Rotation metal-ligand

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. 

The activation barrier to rotation of the cyclopropenyl ligand about the M—C3 axis has been shown to vary dramatically with the nature of the metal-ligand fragment309,314 329. 

The rotation around a metal-ligand single bond is free1391 i. e. /t 2 = 0. 

Steric factors probably prohibit simultaneous rotation of the olefin and alkyne C2 units which would crowd all four metal-bound carbons into the same plane. Separate rotation of each unsaturated ligand was explored theoretically using the EHMO method. Rotation of the olefin destroys the one-to-one correspondence of metal-ligand tt interactions. Overlap of the filled dxz orbital with olefin n is turned off as the alkene rotates 90°, creating a large calculated barrier for olefin rotation (75 kcal/mol). Alkyne rotation quickly reveals an important point the absence of three-center bonds involving dir orbitals allows the alkyne to effectively define the linear combinations of dxy and dyz which serve as dn donor and dir acceptor orbitals for 7T and ttx, respectively. Thus there should be a small electronic barrier to alkyne rotation (the Huckel calculation with fixed metal... 

Dynamic NMR studies of W(CO)(HC=CH)(S2CNEt2)2 and related complexes (58) indicate that the barrier to alkyne rotation is around 11-12 kcal/mol (Table IV). Discordant metal-ligand 77 interactions anticipated as the alkyne rotates away from the ground state orientation are evident in EHMO calculations (Fig. 23). When the alkyne is orthogonal to the M—CO axis the dyz orbital is stabilized by CO it but destabilized by alkyne ir while dxy becomes the lowest lying dir orbital due to... 

The metal is bound to a dummy atom at the centroid of the five-membered rings (Fig. 14.2(c)). The rotation of the ligands around the ligand-metal-ligand axis is easily achieved, and this topology is a reasonable model for the bond-... 

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... 

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