Cluster complexes alkyne derivatives

Fig. 15. Observed bonding modes of alkyne and alkyne-derived ligands in cluster complexes.

The reactivity of clusters containing coordinated alkyne or alkyne-derived ligands has not been widely investigated. This review has indicated that quite a significant number of complexes of this type have now been synthesized, but it is important to remember that quite a large proportion of these clusters are obtained in relatively low yield, and it is perhaps this aspect that has hindered further research into their reaction chemistry. However, over the last several years, an increasing number of publications reporting the reactions of alkyne-substituted... 

The alkyne-Co2(CO)6 complexes 1 are the binuclear cluster complexes of the acetylenic derivatives with the hexacarbonyldicobalt moiety. These complexes can be readily prepared by treatment of alkynes with commercially available octacarbonyldicobalt [Co2(CO)g] and can regenerate the parent triple bond functionality under some mild oxidation conditions. Two synthetically very useful reactions have so far been developed by taking advantage of the characteristic properties of the alkyne-Co2(CO)6 complexes 1 one is so-called Nicholas reaction" and the other is so-called Pauson-Khand reaction (Scheme 1). The alkyne-Co2(CO)6 complexes 1 possessing a hydroxyl group or its equivalent at carbon p- to alkyne moiety (propargyl alcohol derivatives) could easily... 

Surprisingly, in several experiments carried out under a variety of conditions, formation of the / cyclohexyne derivative 19b from cyclohexene and la was never observed. This complex was prepared from cyclohexene with f(C5H5)2Co]/potassium. Reactions with this reagent usually do not proceed cleanly and generate a large amount of insoluble by-products. Nevertheless, separation of the products is usually less laborious, due to the absence of 3 and 4. As a second type of product, the tetranuclear /r4-alkyne cluster complexes 21 were formed in very low yield from the corresponding cycloalkenes and [(C5H5)2Co]/K. ° ... 

The use of Me3NO to induce substitution of dppm (bis(diphenylphosphino)-methane) for CO molecules on dinuclear iron complexes led to insertion of CO into C-C bonds of alkyne-derived metallacycles. Similar behavior was observed when [PPNJCl salts were used to favor the formation of alkyne-substituted triruthenium dppm-containing clusters.I This behavior should be compared with the insertion of CO into allenylidene and phosphido-bridging ligands occurring when dppm coordinates to binuclear ruthenium complexes as shown in Fig. 3. This reaction is a nucleophilic attack of the coordinated allenylidene and phosphido groups on a coordinated CO (see Section 2.8.2.2). 

A discussion of complexes with parallel or perpendicular alkynes or alkyne-derived ligands is in Deabate, S. Giordano, R. Sappa, E. J. Cluster Set. 1997, 4, 407 59. 

In Volume II, which will be published in the near future, the following topics will be covered The Potential Utility of Transition Metal-Alkyne Complexes and Derived Cluster Compounds as Reagents in Organic Synthesis (K. M. Nicholas, M. O. Nestle, and D. Seyferth) Arene Complexes in Organic Synthesis (G. Jaouen) and Oxidation, Reduction, Rearrangement, and Other Synthetically Useful Processes (H. Alper). 

Reaction of Fc2lr cluster (172) with dihydrogen gives complex 184 whereas stepwise addition of H and H results in the formation of 184 and the isomeric hydrido alkyne derivative 185 (Scheme 50). " ... 

Reaction of acetylenic complexes with triosmium dodecacarbonyl leads to a variety of products involving one, two, or three acetylenic units. As with ruthenium, for the monosubstituted alkynes, hydrogen transfer can occur to the metal cluster. Thus, Os3(CO)12 and phenyl-acetylene (L) yield, in refluxing benzene, the derivatives Os3(CO)10L, Os3(CO)10L2, Os3(CO)9L, and HOs3(CO)9(L-H). The general chemistry is summarized in Scheme 2 (131). 

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