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O Ligands (o + ligand)
Selected AbstractsNovel Cyclic 1,2-Diacetals Derived from (2R,3R)-(+)-Tartaric Acid: Synthesis and Application as N,O Ligands for the Enantioselective Alkylation of Benzaldehyde by DiethylzincEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2004M. Teresa Barros Abstract A chiral cyclic 1,2-diacetal derived from tartaric acid was used as the basic structural unit for novel ligands. Monooxazoline carbinols in which the degree of substitution of the alcohol and the nature of the stereocentre in the oxazoline ring were varied were synthesized in moderate to good yields. The influence of these structural factors on asymmetric induction was examined in the enantioselective addition of diethylzinc to benzaldehyde. Up to 60% ee was observed with a secondary or a tertiary alcohol as the metal-chelating group. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Iron(II) Complexes with Bio-Inspired N,N,O Ligands as Oxidation Catalysts: Olefin Epoxidation and cis -DihydroxylationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2008Pieter Abstract The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis -dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [FeII(PrL1)2](BPh4)2 (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [FeII(PrL1)2(MeOH)2](OTf)2 (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15,15,-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [FeII(PrL1)2](OTf)2 (2) and [FeII(PrL1)2](BPh4)2 (3) were tested in olefin oxidation reactions with H2O2 as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis -dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction. [source] Mono-, Di- and Polymeric Calcium and Gadolinium Complexes of the Tripodal Ligand 2,2,,2,,-Nitrilotribenzoic AcidEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2005Stefan Wörl Abstract Three novel carboxylate-bridged complexes incorporating the tripodal N,O ligand 2,2,,2,,-nitrilotribenzoic acid H3L of formula [CaII(H2L)(OH2)4][(H2L)]·4H2O (1), [CaII(OH2)4]-[CaII(L)(OH2)2]2·7H2O (2) and [GdIII(L)(OH2)3]2[GdIII(L)-(OH2)4]2·13H2O (3) were synthesized and characterized by X-ray crystallography. In all three complexes, the ligand H3L binds to the metal centre only by its three carboxylate donors, leaving the bridgehead nitrogen atom nonbonding. The calcium(II) ion in the monomeric complex 1 is distorted pentagonal-bipyramidal coordinated, the +1 charge of the complex cation [CaII(H2L)(OH2)4]+ is balanced by an H2L, anion and both units are connected by hydrogen bonds. The polymeric compound 2 displays a one-dimensional chain structure, in which two [CaII(L)]2, units form a dimeric structure and are connected by hydrated CaII ions. 3 contains two different [GdIII(L)(OH2)n] dimers. In one of them the two GdIII ions are linked by two monoatomic carboxylate O-bridges showing a short Gd···Gd distance of 3.99 Å. In the second, a syn - anti carboxylate 1,3-bridge with a longer Gd···Gd distance of 4.96 Å is observed. Magnetic measurements of 3 show paramagnetic behaviour with weak antiferromagnetic coupling. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Synthesis and Transition Metal Complexes of Novel N,N,O Scorpionate Ligands Suitable for Solid Phase ImmobilisationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2006Eike Hübner Abstract Introduction of an allyl or a hydroxymethyl group to bis(3,5-dimethylpyrazol-1-yl)acetic acid (1) at the bridging carbon atom leads to the new tripodal N,N,O ligands 2,2-bis(3,5-dimethylpyrazol-1-yl)pent-4-enoic acid (Hbdmpzpen) (2) and 2,2-bis(3,5-dimethylpyrazol-1-yl)-3-hydroxypropionic acid (Hbdmpzhp) (3). These ligands exhibit similar chemical behaviour to that of 1, but they have the additional possibility to be immobilised to a solid phase. Esterification of the hydroxymethyl linker of 3 yields 2,2-bis(3,5-dimethylpyrazol-1-yl)-3-acetatopropionic acid (Hbdmpzap) (4). The molecular structures of 2, 3 and 4 all exhibit intramolecular hydrogen bridges. Introduction of a hydroxymethyl group to methyl bis(3,5-dimethylpyrazol-1-yl)acetate (5) yields methyl2,2-bis(3,5-dimethylpyrazol-1-yl)-3-hydroxypropionate(Mebdmpzhp) (6), which can be immobilised on Merrifield polymer to yield modified resin P - 6. To investigate the reactivity of these new ligands, manganese and rhenium complexes of 2, 3 and 4 have been studied. The molecular structures of the two manganese complexes [Mn(bdmpzpen)(CO)3] (7) and [Mn(bdmpzap)(CO)3] (8) have been confirmed by single-crystal X-ray structure determination. Saponification of polymer resin P - 6 and subsequent reaction with [ReBr(CO)5] yields rhenium tricarbonyl complexes anchored on Merrifield polymer (P -Re). Solid phase immobilisation of the [Mn(bdmpzpen)(CO)3] (7) and [Re(bdmpzpen)(CO)3] (9) complexes on 3-mercaptopropyl functionalised silica is initialised by AIBN. The tripodal coordination of manganese and rhenium in these functionalised Merrifield resins (P -Re) and silica (S -Mn, S -Re) is proven by a single A1 and two E signals in the IR spectra that are typical for unsymmetrical "piano stool" type carbonyl complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Modular Routes Towards New N,O-Bidentate Ligands Containing an Electronically Delocalised ,-Enaminone Chelating BackboneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 24 2008Udo Beckmann Abstract Polyketones are synthesised by a transition-metal-catalysed copolymerisation of olefins and carbon monoxide. Nickel complexes with N,O-chelating ligands turned out to be promising catalysts in that field. In this work a series of new N,O ligands with an electronically delocalised ,-enaminone backbone were synthesised and fully characterised. The ligand design was inspired by the ligand found in the most efficient nickel catalyst for polyketone synthesis and developed to a highly modular LEGO® -like arsenal of reactions to versatile substituted ,-enaminone ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Highly Selective Cobalt-Catalyzed Hydrovinylation of StyreneADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Michiel M. Abstract Phosphine complexes of cobalt halide salts activated by diethylaluminum chloride are shown to yield highly active catalysts in the hydrovinylation of styrene, with unprecedented high selectivity to the desired product 3-phenyl-1-butene (3P1B). Double-bond isomerization, a common problem in codimerization reactions, only occurs after full conversion with these catalyst systems, even at elevated temperature. The most active catalysts are based on cobalt halide species combined with either C1 - or C2 -bridged diphosphines, heterodonor P,N or P,O ligands, flexible bidentate phosphine ligands or monodentate phosphine ligands. Kinetic investigations show an order >1 in catalyst, which indicates either the involvement of dinuclear species in the catalytic cycle or partial catalyst decomposition via a bimolecular pathway. [source] | ||||||||||