MONONUCLEAR AND BINUCLEAR MOLYBDENUM COMPLEXES OF THE TRIS(3,5-DIMETHYL-1-PYRAZOLYL)METHANE LIGAND

A series of mononuclear and binuclear molybdenum(0-VI) complexes of the facially coordinating tris(3,5-dimethyl-1-pyrazolyl)methane (L*) ligand have been prepared and structurally and spectroscopically characterized. The oxidation of L*Mo(CO)3 by various oxidants such as SOCl2, Br-2, I-2, and HNO3 affords a variety of mononuclear molybdenum(III and VI) complexes of the type L*MoX(3) (X = Cl, Br, I, and 0). The synthesis of [L*MoOCl2]Cl-+(-) achieved by refluxing a solution of L* and MoCl5 in THF. Oxo-molybdenum(V) complexes of the type [L*MoOX(2)](+) were rapidly generated in solution by the action of 1 equiv of the dianions of catechol, tetrachlorocatechol, and ethanedithiol on [L*MoOCl2]Cl-+(-) in the presence of base. Upon standing, these reaction mixtures produce unsymmetrical dimers having a [Mo2O4](2+) core. The structures of L*MoI3, L*Mo2O4Cl2, and L*Mo2O4(OC6H4O) were determined by X-ray crystallography: L*MoI3 crystallizes in the monoclinic space group P2(1)/n with a = 15.756(1) Angstrom, b = 9.971(1) Angstrom, c = 16.822(1) Angstrom, beta = 102.752(6)0, Z = 4, R = 0.024, and R(w) = 0.036. The molecule adopts the expected fac stereochemistry, and the average Mo-N and Mo-I distances are 2.200(3) and 2.7668(5) Angstrom, respectively. L*Mo2O4Cl2 crystallizes in the orthorhombic space group Pbca with a = 12.800(1) Angstrom, b = 18.530(1) Angstrom, c = 21.197(1) Angstrom, Z = 8, R = 0.034, and R(w) = 0.047. This binuclear complex contains both a six-coordinate molybdenum atom with an N3O3 coordination sphere and a five-coordinate molybdenum atom having O3Cl2 coordination. L*Mo2O4(OC6H4O) crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 7.979(1) Angstrom, b = 16.166(1) Angstrom, c = 21.767(3) Angstrom, Z = 4, R = 0.031, and R(w) = 0.048. This dimer is similar to the above mentioned binuclear complex except that chlorine atoms are replaced by the catecholate moiety. The Mo-95 NMR spectra of the dimeric species show a single peak that is assigned to the five-coordinate center.