Redox reactions via outer sphere charge transfer complexation: the interaction of ferrocenes with σ- and π-type acceptors
作者:H.M.A. Salman、M.R. Mahmoud、M.H.M. Abou-El-Wafa、U.M. Rabie、R.H. Crabtree
DOI:10.1016/j.inoche.2004.07.023
日期:2004.11
Decamethylferrocene Cp-2*,Fe. ferrocene (Cp2Fe), 1,1'-dimethylferrocene. ((MeCP)(2)Fe), and 1,2-diferrocenylethane (Fc(2)C(2)H(4)) were studied as donors for charge transfer complexation with iodine (1,) as a typical sigma-type CT acceptor and with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and p-chloranil (CHL) as typical pi-type CT acceptors. Oxidation of the ferrocenes to the corresponding ferricinium salts is proposed to occur via initial formation of outer sphere charge transfer complexes. UV-Vis spectra for the mixtures of any of the ferrocene donors with 1, or DDQ in CH,C], showed the characteristic bands of the triiodide ion, V and the DDQ(.) anion radical. With CHL, the same behavior occurred only for Cp-2*Fe to give Cp-2*Fe+ and CHL. radicals. Elemental analyses of the isolated solid complexes indicated the formation of [ferrocene]I-3 for ferrocenes and I-2, except for (Fe2C2H4) which gave [(Fc(2)C(2)H(4))]I-5. Ferrocene-DDQ complexes were 1:1 except for (MeCP)2Fe and (Fc,C,H4) which gave 1:2 complexes. By using n-hexane as a non-polar solvent instead of CH2Cl2, the CT band of the Cp-2*Fe adduct has been observed and the formation constant for this CT complexation was found to be 3900 (+/-500) din 3 mol(-1). (C) 2004 Elsevier B.V. All rights reserved.