ELSEVIER Synthetic Metals 84 (1997) 225-226 Electroactive, n-Conjuga’ted Polymers based on Transition Metal-Containing Thiophenes Jerry L. Reddinger and John R. Reynolds Center for Macromolecular Science and Engineering Department of Chemistry, University of Florida, Gainesville, FL 3261 I, USA Abstract A series of heterocycle-based bis(salicylaldimine) complexes have been synthesized and their electrochemical properties investigated. Both nickel and copper complexes of the simplest ligand 1 (SALOTH) were found to undergo electropolymerization to yield durable electro-active films under oxidizing condition. In both cases polymerization desisted upon blocking of the para position of the phenol ring. Hence, it appears that the polymer formed from complexes 2a-b is comprised of phenylene linkages at this site. In stark contrast when the conjugation of the monomer is extended by utilizing a terthiophene core, blocking of the para (complex 6) and both the orfho and para (complex 7) positions did not preclude polymerization. Furthermore, the metal-based oxidation moves to higher potentials, and additional redox processes, not seen in the other systems, grow in at lower potentials. Thus, we believe the polymer structure in these cases to be that of a polythiophene. Keywords: Electrochemical polymerization, Polythiophene and derivatives, metal-containing polymers Introduction There are numerous examples of conducting polymers which contain transition metals within their architecture.’ However, the metallic centers in these systems are appended to the polymer backbone in such a manner that little if any direct electronic communication between the metal and the polymer’s extended n-system can exist. Conversely, metal-containing polymers, in which the metal is directly affixed to the n-conjugated backbone, have the capability of accessing a continuum of redox states afforded by metal-polymer cooperativity. There are few examples of such systems in the current literature. Complexation of preformed polymers has been accomplished using pyridyl and bis(thiazolyl) backbones.* However, the degree of metal incorporation is of great uncertainty when utilizing such an approach. Peng and Yu have recently reported the Heck coupling polymerization of a cationic ruthenium-based monomer.3 Unfortunately, this system is limited to metals that will not decomplex, allowing the polymerization catalyst to chelate to the monomer and be deactivated. Consideration of the features of an ideal system along with such aforementioned factors led us to design a monomer type in which the metal was precomplexed and in conjugation with the reactive core, yet still possessed the ability to undergo electropolymerization. Our group has been involved with the synthesis and electropolymerization of low-oxidation potential monomers for sometime now. Many of these systems are derived from electron-rich thiophene-based monomers that, when polymerized, afford electro-active materials possessing novel electronic properties.4 Using these findings, we opted to meld an electropolymerizable thiophene core with a tetradentate bis(salicylidine)-type ligand system. By utilizing the 3- and 4-positions of the heterocyclic ring as connecting points for the ligand portion, the 2- and 5 positions are left open for further functionalization. 0379-6779/97/$17.00 Q 1997 Else&r Science S.A All rights reserved PIISO3794779(96)03915-X Monomer Synthesis As depicted in Scheme 1, the ligand 1 (SALOTH) was synthesized by the condensation of 3,4- diaminothiophene with salicylaldehyde. Metal complexation was accomplished by adding a hot ethanolic solution of 1 to the desired metal acetate dissolved in hot ethanol. An alternative method, which is shown in Scheme 2, is to first complex the aldehyde and subsequently condense the resulting species with the diamine. Scheme 1. H2 775 NH2 / \ 9: sly”;9 ) S EtOH n I \ S 1 1 WOAch EtOH Q- MINo_p n / \ S 2