In this presentation, I describe solution equilibria studies with a new class of lanthanide and actinide complexes with chelating borohydrides known as phosphinodiboranates. Complexes with the empirical formula M(H3BPtBu2BH3)3, where M = U or Ln, were prepared and shown to exist as dimers in the solid state regardless of metal size. In contrast, the complexes depolymerize to form metal-dependent mixtures of monomers and dimers when dissolved, and both species can be observed by 1H and 11B NMR spectroscopy. This is unusual because most f-element borohydride complexes exchange ligands and B-H-M bonds too rapidly to be seen on the NMR time scale. The monomer/dimer equilibrium in phosphinodiboranate complexes with M = U, Ce, Pr, and Nd were analyzed by VT Q-NMR (variable temperature quantitative NMR) in order to quantify the thermodynamic parameters (ΔH, ΔS, and ΔG) associated with depolymerization as a function of trivalent metal ion. This study has allowed us to assess B-H-M bonding differences between uranium and similarly sized lanthanides.

Solution equilibrium of phosphinodiboranates as an analysis between trivalent lanthanide and uranium B-H-M bonding

ACS Fall 2021

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