Isonitriles cations

Closely related to the hexacyano species are the various isonitrile cations [Mn(CNR)6]+ and [Mn(CNAr)6]+, but these are covered in TreicheFs review.1... 

Since the cyanide anion is an ambident nucleophile, isonitriles R—NC may be obtained as by-products. The reaction pathway to either nitrile or isonitrile can be controlled by proper choice of the counter cation for the cyanide anion. 

Ligand A anionic (e.g., halides, pseudohalides, alkyl, aryl, thiolate, alkoxide) ligand N neutral (e.g., amines, imines, phosphines, carbenes, nitriles, isonitriles, NO, CO) ligand C cationic (e.g., NO+)... 

Iron(ii) complexes of ethylenedithiodiacetic acid, diethylenetrithioacetic acid, and ethylenetetrathiotetra-acetic acid have all been reported. " " Isonitrile and other complexes. Refluxing [Fe(CNMe) ](HSOj2 "hh excess methylamine for 12 h in methanol gives the cation [Fe(CNMe)gNH2Me] which can be precipitated as its PF salt. " The structure of this cation has been determined by X-ray methods and is shown in (52). The location of the protons was confirmed by n.m.r. and the suggested mechanism of formation is as shown. 

Direct reaction of the bis(isonitrile)gold(I) cations with alcohols or amines also gave the biscarbene complexes [Eq. (38)] (132, 141, 142). With bulky C6HnNC, only one carbene moiety was formed (141, 142) under the conditions employed in the preparation of the other biscarbene compounds. 

In contrast to the cationic complexes formed by the more polar isonitriles, e.g., [Co(CNR)s]+, [Mn(CNR)6]+ (12), carbonyl metal cations were for many years considered as incapable of existence. In 1961, however, E. O. Fischer et al. (53) characterized the hexacarbonylmanganese(I) cation [Mn(CO)6]+ from the reaction... 

More recently Behrens and co-workers15 were able to prepare the series of monocyano nitrosyl carbonyls by reactions such as equation (1). The Mn° compounds obtained in this work are listed in Table 6. Na[Mn(CN)(CO)3(NO)] dissolves readily in polar solvents such as water, ethanol, acetone or THF, but the solutions, even in the absence of light and air, are unstable. Crystalline salts, which are air stable, were obtained by adding such a solution to an excess of the appropriate cation. The related isonitrile species were prepared by alkylation of the cyano anions with R304. ... 

Cyanide ions react with the soft alkyl halides in SN2 reactions and with the hard carbocations in SnI reactions to give, almost always, the nitrile 4.27, which is thermodynamically preferred. Isonitrile products are formed along with the nitrile products when the cation is so reactive that the rate has reached the diffusion-controlled limit, and the reversible reaction that would equilibrate the products is too slow. One consequence when reactions are as fast as this is that there is a barrierless combination of ions, and selectivity is not then controlled by the kinetic factors associated with the principle of hard and soft acids and bases. 

Nucleophilic attack at the carbon of a coordinated isonitrile molecule in the complex cations [7r-C5H5Fe(CO)3, j(CNMe),(] (x = 1, 2) using QFjLi produced inter alia the imino derivatives [7r-C5H5Fe(CO)(L)C(C5F5)= NMe] (L = CO, CNMe). Chromatographic separation of the products gave the complex (L = CNMe) in two isomeric forms, shown by IR spectroscopy to arise from cis or trans orientation of the Al-methyl group... 

Addition of azide ion to nitriles, nitrilium ions and isonitriles The addition of the azide anion to nitriles is the most widely used route to 5-substituted tetrazoles (203). This reaction can prove highly sensitive to the nature of the cation and the type of solvent used. It is also sensitive to the nature of the substituent R of the nitrile and it works best when R contains electron-withdrawing groups. In hydroxylic or alcoholic solvents the reaction usually requires a few days at reflux temperatures and the yields may be medium or poor. The best conditions tend to be in dipolar aprotic solvents such as DMF, using ammonium azide as the source of azide ion. The work-up procedures... 

It should be mentioned briefly that solvation phenomena should also influence the outcome in the case of ambident nucleophiles, at least to the extent to which these reagents are sensitive to solvent effects. With an ambident anion, which is not manipulated by countercations (formation of ion pairs), the more electronegative center should attack preferentially. The more this area is blocked by hydrogen bridges formed in protic solvents, or shielded by countercations, the more likely it is that the less electronegative end will react. If dipolar aprotic solvents are used, which can only solvate the cations, a preferential attack of the nonshielded more electronegative center is to be expected. It must be realized, however, that in substitution reactions employing cyanide ions, dipolar aprotic solvents have not been reported to enhance the formation of isonitriles. " ... 

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