Synthesis and investigation of the stability of Ti(III) beta-diketiminato complexes. Structure of the tetrameric non-metallocene titanium fluoride complex (L2)(4)Ti4F6O2 center dot 2toluene supported by the beta-diketiminato ligand

The titanium beta-diketiminato complexes (L1)TiCl2 (1), (L1)TiCl(N2,6-'Pr2C6H3) (2), and (L2)(2)TiCl (3) [L1 = (2,6-'Pr2C6H3)NC(Me)CHC(Me)N(2,6-'Pr2C6H3), L2 = (PrNC)-Pr-i(Me)CHC(Me)(NPr)-Pr-i] have been prepared by the reaction of the lithium salt of the ligand, L, with titanium trichloride. Complex 2 was isolated from supernatant solutions of I containing excess of the (L1)Li salt. The monochloride complex [(L2)TiCl((NPr)-Pr-i)](2) (4) was prepared by reduction of (L2)(2)TiCl2 with the excess of Na/K alloy. Fluorination of the monochloride complex 3 with Me3SnF affords polymeric [(L2)TiF2](n) (5). Oxidation of 5 gives the tetrameric complex, (L2)(4)Ti4F6O2.2toluene (6). Compounds 1-6 were characterized by single crystal X-ray structural analyses, elemental analyses, NMR and mass spectra. The bulky ligand (L1) stabilizes the Ti(III) complex I with an unusual distorted square-planar pyramidal geometry around the titanium atom, by sigma bonding to the metal. The less bulky ligand (L2) in complexes 3, 4 and 6 has mixed sigma and pi coordination to the titanium center. Investigation of the C-C, N-C distances in the NCCCN unit of the coordinated beta-diketiminato ligands (L1) and (L2) demonstrated the localization of the double bonds in the ligand in complexes 1-3 and 6. The stability of the complexes in solution was studied by means of NMR spectroscopy. Complexes 2 and 4 are stable in solution, the polymeric and the tetrameric nature of complexes 5 and 6 is not evident in C6D6 solution. The (L2)2TiCl stoichiometry of the complex is unstable. (C) 2003 Elsevier Science Ltd. All rights reserved.