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. Two ways to activate CO2: Depending on the solvent, dialane [LAl‐AlL] (1; L=dianion of 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene, dpp‐bian) activates carbon dioxide in two different ways. In toluene, a reversible [2+4] cycloaddition gives product 2, whereas in diethyl ether the insertion of CO2 into the Al−N bond is accompanied with irreversible elimination of CO.