Actinide Triamidoamine (TrenR) Chemistry: Uranium and Thorium Derivatives Supported by a Diphenyl‐tert‐Butyl‐Silyl‐Tren Ligand

A series of triamidoamine complexes of uranium and thorium with N-SiPh₂Bu^t substituents are described, including chlorides, azides, cyclometallates.

Abstract

We report the synthesis and characterisation of thorium(IV), uranium(III), and uranium(IV) complexes supported by a sterically demanding triamidoamine ligand with N-diphenyl-tert-butyl-silyl substituents. Treatment of ThCl₄(THF)_3.5 or UCl₄ with [Li₃(Tren^DPBS)] (Tren^DPBS={N(CH₂CH₂NSiPh₂Bu^t)₃}³⁻) afforded [An(Tren^DPBS)Cl] (An=Th, 1Th; U, 1U). Complexes 1An react with benzyl potassium to afford the cyclometallates (Tren^DPBS _cyclomet) [An{N(CH₂CH₂NSiPh₂Bu^t)₂(CH₂CH₂NSiPhBu^tC₆H₄)}] (An=Th, 2Th; U, 2U). Treatment of 1An with sodium azide affords [An(Tren^DPBS)N₃] (An=Th, 3Th; U, 3U). Reaction of 3Th with potassium graphite affords 2Th. In contrast, 3Th reacts with cesium graphite to afford the doubly-cyclometallated (Tren^DPBS _d-cyclomet) ate complex [Th{N(CH₂CH₂NSiPh₂Bu^t)(CH₂CH₂NSiPhBu^tC₆H₄)}₂Cs(THF)₃] (4). In contrast to 3Th, reaction of 3U with potassium graphite produces the uranium(III) complex [U(Tren^DPBS)] (5), and 5 can also be prepared by reaction of potassium graphite with 1U. The loss of azide instead of conversion to nitrides contrasts to prior work when the silyl group is iso-propyl silyl, underscoring how ligand substituents profoundly drive the reaction chemistry. Several complexes exhibit T-shaped meta-C−H⋅⋅⋅phenyl and staggered parallel π–π-stacking interactions, demonstrating subtle weak interactions that drive ancillary ligand geometries. Compounds 1An–3An, 4, and 5 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR spectroscopy, infrared spectroscopy, UV/Vis/NIR spectroscopy, and elemental analyses.

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