Novel 2,6-dimethoxyphenoxy alpha substituted phthalocyaninato metal complexes: Electrochemistry, In situ spectroelectrochemistry and oxygen electrocatalysis

Abstract

Non-peripherally tetra-2,6-dimethoxyphenoxy substituted Co(II) 3, Fe(II) 4, Mn(III) 5, and Ni(II) 6 phthalocyanines were prepared by refluxing the n-pentanol solution of their metal-free analogue H2Pc 2, (obtained by using 3-(2,6-dimethoxyphenoxy)phthalonitrile), metal salts (Co(CH3COO)2.4 H2O, Fe(CH3COO)2, Mn (CH3COO)2.4 H2O or NiCl2) and 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) as the catalyst under N2 atmosphere for 2 h. The molecular structure of metallophthalocyanines 3-6 were explained by common methods which are elemental analysis, MALDI-TOF mass, FTIR, and UV-Vis spectroscopies. The complexes are well dissolved in various solvents (dichloromethane, tetrahydrofuran, dimethylsulfoxide, dimethylformamide, and toluene. Electrochemical redox, electrocatalytic oxygen reducing and electrocolorimetric properties of the phthalocyanine complexes were also measured by voltammetric and in situ UV-Vis spectroelectrochemical techniques. The phthalocyanine complexes displayed highly reversible sequential one-electron redox processes occurring at metal and/or phthalocyanine ring. The association of these processes with net colour changes pointed out their functionality as electrochromic material. Furthermore, the phthalocyanine complexes 3-5 and especially Fe(II)Pc 4, showed striking electrocatalytic oxygen reducing activity, owing to the metal centres with redox activity, increasing their interplay with the O2 molecule.