Investigations of the metal halide catalyzed alkylation reactions of pentaborane(9)

Article abstract of DOI:10.1021/om00156a011

A high-yield route to 1-(isopropyl)pentaborane(9) (1-(i-C₃H₇)B₅H₈) has been developed with use of the early-transition-metal halides HfCl₄ and ZrCl₄ as alkylation catalysts. Comparison studies of the effect of various catalysts and reaction conditions on the catalyzed propylation reaction are discussed. The ZrCl₄-catalyzed alkylation of pentaborane(9) (B₅H₉) with n-ClC₃H₇, i-ClC₃H₇, n-ClC₄H₉, s-ClC₄H₉, and various butenes produces 1-(alkyl)pentaborane(9) compounds in which the secondary alkyl isomer is favored irrespective of the alkyl source. The effect of the ZrCl₄ catalyst and Lewis bases on the isomerization of 1-(i-C₃H₇)B₅H₈ and 1-(n-C₃H₇)B₅H₈ to the other 1-(propyl)pentaborane isomer, and to 2-(propyl)penta-boranes, was also investigated. In the n-propyl chloride alkylation the isomerization of the propyl group appears to occur prior to substitution onto pentaborane, while in the isopropyl chloride case, the isomerization may arise from catalyst interaction with 1-(i-C₃H₇)B₅H₈. The utility of ZrCl₄ and HfCl₄ catalysts for B₅H₉ alkylation with MeCl, EtCl, cyclopentyl chloride, cyclohexyl chloride, CH₂Cl₂, and 2,3-Cl₂C₄H₈ was also examined.