Tetradentate Bis(hydroxamate) and Hydroxamate-Diketonate Ligands and Their Titanium(IV) Complexes

Abstract

A 2,2'-bis(methylene)biphenyl-bridged bis(hydroxamic acid) (HoxH(2)) is prepared by reaction of 2,2'-biphenyldiacetyl chloride with 2 equiv of N-methylhydroxylamine. Use of 1 equiv of CH(3)NHOH gives the cyclic diacylhydroxylamine, which is selectively ring-opened to give a mixed monohydroxamate-monodiketonate ligand HobH(2). Both ligands are metalated by Ti(O(i)Pr)(4) to give the corresponding LTi(O(i)Pr)(2) complexes as exclusively the cis-alpha, (R)-Lambda/(S)-Delta isomers, similar to the previously prepared bis(diketonate) analogues (Bob)TiX(2). The carbonyl oxygens of the hydroxamates in the Hox ligand are constrained to be cis to each other, and the crystal structure of (Hob)Ti(O(i)Pr)(2) suggests that the carbonyl oxygen is a slightly weaker donor than the diketonate oxygen, based on a modest difference in their trans influences. A differential trans effect is also manifest in the observation of only a single geometric isomer of (Hob)Ti(O(i)Pr)(O(3)SCF(3)) and in a 15.6:1 preference for the isomer of (Hob)Ti(OCH(2)CMe(2)CO(2)) in which the alkoxide is trans to the hydroxamate ligand.

Optically active bis(β-diketonate) complexes of titanium

“…Analogous complexes with hydroxamates replacing one or both of the diketonates appear to share these stereochemical features. 6 (1)…”

Molecular titanium–hydroxamate complexes as models for TiO2 surface binding

“…5,10 The mc binding mode is analogous to that of a previously synthesized N-alkyl titanium hydroxamate complex, and in the natural product ferrichrome in which an N-alkyl hydroxamic acid chelates iron. 12,13 They could also bind as monodentate species, likely as the monodeprotonated monodentate species mm. Thus, they could bind in a monoanionic form via deprotonation at O (mc, mb, and mm), or dianionic form via deprotonation at O and N (db, dc).…”

Redox-active tetrahydrosalen (salan) complexes of titanium

“…1 H NMR (CDCl 3 ): d 1. 24 An2N LTiF 2 . An2N LH 2 (0.1000 g, 0.115 mmol), TiF 4 (Strem, 0.0284 g, 0.229 mmol), CH 2 Cl 2 (10 mL), and a stir bar were placed in a 20 mL scintillation vial.…”

“…23 We have previously used the formation of titanium chelates of whydroxycarboxylic acids as a way of probing the effects of ancillary ligation with two groups of dissimilar trans influence. 24 The titanium isopropoxide complexes LTi(O i Pr) 2 react rapidly with ahydroxyisobutyric acid or 2,2-dimethyl-3-hydroxypropanoic acid (hydroxypivalic acid) to form chelated alkoxy-carboxylates with 5-or 6-membered chelate rings, respectively (eqn (2)). NMR spectra of the bromo-substituted and diarylamino-substituted salan complexes are very similar to each other, and in each of the four compounds only one C 1 -symmetric isomer is apparent by NMR.…”