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

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(TrenDPBS)] (TrenDPBS = {N(CH2CH2NSiPh2But)3}3-) afforded [An(TrenDPBS)Cl] (An = Th, 1Th; U, 1U). Complexes 1An react with benzyl potassium to afford the cyclometallates (TrenDPBScyclomet) [An{N(CH2CH2NSiPh2But)2(CH2CH2NSiPhButC6H4)}] (An = Th, 2Th; U, 2U). Treatment of 1An with sodium azide affords [An(TrenDPBS)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 (TrenDPBSd-cyclomet) ate complex [Th{N(CH2CH2NSiPh2But) CH2CH2NSiPhButC6H4)}2Cs(THF)3] (4). In contrast to 3Th, reaction of 3U with potassium graphite produces the uranium(III) complex [U(TrenDPBS)] (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 p-p-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.