Resolution of enantiomers of a series of chiral alkoxy-modified phthalocyaninato nickel(ii) complexes by enantioselective HPLC

Abstract

We have resolved the enantiomers of a series of chiral modified metallophthalocyaninato complexes of nickel bearing alkoxy groups at the 14 and 28 positions on what would otherwise be a normal phthalocyaninato ligand and conforming to the general formula [14,28-(RO)₂Pc]Ni(II), where R = Me, Et, or n-Pr. The complex for which R = n-Pr is reported here for the first time. Resolution of the enantiomers of these complexes was accomplished viaHPLC utilizing an immobilized carbohydrate-based stationary phase, resulting in baseline resolution of peaks corresponding to enantiomers of the complexes, with R_s values in excess of five. Isolation of milligram quantities of the complexes bearing methoxy and n-propoxy groups in high enantiomeric excess has been achieved via semi-preparative-scale HPLC on the same stationary phase. Resolved samples of these compounds do not appear to racemize at an appreciable rate, nor do they readily exchange alkoxy groups with alcohols while stirring in alcoholic solution. The spectroscopic details and the crystallographically-determined solid-state structure for the complex where R = n-Pr are reported, and are highly similar to those that have been observed for the previously reported analogues. It has been shown by NMR that the chirality and C₂ molecular symmetry of the complex bearing n-propoxy groups is maintained in solution.