Probing Electronic Communications in Heterotrinuclear Fe-Ru-Fe Molecular Wires Formed by Ruthenium(II) Tetraphenylporphyrin and Isocyanoferrocene or 1,1′-Diisocyanoferrocene Ligands

Two new heterotrinudear Fe-Ru-Fe complexes of ruthenium(II) tetraphenylporphyrin axially coordinated with a pair of isocyanoferrocene ((FcNC)(2)RuTPP, 1) or 1,1'-diisocyanoferrocene (([C5H4NC](2)Fe)(2)RuTPP, 2) ligands [Fe = ferrocenyl, TPP = 5,10,15,20-tetraphenylporphyrinato(2-) anion] were synthesized and characterized by UV vis, magnetic circular dichroism, NMR, and FTIR spectroscopies as well as by electrospray ionization mass spectrometry and single-crystal X-ray diffraction. Isolation of insoluble polymeric {([C5H4NC](2)Fe)RuTPP}(n), molecular wires (3) was also achieved for the first time. The redox properties of the new trinudear complexes 1 and 2 were probed using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation methods and correlated to those of the bis(tertbutylisocyano)ruthenium(11) tetraphenylporphyrin reference compound, (t-BuNC)(2),RuTPP (4). In all cases, the first oxidation process was attributed to the reversible oxidation of the Ru-II center. The second and third reversible oxidation processes in 1 are separated by similar to 100 mV and were assigned to two single-electron Fe-II/Fe-III couples, suggesting a weak long-range iron iron coupling in this complex. Electrochemical data acquired for 2 are complicated by the interaction between the axial eta(1)-1,1'-diisocyanoferrocene ligand and the electrode surface as well as by axial ligand dissociation in solution. Spectroelectrochemical and chemical oxidation methods were used to elucidate the spectroscopic signatures of the [1](n+), [2](n+), and [4](n+) in solution. DFT and time-dependent DFT calculations aided in correlating the spectroscopic and redox properties of complexes 1, 2, and 4 with their electronic structures.