Oxo‐Entity‐Controlled Diastereomer Peculiarity of Rhenium( V ) Complexes ReOX 2 (P~O)py [X = Cl, Br, I; P~O = (OCMe 2 CMe 2 O)POCMe 2 CMe 2 O(1–); py = pyridine]: Synthesis and Molecular and Crystal Structural Characterization

The stability of diastereomers of ReOX 2 (P~O)py complexes determined by the arrangement of the oxo‐entity O=Re(–O~P) is manifested in molecular recognition and crystallization behavior [X = Cl, Br, I; P~O = (OCMe 2 CMe 2 O)POCMe 2 CMe 2 O(1–); py = pyridine]. With X = Cl and Br both chiral cis [ OC ‐6–52] and achiral trans [ OC ‐6–15] complexes can be obtained concomitantly, while for X = I only a trans complex can be afforded. Molecular structures were characterized using NMR IR and UV/Vis spectroscopic methods with the aid of DFT computational analysis and were ultimately corroborated by the single‐crystal X‐ray diffraction method. These analyses revealed that the most stable diastereomers involve an O=Re(–O~P) oxo arrangement in an axial disposition reinforced with a phosphorus ligating atom mutually cis due to extensive π‐bonding both for chiral cis and achiral trans complexes, regardless of whether X = Cl, Br, or I. However, the disparate intramolecular geometry either cis or trans in the solid state results in enantiomorphic crystals related to space group P 2 1 2 1 2 1 (X = Cl, Br) or crystals pertinent to the centrosymmetric framework P 2 1 /c (X = Cl, Br, I), respectively. Thoughtful analysis of crystal structures reveals a supramolecular architecture due to intermolecular forces involving hydrogen bonding and electric dipole–dipole interactions (among other contact interactions). Thus, chiral cis complexes (X = Cl, Br) show helical crystal packing that succeeds in spontaneous resolution, while trans stereoisomers (X = Cl, Br, I) do not and rather exhibit a zig‐zag supramolecular framework. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)