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Neotectonic features in the Apricena area: stratigraphic keys to distinguish the upper-Pliocene – lower Pleistocene subsidence and the middle – upper Pleistocene uplift phases in the NW part of the Apulian foreland (Gargano, Southern Italy)
No full textEvidenze di neotettonica (Pliocene superiore-Pleistocene superiore) nel settore occidentale del Promontorio del Gargano (Apricena, Italia meridionale)
No full text1,4-bis-difosfino-(Z)-2-buteni, 1,4 disostituiti otticamente puri in qualità di leganti chirali per la catalisi omogenea stereocontrollata con metalli di transizione
No full textLa presente invenzione ha come oggetto leganti 1,4 difosfinici chirali con due stereocentri uniti da un ponte etilenico in grado di coordinare stabilmente un metallo di transizione dando accesso a catalizzatori facilmente ottenibili con alte rese e altrettanto facilmente conservabili e utilizzabili.Come verrà illustrato in seguito, i leganti oggetto dell’invenzione uniscono due caratteristiche essenziali nella loro struttura: una grande rigidezza conformazionale tipica dei leganti a chiralità atropisomerica, dovuta alla presenza di un doppio legame carbonio-carbonio, e una grande flessibilità di sintesi tipica dei leganti con atomi di carbonio stereogenici
Structural variations on chiral ligands : new chelating diphosphines from optically active (1,4)-(Z)-2-butenes
No full textThe asymmetric catalysis by transition metal complexes is recognized an alternative strategy for the preparation of compounds which were believed to be impossible to carry out by conventional methods. The greater part of the transition metals known as excellent catalysts for asymmetric synthesis have optically active diphosphines as source of chirality but in spite of the great variety of chiral ligands available, there is still demand for the development of catalysts which display the requirements of high enantioselectivity, diastereoselectivity and productivity in fine chemicals, fragrances, flavours, agrochemicals.
The development of new catalysts is usually closely connected to the development of new chiral ligands among which optically active diphoshines take the lion’s share but, even if up to now thousands of chiral chelating phosphines are available, only few of them give catalysts with satisfactory enantioselectivity, productivity and process robusteness to find application on industrial scale.
We wish to present a new class of chiral chelating diphosphines derived from (1,4)-(Z)-2-butenes; these ligands would gather the conformational rigidity of the atropisomeric ligands like BINAP or BITIOP with the flexibility and the possibility to modulate the electronic and steric properties typical of the ligands based on chiral sp3 carbon.
The ligands are prepared from the corresponding (1,4)-(Z)-2-butenes ( R = CH3-, C6H5-, (CH3)2CH- ) according to the scheme:
The structure of the palladium(II)Cl2 complexes of the cis,2,5-bis-diphenylphosphino-3-hexene are reported in the following figures
The ruthenium complexes with the optically pure ligands give promising results in the asymmetric hydrogenation of prochiral ketones. Work is in progress to investigate other catalytic reactions like asymmetric hydroformylation with rhodium complexes
DIOPHEP, a chiral diastereoisomer bisphosphine ligands : synthesis and applications in asymmetric hydrogenations
No full textA couple of novel optically active diphosphine ligands, called DIOPHEP, has been designed and synthesized starting from a derivative of tartaric acid. The ligands conjugate the sp3 chirality of the precursor of DIOP with the atropisomeric chirality of a biaryl scaffold. The stereorecognition abilities of DIPHEP-Ru complex catalysts have been investigated in the asymmetric catalytic hydrogenation of some standard substrates suggesting a close relationship between dihedral angles and enantioselectivity
catalisi enantioselettiva : sintesi di istidina non naturale e istidina non naturale deuterata
No full textChiral 1,4-bis-diphosphine ligands from optically active (Z)-olefines
No full textThe catalytic asymmetric hydrogenation of prochiral ketones was carried out with Ru(II) complexes prepared from new chiral diphosphine ligands, cis (R,R)-2,5-bis[(diarylphosphino)]-3-hexenes.
These new ligands were prepared from optically pure (R,R) or (S,S)-Z-3-hexene-2,5 diol and enantiomeric excesses up to 85 % were obtained in the reduction of 2-benzamidomethyl-3-oxobutanoate, starting material for the synthesis of 4-acetoxy-2-azetidinone
Asymmetric Hydrogenation of prochiral Ketones catalyzed by Ru(II)Cl2diphosphine/diamine system
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