Diamido-Ether Uranium(IV) Alkyl Complexes as Single-Component Ethylene Polymerization Catalysts

Abstract

The synthesis and characterization of two new uranium(IV) dialkyl complexes supported by two different diamido ether ligands are reported. The reaction of [{({2,6-iPr2C6H3}N{CH2CH2})2O}UCl2] ([{dippNCOCN}UCl2]) with 2 equiv of KCH2Ph generates the organoactinide [{dippNCOCN}U(CH2Ph)2] (3), which shows an η1-, η2-benzyl arrangement of the alkyl ligands in the solid state. Reaction of [({tBuN(SiMe2)}2O)UCl2] ([{tBuNON}UCl2]) with 2 equiv of LiCH(SiMe3)2 yields the alkyl-bridged uranium dimer [{tBuNON}U{CH(SiMe3)(SiMe2CH2)}]2 (4), which forms via γ C−H activation of the CH(SiMe3)2 substituent. Reaction of 3 and 4 as well as previously reported [{tBuNON}U(CH2SiMe3)2] (1) and [{dippNCOCN}U(CH2SiMe3)2] (2) with 1 atm of ethylene under ambient conditions produced high molecular weight polymers, demonstrating that diamido ether actinide complexes can act as ethylene polymerization catalysts; activities up to 560 g/mol·h·atm using 1 were observed. Reaction of 1 and 2 with 1 atm of ethylene and 1 equiv of B(C6F5)3 demonstrated a 4-fold decrease in activity of the catalyst. Reaction of 1 or 2 with an excess of MMAO or Et2AlCl did not yield any polymer formation upon the addition of ethylene. After reaction of 1 with Et2AlCl, removal of volatiles in vacuo yielded a dark red liquid that, upon standing, formed green crystals of [{tBuNON}U{(μ-Cl)2AlEt2}2] (5), indicating a route for catalyst deactivation by aluminum-based cocatalysts.