Ethene activation and catalytic hydrogenation by a low-valent uranium pentalene complex

The reaction of the uranium(III) complex [U(?8-Pn††)(?5-Cp*)] (1) (Pn†† = C8H4(1,4-SiiPr3)2, Cp* = C5Me5) with ethene at atmospheric pressure produces the ethene-bridged diuranium complex [{(?8-Pn††)(?5-Cp*)U}2(µ-?2:?2-C2H4)] (2). A computational analysis of 2 revealed that coordination of ethene to uranium reduces the carbon–carbon bond order from 2 to a value consistent with a single bond, with a concomitant change in the formal uranium oxidation state from +3 in 1 to +4 in 2. Furthermore, the uranium–ethene bonding in 2 is of the d type, with the dominant uranium contribution being from f–d hybrid orbitals. Complex 2 reacts with hydrogen to produce ethane and reform 1, leading to the discovery that complex 1 also catalyzes the hydrogenation of ethene under ambient conditions.