Syntheses of Functionalized Ferratricarbadecaboranyl Complexes

The reactions of nitriles (RCN) with arachno-4,6-C₂B₇H₁₂^- provide a general route to functionalized tricarbadecaboranyl anions, 6-R-nido-5,6,9-C₃B₇H₉^-, R = C₆H₅ (2^-), NC(CH₂)₄ (4^-), (p-BrC₆H₄)(Me₃SiO)CH (6^-), C₁₄H₁₁ (8^-), and H₃BNMe₂(CH₂)₂ (10^-). Further reaction of these anions with (η⁵-C₅H₅)Fe(CO)₂I yields the functionalized ferratricarbadecaboranyl complexes 1-(η⁵-C₅H₅)-2-C₆H₅-closo-1,2,3,4-FeC₃B₇H₉ (3), 1-(η⁵-C₅H₅)-2-NC(CH₂)₄-closo-1,2,3,4-FeC₃B₇H₉ (5), 1-(η⁵-C₅H₅)-2-[(p-BrC₆H₄)(Me₃SiO)CH]-closo-1,2,3,4-FeC₃B₇H₉ (7), 1-(η⁵-C₅H₅)-2-C₁₄H₁₁-closo-1,2,3,4-FeC₃B₇H₉ (9), and 1-(η⁵-C₅H₅)-2-H₃BNMe₂(CH₂)₂-closo-1,2,3,4-FeC₃B₇H₉ (11). Reaction of 11 with DABCO (triethylenediamine) resulted in removal of the BH₃ group coordinated to the nitrogen of the side chain, giving 1-(η⁵-C₅H₅)-2-NMe₂(CH₂)₂-closo-1,2,3,4-FeC₃B₇H₉ (12). Crystallographic studies of complexes 3, 5, 7, 9, and 11 confirmed that these complexes are ferrocene analogues in which a formal Fe²⁺ ion is sandwiched between the cyclopentadienyl and tricarbadecaboranyl monoanionic ligands. The metals are η⁶-coordinated to the puckered six-membered face of the tricarbadecaboranyl cage, with the exopolyhedral substituents bonded to the low-coordinate carbon adjacent to the iron.