Reaction of a rhodium-miniPHOS complex with dihydrogen: NMR and computational study

Citation
Id. Gridnev et T. Imamoto, Reaction of a rhodium-miniPHOS complex with dihydrogen: NMR and computational study, ORGANOMETAL, 20(3), 2001, pp. 545-549
Citations number
26
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
0276-7333 → ACNP
Volume
20
Issue
3
Year of publication
2001
Pages
545 - 549
Database
ISI
SICI code
0276-7333(20010205)20:3<545:ROARCW>2.0.ZU;2-D
Abstract
The rhodium-MiniPHOS complex [Rh((R,R)-(MeBuPCH2PMeBut)-P-t)(2)](+) BF4- (1 ) is reversibly and stereoselectively hydrogenated at low temperatures to g ive one isomer of cis-dihydride 2a. The second possible diastereomer, 2b, i s 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 H-2 determined by NMR are DeltaH = -7.7 +/- 0.1 kcal mol(-1) and De ltaS = -25 +/- 1 cal mol(-1) K-1. Formation of the trans-dihydride 3 is obs erved at around -20 degreesC. 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 s ubstrate binding when 1 is used as a catalyst for asymmetric hydrogenation.