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

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journal contribution
posted on 05.10.2020, 04:33 by Kenson Ambrose, Jennifer N. Murphy, Christopher M. Kozak
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.