ATTACK OF CADMIUM(II) AND PALLADIUM(II) ON CIS-(R,S)-[PD(EGTA)](2-) -COORDINATION REARRANGEMENTS FACILITATED BY PENDANT CARBOXYLATES

Cd(H2O)(6-8)(2+) reacts with cis-(R, S)-[Pd(egta)](2-) producing equim olar amounts of [Cd(egta)](2-) and [Pd(egta)Cl-2](2-). The progress of the reaction and products have been followed by recording H-1- and C- 13-n.m.r spectra as a function of time. The Pd-II released in forming [Cd(egta)](2-) is thousands of times more reactive than Cd-II, and int ercepts another [Pd(egta)](2-) to form the 2:1 complex [Pd-2(egta)Cl-2 ](2-); the 2:1 complex is not attacked by Cd-II. The role of pendant c arboxylates below the PdN2O2 plane of cis-(R, S)-[Pd(egta)](2-) in sup plying a site for 'docking' of an incoming Cd-II or Pd-II centre, and in leading the metal near the lone pair of rupturing Pd-N bond of [Pd( egta)](2-) or simply by increasing the residence time of Cd-II or Pd-I I nearby to accelerate the number of collisions between the ruptured N -base and external metal ions, is described. Although mixed-metal [Cd( Pd)(egta)] intermediates are required for the reaction, no such specie s achieves a detectably large enough concentration to be seen by H-1-n .m.r. The observed spectra ar the sum of the reactant, [Pd(egta)](2-), and products, [Cd(egta)](2-) and [Pd-2(egta)Cl-2](2-), throughout the time-dependent change.