Diastereoselective Routes to [Amino{σ(P):η 6 -(ansa-phosphinite)benzene} chlororuthenium(II)] PF 6 Salts: Kinetic versus Thermodynamic Preferences Immo Weber, †,⊥ Frank W. Heinemann, † Walter Bauer, ( Stefano Superchi, ‡ Achim Zahl, † Daniela Richter, | and Ulrich Zenneck* ,† Department Chemie und Pharmazie, Erlangen Catalysis Resource Center (ECRC), and Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-UniVersita ¨t Erlangen-Nu ¨rnberg, Egerlandstrasse1, D-91058 Erlangen, and Henkestrasse 42, D-91054 Erlangen, Germany, Dipartimento di Chimica, UniVersita ` della Basilicata, Via Nazario Sauro 85, I-85100 Potenza, Italy, and Computer Chemistry Center and ICMM, Friedrich-Alexander-UniVersita ¨t Erlangen-Nu ¨rnberg, Na ¨gelsbachstrasse 25, D-91052 Erlangen, Germany ReceiVed December 17, 2007 A novel chiral phosphinite derivative was designed as a ligand for Ru 2+ ions to give access to new enantiomerically pure or diastereomerically enriched [{σ(P):η 6 -(ansa-phosphinite)benzene}Ru(II) com- plexes. We are interested in this class of compounds as potential catalysts for enantioselective transfer hydrogenation of organic carbonyl compounds. The preparation of enantiopure (R)-[{σ(P):η 6 -(ansa- phosphinite)benzene}Ru(II)Cl 2 ](6) was achieved in good yeld on the basis of (S)-mandelic acid. Four diastereomeric [{σ(P):η 6 -(ansa-phosphinite)benzene}Ru(II)Cl(NH 2 R)] + complex PF 6 - salts were obtained from neutral 6 by nucleophilic substitution of a chloride ligand with primary amines. For aniline and p-fluoroaniline salts 7 and 8 a significant excess of the (S Ru ,R C )-diastereomers 7S and 8S was observed in the reaction mixtures as the kinetically preferred species, and 7S could be isolated as a pure diastereomer. No diastereoselectivity was observed in the reaction mixtures of (R)- and (S)-1-phenylethylamine salts 9 and 10 right after preparation. 7, 8, and 9 epimerize at the metal center. This leads to a loss of diastereoselectivity of 7S and 8S but enrichment of (R Ru ,R C )-diastereomer 9R. Pure diastereomers 7S, 9R, and 10S as well as a 1:1 diastereomeric mixture 8S/8R have been characterized structurally. The experimental setup allowed detailed insight into the specific X-ray crystallographic, CD, and NMR spectroscopic properties of defined stereoisomers of chiral Ru(II) complexes. The kinetic diastereose- lectivities of 7S and 8S are explained by a H-bond delivery effect, while pure diastereomer salt 9R is configuratively stable. Introduction Configurationally stable hapto-arene complexes with pseudo- tetrahedral chiral metal centers 1 and especially chiral Ru(II) η 6 - arene complexes have gained increasing interest after their discovery by Noyori as enantioselective catalysts for transfer hydrogenations. 2 In the scope of potential enantioselective catalysts an ansa linkage from the η 6 -arene ligand of such complexes via an alkyl chain with a terminal σ-donor func- tionality complexed to the pseudotetrahedral Ru(II) center bears unique structural features: (i) An ansa chain with two to three atoms as covalent links besides the σ-donor functionality stabilizes the η 6 -arene moiety toward substitution. (ii) A chiral ansa chain can serve as a provider of “chiral information” in the sense that it closes up one diastereotopic side of the Ru(II) center and creates a “chiral pocket” around it. 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