Highly trans-stereospecific Isoprene Polymerization by Neodymium Borohydrido Catalysts

Highly stereospecific polymerization of isoprene was achieved using borohydrido neodymium complexes. In combination with stoichiometric amounts of dialkylmagnesium, Nd(BH4)3(THF)3 (1) and Cp*'Nd(BH4)2(THF)2 (2) (Cp*' = C5Me4nPr) afford very efficient catalysts. Activity reaches 37300 g polyisoprene/mol Nd/h. Half-lanthanidocene 2 gives rise to polyisoprene 98.5 % trans-regular, the highest content yet described for a homogeneous organometallic catalyst. NMR experiments argue for the formation of bimetallic Nd(m-BH4)Mg active species

NMR T1-Relaxation Measurements on Paramagnetic Organolanthanides: An Alternative Tool for Structure Determination in Solution

1H NMR investigations were conducted on four paramagnetic organolanthanides all bearing the tetraisopropylcyclopentadienyl Cp4i ligand (Cp4i = HC5iPr4) in order to verify whether or not interactions observed in the solid state were maintained in solution. In some cases, variable temperature experiments were necessary to enhance the resolution and determine the best conditions of study. 1D NMR spectrum could be interpreted in every case. Complementary 2D COSY experiments allowed the full attribution of the signals. T1 (1H) relaxation measurements were determined for all the paramagnetic complexes at the most suitable temperature, and compared to those of the diamagnetic KCp4i. The same tendency was observed, with particular features concerning the isopropyl groups. Among the four methyl groups, one exhibits a much higher T1 value, one a much lower and the two others are intermediate. This was interpreted as the result of a privilegied conformation of the Cp4i ligand: the two a-isopropyl groups take a spatial orientation with one methyl in exo position, opposite to the metal, whereas the methyl groups of the two b-isopropyl are quite equidistant from the metal. Whatever the nature of the metal (Nd, Sm), the oxidation state (SmII, SmIII), or the temperature (298, 363 K), this conformation is retained. The structure in solution seems to be different from that previously determined in the solid state

Structural diversity in the borohydrido lanthanides series: first isolation and X Ray crystal structure of ionic [Sm(BH4)2(THF)5]+[Cp*'Sm(BH4)3]-

International audienceTwo new borohydrido complexes of samarium were prepared: [Sm(BH4)2(THF)5]+[Cp*'Sm(BH4)3]- (1) and Cp*'2Sm(BH4)(THF) (3) (Cp*' = C5Me4nPr). X Ray studies revealed that 1 displays an unprecedented ionic structure comprising a half samarocene moiety, whereas 3 is monomeric and bears a terminal BH4 ligand

Impact of species and antibiotic therapy of enterococcal peritonitis on 30-day mortality in critical care - An analysis of the OUTCOMEREA database

Introduction: Enterococcus species are associated with an increased morbidity in intraabdominal infections (IAI). However, their impact on mortality remains uncertain. Moreover, the influence on outcome of the appropriate or inappropriate status of initial antimicrobial therapy (IAT) is subjected to debate, except in septic shock. The aim of our study was to evaluate whether an IAT that did not cover Enterococcus spp. was associated with 30-day mortality in ICU patients presenting with IAI growing with Enterococcus spp. Material and methods: Retrospective analysis of French database OutcomeRea from 1997 to 2016. We included all patients with IAI with a peritoneal sample growing with Enterococcus. Primary endpoint was 30-day mortality. Results: Of the 1017 patients with IAI, 76 (8%) patients were included. Thirty-day mortality in patients with inadequate IAT against Enterococcus was higher (7/18 (39%) vs 10/58 (17%), p = 0.05); however, the incidence of postoperative complications was similar. Presence of Enterococcus spp. other than E. faecalis alone was associated with a significantly higher mortality, even greater when IAT was inadequate. Main risk factors for having an Enterococcus other than E. faecalis alone were as follows: SAPS score on day 0, ICU-acquired IAI, and antimicrobial therapy within 3 months prior to IAI especially with third-generation cephalosporins. Univariate analysis found a higher hazard ratio of death with an Enterococcus other than E. faecalis alone that had an inadequate IAT (HR = 4.4 [1.3-15.3], p = 0.019) versus an adequate IAT (HR = 3.1 [1.0-10.0], p = 0.053). However, after adjusting for confounders (i.e., SAPS II and septic shock at IAI diagnosis, ICU-acquired peritonitis, and adequacy of IAT for other germs), the impact of the adequacy of IAT was no longer significant in multivariate analysis. Septic shock at diagnosis and ICU-acquired IAI were prognostic factors. Conclusion: An IAT which does not cover Enterococcus is associated with an increased 30-day mortality in ICU patients presenting with an IAI growing with Enterococcus, especially when it is not an E. faecalis alone. It seems reasonable to use an IAT active against Enterococcus in severe postoperative ICU-acquired IAI, especially when a third-generation cephalosporin has been used within 3 months. © 2019 The Author(s)