Imido Complexes of Titanium Bearing η2-Pyrazolato Ancillary Ligand Sets

Treatment of dichlorobis(3,5-di- tert -butylpyrazolato)titanium(IV) with Grignard (CH 3 MgCl, C 6 H 5 CH 2 MgCl) or organolithium (LiCH 2 Si(CH 3 ) 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 -butyl-pyrazolato)titanium(IV) (49%). Analogous methylation of chlorotris(3,5-di- tert -butylpyrazolato)titanium(IV) with CH 3 MgCl afforded methyltris(3,5-di- tert -butylpyrazolato)titanium(IV) (52%). Attempted alkylation of trichloro(3,5-di- tert -butylpyrazolato)titanium(IV) with CH 3 MgCl (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 -butylpyrazolato)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.