Towards magnetic molecule and reagent separation in organic synthesis: Development and use of covalently functionalized nanomagnets

Preparative chemistry combines theoretical complexity and arduous practical work in the laboratory. As a result, chemists often spend long hours waiting for products to react, dry, separate, and crystallize or to be analyzed. Partial relief from waiting comes with today's broad access to efficient and elegant synthetic methods. The present contribution addresses the time-consuming work between the actual chemical reaction steps where labor-intensive work is done manually. Even the most skillful chemists admit that reactions typically run on their own while personal time is largely spent on the workup and, most important, on their planning. This article demonstrates how covalently functionalized cobalt nanomagnets can offer an unconventional way to significantly speed up separation of reagents or products in synthesis. Combining concepts from Merrifield chemistry and making use of novel materials preparation methods, reagents or synthetic intermediates can now be covalently attached to nanomagnets. With a size range of 10-50 nm, the tiny metal particles have sufficient specific surface area to attach molecules at a capacity close to presently used Wang resins or Merrifield chemistry. A synthesis can now be run in the presence of the magnetic helping agents and, if necessary, the tagged compounds can be removed from the reaction mixture within seconds. While magnetic molecule separation is still in its infancy, the present review offers insight into the materials origins and first applications.