Synthesis, characterization, and reactivity of the first uranium metallocene 1,2-bis(diphenylphosphino)acetylene complexes

[Display omitted] •Two metallacyclopropenes, (C5Me4R)2U(η2-Ph2PCCPPh2) (R = Me, Et) were prepared.•The spectra of these compounds and (C5Me5)2U(η2-Me3SiCCSiMe3) are discussed.•The structure of (C5Me4Et)2U(η2-Ph2PCCPPh2) reveals distortions of the coordinated acetylene. Two new uranium metallacyclopropenes, (C5Me4R)2U(η2-Ph2PCCPPh2) (R = Me, Et) were prepared by reducing the corresponding (C5Me4R)2UCl2 complexes with KC8 in the presence of 1,2-bis(diphenylphosphino)acetylene (Ph2PCCPPh2). Both compounds were fully characterized by a combination of elemental analysis and multinuclear NMR, UV–visible–NIR, and IR spectroscopies. Differences in the electronic spectra of these novel compounds and the known (C5Me5)2U(η2-Me3SiCCSiMe3) are discussed. Also presented is the solid-state structure of (C5Me4Et)2U(η2-Ph2PCCPPh2), which reveals significant distortions of the coordinated 1,2-bis(diphenylphosphino)acetylene (Ph2PCCPPh2) ligand.