Self-Assembly of Tricuprous Double Helicates: Thermodynamics,Kinetics,and Mechanism

摘要

We report in this paper the coordination and kinetic properties of two oligobipyridine strands, which contain three 2,2'-bipyridine subunits separated by oxydimethylene bridges, the 4,4'-bis(CONET J-substituted L and the 4,4'-bis(CO_2Et)-substituted L'. Spectrophotometric measurements allowed the characterization of thermodynamic complexes and kinetic intermediates* which are involved in the self-assembly process ofL_2Cu_3 and L_2'Cu_3 helicates. The reaction presents positive cooperativity for the binding of two 2,2'-bipyridine strands to the cuprous cations. While reactive kinetic intermediates* present distorted coordination geometries around Cur, the final rearrangement of the tricuprous bistranded helicates allows more closely tetrahedral coordination of each cation and reduces the interactions. Differences in the bulkiness and electronic properties of the Land L' substituents do not affect significantly the stability of the corresponding helicates, but greatly influence binding rates in the self-assembly process.