Reversible Addition of Carbon Dioxide to Main Group Metal Complexes at Temperatures about 0 °C

The reaction of dialane LAl-AlL] ( 1 ; L=dianion of 1,2-bis(2,6-diisopropylphenyl)imino]acenaphthene, dpp-bian) with carbon dioxide results in two different products depending on solvent. In toluene at temperatures of about 0 °C, the reaction gives cycloadduct L(CO₂)Al-Al(O₂C)L] ( 2 ), whereas in diethyl ether, the reaction affords oxo-bridged carbamato derivative L(CO₂)(Et₂O)Al(μ-O)AlL] ( 3 ). The DFT and QTAIM calculations provide reasonable explanations for the reversible formation of complex 2 in the course of two subsequent (2+4) cycloaddition reactions. Consecutive transition states with low activation barriers were revealed. Also, the DFT study demonstrated a crucial effect of diethyl ether coordination to aluminium on the reaction of dialane 1 with CO₂. The optimized structures of key intermediates were obtained for the reactions in the presence of Et₂O; calculated thermodynamic parameters unambiguously testify the irreversible formation of the product 3 .