Molybdenum complexes multiple

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

There are two well-characterized examples of a naked carbon atom bound by a triple bond to a metal center (Fig 14.3.8). The molybdenum carbide anion [CMo N(R)Ar 3]- (R = C(CD3)2(CH3), Ar = C6H3Me2-3,5), an isoelectronic analog of NMo N(R)Ar 3, can be prepared in a multistep procedure via deprotonation of the d° methylidyne complex HCMo N(R)Ar 3. The Mo=C distance of 171.3(9) pm is at the low end of the known range for molybdenum-carbon multiple bonds. In the diamagnetic, air-stable terminal ruthenium carbide complex Ru(=C )C12(LL/)(L = L = PCy3, or L = PCy3 and L = l,3-dimesityl-4,5-dihydroimidazol-2-ylidene), the measured Ru-C distance of 165.0(2) pm is consistent with the existence of a very short Ru=C triple bond. 

This is a general reaction for alkynes (acetylene, phenylacetylene, diphenylacetylene, cyclodecyne, etc.) that occurs at RT, producing 75% yields of products. The two cobalt atoms and two carbons form a tetrahedron. Analogous iron complexes are prepared in low yield by reaction of diphenylacetylene with Fe3(CO)i2 . Similar molybdenum complexes are prepared by addition of alkynes to molybdenum multiple bonds ... 

We noted earlier that two collinear bonds to metal atoms are formed by 0 in some finite ions and molecules. Examples include compounds of both transition and non-transition metals (Table 11.5). In all cases the short M-0 bonds indicate multiple-bond character though there are still shorter bonds to terminal 0 atoms in some of the molybdenum complexes. Details of some of these complexes are given at (a)-(c). Note the trigonal bipyramidal coordination of A1 in (a). 

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. 

Complexes Involving Multiple Molybdenum-Nitrogen Bonds 1340... 

There are two principal synthetic routes to dicarboxylate complexes. One of these uses an aqueous solution of the alkali metal dicarboxylate and the corresponding metal halide,93 while the other depends upon the dicarboxylic acid reduction of higher oxidation state metals. This reductive property of oxalic acid results in its ready dissolution of iron oxides and hence a cleaning utility in nuclear power plants.94 Mention must also be made of the successful ligand exchange synthesis of molybdenum dicarboxylates, Mo(dicarboxylate)2 H2 O, from the corresponding acetate complex. Unfortunately the polymeric, amorphous and insoluble nature of these complexes has restricted the study of these systems, which may well provide examples of multiple M—M bonding in dicarboxylate coordination chemistry.95... 

The striking advance since 1973 has been the synthesis of homoleptic isocyanides for vanadium and almost all of the post-group-VIA metals up to group IB (see Table I), and this has been helped in some respects by synthetic rationale. For example, the discovery of the simple reductive or nonreduc-tive cleavage of multiple metal-metal bonds in suitable dinuclear complexes of molybdenum and tungsten has provided a high yield route to W(CNPh)6 and [M(CNR)7]2+ (M = Mo, W) and related complexes (5-14). During these studies the series [M(CNR)7]2+ was completed with the isola-... 

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