J . A m . Chem. Soc. 1985, 107, 5283-5285
5283
MS.I6 Ammonia itself reacts with nitrosonium tetrafluoroborate by Pople and co-workers*has shown that linear structure 2 is more stable than the bridged one 3. In the course of nitrogen f i x a t i ~ n ~ ~ ' ~rather violently even at -80 OC to give 89% monolabeled and 1 1% unlabeled dinitrogen. In reaction of bis(trimethylsily1)amine 94% ,H, monolabeled nitrogen was formed, the reaction being somewhat t t NEN-H N=N sluggish at -80 OC. Isocyanic acid reacted very slowly with the 2 3 nitrosonium ion even at room temperature. A competing polymerization of isocyanic acid seem to occur along with the diazoit is highly unlikely that proton transfer to free nitrogen occurs. tization and it was not possible to determine the exact isotope Instead, such proton transfer probably occurs on to coordinated distribution of the evolved nitrogen although it is estimated to be dinitrogen on a suitable transition-metal site such as molybdenum. 390% monolabeled. In continuation of our studies on substituted diazonium ions (such Attempts were made to directly detect the monolabeled dias N2+NH2,I1N2+N02,12 N2+CN,I2N2+FI2,etc.) we would like azonium ion 1 using "N N M R spectroscopy." In a typical to report new results on our attempts to generate diazonium ion experiments 4 0 mg of bis(trimethylsily1)amine was treated with 1 not by direct protonation but by diazotization of ammonia and -100 mg of 95% I5NOBF4- in 2 mL of dichloromethane in a some of its derivatives using nitrosonium tetrafluoroborate salt. 10-mm N M R tube at -80 OC in the N M R probe. The probe It is known that aromatic as well as aliphatic amines and temperature when raised to -40 'C resulted in slow evolution of isocyanates react with NO+ salts, such as NO+BF4- to form the nitrogen gas. Accumulation of l5N data over a period of 30 min corresponding diazonium ions.I3 Weiss recently reported14a useful detected, however, the presence of only ISNO+salt and no signal R N H z NO+BF4- R N + = NBF4- + H,O for 1 could be observed. The failure to detect HN2+ in the described stop-flow experiment seems to indicate that 1 is unstable RN=C=O + NO+BF4- RN' E NBF4- C 0 2 under the reaction conditions. This is in accordance with the additional anhydrous diazotization method by reacting bissilylated known low proton affinity of dinitrogen. amines with NO+ salt. Our studies reported indicate that the parent diazonium ion R-N(Si(CH3)3)2 NO'X1 was in situ formed in the diazotization of ammonia and its derivatives with 15NOfBF4-.However, 1 once formed has very R N + = N X- + [(CH3)3Si]20 short lifetime to be observed by N M R spectroscopy and spontaAs the direct protonation of nitrogen could not be achieved in neously deprotonates to lsN='4N. solution, it occurred to us that the problem could be attacked by generating protonated dinitrogen, Le., the parent diazonium ion Acknowledgment. Support of our work by the National Science via diazotizing ammonia and some of its derivatives. Foundation is gratefully acknowledged. R. Herges is grateful for Using 96% enriched I5NO+BF4-salt15we have indeed succeeded the financial support by a Feodor Lynen grant of the Alexander with diazotization of ammonia, bis(trimethylsilyl)amine, and von Humbold Foundation. isocyanic acid, respectively, resulting in the formation of I 4 N ~ I 5 N . The mono 15N-labelednitrogen gas obtained can be produced only (16) GC-MS analysis was performed on a Hewlett-Packard 5985 A GCthrough the intermediacy of the parent diazonium ion 1. MS spectrometer. I
