Reactions of 1,2-diaminoethane-N,N,N′N′-tetra(N-methylacetamide), L, with potassium tetrachloroplatinate(II). Crystal and molecular structures of Pt(LH−2)Cl2·2H2O, a novel platinum(IV) complex containing deprotonated amide ligands, and of (2H+-L) [PtCl4

Abstract

Abstract Reaction of 1,2-diaminoethane-N,N,N′,N′-tetra(N-methylacetamide), L, with potassium tetrachloroplatinate(II) in aqueous solution afforded the crystalline salt (2H+-L)[PtCl4] and the neutral platinum(IV) complex cis-Pt(LH−2)Cl2·2H2O. The crystal and molecular structure of the latter shows that the chloride ligands are cis, PtCl = 2.308(2) A, and that LH−2 is present as a tetradentate ligand coordinated through its two amino nitrogen atoms, PtN = 2.097(6) A, and two deprotonated amide nitrogens, PtN = 2.032(4) A which are trans to each other. This structure is the first of a platinum(IV) complex containing deprotonated amide ligands and may serve as a model for platinum(IV)-peptide/protein interactions. The fact that this complex is formed without any added oxidant other than air suggests that deprotonated amide groups facilitate the oxidation of platinum(II) to platinum(IV). The CN and CO bond distances in the coordinated, deprotonated amide groups are almost identical to those of the uncoordinated amide groups indicative of similar π electron delocalisation in the NCO groups in both cases. This is in contrast to the situation in a recently reported platinum(II)-amidate complex in which there is considerably greater π electron delocalisation than in the free amide. The crystal structure of (2H+-L)[PtCl4] is also reported, av. PtCl = 2.292 A. Crystal data: cis-Pt(LH−2C2·H2O, monoclinic space group P2/n, 1 = 11.764(4), b = 7.840(1), c = 11.829(3) A , β = 104.09(2)°, Z = 2 ; (2H+-L)[PtCl4], triclinic, space group P1, a = 9035(1), b = 9.316(1), c = 7.308(2) A , α = 100.88(1), β = 106.52(1), γ = 99.96(1)°, Z = 1 .