Substituent exchange reactions of trimeric and tetrameric aryloxycyclophosphazenes with sodium 2,2,2-trifluoroethoxide

Dalton Transactions Pub Date: 2011-12-19 DOI: 10.1039/C1DT11606A

Abstract

Substituent exchange reactions of sodium 2,2,2-trifluoroethoxide with trimeric and tetrameric aryloxycyclophosphazenes with phenoxy, 4-formylphenoxy, 4-cyanophenoxy and 4-nitrophenoxy side groups were conducted at 66 °C in THF and monitored by 31P NMR and mass spectrometry. These are model reactions for their counterparts with high polymeric linear organophosphazenes. The ease of displacement of OAr in cyclic trimeric and tetrameric molecules by CF3CH2O increased significantly with the presence of electron-withdrawing substituents in the polyphosphazene in the order, phenoxy ? 4-formylphenoxy < 4-cyanophenoxy ≈ 4-nitrophenoxy. Fully substituted 2,2,2-trifluoroethoxyphosphazene trimer and tetramer were formed by side group exchange, but these reactions were followed by an attack by the nucleophile on the α-carbon of the 2,2,2-trifluoroethoxy groups linked to phosphorus to give a species in which one trifluoroethoxy group had been replaced by an ONa unit, and bis(trifluoroethyl) ether was formed as a side product. On the other hand, only partly exchanged species were formed when sodium phenoxide reacted with the trifluoroethoxy phosphazene trimer and tetramer, but again a product with an ONa side group was formed eventually together with phenyltrifluoroethyl ether generated viaalpha-carbon attack. The relative sensitivity of 2,2,2-trifluoroethoxy and phenoxyphosphazene cyclic trimers and tetramers to the presence of trifluoroethoxide was established.

Graphical abstract: Substituent exchange reactions of trimeric and tetrameric aryloxycyclophosphazenes with sodium 2,2,2-trifluoroethoxide
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