Copper complexes isocyanide

Figure 41 The copper isocyanide complexes 103 and 104.104 reproduced with permission from ACS publications.

A 2-propenylidene transfer reaction utilizing vinyldiazomethane has been examined under copper-catalyzed conditions. Cu(OTf )2 and Cu(acac-F6)2 have been found to be the catalysts of choice Dichloropropenes transfer 2-propenylidenes to electron-deficient double bonds upon treatment with a copper-isocyanide complex ... 

Copper-vinylcarbenoid intermediates are probably involved in the condensation of allylidene chlorides with electron-poor olefins, mediated by copper isocyanide complexes. ... 

A copper-isocyanide complex functions as a selective catalyst in the Michael reaction, preferentially activating acrylonitrile and its homologues to nucleophilic attack. 

While on the subject of reviews, attention should also be directed to a very recent collection of articles on isocyanide chemistry edited by Ugi 156). This volume is oriented somewhat toward the organic chemistry of isocyanides, but not with the complete exclusion of metal complexes of these species one is directed in particular to the chapters by Vogler (Chapter 10) on coordinated isocyanides and by Saegusa and Ito (Chapter 4) on a-additions to isocyanides. These latter reactions are often catalyzed by copper(I) compounds and occasionally by other metal complexes as well, and it is believed that this catalysis is accomplished by intermediate formation of metal isocyanide complexes. 

Various a-addition reactions are observed to be metal- or acid-catalyzed, or to be uncatalyzed. In this review only the metal-catalyzed reactions will be discussed, since it is generally assumed that metal isocyanide complexes are involved in these systems. A number of metal-catalyzed a-addition reactions have been mentioned recently. Copper(I) oxide seems to be the most commonly used catalyst, although other metal complexes sometimes are satisfactory. Table III presents a partial survey of this work. 

Some infrared data on these catalytic systems also support the intermediate complex formation (123). For a heterogeneous system of Cu metal and cyclohexyl isocyanide one observes, in solution, a vcn absorption at 2180 cm , compared to 2140 cm for the free isocyanide. Absorptions at 2181 and 2192 cm for the systems with CujO and CuCl, respectively, are measured. The solutions in each case have catalytic activity. The suggestion is made that either a copper(O) complex (from Cu metal) or copper(I) isocyanide complex (from CU2O or CuCl) is the catalytic species present. 

It is reported that the intermediate species in the CujO-Icrt-BuNC reaction system can undergo reactions with cyclopentadiene or with indene. The products obtained are C5HjCu(CNBu ) and indenylCu(CNBu )3 132). The postulate that a copper(I) isocyanide complex is the reaction intermediate here is reasonable. 

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. 

There are scattered reports on isocyanide complexes of other metals including copper and gold, vanadium, and several lanthanides and actinides. 

The colorless, diamagnetic copper(I) complex Cu(acac)(CNPh)2 is formed from copper(I) acetylacetonate and phenyl isocyanide (103). The copper(I) complex (CuCl)2(CNCjH,)2pip was isolated (124) it decomposes to C5H, oNCH=NCgH 11. Primarily on this basis, copper(I) complexes are presumed to be intermediates in various -addition reactions to isocyanides (Section III,D). 

Benouazzane, M., Coco, S Espinet, P. and Barbera, J. (2001) Supramolecular organization in copper(I) isocyanide complexes Copper(I) liquid crystals from a simple molecular structure. Journal of Materials Chemistry, 11, 1740-1744. 

Isocyanide complexes of phenylethynyl-, indenyl-, and cyclopentadi-enyl copper have been isolated 86, 172, 246). Organocopper-isocyanide complexes are assumed to be intermediates in certain organic syntheses (245-252). Isocyanides also insert into the aryl-copper bond 281d) [Eq. (35)]. 

A cyclopentadienylcopper-fcr/-butyl isocyanide complex catalyzes the Michael addition of dimethyl methylmalonate to acrylonitrile at room temperature to give an S6% yield of the adduct 249). As the CU2O—BNC complex can also catalyze the addition of indene to methyl acrylate, the intermediate is most likely an organocopper complex. The reactions and kinetic data support the mechanism given by Eq. (118) to (120), involving metalation and nucleophilic attack by the carbanion on the olefin within the complex. Displacement of a solvent ligand by the olefin and coordination of the latter to the copper species are essential features of the mechanism. The rate of reaction is decreased if the compound with the... 

