%0 Journal Article
%T A [2.2]Isoindolinophanyl-Based Carbene (iPC) Ligand: Synthesis, Electronic and Photophysical Properties, and Application in Photocatalysis*.
%A Maity S
%A Muthig AMT
%A Sen I
%A Mrózek O
%A Belyaev A
%A Hupp B
%A Steffen A
%J Angew Chem Int Ed Engl
%V 0
%N 0
%D 2024 Jul 4
%M 38965782
%F 16.823
%R 10.1002/anie.202409115
%X Cyclic amino(alkyl) and cyclic amino(aryl) carbenes (cAACs/cAArCs) have been established as very useful ligands for catalytic and photonic applications of transition metal complexes. Herein, we describe the synthesis of a structurally related sterically demanding, electrophilic [2.2]isoindolinophanyl-based carbene (iPC) with a [2.2]paracyclophane moiety. The latter leads to more delocalized frontier orbitals and intense green fluorescence of (HiPC)OTf (2) from an intra-ligand charge transfer (1ILCT) state in the solid state. Base-promoted synthesis of the free carbene led to an unusual ring expansion and subsequent dimerization reaction, but the beneficial ligand properties can be exploited by trapping in situ at a metal center. The iPC ligand is a very potent π-chromophore, which participates in low energy metal-to-ligand (ML)CT transitions in [RhCl(CO)2(iPC)] (4) and IL-"through-space"-CT transitions in [Au(iPC)2]OTf (5). The steric demand of the iPC leads to high stability of 5 against air, moisture, or solvent attack, and ultralong-lived green phosphorescence with a lifetime of 185 μs is observed in solution. The beneficial photophysical and electronic properties of the iPC ligand, including a large accessible π surface area, were exploited by employing highly efficient energy transfer (EnT) photocatalysis in a [2+2] styrene cycloaddition reaction using 5, which outperformed other established photocatalysts in comparison.