Isocyanides hydrogen bonding

Coco, S., Espinet, E., Espinet, P. and Palape, I. (2007) Functional isocyanide metal complexes as building blocks for supramolecular materials hydrogen-bonded liquid crystals. Dalton Transactions, (30), 3267-3272. 

In this period, the most important reactions of the isocyanides were the formations of tetrazole derivatives from isocyanides and hydrazoic acid, a process introduced in 1910 by Oliveri-Mandala and Alagna, and then in 1921 Passerini introduced the reaction (P-3CR), which was the first 3-component reaction of the isocyanides. In the 1940s Baker,and later Dewar, proposed mechanisms of the P-3CR. The important role of the intermediate hydrogen bond between the carboxylic acid and the carbonyl compound in suitable solvents was mentioned. ... 

Scheme 3 Synthetic aspects of two conceptually different strategies for the introduction of piperazines via isocyanide based MCRs and two representative 3D conformations of 18A (blue) and 18B (cyan). An intramolecular hydrogen bond in compound 18B was shown in red dots...

Distinctly different is the solubility behaviour of poly(a-phenylethyl isocyanide), which can be dispersed truly by thermodynamic mixing. It is soluble is more than 40 solvents, as shown in the mode of representation following Hansen s treatment (27), (Fig. 5). The well known Hildebrand-Scott solubility parameter by this treatment is divided into three indices which separately account for cohesive energy contributions from dispersion, permanent dipole-dipole, and hydrogen bonding forces. Thus, the conventional Hildebrand-Scott parameter equals 9.56 (cal/cm3) for an unfractionated sample of poly(a-phenylethyl iso-... 

Initially, a loosely bound hydrogen bonded adduct 10 is formed, from the carboxyhc acid 8 and the carbonyl compound 6. The next step is the formation of the a-adduct 11 by reaction of the isocyanide with the nucleophilic carboxylate and the electrophilic protonated carbonyl compound. a-Adduct 11 then rearranges to give oc-acyloxy amide 9. 

Whether carbene, germylene, and silylene are justifiable terms for stabilized versions of the reactive species is a very debatable question [28], However, for synthetic chemists, the most important issue is to know whether these stable species feature the reactivity of transient carbenes. Formation of azaphospholidines upon thermolysis (intramolecular carbene insertion into a carbon-hydrogen bond), cyclopropanation reactions, and [l + l]-addition to isocyanides giving keteneimines... 

The mechanism of the Passerini reaction was widely examined. A plausible mechanism that is consistent with experimental data is as follows First, the carbonyl compound and the carboxylic acid forms a hydrogen bonded adduct. Subsequently, the carbon atom of the isocyanide group attacks the electrophilic carbonyl carbon, and also reacts with the nucleophilic oxygen atom of the carboxylic acid. The resulting intermediate cannot be isolated as it rearranges to the more stable a-acyloxycarboxamide in an intramolecular transacylation. 

While insertion of carbon monoxide into metal-hydrogen bonds is an elusive reaction, the analogous insertion with isocyanides and Pt-H compounds occurs readily. For example, [tmns-Pt(CNR)(H)L2]Cl undergoes a retroionization reaction and is converted to the corresponding formamidoyl complexes ... 

I. Alkorta, I. Rozas, J. Elguero. Isocyanides as hydrogen bond acceptors. Theor. Chem. Acc. 99, 116-123 (1998). 

The dimethyl 2-(ferf-butylamino)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahy-dro-4H-chromene-3,4-dicarboxylate was synthesized by the reaction of f erf-butyl isocyanide and dimethyl acetylenedicarboxylate with dime-done in cold CH2C12. Its structure was established by X-ray analysis which revealed that it was stabilized by one intramolecular hydrogen bond and the pyran ring had a distorted boat conformation (05MI545) Condensation of 1 with 2,3-disubstitutedamino-propenoates 454 or N-(2,2-dicyanoethenyl)-2,2-dimethylaminoethyl)aminoacetonitrile in acetic... 

Reviews. - In a recent review Alkorta et a/.191 discuss non-conventional hydrogen bonds (HB), which are much more exotic than the once unconventional C-H - O hydrogen bond. Their survey includes HBs such as C-H - C, where isocyanides, CO or carbanions and zwitterions act as HB acceptors. 

---