A mononuclear manganese(III) complex containing flexible hexadentate chelating ligand has been prepared and characterised by variable temperature single-crystal X-ray diffraction analyses, magnetic, spectroscopic and electrochemical studies. The complex consists MnN4O2...

The three Co(II) complexes [Co(bbp) 2 ][Co(NCS) 4 ]•4DMF (1), [Co(bbp)(NCS) 2 (DMF)]•2DMF (2), and [Co(bbp)(NCS) 2 ](3) have been synthesized and characterized by single-crystal X-ray diffraction, magnetic, and various spectroscopic techniques. Complexes 1 and 3 are obtained by the reaction of Co(NCS) 2 with 2,6-bis(1H-benzo[d]imidazol-2yl)pyridine (bbp), and complex 1 undergoes a structural transformation to form complex 2. A single-crystal X-ray study revealed that complex 1 is comprised of two Co(II) centers, a cationic octahedral Co(II) unit and an anionic tetrahedral Co(II) unit, while the Co(II) ion is in a distorted-octahedral environment in 2. Moreover, in complex 3, the Co(II) ion is in a distorted-square-pyramidal geometry. The effect of coordination geometry on the magnetic properties was studied by both static and dynamic magnetic measurements. Direct current (dc) magnetic susceptibility measurements showed that all of the Co(II) ions are in high-spin state in these complexes. Alternating current (ac) magnetic susceptibility measurements indicated that complexes 2 and 3 display slow relaxation of magnetization in an external dc magnetic field, while complex 1 displayed no such property. EPR experiments and theoretical calculations were consistent with the above findings.

Fe catalyzed carbene insertion reactions present an efficient route for direct CÀ H functionalization. The use of Fe(III) in place of the widely used Fe(II) presents several benefits. However, the mechanistic understanding of Fe(III) severely lags behind Fe(II) complexes. One of the major unsolved issues relates to the formation of bridged versus terminal metallocarbenes. Even though the oxidized bridged carbenoid complexes have been isolated and found to be thermodynamically more stable, they are generally considered a dead end for the catalytic cycle. In the current report, the formation and the subsequent reactions of the bridged carbenoid complexes for an Fe(TPP)Cl catalyzed C(sp 2 )À H insertion are investigated. Using DFT calculations, it is observed that both mono and bis oxidized bridged carbenoid complexes can participate in the catalytic cycle. Importantly, for the first time, a mechanistic pathway showing that these bridged species are not a dead end in Fe catalysis is presented. Their existence in other reactions might be more prevalent than what is currently believed. The current study will have important implications in utilizing Fe(III) complexes for other insertion reactions, especially for heme containing enzymes which necessarily need to be carried out under anaerobic/reducing conditions.