Actinide-Pnictide (An-Pn) Bonds Spanning Non-Metal, Metalloid, and Metal Combinations (An=U, Th; Pn=P, As, Sb, Bi)

The synthesis and characterisation is presented of the compounds [An(Tren(DMBS)){Pn(SiMe3)(2)}] and [An(Tren(TIPS)){Pn(SiMe3)(2)}] [Tren(DMBS)=N(CH2CH2NSiMe2But)(3), An=U, Pn=P, As, Sb, Bi; An=Th, Pn=P, As; Tren(TIPS)=N(CH2CH2NSiPr3i)(3), An=U, Pn=P, As, Sb; An=Th, Pn=P, As, Sb]. The U-Sb and Th-Sb moieties are unprecedented examples of any kind of An-Sb molecular bond, and the U-Bi bond is the first two-centre-two-electron (2c-2e) one. The Th-Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U-Bi complex is the heaviest 2c-2e pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An-An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U-Pn bonds degrade by homolytic bond cleavage, whereas the more redox-robust thorium compounds engage in an acid-base/dehydrocoupling route.