The structure of 1,5-bis(2,6-dimethylphenyl)-3-nitroformazan

Synthesis and Characterization of 3-Cyano- and 3-Nitroformazans, Nitrogen-Rich Analogues of β-Diketimine Ligands

“…The crystal structure of bis(mesityl)-3-nitroformazan 6d is presented in Figure . This compound exists as the closed isomer in the solid state, as was found for the previously structurally characterized bis(2,6-dimethylphenyl) nitroformazan 6c . As is the case for the other closed derivatives, the formazan backbone in 6d is highly delocalized, showing minimal bond-length alternation (N1−N2 1.299(2), N4−N3 1.282(2), N1−C1 1.322(2), N3−C1 1.357(2)Å).…”

“…Diazonium tetrafluoroborate salts were prepared according to literature procedures and used immediately. Formazans 5a , 5b , 5e , and 5f and 6a , 6b , and 6c have been reported previously; however, in all cases, the characterization of these compounds was either not reported or incomplete. NMR spectra were recorded on a 300 or 500 MHz instrument.…”

“…In the nitromethane system, the presence of even ortho- methyl substituents (cf. 5c , 5d ) causes this reaction to fail; the bis(2,6-dimethylphenyl) derivative 6c has been made previously but in 1% yield . However, we have found that the diazonium cations (as their BF 4 − salts) are stable enough in nonaqueous (anhydrous) conditions to couple with deprotonated nitromethane to afford 3-nitroformazans in fair to good yields.…”

“…Of the six nitroformazans prepared, derivatives 6b , 6c , and 6d have been crystallographically confirmed to be closed isomers in the solid state. These derivatives all have visible maxima between 450 and 500 nm and weaker maxima above 550 nm in their diffuse reflectance spectra; subtle variations between the maxima of these compounds may be due to substituent effects (see below).…”

“…Several formazans adopt the trans-syn , s-cis (hereafter referred to as “open”) structure in which the NH proton bridges N1 and N5. This structure is favored by formazans with aryl or bulky alkyl substituents in the 3 position. ,,, Formazans with relatively small R 3 groups (e.g., H, Me, Et, and SMe) crystallize in either the trans-syn , s-trans (“open”) , or trans-anti , s-trans (“linear”) ,– configuration. Among the crystallographically characterized formazan derivatives there are no examples of 3-cyanoformazans and only one 3-nitroformazan (compound 6c ). , Crystal structures of three of the 3-cyanoformazans ( 5d , 5e , and 5f ) and two of the 3-nitroformazans ( 6b and 6d ) have been determined (attempts to grow single crystals of the other derivatives suitable for X-ray studies were not successful).…”