Bimetallic Calcium and Zinc Complexes with Bridged β-Diketiminate Ligands: Investigations on Epoxide/CO₂ Copolymerization

A series of dinucleating bis(β-diketiminate) ligands with rigid bridges has been prepared. In all cases the β-diketiminate unit is 2,6-iPr2C6H3NC(Me)C(H)C(Me)N-(bridge), and the bridges are either para-phenylene, meta-phenylene or 2, 6-pyridylene (the dinucleating ligands are abbreviated as PARA-H2, META-H2 and PYR-H2, respectively). These ligands have been converted to heteroleptic bimetallic calcium and zinc complexes. For calcium, only the PARA-phenylene bridged ligand led to a heteroleptic bimetallic calcium amide complex PARA-[CaN(SiMe3)2·THF]2. For the other ligands, homoleptic complexes have been isolated: META-Ca and PYR-Ca. For zinc, the whole range of heteroleptic amides could be isolated: PARA-[ZnN(SiMe3)2]2, META-[ZnN(SiMe3)2]2, and PYR-[ZnN(SiMe3)2]2. Analogue ethylzinc complexes have been prepared in quantitative yields: PARA-(ZnEt)2, META-(ZnEt)2, and PYR-(ZnEt)2. Reactions of the ethylzinc complexes with SO2 gave access to the ethylsulfinate complexes META-(ZnO2SEt)2 and PYR-(ZnO2SEt)2; fo...