Optically active transition metal complexes.: Part 115.: Synthesis, crystal structure and properties of chiral (η5-C5H5)Ru complexes with pyrrolecarbaldiminato and salicylaldiminato ligands

The chiral complexes CpRu(LL*)PPh3, Cp = eta(5)-C5H5, LL*-1 = anion of 2-N-[(S)-1-phenylethyl]pyrrolecarbaldimine LL*-2 = anion of 2-N-[(R)-hydroxybut-2-yl)]pyrrolecarbaldimine (2a/2b) and LL*-3 = anion of N-[(S)-1-phenylethyl]salicylaldimine (3a/3b), can be prepared by reaction of CpRu(PPh3)(2)Cl and the corresponding ligand HLL* in boiling toluene. An X-ray structure analysis of diastereomerically pure 1a shows S-Ru configuration. The phenyl substituent of the ligand adopts a T-shape arrangement with respect to the Cp ring. The PPh3 ligand is in a right handed propeller conformation. The activation parameters of the epimerization 1a reversible arrow 1b were determined to be Delta H-not equal = (133 +/- 33) kJ mol(-1) and Delta S-not equal = (77 +/- 26) J K-1 mol(-1). The equilibrium ratios are 1a:1b = 86.14, 2a:2b = 1.1 and 3a:3b = 88:12, the attractive interaction between the Cp ring and the phenyl substituent of the chiral center in the chelating ligand LL* favoring one diastereomer of the complexes 1a/1b and 3a/3b. (C) 1998 Elsevier Science S.A. All rights reserved.