Phosphorus–nitrogen compounds: part 63. Mono- and bis-vanillinatobisferrocenyldispiro(N/N)cyclotriphosphazenes and their macrocyclic Schiff-bases: synthesis, structural characterization and isomerism

Abstract

In this study, mono- and bis-vanillinato-ferrocenyldispirophosphazenes and their Schiff-bases were obtained to investigate the optical and structural properties of cyclotriphosphazenes with stereogenic P-atoms. Accordingly, substitution reactions of two equimolar amounts of the potassium salt of 4-hydroxy-3-methoxybenzaldehyde (potassium vanillinate; KOAr) with one equimolar dichloro trans- (1 and 2) and cis-ferrocenyldispirocyclotriphosphazenes (3 and 4) yielded bis-vanillinato trans- (5 and 6) and cis-dispirocyclotriphosphazenes (8 and 9), respectively. In contrast, using equimolar amounts of trans- (2) and cis-dispirocyclotriphosphazenes (4) with an equimolar amount of KOAr produced the corresponding mono-vanillinato ferrocenyldispirocyclotriphosphazenes, 7 and 10. In addition, condensation reactions of bis-vanillinato trans/cis-dispirophosphazenes (5, 6, 8 and 9) and 1,4-diaminobutane gave rise to novel macrocyclic phosphazene Schiff bases, 11, 12, 13 and 14. The characterization of macrocyclic Schiff bases via¹H, ¹³C and ³¹P NMR spectroscopy showed that they were present in solution as a mixture of ZZ (syn–syn), ZE (syn–anti) and EE (anti–anti) isomers. The molecular and crystal structures of bis-vanillinato trans- (6) and cis- (9), and mono-vanillinato cis-dispirophosphazenes (10) were elucidated using the X-ray diffraction technique and their absolute configurations were determined as RR, SR and RS, respectively. All dispirophosphazenes have two stereogenic P-atoms, except 10. In addition to two stereogenic P-atoms, mono-vanillinato phosphazene (10) also has a pseudo-asymmetric P-center. Compound 10 was proven to be chiral using the CSA-added ³¹P NMR spectrum.