Separation of planar chiral ferrocene derivatives on β-cyclodextrin-based polymer supports prepared via ring-opening metathesis graft-polymerization

A series of β-cyclodextrin (β-CD) based chiral stationary phases (CSPs) were synthesized by ring-opening metathesis graft polymerization of various norborn-2-ene (NBE) substituted CDs. Chiral selectors based on endo/exo-6-O-(norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD, tris(endo/exo-6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD, tetrakis(endo/exo-6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD, hexakis(endo/exo-6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD and tetrakis(endo-6-O-norborn-2-ene-5-carboxyl)-β-CD were grafted onto Nucleosil 300-5 using well-established grafting procedures. CSPs were investigated for their separation capabilities for a series of the planar chiral ferrocene derivatives, rac-ferroceno[2,3a]inden-1-one (1a, 1b), rac-6-(3-hydroxy-3-methylbut-1-yn-1-yl)ferroceno[2,3a]inden-1-one (2a, 2b), rac-ferrocene[2,3a]indene (3a, 3b), rac-endo 1-methoxy-1-allylferroceno[2,3a]indene (4a, 4b) and rac-1,4-dihydroxybutylferrocene (5a, 5b). Compounds 1a, 1b and 2a, 2b bearing a carbonyl group were successfully separated on these CSPs, while compounds 3–5 do not undergo enantioselective interaction under the conditions applied. General aspects of separation as well as mechanistic implementations are discussed.