Halogen Bonding in the Decoration of Secondary Coordination Sphere of Zinc(II) and Cadmium(II) Complexes: Catalytic Application in Cycloaddition Reaction of CO 2 with Epoxides.

Three new zinc(II) complexes [Zn(H 2 L 3 ) 2 (H 2 O) 3 ] ( Zn2 ), [Zn(H 3 L 2a )(H 2 O) 3 ] n ( Zn3 ) (H 3 L 2a = 2,4-diiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2 H )-ylidene)hydrazineyl)isophthalate) and [Zn(HL 4 )(DMF)(H 2 O)] n ( Zn4 ) were synthesized by the reaction of Zn(II) salts with 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl) isophthalic acid (H 3 L 3 ), 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2 H )-ylidene)hydrazineyl) isophthalic acid (H 5 L 2 ) (in the presence of NH 2 OH·HCl) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)-2,4,6-triiodoisophthalic acid (H 3 L 4 ), respectively. According to the X-ray structural analysis, the intramolecular resonance-assisted hydrogen bond ring remains intact, with N ··· O distances of 2.562(5) and 2.573(5) Å in Zn2 , 2.603(6) Å in Zn3 , and 2.563(8) Å in Zn4 . In the crystal packing of Zn3 , the cooperation of I ··· O and I ··· I types of halogen bonds between tectons leads to a one-dimensional supramolecular polymer, while I ··· O interactions aggregate 1D chains of coordination polymer Zn4 . These new complexes ( Zn2 , Zn3 , and Zn4 ) and known [Zn(H 3 L 1 )(H 2 O) 2 ] n ( Zn1 ) (H 3 L 1 = 5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2 H )-ylidene) hydrazineyl)isophthalate), {[Zn(H 3 L 1 )(H 2 O) 3 ]·3H 2 O} n ( Zn5 ), [Cd(H 3 L 1 )(H 2 O) 2 ] n ( Cd1 ), {[Cd(HL 3 )(H 2 O) 2 (DMF)]·H 2 O} n ( Cd2 ), [Cd(H 3 L 3 )] n ( Cd-3 ), {[Cd 2 (μ-H 2 O) 2 (μ-H 2 L 4 ) 2 (H 2 L 4 ) 2 ]·2H 2 O} n ( Cd4 ), and {[Cd(H 3 L 1 )(H 2 O) 3 ]·4H 2 O} n ( Cd5 ) were tested as catalysts in the cycloaddition reaction of CO 2 with epoxides in the presence of tetrabutylammonium halides as the cocatalyst. The halogen-bonded catalyst Zn4 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.