Nickel -mediated polymerization

The nickel-mediated polymerization of p-hydroxy-substituted phenyl isocyanide 60 (R=H) afforded the corresponding poly(isocyanide) 65 in a 43% yield after 65 h at room temperature [81]. The polyhydroxylated polymer 65 was oxidized with NaOCl in THF (Scheme 43). The resultant black solid 66,... 

Witte P, Menzel H (2004) Nickel-mediated surface grafting from polymerization of alpha-amino acid-N-carhoxyanhydrides. Macromol Chem Phys 205 1735-1743... 

Scheme 6.79 Hydrosilylation of ketones [164], Dotz benzannulation chemistry [165], cobalt-mediated synthesis of angular [4]phenylenes [166], and nickel-mediated coupling polymerizations [167],...

A proposed mechanism for Ni-mediated polymerization was given by Drenth and Nolte (Scheme 16) [23]. They presumed the involvement of a cationic tetrakis(isocyanide)nickel(II) complex A before the initiation step. 

The details of this mechanism are still unclear, and need to be clarified. However, this asymmetric polymerization system using a nickel catalyst with optically active amines seems to be unique, in that the chiral elements that become apart from the propagating termini control the helical sense of the entire polymer main chain. A similar, but more stereoselective system is discussed below for the Pd-mediated polymerization of diisocyanobenzenes, which is discussed later. 

Living NCA polymerizations of a wide variety of monomers have also been initiated with transition metal catalysts, allowing the preparation of proteins and block copolypeptide-sin high yield with low polydispersity. NCA catalysts have also been employed to produce low-polydispersity protein-synthetic polymer hybrid materials. Using a bifunctional initiator in nickel-mediated NCA polymerization followed by ATRP, poly(Y-benzyl-L-glutamate-l7-methyl methacrylate) (PBLG-b-PMMA) was prepared with polydispersity in the range of 1.2-1.4. ... 

Summary A double-headed initiator was synthesized yielding two functional groups for the initiation of the nickel mediated ring-opening polymerization of y-benzyl-L-glutamate-N-carboxyanhydride and controlled radical polymerization of vinyl monomers via ATRP or NMP. Well-defined block copolymers combining polypeptides and synthetic polymers were obtained. 

Combination of Nickel Mediated NCA Polymerization with ATRP... 

The synthesis of the double-headed initiator 4 (Scheme 2) for the combination of nickel mediated NCA polymerization with ATRP has already been described.f It was... 

The rod-coil block copolymers obtained by the controlled nickel mediated NCA polymerization and subsequent ATRP (PBLG-b-PMMA) were investigated by XRD measurements and AFM after storage in THF vapour. The XRD measurements (not shown) reveal that before treatment... 

Therefore the possibility of combining NMP and nickel mediated NCA polymerization was investigated by synthesizing the double headed initiator 7 with an amido-amidate group and a nitroxide group (Scheme 3). A nitroxide 5 (synthesis according to literature ) was converted withaUoc-L-leucine-A-hydroxysuccinimidyl... 

Mechanism of nickel-mediated cross-coupling polymerization... 

Figure 2.7 Molecular weight vs conversion plots for nickel- and palladium-mediated GRIM polymerization of 2,5-dibromo-3-hexylthiophene). Nickel-mediated GRIM [M]o = 0.1 mol THF [Ni o= 15 x 10 mol L 23°C. Palladium-mediated GRIM [M]o = 0.1 mol [Pd]o = 1.5 x 10 mol 45°C...

Recent achievements in nickel-mediated CHD polymerization involve the development of methylaluminoxane (MAO) activated catalytic systems, which have been studied independently by a few research groups. Although ANiTFA is a good catalyst for CHD polymerization, the complexes discussed below are more active. 

Kros et al. reported a polymer-peptide conjugate prepared via nickel-mediated NCA polymerization and a subsequent polymerization of an isocyanide, again using the nickel complex as initiator [111]. The active catalyst is attacked by the more electrophilic isocyanide and the coordinated amine reacts with the isocyanide to yield a carbene-like initiator for the isocyanide polymerization (see Fig. 14). The product can be purified from free residual homopolymers by selective solvent... 

The coupling of 3-tert-butyl [1 - " C]malonate (393) with the /3-amino acid derivative 395 to give amide 396 was developed as an alternative route to the 1,4 addition of 395 to the corresponding [l- " C]acrylate 394, which might have failed due to radiation-induced polymerization. Subsequent treatment with 2,4-bis(4-methoxyphenyl)-l,3,2,4-dithiadi-phosphetane-2,4-disulfide (Lawesson s reagent) followed by Raney nickel-mediated desulfurization of the thioamide function formed converted 396 into the target /3-amino acid ester 397. Intramolecular ester condensation upon treatment of 397 with sodium methoxide and concluding saponification and decarboxylation of the f-butyl ester function afforded the trisubstituted 4-[2- " C]piperidone derivative 398. 

To the best of our knowledge, there is only one paper by Mullen et al. [ 125] that presents the polymerization of the BIC unit. The semi-ladder polymer was synthesized by a nickel(0)-mediated Yamamoto-type polymerization using dichlorobisindenocarbazole or dibromobisindenocarbazole as precursors. The two polymers were synthesized in good yields (77 and 70%). They both show a strong blue emission in solution with a maximum centered at 445 nm. 

Moreover, semi-ladder polymers based on DIC units were obtained in much more classical ways. 2,11- and 3,10-dichloro DIC derivatives were polymerized through a nickel(0)-mediated Yamamoto polymerization reaction [95]. The resulting polymers are soluble in ODCB and partially soluble in CB. The absorption maxima of the BIC-based polymers clearly indicate a planar structure. The absorption maxima of the polymeric precursors show a primary maximum around 350 nm compared to the ladder-type polymers where the maximum is centered around 470 nm [50]. This significant red shift clearly indicates the higher degree of conjugation in the planar rigid polymers. The fluorescence spectra of those polymers also show the same trend. 

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