Phosphines are widely used as ligands. Their steric and electronic properties can be tuned by changing the substituents at the phosphorus atom. PCl3 and PH3 can be used as precursors for the synthesis of phosphines, but these compounds are difficult to handle and hazardous. Tris(hydroxymethyl)phosphine (THP) could be a safer alternative and can be generated in situ from low-cost tetrakis(hydroxymethyl)phosphonium chloride (THPC).
James D. Nobbs, Martin van Meurs, Institute of Sustainability for Chemicals, Energy, and Environment (ISCE2), Agency for Science, Technology, and Research (A*STAR), Singapore, and colleagues have prepared novel cage-like phosphines, i.e., dioxaphosphabicyclo[2.2.2]octanes (general structure pictured), in a one-pot reaction from THP and different α,β-unsaturated ketones. The team first reacted THPC with KOH as a base in methanol to generate THP. Then they added the α,β-unsaturated ketone and obtained the desired dioxaphosphabicyclo[2.2.2]octane derivative after 16 h at 50 °C.
The phosphines are oxidized very slowly in air, which makes them convenient to handle. They can, however, be converted to the corresponding phosphine oxides using meta-chloroperoxybenzoic acid (m-CPBA). The products have potentially useful properties as ligands, with small tuneable cone angles but similar electronic properties to the widely used PPh3. The team used the new ligands, for example, in the rhodium-catalyzed hydroformylation of 1-octene and in palladium-catalyzed Suzuki–Miyaura couplings.
- Dioxaphosphabicyclooctanes: small caged phosphines from tris(hydroxymethyl)phosphine,
James David Nobbs, Dillon Tay, Yoon Hui Yeap, Yong-Lun Tiong, Suming Ye, Srinivasulu Aitipamula, Cun Wang, Choon Boon Cheong, Martin van Meurs,
Dalton Trans. 2023.