Racemic and chiral expanded salen-type complexes derived from biphenol and binaphthol: Salbip and salbin

The reaction of 2-fluoronitrobenzene with 2,2′-biphenol or (R)-binaphthol, followed by reduction and subsequent reaction of the resulting diamine with two equivalents of a salicylaldehyde, affords expanded salen-type ligands having backbones based on biphenol or binaphthol: salbipH2, (R)-salbinH2 and (R)-salbin(t-Bu)4H2. Deprotonation of these ligands with sodium methoxide or potassium hydride, followed by metallation with M(OAc)2 (M = Mn, Co, Ni, or Cu), affords the corresponding metal complexes in good yield (61–85%). The species containing Mn, Co, and Ni all have distorted octahedral geometry, as determined by X-ray crystallography. The ethereal oxygen atoms occupy two coordination sites with metal–oxygen distances ranging from 2.19 to 2.36 Å. The imine nitrogen atoms are trans to each other in the solid state, an impossible geometry in traditional salen-type complexes. The species containing Cu are distorted square planar and show much longer metal–ethereal oxygen distances ranging from 2.79 to 3.22 Å. The manganese complexes are competent catalysts for the epoxidation of olefins.

Graphical abstractThe reaction of 2-fluoronitrobenzene with 2,2′-biphenol or (R)-binaphthol, followed by reduction and subsequent reaction of the resulting diamine with two equivalents of a salicylaldehyde, affords expanded salen-type ligands which are readily metallated to form salbipM and salbinM complexes (M = Mn, Co, Ni, or Cu).Figure optionsDownload full-size imageDownload as PowerPoint slide