A Uranium(IV) Triamide Species with Brønsted Basic Ligand Character: Metal–Ligand Cooperativity in the f Block

Deprotonation of the tridentate triamine
ligand H3N3Mes ((2,4,6-Me3C6H2N­(H)­CH2CH2)2NH) with 2 equiv of
KCH2Ph followed by treatment with 1 equiv of UCl4 afforded the diamidoamine uranium complex (THF)2UCl2(HN3Mes) (1-THF). This
species was further derivatized with either OPPh3 or KCp* to generate (Ph3PO)­UCl2(HN3Mes) (1-OPPh3) or
Cp*UCl­(HN3Mes) (2-Cl), respectively.
Deprotonation of 2-Cl with nBuLi furnished the uranium­(IV) triamido compound Cp*U­(N3Mes-LiCl­(THF)2) (3-LiCl), which
is stabilized by the presence of LiCl. 3-LiCl reacts
readily with alcohols and thiols, including HOPh, HSPh, and HOtBu, to furnish the respective products Cp*U­(OPh)­(HN3Mes) (2-OPh), Cp*U­(SPh)­(HN3Mes) (2-SPh), and Cp*U­(OtBu)­(HN3Mes) (2-OtBu), which show cooperative
addition of the H–E (E = O, S) bond across the U–N bond,
serving to regenerate the diamidoamine ligand. Similar cooperative
addition was noted for 3-LiCl with benzophenone, furnishing
Cp*U­(N3Mes-OCPh2) (3-OCPh2), which features new U–O and N–C
bonds. The Brønsted basicity of the central nitrogen of 3-LiCl was illustrated by addition of PhOAc, which favored
α-carbon deprotonation over nucleophilic attack at the carbonyl.
All species were subject to a complete spectroscopic and crystallographic
analysis, confirming that the reactivity of 3-LiCl in
fact involves cooperation from the triamido ligand and uranium center.