AMIDE COMPLEXES OF (DIETHYLENETRIAMINE)PLATINUM(II)

The coordination of acetamide and formamide to dienPt(II) is described. Both O- and N-bonded amide complexes are stable and have been isolated. As oxygen donor ligands for dienPt(II), the binding affinity of amides lies between water and the very weakly coordinating acetone. The O-bonded amide complexes [dienPtOC(R)NH2]2+ are the kinetically preferred isomers in acetone but they rearrange very slowly (t1/2 approximately 30 h, 20-degrees-C) and intramolecularly to the thermodynamically more stable N-bonded amide complexes (K = [N] / [O] approximately 30). This is the reverse of relative amide affinities for harder metal ions (e.g. (NH3)5M3+, M = CO(III), Cr(III), Ru(III)) despite comparable polarizing power for dienPt(II). The N-bonded amide isomers exist in solution(acetone, DMSO, water) as the imidol, [dienPtNH=C(OH)R]2+, rather than the amide tautomer, [dienPtNH2COR]2+, whereas the opposite has been observed for N-bonded ureas. The N-bonded amides adopt only one of the two possible geometric isomers which could result from restricted rotation about the amide N=C bond, and they are appreciably acidic (pK(a) 3.8, 20-degrees-C, H2O, I = 0.1 M; R = Me). Complexes of both O- and N-bonded amides are unstable in coordinating solvents (t1/2 < 1 min, O-isomers; t1/2 > 40 h, N-isomers; 20-degrees-, H2O), but no decomposition of the amide ligands was detected during solvolysis (amide release) in either DMSO or water, nor was the Pt(II) susceptible to aerial oxidation as reported for mixtures of amides with cis-diammineplatinum(II). Coordination preferences of amides to "soft" versus "hard" metals are compared.