Electrophilic diiodination reactions of icosahedral closo-1,2-C2B10H12 and closo-1,7-C2B10H12 using 2 molar equiv of iodine monochloride in the presence of catalytic amounts of aluminum chloride yielded the corresponding closo-9,12-I2-1,2-C2B10H10 and closo-9,10-I2-1,7-C2B10H10 complexes in excellent yields. Palladium-mediated cross-coupling reactions of these diiodocarboranes with a variety of alkyl, aralkyl, and aryl Grignard reagents were reinvestigated, and it was demonstrated that the addition of copper(I) iodide as a cocatalyst is crucial to the success of this reaction. A reaction mechanism involving the initial formation of binary organocopper species (RCu; R = alkyl, aralkyl, aryl) followed by the reaction of (σ-carboranyl)palladium iodides (L2Pd(CbI)I and L2Pd(CbR)I; L = PPh3, Cb = closo-1,2-C2B10H10, closo-1,7-C2B10H10) via a four-centered transition state is proposed. The molecular structures of closo-9,10–12-1,7-C2B10H10, 1, and closo-9,10-(C6H5)2-1,7-C2B10H10, 10, have been determined. Crystallographic data are as follows: for 1, monoclinic, space group P21\c, a = 13.2719-(6) Å, b = 14.9718(6) Å, c = 13.4734(6) Å, β = 114.211(1)°, V = 2441.7(3) Å3, Z = 8, ϱcalcd = 2.15 g cm−3, R = 0.043, Rw = 0.064; for 10, tetragonal, space group I41\a, a = 9.446(2) Å, c = 39.949(8) Å, V = 3564.1(1) Å3, Z = 8, ϱcalcd = 1.10 g cm−3, R = 0.056, Rw = 0.063.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry