Cl₃Al-PH₃ Is a Weak Lewis Pair Allowing the Synthesis of Sterically Highly Hindered Primary and Secondary Alkyl Phosphanes

Phosphane (PH₃) gas has the highest phosphorus content of all commercial phosphorus compounds, yet its use for valuable chemicals is very limited. Aluminum chloride and phosphane yield quantitatively the adduct Cl₃Al-PH₃, which is easy to handle and reacts with a large set of alkyl halides to give phosphonium salts that can be converted to primary phosphanes. This sequence has been generalized to access various secondary and some tertiary phosphanes in excellent yields under mild conditions and short reaction times. With unprecedented ease, these reactions allow, in particular, the preparation of sterically demanding phosphanes, which, as ligands, are key components of highly catalytically competent transition metal complexes.