214841-68-6Relevant academic research and scientific papers
Oxidative addition of dihydrogen to [Ir(bisphosphine)(1,5- cyclooctadiene)]BF4 complexes: Kinetic and thermodynamic selectivity
Kimmich, Barbara F. M.,Somsook, Ekasith,Landis, Clark R.
, p. 10115 - 10125 (1998)
The activation of dihydrogen by cationic diphosphine complexes of Rh is the rate-determining and enantiodetermining step in the catalytic asymmetric hydrogenation of prochiral enamides. The addition of H2 to [Ir(bisphosphine)(COD)]+ (COD = 1,5-cyclooctadiene) complexes is examined herein as a model for stereocontrol and dynamic processes related to catalytic hydrogenation. The diastereoselectivity of H2 oxidative addition to form diastereomeric [Ir(chiral bisphosphine)(H)2(COD)]+ complexes at - 80 °C is kinetically controlled and varies substantially with the structure of the diphosphine. In one instance (chiral bisphosphine = CHIRAPHOS), the kinetic and thermodynamic selectivities of H2 addition are inverted; i.e., the dominant kinetic product is thermodynamically less stable than the minor kinetic product. For the [IrH2(Me-DuPhos)- (COD)]+ system, quantitative analysis of the 2D NOE data using two-dimensional conformer population analysis (2DCPA) establishes the absolute stereochemistry and the three- dimensional structures of the predominant conformers. Kinetic analysis of the interconversion of the [IrH2(MeDuPhos)(COD)]+ diastereomers, and of their exchange with D2, reveals a complex pathway for isotope scrambling and diastereomer interconversion that does not involve reductive elimination of H2 to form [Ir(Me-DuPhos)(COD)]+. During the isotope scrambling, exquisite selectivity is seen for exchange in only two ligand sites, one on the Me- DUPHOS ligand and one on the COD ligand.
