735
5254
Z
Ϫ3
O(1A)᎐Pd(A)᎐O(2A) 176.7(2)
O(2B)᎐Pd(B)᎐O(1B) 177.1(2)
O(2B)᎐Pd(B)᎐N(1B) 88.5(2)
O(1B)᎐Pd(B)᎐N(1B) 91.5(2)
O(2B)᎐Pd(B)᎐N(2B) 90.8(2)
O(1B)᎐Pd(B)᎐N(2B) 89.4(2)
N(1B)᎐Pd(B)᎐N(2B) 177.0(2)
D /g cm
c
O(1A)᎐Pd(A)᎐N(1A)
O(2A)᎐Pd(A)᎐N(1A)
O(1A)᎐Pd(A)᎐N(2A)
O(2A)᎐Pd(A)᎐N(2A)
91.5(2)
88.5(2)
88.8(2)
91.4(2)
F(000)
Ϫ1
µ/mm
Total no. reflections
measured
No. reflections used
N(1A)᎐Pd(A)᎐N(2A) 176.6(2)
6257
4310
[
I > 2σ(I)]
Final R1, wR2 [I > 2σ(I)]
all data)
0.0329, 0.0850 0.0361, 0.0742
0.0434, 0.0982 0.0706, 0.1964
Table 6 Selected bond lengths (Å) and angles (Њ) for complex 2a
(
Goodness of fit
1.151
0.987
Pd᎐O(1)
Pd᎐N
1.991(3)
2.051(4)
2.2666(10)
2.2873(12)
N᎐C(7)
1.287(7)
1.438(8)
1.422(7)
1.309(5)
C(6)᎐C(7)
C(1)᎐C(6)
O(1)᎐C(1)
Pd᎐P
Pd᎐Cl
[
{Pd(C,N)(µ-O2CMe)}2]
3a, 4a
–
MeCO2H
O(1)᎐Pd᎐N
O(1)᎐Pd᎐P
N᎐Pd᎐P
89.6(2)
89.13(9)
178.46(12)
O(1)᎐Pd᎐Cl
N᎐Pd᎐Cl
P᎐Pd᎐Cl
176.93(11)
92.61(12)
88.63(4)
n
(
i) thf, LiBu , – 75 °C
HLOH
5a
(
ii) [{Pd(C6H2Me3-2,4,6)(PPh3)(µ-Br)}2]
Et
O
Et
H
O
N
N
H
R
[
{Pd(C3H4R-2)(µ-X)}2]
7
a, R = Me, X = Cl
Pd
O
Pd
O
dbu
8a, R = H, X = Br
R
7
a, R = Me
C,N = C6H4CH=NCH2Ph, 3a
,4-(MeO)2C6H2CH=NC6H4(OMe-2), 4a
8a, R = H
3
Scheme 5
Et
*
The neutral (1b and 2b) and cationic (3b and 4b) palladium
R
O
complexes were prepared by substitution reactions (Scheme 6).
Et
mes
N
R
* O
1
The neutral complexes gave very well defined H NMR spectra
Pd
N
O
at room temperature (Table 2). The resonance of the methyl
O
Ph3P
Pd
bonded to the palladium atom for 2b appeared as a doublet at δ
3
HC
0.58 [ J(PH) = 3.5 Hz]. The value of this coupling constant is as
5
a
N
expected for a cis disposition between the methyl and the phos-
41
(
CH2)n
phorus atom. However, the cationic complexes gave very
broad NMR signals even at Ϫ70 ЊC. Since the neutral com-
plexes are rigid and the substituents in the different ligands were
the same as those used in the rigid N,O* ligand complexes, the
dynamic behaviour in these complexes probably depends on the
trans labilizing effect of the phosphorus atom, which would be
enough to labilize MeCN or the allyl group. These results show
the importance of the electronic factors in the activation pro-
O
R
Et
N
R
Pd
O
3
a, R = H, n = 1
4
a, R = OMe, n = 0
7
a, R = Me
a, R = H
42
8
cesses in this type of asymmetric complexes.
Similar Ph3 P-oxazoline allyl complexes prepared with the
symmetric η -1,3-Ph C H allyl group showed the presence,
Scheme 4 mes = C H Me -2,4,6
2
6
2
3
2
3
3
OP
either in the solid state or in solution, of two diastereoisomers,
exo and endo, depending on the relative position of the sub-
stituent on the chiral carbon with respect to the central C atom
of the allyl moiety. In solution the two isomers occur nearly in
Complexes of L
2
Six-membered metallic rings, containing four sp atoms, were
obtained, with the bidentate anionic moiety N,O*. In particu-
lar, the allyl complexes in solution were rigid on the NMR time-
scale. However, similar complexes with N,O*, N,P * or
N,N * ligands showed non-rigid behaviour. In some cases, it
has been stated that the ligand itself maintains a rigid conform-
ation. In other situations, a twist in the six-membered ring
contributes to the non-rigidity of the complex.
