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(κ2-triphos)­(py)­X3. Oxidation of the P center of the dangling arm of Ir­(κ2-triphos)­(py)­Cl3 yields mer-Ir­(κ2-P,P-triphosO)­(py)­Cl3 (triphosO = MeC­(CH2P­(O)­Ph2)­(CH2PPh2)2), which was characterized by single-crystal X-ray diffraction. mer-Ir­(κ2-triphos)­(py)­Cl3 is also formed when Ir­(triphos)­Cl3 is photolyzed in the presence of py (ϕ = 26%). Both mer-Ir­(κ2-triphos)­(py)­Cl3 and mer-Ir­(κ2-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.