Proximate,syn-Periplanar Bisdiazene Skeletons: Syntheses, Structures, Homoconjugate Reactivity and Photochemistry

Abstract

Rigid NN/NN (diazene/diazene) systems (F) consisting of more or less alkylated DBH and DBO chromophoric units (1, 2, X‐ray structures), with very short π,π distances [d = 2.849 (1a, av.), 2.822 Å (2)] and almost perfect syn‐periplanar π,π alignments [ω = 168.6 (1a), 174.2° (2)] as well as the more flexible, less “proximate” metathesis isomers (3a,c, 27a,c, d >4.6 Å, ω = 90‐100°) have been synthesized. Homoconjugate π,π interaction (in 1, 2, not in 3, 27) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters (1a: <0.3 eV). The potential of the novel syn‐periplanar NN/NN motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all‐cis‐peralkylated tetrazolidines (38, 44) and perhydro‐1,2,4,5‐tetrazines (41, 47) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b‐d, as well as in the DBH/DBO combination 2, and likewise in more ‘distant’ 27 (differently from the analogous CC/CC and NN/CC systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N2‐elimination took place. It is argued that unproductive NN/NN photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.

Raman, FT‐IR, and DFT studies of 3,5‐pyrazoledicarboxylic acid and its Ce(III) and Nd(III) complexes

“…In our spectra no band can be observed in this region in the Raman spectra of H 3 pdc and its complexes. The dimer form is best characterized by the Raman band in the 1680-1640 cm 1 range 28,44,56 and by two IR bands: at about 1290 cm 1 (inplane C-O-H bending mode) and a somewhat weaker band seen at 1440-1395 cm 1 (C-O stretching mode). 57,58 The wavenumber region 2700-2500 cm 1 in IR and Raman spectra, respectively, is typical of strongly hydrogenbonded intermolecular complexes owing to the strong anharmonic coupling (Fermi resonance) of the N-H stretching vibrations with the overtones and combinations of the lower wavenumber modes of the bonded molecules.…”

“…As shown in Table 1, the calculated N1-N2 bond lengths of the H 3 pdc molecule obtained with different methods vary from 131.8-135.7 pm, which is somewhere between the length of an N-N single bond (145 pm) and that of an N N double bond (125 pm). 28 The N1-H12 bond distance in this compound is calculated to be about 101.1-101.3 pm.…”

Theoretical and spectroscopic studies of lanthanum (III) complex of 5-aminoorotic acid

“…Opposite to the IR spectra, in the Raman spectra was observed only a medium band at 1999 cm À1 for the free ligand. The dimer form is best characterized by the Raman bands in the 1680-1640 cm À1 range [96][97][98] and by two IR bands, around 1290 cm À1 (in plane C-O-H bending mode) and between 1440 cm À1 and 1395 cm À1 (C-O stretching mode) (Figs. 5, 6; Table 3) [99,100].…”

Theoretical and spectroscopic studies of new lanthanum(III) complex of orotic acid

“…3). The dimer form is best characterized by the Raman band in the 1680-1640 cm À1 range [84][85][86] and by two IR bands: at about 1290 cm À1 (in plane C-O-H bending mode) and somewhat weaker band, which is seen at 1440-1395 cm À1 (C-O stretching mode) (Figs. 3 and 4; Table 3) [87,88].…”