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

Hydroxamic Acid: An Underrated Moiety? Marrying Bioinorganic Chemistry and Polymer Science

Even 150 years after their discovery, hydroxamic acids are mainly known as the starting material for the Lossen rearrangement in textbooks. However, hydroxamic acids feature a plethora of existing and potential applications ranging from medical purposes to materials science, based on their excellent complexation properties. This underrated functional moiety can undergo a broad variety of organic transformations and possesses unique coordination properties for a large variety of metal ions, for example, Fe(III), Zn(II), Mn(II), and Cr(III). This renders it ideal for biomedical applications in the field of metal-associated diseases or the inhibition of metalloenzymes, as well as for the separation of metals. Considering their chemical stability and reactivity, their biological origin and both medical and industrial applications, this Perspective aims at highlighting hydroxamic acids as highly promising chelators in the fields of both medical and materials science. Furthermore, the state of the art in combining hydroxamic acids with a variety of polymer structures is discussed and a perspective regarding their vast potential at the interface of bioinorganic and polymer chemistry is given.

Molecular titanium-hydroxamate complexes as models for TiO2 surface binding

Hydroxamate binding modes and protonation states have yet to be conclusively determined. Molecular titanium(iv) phenylhydroxamate complexes were synthesized as structural and spectroscopic models, and compared to functionalized TiO2 nanoparticles. In a combined experimental-theoretical study, we find that the predominant binding form is monodeprotonated, with evidence for the chelate mode.

Intermetallic communication in titanium(IV) ferrocenyldiketonates

A tetradentate bis(ferrocenyldiketonate) ligand, Fc(2)BobH(2), is prepared via Claisen condensation of acetylferrocene and 2,2'-biphenyldiacetyl chloride, and is metalated with titanium(IV) isopropoxide to give (Fc(2)Bob)Ti(O(i)Pr)(2) in good yield. The isopropoxide groups are replaced with di(4-nitrophenyl)phosphate groups on treatment with the corresponding acid, and with chlorides on treatment with trimethylsilyl chloride. Metathesis with catechol leads to the bis(o-hydroxyphenoxide) complex rather than the chelating catecholate complex. Hydrolysis selectively gives the mu-oxo trimer (Delta,Delta,Delta)/(Lambda,Lambda,Lambda)-{(Fc(2)Bob)Ti(mu-O)}(3). The solid-state structures of the mu-oxo trimer and the bis(o-hydroxyphenoxide) complex show that the ferrocene substituents are oriented proximal to the biphenyl backbone rather than pointed out toward the exogenous groups. The complexes show dramatic changes in color depending on the bound anions, ranging from the red isopropoxide (lambda(max) = 489 nm) to the green bis(di(4-nitrophenyl)phosphate) (lambda(max) = 653 nm). The oxidation potentials of the ferrocenes show modest shifts based on the titanium environment, but the redox potentials of the two ferrocenes are never separated by more than 60 mV. These results and those of density-functional theory (DFT) calculations indicate that the titanium interacts principally with the lowest unoccupied molecular orbital (LUMO) of the ferrocenyldiketonate and very little with its highest occupied molecular orbital (HOMO).

Methyl 3-[(1-adamantylcarbon-yloxy)amino-carbon-yl]propanoate

In the title compound, C(16)H(23)NO(5), the H-N-O-C torsion angle is 98.6 (1)°, which is of a similar magnitude to other N,O-diacyl-hydroxy-lamines. The N-O distance is 1.4029 (14) Å, which is similar to the N-O distance in other N,O-diacyl-hydroxy-lamines. In the crystal, intermolecular N-H⋯O hydrogen bonds generate chains of molecules.