Actinide borohydrides played a key role in the history of actinide science and are remarkable because of their high coordination numbers and unusual properties. U(BH4)4 and U(BH3Me)4, for example, are highly volatile and were discovered during the Manhattan Project in the search for volatile uranium complexes for isotope separation and uranium enrichment in fissile U-235. Later, X-ray and neutron diffraction studies revealed the inner coordination spheres of these complexes are comprised exclusively of hydrogen atoms. Since the discovery of U(BH4)4 and U(BH3Me)4 during World War II, only three major classes of homoleptic actinide borohydride complexes have been reported: tetrahydroborates (BH4-), alkyltrihydroborates (BH3R-), and aminodiboranates (H3BNR2BH3-). Here we describe a new class of homoleptic actinide and lanthanide borohydride complexes called phosphino-di-boranates (H3BPR2BH3-). Treating UI3(1,4-dioxane)1.5 or NdI3 with three equivalents of K(H3BPtBu2BH3) in Et2O yielded the homoleptic uranium and neodymium complexes U2(H3BPtBu2BH3)6 (1) and Nd2(H3BPtBu2BH3)6 (2). The dimeric structures of 1 and 2 were determined by single-crystal X-ray diffraction studies. Each metal is surrounded by two chelating phosphinodiboranate ligands and two ligands that bridge the metals to form the dimer. The metal-boron distances suggest that U and Nd form 14 M-H-B bonds. Multinuclear NMR and IR spectra of 1 and 2 will be presented, as will novel lanthanide and actinide phosphinodiboranate complexes with different substituents attached to phosphorus.

Homoleptic uranium and lanthanide phosphinodiboranate complexes

255th National Meeting (2018)

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