β-Diiminato Complexes of VIII and TiIII – Formation and Structure of Stable Paramagnetic Dialkylmetal Compounds

(Mono-β-diiminato)titanium(III) and -vanadium(III) dichlorides LMCl2 [L = ArNC(R)CHC(R)NAr–] are easily accessible from the metal trichlorides and LLi in THF. The crystal structures of LVCl2 (Ar = 2,6-iPr2C6H3, R = Me) and LTiCl2 (Ar = 2,4,6-Me3C6H2, R = Me and Ar = 2,4,6-Me3C6H2, R = tBu) reveal tetrahedral metal environments. Treatment of LVCl2 with alkyllithium reagents affords surprisingly stable dialkylvanadium(III) compounds; the structure of LV(nBu)2 (Ar = 2,6-iPr2C6H3, R = Me) is similar to that of the dichloride. The corresponding dialkyltitanium(III) compounds are less stable; only the dimethyl derivatives could be obtained in pure form (from LTiCl2 and MeMgI), and only for ligands bearing 2,6-disubstituted aryl groups. The structure of LTiMe2 (Ar = 2,4,6-Me3C6H2, R = Me) is also similar to that of the dichloride. Reaction of LTiMe2 with B(C6F5)3 produces a catalyst for α-olefin polymerization, but the corresponding VIII derivatives are inactive.