Tungsten complexes multiple bonds

Among the more interesting metal-metal multiple bonded complexes are the hexaalkoxo dinuclear tungsten and molybdenum complexes, fM,(OR),J [Pg.418]

The reactions and nature of multiple bonds between two metal atoms form a lively area of research and debate (1,2). Many examples of triple bonds between metals are known, including the extensively studied molybdenum or tungsten alkoxide, M2(OR)6, and amido, M2(NR2)6, complexes (3). Classic examples of quadruple bonds are epitomized by [Re2Cl8]2 (4) and molybdenum acetate, Mo2(OCOMe)4 (5). 

NMR resonances of the alkylidyne carbon atom and selected IR absorptions for new carbyne complexes are given in Table 11. In other studies, the Mo and NMR spectra of molybdenum and tungsten alkylidyne complexes were determined by Enemark and co-workers (23). The metal atoms in the alkylidyne complexes were found to be less shielded than those in nitrido complexes but more shielded than those in compounds containing metal-metal multiple bonds. 

The C=0 bond in ketones can be cleaved by tungsten complexes with formation of a very strong oxo-tungsten multiple bond as has been studied extensively [119]. 

There are many compounds and complexes of molybdenum in the V and VI oxidation states in which there are one or more oxygen atoms bound to the molybdenum by multiple bonds that can be represented Mo=0, since they are evidently approximately double bonds. There are also oxo species with either linear or non-linear M—O—M bridges. While there are certain resemblances in this oxo chemistry to that of Cr, and while tungsten also forms some analogous compounds, by far the most extensive chemistry is known for molybdenum. Some important relationships have been summarized above in Fig. 26-C-9. 

Tungsten(n) shows much less tendency to M—M multiple bonding. The W2(02CR)4 compounds are much less stable than those of Mo and have not, in fact, been unequivocally shown to be isostructural with them.53 No dinuclear halo complex or allyl derivative of Wn is known. However the Mo111 and W1" alkyls M2(CH2SiMe3)6 are isomorphous and have a short, triple M-—M bond (see page 757) the neopentyls are similar.54... 

---