Chiral Discrimination of Complexes with D3 Symmetry. Synthesis and Characterization of Tris{O,O'-bis[(+)(S)-2-methylbutyl] dithiophosphato}chromium(III) Complexes (ΛΔ){Cr(+)(S)(S)Mebdtp]3} and Λ-(-)589- and Δ-(+)589{Cr[(+)(S)(S)Mebdtp]3} and Crystal Packing ...

Biscarini, Paolo,Franca, Roberto,Kuroda, Reiko

, p. 4618 - 4626 (1995)

Synthesis of the title chiral complex (ΛΔ){Cr[(+)(S)(S)Mebdtp]3}, with (+)(S)(S)Mebdtp(1-) = (+)[(S)-(CH3CH2CHCH3CH2O)2PS2](1-), O,O'-bis[(+)(S)-2-methylbutyl] dithiophosphate ion, as the ligand, was accomplished in solution with various solvents giving rise in all cases toa higher production of Λ-(-)589 {Cr[(+)(S)(S)Mebdtp]3} diastereoisomer than Δ-(+)589{Cr[(+)(S)(S)Mebdtp]3}. The formation reactionwas followed by absorption and CD spectroscopy. The Λ-(S,S)(S,S)(S,S) diastereoisomer proved to have higher stability in all the solvents employed (ethanol, acetone, acetonitrile, benzene, dichloromethane, chloroform, and water). Crystal packing forces seem to favor an equal mixture assembly of Λ- and Δ-{Cr[(+)(S)(S)Mebdtp]3}, as is evident from CD characterization of the solid precipitated from solutions with a slight excess of the Λ(-)-isomer. Configurational inversion was observed in solution and even in the solid state after a long time if the solid was kept at higher temperature and under vacuum, although the chirality favored was different in the two phases. The molecular structure and crystal-packing mode of the related title complex {Cr[ddtp]3}, ddtp(1-) = (C2H5O)2PS2(1- ), (C12H30CrO63P3S6, formula weight 607.64) were determined from single-crystal X-ray diffraction data and refined by full-matrix least squares methods to R = 0.065. Crystals are monoclinic,with a = 14.512(8) ?, b = 13.657(3) ?, c = 14.350(2) ?, β = 90.42(3)°, V = 2844(2) ?**3, Z = 4, and space group C2/c (No. 15). The crystals contained a racemic mixture of Λ- and Δ-Cr[ddtp]3 enantiomers. The discussion based on the structural information of this compound extends to chiral discrimination in the formation reaction, configurational inversion reaction, molecular structure, and crystal packing of (ΛΔ){Cr[(+)-(S)(S)Mebdtp]3}.