Aryl isocyanide complexes

The preparations of a number of rhodium(I) complexes of isocyanides, some of them new, have been described. The newtetrakis(methyl isocyanide) complex, [Rh(CNCH3)4], was isolated as salts of various anions from reactions of RhClj -3H20 or [(l,S-CgH,2)RhCl]2 and this isocyanide ligand (11), and several [Rh(CNR)4]+ alkyl and aryl isocyanide complexes (R= Bu, Pr, /)-C6H4C1, /.-CSH4CH3, and P-C6H4OCH3) have... 

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. 

Some aryl isocyanide complexes of the type [Cr(CNR)6]X3 (X = SbCl6, BET) have recently been reported. Details of the preparations and properties of these complexes are given in Table 3. 

N==Ca+—Aua which makes the isocyanide ligands susceptible to nucleophilic attack and has led to formation of carbene complexes, iminoalkyl complexes and catalytic conversion of isocyanides to formamidines using alkyl or aryl isocyanide complexes of gold(I).301,402 4(y7-409-415 A review of this significant work has been published.16... 

Cyanide, Alkyl Isocyanide and Aryl Isocyanide Complexes 128... 

All the isocyanides have 1 1 stoichiometry with the exception of MeC5H4 and R = 2,6-Me2CeH3 for which both the 1 1 and 1 2 adducts were obtained. Table 6 lists the isocyanide complexes and the vcnr frequencies in the infrared spectrum. The IR spectra showed that vcn increased shghtly for the alkyl iso cyanide complexes and decreased slightly for the aryl isocyanide complexes relative to vcn for the free ligands. The substituents on the cyclo-... 

Preliminary results on the photochemistry of aryl isocyanide complexes [Ru(CNAr)6], particularly for the cation with Ar = xylyl, indicate a more complicated mechanism than for [Fe(CNMe)6], where one simply gets ligand substitution via a reactive d-d excited state. In the ruthenium case this and a parallel TT-TT pathway may well operate in parallel. The range of rate constants for thermal substitution in pentacyanoruthenate(II) complexes [Ru(CN)5L]" is wide. 

In 1975 it was found that cationic aryl isocyanide complexes of rhodium(I) formed aggregates in solution via the formation of weak metal-metal interac-... 

One additional point should be discussed here, concerning the substantial emphasis that has been placed on the differences between alkyl and aryl isocyanides. It has been suggested, primarily on the basis of infrared evidence, that aryl isocyanides are better 7r-acceptors than alkyl isocyanides (90). Qualitatively this difference is easily rationalized. One can see that delocalization of charge into 7r -orbitals on an aryl ring in aryl isocyanide-metal complexes should be possible, whereas no such possibility exists for alkyl isQcyanide-metal complexes this means that aryl isocyanides should be better ir-acceptors. Of course, the simple qualitative model gives one no measure of the relative importance of this effect. 

More important than this, however, is the fact that until recently there have been no substantial differences observed in the chemistry of metal complexes of alkyl and aryl isocyanides. In general, the choice of which isocyanide to use seems to be made largely at random, dictated perhaps by convenience as much as any other factor. Lacking any substantial chemical differences between the two groups of complexes, one might wish to minimize, rather than emphasize, this comparison. However, several observations have recently been made which seem to substantiate the earlier conclusion. 

Reactions of the ferrocyanide ion with alkylating agents, and reactions of iron(II) salts with alkyl or aryl isocyanides, have led to complexes of several types including [FeLJ, [FeLjX], cis- and tranf-FeL4(CN)2 and FeL4X2 this chemistry is reviewed by Malatesta and Bonati (90). There has been some extension of this work. 

A closer look at the thermal behavior variation upon introduction of a second aryl ring (see Figure 8.5 for the behavior of the derivatives with a w-decyloxy chain) reveals very interesting features for the phenyl isocyanide complexes the melting and clearing temperatures decrease in the order Cl > Br > I. This is also the trend of the clearing points for biphenyl isocyanide complexes, but their melting temperatures follow the opposite trend that is, I > Br > Cl. 

Addition of disilanes to isocyanides is catalyzed by palladium complexes, giving A-substituted bis(silyl)imino-methanes (Equation (53)).132 A wide range of isocyanides including aryl isocyanides and alkyl isocyanides can take part in the reaction. However, it is important to note that tert-alkyl isocyanides hardly undergo the bis-silylation reaction. This low reactivity of / r/-alkyl isocyanides allows their use as spectator ligands in the catalytic bis-silylations. 

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