Catenated Metallocycles

Semi-flexible bipyridine derivatives incorporating alkyl spacer groups between the pyridyl rings have been demonstrated to yield dinuclear palladium(II) species related to those discussed in Section 7.2 of this chapter.Thus, insertion of -CHjCHj- or -CH2(CgF4)CH2- groups between the 4- and 4 -positions in the parent bipyridine ligand leads to the formation of 2 2 (metal ligand) complexes of type 32 on reaction of these extended bipyridine derivatives with dinitro(ethane- 

A remarkable medium effect was also demonstrated to influence the position of the above equilibrium. Employment of a more polar medium (a DjO solution of sodium nitrate) pushed the equilibrium strongly towards the catenated form, with greater than 99% of this form being present, even at relatively low concentrations of the above salt. The observation that the change in the equilibrium position is rapid confirmed the inherent lability of the palladium(II)-pyridine linkages in this 

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