Spectroelectrochemical and flash photochemical reduction of 1,4,5,8-tetraazaphenanthrene and 1,4,5,8,9,12-hexaaza-triphenylene mono- and bi-metallic ruthenium(II) complexes

Abstract

The Spectroelectrochemical reduction and photoreduction of [{Ru(phen)₂}₂(hat)]⁺⁴(phen = 1,10-phen-anthroline. hat = 1,4,5,8,9,12-hexaazatriphenylene) and [Ru(tap)₃]²⁺ and [Ru(bipy)₂(tap)]²⁺(bipy = 2,2′-bipyridine, tap = 1,4,5,8-tetraazaphenanthrene) for comparison purposes, have been examined. Hydroquinone (H₂quin) was chosen as the reductant for the photochemical reduction. Laser flash photolysis of these complexes with H₂quin led to two transients. It is shown, on the basis of the Spectroelectrochemical reduction of free tap and hat and the corresponding complexes, that the first transient at ≈500 nm corresponds to the monoreduced complexes [{Ru(phen)₂}₂(hat˙^–)]³⁺, [Ru(tap)₂(tap˙^–)]⁺ and [Ru(bipy)₂(tap˙^–)]⁺ respectively; this is confirmed by the kinetic behaviour of their decays in the presence of oxidante such as benzoquinone (bquin) and O₂. The second transient at ≈350–400 nm has a much longer lifetime and is attributed to the semiquinone Hquin˙, formed from the reduction of bquin (purposely added or present as traces of oxidant in the medium) by the photogenerated reduced complex. For the bimetallic complex an alternative pathway is proposed for the observation of the second transient.