Structurally well-characterized zinc complexes bearing imine-benzotriazole phenoxide ligands: Synthesis, photoluminescent properties and catalysis for carbon dioxide/epoxide coupling

New imine-benzotriazole phenol ligands, RFuIBTP-H were prepared from the condensation of 3-(2H-benzotriazol- 2-yl)-2-hydroxy-5-alkyl-benzaldehyde (R=C1 for alkyl=CH3; R=C8 for alkyl C8H17) with 1-(2-furyl) methylamine (1.1 equiv) in diethyl ether. Air-tolerant zinc complexes of bis-IBTP derivatives were synthesized and structurally characterized. The monomeric and homoleptic zinc complexes ([((IBTP)-I-C1Fu)(2)Zn] (1), [((IBTP)-I-C8Fu)(2)Zn] (2)) resulted from treatment of (IBTP)-I-RFu-H (2.0 equiv) with ZnEt2, in which the metal center is tetra-coordinated with two N, O-bidentate IBTP- ligands. Further reaction of 2 with 4-dimethylaminopyridine (DMAP) or 1-methylimidazole (MeIm) in stoichiometric proportion furnished the penta-coordinated monomeric zinc complexes ([((IBTP)-I-C8Fu)(2)Zn(DMAP)] (3), [((IBTP)-I-C8Fu)(2)Zn(MeIm)] (4)). Optical properties and catalysis of epoxide/carbon dioxide (CO2) coupling of these IBTP-containing zinc complexes were systematically investigated. The luminescent properties showed that Zn complexes 1-4 in solution produce intense blue fluorescence with wavelength of emission maximum in a range 473-482 nm. IBTP-ligated zinc complex 2 is an active catalyst (TOF: 33.3 h(-1)) for the cycloaddition of CO2 with propylene oxide in the presence of n-Bu4NBr to give propylene carbonate (PC) under mild conditions. The single-component character of Zn complex 3 that is extra-coordinated with one DMAP molecule also enabled an efficient preparation of PC without a co-catalyst. (C) 2013 Elsevier B. V. All rights reserved.