Synthesis, characterization, reactivity, identification of isomeric species and crystal structure of dinitrosylmolybdenum(0) complexes of 2-(α-hydroxyalkyl/aryl)benzimidazole

Abstract

Reaction of [Mo0(NO)2(acac)2] (Hacac = acetylacetone) with 2-(α-hydroxymethyl)benzimidazole (Hhmbmz, I), 2-(α-hydroxyethyl) benzimidazole (Hhebmz, II) and 2-(α-hydroxybenzyl)benzimidazole (Hhbbmz, III) at 1:1 ratio in refluxing methanol gives the corresponding dinitrosyl complexes, [Mo0(NO)2(acac)(hmbmz)] (1), [Mo0(NO)2(acac)(hebmz)] (2) and [Mo0(NO)2(acac)(hbbmz)] (3), respectively. Using complex precursor-to-ligands ratio of 1 : 2 with increased refluxing time results in [Mo0(NO)2(hmbmz)2] (4), [Mo0(NO)2(hebmz)2] (5) and [Mo0(NO)2(hbbmz)2] (6). All the complexes exhibit two well-separated sharp bands at 1,617–1,636 and 1,749–1,763 cm−1 in their IR spectra indicating the presence of a cis-Mo(NO)2 structure. Single crystal X-ray study of complexes [Mo0(NO)2(acac)(hmbmz)] and [Mo0(NO)2(hbbmz)2] suggests that NO is coordinated as NO+. The electronic spectra of the dinitrosyl complexes are dominated by one or two strong bands centered at ca. 450 nm due to metal to ligand charge transfer [(Mo → π*(NO)] transitions. Existence of two isomeric species in solution has been identified for some of these complexes. Reactions of nitrosyl complexes 4, 5 and 6 with aqueous 30 % H2O2 result in the removal of both the nitrosyl groups along with the concomitant oxidation and formation of the corresponding oxidoperoxidomolybdenum(VI) complexes. Dinitrosylmolybdenum(0) complexes in two different stoichiometries have been isolated and characterized. Oxidation of nitrosyl complex by H2O2 resulted in the removal of both nitrosyl groups along with the formation of oxidoperoxidomolybdenum(VI) complex.