Alkyl isocyanides, polymerization

Initial attempts to form alkyl isocyanide complexes from metal atoms led to polymerization of the isocyanides (133). However, a recent report suggests that Ni(RNC)4, Fe(RNC)5, and Cr(RNC)6 can be made directly from the respective atoms and RNC at -196°C (98). 

AT-Vinyl-substituted isocyanides 57 have been polymerized in the presence of nickel catalysts, yielding poly(vinyl isocyanide)s [79]. The solubility and stability of these polymers very much depends upon the substituent on the vinyl group. Substituted vinyl isocyanide, (CH3)2C=CHNC, afforded polymers that were soluble in chloroform when freshly prepared, although they became insoluble on standing for several days, even at temperatures of -10 °C. The polymerization of vinyl isocyanide proceeded in hydrocarbon solvents, unlike aryl or alkyl isocyanides, which required an alcoholic solvent for efficient polymerization. 

Mention was made earlier about insertion reactions into nickel alkyl bonds 108, 164), and about polymerizations of oleiins by isocyanide nickel complexes 31,174). 

Rod-like mononuclear derivatives have been prepared by the reaction of a polymeric alkynyl gold(I) complex with isocyanides. The mesomorphic properties of three types ofgold(I) acetylide complexes, namely, [Au(CC-Ar)(CN-Ar)J, [Au(CC-R)(CN-Ar)J and [Au(CC-Ar)(CN-R)] (Ar = aryl with aliphatic chain, R = alkyl chain), have been systematically examined. 

Polyisocyanides have a rigid helical structure with four monomeric units per helix turn [254,255]. The polymers of isocyanides do not display any stereoisomerism, since the carbon atoms in the polymer backbone are not chirotropic. However, it is worth noting that isocyanide polymerisation is stereoselective as regards the screw sense of the polymeric helix (atropisomerism). Therefore, right- and left-handed helices are formed from achiral isocyanides [256], When the monomer is achiral, a racemic mixture of right- and left-handed helices is obtained, e.g. in the case of the polymerisation of t-butylisocyanide [257,258]. When the alkyl... 

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). 

It is relevant to these findings that unhindered or even hindered isocyanides undergo polymerization to poly(iminomethylenes) in the presence of initiators such as the transition metal complexes j -alkyl(trifluoroacetato)nickel(II) or trifluoroacetato-nickel(II) ... 

Polymerization of isocyanides is a thermodynamically feasible process, in agreement with the stoichiometric multiple insertion observed in reactions between metal-alkyl complexes and isocyanides. The entropy loss in the case of isocyanides is lower than for insertion of CO. Isocyanide insertions into palladium-alkyl a bonds are faster than those for the platinum(II) analogues. The latter, on the other hand, usually lead to more stable and better defined products. Insertion of isocyanides into platinum-carbon bonds has been studied extensively Reaction (j) is typical the ionic product was strongly suggested by observation that the compounds isolated under mild conditions are 1 1 electrolytes. 

Complexes of Crlv with alkyl,216 alkylidene,217 or r/-carborane218 ligands are extensively studied as model compounds for Cr-based alkene polymerization catalysts (Section 4.6.5.1.2). These complexes are described in detail in the Comprehensive Organometallic Chemistry series. A CrIV complex with isocyanide ligands is described in Section 4.6.4.2.I. 

Recently, the CpNi system was reinvestigated to reveal the system s catalytic activity toward aryl isocyanides [19]. The CpNiR(PPh3) complexes 3a and 5a-c, where R=methyl or alkynyl group, polymerized p- or ra-substitut-ed aryl isocyanides in THF at room temperature (Scheme 9). Alkyl iso-... 

Reaction of ferrous chloride with cyanide ions in the presence of CO produces a mixture of cyano-carbonyl ions including T[Fe(CN)4(CO)2], /ra 3-[Fe(CN)4(CO)2] , and [Fe(CN)s(CO)] (Scheme H).63.70,7l OT-dicarbonyl compound was also prepared via the reaction of Fe(CO)4l2 with 4 equiv. of MCN (M = Na, K) in MeOH (Scheme Z) Treating [Fe(CN)3(CO)3] with NaCN also produced the m-derivative. As with the previous work reviewed in GOMC II (1982) and COMC (1995), alkylation of these anionic cyano complexes leads to isocyanide derivatives. Similarly, protonation leads to the formation of the bound isocyanic acid. Oxidation of the [Fe(CN)s(CO)] ion gives [Fe(CN)s(CO)]. Two-dimensional polymeric networks were obtained when [Na(DMF)2]2[7ra .f-Fe(GN)4(CO)2] was treated with divalent metal salts in agar gels (Equation (22)). ... 

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