Synthesis, structural characterization and electrochemistry of C,N-chelated organotin(IV) dicarboxylates with ferrocenyl substituents

A set of C,N-chelated organotin(IV) ferrocenecarboxylates, [LCN(n-Bu)Sn(O2CFc)2] (1), [(LCN)2Sn(O2CFc)2] (2), [LCN(n-Bu)Sn(O2CCH2Fc)2] (3), [LCN(n-Bu)Sn(O2CCH2CH2Fc)2] (4), [LCN(n-Bu)Sn(O2CCHdouble bond; length as m-dashCHFc)2] (5), [LCN(n-Bu)Sn(O2CfcPPh2)2] (6), [(LCN)2Sn(O2CfcPPh2)2] (7), and [LCN(n-Bu)2Sn(O2CFc)] (8) (LCN = 2-(N,N-dimethylaminomethyl)phenyl, Fc = ferrocenyl and fc = ferrocene-1,1′-diyl) has been synthesized by metathesis of the respective organotin(IV) halides and carboxylate potassium salts and characterized by multinuclear NMR and IR spectroscopy. The spectral data indicated that the tin atoms in diorganotin(IV) dicarboxylates bearing one C,N-chelating ligand (1 and 3-6) are seven-coordinated with a distorted pentagonal bipyramidal environment around the tin constituted by the n-butyl group, the chelating LCN ligand and bidentate carboxylate. Compounds 2 and 7 possessing two chelating LCN ligands comprise octahedrally coordinated tin atoms and monodentate carboxylate donors, whereas compound 8 assumes a distorted trigonal bipyramidal geometry around tin with the carboxylate binding in unidentate fashion. The solid state structures determined for 1⋅C6D6 and 2 by single-crystal X-ray diffraction analysis are in agreement with spectroscopic data. Compounds 1, 3–5, and 8 were further studied by electrochemical methods. Whereas the oxidations of ferrocene units in bis(carboxylate) 2 and monocarboxylate 8 proceed in single steps, compound 1 undergoes two closely spaced one-electron redox waves due to two independently oxidized ferrocenyl groups. The spaced analogues of 2, compounds 3–5, again display only single waves corresponding to two-electron exchanged.