79201-48-2Relevant academic research and scientific papers
Asymmetric hydrosilation of ketones, catalyzed by rhodium complexes containing chiral chelate ligands. Crystal and molecular structure of (bicyclo[2.2.1]hepta-2,5-diene)[(S)-N,N-dimethyl-1-(o-(diphenylarsino)phenyl) ethylamine]rhodium(I) perchlorate
Payne, Nicholas C.,Stephan, Douglas W.
, p. 182 - 188 (2008/10/08)
Two chiral, bidentate ligands of formula o-(X(C6H5)2)C6H 4CH(CH3)N(CH3)2, amphos (X = phosphorus) and amars (X = arsenic), have been prepared in good yield from (R)- and (S)-1-phenylethylamine. Rhodium complexes of these ligands have been used for the asymmetric hydrosilation of a series of prochiral ketones. For comparison purposes, the reactions were repeated with Rh catalysts containing the chiral, diphosphine species (S,S)-chiraphos and (+)-diop. The maximum enantiomeric excess of 72% was achieved with the amphos catalyst, while, in contrast, the amars catalyst gave no induction. An explanation for this behavior is proposed, on the basis of the results of a three-dimensional single-crystal X-ray study of [Rh(S-amars)(C7H8)]ClO4. The salt crystallizes in space group P1 with two formula units per cell and unit cell dimensions a = 10.154 (6) ?, b = 15.082 (9) ?, c = 9.538 (6) ?, α = 97.64 (1)°, β = 96.05 (1)°, and γ = 74.43 (1)°. The structure has been refined by full-matrix least-squares techniques on F, with the use of 3834 reflections with I > 3σ(I), to a final agreement factor of R1 = 0.059. The two independent chiral cations have essentially square-planar coordination geometries at the Rh atoms (if the diene is viewed as a bidentate chelating ligand), with average Rh-As and Rh-N distances of 2.398 (3) and 2.177 (18) ?, respectively. Each six-membered ring adopts a λ-twist boat conformation. In spite of this, enantiotopic dispositions of the pseudo axial-equatorial arrangements of the phenyl rings are observed in the unit cell, a conformational flexibility which is presumably responsible for the observed optical yields.
