Darstellung,Eigenschaften und Kristallstruktur von Cl3(bpy)Ta  NOCH3, einem Methoxynitrenkomplex des Tantals

Synthesis, Properties, and Crystal Structure of Cl₃(bpy)Ta≡NOCH₃, a Methoxynitrene Complex of Tantalum TaCl₅ reacts in the presence of 2,2′-bipyridine with O-methyl-hydroxylamine or bis(trimethylsilyl)-O-methyl-hydroxylamine to yield the methoxynitrene complex Cl₃(bpy)Ta≡NOCH₃. The red complex decomposes only slowly at moist air. It crystallizes in the monoclinic space group C2/c with the lattice constants a = 1588.5, b = 1515.9, c = 1414.2 pm, β = 122.78°, Z = 8. The monomeric complex exhibits a distorted octahedral coordination for the tantalum atom. The methoxynitrene ligand is coordinated by a Ta? N triple bond resulting in a linear Ta≡N? O arrangement with Ta? N? O = 174.0° and distances Ta? N = 174.4 pm and N? O = 134.8 pm. v(Ta? N) is observed in the i.r. spectrum at 950 cm^?1.     

2, 4-Dimethyl -5 -nitrofuran -3 -carboxylic acid and its derivatives

It is found that 2, 4-dimethyl-5-nitrofuran-3-carboxylic acid and its methyl ester can give comparatively stable anionic groups, which are prepared electrochemically and investigated by EPR. Their lives (80–100 sec) are 4- 5 times greater than the lives of other anionic groups of the 5-nitrofuran series previously studied. Starting from 2, 4-dimethyl-5-nitrofuran-3-carboxylic acid and 2, 4-dimethylfuran-3-carboxylic acid, two new semisynthetic penicillins are prepared, with activities basically extending to Gram-positive microorganisms, including forms of staphylcocci resistant to benzylpenicillin. Introduction of the nitro group into the furan ring increases the stability of penicillin to acid 79-fold. Low toxicity penicillins are synthesized (LD₅₀ 1000–1500 mg/kg).