Synthesis and electrochemical characterization of ruthenium porphyrins containing a bound PF3 axial ligand

The first synthesis and electrochemistry of metalloporphyrins containing a bound PF, axial ligand has been achieved. The investigated compounds are [Ru(por)(PF3)] where por is the dianion of 5,10,15,20-tetraphenyl-, -tetra(p-bromophenyl)-, -tetra(p-methoxyphenyl)-, 2,7,12,17-tetraethyl-3,8,13,18-tetramethyl- or 2,3,7,8,1 2,13,17,18-octaethyl-porphyrin. Each [Ru(por)(PF3)] species was investigated with respect to its spectroscopic and electrochemical properties and the resulting data compared with those for [Ru(por)(CO)] having the same porphyrin ring. A number of similarities exist between the carbonyl and PF3 derivatives in methylene chloride but major differences can be observed in other non-aqueous solutions. The first reduction of each complex is reversible in tetrahydrofuran (thf) and leads to a porphyrin pi-anion radical rather than a ruthenium(I) species as identified by UV/VIS spectroelectrochemistry. Each investigated complex also undergoes two reversible oxidations in dichloromethane, the first of which leads to a porphyrin pi-cation radical. The [Ru(por)(PF3)] derivatives appear to be more stable than the [Ru(por)(CO)] analogues in thf or CH2Cl2, but an electrochemically initiated conversion of [Ru(II)(por)(PF3)(PY)] into [Ru(III)(por)(py)2]+ can be readily accomplished in pyridine (py) or CH2Cl2-pyridine mixtures. This type of reaction has never been seen upon oxidation of a ruthenium(II) porphyrin and was monitored by cyclic voltammetry and UV/VIS spectroelectrochemistry.