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 SCpRRu/RCpSRu. 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.