Synthesis, X-ray structure and properties of a new nitrite-bound copper(II) complex with 2-(3,5- dimethylpyrazol-1-ylmethyl)pyridine in a CuN4(O) coordination

Nitrite and Nitric Oxide Interconversion at Mononuclear Copper(II): Insight into the Role of the Red Copper Site in Denitrification

Nitrite (NO2 - ) and nitric oxide (NO) interconversion is crucial for maintaining optimum NO flux in mammalian physiology. Herein we demonstrate that [L2 CuII (nitrite)]+ moieties (in 2 a and 2 b; where, L = Me2 PzPy and Me2 PzQu) with distorted octahedral geometry undergo facile reduction to provide tetrahedral [L2 CuI ]+ (in 3 a and 3 b) and NO in the presence of biologically relevant reductants, such as 4-methoxy-2,6-di-tert-butylphenol (4-MeO-2,6-DTBP, a tyrosine model) and N-benzyl-1,4-dihydronicotinamide (BNAH, a NAD(P)H model). Interestingly, the reaction of excess NO gas with [L2 CuII (MeCN)2 ]2+ (in 1 a) provides a putative {CuNO}10 species, which is effective in mediating the nitrosation of various nucleophiles, such as thiol and amine. Generation of the transient {CuNO}10 species in wet acetonitrile leads to NO2 - as assessed by Griess assay and 14 N/15 N-FTIR analyses. A detailed study reveals that the bidirectional NOx -reactivity, namely, nitrite reductase (NIR) and NO oxidase (NOO), at a common CuII site, is governed by the geometric-preference-driven facile CuII /CuI redox process. Of broader interest, this study not only highlights potential strategies for the design of copper-based catalysts for nitrite reduction, but also strengthens the previous postulates regarding the involvement of red copper proteins in denitrification.

Involvement of a Formally Copper(III) Nitrite Complex in Proton-Coupled Electron Transfer and Nitration of Phenols

A unique high-valent copper nitrite species, LCuNO2, was accessed via the reversible one-electron oxidation of [M][LCuNO2] (M = NBu4+ or PPN+). The complex LCuNO2 reacts with 2,4,6-tri-tert-butylphenol via a typical proton-coupled electron transfer (PCET) to yield LCuTHF and the 2,4,6-tri-tert-butylphenoxyl radical. The reaction between LCuNO2 and 2,4-di-tert-butylphenol was more complicated. It yielded two products: the coupled bisphenol product expected from a H-atom abstraction and 2,4-di-tert-butyl-6-nitrophenol, the product of an unusual anaerobic nitration. Various mechanisms for the latter transformation were considered.

Structural and Magnetic Properties of Three One-Dimensional Azido-Bridged Copper(II) and Manganese(II) Coordination Polymers

Three one-dimensional (1D) azido-bridged coordination polymers of formula [Cu(L)(N3)2]n (1), [Cu2(Me-L)(N3)4]n (2), and [Mn(L)(N3)2]n (3) have been synthesized and structurally characterized, and their magnetic properties studied, where L and Me-L are 2-(pyrazol-1-ylmethyl)pyridine and 2-(3-methylpyrazol-1-ylmethyl)pyridine, respectively. Compound 1 consists of 1D chains in which the Cu(II) ions with a square pyramidal geometry are alternately bridged by an end-to-end (EE) and an end-on (EO) azido ligands, both adopting a basal-apical disposition. Compound 2 exhibits an unprecedented chain topology built via three different kinds of EO azido bridges. Four Cu(II) ions in the square pyramidal environment are alternately bridged by single and double EO bridges to form a tetranuclear cyclic ring, and neighboring rings are interlinked by double EO bridges to generate a "chain of rings". The intraannular double azido ions are disposed between metal ions in a basal-basal fashion, and the other two kinds of azido ions adopt the basal-apical disposition. Compound 3 consists of 1D concave-convex chains in which cis-octahedrally coordinated Mn(II) ions are alternately bridged by double EE and double EO bridges. There exist pi-pi interactions between the ligands bound to the neighboring Mn(II) ions bridged by the EO bridges. Temperature- and field-dependent magnetic analyses reveal alternate ferromagnetic interactions for 1, dominating ferromagnetic interactions for 2, and alternating ferro- and antiferromagnetic interactions through the EO and EE azido bridges for 3, respectively.