Micellar effect in hydroformylation of high olefin catalysed by water-soluble rhodium complexes associated with sulfonated diphosphines

High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO₄) as the surfactant or methanol as the co-solvent.     

New phosphite-oxazoline ligands for efficient Pd-catalyzed substitution reactions

We have designed and synthesized a new family of readily available highly modular phosphite-oxazoline ligands for the Pd-catalyzed asymmetric allylic substitution reactions. The introduction of a pi-acceptor flexible bulky biphenyl phosphite moiety in the ligand design is highly adventitious in the product outcome. Thus, this ligand series affords excellent reaction rates (TOF's up to >2400 mol.(mol.h)-1) and enantioselectivities (ee's up to >99%) and, at the same time, shows a broad scope for different substrate types.     

Mononuclear Pt(II) and Pd(II) 1,4-dithiolato complexes. Crystal structures of [Pt((−) DIOS) (PPh3)2] and [Pd(S(CH2) 4S)(Ph2P(CH2) 3PPh2)]. Application in styrene hydroformylation

Addition of 1,4-dithiols to dichloromethane solutions of [PtCl₂(P-P)] (P-P = (PPh₃)₂, Ph₂P(CH₂)₃PPh₂, Phd₂P(CH₂)₄PPh₂; 1,4-dithiols = HS(CH₂)₄SH, (−)DIOSH₂ (2,3-O-isopropylidene-1,4-dithiol-l-threitol), BINASH₂ (1,1′-dinaphthalene-2,2′-dithiol)) in the presence of NEt₃ yielded the mononuclear complexes [Pt(1,4-dithiolato)(P-P)]. Related palladium(II) complexes [Pd(dithiolato)(P-P)] (P-P=Ph₂P(CH₂)₃PPh₂, Ph₂P(CH₂)₄PPh₂; dithiolato = ⁻S(CH₂)₄S⁻, (−)-DIOS) were prepared by the same method. The structure of [Pt((−)DIOS)(PPh₃)₂] and [Pd(S(CH₂)₄S)(Ph₂P(CH₂)₃PPh₂)] complexes was determined by X-ray diffraction methods. Pt—dithiolato—SnC1₂ systems are active in the hydroformylation of styrene. At 100 atm and 125°C [Pt(dithiolate)(P-P)]/SnCl₂ (Pt:Sn = 20) systems provided aldehyde conversion up to 80%.     

A rapid and selective HPLC‐UV method for the quantitation of efavirenz in plasma from patients on concurrent HIV/AIDS and tuberculosis treatments

Owing to heterogeneity in therapeutic response, efavirenz is of research and clinical interest. There is a need to quantitate it using noncostly and selective methods. A method for efavirenz quantitation in plasma containing HIV and tuberculosis drugs was developed. Chromatographic separation was carried out using a C₁₈ column. The mobile phase consisted of 0.1% formic acid and acetonitrile, and was pumped at a flow rate of 0.3 mL/min. Efavirenz and ritonavir (internal standard) were monitored at 247 nm. Plasma proteins were precipitated by centrifugation. The analysis time was 6 min. The response was linear (r = 0.9997). The accuracy ranged between 98 and 115% (intraday) and between 99 and 117% (interday). The precision ranged from 1.670 to 4.087% (intraday) and from 3.447 to 13.347% (interday). Recovery ranged from 98 to 132%. Stability ranged between 99 and 123%. The selectivity was proven by analysis of drugs used for the management of HIV/AIDS and tuberculosis. Plasma sample analysis showed an efavirenz retention time of 5.57 min and a peak plasma concentration of 2.4 µg/mL occurring at 2 h. This method is rapid and selective, and thus suitable for monitoring efavirenz in patients with HIV/AIDS alone or co‐infected with tuberculosis in a less resourced setting. Copyright © 2013 John Wiley & Sons, Ltd.     

