A Ferrocene‐Based Phosphane/Borane Frustrated Lewis Pair for Asymmetric Imine Reduction

The α‐phosphanylferrocenecarbaldehyde (pS)‐1 was converted into the β‐styryl derivative (pS)‐4 by Wittig–Horner olefination. Subsequent hydroboration with Piers' borane [HB(C6F5)2] followed by H2 splitting and crystallization gave the phosphonium/hydridoborate product (pS,R)‐5, which was used as a frustrated Lewis pair catalyst for the asymmetric hydrogenation of a series of imines (up to 69 % ee).