Theoretical Study on the Mechanism and Regioselectivity of the Macromolecular Substitution Reactions of [NPCl2]n with Bifunctional Nucleophiles by a Combination of Quantum

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• 作者：Luis M. Frutos ; Gabino A. Carriedo ; M. Pilar Tarazona ; Enrique Saiz
• 刊名：Macromolecules
• 出版年：2009
• 出版时间：November 24, 2009
• 年：2009
• 卷：42
• 期：22
• 页码：8769-8773
• 全文大小：767K
• 年卷期：v.42,no.22(November 24, 2009)
• ISSN：1520-5835

文摘

A combination of molecular dynamics simulations and quantum chemistry calculations affords a good understanding of the reaction between [NPCl₂]_n and the bifunctional nucleophile aminophenol HO−C₆H₄−NH₂ in THF solution and in the presence of alkali carbonates. This reaction is regiospecific at room temperature favoring the attack by the NH₂ group, and only at higher temperatures the attack by the OH is activated. It is also explained why the reaction of HO−C₆H₄−NH₂ with {[NP(O₂C₁₂H₈)]_1−x[NPCl₂]_x}_n and Cs₂CO₃ at reflux proceeds exclusively by the OH giving aryloxyphosphazenes with terminal NH₂ substituents. Molecular dynamics simulations have been performed on model systems consisting on [NPCl₂]_n chains surrounded by aminophenol molecules or ions obtained by deprotonation of either the OH or NH₂ groups. Quantum mechanics calculations consisted in density functional theory (DFT) computation of the reaction mechanism of aminophenol with the phosphoranimine (NH₂)Cl₂P(=NH) as a simple model for the NPCl₂ phosphazene units, using B3LYP approximation with 6-31G(d). Our results provide evidence to support that the macromolecular substitution reactions of poly(dichlorophosphazene) with aryloxide ions are diffusion controlled and governed by the atomic charges, while the reaction with amino-arenes are directed by hydrogen interactions between the NH₂ hydrogens and the phosphazene nitrogen atoms that initiate a lower activation energy stepwise mechanism competing with a concerted mechanism. The combined methodology employed in this work seems to be useful to address the regiochemistry of the macromolecular substitution on polyphosphazenes with heterobifunctional nucleophiles which is a central issue in the design of polymers with predetermined chemical composition and structure.