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]_<i>n</i> with bridging triphos and halide ligands. Refluxing pyridine (py) dissolves the insoluble photoproducts ultimately yielding the dangling triphos complexes <i>mer</i>-Ir­(κ²-triphos)­(py)­X₃. Oxidation of the P center of the dangling arm of Ir­(κ²-triphos)­(py)­Cl₃ yields <i>mer</i>-Ir­(κ²-P,P-triphosO)­(py)­Cl₃ (triphosO = MeC­(CH₂P­(O)­Ph₂)­(CH₂PPh₂)₂), which was characterized by single-crystal X-ray diffraction. <i>mer</i>-Ir­(κ²-triphos)­(py)­Cl₃ is also formed when Ir­(triphos)­Cl₃ is photolyzed in the presence of py (ϕ = 26%). Both <i>mer</i>-Ir­(κ²-triphos)­(py)­Cl₃ and <i>mer</i>-Ir­(κ²-P,P-triphosO)­(py)­Cl₃ 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

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]_<i>n</i> with bridging triphos and halide ligands. Refluxing pyridine (py) dissolves the insoluble photoproducts ultimately yielding the dangling triphos complexes <i>mer</i>-Ir­(κ²-triphos)­(py)­X₃. Oxidation of the P center of the dangling arm of Ir­(κ²-triphos)­(py)­Cl₃ yields <i>mer</i>-Ir­(κ²-P,P-triphosO)­(py)­Cl₃ (triphosO = MeC­(CH₂P­(O)­Ph₂)­(CH₂PPh₂)₂), which was characterized by single-crystal X-ray diffraction. <i>mer</i>-Ir­(κ²-triphos)­(py)­Cl₃ is also formed when Ir­(triphos)­Cl₃ is photolyzed in the presence of py (ϕ = 26%). Both <i>mer</i>-Ir­(κ²-triphos)­(py)­Cl₃ and <i>mer</i>-Ir­(κ²-P,P-triphosO)­(py)­Cl₃ 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

Hydroxo Radicals, C–H Activation, and Pt–C Bond Formation from 77 K Photolysis of a Platinum(IV) Hydroxo Complex

Photolysis (380 nm) of <i>trans</i>,<i>cis</i>-Pt­(PEt₃)₂(Cl)₂(OH)­(4-tft) (4-tft = 4-trifluoromethylphenyl) at 77 K in 2-methyltetrahydrofuran gives triplet emission, platinum­(III), and a hydroxo radical. Benzyl radical emission is observed in toluene from the reaction of a portion of the OH radicals with toluene. Warming the photolyzed solutions gives platinacycle <i>trans</i>-Pt­(CH₂CH₂PEt₂)­(PEt₃)­(Cl)₂(4-tft) by hydrogen-atom abstraction from a PEt₃ ligand and <i>trans</i>-Pt­(PEt₃)₂(Cl)­(4-tft) from net HOCl photoelimination. The platinacycle undergoes thermal reductive elimination at 298 K or photolytic reductive elimination, even at 77 K

Hydroxyl Radical Control through Hydrogen Bonding: Photolysis of Platinum(IV)hydroxido Complexes with Intramolecular H‑Bonding

By introducing hydrogen-bonding groups into the coordination sphere of Pt­(IV) hydroxido complexes photogenerated hydroxyl radicals are tethered and directed to abstract a hydrogen atom from the ethyl group of a triethylphosphine ligand, even at 25 °C, to yield phosphaplatinacycle complexes

Photoreduction of Pt(IV) Halo-Hydroxo Complexes: Possible Hypohalous Acid Elimination

