Properties of Isocyanide Complexes

Figure 8.5 Thermal properties of gold complexes with isocyanides having a phenyl or a biphenyl core.

Synthesis and Properties of Isocyanide and Carbonyl Complexes of Silver 221... 

In the present account, the standard preparations and analytical procedures employed for certain groups of compounds are not recapitulated. The reader is rather directed to the more special properties of the complexes. Many of the simple compounds of isocyanides RNC with R = Me, Et, nPro, iPro, Ph, etc. were published in the early literature.2,3,5 Almost all of the later work is dedicated to complexes of ligands with R groups of a specific shape or functionality which allow an influence on the molecular properties or the association modes. 

Owing to the good ligand properties of isocyanides for complexation of gold(i), complexes of the type [(RNC)2Au]+X are readily available through a variety of synthetic routes. One new approach is the substitution of organic nitriles. The reaction is carried out in acetonitrile and gives quantitative yields (Equation (43)).2... 

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. 

Bocarsly and Mayr first reported the luminescence properties of transition metal alkylidyne see Alkylidyne) complexes [XW(CO)2(L2)(CPh)] (X = hahdes, L2 = TMEDA, (py)2 or dppe). The complexes exhibited broad and stmctureless emission bands at ca. 625-640mn, which was attributable to an excited state of MLCT (dxy(W) - 7r (W=C)) character. With an extension of the alkylidyne unit, the complexes [XW(CO)2 (L2) (C-C6H4-/ -(C=C-C6H4-/ -) -N=C)] (L2 = TMEDA, dppe n = 0, 1) containing an isocyanide moiety have been shown to possess rich luminescence properties. Perturbation of the absorption and emission properties of the complexes by coordination of the isocyanide moiety to metal-containing fragments such as/ac-ReCl(CO)3, cw-PdCb, trans-Vdh, and trans-Vth was also studied. 

Consequently the resistance of the complex to M—CNR bond breaking depends upon electronic configuration of the central atom, properties of isocyanide ligands, reagents that react with the isocyanide products, and properties of products. 

The isocyanide ligand, CNR, is formally isolobal with a carbene ligand. Several studies have investigated iron(Ill) porphyrin isocyanide complexes which have the general formula [FeCPorKCNR) ]. However, these studies have mostly been concerned with spin state and spectroscopic properties rather than chemical transformations and will not be discussed in detail here. Crystallographic details are given for two of the complexes. " ... 

The subjects of structure and bonding in metal isocyanide complexes have been discussed before 90, 156) and will not be treated extensively here. A brief discussion of this subject is presented in Section II of course, special emphasis is given to the more recent information which has appeared. Several areas of current study in the field of transition metal-isocyanide complexes have become particularly important and are discussed in this review in Section III. These include the additions of protonic compounds to coordinated isocyanides, probably the subject most actively being studied at this time insertion reactions into metal-carbon bonded species nucleophilic reactions with metal isocyanide complexes and the metal-catalyzed a-addition reactions. Concurrent with these new developments, there has been a general expansion of descriptive chemistry of isocyanide-metal complexes, and further study of the physical properties of selected species. These developments are summarized in Section IV. 

The existence of copper(I) isocyanide complexes is well documented, of course (90). Such complexes are basically straightforward, having stoichiometries and physical and chemical properties analogous to other copper(I) complexes. It would be somewhat surprising if the studies currently underway on the catalytic systems had not attempted to sketch in this relationship more precisely. No copper(O) isocyanide complexes are known, so such species if they exist here would be particularly interesting their stability is clearly low with respect to ligand dissociation, or they would have been isolated in these studies. 

Several papers have appeared recently comparing various properties of carbonyl metal complexes substituted by various phosphines or phosphite ligands or isocyanides. Angelici and Ingemanson (4) studied the equilibrium... 

Luminescent gold(l) acetylide complexes. Photophysical and photoredox properties and crystal structure of [ Au(C = CPh) 2 (p-Ph2PCH2CH2PPh2)]. Journal of the Chemical Society, Dalton Transactions, 2929-2932 (d) Che, C.-M., Wong, W.-T., Lai, T.-F. and Kwong, H.-L. (1989) Novel luminescent binuclear gold(I) isocyanide complexes. Synthesis, spectroscopy, and X-ray crystal structure of Au2(dmh)(CN)2 (dmb = 1,8-di-isocyano-p-menfhane). Journal of the Chemical Society, Chemical Communications, 243-244. 

Ionic LCs are interesting systems because they combine the properties of LCs with those of ionic liquids. Although alkali metal soaps were among the first thermotropic LCs to be systematically studied, ionic liquid crystalline derivatives have been reported less frequently than those based on neutral molecular and macromolecular species [39]. When the halide of [AuX(CNR)] complexes is substituted by a second isocyanide, ionic complexes [Au(CNR)2][Y] [R = C6H40C H2 + i (27a),... 

Coco, S., Fernandez-Mayordomo, C., Falagan, S. and Espinet, P. (2003) Effect of alkoxy chains on the mesomorphic properties of (p-alkoxy)tetrafluoroarylgold(I) isocyanide complexes. Inorganica Chimica Acta, 350, 366-370. 

No isocyanide complexes have been described for lower oxidation states, probably because the c-donating properties of this kind of ligand are too strong or the w-accepting properties too weak. 

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