651291-86-0Relevant academic research and scientific papers
Optically active transition metal complexes. Part 133. Preparation, epimerization and crystallization of chiral-at-metal rhodium(III) half-sandwich complexes
Brunner, Henri,K?llnberger,Zabel, Manfred
, p. 2639 - 2646 (2003)
The complexes Cp*Rh(beapy)Cl (5) and Cp*Ir(beapy)Cl (6) were synthesized by reaction of [Cp*MCl2]2 (M = Rh, Ir) and the deprotonated ligand Hbeapy, the condensation product of benzylamine and 2-pyrrolcarbaldehyde. In each case two enantiomers (SM) and (RM arise, differing only in the metal chirality. The CH2 group of the benzyl substituent in the ligand forms an AB spectrum which was used for 1H NMR coalescence measurements (Tc=115.1 °C). The half-life for the racemization of Cp*Rh(beapy)Cl (5) was 46 ms at 115.1 °C. Substitution of the chloride ligand in Cp*Rh(pepy)Cl (3), pepy anion of Schiff base (+)-2-N-[(S)-1-phenylethyl]pyrrolcarbaldimine, afforded the complexes Cp*Rh(pepy)Br (7) and Cp*Rh(pepy)I (8). Single crystals of the two compounds contained only one of the two diastereomers. In solution the compounds epimerized via a change of the metal configuration, the half-life for (RRh, SC)-Cp*Rh(NN*)I (8) being 40.8 min at -40 °C in CD2Cl2 solution (obtained by time dependent integration of suitable 1H NMR signals). Reaction of [CpRhCl2]2 with (+)-N-[(S)-1-phenylethyl]salicylaldimine gave CpRh(pesa)Cl (9). Surprisingly, single crystals of 9 contained both diastereomers (RRh,SC) and (SRh,SC) in a 1:1 ratio following the molecular recognition motif of the inverted pianostools. The half-lifes for the epimerization of 9 with respect to the metal center, derived from 1H NMR coalescence experiments, were 31 and 9.2 ms at 11.3 °C (CD2Cl2) for the forward and back reactions, respectively.
