SYNTHESIS AND ELECTROCHEMISTRY OF IRON(II) CLATHROCHELATES

A series of clathrochelates of iron(II) has been prepared from various dioximes (cyclohexanedione dioxime, dimethylglyoxime, and diphenylglyoxime) and boron capping agents (boron halides, borate esters, and boronic acids). New synthetic routes have been developed to introduce various boron substituents (e.g. chloro, bromo, methyl, and hydrido) into these complexes. Cyclic voltammetric studies reveal a pseudoreversible redox couple (Fe(II)/Fe(III)), the potential of which varies over 280 mV as the substituent on the boron cap is changed. The correlation of this potential shift with the Hammett σp parameters of the boron substituents has led to a division of the complexes into two groups (group I = Br, CI, F, OH, OCH3; group II = CH3, H, C6H5, n-C4H9). Both groups show essentially linear redox potential behavior within their group with respect to the Hammett σp parameters. Attempts to correlate the 11B NMR shifts with the redox potential of the Fe(II)/Fe(III) couple have failed to produce interpretable results. Controlled-potential electrolysis studies have not produced stable Fe(III) species. Decomposition occurs during the course of electrolysis, generating electroactive products as evidenced by very large n values (>10). The B-H-capped clathrochelate exhibits remarkable stability in acidic media. Material isolated from refluxing glacial acetic acid (67 h) still possesses a B-H bond as evidenced by infrared studies (vB-H = 2485 cm-1). 11B NMR studies of this complex reveal a crude doublet centered at -13.76 ppm vs. B(OCH3)3; JB-H = 120 Hz. © 1985, American Chemical Society. All rights reserved.