Liquid‐phase stereochemistry of cationic [Rhbisphosphinediene]+ and neutral [RhbisphosphinedieneCl] complexes. 1H, 31P and 13C NMR and molecular mechanics study

Gábor Szalontai, Péter Sándor, J. Bakos

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Abstract

The liquid‐state stereochemistry of cationic [Rh(I)dienebisphosphine]+ and neutral [Rh(I)dienebisphosphineCl] complexes is reported on the basis of their 1H, 13C and 31P NMR spectra. In solution the 400‐MHz 1H spectra indicate C2 symmetry for the cationic species and a strongly solvent‐ and temperature‐dependent equilibrium for the neutral five‐coordinated species. Gas‐phase molecular mechanics calculations on the cationic complexes predict local energy minima for the skew(diequatorial), chair and boat conformations of the six‐membered phosphine chelate. The 2D exchange spectra of the neutral complex prove a slow exchange between identical forms of the bidentate chelate, but no such exchange exists between the diene atom pairs; the origin of the observed pairwise identify of the diene atoms is therefore not fully understood. In principle, several stereoisomers can exist in such complexes, depending on the actual conformation of the bisphosphine chelate and/or on the cis or trans relationship of the fifth coordinating point and the rest of the phosphine. The existence of the traditionally asssumed trigonal‐bipyramidalsquare‐pyramidal equilibrium is unlikely. As an alternative, the fluxional nature of the aliphatic part of the phosphine chelate could explain the phenomena. This motion, however, should be restricted to a chair—boat equilibrium which does not significantly change the axial—equatorial positions of the phenyl rings.

Original languageEnglish
Pages (from-to)449-458
Number of pages10
JournalMagnetic Resonance in Chemistry
Volume29
Issue number5
DOIs
Publication statusPublished - 1991

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Keywords

  • Dynamic H, C and PNMR
  • Liquid‐phase stereochemistry
  • Rh(I) complexes

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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