Valence Tautomerism in Main-Group Complexes? Computational Modeling of Si, Ge, Sn, and Pb Bischelates with o-Iminoquinone Ligands

• Published in: European journal of inorganic chemistry 2016-01, Vol.2016 (2), p.252-258
• Main Authors: Chegerev, Maxim G., Starikova, Alyona A., Piskunov, Alexander V., Cherkasov, Vladimir K.
• Format: Article
• Language: English
• Subjects: Barriers; Computation; Density functional calculations; Germanium; Group 14 elements; Isomers; Ligands; Mathematical models; N,O ligands; O ligands; Silicon; Tautomerism; Tin; Valence isomerization
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201501155

The potential valence tautomeric (VT) properties of bischelate complexes of group 14 elements with 2,6‐di‐tert‐butyl‐4‐[(3,5‐di‐tert‐butyl‐2‐hydroxyphenyl)imino]cyclohexa‐2,5‐dienone (I) and 4,6‐di‐tert‐butyl‐N‐(R)‐o‐aminophenol (II, R = Ph and tBu) were studied computationally. According to DFT B3LYP/6‐311++G(d,p)/SDD calculations, the silicon complexes will be present as SiIV isomers with pseudotetrahedral coordination sites. Geometry optimizations of both lead bischelates I and II result in tetragonal‐pyramidal PbII structures. In the germanium complex I, the energy difference (5.2 kcal mol–1) between the electromeric forms allows the expectation of valence tautomerism, but the large energy barrier of the spin‐forbidden reaction (20.8 kcal mol–1) will complicate the occurrence of a thermally initiated redox process. Tin complex II (R = tBu) is characterized by a narrow energy gap between the tetragonal‐pyramidal and pseudotetrahedral electromeric forms (7.0 kcal mol–1) and a low energy barrier (11.7 kcal mol–1) for their interconversion and, therefore, may be considered as a promising candidate for the observation of thermally driven VT rearrangements. DFT B3LYP/6‐311++G(d,p)/SDD calculations are performed on a series of group 14 bischelate complexes with redox‐active o‐iminoquinone ligands. The possibility of valence tautomeric rearrangements between the tetragonal‐pyramidal and pseudotetrahedral electromeric forms of the tin compound with 4,6‐di‐tert‐butyl‐N‐(tert‐butyl)‐ortho‐aminophenol is shown.