Bifunctional
aluminum complexes supported by novel zwitterionic
NNO-donor scorpionate ligands were found to be efficient bifunctional
catalysts for cyclic carbonate synthesis from terminal and internal
epoxides in good yields and with broad substrate scope. Neutral
scorpionate ligands (1–2) were designed
and used as precursors to obtain two novel zwitterionic NNO-heteroscorpionate
ligands (3–4). Reaction of 3 or 4 with [AlX3] (X = Me, Et) in
a 1:1 or 1:2 molar ratio afforded the mononuclear and dinuclear cationic
aluminum complexes [AlX2{κ2-mbpzbdmape}]I2 (X = Me (5), Et (6)), [AlX2{κ2-mbpzbdeape}]I2 (X = Me (7), Et (8)), [{AlX2(κ2-mbpzbdmape)}(μ-O){AlX3}]I2 (X = Me (9), Et (10)), and [{AlX2(κ2-mbpzbdeape)}(μ-O){AlX3}]I2 (X
= Me (11), Et (12)) with elimination of
the corresponding alkane. These complexes were investigated as catalysts
for cyclic carbonate formation from epoxides and carbon dioxide in
the absence of a co-catalyst. Complex 7 was found to
be the most active catalyst for cyclic carbonate formation from various
epoxides and carbon dioxide.
The coupling reaction of carbon dioxide and terminal, internal, and highly substituted epoxides derived from renewable resources such as furfural, limonene, carvone, carvyl acetate, terpinen-4-ol, or ionone leads to the synthesis of new bioderived cyclic carbonates using an efficient aluminum catalyst under mild and solvent-free reaction conditions. Interestingly, the synthesis of highly substituted bioderived cyclic carbonates can occur with excellent diastereoselectivity, obtaining in some cases one diastereoisomer as the major product. The X-ray crystal structures of two enantiomerically pure carvonebased cyclic carbonates are reported.
The
optimization of an organoaluminum catalytic system for the
copolymerization of epoxides and anhydrides is presented. For this
purpose, the influence of different variables in the process, such
as catalysts, cocatalyst, solvent, or substrates, has been analyzed.
Kinetic studies, a proposal for the catalytic mechanism, and full
characterization of the copolymers obtained are also discussed. Finally,
a new copolymer, poly(limonene succinate), obtained by the optimized
catalytic system is reported.
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