Regioregulated Syntheses of Poly(aminopyridine)s by Pd‐catalyzed Amination Reaction

Abstract

Regioregulated poly(aminopyridine)s were synthesized by a Pd-catalyzed CN coupling reaction. The polymerization using Pd(0) and a bulky monodentate phosphine ligand distinctively produced the para-linked and meta-linked poly(aminopyridine)s, without the need for a protection process. The regioregularity of the polymer was confirmed by (1) H NMR spectroscopy. Model reactions were studied to evaluate the possibility of crosslinkage in the polymer. A large difference in reactivity was observed between 5-amino-2-bromopyridine and 2-amino-5-bromopyridine, which should have afforded same product. Density functional theory (DFT) calculations indicated that electron densities of the Br-bound carbon atom and the pyridine-nitrogen atom determine the reactivity of the monomers.

Preparation of Polyaminopyridines Using a CuI/l-Proline-Catalyzed C-N Polycoupling Reaction

“…However, the reaction time was increased from 40 to 80 hours, Scheme 1. The dark brown powder obtained as product was similar to that reported by both electrochemical [9] and chemical [16] synthesis of PAPy.…”

“…Monomer 1 is more reactive than monomer 2 and this led to the formation of PAPy with higher M n and with a more satisfactory yield (comparison among entries 1/2/3 and 12/13/14). The higher reactivity of the amino-bromopyridine ( 1 ) in comparison to 2 (Scheme 2) was also observed in the synthesis of PAPy by Pd-catalyzed C-N coupling reaction [16]. This behavior was justified by Quantum Chemical calculations as result of partial atomic charges differences in the monomers [16].…”

“…On the other hand, C-H bond activation mediated by Palladium catalysis (Palladium homo-coupling reactions) is an already known reaction and intensively studied nowadays [26,27,28]. In the case of Palladium cross-coupling polymerization reactions, polymer crosslinking may be a real drawback [16]. …”

“…To overcome these drawbacks of catalysis by copper, several Pd-catalyzed C-N formation methods have been developed [14,15]. In this context, the regio-regulated synthesis of PAPy using Pd-catalyzed amination reaction at 110 °C was reported recently [16]. However, industrial use of methods involving Pd is problematic in many cases due to the air and moisture sensitivity, as well as the high costs of Pd catalysts [17].…”

Two-dimensionally extended organic high-spin poly(aminium cationic radical)s and their magnetic force microscopic images

“…[48][49][50][51][52][53] The suitable combination of catalyst and ligand was examined, and the use of P(tBu) 3 as a ligand was found to most effectively improve the reaction yields. 54 However, a part of the products was decomposed during column chromatography on silica gel because of the shallow HOMO levels.…”