Reactions of Isocyanide Complexes

The reaction of isocyanide complexes with nucleophiles gives metal-carbene complexes [49], which constitute an important branch of organometallic chemistry and are effective catalyst systems for a variety of processes [50, 51]. 

Finally, although not a reaction of isocyanide complexes as such, except as labile intermediates, it can be noted that metal hydrido or alkyl compounds can undergo insertion reactions to give acylimidoyl complexes, which can react further ... 

The reactions of isocyanide complexes with nucleophiles parallel the reactions of metal carbonyls. Alcohols were found to add across the carbon-nitrogen bond of complexed isocyanides (Badley et al., 1969, 1971). Amines... 

The reaction of alkoxyarylcarbene complexes with alkynes mainly affords Dotz benzannulated [3C+2S+1C0] cycloadducts. However, uncommon reaction pathways of some alkoxyarylcarbene complexes in their reaction with alkynes leading to indene derivatives in a formal [3C+2S] cycloaddition process have been reported. For example, the reaction of methoxy(2,6-dimethylphenyl)chromium carbene complex with 1,2-diphenylacetylene at 100 °C gives rise to an unusual indene derivative where a sigmatropic 1,5-methyl shift is observed [60]. Moreover, a related (4-hydroxy-2,6-dimethylphenyl)carbene complex reacts in benzene at 100 °C with 3-hexyne to produce an indene derivative. However, the expected Dotz cycloadduct is obtained when the solvent is changed to acetonitrile [61] (Scheme 19). Also, Dotz et al. have shown that the introduction of an isocyanide ligand into the coordination sphere of the metal induces the preferential formation of indene derivatives [62]. 

Several examples of [5C+1S] cycloaddition reactions have been described involving in all cases a 1,3,5-metalahexatriene carbene complex as the C5-syn-thon and a CO or an isocyanide as the Cl-synthon. Thus,Merlic et al. described the photochemically driven benzannulation of dienylcarbene complexes to produce ortho alkoxyphenol derivatives when the reaction is performed under an atmosphere of CO, or ortho alkoxyanilines when the reaction is thermally performed in the presence of an isonitrile [111] (Scheme 63). In related works, Barluenga et al. carried out analogous reactions under thermal conditions [36a, c, 47a]. Interestingly, the dienylcarbene complexes are obtained in a first step by a [2+2] or a [3S+2C] process (see Sects. 2.3 and 2.5.1). Further reaction of these complexes with CO or an isonitrile leads to highly functionalised aromatic compounds (Scheme 63). 

The reaction of the complex [Au(C6E5)(Ph2C=N—N=CPh2)] with 2,6-dimethyl-phenylisocyanide (CNXy) leads to the formation of [Au(CGF5)(CNXy)] [50] by displacement of the ligand. The IR shows an absorption at 2214 cm that is due to the V(CN) of the coordinated isocyanide. 

Aldol reactions of isocyanides with aldehydes are catalyzed by cationic platinum complexes having P-C-P or N-C-N ligands in the presence of a catalytic amount of an amine base to give 2-oxazolines (Equation (126)) 48S>485a>485b Platinum-coordinated a-isocyano carbanions presumably serve as nucleophiles toward aldehydes. Low to moderate enantioselectivities were obtained by using chiral platinum complexes.485 4853... 

Lazar, M. and Angelici, R.J. (2005) Gold metal-catalyzed reactions of isocyanides with primary amines and oxygen analogies with reactions of isocyanides in transition metal complexes. J. Am. Chem. Soc., 128, 10513. 

Scheme 1 Reaction of isocyanide Pd-complex with Ph3Bi...

A less conventional preparation of isocyanide complexes involves the reaction of iron pentacarbonyl with metalated (sodium or lithium derivative) hexamethyldisilazane (162). 

A general procedure has been outlined for the preparation of isocyanide complexes of Wn (equations 23, 24).316 [W(CNR)7]2+ (R = CMe3, C6HU) can also be prepared by reaction of the... 

Alkylation of the cyanide ligands in Ag4M(CN)8 with RX (X = halides) has provided the only route to the complexes M(CN)4(CNR)4 (M = Mo, W R = alkyl, allyl, CH2Ph, CPh3) (72, 73), as direct reaction of isocyanides on the cyanide anions has given only reduced products (74). 

Polymerization reaction of isocyanides RNC is catalyzed by [Fecp(CH2Ph)(CO)]. It proceeds as a result of multistep migration to coordinated ligands and is evidenced by the isolation and identification of the tris(imino) complex (9.164). " ... 

Reactions of metal cyanides with various compounds leading to the preparation of isocyanide complexes have less significance at present, because synthetic methods that utilize isocyanides as substrates have been developed. Nevertheless, metal cyanides are still used in the case of synthesis of complexes with unstable or unattainable isocyanides... 

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. 

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