Synthesis and structural characterization of a face-sharing bioctahedral complex [HB(Me2Pz)3)BH][Br3Mo(μ-Br)3MoTp*] and an edge-sharing tetramolybdenum complex [Mo4(μ3-O)2(μ2-O)2(μ2-OH)2(O)4(Me2PzH)6](Br)4(Me2PzH2)2 (Tp*=hydridotris(3,5-dimethylpyrazolyl)

From a solution prepared by a reaction of Mo2(O2CCH3)4 with KTp* (Tp*=hydridotris(3,5-dimethylpyrazolyl)borate, HB(Me2Pz)3), in diglyme at room temperature followed by addition of excess (CH3)3SiBr to the red solution in refluxing THF, the complexes [HB(Me2Pz)3)BH][Br3Mo(μ-Br)3MoTp*] (1), [Mo4(μ3-O)2(μ2-O)2(μ2-OH)2(O)4(Me2PzH)6](Br)4(Me2PzH2)2 (2) and MoBr2Tp*(Me2PzH) (3), were obtained. Their structures have been determined by X-ray crystallography. The anion of complex 1 consists of two octahedra sharing a common triangular face so those three Br atoms bridge the Mo atoms. The metal centers are also chelated by a tridentate Tp* ligand and coordinated by three Br atoms. Structural comparison of 1 and [HB(Me2Pz)3)BH][Br3Mo(μ-Br)2(μ-H)MoTp*] shows that replacement of the bridging hydride atom by the bromide atom led to the lengthening of the Mo–Mo bond distance by about 0.36 Å. In complex 2, the four octahedra are bridged together through edges. The two molybdenum atoms in the asymmetric unit have different environments although both are formally seven-coordinated. The average oxidation state of molybdenum is +5, and the four electrons available for Mo–Mo bonding form two localized Mo–Mo single bonds. Complex 2 can be classified into the structural type Mo4XaYbZc, in which a+b+c=16. The formation of the cation, [HB(Me2Pz)3)BH]+, 2 and 3 shows the ready cleavage of the B–N bond of the Tp* ligand.