Mild direct amination of benzoxazoles using interpenetrating Cobalt(II)-based metal-organic framework as an efficient heterogeneous catalyst

Based on the acid-base mixed-ligand assembly strategy, a new acid- and base-stable cobalt(II) metal-organic framework {[Co(tcpa)(Fbtx)(H2O)(2)]center dot 0.5H(2)O}(n) (denoted as Co-MOF, Fbtx = 1,4-bis(1,2,4-triazole-1-ylmethyl)-2,3,5,6-tetrafluorobenzene, H(2)tcpa = 3,4,5,6-tetrachloro-phthalic acid) was synthesized under hydrothermal conditions and characterized by various spectral and analytical techniques. Single-crystal X-ray diffraction analysis revealed that Co-MOF features a rare three-dimensional two-fold interpenetrating cds-type framework. The crystalline Co-MOF exhibited excellent activity toward the direct amination of 5-methylbenzoxazoles with TBHP as oxidant and acetic acid as an additive under mild reaction conditions, and various 2-aminobenzoxazoles were synthesized in moderate to good yields under optimized reaction conditions. Furthermore, the Co-MOF catalyst could be easily recovered and reused several times without loss of its crystallinity and activity.