The synthesis, structure, and catalytic properties of Cl‐substituted tridentate ONO Schiff base molybdenum(VI) complexes: Expeditious synthesis of 1,8‐dioxo‐octahydro‐xanthene derivatives

Abstract

A family of molybdenum complexes with a general formula of [MoO2L]2 have been synthesized and fully characterized, where L is a tridentate ONO Schiff base ligand featuring a Cl substituent in different positions on the aromatic ring of salicylidene‐2‐aminophenolato backbone. The solvent molecule stabilized the monomeric structure of [MoO2LD] (D = DMF or DMSO) allowing single‐crystal X‐ray diffraction of the three new complexes. The dimeric complexes are utilized to catalyze the reaction of aldehydes/ketones with dimedone, leading to 1,8‐dioxo‐octahydro‐xanthene derivatives in N,N‐dimethylformamide. We found that their catalytic activity is enhanced by the electron‐withdrawing group of the Cl substituent on the ONO ligand. In addition, the position of the Cl substituent can also positively influence the catalysis performance: (ortho (L1) > para (L3) > meta (L2) ≈ meta (L4)). The high efficiency of the catalysts promises high yields and selectivity with a low catalyst loading and allows a wide substrate scope of aldehydes/ketones for the reaction. In addition, the method employs recrystallization for purifying products and can be easily scaled up to gram levels, indicating a strong potential for industrial utilization.