ИСТИНА

Optically active cyclopalladated compounds (CPCs) have found wide practical use in the stoichiometric and catalytic asymmetric synthesis.All these application spheres require precise knowledge of cyclopalladated catalyst or reagent enantiomeric composition.The most convenient approach to this analytic problem solution seems to be NMR spectroscopy using after enantiomers to diastereomers onversion. Unfortunately, 1H NMR spectroscopy application for enantiopurity determination of CN-CPCs becomes to be very problematic in the case of complicated C,H-skeleton of both, resolving/derivatizing agent and of the azapalladacycle, and due to existence of some mononuclear derivatives of CN-palladacycles as a mixture of geometric isomers.The known readily available phosphinite ligand (1R,2S,5R)-menthyloxydiphenylphosphine was introduced as chiral derivatizing agent for the enantiomeric purity determination of the optically active CN-palladacycles using the 31P NMR spectroscopy. After slight modification, known methods provided the target phosphinite in a crystalline state with chemical purity of >99.5% (1H and 31P NMR data). The examination of (1R)-MenOPPh2 as analytical reagent shows: (i) increasing oxidative and hydrolytic stability of phosphinite coordinated with palladacycles on comparison to free ligand; (ii) its tight and quantitative in situ bonding with the palladium atom; (iii) phosphinite ability for spectral recognition of palladacycle enantiomers; (iv) its ability for the palladacycle recovery from the intermediate adduct, and (v) opportunity to increase the enantiopurity of the palladacycle tested via removing the minor diastereomer of its phosphinite derivative. The most unexpected outcome of our analytic investigations was discovery of the clear dependence of the chemical shifts of phosphinite adduct diastereomers upon the absolute configuration of the palladacycle. Namely, in the spectra of all CPCs of known absolute configuration 31P signal of the (1R)-MenOPPh2 derivatives of (SC)-palladacycles was low field shifted compared to that for the adduct derived from the corresponding (RC)-dimer.