Laboratoire Hétérochimie Fondamentale et Appliquée

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStable CarbenesDidier Bourissou, Olivier Guerret, François P. Gabbaï, and Guy BertrandView Author Information Laboratoire d'Hétérochimie Fondamentale et Appliquée (UPRES-A CNRS 5069), 118 route de Narbonne, Université Paul Sabatier (Bât 2R1), F-31062 Toulouse Cedex 04, France, Centre de Recherche Rhône-Alpes, Elf-Atochem, BP 63, F-69493 Pierre Bénite, France, and Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255 Cite this: Chem. Rev. 2000, 100, 1, 39–92Publication Date (Web):December 22, 1999Publication History Received2 March 1999Published online22 December 1999Published inissue 1 January 2000https://pubs.acs.org/doi/10.1021/cr940472uhttps://doi.org/10.1021/cr940472uresearch-articleACS PublicationsCopyright © 2000 American Chemical SocietyRequest reuse permissionsArticle Views37288Altmetric-Citations3327LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Adducts,Carbene compounds,Ligands,Phosphorus,Substituents Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTControlled Ring-Opening Polymerization of Lactide and GlycolideOdile Dechy-Cabaret, Blanca Martin-Vaca, and Didier BourissouView Author Information Laboratoire Hétérochimie Fondamentale et Appliquée du CNRS (UMR 5069), Université Paul Sabatier, 118, route de Narbonne, 31062 Toulouse Cedex 04, France Cite this: Chem. Rev. 2004, 104, 12, 6147–6176Publication Date (Web):October 5, 2004Publication History Received26 April 2004Published online5 October 2004Published inissue 1 December 2004https://pubs.acs.org/doi/10.1021/cr040002shttps://doi.org/10.1021/cr040002sresearch-articleACS PublicationsCopyright © 2004 American Chemical SocietyRequest reuse permissionsArticle Views34594Altmetric-Citations2015LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Ligands,Monomers,Organic polymers,Plastics,Ring-opening polymerization Get e-Alerts

A cDNA clone encoding a receptor protein which presents all the characteristics of a guanine-nucleotide-binding protein (G-protein)-coupled receptor was isolated from a human brain stem cDNA library. The probe used (HGMP08) was a 600 bp DNA fragment amplified by a low-stringency PCR, using human genomic DNA as template and degenerate oligonucleotide primers corresponding to conserved sequences amongst the known G-protein-coupled receptors. The deduced amino acid sequence encodes a protein of 472 residues which shares 97.3% identity with the rat cannabinoid receptor cloned recently [Matsuda, Lolait, Brownstein, Young & Bronner (1990) Nature (London) 346, 561-564]. Abundant transcripts were detected in the brain, as expected, but lower amounts were also found in the testis. The same probe was used to screen a human testis cDNA library. The cDNA clones obtained were partially sequenced, demonstrating the identity of the cannabinoid receptors expressed in both tissues. Specific binding of the synthetic cannabinoid ligand [3H]CP55940 was observed on membranes from Cos-7 cells transfected with the recombinant receptor clone. In stably transfected CHO-K1 cell lines, cannabinoid agonists mediated a dose-dependent and stereoselective inhibition of forskolin-induced cyclic AMP accumulation. The ability to express the human cannabinoid receptor in mammalian cells should help in developing more selective drugs, and should facilitate the search for the endogenous cannabinoid ligand(s).

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For a while, the reactivity of gold complexes was largely dominated by their Lewis acid behavior. In contrast to the other transition metals, the elementary steps of organometallic chemistry-oxidative addition, reductive elimination, transmetallation, migratory insertion-have scarcely been studied in the case of gold or even remained unprecedented until recently. However, within the last few years, the ability of gold complexes to undergo these fundamental reactions has been unambiguously demonstrated, and the reactivity of gold complexes was shown to extend well beyond π-activation. In this Review, the main achievements described in this area are presented in a historical context. Particular emphasis is set on mechanistic studies and structure determination of key intermediates. The electronic and structural parameters delineating the reactivity of gold complexes are discussed, as well as the remaining challenges.

