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-(OzR–OPh) [OzR = oxazolyl; R = iPr (4), tBu (5); OPh = 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-(OziPr–OPh)}2MCl2] [M = Ti (6), Zr (7), Hf (8)] and [{N,O-(OztBu–OPh)}2MCl2] [M = Ti (9), Zr (10), Hf (11)], respectively. The molecular structures of 6, 7, and 8 were established by X-ray 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.