LEWIS ACIDIC TITANIUM SPECIES - THE SYNTHESIS, STRUCTURE, BONDING AND MOLECULAR MODELING CONSIDERATIONS OF THE COMPLEXES TI(NME2)3CL, TI(NET2)3CL

Reaction of simple amides with TiCl4 affords mixed amido-chloride species Ti(NR2)(4-n)Cl(n). The trisamide-chloride species Ti(NR2)3Cl can be prepared directly employing three equivalents of amide or by reaction Ti(NR2)4 with TiCl4. The compound Ti(NMe2)3Cl, 1, crystallizes in the trigonal space group R3BARc, with a = 11.525(5), c = 14.939(3) angstrom, Z = 6, and V = 1718(1) angstrom 3. The compound Ti(NEt2)3Cl, 2, crystallizes in the monoclinic space group P2(1)/c, with a = 8.385(2) angstrom, b = 15.958(2) angstrom, c = 14.230(4) angstrom, beta = 107.79(1)degrees, Z = 4, and V = 1813(1) angstrom 3. The geometry of the Ti coordination sphere in these complexes is best described as pseudo-tetrahedral. The structural data are consistent with Ti-N multiple bonding. Preliminary results of EHMO calculations are consistent with d-pi-p-pi Ti-N bonding. Attempts to replace the halides with phosphides (LiPR2, R = Me, Et, Ph) led not to the Ti(IV) phosphido species, but rather to redox chemistry yielding Ti(III) amides and P2R4. The barrier to rotation about the Ti-N bonds has been considered. Variable temperature H-1 NMR studies reveal that the barrier is small. Extended Huckel total energy minimization calculations have been performed. In addition, MMX calculations of the barrier to Ti-N rotation are reported. The results of these calculations imply that the rotational barrier is dominated by steric effects.