The role of neutral Rh(PONOP)H, free NMe2H, boronium and ammonium salts in the dehydrocoupling of dimethylamine-borane using the cationic pincer [Rh(PONOP)(η2-H2)]+ catalyst

The σ-amine-borane pincer complex [Rh(PONOP)(η1-H3B·NMe3)][BArF4] [2, PONOP = κ3-NC5H3-2,6-(OPtBu2)2] is prepared by addition of H3B·NMe3 to the dihydrogen precursor [Rh(PONOP)(η2-H2)][BArF4], 1. In a similar way the related H3B·NMe2H complex [Rh(PONOP)(η1-H3B·NMe2H)][BArF4], 3, can be made in situ, but this undergoes dehydrocoupling to reform 1 and give the aminoborane dimer [H2BNMe2]2. NMR studies on this system reveal an intermediate neutral hydride forms, Rh(PONOP)H, 4, that has been prepared independently. 1 is a competent catalyst (2 mol%, ∼30 min) for the dehydrocoupling of H3B·Me2H. Kinetic, mechanistic and computational studies point to the role of NMe2H in both forming the neutral hydride, via deprotonation of a σ-amine-borane complex and formation of aminoborane, and closing the catalytic cycle by reprotonation of the hydride by the thus-formed dimethyl ammonium [NMe2H2]+. Competitive processes involving the generation of boronium [H2B(NMe2H)2]+ are also discussed, but shown to be higher in energy. Off-cycle adducts between [NMe2H2]+ or [H2B(NMe2H)2]+ and amine-boranes are also discussed that act to modify the kinetics of dehydrocoupling

Microwave-Assisted Isomerizations of Epoxides to Allylic Alcohols

The present work reports a study on the isomerization reactions of several alkyl epoxides to the corresponding allylic alcohols or bicyclic alcohols under microwave irradiation. The reaction occurred in the presence of lithium diisopropylamide as a base and different experimental conditions in terms of solvent, amount of the base, times and temperatures. The traditional heating with an oil-bath and the use of alternative organometallic bases, as the Lochmann-Schlosser bases, have been furthermore compared with the microwave heating. The results obtained show that the use of microwave irradiations on promoting the isomerization of epoxides gives access to a series of synthetically useful products, among which allylic alcohols and bicyclic alcohols, depending on the starting substrate

Composés organométalliques en synthèse regio- et énantiosélective (structure et réactivité)

Ce travail présente deux études en chimie organométallique (organolithiens). Dans le premier chapitre, des réactions d'isomérisation réalisées en présence de superbases bimétalliques sont impliquées, et la transformation d'aziridines fonctionnalisées est examinée. Deux voies sont possibles : la b-élimination ou la cyclisation 4-exo intracyclique. Le processus réactionnel étant accompagné de la formation de centre(s) stéréogène(s), une approche asymétrique est explorée avec 3-APLi's. Le deuxième chapitre s'intéresse à l'étude structurale de phosphines (boranes) lithiées dans le but d'aborder la synthèse énantiosélective d'alkylphosphines P-stéréogéniques. Ce travail de thèse a permis d'examiner la structure en solution d'une phosphine borane lithiée modèle (Ph2P(BH3)Li) en solution par spectroscopie RMN multinoyaux (1H, 6Li, 13C, 11B, 31P). L'affinité du phosphure avec le BuLi puis la LDA a ensuite été examinée.Questo lavoro di tesi è stato focalizzato su due tematiche alla chimica degli organometalli (ed in particolare degli organolitio derivati). Nella prima parte sono state studiate le reazioni di isomerizzazione in presenza di superbasi bimetalliche ed è stata esaminata la reattività di aziridine funzionlizzate. Due meccanismi sono possibili : la b-eliminazione e la ciclizzazione 4-exo intramolecolare. Dato che la reazione è accompagnata dalla formazione di uno o più centri stereogenici, è stata anche studiata una versione asimmetrica. La seconda parte descrive uno studio di fosfine-borani litiati. Questo lavoro è parte di un programma consistente nella sintesi di alchifosfine P-stereogeniche enantioarricchite. Il nostro contributo consiste nella determinazione della struttura di una litio fosfide-borano (Ph2P(BH3)Li) grazie alla tecnica di analisi NMR multinucleare (1H, 6Li, 13C, 11B, 31P). È stata anche analizzata l'affinità della lithio fosfide per il BuLi e poi per l'LDA.ROUEN-BU Sciences (764512102) / SudocROUEN-BU Sciences Madrillet (765752101) / SudocSudocFranceF

Rare bone marrow biopsy complication: a challenging case of sacroiliitis and Staphilococcus aureus sepsis

Bone marrow biopsy is a mandatory procedure to diagnose several hematological disorders. This invasive analysis is generally safe and the procedure-related risks are rare and include bleeding at the site of puncture and, very occasionally, local infections. Here, we describe a case of sacroiliitis that occurred as a consequence of bone marrow biopsy

Multinuclear NMR study of PH2P(BH3)Li in THF-d8 solution: new aspects on the reactivity of P-alkylation and reduction reactions

P-chiral phosphide-boranes have been shown to be valuable building blocks in the synthesis of enantiomerically pure phosphines with chirogenic phosphorus centers.1 However, despite the considerable interest towards these compounds no information about their structure and their stability in solution is present in the literature. For this reason a set of heteronuclear (1H, 6Li, 11B, 13C and 31P) NMR experiments in THF-d8 has been conducted on a lithium borylphosphide model: lithium diphenylphosphide borane 1 (Figure 1). These experiments have clearly established that the deprotonation of diphenylphosphine-borane by n-BuLi in THF leads to a disolvated monomer with the lithium cation connected to the hydrides on the boron and two THF molecules. These structural data allowed us also to understand some aspects of its reactivity in the field of P-alkylation and reduction reactions of carbonyl species

Chiral Lithium Amides: Tuning Asymmetric Synthesis on the Basis of Structural Parameters

International audienceAn overview on the structural arrangements adopted by Chiral Lithium Amides (CLAs), alone or in mixed complexes, is presented. These species are important reagents for asymmetric synthesis and understanding their organization is essential to improve their design and the reaction conditions