Rational synthesis of hexanuclear metallacycles by alkylation reactions of an S-bridged Co IIIPd IICo III trinuclear complex containing non-binding thiolato groups

Abstract

The reaction of an S-bridged Co IIIPd IICo III trinuclear complex containing two non-bridging thiolato groups, [Pd{Co(aet) 3} 2] 2+ (aet = 2-aminoethanethiolate), with o-dibromoxylene ( o-xylBr 2) in water produced a cyclic Co III 4Pd II 2 hexanuclear complex, [{Co 2Pd(aet) 4} 2( o-L) 2] 8+ ([ 1] 8+; o-L = o-bis(2-aminoethylthiomethyl)benzene), in which two Co IIIPd IICo III trinuclear units are linked by two o-xyl 2+ moieties through C–S bonds. A similar cyclic Co III 4Pd II 2 complex, [{Co 2Pd(aet) 4} 2( m-L) 2] 8+ ([ 2] 8+; m-L = m-bis(2-aminoethylthiomethyl)benzene), bearing a relatively large cavity that accommodates water molecule(s), was synthesized by the reaction of [Pd{Co(aet) 3} 2] 2+ with m-dibromoxylene ( m-xylBr 2) in water. While [ 1] 8+ afforded only the racemic (Δ 4/Λ 4) isomer, both the racemic ([ 2a] 8+; Δ 4/Λ 4) and the meso ([ 2b] 8+; Δ 2Λ 2) isomers were formed for [ 2] 8+. In addition, the meso [ 2b] 8+ was found to exist as a mixture of two diastereomers, (Δ S ) 2(Λ R ) 2 and (Δ S Δ R )(Λ R Λ S ), which arise from the difference in chiral configurations ( R and S) of asymmetric sulfide S atoms, while the racemic [ 1] 8+ and [ 2a] 8+ existed as a pair of enantiomers, (Δ S ) 4 and(Λ R ) 4, which were optically resolved. The complexes obtained were characterized on the basis of electronic absorption, CD, and NMR spectroscopies, along with single crystal X-ray analyses.