Activation of Enamido Zirconium Complexes for Ethylene Polymerization:  Electrophilic Addition versus Electrophilic Abstraction Reaction

Abstract

Deprotonation of the α-diimine compound {2,6-(CHMe2)2-C6H3}NC(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)-κ2 N,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) in 79%, 94% and 54% yields, respectively. Reaction of the chloride complexes with MeMgBr affords 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, the aluminum atom is coordinated by the methylene functionality of the enamide ligand to form zwitterionic complexes. The solid structure of a zwitterionic complex generated by the addition of Al(C3F5)3 to 8 was determined and confirms the molecular connectivity. The zwitterionic complexes are active to ethylene polymerization, while the ion-paired complexes are sluggish. Complexes 2 and 6 are highly active to the ethylene polymerization when they are activated with MAO.

New Benzylpotassium Reagents and Their Utility for the Synthesis of Homoleptic Uranium(IV) Benzyl Derivatives

“…A variation of Schlosser’s procedure has already been reported for 1- o -Picolyl and 1- p - t Bu. However, we have synthesized these according to the same conditions as for the rest of the 1-Bn ′ family, as the previous procedure for 1- p - t Bu requires potassium 3-methyl-3-pentanolate, which is not commercially available.…”

Synthesis of Imino-Enamido Hafnium and Zirconium Complexes: A New Family of Olefin Polymerization Catalysts with Ultrahigh-Molecular-Weight Capabilities

“…These imino-enamines attracted our interest because they are structurally similar to the imino-amine ligands and contain the cyclohex-2-enylidene backbone which, in principle, should yield configurationally stable complexes. Ligand 9 has been used in the preparation of nickel, , palladium, and aluminum compounds but had not been yet reported in the synthesis of group 4 transition metal complexes . Neutral and cationic nickel complexes with acyclic imino-enamido ligands were reported as well .…”

Remote Activation of Nickel Catalysts for Ethylene Oligomerization

“…[3,5] Zwitterionic initiators, which provide an intermediate choice between cationic and neutral species for specifying reactivity and functionality tolerance, are fewer in number. [6][7][8][9][10] In the case of [{(H 3 C)C[N(C 6 H 5 )]C[O-B(C 6 F 5 ) 3 ]-[N(C 6 H 5 )]-k 2 N,N'}Ni(h 3 -CH 2 C 6 H 5 )], the Lewis acid attaches to a site removed from the trajectory of the incoming substrate and no dissociative process is required for initiation or propagation of oligomerization or polymerization reactions. [11] This complex has found utility in the design of tandem copolymerization reactions for producing branched polyethylene from ethylene alone.…”