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Abstract
A series of four dizinc complexes coordinated by salen or salan ligands, derived from
ortho-vanillin and bearing (±)-trans-1,2-diaminocyclohexane (L1) or 2,2-dimethyl-1,3-propanediamine
(L2) backbones, is reported. The complexes are characterized using a combination of
X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental
analysis. The stability of the dinuclear complexes depends on the ligand structure,
with the most stable complexes having imine substituents. The complexes are tested
as catalysts for the ring-opening copolymerization (ROCOP) of CO2/cyclohexene oxide
(CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity
relationships reveal that the complex having both L2 and imine substituents displays
the highest activity. In the ROCOP of CO2/CHO its activity is equivalent to other
metal salen catalysts (TOF = 44 h(-1) at a catalyst loading of 0.1 mol %, 30 bar of
CO2, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than
other metal salen catalysts (TOF = 198 h(-1) at a catalyst loading of 1 mol % and
100 °C). Poly(ester-block-carbonate) polymers are also afforded using the most active
catalyst by the one-pot terpolymerization of PA/CHO/CO2.