352
Russ.Chem.Bull., Int.Ed., Vol. 54, No. 2, February, 2005
Nindakova and Shainyan
complexes (possibly, only at an early stage) and microꢀ
heterogeneous cobaltꢀcontaining particles, which make a
certain contribution to hydrogenation. In the absence of a
sufficient amount of stabilizing ligands and surfactants,
the latter particles coalesce and precipitate. The fact that
this precipitate contains some nitrogen, hydrogen, and
carbon even after thorough washing and drying suggests
that colloid particles can be modified by chiral diamine
ligands or their fragments. This can also influence the
enantioselective reduction of the substrates.
Methyl αꢀacetamidocinnamate (2) was prepared by a known
procedure,2 m.p. 120—121 °C. Dimethyl itaconate (3) was synꢀ
thesized by refluxing itaconic acid in MeOH with some HCl for
several days. The white crystals that precipitated on cooling
were recrystallized from MeOH, m.p. 38 °C.
2
Modification of sodium borohydride with alcohols (general
i
procedure). A modifying alcohol (MeOH, EtOH, Pr OH)
(
4—20 mmol) or 2 mmol of each alcohol was added to a suspenꢀ
sion of NaBH (0.077 g, 2 mmol) in 15 mL of CHCl (EtOH,
4
3
THF) or in 5 mL of DMF in the reduction of esters of dehydro
acids, and the mixture was stirred for 30 min at ~20 °C under
argon.
Reduction of acetophenone (2) (general procedure). A cooled
solution of complexes 5a—c (0.02—0.05 mmol) and acetopheꢀ
The question of whether the reduction of aryl ketones
and dehydro acids in the presence of cobalt diamine is a
homogeneous or a heterogeneous process would be tackꢀ
led in our further studies.
none (2) (0.5—1 mL) in 9—9.5 mL of a solvent (CHCl , EtOH,
3
THF) was slowly added in an argon flow to a solution of modiꢀ
fied NaBH cooled to –20 °C. The resulting brown solution was
4
Experimental
evacuated to remove the hydrogen evolved and stirred using a
magnetic stirrer for 24—48 h at –20 °C. The degree of converꢀ
sion was determined by GLC analysis of the reaction mixture.
The product was separated from the catalyst and unreacted acꢀ
etophenone by vacuum distillation. The optical yield (ee) was
determined for the highestꢀboiling fraction with the lowest conꢀ
tent of acetophenone (≤10% according to GLC) as the ratio of
the specific rotation calculated with allowance for the content
of 1ꢀphenylethanol to the published value for 1ꢀphenylethanol
Chloroform, CH Cl , toluene, DMF, and acetophenone
2
2
were purified and dehydrated by standard procedures and disꢀ
tilled under argon.
IR spectra were recorded on an IKSꢀ29 instrument in KBr.
GLC analysis was performed on an LKhMꢀ80 chromatograph
2 m × 3 mm columns, 5% SЕꢀ30 on Chromaton NꢀAWꢀDMCS,
heat conductivity detector, helium as the carrier gas). The speꢀ
(
1
4
(
in МеOH) by a previously described procedure.
The reduction of esters of dehydro acids 3 and 4. A solution
of complexes 5a—c (0.02—0.05 mmol) and ester 3 or 4
cific rotation was measured on a Polamat A instrument (с 2—30,
МеOH or CHCl ) at λ = 546 nm. The powder Xꢀray diffraction
3
analysis of solid precipitates was performed on a DRONꢀ3M
Xꢀray diffractometer (CuꢀKα radiation). The micrographs of
the "colloid" cobalt were taken at the Instrument Center "Elecꢀ
tron Microscopy" of the Limnological Institute of the Siberian
Branch of the Russian Academy of Sciences on a 287ꢀfold
Philips´ SEM 525ꢀM scanning electron microscope.
Diamines 1a—d were synthesized as described previously.
