Visible-Light Activation of Diorganyl Bis(pyridylimino) Isoindolide Aluminum(III) Complexes and Their Organometallic Radical Reactivity.

ABSTRACT

We report on the synthesis and characterization of a series of (mostly) air-stable diorganyl bis(pyridylimino) isoindolide (BPI) aluminum complexes and their chemistry upon visible-light excitation. The redox non-innocent BPI pincer ligand allows for efficient charge transfer homolytic processes of the title compounds. This makes them a universal platform for the generation of carbon-centered radicals. The photo-induced homolytic cleavage of the Al-C bonds was investigated by means of stationary and transient UV/Vis spectroscopy, spin trapping experiments, as well as EPR and NMR spectroscopy. The experimental findings were supported by quantum chemical calculations. Reactivity studies enabled the utilization of the aluminum complexes as reactants in tin-free Giese-type reactions and carbonyl alkylations under ambient conditions, which both indicated radical-polar crossover behavior. A deeper understanding of the physical fundamentals and photochemical process was provided, furnishing in turn a new strategy to control the reactivity of bench-stable aluminum organometallics.