Chemistry Reference
In-Depth Information
Me
1,2-insertion
Pd
X
O
Pd
O
X
X = R, OR
Me
+
Pd
X
2,1-insertion
O
Me
Scheme 10.14.
O
O
(R)
(R)
isotactic
(R)
(R)
O
O
O
O
(R)
(R)
syndiotactic
(S)
(S)
O
O
O
O
(R)
(R)
atactic
(S)
(R)
O
O
Figure 10.22.
Possible structures of regioregular CO/propene copolymers.
The use of bis-triaryl diphosphines such as DIOP
65
, BINAP
88
, and BIPHEP
89
(where R = Ph, R ′ = CH
3
, OMe) in CO/propene copolymerization was shown to yield
regioirregular product with low stereoselectivity [87]. However, the substitution of
phenyl rings by alkyl groups (ligands
89
with R = Cy, and
90
) resulted in the production
of highly isotactic (ca. 72% isotacticity) and regioregular copolymers [88,89]. To date,
the most active class of ligands is that of
C
1
- symmetry ferrocenyldiphosphines
96
(Fig.
10.23) [90]. The highest activity was obtained with bulky substituent on the phosphorus
bonded to the chiral carbon and withdrawing groups on the aryl ring of the second
phosphorus atom. A remarkable effect on catalyst activity was revealed by the use of
ligands
97a
and
97b
as the catalyst containing the former ligand
97a
was 84 times more
active than its analogue with
97b
, although highly isotactic materials were obtained in
both cases [91]. Ligands
98
-
100
were also reported to yield highly regio- and stereoregu-
lar copolymers [92] .
The catalysts for the copolymerization of CO with higher aliphatic 1-alkenes showed
slightly lower activity than with propene. However, the regio- and stereoselectivities to
isotactic copolymers achieved are as high as those obtained for propene [93].
10.4.1.4. Asymmetric Copolymerization of CO with Vinylarenes
Unlike aliphatic
olefi ns, the copolymerization of styrene and its derivatives with CO requires the use of
