Bifunctional Acid–Base Ionic Liquid Organocatalysts with a Controlled Distance Between Acid and Base Sites

Bifunctional acid–base ionic liquid organocatalysts with different distances between the two sites have been synthesised, and their activity for the Knoevenagel condensation has been tested. As has been found to be the case with enzymes, the distance between the acidic and basic sites determines the activity of the bifunctional organocatalyst, and at the optimal distance the reaction rate increases by two orders of magnitude with respect to the purely acidic or basic counterpart organocatalysts. The experimental results have been rationalised through the study of the reaction mechanism of the Knoevenagel condensation between malononitrile and benzaldehyde by means of DFT calculations. It has been found that it consists of two consecutive steps. First, deprotonation of malononitrile on the basic site to obtain a methylene carbanion intermediate takes place, and second, co‐adsorption and activation of benzaldehyde on the acid centre of this intermediate followed by the C? C bond‐formation reaction. The calculations and the kinetic study indicate that there is an inversion of the rate‐controlling step when the distance between the acidic and the basic sites is modified, with a direct implication on the reaction rate.     

Die Reduktion von Germanium- und Zinntetrabromid durch Tri-tert-butylphosphin: Brom-tri-tert-butylphosphonium-Salze

Reduction of Germanium and Tin Tetrabromide by Tri-tert-butylphosphine: Bromo-tri-tert-butylphosphonium Ions Tri-tert-butylphosphine react with equimolar amounts of germanium or tin tetrabromide with formation of “1:1 adducts”. The new compounds are characterized as bromo-tri-tert-butylphosphonium salts (t-C₄H₉)₃PBr⁺MBr₃^? by ¹H n.m.r., ³¹P n.m.r., infrared and Raman spectroscopy (M = Ge, Sn).     

Organometallphosphin-substituierte Übergangsmetalkomplexe XVI. Tricarbonyl-tris(organometallphosphin)chrom- und -molybdän komplexe

Two phosphido cobalt carbonyl cluster Co(CO)₆P2 and Co₃(CO)₉PS have been prepared and characterised.     

Building the “Phosphoindigo” Backbone by Oxidative Coupling of Phosphindolin‐3‐ones with Selenium Dioxide

Oxidative coupling of racemic 1‐ethoxy‐1‐oxophosphindolin‐3‐one ( 1 ) and its 5‐CF₃‐derivative 6 with SeO₂ furnishes 1,1′‐diphosphaindigo derivatives 5 and 7 as bis‐phosphinic esters, i. e. as P^V‐compounds. Like indigo and thioindigo, 5 and 7 exist in the E‐configuration; the crude products of 5 and 7 are mixtures of isomers that are trans‐ and cis‐configurated with respect to the relative orientation of the ester groups oat phosphorus. The structure of the centrosymmetric E‐P(R)P′(S) isomer [(E)‐trans‐isomer] of 5 was determined by X‐ray crystallography. Ester cleavage of 5 , followed by addition of triethylamine to bis‐phosphinic acid 9 (the 1,1,1′,1′‐tetroxide of “phosphoindigo”), furnishes the related bis‐triethylammonium salt 10 as a crystalline hydrate that exhibits an extended hydrogen bonding network.     

Spektralphotometrische Untersuchung der Systeme NiF2/Erdalkalifluoride sowie des Systems CaF2/CoF2

The light absorption of the phases occurring in the systemsMF₂/NiF₂ (M=Ba, Sr, Ca) has been investigated. The colour curves of Ba₂NiF₆ (I) and of BaNiF₄ (II) show characteristic differences. The colour curve of SrNiF₄ is similar to that of II. The colour curves of the system CaF₂/NiF₂ are compared with those of the system CaF₂/CoF₂. From the colour curve of the latter system one can unambiguously infer that mixed cristals Ca_1–x Co _x F₂ (x0,01) exist. No evidence could be found for the existence of mixed cristals Ca_1–x Ni _x F₂ by the spectrophtometric method.

---

---

Mit 6 Abbildungen