Cooperative dihydrogen activation with unsupported uranium-metal bonds and characterization of a terminal U(iv) hydride.

Cooperative chemistry between two or more metal centres can show enhanced reactivity compared to the monometallic fragments. Given the paucity of actinide-metal bonds, especially those with group 13, we targeted uranium(iii)-aluminum(i) and -gallium(i) complexes as we envisioned the low-valent oxidation state of both metals would lead to novel, cooperative reactivity. Herein, we report the molecular structure of [(C 5 Me 5 ) 2 (MesO)U-E(C 5 Me 5 )], E = Al, Ga, Mes = 2,4,6-Me 3 C 6 H 2 , and their reactivity with dihydrogen. The reaction of H 2 with the U(iii)-Al(i) complex affords a trihydroaluminate complex, [(C 5 Me 5 ) 2 (MesO)U(μ 2 -(H) 3 )-Al(C 5 Me 5 )] through a formal three-electron metal-based reduction, with concomitant formation of a terminal U(iv) hydride, [(C 5 Me 5 ) 2 (MesO)U(H)]. Noteworthy is that neither U(iii) complexes nor [(C 5 Me 5 )Al] 4 are capable of reducing dihydrogen on their own. To make the terminal hydride in higher yields, the reaction of [(C 5 Me 5 ) 2 (MesO)U(THF)] with half an equivalent of diethylzinc generates [(C 5 Me 5 ) 2 (MesO)U(CH 2 CH 3 )] or treatment of [(C 5 Me 5 ) 2 U(i)(Me)] with KOMes forms [(C 5 Me 5 ) 2 (MesO)U(CH 3 )], which followed by hydrogenation with either complex cleanly affords [(C 5 Me 5 ) 2 (MesO)U(H)]. All complexes have been characterized by spectroscopic and structural methods and are rare examples of cooperative chemistry in f element chemistry, dihydrogen activation, and stable, terminal ethyl and hydride compounds with an f element.