Ligand-based reduction of nitrate to nitric oxide utilizing a proton-responsive secondary coordination sphere.

Utilizing the proton-responsive pyridinediimine ligand [(2,6-PrCH)(N[double bond, length as m-dash]CMe)(N(Pr)CH)(N[double bond, length as m-dash]CMe)CHN] (didpa), the ligand-based reduction of nitrate (NO) to nitric oxide (NO) was achieved. The bioinspired [Fe(Hdidpa)(CO)] was shown to react with tetrabutylammonium nitrate to form the dinitrosyl iron complex [Fe(didpa)(NO)]. The didpa scaffold was shown to provide two electrons for the net reduction of NO to NO in 43% yield.

Nitrite reduction by a pyridinediimine complex with a proton-responsive secondary coordination sphere.

The proton-responsive pyridinediimine ligand, (DEA)PDI (where (DEA)PDI = [(2,6-(i)PrC6H3)(N[double bond, length as m-dash]CMe)(N(Et)2C2H4)(N[double bond, length as m-dash]CMe)C5H3N]) was utilized for the reduction of NO2(-) to NO. Nitrite reduction is facilitated by the protonated secondary coordination sphere coupled with the ligand-based redox-active sites of [Fe(H(DEA)PDI)(CO)2](+) and results in the formation of the {Fe(NO)2}(9) DNIC, [Fe((DEA)PDI)(NO)2](+).

Stabilization of a Zn(ii) hydrosulfido complex utilizing a hydrogen-bond accepting ligand.

Hydrogen sulfide (H2S) has gained recent attention as an important biological analyte that interacts with bioinorganic targets. Despite this importance, stable H2S or HS(-) adducts of bioinorganic metal complexes remain rare due to the redox activity of sulfide and its propensity to form insoluble metal sulfides. We report here reversible coordination of HS(-) to Zn(didpa)Cl2, which is enabled by an intramolecular hydrogen bond between the zinc hydrosulfido product and the pendant tertiary amine of the didpa ligand.

Pyridinediimine Iron Complexes with Pendant Redox-Inactive Metals Located in the Secondary Coordination Sphere.

A series of pyridinediimine (PDI) iron complexes that contain a pendant 15-crown-5 located in the secondary coordination sphere were synthesized and characterized. The complex Fe((15c5)PDI)(CO)2 (2) was shown in both the solid state and solution to encapsulate redox-inactive metal ions. Modest shifts in the reduction potential of the metal-ligand scaffold were observed upon encapsulation of either Na(+) or Li(+).

Probing the Protonation State and the Redox-Active Sites of Pendant Base Iron(II) and Zinc(II) Pyridinediimine Complexes.

Utilizing the pyridinediimine ligand [(2,6-(i)PrC6H3)N═CMe)(N((i)Pr)2C2H4)N═CMe)C5H3N] (didpa), the zinc(II) and iron(II) complexes Zn(didpa)Cl2 (1), Fe(didpa)Cl2 (2), [Zn(Hdidpa)Cl2][PF6] (3), [Fe(Hdidpa)Cl2][PF6] (4), Zn(didpa)Br2 (5), and [Zn(Hdidpa)Br2][PF6] (6), Fe(didpa)(CO)2 (7), and [Fe(Hdidpa)(CO)2][PF6] (8) were synthesized and characterized. These complexes allowed for the study of the secondary coordination sphere pendant base and the redox-activity of the didpa ligand scaffold. The protonated didpa ligand is capable of forming metal halogen hydrogen bonds (MHHBs) in complexes 3, 4, and 6.