Exploiting the Marcus inverted region for first-row transition metal–based photoredox catalysis

Abstract

Second- and third-row transition metal complexes are widely employed in photocatalysis, whereas earth-abundant first-row transition metals have found only limited use because of the prohibitively fast decay of their excited states. We report an unforeseen reactivity mode for productive photocatalysis that uses cobalt polypyridyl complexes as photocatalysts by exploiting Marcus inverted region behavior that couples increases in excited-state energies with increased excited-state lifetimes. These cobalt (III) complexes can engage in bimolecular reactivity by virtue of their strong redox potentials and sufficiently long excited-state lifetimes, catalyzing oxidative C(sp 2 )–N coupling of aryl amides with challenging sterically hindered aryl boronic acids. More generally, the results imply that chromophores can be designed to increase excited-state lifetimes while simultaneously increasing excited-state energies, providing a pathway for the use of relatively abundant metals as photoredox catalysts.

Photocatalytic Reduction of CO2 to HCOOH and CO by a Phosphine‐Bipyridine‐Phosphine Ir(III) Catalyst: Photophysics, Nonadiabatic Effects, Mechanism, and Selectivity

“…Moreover, we estimated the transition‐state barrier of 0.2 kcal/mol and the electronic coupling of 37.4 meV, [103–107] both of which together lead to an ultrafast SET process (Table S5). In addition, the SET process happens in an inverted Marcus region, which was recently exploited for photoredox catalysis by MacMillan et al [108] . Therefore, in the 3 MLCT state, the SET process will occur dominantly.…”

Photocatalytic Reduction of CO2 to HCOOH and CO by a Phosphine‐Bipyridine‐Phosphine Ir(III) Catalyst: Photophysics, Nonadiabatic Effects, Mechanism, and Selectivity

“…Moreover, we estimated the transition‐state barrier of 0.2 kcal/mol and the electronic coupling of 37.4 meV, [103–107] both of which together lead to an ultrafast SET process (Table S5). In addition, the SET process happens in an inverted Marcus region, which was recently exploited for photoredox catalysis by MacMillan et al [108] . Therefore, in the 3 MLCT state, the SET process will occur dominantly.…”

Enhanced Visible Light Absorption in Heteroleptic Cuprous Phenanthrolines

“…Two classes of Cu­(I) bis -phenanthrolines engender either homoleptic or heteroleptic ligand topologies. Homoleptic cuprous phenanthrolines have been studied since the 1970s for their potent photoreducing capabilities, long-lived excited states, and tremendous durability to high-power laser excitation. ,,− Heteroleptic complexes using diimine- and bis -phosphine-type ligands have been growing in interest, especially for applications in dye-sensitized solar cells, − photoredox catalysis, − and the construction of supramolecular donor–acceptor architectures. ,,− The HETPHEN strategy leverages 2,9-mesityl-1,10-phenanthroline (mesPhen), ,, which is unable to form a bis -homoleptic complex but enables the binding of another suitable phenanthroline, assisted through π-interactions with the 2,9-mesityl substituents and the B-ring of the orthogonally coordinated phenanthroline. This platform facilitates a facile pathway for obtaining heteroleptic Cu­(I) complexes with the generic formula [Cu­(mesPhen)­(L)] + , where L is a second and distinct phenanthroline ligand (Chart ).…”