Ferracarborane Benzene Complexes [(η-9-L-7,8-C2B9H10)Fe(η-C6H6)]+ (L = SMe2, NMe3): Synthesis, Reactivity, Electrochemistry, Mössbauer Effect Studies, and Bonding

Abstract

The benzene complexes [(η-9-L-7,8-C2B9R2H8)Fe(η-C6H6)]+ (3a: L = SMe2, R = H; 3b: L = SMe2, R = Me; 3c: L = NMe3, R = H) were prepared by photochemical reaction of [(η5-C6H7)Fe(η-C6H6)]+ with carborane anions [9-L-7,8-C2B9R2H8]− (1a−c) followed by treatment of the (η-9-L-7,8-C2B9R2H8)Fe(η5-C6H7) (2a−c) ferracarboranes formed with HCl. Visible light irradiation of 3a with tBuNC or P(OMe)3 in acetonitrile results in replacement of the benzene ligand, giving the tris(ligand) derivatives [(η-9-SMe2-7,8-C2B9H10)Fe(ligand)3]+ (4, 5). The unsymmetrical carborane complex (η-9-SMe2-7,8-C2B9H10)Fe(η-9-NMe3-7,8-C2B9H10) (6) was obtained by photochemical reaction of 3a with 1c. The structures of 2a, 3aBPh4, and 6 were determined by X-ray diffraction. Temperature-dependent Mössbauer spectroscopy has been used to elucidate the hyperfine parameters and metal atom vibrational amplitudes in a number of these complexes. The redox activity of the ferracarboranes 2a,c and 3a,c has been investigated by electrochemical techniques and compared with that of the related cyclopentadienyl complexes. Electrochemistry gives evidence that the conversion of 2a−c to 3a−c can also be triggered by a two-electron oxidation followed by deprotonation. DFT calculations of the redox potentials and the respective geometrical changes were performed. Data on electrostatic potentials at iron nuclei suggest that anions 1a,c are stronger donors than Cp− in cationic complexes, but weaker donors in the neutral derivatives.