691365-08-9Relevant academic research and scientific papers
[CpRu((R)-Binop-F)(H2O)][SbF6], a New Fluxional Chiral Lewis Acid Catalyst: Synthesis, Dynamic NMR, Asymmetric Catalysis, and Theoretical Studies
Alezra, Valerie,Bernardinelli, Gerald,Corminboeuf, Clemence,Frey, Urban,Kuendig, E. Peter,Merbach, Andre E.,Saudan, Christophe M.,Viton, Florian,Weber, Jacques
, p. 4843 - 4853 (2007/10/03)
The C2-symmetric electron-poor ligand (R)-BINOP-F (4) was prepared by reaction of (R)-BINOL with bis(pentafluorophenyl)-phosphorus bromide in the presence of triethylamine. The iodo complex [CpRu-((R)-BINOP-F)(I)] ((R)-6) was obtained by substitution of two carbonyl ligands by (R)-4 in the in situ-prepared [CpRu(CO)2H] complex followed by reaction with iodoform. Complex 6 was reacted with [Ag(SbF 6)] in acetone to yield [CpRu((R)-BINOP-F)(acetone)][SbF 6] ((R)-7). X-ray structures were obtained for both (R)-6 and (R)-7. The chiral one-point binding Lewis acid [CpRu((R)-BINOP-F)][SbF6] derived from either (R)-7 or the corresponding aquo complex (R)-8 activates methacrolein and catalyzes the Diels-Alder reaction with cyclopentadiene to give the [4 + 2] cycloadduct with an exo/endo ratio of 99:1 and an ee of 92% of the exo product. Addition occurs predominantly to the methacrolein C α-Re face. In solution, water in (R)-8 exchanges readily. Moreover, a second exchange process renders the diastereotopic BINOP-F phosphorus atoms equivalent. These processes were studied by the application of variable-temperature 1H, 31p, and 17O NMR spectroscopy, variable-pressure 31p and 17O NMR spectroscopy, and, using a simpler model complex, density functional theory (DFT) calculations. The results point to a dissociative mechanism of the aquo ligand and a pendular motion of the BINOP-F ligand. NMR experiments show an energy barrier of 50.7 kJ mol-1 (12.2 kcal mol-1) for the inversion of the pseudo-chirality at the ruthenium center.
