With the background that β-diketiminato zinc complexes efficiently catalyze the CO 2 /epoxide copolymerization via a mechanism involving two catalyst molecules, a ligand system containing two parallel β-diiminato binding sites linked by a xanthene backbone ([ R Xanthdim] 2with 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 [ R Xanthdim]H 2 were treated with diethylzinc to yield the complexes [ Me2C6H3 Xanthdim](ZnEt) 2 , 4, and [ F2C6H3 Xanthdim](ZnEt(thf)) 2 , 5, respectively. In order to convert these compounds into polymerization catalysts, they were subsequently treated with SO 2 , 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, as evidenced by the isolation of the tetramer [{[ Me2C6H3 Xanthdim]Zn 2 (µ-O 2 SEt)}µ-O 2 SEt] 4 , 6, and the precipitation of an insoluble solid on storing of such mixtures. 4, 5, and 6 display moderate activities as catalysts for the copolymerization of cyclohexene oxide and CO 2 . A bimodal molecular weight distribution points to two effective mechanisms, one of which probably involves two cooperating Zn centers as anticipated. Possible structural reasons for these catalytic results are discussed.
A novel potential ligand has been designed where two beta-dialdimine units are linked by a xanthene backbone (H2Xanthdim). The synthesis proceeds via a double vinamidinium salt and the products of its hydrolysis (containing eneamine/malonaldehyde units), which were converted into H2Xanthdim via a reaction with 2,3-dimethylaniline. The reaction of H2Xanthdim with n-butyllithium yields ((Et2O)Li)2Xanthdim, which was isolated and crystallized. The crystal structures of both H2Xanthdim and its lithium salt are discussed.
With the background that certain natural systems utilize two Fe(II) centres in their prosthetic groups for the activation of O2, a ligand system containing two parallel beta-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 Fe(II) coordination chemistry in order to study O(2) activation reactions. Hence, the corresponding lithium salts were treated with FeCl2 to yield the complexes [Me2C6H3Xanthdim]Fe2Cl3(Li(thf)3), and [F2C6H3Xanthdim]Fe2Cl3(Li(thf)3), , respectively, each of which comprises Cl-Fe(micro-Cl)Fe-Cl(Li(thf)3) units. and indeed readily react with O2 to give the oxides [RXanthdim]Fe2Cl2O containing Fe(III)-O-Fe(III) moieties. Due to the electron withdrawing F atoms reacts more slowly than . The molecular structures of , and [Me2C6H3Xanthdim]Fe2Cl2O, , as determined by single crystal X-ray diffraction are discussed, and an investigation concerning their magnetic properties revealed an antiferromagnetic coupling of the two iron centres in all complexes; naturally, the strongest coupling is observed for .
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