Photolytic and reductive activations of 2‐arsaethynolate in a uranium–triamidoamine complex. Decarbonylative arsenic‐group transfer reactions and trapping of a highly bent and reduced form

Little is known about the chemistry of the 2‐arsaethynolate anion, but to date it has exclusively undergone fragmentation reactions when reduced. Herein, we report the synthesis of [U(Tren${}^{TIPS}$)(OCAs)] (2, Tren${}^{TIPS}$=N(CH${}_2$CH${}_2$NSiiPr${}_3$)${}_3$), which is the first isolable actinide‐2‐arsaethynolate linkage. UV‐photolysis of 2 results in decarbonylation, but the putative [U(Tren${}^{TIPS}$)(As)] product was not isolated and instead only [{U(TrenTIPS)}${}_2$(μ‐η${}^2$:η${}^2$‐As${}_2$H${}_2$)] (3) was formed. In contrast, reduction of 2 with [U(Tren${}^{TIPS}$)] gave the mixed‐valence arsenido [{U(Tren${}^{TIPS}$)}${}_2$(μ‐As)] (4) in very low yield. Complex 4 is unstable which precluded full characterisation, but these photolytic and reductive reactions testify to the tendency of 2‐arsaethynolate to fragment with CO release and As transfer. However, addition of 2 to an electride mixture of potassium‐graphite and 2,2,2‐cryptand gives [{U(Tren${}^{TIPS}$)}${}_2${μ‐η${}^2$(OAs):η${}^2$(CAs)‐OCAs}][K(2,2,2‐cryptand)] (5). The coordination mode of the trapped 2‐arsaethynolate in 5 is unique, and derives from a new highly reduced and bent form of this ligand with the most acute O‐C‐As angle in any complex to date (O‐C‐As < ≈128°). The trapping rather than fragmentation of this highly reduced O‐C‐As unit is unprecedented, and quantum chemical calculations reveal that reduction confers donor–acceptor character to the O‐C‐As unit. (© 2019 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)