Chemistry is the science of change. But why do chemical reactions take place? Why do chemicals react with each other? The answer is in thermodynamics and kinetics.In a document type is Article, the author is Cundari, Thomas R. and a compound is mentioned, 33100-27-5, 1,4,7,10,13-Pentaoxacyclopentadecane, introducing its new discovery. 33100-27-5
Rhenium-oxo-bis(acetylene) anions. Structure, properties, and electronic structure. Comparison of Re-O bonding with that in other rhenium-oxo complexes
Reduction of Re(O)I(RC?CR)2 (2) or [Re(O)(RC?CR)2]2 by two electrons gives Re(O)(RC?CR)2Na (R = Me, 1a; Et, 1b; Ph, 1c). Compounds 1 are unusual oxo complexes, being highly nucleophilic and strongly reducing. X-ray structures of 1a-crypt and 1c-2MeCN reveal Re(O)(RC?CR)2 units, as isolated anions in the former but, in the latter, connected via Na-O-Na bridges into centrosymmetric dimers. The acetylene ligands lie in a plane that is roughly perpendicular to the Re – O bond, but the C?C vectors are splayed rather than parallel. The bond lengths and angles about rhenium are quite similar in the two structures, and quite close to the values found for 2 in which the splaying occurs to accommodate the iodide ligand. Reduction of 2a to 1a¡¤crypt causes a lengthening of the Re-O bond from 1.697(3) to 1.745(7) A and a drop in nuReO from 975 to 869 cm-1, both indicative of a decrease in the Re-O bond order. The Re-C distances and C?C stretching frequencies both decrease on reduction, indicating increased Re ? acetylene back-bonding in 1. Effective core potential calculations on Re(O)(HC?CH)2- (A), Re(O)H(HC?CH)2 (B), Re(O)Cl4- (C), and Re(O)F5 (D) have been performed with excellent agreement between the calculated structures and experimental crystallographic data (A and B are models for 1 and 2). The Re-O bonds in the high-oxidation-state oxo complexes C and D follow the classical Ballhausen-Gray picture, with little mixing between the Re-O orbitals and orbitals on other ligands. In contrast, the frontier molecular orbitals in A and B exhibit significant delocalization over the rhenium, the oxygen, and the acetylene ligands. In A, the HOMO is an orbital largely Re dx(2)-y(2) in character, accounting for the high nucleophilicity at rhenium in 1. The second-highest molecular orbital, only 0.8 eV below the HOMO, has significant Re-O ?-antibonding and Re-acetylene ?-back-bonding character, which provides a rationalization for the reduced Re-O bond order and strong back-bonding observed. There is also a ligand-based nonbonding orbital delocalized over the oxo and the acetylene ligands, as observed in other three-coordinate compounds involving acetylenes. Connections between the calculated electronic structure and the chemistry of 1 are emphasized.
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Reference£º
Chiral Catalysts,
Chiral catalysts – SlideShare