Diamido-Ether Actinide Complexes as Catalysts for the Intramolecular Hydroamination of Aminoalkenes

Abstract

The synthesis and characterization of a series of new diamido-thorium(IV) and diamido-uranium(IV) halide and alkyl complexes supported by three different diamido-ether ligands are reported. Reaction of ThCl4·2DME with [(RNSiMe2)2O]Li2 ([RNON]Li2) in DME when R = tBu gives [tBuNON]ThCl5Li3·DME (1), when R = iPr2Ph in diethyl ether [iPr2PhNON]ThCl3Li·DME (3) is prepared. Reaction of UCl4 with [iPr2PhNON]Li2 in diethyl ether gives {[iPr2PhNON]UCl2}2 (4). Reaction of ThCl4·2DME with Li2[(iPr2PhNCH2CH2)2O] ([iPr2PhNCOCN]Li2) in DME gives [iPr2PhNCOCN]ThCl2·DME (5). The addition of 2 equiv of LiCH2SiMe3 to 1 and 5 resulted in salt- and base-free [tBuNON]Th(CH2SiMe3)2 (7) and [iPr2PhNCOCN]Th(CH2SiMe3)2 (9), respectively. Complexes 1, 3, 4, 7, and 9, as well as previously reported {[tBuNON]UCl2}2 (2), [tBuNON]U(CH2SiMe3)2 (6), and [iPr2PhNCOCN]U(CH2SiMe3)2 (8) were examined as catalysts for the intramolecular hydroamination of a series of aminoalkenes. Complexes 6–9 were shown to facilitate the formation of 2-methyl-4,4-diphenylpyrrolidine from 2,2-diphenyl-1-amino-4-pentene at room temperature. For 9, this reaction occurs in less than 15 min, while for other dialkyls 6–8, the reaction takes less than 2 h. Dihalides 1 and 2 facilitated the same reaction at 60 °C in 4 h, while 3 and 4 showed no activity under the same conditions. Dialkyl complexes 7–9 were examined for further reactivity with different substrates. The uranium dialkyl 8 was more active than 7 and 9 for the cyclization of 2,2-diphenyl-1-amino-5-hexene and 2,2-diphenyl-1-amino-6-heptene, as well as more active in the cyclization of N-methyl-2,2-diphenyl-1-amino-4-pentene, a secondary amine. All three dialkyls became less active when the steric bulk of the gem-substituents was decreased from diphenyl to cyclopentyl; reactivity further decreased when the steric bulk of the substituents was decreased further to hydrogen.