Organic-Soluble Tri-, Tetra-, and Pentanuclear Titanium(IV) Phosphates

Bulky 2,6-disubstituted aryl esters of phosphoric acid, 2,6-dimethylphenyl phosphate (dmppH2), and 2,6-diisopropylphenyl phosphate (dippH2) react differently with Cp*TiCl3 (Cp* = C5Me5) under identical reaction conditions. While dippH2 and Cp*TiCl3 react in THF at 25 °C to yield air-stable trinuclear titanophosphate cage [(Ti3Cp*Cl(μ2-O)(dipp)2(dippH)4(THF)]·(toluene) (1), the similar reaction involving dmppH2 yields the tetranuclear titanophosphate [Ti4Cl2(μ2-O)2(dmpp)2(dmppH)6(THF)2]·(toluene)2 (2). Interestingly, the change of titanium source to Ti(OiPr)4 in the reaction with dippH2 produces a pentanuclear titanophosphate, [Ti5(μ3-O)(OiPr)6((dipp)6(THF)] (3). Compounds 1−3 were the only products isolated as single crystals from the respective reaction mixtures in 59, 75, and 54% yield, respectively. The new clusters 1−3 have been characterized by elemental analysis, IR and NMR (1H and 31P) spectroscopy, and single crystal X-ray diffraction studies. The structural elucidation reveals that in the reactions leading to 1 and 2, extensive Cp*-Ti bond cleavage occurs, leaving only one residual Cp*-ligand in cluster 1 and none in 2. Closer analysis of the structures of 1−3 shows common structural features which in turn imply that the formation of all three products could have proceeded via a common Ti−O−Ti dimeric building block.