Bulky Phosphinines: From a Molecular Design to an Application in Homogeneous Catalysis

The design and preparation of an asymmetrically substituted and bulky phosphinine was achieved by introducing sterically demanding substituents into specific positions of a rigid phosphorus‐heterocyclic framework. Compound 5 shows, at the same time, axial chirality and a sufficiently high energy barrier for internal rotation to prevent enantiomerization. Both enantiomers of 5 were isolated by means of chiral analytical HPLC, and their absolute configurations could be assigned by combining experimental data and DFT calculations. Despite its substitution pattern, 5 can still coordinate to transition‐metal centers through the lone pair of electrons on the phosphorus atom. Rapid CH activation on the adjacent aryl substituent at the 2‐position of the phosphorus heterocycle was achieved by using [{Cp*IrCl2}2] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) as a metal precursor. A racemic mixture of 5 was applied as a π‐accepting low‐coordinate phosphorus ligand in the Rh‐catalyzed hydroformylation of trans‐2‐octene, which showed a clear preference for the formation of 2‐methyloctanal. Bulky phosphinines: An asymmetrically substituted, bulky, and atropisomeric phosphinine has been prepared and characterized (see figure). Rapid CH activation on the 2‐aryl substituent of the phosphorus heterocycle was achieved with [{Cp*IrCl2}2] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) as a metal precursor. A racemic mixture of the phosphinine acted as a π‐accepting low‐coordinate phosphorus ligand in the Rh‐catalyzed hydroformylation of 2‐octene.