EPR study of pyrrolyl‐1‐oxyl and 3‐pyrrolinyl‐1‐oxyl radicals

Pyrrolyl‐1‐oxyl, 3‐phenylpyrrolyl‐1‐oxyl and a number of deuterium‐substituted derivatives were generated by hydrogen abstraction from the corresponding N‐hydroxypyrroles, and observed by EPR spectroscopy. They were all transient with lifetimes ≤ 10−2 s. The hyperfine splittings showed that unpaired spin was delocalized around the five‐membered ring with significant density at N‐1, C‐3 and C‐4, but very low density at C‐2 and C‐5. N‐Hydroxpyrrole and pyrrolyl‐1‐oxyl were studied by the semi‐empirical AM1 method, and the radical by the INDO method. The transient pyrrolinyl‐1‐oxyl was also generated from the corresponding N‐hydroxypyrroline and observed by EPR spectroscopy.</p

Synthesis, spectroelectrochemistry and thermochromism of regioregular head-to-tail oligo- and poly-[3-aryloxyhexylthiophenes]

The synthesis of regioregular head-to-tail poly(3-[ω-(p- methoxyphenoxy)hexyl]thiophenes) is reported, together with a study of the effect of sterically demanding 3-substituents on its structure and physical properties (conductivity, spectroelectrochemistry and thermochromism). The polymer is deep red when reduced but optically transparent in its oxidised form. The syntheses of the corresponding regioregular dimer and trimer, i.e. 3,4'-di[(p-methoxyphenoxy)hexyl]-2,2'-bithiophene and 3,4',4'-tri[(p- methoxyphenoxy)hexyl]-2,2' : 5',2'terthiophene are also reported.</p

Poly(N-hydroxypyrrole) and poly(3-phenyl-N-hydroxypyrrole):synthesis, conductivity, spectral properties and oxidation

N-Hydroxypyrrole and 3-phenyl-N-hydroxypyrrole were oxidized by (ButO2) in the presence of light to give the transient pyrrolyl-1-oxyl (nitroxide) radicals which were observed by EPR spectroscopy. The corresponding poly(N-hydroxypyrroles) were prepared by chemical oxidation with ferric salts, or, in the case of N-hydroxypyrrole only, by electrochemical oxidation in CH3CN at + 1.2 V versus SCE. The latter polymer had a considerably higher electronic conductivity than the chemically produced polymers (10-4 cf. 10-10 S cm-1), but much lower conductivity than polypyrrole prepared via the same route. It is not clear from the FT-IR spectra of these polymers whether the hydroxyl group survived intact, or whether it was converted back to the amine. Microanalyses showed that the electropolymerized materials had the expected formulation, but chemical polymerization with FeCl3 led to the introduction of one O per monomer unit in the case of pyrrole, and two and three O atoms, respectively, for FeCl3- and Fe(NO3)3-polymerized N-hydroxypyrroles. The EPR spectrum of each polymer consisted of a single featureless band at g = 2.003. The poly(N-hydroxypyrroles) were further oxidized by PbO2 and m-chloroperbenzoic acid (MCPBA) to give polymer containing a strong band at 1720 cm-1 which may be due either to a ketone group (e.g. pyrrolidone) or possibly an oxoammonium (&gt;N+O) species. Microanalyses showed that while electropolymerized polypyrrole had been oxidized by one O atom per monomer, the chemically prepared polymers (FeCl3) had been oxidized up to the same level as the ferric nitrate-prepared polymers (i.e. from two to three O per pyrrole unit). These oxidized polymers were effectively insulators.</p

Synthesis, spectroelectrochemistry and thermochromism of regioregular head-to-tail oligo- and poly-[3-aryloxyhexylthiophenes]

The synthesis of regioregular head-to-tail poly(3-[ω-(p- methoxyphenoxy)hexyl]thiophenes) is reported, together with a study of the effect of sterically demanding 3-substituents on its structure and physical properties (conductivity, spectroelectrochemistry and thermochromism). The polymer is deep red when reduced but optically transparent in its oxidised form. The syntheses of the corresponding regioregular dimer and trimer, i.e. 3,4'-di[(p-methoxyphenoxy)hexyl]-2,2'-bithiophene and 3,4',4'-tri[(p- methoxyphenoxy)hexyl]-2,2' : 5',2'terthiophene are also reported.</p

Poly(N-hydroxypyrrole) and poly(3-phenyl-N-hydroxypyrrole):synthesis, conductivity, spectral properties and oxidation

