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

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.