Chemistry Reference
In-Depth Information
on the exterior of the resin beads [
2
]. The product was then used in free-radical polymerization with
various styrene monomers [
4
]. It was also shown that such resins could be prepared efficiently using
microwave-initiated polymerization [
22
]. Fontaine extended this concept by using atom transfer
radical polymerization initiators to attach poly(2-vinyl-4,4-dimethyl-5-oxazollne) to form grafts that
are efficient nucleophilic scavenging [
25
,
26
]. Preparation of Rasta resin can be illustrated as follows:
Si
+
Cl
H
N
N
Merrifield resin
O
O
Na
NCO
N
O
n
N
O
n
Si
NCO
H
10.1.1.2 Support Materials Other Than Polystyrene
Barett et al. [
27
] as well as Hanson and coworkers [
28
] used low molecular weight polyisobutylene to
form polyisobutylene-supported catalysts:
S
OCH
3
H
P
and
N
Pd
TFA
n
3
n
O
S
OCH
3
An advantage of using polyisobutylene is solubility in a variety of nonpolar solvents at ambient
temperatures. Also, the terminal double bond of polyisobutylene can be readily transformed into
various useful groups for attachment of catalysts or reagents. Thus, polyisobutylene was used as a
catalyst support for anchoring a sulfur-cation-sulfur Pd(II), as shown above. These catalysts were used
to perform allylic substitution, Heck, and Sonogashira reactions [
26
]. Polyisobutylene was also used to
support chiral bisoxazoline ligands for copper-catalyzed cyclopropanation reactions [
27
]. Other uses
