On the mechanism of the reaction of a magnesium(i) complex with CO2: a concerted type of pathway

Abstract

Theoretical mechanistic calculations (DFT) on the reactivity of [{(^DipNacnac)Mg}₂] (^DipNacnac = [(DipNCMe)₂CH]⁻, Dip = C₆H₃ⁱPr₂-2,6) towards CO₂ were carried out in order to rationalise the experimental formation of a carbonate (major product) and an oxalate (minor product). Despite its apparent similarity to f-element reactivity, the magnesium(I) bimetallic complex yields the carbonate through a concerted type of pathway rather than via a transient oxo-bridged intermediate. The latter is destabilised due to the electrostatic repulsion between the two magnesium centres. The small energy barrier difference between carbonate and oxalate formation (∼10 kcal mol⁻¹) may allow for the experimentally observed reactivity to be tuned by changing the sterics and/or electronic properties of the magnesium(I) complex.