Aza annulene

At the beginning of the 70s Beck and co-workers discovered the electrocatalytic activity of dihydro-dibenzo-tetra-aza-annulene 8>12>, and Binder, Sandstede and co-workers that of tetraphenylporphyrine and its tetramethoxy derivative 9,13-15). 

Parallel to this work, catalysts for the anodic oxidation of several fuels were established 10>. Up to now, however, only one chelate is known to catalyze anodic reactions the cobalt complex of dihydro-dibenzo-tetra-aza-annulene. 

Figure 9 shows the results obtained by Sandstede 16) with tetra-(p-methoxy-phenyl)porphyrins on activated carbon in suspension. The activity decreases in the order Co > Fe > Ni Cu. The same sequence of central atoms is observed with tetra-aza-annulene. 

Fig. 25. Potentiodynamic current/voltage curves of monomeric cobalt tetra-aza-annulene. Conditions 2 N H2SO4, 70°C, sweep rate 50 mV/min.

Beck 23,37,38) carried out voltammetric investigations of chelates in solution (phthalocyanine and tetra-aza-annulene in 85—90% H2SO4). The particularly active electrocatalysts (FePc and CoTAA) showed very positive redox potentials and a pronounced positivization of the polarographic oxygen step in 85 % sulfuric acid. On the basis of these results, Beck proposed the following mechanism... 

The structural information obtained from the compound was not sufficiently detailed to eliminate the possibility of a fra/w-double bond in the molecule. The aza-annulene (152b) does, however, exhibit aromatic character. 

Synthesis and Study of Octa-aza Annulene Complexes With Unusual Properties... 

A Hiickel aromatic system with ten electrons (n = 2) can be established with the 9-membered azonine ting system involving the eight pi-electrons of the double bonds and the lone pair on nitrogen. The aU-cis ring (7.10) is known but not stable because of the angle strain as described in the aza-annulenes (Chapter 6). Its proton NMR spectrum... 

Reaction of a nickel(ii) tetra-aza-annulene with NOs" in methanol results in the formation of a dinuclear nickel(iii) complex. In conditions of dilute acid, the reaction is slower than the corresponding reaction of HNO2 (which is reduced to NgO). In the reaction of the related tetra-azacyclotetradecadienenickel(n) ion with HNO3, however, oxidation takes place on the ring with tetraimine formation. ... 

The reaction of Brg (and other oxidants) with organo-bis(dioximato)cobalt(iii) complexes results in one-electron oxidations 4 to generate the cobalt(iv) complex cations [RCo(dmgH)2L]+. In the corresponding reaction with the nickel(ii) tetra-aza-annulene (4) ligand oxidation occurs prior to metal oxidation and a radical cation is formed which rapidly dimerizes to (5), which may be further deprotonated. 

Nikolic S, Trinajstid N (1990) Compact Molecular Codes for Annulenes, Aza-annulenes, Annulenoannulenes, Aza—annulenoannulenes, Cydazines and Aza—cyclazines. Croat Chem Acta 63 155... 

S. Nikobc and N. Trinajstic, Compact molecular codes for annulenes, aza-annulenes, annuleno-annulenes, aza-annulenoannulenes, cyclazines and aza-cyclazines, Croat. Chem. Acta 63 (1990) 155-169. 

Azaadamantanes biocide, 1, 400 mechanism, 1, 401 photoelectron spectroscopy, 2, 142 5-Azaadenines reactions, 5, 878 synthesis, 5, 901 8-Azaadenosines synthesis, 5, 895 Azaallyl cations generation, 7, 73 Aza[10]annulenes bridged... 

Cyclazines may be considered as nitrogen-bridged annulenes rather than as hetarenes and, therefore, are only briefly mentioned in this volume. The chemistry of [3.3.3]cyclazines 1 and aza analogs, e. g. 3, is covered comprehensively in Houben-Weyl, Vol. E7b, p 205 IT. For another recent review, see ref 1. Subsequently, the chemistry of individual types of cyclazines has been reviewed, in particular 2.2.x]cyclazines,1 2 [2.2.2]cyclazines,3 [2.3.x]cyclazines4 and [2.2.3]-cyclazines.5 Moreover, the synthesis and the reactions of [2.2.3]cyclazines and the question of the effect of bcnzannulation have been addressed specifically.6... 

If the cycloaddition and cycloreversion steps occurred under the same conditions, an equilibrium would establish and a mixture of reactant and product olefins be obtained, which is a severe limitation to its synthetic use. In many cases, however, the two steps can very well be separated, with the cycloreversion under totally different conditions often showing pronounced regioselectivity, e.g. for thermodynamic reasons (product vs. reactant stability), and this type of olefin metathesis has been successfully applied to organic synthesis. In fact, this aspect of the synthetic application of four-membered ring compounds has recently aroused considerable attention, as it leads the way to their transformation into other useful intermediates. For example aza[18]annulene (371) could be synthesized utilizing a sequence of [2 + 2] cycloaddition and cycloreversion. (369), one of the dimers obtained from cyclooctatetraene upon heating to 100 °C, was transformed by carbethoxycarbene addition to two tetracyclic carboxylates, which subsequently lead to the isomeric azides (368) and (370). Upon direct photolysis of these, (371) was obtained in 25 and 28% yield, respectively 127). Aza[14]annulene could be synthesized in a similar fashion I28). 

The phthalocyanine [1-4] system is structurally derived from the aza-[18]-annulene series, a macrocyclic hetero system comprising 18 conjugated n-electrons. Two well known derivatives of this parent structure, which is commonly referred to as porphine, are the iron(III)complex of hemoglobin and the magnesium complex of chlorophyll. Both satisfy the Htickel and Sondheimer (4n + 2)- electron rule and thus form planar aromatic systems. 

NMR data for aza[18]annulene 234 show a wide separation between the centers of the inner and outer proton lH NMR multiplets (Ad =11 ppm), indicative of a strong diamagnetic ring current.270 271 The bis-dehydro system 235 with 22 jr-electrons in the aromatic ring is diatropic.272... 

The structures of the dihydro-octa-aza[14]annulene complexes (149) have been reported. The second example of single macrocycles capable of encompassing two metal atoms has been published. The complexes (150) and (151) have been prepared by metal template reactions of acetone and... 

The redox behavior of [MnLY], where L is the dianionic form of dibenzotetramethyltetra-aza[14]annulene and Y is tetrahydrofuran or nothing, has been investigated." A two-electron oxidation and one- and two-electron reductions have been determined for this complex. The... 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

Ogawa et al. (12) used an intramolecular azide-alkene cycloaddition strategy to synthesize the oxygen-bridged aza[15]annulene 52 and the aza[15]annulene dicar-boxylate 55 (Scheme 9.12). 1,3-Dipolar cycloaddition of vinyl azide to the acrylate moiety followed by extrusion of nitrogen gave the aziridine 51. Rearrangement of 51 afforded the aza[15]annulene 52. The same approach was used to synthesize the aza[15]annulene 55. 

Table 2 Selected Spectroscopic Data on the Bridged Aza[10]annulenes (23) (78AG(E)853, 855)...

The interesting, heavily substituted, diatropically delocalized triaza[10]annulenone formulated as shown in (24) is a further known member of the general aza[10]annulene family <71JCS(C)2142>. 

---