Kinetics and mechanism of N2 hydrogenation in bis(cyclopentadienyl) zirconium complexes and dinitrogen functionalization by 1,2-addition of a saturated C-H bond

The rates of hydrogenation of the N2 ligand in the side-on bound dinitrogen compounds, [(eta(5)-C5Me4H)2Zr]2(mu2,eta(2),eta(2)-N2) and [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford the corresponding hydrido zirconocene diazenido complexes have been measured by electronic spectroscopy. Determination of the rate law for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) establishes an overall second-order reaction, first order with respect to each reagent. These data, in combination with a normal, primary kinetic isotope effect of 2.2(1) for H2 versus D2 addition, establish the first H2 addition as the rate-determining step in N2 hydrogenation. Kinetic isotope effects of similar direction and magnitude have also been measured for hydrogenation (deuteration) of the two other zirconocene dinitrogen complexes. Measuring the rate constants for the hydrogenation of [(eta(5)-C5Me5)(eta(5)-C5H2-1,2,4-Me3)Zr]2(mu2,eta(2),eta(2)-N2) over a 40 degrees C temperature range provided activation parameters of deltaH(double dagger) = 8.4(8) kcal/mol and deltaS(double dagger) = -33(4) eu. The entropy of activation is consistent with an ordered four-centered transition structure, where H2 undergoes formal 1,2-addition to a zirconium-nitrogen bond with considerable multiple bond character. Support for this hypothesis stems from the observation of N2 functionalization by C-H activation of a cyclopentadienyl methyl substituent in the mixed ring dinitrogen complexes, [(eta(5)-C5Me5)(eta(5)-C5H2-1,2-Me2-4-R)Zr]2(mu2,eta(2),eta(2)-N2) (R = Me, Ph), to afford cyclometalated zirconocene diazenido derivatives.     

Electroactivity of Nonconjugated Proteins and Peptides. Towards Electroanalysis of All Proteins

Present proteomics and biomedicine require sensitive analytical methods for all proteins. Recent progress in electrochemical analysis of peptides and proteins based on their intrinsic electroactivity is reviewed. Tyrosine and/or tryptophan‐containing proteins are oxidizable at carbon electrodes. At mercury electrodes all peptides and proteins (about 13 peptides and >25 proteins were tested) produce chronopotentiometric peak H at nanomolar concentrations. This peak is sensitive to changes in protein structure. Microliter sample volumes are sufficient for the analysis. Electrochemical methods can be used in studies of nucleic acid‐protein interactions and can be applied in biomedicine. Examples of such applications in neurogenerative diseases and cancer are presented.     

Anil-Synthese. 23. Mitteilung. Über die Herstellung von Styryl- und Stilbenyl-Derivaten des Pyrimidins

Preparation of Styryl and Stilbenyl Derivatives of Pyrimidines 2- and 4-(p-Tolyl)-substituted pyrimidines react with anils of hetero-aromatic aldehydes in the presence of dimethylformamide and potassium hydroxide or potassium t-butoxide to yield the corresponding 2- and 4-[4″-(heteroaryl)stilben-4′-yl]pyrimidines or the 2- and 4-[a-(heteroaryl)-4′-styryl]pyrimidines respectively (‘Anil synthesis’). Furthermore, the Schiff′s bases derived from p-chloroaniline and 4-(pyrimidine-2-yl and 4-yl)benzaldehydes give, with methyl- and with p-tolyl-substituted heterocycles, the corresponding heterocyclic substituted styryl and stilbenyl derivatives. Alkyl-, alkoxy- or phenyl-substituted pyrimidines undergo also the ‘Anil synthesis’.     

Stereoselective Syntheses of Benz[f]isoindoline-Derivatives by Intramolecular Cycloadditions of Styrenes to Olefins

The N-allyl-N-cinnamyl amide 10 undergoes thermal cyclization to a 2:1-mixture of the trans- and cis-benz(f)isoindolines 11a and 12a . By comparison, the thermolysis of the corresponding bis-cinnamylamide 14 proceeds in a highly stereoselective manner to give the cis-fused[4+2]-adduct 16a . Similarly, the trans-fused stereoisomeric adducts 30a and 31a were obtained with high stereochemical control on heating the N-allyl-N-diphenylallyl amide 28 . The thermal transformations 4 → 5 + 6a and 17 → 18a + 20a show the competitive formation of [2+2]-adducts. An alternative approach to (substituted) benz[f]isoindolines 16 via the all-cis-isomer 24a has been developed. The described structures have been assigned on the basis of spectral evidence, chemical correlations and by X-ray-diffraction study of the isomer 16b . These results illustrate the utility of substituent interactions in order to direct intramolecular cyclo-additions at will towards either endo- or exo-products.     

Three remarks on the modular commutator

First a problem of Ralph McKenzie is answered by proving that in a finitely directly representable variety every directly indecomposable algebra must be finite. Then we show that there is no local proof of the fundamental theorem of Abelian algebras nor of H. P. Gumm's permutability results. This part may also be of interest for those investigating non-modular Abelian algebras. Finally we provide a Gumm-type characterization of the situation when twonot necessarily comparable congruences centralize each other. In doing this, we introduce a four variable version of the difference term in every modular variety. A two-terms condition is also investigated.Dedicated to the memory of András HuhnPresented by R. W. Quackenbush.     

Entwurf zur Bodenanalyse

Ohne ZusammenfassungBegutachtet von den Commissionsmitgliedern: Dr. Bretschneider, Dr. Grouven, Professor Dr. Knop, Dr. Peters, Dr. Stohmann und Dr. Zöller.Bei der ersten Wanderversammlung deutscher Agriculturchemiker, welche im Mai 1863 zu Leipzig gehalten wurde, sind zum Behufe der Ausarbeitung gemeinsam zu befolgender Methoden und Untersuchungssysteme Commissionen ernannt worden. Als erste Frucht von deren Arbeiten ist in den Landw. Versuchs-Stationen, dem Organ für wissenschaftliche Forschungen auf dem Gebiete der Landwirthschaft, herausgegeben von Dr. Fr. Nobbe, Band VI, der Entwurf zurBodenanalyse von Dr. Emil Wolff, begutachtet von den andern Commissionsmitgliedern, veröffentlicht worden. Ich theile denselben im Einverständniss mit dem Herrn Verfasser auch an dieser Stelle mit, einerseits um den löblichen Zweck, welchen die Wanderversammlung der deutschen Agriculturchemiker im Auge hat, nach Kräften zu fördern, andererseits die mancherlei neuen Methoden, welche bei agriculturchemischen Untersuchungen in Gebrauch gekommen sind, auch in den Kreisen zu verbreiten, welchen die speciell agriculturchemischen Schriften nicht zu Gesicht kommen. Ich füge hinzu, dass die kleine Modification auf S. 94, sowie die Anmerkungen ebendaselbst in Folge brieflicher Mittheilung des Herrn Prof. Wolff aufgenommen worden sind. Dem Wunsche desselben, dass ich meinerseits Bemerkungen zufügen möchte, werde ich gerne entsprechen, so bald ich Zeit finde, betreffende Experimentaluntersuchungen vorzunehmen. R. F.     

BF3-mediated additions of organolithiums to ketimines: X-ray crystal structures of BF3-ketimine complexes

[reaction: see text] Additions of lithium acetylides and n-BuLi to N-alkyl ketimines mediated by BF(3)-Et(2)O in THF afford hindered tert-alkylamines in moderate to good yields. Stereochemical results and crystal structures of three BF(3)-imine complexes suggest that allylic strain strongly influences conformation and may be an important determinant of reactivity and selectivity.