Chemistry of Dimolybdenum and Ditungsten Hexalkoxides

The chemistry of the M2Xs molecules (M = Mo, W and X = R, OR, NR2, etc.) has continued to develop rapidly, with many of the major advances coming from the laboratory of M. H. Chisholm. There is, in fact, far too much new material to be reviewed comprehensively here. We shall restrict coverage to some of the reaction chemistry of the M2(OR)6 molecules, where particularly important advances have been made, namely, to the reactions of the M2(OR)6 molecules with C=C and C=N bonds. 

With alkynes, R CsCR , the M2(OR)g molecules give a wide variety of products, depending on (a) conditions, (b) the R and R in the alkyne, (c) the OR group in the 

Alkyne scission reactions also occur and some are of exceptional interest and importance. Schrock, et al.166 discovered the following remarkable reaction  

It is important to note that this reaction works only with W2(OCMe3)6 and not with any other M2(OR)6 molecule and that while it appears to be general for aliphatic R it does not proceed for R = QH5. It goes under very mild conditions and is virtually quantitative. Since the (Me3CO)3W=CR compounds are alkyne metathesis catalysts, still other tungsten alkylidyne compounds, not obtainable in the above reaction, can be obtained by the following reaction  

The (Me3CO)3W=CR compounds exist in the solid state as either weakly associated dimers (Structure IV, Fig. 5.4-1) with OR bridges (R = CH3167) or NMe2)l68) or as a tetrahedral monomer in the case of R = C6H5169). 

---