Sponge, proton

Let us start with the discussion of some charged and - for comparison - of some neutral systems exhibiting strong intramolecular formally symmetric NHN 

A recent IR spectroscopic study (solvent CD2CI2) indicated different vibrations for the pyridine and the pyridinium moiety [64]. The exchange rate was estimated to be between 10 and 10 s .  

2 Phenol-Carboxylate versus Carboxylic Acid-Phenolate Complexes 

In a first step, it was possible to identify the NMR parameters and UVA is bands of the complexes AHX of interest. Both single as well as dual UV/Vis absorption 

The finding that in a heteroconjugated anion embedded in a polar environment phenols transfer the proton to the carboxylates is rationalized schematically in 

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PhCH20CH2Cl, Nal, proton sponge [l,8-bis(dimethylamino)naphthalene], 84% yield. BOMBr can also be used. ... 

The Lewis acid of choice for most of the cyclization reactions is ethylaluminum dichloride, because of its exceptional properties it is a mild Lewis acid, and, as an organometallic compound, can serve as a proton sponge , and thereby inhibit competitive protodesilyla-tion37. The desired precursors reacted smoothly with 1.1 equivalents of ethylaluminum dichloride in toluene or dichloromethane at low temperature to generate diastereoselectively the desired spiro[4.5]decanones38. 

Larhed et al. investigated enantioselective Heck reactions with 2,3-dihydrofuran as alkene [86]. In the coupling with phenyl triflate, conditions previously reported by Pfaltz [87] were attempted under microwave irradiation. Interestingly, the catalytic system Pd2(dba)3/(4S)-4-t-butyl-2-[2-(diphenylphosphanyl)phenyl]-4,5-dihydro-l,3-oxazole, identified by the Swiss team, was found suitable for high-temperature microwave-assisted enantioselective Heck reactions (Scheme 76). Using a proton sponge as a base and benzene as a solvent gave the best conversions (Scheme 76). At tempera-... 

Compounds such as 2, 4, and 5 are known as proton sponges. Another type of proton sponge is quino[7,8-A]quinoline (6). Protonation of this compound also gives a stable monoprotonated ion similar to 3, but the steric hindrance found in 2, 4, and 5 is absent. Therefore 6 is a much stronger base than quinoline (7) (p/fg values of the conjugate acids are 12.8 for 6 and 4.9 for 7), but proton transfers are not abnormally slow. 

Evidence for an intermediate metaphosphorimidate is also provided by a three-phase experiment110b,139) treatment of a suspension of the two functionalized polymers 203 and 205 in dioxane with proton sponge leads to formal transfer of a phosphorodiamidate moiety from 203 to 205 with formation of 206. It appears... 

Reaction of Chlorodimethyl(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane with Silica Materials. Chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane (excess) was added to a mixture of amine-functionalized silica with hexanes in a drybox. 2,6-Di-tert-butylpyridine (excess) was added as a proton sponge. The mixture was allowed to react while stirring for 24 h. The solid was filtered and washed with hexanes and THF in the drybox. The solid was then contacted with another aliquot of chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l-yl)silane and the procedure was repeated. 

Behr JP (1997) The proton sponge A trick to enter cells the viruses did not exploit. Chimia 51 34-36... 

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