Reduction Reaction of the Copper(II) Complex Bearing 1,3-Di(pyridine-2-carboxaldimino)propane (pitn) by Decamethylferrocene in Acetonitrile

The reduction reaction of the Cu(II)-pitn complex (pitn = 1,3-di(pyridine-2-carboxaldimino)propane) by decamethylferrocene [Fe(Cp*)(2)] was examined in acetonitrile. The observed pseudo-first-order rate constants exhibited saturation kinetics with increasing excess amount of [Fe(Cp*)(2)]. Detailed analyses revealed that the reaction is controlled by a structural change prior to the electron transfer step, rather than a conventional bimolecular electron transfer process preceded by ion pair (encounter complex) formation. The rate constant for the structural change was estimated to be 275 +/- A 13 s(-1) at 298 K (a dagger H* = 33.3 +/- A 1.0 kJ center dot mol(-1), a dagger S* = 86 +/- A 5 J center dot mol(-1)center dot K-1), which is the fastest among gated reactions involving CuN4 complexes. It was confirmed by EPR measurement and Conflex calculations that the dihedral angle between the two N-N planes is significantly large (40A degrees) in solution whereas it is merely 17.14A degrees in the crystal.