Concentrated hydrogen peroxide addition to <i>trans-</i>Pt­(PEt₃)₂Cl­(R) [<b>1</b> (R = 9-phenanthryl), <b>2</b> (R = 4-trifluoromethylphenyl)] yields hydroxo-hydroperoxo complexes <i>trans-</i>Pt­(PEt₃)₂(Cl)­(OOH)­(OH)­(R) [<b>5</b> (R = 9-phenanthryl), <b>4</b> (R = 4-trifluoromethylphenyl)], where the hydroperoxo ligand is <i>trans</i> to R. Complex <b>5</b> is unstable and reacts with solvent CH₂Cl₂ to give <i>trans</i>,<i>cis</i>-Pt­(PEt₃)₂(Cl)₂(OH)­(9-phenanthryl) (<b>3</b>). Treatment of <b>4</b> with HCl yields analogous <i>trans</i>,<i>cis</i>-Pt­(PEt₃)₂(Cl)₂(OH)­(4-trifluoromethylphenyl) (<b>6</b>) and HBr gives <i>trans</i>-Pt­(PEt₃)₂(Br)­(Cl)­(OH)­(4-trifluoromethylphenyl) (<b>7</b>), where the Br and 4-trifluoromethylphenyl ligands are <i>trans</i>. Photolysis of <b>3</b> or <b>6</b> at 313 or 380 nm causes reduction to <i>trans-</i>Pt­(PEt₃)₂Cl­(R) (<b>1</b> or <b>2</b>, respectively). Expected coproduct HOCl is not detected, but authentic solutions of HOCl are shown to decompose under the reaction conditions. Chlorobenzene and other unidentified products that oxidize PPh₃ to OPPh₃ are detected in photolyzed benzene solutions. Photolysis of <b>3</b> or <b>6</b> in the presence of 2,3-dimethyl-2-butene (TME) yields the chlorohydrin (2-chloro-2,3-dimethyl-3-butanol), 3-chloro-2,3-dimethyl-1-butene, and acetone, all expected products from HOCl trapping, but additional oxidation products are also observed. Photolysis of mixed chloro-bromo complex <b>7</b> with TME yields the bromohydrin (2-bromo-2,3-dimethyl-3-butanol) and <b>2</b>, consistent with <i>cis</i>-elimination of HOBr. Computational results (TDDFT and DFT) and photochemistry of related complexes suggest a dissociative triplet excited state reaction pathway and that HOCl elimination may occur by an incipient hydroxo radical abstraction of an adjacent halogen atom, but a pathway involving hydroxo radical reaction with solvent or TME to generate a carbon-based radical followed by halogen abstraction from Pt cannot be eliminated

Dihydrogen Trioxide (HOOOH) Photoelimination from a Platinum(IV) Hydroperoxo-Hydroxo Complex

Photolysis (380 nm) of <i>trans-</i>Pt­(PEt₃)₂(Cl)­(OH)­(OOH)­(4-trifluoromethylphenyl) (<b>1</b>) at −78 °C in acetone-<i>d</i>₆ or toluene-<i>d</i>₈ yields HOOOH (16–20%) and <i>trans-</i>Pt­(PEt₃)₂(Cl)­(4-trifluoromethylphenyl) (<b>2</b>). Also observed in acetone-<i>d</i>₆ are H₂O₂, (CD₃)₂C­(OH)­(OOH), and (CD₃)₂C­(OOH)₂. Thermal decomposition or room-temperature photolysis of <b>1</b> gives O₂, water, and <b>2</b>. Computational modeling (DFT) suggests two intramolecular hydrogen-bonding-dependent triplet pathways for the photolysis and two possible pathways for the thermolysis, one involving proton transfer from the OOH to the OH ligand and the other homolysis of the Pt–OOH bond, abstraction of the OH ligand, and decomposition of the resulting H₂O₃. Trapping studies suggest the latter pathway

Emissive Biphenyl Cyclometalated Gold(III) Diethyl Dithiocarbamate Complexes

We report here a series of emissive biphenyl cyclometalated gold­(III) diethyl dithiocarbamate complexes having H, CF₃, OMe, and ^tBu substitutions on the biphenyl moiety. Synthesis of these complexes was accomplished by a single-step reaction of the appropriate dilithio-biphenyl reagent with Au­(dtc)­Cl₂ (dtc = diethyl dithiocarbamate). All four complexes exhibit weak room-temperature phosphorescence in solution and much more intense phosphorescence in the solid state and in low-temperature glasses with lifetimes in the microseconds. From experimental data and computational modeling, the emission originates mainly from a metal-perturbed ³(π–π*) state of the biphenyl moiety with a minor contribution from ligand-to-ligand charge transfer. Weak solution emission is attributed to deactivation via a distorted charge-transfer state that is less accessible in the solid state or in a low-temperature glass

Thermal and Photochemical Ring-Bromination in Naphthyl‑, Naphthdiyl‑, and Dicarboximideperyl-Platinum Complexes

