Carbon-bound Ligands

Copper compounds containing carbon-bound ligands, such as cyanide, carbon monoxide, alkyls, and so on are covered elsewhere (see Copper Organometallic Chemistry). 

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). 

Reaction of [Ir(cod)Cl]2 with (6-methyl-2-pyridyl)methyl lithium yields the binuclear species [(cod)Ir(/i-CH2-py-6-Me-C, /V)]2, (401). The Ir centers in (401) are 3.5889(3) A apart, indicating little metal-metal interaction. Treatment of (401) with PPh2Et yields [(cod)Ir(PPh2Et)2(CH2-py-6Me)], which contains the monodentate, carbon-bound pyridylmethyl ligand. 

Contrary to carbon enterosorbents, Enterosgel does not possess an ability for selective removal of albumin-bound ligands regardless of their affinity with the protein carrier - weak (L-tryptophane), medium (sodium caprylate, deoxycholic acid), or strong (indole-3-carboxylic acid and unconjugated bilirubin). It means that if protein-bound toxins are removed by Enterosgel, this occurs simultaneously with adsorption of the carrier protein. 

Table 21.3 Comparative efficacy (M /Mp) of orgatiosilicoti and carbon enterosorbents for removal of protein bound ligands...

Organometallic complexes frequently are susceptible to nucleophilic attack by an external reagent. In some instances the attack takes place on the metal center (see substitution reactions, page 686). while in others it occurs on a bound ligand. Already in this chapter we have seen many instances in which coordinated carbon monoxide undergoes nucleophilic attack. Examples include reactions with H to produce a formyl complex (Eq. 15.19). with R to form an acyl complex (Eq. 15.49). and with OH to give a hydroxycarbonyl complex (Eq. 15.21). 

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