Synthesis of regioregular poly (3-octylthiophene)s via suzuki polycondensation and end-group analysis by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

Regioregular poly(3-octylthiophene)s were synthesized through a palladium-catalyzed Suzuki polycondensation of 2-(5-iodo-4-octyl-2-thienyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane. The effects of the palladium catalyst {tetrakis((triphenylphosphine)palladium(0) [Pd(PPh(3))(4)], palladium(II) acetate [Pd(OAc)2], [1,1 '-bis(diphenylphosphino)ferrocene]dichloropalladium(II) [Pd(dppf)Cl(2)], tris(dibenzylideneacetone)dipalladium(0)), or bis(triphenylphosphine)palladium(II) dichloride [Pd(PPh(3))(2)Cl(2)]} and the reaction conditions (bases and solvents) were investigated. NMR spectroscopy revealed that poly(3-octylthiophene)s prepared via this route were essentially regioregular. According to size exclusion chromatography, the highest molecular weights were obtained with in situ generated Pd(PPh3)4 and tetrakis(tri-o-tolylphosphine)palladium(0) {Pd[P(o-Tol)(3)](4)} catalysts or more reactive, phosphine-free Pd(OAc)(2). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to analyze end groups and allowed the determination of some mechanistic aspects of the Suzuki polycondensation. The polymers were commonly terminated with hydrogen or iodine as a result of deboronation and some deiodination. Pd(PPh(3))(4), Pd(PPh(3))(2)Cl(2), and Pd[P(o-Tol)(3)](4) induced aryl-aryl exchange reactions with the palladium center and resulted in some chains having phenyl- and o-tolyl-capped chain ends. Pd(dpp)Cl(2) yielded only one type of chain, and it had hydrogen end groups.