SYNTHESIS AND CHARACTERIZATION OF 3,6-BIS(3,5-DIMETHYL PYRAZOL-1-YL)PYRIDAZINE (L) DERIVATIVES OF MONONUCLEAR MANGANESE(I) AND GROUP-6 METAL(O) CARBONYL-COMPLEXES - CRYSTAL AND MOLECULAR-STRUCTURES OF [M(CO)4L] (M = CR OR MO)

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 H-1 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 P2(1)/c, with Z = 4 in unit cells of dimensions a = 8.0790(1), b = 19.5539(2), c = 12.5186(1) angstrom, beta = 91.598(1)-degrees (M = Cr) and a = 8.081(1), b = 19.793(2), c = 12.607(6) angstrom, beta = 91.62(3)-degrees (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-degrees 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)-degrees 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)-degrees (M = Mo) with slighter distortions of the mutually cis-carbonyl groups [range 84(1)-87(1)-degrees]. 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.