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J IRAN CHEM SOC
from Aldrich. Chloromethylated polystyrene (2 % cross-
linked with divinylbenzene) was purchased from Merck.
FT-IR spectra were obtained as potassium bromide pellets
in the range 400–4,000 cm-1 with a Perkin Elmer instru-
ment. All GC yields based on starting materials were
obtained by using Teif Gostar Fraz Co with silicon-DC 200
column.
Results and discussion
Aldehydic polystyrene was used as starting reagent to
prepare the catalysts. This reagent was prepared readily by
oxidation of chloromethylated polystyrene. Direct reaction
of aldehydic polystyrene and ethylenediamine in methanol
at reflux conditions resulted in polystyrene–imine–amine
reagent. This functionalized polystyrene was characterized
by FT-IR spectrum and CHN analysis. The carbonyl peak
of aldehydic polystyrene (vCO = 1,699 cm-1)disappeared,
and new peaks appeared at 1,645 cm-1 and 3,422 cm-1
attributed to vC=N of imine and N–H stretching vibrations
of amine of polystyrene–imine–amine bounded resin 2,
respectively. By the reaction of benzaldehyde and
4-nitrobenzaldehyde with resin 2 in dioxane in the presence
of 18-crown-6, polystyrene–diimine resins 3a and 3b were
prepared. CHN analysis of these resins showed 85.21 % C,
7.11 % H, 1.82 % N and 84.12 % C, 7.22 % H, 2.18 % N
for resins 3a and 3b, respectively. In FT-IR spectrums of
resins 3a and 3b, the peaks of NH disappeared that evi-
dently showed the formation of terminal imine bond.
Further evidence for this terminal imine bond formation
was obtained using 4-nitrobenzaldehyde as aldehyde
reagent. For resin 3b, two new strong peaks were produced
at 1,345 and 1,523 cm-1 that corresponded to symmetric
and asymmetric stretching vibration modes of N–O bonds
from –NO2 groups. These diimine linkages were used for
the immobilization of molybdenum hexacarbonyl. To a
solution of molybdenum hexacarbonyl in dioxane refluxed
for 1 h, each of resins 3a and 3b was added in separate
reactions and refluxed for 45 min that resulted in covalent
attachment of molybdenum carbonyl onto diimine poly-
styrenes to give polymer-supported diimine molybdenum
carbonyl resins 3aM and 3bM (Scheme 1). The success of
immobilization was proved by FT-IR spectrum; vCO
(cm-1): 2,070(w), 2,010(m), 1,985 (w), 1,942 (m), 1,895
(s), 1,878 (s), 1,840 (s) for resin 3aM and 2,070 (w), 2,008
(m), 1,980 (w), 1,938 (m), 1,891 (s), 1,882 (s), 1,840 (s) for
resin 3bM. The amount of molybdenum incorporation into
the polymer was also detected by neutron activation anal-
ysis (NAA) which showed values about 3.49 and 4.26 %
for resins 3aM and 3bM, respectively. Based on the local
symmetry of cis-[M(CO)4(L–L)] with C2v point group, four
active bands can be assumed [22]. But here seven bands are
seen for the two supported molybdenum carbonyl resins
3aM and 3bM. For each penta-carbonyl coordination (C4v)
and mer-tri-carbonyl coordination (C2v), three active bands
can be seen in the IR spectrum, respectively [22]. Thus in
addition to the tetra-carbonyl coordination of the supported
ligands (3a and 3b) with the molybdenum carbonyl, the
penta-carbonyl and tri-carbonyl coordination of them can
be also assumed. This suggestion can be confirmed by
comparison of the ratio of N/Mo in the resins 3a and 3b
Functionalization of polystyrene (2)
The aldehydic polystyrene and imine–amine polystyrene
were prepared as we previously described [21].
Preparation of diimine polystyrene resin (3a)
In a 100 mL round-bottom flask containing 60 mL of
dioxane, 3 g of resin 2 was reacted with benzaldehyde in
the presence of 18-crown ether-6 (0.01 g) and refluxed.
After 20 h the content was filtered off and washed
thoroughly with THF and dried in an oven at 90 °C.
Preparation of diimine polystyrene resins(3b)
As described for the preparation of 3a, except that 4-nitro
benzaldehyde was used as aldehyde.
Preparation of polystyrene-supported diimine
molybdenum carbonyl resins 3aM and 3bM
3.5 g of Mo(CO)6 was added to 60 mL of dioxane in
100 mL round-bottom flask and refluxed for 1 h. Then 2 g
of polystyrene–diimine resin was added to this solution and
it was refluxed for 45 min else. The content was cooled to
room temperature, filtered off and thoroughly washed with
THF and dried in an oven at 90 °C.
General procedures of epoxidation of alkenes
To a 25 mL round-bottom flask equipped with a magnetic
stirring bar 4 mL CCl4, 0.5 mmol alkene, 1.5 mmol tert-
butyl hydroperoxide (TBHP) and 0.012 mmol/Mo pre-
catalyst were added and refluxed. The reaction progress
was monitored by GLC.
General procedures for reusability of catalysts
The reusability of the polymer-supported diimine molyb-
denum carbonyl pre-catalysts was studied in repeated
epoxidation reaction of cis-cyclooctene. The reactions were
carried out as described above. At the end of each reaction,
the mixture was filtered, washed with 4 mL CHCl3/THF
(in 1:3 ratio) for five times then, dried in an oven at 80 °C
and reused.
123
Grivani, Gholamhossein
