Alkyl Complexes of Group 4 Metals Containing a Tridentate-Linked Amido−Cyclopentadienyl Ligand: Synthesis, Structure, and Reactivity Including Ethylene Polymerization Catalysis

Abstract

A series of group 4 metal complexes M(η5:η1:η1-C5Me4SiMe2NCH2CH2X)R2 (M = Ti; R = Me, CH2Ph; M = Zr, Hf; R = Me, Et, nPr, nBu, CH2Ph, CH2SiMe3, Ph) containing the tridentate-linked amido−tetramethylcyclopentadienyl ligand C5Me4SiMe2NCH2CH2X (X = OMe, NMe2) were synthesized by alkylation of the dichloro complexes M(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Cl2. The complexes were characterized by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Nuclear Overhauser effect measurements of the dimethyl complexes show that, in solution, the side chains of the zirconium derivatives coordinate intramolecularly, in contrast to the titanium complexes. The crystal structures of the zirconium alkyls Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)R2 (R = Me, Ph) were determined by X-ray diffraction studies. Both complexes adopt a trigonal-bipyramidal structure, with the five-membered ring and the methoxy group in the apical positions. Insertion of carbon monoxide into the hafnium dimethyl and di(n-butyl) complexes led to the η2-acyl derivatives Hf(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)(η2-COR)R (R = Me, nBu). Chloro mono(ethyl) complexes underwent insertion of tert-butyl isonitrile to give η2-iminoacyl derivatives M(η5:η1-C5Me4SiMe2NCH2CH2X){η2-C(NtBu)Et}Cl. The X-ray diffraction structure of the titanium complex Ti(η5:η1-C5Me4SiMe2NCH2CH2OMe){η2-C(NtBu)Et}Cl showed a square-pyramidal configuration with the imino nitrogen trans to the amido nitrogen. The zirconium dimethyl complexes Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Me2 reacted with B(C6F5)3 to form the contact ion pairs [Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2X)Me]+[MeB(C6F5)3]-. Reaction between the titanium dibenzyl Ti(η5:η1-C5Me4SiMe2NCH2CH2X)(CH2Ph)2 and B(C6F5)3 resulted in the clean formation of the solvent-separated ion pair [Ti(η5:η1:η1-C5Me4SiMe2NCH2CH2X)(CH2Ph)]+[(PhCH2)B(C6F5)3]-. When activated with methylaluminoxane, the complexes Ti(η5:η1-C5Me4SiMe2NCH2CH2OMe)Cl2 and M(η5:η1:η1-C5Me4SiMe2NCH2CH2OMe)R2 (M = Zr, Hf; R = Me, nBu) are active in the polymerization of ethylene.