Synthesis and EPR Characterization of “Phosphaverdazyl” Radicals

Abstract

Two tetraazaphosphorines, 1,4,5,6-tetrahydro-1,5-dimethyl-3,6-diphenyl-1,2,4,5,6-tetrazaphosphorine 6-oxide (4) and 1,4,5,6-tetrahydro-1,5-dimethyl-3,3-diphenyl-1,2,4,5,3-tetrazaphosphorine 6-oxide (6), have been prepared and oxidized to form the corresponding stable “phosphaverdazyl” free radicals 5 and 7, respectively. Solution EPR spectra of both radicals were obtained, from which phosphorus hyperfine coupling values of 5.2 G for 5 and ca. 0.2 G for 7 were determined by spectral simulation. The very small value of the latter a(P) was rationalized on the basis of orbital symmetry arguments and infers a planar geometry of the heterocycle. In contrast, the larger a(P) for 5 is indicative of a nonplanar geometry at the phosphorus atom, consistent with structures of related verdazyl radicals. These results represent the first systematic foray into so-called “heteroveradazyl” radicals and demonstrate the utility of incorporating phosphorus as an additional probe for EPR studies.

Ruthenium(III) Catalysed Oxidation of L-Alanine by Alkaline Permanganate: A Kinetic and Mechanistic Approach

“…Such complex formation between substrate and catalyst has also been observed in earlier work [45][46][47][48][49]. This conclusion is supported by earlier observation [52][53][54] . The spectral evidence for complex formation between catalyst and substrate was obtained from the uv-vis spectra of the catalyst and a mixture of catalyst and aminoacid in the alkaline medium.…”

The Diversity of Stable and Persistent Phosphorus-Containing Radicals

“…In dilute solutions, solvation of the lithium cations of 11 occurs, which ruptures the cubic structure forming the solvent-separated ion pair 15 and a molecule of (THF) 3 LiI (27). In dilute solutions, solvation of the lithium cations of 11 occurs, which ruptures the cubic structure forming the solvent-separated ion pair 15 and a molecule of (THF) 3 LiI (27).…”

Can DFT calculations help the molecular designer to construct molecule based magnetic materials?

“…13 and prepared by Hicks et al The structures were unknown, but the ESR spectra gave valuable clues as to their actual geometries in solution. In 9 there is a significant hyperfine coupling of the unpaired electron to the nuclear spin of P [29] whereas in 10 there is no such coupling to phosphorus, but instead an interaction with the amine nitrogen via the N nuclear spin (well reproduced by a simulation of the spectrum) [30]. The question was; exactly what does this mean?…”