58
R.D. Chakravarthy et al. / Inorganica Chimica Acta 376 (2011) 57–63
was used for determining the absolute configuration. The enantio-
meric excess values of sulfoxides were determined by Waters HPLC
system with 2487 detector, 515 pump using CHIRALPAK AS-H,
CHIRALCEL OD-H and CHIRALCEL OJ-H columns. The amino alco-
hols and the corresponding Schiff-bases were prepared by litera-
ture protocols [15–17].
34.46, 35.48, (four peaks for t-Bu group), 74.24 (O-CH2–), 78.37 (–
CH–N@), 119.93, 128.30, 129.35, 129.55, 129.63, 131.70, 136.60,
139.84, 142.99, 167.02 (–C@N). IR (KBr pellet)
m(C@N) 1633;
m
(MoO2) 929, 883 cmÀ1. MS (ESI): m/z = 482 (98MoO2(L4)+H+).
2.2.5. [MoO2(L5)] (5)
2.2. Preparation of the molybdenum complexes
To a methanolic solution of the Schiff base L5(H)2 which was
prepared from 3,5-di-tert-butyl-2-hydroxybenzaldehyde (0.234 g,
1 mmol) and (S)-2-amino-1,1,3-triphenylpropan-1-ol (0.303 g,
1 mmol) by the same method as described above, MoO2(acac)2
(0.326 g, 1 mmol) was added and refluxed for 3 h. The resulting
clear yellow solution was concentrated, washed with cold metha-
nol and dried. The recrystallization for this complex was done in
methanol solvent. Yield: 72%; 1H NMR (CDCl3, 400 MHz): d = 1.21
(s, 9H, t-Bu), 1.37 (s, 9H, t-Bu), 2.85–2.90 (dd, 1H, PhCH2), 2.95–
3.01 (dd, 1H, PhCH2), 5.02–5.05 (dd, 1H, –CH–N@), 6.65–7.57
(18H, (aromatic and –N@CH–) 13C NMR (CDCl3, 100 MHz):
d = 29.83, 31.27, 34.34, 35.38, 39.13, 82.96, 90.48, 118.76, 125.88,
126.38, 127.07, 127.30, 127.63, 127.72, 128.69, 128.94, 130.47,
132.65, 137.08, 140.29, 143.20, 143.52, 144.26, 158.06, 168.16 (–
2.2.1. [MoO2(L1)CH3OH)]ÁCH3OH, ([1Á(CH3OH)]ÁCH3OH)
A mixture of salicylaldehyde (0.610 g, 5 mmol) and (S)-2-ami-
no-3-phenyl-propan-1-ol (0.756 g, 5 mmol) in 20 ml methanol
was heated to reflux for 3 h, which gave the Schiff base L1(H)2.
Then MoO2(acac)2 (1.630 g, 5 mmol) was added and refluxed for
another 3 h. A green solid was obtained by concentrating the meth-
anolic solution, washed with cold methanol and recrystallized
from methanol by slow evaporation. Yield: 51%; 1H NMR (DMSO-
d6, 400 MHz): d = 3.03–3.13 (m, 2H, Ph-CH2–), 4.26–4.31 (m, 2H,
O-CH2–), 4.44–4.46 (m, 1H, –CH–N@), 6.87–7.47 (9H, aromatic),
8.11 (s, 1H, –N@CH–). 13 C NMR (DMSO-d6, 100 MHz): d = 40.00
(Ph-CH2 –), 72.44 (O-CH2 –), 75.82 (–C H–N@), 119.47, 119.57,
120.46, 126.64, 128.51, 129.87, 134.21, 135.04, 138.13, 160.92,
C@N). IR (KBr pellet) m(C@N) 1618; m
(MoO2) 944, 916 cmÀ1. MS
(ESI): m/z = 648 (98MoO2(L5)+H+).
164.16 (–C @N). IR (KBr pellet)
m (C@N) 1635; m(MoO2) 913,
883 cmÀ1. MS (ESI): m/z = 384 (98MoO2(L1)+H+).
