Ambident PCN heterocycles: N- and P-phosphanylation of lithium 1,3-benzazaphospholides

Bhaskar R. Aluri, Sebastian Burck, Dietrich Gudat, Mark Niemeyer, Oldamur Holloczki, Laszlo Nyulaszi, Peter G. Jones, Joachim Heinicke

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15 Citations (Scopus)

Abstract

Synthetic and structural aspects of the phosphanylation of 1,3benzazaphospholides 1L1, ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl-l,3,2-diazaphospholes inspired us to study the coupling of 1 L1 with chlorodiazaphospholene 2, which led to the N-substituted product 3. Reaction of 1L1 with chlorodiphenyl- and chlorodicyclohexylphosphane likewise gave N-phosphanylbenzazaphospholes 4 and 5, whereas with the more bulky di-iert-butyl- and di-1-adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct. Structural information was provided by single-crystal X-ray diffraction and solution NMR spectroscopy experiments. 2D exchange spectroscopy confirmed the existence of two rotamers of the aminophosphane 5 at room temperature; variable-temperature NMR spectroscopy studies of 6 revealed two dynamic processes, low-temperature inversion at ring phosphorus (△H =22 kJ mol-1, △S = 2 JK-1 mol-1) and very low-temperature rotation of the tBu2P group. Quantum chemical studies give evidence that 2-unsubstituted benzazaphospholides prefer N-phosphanylation, even with bulky chlorophosphanes, and that substituents at the 2position of the heterocycle are crucial for the occurrence of P-N rotamers and for switching to alternative P-substitution, beyond a threshold steric bulk, by both P- and 2-position substituents.

Original languageEnglish
Pages (from-to)12263-12272
Number of pages10
JournalChemistry - A European Journal
Volume15
Issue number45
DOIs
Publication statusPublished - Dec 4 2009

Keywords

  • Ambident reactivity
  • Dynamic processes
  • Heterocycles
  • Phosphanes quantum chemistry

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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    Aluri, B. R., Burck, S., Gudat, D., Niemeyer, M., Holloczki, O., Nyulaszi, L., Jones, P. G., & Heinicke, J. (2009). Ambident PCN heterocycles: N- and P-phosphanylation of lithium 1,3-benzazaphospholides. Chemistry - A European Journal, 15(45), 12263-12272. https://doi.org/10.1002/chem.200901753