Sterically Hindered and Robust Pnictogen Ligands Derived from Carboranes:  Synthesis and X-ray Structure Determination of Tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))phosphine, Tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))arsine and Chloro(Tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))phosphine)gold(I)

Sterically hindered phosphine and arsine ligands derived from ortho-carborane were synthesized and characterized by X-ray crystallography. Tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))phosphine, 2 (crystal data, hexagonal, space group P6₃, a = b = 12.251(3) Å, c = 11.514(4) Å, α = β = 90°, γ = 120°, V = 1496.6(7) ų, Z = 2, R₁ = 0.0568) and tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))arsine, 3 (crystal data, hexagonal, space group P6₃, a = b = 12.330(3) Å, c = 11.474(4) Å, α = β = 90°, γ = 120°, V = 1510.7(7) ų, Z = 2, R₁ = 0.0930) were prepared in 82% and 68% yield, respectively. The phosphine ligand is resistant to air-oxidation but was converted to corresponding oxide when heated with hydrogen peroxide. The tertiary carboranyl phosphine reacted with (Tht)AuCl to yield chloro(tris(1‘-methyl(1,2-dicarba-closo-dodecaboran-1-yl))phosphine)gold(I), 4 (crystal data, monoclinic, space group P2₁/c, a = 19.101(4) Å, b = 12.167(2) Å, c = 13.846(3) Å, α = γ = 90°, β = 91.13(3)°, V = 3217.2(11) ų, Z = 4, R₁ = 0.0396) in 82% yield. From the X-ray structure of the gold complex, the cone angle of the phosphine was determined to be 213(2)°, which is among the largest values reported to date.