2,2,6,6-Tetramethyl-l-piperidinyloxy radical

The current progress in the field of controlled radical polymerization has allowed polymer chemists to control some of the radical ROPs. In the first example of such controlled radical ROPs, nitroxyl radical (2,2,6,6-tetramethyl-l-piperidinyloxy TEMPO) was added to the ROP of 2-methylene-1,3-dioxe-pane. The polymerization afforded the corresponding polyester with polydispersity (Mw/Mn) as low as 1.2. Addition of TEMPO was also effective to control the ROP of SOE bearing... 

Developments in the synthesis and characterization of stable silylenes (RiSi ) open a new route for the generation of silyl radicals. For example, dialkylsilylene 2 is monomeric and stable at 0 °C, whereas N-heterocyclic silylene 3 is stable at room temperature under anaerobic conditions. The reactions of silylene 3 with a variety of free radicals have been studied by product characterization, EPR spectroscopy, and DFT calculations (Reaction 3). EPR studies have shown the formation of several radical adducts 4, which represent a new type of neutral silyl radicals stabilized by delocalization. The products obtained by addition of 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) to silylenes 2 and 3 has been studied in some detail. ... 

The Ir11 dimer [Ir(oep)]2 (oep = octaethylporphyrin) has been prepared in low yield by photolysis of (oep)IrCH3 in C6D6.473 This preparation has been improved by Chan et al.474, as shown in Reaction Scheme 24, where TEMPO = 2,2,6,6-tetramethyl-l-piperidinyloxy, free radical. The dimer undergoes several organometallic reactions, including oxidative addition of alkyl C 11 bonds and alkene insertions.475... 

Finally, the use of stable free radical polymerization techniques in supercritical C02 represents an exciting new topic of research. Work in this area by Odell and Hamer involves the use of reversibly terminating stable free radicals generated by systems such as benzoyl peroxide or AIBN and 2,2,6,6-tetramethyl-l-piperidinyloxy free radical (TEMPO) [94], In these experiments, styrene was polymerized at a temperature of 125 °C and a pressure of 240-275 bar C02. When the concentration of monomer was low (10% by volume) the low conversion of PS which was produced had a Mn of about 3000 g/mol and a narrow MWD (PDI < 1.3). NMR analysis showed that the precipitated PS chains are primarily TEMPO capped, and the polymer could be isolated and then subsequently extended by the addition of more styrene under an inert argon blanket. The authors also demonstrated that the chains could be extended... 

In 1993, Georges and coworkers [23,202,203] first succeeded in the synthesis of poly(St) with a narrow molecular weight distribution through the free-radical polymerization process of St. The polymerization was carried out in the presence of BPO and 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO) ... 

Chiral 2-imidazoline dianions undergo one-electron oxidation in the presence of TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy) to form a radical anion that is either trapped stereoselectively by TEMPO or undergoes dimerization. Oxidation of bis-diazene oxides leads to novel (9-stabilized 4N/3e radical cations and 4N/2e dications. These were detected by ESR spectroscopy and cyclic voltammetry. B3LYR/6-31G calculations confirmed the nature of the 4N/3e and 4N/2e systems. ... 

Dimerization of 4-monosubstituted-5(4//)-oxazolones 792 has been reported to occur in the presence of 2,2,6,6-tetramethyl-l-piperidinyloxy, free radical (TEMPO) to give the corresponding 4,4 -bis(oxazolones) 793 (Scheme 7.242). 

Chemicals AIBN CAN DIBAL DMAP DMSO HMPA LAH LDA mCPBA NBS NCS or PCC PDC Py TBAF TEMPO a.a -azobislisobutyronitrile) cerium(IV) ammonium nitrate diisobutylaluminium hydride 4-(dimethylamino)pyridine dimethyl sulfoxide hexamethylphosphoramide lithium aluminum hydride lithium diisopropylamide m-chloroperoxybenzoic acid A-bromosuccinimide A-chlorosuccinimide superoxide anion radical pyridinium chlorochromate pyridinium dichromate pyridine tetrabutylammonium fluoride 2,2,6,6-tetramethyl-l-piperidinyloxy free radical... 

Experimental evidence for the presence of radical intermediates is provided by the identification of expected products from radical rearrangements, by the use of appropriate radical probes and by direct detection by electron spin resonance (ESR). Other mechanistic evidence includes inhibition by radical traps, such as di-t-butylnitroxide (DTBN), TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy), galvinoxyl and oxygen, and by radical anion scavengers such as p-dinitrobenzene (p-DNB). 

The direct oxidation of hydroxyls on inulin allows the potential introduction of carbonyl and carboxyl groups, altering the properties of the polysaccharide and opening additional commercial applications (Bragd et al., 2004). The primary hydroxyl in the C-6 position on the fructofuranoside subunits can be selectively oxidized using 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO). This forms a stable radical that can be oxidized by hypobromite, or similar reagent, to give a nitrosonium... 

Inhibition by radical traps or radical anion scavengers has been extensively used in providing evidence for the mechanism with both aliphatic and aromatic substrates. The most commonly employed inhibitors are compounds that add irreversibly to radicals butylnitroxide (DTBN), 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO), galvinoxyl, etc.] and good reversible electron acceptors such as dinitrobenzenes (DNB) which intercept the radical anions38. 

A stable free radical polymerization using 2,2,6,6-tetramethyl-l-piperidinyloxy with maleic anhydride and styrene was used to prepared moderate molecular weight copolymers with polydispersities less than 1.5. Thermal re-activation of these copolymers in the presence of other monomers produced block polymers. 

Living radical dispersion polymerization is a promising way to expand the design and scope of functional polymer colloids to a wider range of other monomers. The 2,2,6,6-tetramethyl-l-piperidinyloxy (TEMPO)-mediated living radical dispersion polymerization of styrene has been carried out in presence of PS-h-P(PP-aZt-E) in decane at 135 °C [95] or PVP in alcohol-water at 130 °C [96] in order to produce microspheres with a very broad size distribution, consisting of relatively low molecular weight polystyrene (M =10 ) with M /Mn=l.l. 

Tetramethyl-l-piperidinyloxy (TEMPO), a nitroxy radical (Figure 10.3), is an effective catalyst for the oxidation of primary alcohols in the presence of secondary alcohols [9]. Iwabuchi and co-workers reported excellent catalytic activity of 2-azaadamantane-N-oxyl (1-Me-AZADO) towards a variety of alcohols. Oxidation of secondary alcohols was effected by means of 1 mol% of 1-Me-AZADO (Equation 10.4) [10]. 

---