Abstract:

Aryl palladium complex (bt-DTT)Pd(PCy₃)₂Br was synthesized by oxidative addition of 5-bromo-2-trimethylsilanyl-dithieno[2,3-b:2',3'-d]thiophene(bt-DTT-Br) to bis(tericlohexylphosphine)palladium(Pd(PCy₃)₂). X-ray crystal structure analysis reveals that the complex adopts a nearly square-planar geometry around central Pd atom with the expected trans configuration of the phosphine ligands. The complex can initiate the polymerization of AB-type fluorene monomer under heating conditions to afford the polyfluorene with the defined end group of aryl group bt-DTT derived from the complex(bt-DTT)Pd(PCy₃)₂Br. The similar conjugated polymers can also be prepared by employing the aryl palladium complexes in situ generated from bt-DTT-Br/Pd(0)-species as initiators. Polymerization of AB-type fluorene monomers is achieved at room temperature to give the single polyfluorene with the well-defined end groups while initiators are the complexes with the ancillary ligand of tris(2-methylphenyl)phosphine(P(o-tol)₃) or tri-tert-butylphosphine(P(t-Bu)₃). Matrix-assisted laser desorption ionization time-of-flight(MALDI-TOF) mass spectra confirm that the polymers bear a bt-DTT group at one end and a Br/H atom or end-capping group at the other end. Gel permeation chromatography(GPC) analyses demonstrate that molecular mass of polymers increases linearly with increase of the molar ratio of monomer to catalyst, indicating that the polymerizations proceed through the catalyst-transfer mechanism.

Key words: aryl palladium complexes, polyfluorene, catalyst-transfer polymerization, dithieno[2,3-b:2',3'-d]thiophene