We have obtained complexes with an N,P* neutral ligand con-
taining a seven-membered ring and with allyl or methyl groups.
40
the same proportion.
13
12
3
9
Oxidation of styrene
4
0
Recently, chiral ruthenium pyridyloxazoline complexes have
been reported to catalyse the asymmetric epoxidation of olefins
39
43
using sodium periodate as the oxygen donor. Similarly chiral
ruthenium bis(2-pyridyloxazoline) complexes were used as cat-
3
762
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764

View Article Online
OH
+
PPh2Cl
O
N *
Et
toluene,
NEt3
+
Ph2
P
Ph2
P
O
OPPh2
O
O
X
BF4–
3
Pd
[Pd(η -C3H4Me-2)(cod)]BF4
Pd
[
PdCl(X)(cod)]
N
N
Cl
CH2Cl2, r.t.
– cod
CH2Cl2, r.t.
– cod
*
*
Et
Et
O
N
O
*
Et
1b, X = Cl
2b, X = Me
4b
LOP
CH2Cl2, MeCN
AgCl
AgBF4
–
+
Ph2
O
P
Me
BF4–
Pd
N
*
NCMe
Et
O
3b
Scheme 6 r.t. = Room temperature
complex 13a. For chiral salen-based manganese() catalysts
Table 7 Results of styrene oxidation with NaOCl
the presence of bulky groups in the salen ligand is crucial to its
49
stability and selectivity. Bleaching of catalyst 13a occurs a
considerable time before the end of olefin conversion. The
major product of styrene oxidation was styrene oxide but small
amounts of benzaldehyde (1%) and phenylacetaldehyde (1.2%)
were also detected by GC and NMR spectroscopy from the
reaction mixtures. The epoxide was isolated and a fairly low
enantioselectivity [3% enantiomeric excess of (S)-(Ϫ)-styrene
oxide] was detected using a 30 m Carbowax and a 50 m
Cyclodex-β column. This reaction was run several times and
the results were reproducible. An additional analysis was per-
formed to check the optical purity. The isolated epoxide was
reduced to 1-phenylethanol by lithium aluminium hydride and
was analyzed using a 25 m Cyclodex-β column. No enantio-
selectivity was detected within the error of the measurement
by using racemic samples under the same conditions.
a
b
Complex Conversion (%) t/h
Epoxide (%)
Selectivity (%)
1
9
a
a
3
4
12
24
24
3
Traces
Traces
6
—
—
50
c
1
3a
a
b
c
Based on starting styrene. Epoxide yield/% conversion. Side prod-
ucts detected: PhCHO (1%) and PhCH CHO (1.2%).
2
4
4
45
alysts for epoxidations with iodosylbenzene and RCHO/O2.
These results prompted us to study the possibility of using
chiral hydroxyphenyl oxazoline ligands for asymmetric alkene
oxidations.
The activity of complexes 1a, 9a and 13a was investigated
under a standard set of conditions by using catalytic amounts
of the corresponding complex together with styrene as the test
olefin in a biphasic system. In the absence of the catalysts, the
Ϫ
olefin was scarcely oxygenated by ClO alone under identical
reaction conditions. We verified that the simple salt Mn(O C-
Acknowledgements
2
Me) resulted in no epoxidation and styrene oxide was stable
under the reaction conditions. Table 7 summarizes our trials on
the catalytic epoxidation of styrene with NaOCl.
We thank the Generalitat de Catalunya (grant number QFN95-
4708 and 1995SGR 00199) for financial support. We thank Dr.
Ramon Vicente for helpful discussions regarding magnetic
susceptibilities.
2
The nature of the metal has an important influence on the
catalytic properties of the oxazoline complexes. It is also known
that there exist very specific ligand requirements in order for
nickel() species to participate in catalytic epoxidation with
References
Ϫ
46
OCl . Nickel()–1,4,8,11-tetraazacyclotetradecane systems
1 C. G. Frost, J. Howarth and J. M. J. Williams, Tetrahedron:
Asymmetry, 1992, 3, 1089; B. M. Trost, Acc. Chem. Res., 1996, 29,
are active but (5,10,15,20-tetraphenylporphyrinato)nickel() is
3
55; B. M. Trost and D. L. van Vranken, Chem. Rev., 1996, 96, 395.
