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(mu(2),,kappa(2),kappa(2)) 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 P1 and monoclinic P2(1) space groups, respectively. These complexes contain Ti equivalent to O units with distances of 1.624(7) and 1.644(2) A, 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.