Actinide Pnictinidene Chemistry: A Terminal Thorium Parent‐Arsinidene Complex Stabilised by a Super‐Bulky Triamidoamine Ligand

We report the direct synthesis of the terminal pnictidenes [An(Tren(TCHS))(PnH)][M(2,2,2‐cryptand)] (Tren(TCHS)={N(CH(2)CH(2)NSiCy(3))(3)}(3−); An/Pn/M=Th/P/Na 5, Th/As/K 6, U/P/Na 7, U/As/K 8) and their conversion to the pnictides [An(Tren(TCHS))(PnH(2))] (An/Pn=Th/P 9, Th/As 10, U/P 11, U/As 12). Use of the super‐bulky Tren(TCHS) ligand was essential to accessing complete families, and 6 is an unprecedented example of a terminal thorium‐arsinidene complex and only the second structurally authenticated parent terminal arsinidene complex of any metal. Comparison of the terminal Th=AsH unit of 6 to the bridging ThAs(H)K linkage in structurally analogous [Th(Tren(TIPS)){μ‐As(H)K(15‐crown‐5)}] (Tren(TIPS)={N(CH(2)CH(2)NSiPr(i) (3))(3)}(3−)) reveals a stronger Th−As bond in the former compared to the latter, and a large response overall to the nature of the Th=AsH bonding upon removal of the electrostatically‐bound K‐ion; the σ‐bond changes little but the π‐bond is significantly perturbed.