Since the mid 2000's, the incorporation of Lewis acid moieties in ligands for transition metals has been studied extensively. So-called ambiphilic ligands were shown to possess rich and unusual coordination properties and special focus was given to the coordination of Lewis acids as σ-acceptor ligands (concept of Z-type ligands). Recent studies have demonstrated that the presence of Lewis acids at or nearby transition metals can also strongly impact their reactivity. These results are surveyed in this review. The stoichiometric transformations and catalytic applications of complexes deriving from ambiphilic ligands are presented. The different roles the Lewis acid can play are discussed.

Singlet diradicals are usually not energy minima. As observed by femtosecond spectroscopy, they readily couple to form final sigma bonds. Substituent effects allow lifetimes to increase into the microsecond range. Taking advantage of the properties of hetero-elements, a diradical has been prepared that is indefinitely stable at room temperature. The availability of diradicals that can be handled under standard laboratory conditions will lead to further insight into their chemical and physical properties, raising the likelihood of practical applications, especially in the field of molecular materials such as electrical conductors and ferromagnets.

-H auration and reductive elimination, allowing a gold-catalyzed direct arylation of arenes with aryl halides. Key to this discovery is the use of Me-Dalphos, a simple ancillary (P,N) ligand, that allows the bottleneck oxidative addition of aryl iodides and bromides to readily proceed under mild conditions. The hemilabile character of the amino group plays a crucial role in this transformation, as substantiated by density functional theory calculations.Catalysis involving Au(I)/Au(III) cycles are notoriously hampered by the reluctance of Au(I) towards oxidative addition. Here, the authors show that an hemilabile bidentate ligand promotes oxidative addition of aryl halides to Au(I) and the catalytic formation of biaryl coupling products.

Thanks to rational ligand design, the first gold(I) complexes to undergo oxidative addition of aryl iodides were discovered. The reaction proceeds under mild conditions and is general. The ensuing aryl gold(III) complexes have been characterized by spectroscopic and crystallographic means. DFT calculations indicate that the bending induced by the diphosphine ligand plays a key role in this process.

Abstract Bismuth( III ) triflate is a new, cheap and environmentally friendly Lewis acid. The research presented in this microreview is devoted to the evaluation of the scope of the uses of bismuth( III ) triflate in organic synthesis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Monophosphine-boranes were shown to behave as bidentate ambiphilic ligands, whose structural versatility has been illustrated by the preparation of PdII and AuI complexes featuring unusual P --> M-Cl --> B and P --> M --> B interactions, respectively.

The value of gold: The coordination of ambiphilic diphosphanylborane ligands to AuCl provides unusual square-planar gold(I) complexes. Insight is gained on the nature of the gold→borane interactions in these complexes through natural bond orbital (NBO) analysis and 197Au Mössbauer spectroscopy.

The use of organic photocatalysts has revolutionized the field of photoredox catalysis, as it allows access to reactivities that were traditionally restricted to transition-metal photocatalysts. This Minireview reports recent developments in the use of acridinium ions and cyanoarene derivatives in organic synthesis. The activation of inert chemical bonds as well as the late-stage functionalization of biorelevant molecules are discussed, with a special focus on their mechanistic aspects.

Alcohols, in particular polyols, are well-known for the synthesis of metal nanoparticles, often acting as reducing agents, solvents, and stabilizers. Given not only their structural flexibility depending on the number of OH functions and their inherent H bonding interactions, but also the wide range of polyol molecular weights readily available, different physicochemical properties (boiling point, polarity, viscosity) could be exploited toward the synthesis of well-defined nanomaterials. In particular, the relevance of the supramolecular structure of polyols has a fundamental impact on the formation of metal nanoparticles, thereby favoring the dispersion of the nanoclusters. In the field of the metal-based nanocatalysis, palladium occupies a privileged position mainly due to its remarkable versatility in terms of reactivity representing a foremost tool in synthesis. In this review, we describe the controlled synthesis of Pd-based nanoparticles in polyol medium, focusing on the progress in terms of tailoring size, morphology, structure, and surface state. Moreover, we discuss the use of palladium nanoparticles, in a polyol solvent, applied in two of the most relevant Pd-catalyzed processes, i.e., couplings and hydrogenation reactions, including multistep processes.

