Dinuclear Zinc Complexes Based on Parallel β-Diiminato Binding Sites:  Syntheses, Structures, and Properties as CO₂/Epoxide Copolymerization Catalysts

With the background that β-diketiminato zinc complexes efficiently catalyze the CO2/epoxide copolymerization via a mechanism involving two catalyst molecules, a ligand system containing two parallel β-diiminato binding sites linked by a xanthene backbone ([RXanthdim]2- with residues R = 2,3-dimethylphenyl and 2,4-difluorophenyl at the iminato units, respectively) was investigated with respect to its zinc coordination chemistry. The corresponding diimines [RXanthdim]H2 were treated with diethylzinc to yield the complexes [Me2C6H3Xanthdim](ZnEt)2, 4, and [F2C6H3Xanthdim](ZnEt(thf))2, 5, respectively. In order to convert these compounds into polymerization catalysts, they were subsequently treated with SO2, which indeed resulted in the corresponding ethylsulfinates. Due to aggregation via intermolecular bridging of ethylsulfinate ligands, the product after the reaction of 5 represents an insoluble coordination polymer. Aggregation does take place also for the primary product obtained from the reaction of 4, ...