Isocyanide ligands aryls

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... 

Given that the presence of three alkoxy chains in the phenyl group produces such a dramatic change in the properties of the material to the point that columnar mesophases are formed at room temperature, the structure of the aryl isocyanide ligand has been further modified to introduce more paraffinic chains, and examples of metallodendrimers containing monodendrons with an isocyanide group in the focal point, and its gold compound 9, have been reported [26]. 

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. 

Comparison between the half-wave potentials (equations 2 to 4) of [Cr(CNR)6](PF6)2, e.g. for R = Bu , -1.04, -0.28 and 0.84 V (versus SCE),22 with those for [Cr(CNPh)6](PF6)2, i.e. -0.35, 0.25 and 1.00 V,20 shows that alkyl and aryl isocyanides favour respectively the higher and the lower oxidation states as expected from the greater a-donor and weaker jr-acceptor capabilities of the alkyl over the aryl isocyanides. Similarly, the phosphines in the mixed ligand complexes (Table 3), 23 relative to isocyanide ligands, stabilize the Cr111 oxidation state. The great difference in the relative stabilities of Cr—C bonds in the cyano and phenyl isocyanide complexes is indicated by the magnitude of the shift (ca. 2.0 V) between the Cr(CN) "/Cr(CN)r (-1.130 V) and the Cr(CNPh)i+/Cr(CNPh)i+ reduction potentials.28... 

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... 

The labilisation of the coordinative bonds due to the strong cr-donation of the aliphatic isocyanide ligands in 25a,b, which has already been mentioned above, obviously also plays a role again in the reaction of 25a,b with aryl isothiocyanates (Scheme 7). The X-ray structure of 34c, L = Bu NC indicates a [3.2.0] bicyclic complex with a coordinated amido nitrogen and an uncoordinated imine nitrogen (A). However, temperature-dependent NMR spectroscopy indicates a dynamic competition of these two nitrogen atoms for the coordination site. As in all previous cases, the terminally coordinated aliphatic isocyanides do not insert in the initial bicyclo[2.2.1] cycloadduct, but rather an external isothiocyanate is inserted, most likely after precoordination by displacement of the imino group. 

Complexes of this type may contain a variety of orgaiuc residues R, such as alkyl, vinyl, alkynyl or aryl. The neutral donor group L is most commonly a tertiary phosphine or an isocyanide ligand, and polynuclear complexes with bridging polyfunctional donor ligands are also known . From a practical point of view, the series of organogold(I) and isocyanide complexes is of particular interest since some of its members hold promise as precursors for the chemical vapour deposition of gold films. A selection of these and other compounds of the type [RAuL] is presented in Tables 1-3. 

Many papers devoted to electrochemical processes of oxidation and reduction of metal isocyanide complexes have also appeared. It has been found that the ease of oxidation increases when the number of carbonyl ligands in the coordination sphere decreases and as a result of substitution of aryl isocyanides by alkyl isocyanides. Oxidation of [Cr(CNR)6] to [Cr(CNR)6] proceeds more easily in the case of alkyl isocyanides while reduction of Cr(II) complexes to Cr(I) compounds and Cr(I) complexes to Cr(0) compounds takes place more readily for aryl isocyanide ligands. " " " >... 

---