Photoinduced Face-Inversion of Conjugated Tetraene Ligands on a Pd−Pd−Pd Moiety

The linear sandwich tripalladium complexes [Pd₃{Ar(CHCH)₄Ar}₂[BAr_f]₂ (Ar = Ph, p-t-Bu-C₆H₄, p-styryl-C₆H₄) undergo photoinduced isomerization involving face-inversion of the tetraene ligands. Irradiation of these complexes with visible light (>510 nm) resulted in rac (staggered sandwich) to meso (eclipsed sandwich) isomerization. The structures of rac and meso isomers are determined by X-ray crystallographic analyses.