Tetragonal pyramidal intermediates

Pi the Berry step is seen as a double bending of an equatorial and an apical angle. The two apical ligands become equatorial and two equatorial ones go to apical positions. One of the equatorial ligands, the so-called pivot, is on the fourfold axis of the tetragonal pyramidal intermediate state. The connectivity i.e. the number of isomers reached from a given one in one step, is three. 

Reaction (19) causes larger isotope effect determined for product than effect for substrate due to additional fractionation of analysed carbon atom in the side reaction. For mechanistic analysis 13C KIE based on the substrate analysis was used. DFT calculations of isotope effects for each step of the reaction led to conclusion that the rate-determining step involves breaking of the P-C bond in the tetragonal pyramidal intermediate. 

Similar conclusions were drawn from detailed 1 H-NMR-analyses of the dynamic behaviour of the isopropylphenyl derivatives 39h, i where even the (very improbable) possibility of a tetragonal-pyramidal intermediate with freely rotating isopropylphenyl substituents was taken into consideration 81). 

It seemed likely that mechanism B would produce a symmetrical trigonal bipyramid and thus lead to racemization if an optically active substrate was used in the reaction. Mechanism A would certainly lead to total racemization, but mechanism C would not cause loss of optical activity. On the other hand it is possible to draw an asymmetric trigonal pyramid or an asymmetric tetragonal pyramid as a five-coordinate intermediate in mechanism B. The latter seem unlikely in organic solvents with weak donor properties. Furthermore, recent evidence suggests a symmetric trigonal pyramid as an intermediate in the racemization of trisacetylacetonate (50). 

A = distorted trigonal bipyramidal, B = irregular five-coordinate, C = distorted tetrahedral, D = intermediate between trigonal bipyramidal and square pyramidal, E = distorted tetragonal pyramidal, F = pseudooctahedral, G = linear, H = highly distorted tetrahedral. Axial bonds. 

Reaction of a methanolic solution of copper(II) acetate and enantiomerically pure (/ )/(S)-methyl( )-4ethyl-2-oxazolidinylidene)cyanoacetate 64 leads to the coordinatively unsaturated CVsymmetric intermediates (R,Rj-65 and (S,S)-65, which are sterically shielded at one side by two ethyl groups. Therefore, in contrast to the 2D- and 3D-coordination polymers, coordination of (R,R)/(S,S)-65 with only one cyano donor is possible, resulting in the formation of polymers (/>)-oc1[Cu(Li )2] (P-66) and (M)-J[Cu(L5)2] (M)-66) (Scheme 24) ([166, 169, 170] for other chiral lD-coordination polymers of our group, see [171, 172]). The X-ray crystal structure analysis of polymer (P)-66 clearly proves a well-ordered infinite onedimensional architecture. The central copper atoms in (P)- [Cu(L )2] CP-66) are almost tetragonal-pyramidally coordinated, and in contrast to the 2D- and... 

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