191734-12-0Relevant academic research and scientific papers
Synthesis, structures, and properties of encapsulated iron and cobalt metallocenes with highly isopropylated cyclopentadienyl rings
Burkey, David J.,Hays, Melanie L.,Duderstadt, Randall E.,Hanusa, Timothy P.
, p. 1465 - 1475 (1997)
Bis(triisopropylcyclopentadienyl)cobalt, [(i-Pr)3C5H2]2Co, and bis(tetraisopropylcyclopentadienyl)cobalt, [(i-Pr)4C5H]2Co, can be prepared from the reaction of K[(i-Pr)3C5H2] and K[(i-Pr)4C5H], respectively, with CoCl2 in THF. In contrast to [(i-Pr)3C5H2]2Co, solid samples of the encapsulated [(i-Pr)4C5H]2Co are indefinitely stable in air. Bis(triisopropylcyclopentadienyl)iron, [(i-Pr)3C5H2]2Fe, and bis(tetraisopropylcyclopentadienyl)iron, [(i-Pr)4C5H]2Fe, can be oxidized with NOBF4 to give the corresponding ferrocenium salts [(i-Pr)3C5H2]2Fe}-BF4 and {[(i-Pr)4C5H]2Fe}BF4 in high yield. Oxidation of [(i-Pr)3C5H2]2Co and [(i-Pr)4C5H]2-Co with NH4X (X = [PF6]-, [BPh4]-) yields the cobaltocenium complexes {[(i-Pr)3C5H2]2Co}X and {[(i-Pr)4C5H]2Co}X. The oxidation of [(i-Pr)4C5H]2M (M = Fe or Co) is significantly slower than that for [(i-Pr)3C5H2]2M. The single-crystal X-ray structures of the neutral [(i-Pr)3C5H2]2M metallocenes and cationic [(i-Pr)3C5H2]2M}+ and {[(i-Pr)4C5H]2M}+ metallocenes are reported. The structures of the bis(triisopropylcyclopentadienyl)metallocenes are undistorted, with nearly parallel rings and average M-C(ring) distances of 2.05(1) ([(i-Pr)3C5H2]2Fe), 2.08(2)-2.10(2) ({[(i-Pr)3C5H2]2Fe}BF4), 2.122(7) ([(i-Pr)3C5H2]2Co), and 2.05(2) ? ({(i-Pr)3C5H2]2Co}BPh4). In contrast, {[(i-Pr)4C5H]2Fe}BF4 and {[(i-Pr)4C5H]2Co}-PF6 display sterically induced distortions in the M-C(ring) distances (lengthened to 2.14(2) and 2.09(2) ?) and the inter-ring angles (ring normal-M-ring normal angles of 170.7° and 171.5°), making them the most distorted transition metal metallocenium complexes yet reported. The {[(i-Pr)3C5H2]2Co}0/+ and {[(i-Pr)4C5H]2Co)0/+ redox couples have essentially identical electrochemical potentials, despite the two additional electron-donating isopropyl substituents in the latter complexes. Additionally, oxidation of [(i-Pr)4C5H]2Fe is more favorable than expected for a ferrocene with eight alkyl groups. The anomalous electrochemical data can be attributed to the severe steric crowding that is present in the {[(i-Pr)4C5H]2M)0/+ complexes.
