2- imidazolium carboxylate

An analogous reaction was carried out with ter/-butyl alcohol to give the imidazolium carboxylate in 77% yield and the azido formic ester in 85% yield.[l37]... 

Analogously to these reactions of imidazolium carboxylates, the introduction of urethane-type amino-protecting groups can be accomplished with the following mesoionic azolides [194]... 

Reaction of imidazolide with carboxylic acid in a 1 2 ratio at room temperature leads to carboxylic acid antydride and imidazolium carboxylate. 

Scheme 5.4 Formation of 2-dialkyl-imidazolium-carboxylates following the Kolbe-Schmitt synthetic procedure [27].

Scheme 5.8 Formation of sodium carboxylates with 2-dialkyl-imidazolium-carboxylate as the C02-carrier [40].

Figure 4 Histograms of N O hydrogen bonding distances. A systematic dependence of N O distance on ApXa appears in these data. Both X-ray and neutron diffraction data are from the CSD. From top to bottom all N—H O imidazolium-carboxylate, ApXa 3 ammonium-cargoxylate, ApXa 5 amide-amide, ApXa 15 amide-water, ApXa 17. The pXa values used here are based on typical aqueous values.

RHODIUM AND IRIDIUM A-HETEROCYCLIC CARBENE COMPLEXES FROM IMIDAZOLIUM CARBOXYLATES... 

Charge-assisted (-l-)N-H...O(-) hydrogen bonds also promote the formation of ID chains comprising imidazolium and arenecarboxylate ions (Fig. 3f). If dicarboxylic acids are used, the ID chains can be stitched into 2D sheets by Speakman-type -COO . .. HOOC- hydrogen bonds [28]. The imidazolium-carboxylate hydrogen bond has also been used to construct a series of isostrucmral layered materials containing different transition metal ions [29]. 

The enthalpy of vaporization, estimated according to Zaitsau et al. [175] as shown above yielded the ce = Ay// - RT and the ced, which were then used for other purposes by Singh and Kumar [185]. This approach was also used by Xu et al. [202] to obtain the Ay// and values of four imidazolium carboxylate RTlLs... 

A novel synthetic route to NHC complex species involving C-C aetivation of imidazolium carboxylates was also characterized computationally, with the reaction being driven by the release of a CO2 molecule. 

N-oxides, KHSO5 and oxaziridines. Molecular oxygen can also be used in the presence of an electron source. The use of hydrogen peroxide often results in oxidative decomposition of the catalyst due to the potency of this oxidant. However, the introduction of chlorinated porphyrins (1) (Scheme 2.7) allowed for hydrogen peroxide to be used as the terminal oxidant [27]. These catalysts, discovered by Mansuy and coworkers, were demonstrated to resist decomposition, and when used together with imidazole or imidazolium carboxylates as additives, efficient epoxidation of alkenes were achieved (Table 2.3, entries 1 and 2). 

The use of stoichiometric ruthenium-NHC complexes generated in situ from [Ruljd-COCKp-cymene)], an imidazohnm salt [4] or an imidizol(idin)ium-2-carboxylate [4] has been applied in the cyclopropanation of styrene 5 with ethyl diazoacetate (EDA) 6 (Scheme 5.2). No base was necessary when imidazolium-2 carboxylate were employed. The diastereoselectivity was low and the cis/trans ratio was around 50/50 (Table 5.1). Although the diastereoselectivity was moderate, the reaction was highly chemoselectivity as possible side reactions (homologation, dimerisation and metathesis) were totally or partially suppressed. 

Carbamates by Reaction of Imidazole- or Imidazolium-iV-carboxylates. Introduction of Amino Protecting Groups... 

By use of TV-(trifluoroacetyl)- or TV-(trichloroacetyl)-imidazoleare obtained symmetric aliphatic and aromatic anhydrides even from carboxylic acids that do not form insoluble salts in benzene, ether, or THF (Table 13—1). In this case the acid is treated with the imidazolide in a 2 1 molar ratio, and an insoluble imidazolium trifluoro- or tri-chloroacetate is formed. 

Route A 1- is very convenient for the substitution of OH groups by bromide or iodide. The reaction conditions are relatively mild (acetonitrile, room temperature, and reflux for 1—3 h, neutral medium). The activating halide (methyl iodide, ally or benzyl bromide) is added in excess (5 equivalents) or in large excess (10 equivalents) when the resultant halide is nearly as reactive as the activating halide. The imidazolium-iV-carboxylates are the important intermediates, which undergo a displacement reaction to give the halides,... 

If vinylogous imidazole-A-carboxylates (route A) are treated with nucleophiles such as alkoxides or amines, the corresponding vinylogous carbonic esters or amides are obtained. While reaction of the vinylogous imidazole-TV-carboxylate with a thiol (route A) yields the addition product only, that of the corresponding imidazolium compound (route B) leads to the carbonic thioester in a substitution reaction [3]... 

On intuition, a minute amount of water was added to the solvent (ethyl acetate) in the first crystallization experiment containing a molar excess of imidazole corresponding to 1, Regularly shaped crystals were formed within one hour. Such a crystal, subjected to X-ray analysis, has the structure as shown in Fig. 41 U1). Apart from the formation of the expected salt-type associate (carboxylate-imidazolium ion pair, cf. Sect. 4.2.2), two water molecules are present in the asymmetric unit of the crystal structure. This fact called our attention again to the family of serine protease enzymes, where water molecules are reported as being located in the close vicinity of the active sites 115-120),... 

Instead, the conformational characteristics are explained by the stringent requirement of the ionic interaction between the carboxylate/imidazolium ion pair coupled with the attempt of the former group to maintain as many H-bonds as possible (e.g. four H-bonds, cf. Ref. 75c). Such an attempt is obviously supported by the intramolecular H-bond in 1 Im 2 H20. The geometry of the corresponding moieties indicates the presence of strongly interacting ionic species (Fig. 42). 

---