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

Abstract

The first synthesis and electrochemistry of metalloporphyrins containing a bound PF₃ 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 2,3,7,8,12,13,17,18-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 π-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 π-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.