Diamine complexes 5 were prepared by a known procedure
and dried for 8 h in vacuo (3 Torr) at 60—70 °C. Complex 5a
precipitated from suspension of CoCl2 and a solution of the
starting diamine without passing to a CH Cl solution, whereas
(
(
1.5—4 mmol) in 10 mL of DMF or a CHCl —toluene mixture
6 : 1) was slowly added to 15 mL of a solution of modified
3
NaBH4 in DMF or CHCl . After degassing, the mixture was
3
stirred for 9—10 h (in the case of ester 3) or for 24—48 h (in the
case of ester 4). To terminate the reaction, 1—2 mL of a satuꢀ
rated solution of NH4Cl was added. After quenching of the
active components of the reaction mixture, 50 mL of CH2Cl2
and 50 mL of water were added, the organic layer was washed
1
2,13
1
5
with water several times, dried with anhydrous МgSO and the
4
solvent was removed under reduced pressure. The chemical yield
2
2
of ester 3 was determined by GLC, and that of ester 4, by
complexes 5b,c are soluble in CH Cl . Complex 5b was obꢀ
2
2
1
H NMR spectroscopy. The products were isolated and purified
tained as a darkꢀblue oil from which crystals were formed on
storage in the cold for several days.
by column chromatography on silica gel (elution with hexꢀ
ane—AcOEt, 9 : 1).
Dichloro[(4S,5S)ꢀ2,2ꢀdimethylꢀ4,5ꢀbis(aminomethyl)ꢀ1,3ꢀ
dioxolane]cobalt(II) (5a). Yield 81.0%, m.p. 230—232 °C.
Found (%): C, 27.92; H, 5.77; Cl, 25.53; N, 9.23.
C H Cl CoN O . Calculated (%): C, 28.99; H, 5.56; Cl, 24.45;
The optical yields were calculated relative to the specific
2
0
rotation of dimethyl Rꢀ(+)ꢀαꢀmethylsuccinate ([α]546 +7.7
neat)) calculated using the Drude equation based on the folꢀ
(
7
16
2
2
2
2
0
6
23
–
1
lowing data: [α]D +6.44 (neat), K = 3.15•10 , λ0 = 204 nm,
[
alanine ([α]
MeOH))
MeOH)) and Rꢀ(+)ꢀ1ꢀphenylethanol ([α]546 +43.9 (neat)).
The precipitate of the "colloid" cobalt was separated by deꢀ
canting off the catalyzate solution, washed many times with
DMF and CHCl3, and dried in vacuo (5 h, 100 °C, 1 Torr).
Found (%): C, 6.15; H, 2.30; Cl, 2.52; N, 1.89; ash, 74.91.
N, 9.66. IR, ν(N—H)/cm (the absorption bands of the free
2
4
α]D +4.8 (c 2.9, CHCl ); methyl Sꢀ(+)ꢀNꢀacetylphenylꢀ
3
ligand are given in parentheses): 3210 (3190), 3270 (3290),
2
0
20
+19.3 (c 2.0, MeOH), [α]D +16.4 (c 2.0,
Sꢀ(–)ꢀ1ꢀphenylethanol ([α]D
5
46
3
320 (3360).
2
5
20
;
–45.0 (c 5,
Dichloro[(4S,5S)ꢀ2,2ꢀdimethylꢀ4,5ꢀbis(methylaminomethyl)ꢀ
,3ꢀdioxolane]cobalt(II) (5b). Yield 66.5%, m.p. 97—98 °C.
2
6
25
27
1
Found (%): C, 35.00; H, 6.83; Cl, 21.37; N, 8.93.
C H Cl CoN O . Calculated (%): C, 33.98; H, 6.34; Cl, 22.29;
9
20
2
2
2
–
1
N, 8.81. IR, ν(N—H)/cm (the absorption bands of the free
ligand are given in parentheses): 3190 (3273, 3328).
Dichloro[(4S,5S)ꢀ2,2ꢀdimethylꢀ4,5ꢀbis(dimethylaminoꢀ
methyl)ꢀ1,3ꢀdioxolane]cobalt(II) (5c). Yield 70.8%, m.p.
The authors are grateful to E. V. Likhoshvai (Limnoꢀ
logical Institute of the Siberian Branch of the Russian
Academy of Sciences) for taking images by scanning elecꢀ
tron microscopy.
1
66—168 °C. Found (%): C, 37.93; H, 7.22; Cl, 21.42;
N, 7.71. C H Cl CoN O . Calculated (%): C, 38.17; H, 6.99;
1
1
24
2
2
2
Cl, 20.48; N, 8.09.