N-Tetradentate SPANamine Derivatives and Their MnII-Complexes as Catalysts for Epoxidation of Alkenes

A family of manganese complexes containing heterocyclic-based ligands with cytotoxic properties

We describe the synthesis of three new manganese (II) complexes containing the bidentate ligands 2-(1-methyl-3-pyrazolyl)pyridine (pypz-Me) and ethyl 2-(3-(pyridine-2-yl)-1H-pyrazol-1-yl)acetate (pypz-CH₂COOEt), with formula [MnX₂(pypz-Me)₂] (X = Cl^-1, CF₃SO₃^-2) and [Mn(CF₃SO₃)₂(pypz-CH₂COOEt)₂] 3. Complexes 1-3 have been characterized through analytical, spectroscopic and electrochemical techniques, as well as by monocrystal X-ray diffraction analysis. The complexes show a six-coordinated Mn(II) ion though different stereoisomers have been isolated for the three compounds. Complexes 1-3, together with the previously described compounds [MnCl₂(pypz-H)₂] 4, [Mn(CF₃SO₃)₂(pypz-H)₂] 5, [Mn(NO₃)₂(pypz-H)₂] 6, [MnCl₂(H₂O)₂(pypz-H)₂] 7 (pypz-H = 2-(3-pyrazolyl)pyridine) and ([Mn(CF₃SO₃)₂((-)-L)₂] 8, ((-)-L = (-)-pinene[5,6]bipyridine), were tested in vitro for cytotoxic activity against NCI-H460 and OVCAR-8 cancer cell lines. The geometry of a specific compound does not seem to influence its activity in a significant extent. However, among the tested compounds those that display hydrophobic substituents on the pyrazole ring and triflate ions as labile ligands show the best antiproliferative properties. Specifically, compound 8 containing the pinene-bipyridine ligand presents an antiproliferative activity similar to that of cisplatin and higher than that of carboplatin, and displays selectivity for tumour cells. Its antiproliferative effect is due to the generation of ROS species that allow the compound to interact with DNA.

Copper based coordination polymers based on metalloligands: utilization as heterogeneous oxidation catalysts

This work presents two copper-based coordination polymers and their utilization as stable, reusable and heterogeneous catalysts for the epoxidation of olefins using O₂ and for peroxide-mediated oxidation of benzyl alcohols under solvent-free conditions.

Reusable manganese compounds containing pyrazole-based ligands for olefin epoxidation reactions

New robust and effective Mn-pyrazolyl catalysts for olefin epoxidation in [bmim]PF₆ : CH₃CN, with good activity even after several reuses, are described. The cis → trans isomerization in the epoxidation of cis-β-methylstyrene is confirmed through computational calculations.

How does the addition of steric hindrance to a typical N-heterocyclic carbene ligand affect catalytic activity in olefin metathesis?

Density functional theory (DFT) calculations were used to predict and rationalize the effect of the modification of the structure of the prototype 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) N-heterocyclic carbene (NHC) ligand. The modification consists in the substitution of the methyl groups of ortho isopropyl substituent with phenyl groups, and here we plan to describe how such significant changes affect the metal environment and therefore the related catalytic behaviour. Bearing in mind that there is a significant structural difference between both ligands in different olefin metathesis reactions, here by means of DFT we characterize where the NHC ligand plays a more active role and where it is a simple spectator, or at least its modification does not significantly change its catalytic role/performance.

Ruthenium complexes with chiral bis-pinene ligands: an array of subtle structural diversity

A new chiral derivative of the N,N-bis(2-pyridylmethyl)ethylamine (bpea) ligand, Me-pinene[5,6]bpea [(-)-L1], has been prepared from a new aldehyde building block [Me-pinene-aldehyde, (-)-4] arising from the monoterpene chiral pool. The tridentate (-)-L1 ligand has been employed to prepare a new set of Ru-Cl complexes in combination with didentate 2,2'-bipyridine (bpy) with the general formula [RuCl((-)-L1)(bpy)](+). These complexes have been characterized in solution by cyclic voltammetry, UV-vis, and 1D and 2D NMR spectroscopy. Isomeric mixtures of trans,fac-C1a and anti,mer-C1c compounds are formed when (-)-L1 is reacted with a [Ru(bpy)(MeOH)Cl3] precursor. Density functional theory calculations of all of the potential isomers of this reaction have been performed in order to interpret the experimental results in terms of electronic and steric effects and also to unravel the observed isomerization pathway between anti,mer-C1c and trans,fac-C1a.

Complete σ* intramolecular aromatic hydroxylation mechanism through O2 activation by a Schiff base macrocyclic dicopper(I) complex

In this work we analyze the whole molecular mechanism for intramolecular aromatic hydroxylation through O2 activation by a Schiff hexaazamacrocyclic dicopper(I) complex, [Cu(I) 2(bsH2m)](2+). Assisted by DFT calculations, we unravel the reaction pathway for the overall intramolecular aromatic hydroxylation, i.e., from the initial O2 reaction with the dicopper(I) species to first form a Cu(I)Cu(II)-superoxo species, the subsequent reaction with the second Cu(I) center to form a μ-η(2):η(2)-peroxo-Cu(II) 2 intermediate, the concerted peroxide O-O bond cleavage and C-O bond formation, followed finally by a proton transfer to an alpha aromatic carbon that immediately yields the product [Cu(II) 2(bsH2m-O)(μ-OH)](2+).