Synthesis of Mono- and Dihalogenated Derivatives of (Me2S)2B12H10 and Palladium-Catalyzed Boron-Carbon Cross-Coupling Reactions of the Iodides with Grignard Reagents

Two series of compounds, 9-X-1,7-(Me 2 S) 2 B 1 2 H 9 and 9,10-X2-1,7-(Me2S) 2 B 1 2 H 8 (X = Cl, Br, I), have been synthesized from reactions of 1,7-(Me 2 S) 2 B 1 2 H 1 0 with various halogenating reagents. In addition, reactions of 1,7-(Me 2 S) 2 B 1 2 H 1 0 with 2,4-(NO 2 ) 2 C 6 H 3 SCl and PhSeBr resulted in 9-(2',4'-(NO 2 ) 2 C 6 H 3 S)-1,7-(Me 2 S) 2 B 1 2 H 9 and 9,10-(PhSe) 2 -1,7-(Me 2 S) 2 B 1 2 H 8 , respectively. X-ray studies of the dibromo, monoiodo, and aryl thioether derivatives show that electrophilic substitution in 1,7-(Me 2 S) 2 B 1 2 H 1 0 takes place at positions 9 and 10, as in the case of the metacarborane 1,7-C 2 B 1 0 H 1 2 . From 1,12-(Me 2 S) 2 B 1 2 H 1 0 the halides 2-X-1,12-(Me 2 S) 2 B 1 2 H 9 (X = Br, I) were prepared. For both 1,7-and 1,12-(Me 2 S) 2 B 1 2 H 1 0 the best iodination results were obtained using iodine monochloride in refluxing acetonitrile. In the presence of 5 mol % (PPh 3 ) 2 PdCl 2 the iodides 9-1-1,7-(Me 2 S) 2 B 1 2 H 9 , 2-1-1,12-(Me 2 S) 2 B 1 2 H 9 , and 9,10-I 2 -1,7.(Me 2 S) 2 B 1 2 H 8 react with RMgX (R = Me, Ph, Bn; X = Cl, Br) in THF to yield the corresponding B-alkyl-and B-aryl-substituted products in good yields without using Cul as a cocatalyst. The bromo derivative 9-Br-1,7-(Me 2 S) 2 B 1 2 H 9 did not react under similar conditions. No interference from the nearby Me 2 S substituent was observed in palladium-catalyzed substitution of iodide in 2-1-1,12-(Me 2 S) 2 B 1 2 H 9 . Presumably due to the intramolecular activation of an aryl C-H bond of the benzyl substituent in the inermediate palladium complex, the yield of 9,10-Bn 2 -1,7-(Me 2 S) 2 B 1 2 H 8 was significantly lower than those of the dimethyl and diphenyl derivatives. The molecular structures of 9-R-1,7-(Me 2 S) 2 B 1 2 H 9 (R = Ph, Bn) and 2-Bn-1,12-(Me 2 S) 2 B 1 2 H 9 were obtained by single-crystal X-ray analysis.