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

Abstract

The synthesis and characterization of tri- and tetrametaphosphate titanium(IV) oxo and peroxo complexes is described. Addition of 0.5 equiv of [OTi(acac)[subscript 2]][subscript 2] to dihydrogen tetrametaphosphate ([P[subscript 4]O[subscript 12]H[subscript 2][superscript 2–]) and monohydrogen trimetaphosphate ([P[subscript 3]O[subscript 9]H][superscript 2–]) provided a bis(μ[subscript 2],κ[superscript 2],κ[superscript 2]) tetrametaphosphate titanyl dimer, [OTiP[subscript 4]O[subscript 12]][subscript 2][superscript 4–] (1; 70% yield), and a trimetaphosphate titanyl acetylacetonate complex, [OTiP[subscript 3]O[subscript 9](acac)][superscript 2–] (2; 59% yield). Both 1 and 2 have been structurally characterized, crystallizing in the triclinic P1̅ and monoclinic P2[subscript 1] 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 [O[subscript 2]TiP[subscript 4]O[subscript 12]][subscript 2][superscript 4–](3; 61% yield) and [O[subscript 2]TiP[subscript 3]O[subscript 9](acac)][superscript 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)[subscript 3], PPh[subscript 3]) and SMe[subscript 2] at ambient temperature to result in the corresponding organic oxide with regeneration of dimer 1.