Zinc(II) Hexafluoroacetylacetonate Complexes of Alkoxyamines: NMR and Kinetic Investigations. First Step for a New Way to Prepare Hybrid Materials.

Abstract

A series of Zn(hfac)2 alkoxyamines (diethyl(2,2‐dimethyl‐1‐(tert‐butyl‐(1‐pyridylethoxy)amino)propyl)phosphonate) coordinated at ortho, meta and para positions of their pyridyl moiety were prepared and their homolysis rate constants kd measured. Up to a 30‐fold increase in kd was observed for the meta‐(Zn‐RR/SS) and para‐(Zn‐RR/SS) regioisomers. Moreover, the activation is also controlled by the amount of pyridine, used as a ligand competitor. XRD, 1H and 31P NMR spectra show very different structures for each complexes in solid state and in solution depending on the diastereosiomers and on the regioisomers.

How intramolecular hydrogen bonding (IHB) controls the C–ON bond homolysis in alkoxyamines

“…9) are very different for RR/SS-4 and RR/SS-5 in benzene-d 6 , while they are similar in DMSO-d 6 . As similar observations were also reported upon protonation (or other types of activation) of the pyridyl moiety in alkoxyamines, [20][21][22] this change in the signal is ascribed to the occurrence of IHB between the hydroxyl group and the pyridyl moiety (interN in Fig. 8).…”

“…For several years, our group has been promoting the chemical alkoxyamine activation using protonation, 20 oxidation, 20 alkylation, 20 or metal cation coordination. 21,22 However, in our view, activation processes based on physicochemical events cannot be disregarded. Indeed, very recently, 23 a dramatic solvent effect on the C-ON bond homolysis rate constant k d (Scheme 1) has been reported for 1 (Fig.…”

How intramolecular coordination bonding (ICB) controls the homolysis of the C–ON bond in alkoxyamines

“…10,11 Furthermore, formation of complexes of the Zn(hfac) 2 electron acceptor matrix with alkoxyamines has a positive effect on NMP because it enhances initiation efficiency. 12 As we have demonstrated earlier, [7][8][9] alkoxyamine-metal complexes undergo equilibrium dissociation in solution. One can shi this equilibrium by adding a complexation agent for zinc ions, e.g., pyridine (Py) or bi-pyridine.…”

“…1 and 10), supported by 1 H and 31 P NMR analysis (vide supra) in sharp contrast to the interF model of coordination observed for Cu-RS/ SR-B 8 and Zn-RS/SR-C (vide infra). 7 Consequently, a 10-fold increasing in k d is observed upon the coordination of metal cation Zn(II) by 1 in sharp contrast to intraR IHB model RR/SS-2 for which no signicant differences where observed. 14 Moreover, the change in electronegativity at N-atoms due to intraRtype ICB overbalances by 8 kJ mol À1 in E a the entropic cost due to the strongly disfavoured conformation in starting materials accordingly to the geometrical requirements at TS, i.e.…”

Structural, Optical and Thermal Characterization of Wholly Aromatic Poly(ether amide)s Synthesized by Phosphorylation‐Based Condensation Polymerization

“…The improved solubility of polymers and hybrid materials in the presence of salts or acids has been also reported in literatures. [33,34] It is conjectured that the partial solubility of pPEA and coPEA80 in pure solvents of DMAc and DMSO at 25°C originates from the high contents of stiff para-phenylene units in PEA backbones. The intrinsic viscosity of pPEA, mPEA, and coPEAs in NMP solvent was evaluated to be in the range of 0.48-0.97 dl/g.…”