Synthesis, structure and solid-state nuclear magnetic resonance studies of P-chiral (dicyclohexylaminosulfanyl)-[(–)-p-menthan-3-yloxy]phenylthioxophosphorane

Abstract

P-Chiral (R_p)(dicyclohexylaminosulfanyl)[(–)-p-menthan-3-yloxy]phenylthioxophosphorane 1 was synthesized by condensation of (S_p)(–)-p-menthlan-3-yl phenylthiophosphinate 2 and (H₁₁C₆)₂NSBr. The reaction proceeds with retention of configuration at the chiral phosphorus centre. Compound 1 crystallized from chloroform–acetone or chloroform as two polymorphs in proportions depending on the solvent. X-Ray crystallography revealed that in the asymmetric part of the unit cell polymorph 1 contains two independent molecules with anti and syn geometry of the SP–S–N fragment and polymorph 1′ contains only one independent molecule with anti geometry. Preliminary structural results were obtained by analysis of ³¹P cross-polarization magic angle spinning NMR spectra. The SP–S bond angles, P–S and PS bond lengths were established from the anisotropy Δδ and principal components of the chemical shift tensor, δ₂₂ and δ₃₃, respectively. Comparison of geometrical parameters obtained from solid-state NMR spectroscopy with those from X-ray diffraction analysis of single crystals confirms the accuracy of this approach. For the anti SP–S–N conformation the SP–S bond angle is smaller than the tetrahedral value, and the P–S bond length is 2.09 Å. The syn geometry is associated with a larger SP–S valence angle and longer P–S bond. The trend towards planarity is explained in terms of a π contribution to the P–S single bond.