title: Di-μ-oxo dimetal core of Mn(IV) and Ti(IV) as a linker between two chiral salen complexes leading to the stereoselective formation of different M- and P-helical structures.
abstract: Because of restricted rotational freedom along the metal-metal axis, a di-μ-oxo dimetal core could be an excellent building block to create dinuclear compounds with well-defined stereochemistry, but their stereoselective synthesis remains a challenge. We herein report the formation of di-μ-oxo dimanganese(IV) complexes with tetradentate salen ligands bearing different degrees of steric bulk, in order to study stereochemical aspects of the dimerization reaction that potentially generates multiple stereoisomers. X-ray crystallography shows that the di-μ-oxo dimanganese(IV) complex with salen, where salen is (R,R)-N,N'-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, adopts a unique structure in which two salen complexes are arranged in an M-helical fashion. According to the solution study using (1)H, (2)H NMR, and circular dichroism spectroscopies, the dimerization reaction is highly diastereoselective in the presence of the tert-butyl group at the 3/3' position as a determinant steric factor. In contrast, the di-μ-oxo dititanium(IV) complex with the same salen ligand was previously reported to afford an opposite P-helical dimer. The present DFT study clarifies that a less-covalent Ti-O bonding causes a distortion of the di-μ-oxo dititanium(IV) core structure, generating a completely different framework for interligand interaction. The present study provides a solid basis to understand the stereochemistry for the formation of the di-μ-oxo dimetal core.
authors.affiliation: Institute for Molecular Science and Okazaki Institute for Integrative Bioscience , National Institutes of Natural Sciences , Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Kurahashi
authors.forename: Masahiko
authors.initials: M
authors.lastname: Hada
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fujii
mesh_terms: D019281:Dimerization; D005029:Ethylenediamines / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism; D014025:Titanium / Q000737:chemistry*
chemical_list: D005029:Ethylenediamines; D009942:Organometallic Compounds; D008345:Manganese; C011452:disalicylaldehyde ethylenediamine; D014025:Titanium; D010100:Oxygen