Etude de réactions organiques induites par des systèmes qui associent des complexes de métaux de transition et des lanthanides

I.'utilisation des lanthanides et dérivés, en chimie organique s'est considérablement développée. L utilisation en catalyse des dérivés de métaux de transition pour effectuer des transformations très sélectives aussi. Nous avons montré sur quelques cas que l'on pouvait mettre en synergie les lanthanides (métaux et dérivés) et des complexes des métaux de transition. L utilisation du diiodure de samarium en quantité catalytique en présence du mischmétal en tant que co-réducteur dans le système mischmétal/SmI2/Pd(0) nous a permis de réaliser des réactions d'allylation de composés carbonylés à l'aide d'esters variés. Ainsi, une catalyse dite gigogne à été mis en œuvre. Des interprétations mécanistiques ont permis d'expliquer les réactions ainsi réalisées. Avec les systèmes associant SmI2 ou des métaux des lanthanides avec des trichlorures de métaux de transition (Rh, Ru, Ir), nous avons réalisé des isomérisations de liaisons doubles terminaux C=C dans des conditions douces. Cette isomérisation tolère la présence de groupes fonctionnels variés ( hydroxy, carbonyl, ). A partir du dichloro dicyclopentadienyl zirconium que nous avons traité par les métaux des lanthanides légers (Ce, La, mischmétal), nous avons pu accéder à un réactif présentant beaucoup d'analogies avec le réactif de Negishi. Ainsi, des réactions de dimérisation d'alcynes ont été réalisées.The use of lanthanids and derived, in organic chemistry is considerably developed. The use in catalysis of derived from transition metal to carry out very selective transformations too. We showed on some cases that lanthanides (metals and derived) and transition complexes metals could be putting of synergy. The use of samarium diiodide in catalytic amounts together mischmetall as coreductant in the system mischmetall/SmI2/Pd(0) allowed us to carry out reactions of allylation of carbonyl compounds using varied esters. Thus, a catalysis known as "multi-stage" is described. Mechanistic interpretations made it possible to explain the reactions thus carried out. With the systems associating SmI2 or lanthanids metals with trichlorides of transition metal (Rh, Ru, Ir), we carried out isomerization of double bond C=C under soft conditions. This isomerization tolerates the presence of varied functional groups (hydroxy, carbonyl ). From the dichloro dicyclopentadienyl zirconium that we treated by metals of light lanthanids (La, Ce, mischmetall), we could reach a reagent which presenting many analogies with the reagent of Negishi. Thus reactions of alkynes dimerisation were realized.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Farmers’ knowledge, perceptions and management practices for termite pests of maize in Southern Benin

Termite (Isoptera: Termitidae) infestation is an important constraint of maize production in Benin. A survey of 300 households was conducted in 2018 throughout 30 villages in Southern Benin to evaluate farmers’ knowledge, perceptions and management practices of maize termite pests using focus group discussions and individual interviews with a semi-structured questionnaire. The results showed that for most of the farmers, maize is the most susceptible crop to termite attacks and the maturation developmental stage having the highest termite abundance and damage. A total of 43 different names of maize termite pests corresponding to 8 species were recorded in the study area. Size and colour were the main criteria used by farmers to classify and identify maize termite pests. Amitermes evuncifer was perceived as the most damaging to maize during vegetative and maturation stages, while Macrotermes bellicosus was perceived by famers (32.5%) as most damaging during seedling and flowering maize development stages. Erratic rainfall was perceived by maize producers as the most important factor favouring termite infestation in maize fields. The majority of the local maize is considered by farmers as susceptible to termites. The use of synthetic insecticides was the main method to control termites. Four of the 20 pesticides used by farmers have active ingredients that have been listed as highly hazardous (class Ib) by the World Health Organization (WHO). Farmers training on the danger and impact of misuse of insecticides on the development of termite insecticide resistance was recommended. The development of an integrated termite management strategy is discussed and the future research for its implementation identified