Binding and redox properties of iron(II) bonded to an oxo surface modeled by calix[4]arene

Article abstract of DOI:10.1021/ic991467h

The syntheses of the parent compounds [{p-Bu(t) - calix[4] - (O)₂(OR)₂}Fe - L] [R = Me, L = THF, 5; R = Bu(n), L = THF, 6; R = PhCH₂, L = THF, 7; R = SiMe₃, L = none, 8] have been performed by reacting the protonated form of the dialkylcalix[4]arene with [Fe₂Mes₄] [Mes = 2,4,6-Me₃C₆H₂]. All of them undergo one-electron oxidative functionalization. By use of different oxidizing agents, the following iron(III) derivatives have been obtained: [{p-Bu(t) - calix[4] - (O)₂(OR)₂}Fe - X] [X = Cl, R = Me, 9; X = I, R = Me, 10] and [{p-Bu(t) - calix[4] - (O)₂(OR)₂}₂Fe₂(μ-X] [X = O, R = Me, 11; X = O, R = Bu(n), 12; X = S, R = Me, 13], 9 and 10 being particularly appropriate for a further functionalization of the metal. The last three display typical antiferromagnetic behavior [J = - 78.6 cm^-1, 11; J = - 64.1 cm^-1, 13]. In the case of 7 and 8, the reaction with O₂ led to the dealkylation of one of the alkoxo groups, with the formation of a dimeric iron(III) derivative {[μ-p-Bu(t) - calix[4] - (O)₃(OR)}₂Fe₂] [R = PhCH₂, 14; R = SiMe₃, 15] [J = - 9.8 cm^-1]. The reaction of the parent compounds with Bu(t)NC and diazoalkanes led to the formation of [Fe = C] functionalities supported by a calix[4]arene oxo surface. The following compounds have been isolated and characterized: {[p-Bu(t) - calix[4] - (O)₂(OR)₂}Fe = CNBu(t)] [R = SiMe₃, 16, v(CN) = 2175 cm^-1], {[p-Bu(t) - calix[4] - (O)₂(OR)₂}Fe = CPh₂] [R = Me, 17; R = PhCH₂, 18; R = SiMe₃, 19]. The three carbene complexes 17 - 19 display quite an unusual high-spin state, which is a consequence of the formation of a weak π interaction between the metal and the carbene carbon, as confirmed by the extended Huckel calculations. The carbene functionality has been removed from the iron center in the reaction with O₂ and HCl. The proposed structures have been supported by X-ray analyses of complexes 8, 9, 12, 14, 16, 17, and 19.