C. Charrier

Réarrangement du type σ-π de complexes homoallyliques du molybdéne: formation de complexes π-allyliques

Abstract Substituted π-allylmolybdenum complexes are obtained by reacting(π-cyclopentadienylmolybdenumtricarbonyl) sodium with homoallylbromides. Anti - and syn -forms of these complexes areisolated. A mechanism with a σ-π-intermediate is proposed.

Insertion d'allenes : II. Cyclisation d'halogénures éthyléniques et alléniques avec le tétracarbonylferrate de sodium (Fe(CO)42-, 2 Na+. Formation de cétones cycliques☆

Abstract The cyclisation of previously described ω-unsaturated η 1 -alkyl ligands has been extended using the versatile Fe(CO) 4 metallic fragment. Treatment of the homoallenic halide 5-bromo-1,2-pentadiene with disodium tetracarbonylferrate (Fe(CO) 4 2- , 2 Na + gives, after protonation, 2-methylcyclopentenone in 30–40% yield. The structure and reactivity of the reaction intermediate, subsequent to the cyclisation step, suggest delocalisation of electronic density onto the organic ligand. The metallic reagent converts some alkenyl halides into cyclic ketones in low to moderate yields.

Insertion d'allenes

Abstract η 3 -Allylcyclopentenone complexes of molybdenum and tungsten are obtained by treating homoallenic bromides with η 5 -cyclopentadienyl-molybdenum or -tungsten tricarbonyl anions. Conformational equilibria were observed and studied by NMR. The results can be explained by assuming that the dominant factor is a steric interaction between the cyclopentadienyl ring and the substituents on the η 3 -allyl ligand. According to the NMR data one of the compounds was in a B exo conformation. This conclusion was asserted by an independent study using X-ray diffraction techniques.

Alcoxycarbonylation : I. Alcoxycarbonylation de complexes σ-propargyliques du molybdene, du tungstene et du manganese

Abstract σ-Propargylic molybdenum, tungsten or manganese carbonyl complexes are alkoxycarbonylated by alcohols, water and thiols, yielding π-allyl complexes in most cases. The reaction of the σ-2-propynylmolybdenum complex with alcohols yields carbenoid complexes or π-allyl complexes if propargyl bromide is added.

Formation de cétones cycliques à partir du dianion du fer tétracarbonyle

Abstract Sodium tetracarbonyl ferrate(—II) converts γ-ethylenic bromides and tosylates into cyclohexanones and β-allenic bromides into cyclopentenones in moderate yields.