Control of Stereochemistry at the Metal Center in Planar-Chiral Cyclopentadienyl Ruthenium Complexes with Anchor Phosphine on Complexation with Salicylideneaminato Ligands

Reactions of planar-chiral cyclopentadienyl-phosphine ruthenium complexes [η5,η1-{C5H2(Me)(R)COO(CH2)2PPh2}Ru(MeCN)2][PF6] (1a, R = Me; 1b, R = Ph) with sodium salicylideneaminato (2) led to the formation of salicylideneaminato complexes (3 and 4, R = Me; 5 and 6, R = Ph) inducing metal-centered chirality with a high selectivity (up to >99% de). The diastereoselectivity of products did not depend on the substituent on aromatic ring of salicylideneaminato ligands, but upon the substituents on the cyclopentadienyl group and on nitrogen of the imino group. X-ray diffraction and NMR studies including NOE measurements revealed that the configuration of the major isomers is S Cp R Ru/R Cp S Ru. Similar reactions of planar-chiral cyclopentadienyl ruthenium complexes [η5-{C5H2(Me)(R)COOEt}Ru(PPh3)(MeCN)2][PF6] (7) (7a, R = Me; 7b, R = Ph) having no anchor phosphine ligands with 2 also gave salicylideneaminato complexes (8 and 9) with a low selectivity. Epimerization of a pure sample of the major product 5a into a diastereomeric mixture of 5a and 6a showed that the diastereoselectivity at the ruthenium center is governed by the difference in thermodynamic stability between 3 and 4, or 5 and 6.