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SM ISO690:2012 MAKAEV, Fliur, BARBA, Alic, BARBA, Alic. 31P NMR investigation of new P*-chiral phosphates. In: NANO: - 2016: Ethical, Ecological and Social Problems of Nanoscience and Nanotechnologies, Ed. 2016, 11-14 mai 2016, Chişinău. Chișinău, Republica Moldova: 2016, p. 36. |
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NANO 2016 | ||||||
Conferința "NANO-2016: Ethical, Ecological and Social Problems of Nanoscience and Nanotechnologies" 2016, Chişinău, Moldova, 11-14 mai 2016 | ||||||
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Pag. 36-36 | ||||||
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Chiral phosphites represent an important type of chirality transfer agents for asymmetric catalysis. The most important advantages of phosphite-type ligands include their pronounced π-acidity, oxidation stability, as well as their synthetic availability and low cost. Correspondingly, the idea of designing P-monodentate phosphites that possess a P*stereocenter is rather attractive, since ligands with asymmetric donor centers are particularly efficient stereoinductors. Nevertheless, there are rather sufficiently limited number of very promising P*-chiral monodentate phosphite-type ligands. Herein we report the 31P NMR investigation of new synthesized [1] P*-chiral phosphites based on terpene - α-pinene 1, 2-carene 2 and 3-carene 3 as one of cheapest natural optically active auxiliaries. The 31P NMR spectroscopic data for 4-7 are summarized in Table 1. Compound 6 with NEt2 exocyclic fragment is formed as single stereoisomer, while 4, 5 and 7 each contain from 3 to 34% of the second epimer by P* - stereocentre. To estimate steric demands of ligands 4-7, we calculated their Tolman’s angles [2] by the reported method using of semiempirical quantum mechanical AM1 techniques with full optimization of geometrical parameters [3]. The obtained results (Table 1) show that the steric demands of 4-7 vary over a rather wide range between 90° and 122°.tableTable 1. 31Р NMR chemical shifts (CDCl3) and cone angles (deg) of phosphites 1-4. |
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