U. Burckhardt, M. Baumann and A. Togni, Tetrahedron: Asymmetry,
997, 8, 155.
completely inactive. Square-planar nickel complexes containing
2
3
47
N O2 co-ordination sites, i.e. [Ni(salen)] [H salen = N,NЈ-
2
2
1
bis(salicylidene)ethane-1,2-diamine] or salen analogues such
H. Nishiyama, M. Kondo, T. Nakamura and K. Itoh, Organo-
metallics, 1991, 10, 500; H. Nishiyama, S. Yamaguchi, S. B. Park
and K. Itoh, Tetrahedron: Asymmetry, 1993, 4, 143; H. Brunner
and C. Henrichs, Tetrahedron: Asymmetry, 1995, 6, 653.
L. M. Newman, J. M. J. Williams, R. McCague and G. A. Potter,
Tetrahedron: Asymmetry, 1996, 7, 1597.
S. B. Park, N. Sakata and H. Nishiyama, Chem. Eur. J., 1996, 2, 303;
Y. Uozumi, H. Kyota, E. Kishi, K. Kitayama and T. Hayashi,
Tetrahedron: Asymmetry, 1996, 7, 1603.
48
as [Ni(babp)] {H babp = N,NЈ-[6,6Ј-(2,2Ј-bipyridyl)]dibenz-
2
imidic acid} were reported to catalyse alkene oxidation using
NaOCl under phase-transfer conditions, although the latter
complex required much longer induction periods. The square-
planar palladium and nickel complexes 1a and 9a were not
effective under the experimental conditions.
4
5
Modest conversions and selectivities were observed with
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764
3763

View Article Online
6
D. A. Evans, J. A. Murry, P. von Matt, R. D. Norcross and
S. J. Miller, Angew. Chem., Int. Ed. Engl., 1995, 34, 798; A. K.
Ghosh, P. Mathivanan, J. Cappiello and K. Krishann, Tetrahedron:
Asymmetry, 1996, 7, 2163.
M. D. Santana, A. Rufete, G. Sánchez, G. García, G. López,
J. Casabó, E. Molins and C. Miravitlles, Inorg. Chim. Acta, 1997,
255, 21.
29 D. Drew and J. R. Doyle, Inorg. Synth., 1990, 28, 348.
30 R. E. Rülke, J. M. Ernsting, A. L. Spek, C. J. Elsevier, P. W. N. M.
van Leeuwen and K. Vrieze, Inorg. Chem., 1993, 32, 5769.
31 D. A. White, Inorg. Synth., 1972, 13, 61.
32 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
33 G. M. Sheldrick, SHELXL 93, a computer program for crystal
structure refinement, University of Göttingen, 1993.
34 International Tables for X-Ray Crystallography, Kynoch Press,
Birmingham, 1974, vol. 4, pp. 99, 100 and 149.
35 H. D. Flack, Acta Crystallogr., Sect. A, 1983, 39, 876.
36 J. A. Smegal and C. L. Hill, J. Am. Chem. Soc., 1983, 105, 3515.
37 X. Shi Tan, D. Feng Xiang, W. Xia Tang and M. Qin Chen,
Polyhedron, 1997, 16, 1273.
38 R. Vicente, A. Escuer, X. Solans and M. Font-Bardía, Inorg. Chim.
Acta, 1996, 248, 59.
7
8
M. Sperrle, A. Aeby, G. Consiglio and A. Pfaltz, Helv. Chim. Acta,
1
996, 79, 1387.
S. Bennett, S. M. Brown, G. Conole, M. Kessler, S. Rowling, E. Sinn
and S. Woodward, J. Chem. Soc., Dalton Trans., 1995, 367; L. F.
Szczepura, S. M. Maricich, R. F. See, M. R. Churchill and K. J.
Takeuchi, Inorg. Chem., 1995, 34, 4198.
9
O. Loiseleur, P. Meier and A. Pfaltz, Angew. Chem., Int. Ed. Engl.,
1
996, 35, 200.
0 H. Eichelmann and H. J. Gais, Tetrahedron: Asymmetry, 1995, 6,
43.
1
6
1
1
1 P. S. Pregosin and R. Salzmann, Coord. Chem. Rev., 1996, 155, 35.
2 J. Sprinz, M. Kiefer, G. Helmchen, M. Reggelin, G. Hutter, O.
Walter and L. Zsolnai, Tetrahedron Lett., 1997, 38, 1523.
