Carbonyl clusters substituted

Ni(CO)4 -H 4 PCCHaCHaCNla Ni4(CO)6[P(CH2CH2Clsr)3]4 -H 10 CO (27) The carbonyl clusters substituted by ligands with Group V donor atoms are listed in Table V along with their preparations and references to structural studies. 

Carbonyl Clusters Substituted by Ligands with an Organic n System... 

Trinuclear Carbonyls and Substituted Carbonyls for Heteronuclear Clusters... 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

With more and more clusters becoming available, the synthetic chemistry of clusters turns more to the use of clusters as starting materials. Thus, there is an extensive literature on CO substitutions in metal carbonyl clusters and on the organic chemistry of methinyltricobalt enneacarbonyls. Reactions of this type are dealt with in part in Chapter 2.5. and in detail in Chapter 3. 

Oxidation of the tetracobalt clusters is made easier by the successive phosphine substitution. The anion radical derived from the 0/ — 1 redox couple of the cluster is substitution-ally labile. The cyclic voltammetric pattern of tetracobalt carbonyl cluster is shown in Figure 3. 

The first class of reactions, direct transfer of an oxygen atom from the oxidant to carbon monoxide, has not been commonly observed as a reaction catalyzed by metal complexes in solution. One example, derived from a preparative procedure developed to substitute carbonyls with other ligands (90), is the reaction of trimethylamine oxide, Me3NO, with carbonyl clusters such as Os3(CO)12 in the presence of excess CO. The net reaction is shown as (27). 

Anionic clusters are good nucleophiles (see Section III,A) and are often easy to make. On the other hand, the electrophilic nature of most monometallic complexes is obvious from ligand substitutions. The combination of these properties makes a strategy for cluster expansion. This strategy was used for the first time by Hieber (130) in making Fe4(CO)fc from Fe3(CO),7 and Fe(CO)s. It is probably active in many syntheses of large metal carbonyl clusters because the Re, Os, Rh, Ir, Ni, and Pt clusters involved are almost always anionic. However, simple stoichiometries can rarely be written for such reactions (122). This route makes mixed metal clusters accessible, e.g.,... 

Homogeneous Catalytic Oxidation with Phosphine-Substituted Complexes of Rhodium Carbonyl Clusters... 

Exclusive formation of silylstyrenes 76 is achieved when the reactions of styrene and 4-substituted styrenes with HSiEt3 are catalyzed by Fe3(CO)i2 or Fe2(CO)9100. Other iron-triad metal carbonyl clusters, Ru3(CO)i2 and Os3(CO)i2, are also highly active catalysts, but a trace amount of hydrosilylation product 77 is detected in the Ru-catalyzed reactions and the Os-catalyzed reactions are accompanied by 3-12% of 77 (equation 31)100. Mononuclear iron carbonyl, Fe(CO)5, is found to be inactive in this reaction100. 

In 1962, Dahl had also structurally characterized Fej(CO)i5C, the first high nuclearity carbide (26). This compound was originally prepared in extremely low yields (0.5%) by the reaction of Fe3(CO)i2 with substituted acetylenes, and, probably due to the peculiarity of this synthesis, was considered for some time much more a curiosity rather than being recognized as the precursor of today s large family of carbide-carbonyl clusters. 

The carbide-centered polynuclear transition-metal carbonyl clusters exhibit a rich variety of structures. A common feature to this class of carbide complexes is that the naked carbon is wholly or partially enclosed in a metal cage composed of homo/hetero metal atoms, and there is also a subclass that can be considered as tetra-metal-substituted methanes. The earliest known compound of this kind is FesC(CO)i5, in which the carbon atom is located at the center... 

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