A suspension of polymeric cupric dimethoxide in pyridine reacts with CO2 to yield the cupric methyl carbonate. The CO2 moiety is, however, very labile the insertion could be reversed by heating the reaction mixture at 80" under a stream of nitrogen [SO]. Another reversible carbon dioxide carrier was found in copper(I) rerr-butoxide, which was stabilized by rerr-butyl isocyanide. The rerr-butyl carbonato complex was formed during the reaction with CO2 [811. Carbon dioxide also reacts with ROCu(PPh3)2 0 produce (ROCOj)Cu(PPhj>3, Hydrolysis or thermolysis of these alkylcarbonato complexes gives the binuctear carbonato copper (I) complex (PPhj>2 CuCK Oj Cu(PPhj)2, which can be further convened into the bicarbonate complex f(HC)C02)Cu(PPh3)3] by reaction with CO2 in moist solvents [82],... 

Polymeric complexes are formed when copper(I) cyanide reacts with ammonia or alkyl and aryl isocyanides. The ammine complex consists of Cu-C-N-Cu-C helices linked by metal-metal bonds to form sheets. The NH3 ligands bond normal to the copper atoms and interlock with NH3 protrusions of other sheets (94). Complex CuCN(Bu"NC) is polymeric (272), and the ethyl, propyl, and 2-butyl isocyanide complexes are also known (139). 

Unlike the different behaviour of iron and copper complexes of cyanides, the corresponding isocyanide complexes behave similarly. 

Despite being three-coordinate in the solid, (18) (20), (30), (31) or other compounds closely related to (g) (11), " " (19) and (30) will readily add a monodentate ligand such as Cl , CO, MeCN, or PPhs, or an endogenous alkene, imine, phenoxide, or thioether donor, to afford four-coordinate products. This affinity for a fourth donor mimics the ability of CO and isocyanides to bind to the Cuh site. " However, given the spectroscopic inertness of Cu(I), this affinity for exogenous ligands means that (8)-(31) cannot be assumed to be three-coordinate in solution, particularly in donor solvents such as MeCN. Compounds (8)-(ll) and copper(I) complexes of several other A-alkyl- A(2- pyrid-2-yl ethyl)amines, (13), ... 

Indeed, some copper-pyrazolato complexes allowed the catalytic oxidation of organic substrates such as primary and secondary amines, isocyanides and phosphines in mild conditions. 

At present, this method is often used for the preparation of isocyanide complexes. During reaction, the addition of the ligand may take place without the change of the oxidation state. However, in many cases, reduction of the metal occurs, and complexes in which the transition element has a lower oxidation state than the starting compound are obtained. Copper (I) salts coordinate one to four RNC molecules to give [CuX(CNR) ] and [Cu(CNR)4]X. Copper(II) salts are readily reduced by isocyanides to Cu(I) compounds. However, copper(II) chlorate or tetrafluoroborate and tert-dikyl isocyanide give the cationic complex [Cu(CNR)4]X2. This compound must immediately be separated from the reaction mixture in order to avoid its reduction. 

Isocyanide complexes of copper, silver, and iron decompose to give off free isocyanide ligands while heated, for instance,... 

Coco, S., Cordovdla, C., Donnio, B., Espinet, P., Garda-Casas, M.J. and Gudlon, D. (2008) Self-Organization of Dendritic Supermolecules, Based on Isocyanide-Gold(I), -Copper(l), -Palladium(II), and -Platinum(ll) Complexes, into Micellar Cubic Mesophases. Chemistry - A European Journal, 14, 3544-3552. 

The cyanide ion is an ambident nucleophile and isocyanides may be side products. If the preparation of isocyanides is desired, they can be made the main products by the use of silver or copper(I) cyanide1577 (p. 368). Vinylic bromides can be converted to vinylic cyanides with CuCN,1578 with KCN, a crown ether, and a Pd(0) complex,1579 with KCN and a Ni(0) catalyst,15 1 or with K4Ni2(CN)6.1581 Tertiary halides can be converted to the corresponding nitriles by treatment with trimethylsilyl cyanide in the presence of catalytic amounts of SnCl4 RjCCl + Me3SiCN — R3CCN.1582... 

Reaction of the Schiff base ligand A,Ar -bis(o-diphenylphosphinobenzylidene)(ethylene-diamine (49 en=P2) with AgBF4 produced a pale yellow salt. The IR spectrum of this complex showed strong bands due to the imino and BF4 group (v(C=N) 1653 cm-1, v(BFj) 1080 cm-1). The crystal structure of the Cu1 analogue was reported and the copper ion was found to adopt a severely distorted tetrahedral geometry. This strain was manifested in its reactivity since both the copper and silver complex reacted with f-butyl isocyanide. In the case of silver(I) a five-coordinate adduct was obtained, [Ag(en=P2)(Bu NC)]BF4.396... 

Copper(I) pyrazolates react with neutral ligands (L), such as 1,10-phenan-throline and cyclohexyl isocyanide, giving binuclear complexes of general formula [Cu(pzXL)]2.9,10 Solutions of [Cu(dmpz)]3 in pyridine rapidly absorb oxygen in the presence of water, giving the blue octanuclear hydroxo-... 

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