Chiral Induction via the Disassembly of Diruthenium(II,III) Tetraacetate by Chiral Diphosphines

Abstract

[Ru(2)(μ-O(2)CCH(3))(4)(MeOH)(2)](PF(6)) reacts with chiral diphosphines (R,R)- and (S,S)-chiraphos, leading to disassembly and production of the enantiomers Λ-[Ru(η(2)-O(2)CCH(3))(η(2)-(R,R)-chiraphos)(2)](PF(6)) and Δ-[Ru(η(2)-O(2)CCH(3))(η(2)-(S,S)-chiraphos)(2)](PF(6)) in high yield and purity. X-ray crystallography and solid-state circular dichroism (CD) show that only the indicated isomers are present in the solid state. Solution CD measurements also indicate their predominance in solution.

Chiral Induction at Octahedral Ru(II) via the Disassembly of Diruthenium(II,III) Tetracarboxylates Using a Variety of Chiral Diphosphine Ligands

“…In all cases, the CD signal for the free ligands lie below 290 nm . As well, none of the solution CD signals changed over a period of at least 5 days at room temperature, supporting our earlier conclusion that the rate of epimerization at the relatively inert Ru(II) centers is quite slow if it occurs at all. Let us now deal with each complex (or pair of complexes) in a bit more detail.…”

“…In our preliminary Communication, R,R- and S,S -Chiraphos ligands induced Λ and Δ chirality, respectively, when reacted with [Ru 2 (μ-O 2 CCH 3 ) 4 ­(MeOH) 2 ](PF 6 ) to form Λ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - R,R -Chiraphos) 2 ](PF 6 ) and Δ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - S,S -Chiraphos) 2 ](PF 6 ). When we introduce the larger phenyl R-group into the starting dimer, a similar disassembly takes place in this study, and the products have the same stereochemistry; i.e., R,R -Chiraphos induces Λ chirality at the metal to form Λ- R,R -III , and S,S- Chiraphos induces Δ chirality to form Δ- S,S -III .…”

“…Subsequent reaction of either the acetate or benzoate diadduct with the appropriate chiral (or achiral) diphosphine yielded the desired products. A detailed outline of the mechanism of this reaction is reported elsewhere, and a discussion of the possibility of any epimerization processes is given in our earlier communication . The benzoate diadduct yielded the Ru(II) complexes [Ru(η 2 -O 2 CC 6 H 5 )­(η 2 -dppe) 2 ](PF 6 ) II , Λ-[Ru(η 2 -O 2 CC 6 H 5 )­(η 2 - R,R -Chiraphos) 2 ](PF 6 ) Λ- R , R -III , Δ-[Ru(η 2 -O 2 CC 6 H 5 )­(η 2 - S , S -Chiraphos) 2 ](PF 6 ) Δ- S,S -III , Λ-[Ru(η 2 -O 2 CC 6 H 5 )­(η 2 - S,S - o-tolyl- Dipamp) 2 ](PF 6 ) “ Λ- S,S -IV ”, and Δ-[Ru(η 2 -O 2 CC 6 H 5 )­(η 2 - R,R - o-tolyl- Dipamp) 2 ](PF 6 ) “ Δ- R,R- IV ”, whereas the acetate diadduct was converted to Λ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - S,S - o-tolyl- Dipamp) 2 ](PF 6 ) “ Λ- S,S -V ”, Δ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - R,R - o-tolyl- Dipamp) 2 ](PF 6 ) “ Δ- R,R- V ”, and Λ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - R -Prophos) 2 ](PF 6 ) Λ- R -VI .…”

“…In an earlier communication in this journal, we reported on the reaction of the diruthenium(II,III) tetraacetate core with the chiral diphosphines R,R - and S,S- Chiraphos (see ligand structures in Chart ), which through chiral induction led to the complexes Λ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - R,R -Chiraphos) 2 ](PF 6 ), and Δ-[Ru(η 2 -O 2 CCH 3 )­(η 2 - S,S -Chiraphos) 2 ](PF 6 ), respectively, with very high diastereoselectivity . We extend this work here to study the effect on the chiral induction process of (a) changing the carboxylate R group from -CH 3 to -C 6 H 5 , (b) moving the chiral center(s) from the spacer ethylene group in Chiraphos to the coordinating phosphorus atoms in the Dipamp ligands, and (c) reducing the number of chiral centers from 2 to 1 in the ligand Prophos.…”

Chirality transfer based on reversible C–C bond formation/breaking in nickel(ii) complexes

“…2 In coordination chemistry, considerable interest has been directed toward the chirality transfer from a tetrahedral centre of an organic ligand to an octahedral metal centre, and steric factors that govern the chiral selective formation of metal complexes have been extensively investigated. 3 The chirality transfer between metal centres has also been observed in the formation of multinuclear complexes with a helical chirality. 4 Recently, the chiral-auxiliarymediated asymmetric synthesis based on an efficient chirality transfer was reported in an octahedral ruthenium polypyridyl system.…”