Organic-soluble tri-, tetra-, and pentanuclear titanium(IV) phosphates

Abstract

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.