Molybdenum ligand complexes

More recendy, molecular molybdenum-sulfur complexes and clusters have been used as soluble precursors for M0S2 in the formulation of lubricating oils for a variety of appHcations (70). Presumably, the oil-soluble molybdenum—sulfur-containing precursors decompose under shear, pressure, or temperature stress at the wear surface to give beneficial coatings. In several cases it has been shown that the soluble precursors are trifunctional in that they not only display antifriction properties, but have antiwear and antioxidant characteristics as weU. In most cases, the ligands for the Mo are of the 1,1-dithiolate type, including dithiocarbamates, dithiophosphates, and xanthates (55,71). 

Fig. 2. The Schrock cycle with its intermediates, based on the molybdenum(III) complex [Mo(HIPTN3N)] containing the triamidoa-mine ligand HIPTN3N (hexaisopropylterphenyl-triamidoamine) (2).

C). The exact role of the base is not clear, but it may accelerate the formation of the molybdenum alkoxide complex from a bound alcohol ligand. 

In recent work, Ashe et al. have prepared a series of molybdenum tricarbonyl complexes of C6H6B-R ligands.142 X-ray diffraction data on [H6C6B-N(CHMe2)2]Mo(CO)3 123 revealed that the metal is coordinated to the six ring carbons but not to boron. 

Direct comparisons of the stability constants for formation of the dmpp complexes of molybdenum(VI) with those for uranium(VI) are not possible. The mono-ligand complexes have different stoichiometries, MoOaldmpp) versus U02(dmpp), while although log P2 is available for Mo02(dmpp)2 (175) the value of 40.2 refers to formation from Mo04 rather than from MoOg laq), and U02(dmpp)2 is too sparingly soluble for its formation constant to be determined (231). 

N-Donor Ligands. The full account of the crystal structure of [Mo02(8-hydroxyquinolate)2] has been published. The dimensions of the M0O2 unit are O—Klo—O = 104.C and Mo—O = 171(2) pm. The electrochemistries of this and the related molybdenum(v) complex. [ MoO(8-hydroxyquino-late)2 2 0], have been investigated as simple models of molybdenum-fluoro-protein enzymes (p. 146). Reduction of the molybdenum(vi) complex occurs in two one-electron steps with solvent attack of the reduced intermediates and displacement of the 8-hydroxyquinolato-groups. ... 

In seven-coordinate molybdenum peroxo complexes of the type Mo(0)(02)2L2, there is the problem of dissociation of the complex in the case of monodentate ligands like pyridine, HMPA, DMF or H2O. Bidentate hgands like 2,2 -bipyridine, on the other hand, tend to give insoluble complexes. A solution to this problem was presented by Thiel in 1997 and 1998 . His group utilized the Mo-diperoxo complex 160 bearing a pyrazolylpyridine ligand. 

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