Isocyanide-based polymers

We shall focus here on the synthesis of the isocyanide-containing polymer. Several reactions of the polymer with the metal vapors of Cr, Fe and Ni using a matrix-scale modeling technique, as well as synthetic-scale metal vapor methods, are then presented in order to demonstrate the reactivity of the isocyanide groups on the polymer. Finally, preliminary studies of the reactivity of the polymer-based metal complexes are described. 

The employment of MCRs is expected to overcome the drawbacks of click reactions because many MCRs proceed with common functional compounds such as aldehydes, ketones, and amines, which are commercially available in most cases. Hence, polymer chemists are currently examining and starting to take advantage of the synthetic utility of MCRs for polymer synthesis [42, 43]. Although the main MCRs used in polymer science are isocyanide-based reactions such as the Passerini and Ugi reactions, this chapter will focus on metal-catalyzed MCRs in the area of polymer chemistry. 

Prior to discussing the current state of MCRs in polymer S3mthesis, the classification of MCRs should be addressed. In spite of the large number of MCRs, these reactions can be divided into three groups (1) isocyanide-based MCRs (IMCRs), (2) non-isocyanide-based MCRs, and (3) metal-catalyzed MCRs (MC-MCRs). The MCR classification and a few examples are listed in Scheme 2. 

To furnish a convenient reaction platform, polymer chemists have explored the utility of non-isocyanide-based MCRs in order to avoid the use of isocyanides. For example, Tao and coworkers focused intensively on the employment of non-isocyanide MCRs such as the BigineUi reaction [70] and the three-compmient reaction between aldehydes, amines, and mercaptoacetic acid [71]. In additimi, the utility of the Kabachnik-Fields reaction was demonstrated independently by the groups of Theato [72] and Tao [73]. To be precise, Kakuchi and Theato showed that the Kabachnik-Fields post-polymerization modification reaction on poly(4-vinyl benzaldehyde) with amines and phosphites proceeded very efficiently to afford polymers featuring a-amino phosphonate pendant groups (Scheme 3) [72]. Furthermore, the group of Tao succeeded in synthesizing polymeric a-amino phosphonates via concurrent Kabachnik-Fields reactions of vinyl compounds and RAFT polymerization of the vinyl monomers in a one-pot process [73]. 

Schmidt S, Koldevitz M, Noy J-M, Roth PJ (2015) Multiccunponcmt isocyanide-based synthesis of reactive styrenic and (meth)acrylic monomers and their RAFT (co)polymerization. Polym Chem 6 44-54... 

An alternative approach towards the PASP synthesis of isocyanides was developed by Bradley [100,101]. It involved the use of a polymer-supported sul-fonyl chloride in the presence of base to afford the dehydration of formamides (Scheme 21). The formamides required could be easily prepared by reaction of the corresponding amines with a formylated benzotriazole resin. Opti-... 

Homopolymers of simple alkyl and aryl isocyanides (Mv.p.osm > 1000-4000) are insoluble in all common solvents. This statement, however, requires elaboration of the fact that trichloroacetic acid successfully disperses these polymers. Observations with poly(cr-toluyl isocyanide) are informative, since the polymer is canary yellow in color, and turns to dark brown in trichloroacetic acid—acting in the manner of an acid-base indicator dye. Dilution with water of the trichloroacetic acid solution of poly(aqueous alkali produces the original yellow color. It appears that the polyisocyanide is dispersed in trichloroacetic acid as a pro-tonated species. Conductimetric experiments on poly(a-phenylethyl isocyanide) in dichloroacetic acid confirm this view (25). 

The synthesis of optically active polymers is an important area in macromolecular science, as they have a wide variety of potential applications, including the preparation of CSPs [31-37]. Many of the optically active polymers with or without binding to silica gel were used as CSPs and commercialized [38]. These synthetic polymers are classified into three groups according to the methods of polymerization (1) addition polymers, including vinyl, aldehyde, isocyanide, and acetylene polymers, (2) condensation polymers consisting of polyamides and polyurethanes, and (3) cross-linked gels (template polymerization). The art of the chiral resolution on these polymer-based CSPs is described herein. 

Similar behaviour to carbon monoxide is displayed by other heterounsatur-ated monomers of carbene-like structure, isocyanides, which homopolymerise in the presence of nickel-based catalysts, yielding polymers with a carbon-carbon main chain, poly(iminomethylene)s [60],... 

Covalent bonding Tyrosine-based isocyanide polymer 4-(3-Br-n-propoxy)phenyl-substituted porphyrin van der Made et al. (117)... 

Isocyanide polymerization has also been used to polymerize peptide-based monomers. Cornelissen et al. [31,32] prepared oligopeptides based on alanine and functionalized the N-terminus with an isocyanide moiety. These monomers were subsequently polymerized using a Ni catalyst into /3-helical poly isocyanopeptides with the dipeptides in the side chain. It was found that these polymers formed rigid rods, which were revealed by AFM to have extremely long persistence lengths. This rigidity was caused by the formation of /5-sheets between the alanines in the side chain. The same group... 

Isocyanide complexes have found numerous applications in organic synthesis and catalysis. Isocyanides undergo polymerization in the presence of many transition metal complexes, for instance, metal carbonyls, metallocenes, cyclopentadienyl carbonyls, nickel(II), palladium(II), and cobalt(II) complexes. Exceptionally high activity is exhibited by nickel and cobalt carbonyls. The resulting polymers are Schiff bases ... 

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