Eight-Coordinate [Bis(oxyiminodiacetate)-titanium(iv)]~(2-) and Nine-Coordinate [Bis(oxyiminodiacetate)aquazirconium(IV)]~(2-); Variation in Coordination Mode in Amavadin-Like Complexes

摘要

The synthesis and single-crystal X-ray characterization of [NH_4][NMe_4][V(hida)_2], (hida)~(3-) = oxyiminodiacetate, was important in the development of our understanding of the structure of amavadin (H_2[V(S,S-hidpa)_2], (hidpa)~(3-) = oxyimino-2,2'-dipropionate), the form in which vanadium is accumulated in Amanita muscaria. We have confirmed the nature of isolated amavadin, which possesses a novel, eight-coordinate structure. Each (hidpa)~(3-) ligand binds to vanadium through two unidentate carboxylate groups and an eta~2-N,O moiety; the two eta~2-N,O groups are mutually trans and oriented at about 90° to one another. The relative orientations of the two eta~2-N,O groups define the A and A isomers at the stereogenic metal center; amavadin as isolated contains an equal mixture of the two diastereoisomers, [trangle open, A-V(S,S-hidpa)_2]~(2-). We have extended this chemistry to other early transition metals, including Mo, Nb, and Ta. Herein we report the synthesis and characterization of (hida)~(3-) complexes of the Group 4 metals Ti and Zr, which further develops the coordination chemistry of the oxyiminodicarboxylate ligands.