Secondary Phosphines Bearing N-Heterocyclic Imine Groups: Polarity Umpolung of Highly Electron-Rich P-H Bonds

The synthesis and reactivity of secondary phosphines carrying two N-heterocyclic imine substituents are reported. These highly electron-rich phosphines feature a polarized P-H bond, with computational studies revealing their dual nature as excellent hydride donors and superbasic phosphorus nucleophiles. Experimental investigations demonstrated their ability to transfer a hydride, proton, or hydrogen atom, depending on the reaction partner, as well as their reactivity in hydrophosphination reactions. The hydrophosphination of nonactivated alkynes proceeded under mild, metal-free conditions, yielding alkenylphosphine intermediates that partly rearranged into azaphosphole heterocycles.