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]24– (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]24–(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.