Heterobifunctional ligands

Lali A, Balan S, John R, D Souza F (1998), Carboxymethyl cellulose as a new heterobifunctional ligand carrier for affinity precipitation of proteins, Bioseparation 7 195-205. 

FIGURE 18.6 Structure of the heterobifunctional ligand that drive the assembly of IgM-CD22 complexes. 

The use of heterobifunctional ligands is a very convenient method to link two different transition metals. Heterobimetallic Ti-Zr complexes (Scheme 687) have been prepared by the reaction of Cp[(C5H4)2SiMe2]ZrCl with (C5H4R)TiCl3 in toluene under reflux. In the presence of MAO, these complexes are highly active catalysts for the polymerization of ethylene.1735... 

Fig. 6 Utility of the heterobifunctional PEG. Two different components such as drug and ligand can be introduced at the different ends of PEG...

PEG polymer has to be suitably functionalized at one or both terminals. PEGs that are activated at each terminus with the same reactive moiety are known as homobifunctional. If the functional groups present are different, then the PEG derivative is referred as heterobifunctional or heterofunctional. Chemically activated PEG polymer derivatives are used to attach the PEG to the desired molecule or ligand. 

The complex resulting from triple C-H/N-H activation can be heterobifunc-tionalized by successive addition of CO2 (carboxylation of the hexamethylbenzene ligand) and water (acidic hydrolysis of the imine to the aldehyde on the Cp substituent). This heterobifunctional complex is very useful for the branching to nano-scopic substrates and yet keep the solubility in aqueous media by means of the carboxylate group. Use of this functionalized electron-reservoir system in redox catalysis is promising. Thus, from the starting 18-electron complex, the overall heterobifunctionalization can be carried out in one pot as shown in Scheme 16 [177, 178]. 

Yb(THF)]2 (Figure 108b) containing the heterobifunctional tetramethylcyclopentadienyl-silanolate ligand has also been reported. 

Contrary to the rules of Davies and co-workers, attack by CN on the complexes (64a) (R = CH2Ph) and (64b) [R = CHS(CH2)3S] occurs on the odd cyclohexadienyl ring rather than the even benzene ligand, despite the presence of the bulky R group on the dienyl moiety see q. (22). The heterobifunctional... 

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