Chromium complexes alkyl isocyanides

The metal-free eyclobutane-1,2-dioxime can be generated by oxidative displacement. It is interesting to note that, unlike ketene dimerization, head-to-head dimerization takes place here. The chromium ketenimine complex 20 is prepared by reaction of the Fischer-type chromium carbene complex with alkyl isocyanides.60 A cyclobutane-1,2,3,4-tetraimine 24 has been reported from the reaction of the ketenimine phosphonium ylide 22.61 Bisimine 23 has been proposed as the intermediate in this transformation. 

Some recent advances are the isolation of aryl isocyanide complexes of chromium(III) Cr(CNAr)6]X3, and six- and seven-coordinate alkyl isocyanide complexes of chromium(II) Cr(CNR)6j7]X2. All but the chromium(O) and the seven-coordinate chromium(II) complexes lave less than 18 electrons in the valency shell. 

There are Cr° and Cr complexes of both aryl and alkyl isocyanides (RNC) as well as cyanides because of their Cr-C linkages, these are described elsewhere see Chromium Organometallic Chemistry). 

Chromium(I) complexes, 702 alkyl isocyanides, 704-709 aryl isocyanides, 704-709 2,2 -bipyridyl, 709 electrochemistry, 713 electronic spectra, 712 ESR spectra, 712 IR spectra, 712 magnetic properties, 710 synthesis, 709 cyanides, 703 fluorophosphine, 716 isocyanides crystallography, 708 electrochemistry, 709 spectroscopy, 708 synthesis, 707 1,10-phenanthroline, 709 electrochemistry, 713 electronic spectra, 712 ESR spectra, 712 IR spectra, 712 magnetic properties, 710 synthesis, 709 tertiary phosphines dinitrogen, 713 tris(bipyridyl)... 

G. Simonneaux et al. (57) published the synthesis and complexation to ruthenium(II) and iron(in) m 5(9-tetraphenylporphyrins of two new fluorinated alkyl isocyanides, 2-monofluoroethyl isocyanide and 2,2,2-trifluoroethyl isocyanide. A new synthesis of trifluoromethyl isocyanide, pentafluoroethyl isocyanide and heptafluoropropyl isocyanide from R-N=Cp2 (R = CF3, C2F5, C3F7) using triphenyl phosphine has been reported (58). Geometries and HOMO and LUMO energies of fluorinated vinyl isocyanides have been calculated (59). Pentacarbonyl chromium complexes of both isomers of the first fluorinated diisocyanide, l,2-diisocyano-l,2,3,3,4,4-hexafluoro cyclobutane have been isolated from a [2+2] cycloaddition reaction of pentacarbonyl(trifluorovinyl isocyanide) chromium. The structure of the cis isomer has been elucidated by X-ray crystallography (60),... 

Among the types of complexes found here are formyl, acyl, alkyl, and aryl carbonyls, carbonyl cyanides," " carbonyl isocyanides and acetylides," and thiocarbonyl and seleno-carbonyl complexes." Of the greatest significance, however, are the chromium carbenes, for example, (CO)sCr=C(OR)R". This chemistry has been thoroughly reviewed " nevertheless, these compounds will be briefly discussed here. 

The nitrogen atom in a-ferrocenylalkylamines generally shows the same reaction pattern as that in other amines alkylation and acylation do not provide synthetic problems. Due to the high stability of the a-ferrocenylalkyl carbocations, ammonium salts readily lose amine and are, therefore, important synthetic intermediates. Acylation of primary amines with esters of formic acid gives the formamides, which can be dehydrated to isocyanides by the standard POClj/diisopropylamine technique (Fig. 4-16) [92]. Chiral isocyanides are obtained from chiral amines without any racemization during the reaction sequence. The isocyanides undergo normal a-addition at the isocyanide carbon, but could not be deprotonated at the a-carbon by even strong bases. This deviation from the normal reactivity of isocyanides prompted us to study the electrochemistry of these compounds, but no abnormal redox behaviour, compared with that of other ferrocene derivatives, was detected [93]. The isocyanides form chromium pentacarbonyl complexes on treatment with Cr(CO)s(THF) (Fig. 4-16) and electrochemistry demonstrated that there is no electronic interaction between the two metal centres. 

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