Equatorial ligands

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. 

Pj a twist permuting one apical and two equatorial ligands ( 2=6) P3 a twist permuting one apical and one equatorial ligand ( 3=6) F4, two simultaneous twists each involving one apical and one equatorial ligand ( 4 = 3)... 

These complexes may be either six-coordinate with an octahedral configuration or five-coordinate with a square-pyramidal configuration, in which the organo ligand occupies the apical position a few form dimers through the interaction of each cobalt with a coordinated atom of the equatorial ligand of the other half (see Section In virtually all groups... 

Most of the tetradentate equatorial ligands have a complex structure and, since their systematic names are often cumbersome, abbreviations and... 

Costa and co-workers have compared the effect of different equatorial ligands on the relative stability of the five- and six-coordinate forms by studying the tendency of the five-coordinate acetylcobalt complexes to bind... 

Isomers are, of course, possible when the equatorial ligand lacks a plane of symmetry, as in the corrinoids [see (HI)]. All the acetamide side chains project to one side of the corrin ring, which we shall call the upper side, and all the propionamide side chains and the nucleotide side chain to the lower side. Isomers are then theoretically possible whenever the two axial ligands are different, and their existence has been shown experimentally for corrinoids where one axial ligand is CN , Me, or Et and the other is H2O or is absent [for further details see Section 8.2 of ref. (136)]. Salen and BAE also show minor deviations from planarity due to the bending of the two halves (mentioned above in Section II,B,2) and to torsion about the C—C bonds in the ethylene bridge (see references in Table I), but these are not expected to give rise to separable isomers. 

The Preparation and Characterization of Organocobalt(III) Complexes of the General Formula [RCo" (L )X] where L4 is the equatorial ligand (Corrin, etc.) and X is the unidentate axial ligand (.S,6-dimethylbenzimidazole, HjO or absent, where L is corrin otherwise as stated in the table). 

This section deals with reactions which involve only the organo-ligand, whether unmodified or modified by the loss or gain of a proton, and the cobalt. After considering established and possible mechanisms (Section B,l) we list examples to show how reactivity is influenced by different functional groups and substituents (Section B,2), and by changes in the axial and equatorial ligands (Section B,3). 

Most of the examples listed are pentacyanide, corrinoid, or DMG complexes. The axial ligands are not identified in the tables, but are as follows corrinoids, 5,6-dimethylbenziminazole (cobalamins), H O or none (cobinamides), (DMG)2, usually pyridine or H2O, less frequently NHj, imidazole, benzimidazole, PBuj, etc. The nature of the axial and equatorial ligands may have a striking effect on reactivity, but few direct comparisons are available these are discussed in the next section. 

Figure 9.11 Contour maps of p and L for PF5 (a) in the equatorial plane and (b) in the axial plane through an equatorial ligand.

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