Easy Access to Phosphine‐Borane Building Blocks

In this paper, we highlight the synthesis of a variety of primary phosphine‐boranes (RPH(2)⋅BH(3)) from the corresponding dichlorophosphines, simply by using Li[BH(4)] as reductant and provider of the BH(3) protecting group. The method offers facile access not only to alkyl‐ and arylphosphine‐boranes, but also to aminophosphine‐boranes (R(2)NPH(2)⋅BH(3)) that are convenient building blocks but without the protecting BH(3) moiety thermally labile and notoriously difficult to handle. The borane‐protected primary phosphines can be doubly deprotonated using n‐butyllithium to provide soluble phosphanediides Li(2)[RP⋅BH(3)] of which the phenyl‐derivative Li(2)[PhP⋅BH(3)] was structurally characterized in the solid state.