Synthesis and characterization of 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (L) derivatives of mononuclear manganese(I) and Group 6 metal(0) carbonyl complexes. Crystal and molecular structures of [M(CO)4L](M = Cr or Mo)

Abstract

Treatment of [M(CO)₆](M = Cr, Mo or W) or [MnBr(CO)₅] with 3,6-bis(3,5-dimethylpyrazol-1-yl)pyridazine (L) in refluxing tetrahydrofuran or toluene (M = Cr or W) gives, respectively, [M(CO)₄L] and [MnBr(CO)₃L]. Infrared and ¹H NMR spectra indicate that the tetradentate heterocycle acts only as a monochelate ligand forming mononuclear complexes. The crystal structures of [M(CO)₄L](M = Cr or Mo) have been determined by X-ray diffraction. Crystals are isotypic, monoclinic, space group P2₁/c, with Z= 4 in unit cells of dimensions a= 8.0790(1), b= 19.5539(2), c= 12.5186(1)Å, β= 91.598(1)°(M = Cr) and a= 8.081(1), b= 19.793(2), c= 12.607(6)Å, β= 91.62(3)°(M = Mo). The structures have been solved by Patterson methods and DIRDIF. Final conventional agreement factors were R= 0.043, R′= 0.038 for M = Cr and R= 0.051, R′= 0.038 for M = Mo. The structures consist of distorted octahedral arrangements with four carbonyl groups and two nitrogen atoms of the ligand L around each metal atom, and the unco-ordinated nitrogen atom of the pyrazolyl group twisted by almost 180° with respect to the corresponding one in the co-ordinated ring. The ligand, which is almost planar, forms a monochelate ring with small bite angles N–M–N 75.2(1) and 71.0(3)° for Cr and Mo respectively. Deviation from the linearity of the mutually trans-carbonyl groups is revealed by the C–M–C bond angles of 166.7(2)(M = Cr) and 167.0(6)°(M = Mo) with slighter distortions of the mutually cis-carbonyl groups [range 84(1)–87(1)°]. Cyclic voltammetric studies in CH₂Cl₂ show single non-reversible redox waves in accord with the observed energies of the metal-to-ligand charge transfer absorptions in the electronic spectra.