Aluminum complexes bearing fonctionalized trisamido ligands and their reactivity in the polymerization of ε-caprolactone and rac-lactide

The addition of 1 and 2 equivalents of AlMe3 to cis,cis-C6H9(NHCH2C6H4-o-R)3 (R = PPh2 (3) and SPh (4)) gives complexes [cis,cis-C6H9(NCH2C6H4-o-R-κN)2(NHCH2C6H4-o-R-κN)]AlMe (R = PPh2 (7) and SPh (8)) and [cis,cis-C6H9(NCH2C6H4-o-R)3-κ5μ2N]Al2Me3 (R = PPh2 (5) and SPh (6)), respectively. The bimetallic complexes are active in the polymerization of ε-caprolactone and rac-lactide whereas the monometallic complexes are not, although no cooperative behaviour is observed between the two aluminium atoms of 5 and 6. The polycaprolactone samples, which were characterized using 1H NMR, MALDI-TOF, and SEC, show the presence of residual ligands 3 or 4 bound to the polymer and the in situ NMR studies confirm that the insertion occurs in an Al–N bond

(η4-Cyclo­octa-1,5-diene)diiodidoplatinum(II)

The monoclinic title complex, [PtI2(C8H12)], characterized by a twisted cyclo­octa­diene ring, is similar to its Cl and Br ortho­rhom­bic homologues. The observed Pt—I bond distances of 2.6094 (5) and 2.6130 (5) Å are in the expected range for PtI2 complexes. The C=C double bonds in the mol­ecule differ significantly [1.373 (10) and 1.403 (10) Å]. As expected for a platinum(II) complex, the PtII atom is in a square-planar environment (ΣPtα= 359.71°)

Management and treatment in patients with an indication of a chemotherapy and with a chronic viral hepatitis

En raison de la fréquence des cancers et des infections virales chroniques B et C dans la population générale, la coexistence de ces deux états pathologiques est fréquente. Elle peut se compliquer d’exacerbations de la maladie hépatique (réactivation, arrêt de la multiplication virale, accompagnées ou non de séroréversion ou de séroconversion) sous forme d’hépatite aiguë ou chronique pouvant évoluer à court terme vers une forme fulminante ou à long terme vers la cirrhose. Ces complications peuvent être facilement prévenues par : – le dépistage systématique des hépatites virales B et C : 1) chez tout patient devant recevoir une chimiothérapie ; et 2) pendant la chimiothérapie ou au décours de celle-ci en cas de cytolyse et/ou de cholestase, – et par l’institution d’un traitement préemptif par analogues nucléosidiques ou nucléotidiques au cours des hépatites virales B chroniques. Ceci permet de limiter la morbidité et la mortalité chez ces patients, induites, d’une part, par les complications hépatiques et, d’autre part, par la diminution de l’efficacité des chimiothérapies, trop souvent modifiées ou retardées par ces complications.Because of their prevalence in general population, the co-existence of cancers and chronic viral hepatitis are relatively high, and could lead to exacerbation of liver disease (HBV reactivation, discontinuation of HBV replication, sometimes associated with HBe or HBs seroreversion or seroconversion). These forms of acute or chronic hepatitis could evoluate to cirrhosis or fulminant hepatitis form. These complications could easily be prevented by: – the routine screening of hepatitis B and C in: 1. all patients who have to receive chemotherapy; 2. during the chemotherapy or during the follow-up after its discontinuation, in case of elevation of alanine aminotransferase and aspartate aminotransferase, or occurrence of cholestasis, – apre-emptive treatment with nucleoside or nucleotide analogs in all patients with chronic hepatitis B. These recommendations allow to decrease the morbidity and the mortality, explained, in one hand, by the specific liver complications and, in other hand, by the decrease of the efficacy of chemotherapies, more often delayed or discontinuated because of them

Confinement of the Grubbs catalyst in alkene-functionalized mesoporous silica

Herein, we report on the impact of alkyl chain length of olefin moieties anchored into silica mesopores on the confinement behavior and stability of the first-generation Grubbs catalyst, i.e., [RuCl2(C(H)(Ph))(PCy3)2] . In this contribution, ordered mesoporous SBA-15 silica materials were functionalized with alkenyl-trichlorosilanes exhibiting different carbon chain lengths, e.g., vinyl- (C2), allyl- (C3), hexenyl- (C6) and octenyl- (C8) trichlorosilanes. Subsequently, the Grubbs I catalyst was incorporated into these different host materials in the presence of organic solvent. The thus-obtained materials, before and after interaction with Grubbs I, were characterized by a variety of methods, including N2 physisorption, thermogravimetric analyses, solid state NMR (13C, 31P and 29Si) and attenuated total reflectance (ATR) infra-red spectroscopy. Our investigations reveal a pronounced dependence of the Grubbs surface stability as a function of the grafted alkyl chain length of the alkene moieties. The nature of the immobilized Ru-based species is function of the surface modification and the presence of residual silanol groups

Coordination chemistry of neutral (Ln)–Z amphoteric and ambiphilic ligands

This review focuses on the coordination chemistry of neutral ambiphilic and amphoteric ligands. The various designs of molecules having both donor and acceptor moieties and the strategies to prevent self‐aggregation and favour transition‐metal coordination will be discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008

Synthesis and solid-state characterization of platinum complexes with hexadentate amino- and iminophosphine ligands

