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

Abstract

We report the direct synthesis of the terminal pnictidenes [An(Tren^TCHS )(PnH)][M(2,2,2-cryptand)] (Tren^TCHS ={N(CH₂ CH₂ NSiCy₃ )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 )(PnH₂ )] (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(CH₂ CH₂ NSiPrⁱ 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.

Keywords: Actinides; Arsinidene; Density Functional Theory; Multiple Bonds; Phosphinidene.