Photoredox Catalysis Mediated by Tungsten(0) Arylisocyanides in 1,2-Difluorobenzene.

We have studied the photochemical cyclization of 1-(2-iodobenzyl)-pyrrole (IBP) and 1-(2-bromobenzyl)-pyrrole (BBP) to 5 H -pyrrolo[2,1- a ]isoindol catalyzed by W(CNDipp) 6 (CNDipp = 2,6-diisopropylphenylisocyanide) in 1,2-difluorobenzene (DFB). Irradiation (445 nm) of W(CNDipp) 6 (5 mol %) in DFB solution converted 78% of IBP (50 mM) to product after 1 h (16 turnovers). Addition of tetra- n -butyl ammonium hexafluorophosphate (TBAPF 6 ) (0.2 M) to the DFB solution led to rapid photoinduced disappearance of W(CNDipp) 6 but, remarkably, did not inhibit photochemical cyclization of IBP, indicating that IBP cyclization could be driven by a nonluminescent photocatalyst.