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The radical cation and anion of the title compound were obtained either by treatment with mercury trifluorocatetate in trifluoroacetic acid or by reduction with potassium in tetrahydrofurane. For both species the ESR spectra indicated magnetic non-equivalence of the two phosphorus atoms, as well as of the two methyl groups. Spectra attributed to the corresponding spin adducts were also observed when reacting the title compound with in situ-generated alkoxyl and thiyl radicals. MO calculations carried out for both the ionic radicals and the neutral spin adducts led to questioning the actual nature of some of the latter species.

This paper is aimed at providing an overview of our studies on the title compounds as spin trapping agents, and at emphasising the links between purely cognitive, academic research and industrial applications. Phosphoryl- and thiophosphoryl-dithioformates exhibit a comparable and interesting spin trapping ability, their efficiency being analogous to that of some aromatic thioketones. The spectral hyperfine structure may provide valuable information on the nature of the trapped radical but the phosphorus hfs constant cannot be used as an useful indicator. Thionformates are less efficient spin traps than the corresponding dithioformates, being inert towards stabilised radicals such as benzyl or relatively hindered radicals as tert-butoxyl. In no case could spin adducts to thiolformates be detected, this being an indication that their carbonyl group is significantly deactivated with respect to that of organic and organometallic ketones. Because of their ability in trapping either alkyl or alkoxy radicals both kind of dithioformates were exploited as stabilisers in the processing of such polymers as polypropylene, but their outstanding performance could not compensate for some organoleptic drawbacks that were intrinsic of the thiocarbonyl function. A much more promising application of dithioesters is instead their use as RAFT chain transfer agents in the controlled polymerisation of styrene. Preliminary experiments with benzyl diethoxyphosphoryldithioformate have afforded polystyrene with a polydispersity as low as 1.17, but further studies are needed to fully elucidate the RAFT-polymerisation mechanism and to optimise its outcome.

Five new phosphoryldithioformates bearing different substituents on the phosphoryl group have been synthesised and exploited as spin trapping agents in ESR experiments. While the dilauroxy substituted compound led to the observation of ESR spectra indicating photolability of either the compound as such or of its radical adducts, the three diaryloxy-phosphoryl dithioformates exhibited an excellent spin trapping ability, thus proving an attractive alternative to previously described members of this family. This was also the case for the di(2-menthoxy)phosphoryl derivative which led in all cases to very persistent radical adducts. The low melt-flow index values measured in the extrusion of polypropylene with variable additions of some of the dithioformates investigated in this and in previous studies indicated that the tested compounds have a remarkable ability to act as process stabilisers.

The addition of silyl and germyl radicals to a series of substituted cyclopentenones and cyclohexenones has been investigated using EPR spectroscopy. At low temperatures the 3-position is the preferred site for addition unless it is substituted or sterically hindered in which case addition occurs at the carbonyl oxygen. The latter process is also favoured at higher temperatures but no evidence has been obtained for either addition at the 2-position or for an intramolecular migration following initial attack at the 3- or 2-position.

Electron paramagnetic resonance has been used to characterise free radicals formed by the reaction of photochemically generated tert-butoxyl radicals with a range of methyl substituted cyclopentenones and cyclohexenones. The spectra have been interpreted using computer analysis and simulation and assigned to cyclic allylic and alkyl radicals formed by abstraction of a hydrogen atom. The 1-oxocyclohept-2-en-4-yl radical derived by abstraction of bromine from 4-bromocyclohept-2-enone exhibits a temperature dependent EPR spectrum attributed to ring inversion.

The addition of a variety of radicals to triphenylmethyl l, allyl 2, benzyl 3 and but-3-enyl (diethoxyphosphoryl)dithioformate 4 has been investigated by EPR spectroscopy. Reactions with the first substrate always led to displacement of the triphenylmethyl radical; release of the allylic or benzylic moieties from 2 and 3 was observed above 243 K under photolytic conditions, while at lower temperatures or in the dark the adducts resulting from thiophilic addition of the radicals were detected. The weak EPR spectra detected when reacting dithioformates 1–4 and methyl(diethoxyphosphono)dithioformate 5 with Grignard reagents are attributed to the radical anions of the starting compounds and to their ion pairs with magnesium cations.

3,5-Di-tert-butylthiobenzoyltriphenylsilane (DBTBTPS) has been synthesized and tested as a spin trapping agent for electron spin resonance studies. Upon reaction with a variety of radicals of different nature inside the cavity of the ESR spectrometer, DBTBTPS leads to the observation of rather persistent spectra which in nearly all cases allow the unambiguous identification of the trapped species. DBTBTPS is somewhat less stable than thiobenzoyltriphenylsilane (TBTPS), the unsubstituted thiobenzoyltriphenylsilane; yet, as it affords spin adducts whose spectra are characterized by a smaller number of lines, it may prove more useful than TBTPS itself when dealing with radicals leading to species with a large number of magnetically active nuclei interacting with the unpaired electron.

The direct EPR detection of thioacyl radicals has been reported only once, while thioacyl nitroxides remain an elusive species. We failed to detect the thioacyl radicals from two thioaldehydes and from phosphoryldithioformates but have obtained EPR evidence that thioacyl radicals react with 2-methyl-2-nitrosopropane to give thiocarbonyloxyaminyls rather than thioacyl nitroxides. The results of DFT calculations support this unexpected reactivity of thioacyls, while making questionable their previous EPR identification.

