Electropolymerization of Pd(II) complexes containing phosphinoterthiopheneligands

A series of Pd complexes of 3'-diphenylphosphino-2,2:5'2"-terthiophene (1a, dppterth) in which the metal is coordinated in three different modes have been,prepared and electropolymerized, resulting in the formation of conduct ive thin films. In [Pd-2(mu -Cl-2)(dppterth-P,C-3)(2)] (3a), the metal is P ,C-coordinated, in. [PdCl2(dppterth-P)(2)] (4a) the coordination is monoden tate via the phosphine, and in [Pd(dppterth-P,C-3)(dppterth-P, S-1)] [PF6] (5a) both P,C- and P,S-coordination modes are found. In 5a, the coordinated thiophene is hemilabile and may be displaced by reaction with more strongl y coordinating ligands such as isocyanides, To probe the effect of blocking the a-position of the terthienyl moiety with methyl groups, 3'-diphenylpho sphino-5-methyl-2,2':5'2"-terthiophene (1b, Me-dppterth) and 3'-diphenylpho sphino-5,5"-dimethyl-2,2':5'2"-terthiophene (1c, Me-2-dppterth) were prepar ed, and the corresponding series of Pd complexes was synthesized. One of th ese complexes, [Pd(Me-2-dppterth-P,C-3)(Me-2-dppterth-P,S-1)] [PF6] (5c), h as been crystallographically characterized. The electropolymerized films pr epared, from 5a react with isonitriles, and shifts in the absorption spectr a of the electropolymerized materials are observed upon reaction. A Pd comp lex has also been prepared from 5-diphenylphosphino-2,2':5,'2"-terihiophene (2, 5dppterth), and this complex has been electropolymerized. All the elec tropolymerized thin films have been characterized using EDX analysis, which demonstrates good correspondence with the elemental analysis of the respec tive monomers, and the maximum conductivities of the films are near 10(-4) S cm(-1). Comparing the electropolymerization behavior of the complexes, al ong with their electrochemical and spectroscopic data, allows conclusions t o be drawn regarding the involvement of pi -delocalization and the metal gr oup in the conductivity of the Materials.