4,563 research outputs found
Gold(I) complexes in ionic liquids: an efficient catalytic system for the C-H functionalization of arenes and heteroarenes under mild conditions
No full textNovel gold complexes with di(N-heterocyclic carbene) ligands: synthesis and applications
No full textIn the last twenty years, N-heterocyclic carbenes (NHC) have gained general attention as a class of ligands alternative or complementary to the classical ones, based on phosphorous (phosphines, phosphites, etc.) or nitrogen (amines, imines, etc.) donor atoms. In particular, a growing number of new technological applications based on Au(I)- or Au(III)-NHC complexes has appeared. Noteworthy, up to now the majority of these examples deals with N-heterocyclic monocarbene gold complexes.
This PhD thesis is focused on the chemistry of gold complexes with di(NHC) ligands (di(NHC) = di(N-heterocylic carbene)) with particular reference to their synthesis and to the determination of a possible relation between their structure, properties and reactivity.
In particular the obtained results are divided in three main chapters: i) Synthesis and characterization of the gold(I) di(NHC) complexes; ii) Oxidation of the gold(I) di(NHC) complexes; iii) Synthesis and reactivity of silver and gold complexes with novel di(NHC) ligands obtained via click reaction.
i) Synthesis and characterization of the gold(I) di(NHC) complexes.
Gold(I) complexes with different functionalized N-heterocyclic di(NHC) ligands have been prepared by direct deprotonation of the diimidazolium salts, that are the di(NHC) ligand precursors, in the presence of AuCl(SMe2) and of a mild base (NaOAc). In the adopted synthetic conditions, dinuclear dicationic gold(I) complexes presenting a metallamacrocyclic structure with two bridging di(NHC) ligands have been obtained in good yields.
The photoluminescence and electrochemical properties of the synthesized complexes are strongly influenced by the structure of the di(NHC) ligand employed, in particular by the bridge present between the two imidazole-2-ylidene rings. Remarkably we identified complex 3 (Y = (CH2)3) as a very strong solid state emitter with an almost unitary quantum yield of emission (Фem = 96 %). The ligands of complex 3 were functionalized with different wingtip substituents, bearing long aliphatic chains of different length, with the aim of obtaining luminescent liquid crystals. The new complexes of this type behave as thermotropic materials, differing from the parent compound 3.
ii) Oxidation of the gold(I) di(NHC) complexes.
The reactivity of the gold(I) complexes toward oxidative addition of halogen is strongly influenced by the employed halogen and by the structure of the di(NHC) ligand. In general stable Au(III)/Au(III) complexes were obtained; however with the bulkier iodine a mixed valence Au(I)/Au(III) complex is isolated. Moreover the presence of the propylene bridge in the di(NHCs) favors the formation rather novel Au(II)/Au(II) complexes. The nature and the geometry of the obtained products have been fully elucidated in several cases by X-ray analysis.
iii) Synthesis and reactivity of silver and gold complexes with novel di(NHC) ligands obtained via click reaction.
The copper(I) catalyzed azide alkyne cycloaddition was used to introduce new functionalities (benzyl or polyethyleneglycole chain substituted triazole) on the peripheral positions of the bis(1-methylimidazole)propane core. Using the optimized reaction condition it was possible to prepare the corresponding gold(I) and gold(III) complexes. The in vitro cytotoxic activity of the functionalized gold(III) di(NHC) complexes was evaluated on a series of different neoplastic cell lines and on two healthy cell lines; The functionalized complexes are more active than the parent unfunctionalized ones and they express cytotoxicity preferentially towards the neoplastic cells
Poly-NHC Complexes of Transition Metals: Recent Applications and New Trends
No full textThe most significant recent developments in the chemistry of transition metal complexes with poly-N-heterocyclic carbene ligands (poly-NHCs) are reviewed herein. In particular, attention is focussed on the preparation of novel poly-NHCs, on their coordination chemistry towards transition metal centers as well as on the applications of the resulting complexes, which nowadays range from catalysis to photophysics and medicinal chemistry. The goal is to highlight the most important recent achievements in this complex field and to give to the reader an overview on the broad chemistry of these compounds
Advances in Transition-Metal-Catalysed Alkyne Hydroarylations
No full textWe present herein a personal account of our achievements in the development of novel catalytic systems based on late-transition-metal complexes for the hydroarylation of alkynes. In particular, our targets were intermolecular hydroarylation reactions with arene or heteroarene substrates devoid of directing groups. We have shown that complexes of palladium, platinum or gold with N-heterocyclic carbene (NHC) ligands can be particularly useful catalysts for this reaction; the NHC ligand imparts greater stability to the complex and renders the catalytic system more productive. Furthermore, we have identified promoters and reaction media that allow to significantly improve the catalytic activity under mild conditions, to control the reaction chemoselectivity and to steer it towards more complex products; thus making this reaction considerably more attractive for the synthetic chemist
AAJR Baron Book Prize
No full textThe American Academy for Jewish Research invites submissions for the Salo Wittmayer Baron Book Prize. The Baron Book Prize ($3,000) is awarded annually to the author of an outstanding first book in Jewish studies. Eligibility: An academic book, in English, in any area of Jewish studies published in calendar year 2023. The work must be the author’s first scholarly book. Authors must have received their Ph.D. within the previous ten years, no earlier than 2013. Deadline: Submissions..
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