Cyclo- and Polyphosphazenes with Redox Active Substituents

GRAPHICAL ABSTRACT

Abstract

This paper focuses on phosphazenes containing one of two organometallic functionalities, either the tetrahedral cluster obtained from the reaction of dicobalt octacarbonyl with an ethynyl or the ferrocene entity, which provide well-behaved reduction and oxidation processes, respectively. The cyclic voltammetry of N₃P₃F₅CCPhCo₂(CO)₆ shows a reversible reduction to the moderately stable radical anion. A frozen solution EPR spectrum of the radical ion shows that the unpaired electron is localized on the cobalt carbonyl fragment. The corresponding geminal disubstituted analog undergoes two reversible one electron reductions. A polymer with a N₃P₃F₄CCPhCo₂(CO)₆ substituent also undergoes a reversible one electron reduction giving the polymer radical anion. Introduction of a ferrocene unit was accomplished via the reaction of N-(ferrocenylmethyl)-N-methylamine, CpFeC₅H₄CH₂N(Me)H, with hexachlorocyclotriphosphazene and poly(dichlorophosphazenes). Each cyclophosphazene with multi ferrocene substituents shows only one reversible one electron oxidation indicating electronic isolation of the multiple redox centers. Poly(phosphazenes) containing the ferrocene unit and trifluoroethoxy, phenoxy, and methoxyethoxyethoxy (MEEP) cosubstituents have been studied as electron-transfer mediators in a glucose sensor array using cyclic, steady state, and constant potential voltammetry. The MEEP system is one hundred fold more effective than the other polymers which can be understood in terms of the hydrophilic interactions of the MEEP group and glucose oxidase.

Keywords:

• Cyclophosphazenes
• redox
• electrochemistry