Easy Access to Phosphine-Borane Building Blocks

In this paper, we highlight the synthesis of a variety of primary phosphine‐boranes (RPH₂⋅BH₃) from the corresponding dichlorophosphines, simply by using Li[BH₄] as reductant and provider of the BH₃ protecting group. The method offers facile access not only to alkyl‐ and arylphosphine‐boranes, but also to aminophosphine‐boranes (R₂NPH₂⋅BH₃) that are convenient building blocks but without the protecting BH₃ moiety thermally labile and notoriously difficult to handle. The borane‐protected primary phosphines can be doubly deprotonated using n‐butyllithium to provide soluble phosphanediides Li₂[RP⋅BH₃] of which the phenyl‐derivative Li₂[PhP⋅BH₃] was structurally characterized in the solid state.