Influence of Changing the Remote Substituents on Charge Transfer Properties of Cyanide-Bridged Trinuclear Fe−Ru−Fe Complexes

Abstract

To investigate the effect of ligand remote (>10 Å) substituents on the bridging metal center on the metal-to-metal charge transfer (MMCT) properties in cyanidometa-bridged complexes, a series of new cyanidometal-bridged complexes and their one-electron and two-electron oxidation products have been synthesized and well characterized (namely, trans-[Cp(dppe)Fe−NC−(L)Ru(PPh3)−CN−Fe(dppe)Cp][PF6]n (n=2, 3, 4) (L=dmptpy, 1[PF6]n; L=meoptpy, 2[PF6]n; L=t-Buptpy, 3[PF6]n) (Cp=1,3-cyclopentadiene, dppe=1,2-bis(diphenylphosphino)ethane, PPh3=triphenylphosphine, dmptpy=4′-(4-dimethylaminophenyl)-2,2′,6′,2′′-terpyridine, meoptpy=4′-(4-methoxyphenyl)-2,2′,6′,2′′-terpyridine, t-Buptpy=4′-(4-tertbutylphenyl)-2,2′,6′,2′′-terpyridine)). The investigations suggest that the cyanido-stretching (νCN) vibration energy for the complexes is unsensitive to the electron-donating ability change of the remote substituents of the cyanidometal bridging auxiliary ligand from tertbutyl, methoxy to dimethylamino group. However, the MMCT energies of the one- and two-electron oxidation complexes are still sensitive to the remote substituents of the ligand on the bridging metal center, and decreases with the increase of the electron-donating ability of the remote substituents from tertbutyl, methoxy to dimethylamino group. All one-electron and two-electron oxidation products belong to Class II mixed valence compounds according to the classification of Robin and Day.