Cluster complexes alkylidynes

Ma-ALKYLIDYNE-TRIS(TRICARBONYLCOBALT) COMPOUNDS ORGANOCOBALT CLUSTER COMPLEXES... 

The interconversion of alkylidyne, alkylidene, vinylidene, and alkyne ligand moieties in a single cluster complex has been demonstrated on the oxo-alkylidyne cluster 198 via hydrogenation, protonation, or thermolysis. 

A review article illustrates the use of W(CO)2(CR)Cp as precursor for the synthesis of heteronuclear cluster complexes in which the y3 CR ligand is often present.Addition of Fe2(CO)9 to Mo(CO)2(Ctol)Cp affords the y-alkylidyne... 

The Iron Triad.—Mild protonation of the anion [Fe4(CO)u(/t-CO)(/e3-COMe)] yields [Fe4H(CO)i2(i -COMe)], which in turn reacts with strong acid to generate methane from the iy -COMe liquid X-ray crystal structures are reported for both iron complexes. Methods for the s mthesis of triangular metal-cluster complexes containing iUg-alkylidyne ligands have been reported and structures of this tsrpe have been established by X-ray diffraction methods for... 

An acetylide cluster, CpWRu2(CO)3(CCPh), was treated with 1 equivalent of Ru3(CO)i2 to give two carbido-alkylidyne cluster complexes, CpWRu4(/i5-C)(CO)i2(ju-CPh) and CpWRu5(/i6-C)(CO)i4(ju-CPh), as shown in Scheme 11 [35]. It is interesting to note that this cleavage is reversible. 

Further developments are likely as the chemistry of the compounds described above is explored. Moreover, entirely new dimensions may be added. For example, the synthesis of tungsten-alkylidyne complexes with carba-borane ligands with cage structures smaller than the icosahedral C2B9 fragment should result in the isolation of new electronically unsaturated metal cluster and electron-deficient molecules of types as yet unknown. 

Complex 2 is a potent cluster precursor. The isolobal relationship (194) between diarylalkynes and the alkylidynes CpW(CO)2(=CR) is now quite well known (195). Since 2 and 3 readily add alkynes, one might reason that alkylidynes CpW(CO)2(=CR) will also add across the M=M bonds of 2 or 3. In fact, this happens, and in quantitative yield for 2, when the product is 73. The yield of 74 in the tungsten reaction is less impressive, but it is obtained in higher yield in the reaction of Cp2W2(CO)4-(fi-rf-RCCR) with CpW(CO)2(=CR). The behavior of the chromium system is quite different, the product being the /x-alkyne species Cp2-W2(CO)4(jU-i72-RCCR). Remarkably, 1 is catalytic for this dimerization (196). 

Several factors affect the nature of the products in a reaction between a transition metal cluster and an alkyne or alkene. In this section, the various synthetic routes to alkyne or alkene-substituted clusters will be presented, and these will be used to analyze the changes in reactivity of the cluster systems when one or more of the important reaction parameters is altered. In order to simplify the discussion, tri-, tetra-, and higher nuclearity clusters will be treated separately. Finally, in this section, there is a brief description of the chemistry of alkylidyne-substituted clusters since synthetic routes to alkyne-containing complexes may involve these species. 

A number of elegant syntheses of mixed-metal clusters have been accomplished through the condensation of unsaturated metal complexes with metal donors. For example, condensation of the unsaturated cluster H20s3(CO)io with the alkylidyne see Alkylidyne) complex CpW(CO)2(CR) produces H20s3W(/u.3-CR)(C0)i2. Metal-metal, metal-carbon, or carbon-carbon multiple bonds may serve as the sites for metal fragment condensation. Other examples are shown in equations (80 and (9). 

Of the large number of /u.3-alkylidyne clusters known, only the title complexes have had their photochemical properties reported (194). The structure of CH3CCo3(CO)9 (163) consists of a triangle of metal-metal... 

---