Topic
Ligand
About: Ligand is a research topic. Over the lifetime, 67732 publications have been published within this topic receiving 1359684 citations. The topic is also known as: complexing agent & ligands.
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TL;DR: A high-resolution crystallographic analysis of the nitrogenase MoFe-protein reveals a previously unrecognized ligand coordinated to six iron atoms in the center of the catalytically essential FeMo-cofactor, consistent with this newly detected component being a light element, most plausibly nitrogen.
Abstract: A high-resolution crystallographic analysis of the nitrogenase MoFe-protein reveals a previously unrecognized ligand coordinated to six iron atoms in the center of the catalytically essential FeMo-cofactor. The electron density for this ligand is masked in structures with resolutions lower than 1.55 angstroms, owing to Fourier series termination ripples from the surrounding iron and sulfur atoms in the cofactor. The central atom completes an approximate tetrahedral coordination for the six iron atoms, instead of the trigonal coordination proposed on the basis of lower resolution structures. The crystallographic refinement at 1.16 angstrom resolution is consistent with this newly detected component being a light element, most plausibly nitrogen. The presence of a nitrogen atom in the cofactor would have important implications for the mechanism of dinitrogen reduction by nitrogenase.
940 citations
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TL;DR: In this article, a single-crystal X-ray diffraction study has been performed on 6.5-C5Me5-RuCl2(C(H)Ph)(PCy3)2 (1) and the carbene ligand 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes)Cl (3) in 86% isolated yield, where the thermochemical information is used to predict the magnitude of the enthalpic driving force behind substitution reactions
Abstract: The reaction of [Cp*RuCl]4 (1; Cp* = η5-C5Me5) with the carbene ligand 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) affords a coordinatively unsaturated Cp*Ru(IMes)Cl (3) complex in 86% isolated yield. Solution calorimetric results in this system provide information concerning the electron donor properties of the carbene ligand, which are very similar to those of PCy3. Structural information from single-crystal X-ray studies for complex 3 allows the determination of steric parameters associated with this ligand. The thermochemical information is used to predict the magnitude of the enthalpic driving force behind substitution reactions involving RuCl2(C(H)Ph)(PCy3)2 (1) and the carbene ligand, IMes, affording the RuCl2(C(H)Ph)(PCy3)(IMes) (6) complex in high yield. A similar mixed carbene/phosphine ruthenium complex, RuCl2(C(H)Ph)(PPh3)(IMes), can also be isolated from RuCl2(C(H)Ph)(PPh3)2 and the IMes ligand. A single-crystal X-ray diffraction study has been performed on 6. The thermal stabilit...
920 citations
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887 citations
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TL;DR: The highly ordered amide groups in the channels play an important role in the interaction with the guest molecules, which was confirmed by thermogravimetric analysis, adsorption/desorption measurements, and X-ray crystallography.
Abstract: To create a functionalized porous compound, amide group is used in porous framework to produce attractive interactions with guest molecules. To avoid hydrogen-bond formation between these amide groups our strategy was to build a three-dimensional (3D) coordination network using a tridentate amide ligand as the three-connector part. From Cd(NO3)2·4H2O and a three-connector ligand with amide groups a 3D porous coordination polymer (PCP) based on octahedral Cd(II) centers, {[Cd(4-btapa)2(NO3)2]·6H2O·2DMF}n (1a), was obtained (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-pyridyl)amide]). The amide groups, which act as guest interaction sites, occur on the surfaces of channels with dimensions of 4.7 × 7.3 A2. X-ray powder diffraction measurements showed that the desolvated compound (1b) selectively includes guests with a concurrent flexible structural (amorphous-to-crystalline) transformation. The highly ordered amide groups in the channels play an important role in the interaction with the guest molec...
883 citations
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TL;DR: A range of novel catalytic reactions that were developed guided by these new modes of metal-ligand cooperation are described, including a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex.
Abstract: In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on “cooperating” ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation.We have discovered a new mode of metal–ligand cooperation, involving aromatization–dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H–H, C–H (sp2 and sp3), O–H, and N–H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process,...
877 citations