Direct studies of 1,1-diazenes. Syntheses, infrared and electronic spectra, and kinetics of the thermal decomposition of N-(2,2,6,6-tetramethylpiperidyl)nitrene and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene

Abstract

The syntheses, direct spectroscopic observation, and kinetics of thermal decomposition of the persistent 1,l-diazenes, N-(2,2,6,&tetramethyIpiperidyl)nitrene (4) and N-(2,2,5,5-tetramethylpyrrolidyl)nitrene (5) are reported. The electronic absorption spectrum of 4 at -78 "C reveals a structured absorption for the n,a* transition: A, , , = 543 nm, A, , o = 620 nm, and emax = 18 f 3 in Et20; A, , , = 541 nm and &, o = 610 nm in CH2CI2; A, , , = 526 nm and A, , o = 592 nm in i-PrOH. The electronic absorption spectrum of 1,l-diazene 5 at -78 "C reveals a structured absorption band for the n,a* transition: A, , , = 497 nm and b,o = 572 nm and e , , = 20 3 in CH2CI2; A, , , = 487 nm and Ao,o = 552 nm in i-PrOH. The infrared spectrum of 4 shows a strong absorption at 1595 cm-' (R2I4N=l4N stretch) and provides evidence that 1,l-diazene 4 has considerable N=N double-bond character in the ground state. The infrared spectrum of 5 shows a strong absorption at 1638 cm-' (R2l4N=I4N stretch). The unimolecular rate of thermal decomposition of 4 is sensitive to solvent, the rate increasing with decreasing solvent polarity (kd = 1.0, 1.7,4.8 in THF, Et20, and hexane, respectively). The activation parameters for the unimolecular fragmentation of 1,l-diazene 4 are as follows: log A = 11.6 0.5 and E, = 16.9 * 0.7 kcal mol-' in hexane; log A = 13.7 f 0.3 and E, = 20.0 f 0.4 kcal mo1-l in EtzO; log A = 13.6 f 0.3 and E , = 20.1 f 0.4 kcal mo1-I in THF. The activation parameters for the bimolecular dimerization of 4 are log A = 3.8 f 0.7 and E, = 6.4 f 0.9 kcal mol-' in CDC13. The unimolecular rate of thermal decomposition of 5 is sensitive to solvent, the rate increasing with decreasing solvent polarity, krcl = 1.0, 2.4, and 5.1 for THF, Et20, and hexane, respectively. The activation parameters for the unimolecular fragmentation of 1,l-diazene 5 are as follows: log A = 10.9 f 0.3 and E , = 16.8 i 0.5 kcal mol-' in hexane; log A = 12.4 f 0.4 and E , = 19.0 i 0.6 kcal mol-' in Et20; log A = 12.1 f 0.3 and E , = 19.1 * 0.4 kcal mol-' in THF. At -41.1 "C the bimolecular rate constant for the dimerization of 5 is 8.5 X 0002-7863/82/1504-0766%01.25/0 0 1982 American Chemical Society

Heteroatom Substitution at Amide Nitrogen—Resonance Reduction and HERON Reactions of Anomeric Amides

“…In a polar solvent such as methanol, N -methylaniline attacks the amide nitrogen, replacing the acetoxyl side chain to form an unstable intermediate, N -butoxy- N -( N ′-methylanilino)benzamide 36 , which undergoes the HERON reaction to form butyl benzoate 37 , and an aminonitrene, 1-methyl-1-phenyldiazene 38 (Scheme 7 i). Aminonitrenes are highly reactive intermediates with a singlet ground state, which persist long enough under reaction conditions to dimerise to tetrazenes [114,115,116,117], in this case, 39 (Scheme 7 ii) [44,47]. N , N ′-Diacyl- N , N ′-dialkoxyhydrazines 40 , the only forms of N -alkoxy- N -aminoamides 2d to have been isolated, undergo tandem HERON reactions to form two equivalents of ester 41 and a molecule of nitrogen; the N -acyl- N -alkoxyaminonitrenes 42 , formed in this HERON reaction, rapidly undergo a second rearrangement to form a molecule of nitrogen and ester before dimerisation of the N -acyl- N -alkoxyaminonitrene can occur (Scheme 8) [56,76].…”

Interactions between Functional Groups Part IV. The responses of four diazonium groups to adjacent electron‐rich atoms in peri‐substituted naphthalene and quinoline derivatives

“…~ All four cations 1 4 exhibit similar attractive interactions between an electron-rich atom (1, 4 : 0 , 2:S, 3:N) and the a-N-atom of the diazonium group. Structural details are summarized in Table 1.…”

Redox Non‐Innocent Behavior of a Terminal Iridium Hydrazido(2−) Triple Bond

“…Exposure of aC 6 D 6 solution of 6 to an atmosphere of CO yields ad eep red solution, which over time results in the formation of Cp*Ir(CO) 2 and several organic byproducts, which were identified as decomposition products of free N-(2,2,6,6-tetramethylpiperidyl)nitrene. [33] In this case,w ep ropose that coordination of CO leads to charge transfer from the hydrazido N b lone pair to the Ir, formally reducing it from Ir III to Ir I .T hen, the resulting 1,1-isodiazene can be displaced by CO,f orming Cp*Ir(CO) 2 and the free nitrene,w hich decomposes in solution. In comparison, Cp*IrNtBu and other related imido complexes react with CO to form h 2 -bound organoisocyanates, [11] Thus,u nlike normal terminal imidos, the nitrogen ligand of 6 undergoes CO-induced tautomerization rather than reacting directly with CO.Reactions of 6 with other Ldonors such as PMe 3 or outer-sphere oxidants such as [Fc] + [PF 6 ] À also generate product mixtures from diazene decomposition, and traces of the analogous reduced product Cp*Ir(PMe 3 ) 2 were detectable by NMR.…”