3,5-Di-tert-butyl-3‘-(N-tert-butyl-N-aminoxy)-4-oxybiphenyl:  A Heterospin Diradical with Temperature Dependent Behavior

Abstract

The title diradical was synthesized and investigated by ESR and UV−vis spectroscopy. It was found to have a lifetime of weeks even in the presence of oxygen, and even survives brief heating in toluene up to about 60 °C. In the UV−vis spectrum, the diradical showed reversible thermochromic behavior in the −10 to 50 °C range. In the ESR spectrum, hyperfine analysis showed nearly isolated behavior by the phenoxyl and nitroxide spin carrying units. Upon warming, additional, broad lines appeared at the expense of the lower temperature lines. This temperature behavior was reversible over the 0 to 50 °C range, so long as the raised temperatures were not maintained for long time periods. The spectral behavior is interpreted as being due to temperature-dependent conformational effects on the exchange coupling between the spin carrying units, i.e., J-modulated exchange behavior.

Synthesis and characterisation of some novel hetero-diradicals containing linked hydrazyl and aminoxyl (nitroxide) moieties

“…We also found that the monoradicals and diradicals could be reduced to the corresponding parent hydroxylamine-hydrazines [11][12][13], using ascorbic acid, cysteine, glutathione or, even better sodium ascorbate, as judged by TLC, UV-Vis and EPR spectroscopy. The diradicals were found to be selectively reduced by hydroquinone to the corresponding monoradicals.…”

“…2-4], the bis-phenoxyl 5 and bis-semiquinone 6 and the bis-hydrazyl 7. [6][7][8][9][10][11][12][13][14] A much smaller number of hetero-diradicals have been reported; 15 some recent examples include the phenoxy-nitroxide 8 and the semiquinone-nitroxide 9. The vast majority of the diradicals so far described have either a conjugated bridge, as in 4, 9 or a very flexible link as in the bis-nitroxide 10 studied by Falle and Luckhurst.…”

Trends in Metal−Biradical Exchange Interaction for First-Row MII(Nitronyl Nitroxide-Semiquinone) Complexes

“…Ligand Design Elements. Heterospin organic molecules are those with multiple, different spin-containing moieties. ,,− To prepare robust, high-spin structures an active atom (one with positive spin density) of one radical group must be attached to an inactive atom (one with negative spin density) of another radical group. − This is the case for our NN-SQ ligand: nitronyl-nitroxides are known to have large negative spin density at the middle carbon of the ONCNO chain, and SQ has positive spin density at the C5 position …”

Syntheses of Sterically Hindered Zwitterionic Pyridinium Phenolates as Model Compounds in Nonlinear Optics

“…Boronic acid 16 was then synthesized according to the method published by Liao et al by lithium-halogen exchange in THF, followed by reaction with triisopropylborate at -78°C. [19] Finally, boronic acid 16 was converted into ester 7 at room temperature in THF by reaction with pinacol in the presence of molecular sieves. [20] Eventually, the synthesis of boronic ester 7 was performed in 57 % overall yield from bromoanisole 3 and in a 77 % yield from 2,6-di-tert-butylphenol.…”