N-Hydroxypyrrole and 3-phenyl-N-hydroxypyrrole were oxidized by (ButO2) in the presence of light to give the transient pyrrolyl-1-oxyl (nitroxide) radicals which were observed by EPR spectroscopy. The corresponding poly(N-hydroxypyrroles) were prepared by chemical oxidation with ferric salts, or, in the case of N-hydroxypyrrole only, by electrochemical oxidation in CH3CN at + 1.2 V versus SCE. The latter polymer had a considerably higher electronic conductivity than the chemically produced polymers (10-4 cf. 10-10 S cm-1), but much lower conductivity than polypyrrole prepared via the same route. It is not clear from the FT-IR spectra of these polymers whether the hydroxyl group survived intact, or whether it was converted back to the amine. Microanalyses showed that the electropolymerized materials had the expected formulation, but chemical polymerization with FeCl3 led to the introduction of one O per monomer unit in the case of pyrrole, and two and three O atoms, respectively, for FeCl3- and Fe(NO3)3-polymerized N-hydroxypyrroles. The EPR spectrum of each polymer consisted of a single featureless band at g = 2.003. The poly(N-hydroxypyrroles) were further oxidized by PbO2 and m-chloroperbenzoic acid (MCPBA) to give polymer containing a strong band at 1720 cm-1 which may be due either to a ketone group (e.g. pyrrolidone) or possibly an oxoammonium (&gt;N+O) species. Microanalyses showed that while electropolymerized polypyrrole had been oxidized by one O atom per monomer, the chemically prepared polymers (FeCl3) had been oxidized up to the same level as the ferric nitrate-prepared polymers (i.e. from two to three O per pyrrole unit). These oxidized polymers were effectively insulators.</p

Cyclic voltammetry and spectroelectrochemical study of nickel and cobalt diphenyltetraazaannulene complexes

The absorption spectra. cyclic voltammetry and spectroelectrochemistry of [Ni(II)DPTAA] and [Co(II)DPTAA] (DPTAA = 6,13-diphenyldibenzo[b,i][1,4,8,11] tetraaza[14]annulene) complexes in DMF are reported in detail. The ligand oxidation is observed for [Ni(II)DPTAA] at +0.70 V vs. SCE whereas Ni2(+/+) occurs at - 1.60 V. For [Co(II)DPTAA], a ligand oxidation redox couple is seen at +0.56 V while the Co2+/+ and Co2+/3+ redox couples appear at -1.21 and +0.24 V, respectively. All observed redox couples are assigned to reversible one-electron processes on account of peak separations and scan-rate dependency. These processes were further investigated by spectroelectrochemistry for [Co(II)DPTAA]. For [Co(II)DPTAA], axial ligation of pyridine was found to shift the Co2+/3+ redox couple more negative. while the ligand oxidation was shifted to more positive potentials. From a spectrophotometric titration of [Co(II)DPTAA] with pyridine an equilibrium constant, K-f, was determined for the binding of pyridine to [Co(II)DPTAA]. This was found to be 10.2 dm(3) mol(-1), slightly lower than that of [Co(II)TAA], indicating the influence of the phenyl groups. From this value and shifts in the Co2+/3+ redox couple upon ligation, an equilibrium constant for the binding of pyridine to [Co(III)DPTAA], K'(f), was found to be 5.06 x 10(6) dm(3) mol(-1). (c) 2007 Elsevier B.V. All rights reserved.</p

Aminoxyl functionalized polythiophene:Synthesis and electrochemical applications

2,2,6,6-Tetramethyl-4-[4-(3-thienyl)butoxycarbonyl]piperidin-1-yloxyl and the corresponding N-hydroxytosylate salt have been prepared and polymerized in good yields by chemical and electrochemical methods. The chemically prepared tetramethylpiperidin-1-yloxyl (TEMPO)-substituted polythiophenes had electronic conductivities, when doped with iodine, of ca. 10-3 S cm-1 and were paramagnetic. Electrochemically deposited polymers showed reversible waves at 0.59 V vs. Ag/AgCl in their cyclic voltammograms. Preparative-scale experiments with a platinum electrode coated with electrodeposited polymer showed that efficient oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde could be achieved by a much lower potential to that required without mediation.</p

Aminoxyl functionalized polythiophene:Synthesis and electrochemical applications

2,2,6,6-Tetramethyl-4-[4-(3-thienyl)butoxycarbonyl]piperidin-1-yloxyl and the corresponding N-hydroxytosylate salt have been prepared and polymerized in good yields by chemical and electrochemical methods. The chemically prepared tetramethylpiperidin-1-yloxyl (TEMPO)-substituted polythiophenes had electronic conductivities, when doped with iodine, of ca. 10-3 S cm-1 and were paramagnetic. Electrochemically deposited polymers showed reversible waves at 0.59 V vs. Ag/AgCl in their cyclic voltammograms. Preparative-scale experiments with a platinum electrode coated with electrodeposited polymer showed that efficient oxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde could be achieved by a much lower potential to that required without mediation.</p