AMMONIA AND CARBON-DIOXIDE FROM UREA - A MULTINUCLEAR NMR-STUDY OF THE ACTIVATION OF UREA BY PLATINUM(II)

Isotopically enriched (98% N-15, 99% C-13) urea, (NH2CONH2)-N-15-C-13-N-15, reacts with [dienPtOH(2)](2+) in acetone to form principally (CO2)-C-13, (NH4+)-N-15, and [dienPt(15)NH(3)](2+) The reaction was monitored by combined one- and two-dimensional multinuclear (H-1, C-13, N-15) NMR spectroscopy. The initial product was [dienPtOC(NH2)(2)](2+), in addition to a fluxional species detected spectroscopically at low temperature, which undergoes O- to N-linkage isomerization to [dienPtNH(2)CONH(2)](2+) The latter complex, unlike the crystallographically characterized [dienPtNH(2)CONMe(2)](2+), decomposes to CO2, NH4+, and [dienPtNH(3)](2+). [dienPtNCO](2+) was detected as an intermediate by C-13 NMR spectra and may be formed directly from [dienPtNH(2)CONH(2)](2+) or its tautomer [dienPtNH=C(OH)NH2](2+) by elimination of ammonia or indirectly after hydrolysis to [dienPtNH(2)CO(2)](+) through elimination of water. Addition of acid and water to acetone solutions of [dienPtNCO](2+) rapidly produces [dienPtNH(3)](2+) and CO2. The mechanism of the reaction is discussed.