Chromium Diamino-bis(phenolate) Complexes as Catalysts for the Ring-Opening Copolymerization of Cyclohexene Oxide and Carbon Dioxide

Chromium diamino-bis­(phenolate) complexes, CrXL [where L = 6,6′-((1,4-diazepane-1,4-diyl)­bis­(methylene))­bis­(2,4-di­methyl­phenolato) and X = Cl^– (1), OH^– (2), and N₃^– (3)], were prepared and characterized by MALDI-TOF MS and single-crystal X-ray diffraction. Complex 1 crystallized as two linkage isomers, specifically a green chloride-bridged dimer (1) and a pink asymmetrically bridged isomer exhibiting one chloride bridging atom and one bridging phenolate oxygen (1′). Adventitious moisture during sample handling causes the formation of hydroxide-containing complex 2. The reaction of 1 with PPNN₃ (where PPN = bis­(triphenylphosphine)­iminium) permits the isolation of a crystalline chromium azide complex, 3, which was structurally authenticated. Complex 1 showed good activity toward the ring-opening copolymerization of cyclohexene oxide and carbon dioxide with an added chloride, azide, or 4-(dimethylamino)­pyridine (DMAP) cocatalyst to give a completely alternating polycarbonate with a narrow molecular weight dispersity.