β-diketonate derivatives of titanium alkoxides:: X-ray crystal structures and solution dynamics of the binuclear complexes [{Ti(OR)3(dik)}2]

The crystal structures of the 2,4-pentanedionato (acetylacetonato, acac) and 2,2,6,6-tetra-methylheptane-3,5-dionato (tmhd) compounds (tmhd) compounds [{Ti(OR)(3)(dik)}(2)] (dik = acad, R = Me, Et, Pr-i; dik = tmhd, R = Me, Pr-n, Pr-i), obtained from reactions between Ti(OR)(4) and one equivalent of dikH, have been determined for the first time. In the solid state? these compounds adopt centrosymmetric, alkoxide-bridged binuclear structures which in solution undergo ligand redistribution to give mixtures of [{Ti(OR)(3)(dik)}(2)], [Ti(OR)(2) (dik)(2)] and Ti(OR)(4). When R = Pr-i, the equilibrium favours the mononuclear compounds, whereas when R = Me, Et or Pr-n the binuclear compounds can be observed in the H-1 NMR spectra. Variable-temperature H-1 NMR spectra provide an insight into the dynamic behaviour of the methoxides [{Ti(OMe)(3)(dik)}(2)], and possible ligand exchange mechanisms are discussed. No conclusive evidence was obtained for the existence of dimeric or monomeric [Ti(OBut)(3)(dik)] in the solid state or in solution. (C) 1998 Elsevier Science Ltd. All rights reserved.