Spectroscopic and Computational Studies of Spin States of Iron(IV) Nitrido and Imido Complexes.

High-oxidation-state metal complexes with multiply bonded ligands are of great interest for both their reactivity as well as their fundamental bonding properties. This paper reports a combined spectroscopic and theoretical investigation into the effect of the apical multiply bonded ligand on the spin-state preferences of threefold symmetric iron(IV) complexes with tris(carbene) donor ligands. Specifically, singlet (S = 0) nitrido [{PhB(Im)}FeN], R = Bu (1), Mes (mesityl, 2) and the related triplet (S = 1) imido complexes, [{PhB(Im)}Fe(NR')], R = Mes, R' = 1-adamantyl (3), Bu (4), were investigated by electronic absorption and Mössbauer effect spectroscopies.

Crystal structures of bis- and hexakis[(6,6'-di-hydroxy-bipyridine)copper(II)] nitrate coordination complexes.

Two multinuclear complexes synthesized from Cu(NO3)2 and 6,6'-di-hydroxy-bipyridine (dhbp) exhibit bridging nitrate and hydroxide ligands. The dinuclear complex (6,6'-di-hydroxy-bipyridine-2κ(2) N,N')[μ-6-(6-hy-droxy-pyridin-2-yl)pyridin-2-olato-1:2κ(3) N,N':O (2)](μ-hydroxido-1:2κ(2) O:O')(μ-nitrato-1:2κ(2) O:O')(nitrato-1κO)dicopper(II), [Cu2(C10H7N2O2)(OH)(NO3)2(C10H8N2O2)] or [Cu(6-OH-6'-O-bpy)(NO3)(μ-OH)(μ-NO3)Cu(6,6'-dhbp)], (I), with a 2:1 ratio of nitrate to hydroxide anions and one partially deprotonated dhbp ligand, forms from a water-ethanol mixture at neutral pH. The hexa-nuclear complex bis-(μ3-bi-pyridine-2,2'-diolato-κ(3) O:N,N':O')tetra-kis-(6,6'-di-hydroxy-bipyridine-κ(2) N,N')tetra-kis-(μ-hydroxido-κ(2) O:O')bis-(methanol-κO)tetra-kis-(μ-nitrato-κ(2) O:O')hexa-copper(II), [Cu6(C10H6N2O2)2(CH4O)2(OH)4(NO3)4(C10H8N2O2)4] or [Cu(6,6'-dhbp)(μ-NO3)2(μ-OH)Cu(6,6'-O-bpy)(μ-OH)Cu(6,6'dhbp)(CH3OH)]2, (II), with a 1:1 NO3-OH ratio and two fully protonated and fully deprotonated dhbp ligands, was obtained by methanol recrystallization of material obtained at pH 3.

Studies of the pathways open to copper water oxidation catalysts containing proximal hydroxy groups during basic electrocatalysis.

Water oxidation can lead to a sustainable source of energy, but for water oxidation catalysts to be economical they must use earth abundant metals. We report here 2:1 6,6'-dihydroxybipyridine (6,6'-dhbp)/copper complexes that are capable of electrocatalytic water oxidation in aqueous base (pH = 10-14). Two crystal structures of the complex that contains 6,6'-dhbp and copper(II) in a ratio of 2:1 (complex 1) are presented at different protonation states.

Ruthenium dihydroxybipyridine complexes are tumor activated prodrugs due to low pH and blue light induced ligand release.

Ruthenium drugs are potent anti-cancer agents, but inducing drug selectivity and enhancing their modest activity remain challenging. Slow Ru ligand loss limits the formation of free sites and subsequent binding to DNA base pairs. Herein, we designed a ligand that rapidly dissociates upon irradiation at low pH.

Iridium dihydroxybipyridine complexes show that ligand deprotonation dramatically speeds rates of catalytic water oxidation.

We report highly active iridium precatalysts, [Cp*Ir(N,N)Cl]Cl (1-4), for water oxidation that are supported by recently designed dihydroxybipyridine (dhbp) ligands. These ligands can readily be deprotonated in situ to alter the electronic properties at the metal; thus, these catalyst precursors have switchable properties that are pH-dependent. The pKa values in water of the iridium complexes are 4.

Thermodynamics of hydrogen atom transfer to a high-valent iron imido complex.

Thermodynamic investigations relevant to hydrogen atom transfer by the high-valent iron imido complex [LMesFe[triple bond]NAd]OTf have been undertaken. The complex is found to be weakly oxidizing by cyclic voltammetry (E1/2 = -0.98 V vs Cp2Fe+/Cp2Fe in MeCN).

A new synthetic route to bulky "second generation" tris(imidazol-2-ylidene)borate ligands: synthesis of a four coordinate iron(II) complex.

A bulky tripodal tris(carbene)borate ligand, prepared from 1-tert-butylimidazole, is cleanly transferred to iron(II) by a magnesium reagent.