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. (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH)