title: Synthesis and characterization of 3-cyano- and 3-nitroformazans, nitrogen-rich analogues of beta-diketimine ligands.
abstract: The synthesis and characterization of several formazans containing strong electron-withdrawing substituents (cyano and nitro) in the 3 position of the ligand backbone are described. Reactions of aryldiazonium cations with the conjugated bases of either cyanoacetic acid or nitromethane lead to 1,5-diaryl-3-cyano- or 3-nitroformazans, respectively. When these reactions are carried out in aqueous conditions, the range of aromatic groups is limited by the stability of the diazonium salt. However, 3-nitroformazans containing bulky substituents on the nitrogen atoms (2,6-dimethylphenyl, 2,4,6-trimetyhlphenyl, 2,6-diisopropylphenyl, and 3,5-ditert-butylphenyl) could be made by performing the reactions under nonaqueous and anhydrous conditions. NMR and electronic spectroscopic studies indicate that the 3-nitroformazans exist exclusively as closed ( trans-syn, s-cis) isomers whereas the 3-cyanoformazans exist as mixtures of isomers which are substrate-dependent. The crystal structures of five of the formazans are presented: two 3-nitroformazans, both of which are closed, and three 3-cyanoformazans, two of which are closed and one of which adopts an open ( trans-syn, s-trans) structure. Solid state (diffuse reflectance) spectroscopy has been employed to ascertain the isomeric preferences of the other formazans which could not be crystallographically characterized.
authors.affiliation: Department of Chemistry, University of Victoria, Victoria, British Columbia, Canada.
authors.forename: Joe B
authors.initials: JB
authors.lastname: Gilroy
authors.forename: Peter O
authors.initials: PO
authors.lastname: Otieno
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ferguson
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Robin G
authors.initials: RG
authors.lastname: Hicks