Transition metal alkene complex

Summary

In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. The inventory is large. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products. Monoalkenes The simplest monoalkene is ethene. Many complexes of ethene are known, including Zeise's salt (see figure), Rh2Cl2(C2H4)4, Cp*2Ti(C2H4), and the homoleptic Ni(C2H4)3. Substituted monoalkene include the cyclic cyclooctene, as found in chlorobis(cyclooctene)rhodium dimer. Alkenes with electron-withdrawing groups commonly bind strongly to low-valent metals. Examples of such ligands are TCNE, tetrafluoroethylene, maleic anhydride, and esters of fumaric acid. These acceptors form adducts with many zero-valent metals. Dienes, trienes, polyenes, keto-alkenes, and other complicated alkene ligands Butadiene, cyclooctadiene, and norbornadiene are well-studied chelating agents. Trienes

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A novel synthetic strategy for getting low-valent metals in an oxo environment

Geoffroy Guillemot

EPFL2002

The oligomerization of propene was investigated over a series of nickel ion-exchanged Na-X zeolites with varying Ni loadings. Catalyst characterization by temperature-programmed reduction, elemental analysis, and XANES indicates that all of the exchanged Ni is present as Ni2+ that charge-compensates two exchange sites. The selectivity to propene oligomers remained greater than 98% for all Ni-Na-X catalysts with dimers being the main product. In contrast, the activity of Ni-Na-X was determined to depend strongly on Ni loading. At low to intermediate Ni loadings, the catalyst activates, reaches a maximum activity, and then deactivates with further time on stream. The rates of activation and deactivation are functions of the Ni content in the zeolite and both increase with increasing Ni loading. Stable activity was achieved for low Ni loadings (

Academic Press Inc Elsevier Science2012

The thesis deals with the development of transition metal-catalyzed difunctionalization of alkenes and alkynes, which can be categorized into two major topics: (1) palladium-catalyzed diamination of alkynes for the synthesis of tetracycles; (2) copper-catalyzed cyanoalkylation-initiated double functionalization of alkenes. The first part of this thesis describes the synthesis of free NH tetracyclic indoles by palladium-catalyzed diamination of triple bonds. In the presence of palladium catalyst, 1,2-diarylethynes bearing an N-methyl-N-[2-(methoxy-carbonyl)ethyl]amino and an aminocarbonyl/aminosulfonyl group at the ortho positions of the two aromatic rings underwent double cyclization in a highly ordered fashion to afford N-2-(methoxycarbonyl)ethylaed indolo[3,2-c]isoquinolinone or indolobenzothiazine S,S-dioxide with complete chemoselectivity. Subsequently, the N-[2-(methoxycarbonyl)ethyl] group is readily removed under basic conditions (DBU, DMF, 120 °C) to afford tetracycles with indolyl nitrogen unprotected. We subsequently developed a transition metal-free diamination process to access the tetracyclic quindolinones. In the presence of acetic acid and a hydride donor (Hantsch¿s ester) under oxygen atmosphere, double cyclization of 1,3-diarylprop-2-yn-1-ones bearing an N,N-dialkylated amino and an N-monoalkylated amino groups at ortho positions of aromatic rings occurred smoothly to provide tetracyclic quindolinones. In the second part of thesis, copper-catalyzed cyanoalkylative difunctionalization of alkenes with alkylnitriles as alkylative reagents was addressed. We developed catalytic conditions (copper salt, ligand, peroxide, base) that allowed us to convert unactivated alkenes to 1,2-difunctionalized alkanes or its cyclic variants. The domino process proceeded through following key elementary steps: a) generation of cyanolakyl radicals; b) addition of cyanoalkyl radical to unactivated double bond; c) interception of this adduct radical by a suitable reagent, or more frequently, oxidation of adduct radical to carbenium; d) trapping of the carbocation by an internal/or external nucleophile. By applying this strategy, a series of value-added molecules such as dihydroisobenzofurans, gamma-lactones, aziridines and gamma-azidobutyronitriles, were readily synthesized from simple alkenes.

EPFL2017