Molybdenum oxo and imido complexes of beta-diketiminate ligands: synthesis and structural aspects

Treatment of MoO2(eta2-Pz)2] (Pz = 3,5-di-tert-butylpyrazolate) with the diketiminate ligand NacNacH (NacNac = CHC(Me)NAr]2-, Ar = 2,6-Me2C6H3) at 55 degrees C leads under reduction of the metal to the formation of the dimeric molybdenum(V) compound {MoO2(NacNac)}2] (1). The compound was characterized by spectroscopic means and by X-ray crystal structure analysis. The dimer consists of a Mo2O4]2+ core with a short Mo-Mo bond (2.5591(5) A) and one coordinated diketiminate ligand on each metal atom. The reaction of MoO2(eta2-Pz)2] with NacNacH in benzene at room temperature leads to a mixture of 1 and the monomeric molybdenum(VI) compound MoO2(NacNac)(eta2-Pz)] (2). From such solutions, yellow crystals of 2 suitable for X-ray structural analysis were obtained revealing the coordination of one bidentate NacNac and one eta2-coordinate Pz ligand. This renders the two oxo groups inequivalent. Further high oxidation state molybdenum compounds containing the NacNac ligand were obtained by the reaction of Mo(NAr)2Cl2(dme)] (Ar = 2,6-Me2C6H3) and Mo(N-t-Bu)2Cl2(dme)] (dme = dimethoxyethane) with 1 equiv of the potassium salt NacNacK forming Mo(NAr)2Cl(NacNac)] (3) and Mo(N-t-Bu)2Cl(NacNac)] (4), respectively, in good yields. The X-ray structure analysis of 3 revealed a penta-coordinate compound where the geometry is best described as trigonal-bipyramidal.