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

Abstract

Abstract:The potential valence tautomeric (VT) properties of bischelate complexes of group 14 elements with 2,6-di-tertbutyl-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 Si IV isomers with pseudotetrahedral coordination sites. Geometry optimizations of both lead bischelates I and II result in tetragonal-pyramidal Pb II structures. In the germanium complex I, the energy difference (5.2 kcal mol -1

Redox Isomerism in Main‐Group Chemistry: Tin Complex with o‐Iminoquinone Ligands

“…Data obtained indicate that dissolution of the diamagnetic compound 1a in toluene is accompanied by the occurrence of redox‐isomeric rearrangement, with the formation of 1b comprising the tin ion in oxidation state +2 and ligands in o ‐iminosemiquinonate form (Scheme ). Notably, previous quantum‐chemical calculations suggest that the diradical 1b should be preferable to the pseudotetrahedral diamagnetic 1a . However, as we can see, in a frozen matrix, the distribution of the diradical structure amounts to only 11 %.…”

“…We can assume two possible mechanisms for this interconversion of paramagnetic 1b into diamagnetic 1a . The repulsion of two sterically hindered o ‐iminosemiquinonate ligands and a lone pair from tin(II) leads to the distortion of the initial pyramidal geometry to a pseudotetrahedral one (predicted by calculations through MECP geometry). Such rearrangement causes the electron transfer from the divalent metal to the radical‐anionic ligands.…”

“…[7] Recently, we reported a quantum chemical investigation of the possibility of the occurrence of VT in group 14 (E = Si, Ge, Sn, Pb) element derivatives with redox-active o-indophenols and o-aminophenols. [8] It was shown that the bis-chelate tin complex 1, based on 4,6-di-tert-butyl-N-(tert-butyl)-o-aminophenol is characterized by a narrow energy gap (7.0 kcal mol -1 ) between the pseudotetrahedral 1a and the tetragonal-pyramidal 1b electromeric [9] forms and a low-energy barrier for their interconversion (11.7 kcal mol -1 ). Notably, according to the calculations, the diradical tin(II) structure 1b is a ground state with respect to the pseudotetrahedral diamagnetic 1b.…”

Multiple Reactivity of SnII Complexes Bearing Catecholate and o‐Amidophenolate Ligands

“…The presence of these compounds in the reaction mixture can be explained by symmetrisation of complexes 8 and 9 in solution with the subsequent formation of ( RO ) 2 Sn and diradical species of low‐valence tin – compounds 10 and 11 . Species 10 and 11 undergo intramolecular redox transformations, (Scheme ) to produce diamagnetic Cat 2 Sn(THF) 2 and AP 2 Sn · THF.…”

Structural Changes in Five‐Coordinate Bromido‐bis(o‐iminobenzo‐semiquinonato)iron(III) Complex: Spin‐Crossover or Ligand‐Metal Antiferromagnetic Interactions?

“…[1][2][3][4][5][6][7] Complexes of transition elements with such type ligands are important objects from the fundamental and applied points of view. Detailed investigation of magnetic properties, electrochemical and spectroscopic features allowed ones to discover such unique phenomena as redox-isomerism (or valencetautomerism), [3,[8][9][10][11][12][13][14][15] photo and termomechanical effects. [16,17] Moreover, o-benzoquinone and o-iminobenzoquinone complexes were found to demonstrate a spin-crossover effect [18][19][20][21][22][23] and different types of inter-or intramolecular magnetic exchange interactions.…”