174677-63-5Relevant academic research and scientific papers
Enantioselective π-complexation. Synthesis of enantiomerically pure planar chiral ruthenocenes
Koelle, Ulrich,Bücken, Karin,Englert, Ulli
, p. 1376 - 1383 (2008/10/08)
Reaction of half-sandwich complexes Cp*RuL2ch, featuring a chiral auxiliary ligand L2ch, with prochiral cyclopentadienides Cppc- gave enantiomerically pure (>95% ee) or enriched ruthenocenes Cp*RuCppc 4. For the chiral auxiliary L2ch were tested a pyridyloxazoline (ref 15), the diolefin nopadiene (ref 16), and the amino acids methionine and proline, which form relatively labile complexes with the Ru(II) fragment Cp*Ru+. For the prochiral cyclopentadienide CppcLi, Li derivatives of 1-tert-butyl-3-methylcyclopentadienide, 1-tert-butylindenyl, and 1- tert-butyl-3-benzylindenyl were used. Determination of enantiomeric excess was achieved through a derivatization procedure generating fulvene cation complexes [CppcRuC5-Me4=CH2]+ (5), which, after the addition of (S)-α-phenylethylamine, yield mixtures of diastereoisomers CppcRuC5H4CH2NHCH(Me)Ph (6). The absolute configuration of 4c (Cppc = 1-tert-butyl-3-benzylindenyl) was determined by X-ray structure analysis of the respective fulvene salt. Asymmetric induction was greatest with the amino acids and was reverted with the epimeric amino acid; thus, (S)-proline or -methionine gave (S)-ruthenocene 4c and vice versa.
