Lithiation of tricarbonylchromium complexes with polyaromatic carbo-and heterocyclic ligands. DFT study

Abstract

The reactions of tricarbonylchromium complexes of polyaromatic carbo-and heterocyclic derivatives with BunLi was studied by the density functional theory. The kinetic and thermodynamic factors for controlling the direction and selectivity of metallation were calculated for the model biphenylenetricarbonylchromium complex. Both approaches indicate that lithiation occurs exclusively at the aromatic ring bonded to the transition metal, which agrees with experimental data, while the selectivity inside this ring is determined more exactly by the thermodynamic factor. The solvation effects were simulated for the lithium salt of the tricarbonylnaphthalenechromium complex in which the lithium atom is localized in position 1 of the coordinated ring. The simulation showed the stable coordination of the lithium atom with two THF molecules, and the addition of the next THF molecule is thermodynamically unfavorable. The results of calculation of the relative energies for all possible THF-solvated lithium salts of the tricarbonylchromium complexes of biphenyl, naphthalene, biphenylene, and dibenzothiophene indicate that the difference in energies Δ E ≤ 1 kcal mol−1 corresponds to the experimentally observed absence of selectivity, while the difference more than 2.5 kcal mol−1 corresponds to the selectivity of the reaction. No additional coordination of the lithium atom to the free electron pair of the heteroatom was observed for the sulfur-containing dibenzothiophene complex. Similar calculations show that double metallation in the dibenzothiophene complex occurs at positions 1 and 4. The developed approach enables one to predict the direction and selectivity of metallation reactions of transition metal complexes with different arenes.