✍ Scribed by Gábor Szalontai; Péter Sándor; József Bakos
No coin nor oath required. For personal study only.
The liquid‐state stereochemistry of cationic [Rh(I)dienebisphosphine]^+^ and neutral [Rh(I)dienebisphosphineCl] complexes is reported on the basis of their ^1^H, ^13^C and ^31^P NMR spectra. In solution the 400‐MHz ^1^H spectra indicate C~2~ 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‐bipyramidalsquare‐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.
📜 SIMILAR VOLUMES
## Abstract The chiral (π‐allyl)Pd(II) complex [Pd(η^3^CH~3~CHCHCH~2~)(__S, S__‐Chiraphos)]CF~3~SO~3~ was shown to exist in four isomeric forms (two diastereomeric and two geometric). Aspects of their three‐dimensional structures were elucidated using ^1^H, ^13^C and ^31^P one‐ and two‐dimensional