Formation and structural properties of salicylaldiminato complexes of zirconium and titanium

The metallocene cation [Cp2ZrCH3(THF)(+)] (2, with BPh4- anion) reacts with N-isopropylsalicylaldimine (1a) by liberation of methane and formation of the pseudotetrahedral [(kappa O,kappa N-salicylaldiminato)ZrCp2+] complex 3 that was characterized by X-ray diffraction. Deprotonation of la by treatm ent with n-butyllithium yields the corresponding lithiated reagent 4a, that exhibits a tetrameric structure in the crystal, featuring a cubic Li4O4 co re structure. Treatment of 4a with Zr(NMe2)(2)Cl-2(dme) (5) yields the octa hedral bis(N-isopropylsalicylaldiminato)Zr(NMe2)(2) complex 7a. The X-ray c rystal structure analysis of 7a has revealed that the aldiminato oxygen ato ms of the kappa O,kappa N-chelate ligand are oriented trans to each other a t the central metal atom. Treatment of the N-isopropyl, the N-cyclohexyl- a nd the N-(2,6-diisopropylphenyl)salicylimines (1a,b,d) with the reagent Zr( NMe2)(4) (6) directly results in the formation of the respective octahedral (lig)(2)Zr(NMe2)(2) complexes 7a, 7b (also characterized by X-ray diffract ion), and 7d in good yields. Treatment of 7b and 7d with Me3Si-Cl replaced the -NMe2 substituents by chloride to yield the corresponding lig(2)ZrCl(2) complexes 8b and Sd, respectively. The X-ray crystal structure analysis of 8d showed an octahedral coordination with the aldiminato nitrogen atoms of the KO,kappa N-chelate ligands now being trans-oriented at zirconium. Comp lex 8b undergoes an enantiomerization process that is followed by dynamic N MR spectroscopy (Delta G(emnant)(not equal) (268 K) approximate to 12 kcal mol(-1)). Titanium tetrachloride forms a neutral 1:2 adduct with 1d. The NM R analysis and X-ray crystal structure analysis of the resulting bisbetaine -type adduct 9d reveals the formation of an octahedral titanium complex tha t contains two trans-Ti-O(aryl) bonds. The phenolic hydrogen atoms were tra nsferred to the aldimine nitrogens to form an intramolecular iminium salt. Two equivalents of HCl are removed from 9d by treatment with NEt3 to yield the bis[N-(2,6-diisopropylphenyl)salicylaldiminato]TiCl2 complex 10d (chara cterized by X-ray diffraction). In a one-pot procedure TiCl4, reacts with N -phenylsalicylaldimine (Ic) and triethylamine in a 1:2:2 ratio to directly yield the corresponding (kappa O,kappa N-lig)(2)TiCl2 complex 10c. The X-ra y crystal structure analysis of 10c reveals a trans-orientation of ligand o xygen atoms, just like in the adduct intermediate 9. Upon activation with m ethylalumoxane the complexes Sd, 10c, and 10d form catalysts for the polyme rization of ethene. (C) 2000 Elsevier Science S.A. All rights reserved.