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(mu-oxo)trititanium(IV,IV,IV) complex [Ti3L3(mu-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 boolean AND O chelate loops (lambda) as well as the six-membered non-planner chair-like (Ti-mu-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(O-phenolato-O-phenolato) binding mode by unequivocally locating one O-phenolato in an axial position and the other O-phenolato in an equatorial plane. (c) 2006 Elsevier B.V. All rights reserved.