Triphos iridium(III) halide complex photochemistry: triphos arm dissociation

Photolysis of Ir(triphos)X3 (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane; X = Cl, Br) yields an insoluble product believed to be oligomeric [Ir(triphos)X3]n with bridging triphos and halide ligands. Refluxing pyridine (py) dissolves the insoluble photoproducts ultimately yielding the dangling triphos complexes mer-Ir(κ(2)-triphos)(py)X3. Oxidation of the P center of the dangling arm of Ir(κ(2)-triphos)(py)Cl3 yields mer-Ir(κ(2)-P,P-triphosO)(py)Cl3 (triphosO = MeC(CH2P(O)Ph2)(CH2PPh2)2), which was characterized by single-crystal X-ray diffraction. mer-Ir(κ(2)-triphos)(py)Cl3 is also formed when Ir(triphos)Cl3 is photolyzed in the presence of py (ϕ = 26%). Both mer-Ir(κ(2)-triphos)(py)Cl3 and mer-Ir(κ(2)-P,P-triphosO)(py)Cl3 photoisomerize in pyridine to their thermally unstable fac-isomers. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations suggest triphos ligand arm dissociation occurs along a triplet pathway from an initial Franck-Condon ligand-field excited state that relaxes to a Jahn-Teller axially distorted octahedral triplet with a long Ir-P bond. Subsequent triphos arm dissociation yields a distorted trigonal-bipyramidal triplet that undergoes intersystem crossing to a square pyramidal singlet.