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Salen ligand
Salen is the abbreviation for a popular chelating ligand used in coordination chemistry and homogeneous catalysis. The name salen is a contraction for salicylic aldehyde and ethylene diamine, which are the precursors to the ligand. As an anionic tetradendate ligand, salen2- resembles other quasi-planar ligands including those that are macrocyclic, such as porphyrinate, corrin, and bis(dimethylglyoximate. Salen together is a preeminent example of a Schiff base. Additional recommended knowledgeThe ligand salenH2 was first prepared by Pfeiffer.[1] It is often generated in situ followed by the addition of the metal salt, but the ligand is also easily prepared as a pure organic compound, as well as being commercially available.[2] Coordination chemistrySalenH2 forms complexes with most transition metals. In most cases, the metal adopts square pyramidal or octahedral coordination, M(salen)L and M(salen)L2. Illustrative examples include VO(salen) and Co(salen)Cl(pyridine). Low-spin d8 metal ions form square planar complexes (see picture at lower right), such as Ni(salen). Salen-related ligandsNumerous variations of salen are known with diverse substituents. For example the ligand abbreviated "Salph" is derived from the condensation of 1,2-phenylenediamine and salicyaldehyde. Chiral versions the salen motif are derived from chiral 1,2-diamines, such as the C2-symmetric 1,2-aminocyclohexane. When the aldehyde is 3,5-di-tert-butylsalicylaldehdye one obtains a ligand that was popularized by Eric Jacobsen. Complexes of this ligand with Cr, Mn, Co, Al have proven useful for diverse asymmetric transformations. For example, see the Jacobsen epoxidation.[3] Analogues of the salenH2 are also derivable by condensation of acetylacetone and ethylene diamine. References
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Salen_ligand". A list of authors is available in Wikipedia. |