Ligand with ionic side groups

More recently, the Cole-Hamilton group has been able to develop a continuous-flow process on the basis of a similar concept, using phosphine ligands modified with ionic side groups to disperse and immobilize the catalyst in the liquid product phase [5]. 

The equilibrium reaction between neutral hexacoordinate chelates and pentacoordinate siliconium halide salts is discussed in Section III.A.4 (Eq. 17). This reaction can be driven completely to the ionic side by replacement of the chloro ligand by better leaving groups triflate and bromide (Eq. (18), listed again with compound labels see Section III.A.4.iv). The products of this counterion-exchange reaction are stable siliconium salts 90(OTf)-92(OTf), 90(Br)-92(Br), which no... 

When X is a bulky group (X = cyclohexyl, /-butyl), the equilibrium reaction (Eq. 1) is shifted con jletely toward the ionic side even at room ten erature. This is evident from the Si NMR chemical shifts of the mixtures of 1 and 2 (Table 1), which are characteristic of pentacoordination and prove that the equilibrium leans heavily toward 2. Apparently, the proximity of the bulky /-butyl and dimethylamino groups in 1 to the halogeno-ligand forces the latter to dissociate preferentially even at room temperature, in contrast to complexes with small X ligands, which ionize at lower temperature. 

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