Group VB Vanadium

Of the group VB elements, tt complexes have been reported only for vanadium. The complexes (diolefin)V(CO)2(C6H5) obtained by UV irradiation of V(CO)4(C5H5) with butadiene, 2,3-dimethylbutadiene, and 1,3-cyclohexadiene have been reviewed earlier (219, 268). 

Although many stable cycloolefin complexes of the group VIB metals have been reported (47, 268), it is only recently that tt complexes of the simple monoolefins such as ethylene have been isolated (148, 195, 203, 572). 

With several functionally substituted ethylenes, stable tt complexes of molybdenum and tungsten of the general form L M(CO)g 2 can be prepared, according to Eq. (1)  

From the reaction of vinyl methyl ketone with (CH3CN)3M(CO)3, (M = Cr or Mo), King (348) has isolated the complexes, (vinyl methyl ketone)3M, as yellow volatile solids. Although the molybdenum complex 

The failure to obtain complexes containing tnore than two acrylonitrile ligands by displacement of carbon monoxide from M(CO)6 may be due to the fact that either tlie complex or the ligands cannot withstand the rigorous reaction conditions. It is possible, however, to prepare the series (AN) M(CO)g (w = 1, 2, or 3 AN = acrylonitrile M = Cr, Mo, or W) in good yields by displacement of acetonitrile under mild conditions from its corresponding complexes (508, 571). 

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