HEMOLEPTIC 1,4-DIAZADIENE COMPOUNDS OF EA RLY TRANSITION-METALS - SYNTHESES, PROPERTIES AND STRUCTURES OF (DAD)(2)TI AND (DAD)(3)TI

Syntheses and structures of homoleptic 1,4-diaza-1,3-diene (DAD) compl exes of titanium are described. The spiranoid DAD complexes of formula (DAD)(2)Ti 3a-c are formed by reaction of TiCl4.2THF with the disodiu m salts Na(2)DAD 2a-c or by reduction of TiC1(4).2THF with magnesium i n presence of two equivalents of DAD 1a-c The endiamide complexes 3a-c are thermally stable, very sensitive to oxygen and water, and soluble in all common organic solvents. An X-ray crystal structure determinat ion of 3c reveals the titanium atom to be in a strongly distorted tetr ahedral environment. The two five-membered metallacyclic Ti(NC=CN) rin gs are folded along the N,N' axis. Temperature-dependent H-1 NMR spect ra of 3a-c indicate a rapid intramolecular inversion of this non-plana r ring system in solution even at room temperature. Reduction of TiCl4 .2THF with magnesium in presence of excess DAD 1d-fleads to the format ion of the blue-violet complexes (DAD)(3)Ti 4d-f. At low temperatures three sterically crowded DAD ligands cause a rigid conformation as dem onstrated by their unique low temperature H-1 NMR spectra.