Chromium cyano complexes

The coordination chemistry of molybdenum reported during 1991 is reviewed, 20 as is the organometallic literature of the chromium triad reported during 1992.321 There is much material of interest in a review of chromium (II) based methods for C-C bond formation322 and a short review of recent developments in the use of chromium carbene complexes in organic synthesis.323 There is some material of interest in a review of peroxo and superoxo complexes of Cr, Mo and W324 and a review of chromium (III) cyano-am(m)ine complexes.325... 

When it is heated above 196°C, the mixture of this compound with chromium trioxide combusts. When it is submitted to friction or impact, the same mixture detonates violently. The same happens if it is heated with sodium nitrite. Nitrite gives rise to a detonation with potassium hexacyanoferrate (II) too. The dangerous site of these complex anions is the cyano group. 

In isolation the electron distribution in the trivalent chromium (III) ion consists of three unpaired electrons in the d shell, as indicated in line (a) of Table 5.1. In line (b) the six electron pairs donated to the central chromium atom by oxygen atoms of water molecules give rise to sp3d2 hybridisation. This is characteristic of an octahedral structure. A similar situation arises with the trivalent cobalt(III) complex in line (e), where each of the three t2g levels is doubly occupied by an electron pair from each cyano ligand. 

An interesting chromium system example is represented by complex 145. Addition of cyano-Gilman cuprates occurred with complete diastereoselectivity to give conjugate adducts 146 (Scheme 6.28). Interestingly, the opposite diastereomer was accessible by treatment of enone 145 with a titanium tetrachloride/Grignard reagent combination [71c]. 

Although the range of reported acidoammine/amine chromium(III) complexes is quite extensive, only a few such cyano species have so far been prepared, due mainly to the difficulties associated with the CN- anation of the appropriate aqua complexes. These difficulties stem largely from the ionization of coordinated water in the presence of CN-. This not only generates a leaving group of greater nucleophilicity but also makes complex... 

Thermal deamination of tris(ethylenediamine)chromium(III) complexes is a standard preparative method for cis- and trans-diacidobis(ethylenediamine) complexes421,422 and the thermal behaviour of the starting materials has been related to their crystal structures.423 The cyano complex cis-[Cr(CN)2(en)2]C104 in DMSO undergoes stepwise reduction III— 11 — I at the DME. The standard redox potential for the Cr /Cr11 couple is -1.586 V (versus SCE). 

As discussed above, the ligands that have been typically utilized for the preparation of chromium nitrides are multidentate. Consequently, ligand exchange reactions of such complexes are difficult and rare. Wieghardt and co-workers have reported such a process, however, for the synthesis of a nitrido chromium cyanide complex 43 (Eq. (13)) [18]. Thus, treatment of CrN(salen) 42 with excess sodium cyanide and tetramethyl ammonium chloride results in the formation of a six-coordinate penta-cyano chromium nitride [21]. 

Low electron density of the aromatic ring is also achieved by complex-ing with transition metals. In chromium tricarbonyl fluorobenzene, the fluorine is replaced by a cyano group under very mild conditions [93],... 

Chloroperoxidase catalysis by, 58, 302 in chlorination of pyrazoles, 57, 337 Chlorophyll, thioaldehyde synthetic intermediate to, 55, 3 Chlorosulfonyl isocyanate, reaction with 2-arylhydrazono-3-oxobutanoate, 59, 148 Chromatography, of [l,2,4]triazolo[l,5-a]-pyrimidines, 57, 106 Chrom-3-enes, see 2//-l-Benzopyrans Chromium tricarbonyl complexes of 3,5-diphenyl-l-(alkyl- or oxido-)-thiabenzenes, 59, 206, 227 indoles, lithiation of, 56, 181, 184 of pyridine, 58, 160 pyridines, lithiation of, 56, 230, 239 of 2f/-thiopyrans, 59, 227 Chromones, see l-Benzopyran-4-ones Cinnamonitrile, a-cyano-, condensations with thio-, seleno-amides, 59, 184, 186 Cinnoline, nitration, MO calculation, 59, 302... 

Cyano- and thiocyanato-complexes of chromium are also common. Among the more interesting of these is Reinecke s salt, NH4[Cr(NH3)2(SCN)4]H20, made by adding (NH4)2Cr207 slowly to melted NH4SCN, washing with, and recrystallising from, alcohol. The octahedral ion has the form shown in Fig. 246. 

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