Improved Photocatalysis in Diisocyanide-Supported Heteroleptic Four-Coordinate Copper(I) β-Diketiminate Complexes

Developing robust, sustainable molecular photosensitizers that combine strong visible-light absorption, long excited-state lifetimes, and potent redox reactivity remains a fundamental challenge in photoredox catalysis. Cu(I) complexes are promising earth-abundant alternatives to precious-metal photocatalysts, motivating fundamental investigations into their excited-state properties and photocatalytic reactivity. Here we report a new class of heteroleptic four-coordinate Cu(I) complexes supported by chelating diisocyanide ligands, one with a m-terphenyl (CNAr3NC) core and an analogue with a m-quinquephenyl core (CNAr5NC), in combination with a β-diketiminate ligand with 2,6-dimethylphenyl N-substituents (dmp-NacNac). With more sterically encumbered or electron-rich β-diketiminate ligands, diisocyanide-bridged, three-coordinate dicopper complexes are formed instead. The four-coordinate complex supported by the quinquephenyl-based diisocyanide CNAr5NC, Cu2, exhibits strong visible absorption, an excited-state lifetime over twice as long as the m-terphenyl CNAr3NC analogue (103 ns vs 48 ns), and a highly reducing excited-state oxidation potential (*Eox = -2.4 V vs Fc+/0). As a result, Cu2 is active for visible-light photocatalytic E/Z isomerization of stilbene and reductive photoredox transformations of substituted benzophenone derivatives. In the latter application, Cu2 outperforms a related three-coordinate monoisocyanide-terminated analogue, affording higher yields of photohydrogenation and hydrodehalogenation products with lower catalyst loadings.