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

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