Azide complexes photolysis

More unusual are the reactions between CO, CO2, and SO2 and [Ni(L)(S3)] complexes with L = N2 and N(SiMe3)2. The azide complex (NBu4)[Ni(N3) (S3)] is inert toward UV photolysis and thermolysis, however, it readily reacts with CO under standard conditions according to Eq. 37 (119). 

The photolysis of azide complexes induced by LMCT excitation leads to a variety of products depending on the specific complex and reaction conditions. The azide radical which is formed in the primary photochemical step is known to be very labile [105]. It eliminates nitrogen. The nitrogen atoms which are thus formed can be detected by ESR spectroscopy at low temperatures. In simple cases the photolysis of azide complexes yields only the reduced metal and molecular nitrogen, e.g., equation (14) ... 

The Fe(III)-azide(cyclam-acetato) complex, as seen earlier, serves as a precursor for generation of the superoxidized Fe(V)-nitrido(cyclam-acetato) complex by means of photolysis with 420 nm light [63, 108] (Fig. 5). 

High-valent iron also occurs in -nitrido bridged dimers with linear [Fe °-N=Fe" ]" and [Fe =N=Fe ] " cores [209, 210] (and references therein). Such compounds have been prepared first by thermolysis [247] or photolysis [248] of iron(III)-porphyrin complexes with an azide ligand, (N3). Mixed-valent iron-nitrido porphyrin dimers exhibit valence delocalization as can be inferred from the... 

On the other hand, thermolysis of ferrocenylsulpkonyl azide (14) in aliphatic solvents may lead to the predominant formation of the amide (16) 17>. A 48.4% yield of (16) was obtained from the thermolysis in cyclohexane while an 85.45% yield of 16 was formed in cyclohexene. Photolysis of 14 in these solvents led to lower yields of sulphonamide 32.2% in cyclohexane, 28.2% in cyclohexene. This suggests again that a metal-nitrene complex is an intermediate in the thermolysis of 14 since hydrogen-abstraction appears to be an important made of reaction for such sulphonyl nitrene-metal complexes. Thus, benzenesulphonamide was the main product (37%) in the copper-catalyzed decomposition of the azide in cyclohexane, and the yield was not decreased (in fact, it increased to 49%) in the presence of hydroquinone 34>. On the other hand, no toluene-sulphonamide was reported from the reaction of dichloramine-T and zinc in cyclohexane. 

Ru(edta)(H20)] reacts very rapidly with nitric oxide (171). Reaction is much more rapid at pH 5 than at low and high pHs. The pH/rate profile for this reaction is very similar to those established earlier for reaction of this ruthenium(III) complex with azide and with dimethylthiourea. Such behavior may be interpreted in terms of the protonation equilibria between [Ru(edtaH)(H20)], [Ru(edta)(H20)], and [Ru(edta)(OH)]2- the [Ru(edta)(H20)] species is always the most reactive. The apparent relative slowness of the reaction of [Ru(edta)(H20)] with nitric oxide in acetate buffer is attributable to rapid formation of less reactive [Ru(edta)(OAc)] [Ru(edta)(H20)] also reacts relatively slowly with nitrite. Laser flash photolysis studies of [Ru(edta)(NO)]-show a complicated kinetic pattern, from which it is possible to extract activation parameters both for dissociation of this complex and for its formation from [Ru(edta)(H20)] . Values of AS = —76 J K-1 mol-1 and A V = —12.8 cm3 mol-1 for the latter are compatible with AS values between —76 and —107 J K-1mol-1 and AV values between —7 and —12 cm3 mol-1 for other complex-formation reactions of [Ru(edta) (H20)]- (168) and with an associative mechanism. In contrast, activation parameters for dissociation of [Ru(edta)(NO)] (AS = —4JK-1mol-1 A V = +10 cm3 mol-1) suggest a dissociative interchange mechanism (172). 

In more recent studies, Jacobs, Tompkins and Young [136] examined the rate of evolution of nitrogen from barium azide as a criterion of the rate of photolysis, and have shown the reaction to be more complex than was previously indicated. A mechanism for the photolysis involving the production and reaction of both exci-tons and positive holes has been formulated. 

Photolysis of the azide 54 in benzene gave the tctrahydro-l,3-oxazepine 55 in moderate yield. The rearrangement proceeded by migration of the endocyclic carbon atom attached to the anomeric center, independent of the anomeric configuration (Equation 10). Unfortunately, when the nitrile group was replaced either by a carboxamido or a tetrazolyl group, complex mixtures of products resulted <2000TA533>. 

Photolysis of 4-phenyl- and 4-methoxyphenyl azides gave good yields of azo compounds, whereas phenyl, 4-nitrophenyl and 4-chlorophenyl azide gave undefined products . Photolysis of 4-methoxyphenyl azide in benzene gave only 18% yield of azo compound (4-azidobiphenyl gave 81%), but in solvents such as tetra-hydrofuran and methylsulphide, the yields of the azo compound were 80-90%. It was felt that complexing of the nitrene with solvent lone pairs of electrons stabilized this species and enhanced the probability of azo compound formation . 

When stripped to its naked minimum, the thermal chemistry of aryl azides is deceptively simple. Excluding those compounds bearing reactive ortho substituents [3] and reactions carried out in the presence of active olefins [4], the thermolysis of an aryl azide simply causes unimolecular loss of nitrogen. The complexity arises in subsequent steps where intervention of the various intermediates shown in Figure 1 has been postulated to precede formation of isolatable products. The photolysis of aryl azides is further complicated by the inclusion of reactions originating from electronically excited singlet and triplet states of the azide itself [5]. In essence, a clear understanding of aryl azide chemistry requires the description of the participation and role of each of these reactive intermediates under various reaction conditions. 

Flash photolysis of an oxygen-free benzene solution of 2-naphthyl azide leads to the slow appearance of 2-azonaphthalene from a precursor having a lifetime of several hundred microseconds. In contrast, irradiation of 1-naphthyl azide under these conditions shows more complex behavior. In the... 

The discovery of the temperature dependence of the photochemistry of phenyl azide prompted Leyva and Platz [85] to reexamine the photochemistry of 1-naphthyl azide. As mentioned previously photolysis of 1-naphthyl azide at 298 K in the presence of diethylamine fails to produce an azepine adduct, instead only a trace of diamine 9 is observed along with small amounts of azonaphthalene [51, 57, 91], The major product is 1-naphthy-lamine. Carroll et al. [51] improved the yield of diamine adduct with piperidine by adding N, N, N, N tetramethylethylenediamine (TMEDA) to complex with singlet 1-naphthyl nitrene. TMEDA did not improve the yield of diethylamine adduct, however. 

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