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))Cl-2 center dot 2H(2)O, a novel platinum(IV) complex containing deprotonated amide ligands, and of (2H(+)-L)[PtCl4]

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))Cl-2 . 2H(2)O. The crystal and molecular structure of the latter shows that the chloride ligands are cis, Pt-Cl=2.308(2) Angstrom, and that LH(-2) is present as a tetradentate ligand coordinated through its two amino nitrogen atoms, Pt-N=2.097(6) Angstrom, and two deprotonated amide nitrogens, Pt-N=2.032(4) Angstrom 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(N)-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 rr 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 pi electron delocalisation than in the free amide. The crystal structure of (2H(+)-L)[PtCl4] is also reported, av. Pt-Cl=2.292 Angstrom. Crystal data: cis-Pt(LH(-2))Cl-2 . H2O, monoclinic, space group P2/n, a=11.764(4), b=7.840(1), c=11.829(4) Angstrom, beta=104.09(2)degrees, Z=2; (2H(+)-L)[PtChl(4)], triclinic, space group P1, a=9.035(1), b=9.316(1), c=7.308(2) Angstrom, alpha=100.88(1), beta=106.52(1), gamma=99.96(1)degrees, Z=1.