Lewis bases 2,6-lutidine

Well-defined macromonomers of poly(BVE), poly(IBVE), and poly(EVE) with co-methacrylate end group [91] were prepared by living cationic polymerization of the corresponding monomers initiated by trifluoromethanesulfonic add in CH2C12 at -30 °C in the presence of thiolane as a Lewis base. After complete conversion, the polymers were quenched with 37 in the presence of 2,6-lu-tidine or with 41 to produce macromonomers with Mn up to 10,000 g mol-1, with narrow MWD, bearing one polymerizable methacrylate function per molecule. The same polymers were also quenched with 38 in the presence of 2,6-lutidine to give poly(vinyl ether)s with an allylic terminal group. 

In an important experiment, Mukaiyama and coworkers enolized carbonyl compounds under much milder conditions (low temperatures) with dialkylboryl triflate and a sterically hindered tertiary amine base such as 2,6-lutidine (2,6-dimethylpyridine) or diisopropylethylamine (DPEA).95-97 Less-hindered bases led to formation of a stable borane-amide complex (Lewis acid-Lewis base) and prevented the reaction with the carbonyl compound. Masamune et al,98 and Evans et a/.99100 carried out a study to investigate the reasons for the selective enolate formation. They showed that it depends on the boron ligand, base, solvent and the group attached to the carbonyl moiety. Ketones give (Z)-enolates with often excellent selectivity, whereas r-butyl thiolates give selectively the ( )-enolates (equations 32 and 33).100 101 Evans suggests that reactions with 9-BBN triflate are often under thermodynamic control.15 In equation... 

Ephritikhine and coworkers investigated the reactivity of U(III) metallocene towards various pyridine-based azine molecules and reported the Lewis base adducts [(C5H4R)3ULj (L = pyridine, 3-picoline, 3,5-lutidine, 3-chloropyridine, pyridazine, pyrimidine, pyrazine, 3,5-dimethylpyrazine and 5-triazine). Except in the cases of L = 3-chloropyridine, pyridazine, pyrazine and 5-triazine, the U(lll) center was found to be oxidized (Scheme 10) [ 145). 

The complexes [(C5H4-f-Bu)3UL] (L = pyridine, picoline) and [(C5H4SiMe3)3UL] (L = pyridine, lutidine, pyrimidine, and dimethylpyrazine) have been characterized by single crystal X-ray crystallography (Table 4). All the mononuclear complexes were found in the familiar pseudotetrahedral arrangement of the three ri -cyclopentadienyl ligands and the coordinated Lewis base. 

The conductivity of polymer 114 constituted by a Co(II)-salen-3,4-ethylenedioxythiophene polymer backbone has been shown to be sensitive when exposed to Lewis bases, such as pyridine and 2,6-lutidine [230]. This polymer was recently used as reversible chemoresistive sensor for nitric oxide (NO) [231] as well as catalyst for the reduction of O2 [232]. 

Other examples involve combinations of sterically hindered Af-heterocyclic Lewis bases and B(C5F5)3 that also form frustrated Lewis pair systems capable of activating hydrogen [153,154]. This was danonstrated, for example, for the lutidine-tri(pentafluorophenyl)borane system shown in Scheme 16.1. 

To prove their hypothesis, Bamford and Block (51) applied the diagnostic test previously designed by Gold and Jefferson (58) in their studies of hydrolysis of carboxylic anhydrides catalysed by tertiary bases. The technique employed involves the use of a series of tertiary bases having different relative abilities to assodate with Lewis acids and to act as Bronsted bases. Pyridine, a-picoline and 2,6-lutidine form... 

Similarly, Karge et al. [398] employed pyridine and 2,6-di-tert-butylpyridine to differentiate between internal and external acid sites of zeolite crystallites. In this respect, another possibility is the use of lutidine [139] or quinoline. The latter probe was employed by Corma et al. [693] for the determination of external Bronsted and Lewis acid sites of H, Na-Y and Al, Na-Y zeolites (cf. also [694,695]). For a characterization of the external Bronsted and Lewis acidity of ZSM-5 samples, Keskinen et al. [696] utilized as sufficiently bulky bases trimethylsi-lyldiethylamine and, like Karge et al. [398], 2,6-di-ferf-butylpyridine. For the discrimination of external from internal acid sites of shape-selective H-ZSM-5 catalysts,Take et al. [135] utilized pyridine andabulkytrialkylamine (e.g.,Et3N, n-Pr3N and n-Bu3N) as a pair of probes, with the former indicating the total amount of acid sites. For quantitative evaluation they determined the extinction... 

A widely used class of compounds are pyridine and alkylpyridines, including 2,6-lutidine, 2,4,6-coUidine, DTBP, quinoline, 4-methylquinohne, and 2,4-dimethyl-quinoline (565,582). These molecules interact with acidic hydroxyls through their N-atoms with formation of protonated species. Because they are strong bases, the possibility to extract protons from their original positions cannot be ruled out. An advantage (but in some cases disadvantage) of many pyri dines with bulky substituents is that, for steric reasons, they do not interact with Lewis acid sites through the N-atoms, or this interaction at least is hindered. 

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