The synthesis and characterization of sterically hindered carboranylphosphine ligands

Sterically hindered phosphine ligands occupy a central role in coordination chemistry. Their usefulness has been demonstrated in the isolation of coordinatively unsaturated metal complexes and in palladium-catalyzed cross-coupling reactions. The most electron-rich phosphines are also sensitive to oxidation. Ideally, such ligands would be both sterically hindered and resistant toward oxidation.;Three classes of carboranylphosphine ligands were prepared, in which one, two or three carborane cages were incorporated around a central phosphorus atom. Once prepared, the reactivity of the phosphine ligands was probed by screening them for their resistance to oxidation, by preparing phosphine oxides and Au(I) complexes. Selected derivatives were screened for their activity in the Suzuki cross-coupling of aryl halides and aryl boronic acids. The phosphine ligand which displayed the best reactivity and resistance toward oxidation, (1,12-dicarba-closo-dodecaboran-1-yl)diphenylphosphine, was used to prepare novel gold nanoparticles.;Carboranes, which are icosahedral clusters of carbon, hydrogen and boron, are ideal synthons for the preparation of electron-rich, sterically hindered ligands. Carboranes possess tremendous synthetic versatility, are highly robust and are sterically bulky. Addition of carborane groups to a phosphorus centre should provide ligands which are sterically hindered and highly robust.