2.2.2. [MoO2(L2)(CH3OH)]ÁH2O ([2Á(CH3OH)]ÁH2O)
2.2.6. [MoO2(L6)] (6)
This complex was prepared by the same procedure employed
for making [MoO2(L1)CH3OH)]ÁCH3OH except that (S)-2-amino-2-
phenylethanol was used instead of (S)-2-amino-3-phenyl propan-
1-ol. Yield: 60%; 1H NMR (CDCl3, 400 MHz): d = 4.61–4.66 (t, 1H,
O-CH2–), 4.93–4.97 (dd, 1H, O-CH2–), 5.18–5.21 (m, 1H, –CH–
N@), 6.73–7.45 (9H, aromatic), 8.10 (s, 1H, –N@CH–). 13C NMR
(CDCl3, 100 MHz): d = 74.06 (O-CH2–), 79.05 (–CH–N@), 119.59,
120.48, 129.33, 129.53, 129.80, 134.15, 135.77, 136.05, 160.66,
This complex was prepared by the method similar to that of
[MoO2(L5)] except that (S)-2-amino-1,1,2-triphenylethanol was
used instead of (S)-2-amino-1,1,3-triphenylpropan-1-ol (0.289 g,
1 mmol). A green solid was obtained by concentrating the metha-
nolic solution, washed with cold methanol and dried. Yield: 39%;
1H NMR (CDCl3, 400 MHz): d = 1.27 (s, 9H, t-Bu), 1.37 (s, 9H, t-
Bu), 6.21 (s, 1H, –CH–N@), 7.03–7.66 (17H, aromatic), 8.74 (s,
1H,–N@CH–). 13C NMR (CDCl3, 100 MHz): d = 29.86, 31.30, 34.49,
35.47 (four peaks for t-Bu group), 84.67, 91.17, 119.43, 126.38,
126.63, 126.90, 127.73, 127.92, 127.99, 128.35, 128.69, 128.72,
128.91, 133.67, 139.05, 140.92, 143.38, 143.46, 143.60, 143.68,
164.81 (–C@N). IR (KBr pellet)
m(C@N) 1626; m(MoO2) 931,
912 cmÀ1. MS (ESI): m/z = 370 (98MoO2(L2)+H+).
2.2.3. [MoO2(L3)] (3)
158.80, 170.80 (–C @N). IR (KBr pellet)
m (C@N) 1612; m(MoO2)
To a methanolic solution of the Schiff base L3(H)2 which was
prepared from salicylaldehyde (0.122 g, 1 mmol) and (S)-2-ami-
no-1,1,3-triphenylpropan-1-ol (0.303 g, 1 mmol) by the same
method as described above, MoO2(acac)2 (0.326 g, 1 mmol) was
added and refluxed for 3 h. The complex thus formed by concen-
trating the resulting solution was washed with methanol and
dried. Yield: 84%; 1H NMR (DMSO-d6, 400 MHz): 1H NMR:
d = 2.27–2.30 (d, 1H, Ph-CH2–), 3.00–3.03 (1H, Ph-CH2–), 5.27–
5.29 (d, 1H, –CH–N@), 6.76–7.67 (aromatic and –N@CH–). 13C
NMR (DMSO-d6, 100 MHz): d = 37.74 (Ph-CH2–), 76.81, 88.71,
119.02, 119.15, 120.72, 125.85, 126.27, 126.36, 126.75, 127.59,
127.98, 128.16, 130.06, 133.87, 134.84, 137.99, 143.97, 145.80,
942, 915 cmÀ1. MS (ESI): m/z = 634 (98MoO2(L6)+H+).
2.3. Crystal structure determination
Crystals suitable for X-ray measurement were grown from
methanol by slow evaporation method. Crystallographic data for
complexes 1, 2, 4 and 5 along with other experimental details
are summarized in Table 1. The structures were solved by direct
methods (SHELXS-97 and SHELXL-97) and refined by full-matrix least
squares methods [18]. Perspective view of the complexes is given
in Figs. 1–4 were drawn with ORTEP-3 for windows.
161.61, 164.35 (–C@N). IR (KBr pellet)
m(C@N) 1618; m(MoO2)
941, 915 cmÀ1
.
2.2.4. [MoO2(L4)(CH3OH)] ([4Á(CH3OH)]ÁH2O)
2.4. Catalytic sulfoxidation
A solution of the Schiff base L4(H)2 was prepared by condensa-
tion of 3,5-di-tert-butyl-2-hydroxybenzaldehyde (0.468 g, 2 mmol)
with (S)-2-amino-2-phenylethanol (0.274 g, 2 mmol) in methanol
for 3 h under refluxed condition. MoO2(acac)2 (0.652 g, 2 mmol)
was added to the resulting solution and refluxed for another 3 h.
The product thus obtained on evaporation of methanol was
washed with cold methanol and dried. This material was recrystal-
lized form methanol by slow evaporation method and dried to af-
ford the compound. Yield: 67%; 1H NMR (CDCl3, 400 MHz): d = 1.26
(s, 9H, t-Bu), 1.38 (s, 9H, t-Bu), 4.63–4.68 (t, 1H, O-CH2–), 4.92–4.96
(dd, 1H, O-CH2–), 5.15 (m, 1H, –CH–N@), 7.01–8.19 (7H, aromatic),
8.20 (s, 1H, –N@CH–). 13C NMR (CDCl3, 100 MHz): d = 29.90, 31.45,
A mixture of molybdenum–Schiff base complex (5 mol%) and
phenyl methyl sulfide (0.248 g, 2 mmol) in 5 ml of dichlorometh-
ane was stirred at 0 °C. Then 30% hydrogen peroxide (0.226 ml,
2 mmol) was added slowly into the reaction mixture. Stirring
was continued for 10–48 h as per requirement. Reaction progress
was monitored by TLC. The resulting solution was diluted with
water and extracted with dichloromethane. The organic layer
was dried over anhydrous sodium sulfate, concentrated and the
resulting crude product obtained was purified by column chroma-
tography to get the pure sulfoxide. The ee of the sulfoxides were
determined by HPLC method.