Umsetzung von Brenzcatechinen mit diarylborinsäuren zu paramagnetischen boratkomplexen

Diaryl borinic acids react smoothly in organic solvents with catechols to stable paramaagnetic complexes. The ESR spectra of the solutions show the hydrogen HFS of the catechol and the coupling with the ¹¹B and ¹⁰B nuclei.     

NMR-spektroskopie an paramagnetischen komplexen : XVIII. Kobaltocene: Nicht-starre paramagnetische π-komplexe

Temperature dependent paramagnetic ¹³C and ¹H NMR spectra of six cobaltocenes (RC₅H₄)₂Co (R = H, Me, Et, i-Pr, n-Bu, t-Bu) are reported. The signals for the substituted five-ring carbons as well as for the substituent ¹³C and ¹H nuclei which are separated from the five-ring by two bonds show a strong departure from the Curie law. This is due to a time-dependent change of the interaction between the five-ring carbons and the metal classifying cobaltocenes as nonrigid molecules. It introduces the previously unknown dynamic paramagnetic ¹³C NMR.     

Isolierung und kristallstrukturanalyse eines titantetrachlorid-komplexes eines 1,3-diketons

Titanium tetrachloride forms a crystalline adduct with 3,3-dimethyl-2,4-pentanedione ($\text{2}$). This observation together with the structural data of complex $\text{4}$ can help to understand the directive force of TiCl₄ in stereoselective reductions of diketones.     

Kristallstruktur eines Lithiumsilylamidbutanids

Crystal Structure of a Lithiumsilylamidebutanide Colorless single crystals of {Li₆[Me₂(H)Si—N—Si(H)—(CHMe₂)₂]₂[n‐C₄H₉]₄} ( 1 ) were obtained from a solution of Me₂(H)SiN(Li)Si(H)(CHMe₂)₂ and n‐C₄H₉Li in n‐hexane. The X‐ray analysis showed that the core of 1 is a distorted octahedron of lithium atoms with ten long and with two short LiÄLi distances. Four of the eight triangular Li₃ faces are capped by an n‐butyl group. The nitrogen atoms of the amide groups are situated about opposite edges of adjacent unoccupied Li₃ faces. (Si)H····Li interactions exist between the hydridic H atom of each Me₂(H)Si group and one Li atom.     

Nmr spektroskopie an paramagnetischen komplexen : XXVI. Paramagnetische peralkyl-metallocene. Synthese,stereochemie und elektronische eigenschaften

The paramagnetic metallocenes (EtMe₄)Cp₂M, M  V, VBr, Cr, Co, Ni have been synthesized starting from the THF adducts of MCl₂. A detailed ¹H and ¹³C NMR study shows that there are two main effects of peralkylation: a change in redox properties and steric repulsion. The reducing power for M  Co, Ni is enhanced and hindered rotation is found for the ethyl group with Cβ being turned away from the metal. Cβ allows to determine selectively the sign of the electron spin density in the ligand π-system. This offers a general way to investigate the spin delocalisation as shown for bent vanadocenes. The limits of the NMR analysis are discussed.