Despite the abundance of f-block-cyclopentadienyl, arene, cycloheptatrienyl and cyclo-octatetraenide complexes, cyclobutadienyl derivatives are unknown in spite of their prevalence in the d-block. Here we report that reductive [2+2]-cycloaddition reactions of diphenylacetylene and (2,2-dimethylpropylidyne) phosphine with uranium(V)-inverted sandwich 10π-toluene tetra-anion complexes results in the isolation of inverted sandwich cyclobutadienyl and diphosphacyclobutadienyl dianion uranium(IV) complexes. Computational analysis suggests that the bonding is predominantly electrostatic. Although the ψ 4 molecular orbital in the cyclobutadienyl and diphosphacyclobutadienyl ligands exhibits the correct symmetry for δ-bonding to uranium, the dominant covalent contributions arise from π-bonding involving ψ 2 and ψ 3 orbital combinations. This contrasts with uranium complexes of larger arenes and cyclo-octatetraenide, where δ-bonding dominates. This suggests that the angular requirements for uranium to bond to a small four-membered ring favours π-bonding, utilizing 5f-instead of 6d-orbitals, over δ-bonding that is favoured with larger ligands, where 6d-orbitals can become involved in the bonding. © 2013 Macmillan Publishers Limited.
CITATION STYLE
Patel, D., McMaster, J., Lewis, W., Blake, A. J., & Liddle, S. T. (2013). Reductive assembly of cyclobutadienyl and diphosphacyclobutadienyl rings at uranium. Nature Communications, 4. https://doi.org/10.1038/ncomms3323
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