Chiral Metal Chelating Stationary Phases

The stationary phases so far considered were found unsuitable for the separation of unsaturated hydrocarbons, ethers and ketones, etc. Schurig and Gil-Av (28) considered that such materials might interact with optically active organometalic agents and provide a basis for chiral selectivity. Schurig and Gil-Av used dicarbonylrhodium (I)-3-trifluoroacetyl-(1R)-camphorate as a stationary phase coated on the inside of stainless steel capillary tube to separate a racemic mixture of 3-methylcyclopentene.

The work on dicarbonylrhodium (I)-3-trifluoroacetyl-(1R)-camphorate inspired further studies on the use of metal chelates for chiral separations. One chelate that showed promise was the manganese chelate (28 ), the structure of which is shown below.

An example of the separation of the enantiomers of some alkyloxiranes using these columns is shown in figure 42. Another interesting example of a chelating agent used for chiral selectivity is that of the aliphatic diolacetonides.

where R = CF₂CF₂CF₃ and M is manganese.

Glass Column 42cm long, 0.25mm I.D. coated with the manganese complex in OCV-101and operated at 40 C. Courtesy J.Chem.Soc.(ref.28)

Figure 42. The Separation of the Enantiomers of Some Alkyloxiranes

The chelate was incorporated into the polysiloxane OV101 (which is dispersive in character) and the basic structure of the chelating agent is shown below.

An example of the use of an aliphatic diolacetonides for the separation of some diol acetonides is shown in figure 43.

Column length 40 m, Column Diameter ).25mm Operating temperature 80 C Courtesy of Anal. Chem. (ref 29)

Figure 43. The Separation of Some Diol Acetonides