Tetraaza annulene

Darensbourg, D.J., Fitch, S.B., 2007. (Tetramethyl tetraaza annulene)chromium chloride a highly active catalyst for the alternating copolymerization of epoxides and carbon dioxide. Inorganic Chemistry 46, 5474—5476. 

The 7/NMR spectrum displays signals of shielded protons = - 2.35, integral level 1) and of deshielded ones = 10.45 and 9.39, integral levels 1 1). This reflects a ring current due to aromaticity as described for annulenes and porphyrins in section 2.5.2. To conclude, the reaction involves an oxidative cyclisatlon of 2,5-bis(2-pyrrolylmethyl)-17/-pyrrole 2 with 47/-trlazole-3,5-dlaldehyde 3 to the corresponding 2,3-diazaporphyrin 4, following the 3-t-l pathway of porphyrin synthesis. Two non-equivalent tautomers may exist these are the diaza[ 18]annulene 4a and the tetraaza[18]annulene 4b. 

The equivalence of the inner NH protons (Sm = - 2.35) as well as correlation signals with the pyrrolic carbons only (5c = 143.8, 141.6, 139.8 and 136.7) provide evidence for the diaza[18]-annulene tautomer 4a. Two separate NT/ proton signals and cross signals with the a-carbon atoms (5c = 159.3) of the triazole ring are expected, in contrast, for the tetraaza[18]annulene tautomer 4b. 

Extensive work has been carried out on microsensors built from electropolymerized nickel porphyrin films.328,329 Films of Prussian blue (Fe4[Fe(CN)6]3) 345 metal-salen complexes (M = Co, Fe, Cu, Mn)346 or the ferrocene-containing Nin-tetraaza[14] annulene (24),347 also exhibit interesting activity for NO electrooxidation and sensing. 

TTAA l,8-dihydro-5,7,12,14-tetramethyldibenso (b,i)-(l, 4,8,1 l-tetraazacyclotetradeca-4,6,11,13-tetraene- 5N4 (tetramethyldibenzo-tetraaza(14)annulene). 

There are some examples of macrocyclic complexes of germanium, tin and lead reported in the recent literature. Several crown ethers73,75, tetraaza macrocycles76 [for instance dibenzotetramethyltetraaza[14]annulene (TMTAA)], cyclic polyamines (polyazacycloalkanes)77-80 or, as already mentioned above, poly(pyrazolyl)borate were... 

Complexes with the tetradentate tetraaza[14]annulenes (163) and (164) ( = H2L), studied by spectroscopy,892 were formulated as [VOL], probably similar to the complexes with porphyrins. v(V=0) was at 967 and 940cm-1 for (163) and (164). In the ESCA spectra, the nitrogen donors are equivalent.892... 

A logical extension of the condensation reactions which yield multidentate nitrogen donors is the formation of macrocyclic ligands. The preference of palladium for square planar coordination makes it an ideal metal for the formation of complexes of these ligands. Thus palladium porphyrins are very stable and resistant to demetallation.281 Both 14- and 16-atom macrocycles have been used to form complexes. The ligand l,8-dihydro-5,7,12,14-tetramethyl-dibenzo[b,i][l,4,8,ll]tetraaza[14]annulene reacts with [PdCl2(PhCN)2] to yield the complex (46). 

Apparently, the first examples of [16]annulenoid porphyrin derivatives were obtained by Eschenmoser and coworkers during their work on corphin (21, Fig. 15), a peripherally reduced porphyrin derivative [91]. Free base corphin has the appropriate oxidation level to adopt a tetraaza[16]annulene structure, but it actually exists as the cross-conjugated tautomer 21. However, some of the complexes of corphin with divalent metals (such as Zn or Pd) were shown to have the symmetrical structure 22, and their H NMR spectra revealed a modest paratropic ring current, comparable with that of [16]annulene [92-94],... 

A stable germylene containing tetraaza macrocyle, i.e. dibenzotetraaza[14]annulene (tmtaa), and a variety of cyclic germylenes (such as 30) readily act as two electron donors to form a variety of metal complexes101,140-144. 

The nearly planar structure of Pd(II) complex 123 enabled a twofold connection of the bicyclic units in imino ether condensations brought about by Meerwein s salt and diisopropylethylamine in methylene chloride. Protonation of 124 (Scheme 14) generates a Pd(II) complex (125) of an octahy-droporphyrin, with complete saturation of the peripheral double bonds containing the 7t-system of l,5,9,13-tetraaza[16]annulene (68AG622). 

The black coloured -oxo-bridged Ni-tetraaza (14) annulene (69) was formed by heating Ni(OH)2Taa (oxidized NiTaa) at 473 K in bulk (Eq. 29) But the structure was only confirmed by elementary analysis and tte amount of eliminated H2O. 

Monocyclic, bicyclic and polymeric tetraaza(14)annulene ligands and their metal chelates (113)-(117) were prepared firom propynal and amines (Eq. 60) ... 

Dynamics of nano- to picosecond proton transfer processes in the N labeled polycrystalline tetraaza[14]annulene have been studied by a combination of 9.1 MHz N Ti relaxation time measurements under CPMAS conditions and by 46 MHz H Ti relaxation time measurements of a static sample of a doubly deuterated sample. 

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