Cyclophosphazene hydrazides as scaffolds for multi-ferrocenyl assemblies: synthesis, structure, and electrochemistry

Abstract

Reactions of N-methylhydrazine with chlorocyclophosphazenes, N₃P₃Cl₆ (1), N₃P₃(OPh)Cl₅ (2), gem-N₃P₃Ph₂Cl₄ (3), spiro-N₃P₃(O₂C1₁₂H₈)₂Cl₂ (4), N₃P₃(OPh)₅Cl (5), and diphenylphosphinic chloride, Ph₂P(O)Cl (6), proceed in a regiospecific manner to afford the products N₃P₃[N(Me)NH₂]₆ (1a), N₃P₃(OPh)[N(Me)NH₂]₅ (2a), gem-N₃P₃Ph₂[N(Me)NH₂]4 (3a), spiro-N₃P₃(O₂C1₂H₈)₂[N(Me)NH₂]₂ (4a), N₃P₃(OPh)₅[N(Me)NH₂] (5a), and Ph₂P(O)[N(Me)NH₂] (6a). The terminal NH₂ groups in all of these compounds are reactive and have been used in the condensation reaction involving ferrrocene-2-carboxaldehyde to afford the corresponding hydrazones N₃P₃[N(Me)N=CHC₅H₄FeC₅H₅]₆ (1b), N₃P₃(OPh)[ N(Me)N=CHC₅H₄FeC₅H₅]₅ (2b), gem-N₃P₃Ph₂[N(Me)N=CHC₅H₄FeC₅H₅]₄ (3b), spiro-N₃P₃(O₂C₁₂H₈)₂[N(Me)N=CHC₅H₄FeC₅H₅]₂ (4b), N₃P₃(OPh)₅[N(Me)N=CHC₅H₄FeC₅H₅] (5b), and Ph₂P(O)[ N(Me)N=CHC₅H₄FeC₅H₅] (6b). The structures of 1-6(a,b) have been determined by the use of multinuclear NMR, mass spectroscopy, and elemental analysis. X-ray crystal structures of 1b, 3b, 4b, 5b, and 6b have also been determined, which confirm their molecular structures. Cyclic voltammetric experiments on the ferrocenyl derivatives 1b-6b reveal an essentially reversible oxidation peak. Further, all of these are electrochemically quite robust and do not decompose on oxidation.