Abstract
A series of enantiomerically-pure ruthenium tricarbonyl cyclopentadienone complexes were prepared via the cyclisation of C2-symmetric dialkynes with Ru3(CO)12. Four complexes were characterised by X-ray crystallography and a hydride derivative of one of these was characterised. The complexes were tested in the asymmetric hydrogenation and transfer hydrogenation of acetophenone. Whilst the catalysts were active, acetophenone was reduced in low ee, however a reduction product of up to 46% ee could be obtained when a mild base (iPr2NEt or pyridine) was added to the reaction.
Highlights
Asymmetric Ruthenium Tricarbonyl Cyclopentadienone Complexes; Synthesis and Application to Asymmetric Hydrogenation of Ketones
The OHs were located in a difference map but placed at calculated positions during the refinement. They form short contacts tabulated below Specified hydrogen bonds D-H H...A D...A
The puckering of the ring because of the C=O is described by the angle between mean planes through the diene and a mean plane through the C=O and its two alpha carbons Mean plan C2 C3 C8 C9 to mean plane C2 C1 O1 C9 is 13.287 ( 0.084 ) degrees The angle of the phenyl groups to the mean plane of the diene is mean plane C16 C21 C20 C19 C18 C17 to mean plane C2 C3 C8 C9 is 42.522 ( 0.094 ) degrees and mean plane C10 C15 C14 C13 C12 C11 to mean plane C2 C3 C8 C9 is 75.227 ( 0.082 )
Summary
OH Ru complex 13a Selected expansions: OH Ru2 complex 14 1H NMR H (500 MHz, CDCl3): S8. OBn Ru complex 13b Selected expansions: OBn2Ru hydride complex 15 1H NMR H (500 MHz, CDCl3): S19. OTBS Ru complex 13c Selected expansions: OMe ligand 12d 1H NMR H (500 MHz, CDCl3): S31. The Flack parameter (and Hooft y) are a measure of the confidence you can have in the assignment of the handedness of the crystal chosen. Flack parameter -0.038(5) (Shelx2014) which is small(ish) with a small error so you can be happy with the assignment of the handedness of the crystal chosen ( it matches the configuration of the starting diol) Hooft y parameter -0.040(3) (Olex). Crystal Data for C24H18O6Ru (M =503.45 g/mol): tetragonal, space group I4 The final R1 was 0.0178 (I > 2σ(I)) and wR2 was 0.0447 (all data)
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