C–C bond cleavage and carbonylation enabled by an NNN-pincer uranium scaffold via metal–arene interaction

Abstract

Metal–arene complexes have recently attracted an increasing interest in f-element chemistry, but the functionalization of arenes mediated by uranium–arene interactions is limited to a single example. Here, we report a new uranium–biphenylene complex supported by a bulky rigid trianionic NNN-pincer ligand in which the uranium–arene interaction is able to promote C–C bond cleavage and functionalization with CO under mild conditions to yield a U-bound 9-fluorenone. Reduction of the U(IV)-pincer complex [NNN-U(THF)Cl₂K(THF)₃]₂ (1) with KC₈, in the presence of biphenylene, results in the terminal arene complex [NNN-U(THF)(biphenylene)][K(THF)₅] (3). DFT studies of 3 indicate the presence of two unpaired electrons located at the uranium center, in line with a U(IV) and a biphenylene dianion. Complex 3 undergoes C_aryl–C_aryl bond cleavage of the biphenylene ligand, affording [NNN-U(THF)(2,2′-biphenyl)][K(THF)₂] (4). DFT studies indicated that, due to the interaction between the biphenylene dianion and the uranium, a concerted ring opening reaction can occur on the strained four members ring to yield 4 while the uranium center retains a +IV oxidation state. Complex 4 undergoes facile CO insertion into the U–C_aryl bond, followed by the C_aryl–C_carbonyl bond formation, yielding [NNN-U(THF)₂(fluorenone)][K(THF)₄] (5). This work demonstrates the potential of uranium–arene interactions to promote arene activation and functionalization.