Hexadentate ligands cis,cis-C6H9(N[double bond, length as m-dash]CHC6H4(PPh2))3 (1) and cis,cis-C6H9(NHCH2C6H4(PPh2))3 (2) were synthesized starting from cis,cis-1,3,5-triaminocyclohexane, and characterized using NMR spectroscopy and single-crystal X-ray diffraction. These ligands can bind both Pt(0) and Pt(II) metal centers using either or both of the soft phosphine moieties and the hard amine/imine moieties. In many cases the resulting complexes are negligibly soluble; hence, 31P and 195Pt solid-state NMR (SSNMR) spectroscopy was applied to analyse the bonding modes of the hexadentate ligands. The 195Pt SSNMR spectroscopy of these complexes is particularly challenging, since 1H–195Pt cross polarization is extremely inefficient, the 195Pt longitudinal relaxation times are extremely long and the 195Pt powder patterns are expected to be quite broad due to platinum chemical shift anisotropy. It is demonstrated that the ultra-wideline 195Pt SSNMR spectra can be efficiently acquired with a combination of frequency-stepped piecewise acquisitions and cross-polarization/Carr–Purcell Meiboom–Gill (CP/CPMG) NMR experiments. The 195Pt and 31P SSNMR data are correlated to important structural features in both Pt(0) and Pt(II) specie

Reactivity of a Functionalized Trisamido Ligand with Zr(NMe2)4 and GaMe3

NMR study of the reactivity of multifunctional ligand cis,cis-C6H9(NHCH2C6H4-o-PPh2)3 (1) with GaMe3 and Zr(NMe2)4 was carried out, yielding [cis,cis-(κN-NHCH2C6H4-o-PPh2)(κN-NCH2C6H4-o-PPh2)2C6H9]GaMe (2) and [cis,cis-(NCH2C6H4-o-PPh2)3C6H9]Ga2Me3 (3), and [cis,cis-(NCH2C6H4-o-PPh2)3C6H9]Zr(NMe2) (4), respectively. The spectral properties of 2 and 3 are very similar to that observed for the equivalent aluminum species already reported, but form at a much slower rate which allows for the observation of a GaMe3⋅1 adduct. Species 4 undergoes coordination/displacement of one of the phosphine arms, which was observed using both NMR spectroscopy and DFT analyses

On the interaction of phosphines with high surface area mesoporous silica

To increase the efficiency and selectivity of homogeneous catalysts, particularly useful in the synthesis of fine chemicals and drugs, fine tuning of the steric and electronic properties of the complexes can be achieved by modification of the ligands in the coordination sphere of the metal center. Considerable efforts have been devoted in order to immobilize such well-defined catalysts on solid substrates, e.g., silica, to facilitate catalysts’ recovery and to reduce contamination of desired products by metallic impurities. However, the presence of the silica surface can play a very important role in tuning the electronic properties of the metal, its steric environment, or in participating in the reactivity of the complex. In this context, several moieties have been used to anchor metallic catalysts on surfaces, but one of the most interesting is phosphine. Herein, we report on the addition of PPh2Cl which leads to the grafting and the oxidation of the phosphine species, even in absence of oxygen, and that the nature of the surface plays an important role in secondary interactions, e.g., hydrogen bonding, and modifies the spectroscopic properties of the functional groups on the surface. In particular, the chemical shift of the phosphorous resonance in the P NMR spectra is altered by hydrogen bonding between available silanol or water molecules present on the silica surface and the phosphorous oxide. The DFT models developed for this process are in direct accordance with the experimental results and demonstrate firmly that the oxidation of the phosphine after grafting of ClPR2 is highly favored thermodynamically and occurs with the formation of Si-Cl bonds on the surface. Passivation of the surface with hexamethyldisilazane limits the extent of the H-bonding between the surface and the oxide, but also leads to some substitution reaction between bound phosphorous species and the trimethylsilyl (TMS) moieties. These findings offer new knowledge critical to fully ascertain the environment and the stability of immobilized phosphine-containing catalytic systems and, thus, further broaden the range of their reactivity

Substantiating the influence of pore surface functionalities on the stability of grubbs catalyst in mesoporous SBA-15 silica

The influence of pore surface functionalities in mesoporous SBA‐15 silica on the stability of a model olefin metathesis catalyst, namely Grubbs I, is substantiated. In particular, it is demonstrated that the nature of the interaction between the ruthenium complex and the surface is strongly depending on the presence of surface silanols. For this study, differently functionalized mesoporous SBA‐15 silica materials were synthesized according to standard procedures and, subsequently, the Grubbs I catalyst was incorporated into these different host materials. All of the materials were thoroughly characterized by elemental analyses, nitrogen physisorption at −196 °C, thermogravimetric analyses, solid‐state NMR spectroscopy, and infrared spectroscopy (ATR‐IR). By such in‐depth characterization of the materials, it became possible to achieve models for the surface/catalyst interactions as a function of surface functionalities in SBA‐15; for example, in the case of purely siliceous silanol‐rich SBA‐15, octenyl‐silane modified SBA‐15, and silylated equivalents. It was evidenced that large portions of the chemisorbed species that are detected spectroscopically arise from interactions between the tricyclohexylphosphine and the surface silanols. A catalytic study using diethyldiallylmalonate in presence of the various functionalized silicas shows that the presence of surface silanols significantly decreases the longevity of the ring‐closing metathesis catalyst, whereas the passivation of the surface by trimethylsilyl groups slows down the catalysis rate, but does not affect significantly the lifetime of the catalyst. This contribution thus provides new insights into the functionalization of SBA‐15 materials and the role of surface interactions for the grafting of organometallic complexes