Coordination Chemistry Solutions: #15

15.* (1994 2 5C) A. Describe how to resolve a racemic mixture of Ru(bipy)₃²⁺ into its two enantiomers, and how to make sure that your separation procedure has worked.

(1) Add a chiral reagent (for example l-tartrate) to a solution of the Ru(bipy)₃²⁺ racemic mixture. The tartrate is needed to form diastereomeric salts in the solution. These salts have different physical properties since they are diastereomers.

(2) Separate the two salts through differences in their physical properties. In this case, we know that the solubility of the two salts is very different. One of the salts is insoluble and can be filtered out of the mixture, leaving the other salt still dissolved in solution.

(3) After recovering and washing the insoluble diastereomeric salt, the pure enantiomer can be recovered by recrystallizing as the dibromide salt. The optical purity of the dibromide salt can be verified by measuring its optical rotation in a solution of known concentration in water. If the solution rotates plane polarized light then at least a partial separation has occurred. If no rotation is observed then a racemic mixture is still present.

The exact enantiomer recovered can be determined by verifying which direction the plane-polarized light is rotated.