C₂-symmetric group 4 metal complexes adorned with chiral N,O chelates: Synthesis and structural characterization of helical hexacoordinate metal dichlorides derived from 6-isopropyl-3-methyl-2-(4-isopropyl-4,5- dihydrooxazol-2-yl)phenol ligands

A series of group 4 metal complexes containing [6-isopropyl-3-methyl-2-(4- R-4, 5-dihydrooxazol-2-yl)phenol] ligands, N,O-(Oz^R-O^ph) [Oz^R = oxazolyl; R = iPr (4), tBu (5); O^ph = phenolate] was prepared. The reaction of the lithium salts of compounds 4 and 5 with MCl₄, (M = Ti, Zr, Hf) in 2:1. ratio afforded the corresponding hexacoordinate metal complexes of the types [{N,O-(Oz^iPr-O ^ph)}₂MCl₂] [M = Ti (6), Zr (7), Hf (8)] and [{N,O(Oz^tBu-O^ph)}₂MCl₂] [M = Ti (9), Zr (10), Hf(11)], respectively. The molecular structures of 6, 7, and 8 were established by Xray structural studies. The structures showed a helical screw-shaped molecular entity with two alternating N,O-chelating ancillary ligands and two cis-chlorido ligands at the metal centers. In the case of compound 6, chiral locking by two N,O-chelating ligands at the titanium resulted in unusual air stability. The cyclic voltammogram showed electrochemically quasireversible reduction for compound 6, whereby the half-life of the reduction state was about 3 s.