612
polycarbonates [70], and isocyanate-free polyurethanes [71], polar aprotic solvents
[72, 73], alkylating agents, electrolyte components, and scaffolds for biologically
active pharmaceutical agents [74–81]. In addition to the epoxide and diols, the
cyclic carbonate can also be achieved from alkene via oxidative carboxylation and
from ketals in presence of a suitable catalyst (Scheme 1). The catalytic conversion
of epoxide to cyclic carbonate is feasible, whereas the conversion of diol to cyclic
carbonate is challenging. The synthesis of cyclic carbonates from epoxides is an
established industrial reaction that is used in the synthesis of aromatic polycarbonates [70]. The cycloaddition of CO 2 to internal epoxides has received increasing
attention in recent years as these compounds can be used as synthons for isocyanate-free polyurethane synthesis. In addition, there are few reports available on the
asymmetric cyclic carbonate.
3.1.2 Metal Complexes as Catalysts
The homogenous catalytic system incorporating salen, salphen, and porphyrinbased metal complexes with a wide choice of Lewis acids has been investigated for
the efficient synthesis of cyclic carbonate utilizing CO 2 [82, 83]. Among the several
metal ions, the aluminum and magnesium complexes are well explored when compared to other metal complexes. In addition to the catalyst, the tetrabutylammonium
salts are used for the epoxide ring opening and carbon dioxide activation. Very few
catalysts are working under ambient conditions either atmospheric temperature or
pressure.
M. North and co-workers have reported a series of μ-oxo-bridged bimetallic
aluminum-salen complexes (Scheme 2) which are working as catalysts under minimum pressure (1 bar CO 2 ) in RT. The bimetallic aluminum catalysts (1–6) are
O
R
R
OH
OH
R
O
O
O
R
O
O
[O]
Dehydrating
agent
Catalyst
CO 2
Catalyst
CO 2
Catalyst
CO 2
Catalyst
CO 2
O
Epoxide
Alkene
Cyclic ketal
Diol
Scheme 1 Cyclic
carbonates synthesis from
various organic
substrates and CO 2
R. Arunachalam et al.
polycarbonates [70], and isocyanate-free polyurethanes [71], polar aprotic solvents
[72, 73], alkylating agents, electrolyte components, and scaffolds for biologically
active pharmaceutical agents [74–81]. In addition to the epoxide and diols, the
cyclic carbonate can also be achieved from alkene via oxidative carboxylation and
from ketals in presence of a suitable catalyst (Scheme 1). The catalytic conversion
of epoxide to cyclic carbonate is feasible, whereas the conversion of diol to cyclic
carbonate is challenging. The synthesis of cyclic carbonates from epoxides is an
established industrial reaction that is used in the synthesis of aromatic polycarbonates [70]. The cycloaddition of CO 2 to internal epoxides has received increasing
attention in recent years as these compounds can be used as synthons for isocyanate-free polyurethane synthesis. In addition, there are few reports available on the
asymmetric cyclic carbonate.
3.1.2 Metal Complexes as Catalysts
The homogenous catalytic system incorporating salen, salphen, and porphyrinbased metal complexes with a wide choice of Lewis acids has been investigated for
the efficient synthesis of cyclic carbonate utilizing CO 2 [82, 83]. Among the several
metal ions, the aluminum and magnesium complexes are well explored when compared to other metal complexes. In addition to the catalyst, the tetrabutylammonium
salts are used for the epoxide ring opening and carbon dioxide activation. Very few
catalysts are working under ambient conditions either atmospheric temperature or
pressure.
M. North and co-workers have reported a series of μ-oxo-bridged bimetallic
aluminum-salen complexes (Scheme 2) which are working as catalysts under minimum pressure (1 bar CO 2 ) in RT. The bimetallic aluminum catalysts (1–6) are
O
R
R
OH
OH
R
O
O
O
R
O
O
[O]
Dehydrating
agent
Catalyst
CO 2
Catalyst
CO 2
Catalyst
CO 2
Catalyst
CO 2
O
Epoxide
Alkene
Cyclic ketal
Diol
Scheme 1 Cyclic
carbonates synthesis from
various organic
substrates and CO 2
R. Arunachalam et al.