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. Here, we report the synthesis of [U(Tren TIPS )(OCAs)] ( 2 , Tren TIPS = N(CH 2 CH 2 NSiPr i 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(Tren TIPS )} 2 (m-h 2 :h 2 -As 2 H 2 )] ( 3 ) was detected. In contrast, reduction of 2 with [U(Tren TIPS )] gave the mixed-valence arsenido [{U(Tren TIPS )} 2 (m-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 {m-h 2 (OAs):h 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 Ð ~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.