Computational prediction of cyclometalated IrIII, RhIII and CoIII amido complexes to capture up to three CO2 molecules

Abstract

An organometallic complex showing the ability to capture up to three CO₂ molecules is unprecedented in chemistry while with convincing theoretical evidence we show that [(CH₃)₂PCH₂NH₂] (pcn) based cyclometalated Ir(III), Rh(III) and Co(III) amido complexes can perform such a reaction under mild conditions. The CO₂ capture in these complexes occurs via three successive CO₂ insertion steps into the M–N(amido) bonds which are driven by modest activation barriers (14.5 to 23.1 kcal mol⁻¹) and highly exothermic products (−18.4 to −47.4 kcal mol⁻¹). The Rh(III) is more effective than Co(III) and Ir(III) and solvation by acetonitrile further enhances the CO₂ insertion ability of all three complexes. The feasibility of the successive CO₂ insertion reactions has been explained on the basis of the synergistic effect induced by the pcn ligand, viz. the nucleophilic affinity of the nitrogen atom, the ring strain of the [η²-NHCH₂P(CH₃)₂] moiety and the electronic effect of the phosphorous atom.