Synthesis and investigation of the stability of Ti(III) β-diketiminato complexes. Structure of the tetrameric non-metallocene titanium fluoride complex (L2) 4Ti 4F 6O 2·2toluene supported by the β-diketiminato ligand

Abstract

The titanium β-diketiminato complexes (L1)TiCl 2 ( 1), (L1)TiCl(N2,6- i Pr 2C 6H 3) ( 2), and (L2) 2TiCl ( 3) [L1=(2,6- i Pr 2C 6H 3)NC(Me)CHC(Me)N(2,6- i Pr 2C 6H 3), L2= i PrNC(Me)CHC(Me)N i Pr] 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 1 containing excess of the (L1)Li salt. The monochloride complex [(L2)TiCl(N i Pr)] 2 ( 4) was prepared by reduction of (L2) 2TiCl 2 with the excess of Na/K alloy. Fluorination of the monochloride complex 3 with Me 3SnF affords polymeric [(L2)TiF 2] n ( 5). Oxidation of 5 gives the tetrameric complex, (L2) 4Ti 4F 6O 2·2toluene ( 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 1 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 σ and π coordination to the titanium center. Investigation of the CC, NC distances in the NCCCN unit of the coordinated β-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 C 6D 6 solution. The (L2) 2TiCl stoichiometry of the complex is unstable.