Brominated polycyclic aromatic compounds are important synthons, but their synthesis can be difficult. Herein, we report that Pt­(IV) centers σ-bonded to naphthalene and a dicarboximideperylene activate the ring systems to selective thermal and photochemical bromination. Thus, <i>trans</i>-Pt­(PEt₃)₂(Br)₃­(4-bromo-1-naphthyl) and Br₂ give <i>trans</i>-Pt­(PEt₃)₂(Br)₃­(7,4-dibromo-1-naphthyl). Introduction of a second Pt­(IV) center is achieved by double oxidative addition of 1,4-dibromonaphthalene to 2Pt­(PEt₃)₄. Bromination of [<i>trans</i>-Pt­(PEt₃)₂Br]₂­(1,4-naphthdiyl) yields [<i>trans</i>-Pt­(PEt₃)₂(Br)₃]₂­(1,4-naphthdiyl), which further brominates on the ring to give [<i>trans</i>-Pt­(PEt₃)₂(Br)₃]₂­(6,7-dibromo-1,4-naphthdiyl). Photoreduction of the Pt­(IV) centers with 1-hexene gives first mixed-valent [<i>trans</i>-Pt­(PEt₃)₂(Br)₃]­[<i>trans</i>-Pt­(PEt₃)₂(Br)]­(6,7-dibromo-1,4-naphthdiyl) and then [<i>trans</i>-Pt­(PEt₃)₂Br]₂­(6,7-dibromo-1,4-naphthdiyl). Photoreduction of <i>trans</i>-Pt­(PEt₃)₂(Br)₃(PMI) (PMI = <i>N</i>-(2,5-di<i>-tert</i>-butylphenyl)­perylen-3-yl-9,10-dicarboximide) without 1-hexene slowly gives ring-bromination at the PMI 12-position. HOTf treatment cleaves the Pt–PMI bond to give 12-bromo-<i>N</i>-(2,5-di<i>-tert</i>-butylphenyl)­perylene-9,10-dicarboximide. The reaction chemistry indicates that the Pt­(IV) center is equivalent to a bulky, electron-donating group for the naphthalene and PMI ring systems

Emissive Biphenyl Cyclometalated Gold(III) Diethyl Dithiocarbamate Complexes

We report here a series of emissive biphenyl cyclometalated gold­(III) diethyl dithiocarbamate complexes having H, CF₃, OMe, and ^tBu substitutions on the biphenyl moiety. Synthesis of these complexes was accomplished by a single-step reaction of the appropriate dilithio-biphenyl reagent with Au­(dtc)­Cl₂ (dtc = diethyl dithiocarbamate). All four complexes exhibit weak room-temperature phosphorescence in solution and much more intense phosphorescence in the solid state and in low-temperature glasses with lifetimes in the microseconds. From experimental data and computational modeling, the emission originates mainly from a metal-perturbed ³(π–π*) state of the biphenyl moiety with a minor contribution from ligand-to-ligand charge transfer. Weak solution emission is attributed to deactivation via a distorted charge-transfer state that is less accessible in the solid state or in a low-temperature glass

Photoreduction of Pt(IV) Chloro Complexes: Substrate Chlorination by a Triplet Excited State

The Pt­(IV) complexes <i>trans</i>-Pt­(PEt₃)₂­(Cl)₃(R) <b>2</b> (R = Cl, Ph, 9-phenanthryl, 2-trifluoromethylphenyl, 4-trifluoromethylphenyl, 3-perylenyl) were prepared by chlorination of the Pt­(II) complexes <i>trans</i>-Pt­(PEt₃)₂(R)­(Cl) <b>1</b> with Cl₂(g) or PhICl₂. Mixed bromo–chloro complexes <i>trans,trans</i>-Pt­(PEt₃)₂(Cl)₂­(Br)­(R) (R = 9-phenanthryl, 4-trifluoromethylphenyl), <i>trans,cis</i>-Pt­(PEt₃)₂(Cl)₂(Br)­(4-trifluoromethylphenyl), <i>trans,trans</i>-Pt­(PEt₃)₂(Br)₂­(Cl)­(R) (R = 9-phenanthryl), and <i>trans,cis</i>-Pt­(PEt₃)₂(Br)₂(Cl)­(4-trifluoromethylphenyl) were obtained by halide exchange or by oxidative addition of Br₂ to <b>1</b> or Cl₂ to <i>trans</i>-Pt­(PEt₃)_2­(R)­(Br). Except for <b>2</b> (R = Ph, 4-trifluoromethylphenyl), all of the Pt­(IV) complexes are photosensitive to UV light and undergo net halogen reductive elimination to give Pt­(II) products, <i>trans</i>-Pt­(PEt₃)₂­(R)­(X) (X = Cl, Br). Chlorine trapping experiments with alkenes indicate a reductive-elimination mechanism that does not involve molecular chlorine and is sensitive to steric effects at the Pt center. DFT calculations suggest a radical pathway involving ³LMCT excited states. Emission from a triplet is observed in glassy 2-methyltetrahydrofuran at 77 K where photoreductive elimination is markedly slowed