Trinuclear Mn2+/Zn2+ based microporous coordination polymers as efficient catalysts for ipso-hydroxylation of boronic acids

Abstract

Two microporous coordination polymers based on hourglass trinuclear building units, [Mn₃(bpdc)₃(bpy)]·2DMF and [Zn₃(bpdc)₃(bpy)]·2DMF·4H₂O (bpdc = 4,4′-biphenyl dicarboxylic acid, bpy = 4,4′-bipyridine), have been synthesized under solvothermal conditions employing DMF as the solvent. Each structure consists of two crystallographically distinct M²⁺ (M1 and M2) centers that are connected via carboxylate bridges from six bpdc ligands, generating a trinuclear metal cluster, [M₃(bpdc)₃(bpy)]. Cluster representation of the structure resulted in an interpenetrated net of rare hex topological type. Catalytic activities of the CPs have been assessed for the oxidative hydroxylation of phenylboronic acids (PBAs) using aqueous hydrogen peroxide (H₂O₂). Various substituted aryl/hetero-arylboronic acids RB(OH)₂ [R = phenyl, 2,4-difluorophenyl, 4-aminophenyl, 2-thiophene etc.] underwent ipso-hydroxylation smoothly at room temperature to generate the corresponding phenols in excellent yields. The main advantages of this protocol are the aqueous medium reaction, heterogeneous catalytic system, and short reaction time with excellent yield.