| Autor: |
Gridnev, I. D., Imamoto, T. |
| Zdroj: |
Organometallics; February 2001, Vol. 20 Issue: 3 p545-549, 5p |
| Abstrakt: |
The rhodium−MiniPHOS complex [Rh((R,R)-MeButPCH2PMeBut)2]+BF4- (1) is reversibly and stereoselectively hydrogenated at low temperatures to give one isomer of cis-dihydride 2a. The second possible diastereomer, 2b, is not observed experimentally. DFT calculations suggest that 2b is 3.5 kcal mol-1 less stable than 2a. The parameters of the equilibrium between 2a, 1, and H2 determined by NMR are ΔH = −7.7 ± 0.1 kcal mol-1 and ΔS = −25 ± 1 cal mol-1 K-1. Formation of the trans-dihydride 3 is observed at around −20 °C. Most probably 3 is formed by isomerization of 2a or 2b. This isomerization involves reversible dissociation of the Rh−P bond. Similar dissociation of the Rh−P bond in 2a might make possible the substrate binding when 1 is used as a catalyst for asymmetric hydrogenation. |
| Databáze: |
Supplemental Index |
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