Dipotassiumtetrachloride-bridged dysprosium metallocenes: a single-molecule magnet.

The present work describes the dynamic magnetic properties of the complex [(CpAr3)4DyIII2Cl4K2]·3.5(C7H8) (1), synthesized by employing a tri-aryl-substituted cyclopentadienyl ligand (CpAr3), [4,4'-(4-phenylcyclopenta-1,3-diene-1,2-diyl)bis(methylbenzene) = CpAr3H]. Each Dy(III)-metallocene weakly couples via K2Cl4, displaying slow relaxation of magnetization below 14.5 K under zero applied dc field via KD3 energy levels with an energy barrier of 136.9/133.7 cm-1 on the Dy sites. The single-ion axial anisotropy energy barrier is reduced by geometrical distortion due to the coordination of two chloride ions at each Dy centre.

Synthesis, oligomerization and catalytic studies of a redox-active Ni4-cubane: a detailed mechanistic investigation.

A robust tetrameric nickel complex [Ni4((Oal -)2L-Me)4(s)4] (3) (s = solvent) with cubane-like Ni4O4 core topology was isolated as a light greenish-orange crystalline solid in excellent yield. The mechanism of formation of 3 involving the two chloride-containing precursors [Ni4((Oal -)2L-Me)4(s)4]·2MeOH (1) and [Ni4((O-)2L-Me)3((Oal -)(OH)L-Me)Cl] (2) was studied by ESI mass spectrometry and confirmed by the solid state isolation and single-crystal X-ray diffraction. The challenging ligand fields containing mono/di-anionic O2N donating atoms and/or chloride ions stabilized the pentacoordinate Ni(ii) ions in 1-2 upon controlling the experimental conditions. Complexes 1-3 have been characterized by NMR, UV-Vis and mass spectrometric analysis. Complex 3 was found to be redox active by cyclic voltammetry (CV) studies. Theoretical calculations were carried out to shed light on the effects of ligand fields on the stability of complexes 1-3. Complex 3 was found to be a potential catalyst for the diastereoselective cyclopropanation of heteroarenes with good to excellent yields. The ESI mass spectrometric analysis revealed the existence of solution dynamics and oligomerization of 3 in solution. Mechanistic investigation of the catalytic cycle revealed that complex 3 and its various oligomers bind to the diazoester employed, followed by dissociative insertion of the respective carbene moieties to the C2-C3 double bond of the involved aromatic heterocycle, leading to the diastereoselective cyclopropanation.