Nitrile Coupling Mediated by Cyclometalated Uranium Alkyl Complex: The Ketimide-Enamine Seesaw Mechanism

Metal alkyls play a crucial role in synthetic chemistry. Although s-, p-, and d-block metal alkyls have been extensively investigated, the reactivity of f-block actinide alkyls has received relatively limited attention. In this work, we systematically investigate the insertion reactivity of a four-membered cyclometalated uranium(IV) alkyl complex (<b>1</b>) with various nitriles, including 2-naphthonitrile, 4-cyanopyridine, and 2-cyanopyridine, yielding coupled products <b>2</b>-<b>4</b>, respectively. Mechanistic studies reveal that stoichiometric nitrile addition generates a uranium-ketimide intermediate (<b>5</b>), which undergoes facile 1,3-H migration at room temperature to produce a uranium-enamine complex (<b>6</b>). Further reactions of the uranium-ketimide complex <b>5a</b> with 2-naphthonitrile, 4-cyanopyridine, and 2-cyanopyridine yield complexes <b>2</b>, <b>7</b>, and <b>8</b>, respectively. In contrast, reactions of the uranium-enamine complex <b>6a</b> with the same nitriles result in complexes <b>9</b>, <b>10</b>, and <b>11</b>, all of which feature a β-diketiminate ligand formed by nitrile coupling with the 2-naphthonitrile motif of <b>6a</b>. Theoretical analyses highlight the critical role of the 1,3-migration intermediate <b>6a</b> in facilitating nitrile coupling reactions. These results suggest a ketimide-enamine seesaw mechanism for the nitrile coupling in this system. Moreover, the uranium-enamine complex <b>6a</b> exhibits broad electrophile compatibility, efficiently engaging in cross-coupling reactions with benzophenone and CS₂.