A TEMPERATURE-DEPENDENT DYNAMIC REARRANGEMENT OF CIS-(R,S)-[PD(EGTA)](2-) (EGTA(4-)=GLYCINE, EDIYLBIS(OXY-2,1-ETHANEDIYL)BIS[N-CARBOXYMETHYL])) IN AQUEOUS-SOLUTION

The cis-(R,S)-[Pd(egta)](2-) complex? egta(4-) = glycine, ediylbis(oxy -2,1-ethanediyl)bis[N-carboxymethyl]), has been examined by H-1- and C -13-n.m.r. methods over the 18.0 to 95.0 degrees C range in D2O. A dyn amic process occurs above 65 degrees C which makes the protons on the NCH2 functionalities of the egta tether become H-1-n.m.r. equivalent. The two states that inter-convert coalesce at 81 degrees C. Evidence f rom C-13-n.m.r. spectra obtained at 81 degrees C show that the in-plan e coordinated carboxylates are not lost, but rather a pendant carboxyl ate becomes attached with loss of the central imino donor. The resulta nt palladium(II)NO3 intermediate is able to reform cis-(R,S)-[Pd(egta) ](2-) or, presumably, give trans-(R,R)-[Pd(egta)](2-). The rate limiti ng step occurs with a rate constant of 178 s(-1) at 81 degrees C and a n activation energy of 20.5 kJ/mol. However: competitive aquation of g lycinato donors above 85 degrees C prevents isolation of a stable tran s-(R,R)-[Pd(egta)](2-) isomer.