C–H benzylic oxidation promoted by dinuclear iron DBDOC iminopyridine complexes

Dinuclear Iron Complexes of Iminopyridine-Based Ligands as Selective Cytotoxins for Tumor Cells and Inhibitors of Cancer Cell Migration

A family of dinuclear iron (II) compounds with iminopyridine-based ligands displays selective cytotoxic activity against cancer cell lines. All compounds have IC₅₀ values 2-6 fold lower than that of cisplatin, and 30-90 fold lower than that of carboplatin for the tumor cell lines assayed. Comparing the IC₅₀ values between tumor and non-tumor cell lines, the selectivity indexes range from 3.2 to 34, compound 10, [Fe₂(4)₂(CH₃CN)₄](BF₄)₄, showing the highest selectivity. Those compounds carrying substituents on the iminopyridine ring show the same cytotoxicity as those without substituents. However, the electronic effects of the substituents on position 6 may be important for the cytotoxicity of the complexes, and consequently for their selectivity. All compounds act over DNA, promoting cuts on both strands in the presence of reactive oxygen species. Since compound 10 presented the highest selectivity, its cytotoxic effect was further characterized. It induces apoptosis, affects cell cycle phase distribution in a cell-dependent manner, and its cytotoxic effect is linked to reactive oxygen species generation. In addition, it decreases tumor cell migration, showing potential antimetastatic effects. These properties make compound 10 a good lead antitumor agent among all compounds studied here.

Solution-State Spin Crossover in a Family of [Fe(L)2(CH3CN)2](BF4)2 Complexes

We report herein on five new Fe(II) complexes of general formula [Fe(L)2(NCCH3)2](BF4)2•xCH3CN (L = substituted 2-pyridylimine-based ligands). The influence of proximally located electron withdrawing groups (e.g., NO2, CN, CF3, Cl, Br) bound to coordinated pyridylimine ligands has been studied for the effect on spin crossover in their Fe(II) complexes. Variable-temperature UV-visible spectroscopic studies performed on complexes with more strongly electronegative ligand substituents revealed spin crossover (SCO) in the solution, and thermodynamic parameters associated with the spin crossover were estimated.

Transition-Metal-Free C(sp³)⁻H Oxidation of Diarylmethanes

An efficient direct C(sp3)–H oxidation of diarylmethanes has been demonstrated by this study. This method employs environment-friendly O₂ as an oxidant and is promoted by commercially available MN(SiMe₃)₂ [M = K, Na or Li], which provides a facile method for the synthesis of various diaryl ketones in excellent yields. This protocol is metal-free, mild and compatible with a number of functional groups on substrates.

Cu(I) Coordination Polymers as the Green Heterogeneous Catalysts for Direct C-H Bonds Activation of Arylalkanes to Ketones in Water with Spatial Confinement Effect

To develop coordination polymers (CPs) as catalysts to selectively catalyze the reaction of C-H bond activation of arylalkanes to their homologous ketones, three new Cu(I)-based coordination polymers (Cu^I-CPs) [CuI(aas-TPB)]_n (1), [CuBr(ass-TPB)CH₃CN]_n (2), and {[Cu(ass-TPB)]Cl}_n (3) (TPB = N,N,N-tris(3-pyridinyl)-1,3,5-benzenetricarboxamide) were synthesized. Structural variations from a herringbone fashion one-dimensional framework of 1 to a two-dimensional framework of 2 containing a 48-membered macrocycle and a cationic three-dimensional framework of 3 filled with Cl^- anions were observed arising from the different halogen ions (I^-, Br^-, and Cl^-). 1-3 were used as the green heterogeneous catalysts to catalyze direct C-H bond activation reactions of arylalkanes to ketones under mild reaction conditions with water as solvent. Handy product separation, convenient reaction procedures, and recyclability of these catalysts make the catalytic system fascinating. Moreover, the Cu^I-CPs performed the reaction with high regioselectivity due to the unique spatial confinement effect of CPs.

The cumene/O2 system: a very simple tool for the radical chain oxidation of some functional groups

Due to the relative stability of the cumyl radical, cumenes and α-methyl-styrenes are ideally structured to directly harvest the oxidizing reactivity of O2 and initiate radical chain reactions in catalyst-free conditions. In the absence of additional substrates, these processes can lead to acetophenones. In the presence of substrates, the cumene oxidation process can be intercepted in various chain reactions, affording very simple protocols for functional group oxidation.

Novel iminopyridine derivatives: ligands for preparation of Fe(ii) and Cu(ii) dinuclear complexes

A series of imino- and amino-pyridine ligands based on dihydrobenzofurobenzofuran (BFBF) and methanodibenzodioxocine (DBDOC) backbones have been synthesized. These ligands form exclusively dinuclear complexes with metals such as iron(II) and copper(II). The structures for complexes 15, 16, 18, 19, 20, 21, 23, and 24 were determined by X-ray crystallography. The complexes show large distances for the metal nuclei and different geometries depending on the nature of the metal. An octahedral geometry was observed for the iron(II) complexes, while copper(II) complex 24 showed a distorted trigonal bipyramidal geometry. The iron(II) complexes showed activity as catalysts in the cycloaddition of CO2 to epoxides, obtaining moderate yields of cyclic carbonates.

C-H Bond Oxidation Catalyzed by an Imine-Based Iron Complex: A Mechanistic Insight

A family of imine-based nonheme iron(II) complexes (LX)2Fe(OTf)2 has been prepared, characterized, and employed as C-H oxidation catalysts. Ligands LX (X = 1, 2, 3, and 4) stand for tridentate imine ligands resulting from spontaneous condensation of 2-pycolyl-amine and 4-substituted-2-picolyl aldehydes. Fast and quantitative formation of the complex occurs just upon mixing aldehyde, amine, and Fe(OTf)2 in a 2:2:1 ratio in acetonitrile solution. The solid-state structures of (L1)2Fe(OTf)(ClO4) and (L3)2Fe(OTf)2 are reported, showing a low-spin octahedral iron center, with the ligands arranged in a meridional fashion. (1)H NMR analyses indicate that the solid-state structure and spin state is retained in solution. These analyses also show the presence of an amine-imine tautomeric equilibrium. (LX)2Fe(OTf)2 efficiently catalyze the oxidation of alkyl C-H bonds employing H2O2 as a terminal oxidant. Manipulation of the electronic properties of the imine ligand has only a minor impact on efficiency and selectivity of the oxidative process. A mechanistic study is presented, providing evidence that C-H oxidations are metal-based. Reactions occur with stereoretention at the hydroxylated carbon and selectively at tertiary over secondary C-H bonds. Isotopic labeling analyses show that H2O2 is the dominant origin of the oxygen atoms inserted in the oxygenated product. Experimental evidence is provided that reactions involve initial oxidation of the complexes to the ferric state, and it is proposed that a ligand arm dissociates to enable hydrogen peroxide binding and activation. Selectivity patterns and isotopic labeling studies strongly suggest that activation of hydrogen peroxide occurs by heterolytic O-O cleavage, without the assistance of a cis-binding water or alkyl carboxylic acid. The sum of these observations provides sound evidence that controlled activation of H2O2 at (LX)2Fe(OTf)2 differs from that occurring in biomimetic iron catalysts described to date.