C-2-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

Abstract

A series of group 4 metal complexes containing [6-iso-propyl- 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)}(2)MCl2] [M = Ti (6), Zr (7), Hf (8)] and [{N,O-(Oz(tBu)-O-Ph)}(2)MCl2] [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.