DIAZADIENE COMPLEXES OF GROUP-4 METALS .1. SYNTHESIS OF MONO(DIAZADIENE), BIS(DIAZADIENE) AND TRIS(DIAZADIENE)TITANIUM COMPLEXES AND THE STRUCTURE OF DIAZADIENEDICHLOROTITANIUM

Exhaustive reduction of diazadienes (dad = R-N = CH-CH = N-R, R = Bu(t), Pr(i)) with lithium and subsequent addition of titanium tetrachloride yields the homoleptic diazadiene-titanium complexes [(dad)2Ti] (1, 2) and (dad)3 Ti (3) (R = Pr(i)). Complexes (dad)TiCl2 (4, 5) are similarly formed from a 1:1 reaction of Li2[dad] with TiCl4. Substitution reaction of 4 (R = Bu(t)) afford complexes (dad)TiCl(X) (6-8) (X = N(SiMe3)2, C5H5, CH2CMe3). All compounds are volatile, soluble in unpolar solvents, and intensely coloured. A structure investigation by X-ray diffraction was performed for (Bu(t)dad)Ticl2 (4): space group P4(2)/n, a = 14.774(3), b = 14.792(4), c = 13.322(2) angstrom. It shows a five-coordinate chloro-bridged dimer. The Ti2Cl2 ring is folded along a line through the chlorine atoms, the TiNCCN chelate is folded along a line through the nitrogen atoms, which do not deviate strongly from sp2 geometry. The bond lengths within the chelate indicate only a partial reduction of the dad. Symmetry arguments and data from the NMR and electronic spectra give indications as to the oxidation state of the metal and dad in the homoleptic complexes as well.