| Abstract
| - Bis(enamido)zirconium and -hafnium complexes have been synthesized which have electron-rich methylene carbons in the ligand frame. Addition of Al(C6F5)3 to the complexes affords maily zwitterionic complexes by electrophilic addition to the methylene carbon on the enamido ligand, while addition of B(C6F5)3 gives ion-paired complexes by electrophilic abstraction of alkyl. Ethylene polymerization studies for the zwitterionic and ion-paired complexes are reported. Some complexes are highly active when activated with MAO.
- Deprotonation of the α-diimine compound {2,6-(CHMe2)2-C6H3}NC(CH3)C(CH3)N{2,6-(CHMe2)2-C6H3} with excess KH in THF gives dipotassium N,N‘-(1,2-dimethylene-1,2-ethanediyl)bis(2,6-diisopropylanilide) (1) in 75% yield. Reaction of 1 with bis(2-picolyl)zirconium dichloride generated in situ by the reaction of ZrCl4 and 2 equiv of (2-picolyl)potassium affords [N,N‘-(1,2-dimethylene-1,2-ethanediyl)bis(2,6-diisopropylanilido)-κ2N,N‘]bis(2-picolyl)zirconium(IV) (2) in 35% yield. Similar reaction of 1 with LMCl3 (L =Cp, Cp*; M = Zr, Hf) gives the desired complexes {2,6-(CHMe2)2-C6H3}NC(CH2)C(CH2)N{2,6-(CHMe2)2-C6H3}MLCl (L = Cp*, M = Zr, 4; L = Cp*, M = Hf, 5; L = Cp, M = Zr, 6) in79%, 94% and 54% yields, respectively. Reaction of the chloride complexes with MeMgBraffords the corresponding methyl complexes {2,6-(CHMe2)2-C6H3}NC(CH2)C(CH2)N{2,6-(CHMe2)2-C6H3}MLMe (L = Cp*, M = Zr, 7; L = Cp*, M = Hf, 8; L = Cp, M = Zr, 9) in 63%,69% and 90% yields, respectively. The solid-state structure of 7 was determined. When 2, 7,or 9 is treated with 1 equiv of B(C6F5)3, one observes formation of the picolyl- or methyl-abstracted ion-paired complex in NMR spectra. When Al(C6F5)3 is added to 2, 8, or 9, thealuminum atom is coordinated by the methylene functionality of the enamide ligand to formzwitterionic complexes. The solid structure of a zwitterionic complex generated by theaddition of Al(C3F5)3 to 8 was determined and confirms the molecular connectivity. Thezwitterionic complexes are active to ethylene polymerization, while the ion-paired complexesare sluggish. Complexes 2 and 6 are highly active to the ethylene polymerization when theyare activated with MAO.
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