Pyrazolone Containing Azine Based Molybdenum Complexes Having μ‐O{MoO2}2 Core and their Catalytic Applications for the Cycloaddition of CO2 with Epoxides to Cyclic Carbonates

Abstract

AbstractTetradentate ONNO donor ligands H2hz(fp)2 (I), H2hz(butp)2 (II) and H2hz(bp)2 (III) synthesized by the reaction of hydrazine hydrate with 4‐formyl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (fp), 4‐butyryl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (butp) and 4‐benzoyl‐3‐methyl‐1‐phenyl‐5‐pyrazolone (bp), respectively, react with [MoVIO2(acac)2] in 1 : 2 molar ratio in refluxing methanol to give binuclear complexes [(μ‐O){MoVIO2(H2O)}2hz(fp)2] (1) and [(μ‐O){MoVIO2(H2O)}2hz(butp)2] (2) and [(μ‐O){MoVIO2(H2O)}2hz(bp)2] (3). All ligands and complexes are characterized by several techniques that include, FT‐IR, UV/Vis, 1H NMR, 13C NMR spectroscopy, elemental and thermal analysis, and single crystal X‐ray analysis of 2 and 3. Ligands coordinate through a set of ON functionalities of the same ligand to two MoVIO2 groups attached through an oxido‐bridge. Additional coordination of water to each vanadium makes each of them to maintain an octahedral geometry. Azine moiety coordinates to two molybdenum through the symmetrical μ‐{η2‐(N−N)} fashion. Catalytic activity of these complexes was studied for the cycloaddition of CO2 with epoxides. A pressure of 4 bar CO2, 3.0 mg catalyst, 1 mmol of tetrabutylammonium bromide (TBAB) at 120 °C for 6 h were found to be most suited reaction condition for 10 mmol epoxide. Under the optimized reaction conditions, the product yield and selectivity of alkene carbonate for all complexes were investigated. As high as 96 % yield with almost 99 % selectivity for styrene carbonate under these optimized reaction conditions was achieved.