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

Abstract

AbstractThe 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.