Triphos Iridium(III) Halide Complex Photochemistry:
Triphos Arm Dissociation
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Abstract
Photolysis
of Ir(triphos)X<sub>3</sub> (triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane;
X = Cl, Br) yields an insoluble product believed to be oligomeric
[Ir(triphos)X<sub>3</sub>]<sub><i>n</i></sub> with bridging
triphos and halide ligands. Refluxing pyridine (py) dissolves the
insoluble photoproducts ultimately yielding the dangling triphos complexes <i>mer</i>-Ir(κ<sup>2</sup>-triphos)(py)X<sub>3</sub>. Oxidation
of the P center of the dangling arm of Ir(κ<sup>2</sup>-triphos)(py)Cl<sub>3</sub> yields <i>mer</i>-Ir(κ<sup>2</sup>-P,P-triphosO)(py)Cl<sub>3</sub> (triphosO = MeC(CH<sub>2</sub>P(O)Ph<sub>2</sub>)(CH<sub>2</sub>PPh<sub>2</sub>)<sub>2</sub>), which was characterized by
single-crystal X-ray diffraction. <i>mer</i>-Ir(κ<sup>2</sup>-triphos)(py)Cl<sub>3</sub> is also formed when Ir(triphos)Cl<sub>3</sub> is photolyzed in the presence of py (ϕ = 26%). Both <i>mer</i>-Ir(κ<sup>2</sup>-triphos)(py)Cl<sub>3</sub> and <i>mer</i>-Ir(κ<sup>2</sup>-P,P-triphosO)(py)Cl<sub>3</sub> photoisomerize in pyridine to their thermally unstable <i>fac</i>-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
