Terminal Titanyl Complexes of Tri- and Tetrametaphosphate: Synthesis, Structures, and Reactivity with Hydrogen Peroxide

The synthesis and characterization of tri- and tetrametaphosphate titanium­(IV) oxo and peroxo complexes is described. Addition of 0.5 equiv of [OTi­(acac)₂]₂ to dihydrogen tetrametaphosphate ([P₄O₁₂H₂]^2–) and monohydrogen trimetaphosphate ([P₃O₉H]^2–) provided a bis­(μ₂,κ²,κ²) tetrametaphosphate titanyl dimer, [OTiP₄O₁₂]₂^4– (1; 70% yield), and a trimetaphosphate titanyl acetylacetonate complex, [OTiP₃O₉(acac)]^2– (2; 59% yield). Both 1 and 2 have been structurally characterized, crystallizing in the triclinic P1̅ and monoclinic P2₁ space groups, respectively. These complexes contain TiO units with distances of 1.624(7) and 1.644(2) Å, respectively, and represent rare examples of structurally characterized terminal titanyls within an all-oxygen coordination environment. Complexes 1 and 2 react with hydrogen peroxide to produce the corresponding peroxotitanium­(IV) metaphosphate complexes [O₂TiP₄O₁₂]₂^4–(3; 61% yield) and [O₂TiP₃O₉(acac)]^2– (4; 65% yield), respectively. Both 3 and 4 have been characterized by single-crystal X-ray diffraction studies, and their solid-state structures are presented. Complex 3 functions as an oxygen atom transfer (OAT) reagent capable of oxidizing phosphorus­(III) compounds (P­(OMe)₃, PPh₃) and SMe₂ at ambient temperature to result in the corresponding organic oxide with regeneration of dimer 1.