ESR studies carried out during the reaction of ferrocenoylsilanes with Grignard reagents at low temperature led to the detection of the radical anions of the former compounds. Cyclic voltammetric experiments indicate that the observed radical anions are likely to originate through an inner-sphere electron transfer process. Different radical species were observed upon annealing, originating from destruction of the ferrocenyl moiety. Paramagnetic species were also detected on reacting ferrocenoylsilanes with LiAlH4. Copyright © 2004 John Wiley & Sons, Ltd.

The identification of the species observed by EPR spectroscopy in the SmI(2)-promoted coupling of N-(N', N'-dialkylaminoalkyl)benzotriazoles as substituted benzyl radicals is disputed on the basis of results obtained studying the model radical derived from tribenzylamine.

The reduction of a number of phosphoryl- and thiophosphoryl formates, monothioformates and dithioformates has been studied by means of cyclic voltammetry and EPR spectroscopy. The reduction potentials of all dithioformates are close to −1 V vs. SCE, and increase for S-alkyl monothioformates and even more for O-alkyl monothioformates. The radical anions of the compounds bearing the thiocarbonyl function have been characterised by means of EPR spectroscopy, whereas those of the compounds having the carbonyl function underwent decomposition before detection. Reduction at higher potentials led in most cases to the detection of paramagnetic dianions derived from fragmentation of the initially formed radical anions.

The paramagnetic species detected by EPR spectroscopy upon electrochemical reduction of bis(2,4,7-tri-tert-butyl-phenyl)-1,3-diphosphaallene in THF solution has been unambiguously identified as the title radical, the identi-fication being supported by DFT calculations

The radical ions from 5-nitrospiro[indoline-2,3′-naphthopyran]1, 8′-nitrospiro[indoline-2,3′-naphthopyran]2, and 5,8′-dinitrospiro[indoline-2,3′-naphthopyran]3 have been investigated electrochemically and by means of electron paramagnetic resonance spectroscopy.The first reduction potentials of these compounds reflect the position of the nitro groups and vary between –1.532 V for 1 and –1.273 V for 2vs. SCE, while 3 exhibits two reduction waves at, potentials similar to those of 1 and 2, suggesting no or very little interaction between the two moieties of the molecules. The oxidation potentials are dominated by the indolinic moiety increasing in the order 2 < 1 < 3.The reduction with butoxide in DMF leads to the EPR observation of the expected radical anions of 1 and 2, while the spectrum observed with 3 shows, against expectations, reduction of the indolinic moiety. Photoreduction with Bu4NBH4 in THF affords the radical anions of 2 and 3 but not of 1, the measured hfs constants being similar to those measured in DMF without light. Addition of in situ generated triphenylgermyl radicals to 1–3 affords rather persistent germyloxy-aminoxyls which give identical spectra both under UV irradiation and in the dark.

Some mechanistic considerations based on the results of an ESR spectroscopic study of the IBDA (iodosobenzene diacetate) induced iododecarboxylation of several aliphatic carboxylic acids are reported. Both acetoxy units in IBDA are replaced by carboxylate groups in the first step of the reaction, forming a hypervalent iodine complex which then undergoes homolytic photodegradation. The R. radicals deriving from decarboxylation of the starting acids have been trapped by means of thiobenzoyl triphenylsilane and identified using ESR spectroscopy.

The synthesis, solution behavior and photophysical properties of several heteronuclear bimetallic d/f complexes that utilise a Ru-II bis-terpyridine moiety as the sensitiser for Eu-III, Nd-III and Yb-III luminescence are reported and compared to a Gd-III analogue. The former compounds display sensitised emission in the visible and near-infrared (NIR) regions depending on the choice of the Ln(III) cation. We illustrate that sensitised lanthanide emission can operate by two distinctly different pathways that involve either the triplet ligand-centred ((LC)-L-3) excited state of the organic ligand or the triplet metal-to-ligand charge transfer ((MLCT)-M-3) excited state of the Ru-II complex. Owing to the electronic structure of this antenna and the higher density of metal-centred accepting states, a higher sensitization efficiency with Nd-III was observed than with Yb-III and Eu-III. Lastly, we have observed unusual sensitised emission from the upper (F-4(5/2), H-2(9/2)) excited state of Nd-III at approximately 800 nm, which we report here for the first time from a molecular species in solution.

A wide variety of radicals has been added to three relatively stable thiocarbonyl compounds, namely thiobenzoyltriphenylsilane (TBTPS), 2,4,6-tri-t-butylthiobenzaldehyde (TBTBA), and tris(trimethylsilyl)ethan-ethial or trisylthioaldehyde (TSTA), in order to test their ability to act as radical scavengers and the possibility of using them as spin-trapping agents. Reactions with radicals centred at elements from Groups IV to VI afforded in all cases persistent spin adducts which were studied by e.s.r. spectroscopy. In particular the adducts with TBTPS showed well resolved e.s.r. spectra for which the hyperfine pattern allowed in most cases an unambiguous identification of the trapped radical. The decay of some of the TBTA and TSTA adducts has been monitored, and the rate constants for the process determined. The rate of addition of the t-butoxyl and pivaloyl radicals to TSTA were also measured as (1.2 ± 0.5)× 107 and (1.9 ± 0.5)× 106 dm3 mol–1 s–1, respectively.