Rotation metal/ligand bond

Diasteroisomers, also known as geometric isomers, have different relative orientations of their metal-ligand bonds. Enantiomers are stereoisomers whose molecules are nonsuperposable mirror images of each other. Enantiomers have identical chemical and physical properties except for their ability to rotate the plane of polarized light by equal amounts but in opposite directions. A solution of equal parts of an optically active isomer and its enantiomer is known as a racemic solution and has a net rotation of zero. 

Since is a rotation matrix, the rf-orbital di) can be represented in polar coordinates, with Z-axis along the metal-ligand bond, as... 

Line shape analysis has been utilized to detect and elucidate dynamics of ligands bound to metals. For iron porphyrin models of metalloproteins, axial imidazole ligands may rotate relative to the heme axes linebroadening of heme substituents resulting from this process can be observed at low temperature. Such ligand motion is not commonly observed within metalloproteins because of constraints of the protein structure and metal-ligand bonding. NMR studies of... 

DDQ, TCNQ, etc., yield cyclopropanes stereochemical studies show that the reductive elimination is either concerted with the oxidation step or that C—C coupling following the first Ti—C bond cleavage is faster than C—C bond rotations (4/). It is currently believed that these reactions proceed via outer-sphere one-electron oxidation from a metal-ligand bond. In the case of Zr, this is followed by loss of an R radical and trapping... 

Another dynamic intramolecular effect has to be considered when prochiral olefins such as propylene are polymerized the intramolecular rotation of the indenyl ligands around the metal—ligand bond axis can change the symmetry of the corresponding metallocene complex rac or mesd) continuously ( oscillating catalysts 4-77) produce polymers... 

Ligand Rotations about the Metal-Ligand Bond. 341... 

The bonding of a triplet carbene is less closely related to the metal-ligand bonds discussed thus far. The carbenes in these complexes are considered dianionic. With this assignment of electrons and charges, the a- and ir-orbitals of this dianionic fragment can be considered to bind the metal by donation of two electron pairs, one into each of the unoccupied orbitals of the metal of a- and ir-symmetry. These carbene ligands have ir-bonds that are stronger than those in Fischer carbenes, but much weaker than those in alkenes. The barrier to rotation in these complexes is t5q)ically 19 kcal/mol. - ... 

In this complex, the molecule of coordinated ethylene occupies a single coordination site and is oriented perpendicularly to the plane of the square anion. In both complexes mentioned above (i.e., the complexes with two-center ligands and the olefin rr complexes), the bonding of ligands to the central atom occurs via the dihapto type. Moreover, the rotation of olefin about the metal-ligand bond was observed both in Zeise s salt and in some other ir complexes. Thus, the free energies for the activation of olefin (L) rotation in complexes (PR3)PtCl2 -L and PtCl(acac) - L depend on the nature of R and L, and vary within 44.4-67 kJ mol (10.6 16 kcal mol ) [80]. 

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