An investigation of mononuclear and binuclear palladium(II) complexes of egta (egta = glycine, N,N '-(1,2-ethanediylbis(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) by H-1-, C-13- and N-15-nmr methods

1:1 and 2:1 palladium(II) complexes of egta(4-) (egta(4-) = glycine, N,N'-( 1,2-ethanediylbis)(oxy-2,1-ethanediyl)bis[N-carboxymethyl]) were prepared b y 1:1 and 2:1 addition of K2PdCl4 to K(4)egta, and examined by H-1-, C-13- and N-15-n.m.r. methods. The 1:1 complex, [Pd(egta)](2-) in solution, utili zes a square-planar coordination comprised of two nitrogen and two glycinat o carboxylate donors of egta(4-), leaving two glycinato carboxylates pendan t. The complex has a cis-(R,S) stereochemistry which places both pendant ca rboxylates below the PdN2O2 square plane and the tether backbone of egta(4- ) in the "up, up" sense above the same plane. The cis-(R,S) assignment was assisted by computer simulations of the C-13-n.m.r. spectrum for four possi ble isomers. Only cis-(R,S) and trans-(R,R) calculated C-13-spectra were co mpatible with the observed C-13-n.m.r. pattern. The HH NOESY spectrum of [P d(egta)](2-) detects long range coupling of the backbone -OCH2CH2O- linkage with both coordinated and pendant glycinato CH2 moieties. The cis-(R,S) is omer's tortional movements allow such contacts whereas a trans-(R,R) isomer does not. The 2:1 complex, [Pd-2(egta)(H2O)(2)] in solution has an extende d-chain structure with each palladium(II) center coordinated in the mer-imi nodiacetate-like coordination with two bound glycinato-functionalities.