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-doclecaboran-1-yl)) phosphine, 2 (crystal data, hexagonal, space group P6(3), a = b = 12.251(3) Angstrom, c = 11.514(4) Angstrom, alpha = beta = 90degrees, gamma = 120degrees, V = 1496.6(7) Angstrom(3), Z = 2, R-1 = 0.0568) and tris(1'- methyl (1,2-dicarba-closo-dodecaboran-1-yl))arsine, 3 (crystal data, hexagonal, space group P6(3), a = b = 12.330(3) Angstrom, c = 11.474(4) Angstrom, alpha = beta = 90degrees, gamma = 120degrees, V = 1510.7(7) Angstrom(3), Z = 2, R-1 = 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 (l), 4 (crystal data, monoclinic, space group P2(1)/c, a = 19.101(4) Angstrom, b = 12.167(2) Angstrom, c = 13.846(3) Angstrom, alpha = gamma = 90degrees, beta = 91.13(3) degrees, V = 3217.2 (11) Angstrom(3), Z = 4, R-1 = 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)degrees, which is among the largest values reported to date.