1
1
1
1
3 H. Yang, M. A. Khan and K. M. Nicholas, Organometallics, 1993,
1
2, 3485.
4 H. Yang, M. A. Khan and K. M. Nicholas, J. Mol. Catal., 1994, 91,
19.
39 P. von Matt, G. C. Lloyd-Jones, A. B. E. Minidis, A. Pfaltz, L.
Macko, M. Neuburger and M. Zchnde, Helv. Chim. Acta, 1995, 78,
265.
3
5 K. Ohkita, H. Kurosawa, T. Hasegawa, T. Hirao and I. Ikeda,
Organometallics, 1993, 12, 3211.
6 P. G. Cozzi, E. Gallo, C. Floriani, A. Chiesi-Villa and C. Rizzoli,
Organometallics, 1995, 14, 4994.
7 T. G. Gant and A. I. Meyers, Tetrahedron, 1994, 50, 2297.
8 A. Pfaltz, Acta Chem. Scand., 1996, 50, 189.
9 T. P. Ward, Organometallics, 1996, 15, 2836.
0 D. D. Perrin, W. L. F. Armarego and D. R. Perrin, Purification of
Laboratory Chemicals, Pergamon, Oxford, 3rd edn., 1988.
1 C. Bolm, K. Weickhardt, M. Zehnder and T. Ranff, Chem. Ber.,
40 N. Baltzer, L. Macko, S. Schaffner and M. Zehnder, Helv. Chim.
Acta, 1996, 79, 803.
41 G. P. C. M. Dekker, C. J. Elsevier, K. Vrieze and P. W. N. M. van
Leeuwen, Organometallics, 1992, 11, 1598; G. P. C. M. Dekker,
A. Buijs, C. J. Elsevier, K. Vrieze, P. W. N. M. van Leeuwen,
W. J. J. Smeets, A. L. Spek, Y. F. Wang and C. H. Stam, Organo-
metallics, 1992, 11, 1937.
1
1
1
2
42 J. M. J. Williams, Synlett, 1996, 705.
43 R.-Y. Yang, and L.-X. Dai, J. Mol. Catal., 1994, 87, L1.
44 S.-B. Nishiyama, M. Park, K. Haga, K. Aoki and K. Itoh, Chem.
Lett., 1994, 1111.
45 S. Bennett, S. M. Brown, G. Conole, M. Kessler, S. Rowling, E. Sinn
and S. Woodward, J. Chem. Soc., Dalton Trans., 1995, 367.
46 J. F. Kinneary, J. S. Albert and C. J. Burrows, J. Am. Chem. Soc.,
1988, 110, 6124.
47 H. Yonn and C. J. Burrows, J. Am. Chem. Soc., 1988, 110, 4987.
48 M. Yamada, S. Ochi, H. Suzuki, A. Hisazumi, S. Kuroda and
I. Shimao, J. Mol. Catal., 1994, 87, 195.
2
1
991, 124, 1173; J. V. Allen and J. M. J. Williams, Tetrahedron:
Asymmetry, 1994, 5, 277.
2 S. Baba, T. Ogura and S. Kawaguchi, Bull. Chem. Soc. Jpn., 1974,
2
2
2
4
7, 665.
3 J. Albert, J. Granell and J. Sales, J. Organomet. Chem., 1984, 273,
93.
3
4 J. Albert, J. Granell, R. Moragas, M. Font Bardia and X. Solans,
J. Organomet. Chem., 1996, 522, 59.
2
2
2
5 V. V. Grushin and H. Alper, Organometallics, 1993, 12, 1890.
6 Y. Tatsuno, T. Yoshida and S. Otsuka, Inorg. Synth., 1990, 28, 342.
7 A. Escuer, J. Ribas, R. Vicente, C. Faulmann, D. de Montauzon and
P. Cassoux, Polyhedron, 1991, 10, 2025.
49 W. Zhang and E. N. Jacobsen, J. Org. Chem., 1991, 56, 2296; E. N.
Jacobsen, W. Zhang, A. R. Mucci, J. R. Ecker and L. Deng, J. Am.
Chem. Soc., 1991, 113, 7063.
2
8 G. López, G. García, G. Sánchez, J. García, J. Ruiz, J. A. Hermoso,
A. Vegas and M. Martínez-Ripoll, Inorg. Chem., 1992, 31, 1518;
Received 6th June 1997; Paper 7/03951D
3
764
J. Chem. Soc., Dalton Trans., 1997, Pages 3755–3764