Imido Complexes of Titanium Bearing η²-Pyrazolato Ancillary Ligand Sets

Abstract

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-butyl-pyrazolato)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-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.

Simple Syntheses, Structural Diversity, and Tishchenko Reaction Catalysis of Neutral Homoleptic Rare Earth(II orIII) 3,5-Di-tert-butylpyrazolates—The Structures of [Sc(tBu2pz)3], [Ln2(tBu2pz)6] (Ln=La, Nd, Yb, Lu), and [Eu4(tBu2pz)8]

“…Although 1 has a similar molecular array to those of the recently determined [M(h 2 -tBu 2 pz) 3 ] complexes (M Al [15] or Ti [13] ), it is not isomorphous with them. Nevertheless, the angles between the centres of the N À N bonds [N(n0); e.g., N(10) is the centre of the bond between N(11) and N (12); (N(10)-Sc-N (20) 118.2; 121.58; S 360.08] are only slightly divergent from 1208, and the ScÀN(n0) lengths show little variation (average 1.987(4) ). P2 1 /c for 1).…”

“…For the m-h 2 :h 2 ligands, bridging is highly symmetrical with differences between Ln À N(1n) and Ln*ÀN(1n) (n 1 or 2) 0.01 for 3, 5, and 8, but slightly larger (ca. However, chelation is unsymmetrical with differences between LnÀN(11) and LnÀN (12) and between Ln*ÀN(11) and Ln*ÀN(12) of 0.145, 0.15 (2), 0. However, chelation is unsymmetrical with differences between LnÀN(11) and LnÀN (12) and between Ln*ÀN(11) and Ln*ÀN(12) of 0.145, 0.15 (2), 0.…”

“…However, chelation is unsymmetrical with differences between LnÀN(11) and LnÀN (12) and between Ln*ÀN(11) and Ln*ÀN(12) of 0.145, 0.15 (2), 0. Whilst LnÀN (11) and Ln*ÀN (12) show the expected decrease (0.18, 0.17 ) from 2 to 5, the decrease for LnÀN (12) is unusually small (0.13 ) and for Ln*ÀN(11) unusually large (0.23 ). Whilst LnÀN (11) and Ln*ÀN (12) show the expected decrease (0.18, 0.17 ) from 2 to 5, the decrease for LnÀN (12) is unusually small (0.13 ) and for Ln*ÀN(11) unusually large (0.23 ).…”

A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

“…Beyond acid-base chemistry, alkyllithium reagents have been exploited in inorganic and organometallic chemistry as a means to provide carbonbased ligands 11,12 , transmetallate reagents in catalysis [13][14][15] , or facilitate organometallic reactivity by photolytic M-Me bond homolysis 16,17 . While alkyllithium reagents are thermodynamically very strong bases, their reactivity can be sluggish in some reactions, requiring optimization of reaction conditions 18 .…”

1,2-Bis(trimethylsilyl)hydrazido Titanium Complexes

“…[6] A further class of titanium complexes has been described by Winter et al and by Mösch-Zanetti et al Their complexes bear η 2 -pyrazolato ligands rather than hydrazido ligands and no cyclopentadienyl ligands are used to stabilize them. [7,8] We report herein on the synthesis and characterization of novel bis(trimethylsilyl)hydrazido titanium complexes withTiCl 4 with two equivalents of hydrazine. According to the results of single-crystal X-ray diffraction investigations, complexes 1 and 3 feature an η 2 -coordination of the hydrazido moiety to the titanium.…”