2,2 ,6,6 -tetramethyl-l-piperidinyloxy

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... 

Sodium 4-oxy-2,2,6,6-tetramethyl-l-piperidinyloxy, TEMPONa, was used as a bifunctional initiator for the synthesis of PEO-fc-PS block copolymers [133]. Initially the ROP of EO was performed in THF at 60 °C to provide narrow molecular weight distribution chains with terminal TEMPO moieties. Using these functionalized PEO chains the polymerization of styrene was... 

Miktoarm stars of the A(BC)2 type, where A is PS, B is poly(f-bulyl acrylate) (PtBA), and C is PMMA [161] have been synthesized, by using the trifunctional initiator 2-phenyl-2-[(2,2,6,6-tetramethyl)-l-piperidinyloxy] ethyl 2,2-bis[methyl(2-bromopropionato)] propionate (NMP, ATRP) (Scheme 86). In the first step, a PS macroinitiator with dual < -bromo functionality was obtained by NMP of styrene in bulk at 125 °C. This precursor was subsequently used as the macroinitiator for the ATRP of ferf-bulyl acry-... 

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. ... 

The SFRP or NMP has been studied mainly using the stable free radical TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxy) or its adducts with, e.g., styrene derivatives. It is based on the formation of a labile bond between the growing radical chain end or monomeric radical and the nitroxy radical. Monomer is inserted into this bond when it opens thermally. The free radical necessary to start the reaction can be created by adding a conventional radical initiator in combination with, e.g., TEMPO or by starting the reaction with a preformed adduct of the monomer with the nitroxy radical using so-called unimolecular initiators (Hawker adducts). 

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). 

The structure of the 2,2,6,6-tetramethyl-l-piperidinyloxy intermediate, (I), provided by the author is illustrated below. 

TEMPO Tentagel Teoc TES Tf TFA TFFH 2,2,6,6-tetramethyl-l-piperidinyloxy PEG-grafted cross-linked polystyrene 2-(trimethylsilyl)ethoxycarbonyl triethylsilane trifluoromethanesulfonyl trifluoroacetic acid tetramethylfluoroformamidinium hexafluorophosphate, [(Me2N)2CF] [P F ]... 

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). 

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