Imido complexes of titanium bearing η2-pyrazolato ancillary ligand sets

Treatment of dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) with Grignard (CH3MgCl, C6H5CH2MgCl) or organolithium (LiCH2Si(CH3)(3)) reagents (2 equiv) afforded the dialkyl derivatives dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (93%); dibenzylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (43%), and bis(methyltrimethylsilyl)bis(3,5-di-tert-butylpyrazolato)titanium(IV) (49%). Analogous methylation of chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) with CH3MgCl afforded methyltris(3,5-di-tert-butylpyrazolato)titanium(IV) (52%). Attempted alkylation of trichloro(3,5-di-tert-butylpyrazolato)titanium(IV) with CH3MgCl (3 equiv) afforded dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) (35%), along with extensive decomposition. This experiment indicates that trimethyl(3,5-di-tert-butylpyrazolato)titanium(IV) is unstable at ambient temperature. The reactivity of dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) and dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) toward primary amines was studied. Treatment of dichlorobis(3,5-di-tert-butylpyrazolato) titanium(IV) with excess tert-butylamine afforded tert-butylimido(chloro)(3,5-di-tert-butyl pyrazolato)titanium(IV) dimer (10%), chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV)(56%), and tert-butylammonium chloride (85%). Analogous treatment of dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) with tert-butylamine gave the monomeric imido complex tert-butylimidobis(3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) (33%). Addition of pyridine to the reaction between dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) and tert-butylamine or isopropylamine afforded the pyridine adducts tert-butylimidobis(3,5-di-tert-butylpyrazolato)(pyridine)titanium(IV) (80%) and isopropylimidobis (3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) (46%), respectively. Treatment of dimethylbis(3,5-di-tert-butylpyrazolato)titanium(IV) with 1-amino-4-methylpiperazine led to the hydrazide(1-) complex 1-amido-4-methylpiperazine(methyl)bis(3,5-di-tert-butylpyrazolato)titanium(IV) (64%), which contains both a titanium-methyl bond and a primary hydrazide(1-) ligand. It is proposed that the thermal stability of this compound arises from bidentate coordination of the hydrazide(1-) ligand, which places the reactive nitrogen-hydrogen bond distal to the titanium-methyl bond. The reactivity of tert-butylimidobis(3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) toward acetylenes, nitriles, and ketones is discussed. The X-ray crystal structures of bis(methyltrimethylsilyl)bis(3,5-di-tert-butyl-pyrazolato)titanium(IV), tert-butylimido(chloro)(3,5-di-tert-butylpyrazolato)titanium(IV) dimer, and isopropylimidobis(3,5-di-tert-butylpyrazolato)(tert-butylamine)titanium(IV) were determined.