Liaison carbone-azote | EPFL Graph Search

En chimie, une liaison carbone-azote est la liaison covalente entre un atome de carbone et un atome d'azote. La liaison carbone-azote est l'une des liaisons les plus abondantes en chimie organique et en biochimie. Le carbone possède quatre électrons de valence et est la plupart du temps tétravalent, sauf dans les cas où il forme une liaison double (alcène, carbonyle, imine, etc.) où il devient trivalent, et les cas plus rares où il forme une liaison triple (alcyne, nitrile) où il devient divalent. Les composés où le carbone porte un doublet libre sont extrêmement rares et en général assez instables. L'azote possède cinq électrons de valence et dans les amines simples, il est trivalent, portant les deux électrons restant en doublet libre. Par ce doublet libre, l'azote peut former une liaison additionnelle avec un hydrogène (ion ammonium) ou une autre chaine alkyle (ion ammonium quaternaire) et dans ces cas devient tétravalent et porteur d'une charge positive. Beaucoup de composés de l

Synthetic methodologies for C-C and C-N bond formation involving alkyl radicals

Guido Barzanò

C-C and C-N bonds are some of the most common structures in molecules ranging from drugs to catalysts and to food additives. Many coupling reactions were developed to form these types of bonds with excellent selectivity and good performance. Still, the synthesis of some of those species either depends on traditional methods or requires expensive and rare reagents and catalysts. The use of precious metals in chemistry, and particularly in the industry, can make molecular synthesis expensive and energy-intensive since the extraction of those materials is costly. Moreover, in homogeneous catalysis, the recovery of metal-based catalysts is almost impossible, making these processes unsustainable for the future. Thus, the discovery of chemical reactions that donât involve precious materials is indispensable. This thesis concentrates on the development of two chemical transformations, one performing an sp2-sp3 radical reductive coupling, one performing a photocatalyzed alkyl amination, involving inexpensive reagents and catalysts. The first chapter reviews the existing methodologies which use alkyl radicals to form carbon-carbon and carbon-nitrogen bonds. Alkyl radicals are formed from alkyl halides and pseudo-halides (Acids, esters, tosylates, etc.) via oxidation or reduction performed by metal or photoredox catalyst. The wide variety of available methodologies was illustrated, highlighting the advantages and weaknesses of each reaction. The second chapter of this dissertation is devoted to the development of a new iron-based catalytic method to form stereoselectively Z-alkene boron species from the corresponding boron-alkyne. This novel stereoselective method opens a new way to obtain these types of molecules with cheap reagents, in high yields, with excellent stereoselectivity (Z:E ratio >10:1), and with good tolerance of functional group. The reaction is radical based, avoiding the problem of beta-hydride elimination, which usually occurs in ionic reactions involving metal centers. In order to prove the versatility of this method, the vinyl boron compound formed from this reaction was used for further functionalizations. The formal total synthesis of a 5-HT2c receptor agonist was successfully performed, improving the overall yield of the process, and avoiding the use of expensive and polluting chemicals. The third chapter of this thesis is concentrated on the development of a tandem photoredox/metal base catalyzed functionalization of anilines and imines with alkyl carboxylic esters. In this reaction, no late transition metal is used, and the traditional metal-based photocatalyst is substituted with an inexpensive and more efficient organic dye. The alkylation of amines is a challenging topic in organic chemistry and classical nucleophilic substitution lacks selectivity and scope. Harvesting visible light with a photoredox catalyst opens the possibility to a radical pathway, making this coupling easy and with high tolerance for functional groups. In order to understand the catalytic cycle of the reaction, additional mechanistic studies were conducted, leading to some insight on how this reaction works.

EPFL2020

Crystalline and Soft Materials Based on Dative Boron-Nitrogen Bonds

Nicolas Luisier

The thesis describes the utilization of dative boron-nitrogen bond is used for the construction of new materials. In chapter 2.1, the synthesis of new organogels based on bisimidazolyl ligands and diboronate esters is described. Gels with a critical gel concentration as low as 0.02 wt% were obtained. The high tunability of the system allowed the development of a light-responsive gel by means of an azobenzene spacer. Structural characterization was performed by electron microscopy, rheology and X-ray analysis to better understand the aggregation of the polymer components. The association of imidazole and arylboronate esters is investigated with isothermal titration calorimetry and NMR titrations. It is shown that the association constant of imidazole is on average two orders of magnitude higher than the one of pyridyl analogues. In the second part of this chapter, the simultaneous utilization of boronate esters, imine bonds and dative boron-nitrogen bonds was exploited for the fabrication of a four-component organogel in one step. It is demonstrated that each reversible interaction can be addressed selectively by using an appropriate stimulus. In one case, the mechanical resistance of the gel could be significantly increased by a transesterification reaction between two catechols. The synthesis of self-complementary monomers for the formation of supramolecular polymers in solution is described in chapter 2.2. Analysis by DOSY NMR revealed the formation of large assemblies from monomers composed of two imidazolyl end groups and one boronate ester. In the last chapter, the directionality of the boron-nitrogen bond is explored through the de-sign and synthesis of two new tripyridyl ligands and their coordination to diboronate esters. The formation of crystalline polymers is studied by X-ray crystallography. For the first time, polymers composed of chains of macrocycles based on boron-nitrogen bond are observed.

EPFL2016

Supramolecular polymers based on dative boron–nitrogen bonds

Nicolas Luisier, Kay Severin, Erin Sheepwash

Heteroditopic monomers containing an arylboronate ester and a dialkyl-4-aminopyridine group aggregate via dative boron–nitrogen bonds to give main chain supramolecular polymers. The degree of polymerization can be tuned by changing the electronic and steric properties of the boronate ester.