Halogen Bonding in the Decoration of Secondary Coordination Sphere of Zinc(II) and Cadmium(II) Complexes: Catalytic Application in Cycloaddition Reaction of CO with Epoxides.

Three new zinc(II) complexes [Zn(HL)(HO)] (), [Zn(HL)(HO)] () (HL = 2,4-diiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2)-ylidene)hydrazineyl)isophthalate) and [Zn(HL)(DMF)(HO)] () were synthesized by the reaction of Zn(II) salts with 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl) isophthalic acid (HL), 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2)-ylidene)hydrazineyl) isophthalic acid (HL) (in the presence of NHOH·HCl) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)-2,4,6-triiodoisophthalic acid (HL), respectively. According to the X-ray structural analysis, the intramolecular resonance-assisted hydrogen bond ring remains intact, with NO distances of 2.562(5) and 2.573(5) Å in , 2.603(6) Å in , and 2.563(8) Å in . In the crystal packing of , the cooperation of IO and II types of halogen bonds between tectons leads to a one-dimensional supramolecular polymer, while IO interactions aggregate 1D chains of coordination polymer . These new complexes (, , and ) and known [Zn(HL)(HO)] () (HL = 5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2)-ylidene) hydrazineyl)isophthalate), {[Zn(HL)(HO)]·3HO} (), [Cd(HL)(HO)] (), {[Cd(HL)(HO)(DMF)]·HO} (), [Cd(HL)] (), {[Cd(μ-HO)(μ-HL)(HL)]·2HO} (), and {[Cd(HL)(HO)]·4HO} () were tested as catalysts in the cycloaddition reaction of CO with epoxides in the presence of tetrabutylammonium halides as the cocatalyst. The halogen-bonded catalyst is the most efficient one in the presence of tetrabutylammonium bromide by affording a high yield (85-99%) of cyclic carbonates under solvent-free conditions after 48 h at 40 bar and 80 °C.