Long-Lived Charge-Transfer States of Nickel(II) Aryl Halide Complexes Facilitate Bimolecular Photoinduced Electron Transfer

Here
we investigate the photophysics and photochemistry of Ni­(II)
aryl halide complexes common to cross-coupling and Ni/photoredox reactions.
Computational and ultrafast spectroscopic studies reveal that these
complexes feature long-lived 3MLCT excited states, implicating
Ni as an underexplored alternative to precious metal photocatalysts.
Moreover, we show that 3MLCT Ni­(II) engages in bimolecular
electron transfer with ground-state Ni­(II), which enables access to
Ni­(III) in the absence of external oxidants or photoredox catalysts.
As such, it is possible to facilitate Ni-catalyzed C–O bond
formation solely by visible light irradiation, thus representing an
alternative strategy for catalyst activation in Ni cross-coupling
reactions.