Unique tripodal chiral tertiary amine, 2,6-trans-1,2,6-trisubstituted piperidine with pyridine and bis(phenol) donor groups: Its stereoselective coordination to titanium(IV) ion

A new optically active functionalized tertiary amine, (2R,6R)-2,6-bis(2-hydroxyphenyl)-1-(2-pyridylmethyl)piperidine {(R,R)-1}, was synthesized and its complexation behavior as a tripodal ligand was elucidated with titanium(IV) ion. Protonolysis of Ti(OPr-i)4 with (R,R)-1 and H2O in a stepwise manner led to the formation of C3-symmetric tris(μ-oxo)trititanium(IV,IV,IV) complex [Ti3L3(μ-O)3] {L = diphenolato anion of (R,R)-1} with unified chiralities induced at the metal center (A) and by the conformations of the N∧O chelate loops (λ) as well as the six-membered non-planner chair-like (Ti-μ-O)3 ring core as defined by X-ray crystallography. These stereochemical issues are principally regulated by the stereogenic centers on the ligand and a chair conformation of the piperidine skeleton, which settle an enantiotopos-differentiating cis(Ophenolato–Ophenolato) binding mode by unequivocally locating one Ophenolato in an axial position and the other Ophenolato in an equatorial plane.

A new chiral tertiary amine (H2L) based on 2,6-trans-disubstituted piperidine scaffold appended with pyridine and bis(phenol) functionalities was synthesized and demonstrated to work as a tetradentate tripodal ligand, forming [Ti3L3(μ-O)3] with unified chiralities induced at the metal center by the N∧O chelate and the chair-like (Ti-μ-O)3 ring conformations.Figure optionsDownload as PowerPoint slide