Characterisation of tridentate macrocyclic complexes of molybdenum(0) with tetra-aza macrocycles. Crystal structure of [ Mo(CO)3L1](L1= C-meso-5,5,7,12,12,14-hexamethyl-1,4,8,11 -tetra-azacyclotetradecane)

Abstract

The tetra-aza macrocyclic ligands L¹(C-meso) and L²(C-racemic)(5,5,7,12,12,14-hexamethyl- 1,4,8,11 -tetra-azacyclotetradecane) react with [Mo(CO)₆] in dry dimethylformamide to give the diamagnetic [ Mo(CO)₃L¹] and [ Mo(CO)₃L²] respectively in which the potentially quadridentate ligand is tridentate. The [ Mo(CO)₃L¹] complex has been characterised by X-ray crystallography. It crystallises as yellow needles [monoclinic, a= 8.699(2), b= 19.839(4), c= 12.518(2)Å, β= 90.79(1)°; R converged to 0.022 for 2 243 independent reflections for which I/σ(I) > 6.01]. The crystal structure establishes that the ligand L¹ co-ordinates via N(1), N(4), and N(8). Hydrogen bonding N(11)⋯ H–N(1) occurs within the complex. Cyclic voltammograms of both complexes determined using MeNO₂ solvent display a quasi-reversible one-electron oxidation process corresponding to the Mo^(O)/Mo^(I) oxidation, with E_½=–0.28 (L¹) and =–0.27 V (L²) versus ferrocene—ferrocenium.