Synthesis and Properties in Solution of Rodlike, 2,2‘:6‘,2‘ ‘-Terpyridine-Based Ruthenium(II) Coordination Polymers

Abstract

Rodlike ruthenium(II) coordination polymers have been prepared via the conversion of 4,4‘ ‘-bis(2,2‘:6‘,2‘ ‘-terpyridine)-2‘,5‘-dihexyl-p-terphenyl and an appropriately reactive ruthenium(III) species in 1-butanol/DMA. The diamagnetic polymers readily dissolve in polar organic solvents, and their homogeneous constitution could thus be proven and their degrees of polycondensation could be estimated to be P_n ≥ 30, using ¹H and ¹³C NMR spectroscopy. The Pd-catalyzed polycondensation of bis[4‘-(p-bromophenyl)-2,2‘:6‘,2‘ ‘-terpyridine]ruthenium(II) tetrafluoroborate and 2,5-dihexylbenzene-1,4-diboronic acid, on the other hand, which should lead to a constitutionally identical polymer, only resulted in oligomers under all tested conditions. The intrinsic viscosity [η] of the high-molecular-weight polymers (determined in 0.02 M NH₄PF₆/DMA) is of the order of 300 mL g^-1. In salt-free DMA solution and thus at low ionic strengths, the polymers display the characteristic polyelectrolyte behavior in viscosity experiments which becomes more and more pronounced with increasing P_n. The UV−vis absorption spectra recorded in DMA solution do not show any evidence of intramolecular electronic interactions of the metal centers along the polymer chains: on the contrary, the coordination polymers behave like sequences of electronically independent ruthenium(II) complexes.