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A comparison of the solution behavior of Pt(II) complexes of N,N′- and N,N-ethylenediaminediacetate (edda and uedda)

1996; Elsevier BV; Volume: 244; Issue: 1 Linguagem: Inglês

10.1016/0020-1693(95)04762-x

1873-3255

Rex E. Shepherd⊛, Songsheng Zhang, Richard A. Kortes, Fu‐Tyan Lin, Chris Maricondi,

Ferrocene Chemistry and Applications

Pt(II) complexes of N,N′-ethylenediaminediacetate (edda) and N,N-ethylenediaminediacetate (uedda) have been prepared from K2PtCl4 by stepwise addition of the nitrogen backbone donors at pH ∼ 2.9 (50–60 °C, 60 h) and further coordination of the deprotonated carboxylate donors at pH ≥ 4 (65–75 °C, 24 h). Coordination of the glycinato donors was shown by 1H and 13C NMR and IR methods. The symmetrical edda ligands form 38.3% (R,R)/(S,S)-[Pt(edda)] isomers and 61.7% meso (R,S)/(S,R)-[Pt(edda)] isomers. All four forms of [Pt(edda)] undergo aquation of one in-plane glycinato donor in 72 h as detected by the appearance of a 13-line 1H NMR pattern which may be deconvoluted into four AB glycinato sets. These results are indicative of pendant or ion-paired glycinato donor for [Pt(edda) (H2O)] which is placed either on the same side, or the opposite side, of the PtN2O2 plane and coordinated glycinato donor. 195Pt NMR shows that H2O is actually replaced by Cl−, i.e.[Pt(edda)Cl]−. The unsymmetrical [PtII(uedda) X] (X = H2O, Cl−, OH−) complex exhibits no major change over long time intervals (≥ 10 days, pD ∼ 6). The presence of a minor species at 15% abundance may be a similarly structured species as for [Pt(edda)(H2O)] with a pendant glycinato functionality. The major complex in solution is shown by the 1H NMR with [NaCl] and [NaClO4]-dependence studies to be [Pt(uedda)(H2O)] at low [Cl−] and [Pt(uedda)Cl]− at 1.0 M Cl−. 195Pt NMR confirms the formulation of X = H2O at low [Cl−]. 1H and 13C NMR evidence supports one axially associated and one in-plane coordinated glycinato donor each for the major [Pt(uedda)(H2O)] complex. The 13C NMR shows only one type of glycinato donor with a chemical shift of 189.3 ppm for the major species, and two types for the 15% species (185.6 and 170.5 ppm). The major species of [Pt(uedda)(H2O)] has only one type of carboxylate stretch in the IR spectra (1661 cm−1; shoulder feature at 1639 cm−1) which compares favorably with the fully-coordinated pair of glycinato donors of [Pt(edda)] (1640 cm−1). It is proposed that the structures of [Pt(uedda)(H2O] and [Pt(uedda)Cl]− are pseudo-square pyramids which illustrates the capacity of Pt(II) to adopt five-coordinate, 18-electron complexes when a suitable chelate ligand offers a fifth associable donor. These species are similar to the five-coordinate intermediates of ligand substitution reactions of typical square-planar Pt(II) complexes.