Oxygen versus nitrogen coordination of a urea to (diethylenetriamine)platinum(II)

摘要: Syntheses and properties of isomeric(diethylenetriamine)platinum(II) complexes 1,1-dimethylurea (DMU)bound through oxygen or nitrogen are reported. Isomers were distinguished by a combination NMR (H-1, C-13) IR spectroscopy, acidity reactivity measurements, an isomer selective synthetic route. The oxygen-bonded DMU compound, [dienPtOC(NH2)NMe2]2+, is the kinetically preferred product from stoichiometric reaction with [dienPtOH2]2+ in acetone. This form then rearranges (t1/2 approximately 18 min, 22-degrees-C) to slightly more thermodynamically stable nitrogen-bonded linkage (K(NO) = [N-isomer]/[0-isomer] 3). reverse isomerization N-bonding O-bonding was also detected. NMR(H-1, spectroscopy proved that N-bonded complex, which independently selectively synthesized base hydrolysis cyanamide precursor [dienPtN CNMe2]2+, exists solution solid state as unusual amide tautomer [dienPtNH2COR]2+ (R NMe2), rather than imidol [dienPtNH:C(OH)R]2+ observed for acetamide Me). ligand much acidic (pK(a) 5.6, H20,20-degrees-C) 0-bonded greater-than-or-equal-to 11 (est)), indicating greater resonance stabilization deprotonated urea [dienPtNHCONMe2]+ versus [dienPtOC(NMe2)NH]+, but less [dienPtNH: C(OH)Me]2+ 3.8), where proton on instead nitrogen. Both 50-fold faster solvolysis NMe2, k 5 x 10(-4) S-1; R Me, 1 X 10(-5) H2O, pH 2.5, 40.0-degrees-C) 100-fold rate difference 6.4 s-1; 6.8 10(-6) acetone, attributed requirement migration between tautomers form. likely proceed via only. O-bonded displaced (water, DMSO; t1/2 < platinum coordinating solvents.