Bicyclo[1.1.1]pentyl Substituents in Phosphorus and Aluminum Organometallics

Abstract

The use of organophosphines as ligands in organometallic chemistry has been an enabling technology in catalysis with applications spanning from hydroformylation to cross-coupling chemistry. However, few homoleptic tri-tert-alkylphosphines have been reported despite the importance of the archetype PtBu3. Tris(bicyclo[1.1.1]pentyl)phosphine PBcp3 can be prepared by radical addition of PH3 to [1.1.1]propellane, giving the smallest tri-tert-alkylphosphine known. 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. Additionally, the primary phosphine reagent iPr2NPH2·BH3 can serve as a doubly protected PH2Cl proxy, enabling the synthesis of bis(bicyclo[1.1.1]pentyl)chlorophosphine (Bcp2PCl) for the first time. Bcp2PCl serves as a general reagent for the preparation of a family of bis(bicyclo[1.1.1]pentyl) alkyl- and arylphosphines, including new members of privileged phosphine ligand scaffolds. Organoaluminum compounds are another useful class of organometallic reagents which allow transfer of substituents to various substrates. Addition of [1.1.1]propellane to aluminum hydrides provides access to bicyclo[1.1.1]pentyl aluminum compounds, and these reagents can provide synthetic routes to organic bicyclo[1.1.1]pentyl products through carbonyl addition and cross coupling methodologies.