Core–shell nanogels by RAFT crosslinking polymerization: Synthesis and characterization

A synthetic methodology is described for the preparation of core–shell nanogels by reversible addition‐fragmentation chain transfer. Well‐defined macro chain transfer agents (macro‐CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro‐CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core‐crosslinked star to a core–shell nanogel. Controlling the molecular weight of the macro‐CTA and the type of comonomer in the core forming step, core–shell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

C2-symmetric diphosphinite ligands derived from carbohydrates. The strong influence of remote stereocenters on asymmetric rhodium-catalyzed hydrogenation

Modular ligands of C(2) symmetry (13a-e, 14a,b,d, and ent-9), systematically modified at positions 2 and 5, were easily prepared from d-glucosamine, D-glucitol, and tartaric acid, respectively. The application of these ligands in the rhodium-catalyzed hydrogenation of methyl acetamidoacrylate, methyl acetamidocinnamate, and dimethyl itaconate shows that both the configuration and the substituents at positions 2 and 5 of the tetrahydrofuran backbone have a strong influence on the enantioselectivty of the processes.     

Preparation of α,ω‐telechelic hexyl acrylate polymers with ?OH, ?COOH,and ?NH2 functional groups by RAFT

The design, synthesis, and use of two new, stable, functionalized chain transfer agents (CTA's) containing OH and amine end groups for the RAFT polymerization is reported: 2‐hydroxyethoxy‐carbonylphenylmethyl dithiobenzoate and 2‐(2‐(tert‐butoxycarbonyl)ethylamino)‐2‐oxo‐1‐phenylethyl benzodithioate, respectively. The RAFT polymerization of n‐hexyl acrylate (HA) using those CTA's, were compared to several other functionalized dithiobenzoate esters reported in the literature containing COOH and Ester groups. The performances of the dithiobenzoates were compared in terms of kinetics and molecular weight distribution control. Good control in polymerization of n‐hexyl acrylate with a linear increase of M_n with conversion mantaining polydispersity indices (PDI) below 1.1 was obtained by use of the new functionalized CTA's developed and also by use of some other CTA's tested, to produce well‐defined linear polymers with one specific chain‐end functionality: ? OH, ? COOH or Amine. Using a postpolymerization reaction with functionalized azocompounds in a 5 to 1 ratio, α,ω‐telechelic polymers, with ? OH or ? COOH as functional group at the second end were obtained. By using this synthetic strategy α,ω‐homotelechelic and heterotelechelic polymers were readily prepared. The chemical availability of functional end‐groups in the telechelics was demonstrated by reaction with methacrylic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3033–3051, 2010     

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes [Pd(O₃SCH₃)(L‐L)][O₃SCH₃] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O₃SCH₃)(L‐ L)][O₃SCH₃], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism.     

Efficient recycling of a chiral palladium catalytic system for asymmetric allylic substitutions in ionic liquid

Chiral carbohydrate-based diphosphites were used for Pd-catalysed asymmetric allylic substitution (alkylation, amination, phosphination) in neat ionic liquids (ILs). Pyrrolidinium-based IL led to the best activities, allowing an efficient catalyst immobilization. In the allylic amination (TOF > 3100 h(-1)), the catalyst could be recycled nine times preserving both activity and enantioselectivity.     

Pd-catalysed asymmetric mono- and bis-alkoxycarbonylation of vinylarenes

The asymmetric alkoxycarbonylation of vinylarenes catalysed by palladium complexes bearing chiral phosphine ligands has attracted much attention over the last decades. The products of both mono- and bis(alkoxycarbonylation) reactions are important intermediates in the syntheses of pharmaceuticals such as 2-arylpropionic acids, the most important class of non-steroidal anti-inflammatory drugs. In this article, a general overview of the topics will be presented and the recent advances in this field will be particularly detailed. Besides the term alkoxycarbonylation, hydroesterification and hydroalkoxycarbonylation are also used in the literature to describe this reaction. Furthermore, more specific terms such as methoxycarbonylation can be found. In this report, the term alkoxycarbonylation will be used as the general term, and specific terms will be used to unambiguously define which reaction is meant.