Chemistry Reference
In-Depth Information
The excited oxygen in turn hydroperoxidizes olefins. The structure of polymer-bound Rose Bengal
can be illustrated as follows:
I
O
O
O
I
Cl
O
Cl
Cl
Cl
I
ONa
I
polymer bound Rose Bebgal
The photosensitized hydroperoxidation reaction of olefins [
53
] can be shown as follows:
hν,
O
O*
Rose Bengal
P
O
OH
Metathesis catalysts including Grubbs ruthenium catalyst (see Chap.
5
) are hard to separate from
the reaction products. Chemists therefore sought ways to overcome this problem by immobilizing the
catalyst on various supports. Buchmeister recently reviewed various polymer-supported metathesis
catalysts [
54
]. A few are reported here. Early, Grubbs described a phosphine-derivatized polystyrene-
supported catalyst [
55
]
iBuAl Cl
2
W
CO
OC
CO
Similarly, a Grubbs type ruthenium catalyst on a phosphine-derivatized polystyrene [
56
] can be
illustrated as follows:
Cl
PR
2
PR
2
n
Ru
n
Cl
This catalyst, however, turned out to be considerably less active in ring opening metathesis
polymerization of norborn-2-ene and in metathesis polymerization of
cis-
2-pentene. Better results
were obtained when a ruthenium-based metathesis type catalyst was immobilized via an
N
-heterocy-
clic carbene [
57
]. Additional improvements in performance were obtained when the catalyst was
immobilized on a monolithic silica rods:
