The synthesis, structure and ethene polymerisation catalysis of mono(salicylaldiminato) titanium and zirconium complexes

Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, UK NR4 7TJ.
Dalton Transactions (Impact Factor: 4.1). 03/2005; DOI: 10.1039/b414229b
Source: PubMed

ABSTRACT The silyl ethers 3-But-2-(OSiMe3)C6H3CH=NR (2a-e) have been prepared by deprotonation of the known iminophenols (1a-e) and treatment with SiClMe3 (a, R = C6H5; b, R = 2,6-Pri2C6H3; c, R = 2,4,6-Me3C6H2; d, R = 2-C6H5C6H4; e, R = C6F5). 2a-c react with TiCl4 in hydrocarbon solvents to give the binuclear complexes [Ti{3-But-2-(O)C6H3CH=N(R)}Cl(mu-Cl3)TiCl3] (3a-c). The pentafluorophenyl species 2e reacts with TiCl4 to give the known complex Ti{3-But-2-(O)C6H3CH=N(R)}2Cl2. The mononuclear five-coordinate complex, Ti{3-But-2-(O)C6H3CH=N(2,4,6-Me3C6H2)}Cl3 (4c), was isolated after repeated recrystallisation of 3c. Performing the dehalosilylation reaction in the presence of tetrahydrofuran yields the octahedral, mononuclear complexes Ti{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (5a-e). The reaction with ZrCl4(THF)2 proceeds similarly to give complexes Zr{3-But-2-(O)C6H3CH=N(R)}Cl3(THF) (6b-e). The crystal structures of 3b, 4c, 5a, 5c, 5e, 6b, 6d, 6e and the salicylaldehyde titanium complex Ti{3-But-2-(O)C6H3CH=O}Cl3(THF) (7) have been determined. Activation of complexes 5a-e and 6b-e with MAO in an ethene saturated toluene solution gives polyethylene with at best high activity depending on the imine substituent.

  • [Show abstract] [Hide abstract]
    ABSTRACT: A series of new half-sandwich titanocene [(η5-C5H5)TiLCl2] (1) and nonorganometallic titanium complexes [TiLCl3(THF)] (2) and [TiL2Cl2] (3) containing 5-(2-hydroxyphenyl)tetrazole (LH) were synthesized in high yield and fully characterized by various spectroscopic methods and X-ray crystallography. In all complexes, the ligand L acted as a monoanionic bidentate ligand and hydrogen bonding between the oxygen of the tetrahydrofuran and hydrogen of the tetrazolyl unit was observed. In the cycloaddition of CO2 to propylene oxide, complex 3 showed the highest activity among the reported Ti complexes.
    Organometallics 08/2013; 32(15):4452–4455. DOI:10.1021/om400605k · 4.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The coordination chemistry of the multidentate tethered amidine-phenol {4,6-tBu2C6H2O(2-C(NR)═NR}H2 ({LONR}H2, R = iPr, 2,6-iPr2C6H3 (Ar)) and new guanidine-phenol {4,6-tBu2C6H2ON(C6H5)(2-C(NR)═NR}H2 ({LON(Ph)NiPr}H2) pro-ligands with group 4 metals has been studied. σ-Bond and salt metathesis reactions were explored to coordinate these (pro)ligands onto zirconium and hafnium. Alkane elimination reactions between {LONR}H2 and Zr(CH2Ph)4 afforded mixed-ligand monobenzyl {LOHNR}{LONR}Zr(CH2Ph) (R = iPr; 1) and monoligand tribenzyl {LOHNAr}Zr(CH2Ph)3 (R = Ar; 2) complexes, respectively. Alkane and amine elimination reactions between {LON(Ph)NiPr}H2 and Zr(CH2Ph)4 or Hf(NMe2)4 unexpectedly resulted in cleavage of the ligand backbone and eventual isolation of {(Ph)NC6H2(tBu)2O}Zr{(iPrN)2CCH2Ph}2 (3) and {(Ph)NC6H2(tBu)2O}Hf{(iPrN)2CNMe2}2 (4), respectively. Salt metathesis reactions between {LONR}Li2 and ZrCl4(THF)n (n = 0, 2), conducted in 1:1 ratios, led upon crystallization to diverse chloro complexes: [{LONiPr}ZrCl]3(μ3-O)(μ3-Cl) (5), [{LONAr}2ZrCl(μ2-Cl)]2[{LHONAr}ZrCl(μ2-Cl)](μ3–OH) (6), and {LOHNAr}ZrCl3(THF) (7). Similar salt metathesis reactions between the monolithium salts {LHONR}Li and ZrCl4, conducted in 2:1 ratios, allowed the selective preparation of bis(phenoxy-amidine) complexes with pendant amino groups {LOHNR}2ZrCl2 (R = iPr, 8; R = Ar, 9). All complexes were authenticated by elemental analysis, X-ray crystallography, and NMR spectroscopy. Complexes 5, 6, 8, and 9, upon activation with MAO, showed poor to moderate productivities (4–172 (kg of PE) mol–1 h–1) in the polymerization of ethylene, giving linear polymers with large polydispersities.
    Organometallics 03/2012; 31(8):3228–3240. DOI:10.1021/om300076j · 4.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Group 4 metal complexes bearing new phenoxy(benzimidazolyl)-imine, -amine and -amide ligands have been synthesized. A series of metal chloride derivatives has been prepared via treatment of MCl4(THF)2 (M = Ti, Zr, Hf) with the in situ generated sodium salt of the (benzimidazolyl)imine phenol 1. Reaction of the pro-ligand 2 with TiCl4(THF)2 afforded the corresponding complex 8 in which the amine proton remains bound to the nitrogen donor. Benzyl complexes of zirconium and hafnium were synthesized via treatment of pro-ligands 1 and 2 with M(CH2Ph)4 precursors. The complexes [NNO]M(CH2Ph)3 (6 M = Zr, 7 M = Hf) were found to undergo benzyl migration from the metal centre to the imine carbon of the ligand backbone giving complexes 11 and 12; the migration follows first order kinetics. The reaction of 1 with Ti(NMe2)4 led to the formation of an unusual C–C coupled product in which a new piperazine ring has formed. Complexes 11 and 12 undergo related transformations, leading to analogous C–C coupled products which were characterized by X-ray crystallography. Deuterium labelling experiments were carried out to determine the mechanistic pathway of the reactions. Chloride and benzyl complexes 3–12 were screened as pre-catalysts for olefin polymerization.
    Journal of Organometallic Chemistry 03/2009; 694(5):703–716. DOI:10.1016/j.jorganchem.2008.11.064 · 2.30 Impact Factor