Chemistry Reference
In-Depth Information
BArF
(BF
4
)
2
O
O
BArF
Ph
O
N
N
N
N
N
N
CH
2
OMe
R
Pd
R
Ph
Pd
Pd
MeCN
R=
i
Pr, Me
Me
MeCN
NCMe
MeCN
Me
102
103
101
BArF
O
O
Me
Me
N
N
O
O
N
N
i
Pr
i
Pr
O
O
Pd
N
N
Me
Me
NCMe
104
106
105
Figure 10.24.
Some systems used in Pd-catalyzed CO/styrene copolymerization.
R
Ph
N
N
N
Ph
R=H
107a
R=Bn
107b
R=Me
107c
R=Ts
107d
R=Tf
107e
Figure 10.25.
N - N
′
ligands used in CO/TBS copolymerization.
production of highly isotactic optically active copolymers of CO and styrene or 4-
methylstyrene was reported by using a bisoxazoline catalytic system (complex
104
,
Fig. 10.24) [103]. By using palladium complexes bearing chiral diketimines or dialdi-
mines, productivities as high as 21 g CP/g Pd h for average molecular weight copolymers
were obtained at room temperature under a constant CO pressure of 1 bar [104].
Brookhart achieved the production of stereoblock polyketones by exchanging ligands
during the catalytic reaction [105]. The use of systems bearing the atropoisomeric ligands
105 - 106
derived from bipyridine was also reported to be very active in this reaction
under mild conditions [106]. However, with these systems, low asymmetric induction
was observed, together with short isotactic sequences in the copolymer chain.
Claver and coworkers investigated the alternating CO/4-
t -
butylustyrene (TBE) copo-
lymerization reaction using systems bearing chelating asymmetric bisnitrogen
N - N ′
ligands (Fig. 10.25 ).
Productivities between ca. 2 and 30 g CP/g Pd h were achieved with molecular weights
comprised between 17,000 up to ca. 80,000 under mild conditions (P
CO
= 1 bar, RT, TBS/
Pd = 620). The catalysts bearing the less basic imidazol moieties
107d
and
107e
were
found to be the most active [107].
