General Method for the Selective Functionalization of Cyclopentadienyliron Tricarbadecaboranyl Complexes via Halogenation and Sonogashira Coupling Reactions

A general method for the selective functionalization of cyclopentadienyliron tricarbadecaboranyl complexes has been developed that employs selective halogenation of the tricarbadecaboranyl ligand followed by Sonogashira coupling reactions. The reaction of N-chloro (NCS) or N-bromosuccinimide (NBS) with 1-(η5-C5H5)-2-Ph-closo-1,2,3,4-FeC3B7H9 (2) resulted in selective halogenation at the B6-boron of the tricarbadecaboranyl ligand to form 1-(η5-C5H5)-2-Ph-6-X-closo-1,2,3,4-FeC3B7H8 (X = Cl (3), Br (4)), respectively. 4 was also formed selectively by the reaction of 2 with Br2. The AlCl3-catalyzed reaction of 2 with ICl gave an easily separated mixture of 1-(η5-C5H5)-2-Ph-6-I-closo-1,2,3,4-FeC3B7H8 (5), 1-(η5-C5H5)-2-Ph-11-I-closo-1,2,3,4-FeC3B7H8 (6), and 1-(η5-C5H5)-2-Ph-6-I-11-I-closo-1,2,3,4-FeC3B7H7 (7). Reaction of 5 with terminal acetylenes in the presence of (PPh3)2PdCl2/CuI in Et2NH solvent yielded a series of acetylene-functionalized metallatricarbadecaboranyl complexes, 1-(η5-C5H5)-2-Ph-6-(RCC)-closo-1,2,3,4-FeC3B7H8 (R = Ph (8), (CH3)3Si (9), CH2OC(O)CH2CH3 (11), (η5-C5H4)Fe(η5-C5H5) (12)). 9 reacted with fluoride ion to give the deprotected acetylene complex 1-(η5-C5H5)-2-Ph-6-(HCC)-closo-1,2,3,4-FeC3B7H8 (10). The structures of 3−12 have been crystallographically determined.