The phosphonium borane [1-Mes2B-2-MePh2P-(C6H4)]+ ([2]+) has been synthesized as an iodide salt by alkylation of 1-Mes2B-2-Ph2P-(C6H4) with MeI. This novel cationic borane complexes fluoride to afford the corresponding zwitterionic fluoroborate complex 1-FMes2B-2-MePh2P-(C6H4) (2-F) with a binding constant in MeOH exceeding that of 1-Mes2B-4-MePh2P-(C6H4) ([1]+) by at least 4 orders of magnitude. Structural and computational results indicate that the high fluorophilicity of [2]+ arises from both Coulombic and cooperative effects which lead to formation of a B-F-->P interaction with a F-->P distance of 2.666(2) A. These results, which are supported by NBO and AIM analyses, show that the latent phosphorus-centered Lewis acidity of the phosphonium moiety in [2]+ can be exploited to enhance fluoride binding via chelation.

The ambiphilic triphosphine-borane ligand 1 {TPB = [o-iPr2P-(C6H4)3B} readily coordinates to all group 10 and 11 metals to afford a complete series of metal boratranes (TPB)[M] 2-8 (2: M = Ni, 3: M = Pd, 4: M = Pt, 5: M = CuCl, 6: M = AgCl, 7: M = AuCl, 8: M = Au+). Spectroscopic and structural characterization unambiguously establishes the presence of M-B interactions in all of these complexes. The first evidence for borane coordination to copper and silver is provided, and the Au-->B interaction is shown to persist upon chloride abstraction. Experimental and theoretical considerations indicate that the M-->B interaction is strongest in the Pt and Au complexes. The influence of the oxidation state and charge of the metal is substantiated, and the consequences of relativistic effects are discussed. The coordination of the sigma-acceptor borane ligand is found to induce a significant bathochromic shift of the UV-vis spectra, the Ni, Pd, and Pt complex presenting strong absorptions in the visible range. In addition, all of the group 10 and 11 metal boratranes adopt C3 symmetry both in the solid state and in solution. The central M-->B interaction is found to moderately influence the degree of helicity and configurational stability of these three-bladed propellers, and DFT calculations support a dissociative pathway for the inversion process.

To and fro: Diphosphanylborane derivative 1 behaves as a tridentate, ambiphilic ligand towards rhodium(I) fragments (see picture). The presence of metal→borane interactions in the resulting square-pyramidal complexes is highlighted by structural analyses and DFT calculations.

The combination of trifluoromethanesulfonic acid (as a catalyst) and a protic reagent (such as water, 2-propanol, or 1-pentanol as an initiator) efficiently initiates the cationic polymerization of lactide in dichloromethane solution at room temperature. Polylactides (PLAs) with molar masses up to 20 000 were obtained via an activated-monomer mechanism. 1 H NMR spectroscopy and electrospray-ionization mass spectrometry of PLA oligomers demonstrated the quantitative incorporation of the protic initiator in the polymer chains and showed that transesterification reactions did not occur to a significant extent. The controlled character of the polymerization was indicated by the linear relationships of the number-average molar mass vs monomer conversion and monomer-to-initiator ratio. Kinetic measurements revealed a first-order dependence on monomer concentration. Moreover, no noticeable epimerization of the stereogenic carbon atom was observed in these polymerization conditions, as deduced from 1 H NMR analysis of a poly( l -lactide) sample.

Abstract The use of metallic nanoparticles in catalysis under homogeneous conditions leads to a discussion of their catalytic nature: whether the catalyst behaves as a molecular species or, on the contrary, the metallic surface is directly involved in the reactivity. This dilemma is intrinsically associated to the kinetic stability of the nanoclusters, favouring their agglomeration, and also to the formation of molecular species by reaction of the atoms placed at low‐coordination positions at the metallic surface. In particular, for palladium‐catalyzed processes, a large number of contributions have been reported in the last decade involving nanoparticles, but few of them analyze the mechanistic aspects. The present review aims to collect the more relevant research carried out in catalysis involving palladium nanoparticles in the liquid phase and addressing the nature of the catalytically active species. This kind of work is mainly focused on hydrogenation and C–C coupling processes.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Dual systems combining Zn(C6F5)2 with an organic base (an amine or a phosphine) promote the controlled ring-opening polymerization of lactide and ε-caprolactone. The Lewis pairs cooperate to activate the monomers, affording well-defined high molecular weight cyclic polyesters. Efficient chain-extension gives access to cyclic block copolymers.