Uranium versus Thorium: Synthesis and Reactivity of [η -1,2,4-(Me C) C H ] U[η -C Ph ].

The synthesis, electronic structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Addition of diphenylacetylene (PhC≡CPh) to the uranium phosphinidene metallocene [η -1,2,4-(Me C) C H ] U=P-2,4,6-tBu C H (1) yields the stable uranium metallacyclopropene, [η -1,2,4-(Me C) C H ] U[η -C Ph ] (2). Based on density functional theory (DFT) results the 5f orbital contributions to the bonding within the metallacyclopropene U-(η -C=C) moiety increases significantly compared to the related Th compound [η -1,2,4-(Me C) C H ] Th[η -C Ph ], which also results in more covalent bonds between the [η -1,2,4-(Me C) C H ] U and [η -C Ph ] fragments. Although the thorium and uranium complexes are structurally closely related, different reaction patterns are therefore observed. For example, 2 reacts as a masked synthon for the low-valent uranium(II) metallocene [η -1,2,4-(Me C) C H ] U when reacted with Ph E (E=S, Se), alkynes and a variety of hetero-unsaturated molecules such as imines, ketazine, bipy, nitriles, organic azides, and azo derivatives. In contrast, five-membered metallaheterocycles are accessible when 2 is treated with isothiocyanate, aldehydes, and ketones.