First direct discrimination of chiral phosphorus thionate (P=S) derivatives by multinuclear magnetic resonance spectroscopy in the presence of a chiral dirhodium complex

Abstract

Enantiomeric ratios of compounds with P=S functionalities can be determined by 1H, 13C, and 31P NMR spectroscopic inspection of their diastereomeric complexes with (R)-Rh2(MTPA)4 (MTPA-H identical with methoxytrifluoromethylphenylacetic acid; Mosher's acid). This is the first facile and rapid spectroscopic method for chiral recognition in this class of compounds. Whereas complexation shifts Deltadelta are moderate or even negligible, significant signal dispersions Delta(nu) can be observed. Some rationalization about the complexation mode is presented. The NMR spectral characteristics of the free P=S compounds 1-9 are described in detail.

First direct discrimination of chiral phosphine selenide (P=Se) derivatives by multinuclear magnetic resonance spectroscopy in the presence of a chiral dirhodium complex

“…In accordance with our previous observations for other ligands, 5,6 Dd-values are small (<0.5 ppm) or even negligible for 1 H signals. They are larger for 13 C (up to )4 ppm) and 31 P (up to +5.9 ppm), a fact which is expected, considering the much larger chemical shift range of these two nuclei.…”

“…In our experience, 5,6,11 acetone does not significantly compete with the ligands in adduct formation.…”

Phenylselenenylalkanes, their adducts with the dirhodium complex Rh2(MTPA)4 and ligand exchange mechanisms in solution as studied by 1H, 13C and 77Se NMR spectroscopy

“…Standards were internal TMS (υ D 0) for 1 H and for 13 C, and external (PhSe) 2 (υ D 463) corresponding to (CH 3 All samples were prepared by mixing 45.2 mg (0.04 mmol) of Rh-Rh and the appropriate molar equivalent of the respective selenide in 0.7 ml of CDCl 3 , adding 7 µl (1 drop) of acetone-d 6 to increase the solubility of Rh-Rh. 4,5 The concentrations in the probes of the free ligands were similar.…”

Chiral phospholene and phospholane chalcogenides: Stereochemistry and chiral recognition by multinuclear NMR spectroscopy of their Rh2[(R)‐MTPA]4 adducts

“…Therefore, we call the difference of the chemical shifts in these adducts as compared to the corresponding values of the free ligands "adduct formation shifts," ⌬␦ (in ppm). It should be noted that, according to our previous work on dirhodium adducts with related ligands, [1][2][3] it can be gen- erally assumed that the experimental set-up (1:1 molar ratio) leads to a predominance of 1:1-adducts in the equilibrium, as shown in Scheme 2. 4 The ligands 1-12 are chiral and the compounds exist as racemates, whereas Rh* is enantiopure.…”

“…1 Very recently, we reported that this "dirhodium method" is the only direct technique for chiral phosphine sulfides (P=S) 2 and phosphine selenides (P=Se). 3 In continuation of our studies we investigated a series of cyclic phospholenechalcogenides 1-11 and one phospholane oxide 12 (Scheme 1).…”