A. Aktas¸ et al. / Journal of Organometallic Chemistry 815-816 (2016) 1e7
3
products.
In order to finding optimum conditions of reaction, the oxida-
tion of benzyl alcohol was utilized for model reaction. The reaction
was performed in the absence and the presence of the Co(II) and
Fe(II) phthalocyanine catalysts (Table 1). The reaction was slowly
proceeding in the absence catalysts and benzaldehyde yield was
obtained low but yields of products were obtained excellent in the
presence the catalysts after 3 h. In the other blank reactions (using
no oxidants) there were no product detectable (Table 2). These are
proved that presence of the catalyst and oxidant are essential for
the oxidation. The conversion of benzyl alcohol and the selectivity
to benzaldehyde with Co(II) and Fe(II) phthalocyanines at 50 ꢀC are
shown in Table 1.
Table 1 indicate that the conversion of benzyl alcohol increased
with the reaction processing and reached the high conversion of
97% with complex 2 (Fig 4a) and 94% with complex 3 (Fig 4b) after
reaction for 180 min, and then remained stable with a slight
increased. On the other hand, the obvious decrease in selectivity to
benzaldehyde is due to a further oxidation of benzaldehyde to
benzoic acid. Based on the results of conversion and selectivity,
180 min was selected as the optimal reaction time.
Table 1 shows the changes in the conversion of benzyl alcohol by
Varying the substrat/catalyst molar ratio from 600 to 1600 at 50 ꢀC.
The results indicate that the conversion of benzyl alcohol decreased
with an increasing subs/cat ratio. Lower conversion of benzyl
alcohol with higher mass of substrate and lower mass of catalyst
was due to the fewer catalytic sites. This study shows that only 600
subs/cat ratio was needed for the reaction to reach an optimum
conversion of benzyl alcohol (97% for complex 2 and 94% for
complex 3) compared the our works in previous [34,35].
The amount of oxidant (TBHP) is an important factor that in-
fluences the conversion and selectivity in selective oxidation re-
actions. The influence of the substrate to oxidant molar ratio was
next examined and the results are presented in Table 2. The con-
version of benzyl alcohol decreases from 97% to 51% for complex 2
and 94%e43% for complex 3 on increasing the TBHP:benzyl alcohol
mole ratio from 0.83 to 3.3. Benzyl alcohol conversion reaches 97%
for complex 2 and 94% for complex 3, when the substrate to oxidant
ratio is increased to 0.83 with the highest TON and TOF values (582,
194 for complex 2 and 564, 188 for complex 3). The above result
clearly points out that an increase in the TBHP content significantly
decreases the benzyl alcohol conversion [36]. The selectivity for
benzaldehyde is about 83.5% for complex 2 and 82.9% for complex
3 at this oxidant content. When still more oxidant is used, the
selectivity decreases at TBHP:BzOH mole ratio of 3.3. Therefore, a
Fig. 2. UVeVis spectrum in THF for phthalocyanine complexes 2 and 3.
1576.36 [MþH]þ (Fig. S2) respectively, confirmed the proposed
structures.
UVeVis spectra of metallophthalocyanines display typical two
strong absoption region which is characteristic Q and B bands, one
of them in the UV region at about 300e350 nm (B band) and the
other in the visible part of the spectrum at around 600e700 nm (Q
band). The electronic absoption spectra of cobalt and iron phtha-
locyanines 2 and 3 were studied in THF at room temperature
(Fig. 2). UVeVis spectra of iron and cobalt phthalocyanines intense
single Q band absorptions appeared at 664 nm for 2, at 704 nm for 3
with the shoulders at around 625 nm for 2, at 572 nm for 3 and the
B bands were observed at between 327 and 360 nm, respectively.
3.2. Catalytic studies
The catalytic activities of the phthalocyanine complexes were
explored for the oxidation of benzyl alcohol. All the oxidation re-
actions data were given in Tables 1e4. In experiments maintained
3 h oxidant and auxiliary chemicals on the conversion and yields
were investigated. Benzyl alcohol can be turned into various
organic compounds in oxidation reactions. In this work, three
fragments (benzaldehyde as major product, benzoquinone and
benzoic acid as minor products) were determined due to the attack
by catalytically active species (Fig. 3). Besides, the by-product also
included a small amount of benzyl benzoate in the reaction
Table 1
Amount of substrate effect of benzyl alcohol oxidation with complex 2 and 3.
Catalyst
Subs./Cat.
600/1
Aldehydea
Quinoneb
Acidc
Tot.Conv. (%)
TONd
TOFe (hꢁ1
)
2
3
2
3
2
3
2
3
81
78
65
69
57
54
47
45
34
32
e
8
9
8
9
8
9
6
7
5
6
e
8
7
7
7
6
7
6
6
6
5
e
97
94
80
85
71
70
59
58
45
43
e
582
564
640
680
710
700
708
696
720
688
e
194
188
213
226
236
233
236
232
240
229
e
800/1
1000/1
1200/1
1600/1
600/1
2
3
Without catalysts
Conversion was determined by GC.
a
Yield of Benzaldehyde.
Yield of Benzoquinone.
Yield of Benzoic Acid.
b
c
d
TON ¼ mole of product/mole of catalyst.
e
TOF ¼ mole of product/mole of catalyst x time.