Treatment of [MoO2( eta(2)- PZ)(2)] (Pz = 3,5-di-tert-butylpyrazolate) with the diketiminate ligand NacNacH (NacNac = CH[C(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) angstrom) and one coordinated diketiminate ligand on each metal atom. The reaction Of [MoO2 (eta(2)-PZ)(2)] with NacNacH in benzene at room temperature leads to a mixture of 1 and the monomeric molybdenum(VI) compound [MoO2(NacNac)(eta(2)-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 eta(2)-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)(2)Cl-2(dme)] (Ar = 2,6-Me2C6H3) and [Mo(N-t-Bu)(2)Cl-2(dme)] (dme = dimethoxyethane) with 1 equiv of the potassium salt NacNacK forming [Mo(NAr)(2)Cl(NacNac)] (3) and [Mo(N-t-Bu)(2)Cl(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-bi pyramidal.