Associative ligand exchange

Figure 3.4 a Dissociative and b associative ligand exchange from Ni(CO)4. 

Competition for Al3+ between F" and a different ligand (e.g., oxalate, C2Ol ) can be pictured in terms of the associative ligand-exchange reaction 811... 

The appropriateness of this speciation calculation from the kinetics standpoint can be assessed by considering the associative ligand-exchange reaction (cf. Eq. 2.12) ... 

Figure 4 is probably the most appropriate form for associative ligand exchange at nickel(II) complexes, well represented by 5-coordinate structures of both types 54, 55). 

Pseudorotation and the Stereoretentive Nature of Associative Ligand Exchange... 

Stereoselective Associative Ligand Exchange of 4-coordinate Square Planar Complex... 

In associative ligand exchange, the intervention of hexacoordinated intermediates has been demonstrated in various intermolecular ligand exchange processes at five-coordinated silicon compounds (286,355) (eq. [114]). 

This means that gold(I) compounds can undergo associative ligand exchange reactions with cysteine-rich peptides and proteins such as glutathione, metallothionein and albumin28,29, particularly where the p/fsH is low, e.g. the Cys-34 of albumin30. 

Organometallic compounds with a 17-electron configuration are often labile toward associative ligand exchange. Radical chain mechanisms are well established for phosphine substitution on metal carbonyl hydrides (Scheme 23), the 17-electron chain carrier being in most cases non hydridic. This mechanism, however, was also shown to operate for OsH2(CO)4 via the 17-electron hydride complex OsH(CO)4 [137]. Thus, phosphine addition to the radical prevails over the dimerization, which indeed occurs in the absence of phosphine [33] (section 6.5.7), and over other possible decomposition pathways. The second step of the chain propagation process in Scheme 23, for this osmium system, is another example of atom transfer to a hydride radical (section 6.5.6). 

The relationship of these compounds to the reaction intermediates of associative ligand exchange processes of 4-coordinate species makes their formations and reactions a rewarding area for study. This time there has been a great deal of structural activity in this field, and the results relate directly to many fundamental mechanistic questions. 

The demonstration of a new photobleaching pathway for /ac-[ReBr(bipy)-(00)3], involving the use of triethylamine in DMF, is of interest in relation to nucleophilic attack at iron(II)-diimine complexes (see Section 8.2.2 below), for the mechanism involves ethylation of coordinated 2,2 -bipyridyl. Finally, the [ReO(MeC=CMe)2(py)] cation undergoes associative ligand exchange, with retention of configuration. 

Associative Ligand Exchange at Square-Planar Platinum(II)... 

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