2,2 -Bipyridine molybdenum complex

The synthesis of polydiacetylenes with bipyridine metal complexes in their sidechains has been achieved by Lindsell and cowoikers (Scheme 17). Complexes of nickel, copper, ruthenimn, and molybdenum were synthesized and the nonlinear optical properties of the resulting polymers examined. 

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. 

Note that these compounds are not enantiomers, but true diastereomers with different properties, and they may be separated by fractional crystallization. The asymmetric carbon atom has an 5 configuration in both diastereomers, but the chirality about the molybdenum atom is different. Thus the asymmetric carbon aids in the resolution of the molybdenum center, but its presence is not necessary for the complex to be chiral. It is merely necessary for the Schiff base to be unsymmetric, i.e., have one pyridine nitrogen and one imino nitrogen. If the bkJentate ligand had been ethylenediamine, bipyridine, or the oxalate ion, there would have been a mirror plane and no duality at the molybdenum. 

Because of their properties they are widely used in electrochemistry, in electrophotography, as well as in photocatalysis and photochemical water cleavage. Thus Hennig and Rehorek in 1986 reported the sensitization of photochemical reactions by Prussian blue analogues of molybdenum octacyanide, and Kaneko and his group in 1984 found that water can be photolyzed with visible light in presence of Pmssian blue and tris (2, 2 -bipyridine) ruthenium (II) complex. 

Binuclear complexes with 17e molybdenum fragments of the type Mo(NO)Tp Cl or MoOTp Cl lead to larger couplings, as shown by Ward, McCleverty and coworkers. With 4,4 -bipyridine or 4,4 -bipyridylethylene as bridges (Rmm = 113 and 13.8 A resjjectively), the couplings (-33 and —18 cm" ) could be measured by... 

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