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 degrees 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(mu-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.

Automated summary

The reaction of the dialane with carbon dioxide produces two different products depending on the solvent used, with cycloadduct formed in toluene and oxo-bridged carbamato derivative in diethyl ether. DFT and QTAIM calculations explain the reversible formation of complex 2, with low activation barrier transition states identified. The study also highlights the crucial role of diethyl ether coordination to aluminum in the reaction with CO2, leading to the irreversible formation of product 3.