Towards New Reactive Phosphenium Cations

Electronically stabilized phosphenium cations of type (1) have been known for about 40 years. These molecules showed interesting chemistry as π-accepting ligands in electron rich transition metal complexes. Their reactivity with small molecules was also probed, however, turned out to be rather limited. This motivated us to design new reactive phosphenium cations capable of activating small molecules, such as H₂, CO, NH₃, R₃SiH etc. and hopefully transform them to value-added products. We present two distinct approaches to achieve the desired goals. The first approach is to synthesize sterically encumbered phosphenium cations (2) which are not stabilized electronically, and thus expected to be more reactive towards small molecules. Noteworthy, phosphenium cations of type 2 are still unknown. The second approach is to synthesize geometrically constrained phosphenium cations (3), which based on computations should be more reactive than 1. Advances in synthesis and utility of 2 and 3 along with theoretical predictions are presented herein.