CARBON-DIOXIDE FIXATION BY CP2(ETA(3)-ALLYL)TI COMPLEXES GENERATED FROM VARIOUS DIENES

Cp2(eta3-allyl)Ti complexes having a variety of substituents on their allyl moieties were prepared from corresponding dienes, Cp2TiCl2, and Grignard reagents and were subjected to reaction with carbon dioxide. The reaction of CO2 took place in a highly regioselective manner to give a single beta, gamma-unsaturated carboxylic acid of a few possible regioisomeric products after hydrolytic workup of the titanium carboxylates. For example, 2-alkylbutadienes selectively yielded Cp2(eta3-1-methyl-2-alkylallyl)Ti complexes which were found to react with CO2 again in a highly regioselective manner to give 2-methyl-3-methylenealkanoic acids as the sole product. A few substituents or their functional groups on the allyl ligand blocked the formation of carboxylic acid, which was discussed in terms of steric and electronic factors. Asymmetric, carbon dioxide insertion reactions were also demonstrated with chiral (neomenthyl-Cp)2(eta3-allyl)Ti complexes and provided the carboxylic acids in up to 19% optical purity.