Isonitriles, polymerization

Polymeric (isocyanide)gold(i) aryls ( gold oligo-phenylene-ethynylene-isonitriles ) were tested as electrical conductors at metal-molecule-metal junctions (7r-conjugated molecular wires), but the preparation, structure, and properties of the materials were not fully disclosed (Scheme 52).218... 

Polymerization of optically active isonitiiles, 72, also leads to the formation of helical polymers with a preferential screw sense (219-222). Various factors distinguish this system from the preceding ones In the isonitrile case no new stereogenic atoms are formed during polymerization the helices are rigid and there is no indication of conformational equilibrium in the system the formation of a preferential screw sense is very probably a kinetically controlled process. 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

Esterification of Hexacyanoferric(II) Acid. When hexacyanoferric (II) acid is heated with ethyl alcohol, esterification of the acid takes place (15, 21). The initial partially esterified hexacyanoferric (II) acid polymerizes with the evolution of hydrogen cyanide or is further esterified. Both reactions appear to take place concurrently. Addition of hydrogen cyanide to the reaction mixture causes liberation of ethyl isonitrile from the complex. Hence it is possible to synthesize isonitriles on a continuous basis—i.e., esterification of the strong hexacyanoferric (II) acid, replacement of the isonitrile in the complex by hydrogen cyanide, re-esterification, etc. (15). The over-all reaction is complex, and the precise course of the reaction has not been elucidated. 

In a simple displacement of benzyl isonitrile by K14CN from II, all the labeled atoms should appear in the isonitrile complex and none in the benzyl isonitrile. But the label was present in all of the products isolated and in each to a different extent. For example, the benzyl isonitrile was more radioactive than the N-benzyl formamide which must have been formed by addition of water to benzyl isonitrile. The results indicate that the internal isomerization (III V, Equation 7), the generation of benzyl isonitrile and N-benzyl formamide, and the polymerization of benzyl isonitrile are concomitant reactions. 

Organometallic Compounds. The predominant oxidation states of iridium in organometallics are +1 and +3. Iridium forms mononuclear and polynuclear carbonyl complexes including IrCl(P(C6H5)3)2(CO)2] [14871-41-1], [Iu,Cl4(CO)2] [12703-90-1], [Ir4(CO)12] [18827-81-1], and the conducting, polymeric [IrCl(CO)3]K [32594-40-4]. Isonitrile and carbene complexes are also known. 

An example of termination by formation cyclic trimers is reported in a recent publication by Shashoua et al. (12 a) describing anionic polymerization of mono-isonitriles to nylons-1. The trimerisation competes with further propagation steps and seems to be favored by higher temperature. 

This chapter contains a survey of free-radical-mediated multicomponent reactions (MCRs), which permit the coupling of three or more components. Even though they are not technically classified as MCRs, remarkable intramolecular radical cascade processes have been developed. Some examples, such as those shown in Scheme 6.3, use an isonitrile or acrylonitrile as the intermolecular component for each reaction [6]. These examples demonstrate the tremendous power of the combination of inter- and intramolecular radical cascade processes in organic synthesis. Readers are advised to be aware of remarkable intramolecular aspects of modem radical chemistry through excellent review articles published elsewhere [1, 7]. It should also be noted that there has also been remarkable progress in the area of living radical polymerizations, but this will not be covered here. 

The weak step in this synthesis is the radical addition to the isonitrile. Isonitriles that are sufficiently radicophilic are also easily polymerized. So we decided to develop a better procedure. The sulfonylcyanide function shows some radical behavior.60 This, in principle, can be utilized for constructing a radical chain process. We decided to compare the well-known... 

Under VI we find that hydrogen chloride does add reversibly and stoichiometrically to hydrocyanic acid, but not to give pentavalent nitrogen. It forms amino-formyl chloride, H2C(C1) NH. This substance would undoubtedly add hydrogen chloride to the nitrogen if it did not polymerize. The polymerization products of the nitriles, isonitriles, cyanates and isocyanates have not been studied with any satisfactory degree of care. 

The THT and SMe2 adducts have structures of the type (18-B-V). Their chemistry has been extensively studied and it is summarized in Fig. 18-B-7. The diverse, and in some cases unique, reactivity of these compounds includes substitution with preservation of the geometry or with conversion to (MX4)2(/t-X)2 species, oxidative-addition,53 cluster formation, splitting of C—N bonds,54 and above all coupling of the molecules with triply bonded carbon atom.55 They catalytically trimerize and polymerize terminal acetylenes, and dimerize nitriles and isonitriles with incorporation of the new ligand into the complex. Another remarkable reaction of M2C16L3 is the metathesis of M=M and N=N bonds into two M=N bonds upon reaction with azobenzene. 

Carbon-transition metal bonds can also be formed by cocondensing transition-metal atoms with isonitriles. Thus, using Ni and Fe with t-butyl isocyanide, methyl isocyanide, cyclohexyl isocyanide and vinyl isocyanide the NiL4 and FeL, complexes are formed. Palladium cocondensed with isonitriles yields PdLj polymeric structures with terminal and bridged isonitrile ligands ... 

Very common Cl fragments bound to a polymeric support are carbenoids. The simplest carbenoid is CO itself, which can be used in transition metal-catalyzed insertions between benzofuran-3yl palladium and a nucleophile such as trifluoroethanol [161]. One of the most common carbenoids is isonitrile, which is used in a large number of multicomponent reactions. Diazoalkanes have often been used as carbene precursors, since they can be readily obtained from support-bound anions and sulfonyl azides [252]. Commonly, diazoalkanes are converted transi-... 

Thus a support-bound benzylpiperazine (282) was allowed to undergo a Man-nich reaction with formaldehyde and a-keto-aldehyde hydrazones. Upon addition of 1,2-dibromo-ethane (388) the support-bound piperazine tether is N, N -dialky-lated to give a quinuclidinium species (389). Subsequent Hoffmann elimination released a diazaalkadiene (390) from the polymeric support, allowing it to react with isonitriles to give pyrazoles (395). With electron-rich dienophiles, HDA reactions were also reported to have been performed to yield compound (393) (Scheme 80). 

We have shown in this review that neutral and cationic organoactinide complexes have been extensively studied, in the last decade, as catalysts for several organic transformations [9-12, 111]. Polymerization of alkenes[112,113], oligomerization of terminal alkynes [55, 114], hydrosilylation of terminal alkynes [41], and 1,1-insertion of isonitriles into terminal alkynes [28] comprise some other studied processes not presented here. However, due to the high oxophilicity of the actinide complexes (as mentioned above), substrates containing oxygen have been excluded because of the expected and predictable oxygen—actinide interaction. 

VL8 Synthesis of Oligomeric and Polymeric Materials via Palladium-Catalyzed Successive Migratory Insertion of Isonitriles... 

Multiple, successive insertion of isonitriles into the palladium-carbon o--bond has also been found with organopalladium(II)bis(phosphine) complexes. However, unlike the Ni- catalyzed polymerization, only single, double, and triple insertion reactions of isonitriles have been reported for Pd-mediated reactions. For instance, reaction of methylpalladium(II) complex 2 with cyclohexyl isonitrile in ratios of 1 1, 1 2, and 1 3 afforded selectively single (3), double (4), and triple (5) insertion products, respectively (Scheme 3). However, no further insertion of cyclohexyl isonitrile to 5 took place. No reactivity of the triple insertion complex 5 was explained by the intramolecular coordination of the nitrogen atom of the third imino group, which formed a stable five-mem-bered chelating palladium complex. 

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