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

## TL;DR

A uranium complex with a special ligand can break and modify carbon-carbon bonds in arenes under mild conditions.

## Contribution

A new uranium complex enables C–C bond cleavage and CO functionalization of arenes via uranium–arene interactions.

## Key findings

- The uranium–arene complex promotes C–C bond cleavage of biphenylene.
- CO insertion into the U–C bond forms a U-bound fluorenone under mild conditions.
- DFT studies confirm uranium retains +IV oxidation state during the process.

## 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 Caryl–Caryl 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–Caryl bond, followed by the Caryl–Ccarbonyl 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.

Enabled by a bulky rigid trianionic NNN-pincer ligand, the uranium–arene interaction results in the facile cleavage of the biphenylene C–C bond and the functionalization with CO under mild conditions to yield a U-bound 9-fluorenone.