Diimide, trapped

Beton and co-workers extended the hydrogen bonding approach to two-component systems, generating a number of structures that utilise different molecular motifs.24 26 In the case of perylene tetracarboxylic diimide (PTCDI) co-adsorbed with melamine (1,3,5-triazine-2,4,6-triamine) on a silver-terminated silicon surface, a network is formed in which the straight edges correspond to PTCDI with melamine at the vertices (Figure 11.6). The network shows large-area pores that the authors used to trap heptamers of C6o molecules. 

Since the corresponding endoperoxide precursors are all too unstable for isolation, the diimide reduction constitutes an important chemical structure confirmation of these elusive intermediates that are obtained in the singlet oxygenation of the respective 1,3-dienes. However, the aza-derivative 14 and the keto-derivative 15 could not be prepared,17> because the respective endoperoxides of the pyrroles 18) and cyclopentadienones suffered complex transformations even at —50 °C, so that the trapping by the diimide reagent was ineffective. 

The bicyclic peroxide 11 was prepared via diimide reduction of the endoperoxide derived from spirocyclopentadiene (Eq. 8)21>. As before, at elevated temperature the labile endoperoxide rearranges into diepoxide and ketoepoxide,22) but diimide reduction at —78 °C allows trapping leading to the highly strained bicyclic peroxide 11. 

The thiophene endoperoxides ate considerably more labile than the furan endo-peroxides 26), but diimide is sufficiently reactive even at —30 to —50 °C to trap them in the form of thiaozonides 13. 

In addition to the photoxygenation/diimide (equation 6),16) silver salt (Eq. 22), 36) and triflate (Eq. 44)s6> routes, 9 has also been prepared by benzophenone-sensitized photodecomposition of the corresponding azo compound 59 and trapping of the resultant triplet diradical with oxygen (Eq. 45) 57). 

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

Alkyl-5-alkyliminothiatriazolines (50) decompose slowly around 40-60 "C and rapidly at 125°C with formation of sulfur, nitrogen, and carbodiimide (51) (Equation (4)). However, the carbo-diimides (51) formed react with undecomposed thiatriazoline (50), which in part explains the low yields of isolable carbodiimide. It has not been possible by trapping experiments to decide whether the decomposition involves an intermediate as addition of electron-rich alkenes or heterocumulenes induces immediate nitrogen evolution in a bimolecular reaction (see Section 4.19.5.2) <78JCS(P1)1440>. 

The use of diimide to selectively reduce the C=C bond in bicyclic systems has received great attention as an efficient route to prostaglandin endoperoxides [86b]. It can be employed also at low temperatures and photooxygenation at —78 °C followed by diimide reduction at the same temperature has been used to trap unstable singlet oxygen adducts [73b,86d],... 

There are three isomeric structures for diimide, N2H2 cis- and fran -diimide (1 and 2), and 1,1-diimide (aminonitrene 3), Diimide has been generated and trapped at low temperatures from the gas-phase electric discharge of hydrazine, and by the thermal decomposition of metal salts of p-toluenesulfonyl hydrazide. A careful analysis of the available spectroscopic data has indicated the formation and presence only of (2). ° 1,1-Diimide (3) has been recently generated by the low temperature photochemi-... 

Since there are 12 valency electrons in NgHg, Walsh (2) has predicted a bent ground state, existing in either a cis or a trans configuration for diimide. Blau and Hochheiraer (4) have measured the infrared spectrum of diimide which was frozen in a cold trap as one of the decomposition products of N H. The spectrum of the solid at liquid nitrogen temperature agrees with... 

The desulfurization of episulfides by d.v-oxaziridine (56) appears to be a general reaction affording the alkene, dimethylsulfur diimide (MeN=S=NMe), and azomethane (MeN=NMe) (80JOC1691). These latter products are formed via the intermediate thionitrosomethane (59) (Equation (8)) which was trapped with 2,3-butadiene to give the cyclic sulfenamide (60) in 22-33% yield. The alkenes are formed in good to excellent yield (80-90%) with retention of configuration. 

Irradiation of oxygenated solutions of a-terpinene (56) in the presence of perylene diimide or 9,10-dicyanoanthracene leads to the formation of p-cymene (57) in a process which occurs by an exciplex rather than by 02( Ag) pathways. Hydroperoxy radicals may be involved in a quantum yield amplification process, and it is speculated that O2 quenching of the exciplex, or proton transfer within the exciplex, followed by trapping of the semi-reduced perylene diimide by molecular oxygen are possibilities. 

Singlet oxygen adds across the 2- and 5-positions of alkyl- and phenyl-substituted thiophenes the further decomposition of the adducts is complex, but their existence has been neatly demonstrated via trapping by diimide reduction. ... 

Kinetic studies of the reaction between the a-nucleophile hydroxylamine and tri-2-pyridyl phosphate (TPP) (54) showed that an initial rapid reaction occurred via a general base-catalysed attack of TPP by the ammonia oxide tautomer of hydroxylamine TlgN -O to form a transient 0-phosphorylated derivative (55) (Scheme 19), which is trapped by the NH2OH in solution to generate diimide (56) and DPP (Scheme 20). 

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