A new poly(3-alkylthiophene) synthesis via Pd-catalyzed coupling of thienyl mercuric chlorides

A new coupling reaction based on the Pd-catalyzed reductive coupling of thienyl mercuric chlorides is described. A variety of substituted thiophenes react with HgCl2 to produce thienyl mercuric chlorides. The degree of substitution can be controlled by the choice of temperature, solvent, and reaction time, and the resulting chloromercuri thiophenes or bis(chloromercuri)thiophenes are stable to air and water. Heating the thienyl mercuric chlorides in pyridine solvent with Cu powder and PdCl2 catalyst gave good yields of the coupled thiophenes. Poly(alkyl)thiophenes, poly(alkyl thienylacetate esters), and copolymers of alkylthiophenes with unsubstituted thiophene were formed in good yields. Molecular weights, M(w), were in the range 5300-83000. This coupling reaction was demonstrated to be compatible with the presence of an electrophilic substituent that is attacked by more nucleophilic intermediates, e.g., thienyllithium or thienyl Grignard reagents. Thus, this synthesis should be compatible with substituents known to be unreactive toward arylmercuric chlorides or arylpalladium compounds and is therefore complementary to the organometallic coupling schemes currently in use.