New Reaction Products of Acetylacetone with Semicarbazide Derivatives

A new approach is suggested herein for the synthesis of pyrazole derivatives by reacting 4-nitrosemicarbazide with acetylacetone. Additional studies were done on the reaction of acetylacetone with semicarbazide and its derivatives (4-aminosemicarbazide, methylsemicarbazide, and dimethylsemicarbazide). The study on the reaction with acetylacetone resulted in monocyclic 3,5-dimethyl-N-nitropyrazole-1-carboxamide, monocyclic 5-hydroxy-3,5-dimethyl-2-pyrazoline, and bicyclic bis(3,5-dimethylpyrazole-1-carbonyl)hydrazine, and conditions for the formation of acetone semicarbazone were identified. The structures of the resultant compounds were validated by physicochemical analytical methods, including X-ray diffraction. The computer-aided screening in the PASS prediction software discovered a high biological activity of the newly obtained compounds.

Backbone Dehydrogenation in Pyrrole-Based Pincer Ligands

Treatment of both [CoCl( ^tBuPNP)] and [NiCl( ^tBuPNP)] ( ^tBuPNP = anion of 2,5-bis((di- tert-butylphosphino)methyl)pyrrole) with one equivalent of benzoquinone affords the corresponding chloride complexes containing a dehydrogenated PNP ligand, ^tBudPNP ( ^tBudPNP = anion of 2,5-bis((di- tert-butylphosphino)methylene)-2,5-dihydropyrrole). Dehydrogenation of PNP to dPNP results in minimal change to steric profile of the ligand but has important consequences for the resulting redox potentials of the metal complexes, resulting in the ability to isolate both [CoH( ^tBudPNP)] and [CoEt( ^tBudPNP)], which are more challenging (hydride) or not possible (ethyl) to prepare with the parent PNP ligand. Electrochemical measurements with both the Co and Ni dPNP species demonstrate a substantial shift in redox potentials for both the M(II/III) and M(II/I) couples. In the case of the former, oxidation to trivalent Co was found to be reversible, and subsequent reaction with AgSbF₆ afforded a rare example of a square-planar Co(III) species. Corresponding reduction of [CoCl( ^tBudPNP)] with KC₈ produced the diamagnetic Co(I) species, [Co(N₂)( ^tBudPNP)]. Further reduction of the Co(I) complex was found to generate a pincer-based π-radical anion that demonstrated well-resolved EPR features to the four hydrogen atoms and lone nitrogen atom of the ligand with minor contributions from cobalt and coordinated N₂. Changes in the electronic character of the PNP ligand upon dehydrogenation are proposed to result from loss of aromaticity in the pyrrole ligand, resulting in a more reducing central amido donor. DFT calculations on the Co(II) complexes were performed to shed further insight into the electronic structure of the pincer complexes.

Crystal structure of 4'-bromo-2,5-dihy-droxy-2',5'-dimeth-oxy-[1,1'-biphen-yl]-3,4-dicarbo-nitrile

In the crystal of the title substituted hemibi-quinone derivative, C16H11BrN2O4 or [BrHBQH2(CN)2], the substituted benzene rings are rotated about the central C-C bond, forming a dihedral angle of 53.59 (7)°. The ring systems inter-act through an intra-molecular O-H⋯Ometh-oxy hydrogen bond, which induces a geometry quite different from those in previously reported hemibi-quinone structures. In the crystal, the mol-ecules associate through an inter-molecular O-H⋯Nnitrile hydrogen bond, forming chains which extend along [100] and are inter-linked through very weak C-H⋯N hydrogen bonds, giving a overall two-dimensional structure lying parallel to (010).

Group 9 and 10 complexes with the bidentate di(1H-indazol-1-yl)methane and di(2H-indazol-2-yl)methane ligands: synthesis and structural characterization

Ni, Pd and Co bis(indazol-1-yl)methane complexes assemble into 3D-networks based on intermolecular electrostatic, H-bonds and aromatic interactions.