Chirality in the Photochemical mer→fac Geometrical Isomerization of Tris(1‐phenylpyrazolato,N,C2′)iridium(III)

Irradiation of the optically resolved mer‐Δ isomer of tris(1‐phenylpyrazolato,N,C2′)iridium(III) with 366‐nm light in CH3CN purged by argon at 25 °C gave 59 % fac‐Δ and 41 % fac‐Λ (18 % ee) at the end of geometrical isomerization. Formation of the intermediate mer‐Λ species was not observed, which is quite characteristic when compared with the corresponding thermal isomerization reaction. This enantiomeric photoisomerization is rationally explained by a mechanism based on Ir–N bond dissociation at the top or bottom axial ligand. This reaction mechanism is explained by the potential energy surface of the triplet excited state.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)