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

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.