Tris(bicyclo[1.1.1]pentyl)phosphine: An Exceptionally Small Tri-tert-alkylphosphine and Its Bis-Ligated Pd(0) Complex

Tris(bicyclo[1.1.1]pentyl)phosphine can be prepared by radical addition of PH3 to [1.1.1]propellane, giving the smallest tri-tert-alkylphosphine known. PBcp3 is substantially smaller than PCy3 and is comparable in electron-donating power to PEt3. It gives a bis-ligated Pd(0) complex Pd(PBcp3)2 that is exceptionally reactive toward alkyl halide oxidative addition and functions as a general ligand for palladium-catalyzed cross-coupling of sp3 electrophiles. Radical addition of [1.1.1]propellane to phenylphosphine gives the bis(bicyclo[1.1.1]pentyl)phosphine derivative PBcp2Ph, illustrating the generality of this approach to bicyclopentylphosphine synthesis.