Phenol oxidation using ruthenium and iridium catalysis

Abstract

We synthesised 4 different tri-substituted phenols: A (2-(pent-4-en-1-yl)phenol, B (4-methoxy-2-(pent-4-en-1-yl)phenol, C (curcuphenol), and D (curcuphenol). While phenols A, B, and C possessed terminal olefins, phenol D possessed a di-methyl substituted olefin. In order to catalyse the photochemical cycloaddition of these phenols, [Ir(dF(CF[subscript 3])ppy)[subscript 2](dtbbpy)(PF[subscript 6]), Ru(bpy)[subscript 3](BF[subscript 4])[subscript 2], and Ru(bpy)[subscript 3]Cl[subscript 2] catalysts were synthesised. Subsequently, we explored the Ir and Ru catalysed photochemical oxidation of each phenol, with the aim of synthesising [5 + 2] cycloaddition bridged bicyclic systems. While cycloadducts were not observed, it became apparent that the reduction of the metal centre before interaction with the phenol might not be a plausible pathway. Thus, future endeavours will include the use of cationic moieties and salts, to elicit metal oxidation prior to phenol-metal interaction in order to foster the formation of a pentadienyl radical cation intermediate. It is envisaged that this pathway will favour cycloaddition.