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

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.