Electron-deficient organouranium chemistry: synthesis and reactivity of monocyclopentadienyldiphenylphosphidouranium trisborohydrides [C5R4PPh2U(BH4)3] (R = H or CH3) and of their borane adducts

Abstract The reactivity of the monocyclopentadienyl complex [(C 5 H 4 PPh 2 )U(BH 4 ) 3 ] and of its borane adduct [(C 5 H 4 PPh 2 ·BH 3 )U(BH 4 ) 3 ] strongly suggest that in solutions these complexes are in equilibrium with the biscyclopentadienyls [(C 5 H 4 PPh 2 ) 2 U(BH 4 ) 2 ] and [(C 5 H 4 PPh 2 ·BH 3 ) 2 U(BH 4 ) 2 ] and uranium tetraborohydride [U(BH 4 ) 4 ] which is the most reactive species in such systems. Both rearrange in the presence of neutral ligands and are only characterizable in solution. The analogue tetramethylcyclopentadienyl [(C 5 Me 4 PPh 2 ·BH 3 )U(BH 4 ) 3 ] a model of monolinked dimetallics, is stable and has been isolated.