Five- and six-coordinate group 4 compounds stabilized by beta-ketiminate and diketiminate ligands: Syntheses and comparisons between solid-state and solution structures

The preparation and reaction chemistry of beta-diketiminate titanium and zi rconium complexes is described. Amine elimination reactions work well for i ntroducing Tolnacnac or Tolnacac to the metal centers (TolnacnacH = 2-(p-to lylamino)-4-(p-tolylimino)-2-pentene; TolnacacH = 4-p-toluidinopent-3-en-2- one). In certain cases, the iminium salt of the diketimine can be used to c ircumvent the unfavorable reaction kinetics. Salt elimination reactions sta rting from group 4 metal halides and beta-diketiminate lithium reagents are the most versatile method for introducing beta-diketiminate ligands to the metal. For (beta-diketiminate)MCl3 compounds (M = Ti, Zr) eta(5)- and eta( 2)-coordination modes can be controlled by modifying the diketiminate ligan ds. Several structures of five- and six-coordinate metal complexes were sol ved by X-ray diffraction methods. Five-coordinate metal complexes adopt bot h trigonal bipyramidal and square pyramidal geometries, and the six-coordin ate metal complexes possess pseudooctahedral metal centers. For (Tolnacnac) (2)ZrXz (X = Cl, OR, NMe2) the activation parameters for Delta/Delta conver sion have been probed by dynamic NMR and are consistent with a Bailar-twist mechanism. At a common temperature, the isomerization rates follow the ord er Cl > OR > NMe2.