EPR/ENDOR detection of stable TiIII and TiIV radical products generated by single electron transfer from (PriO)3TiCH3
Abstract
Single electron transfer reactions between the stereoselective carbanion source methyltriisopropoxy-titanium(IV) as donor and α-diimines, ketones or α-dicarbonyls as π acceptor substrates exhibit a dichotomy with respect to the EPR-detectable paramagnetic ‘escape’ products. Substrates with very negative reduction potentials such as 2,2′-bipyridine yield TiIII species, whereas more easily reducible molecules such as dinucleating 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine react to yield EPR-detectable TiIV complexes of the corresponding anion radicals. A very stable paramagnetic product has been isolated from the reaction between 3,5-di-tert-butyl-o-quinone (dtbq) and (PriO)3TiCH3; this first thermally stable, but apparently configurationally labile, TiIV semiquinone complex [(dtbq–1)Ti(OPri)3]˙ was studied by UV–VIS–NIR absorption and EPR/ENDOR spectroscopy.