Multinuclear NMR (N-15, C-13, H-1) was used to study the reactions of [Pd(en)(H2O)2]2+ (1) with ligands that model peptides. N-acetylglycine (H-2acgly) with 1 in strongly acidic solution (pH 1.2) gave [Pd(en)(Hacgly-O)(H2O)]+ and other complexes with acetylglycine bound only through carboxylate-O. At higher pH (7-10) the chelate complex [Pd(en)(acgly-N,O)] predominated. With glycinamide (N(1)H2CH2C(O)N(2)H2, Hglyam) at pH 4-10, [Pd(en)(glyam-N(1),N(2))]+ was formed. At lower pH (1-3), this complex was in equilibrium with its protonated form, [Pd(en)(Hglyam-N(1),N(2))]2+, and with [Pd(en)(Hglyam-N(1),O)]2+ and [Pd(en)(Hglyam-N(1))(H2O)]2+. With N-glycylglycine(+N(1)H3CH2C(O(1))N(2)HCH2CO2-, H-2digly), the N(1)N(2)-chelate complex[Pd(en)(digly-N(1)N(2))] predominated under most conditions, but under strongly acidic conditions (pH 1), peaks were also present in NMR spectra which were assigned to [Pd(en)(H2digly-N(1)O(1))]2+. When 1 was present in initial excess, the free carboxylate group in the N(1),N(2)-chelate complex bound to Pd(en)(H2O)2+. The dinuclear complex [{Pd(en)}2(digly)]2+, with one Pd atom bound to N(1) and O(1), and the second Pd atom bound to N(2) and carboxylate O, also formed.