Three WERNER TYPE METAL COMPLEXES

The three-center metal-H2 interaction complements classical Werner-type coordination complexes where a ligand donates electron density through its nonbonding electron pair(s) and jt-complexes such as olefin complexes in which electrons are donated from bonding jt-electrons (Scheme 5.5). 

Seventeen years is a long time between editions of a book. In order to add some of the vast amount of new material which has been published in that time, I have needed to abridge the older edition and in so doing apologise to oldtimers (myself included ) whose work may have been removed or modified. Nevertheless, the approach used is unchanged. In the first three chapters I have dealt with the acquisition of experimental data and discussed use for building up the rate law and in the deduction of mechanism. In the second part of the book, the mechanistic behavior of transition metal complexes of the Werner type is detailed, using extensively the principles and concepts developed in the first part. 

Octahedral Six Coordinate In addition to the tris-bidentate complexes and the unidentate complexes discussed above, there are many other examples of chiral metal complexes that are based on octahedral geometry. For example, there are a number of reports of edge-sharing binuclear structures containing four bidentate chelates. The individual metal centers in these binuclear species can exist as either A or A enantiomers, and, therefore, the overall structure can be chiral AA and AA, or the achiral (meso) AA pair as illustrated in Figure 5.12a and b. Studies of complexes of this type were important in the proof of Werner s coordination theory. In these pioneering studies, Werner was able to prove by experiment the existence of the three isomers (AA, AA, and AA) of [Co2(p-NH2)( l-NC>2)(en)2]4 +. 23 For Cr(III) complexes, Werner showed that the / >.vo-AA- Cr2(p-OH)2(en)414 1 may be prepared by... 

As noted earlier, there is an experimental distinction between the substitution reactions of labile and inert complexes. The formation of labile complexes is virtually instantaneous upon mixing of the reactants, so that there are few practical difficulties in their preparation, but three points must be remembered. First, for classical, Werner-type, complexes it is found in practice that it is difficult to prepare such complexes with several different non-ionic ligands bonded to the same metal atom, although it is much easier to prepare complexes in which an anionic species is coordinated together with a neutral ligand. Secondly, although it may be possible to isolate and characterize a solid complex, quite a different complex may be the predominant species in solution. So, the blue complex Cs2[CoCl4] crystallizes... 

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