Synthesis, spectral and electrochemical properties of a new family of pyrrole substituted cobalt, iron, manganese, nickel and zinc phthalocyanine complexes

Abstract

A new family of pyrrole substituted metallophthalocyanine complexes, namely cobalt(II), iron(II), manganese(III), nickel(II) and zinc(II) tetrakis-4-(pyrrol-1-yl)phenoxy phthalocyanines (noted as M ( TPhPyrPc ), where M is the metallic cation) have been synthesized and fully characterized. In particular, the UV-visible spectra of the iron and nickel complexes showed extensive aggregation even at low concentrations. The cyclic voltammetry of the cobalt, iron and manganese complexes showed three to four redox couples assigned to metal and ring based processes. Spectroelectrochemistry of the manganese derivative confirmed that the synthesized complex is Mn III( TPhPyrPc -2) and that the reduction of Mn II( TPhPyrPc -2) to be centred on the ring and rather than on the metal, forming the Mn II( TPhPyrPc -4) species. Also, the electrochemical polymerization of these newly synthesized pyrrole-substituted phthalocyanines has been demonstrated in the case of the cobalt complex and the electrocatalytic activity of the obtained film has been tested towards the oxidation of L-cysteine.

Synthesis and electrochemical properties of benzyl-mercapto and dodecyl-mercapto tetrasubstituted manganese phthalocyanine complexes

“…Manganese phthalocyanine complexes have very interesting electrochemistry due to the fact that manganese metal exhibits variable oxidation states ranging from Mn I to Mn IV in MPc complexes [10], [11], [12], [13] and [14]. This makes manganese phthalocyanine complexes potential catalysts for many reactions.…”

Electropolymerized Pyrrole-Substituted Manganese Phthalocyanine Films for the Electroassisted Biomimetic Catalytic Reduction of Molecular Oxygen

“…Typical spectra for three films of poly-MnTPhPyrPc of different thickness on ITO (prepared by 15, 30 and 50 electropolymerizing scans, respectively) are illustrated in Figure 2a. The dashed line corresponds to the absorption spectra of MnTPhPyrPc monomer in a 10 À5 mol L À1 DCM þ 0.1 mol L À1 Bu 4 NBF 4 solution and shows the typical Mn III Pc band at 729 nm [20]. The UV-vis spectra obtained for the polymer films are similar to monomer species, but exhibit a notorious broad-ening of the band along with a red shift by ca.…”

“…Bu 4 NBF 4 solution containing 3 mmol L À1 of the complex by repeated potential scans between 0.2 Vand þ 1.2 V (vs. Ag/AgCl) at 200 mV/s, as we have recently shown in the case of the cobalt analog [20]. The build up of the electropolymerized film can be followed by the increase in currents of the voltammogram envelop (data not shown) which indicates that a deposit was formed on the electrode as a consequence of electrochemical polymerization of the attached pyrrole groups due to their irreversible oxidation.…”

“…Also, we and others have provided the first and rare examples involving the electroassisted activation of molecular oxygen by manganese porphyrins and Schiff bases as enzyme models, either in solution or supported electropolymerized films, for the catalytic oxidation of selected hydrocarbons [6 -17]. In that case, the use of "activator" such as acetic acid or benzoic anhydride is needed and the proposed mechanism suggested the generation of the metal-oxo active species, in view of the modifications of the cyclic and hydrodynamic voltammograms [6 -19].In a very recent paper, we have reported on the synthesis and spectroelectrochemical characterization of a new family of pyrrole-substituted metallophthalocyanines [20]. As part of our work devoted to the electrochemical elaboration and characterization of biomimetic models, we are reporting here on the first results obtained with an electropolymerizable pyrrole-substituted manganese phthalocyanine, noted Mn(TPhPyrPc) (see structure, Fig.…”

“…Curve 1 in Figure 2c is related to the thinner film (prepared by 15 electropolymerizing scans). It shows a reversible couple of peaks centred at À 0.17 V (vs. Ag/AgCl) which can be related to the Mn III /Mn II redox process of the phthalocyanine, by reference to the behaviour of the monomer complex either in DCM (data not shown) or in DMF [20] solution, and to previously reported studies of Mn phthalocyanine in various conditions [21]. It is noteworthy that there is a loss of reversibility of the observed redox process, as the film grows (curves 2 and 3).…”