Activated Mn-MACHO Complexes Form Stable CO₂ Adducts

Manganese(I) carbonyl complexes bearing a MACHO-type ligand (HN(CH₂ CH₂ PR₂ )₂ ) readily react in their amido form with CO₂ to generate 4-membered {Mn-N-C-O} metallacycles. The stability of the adducts decreases with the steric demand of the R groups at phosphorous (R=isopropyl>adamantyl). The CO₂ -adducts display generally a lower reactivity as compared to the parent amido complexes. These adducts can thus be interpretated as masked forms of the active amido catalysts and potentially play important roles as off-loop species or branching points in catalytic transformations of carbon dioxide.