Structurally diverse aggregating condensations of Ti(IV) catecholates

The simple 1:1 reaction of naphthalene-2,3-diol (H2Np) with Ti(OiPr)4 has a complicated outcome, one rich in diversity and elucidated in this paper by X-ray crystallography and NMR spectroscopy. The reaction in CDCl3 produces a crystalline precipitate, which was found to be the symmetrical dimer [TiNp(OiPr)2]2(HOiPr)2 whose coordinated HOiPr units are hydrogen bonded to OiPr groups (A). A second crystal was also harvested and found to be a partially hydrolyzed 6:6 assembly [Ti3(mu3-O)(mu-Np)2(Np)(mu-OiPr)(OiPr)(HOiPr)2(mu-O)]2 (B) constructed of mu-oxo-linked inverted halves, each a 3:3 assembly anchored by a mu3-oxo group. The supernatant was deduced to contain a soluble 3:3 product [TiNp(OiPr)2]3(HOiPr) possessing the same stereochemistry as B and its likely hydrolysis precursor. When A was redissolved, it produced what appeared to be a 4:4 condensation product, which was also present in the supernatant when the reaction was conducted in the presence of HOiPr-absorbing 13X molecular sieves, or when the reaction mixture was heated. In an analogous reaction, Ti(OtBu)4 produced only an A-like dimeric product possessing pentacoordinate metal centers.