Tautomerism in silicon-containing free radicals

The Reaction of 3,6‐di‐tert‐butyl‐o‐benzoquinone with tin amalgam: Synthesis and structure of tin catecholato complexes

“…In previous papers [6,7], a number of osemiquinonate tin derivatives have been described using the reaction of tin metal or amalgam with 3,5-and 3,6-di-tert-butyl-o-benzoquinones. Authors [6] have proposed the formation of bis(osemiquinonato)tin(II) derivative on the basis of EPR spectroscopy data.…”

“…Authors [6] have proposed the formation of bis(osemiquinonato)tin(II) derivative on the basis of EPR spectroscopy data. But no evidence for such compounds was provided.…”

“…The X-ray analysis also confirms catecholate type of quinonoid ligands in 1, 2 and 5 (see below). All o-semiquinonate tin derivatives obtained in previous works [6,7] show EPR spectra with hyperfine coupling (hfc) constants with magnetic isotopes 117,119 Sn about 5-7 G. These values are typical for tin(IV) osemiquinonate species [9]. Paramagnetic tin(II) SCHEME 1 SCHEME 2 SCHEME 3 complexes have hfc constants with tin magnetic isotopes about 150 G [10,11].…”

“…The reaction between tin and o-chloranil in refluxing toluene produces bis(tetrachlorocatecholate)tin(IV) [5]. Different o-semiquinonate and catecholate tin species were postulated in reaction mixtures of tin and tert-butyl substituted o-quinones by use of various spectroscopic methods but no solid products were obtained [6,7].…”

Structure and Dynamics of Bis(triphenylphosphine)-3,6-di-tert-butyl-o-semiquinone Radical Anion Complexes of Ag+ and Cu+

“…10 The value a( 1 H) ) 3.17 G for the silver complex is close to the values of a( 1 H) ) 3.0-3.3 G for SQ •-radicals with alkali metals, 10 which shows that the O-Ag chemical bond in the silver complex is essentially ionic. For comparison, we can mention that, for 3,6-di-tert-butyl-2-Roxyphenoxide radicals (SQ • R) with covalent chemical bonds O-R, a( 1 H) > 3.90 G. 12,13,17 As can be seen from Figure 1, with the temperature lowering, the central component (with total value of nuclear spin projection ∑m I ( 1 H) ) 0) of the triplet due to the two protons experiences faster broadening than the components with ∑m I ( 1 H) ) (1. This can be visualized by noticing the change in the amplitude ratio of the proton triplet components in the EPR spectra (marked with dots in Figure 1) from 1:2:1 at high temperatures to about 1:1:1 at 190 K in toluene ( Figure 1).…”