Optically active Pt-terpyridyl coordination assemblies derived from planar chiral metallothioligands

A novel enantioselective synthetic procedure to obtain chiral coordination compounds is described. The designed optically active organometallic thioligands (pR, R)-2 and (pS, S)-2 react with Pt(terpy) building blocks to give the related enantiopure coordination assemblies (pR, R)-3 and (pS, S)-3 as confirmed by the induced circular dichroism traces. [Display omitted] Optically active halogenated arenes containing stereogenic benzylic alcohol reacts with [CpRu(CH3CN)3][PF6] to give the major diastereomer with 90% de, in which the metal center is preferentially placed on one face of the arene ring. Thus starting with (S)-1-(2-chlorophenyl)ethanol the metal complex (pS, S)-[CpRu(HO(CH3)CH-C6H4-Cl)][PF6] (pS, S)-1 was obtained in good yield, while the (R)-alcohol provided (pR, R)-[CpRu(HO(CH3)CH-C6H4-Cl)][PF6] (pR, R)-1 metal complex. These compounds display planar and central chiralities. For comparison purposes the analogous racemic compound (rac)-[CpRu(HO(CH3)CH-C6H4-Cl)][PF6] (rac)-1 was also prepared in good yield as well. Subsequent treatment of enantiopure and racemic complexes 1 with NaSH in THF allows halogen displacement to occur at room temperature and generates the related enantiopure neutral metallothioligands of the type (pS, S)-[CpRu(HO(CH3)CH-C6H4-S)], (pS, S)-2, (pR, R)-[CpRu(HO(CH3)CH-C6H4-S)] (pR, R)-2, and (rac)-[CpRu(HO(CH3)CH-C6H4-S)] (rac)-2 (S = sulfur). These metallothioligands react rapidly with [(MeCN)Pt(terpy)][OTf]2 building blocks to give the chiral coordination assemblies [Pt(terpy)-(pS,S)-2][OTf]2 (pS,S)-3, [Pt(terpy)-(pR,R)-3][OTf]2 (pR,R)-3 and the related racemic complex (rac)-3 in which the metal-chromophore is now placed in a chiral environment. The molecular structures of (rac)-3 and the enantiopure heterobimetallic complex (pR,R)-3 were determined and show different arrangements at the supramolecular level depending on whether a homochiral or heterochiral assembly is obtained. The induced circular dichroism curves for the right-handed (pR,R)-3 and left-handed (pS,S)-3 bimetallic complexes displayed mirror image Cotton bands, confirming the enantiomeric relationship between both compounds. Our method provides an entry to the preparation of a wide range of optically pure coordination compounds with potentially important properties.